U.S. patent application number 17/271505 was filed with the patent office on 2021-07-01 for methods of making honeycomb bodies having inorganic filtration deposits.
The applicant listed for this patent is CORNING INCORPORATED. Invention is credited to Yunfeng Gu, Mark Alan Lewis, Cai Liu, Dale Robert Powers, Todd Parrish St Clair, Jianguo Wang, Huiqing Wu, Xinfeng Xing, Danhong Zhong.
Application Number | 20210197105 17/271505 |
Document ID | / |
Family ID | 1000005506670 |
Filed Date | 2021-07-01 |
United States Patent
Application |
20210197105 |
Kind Code |
A1 |
Gu; Yunfeng ; et
al. |
July 1, 2021 |
METHODS OF MAKING HONEYCOMB BODIES HAVING INORGANIC FILTRATION
DEPOSITS
Abstract
Methods for applying a surface treatment to a plugged honeycomb
body comprising porous wall includes: atomizing particles of an
inorganic material into liquid-particulate-binder droplets
comprised of an aqueous vehicle, a binder material, and the
particles, evaporating substantially all of the aqueous vehicle
from the droplets to form agglomerates comprised of the particles
and the binder material, and depositing the agglomerates onto the
porous walls of the plugged honeycomb body, wherein the
agglomerates are disposed on, or in, or both on and in, the porous
walls. Plugged honeycomb bodies comprising porous walls and
inorganic material deposited thereon are also disclosed.
Inventors: |
Gu; Yunfeng; (Painted Post,
NY) ; Lewis; Mark Alan; (Horseheads, NY) ;
Liu; Cai; (Suzhou City, CN) ; Powers; Dale
Robert; (Painted Post, NY) ; St Clair; Todd
Parrish; (Painted Post, NY) ; Wang; Jianguo;
(Horseheads, NY) ; Wu; Huiqing; (Shanghai, CN)
; Xing; Xinfeng; (Shanghai, CN) ; Zhong;
Danhong; (Elmira, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING INCORPORATED |
Corning |
NY |
US |
|
|
Family ID: |
1000005506670 |
Appl. No.: |
17/271505 |
Filed: |
August 30, 2019 |
PCT Filed: |
August 30, 2019 |
PCT NO: |
PCT/US2019/049213 |
371 Date: |
February 25, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62726192 |
Aug 31, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 39/2079 20130101;
B01D 46/2418 20130101; B01D 2046/2433 20130101 |
International
Class: |
B01D 39/20 20060101
B01D039/20; B01D 46/24 20060101 B01D046/24 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2018 |
CN |
PCT/CN2018/103807 |
Claims
1.-97. (canceled)
98. A filtration article comprising: a honeycomb filter body
comprising porous walls having pores; and inorganic deposits
comprising inorganic material nanoparticles and a binder disposed
within the honeycomb filter body; wherein the inorganic deposits
comprise a network of aggregated agglomerates of the inorganic
material nanoparticles and the binder, the binder comprising a
water soluble binder.
99. The filtration article of claim 98, wherein the agglomerates
are comprised of nanoparticles of inorganic material and the
network of agglomerates comprises aggregates of agglomerates.
100. The filtration article of claim 99, wherein the network of
agglomerates comprises clusters or chains of the aggregates.
101. The filtration article of claim 100, wherein at least a
portion of the clusters or chains are disposed within the pores in
or below the surface of the porous walls, at least a portion of the
clusters or chains, are disposed on the surface of the porous
walls.
102. The filtration article of claim 100, wherein a portion of the
clusters are porous clusters comprising exposed aggregates of
agglomerates.
103. The filtration article of claim 102, wherein the porous
clusters comprise one or more chains of two or agglomerates, each
chain extending in an outward direction from the porous walls.
104. The filtration article of claim 102, wherein the porous
clusters comprise a plurality of the outwardly extending chains
collectively providing a morphology resembling a member of the
group consisting of fingers, tufts, and sponges.
105. The filtration article of claim 98, wherein the inorganic
material comprises one or more of ceramic particles, metal oxide
particles and refractory metal oxide particles.
106. The filtration article of claim 98, wherein the inorganic
material comprises alumina.
107. The filtration article of claim 98, wherein the inorganic
material is present on the honeycomb filter body in a loading of
from 0.1 to 20 g/L to 0.1 to 5 g/L.
108. The filtration article of claim 98, wherein the inorganic
material is present on the honeycomb filter body in a loading of
from 0.1 to 5 g/L to 0.1 to 2 g/L.
109. The filtration article of claim 98, wherein water soluble
binder comprises a silicon-containing binder.
110. The filtration article of claim 98, wherein the binder
comprises a silicate or an aluminate.
111. The filtration article of claim 98, wherein the binder
comprises sodium silicate.
112. The filtration article of claim 98, wherein the binder is
present in an amount in a range of from 5 wt % to about 30 wt % of
the inorganic material on the honeycomb filter body.
113. The filtration article of claim 98, wherein the inorganic
deposits are free of rare earth oxides, platinum group metals, and
molecular sieves.
Description
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn. 119 of U.S. Provisional Application No. 62/726,192
filed on Aug. 31, 2018, and to International Application No.
PCT/CN2018/103807 filed on Sep. 3, 2018, the contents of which are
incorporated herein by reference in their entireties.
BACKGROUND
Field
[0002] The present specification relates to methods of making
porous bodies, such as porous ceramic honeycomb bodies, which
comprise inorganic deposits, the deposits comprised of an inorganic
filtration material.
Technical Background
[0003] Wall-flow filters are employed to remove particulates from
fluid exhaust streams, such as from combustion engine exhaust.
Examples include diesel particulate filters used to remove
particulates from diesel engine exhaust gases and gasoline
particulate filters (GPF) used to remove particulates from gasoline
engine exhaust gases. Exhaust gas to be filtered enters inlet cells
and passes through the cell walls to exit the filter via outlet
channels, with the particulates being trapped on or within the
inlet cell walls as the gas traverses and then exits the
filter.
SUMMARY
[0004] Aspects of the disclosure pertain to porous bodies and
methods for their manufacture and use.
[0005] In one aspect, a method is disclosed herein for applying
inorganic deposits to a honeycomb filter body, such as a plugged
honeycomb filter body, the filter body comprising porous walls, the
method comprising: atomizing a feed mixture into
liquid-particulate-binder droplets, the feed mixture being
comprised of an aqueous vehicle, a binder material, and particles
of an inorganic material; aerosolizing the
liquid-particulate-binder droplets, with, for example, a gaseous
carrier stream; removing, e.g. evaporating, substantially all of
the aqueous vehicle from the droplets to form aerosolized
particulate-binder agglomerates comprised of the particles and the
binder material; directing the aerosolized agglomerates onto the
porous walls of the honeycomb filter body, thereby depositing the
agglomerates on, or in, or both on and in, the porous walls. In
specific embodiments, the method further comprises heating the
honeycomb filter body containing the agglomerates for a time and at
a temperature sufficient to cause the binder to bind the
agglomerates to the porous walls, or to bind at least some of the
agglomerates to each other, or both. In some embodiments, the
method further comprises heating the honeycomb filter body
containing the agglomerates for a time and at a temperature
sufficient to cause the binder to break down. In some embodiments,
the binder material comprises silicon, and the method further
comprises heating the honeycomb filter body containing the
agglomerates for a time and at a temperature sufficient to form
silica from the binder material. In one or more embodiments, the
binder material is a silicon-containing compound. In one or more
embodiments, the silicon-containing compound is comprised of a
siloxane or polysiloxane, silicone, a silicate, or a combination
thereof. In one or more embodiments, the silicon-containing
compound is comprised of a silicone compound, polysiloxane,
silicone resin, siloxane, alkoxysiloxane, or combinations thereof.
In one or more embodiments, the silicon-containing compound is
comprised of a silicate, an alkaline silicate, a sodium silicate,
or combinations thereof.
[0006] In another aspect, a method is disclosed herein for making a
honeycomb filtration body which comprises: mixing together
particles of an inorganic material with an aqueous vehicle and a
binder material to form a liquid-particulate-binder mixture, for
example, a suspension, or a colloid; atomizing the
liquid-particulate-binder mixture with an atomizing gas to form
liquid-particulate-binder droplets comprised of the aqueous
vehicle, the binder material, and the particles, by, for example,
directing the liquid-particulate-binder mixture into an atomizing
nozzle and atomizing with a forced atomizing gas; aerosolizing the
droplets with a gaseous carrier stream and conveying the droplets
toward the honeycomb body with a carrier gas flow through a duct
close coupled with the honeycomb filter body, the carrier gas flow
comprising the gaseous carrier stream. In one or more embodiments,
the duct has an outlet end proximate the honeycomb filter body,
wherein an internal surface of the duct defines a chamber. In one
or more embodiments, the carrier gas flow further comprises the
atomizing gas. The method further comprises evaporating
substantially all of the aqueous vehicle from the aerosolized
droplets to form aerosolized particulate-binder agglomerates
comprised of the particles and the binder material and depositing
the agglomerates onto the porous walls of the honeycomb filter
body. In one or more embodiments, the deposited agglomerates are
disposed on, or in, or both on and in, the porous walls. In one or
more embodiments, the carrier gas flow further comprises a vapor
phase of the aqueous vehicle. In one or more embodiments, the
carrier gas flow passes through the walls of the honeycomb filter
body while the agglomerates are being deposited onto the porous
walls of the honeycomb filter body by the atomizing gas.
[0007] In one or more embodiments, the carrier gas stream is
delivered to the chamber of the duct in an annular flow surrounding
the atomizing nozzle in a co-flow around droplets exiting the
nozzle. In one or more embodiments, substantially all of the
aqueous vehicle is evaporated from the droplets to form aerosolized
particulate-binder agglomerates comprised of the particles and the
binder material; aerosolized aggregates of particulate-binder
agglomerates are made; and the aggregates and individual, for
example, non-aggregated, agglomerates are deposited onto the porous
walls of the honeycomb filter body. In one or more embodiments, the
deposited aggregates and agglomerates are disposed on, or in, or
both on and in, the porous walls. In one or more embodiments,
during the depositing, the duct is in sealed fluid communication
with the honeycomb filter body.
[0008] Additional features and advantages will be set forth in the
detailed description, which follows, and in part will be readily
apparent to those skilled in the art from that description or
recognized by practicing the embodiments described herein,
comprising the detailed description, which follows, the claims, as
well as the appended drawings.
[0009] It is to be understood that both the foregoing general
description and the following detailed description describe various
embodiments and are intended to provide an overview or framework
for understanding the nature and character of the claimed subject
matter. The accompanying drawings are included to provide a further
understanding of the various embodiments, and are incorporated into
and constitute a part of this specification. The drawings
illustrate the various embodiments described herein, and together
with the description serve to explain the principles and operations
of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a flowchart depicting an exemplary embodiment of a
process of forming material according to embodiments disclosed
herein;
[0011] FIG. 2 schematically depicts an apparatus for depositing
inorganic material according to embodiments disclosed herein;
[0012] FIG. 3 schematically depicts an apparatus for depositing
inorganic material according to embodiments disclosed herein;
[0013] FIG. 4 schematically depicts an apparatus for depositing
inorganic material according to embodiments disclosed herein;
[0014] FIG. 5 schematically depicts an apparatus for depositing
inorganic material according to embodiments disclosed herein;
[0015] FIG. 6 schematically depicts an apparatus for depositing
inorganic material according to embodiments disclosed herein;
[0016] FIG. 7 schematically depicts an unplugged honeycomb
body;
[0017] FIG. 8 schematically depicts a wall-flow particulate filter
according to embodiments disclosed and described herein;
[0018] FIG. 9 is a cross-sectional longitudinal view of the
particulate filter shown in FIG. 8;
[0019] FIG. 10 schematically depicts a wall of a honeycomb body
with particulate loading;
[0020] FIG. 11 is a flowchart depicting an exemplary embodiment of
an aqueous-based process of forming material according to
embodiments disclosed herein;
[0021] FIG. 12 is a graph showing filtration efficiency before and
after curing for various samples prepared according to embodiments
disclosed herein;
[0022] FIG. 13 is a graph showing pressure drop before and after
curing for various samples prepared according to embodiments
disclosed herein;
[0023] FIG. 14A is an SEM photograph showing alumina agglomerates
generated from ethanol-based suspension (DK-2405-5%);
[0024] FIG. 14B is an SEM photograph showing alumina agglomerates
generated from an aqueous-based suspension (Allied-880-20%);
[0025] FIG. 14C is an SEM photograph showing alumina agglomerates
generated from an aqueous-based suspension (DK-880-20%);
[0026] FIG. 14D is an SEM photograph showing alumina agglomerates
generated from an aqueous-based suspension (DK-880-50%);
[0027] FIG. 14E is an SEM photograph showing alumina agglomerates
generated from an aqueous-based suspension (DK-9950-50%);
[0028] FIG. 14F is an SEM photograph showing alumina agglomerates
generated from an aqueous-based suspension (DK-2404-20%);
[0029] FIG. 15A is a graph showing an aqueous process and
ethanol-based process in terms of FE/dP performance for various
samples prepared according to embodiments disclosed herein;
[0030] FIG. 15B is a graph showing an aqueous process and
ethanol-based process in terms of FE versus deposit loading for
various samples prepared according to embodiments disclosed
herein;
[0031] FIG. 16A is an SEM photograph showing alumina agglomerates
generated from ethanol-based suspension;
[0032] FIG. 16B is an SEM photograph showing alumina agglomerates
generated from an aqueous-based suspension and deposited on a
porous ceramic wall;
[0033] FIG. 16C is a graph showing particle size of agglomerates
for agglomerates produced by an ethanol-based process and an
aqueous-based process;
[0034] FIG. 16D is a graph showing agglomerate accumulative size
distribution produced by an ethanol-based process and an
aqueous-based process;
[0035] FIG. 17A is a graph showing the impact of different thermal
treatment temperatures on the durability of filtration efficiency
with respect to water resistance for samples prepared according to
embodiments disclosed herein;
[0036] FIG. 17B is a graph showing the impact of different thermal
treatment temperatures on pressure drop with respect to water
resistance for samples prepared according to embodiments disclosed
herein;
[0037] FIG. 18A is a graph showing the impact of thermal treatment
on filtration efficiency at different heat treatment temperatures
on water resistance for samples prepared according to embodiments
disclosed herein;
[0038] FIG. 18B is a graph showing the impact of thermal treatment
on pressure drop at different for samples prepared according to
embodiments disclosed herein;
[0039] FIG. 19 is a graph showing filtration efficiency after
various durability tests including a high flow test, a cold
vibration test, a vehicle test, and a two stage water resistance
test;
[0040] FIG. 20 is an SEM photograph of a top view of an inlet
region of an inlet channel of a plugged honeycomb body prepared
according to embodiments disclosed herein;
[0041] FIG. 21 is an SEM photograph of a cutaway side view of an
inlet region of an inlet channel of a plugged honeycomb body
prepared according to embodiments disclosed herein;
[0042] FIG. 22 is an SEM photograph of a top view of a middle
region of an inlet channel of a plugged honeycomb body prepared
according to embodiments disclosed herein;
[0043] FIG. 23 is an SEM photograph of a cutaway side view of a
middle region of an inlet channel of a plugged honeycomb body
prepared according to embodiments disclosed herein;
[0044] FIG. 24 is an SEM photograph of a top view of an outlet
region of an inlet channel of a plugged honeycomb body prepared
according to embodiments disclosed herein;
[0045] FIG. 25 is an SEM photograph of a cutaway side view of an
outlet region of an inlet channel of a plugged honeycomb body
prepared according to embodiments disclosed herein;
[0046] FIG. 26 is an SEM photograph of a magnified cutaway side
view of an outlet region of an inlet channel of a plugged honeycomb
body prepared according to embodiments disclosed herein;
[0047] FIG. 27 is the SEM photograph of FIG. 26 with the colors
reversed;
[0048] FIG. 28A is a portion of the SEM photograph of FIG. 27 with
dashed lines surrounding an aggregate 1500;
[0049] FIG. 28B is a schematic representation of the agglomerates
1502 forming the aggregate 1500 region outlined by the dashed lines
in FIG. 28A;
DETAILED DESCRIPTION
[0050] Reference will now be made in detail to embodiments of
methods for forming honeycomb bodies comprising a porous honeycomb
body comprising inorganic deposits (or "filtration deposits") on,
or in, or both on and in, the porous ceramic walls of the honeycomb
body matrix, embodiments of which are illustrated in the
accompanying drawings. Filtration deposits comprise material that
was deposited into the honeycomb body, as well as compounds that
may be formed, for example, by heating, from one or materials that
were originally deposited. For example, a binder material may be
transformed by heating into an organic component which is
eventually burned off or volatilized, while an inorganic component
(such as silica) remains contained within the honeycomb filter
body. Whenever possible, the same reference numerals will be used
throughout the drawings to refer to the same or like parts.
[0051] Definitions
[0052] As used in this specification and the appended claims, the
singular forms "a", "an", and "the" encompass embodiments having
plural referents, unless the content clearly dictates otherwise. As
used in this specification and the appended claims, the term "or"
is generally employed in its sense including "and/or" unless the
content clearly dictates otherwise.
[0053] As used herein, "have", "having", "include", "including",
"comprise", "comprising" or the like are used in their open ended
sense, and generally mean "including, but not limited to".
[0054] A "honeycomb body," as referred to herein, comprises a
ceramic honeycomb structure of a matrix of intersecting walls that
form cells which define channels. The ceramic honeycomb structure
can be formed, extruded, or molded from a plasticized ceramic or
ceramic-forming batch mixture or paste. A honeycomb body may
comprise an outer peripheral wall, or skin, which was either
extruded along with the matrix of walls or applied after the
extrusion of the matrix. For example, a honeycomb body can be a
plugged ceramic honeycomb structure which forms a filter body
comprised of cordierite or other suitable ceramic material. A
plugged honeycomb body has one or more channels plugged at one, or
both ends of the body.
[0055] A honeycomb body disclosed herein comprises a ceramic
honeycomb structure comprising at least one wall carrying one or
more filtration material deposits which is configured to filter
particulate matter from a gas stream. The filtration material
deposits can be in discrete regions or in some portions or some
embodiments can form one or more layers of filtration material at a
given location on the wall of the honeycomb body. The filtration
material deposits according to some embodiments comprise inorganic
material, in some embodiments organic material, and in some
embodiments both inorganic material and organic material. For
example, a honeycomb body may, in one or more embodiments, be
formed from cordierite or other porous ceramic material and further
comprise inorganic material deposits disposed on or below wall
surfaces of the cordierite honeycomb structure.
[0056] In some embodiments, the filtration material comprises one
or more inorganic materials, such as one or more ceramic or
refractory materials.
[0057] As used herein, "green" or "green ceramic" are used
interchangeably and refer to an unsintered or unfired material,
unless otherwise specified.
[0058] Methods
[0059] Aspects of the disclosure pertain to methods of forming
porous bodies, such as porous ceramic honeycomb bodies, comprising
a material such as a filtration material such as a inorganic
material such as a ceramic or refractory material or even a porous
ceramic or refractory material. In specific embodiments, the
filtration material is an aerosol-deposited filtration material. In
some preferred embodiments, the filtration material comprises a
plurality of inorganic particle agglomerates, wherein the
agglomerates are comprised of inorganic, such as ceramic or
refractory, material. In some embodiments, the agglomerates are
porous, which may allow gas to flow through the agglomerates.
[0060] Aerosol deposition enables deposition of filtration material
onto the porous ceramic walls, which can be discrete regions as
small as a single agglomerate or larger such as a plurality of
agglomerates, and in some embodiments is in the form of a porous
layer of filtration material, on or in, or both on and in, at least
some surfaces of the walls of the ceramic honeycomb body. In
certain embodiments, an advantage of the aerosol deposition method
according to one or more embodiments is that ceramic honeycomb
bodies with enhanced filtration performance can be produced
economically, and/or more efficiently.
[0061] In certain embodiments, an aerosol deposition process
disclosed herein comprises: mixture preparation (e.g., inorganic
material, liquid vehicle, and binder), atomizing the mixture with
an atomizing gas with a nozzle to form agglomerates and/or
aggregates, comprised of the inorganic material, the aqueous
vehicle, and the binder if any, drying the agglomerates and/or
aggregates in the presence of a carrier gas or a gaseous carrier
stream, depositing the aggregates and/or agglomerates onto the
honeycomb bodies, and optionally curing the material. In some
embodiments, walls of the apparatus can be heated to assist in
drying the aggregates and/or agglomerates.
[0062] In various embodiments, the carrier gas can be heated in
addition to, or rather than, heating walls of the apparatus, such
that liquid vehicle can evaporate from the agglomerates faster,
which in turn allows agglomerates to be generated more efficiently.
A heated gaseous carrier stream carries the both atomized droplets
and the agglomerates formed through the apparatus and into the
honeycomb body. In some embodiments, atomizing gas is heated, alone
or in combination with heating the carrier gas. In some
embodiments, co-flowing the aerosolized droplets and/or
agglomerates and the gaseous carrier stream in substantially the
same direction into a chamber of an apparatus may help to reduce
material loss or overspray on walls of the apparatus. Furthermore,
a convergent section can be added to the apparatus before the
agglomerates enter the ceramic honeycomb body in order to help the
gas flow and particle tracking to be more uniform across the
apparatus. An inner diameter of the end of the convergent section
can be slightly larger than an outer diameter of the ceramic
honeycomb body outer diameter in order to reduce or eliminate
boundary effects of non-uniform particle deposition.
