U.S. patent application number 13/444129 was filed with the patent office on 2013-02-28 for method of conditioning an internal combustion engine.
This patent application is currently assigned to Cerion Technology, Inc.. The applicant listed for this patent is KENNETH REED. Invention is credited to KENNETH REED.
Application Number | 20130047945 13/444129 |
Document ID | / |
Family ID | 39157580 |
Filed Date | 2013-02-28 |
United States Patent
Application |
20130047945 |
Kind Code |
A1 |
REED; KENNETH |
February 28, 2013 |
METHOD OF CONDITIONING AN INTERNAL COMBUSTION ENGINE
Abstract
A method of improving the efficiency of a diesel engine provided
with a source of diesel fuel includes the steps of: a) adding to
the diesel fuel a reverse-micellar composition having an aqueous
first disperse phase that includes a free radical initiator and a
first continuous phase that includes a first hydrocarbon liquid, a
first surfactant, and optionally a co-surfactant, thereby producing
a modified diesel fuel; and b) operating the engine, thereby
combusting the modified diesel fuel. The efficiency of a diesel
engine provided with a source of diesel fuel and a source of
lubricating oil can also be improved by modifying the lubricating
oil by the addition of a stabilized nanoparticulate composition of
cerium dioxide. The efficiency of a diesel engine can also be
improved by adding to the diesel fuel a reverse-micellar
composition that includes an aqueous disperse phase containing
boric acid or a borate salt.
Inventors: |
REED; KENNETH; (Rochester,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
REED; KENNETH |
Rochester |
NY |
US |
|
|
Assignee: |
Cerion Technology, Inc.
Rochester
NY
|
Family ID: |
39157580 |
Appl. No.: |
13/444129 |
Filed: |
April 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12440171 |
Sep 4, 2009 |
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PCT/US07/77543 |
Sep 4, 2007 |
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13444129 |
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60824514 |
Sep 5, 2006 |
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60911159 |
Apr 11, 2007 |
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60938314 |
May 16, 2007 |
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Current U.S.
Class: |
123/1A |
Current CPC
Class: |
C10L 1/10 20130101; C10N
2040/25 20130101; C10M 2201/062 20130101; Y02T 50/678 20130101;
C10L 1/2222 20130101; C10L 10/02 20130101; C01F 17/235 20200101;
C01P 2002/72 20130101; C10L 1/1233 20130101; C10L 1/1616 20130101;
C10L 1/125 20130101; B82Y 30/00 20130101; B01F 7/164 20130101; B01J
23/10 20130101; C10L 1/103 20130101; C01P 2004/64 20130101; C10L
10/12 20130101; C10L 1/1811 20130101; C10L 1/1608 20130101; B01F
3/0807 20130101; C01P 2004/52 20130101; C01P 2004/04 20130101; C10L
1/19 20130101; C10L 1/1258 20130101; C10L 10/08 20130101; B01J
13/0086 20130101; B01J 13/0047 20130101; C10N 2030/06 20130101;
C10L 1/1883 20130101; C01F 17/206 20200101; C10L 1/2437 20130101;
C10L 1/1824 20130101; C10L 1/1881 20130101; C10L 1/1985 20130101;
C10M 2201/062 20130101; C10N 2010/06 20130101; C10N 2020/06
20130101; C10M 2201/062 20130101; C10N 2010/06 20130101; C10N
2020/06 20130101 |
Class at
Publication: |
123/1.A |
International
Class: |
F02B 43/02 20060101
F02B043/02 |
Claims
1. A method of improving the efficiency of a diesel engine provided
with a source of diesel fuel, said method comprising the steps of:
a) adding to said diesel fuel a reverse-micellar composition
comprising: i) an aqueous first disperse phase comprising a free
radical initiator; and ii) a first continuous phase comprising a
first hydrocarbon liquid, a first surfactant, and optionally a
co-surfactant, thereby producing a modified diesel fuel; and b)
operating said engine, thereby combusting said modified diesel
fuel.
2. The method according to claim 1, wherein said diesel fuel is
selected from the group consisting of D2 diesel, low sulfur diesel,
ultra low sulfur diesel, and biodiesel.
3. The method according to claim 1, wherein said free radical
initiator is selected from the group consisting of stabilized
hydrogen peroxide, t-butyl hydroperoxide, and mixtures thereof.
4. The method according to claim 1, wherein said first hydrocarbon
liquid comprises a hydrocarbon containing about six to about twenty
carbon atoms.
5. The method according to claim 4, wherein said first hydrocarbon
liquid is selected from the group consisting of toluene, octane,
decane, D2 diesel fuel, low sulfur diesel, ultra low sulfur diesel,
biodiesel, and mixtures thereof.
6. The method according to claim 1, wherein said first surfactant
and said co-surfactant contain only the elements C, H, and O.
7. The method according to claim 1, wherein said modified diesel
fuel contains less than about 500 ppm water.
8. A method of improving the efficiency of a diesel engine wherein
said engine is provided with a source of diesel fuel and a source
of lubricating oil, said method comprising the steps of: a) adding
to said diesel fuel a reverse-micellar composition comprising: i)
an aqueous first disperse phase comprising a free radical
initiator; and ii) a first continuous phase comprising a first
hydrocarbon liquid, a first surfactant, and optionally a
co-surfactant, thereby producing a modified diesel fuel; b) adding
to the lubricating oil a stabilized nanoparticulate composition of
cerium dioxide, thereby producing a modified lubricating oil; and
c) operating said engine, thereby combusting said modified diesel
fuel in said engine and lubricating said engine using said modified
lubricating oil.
9. The method according to claim 8, wherein said free radical
initiator is selected from the group consisting of stabilized
hydrogen peroxide, t-butyl hydroperoxide, and mixtures thereof.
10. The method according to claim 8, wherein said stabilized
nanoparticulate composition comprises cerium dioxide nanoparticles
having a mean hydrodynamic diameter of about 1 nm to about 15
nm.
11. The method according to claim 10, wherein said stabilized
nanoparticulate composition comprises cerium dioxide nanoparticles
having a mean hydrodynamic diameter of about 6 nm.
12. The method according to claim 8, wherein said first surfactant
and said co-surfactant comprise only the elements C, H, or O.
