U.S. patent application number 17/579633 was filed with the patent office on 2022-05-12 for purification and enrichment of boron nitride nanotube feedstocks.
The applicant listed for this patent is Government of the United States, as represented by the Secretary of the Air Force, Government of the United States, as represented by the Secretary of the Air Force. Invention is credited to Jeffrey R. Alston, Jason T. Lamb.
Application Number | 20220144636 17/579633 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-12 |
United States Patent
Application |
20220144636 |
Kind Code |
A1 |
Alston; Jeffrey R. ; et
al. |
May 12, 2022 |
Purification and Enrichment of Boron Nitride Nanotube
Feedstocks
Abstract
A method for purifying a boron nitride nanotube feedstock is
disclosed, including an initial step of mixing a boron nitride
nanotube (BNNT) feedstock with a solvent to form an initial
mixture. This BNNT feedstock is made up of hexagonal boron nitride
(h-BN) particles and less than about 50 weight percent BNNTs on a
dry basis. This initial mixture is then sonicated within a
treatment vessel using an ultrasonic probe. At least a portion of
the initial mixture is filtered out of the treatment vessel and
across a nanoporous membrane at the same as the sonication. In this
manner, the method provides a filtrate which is enriched in h-BN
particles relative to the initial mixture and a retentate which is
enriched in BNNTs relative to the initial mixture.
Inventors: |
Alston; Jeffrey R.; (High
Point, NC) ; Lamb; Jason T.; (Huntersville,
NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Government of the United States, as represented by the Secretary of
the Air Force |
Wright-Patterson AFB |
OH |
US |
|
|
Appl. No.: |
17/579633 |
Filed: |
January 20, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16245821 |
Jan 11, 2019 |
11254571 |
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17579633 |
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International
Class: |
C01B 21/064 20060101
C01B021/064; B01D 71/36 20060101 B01D071/36; B01D 11/02 20060101
B01D011/02 |
Goverment Interests
GOVERNMENT INTEREST
[0001] The invention described herein may be manufactured, used,
and licensed by or for the Government of the United States for all
governmental purposes without the payment of any royalty.
Claims
1. A system for purifying a boron nitride nanotube feedstock
comprising: a treatment vessel having an interior volume for
receiving an initial mixture of a boron nitride nanotube (BNNT)
feedstock with a solvent, the BNNT feedstock comprising hexagonal
boron nitride (h-BN) particles and less than about 50 weight
percent BNNTs on a dry basis a nanoporous membrane in flow
communication with the treatment vessel interior volume; and an
ultrasonic mixing probe disposed within the treatment vessel
interior volume, wherein the initial mixture of the boron nitride
nanotube (BNNT) feedstock with the solvent is sonicated within the
treatment vessel interior volume while, at the same time, at least
a portion of the mixture is filtered across the nanoporous membrane
and out of the treatment vessel to provide a filtrate.
2. The system of claim 1, wherein the initial mixture further
comprises a non-metal containing surfactant.
3. The system of claim 1, wherein the retentate comprises at least
90 weight percent BNNTs on a dry basis.
4. The system of claim 1, wherein the solvent comprises at least
one polar aprotic solvent.
5. The system of claim 1, wherein the nanoporous membrane comprises
polytetrafluoroethylene.
6. The system of claim 1, wherein the nanoporous membrane comprises
a plurality of pores, the pores having an average pore size from
about 0.1 .mu.m to about 100 .mu.m.
7. The system of claim 1, further comprising a receiving vessel for
collecting filtrate from the nanoporous membrane, wherein the
receiving vessel is maintained at a sub-atmospheric pressure in
order to draw filtrate across the membrane.
8. The system of claim 1, further comprising a solvent supply
reservoir and a solvent supply line for adding makeup solvent to
the mixture in the treatment vessel.
Description
FIELD OF THE INVENTION
[0002] The present disclosure relates to the field of
nanomaterials, and more specifically to a method for purifying a
boron nitride nanotube feedstock.