[0063] In an atomizing nozzle, or atomizer, high pressure and/or
high speed atomizing gas can be used to break-up the suspension,
which contains a mixture of liquid vehicle, binder, and solid
particles, into small liquid droplets, for example with average
droplet size of 4-6 micrometers. Heating of these liquid droplets
and quick evaporation of the aqueous vehicle creates porous
inorganic agglomerates before depositing on the honeycomb body
walls as a porous inorganic feature or structure. In some
embodiments more than one nozzle is utilized, even in some cases
under the same operating conditions, such that the liquid flow
through each nozzle is reduced and droplet sizes can be
smaller.
[0064] According to one or more embodiments, a process is disclosed
herein comprising forming an aerosol with a binder, which is
deposited on a honeycomb body to provide a high filtration
efficiency material, which may be present in discrete regions
and/or in some portions or some embodiments in an inorganic layer,
on the honeycomb body to provide a particulate filter. According to
one or more embodiments, the performance is >90% filtration
efficiency with a <10% pressure drop penalty compared to the
bare filter. According to one or more embodiments, as shown in FIG.
1, the process 400 comprises the steps of mixture preparation 405,
atomizing to form droplets 410, intermixing droplets and a gaseous
carrier stream 415; evaporating liquid vehicle to form agglomerates
420, depositing of material, e.g., agglomerates, on the walls of a
wall-flow filter 425, and optional post-treatment 430 to, for
example, bind the material on, or in, or both on and in, the porous
walls of the honeycomb body. Aerosol deposition methods form of
agglomerates comprising a binder can provide a high mechanical
integrity even without any high temperature curing steps (e.g.,
heating to temperatures in excess of 1000.degree. C.), and in some
embodiments even higher mechanical integrity after a curing step
such as a high temperature (e.g., heating to temperatures in excess
of 1000.degree. C.) curing step. In the process in FIG. 1, the
aerosol deposition forms inorganic material deposits, which in some
specific embodiments are porous material deposits. In some
embodiments, the material deposits are in the form of discrete
regions of filtration material. In some embodiments, at least some
portions of the material deposits may be in the form of a porous
inorganic layer.
[0065] In various embodiments, the process further includes
part-switching such that depositing of agglomerates onto the porous
walls of a plugged honeycomb body is conducted semi-continuously or
continuously, which reduces idle time of the equipment. In one or
more embodiments, the part-switching is timed so that deposition is
essentially continuous into and/or onto a plurality of ceramic
honeycomb bodies. Reference to continuous means that the operating
equipment is maintained under operating temperatures and pressures
and raw material supply flow, and that the flow of the gaseous
carrier stream and agglomerates into a part such as a wall-flow
filter is interrupted only to switch out a loaded part for an
unloaded part. Semi-continuous allows also for minor interruptions
to the raw material supply flow and adjustments to operating
temperatures and pressures. In one or more embodiments,
semi-continuous flow means that flow is interrupted for greater
than or equal to 0.1% to less than or equal to 5% of an operating
duration, including greater than or equal to 0.5%, greater than or
equal to 1%, greater than or equal to 1.5%, greater than or equal
to 2%, greater than or equal to 2.5%, and/or less than or equal to
4.5%, less than or equal to 4%, less than or equal to 3.5%, less
than or equal to 3%. In one or more embodiments, flow is continuous
for greater than or equal to 95% to less than or equal to 100% of
an operating duration, including greater than or equal to 96%,
greater than or equal to 97%, greater than or equal to 98%, greater
than or equal to 99%, greater than or equal to 99.5%, and/or less
than or equal to 99.9%, less than or equal to 99%, less than or
equal to 98%, less than or equal to 97%.
[0066] Mixture preparation 405. Commercially available inorganic
particles can be used as a raw material in a mixture in the
formation of an inorganic material for depositing. According to one
or more embodiments, the particles are selected from
Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2, CeO.sub.2, ZrO.sub.2, SiC,
MgO and combinations thereof. In one or more embodiments, the
mixture is a suspension. The particles may be supplied as a raw
material suspended in an aqueous vehicle to which a further liquid
vehicle is optionally added.
[0067] Thus, in some embodiments, the mixture is aqueous-based; for
example, an aqueous vehicle of the suspension may be water. In one
or more embodiments, the aqueous vehicle consists essentially of
water.
[0068] In some embodiments, the suspension comprises by weight:
5-20% particles and 80-95% liquid, and all values and subranges
therebetween. In an embodiment, the suspension comprises by weight:
11 percent.+-.1% alumina and 89 percent.+-.1% water.
[0069] In one or more embodiments, the particles have an average
primary particle size in a range of from about 10 nm to 4 about
micrometers, about 20 nm to about 3 micrometers or from about 50 nm
to about 2 micrometers, or from about 50 nm to about 900 nm or from
about 50 nm to about 600 nm. In specific embodiments, the average
primary particle size is in a range of from about 100 nm to about
200 nm, for example, 150 nm. The average primary particle size can
be determined as a calculated value from the BET surface area of
the aerosol particles, which in some embodiments is 10 m.sup.2/g
currently.
[0070] In one or more embodiments, the primary particles comprise a
ceramic particle, such as an oxide particle, for example
Al.sub.2O.sub.3, SiO.sub.2, MgO, CeO.sub.2, ZrO.sub.2, CaO,
TiO.sub.2, cordierite, mullite, SiC, aluminum titanate, and mixture
thereof.
[0071] The mixture is formed using a solvent which is added to
dilute the suspension if needed. Decreasing the solids content in
the mixture could reduce the aggregate size proportionally if the
droplet generated by atomizing has similar size. The solvent should
be miscible with suspension mentioned above, and be a solvent for
binder and other ingredients.
[0072] Binder is optionally added to reinforce the agglomerates and
to provide a stickiness or tackiness, and can comprise inorganic
binder, to provide mechanical integrity to deposited material. The
binder can provide binding strength between particles at elevated
temperature (>500.degree. C.). The starting material can be
organic. After exposure to high temperature in excess of about
150.degree. C., the organic starting material will decompose or
react with moisture and oxygen in the air, and the final deposited
material composition could comprise Al.sub.2O.sub.3, SiO.sub.2,
MgO, CeO.sub.2, ZrO.sub.2, CaO, TiO.sub.2, cordierite, mullite,
SiC, aluminum titanate, and mixture thereof. One example of a
suitable binder is Dowsil.TM. US-CF-2405 and Dowsil.TM. US-CF-2403,
both available from The Dow Chemical Company. An exemplary binder
content is in the range of greater than or equal to 5% by weight to
less than or equal to 25% by weight of the particle content. In an
embodiment, the binder content is 15 to 20% by weight .+-.1%.
[0073] Catalyst can be added to accelerate the cure reaction of
binder. An exemplary catalyst used to accelerate the cure reaction
of Dowsil.TM. US-CF-2405 is titanium butoxide. An exemplary
catalyst content is 1% by weight of the binder.
[0074] Stirring of the mixture or suspension during storage and/or
awaiting delivery to the nozzle may be conducted by using desired
stirring techniques. In one or more embodiments, stirring is
conducted by a mechanical stirrer. In an embodiment, the use of a
mechanical stirrer facilitates reduction and/or elimination of
potential contaminations from plastic-coated mixing rods, which are
in contact with a holding vessel, used in magnetic stirring
systems.
[0075] Atomizing to form droplets 410. The mixture is atomized into
fine droplets by high pressure gas through a nozzle. One example of
the nozzle is 1/4J-SS+SU11-SS from Spraying Systems Co. This setup
is comprised of a nozzle body along with fluid cap 2050 and air cap
67147. The atomizing gas can contribute to breaking up the
liquid-particulate-binder stream into the droplets.
[0076] In one or more embodiments, the nozzle herein is a nozzle
that utilizes internal mixing, for example, internal mixing nozzles
the part numbers are given above. In one or more embodiments, the
nozzle herein is a nozzle that utilizes external mixing, for
example, Spraying Systems external mix nozzle setup: 1/4J-SS+SU1A
which is made up of a 64 aircap and a 1650 fluid cap. Another
useful setup consists of a 64 aircap and a 1250 fluid cap. External
mix nozzles can be advantageous to allow for smaller particle sizes
with tighter particle size distribution which improves material
utilization and filtration efficiency. External mix nozzles tend to
clog less often as compared to internal mix nozzles. In one or more
embodiments, the nozzles herein are converging nozzles. As used
herein, converging nozzles refer to nozzles having fluid flow
passages whose cross-sectional areas decrease from inlet to outlet
thereby accelerating flow of the fluids. Converging nozzles may be
internally mixed or externally mixed.
[0077] In one or more embodiments, the liquid-particulate-binder
droplets are directed into the chamber by a nozzle.
[0078] In one or more embodiments, the liquid-particulate-binder
droplets are directed into the chamber by a plurality of nozzles.
In one or more embodiments, atomizing the plurality of
liquid-particulate-binder streams occurs with a plurality of
atomizing nozzles. The plurality of nozzles may include 2 or more
nozzles, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8
or more, 9 or more, 10 or more, and the like. The plurality of
nozzles may be evenly spaced within the chamber. In one or more
embodiments, each of the plurality of nozzles is angled toward a
center of the apparatus. The angle of the nozzles may be acute,
ranging from less than 90.degree. to greater than 10.degree.
relative to a side wall of the apparatus, and all values and
subranges therebetween, including 20.degree. to 45.degree..
[0079] The pressure of the atomizing gas may be in the range of 20
psi to 150 psi. The pressure of the liquid may be in the range of 1
to 100 psi. The average droplet size according to one or more
embodiments may be in the range of from 1 micrometer to 40
micrometers, including for example, in a range of greater than or
equal to 1 micrometer to less than or equal to 15 micrometers;
greater than or equal to 2 micrometers to less than or equal to 8
micrometers; greater than or equal to 4 micrometers to less than or
equal to 8 micrometers; and greater than or equal to 4 micrometers
to less than or equal to 6 micrometers; and all values and
subranges therebetween. The droplet size can be adjusted by
adjusting the surface tension of the mixture, viscosity of the
mixture, density of the mixture, gas flow rate, gas pressure,
liquid flow rate, liquid pressure, and nozzle design. In one or
more embodiments, the atomizing gas comprises nitrogen. In one or
more embodiments, the atomizing gas may consist essentially of an
inert gas. In one or more embodiments, the atomizing gas may is
predominantly one or more inert gases. In one or more embodiments,
the atomizing gas may is predominantly nitrogen gas. In one or more
embodiments, the atomizing gas may is predominantly air. In one or
more embodiments, the atomizing gas may consist essentially of
nitrogen or air. In one or more embodiments, the atomizing gas may
be dry. In one or more embodiments, the atomizing gas may comprise
essentially no liquid vehicle upon entry to the chamber.
[0080] In some embodiments, the suspension flow rate is in the
range of 10 to 25 g/minute, including all values and subranges
therebetween, including 18 g/min.
[0081] In some embodiments, the atomizing gas flow rate nitrogen
flow rate is in the range of 2 to 10 Nm.sup.3/hr, including all
values and subranges therebetween, including 5-6 Nm.sup.3/hr.
[0082] Suspension flow and corresponding agglomerate size may be
controlled by a pressure control system or a flow control system,
as appropriate to the apparatus. For a pressure control system, a
pressure controller is in communication with a delivery conduit
such as tubing or piping and a suspension of primary particles in a
liquid is introduced into the delivery conduit, which is then
flowed to the nozzle. For a flow control system, an injector pump
is provided, which delivers the suspension of primary particles in
a liquid to the nozzle. Atomizing gas is typically separately
supplied to the nozzle. In a preferred embodiment, a pump directs
the liquid-particulate-binder mixture to the atomizing nozzle at a
substantially constant flow rate. A constant flow rate can be
advantageous as opposed to maintaining a constant pressure because
the constant flow rate can help reduce variability in the particle
sizes which, in turn, improves material utilization.
[0083] In one or more embodiments, the suspension comprises an
inorganic material, an aqueous vehicle, and in some embodiments, a
binder, which is supplied to the nozzle as a
liquid-particulate-binder stream. That is, particles of an
inorganic material can be mixed with an aqueous vehicle and a
binder material to form a liquid-particulate-binder stream. The
liquid-particulate-binder stream is atomized with the atomizing gas
into liquid-particulate-binder droplets by the nozzle. In one or
more embodiments, the liquid-particulate-binder stream is mixed
with the atomizing gas. In one or more embodiments, the
liquid-particulate-binder stream is directed into the atomizing
nozzle thereby atomizing the particles into
liquid-particulate-binder droplets. The liquid-particulate-binder
droplets are comprised of the aqueous vehicle, the binder material,
and the particles.
[0084] In one or more embodiments, the liquid-particulate-binder
stream mixes with the atomizing gas via the atomizing nozzle. In
one or more embodiments, the liquid-particulate-binder stream
enters the atomizing nozzle. In one or more embodiments, the mixing
of the liquid-particulate-binder stream with the atomizing gas
occurs inside the atomizing nozzle. In one or more embodiments, the
mixing of the liquid-particulate-binder stream with the atomizing
gas occurs outside the atomizing nozzle.
[0085] Intermixing droplets and gaseous carrier stream 415. The
droplets are conveyed toward the honeycomb body by a gaseous
carrier stream. In one or more embodiments, the gaseous carrier
stream comprises a carrier gas and the atomizing gas. In one or
more embodiments, at least a portion of the carrier gas contacts
the atomizing nozzle. In one or more embodiments, substantially all
of the aqueous vehicle is evaporated from the droplets to form
agglomerates comprised of the particles and the binder
material.
[0086] In one or more embodiments, the gaseous carrier stream is
heated prior to being mixed with the droplets. In one or more
embodiments, the gaseous carrier stream is at a temperature in the
range of from greater than or equal to 50.degree. C. to less than
or equal to 500.degree. C., including all greater than or equal to
80.degree. C. to less than or equal to 300.degree. C., greater than
or equal to 50.degree. C. to less than or equal to 150.degree. C.,
and all values and subranges therebetween. Without being held to
theory, it is believed that an advantage of a higher temperature is
that the droplets evaporate faster and when the liquid is largely
evaporated, they are less likely to stick when they collide. In
certain embodiments, smaller agglomerates contribute to better
filtration material deposits formation. Furthermore, it is believed
that if droplets collide but contain only a small amount of liquid
(such as only internally), the droplets may not coalesce to a
spherical shape. In some embodiments, non-spherical agglomerates
may provide desirable filtration performance.
[0087] In one or more embodiments, the atomizing gas is heated to
form a heated atomizing gas, which is then flowed through and/or
contacted with the nozzle. In one or more embodiments, the heated
atomizing gas is at a temperature in the range of from greater than
or equal to 50.degree. C. to less than or equal to 500.degree. C.,
including all greater than or equal to 80.degree. C. to less than
or equal to 300.degree. C., greater than or equal to 50.degree. C.
to less than or equal to 150.degree. C., and all values and
subranges therebetween.
[0088] In one or more embodiments, both the carrier gas and the
atomizing gas are independently heated and contacted with the
nozzle. In one or more embodiments, the gaseous steam is heated,
but the atomizing gas and the nozzle are maintained at a low
temperature (approximately equal to room temperature, e.g.,
25-40.degree. C.). In one or more embodiments, the atomizing nozzle
is cooled during the atomizing. In one or more embodiments, a
temperature of the atomizing nozzle is maintained below a boiling
point of the aqueous vehicle.
[0089] The carrier gas is supplied to the apparatus to facilitate
drying and carrying the liquid-particulate-binder droplets and
resulting agglomerates through the apparatus and into the honeycomb
body. In one or more embodiments, the carrier gas is predominantly
an inert gas, such as nitrogen. In one or more embodiments, the
carrier gas consists essentially of an inert gas. In one or more
embodiments, the carrier gas is predominantly one or more inert
gases. In one or more embodiments, the carrier gas is predominantly
nitrogen gas. In one or more embodiments, the carrier gas is
predominantly air. In one or more embodiments, the carrier gas
consists essentially of nitrogen or air. In one or more
embodiments, the carrier gas is dry. In one or more embodiments,
the carrier gas comprises essentially no liquid vehicle upon entry
to the chamber. In one or more embodiments, the carrier gas
comprises less than 5 weight percent water vapor. In one or more
embodiments, the carrier gas is heated prior to being mixed with
the droplets. In one or more embodiments, the carrier gas is at a
temperature in the range of from greater than or equal to
50.degree. C. to less than or equal to 500.degree. C., including
all greater than or equal to 80.degree. C. to less than or equal to
300.degree. C., greater than or equal to 50.degree. C. to less than
or equal to 150.degree. C., and all values and subranges
therebetween.
[0090] In one or more embodiments, the atomizing gas and the
carrier gas are independently delivered to the apparatus at a
pressure of greater than or equal to 90 psi, including greater than
or equal to 95 psi, greater than or equal to 100 psi, greater than
or equal to 105 psi, greater than or equal to 100 psi, greater than
or equal to 115 psi, or greater than or equal to 120 psi. In one or
more embodiments, a booster provides the atomizing gas and the
carrier gas at a desired pressure.
[0091] The apparatus can comprise a diffusing area downstream of
the nozzle. At least some of the intermixing of the gaseous carrier
stream with the liquid-particulate-binder droplets occurs in the
diffusing area.
[0092] Upon intermixing of the gaseous carrier stream with the
liquid-particulate-binder droplets inside the chamber, a
gas-liquid-particulate-binder mixture is formed. The
gas-liquid-particulate-binder mixture is heated at the intermixing
zone. In one or more embodiments, droplets of liquid containing
particles and binder are present during the intermixing. In one or
more embodiments, the gaseous carrier stream is heated prior to
intermixing with the liquid-particulate-binder droplets.
[0093] In an embodiment, the carrier gas is delivered to the
chamber in an annular co-flow surrounding the nozzle. In an
embodiment, the carrier gas is delivered to a chamber of the duct
in an annular flow surrounding the nozzle in a co-flow around the
droplets at the end of the nozzle.
[0094] Evaporation to Form Agglomerates 420. To avoid liquid
capillary force impact which may form non-uniform material which
may result in high pressure drop penalty, the droplets are dried in
an evaporation section of the apparatus, forming dry solid
agglomerates, which may be referred to as secondary particles, or
"microparticles" which are made up of primary nanoparticles and
binder-type material. The aqueous vehicle, or solvent, is
evaporated and passes through the honeycomb body in a gaseous or
vapor phase so that liquid solvent residual or condensation is
minimized during material deposition. When the agglomerate is
carried into the honeycomb body by gas flow, the residual liquid in
the inorganic material should be less than 10 wt %. In some
embodiments, all liquid is evaporated as a result of the drying and
are converted into a gas or vapor phase. The liquid residual in
some embodiments includes solvent in the mixture such water
condensed from the gas phase. Binder is not considered as liquid
residual, even if some or all of the binder may be in liquid or
otherwise non-solid state before cure. In one or more embodiments,
a total volumetric flow through the chamber is greater than or
equal to 5 Nm.sup.3/hour and/or less than or equal to 200
Nm.sup.3/hour; including greater than or equal to 20 Nm.sup.3/hour
and/or less than or equal to 100 Nm.sup.3/hour; and all values and
subranges therebetween. Higher flow rates can deposit more material
than lower flow rates. Higher flow rates can be useful as larger
cross-sectional area filters are to be produced. Larger
cross-sectional area filters may have applications in filter
systems for building or outdoor filtration systems.
[0095] In one or more embodiments, substantially all of the aqueous
vehicle is evaporated from the droplets to form agglomerates of the
particles and the binder material, the agglomerates being
interspersed in the gaseous carrier stream. In one or more
embodiments, the apparatus has an evaporation section having an
axial length which is sufficient to allow evaporation of at least a
portion of the aqueous vehicle, including a substantial portion
and/or all of the aqueous vehicle from the agglomerates.
[0096] Regarding flow, in an embodiment, a path of the droplets and
a path of the gaseous carrier stream are substantially
perpendicular prior to entering the evaporation section. In one or
more embodiments, the carrier gas contacts the atomizing nozzle by
way of a first path, and wherein a path of the droplets and a
second path of the carrier gas are substantially perpendicular to
each other prior to entering the evaporation section of the
duct.
[0097] In another embodiment, a path of the droplets and a path of
the gaseous carrier stream are substantially parallel upon entering
the evaporation section. In one or more embodiments, a path of the
droplets and a path of the gaseous carrier stream are substantially
parallel to each other upon entering the evaporation section of the
duct. In one or more embodiments, a path of the droplets and a path
of the carrier gas are substantially parallel to each other upon
entering an evaporation section of the duct.
[0098] In an embodiment, the gaseous carrier stream exits the
chamber in a direction substantially parallel to gravity. In an
embodiment, the gaseous carrier stream exits the chamber in a
substantially downward direction. In an embodiment, the gaseous
carrier stream exits the chamber in a substantially upward
direction.
[0099] Deposition in honeycomb body 425. The secondary particles or
agglomerates of the primary particles are carried in gas flow, and
the secondary particles or agglomerates, and/or aggregates thereof,
are deposited on inlet wall surfaces of the honeycomb body when the
gas passes through the honeycomb body. In one or more embodiments,
the agglomerates and/or aggregates thereof are deposited onto the
porous walls of the plugged honeycomb body. The deposited
agglomerates may be disposed on, or in, or both on and in, the
porous walls. In one or more embodiments, the plugged honeycomb
body comprises inlet channels which are plugged at a distal end of
the honeycomb body, and outlet channels which are plugged at a
proximal end of the honeycomb body. In one or more embodiments, the
agglomerates and/or aggregates thereof are deposited on, or in, or
both on and in, the walls defining the inlet channels.