13. The method according to claim 8, wherein said reverse-micellar
composition includes an alcohol as a co-surfactant.
14. The method according to claim 8, wherein said modified diesel
fuel contains less than 500 about ppm water.
15. The method according to claim 8, wherein said reverse-micellar
composition further includes an aqueous second disperse phase.
16. A method of improving the efficiency of a diesel engine
provided with a source of diesel fuel, said method comprising the
steps of: a) adding to said diesel fuel a first reverse-micellar
composition comprising: i) an aqueous first disperse phase
comprising boric acid or a borate salt; and ii) a first continuous
phase comprising a first hydrocarbon liquid, a first surfactant,
and optionally a co-surfactant; and b) operating said engine.
17. The method according to claim 16, wherein said diesel fuel is
selected from the group consisting of D2 diesel, low sulfur diesel,
ultra low sulfur diesel, and biodiesel.
18. The method according to claim 16, wherein said first
hydrocarbon liquid comprises a hydrocarbon containing about six to
about twenty carbon atoms.
19. The method according to claim 18, wherein said first
hydrocarbon liquid is selected from the group consisting of
toluene, octane, decane, D2 diesel fuel, low sulfur diesel, ultra
low sulfur diesel, biodiesel, and mixtures thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of Ser. No. 12/440,182
filed Sep. 4, 2009 which is a National Stage Application of
PCT/US200777543, filed Sep. 4, 2009 and claims the benefit of
priority from: Provisional Application Ser. No. 60/824,514,
CERIUM-CONTAINING FUEL ADDITIVE, filed Sep. 5, 2006; Provisional
Application Ser. No. 60/911,159, REVERSE MICELLAR FUEL ADDITIVE
COMPOSITION, filed Apr. 11, 2007; and Provisional Application Ser.
No. 60/938,314, REVERSE MICELLAR FUEL ADDITIVE COMPOSITION, filed
May 16, 2007, the disclosures of which are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to internal combustion engines
and, in particular, to the conditioning of such engines through the
use of fuel additives to improve their efficiency.
BACKGROUND OF THE INVENTION
[0003] Diesel fuel ranks second only to gasoline as a fuel for
internal combustion engines. Trucks, buses, tractors, locomotives,
ships, power generators, etc, are examples of devices that use
diesel fuel. Passenger cars and sport utility vehicles are another
area of potential growth for the use of diesel engines that can
provide improved fuel efficiency, especially where high torque at
relatively low rpm is desired.
[0004] Diesel fuel is principally a blend of petroleum-derived
compounds called middle distillates (heavier than gasoline but
lighter than lube oil). Diesel fuel is designed to operate in a
diesel engine, where it is injected into the compressed,
high-temperature air in the combustion chamber and ignites
spontaneously. This differs from gasoline, which is pre-mixed with
air and ignited in a gasoline engine by the spark plugs. D2 diesel
fuel conforms to specification D 975 set by the American Society
for Testing and Materials (ASTM).
[0005] Unlike gasoline engines that operate by spark ignition,
diesel engines employ compression ignition. In order to avoid long
ignition delays resulting in rough engine operation, as well as to
minimize misfiring and uneven or incomplete combustion which
results in smoke in the exhaust gases that causes a major
environmental problem, it is highly desirable to improve the
burning quality of diesel fuels to minimize environmental
pollutants such as hydrocarbons, carbon monoxide, particulate
matter (commonly called soot), etc.
[0006] Cetane is an alkane molecule that ignites very easily under
compression, so it is assigned a cetane number (CN) of 100. In
general, the cetane number (CN) depends primarily on its
hydrocarbon composition. Saturated hydrocarbons, particularly those
with straight, open chains, have relatively high cetane numbers,
whereas unsaturated hydrocarbons have relatively low cetane
numbers. All other hydrocarbons in diesel fuel are indexed to
cetane as to how well they ignite under compression. The cetane
number therefore measures how quickly the fuel starts to burn
(auto-ignites) under diesel engine conditions. Since there are
hundreds of components in diesel fuel, with each having a different
cetane quality, the overall cetane number of the diesel is the
average cetane quality of all the components. Cetane improvers act
to increase the effective cetane number of the fuel.
[0007] It is necessary to recognize that the relationship between
the CN of diesel fuel and its performance cannot be equated in any
way to the octane number of a gasoline and its performance in a
spark-ignition engine. Raising the octane number allows an increase
in the compression ratio and thus provides increased power and fuel
economy at a particular fuel load. In contrast, in diesel engines,
the desired CN provides good ignition at high loads and low
atmospheric temperature. High cetane fuels eliminate engine
roughness and diesel knock, allow engines to be started at lower
temperatures, provide faster engine warm-up without misfiring or
producing smoke and reduce formation of harmful deposits. On the
other hand, too high cetane fuels can result in incomplete
combustion and exhaust smoke due to too brief of an ignition delay
which does not allow proper mixing of the fuel and air.
[0008] Commercial diesel fuels have CN numbers of at least 40. The
suitable diesel fuel has appropriate volatility, pour and cloud
point, viscosity, gravity, flash point and contain only small but
tolerable levels of sulfur. It is also important that carbon,
residue formation and ash content should be kept low
[0009] During the normal course of operation, diesel engines often
develop carbon deposits on the walls of their cylinders due to
incomplete combustion of fuel. These deposits can increase engine
wear and, because of friction induced by the deposits, decrease
engine efficiency. Incomplete fuel combustion can also lead to the
environmentally harmful emission of particulate materials, also
referred to as soot. Thus, fuel additives that increase fuel
combustion, protect the cylinder walls of diesel engines, and
decrease engine friction, resulting in greater fuel efficiency, are
highly desirable.
[0010] Sanduja et al., U.S. Pat. No. 6,645,262, the disclosure of
which is incorporated herein by reference, describes liquid
hydrocarbon fuel concentrates, including low-sulfur diesel fuel
concentrates, that include a suspension of particulate boric acid
for the purpose of increasing lubricity and reducing engine
wear.
[0011] Olah, U.S. Pat. No. 5,520,710, the disclosure of which is
incorporated herein by reference, describes diesel fuel additives
that are dissolved in the fuel and homogeneously distributed and
include a dialkyl, alkyl-cycloalkyl, or dicycloalkyl ether compound
together an alkyl or dialkyl peroxide compound for the purposes of
enhancing cetane numbers and improving fuel combustion.