BACKGROUND OF THE INVENTION
[0003] Boron nitride nanotubes (BNNTs) are a relatively new
category of nanomaterials which are of both commercial and research
interest. To date, methods for the preparation of BNNTs have
generally fallen into two broad categories: (1) methods which
produce small quantities of relatively high purity BNNTs and (2)
methods which produce larger quantities of BNNTs, but with a lower
BNNT purity (i.e. more impurities are included with the BNNTs in
the final product mixture). Such high quantity, low purity methods
typically provide a BNNT feedstock which is made up of 50 weight
percent BNNTs or less. The remainder of the BNNT feedstock is made
up of undesirable side products. In many instances, the feedstock
may include 20 weight percent or more of hexagonal boron nitride
(h-BN), with amorphous boron and boron nitride derivatives making
up the balance of the mixture. Neither method has thus far proven
to satisfactorily provide large quantities of relatively high
purity BNNTs at a commercially reasonable price point.
[0004] Thus, there is a continuing need for novel methods and
systems for providing large quantities of relatively high purity
BNNTs, and preferably at a lower price point.
SUMMARY OF THE INVENTION
[0005] In response to these issues, the present disclosure
provides, in a first aspect, a method for purifying a boron nitride
nanotube feedstock. In accordance with one embodiment of the
present disclosure, this method includes an initial step of mixing
a boron nitride nanotube (BNNT) feedstock with a solvent to form an
initial mixture. This BNNT feedstock is made up of hexagonal boron
nitride (h-BN) particles and less than about 50 weight percent
BNNTs on a dry basis. According to the method, this initial mixture
is then sonicated within a treatment vessel using an ultrasonic
probe. The method also includes a step of filtering at least a
portion of the initial mixture out of the treatment vessel and
across a nanoporous membrane at the same time as the sonication. In
this manner, the method provides a filtrate which is enriched in
h-BN particles relative to the initial mixture and a retentate
which is enriched in BNNTs relative to the initial mixture.
[0006] In certain embodiments, the solvent is made up of at least
one polar aprotic solvent. Further, in some embodiments, the
solvent is more particularly made up of a mixture of at least two
solvents selected from the group consisting of tetrahydrofuran
(THF), N-methyl-2-pyrrolidone (NMP), N,N'-dimethylformamide (DMF),
acetone, N,N'-dimethyl acetamide (DMAc), dimethylsulfoxide (DMSO),
dichloromethane DCM), toluene, isopropanol, ethanol, and hexane. In
some instances, the solvent is made up of a mixture of
dimethylformamide and acetone.
[0007] In some embodiments, the initial mixture may also include a
non-metal containing surfactant.
[0008] In certain embodiments, the retentate is made up of at least
90 weight percent BNNTs on a dry basis. In some instances, the
retentate is made up of at least 98 weight percent BNNTs on a dry
basis.
[0009] According to some embodiments, the nanoporous membrane is
made up of polytetrafluoroethylene (PTFE). Further, in certain
embodiments, the nanoporous membrane includes a plurality of pores,
with these pores having an average pore size from about 0.1 .mu.m
to about 100 .mu.m.
[0010] In some embodiments, a sub-atmospheric pressure is
established across the membrane in order to draw filtrate across
the membrane.
[0011] According to some embodiments, the method includes a further
step of adding makeup solvent to the mixture during the filtering
step so that the volume of the mixture in the treatment vessel
remains substantially constant.
[0012] In a second aspect, the present disclosure provides a system
for purifying a boron nitride nanotube feedstock. In accordance
with one embodiment of the present disclosure, this system includes
a treatment vessel having an interior volume for receiving an
initial mixture of a boron nitride nanotube (BNNT) feedstock with a
solvent. This BNNT feedstock is made up of hexagonal boron nitride
(h-BN) particles and less than about 50 weight percent BNNTs on a
dry basis. According to the present disclosure, the system also
includes a nanoporous membrane in flow communication with the
treatment vessel's interior volume; and an ultrasonic mixing probe
disposed within the treatment vessel's interior volume. In
accordance with the present disclosure, an initial mixture of a
boron nitride nanotube (BNNT) feedstock with a solvent is sonicated
within the treatment vessel interior volume while, at the same
time, at least a portion of the mixture is filtered across the
nanoporous membrane and out of the treatment vessel to provide a
filtrate.