[0100] The flow can be driven by a fan, a blower or a vacuum pump.
Additional air can be drawn into the system to achieve a desired
flow rate. A desired flow rate is in the range of 5 to 200
m.sup.3/hr.
[0101] One exemplary honeycomb body is suitable for use as a
gasoline particular filter (GPF), and has the following
non-limiting characteristics: diameter of 4.055 inches (10.3 cm),
length of 5.47 inches (13.9 cm), cells per square inch (CPSI) of
200, wall thickness of 8 mils (203 micrometers), and average pore
size of 14 .mu.m.
[0102] In one or more embodiments, the average diameter of the
secondary particles or agglomerates is in a range of from 300 nm
micrometer to 10 micrometers, 300 nm to 8 micrometers, 300 nm
micrometer to 7 micrometers, 300 nm micrometer to 6 micrometers,
300 nm micrometer to 5 micrometers, 300 nm micrometer to 4
micrometers, or 300 nm micrometer to 3 micrometers. In specific
embodiments, the average diameter of the secondary particles or
agglomerates is in the range of 1.5 micrometers to 3 micrometers,
including about 2 micrometers. The average diameter of the
secondary particles or agglomerates can be measured by a scanning
electron microscope.
[0103] In one or more embodiments, the average diameter of the
secondary particles or agglomerates is in a range of from 300 nm to
10 micrometers, 300 nm to 8 micrometers, 300 nm to 7 micrometers,
300 nm to 6 micrometers, 300 nm to 5 micrometers, 300 nm to 4
micrometers, or 300 nm to 3 micrometers, including the range of 1.5
micrometers to 3 micrometers, and including about 2 micrometers,
and there is a ratio in the average diameter of the secondary
particles or agglomerates to the average diameter of the primary
particles of in range of from about 2:1 to about 67:1; about 2:1 to
about 9:1; about 2:1 to about 8:1; about 2:1 to about 7:1; about
2:1 to about 6:1; about 2:1 to about 5:1; about 3:1 to about 10:1;
about 3:1 to about 9:1; about 3:1 to about 8:1; about 3:1 to about
7:1; about 3:1 to about 6:1; about 3:1 to about 5:1; about 4:1 to
about 10:1; about 4:1 to about 9:1; about 4:1 to about 8:1; about
4:1 to about 7:1; about 4:1 to about 6:1; about 4:1 to about 5:1;
about 5:1 to about 10:1; about 5:1 to about 9:1; about 5:1 to about
8:1; about 5:1 to about 7:1; or about 5:1 to about 6:1, and
including about 10:1 to about 20:1.
[0104] In one or more embodiments, the depositing of the
agglomerates onto the porous walls further comprises passing the
gaseous carrier stream through the porous walls of the honeycomb
body, wherein the walls of the honeycomb body filter out at least
some of the agglomerates by trapping the filtered agglomerates on
or in the walls of the honeycomb body.
[0105] In one or more embodiments, the depositing of the
agglomerates onto the porous walls comprises filtering the
agglomerates from the gaseous carrier stream with the porous walls
of the plugged honeycomb body.
[0106] Post-Treatment 430. A post-treatment may optionally be used
to adhere the agglomerates to the honeycomb body, and/or to each
other. That is, in one or more embodiments, at least some of the
agglomerates adhere to the porous walls. In one or more
embodiments, the post-treatment comprises heating and/or curing the
binder when present according to one or more embodiments. In one or
more embodiments, the binder material causes the agglomerates to
adhere or stick to the walls of the honeycomb body. In one or more
embodiments, the binder material tackifies the agglomerates.
[0107] Depending on the binder composition, the curing conditions
are varied. According to some embodiments, a low temperature cure
reaction is utilized, for example, at a temperature of
.ltoreq.100.degree. C. In some embodiments, the curing can be
completed in the vehicle exhaust gas with a temperature
.ltoreq.950.degree. C. A calcination treatment is optional, which
can be performed at a temperature .ltoreq.650.degree. C. Exemplary
curing conditions are: a temperature range of from 40.degree. C. to
200.degree. C. for 10 minutes to 48 hours.
[0108] In one or more embodiments, the agglomerates and/or
aggregates thereof are heated after being deposited on the
honeycomb body. In one or more embodiments, the heating of the
agglomerates causes an organic component of the binder material to
be removed from the deposited agglomerates. In one or more
embodiments, the heating of the agglomerates causes an inorganic
component of the binder material to physically bond the
agglomerates to the walls of the honeycomb body. In one or more
embodiments, the heating of the agglomerates causes an inorganic
component of the binder to form a porous inorganic structure on the
porous walls of the honeycomb body. In one or more embodiments, the
heating of the deposited agglomerates burns off or volatilizes an
organic component of the binder material from the deposited
agglomerates.
[0109] In an aspect, a method for applying a surface treatment to a
plugged honeycomb body comprising porous walls comprises: mixing
particles of an inorganic material with an aqueous vehicle and a
binder material to form a liquid-particulate-binder stream; mixing
the liquid-particulate-binder stream with an atomizing gas,
directing the liquid-particulate-binder stream into an atomizing
nozzle thereby atomizing the particles into
liquid-particulate-binder droplets comprised of the aqueous
vehicle, he binder material, and the particles; conveying the
droplets toward the plugged honeycomb body by a gaseous carrier
stream, wherein the gaseous carrier stream comprises a carrier gas
and the atomizing gas; evaporating substantially all of the aqueous
vehicle from the droplets to form agglomerates comprised of the
particles and the binder material; depositing the agglomerates onto
the porous walls of the plugged honeycomb body; wherein the
deposited agglomerates are disposed on, or in, or both on and in,
the porous walls.
[0110] In another aspect, methods for forming a honeycomb body
comprise: supplying a suspension to a nozzle that is in fluid
communication with a duct comprising an evaporation section, the
suspension comprising an inorganic material, a binder material, and
an aqueous vehicle; supplying a carrier gas to the duct; contacting
the nozzle with the carrier gas; in the evaporation section,
evaporating at least a portion of the aqueous vehicle thereby
forming agglomerates of the inorganic material; depositing the
agglomerates on walls of the honeycomb body; and binding the
inorganic material to the honeycomb body to form a porous inorganic
material. The porous inorganic material may comprise primary
particles and agglomerates of these primary particles.
[0111] A further aspect is: a method for applying an inorganic
material to a plugged honeycomb body comprising porous walls, the
method comprising: supplying a suspension comprising particles of
the inorganic material and an aqueous vehicle to a nozzle that is
in fluid communication with a duct comprising an evaporation
section; atomizing the suspension with an atomizing gas to form
droplets; supplying a heated carrier gas; intermixing a gaseous
carrier stream including the heated carrier gas with the droplets
inside a chamber of the duct to form a
gas-liquid-particulate-binder mixture; evaporating at least a
portion of the aqueous vehicle from the droplets to form
agglomerates of the particles, the agglomerates being interspersed
in the gaseous carrier stream; passing the agglomerates and the
gaseous carrier stream into the plugged honeycomb body in fluid
communication with the duct such that the gaseous carrier stream
passes through porous walls of the plugged honeycomb body, and the
walls of the plugged honeycomb body trap the agglomerates, wherein
the agglomerates and/or aggregates thereof are deposited on or in
the walls of the honeycomb body.
[0112] Apparatus
[0113] Examples of apparatuses that may used for processes to
deposit inorganic material with binder on ceramic honeycomb bodies
are shown in FIGS. 2-6. Generally, apparatuses suitable for methods
herein include a duct that defines a chamber. The duct may have
several sections defining differing spaces and chambers. In one or
more embodiments, the droplets and the gaseous carrier stream are
conveyed through a duct having an outlet end proximate a plugged
honeycomb body. The duct may comprise a converging section for
engaging a proximal end of the honeycomb body. A converging section
is advantageous in that fluid convection flow is enhanced. The duct
may be in sealed fluid communication with the plugged honeycomb
body during the depositing step. In one or more embodiments, the
duct is adiabatic, or essentially adiabatic. In some embodiments,
the nozzle temperature is regulated to achieve favorable
atomization.
[0114] In some embodiments, a round cross-section chamber can
facilitate keeping agglomerates entrained in the gaseous carrier
stream. In various embodiments, a round cross-sectional duct
reduces and/or prevents recirculation regions or "dead-zones" that
can be the result of, for example, corners being present.
[0115] In one or more embodiments, an average temperature of walls
of the duct is less than a temperature of the gaseous carrier
stream. In one or more embodiments, an average temperature of walls
of the duct is greater than a temperature of the gaseous carrier
stream.
[0116] In the following, Apparatuses A-D (FIGS. 2-3 and 5-6)
schematically show co-flow where a path of the droplets and a path
of the gaseous carrier stream are substantially parallel upon
entering the evaporation section. Apparatus "T" (FIG. 4) shows the
carrier gas contacting an atomizing nozzle by way of a first path,
and wherein a path of the droplets and a second path of the carrier
gas are substantially perpendicular to each other prior to entering
the evaporation section of the duct.
[0117] FIG. 2 shows an apparatus 500, Apparatus "A", for forming
honeycomb bodies, the apparatus 500 comprising a duct 551, a
deposition zone 531, an exit zone 536, an exit conduit 540, and a
flow driver 545.
[0118] The duct 551 spans from a first end 550 to a second end 555,
defining a chamber of the duct comprising: a plenum space 503 at
the first end 550 and an evaporation chamber 523 downstream of the
plenum space 503. In one or more embodiments, the duct 551 is
essentially adiabatic. That is, the duct 551 may have no external
sources of heat. The evaporation chamber 523 is defined by an
evaporation section 553 of the duct 551, which in this embodiment;
comprises a first section of non-uniform diameter 527 and a second
section of substantially uniform diameter 529. The evaporation
section 553 comprises an inlet end 521 and an outlet end 525. The
first section of non-uniform diameter 527 has a diameter that
increases from the inlet end 521 toward the section of uniform
diameter 529, which creates a diverging space for the flow to
occupy.
[0119] A carrier gas is supplied to the duct 551 by a conduit 501,
which may have a heat source to create a heated carrier gas 505. An
atomizing gas 515 and a suspension 510 are separately supplied by
individual delivery conduits such as tubing or piping to a nozzle
520, which is at the inlet end 521 of the evaporation section 553
and is in fluid communication with the duct 551, specifically in
this embodiment with the evaporation chamber 523. The suspension
510 is atomized in the nozzle 520 with the atomizing gas 515. In
one or more embodiments, the suspension 510 comprises an inorganic
material, an aqueous vehicle, and a binder, as defined herein,
which as supplied to the nozzle is a liquid-particulate-binder
stream. The liquid-particulate-binder stream is atomized with the
atomizing gas 515 into liquid-particulate-binder droplets by the
nozzle 520.
[0120] In one or more embodiments, the heated carrier gas 505 flows
over the nozzle 520. The atomizing gas 515 can be heated to form a
heated atomizing gas. Temperature of the nozzle may be regulated as
desired.
[0121] Outlet flow from the nozzle 520 and flow of the heated
carrier gas 505 are both in a "Z" direction as shown in FIG. 2.
There may be a diffusing area 522 downstream of the nozzle where at
least some intermixing occurs. In this embodiment, the diffusing
area 522 is located in the evaporation chamber 523, but in other
embodiments, the diffusing area 522 may be located in the plenum
space 503 depending on the location of the nozzle.
[0122] The outlet flow of from the nozzle intermixes with the
heated carrier gas 505, thereby forming a
gas-liquid-particulate-binder mixture, which flows through the
chamber of the duct 551. Specifically, the
gas-liquid-particulate-binder mixture flows through the evaporation
chamber 523 of the evaporation section 553 and into the deposition
zone 531 at the outlet end 525 of the evaporation section 553. At
the intermixing, the gas-liquid-particulate-binder mixture is
heated inside the chamber by the heated carrier gas.
[0123] In this embodiment, the outlet flow of the nozzle and the
heated carrier gas enter the evaporation chamber 523 of the
evaporation section 553 from substantially the same direction. In
the evaporation chamber 523, substantially all of the aqueous
vehicle from the droplets is evaporated thereby forming
agglomerates of the particles and the binder material, the
agglomerates being interspersed in a gaseous carrier stream, which
is comprised of the carrier gas and the atomizing gas.
[0124] The deposition zone 531 in fluid communication with the duct
551 houses a plugged ceramic honeycomb body 530, for example, a
wall-flow particulate filter. The deposition zone 531 has an inner
diameter that is larger than the outer diameter of the ceramic
honeycomb body 530. To avoid leakage of the gases carrying the
ceramic powders, the ceramic honeycomb body 530 is sealed to the
inner diameter of deposition zone 531, a suitable seal is, for
example, an inflatable "inner tube". A pressure gauge, labelled as
"PG" measures the difference in the pressure upstream and
downstream from the particulate filter.
[0125] The gas-liquid-particulate-binder mixture flows into the
ceramic honeycomb body 530 thereby depositing the inorganic
material of the suspension on the ceramic honeycomb body.
Specifically, the agglomerates and the gaseous carrier stream pass
into the honeycomb body such that the gaseous carrier stream passes
through the porous walls of the honeycomb body, and the walls of
the honeycomb body trap the agglomerates, wherein the agglomerates
and/or aggregates thereof are deposited on or in the walls of the
honeycomb body. The inorganic material binds to the ceramic
honeycomb body upon post-treatment to the ceramic honeycomb body.
In an embodiment, binder material causes the agglomerates to adhere
or stick to the walls of the honeycomb body.
[0126] Downstream from the ceramic honeycomb body 530 is an exit
zone 536 defining an exit chamber 535. The flow driver 545 is
downstream from the ceramic honeycomb body 530, in fluid
communication with the deposition zone 531 and the exit zone 536 by
way of the exit conduit 540. Non-limiting examples of flow drivers
are: fan, blower, and vacuum pump. The aerosolized suspension is
dried and deposited on one or more walls of the particulate filter
as agglomerates of filtration material, which is present as
discrete regions of filtration material, or in some portions or
some embodiments as a layer, or both, wherein the agglomerates are
comprised of primary particles of inorganic material.
[0127] Flow through embodiments such as apparatus 500 is considered
in a downward direction, for example, substantially parallel to the
direction of gravity. In other embodiments, the apparatus is
configured such that flow is directed in a substantially upward or
vertical direction.
[0128] In FIG. 3, an apparatus 600, Apparatus "B", for forming
honeycomb bodies is shown comprising a duct 651, a deposition zone
631, an exit zone 636, an exit conduit 640, and a flow driver
645.
[0129] The duct 651 spans from a first end 650 to a second end 655,
defining a chamber of the duct comprising: a plenum space 603 at
the first end 650 and an evaporation chamber 623 downstream of the
plenum space 603. In one or more embodiments, the diameter of the
duct 651 defining the plenum space 603 can be equal to the diameter
of the evaporation section 653 of the duct 651 defining the
evaporation chamber 623. In one or more embodiments, the duct 651
is essentially adiabatic. That is, the duct 651 may have no
external sources of heat. The evaporation chamber 623, in this
embodiment, comprises a single section of substantially uniform
diameter 629. The evaporation section 653 comprises an inlet end
621 and an outlet end 625.
[0130] A carrier gas is supplied to the duct 651 by a conduit 601,
which may have a heat source to create a heated carrier gas 605. An
atomizing gas 615 and a suspension 610 are separately supplied by
individual delivery conduits such as tubing or piping to a nozzle
620, which is at the inlet end 621 of the evaporation section 653
and is in fluid communication with the duct 651, specifically in
this embodiment with the evaporation chamber 623. The suspension
610 is atomized in the nozzle 620 with the atomizing gas 615. In
one or more embodiments, the suspension 610 comprises an inorganic
material, an aqueous vehicle, and a binder, as defined herein,
which as supplied to the nozzle is a liquid-particulate-binder
stream. The liquid-particulate-binder stream is atomized with the
atomizing gas 615 into liquid-particulate-binder droplets by the
nozzle 620.
[0131] In one or more embodiments, the heated carrier gas 605 flows
over the nozzle 620. The atomizing gas 615 can be heated to form a
heated atomizing gas. The temperature of the nozzle may be
regulated as desired.
[0132] Outlet flow from the nozzle 620 and flow of the heated
carrier gas 605 are both in a "Z" direction as shown in FIG. 3. In
specific embodiments, a diffusing area 622 is downstream of the
nozzle where at least some intermixing occurs. In this embodiment,
the diffusing area 622 is located in the evaporation chamber 623,
but in other embodiments the diffusing area may be located in the
plenum space 603 depending on the location of the nozzle.
[0133] The outlet flow from the nozzle intermixes with the heated
carrier gas 605, thereby forming a gas-liquid-particulate-binder
mixture, which flows through the chamber of the duct 651.
Specifically, the gas-liquid-particulate-binder mixture flows
through the evaporation chamber 623 of the evaporation section 653
and into the deposition zone 631 at the outlet end 625 of the
evaporation section 653. At the intermixing, the
gas-liquid-particulate-binder mixture is heated inside the chamber
by the heated carrier gas.
[0134] In this embodiment, the outlet flow of the nozzle and the
carrier gas enter the evaporation chamber 623 of the evaporation
section 653 from substantially the same direction. In the
evaporation chamber 623, substantially all of the aqueous vehicle
from the droplets is evaporated thereby forming agglomerates of the
particles and the binder material, the agglomerates being
interspersed in a gaseous carrier stream, which is comprised of the
carrier gas and the atomizing gas.
[0135] The deposition zone 631 in fluid communication with the duct
651 houses a plugged ceramic honeycomb body 630, for example, a
wall-flow particulate filter. The deposition zone 631 has an inner
diameter that is larger than the outer diameter of the ceramic
honeycomb body 630. To avoid leakage of the gases carrying the
ceramic powders, the ceramic honeycomb body 630 is sealed to the
inner diameter of the deposition zone 631, a suitable seal is, for
example, an inflatable "inner tube". A pressure gauge, labelled as
"PG" measures the difference in the pressure upstream and
downstream from the particulate filter. The
gas-liquid-particulate-binder mixture flows into the ceramic
honeycomb body 630 thereby depositing the inorganic material of the
suspension on the ceramic honeycomb body. Specifically, the
agglomerates and the gaseous carrier stream pass into the honeycomb
body such that the gaseous carrier stream passes through the porous
walls of the honeycomb body, and the walls of the honeycomb body
trap the agglomerates, wherein the agglomerates are deposited on or
in the walls of the honeycomb body. The inorganic material binds to
the ceramic honeycomb body upon post-treatment to the ceramic
honeycomb body. In an embodiment, binder material causes the
agglomerates to adhere or stick to the walls of the honeycomb
body.
[0136] Downstream from the ceramic honeycomb body 630 is an exit
zone 636 defining an exit chamber 635. The flow driver 645 is
downstream from the ceramic honeycomb body 630, in fluid
communication with the deposition zone 631 and the exit zone 636 by
way of the exit conduit 640. Non-limiting examples of flow drivers
are: fan, blower, and vacuum pump. The aerosolized suspension is
dried and deposited on one or more walls of the particulate filter
as agglomerates of filtration material, which is present as
discrete regions of filtration material, or in some portions or
some embodiments as a layer, or both, wherein the agglomerates are
comprised of primary particles of inorganic material.
[0137] Flow through embodiments such as apparatus 600 is considered
in a downward direction, for example, substantially parallel to the
direction of gravity. In other embodiments, the apparatus is
configured such that flow is directed in a substantially upward or
vertical direction.
[0138] In FIG. 4, an apparatus 900, Apparatus "T", for forming
honeycomb bodies is shown comprising a duct 951, a deposition zone
931, an exit zone 936, an exit conduit 940, and a flow driver
945.
[0139] The duct 951 spans from a first end 950 to a second end 955
including a right cylindrical section 928, all defining a chamber
of the duct comprising: a first plenum space 903 at the first end
950, an evaporation chamber 923 downstream of the plenum space 603,
and a second plenum space 929 defined by the right cylindrical
section 928. In one or more embodiments, the diameter of the duct
951 defining the plenum space 903 can be equal to the diameter of a
first inlet location 921 of an evaporation section 953 of the duct
951. In one or more embodiments, the duct 951 is essentially
adiabatic. That is, the duct 951 may have no external sources of
heat. The evaporation chamber 923 is defined by the evaporation
section 953 of the duct 951. The evaporation section 953 comprises
the first inlet location 921 from the first plenum space 903, a
second inlet location 924 from the second plenum space 929, and an
outlet end 925. In some embodiments, some evaporation may occur in
at least a portion of second plenum space 929 defined by the right
cylindrical section 928.
[0140] A carrier gas is supplied in a first path to the duct 951 by
a conduit 901, which may have a heat source 906a to create a
primary heated carrier gas 905a that enters the first plenum space
903, and optionally another secondary heated carrier gas 905b that
enters the second plenum space 929 by a second path. An atomizing
gas 915 and a suspension 910 are separately supplied by individual
delivery conduits such as tubing or piping to a nozzle 920, which
is in the second plenum space 929 of the right cylindrical section
928 and is in fluid communication with the evaporation chamber 923
of the evaporation section 953. The suspension 910 is atomized in
the nozzle 920 with the atomizing gas 915. In one or more
embodiments, the suspension 910 comprises an inorganic material, an
aqueous vehicle, and a binder, as defined herein, which as supplied
to the nozzle is a liquid-particulate-binder stream. The
liquid-particulate-binder stream is atomized with the atomizing gas
915 into liquid-particulate-binder droplets by the nozzle 920.
[0141] In one or more embodiments, the secondary heated carrier gas
905b flows over the nozzle 920 Temperature of the nozzle may be
regulated as desired.