[0012] Peters et al., U.S. Pat. No. 6,158,397, the disclosure of
which is incorporated herein by reference, describes a process for
reducing soot in diesel engine exhaust gases wherein a fluid
containing a peroxide compound, preferably aqueous hydrogen
peroxide, is separately fed into the combustion chamber after the
start of the injection and combustion of the fuel, preferably
following the combustion phase.
[0013] Cunningham, U.S. Pat. No. 5,405,417, the disclosure of which
is incorporated herein by reference, describes a fuel composition
comprising a middle distillate base fuel having a sulfur content of
less than 500 ppm and a clear cetane number in the range of 30 to
60, and a minor amount of at least one peroxy ester combustion
improver such as t-butyl peroxyacetate dissolved therein.
[0014] Olsson et al., U.S. Pat. No. 5,105,772, the disclosure of
which is incorporated herein by reference, describes a process for
improving combustion in an engine that comprises: injecting a
liquid composition that includes a peroxide or a peroxo compound
into an engine combustion chamber, and passing a portion of the
composition through the exhaust outlet valve as the engine goes
from the exhaust phase to the intake phase, the passing occurring
during the step of injecting.
[0015] Mellovist et al., U.S. Pat. No. 4,359,969, the disclosure of
which is incorporated herein by reference, describes a method of
improving fuel combustion that comprises: introducing a liquid
composition consisting essentially of 1-10% hydrogen peroxide,
50-80% water, and 15-45% of a C.sub.1-C.sub.4 aliphatic alcohol,
all by volume, in the form of fine droplets into the air intake
manifold of an engine, where the droplets mix with air or fuel-air
mixture prior to entering the combustion chamber. Preferably, the
liquid composition also contains up to 5% of a thin lubricating oil
and up to 1% of an anticorrosive.
[0016] Kracklaurer, U.S. Pat. No. 4,389,220, the disclosure of
which is incorporated herein by reference, describes a method of
conditioning diesel engines in which a diesel engine is operated on
a diesel fuel containing from about 20-30 ppm of dicyclopentadienyl
iron for a period of time sufficient to eliminate carbon deposits
from the combustion surfaces of the engine and to deposit a layer
of iron oxide on the combustion surfaces, which layer is effective
to prevent further buildup of carbon deposits. Subsequently, the
diesel engine is operated on a maintenance concentration of from
about 10-15 ppm of dicyclopentadienyl iron or an equivalent amount
of a derivative thereof on a continuous basis. The maintenance
concentration is effective to maintain the catalytic iron oxide
layer on the combustion surfaces but insufficient to decrease
timing delay in the engine. The added dicyclopentadienyl iron may
produce iron oxide on the engine cylinder surface
(Fe.sub.2O.sub.3), which reacts with carbon deposits (soot) to form
Fe and CO.sub.2, thereby removing the deposits. However, this
method may accelerate the aging of the engine by formation of
rust.
[0017] Valentine, et al., U.S. Patent Appl. Publ. No. 2003/0148235,
the disclosure of which is incorporated herein by reference,
describe specific bimetallic or trimetallic fuel-borne catalysts
for increasing the fuel combustion efficiency. The catalysts reduce
fouling of heat transfer surfaces by unburned carbon while limiting
the amount of secondary additive ash which may itself cause
overloading of particulate collector devices or emissions of toxic
ultra fine particles when used in forms and quantities typically
employed. By utilizing a fuel containing a fuel-soluble catalyst
comprised of platinum and at least one additional metal comprising
cerium and/or iron, production of pollutants of the type generated
by incomplete combustion is reduced. Ultra low levels of nontoxic
metal combustion catalysts can be employed for improved heat
recovery and lower emissions of regulated pollutants. However, fuel
additives of this type, in addition to using the rare and expensive
metals such as platinum, can require several months before the
engine is "conditioned". By "conditioned" is meant that all the
benefits of the additive are not obtained until the engine has been
operated with the catalyst for a period of time. Initial
conditioning may require 45 days and optimal benefits may not be
obtained until 60-90 days. Additionally, free metal may be
discharged from the exhaust system into the atmosphere, where it
may subsequently react with living organisms.
[0018] Cerium dioxide is widely used as a catalyst in converters
for the elimination of toxic exhaust emission gases and the
reduction in particulate emissions in diesel powered vehicles.
Within the catalytic converter, the cerium dioxide can act as a
chemically active component, acting to release oxygen in the
presence of reductive gases, as well as to remove oxygen by
interaction with oxidizing species.
[0019] Cerium dioxide may store and release oxygen by the
reversible process shown in equation 1.
2CeO.sub.2.rarw..fwdarw.Ce.sub.2O.sub.3+1/2O.sub.2 (eq. 1)
[0020] The redox potential between the Ce.sup.3- and Ce.sup.4+ ions
lies between 1.3 and 1.8V and is highly dependent upon the anionic
groups present and the chemical environment (CERIUM: A Guide to its
Role in Chemical Technology, 1992 by Molycorp, Inc, Library of
Congress Catalog Card Number 92-93444)), This allows the foregoing
reaction to easily occur in exhaust gases. Cerium dioxide may
provide oxygen for the oxidation of CO or hydrocarbons in an oxygen
starved environment, or conversely may absorb oxygen for the
reduction of nitrogen oxides (NOx) in an oxygen rich environment.
Similar catalytic activity may also occur when cerium dioxide is
added as an additive to fuel, for example, diesel or gasoline.
However, for this effect to be useful, the cerium dioxide must be
of a particle size small enough, i.e., nanoparticulate (<100
nm), to remain in a stable dispersion in the fuel. In addition, as
catalytic effects depend on surface area, the small particle size
renders the nanocrystalline material more effective as a catalyst.
The incorporation of cerium dioxide in fuel serves not only to act
as a catalyst to reduce toxic exhaust gases produced by fuel
combustion, for example, by the "water gas shift reaction"
CO+H.sub.2O--<CO.sub.2+H.sub.2,
but also to facilitate the burning off of particulates that
accumulate in the particulate traps typically used with diesel
engines.