[0013] In some embodiments, the initial mixture may also include a
non-metal containing surfactant.
[0014] According to some embodiments, the retentate is made up of
at least 90 weight percent BNNTs on a dry basis. In some instances,
the retentate is made up of at least 98 weight percent BNNTs on a
dry basis.
[0015] In some embodiments, the solvent is made up of at least one
polar aprotic solvent.
[0016] In certain embodiments, the nanoporous membrane is made up
of polytetrafluoroethylene (PTFE). Further, in certain embodiments,
the nanoporous membrane includes a plurality of pores, with these
pores having an average pore size from about 0.1 .mu.m to about 100
.mu.m.
[0017] According to some embodiments, the system may also include a
receiving vessel for collecting filtrate from the nanoporous
membrane and this receiving vessel may be maintained at a
sub-atmospheric pressure in order to draw filtrate across the
membrane.
[0018] In certain embodiments, the system may also include a
solvent supply reservoir and a solvent supply line for adding
makeup solvent to the mixture in the treatment vessel.
[0019] In a further aspect, the present disclosure provides method
for suspending a boron nitride nanotube feedstock. In accordance
with one embodiment of the present, this method includes an initial
step of mixing a boron nitride nanotube (BNNT) feedstock with a
solvent to form an initial mixture. This BNNT feedstock is made up
of hexagonal boron nitride (h-BN) particles and less than about 50
weight percent BNNTs on a dry basis. According to the method, this
initial mixture is then sonicated within a treatment vessel using
an ultrasonic probe to suspend the BNNTs.
[0020] In accordance with certain embodiments, the solvent is made
up of at least one polar aprotic solvent. Further, in some
embodiments, the solvent is more particularly made up of a mixture
of at least two solvents selected from the group consisting of
tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP),
N,N'-dimethylformamide (DMF), acetone, N,N'-dimethylacetamide
(DMAc), dimethylsulfoxide (DMSO), dichloromethane (DCM), toluene,
isopropanol, ethanol, and hexane. In some instances, the solvent is
made up of a mixture of dimethylformamide and acetone.
[0021] According to some embodiments, the initial mixture may also
include a non-metal containing surfactant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Other embodiments of the invention will become apparent by
reference to the detailed description in conjunction with the
figures, wherein elements are not to scale so as to more clearly
show the details, wherein like reference numbers indicate like
elements throughout the several views, and wherein:
[0023] FIG. 1. is a diagram of an apparatus for use in purifying a
boron nitride nanotube feedstock according to one embodiment of the
present disclosure; and
[0024] FIG. 2 is a diagram of membrane for use in purifying a boron
nitride nanotube feedstock according to one embodiment of the
present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0025] In one aspect, the present disclosure provides a method for
purifying a boron nitride nanotube feedstock. In general, this
method includes: (1) mixing a boron nitride nanotube (BNNT)
feedstock with a solvent, (2) sonicating this mixture within a
treatment vessel, and (3) filtering at least a portion of this
mixture out of the treatment vessel and across a nanoporous
membrane at the same time as the sonication. Thus, a filtrate is
provided which is enriched in hexagonal boron nitride (h-BN)
particles relative to the initial mixture, and a retentate is
provided which is enriched in BNNTs relative to the initial
mixture.
[0026] In a second aspect, the present disclosure also provides a
system 10 for purifying a BNNT feedstock. As illustrated in FIG. 1,
this system 10 includes a treatment vessel 12 having an interior
volume for receiving an initial mixture 14 of a BNNT feedstock with
a solvent. This BNNT feedstock is made up of hexagonal boron
nitride (h-BN) particles and less than about 50 weight percent
BNNTs on a dry basis. According to the present disclosure, the
system 10 also includes a nanoporous membrane 16 in flow
communication with the interior volume of the treatment vessel 12;
and an ultrasonic mixing probe 18 disposed within the treatment
vessel interior volume. In accordance with the present disclosure,
the initial mixture 14 of a boron nitride nanotube (BNNT) feedstock
with a solvent is sonicated within the treatment vessel interior
volume while, at the same time, at least a portion of the mixture
14 is filtered across the nanoporous membrane 16 and out of the
treatment vessel 12 to provide a filtrate.