[0142] Outlet flow from the nozzle 920 and, when present, flow of
the secondary heated carrier gas 905b are both is in an "X"
direction as shown in FIG. 4. Flow of the primary heated carrier
gas 905a is in a "Z" direction as shown in FIG. 4. There may be a
diffusing area 922 downstream of the nozzle where at least some
intermixing occurs. In this embodiment, the diffusing area 922 is
located at least partially in the second plenum space 929, but in
other embodiments, the diffusing area 922 may be located in
evaporation chamber 923 depending on the location of the
nozzle.
[0143] The outlet flow of from the nozzle intermixes with the
heated carrier gases 905a and 905b, thereby forming a
gas-liquid-particulate-binder mixture, which flows through the
chamber of the duct 951. Specifically, the
gas-liquid-particulate-binder mixture flows through the evaporation
chamber 923 of the evaporation section 953 and into the deposition
zone 931 at the outlet end 925 of the evaporation section 953. At
the intermixing, the gas-liquid-particulate-binder mixture is
heated inside the chamber by the heated carrier gas.
[0144] In this embodiment, the outlet flow of the nozzle and the
primary carrier gas 905a enter the evaporation chamber 923 of the
evaporation section 953 from substantially perpendicular
directions. In the evaporation chamber 923, substantially all of
the aqueous vehicle from the droplets is evaporated thereby forming
agglomerates of the particles and the binder material, the
agglomerates being interspersed in a gaseous carrier stream, which
is comprised of the carrier gases and the atomizing gas.
[0145] The deposition zone 931 in fluid communication with the duct
951 houses a plugged ceramic honeycomb body 930, for example, a
wall-flow particulate filter. The deposition zone 931 has an inner
diameter that is larger than the outer diameter of the ceramic
honeycomb body 930. To avoid leakage of the gases carrying the
ceramic powders, the ceramic honeycomb body 930 is sealed to the
inner diameter of the deposition zone 931, a suitable seal is, for
example, an inflatable "inner tube". A pressure gauge, labelled as
"PG" measures the difference in the pressure upstream and
downstream from the particulate filter. The
gas-liquid-particulate-binder mixture flows into the ceramic
honeycomb body 930 thereby depositing the inorganic material of the
suspension on the ceramic honeycomb body. Specifically, the
agglomerates and the gaseous carrier stream pass into the honeycomb
body such that the gaseous carrier stream passes through the porous
walls of the honeycomb body, and the walls of the honeycomb body
trap the agglomerates, wherein the agglomerates are deposited on or
in the walls of the honeycomb body. The inorganic material binds to
the ceramic honeycomb body upon post-treatment to the ceramic
honeycomb body. In an embodiment, binder material causes the
agglomerates to adhere or stick to the walls of the honeycomb
body.
[0146] Downstream from the ceramic honeycomb body 930 is an exit
zone 936 defining an exit chamber 935. The flow driver 945 is
downstream from the ceramic honeycomb body 930, in fluid
communication with the deposition zone 931 and the exit zone 936 by
way of the exit conduit 940. Non-limiting examples of flow drivers
are: fan, blower, and vacuum pump. The aerosolized suspension is
dried and deposited on one or more walls of the particulate filter
as agglomerates of filtration material, which is present as
discrete regions of filtration material, or in some portions or
some embodiments as a layer, or both, wherein the agglomerates are
comprised of primary particles of inorganic material.
[0147] Overall flow through embodiments such as apparatus 900 is
considered in a downward direction, for example, substantially
parallel to the direction of gravity. In other embodiments, the
apparatus is configured such that flow is directed in a
substantially upward or vertical direction.
[0148] FIG. 5 shows an apparatus 700, Apparatus "C", for forming
honeycomb bodies, the apparatus 700 comprising a duct 751, a
deposition zone 731, an exit zone 736, an exit conduit 740, and a
flow driver 745.
[0149] The duct 751 spans from a first end 750 to a second end 755,
defining a chamber of the duct comprising: a plenum space 703 at
the first end 750 and an evaporation chamber 723 downstream of the
plenum space 703. In one or more embodiments, the diameter of the
duct 751 defining the plenum space 703 can be equal to the diameter
of an evaporation section 753 at an inlet end 721. In one or more
embodiments, the duct 751 is essentially adiabatic. That is, the
duct 751 may have no external sources of heat. The evaporation
chamber 723 is defined by the evaporation section 753 of the duct
751, which in this embodiment, comprises a first section of
non-uniform diameter 727 and a second section of substantially
uniform diameter 729. The evaporation section 753 comprises the
inlet end 721 and an outlet end 725. The first section of
non-uniform diameter 727 has a diameter that decreases from the
outlet end 725 toward the section of uniform diameter 729, which
creates a converging space for the flow as it enters the deposition
zone 731.
[0150] A carrier gas is supplied to the duct 751 by a conduit 701,
which may have a heat source to create a heated carrier gas 705. An
atomizing gas 715 and a suspension 710 are separately supplied by
individual delivery conduits such as tubing or piping to a nozzle
720, which is at the inlet end 721 of the evaporation section 753
and is in fluid communication with the duct 751, specifically in
this embodiment with the evaporation chamber 723. The suspension
710 is atomized in the nozzle 720 with the atomizing gas 715. In
one or more embodiments, the suspension 710 comprises an inorganic
material, an aqueous vehicle, and a binder, as defined herein,
which as supplied to the nozzle is a liquid-particulate-binder
stream. The liquid-particulate-binder stream is atomized with the
atomizing gas 715 into liquid-particulate-binder droplets by the
nozzle 720.
[0151] In one or more embodiments, the heated carrier gas 705 flows
over the nozzle 720. The atomizing gas 715 can be heated to form a
heated atomizing gas. Temperature of the nozzle may be regulated as
desired.
[0152] Outlet flow from the nozzle 720 and flow of the heated
carrier gas 705 are both in a "Z" direction as shown in FIG. 5.
There may be a diffusing area 722 downstream of the nozzle where at
least some intermixing occurs. In this embodiment, the diffusing
area 722 is located in the evaporation chamber 723, but in other
embodiments, the diffusing area may be located in the plenum space
703 depending on the location of the nozzle.
[0153] The outlet flow of from the nozzle intermixes with the
heated carrier gas 705, thereby forming a
gas-liquid-particulate-binder mixture, which flows through the
chamber of the duct 751. Specifically, the
gas-liquid-particulate-binder mixture flows through the evaporation
chamber 723 of the evaporation section 753 and into the deposition
zone 731 at the outlet end 725 of the evaporation section 753. At
the intermixing, the gas-liquid-particulate-binder mixture is
heated inside the chamber by the heated carrier gas.
[0154] In this embodiment, the outlet flow of the nozzle and the
heated carrier gas enter the evaporation chamber 723 of the
evaporation section 753 from substantially the same direction. In
the evaporation chamber 723, substantially all of the aqueous
vehicle from the droplets is evaporated thereby forming
agglomerates of the particles and the binder material, the
agglomerates being interspersed in a gaseous carrier stream, which
is comprised of the carrier gas and the atomizing gas.
[0155] The deposition zone 731 in fluid communication with the duct
751 houses a plugged ceramic honeycomb body 730, for example, a
wall-flow particulate filter. The deposition zone 731 has an inner
diameter that is larger than the outer diameter of the ceramic
honeycomb body 730. To avoid leakage of the gases carrying the
ceramic powders, the ceramic honeycomb body 730 is sealed to the
inner diameter of the deposition zone 731, a suitable seal is, for
example, an inflatable "inner tube". A pressure gauge, labelled as
"PG" measures the difference in the pressure upstream and
downstream from the particulate filter. The
gas-liquid-particulate-binder mixture flows into the ceramic
honeycomb body 730 thereby depositing the inorganic material of the
suspension on the ceramic honeycomb body. Specifically, the
agglomerates and the gaseous carrier stream pass into the honeycomb
body such that the gaseous carrier stream passes through the porous
walls of the honeycomb body, and the walls of the honeycomb body
trap the agglomerates, wherein the agglomerates and/or aggregates
thereof are deposited on or in the walls of the honeycomb body. The
inorganic material binds to the ceramic honeycomb body upon
post-treatment to the ceramic honeycomb body. In an embodiment,
binder material causes the agglomerates to adhere or stick to the
walls of the honeycomb body.
[0156] Downstream from the ceramic honeycomb body 730 is an exit
zone 736 defining an exit chamber 735. The flow driver 745 is
downstream from the ceramic honeycomb body 730, in fluid
communication with the deposition zone 731 and the exit zone 736 by
way of the exit conduit 740. Non-limiting examples of flow drivers
are: fan, blower, and vacuum pump. The droplets of the atomized
suspension are aerosolized and dried and deposited on one or more
walls of the particulate filter as agglomerates of filtration
material, which is present as discrete regions of filtration
material, or in some portions or some embodiments as a layer, or
both, wherein the agglomerates are comprised of primary particles
of inorganic material.
[0157] Flow through embodiments such as apparatus 700 is considered
in a downward direction, for example, substantially parallel to the
direction of gravity. In other embodiments, the apparatus is
configured such that flow is directed in a substantially upward or
vertical direction.
[0158] FIG. 6 shows an apparatus 800, Apparatus "D", for forming
honeycomb bodies, the apparatus 800 comprising a duct 851, a
deposition zone 831, an exit zone 836, an exit conduit 840, and a
flow driver 845.
[0159] The duct 851 spans from a first end 850 to a second end 855,
defining a chamber of the duct comprising: a plenum space 803 at
the first end 850 and an evaporation chamber 823 downstream of the
plenum space 803. In one or more embodiments, the duct 851 is
essentially adiabatic. That is, the duct 851 may have no external
sources of heat. The evaporation chamber 823 is defined by an
evaporation section 853 of the duct 851, which in this embodiment,
comprises a first section of non-uniform diameter 827 and a second
section of substantially uniform diameter 829. The evaporation
section 853 comprises an inlet end 821 and an outlet end 825. The
first section of non-uniform diameter 827 has a diameter that
decreases from the outlet end 825 toward the section of uniform
diameter 829, which creates a converging space for the flow as it
enters the deposition zone 831. In some embodiments, the
evaporation section 853 is configured to have a single section of
substantially uniform diameter analogous to Apparatus "B".
Alternatively, the evaporation section 853 has a section of
non-uniform diameter that increases from the inlet end 821 toward a
section of uniform diameter analogous to Apparatus "A."
[0160] A carrier gas is supplied to the duct 851 by a conduit 801,
which may have a heat source to create a heated carrier gas 805. An
atomizing gas 815 and a suspension 810 are separately supplied by
individual delivery conduits such as tubing or piping to a
plurality of nozzles 820a, 820b, and 820c, which are in fluid
communication with the plenum space 803. Each nozzle has an inflow
of the atomizing gas e.g., 815a supplies the nozzle 820a and 815b
supplies the nozzle 820b. Each nozzle has an inflow of the
suspension e.g., 810a supplies the nozzle 820a and 810b supplies
the nozzle 820b. Optionally, each nozzle has a supply of the heated
carrier gas, e.g., 802a supplies the nozzle 820a and 802b supplies
the nozzle 820b. While the embodiment of FIG. 6 shows three
nozzles, in other embodiments, a plurality of nozzles of any number
is be used. The suspension 810 is atomized in the nozzle 820 with
the atomizing gas 815. In one or more embodiments, the suspension
810 comprises an inorganic material, an aqueous vehicle, and a
binder, as defined herein, which as supplied to the nozzle is a
liquid-particulate-binder stream. The liquid-particulate-binder
stream is atomized with the atomizing gas 815 into
liquid-particulate-binder droplets by the nozzle 820.
[0161] In one or more embodiments, the heated carrier gas 805 and
optionally 802a and 802b flow over the nozzles. The atomizing gas
815a and 815b can be heated to form a heated atomizing gas.
Temperatures of the nozzles may be regulated, individually or
collectively, as desired.
[0162] Flow of the heated carrier gas 805 is in a "Z" direction as
shown in FIG. 6. While outlet flow from the nozzles 820a, 820b, and
820c may be angled towards a center of the duct 851, upon
intermixing with the heated carrier gas 805, the outlet flow of the
nozzles will generally be in the "Z" direction. There may be a
diffusing area 822 downstream of the nozzles where at least some
intermixing occurs. In this embodiment, the diffusing area 822 is
located in the plenum space 803, but in other embodiments, the
diffusing area may be located in the evaporation chamber 823
depending on the location of the nozzles.
[0163] The outlet flow of from the nozzles intermixes with the
heated carrier gas 805, thereby forming a
gas-liquid-particulate-binder mixture, which flows through the
chamber of the duct 851. Specifically, the
gas-liquid-particulate-binder mixture flows through the evaporation
chamber 823 of the evaporation section 853 and into the deposition
zone 831 at the outlet end 825 of the evaporation section 853. At
the intermixing, the gas-liquid-particulate-binder mixture is
heated inside the chamber by the heated carrier gas.
[0164] In this embodiment, the outlet flow of the nozzles and the
heated gas enter the evaporation chamber 823 of the evaporation
section 853 from substantially the same direction. In the
evaporation chamber 823, substantially all of the aqueous vehicle
from the droplets is evaporated thereby forming agglomerates of the
particles and the binder material, the agglomerates being
interspersed in a gaseous carrier stream, which is comprised of the
carrier gas and the atomizing gas.
[0165] The deposition zone 831 in fluid communication with the duct
851 houses a plugged ceramic honeycomb body 830, for example, a
wall-flow particulate filter or "wall-flow filter." The deposition
zone 831 has an inner diameter that is larger than the outer
diameter of the ceramic honeycomb body 830. To avoid leakage of the
gases carrying the ceramic powders, the ceramic honeycomb body 830
is sealed to the inner diameter of deposition zone 831, a suitable
seal is, for example, an inflatable "inner tube". A pressure gauge,
labelled as "PG" measures the difference in the pressure upstream
and downstream from the particulate filter. The
gas-liquid-particulate-binder mixture flows into the ceramic
honeycomb body 830 thereby depositing the inorganic material of the
suspension on the ceramic honeycomb body. Specifically, the
agglomerates and the gaseous carrier stream pass into the honeycomb
body such that the gaseous carrier stream passes through the porous
walls of the honeycomb body, and the walls of the honeycomb body
trap the agglomerates, wherein the agglomerates and/or aggregates
thereof are deposited on or in the walls of the honeycomb body. The
inorganic material binds to the ceramic honeycomb body upon
post-treatment to the ceramic honeycomb body. In an embodiment,
binder material causes the agglomerates to adhere or stick to the
walls of the honeycomb body.
[0166] Downstream from the ceramic honeycomb body 830 is an exit
zone 836 defining an exit chamber 835. The flow driver 845 is
downstream from the ceramic honeycomb body 830, in fluid
communication with the deposition zone 831 and the exit zone 836 by
way of the exit conduit 840. Non-limiting examples of flow drivers
are: fan, blower, and vacuum pump. The droplets of the atomized
suspension are aerosolized and dried and deposited on one or more
walls of the particulate filter as agglomerates of filtration
material, which is present as discrete regions of filtration
material, or in some portions or some embodiments as a layer, or
both, wherein the agglomerates are comprised of primary particles
of inorganic material.
[0167] Flow through embodiments such as apparatus 800 is considered
in a downward direction, for example, substantially parallel to the
direction of gravity. In other embodiments, the apparatus may be
configured such that flow is directed in a substantially upward or
vertical direction.
[0168] General Overview of Honeycomb Bodies
[0169] The ceramic articles herein comprise honeycomb bodies
comprised of a porous ceramic honeycomb structure of porous walls
having wall surfaces defining a plurality of inner channels.
[0170] In some embodiments, the porous ceramic walls comprise a
material such as a filtration material which may comprise in some
portions or some embodiments a porous inorganic layer disposed on
one or more surfaces of the walls. In some embodiments, the
filtration material comprises one or more inorganic materials, such
as one or more ceramic or refractory materials. In some
embodiments, the filtration material is disposed on the walls to
provide enhanced filtration efficiency, both locally through and at
the wall and globally through the honeycomb body, at least in the
initial use of the honeycomb body as a filter following a clean
state, or regenerated state, of the honeycomb body, for example
such as before a substantial accumulation of ash and/or soot occurs
inside the honeycomb body after extended use of the honeycomb body
as a filter.
[0171] In one aspect, the filtration material is present in some
portions or some embodiments as a layer disposed on the surface of
one or more of the walls of the honeycomb structure. The layer in
some embodiments is porous to allow the gas flow through the wall.
In some embodiments, the layer is present as a continuous coating
over at least part of the, or over the entire, surface of the one
or more walls. In some embodiments of this aspect, the filtration
material is flame-deposited filtration material.
[0172] In another aspect, the filtration material is present as a
plurality of discrete regions of filtration material disposed on
the surface of one or more of the walls of the honeycomb structure.
The filtration material may partially block a portion of some of
the pores of the porous walls, while still allowing gas flow
through the wall. In some embodiments of this aspect, the
filtration material is aerosol-deposited filtration material. In
some preferred embodiments, the filtration material comprises a
plurality of inorganic particle agglomerates, wherein the
agglomerates are comprised of inorganic or ceramic or refractory
material. In some embodiments, the agglomerates are porous, thereby
allowing gas to flow through the agglomerates.
[0173] In some embodiments, a honeycomb body comprises a porous
ceramic honeycomb body comprising a first end, a second end, and a
plurality of walls having wall surfaces defining a plurality of
inner channels. A deposited material such as a filtration material,
which may be in some portions or some embodiments a porous
inorganic layer, is disposed on one or more of the wall surfaces of
the honeycomb body. The deposited material such as a filtration
material, which may be a porous inorganic layer has a porosity as
measured by mercury intrusion porosimetry, SEM, or X-ray tomography
in a range of from about 20% to about 95%, or from about 25% to
about 95%, or from about 30% to about 95%, or from about 40% to
about 95%, or from about 45% to about 95%, or from about 50% to
about 95%, or from about 55% to about 95%, or from about 60% to
about 95%, or from about 65% to about 95%, or from about 70% to
about 95%, or from about 75% to about 95%, or from about 80% to
about 95%, or from about 85% to about 95%, from about 30% to about
95%, or from about 40% to about 95%, or from about 45% to about
95%, or from about 50% to about 95%, or from about 55% to about
95%, or from about 60% to about 95%, or from about 65% to about
95%, or from about 70% to about 95%, or from about 75% to about
95%, or from about 80% to about 95%, or from about 85% to about
95%, or from about 20% to about 90%, or from about 25% to about
90%, or from about 30% to about 90%, or from about 40% to about
90%, or from about 45% to about 90%, or from about 50% to about
90%, or from about 55% to about 90%, or from about 60% to about
90%, or from about 65% to about 90%, or from about 70% to about
90%, or from about 75% to about 90%, or from about 80% to about
90%, or from about 85% to about 90%, or from about 20% to about
85%, or from about 25% to about 85%, or from about 30% to about
85%, or from about 40% to about 85%, or from about 45% to about
85%, or from about 50% to about 85%, or from about 55% to about
85%, or from about 60% to about 85%, or from about 65% to about
85%, or from about 70% to about 85%, or from about 75% to about
85%, or from about 80% to about 85%, or from about 20% to about
80%, or from about 25% to about 80%, or from about 30% to about
80%, or from about 40% to about 80%, or from about 45% to about
80%, or from about 50% to about 80%, or from about 55% to about
80%, or from about 60% to about 80%, or from about 65% to about
80%, or from about 70% to about 80%, or from about 75% to about
80%, and the deposited material such as a filtration material,
which may be a porous inorganic layer that has an average thickness
of greater than or equal to 0.5 .mu.m and less than or equal to 50
.mu.m, or greater than or equal to 0.5 .mu.m and less than or equal
to 45 .mu.m, greater than or equal to 0.5 .mu.m and less than or
equal to 40 .mu.m, or greater than or equal to 0.5 .mu.m and less
than or equal to 35 .mu.m, or greater than or equal to 0.5 .mu.m
and less than or equal to 30 .mu.m, greater than or equal to 0.5
.mu.m and less than or equal to 25 .mu.m, or greater than or equal
to 0.5 .mu.m and less than or equal to 20 .mu.m, or greater than or
equal to 0.5 .mu.m and less than or equal to 15 .mu.m, greater than
or equal to 0.5 .mu.m and less than or equal to 10 .mu.m. Various
embodiments of honeycomb bodies and methods for forming such
honeycomb bodies will be described herein with specific reference
to the appended drawings.
[0174] The material in some embodiments comprises a filtration
material, and in some embodiments comprises an inorganic filtration
material. According to one or more embodiments, the inorganic
filtration material provided herein comprises discrete regions
and/or a discontinuous layer formed from the inlet end to the
outlet end comprising discrete and disconnected patches of material
or filtration material and binder comprised of primary particles in
secondary particles or agglomerates that are substantially
spherical. In one or more embodiments, the primary particles are
non-spherical. In one or more embodiments, "substantially
spherical" refers to agglomerate having circularity in cross
section in a range of from about 0.8 to about 1 or from about 0.9
to about 1, with 1 representing a perfect circle. In one or more
embodiments, 75% of the primary particles deposited on the
honeycomb body have a circularity of less than 0.8. In one or more
embodiments, the secondary particles or agglomerates deposited on
the honeycomb body have an average circularity greater than 0.9,
greater than 0.95, greater than 0.96, greater than 0.97, greater
than 0.98, or greater than 0.99.
[0175] Circularity can be measured using a scanning electron
microscope (SEM). The term "circularity of the cross-section (or
simply circularity)" is a value expressed using the equation shown
below. A circle having a circularity of 1 is a perfect circle.