[0021] Cerium dioxide nanoparticles are particles that have a mean
diameter of less than 100 nm. For the purposes of this disclosure,
unless otherwise stated, the diameter of a nanoparticle refers to
its hydrodynamic diameter, which is the diameter determined by
dynamic light scattering technique and includes molecular
adsorbates and the accompanying solvation shell of the particle.
Alternatively, the geometrical particle diameter bay be estimated
using transmission electron micrography.
[0022] Vehicle on-board dosing systems that dispense cerium dioxide
into the fuel before it enters the engine are known, but such
systems are complicated and require extensive electronic control to
feed the appropriate amount of additive to the fuel. To avoid such
complex on-board systems, cerium dioxide nanoparticles can also be
added to fuel at an earlier stage to achieve improved fuel
efficiency. They can, for example, be incorporated at the refinery,
typically along with processing additives such as, for example,
cetane improvers or added at a fuel distribution tank farm.
[0023] Cerium dioxide nanoparticles can also be added at a fuel
distribution center, where it can be rack injected into large
(.about.100,000 gal) volumes of fuel or at a smaller fuel company
depot, which would allow customization according to specified
individual requirements. In addition, the cerium dioxide may be
added at a filling station during delivery of fuel to a vehicle,
which would have the potential advantage of improved stabilization
of the particle dispersion.
[0024] Fuel additives, such as PuriNOx.TM. manufactured by Lubrizol
Corporation, have been developed that are useful for the reduction
of NOx and particulate material emissions, however, the composition
of these fuel additives often includes 15-20% water. This
"emulsified" fuel additive is commonly mixed with fuel at a level
of 5-10%. The resulting high water content can lead to a loss in
engine power and lower fuel economy. Thus it would be desirable to
formulate a fuel additive that afforded reduction in nitrogen oxide
and particulate material emissions, while simultaneously
maintaining optimum engine performance.
[0025] Cerium nanoparticles and the associated free radical
initiators (incorporated into reverse micelles), as described
below, can provide a possible solution to this problem.
[0026] Cerium nanoparticles can form a ceramic layer on the engine
cylinders and moving parts essentially turning the engine into a
catalytic device. Their catalytic efficiency derives from the fact
that they provide a source of oxygen atoms during combustion by
undergoing reduction according to the equation (1). This results in
better fuel combustion and reduced levels of particulate material
emissions. Additionally, when used as a fuel additive, these
nanoparticles can provide improved engine performance by reducing
engine friction. As an alternative mode of introduction, cerium
dioxide nanoparticles can be added to the lube oil and act as a
lubricity enhancing agent to reduce internal friction. This will
also improve fuel efficiency.
[0027] Although substantially pure cerium dioxide nanoparticles are
beneficially included in fuel additives, it may be of further
benefit to use cerium dioxide doped with components that result in
the formation of additional oxygen vacancies being formed.
[0028] For this to occur, the dopant should be divalent or
trivalent, i.e., a divalent or trivalent ion of an element that is
a rare earth metal, a transition metal or a metal of Group IIA,
IIB, VB, or VIB of the Periodic Table, and of a size that allows
incorporation of the ion in a lattice position within the surface
or sub-surface region of the cerium dioxide nanoparticles. This
substitutional ion doping is preferred to interstitial ion doping,
where the dopants occupy spaces between the normal lattice
positions.
The following publications, the disclosures all of which are
incorporated herein by reference, describe fuel additives
containing cerium oxidic compounds.
[0029] Hawkins et al., U.S. Pat. No. 5,449,387, discloses a cerium
(IV) oxidic compound having the formula:
(H.sub.2O).sub.p[CeO(A).sub.2(AH).sub.n].sub.m
in which the radicals A, which are the same or different, are each
an anion of an organic oxyacid AH having a pK.sub.a greater than 1,
p is an integer ranging from 0 to 5, n is a number ranging from 0
to 2, and m is an integer ranging from 1 to 12. The organic oxyacid
is preferably a carboxylic acid, more preferably, a
C.sub.2-C.sub.20 monocarboxylic acid or a C.sub.4-C.sub.12
dicarboxylic acid. The cerium-containing compounds can be employed
as catalysts for the combustion of hydrocarbon fuels.
[0030] Valentine et al., U.S. Pat. No. 7,063,729, discloses a
low-emissions diesel fuel that includes a bimetallic, fuel-soluble
platinum group metal and cerium catalyst, the cerium being provided
as a fuel-soluble hydroxyl oleate propionate complex.
[0031] Chopin et al., U.S. Pat. No. 6,210,451, discloses a
petroleum-based fuel that includes a stable organic sol that
comprises particles of cerium dioxide in the form of agglomerates
of crystallites (preferred size 3-4 nm), an amphiphilic acid system
containing at least one acid whose total number of carbons is at
least 10, and an organic diluent medium. The controlled particle
size is no greater than 200 nm.
[0032] Birchem et al., U.S. Pat. No. 6,136,048, discloses an
adjuvant for diesel engine fuels that includes a sol comprising
particles of oxygenated compound having a d90 no greater than 20
nm, an amphiphilic acid system, and a diluent. The oxygenated metal
compound particles are prepared from the reaction in solution of a
rare earth salt such as a cerium salt with a basic medium, followed
by recovery of the formed precipitate by atomization or freeze
drying.
[0033] Lemaire et al., U.S. Pat. No. 6,093,223, discloses a process
for producing aggregates of ceric oxide crystallites by burning a
hydrocarbon fuel in the presence of at least one cerium compound.
The soot contains at least 0.1 wt. % of ceric oxide crystallite
aggregates, the largest particle size being 50-10,000 angstroms,
the crystallite size being 50-250 angstroms, and the soot having an
ignition temperature of less than 400.degree. C.
[0034] Hazarika et al., U.S. Patent Appl. Publ. No. 2003/0154646,
discloses a method of improving fuel efficiency and/or reducing
fuel emissions of a fuel burning apparatus, the method comprising
dispersing at least one particulate lanthanide oxide, particularly
cerium dioxide, in the fuel, wherein the particulate lanthanum
oxide is coated with a surfactant selected from the group
consisting of alkyl carboxylic anhydrides and esters having at
least one C.sub.10 to C.sub.30 alkyl group.