[0027] In the first step of the aforementioned method, a BNNT
feedstock is combined with a solvent to provide an initial mixture
14 in the interior volume of the treatment vessel 12. This BNNT
feedstock typically has a relatively low initial purity. Generally,
the composition of the initial BNNT feedstock includes less than
about 50 weight percent BNNT. The remainder of the BNNT feedstock
is made up of undesirable side products. In many instances, the
feedstock may include 20 weight percent or more of hexagonal boron
nitride (h-BN), with amorphous boron and boron nitride derivatives
making up the balance of the mixture 14.
[0028] The solvent for the initial mixture 14 typically is made up
of at least one polar aprotic solvent. In some embodiments, this
solvent is more particularly a mixture of at least two solvents
selected from the group consisting of tetrahydrofuran (THF),
N-methyl-2-pyrrolidone (NMP), N,N'-dimethylformamide (DMF),
acetone, N,N'-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO),
dichloromethane (DCM), toluene, isopropanol, ethanol, and hexane.
In some instances, the solvent is made up of a mixture of
dimethylformamide and acetone.
[0029] In some embodiments, the initial mixture 14 may also include
a surfactant to improve dispersion of the BNNTs in the solvent.
This surfactant is generally a non-metal containing surfactant.
Examples of suitable surfactants include sorbitan esters (Spans),
polyoyxethylene sorbitan esters (Tweens), and alkylaryl polyether
alcohols. In some instances, protein-based stabilizers or DNA or
RNA based stabilizer may also be used as a dispersant. For
instance, phospholipids, lecithin (from eggs), or ranasmurfin (frog
protein) may be used as a dispersant in certain embodiments.
[0030] The initial mixture 14 is then ultrasonically sonicated in a
treatment vessel 12. The treatment vessel 12 may be the same as
that in which the initial mixture 14 was originally prepared, or
the mixture 14 may be transferred to a different vessel 12.
[0031] The sonication is accomplished by inserting an ultrasonic
probe 18 into the mixture 14, which vibrates at an ultrasonic
frequency in excess of about 20,000 Hertz, and generally from about
20,000 to about 40,000 Hertz. This vibrational energy is
transferred to the mixture 14 within the treatment vessel 12 and
acts to disperse and suspend the BNNTs and other particles within
the solvent.
[0032] According to the present disclosure, at least a portion of
the initial mixture 14 is filtered out of the treatment vessel 12
at the same as the mixture 14 is being sonicated. In this regard, a
lower portion of the treatment vessel 12 includes a nanoporous
membrane 16 in flow communication with the treatment vessel 12
interior volume, and this nanoporous membrane 16 includes a
plurality of pores. A portion of the mixture 14 passes across this
nanoporous membrane 16 (i.e. through the pores) as it is filtered
out of the treatment vessel 12.
[0033] In some instances, these pores may have an average pore size
from about 0.1 .mu.m to about 100 .mu.m. Further, the nanoporous
membrane 16 is typically formed from a polymeric material.
According to some embodiments, the nanoporous membrane 16 may for
instance be made up of polytetrafluoroethylene (PTFE).
[0034] In this manner, the portion of the initial mixture 14 which
passes through the nanoporous membrane 16 may be collected as a
filtrate, with the remaining portion of the mixture 14 left in the
treatment vessel 12 being a corresponding retentate. According to
the present disclosure, the composition of the filtrate is enriched
in h-BN particles relative to the initial mixture 14, while the
composition of the retentate is enriched in BNNTs relative to the
initial mixture 14.