Circularity=(4.pi..times.cross-sectional area)/(length of
circumference of the cross-section).
[0176] A honeycomb body of one or more embodiments may comprise a
honeycomb structure and deposited material such as a filtration
material disposed on one or more walls of the honeycomb structure.
In some embodiments, the deposited material such as a filtration
material is applied to surfaces of walls present within honeycomb
structure, where the walls have surfaces that define a plurality of
inner channels.
[0177] The inner channels, when present, may have various
cross-sectional shapes, such as circles, ovals, triangles, squares,
pentagons, hexagons, or tessellated combinations or any of these,
for example, and may be arranged in any suitable geometric
configuration. The inner channels, when present, may be discrete or
intersecting and may extend through the honeycomb body from a first
end thereof to a second end thereof, which is opposite the first
end.
[0178] With reference now to FIG. 7, a honeycomb body 100 according
to one or more embodiments shown and described herein is depicted.
The honeycomb body 100 may, in embodiments, comprise a plurality of
walls 115 defining a plurality of inner channels 110. The plurality
of inner channels 110 and intersecting channel walls 115 extend
between first end 105, which may be an inlet end, and second end
135, which may be an outlet end, of the honeycomb body. The
honeycomb body may have one or more of the channels plugged on one,
or both of the first end 105 and the second end 135. The pattern of
plugged channels of the honeycomb body is not limited. In some
embodiments, a pattern of plugged and unplugged channels at one end
of the honeycomb body may be, for example, a checkerboard pattern
where alternating channels of one end of the honeycomb body are
plugged. In some embodiments, plugged channels at one end of the
honeycomb body have corresponding unplugged channels at the other
end, and unplugged channels at one end of the honeycomb body have
corresponding plugged channels at the other end.
[0179] In one or more embodiments, the honeycomb body may be formed
from cordierite, aluminum titanate, enstatite, mullite, forsterite,
corundum (SiC), spinel, sapphirine, and periclase. In general,
cordierite has a composition according to the formula
Mg.sub.2Al.sub.4Si.sub.5O.sub.18. In some embodiments, the pore
size of the ceramic material, the porosity of the ceramic material,
and the pore size distribution of the ceramic material are
controlled, for example by varying the particle sizes of the
ceramic raw materials. In addition, pore formers can be included in
ceramic batches used to form the honeycomb body.
[0180] In some embodiments, walls of the honeycomb body may have an
average thickness from greater than or equal to 25 .mu.m to less
than or equal to 250 .mu.m, such as from greater than or equal to
45 .mu.m to less than or equal to 230 .mu.m, greater than or equal
to 65 .mu.m to less than or equal to 210 .mu.m, greater than or
equal to 65 .mu.m to less than or equal to 190 .mu.m, or greater
than or equal to 85 .mu.m to less than or equal to 170 .mu.m. The
walls of the honeycomb body can be described to have a base portion
comprised of a bulk portion (also referred to herein as the bulk),
and surface portions (also referred to herein as the surface). The
surface portion of the walls extends from a surface of a wall of
the honeycomb body into the wall toward the bulk portion of the
honeycomb body. The surface portion may extend from 0 (zero) to a
depth of about 10 .mu.m into the base portion of the wall of the
honeycomb body. In some embodiments, the surface portion may extend
about 5 .mu.m, about 7 .mu.m, or about 9 .mu.m (i.e., a depth of 0
(zero)) into the base portion of the wall. The bulk portion of the
honeycomb body constitutes the thickness of wall minus the surface
portions. Thus, the bulk portion of the honeycomb body may be
determined by the following equation:
t.sub.total-2t.sub.surface
where t.sub.total is the total thickness of the wall and
t.sub.surface is the thickness of the wall surface.
[0181] In one or more embodiments, the bulk of the honeycomb body
(prior to applying any filtration material) has a bulk mean pore
size from greater than or equal to 7 .mu.m to less than or equal to
25 .mu.m, such as from greater than or equal to 12 .mu.m to less
than or equal to 22 .mu.m, or from greater than or equal to 12
.mu.m to less than or equal to 18 .mu.m. For example, in some
embodiments, the bulk of the honeycomb body may have bulk mean pore
sizes of about 10 .mu.m, about 11 .mu.m, about 12 .mu.m, about 13
.mu.m, about 14 .mu.m, about 15 .mu.m, about 16 .mu.m, about 17
.mu.m, about 18 .mu.m, about 19 .mu.m, or about 20 .mu.m.
Generally, pore sizes of any given material exist in a statistical
distribution. Thus, the term "mean pore size" or "d50" (prior to
applying any filtration material) refers to a length measurement,
above which the pore sizes of 50% of the pores lie and below which
the pore sizes of the remaining 50% of the pores lie, based on the
statistical distribution of all the pores. Pores in ceramic bodies
can be manufactured by at least one of: (1) inorganic batch
material particle size and size distributions; (2) furnace/heat
treatment firing time and temperature schedules; (3) furnace
atmosphere (e.g., low or high oxygen and/or water content), as well
as; (4) pore formers, such as, for example, polymers and polymer
particles, starches, wood flour, hollow inorganic particles and/or
graphite/carbon particles.
[0182] In specific embodiments, the mean pore size (d50) of the
bulk of the honeycomb body (prior to applying any filtration
material) is in a range of from 10 .mu.m to about 16 .mu.m, for
example 13-14 .mu.m, and the d10 refers to a length measurement,
above which the pore sizes of 90% of the pores lie and below which
the pore sizes of the remaining 10% of the pores lie, based on the
statistical distribution of all the pores is about 7 .mu.m. In
specific embodiments, the d90 refers to a length measurement, above
which the pore sizes of 10% of the pores of the bulk of the
honeycomb body (prior to applying any filtration material) lie and
below which the pore sizes of the remaining 90% of the pores lie,
based on the statistical distribution of all the pores is about 30
.mu.m. In specific embodiments, the mean or average diameter (D50)
of the secondary particles or agglomerates is about 2 micrometers.
In specific embodiments, it has been determined that when the
agglomerate mean size D50 and the mean wall pore size of the bulk
honeycomb body d50 is such that there is a ratio of agglomerate
mean size D50 to mean wall pore size of the bulk honeycomb body d50
is in a range of from 5:1 to 16:1, excellent filtration efficiency
results and low pressure drop results are achieved. In more
specific embodiments, a ratio of agglomerate mean size D50 to mean
wall pore size of the bulk of honeycomb body d50 (prior to applying
any filtration material) is in a range of from 6:1 to 16:1, 7:1 to
16:1, 8:1 to 16:1, 9:1 to 16:1, 10:1 to 16:1, 11:1 to 16:1 or 12:1
to 6:1 provide excellent filtration efficiency results and low
pressure drop results.
[0183] In some embodiments, the bulk of the honeycomb body may have
bulk porosities, not counting a coating, of from greater than or
equal to 50% to less than or equal to 75% as measured by mercury
intrusion porosimetry. Other methods for measuring porosity include
scanning electron microscopy (SEM) and X-ray tomography, these two
methods in particular are valuable for measuring surface porosity
and bulk porosity independent from one another. In one or more
embodiments, the bulk porosity of the honeycomb body may be in a
range of from about 50% to about 75%, in a range of from about 50%
to about 70%, in a range of from about 50% to about 65%, in a range
of from about 50% to about 60%, in a range of from about 50% to
about 58%, in a range of from about 50% to about 56%, or in a range
of from about 50% to about 54%, for example.
[0184] In one or more embodiments, the surface portion of the
honeycomb body has a surface mean pore size from greater than or
equal to 7 .mu.m to less than or equal to 20 .mu.m, such as from
greater than or equal to 8 .mu.m to less than or equal to 15 .mu.m,
or from greater than or equal to 10 .mu.m to less than or equal to
14 .mu.m. For example, in some embodiments, the surface of the
honeycomb body may have surface mean pore sizes of about 8 .mu.m,
about 9 .mu.m, about 10 .mu.m, about 11 .mu.m, about 12 .mu.m,
about 13 .mu.m, about 14 .mu.m, or about 15 .mu.m.
[0185] In some embodiments, the surface of the honeycomb body may
have surface porosities, prior to application of a filtration
material deposit, of from greater than or equal to 35% to less than
or equal to 75% as measured by mercury intrusion porosimetry, SEM,
or X-ray tomography. In one or more embodiments, the surface
porosity of the honeycomb body may be less than 65%, such as less
than 60%, less than 55%, less than 50%, less than 48%, less than
46%, less than 44%, less than 42%, less than 40%, less than 48%, or
less than 36% for example.
[0186] Referring now to FIGS. 8 and 9, a honeycomb body in the form
of a particulate filter 200 is schematically depicted. The
particulate filter 200 may be used as a wall-flow filter to filter
particulate matter from an exhaust gas stream 250, such as an
exhaust gas stream emitted from a gasoline engine, in which case
the particulate filter 200 is a gasoline particulate filter. The
particulate filter 200 generally comprises a honeycomb body having
a plurality of channels 201 or cells which extend between an inlet
end 202 and an outlet end 204, defining an overall length La (shown
in FIG. 9). The channels 201 of the particulate filter 200 are
formed by, and at least partially defined by a plurality of
intersecting channel walls 206 that extend from the inlet end 202
to the outlet end 204. The particulate filter 200 may also include
a skin layer 205 surrounding the plurality of channels 201. This
skin layer 205 may be extruded during the formation of the channel
walls 206 or formed in later processing as an after-applied skin
layer, such as by applying a skinning cement to the outer
peripheral portion of the channels.
[0187] An axial cross section of the particulate filter 200 of FIG.
8 is shown in FIG. 9. In some embodiments, certain channels are
designated as inlet channels 208 and certain other channels are
designated as outlet channels 210. In some embodiments of the
particulate filter 200, at least a first set of channels may be
plugged with plugs 212. Generally, the plugs 212 are arranged
proximate the ends (i.e., the inlet end or the outlet end) of the
channels 201. The plugs are generally arranged in a pre-defined
pattern, such as in the checkerboard pattern shown in FIG. 8, with
every other channel being plugged at an end. The inlet channels 208
may be plugged at or near the outlet end 204, and the outlet
channels 210 may be plugged at or near the inlet end 202 on
channels not corresponding to the inlet channels, as depicted in
FIG. 9. Accordingly, each cell may be plugged at or near one end of
the particulate filter only.
[0188] While FIG. 8 generally depicts a checkerboard plugging
pattern, it should be understood that alternative plugging patterns
may be used in the porous ceramic honeycomb article. In the
embodiments described herein, the particulate filter 200 may be
formed with a channel density of up to about 600 channels per
square inch (cpsi). For example, in some embodiments, the
particulate filter 100 may have a channel density in a range from
about 100 cpsi to about 600 cpsi. In some other embodiments, the
particulate filter 100 may have a channel density in a range from
about 100 cpsi to about 400 cpsi or even from about 200 cpsi to
about 300 cpsi.
[0189] In the embodiments described herein, the channel walls 206
of the particulate filter 200 may have a thickness of greater than
about 4 mils (101.6 micrometers). For example, in some embodiments,
the thickness of the channel walls 206 may be in a range from about
4 mils up to about 30 mils (762 micrometers). In some other
embodiments, the thickness of the channel walls 206 may be in a
range from about 7 mils (177.8 micrometers) to about 20 mils (508
micrometers).
[0190] In some embodiments of the particulate filter 200 described
herein the channel walls 206 of the particulate filter 200 may have
a bare open porosity (i.e., the porosity before any coating is
applied to the honeycomb body) % P.gtoreq.35% prior to the
application of any coating to the particulate filter 200. In some
embodiments the bare open porosity of the channel walls 206 may be
such that 40%.ltoreq.% P.ltoreq.75%. In other embodiments, the bare
open porosity of the channel walls 206 may be such that
45%.ltoreq.% P.ltoreq.75%, 50%.ltoreq.% P.ltoreq.75%, 55%.ltoreq.%
P.ltoreq.75%, 60%.ltoreq.% P.ltoreq.75%, 45%.ltoreq.% P.ltoreq.70%,
50%.ltoreq.% P.ltoreq.70%, 55%.ltoreq.% P.ltoreq.70%, or
60%.ltoreq.% P.ltoreq.70%.
[0191] Further, in some embodiments, the channel walls 206 of the
particulate filter 200 are formed such that the pore distribution
in the channel walls 206 has a mean pore size of .ltoreq.30
micrometers prior to the application of any coatings (i.e., bare).
For example, in some embodiments, the mean pore size may be
.gtoreq.8 micrometers and less than or .ltoreq.30 micrometers. In
other embodiments, the mean pore size may be .gtoreq.10 micrometers
and less than or .ltoreq.30 micrometers. In other embodiments, the
mean pore size may be .gtoreq.10 micrometers and less than or
.ltoreq.25 micrometers. In some embodiments, particulate filters
produced with a mean pore size greater than about 30 micrometers
have reduced filtration efficiency while with particulate filters
produced with a mean pore size less than about 8 micrometers may be
difficult to infiltrate the pores with a washcoat containing a
catalyst. Accordingly, in some embodiments, it is desirable to
maintain the mean pore size of the channel wall in a range of from
about 8 micrometers to about 30 micrometers, for example, in a
range of from 10 micrometers to about 20 micrometers.
[0192] In one or more embodiments described herein, the honeycomb
body of the particulate filter 200 is formed from a metal or
ceramic material such as, for example, cordierite, silicon carbide,
aluminum oxide, aluminum titanate or any other ceramic material
suitable for use in elevated temperature particulate filtration
applications. For example, the particulate filter 200 may be formed
from cordierite by mixing a batch of ceramic precursor materials
which may include constituent materials suitable for producing a
ceramic article which predominately comprises a cordierite
crystalline phase. In general, the constituent materials suitable
for cordierite formation include a combination of inorganic
components including talc, a silica-forming source, and an
alumina-forming source. The batch composition may additionally
comprise clay, such as, for example, kaolin clay. The cordierite
precursor batch composition may also contain organic components,
such as organic pore formers, which are added to the batch mixture
to achieve the desired pore size distribution. For example, the
batch composition may comprise a starch which is suitable for use
as a pore former and/or other processing aids. Alternatively, the
constituent materials may comprise one or more cordierite powders
suitable for forming a sintered cordierite honeycomb structure upon
firing as well as an organic pore former material.
[0193] The batch composition may additionally comprise one or more
processing aids such as, for example, a binder and an aqueous
vehicle, such as water or a suitable solvent. The processing aids
are added to the batch mixture to plasticize the batch mixture and
to generally improve processing, reduce the drying time, reduce
cracking upon firing, and/or aid in producing the desired
properties in the honeycomb body. For example, the binder can
include an organic binder. Suitable organic binders include water
soluble cellulose ether binders such as methylcellulose,
hydroxypropyl methylcellulose, methylcellulose derivatives,
hydroxyethyl acrylate, polyvinyl alcohol, and/or any combinations
thereof. Incorporation of the organic binder into the plasticized
batch composition allows the plasticized batch composition to be
readily extruded. In some embodiments, the batch composition may
include one or more optional forming or processing aids such as,
for example, a lubricant which assists in the extrusion of the
plasticized batch mixture. Exemplary lubricants can include tall
oil, sodium stearate or other suitable lubricants.
[0194] After the batch of ceramic precursor materials is mixed with
the appropriate processing aids, the batch of ceramic precursor
materials is extruded and dried to form a green honeycomb body
comprising an inlet end and an outlet end with a plurality of
channel walls extending between the inlet end and the outlet end.
Thereafter, the green honeycomb body is fired according to a firing
schedule suitable for producing a fired honeycomb body. At least a
first set of the channels of the fired honeycomb body are then
plugged in a predefined plugging pattern with a ceramic plugging
composition and the fired honeycomb body is again fired to ceram
the plugs and secure the plugs in the channels.
[0195] In various embodiments the honeycomb body is configured to
filter particulate matter from a gas stream, for example, an
exhaust gas stream from a gasoline engine. Accordingly, the mean
pore size, porosity, geometry and other design aspects of both the
bulk and the surface of the honeycomb body are selected taking into
account these filtration requirements of the honeycomb body. As an
example, and as shown in the embodiment of FIG. 10, a wall 310 of
the honeycomb body 300, which can be in the form of the particulate
filter as shown in FIGS. 8 and 9, has filtration material deposits
320 disposed thereon, which in some embodiments is sintered or
otherwise bonded by heat treatment. The filtration material
deposits 320 comprise particles 325 that are deposited on the wall
310 of the honeycomb body 300 and help prevent particulate matter
from exiting the honeycomb body along with the gas stream 330, such
as, for example, soot and/or ash, and to help prevent the
particulate matter from clogging the base portion of the walls 310
of the honeycomb body 300. In this way, and according to
embodiments, the filtration material deposits 320 can serve as the
primary filtration component while the base portion of the
honeycomb body can be configured to otherwise minimize pressure
drop for example as compared to honeycomb bodies without such
filtration material deposits. The filtration material deposits are
delivered by the aerosol deposition methods disclosed herein.
[0196] As mentioned above, the material, which in some portions or
some embodiments may be an inorganic layer, on walls of the
honeycomb body is very thin compared to thickness of the base
portion of the walls of the honeycomb body. As will be discussed in
further detail below, the material, which may be an inorganic
layer, on the honeycomb body can be formed by methods that permit
the deposited material to be applied to surfaces of walls of the
honeycomb body in very thin applications or in some portions,
layers. In embodiments, the average thickness of the material,
which may be deposit regions or an inorganic layer, on the base
portion of the walls of the honeycomb body is greater than or equal
to 0.5 .mu.m and less than or equal to 50 .mu.m, or greater than or
equal to 0.5 .mu.m and less than or equal to 45 .mu.m, greater than
or equal to 0.5 .mu.m and less than or equal to 40 .mu.m, or
greater than or equal to 0.5 .mu.m and less than or equal to 35
.mu.m, or greater than or equal to 0.5 .mu.m and less than or equal
to 30 .mu.m, greater than or equal to 0.5 .mu.m and less than or
equal to 25 .mu.m, or greater than or equal to 0.5 .mu.m and less
than or equal to 20 .mu.m, or greater than or equal to 0.5 .mu.m
and less than or equal to 15 .mu.m, greater than or equal to 0.5
.mu.m and less than or equal to 10 .mu.m.
[0197] As discussed above, the deposited material, which may in
some portions or some embodiments be an inorganic layer, can be
applied to the walls of the honeycomb body by methods that permit
the inorganic material, which may be an inorganic layer, to have a
small mean pore size. This small mean pore size allows the
material, which may be an inorganic layer, to filter a high
percentage of particulate and prevents particulate from penetrating
honeycomb and settling into the pores of the honeycomb. The small
mean pore size of material, which may be an inorganic layer,
according to embodiments increases the filtration efficiency of the
honeycomb body. In one or more embodiments, the material, which may
be an inorganic layer, on the walls of the honeycomb body has a
mean pore size from greater than or equal to 0.1 .mu.m to less than
or equal to 5 .mu.m, such as from greater than or equal to 0.5
.mu.m to less than or equal to 4 .mu.m, or from greater than or
equal to 0.6 .mu.m to less than or equal to 3 .mu.m. For example,
in some embodiments, the material, which may be an inorganic layer,
on the walls of the honeycomb body may have mean pore sizes of
about 0.5 .mu.m, about 0.6 .mu.m, about 0.7 .mu.m, about 0.8 .mu.m,
about 0.9 .mu.m, about 1 .mu.m, about 2 .mu.m, about 3 .mu.m, or
about 4 .mu.m.
[0198] Although the deposited material, which may be an inorganic
layer, on the walls of the honeycomb body may, in some embodiments,
cover substantially 100% of the wall surfaces defining inner
channels of the honeycomb body, in other embodiments, the material,
which may be an inorganic layer, on the walls of the honeycomb body
covers less than substantially 100% of the wall surfaces defining
inner channels of the honeycomb body. For instance, in one or more
embodiments, the deposited material, which may be an inorganic
layer, on the walls of the honeycomb body covers at least 70% of
the wall surfaces defining inner channels of the honeycomb body,
covers at least 75% of the wall surfaces defining inner channels of
the honeycomb body, covers at least 80% of the wall surfaces
defining inner channels of the honeycomb body, covers at least 85%
of the wall surfaces defining inner channels of the honeycomb body,
covers at least 90% of the wall surfaces defining inner channels of
the honeycomb body, or covers at least 85% of the wall surfaces
defining inner channels of the honeycomb body.
[0199] As described above with reference to FIGS. 9 and 9, the
honeycomb body can have a first end and second end. The first end
and the second end are separated by an axial length. In some
embodiments, the filtration material deposits on the walls of the
honeycomb body may extend the entire axial length of the honeycomb
body (i.e., extends along 100% of the axial length). However, in
other embodiments, the material, which may be an inorganic layer,
on the walls of the honeycomb body extends along at least 60% of
the axial length, such as extends along at least 65% of the axial
length, extends along at least 70% of the axial length, extends
along at least 75% of the axial length, extends along at least 80%
of the axial length, extends along at least 85% of the axial
length, extends along at least 90% of the axial length, or extends
along at least 95% of the axial length.
[0200] In embodiments, the material, which may in some portions or
some embodiments be an inorganic layer, on the walls of the
honeycomb body extends from the first end of the honeycomb body to
the second end of the honeycomb body. In some embodiments, the
material, which may be an inorganic layer, on the walls of the
honeycomb body extends the entire distance from the first surface
of the honeycomb body to the second surface of the honeycomb body
(i.e., extends along 100% of a distance from the first surface of
the honeycomb body to the second surface of the honeycomb body).