[0035] Collier et al., U.S. Patent Appl. Publ. No. 2003/0182848,
discloses a diesel fuel composition that improves the performance
of diesel fuel particulate traps and contains a combination of 1-25
ppm of metal in the form of a metal salt additive and 100-500 ppm
of an oil-soluble nitrogen-containing ashless detergent additive.
The metal may be an alkali metal, an alkaline earth metal, a metal
of Group IVB, VIIB, VIIIB, IB, IIB, or any of the rare earth metals
having atomic numbers 57-71, especially cerium, or mixtures of any
of the foregoing metals.
[0036] Collier et al., U.S. Patent Appl. Publ. No. 2003/0221362,
discloses a fuel additive composition for a diesel engine equipped
with a particulate trap, the composition comprising a hydrocarbon
solvent and an oil-soluble metal carboxylate or metal complex
derived from a carboxylic acid containing not more than 125 carbon
atoms. The metal may be an alkali metal, an alkaline earth metal, a
metal of Group IVB, VIIB, VIIIB, IB, IIB, or a rare earth metal,
including cerium, or mixtures of any of the foregoing metals.
[0037] Caprotti et al., U.S. Patent Appl. Publ. No. 2004/0035045,
discloses a fuel additive composition for a diesel engine equipped
with a particulate trap. The composition comprises an oil-soluble
or oil-dispersible metal salt of an acidic organic compound and a
stoichiometric excess of metal. When added to the fuel, the
composition provides 1-25 ppm of metal, which is selected from the
group consisting of Ca, Fe, Mg, Sr, Ti, Zr, Mn, Zn, and Ce.
[0038] Caprotti et al., U.S. Patent Appl. Publ. No. 2005/0060929,
discloses a diesel fuel composition stabilized against phase
separation that contains a colloidally dispersed or solubilized
metal catalyst compound and 5-1000 ppm of a stabilizer that is an
organic compound having a lipophilic hydrocarbyl chain attached to
at least two polar groups, at least one of which is a carboxylic
acid or carboxylate group. The metal catalyst compound comprises
one or more organic or inorganic compounds or complexes of Ce, Fe,
Ca, Mg, Sr, Na, Mn, Pt, or mixtures thereof.
[0039] Wakefield, U.S. Pat. No. 7,169,196 B2, discloses a fuel
comprising cerium dioxide particles that have been doped with a
divalent or trivalent metal or metalloid that is a rare earth
metal, a transition metal, or a metal of Group IIa, IIIB, VB, or
VIB of the Periodic Table.
[0040] Caprotti et al., U.S. Patent Appl. Publ. No. 2006/0000140,
discloses a fuel additive composition that comprises at least one
colloidal metal compound or species and a stabilizer component that
is the condensation product of an aldehyde or ketone and a compound
comprising one or more aromatic moieties containing a hydroxyl
substituent and a further substituent chosen from among
hydrocarbyl, --COOR, or --COR, R being hydrogen or hydrocarbyl. The
colloidal metal compound preferably comprises at least one metal
oxide, preferred oxides being iron oxide, cerium dioxide, or
cerium-doped iron oxide.
[0041] Scattergood, International Publ. No. WO 2004/065529,
discloses a method for improving the fuel efficiency of fuel for an
internal combustion engine that comprises adding to the fuel cerium
dioxide and/or doped cerium dioxide and, optionally, one or more
fuel additives.
[0042] Anderson et al., International Publ. No. WO 2005/012465,
discloses a method for improving the fuel efficiency of a fuel for
an internal combustion engine that comprises lubricating oil and
gasoline, the method comprising adding cerium dioxide and/or doped
cerium dioxide to the lubricating oil or the gasoline.
[0043] Cerium-containing nanoparticles can be prepared by a variety
of techniques known in the art. Regardless of whether the
synthesized nanoparticles are made in a hydrophilic or hydrophobic
medium, the particles normally require a stabilizer to prevent
undesirable agglomeration. The following publications, the
disclosures all of which are incorporated herein by reference,
describe some of these synthetic techniques.
[0044] Talbot et al., U.S. Pat. No. 6,752,979, discloses a method
of producing metal oxide particles having nano-sized grains that
consists of: mixing a solution containing one or more metal cations
with a surfactant under conditions such that surfactant micelles
are formed within the solution, thereby forming a micellar liquid;
and heating the micellar liquid to remove the surfactant and form
metal oxide particles having a disordered pore structure. The metal
cations are selected from the group consisting of cations from
Groups 1A, 2A, 3A, 4A, 5A, and 6A of the Periodic Table, transition
metals, lanthanides, actinides, and mixtures thereof. Preparations
of particles of cerium dioxide and mixed oxides containing cerium
and one or more other metals are included in the illustrative
examples.
[0045] Chane-Ching et al., U.S. Pat. No. 6,271,269, discloses a
process for preparing storage-stable organic sols that comprises:
reacting a base reactant with an aqueous solution of the salt of an
acidic metal cation to form an aqueous colloidal dispersion
containing excess hydroxyl ions; contacting the aqueous colloidal
dispersion with an organic phase comprising an organic liquid
medium and an organic acid; and separating the resulting
aqueous/organic phase mixture into an aqueous phase and a product
organic phase. Preferred metal cations are cerium and iron cations.
The colloidal particulates have hydrodynamic diameters in the range
of 50-2000 angstroms.
[0046] Chane-Ching, U.S. Pat. No. 6,649,156, discloses an organic
sol containing cerium dioxide particles that are made by a thermal
hydrolysis process; an organic liquid phase; and at least one
amphiphilic compounds chosen from polyoxyethylenated alkyl ethers
of carboxylic acids, polyoxyethylenated alkyl ether phosphates,
dialkyl sulfosuccinates, and quaternary ammonium compounds. The
water content of the sols may not be more than 1%. The mean
crystallite size is about 5 nm, while the particle agglomerates of
these crystallites range in size from 200 to 10 nm.
[0047] Chane-Ching, U.S. Pat. No. 7,008,965, discloses an aqueous
colloidal dispersion of a compound of cerium and at least one other
metal, the dispersion having a conductivity of at most 5 mS/cm and
a pH between 5 and 8.