[0035] Again, the initial mixture 14 will typically be made up of
less than about 50 weight percent BNNTs on a dry basis. After
sonication and filtration, however, the final retentate may in some
instances be made up of at least 90 weight percent BNNTs on a dry
basis. In some instances, the retentate is made up of at least 98
weight percent BNNTs on a dry basis.
[0036] Without being bound by theory, it is believed that the BNNTs
are longer particles than the h-BN particles and other impurities.
Thus, the BNNT particles 20 have a relatively higher aspect ratio,
while the h-BN particles 22 have a relatively lower aspect ratio,
as illustrated diagrammatically in FIG. 2. Thus, it is believed
that the h-BN particles 22 more easily pass through the nanopores
of the membrane 16, as compared to the high aspect ratio BNNT
particles 20. Consequently, after filtration, the filtrate is
enriched in h-BN particles and depleted in BNNTs relative to the
initial mixture 14, while the retentate is enriched in BNNTs and
depleted in h-BN particles relative to the initial mixture 14.
[0037] Additionally, in some embodiments, a sub-atmospheric (i.e.,
vacuum) pressure may be established across the membrane 16 in order
to draw filtrate across the membrane 16 and out of the treatment
vessel 12 at a faster rate. Referring back to FIG. 1, the system 10
may also include a receiving vessel 24 for collecting filtrate from
the nanoporous membrane 16 and this receiving vessel 24 may be
maintained at a sub-atmospheric pressure in order to draw filtrate
across the membrane 16.
[0038] Moreover, according to some embodiments, the method may also
include a further step of adding makeup solvent to the mixture 14
during the filtering step. For instance, the system 10 may also
include a solvent supply reservoir 26 and a solvent supply line 28
for adding makeup solvent to the mixture 14 in the treatment vessel
12. In certain embodiments the makeup solvent is added at a rate
such that the volume of the mixture 14 in the treatment vessel 12
remains substantially constant. More particularly, in certain
embodiments the makeup solvent is added at a rate such that the
volume of the mixture 14 in the treatment vessel 12 remains within
+/-10% of the initial mixture 14 volume during the filtering
step.
[0039] In a further aspect, the present disclosure provides a
method for suspending a boron nitride nanotube feedstock. In
accordance with one embodiment of the present, this method includes
an initial step of mixing a BNNT feedstock with a solvent to form
an initial mixture 14, as described above. This BNNT feedstock is
made up of hexagonal boron nitride (h-BN) particles and less than
about 50 weight percent BNNTs on a dry basis. According to the
method, this initial mixture 14 is then sonicated within a
treatment vessel 12 using an ultrasonic probe 18 to suspend the
BNNTs.
[0040] Suitable solvents for use in this method are generally the
same as those described above. Typically, the solvent is made up of
at least one polar aprotic solvent. For instance, the solvent may
be made up of a mixture of at least two solvents selected from the
group consisting of are tetrahydrofuran (THF),
N-methyl-2-pyrrolidone (NMP), N,N'-dimethylformamide (DMF),
acetone, N,N'-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO),
dichloromethane (DCM), toluene, isopropanol, ethanol, and hexane.
In some instances, the solvent is made up of a mixture of
dimethylformamide and acetone. The initial mixture may also include
a non-metal containing surfactant.
[0041] As used herein and in the appended claims, the singular
forms "a", "an" and "the" include plural reference unless the
context clearly dictates otherwise. As well, the terms "a" (or
"an"), "one or more" and "at least one" can be used interchangeably
herein. It is also to be noted that the terms "comprising",
"including", "characterized by" and "having" can be used
interchangeably.
[0042] While the present invention has been illustrated by the
description of one or more embodiments thereof, and while the
embodiments have been described in considerable detail, they are
not intended to restrict or in any way limit the scope of the
appended claim to such detail. Additional advantages and
modification will be readily apparent to those skilled in the art.
The invention in its broader aspects is therefore not limited to
the specific details, representative compositions, and methods and
illustrative examples shown and described. Accordingly, departures
may be made from such details without departing from the scope or
the spirit of the general inventive concept exemplified herein.
* * * * *