However, in one or more embodiments, the layer or material, which
may be an inorganic layer, on the walls of the honeycomb body
extends along 60% of a distance between the first surface of the
honeycomb body and the second surface of the honeycomb body, such
as extends along 65% of a distance between the first surface of the
honeycomb body and the second surface of the honeycomb body,
extends along 70% of a distance between the first surface of the
honeycomb body and the second surface of the honeycomb body,
extends along 75% of a distance between the first surface of the
honeycomb body and the second surface of the honeycomb body,
extends along 80% of a distance between the first surface of the
honeycomb body and the second surface of the honeycomb body,
extends along 85% of a distance between the first surface of the
honeycomb body and the second surface of the honeycomb body,
extends along 90% of a distance between the first surface of the
honeycomb body and the second surface of the honeycomb body, or
extends along 95% of a distance between the first surface of the
honeycomb body and the second surface of the honeycomb body.
[0201] The selection of a honeycomb body having a low pressure drop
in combination with the low thickness and porosity of the
filtration material on the honeycomb body according to embodiments
allows a honeycomb body of embodiments to have a low initial
pressure drop when compared to other honeycomb bodies. In
embodiments, the loading of the layer is in a range of from 0.3 to
30 g/L on the honeycomb body, such as in a range of from 1 to 30
g/L on the honeycomb body, or in a range of from 3 to 30 g/L on the
honeycomb body. In other embodiments, the loading of the layer is
in a range of from 1 to 20 g/L on the honeycomb body, such as in a
range of from 1 to 10 g/L on the honeycomb body, or from 0.1 to 10
g/L, or from 0.1 to 5 g/L. In specific embodiments, the loading of
the layer is in a range of from 1 to 9 g/L, 1 to 8 g/L, 1 to 7 g/L,
1 to 8 g/L, 1 to 5 g/L, 1 to 4 g/L, 1 to 3 g/L, 2 to 10 g/L, 2 to 9
g/L, 2 to 8 g/L, 2 to 7 g/L, 2 to 6 g/L, 2 to 5 g/L, 2 to 4 g/L, 3
to 10 g/L, 3 to 9 g/L, 3 to 8 g/L, 3 to 7 g/L, 3 to 6 g/L, 3 to 5
g/L, 4 to 10 g/L, 4 to 9 g/L 4 to 8 g/L, 4 to 7 g/L, or 4 to 6 g/L
on the honeycomb body. In some embodiments, the increase in
pressure drop across the honeycomb due to the application of the
porous layer across is less than 20% of the uncoated honeycomb. In
other embodiments that increase can be less than or equal to 9%, or
less than or equal to 8%. In other embodiments, the pressure drop
increase across the honeycomb body is less than or equal to 7%,
such as less than or equal to 6%. In still other embodiments, the
pressure drop increase across the honeycomb body is less than or
equal to 5%, such as less than or equal to 4%, or less than or
equal to 3%.
[0202] Without being bound to any particular theory, it is believed
that small pore sizes in the filtration material deposits on the
walls of the honeycomb body allow the honeycomb body to have good
filtration efficiency even before ash or soot build-up occurs in
the honeycomb body. The filtration efficiency of honeycomb bodies
is measured herein using the protocol outlined in Tandon et al., 65
CHEMICAL ENGINEERING SCIENCE 4751-60 (2010). As used herein, the
initial filtration efficiency of a honeycomb body refers to a new
or regenerated honeycomb body that does not comprise any measurable
soot or ash loading. In embodiments, the initial filtration
efficiency (i.e., clean filtration efficiency) of the honeycomb
body is greater than or equal to 70%, such as greater than or equal
to 80%, or greater than or equal to 85%. In yet other embodiments,
the initial filtration efficiency of the honeycomb body is greater
than 90%, such as greater than or equal to 93%, or greater than or
equal to 95%, or greater than or equal to 98%.
[0203] The material, which is in some embodiments an inorganic
filtration material, on the walls of the honeycomb body according
to embodiments is thin and has a porosity, and in some embodiments
also has good chemical durability and physical stability. The
chemical durability and physical stability of the filtration
material deposits on the honeycomb body can be determined, in
embodiments, by subjecting the honeycomb body to test cycles
comprising burn out cycles and an aging test and measuring the
initial filtration efficiency before and after the test cycles. For
instance, one exemplary method for measuring the chemical
durability and the physical stability of the honeycomb body
comprises measuring the initial filtration efficiency of a
honeycomb body; loading soot onto the honeycomb body under
simulated operating conditions; burning out the built up soot at
about 650.degree. C.; subjecting the honeycomb body to an aging
test at 1050.degree. C. and 10% humidity for 12 hours; and
measuring the filtration efficiency of the honeycomb body. Multiple
soot build up and burnout cycles may be conducted. A small change
in filtration efficiency (.DELTA.FE) from before the test cycles to
after the test cycles indicates better chemical durability and
physical stability of the filtration material deposits on the
honeycomb body. In some embodiments, the .DELTA.FE is less than or
equal to 5%, such as less than or equal to 4%, or less than or
equal to 3%. In other embodiments, the .DELTA.FE is less than or
equal to 2%, or less than or equal to 1%.
[0204] In some embodiments, the filtration material deposits on the
walls of the honeycomb body may be comprised of one or a mixture of
ceramic components, such as, for example, ceramic components
selected from the group consisting of SiO.sub.2, Al.sub.2O.sub.3,
MgO, ZrO.sub.2, CaO, TiO.sub.2, CeO.sub.2, Na.sub.2O, Pt, Pd, Ag,
Cu, Fe, Ni, and mixtures thereof. Thus, the filtration material
deposits on the walls of the honeycomb body may comprise an oxide
ceramic. As discussed in more detail below, the method for forming
the filtration material deposits on the honeycomb body according to
embodiments can allow for customization of the filtration material
composition for a given application. This may be beneficial because
the ceramic components may be combined to match, for example, the
physical properties--such as, for example coefficient of thermal
expansion (CTE) and Young's modulus, etc.--of the honeycomb body,
which can improve the physical stability of the honeycomb body. In
some embodiments, the filtration material deposits on the walls of
the honeycomb body may comprise cordierite, aluminum titanate,
enstatite, mullite, forsterite, corundum (SiC), spinel, sapphirine,
and periclase.
[0205] In some embodiments, the composition of the filtration
material deposits on the walls of the honeycomb body is the same as
the composition of the honeycomb body. However, in other
embodiments, the composition of the filtration material is
different from the composition of the walls of the matrix of the
honeycomb body.
[0206] The properties of the filtration material deposits and, in
turn, the honeycomb body overall are attributable to the ability of
applying a sparse or thin porous filtration material having small
median pore sizes relative to the host honeycomb body.
[0207] In some embodiments, the method of forming a honeycomb body
comprises forming or obtaining a mixture or a suspension that
comprises a ceramic precursor material and a solvent. The ceramic
precursor material of the filtration material precursor comprises
ceramic materials that serve as a source of, for example,
SiO.sub.2, Al.sub.2O.sub.3, TiO.sub.2, MgO, ZrO.sub.2, CaO,
CeO.sub.2, Na.sub.2O, Pt, Pd, Ag, Cu, Fe, Ni, and the like.
[0208] In one or more embodiments, the suspension is atomized with
an atomizing gas to form liquid-particulate-binder droplets
comprised of the aqueous vehicle, the binder material, and the
particles, is directed to a honeycomb body, Agglomerates formed
upon removal or evaporation of the aqueous vehicle are then
deposited on the honeycomb body. In some embodiments, the honeycomb
body may have one or more of the channels plugged on one end, such
as, for example, the first end of the honeycomb body during the
deposition of the aerosol to the honeycomb body. The plugged
channels may, in some embodiments, be removed after deposition of
the aerosol. But, in other embodiments, the channels may remain
plugged even after deposition of the aerosol. The pattern of
plugging channels of the honeycomb body is not limited, and in some
embodiments all the channels of the honeycomb body may be plugged
at one end. In other embodiments, only a portion of the channels of
the honeycomb body may be plugged at one end. In such embodiments,
the pattern of plugged and unplugged channels at one end of the
honeycomb body is not limited and may be, for example, a
checkerboard pattern where alternating channels of one end of the
honeycomb body are plugged. By plugging all or a portion of the
channels at one end of the honeycomb body during deposition of the
aerosol, the aerosol may be evenly distributed within the channels
of the honeycomb body.
[0209] According to one or more embodiments, binders with high
temperature (e.g., greater than 400.degree. C.) resistance are
included in the agglomerates and filtration material deposits to
enhance integrity of the agglomerates and deposits even at high
temperatures encountered in exhaust gas emissions treatment
systems. In specific embodiments, a filtration material can
comprise about 5 to 25 wt % Dowsil US-CF-2405, an alkoxy-siloxane
resin. The microstructure of the filtration material deposits was
similar to the as-deposited morphology after the various tests
described below. The inorganic binders Aremco Ceramabind.TM. 644A
and 830 could also be used in in one or more embodiments. The
filtration efficiency of both samples were higher than 60% after
the high flow blowing test, a high flow test at 850 Nm.sup.3/h. The
tests demonstrated that the binders, including organic and
inorganic binders, caused the primary particles to bind together to
form secondary particles (also called agglomerates), which were
bound to the filter walls, even when exposed to high temperatures
encountered in engine exhaust gas streams. According to one or more
embodiments, other inorganic and organic binders such as silicate
(e.g. Na.sub.2SiO.sub.3), phosphate (e.g. AlPO.sub.4,
AlH.sub.2(PO.sub.4).sub.3), hydraulic cement (e.g. calcium
aluminate), sol (e.g. mSiO.sub.2.cndot.nH.sub.2O,
Al(OH).sub.x.cndot.(H.sub.2O).sub.6-x) and metal alkoxides, could
also be utilized, for example to increase mechanical strength by an
appropriate curing process.
[0210] Aqueous-Based Methods
[0211] According to one or more embodiments, a method of
aqueous-based aerosol deposition of inorganic material on porous
walls of a plugged honeycomb body are disclosed. The porous walls
of the plugged honeycomb body form a plurality of channels in the
honeycomb body. In specific embodiments, an aqueous-based
suspension of inorganic material and binder passes through a nozzle
and provides a flow of aerosol particles after contact with a gas
stream and heat before being forced into the opening channels of
the honeycomb body. A layer of inorganic material is then deposited
on the porous walls with some agglomerates or inorganic material
getting into pores. An off-line heat treatment process may be
applied for curing of the layer, which in some embodiments forms a
membrane. According to one or more embodiments, the honeycomb
bodies made and described herein, both before and after curing,
exhibit significantly higher filtration efficiency and/or better
FE/dP trade-off than bare honeycomb body substrate parts.
[0212] Referring now to FIG. 11, according to one or more
embodiments, a process 4100 comprises the steps of aqueous
suspension preparation 1405, atomizing to form droplets 1410,
intermixing droplets and a gaseous carrier stream 1415; evaporating
liquid vehicle to form agglomerates 1420, depositing of material,
e.g., agglomerates, on the walls of a wall-flow filter 1425, and
optional post-treatment 1430 to, for example off-line curing, bind
the material on, or in, or both on and in, the porous walls of the
honeycomb body. Aerosol deposition methods form of agglomerates
comprising a binder can provide a high mechanical integrity even
without any high temperature curing steps (e.g., heating to
temperatures in excess of 1000.degree. C.), and in some embodiments
even higher mechanical integrity after an optional off-line curing
step such as a high temperature (e.g., heating to temperatures in
excess of 1000.degree. C.) curing step. In one or more embodiments,
"off-line" refers to a curing process that is performed separately
form the aerosol deposition apparatus, such as in a separate
apparatus.
[0213] In one or more embodiments, stable aqueous-based inorganic
material suspension or slurry is made by mixing powder of inorganic
material (e.g., alumina) with deionized water and aqueous-based
binder. In some embodiments, such a suspension is made by diluting
a commercially available aqueous-based organic matter suspension
(e.g., aqueous-based alumina suspension with deionized water) and
then adding an aqueous-based binder.
[0214] In some embodiments, it may be desirable to add a
dispersant. The inorganic material is in the form of particles that
are spherical, rod-like, flat or irregular with the primary
particle size of 30 nm to 500 nm. The concentration of the
inorganic material according to one or more embodiments is varied
in the range of 1% to 20% by weight of the suspension. Exemplary
ranges of inorganic material in weight % are 1-2%, 1-3%, 1-4%,
1-5%, 1-6%, 1-8%, 1-9%, 1-10%, 1-15%, 1-20%, 2-3%, 2-4%, 2-5%,
2-6%, 2-8%, 2-9%, 2-10%, 2-15%, 2-20%, 3-4%, 3-5%, 3-6%, 3-8%,
3-9%, 3-10%, 3-15%, 3-20%, 4-5%, 4-6%, 4-8%, 4-9%, 4-10%, 4-15%,
4-20%, 5-6%, 5-8%, 5-9%, 5-10%, 5-15%, 5-20%, 10-15%, 10-16%,
10-17%, 10-18%, 10-19%, 10-20%, 15-18%, 15-19% and 15-20%. In one
or more embodiments, the binder comprises inorganic or organic
materials. Non-limiting examples of inorganic include silica,
titania, silicates, aluminates, phosphate or hydraulic cement.
Non-limiting examples of organic binder include silicone resin,
polyvinyl alcohol (PVA) or polyethylene glycol (PEG). The
concentration of binder may be in the range of 5%-100% by weight of
alumina. Exemplary ranges of binder by weight of inorganic material
in weight % are 5-100%, 10-100%, 15-100%, 20-100%, 25-100%,
30-100%, 35-100%, 40-100%, 45-100%, 50-100%, 55-100%, 60-100%,
5-90%, 10-90%, 15-90%, 20-90%, 25-90%, 30-90%, 35-90%, 40-90%,
45-90%, 50-90%, 55-90%, 60-90%, 5-80%, 10-80%, 15-80%, 20-80%,
25-80%, 30-80%, 35-80%, 40-80%, 45-80%, 50-80%, 55-80%, 60-80%,
5-70%, 10-70%, 15-70%, 20-70%, 25-70%, 30-70%, 35-70%, 40-70%,
45-70%, 50-70%, 55-70%, 60-70%, 5-60%, 10-60%, 15-60%, 20-60%,
25-60%, 30-60%, 35-60%, 40-60%, 45-60%, 50-60%, 55-60%, 5-50%,
10-50%, 15-50%, 20-50%, 25-50%, 30-50%, 35-50%, 40-50%, 45-50%,
5-40%, 10-40%, 15-40%, 20-40%, 25-40%, 30-40%, 35-40%, 5-30%,
10-30%, 15-30%, 20-30%, 25-30%, 5-25%, 10-25%, 15-25%, 20-25%,
1-20%, 2-20%, 3-20%, 4-20% 5-20%, 6-20%, 7-20%, 8-20%, 9-20%,
10-20%, 1-15%, 2-15%, 3-15%, 4-15% 5-15%, 6-15%, 7-15%, 8-15%,
9-15%, 10-15%, 1-10%, 2-10%, 3-10%, 4-10%, 5-10%, 6-10%, 7-10% and
8-10%. In one or more embodiments, mixing is performed mechanically
or acoustically. The as-prepared suspension according to some
embodiments is stable for at least 1 hour without clear
settlement.
[0215] In some embodiments, a tape test may be used to roughly
evaluate effectiveness of different binders and to decide the
amount of binders to be added in the suspension. A layer of wet
coating of a sample suspension is prepared according to embodiments
described herein and then is applied on one microscope slide with
use of as-prepared inorganic material suspension. After drying, the
coated slide is placed in the oven and heated to curing temperature
for a period of time in the range of 10 minutes up to 2 hours.
Curing temperature and profile will depend on the binder used.
After curing, a piece of regular tape such as Highland.TM.
transparent tape is pressed against the cured coating, and then is
lifted off from the coating. According to some embodiments, if
particles of inorganic material are observed on the tape, the
cohesive strength of the cured suspension is not acceptable. More
binder or a different binder can be used, and the test can be
repeated.
[0216] FIG. 4, discussed above, illustrates a schematic of a
deposition system that can be used for aerosol deposition an
aqueous-based suspension containing inorganic material according to
one or more embodiments. In FIG. 4, the suspension is contained in
a suspension container 902, and liquid pressure was applied and
controlled by a gas supply 902, which in some embodiments is in the
form of a cylinder. In one or more embodiments, pressure is
controlled by a digital automatic pressure regulator or a piezo
actuator valve. Atomization gas according to one or more
embodiments comprises nitrogen or air. A first heat source 906a
heats carrier gas 905a that enters the first plenum space 903. A
second heat source 906b is positioned downstream from the nozzle
920 to heat the suspension 910 that is atomized in the nozzle 920.
A third heat source 906c is positioned in the evaporation chamber
923, and the outlet flow of the nozzle and the primary carrier gas
905a enter the evaporation chamber 923 of the evaporation section
953.
[0217] In one or more embodiments, an aqueous-based aerosol
deposition process and products made thereby are provided, which
provide plugged honeycomb bodies comprising porous walls and
inorganic material deposited thereon exhibiting significantly
higher filtration efficiency and minimal backpressure penalty than
those prepare by other methods. Such honeycomb bodies in some
embodiments exhibit higher durability in certain tests described
further below, including a vibration test, a vehicle test and water
durability tests.
[0218] In specific embodiments, a process is provided comprising
flowing an aqueous suspension of inorganic material (e.g., alumina
nanoparticles) in a suspension comprising a binder comprising
(e.g., a water soluble silicate binder) through a spray nozzle to
provide a flow of aerosol particles which form agglomerates after
contact with a drying gas stream. In specific embodiments, the
agglomerates are then forced into the opening channels of plugged
honeycomb bodies and on and/or in the surface of porous walls which
form the channels. In some embodiments, the agglomerates contact
surface pores first. In one or more embodiments, an off-line heat
treatment process is utilized for binder curing and deposit
strengthening. After deposition and thermal treatment, the filter
parts show improved filtration efficiency or FE/dP trade-off
performance compared to bare plugged honeycomb bodies. The plugged
honeycomb bodies made according to the methods made herein pass
various durability tests including water resistance tests with a
thermal treatment. A water soluble binder or aqueous-compatible
binder is used according to one or more embodiments. The aqueous
process according to one or more embodiments forms deposits having
a microstructure of densely packed agglomerates.
[0219] According to one or more embodiments, the aqueous-based
process provides a less complex and less expensive process than an
ethanol-based process. In some embodiments, lower deposited loading
by an aqueous-based process results in similar FE/dP performance
compared to an ethanol-based process, which results in lower
materials cost, shorter deposition time, and higher production
rate. In some embodiments, higher FE could be achieved with the
same loading compared to the ethanol-based process. In some
embodiments, the morphology of the deposited inorganic material can
be adjusted to be similar for an ethanol-based process and an
aqueous based process.
[0220] Plugged Honeycomb Bodies Comprising Inorganic Material
[0221] Embodiments of the disclosure pertain to plugged honeycomb
bodies comprising porous walls and inorganic material deposited on
or in or both on and in the porous walls, which provide a
filtration article configured to filter particulate from an exhaust
gas stream. In specific embodiments, the filtration article
comprises a gasoline particulate filters (GPF) used to remove
particulates from gasoline engine exhaust gases. Exhaust gas to be
filtered enters inlet cells and passes through the cell walls to
exit the filter via outlet channels, with the particulates being
trapped on or within the inlet cell walls as the gas traverses and
then exits the filter. According to one or more embodiments, porous
walls of the filtration article having inorganic material deposited
on or in or both on and in the porous walls provide improved
filtration efficiency and excellent durability, including
durability when exposed to water.
[0222] In one or more embodiments the inorganic material comprises
particulate or primary particles of inorganic material (e.g.
alumina), particulate-binder agglomerates (referred to as
"agglomerates") comprised of the particles and the binder material,
and aggregates of particulate-binder agglomerates. In one or more
embodiments, the "particulate" or "primary particle" refers to the
smallest discrete mass of inorganic material. In one or more
embodiments, "agglomerate" refers to a mass of primary particles or
particulate and binder, wherein the primary particles or
particulate are held together by the binder. In one or more
embodiments, "aggregates of particulate-binder agglomerates" or
"aggregates of primary particle-binder agglomerates" (referred to
as "aggregates") refers to a clustered mass of individual
particulate-binder agglomerates or primary particle-binder
agglomerates, which are held together by binder. In one or more
embodiments, some of the aggregates and individual, for example,
non-aggregated, agglomerates are deposited onto the porous walls of
the honeycomb filter body. In one or more embodiments, at least a
portion of the primary particles or the particulate are present in,
on or both in and on the porous walls as discrete masses that are
not part of agglomerate or aggregate. In one or more embodiments,
at least a portion of the particulate-binder agglomerates or the
primary particle-binder agglomerates are present in, on or in and
on the porous walls as discrete masses that are not part of an
aggregate.
[0223] In one or more embodiments, the inorganic material in or on
or in and one the porous walls of the filtration article in the
form of a plugged honeycomb body is present "clusters" or "chains"
of agglomerates and/or aggregates. In some embodiments, the cluster
or chains provide an inorganic material morphology that is one or
more of finger-shaped, fibril-shaped, or sponge-like, such as for
example, a morphology resembling a sea wool sponge.