[0048] Chane-Ching, U.S. Patent Appl. Publ. No. 2004/0029978
(abandoned Dec. 7, 2005), discloses a surfactant formed from at
least one nanoparticle that has amphiphilic characteristics and is
based on a metal oxide, hydroxide and/or oxyhydroxide, on the
surface of which organic chains with hydrophobic characteristics
are bonded. The metal is preferably selected from among cerium,
aluminum, titanium or silicon, and the alkyl chain comprises 6-30
carbon atoms, or polyoxyethylene monoalkyl ethers of which the
alkyl chain comprises 8-30 carbon atoms and the polyoxyethylene
part comprises 1-10 ethyoxyl groups. The particle is an isotopic or
spherical particle having an average diameter of 2-40 nm.
[0049] Blanchard et al., U.S. Patent Appl. Publ. No. 2006/0005465,
discloses an organic colloidal dispersion comprising: particles of
at least one compound based on at least one rare earth, at least
one acid, and at least one diluent, wherein at least 90% of the
particles are monocrystalline. Example 1 describes the preparation
of a cerium dioxide colloidal solution from cerium acetate and an
organic phase that includes Isopar hydrocarbon mixture and
isostearic acid. The resulting cerium dioxide particles had a
d.sub.50 of 2.5 nm, and the size of 80% of the particles was in the
range of 1-4 nm.
[0050] Zhou et al., U.S. Pat. No. 7,025,943, discloses a method for
producing cerium dioxide crystals that comprises: mixing a first
solution of a water-soluble cerium salt with a second solution of
alkali metal or ammonium hydroxide; agitating the resulting
reactant solution under turbulent flow conditions while
concomitantly passing gaseous oxygen through the solution; and
precipitating cerium dioxide particles having a dominant particle
size within the range of 3-100 nm. In Example 1, the particle size
is stated to be around 3-5 nm.
[0051] Noh et al., U.S. Patent Appl. Publ. No. 2004/0241070,
discloses a method for preparing single crystalline cerium dioxide
nanopowder comprising: preparing cerium hydroxide by precipitating
a cerium salt in the presence of a solvent mixture of organic
solvent and water, preferably in a ratio of about 0.1:1 to about
5:1 by weight; and hydrothermally reacting the cerium hydroxide.
The nanopowder has a particle size of about 30-300 nm.
[0052] Chan, U.S. Patent Appl. Publ. No. 2005/003 1517, discloses a
method for preparing cerium dioxide nanoparticles that comprises:
rapidly mixing an aqueous solution of cerium nitrate with aqueous
hexamethylenetetramine, the temperature being maintained at a
temperature no higher than about 320.degree. K while nanoparticles
form in the resulting mixture; and separating the formed
nanoparticles. The mixing apparatus preferably comprises a
mechanical stirrer and a centrifuge. In the illustrative example,
the prepared cerium dioxide particles are reported to have a
diameter of about 12 nm.
[0053] Ying et al., U.S. Pat. Nos. 6,413,489 and 6,869,584,
disclose the synthesis by a reverse micelle technique of
nanoparticles that are free of agglomeration and have a particle
size of less than 100 nm and a surface area of at least 20
m.sup.2/g. The method comprises introducing a ceramic precursor
that includes barium alkoxide and aluminum alkoxide in the presence
of a reverse emulsion.
[0054] Illustrative example 9 of U.S. Pat. Nos. 6,413,489 and
6,869,584 describes the inclusion of cerium nitrate in the emulsion
mixture to prepare cerium-doped barium hexaaluminate particles,
which were collected by freeze drying and calcined under air to
500.degree. C. and 800.degree. C. The resulting particles had grain
sizes of less than 5 nm and 7 nm at 500.degree. C. and 800.degree.
C., respectively. Illustrative example 10 describes the synthesis
of cerium-coated barium hexaaluminate particles. Following
calcination, the cerium-coated particles had grain sizes of less
than 4 nm, 6.5 nm, and 16 nm at 500.degree. C., 800.degree. C., and
1100.degree. C., respectively.
[0055] A related publication, Ying et al., U.S. Patent Appl. Publ.
No. 2005/0152832, discloses the synthesis, by a reverse micelle
technique within an emulsion having a 1-40% water content, of
nanoparticles that are free of agglomeration and have a particle
size of less than 100 nn. The nanoparticles are preferably metal
oxide particles, which can be used to oxidize hydrocarbons.
[0056] Illustrative Examples 9 and 10 of U.S. Patent Appl. Publ.
No. 2005/0152832 describe the preparation of, respectively,
cerium-doped and cerium-coated barium hexaaluminate particles.
Example 13 describes the oxidation of methane with the
cerium-coated particles.
[0057] Hanawa et al., U.S. Pat. No. 5,938,837, discloses a method
for preparing cerium dioxide particles, intended primarily for use
as a polishing agent, that comprises mixing, with stirring, an
aqueous solution of cerous nitrate with a base, preferably aqueous
ammonia, in such a mixing ratio that the pH value of the mixture
ranges from 5 to 10, preferably 7 to 9, then rapidly heating the
resulting mixture to a temperature of 70-100.degree. C., and
maturing the mixture of cerous nitrate with a base at that
temperature to form the grains. The product grains are uniform in
size and shape and have an average particle size of 10-80 nm,
preferably 20-60 nm.
[0058] European Patent Application EP 0208580, published 14 Jan.
1987, inventor Chane-Ching, applicant Rhone Poulenc, discloses a
cerium (IV) compound corresponding to the general formula
Ce(M).sub.x(OH).sub.y(NO.sub.3).sub.2
wherein M represents an alkali metal or quaternary ammonium
radical, x is between 0.01 and 0.2, y is such that y=4-z+x, and z
is between 0.4 and 0.7. A process for preparing a colloidal
dispersion of the cerium (IV) compound produces particles with a
hydrodynamic diameter between about 1 nm and about 60 nm, suitably
between about 1 nm and about 10 nm, and desirably between about 3
nm and 8 nm.
[0059] The doping of cerium dioxide with metal ions (reported as
early as 1975) and the resultant dopant effects on the electronic
and oxygen diffusion properties are well described by Trovarelli,
Catalysis by Ceria and Related Materials, Catalytic Science Series,
World Scientific Publishing Co., 37-46 (2002) and references cited
therein.
[0060] S. Sathyamurthy et al., Nano Technology 16, (2005), pp
1960-1964, describes the reverse micellar synthesis of CeO.sub.2
from cerium nitrate, using sodium hydroxide as the precipitating
agent and n-octane containing the surfactant cetyltrimethylammonium
bromide (CTAB) and the cosurfactant 1-butanol as the oil phase. The
resulting polyhedral particles had an average size of 3.7 nm, but
the reaction would be expected to proceed in low yield.
[0061] S. Seal et al., Journal of Nano Particle Research, (2002), p
438, describes the preparation from cerium nitrate and ammonium
hydroxide of nanocrystalline ceria particles for a high-temperature
oxidation-resistant coating using an aqueous microemulsion system
containing AOT as the surfactant and toluene as the oil phase. The
ceria nanoparticles formed in the upper oil phase of the reaction
mixture had a particle size of 5 nm.
[0062] Pang et al., J. Mater. Chem., 12 (2002), pp 3699-3704,
prepared Al.sub.2O.sub.3 nanoparticles by a water-in-oil
microemulsion method, using an oil phase containing cyclohexane and
the non-ionic surfactant Triton X-114, and an aqueous phase
containing 1.0 M AlClO.sub.3. The resulting Al.sub.2O.sub.3
particles, which had a particle size of 5-15 nm, appeared to be
distinctly different from the hollow ball-shaped particles of
submicron size made by a direct precipitation process.
[0063] Cuif et al, U.S. Pat. No. 6,133,194, the disclosure of which
is incorporated herein by reference, describes a process that
comprises reacting a metal salt solution containing cerium,
zirconium, or a mixture thereof, a base, optionally an oxidizing
agent, and an additive selected from the group consisting of
anionic surfactants, nonionic surfactants, polyethylene glycols,
carboxylic acids, and carboxylate salts, thereby forming a product.
The product is subsequently calcined at temperatures >500 C
(which would effectively carbonize the claimed surfactants).
[0064] Hazbun et al., U.S. Pat. No. 4,744,796, the disclosure of
which is incorporated herein by reference, describes a
microemulsion fuel composition that includes a hydrocarbon fuel and
a cosurfactant combination of t-butyl alcohol and at least one
amphoteric, anionic, cationic, or nonionic surfactant. Preferred
surfactants are fatty acids or fatty acid mixtures.
[0065] Hicks et al., U.S. Patent Appl. Publ. No. 2002/0095859, the
disclosure of which is incorporated herein by reference, describes
additive compositions for liquid hydrogen fuels that include one or
more surfactants selected from the group consisting of amphoteric,
anionic, cationic, or nonionic surfactants, and optionally one or
more cosurfactants selected from the group consisting of alcohols,
glycols, and ethers.
[0066] As described previously, various methods and apparatus have
been reported for preparing cerium nanoparticles including those
described by Chane-Ching, et al., U.S. Pat. No. 5,017,352; Hanawa,
et al., U.S. Pat. No. 5,938,837; Melard, et al., U.S. Pat. No.
4,786,325; Chopin, et al., U.S. Pat. No. 5,712,218; Chan, U.S.
Patent Appl. Publ. No. 2005/0031517; and Zhou, et al., U.S. Pat.
No. 7,025,943, the disclosures of which are incorporated herein by
reference. However, current methods do not allow the economical and
facile preparation of cerium nanoparticles in a short period of
time at very high suspension densities (greater than 0.5 molal,
i.e., 9 wt. %) that are sufficiently small in size (less than 8 nm
in mean diameter), uniform in size frequency distribution
(coefficient of variation [COV] of less than 15%, where COV is the
standard deviation divided by the mean diameter), and stable for
many desirable applications.
[0067] A typical chemical reactor that might be used to prepare
cerium dioxide includes a reaction chamber that includes a mixer
(see, for example, FIG. 1 in Zhou et al. U.S. Pat. No. 7,025,943).
A mixer typically includes a shaft, and propeller or turbine blades
attached to the shaft, and a motor that turns the shaft, such that
the propeller is rotated at high speed (1000 to 5000 rpm). The
shaft can drive a flat blade turbine for good meso mixing (micro
scale) and a pitched blade turbine for macro mixing (pumping fluid
through out the reactor).
[0068] Such a device is described in Antoniades, U.S. Pat. No.
6,422,736, entitled "Scaleable Device Impeller Apparatus For
Preparing Silver Halide Grains." This type of reactor is useful for
fast reactions such as that shown by the equation below, wherein
the product, AgCl, is a crystalline material having a diameter on
the order of several hundred nanometers up to several thousand
nanometers.
AgNO.sub.3+NaCl.fwdarw.AgCl+NaNO.sub.3
[0069] Cerium dioxide particles prepared using this type of mixing
are often too large to be useful for certain applications. It is
highly desirable to have the smallest cerium dioxide particles
possible as their catalytic propensity (ability to donate oxygen to
a combustion system, i.e., equation 1) increases with decreasing
particle size, especially for particles having a mean diameter of
less than 10 nm.
[0070] A schematic example of a batch reactor that can be used to
produce cerium dioxide nanoparticles is shown in FIG. 1. The
reactor (10) includes inlet ports (11, and 12) for adding
reactants, a propeller, shaft, and motor, 15, 14, and 13, for
mixing. The reaction mixture 18 is contained in a reactor vessel
16. Addition of reactants, such as cerium nitrate, an oxidant, and
hydroxide ion, can result in the formation of nanoparticles. The
particles initially form as very small nuclei. Mixing causes the
nuclei to circulate, shown by the dashed arrows (17) in FIG. 1. As
the nuclei continuously circulate through the reactive mixing
regime they grow (increase in diameter) as they incorporate fresh
reactants. Thus, after an initial steady state concentration of
nuclei is formed, this nuclei population is subsequently grown into
larger particles in a continuous manner. This nucleation and growth
process is not desirable if one wishes to limit the final size of
the particles while still maintaining a high particle suspension
density. Such a batch reactor is not useful for producing a high
yield (greater than 1 molal) of cerium dioxide nanoparticles that
are very small, for example, less than 10 nm in a reasonably short
reaction time (for example, less than 60 minutes).