[0224] As discussed herein, according to embodiments, the inorganic
material is formed from a suspension comprised of nanoparticles
(e.g., inorganic particles, ceramic particles, refractory
particles, alumina particles, etc.), binder (e.g., a
silicon-containing binder and/or an aqueous binder, and liquid
vehicle (e.g., an alcohol or water). The suspension is delivered to
a nozzle which sprays droplets of the suspension with a gas flow
assist. The liquid vehicle is evaporated from the droplets to form
spherical agglomerates of the nanoparticles. The binder serves as
one or more of an agglomerate promoter, an aggregate promoter, a
chain promoter and a cluster promoter. Some spherical agglomerates
are conveyed to the porous ceramic walls and lodge either on the
surface of the porous ceramic walls (on, in, or over surface pores
present on the walls), or in pores inside the porous ceramic walls
(below the surface of the porous ceramic walls), or into contact
with other previously deposited agglomerates which are disposed
either in or on the porous ceramic walls, so as to form aggregates
of spherical agglomerates therein, or thereon. Other spherical
agglomerates come into contact with still other spherical
agglomerates while being conveyed toward the honeycomb filter body
so as to form aggregates of spherical agglomerates, wherein the
aggregates are then conveyed toward the porous ceramic walls and
the aggregates then lodge either on the surface of the porous
ceramic walls (on, in, or over surface pores present on the walls),
or in pores inside the porous ceramic walls (below the surface of
the porous ceramic walls), or into contact with other previously
deposited agglomerates or aggregates which are disposed either in
or on the porous ceramic walls, so as to form aggregates of
spherical agglomerates therein, or thereon.
[0225] Thus, according to one or more embodiments, the inorganic
deposits are comprised of individual agglomerates of nanoparticles
(e.g., spherical agglomerates of nanoparticles), aggregates of
agglomerates, and/or porous clusters or chains of aggregates of
spherical agglomerates, wherein some clusters or chains are
disposed within pores in or below the surface of the porous ceramic
wall, and/or wherein some clusters are disposed on the surface of
the porous ceramic wall. In some embodiments, some of the porous
clusters are porous clusters or cluster islands comprising exposed
aggregates of agglomerates (e.g., spherical agglomerates). In some
embodiments, the porous clusters or cluster islands comprise one or
more chains of two or agglomerates, each chain extending in a
substantially outward direction from the porous ceramic wall. In
some embodiments, a plurality of the outwardly extending chains
collectively provides a morphology resembling a member of the group
consisting of fingers, tufts, sponges (e.g., a sea wool sponge) and
fans. In some embodiments, at least one chain includes a free end
of the chain projecting above the surface of the porous ceramic
wall. In some embodiments, the inorganic material on the honeycomb
body is present as inorganic deposits comprising a network of
aggregated spherical agglomerates of inorganic material
particles.
[0226] In embodiments, the loading of the inorganic material
present on the honeycomb body in a range of from 0.3 to 30 g/L on
the honeycomb body, such as in a range of from 1 to 30 g/L on the
honeycomb body, or in a range of from 3 to 30 g/L on the honeycomb
body. In other embodiments, the loading of the inorganic material
is in a range of from 1 to 20 g/L on the honeycomb body, such as in
a range of from 1 to 10 g/L on the honeycomb body. In specific
embodiments, the loading of the inorganic material is in a range of
from 1 to 9 g/L, 1 to 8 g/L, 1 to 7 g/L, 1 to 8 g/L, 1 to 5 g/L, 1
to 4 g/L, 1 to 3 g/L, 2 to 10 g/L, 2 to 9 g/L, 2 to 8 g/L, 2 to 7
g/L, 2 to 6 g/L, 2 to 5 g/L, 2 to 4 g/L, 3 to 10 g/L, 3 to 9 g/L, 3
to 8 g/L, 3 to 7 g/L, 3 to 6 g/L, 3 to 5 g/L, 4 to 10 g/L, 4 to 9
g/L 4 to 8 g/L, 4 to 7 g/L, or 4 to 6 g/L on the honeycomb body.
Loading of the inorganic material is weight of added material in
grams divided by the geometric part volume in liters. The geometric
part volume is based on outer dimensions of the honeycomb filter
body (or plugged honeycomb body).
[0227] In one or more embodiments, the particles of the inorganic
material have a surface area in a range of from 5 m.sup.2/g to 15
m.sup.2/g, 5 m.sup.2/g to 14 m.sup.2/g, 5 m.sup.2/g to 13
m.sup.2/g, 5 m.sup.2/g to 12 m.sup.2/g, 5 m.sup.2/g to 12
m.sup.2/g, or 5 m.sup.2/g to 10 m.sup.2/g.
[0228] In one or more embodiments the inorganic material deposits
on the honeycomb body are free from rare earth oxides such as
ceria, lanthana and yttria. In one or more embodiments the
inorganic material is free from catalyst, for example, an oxidation
catalyst such as a platinum group metal (e.g., platinum, palladium
and rhodium) or a selective catalytic reduction catalyst such as a
copper, a nickel or an iron promoted molecular sieve (e.g., a
zeolite).
[0229] In one or more embodiments, prior to heat treatment of the
honeycomb body comprising inorganic material on or in or on and in
the porous wall, the honeycomb body further comprises a water
soluble binder, for example a water soluble silicon-containing
binder, a water soluble silicate binder (e.g., metal silicate
binder such as sodium silicate), a water soluble aluminate binder
(e.g., metal aluminate binder such as sodium aluminate). In one or
more embodiments, the binder is present in a range of from 5 wt %
to 40 wt %, 5 wt % to 35 wt %, 5 wt % to 30 wt %, 5 wt % to 25 wt
%, 5 wt % to 20 wt %, 5 wt % to 15 wt % or 5 wt % to 10 wt % based
on the weight of the organic material on the honeycomb body. In one
or more embodiments, the binder or binder material is provided by a
precursor binder or precursor binder material. In one or more
embodiments, the precursor binder or precursor binder material is
silicon-containing. In one or more embodiments, the
silicon-containing precursor binder is a silicone resin, or a
siloxane, or an alkalisiloxane, or an alkoxysiloxane, or a
silicate, e.g., an alkaline silicate or sodium silicate. In one or
more embodiments, the silicon-containing precursor binder is
comprised of an inorganic component and an organic component. In
one or more embodiments, the silicon-containing precursor binder
transitions to silica upon application of heat. In one or more
embodiments, the silicon-containing precursor binder is comprised
of an inorganic component and an organic component, and wherein
upon application of heat the organic component is driven off and
the inorganic component transitions to silica.
EXAMPLES
[0230] Embodiments will be further understood by the following
non-limiting examples.
[0231] Wall-flow filters. The diameter and length of the wall-flow
filter substrates used in the examples were 4.055'' and 5.47''. The
CPSI and wall thickness were 200 and 8 mils. The pore size was 14
micrometers.
[0232] Raw Materials. Unless specified otherwise in the examples,
the following raw materials were used. The inorganic material being
deposited was alumina, the atomizing gas was nitrogen, and a binder
was present. The carrier gas was either air or nitrogen.
[0233] Raw Material Utilization. Raw material utilization was
determined by determining the weight gain of the honeycomb and
comparing that to a calculated amount of ceramic put into the
process. For example, if the weight gain was equal to the amount of
ceramic put into the process, then the utilization was calculated
as 100%; or if the weight gain were only one half of the of ceramic
put into the process, the utilization was calculated to be 50%.
[0234] According to one or more embodiments, a honeycomb filter
body comprising inorganic deposits disposed within the honeycomb
filter body to create a filtration article is characterized
according to the following tests.
[0235] Smoke Filtration Efficiency (FE)
[0236] The smoke filtration efficiency performance of the deposited
inorganic material disposed within the honeycomb filter bodies was
evaluated using a smoke filtration test.
[0237] The filtration efficiency (in percent %) is calculated
as:
FE = ( 1 - c outlet c inlet ) * 1 0 0 , ##EQU00001##
where C is the smoke concentration on the outlet and inlet side of
the part, respectively.
[0238] Two particle counter units (Lighthouse 2016, USA) are used
simultaneously at upstream and downstream positions with respect to
the article at the underfloor position of a dilution chamber. A
cigarette is lit in a smoke generator to provide desired quantity
of soot particles into the dilution chamber and the concentration
is maintained at a certain level (500,000 particles/cm.sup.3)
before the smoke travels into the inlet side of the tunnel. The
flow is driven by a blower which carries the soot particles through
the tunnel and eventually into the wall flow filter parts. When the
concentration at upstream of GPF reaches a stable state, the two
particle counters reset to begin counting for 60 seconds and
filtration efficiency (FE) was calculated based on the differential
of total particle count of 0.3 .mu.m and above. The pressure drop
(dP) measured by pressure gauges located upstream and downstream
from the article is also recorded at a fixed flow of 51
Nm.sup.3/hr.
[0239] Pre-Test Canning. During pre-test canning, an article is
wrapped in a ceramic fiber mat material and then placed into a
metal can. The article, mat and can assembly are heated in an oven
to 650.degree. C. and held at 650.degree. C. for a duration. The
mat expands to help hold the article in place within the can. This
process is referred to as mat popping as the mat expands, it "pops"
inside the can to fit the article in place. The duration of the
pre-test canning is chosen based on the subsequent test being
conducted.
[0240] Post-Test Cleanout. After a test is conducted, the following
steps are completed to achieve post-test cleanout of the article.
The article, mat and can assembly are placed in an oven at
650.degree. C. and held at 650.degree. C. for a duration, usually
about 6 hours so that the soot that was loaded into the article is
burned out of the article.
[0241] Clean Filtration Efficiency
[0242] As used herein, the "clean filtration efficiency" of a
honeycomb body or filtration article refers to a new or regenerated
honeycomb body that does not comprise any measurable soot loading.
In embodiments, the clean filtration efficiency of the honeycomb
body or filtration article is greater than or equal to 70%, such as
greater than or equal to 80%, or greater than or equal to 85%. In
yet other embodiments, the initial filtration efficiency of the
honeycomb body or filtration article is greater than 90%, such as
greater than or equal to 93%, or greater than or equal to 95%, or
greater than or equal to 98%.
[0243] As used herein, "Clean Filtration Efficiency Test" refers to
testing an article as follows.
[0244] After pre-test canning for 6 hours, an air stream is
supplied by a blower upstream of the article at a ramped rate, and
clean pressure drop is measured across the filter using a
differential pressure sensor/gauge at room temperature (about
25.degree. C.). The flow rate of the air stream was ramped from
25.5 m.sup.3/h to 356.8 m.sup.3/h over 10 step increases, where the
flow rate was maintained for one minute at each new step increase.
Each step increase was in a range of about 8 to 68 m.sup.3/h. Next,
an air stream containing soot particles at a concentration of 8
mg/m.sup.3 and a flow rate of 22.5 m.sup.3/h is introduced upstream
of the filter for 45 minutes. The soot is generated at .about.110
nm particle size from a commercially-available propane burner.
Clean filtration efficiency at 30.degree. C. is determined by
measuring the difference between a number of particulates that are
introduced into the article and a number of particulates that exit
the article before and after exposure to the flow conditions. After
the clean filtration efficiency is measured, post-test cleanout is
conducted for 6 hours.
[0245] Water Exposure Tests
[0246] Several assessment protocols for understanding the
durability of the filtration articles disclosed herein were
utilized. Analysis of impact of water exposure of varying
intensities on honeycomb filter bodies having aerosol-deposited
inorganic material is an indication of the durability of the
filtration articles.
[0247] Water Soak Test
[0248] As used herein, "Water Soak Test" refers to testing an
article as follows.
[0249] To simulate conditions where a vehicle exhaust pipeline has
seen incoming water source in an underfloor condition, the water
soak test was conducted.
[0250] An article is first measured for baseline FE/dP measurement
by the clean filtration efficiency test.
[0251] Next, the article is weighed at 75.degree. C. to determine
an initial weight. The article is then placed on its side in a
petri dish, skin layer side, to simulate an underfloor position of
the filter in a vehicle exhaust system and soaked in a quantity of
deionized water for 2 hours. After the part soaks up water to a
target amount, it is dried at 75.degree. C. until completely dry
(weight goes back to as-deposited state). The target quantity of
water may be premeasured. For example, nominally 300 grams of water
may be used. In one or more embodiments, there is a water
absorption level that can be described as a percentage of a
distance along a diameter of the article face the water absorbed,
e.g., 1/2 to 3/4 of a filter diameter. The article is then dried in
a furnace for 5-6 hours at 100.degree. C. until the initial weight
is achieved. Next, clean filtration efficiency is measured. For
evaluating clean filtration efficiency, an air stream containing
soot particles at a concentration of 8 mg/m.sup.3 and a flow rate
of 22.5 m.sup.3/h is introduced upstream of the filter for 45
minutes. The soot is generated at .about.110 nm particle size from
a commercially-available propane burner. Clean filtration
efficiency at 30.degree. C. is determined by measuring the
difference between a number of particulates that are introduced
into the article and a number of particulates that exit the
article. After the filtration efficiency is measured, post-test
cleanout is conducted for 6 hours. Filtration efficiency at 0 g/L
soot is compared before and after the article is exposed to the
water soak test.
[0252] Water Immersion Test
[0253] Another method for evaluating durability of a filtration
article is the water immersion test, where a part is completely
soaked in water to imitate the worst case scenario where an exhaust
pipeline is submerged in water.
[0254] As used herein, "Water Immersion Test" refers to testing an
article as follows.
[0255] An article is first measured for baseline FE/dP measurement
by the clean filtration efficiency test.
[0256] Next, the article is weighed at 75.degree. C. to determine
an initial weight. The article with inlet end face down is slowly
immersed into a vessel of water over a duration of time. The
quantity of water depends on the size of the article in order to
fully immerse the article. The sample remains still in the water
for 1 minute and then is slowly removed from the water and allowed
to sit for 2 hours. The article is weighed. Then the filter is
dried in a furnace for 5-6 hours at 100.degree. C. until the
initial weight is achieved. Another clean filtration efficiency
measurement is conducted to evaluate the filtration efficiency
change after exposure to water.
[0257] Water Nebulizer Test
[0258] As used herein, "Water Nebulizer Test" refers to testing an
article as follows. The article is placed in a can which contains a
bladder. The bladder is inflated with air to hold the filter in
place. Next, clean pressure drop is measured across the filter
using a differential pressure sensor/gauge at room temperature
(about 25.degree. C.). The flow rate of the exhaust gas upstream
from the assembly is ramped from 25.5 Nm.sup.3/h to 356.8
Nm.sup.3/h over 10 step increases, where the flow rate was
maintained for one minute at each new step increase. Each step
increase is in a range of about 8-68 Nm.sup.3/h. Next, filtration
efficiency is measured at 30.degree. C., with the exhaust flow rate
at 21 Nm.sup.3/h and 120 nm median particle diameter soot particles
at a concentration of 8.5 mg/m.sup.3 introduced upstream of the
filter using a propane burner for 45 minutes. Particle mass and
particle number is measured upstream and downstream of the filter
using a AVL microsoot sensor and TSI Engine Exhaust Particle Sizer
(EEPS), respectively. After the filtration efficiency is measured,
the article is removed from the can and placed in an oven at
650.degree. C. and held at 650.degree. C. for 9 hours so that the
soot that was loaded into the article was burned out of the
honeycomb.
[0259] The article is weighed at room temperature. The article is
exposed to a fine mist or spray of water using a nebulizer or
atomizer as described in U.S. Pat. No. 7,520,918 until the part is
exposed to 15 g/L of water. Next the article is dried in an oven
using 250.degree. C. for 3 hours. Then, the article and can
assembly are tested for filtration efficiency at 21 Nm.sup.3/hr at
30.degree. C. and 8.5 mg/m.sup.3 and the filtration efficiency at 0
g/L soot is compared to that measured before the 650.degree. C.
heat treatment and nebulizer water exposure. Then, a cleanout
procedure is performed on the article in an oven at 650.degree. C.
for 12 hours. The filter is then removed from the can and exposed
to a fine mist or spray of water using a nebulizer or atomizer as
described in U.S. Pat. No. 7,520,918 until the part was exposed to
15 g/L of water. Next the article is dried in an oven using
650.degree. C. for 9 hours. Then, the article and can assembly are
tested for filtration efficiency at 21 Nm.sup.3/hr at 30.degree. C.
and 8.5 mg/m.sup.3. Filtration efficiency at 0 g/L soot measured
after the second nebulizer water exposure is compared to the
baseline filtration efficiency at 0 g/L soot prior to the first
650.degree. C. heat treatment and nebulizer water exposure.
[0260] High Flow Test
[0261] As used herein, "High Flow Test" refers to testing an
article as follows.
[0262] An article is first measured for baseline FE/dP measurement
by the clean filtration efficiency test.
[0263] Thereafter, high flow is introduced to the article. The flow
rate of the exhaust gas upstream from the assembly is ramped from
85 m.sup.3/h to 850.8 m.sup.3/h over 10 step increases at about
25.degree. C., where the flow rate was maintained for one minute at
each new step increase. Each step increase was in a range of about
85-170 m.sup.3/h. Next, an air stream containing soot particles at
a concentration of 8 mg/m.sup.3 and a flow rate of 22.5 m.sup.3/h
is introduced upstream of the filter for 45 minutes. The soot is
generated at .about.110 nm particle size from a
commercially-available propane burner. Clean filtration efficiency
at 30.degree. C. is determined by measuring the difference between
a number of particulates that are introduced into the article and a
number of particulates that exit the article before and after
exposure to the flow conditions. After the filtration efficiency is
measured, post-test cleanout is conducted for 6 hours. Filtration
efficiency at 0 g/L soot is compared before and after the article
is exposed to the high flow test .
[0264] Soot Loaded Pressure Drop Test
[0265] After pre-test canning for 6 hours, soot is loaded into the
article with a flow rate of an exhaust gas upstream from the
assembly ramped from 25.5 m.sup.3/h to 356.8 m.sup.3/h over 10 step
increases at about 25.degree. C., where the flow rate was
maintained for one minute at each new step increase. Each step
increase was in a range of about 8-68 m.sup.3/h. Soot loading was
increased from 0 g/L to 3 g/L. A soot loaded pressure drop is
measured across the filter using a differential pressure
sensor/gauge at room temperature (about 25.degree. C.) after the
filter is loaded with soot. After the soot loaded pressure drop was
measured, post-test cleanout is conducted for 6 hours.
[0266] Cold Vibration Test
[0267] An article is placed on a shaker table which vibrates in 2
directions and is vibrated at 706 m/s.sup.2, 200 Hz for 2 hours
along the longitudinal and cross-sectional axis.
[0268] Vehicle Test
[0269] A canned article is installed on a vehicle which is driven
on the highway simulating acceleration followed by a "fuel cut," or
reduction in speed. The article experiences short pulses of high
temperature and high flow rate 5 times targeting 1000 m.sup.3/h for
30 seconds or more.
Example 1
[0270] An aqueous-based suspension was prepared using
Ceramabind.TM. 880 binder, Allied 0.3 .mu.m alumina suspension as
an inorganic material for the suspension. Ceramabind.TM. 880
purchased from Aremco is high temperature, water-dispersible
silicone resin. It cures at 232.degree. C. in 1 hour or 249.degree.
C. in 45 minutes. It has a pH=6.5 and a solids content of 50% by
weight. Allied 0.3 .mu.m alumina suspension purchased from Allied
High Tech has median particle size of 0.3 .mu.m or 300 nm. It
contains 18.2% alumina and 81.8% distilled water by weight. It has
pH=9 and is fully miscible in water. In this example, four dilute
alumina suspensions were prepared with dilution of as-received
Allied 0.3 um alumina suspension with deionized (DI) water followed
by addition of different amounts of Ceramabind.TM. 880. All four
samples had the same alumina concentration of 3% but different
concentrations of the binder, 10%, 30%, 50%, and 100% by weight of
alumina, respectively. The pH value was measured for each sample as
listed in Table 1. The stability of the suspension with 10% binder
was acceptable, and the sample showed no clear separation for 1-2
hours. The other suspension samples with more binder had good
stability, and the samples showed no clear separation for more than
4 hours. The tape test showed that the samples with addition of
binder up to 50% did not pass the test, and the sample with 100%
binder passed the test. However, the tape test is not considered to
be a definitive test as to whether the suspension will work in the
manufacture of
TABLE-US-00001 TABLE 1 Ceramabind .TM. 880 and Allied 0.3 um
alumina suspension Sample ID 1-C 1-D 1-F 1-G Binder concentration
(by 10% 30% 50% 100% wt % of alumina) Alumina concentration, 3.1%
3.1% 3.2% 3.2% wt % pH value 8.0 8.0 7.9 7.7 Stability of
suspension OK Good Good Good Tape test Failed Failed Failed
Passed
Example 2
[0271] An aqueous-based suspension was prepared comprising a
suspension of BINDZIL 9950 colloidal silica and Sky Spring alumina
powder. The binder BINDZIL 9950 colloidal silica was purchased from
AkzoNoble contains 50% of silica in water with colloidal particles
in sizes in a range of 10-20 nm. It has a pH=9 and a specific
surface area of 80 m.sup.2/g. SkySpring alpha-alumina powder
purchased from SkySpring Nanomaterials, Inc. has average alumina
particle size of 150 nm and specific surface area of 10 m.sup.2/g.
In this example, 5 dilute alumina suspensions were prepared by
mixing SkySpring alumina powder with DI water followed by addition
of different amounts of BINDZIL 9950 colloidal silica. All 4
samples had the same alumina concentration of 10% but different
concentrations of the binder, 20%, 30%, 50%, and 100% by weight of
alumina, respectively, as listed in Table 2. The stability of the
suspensions was good and the samples kept no clear separation for
more than 4 hours. The tape test showed that the samples with
addition of binder up to 50% didn't pass the test, and the sample
with 100% binder barely passed the test.
TABLE-US-00002 TABLE 2 BINDZIL 9950 colloidal silica and Sky Spring
alumina powder Sample ID 5-D 5-E 5-B 5-C Binder concentration (by
20% 30% 50% 100% wt % of alumina) Alumina concentration, wt % 10%
10% 10% 10% Stability of suspension Good Good Good Good Tape test
Failed Failed Failed Barely passed
Example 3
[0272] An ethanol-based aerosol deposition experiment was performed
on the same type of wall-flow filter substrates used in Examples 1
and 2.
[0273] 150 nm Al.sub.2O.sub.3 of an ethanol suspension (30 wt. %
solids, Beijing Dk Nano technology Co. LTD
http://www.nanoinglobal.com/en/ProductShow.asp?ID=189) was diluted
to 11 wt. % by ethanol (AR, Sinopharm Group Co. LTD). Dowsil 2405
was added as binder.
[0274] A two-phase fluid nozzle (1/4J-SS+SU11-SS, Spraying Systems
Co.) was used to atomize the solution. The atomizing gas was
nitrogen at 91.5 psi, and the liquid atomizing speed was 18
ml/min.
[0275] The droplets were dried in the deposition chamber as shown
in FIG. 4. The gas flow and the droplets were heated up by the
heaters placed around the chamber. The setting temperatures were
350.degree. C., 350.degree. C. and 120.degree. C. for the heat
sources 906a, 906b and 906c as shown in FIG. 4.
[0276] The flow was driven by a fan (TBR R11Q CL.HP from Twin city
fan (Shanghai) Co. Ltd.) at 2518 RPM. The total flow rate was 21.5
Nm.sup.3/h. Additional air was sucked in the system to make up the
total flow required. The final Al.sub.2O.sub.3 loading was 4.4
g/part. After deposition, the parts were cured at 200.degree. C.
for one hour.
[0277] Next, 300 nm median cigarette smoke particulate was used to
measure the filtration efficiency. The upstream concentrations were
500,000 particles over 30 seconds which is equal to approximately
353 particles/cc with a 0.1 cfm flow rate into a Lighthouse
Handheld 3016 particle counter. The particle number was collected
for 30 seconds upstream and 30 seconds downstream. The total test
was completed in about 1-2 minutes. The air velocity was 51
m.sup.3/h. The filtration efficiency was calculated based on
reduction of particulate number concentration at downstream. The
pressure drop was measured at the same flow rate by differential
pressure gauge. The filtration efficiency was 80% and the pressure
drop was 195 Pa.
Example 4
[0278] Aqueous-based aerosol deposition experiments on a wall-flow
filter.
[0279] Two kinds of Al.sub.2O.sub.3 aqueous suspensions were used.
One suspension was Allied 0.3 .mu.m alumina suspension, and the
other was 0.15 .mu.m alumina suspension (30 wt. % solids, Beijing
DK Nano technology Co. LTD
http.//www.nanoinglobal.com/en/ProductShow.asp?ID=189). The
suspension was diluted with DI water and mixed with binder to form
a solution composition as shown in Table 3.
[0280] A two-phase fluid nozzle (1/4J-SS+SU11-SS, Spraying Systems
Co.) was used to atomize the solution. The atomizing gas was
nitrogen, the liquid pressure was adjusted to achieve liquid flow
rate at about 10 ml/min as listed in Table 3. The droplet was dry
in the deposition chamber as shown in FIG. 1. The gas flow and the
droplets were heated up by the heaters placed around the chamber.
The setting temperatures of for the heat sources 906a, 906b and
906c as shown in FIG. 4 were 350.degree. C., 350.degree. C. and
300.degree. C. The flow was driven by a fan (TBR R11Q CL.HP from
Twin city fan (Shanghai) Co. Ltd.) at the RPM of 2518. The total
flow rate was 21.5 Nm.sup.3/h. Additional air was sucked in the
system to make up the total flow required.
[0281] After deposition, the parts were cured for 1 hour at
temperature listed in table 3. Filtration efficiency was measured
using 300 nm median particle size cigarette smoke particulate. The
procedure was described above, and the FE and dP comparison are
illustrated in FIGS. 12 and 13. All of the samples had higher
filtration efficiency compared to the uncoated honeycomb body.
There were few differences before and after cure.
TABLE-US-00003 TABLE 3 Alumina aerosol depositing and curing
conditions Solid Binder content Loading of vs Atomization
Atomization Cure Sample Al.sub.2O.sub.3 Al.sub.2O.sub.3 Binder
Al.sub.2O.sub.3 N.sub.2 pressure Liquid flow Loading Temp and ID
suspension (wt %) Composition (wt %) (psi) rate (g/min) (g/part)
Time DK-2405- DK 0.15 .mu.m 11% Dow sil 2405 5% 91.5 18 4.4
200.degree. C. * 1 h 5% (ethanol-based) Allied- Allied 0.3 .mu.m 5%
Ceramabind .TM. 20% 91.5 10 7.0 230.degree. C. * 1 h 880-20%
(aqueous-based) 880 DK-880- DK 0.15 .mu.m 5% Ceramabind .TM. 20%
92.5 10 5.5 20% (aqueous-based) 880 DK-880- DK 0.15 .mu.m 5%
Ceramabind .TM. 50% 90.9 12 6.0 50% (aqueous-based) 880 DK-9950- DK
0.15 .mu.m 5% BINDZIL 20% 91.6 10 4.7 250.degree. C. * 1 h 20%
(aqueous-based) 9950 DK-9950- DK 0.15 .mu.m 5% BINDZIL 50% 91.5 10
5.5 50% (aqueous-based) 9950 DK-2404- DK 0.15 .mu.m 5% Dow Corning
.RTM. 20% 92.4 11 4.7 200.degree. C. * 1 h 20% (aqueous-based)
IE-2404
[0282] FIGS. 14A-D show SEM images of the morphology of alumina
agglomerates formed from ethanol-based and aqueous-based
suspensions. The aqueous-based process generated agglomerates that
were less than 10 micrometers, similar to the ethanol based process
(e.g, DK-2405-5%). The agglomerate sizes were controlled for the
aqueous-based samples made using the DK binders, especially the
samples made by DK suspensions through adjusting batch formulation
(such as lowering alumina concentration) and atomization conditions
(such as lowering liquid flow rate).
Example 5
[0283] Sodium silicate solution purchased from Sigma-Aldrich is
reagent grade and contains about 10.6% Na.sub.2O and about 26.5%
SiO.sub.2. It has density of 1.39 g/mL at 25.degree. C. and a pH
value of 12.9. An alumina suspension purchased from Beijing DK Nano
technology Co. LTD ("DK suspension") has a solid concentration of
21.7% and pH of about 9 and alumina nanoparticles of around 150 nm
in size. Seven samples were prepared by mixing 5 grams of the DK
suspension with different quantities of sodium silicate solution as
shown in Table 1, followed by Vortex mixing for 10 seconds at a
speed of 3000 rpm. The resulting suspensions were applied on glass
slides to form a thin layer coating followed by a thermal drying
step. The tape test showed that the samples without or with 5.1%
binder didn't pass the test, and the samples with 7.7% or more
binder passed the test.
TABLE-US-00004 TABLE 4 Binder test on sodium silicate for DK
alumina suspension Sample ID #8-1 #8-2 #8-3 #8-4 #8-5 #8-6 #8-7
21.7% DK 5.01 5.01 5.06 5.05 5.05 5.01 5.01 aqueous suspension, g
Sodium 0 0.15 0.23 0.29 0.38 0.38 0.78 silicate solution, g Binder
0% 5.1% 7.7% 9.8% 12.9% 13.1% 26.6% concentration (by wt % of
alumina) Tape test Failed Failed Passed Passed Passed Passed
Passed
Example 6
[0284] A series of aqueous-based aerosol deposition experiments was
performed on wall-flow filters. The wall-flow filters had a
diameter of 4.055 inches (10.3 cm), length of 5.47 inches (13.9
cm), cells per square inch (CPSI) of 200, wall thickness of 8 mils
(203 micrometers), and average pore size of 14 .mu.m. The same 0.15
.mu.m alumina suspension (21.7 wt. % solids, Beijing DK Nano
technology Co. LTD
http://www.nanoinglobal.com/en/ProductShow.asp?ID=189) was used for
each sample shown in Table 5. The suspension was diluted with DI
water and mixed with binder to form a solution composition as shown
in Table 5.
[0285] A two-phase fluid nozzle (2050/70, 1/4J-SS+SU11-SS, Spraying
Systems Co.) was used to atomize the suspension and the atomizing
gas was nitrogen. The suspension was delivered to the nozzle at a
flow rate of 10 ml/min by a syringe pump as listed in Table 5.
[0286] The droplets were formed and dried into alumina agglomerates
in the deposition chamber as shown in FIG. 3. A heat source 606 in
the form of electrical resistance heating tapes was positioned in
the evaporation section 653 before the outlet end 625. The drying
gas was heated to 220.degree. C. by the heating transmitter and the
chamber mixing temperature was maintained at 120.degree. C. to
evaporate water, while chamber surface heating tapes were set at
130.degree. C. Gas flow was driven by a fan (TBR R11Q CL.HP from
Twin city fan (Shanghai) Co. Ltd.) at a RPM of 2518. The total flow
rate is 40 Nm.sup.3/h. Additional air was sucked in the system to
make up the total flow required. After deposition, the parts were
then thermally treated at the different temperatures in the range
of 250.degree. C. to 1100.degree. C. for 1 hour.
TABLE-US-00005 TABLE 5 Suspension composition and deposition
process parameters used for making one set of embodiments of
filters by ethanol-based process and aqueous-based process.
Ethanol- Aqueous- based based Alumina solids loading wt. % 11% 5%
Binder 2405 sodium silicate Binder concentration wt. % 15% 10%~30%
(vs. Alumina) Suspension flow rate (ml/min) 10 10 Atomizing gas
flow rate (Nm.sup.3/h) 5.00 5.00 Total carrier gas flow
(Nm.sup.3/h) 40 40 Heating transmitter setting 220 220 temperature
(.degree. C.) Chamber surface heating tape 130 130 setting
temperature (.degree. C.)
[0287] Filtration efficiency was tested with 300 nm median particle
size cigarette smoke particulate. The procedure was described
above, and the FE vs. dP and FE vs. Loading are illustrated in FIG.
15A and FIG. 15B. All of the samples had higher filtration
efficiency compared to the uncoated wall-flow filter. There were
differences for the samples before and after cure. The pressure
drop penalty was comparable with ethanol-based process at similar
filtration efficiency level.
[0288] A two-stage water resistance test was performed using a
two-stage water nebulization test and full water immersion FE/dP
performance was measured before and after mist soaking or full
water immersion followed by full drying. The water nebulization
test was conducted in such way that deposited channels faced the
flow of mist so deposited agglomerates directly contact water
droplets (mist) and suction and keep the water droplets in the
pores due to pore capillary force. The two-stage water nebulization
test included a first stage with 15-20 g water takeup and a second
stage with 60-70 g water takeup if the first stage test passed. The
full water immersion test was conducted by fully immersing the
filter into a tank of water for several minutes and water takeup
was at least 300 g for the substrates.
[0289] FIGS. 15A and 15B show performance of parts with deposits
from the aqueous-based process and the ethanol-based process in
terms of FE/dP performance as well as FE as a dependence of deposit
loading. The suspension and processing conditions are shown in
Table 5. FIG. 15A shows similar FE-dP trend for the two processes.
FIG. 15B indicates that at the same deposit loading, the aqueous
process gave higher FE value. As an example, a 3 g/L loading of
deposits, the aqueous-based process produced 90% FE, while
ethanol-based process resulted in 84% FE.
[0290] FIGS. 16A and 16B show morphology and size of alumina
agglomerates formed on the surface of wall-flow filter for the
aqueous-based process deposits and ethanol-based process. It can be
seen that aqueous-based process forms a deposit microstructure of
packed spherical agglomerates with some partially penetrating into
pores of the honeycomb wall.
[0291] For these specific examples and these specific process
conditions, another difference that was observed is that aqueous
process led to larger agglomerates than ethanol-based process. As
shown in FIG. 16B, the agglomerate sizes respectively were 1.72
.mu.m and 1.78 .mu.m for ethanol-based process and aqueous process.
However, further experimentation with fluid flows (gas and
suspension) and nozzle design changes indicated that similar
agglomerate sizes could be achieved between the two processes.
[0292] Table 6 lists FE/dP performance of filters made with
different quantities of sodium silicate binder, 10 wt %, 20 wt %,
and 30 wt %, respectively.
TABLE-US-00006 TABLE 6 As-deposit FE/dP performance of the filter
parts made with 10%, 20%, and 30% sodium silicate binder (by weight
of alumina) Deposit 300 nm Aluminum Binder Chamber loading, smoke
dP, conc. conc. temp. .degree. C. g/L FE Pa L-190411- 5% 10% 20
4.05 89.2% 232 01 L-190411- 5% 10% 120 3.45 87.8% 233 02 L-190408-
5% 20% 120 3.79 95.7% 263 01 L-190408- 5% 20% 120 3.45 94.7% 246 02
L-190408- 5% 20% 120 3.28 91.2% 238 03 L-190408- 5% 20% 120 3.28
90.1% 234 04 L-190409- 5% 30% 120 4.31 92.9% 245 01 L-190409- 5%
30% 20 4.31 92.6% 237 02
[0293] FIG. 16C is a graph showing the agglomerate size
distribution of the aqueous-based and ethanol based examples. The
agglomerate size was measured using scanning electron microscope.
FIG. 16D is a graph showing agglomerate accumulative size
distribution between the embodiments of the two processes. Data for
the ethanol-based process is shown in the dotted lines, and data
for the aqueous-based process is shown in the solid line. Table 7
shows further details of the particle size for both processes. The
values d10, d50 and d90 refer to the diameter at which 10%, 50% and
90% of the sample's deposited mass is comprised of particles with a
diameter less than the provided value.
TABLE-US-00007 TABLE 7 Ethanol-Based Aqueous-Based d10, micrometers
0.752 1.099 d50, micrometers 1.083 1.72 d90, micrometers 1.561
2.693
[0294] FIGS. 17A and 17B show the impact of thermal treatment
temperature on water resistance. The samples were made with the
same 5 wt % alumina suspension with 20 wt % sodium silicate binder
except for one sample, L-0411-02 as shown in Table 8. It can be
seen that thermal treatment at temperature of 600.degree. C. or
higher, preferably 650.degree. C. or higher, significantly improves
the water resistance of FE performance, preferably with FE drop
less than 6% after exposure to one of the water resistance tests
(Neb-1, Neb-2, Water Immersion). Higher temperature thermal
treatments resulted in less reduction in FE after being exposed to
a water test. For example, there was no FE drop for 1100.degree.
C.-treated filter, and net total drop by 5.9% for 650.degree.
C.-treated sample, after completion of a two-stage nebulization
test and full water immersion test. The 425.degree. C.-treated
filter lost 36% in net FE after exposure to water immersion. In
some embodiments, the porous ceramic honeycomb body comprising
agglomerates comprised of 1-15 wt % alumina nanoparticles and 5-25
wt % binder is heat treated by raising the temperature of the
honeycomb body comprising alumina nanoparticles to a maximum
temperature of 600 to 1200.degree. C., for example 650 to
1100.degree. C. for a period of 1 to 24 hours.
TABLE-US-00008 TABLE 8 List of the samples made from aqueous-based
process and thermally treated at different temperature after
deposition. Deposit Thermal Aluminum Binder Chamber loading,
treatment Sample ID conc. conc. temp. .degree. C. g/L temp.
.degree. C. L-190411-02 5% 10% 120 3.96 1100 L-190416-01 5% 20% 120
3.99 910 L-190416-02 5% 20% 120 4.10 910 L-190416-03 5% 20% 120
4.21 650 L-190416-04 5% 20% 120 4.07 650 L-190416-05 5% 20% 120
4.23 425 L-190416-06 5% 20% 120 4.10 425 L-190408-04 5% 20% 120
3.26 250
[0295] We have found that thermal treatment after deposition might
reduce FE, dP, or both FE and dP, as shown in FIGS. 18A and 18B. As
shown in FIG. 18A, lower treatment temperatures for the Examples
from Table 8 caused lower drops in filtration efficiency due to the
thermal treatment (less FE drop); for example, an 1100.degree.
C.-treatment reduced FE value of the filter by 6.3%, and after
650.degree. C.-treatment a similarly alumina loaded filter
experienced a drop in FE of about 2% (the two examples in FIG. 18A
showing net decrease in FE of 2.2%-2.5%). As shown in FIG. 18B,
lower treatment temperatures for the Examples from Table 8 showed
an increase in pressure drop across the filter for lower thermal
treatment temperatures (below 600.degree. C., or in the range of
400-600.degree. C. wherein FIG. 18B shows two examples at thermal
treatment temperatures of 425.degree. C.), whereas higher thermal
treatment temperatures resulted in reductions in pressure drop as
compared to the as-deposited state, with the examples in FIG. 18B
showing a reduction in pressure drop of 10 Pa or more for thermal
treatment temperatures of greater than 600 C, with examples in FIG.
18B corresponding to 650, 910, and 1100.degree. C. Thus, a maximum
thermal treatment temperature of 600-700.degree. C., and preferably
625-675.degree. C., showed a small reduction in FE, along with an
advantageous reduction in pressure drop, after thermal
treatment.
[0296] FIG. 19 shows the smoke FE data measured after thermal
treatment and each of the durability (e.g. water resistance) tests.
The water resistance tests include 3-steps: 1) a first nebulizer
test with 15-20 g water loading; 2) a second water nebulizer test
with 60-70 g water loading; 3) a water soak test with water loading
>300 g. The total FE net loss during the tests was 1.66% for a
250.degree. C.-treated filter and 8.74% for a 650.degree.
C.-treated filter. It should be noted that the 250.degree.
C.-treated sample had exposure to 650.degree. C. for 10 hours
during hot canning before the vehicle test and the water test,
which benefitted deposit strength and water resistance.
Example 7
Morphology of Inorganic Deposits
[0297] This example demonstrates the morphology of filtration
articles, for example, a plugged honeycomb body having inorganic
material deposited on or in or on and in the porous walls of the
plugged honeycomb body. Such a morphology is achieved by an aerosol
deposition process of inorganic material.
[0298] An ethanol-based aerosol deposition experiment was performed
on wall-flow filter substrates having a diameter of 4.252'' and a
length of 4.724'' having 200 CPSI, a wall thickness of 8 mils, and
an average pore size of 13.5 .mu.m and average porosity of 55%.
Inorganic material was deposited to a loading of 6.95 g/L. A
co-flow type chamber similar to the chamber shown in FIG. 5 was
used with 11% solids alumina (DK-2405), 15% Dow 2405 binder, the
spraying nozzle an external mix nozzle (SU1A, 2050/7). The liquid
flow rate was 24 g/min with 8 g/min through three nozzles.
Atomizing gas flow rate was 30 Nm.sup.3/hour total, with 10
Nm.sup.3/hour through each of 3 nozzles. Carrier gas flow rate was
70 Nm.sup.3/hour. A heat transmitter 706a was used to increase the
inlet temperature above the nozzle 720. The setpoint of the heat
transmitter 706a was 230.degree. C. to provide a measured
temperature of about 150.degree. C. A first heater 706b was set at
270.degree. C. (150.degree. C. actual), a second heater 706c was
set at 300.degree. C. (155.degree. C. actual) and a third heater
706d was set at 300.degree. C. (120.degree. C. actual).
[0299] SEM photographs of the wall flow filter containing the
aerosol-deposited alumina were obtained on the wall flow filter
were obtained as follows.
[0300] FIG. 20 is an SEM photograph of a top view of an inlet
region of an inlet channel;
[0301] FIG. 21 is an SEM photograph of a cutaway side view of an
inlet region of an inlet channel;
[0302] FIG. 22 is an SEM photograph of a top view of a middle
region of an inlet channel;
[0303] FIG. 23 is an SEM photograph of a cutaway side view of a
middle region of an inlet channel;
[0304] FIG. 24 is an SEM photograph of a top view of an outlet
region of an inlet channel;
[0305] FIG. 25 is an SEM photograph of a cutaway side view of an
outlet region of an inlet channel;
[0306] FIG. 26 is an SEM photograph of a magnified cutaway side
view of an outlet region of an inlet channel;
[0307] FIG. 27 is the SEM photograph of FIG. 26 with the colors
reversed;
[0308] FIG. 28A is a portion of the SEM photograph of FIG. 27 with
dashed lines surrounding an aggregate 1500; and
[0309] FIG. 28B is a schematic representation of the agglomerates
1502 forming the aggregate 1500 region outlined by the dashed lines
in FIG. 28A.
[0310] As best seen in FIGS. 26, 27, and 28A-B, the inorganic
material on the porous walls comprises particulate or primary
particles of inorganic material (in this specific example,
alumina), particulate-binder agglomerates comprised of the
particles and the binder material and aggregates of
particulate-binder agglomerates. The inorganic material in or on or
in and one the porous walls of the filtration article in the form
of a plugged honeycomb body is present "clusters" or "chains" of
agglomerates and/or aggregates. In some embodiments, the cluster or
chains provide an inorganic material morphology that is one or more
of finger-shaped, fibril-shaped, or sponge-like, such as for
example, a morphology resembling a sea wool sponge.
[0311] It will be apparent to those skilled in the art that various
modifications and variations can be made to the embodiments
described herein without departing from the spirit and scope of the
claimed subject matter. Thus, it is intended that the specification
cover the modifications and variations of the various embodiments
described herein provided such modification and variations come
within the scope of the appended claims and their equivalents.
* * * * *
References