[0071] An example of this nucleation and growth process applied to
the aqueous precipitation of CeO.sub.2 is the work of Zhang et al.,
J. Appl. Phys., 95, 4319 (2004) and Zhang, et al., Applied Physics
Letters, 80, 127 (2002). Using cerium nitrate hexahydrate as the
cerium source (very dilute at 0.0375M) and 0.5 M
hexamethylenetetramine as the ammonia precursor, 2.5 to 4.25 nm
cerium dioxide particles are formed in times that are less than 50
minutes. These particles are subsequently grown to 7.5 nm or
greater using reaction times on the order of 250 minutes (or 600
minutes depending upon growth conditions). The limitations of
particle size, concentration and reaction time would exclude this
process from consideration as an economically viable route to bulk
commercial quantities of CeO.sub.2 nanoparticles.
[0072] I. H. Leubner, Current Opinion in Colloid and Interface
Science, 5, 151-159 (2000), Journal of Dispersion Science and
Technology, 22, 125-138 (2001) and ibid. 23, 577-590 (2002), and
references cited therein, provides a theoretical treatment that
relates the number of stable crystals formed with molar addition
rate of reactants, solubility of the crystals and temperature. The
model also accounts for the effects of diffusion, kinetically
controlled growth processes, Ostwald ripening agents and growth
restrainers/stabilizers on crystal number. High molar addition
rates, low temperatures, low solubility, and the presence of growth
restrainers all favor large numbers of nuclei and consequently
smaller final grain or particle size
[0073] In contrast to batch reactors, colloid mills typically have
flat blade turbines turning at 10,000 rpm, whereby the materials
are forced through a screen whose holes can vary in size from
fractions of a millimeter to several millimeters. Generally, no
chemical reaction is occurring, but only a change in particle size.
In certain cases, particle size and stability can be controlled
thermodynamically by the presence of a surfactant. For example,
Langer et al., in U.S. Pat. No. 6,368,366 and U.S. Pat. No.
6,363,237, incorporated herein by reference, describe an aqueous
microemulsion in a hydrocarbon fuel composition made under high
shear conditions. However, the aqueous particle phase (the
discontinuous phase in the fuel composition) has a large size, on
the order of 1000 nm.
[0074] Colloid mills are not useful for reducing the particle size
of large cerium dioxide particles because the particles are too
hard to be sheared by the mill in a reasonable amount of time. The
preferred method for reducing large, agglomerated cerium dioxide
particles from the micron size down into the nanometer size is
milling for several days on a ball mill in the presence of a
stabilizing agent. This is a time consuming, expensive process that
invariably produces a wide distribution of particle sizes. Thus,
there remains a need for an economical and facile method to
synthesize large quantities (at high suspension densities) of very
small nanometric particles of cerium dioxide with a uniform size
distribution.
[0075] Aqueous precipitation may offer a convenient route to cerium
nanoparticles. However, to be useful as a fuel-borne catalyst for
fuels, cerium dioxide nanoparticles must exhibit stability in a
nonpolar medium (for example, diesel fuel). Most stabilizers used
to prevent agglomeration in an aqueous environment are ill suited
to the task of stabilization in a nonpolar environment. When placed
in a nonpolar solvent, such particles tend to immediately
agglomerate and, consequently, lose some, if not all, of their
desirable nanoparticulate properties. Thus it would be desirable to
form stable cerium dioxide particles in an aqueous environment,
retain the same stabilizer on the particle surface, and then be
able to transfer these particles to a nonpolar solvent, wherein the
particles would remain stable and form a homogeneous mixture. In
this simplified and economical manner, one could eliminate the
necessity for changing surface stabilizer's affinity from polar to
non-polar. Changing stabilizers can involve a difficult
displacement reaction or separate, tedious isolation-redispersal
methods (for example, precipitation and subsequent redispersal with
the new stabilizer using ball milling).
[0076] Thus, there remains a need for an efficient and economical
method to synthesize stable cerium dioxide nanoparticles in a
polar, aqueous environment, and then transfer these particles to a
non-polar environment wherein a stable homogeneous mixture is
formed.
[0077] For some applications, it may even be desirable to have some
relatively low level of water present during the combustion process
of an internal combustion engine. The previously mentioned, Hicks
et al., U.S. Patent Appl. Publ. No. 2002/0095859 suggests that as
little as 5 to 95 ppm water (as a microemulsion) improves
hydrocarbon fuel combustion via the reduction of cyclic dispersion
(variability between compression cycles).
[0078] Water added to diesel fuel is thought to improve combustion
in three ways: [0079] 1. Water promotes a finer, more even spray
pattern for more complete combustion. [0080] 2. Water lowers the
combustion temperature to reduce nitrous oxide emissions (flame
temperature of 2900.degree. F.). [0081] 3. Water delays combustion
slightly to reduce particulate emissions.
[0082] J. Ying et al in WO 98/18884 describe a thermally and
temporally stable water-in-fuel emulsion having micelle size of
<100 nm and including water in an amount of at least 8 wt.
percent. As there was no attendant measurement of engine power, the
claimed 85-90% reductions in particulate emissions may have been an
artifact of the loss of engine power and thus been an unacceptable
trade-off of power for emissions reduction. Fuel additives that
include cerium dioxide nanoparticles, wherein nanoparticles
typically have a mean diameter of 100 nm or less, stabilized with a
surfactant, such as sodium dodecyl succinate, and optionally
containing copper, are known. These types of fuel additives also
have a long conditioning period.
[0083] The use of cerium nanoparticles to provide a high
temperature oxidation resistant coating has been reported, for
example, see "Synthesis Of Nano Crystalline Ceria Particles For
High Temperature Oxidization Resistant Coating," S. Seal et al.,
Journal of Nanoparticle Research, 4, 433-438 (2002). The deposition
of cerium dioxide on various surfaces has been investigated,
including Ni, chromia and alumina alloys, and stainless steel and
on Ni, and Ni--Cr coated alloy surfaces. It was found that a cerium
dioxide particle size of 10 nm or smaller is desirable. Ceria
particle incorporation subsequently inhibits oxidation of the metal
surface.
[0084] In addition, the extent to which CeO.sub.2 can act as a
catalytic oxygen storage material, described by equation 1, is
governed in part by the CeO.sub.2 particle size. At 20 nm particle
sizes and below, the lattice parameter increases dramatically with
decreasing crystallite size (up to 0.45% at 6 nm, see for example
Zhang, et al., Applied Physics Letters, 80 1, 127 (2002)). The
associated size-induced lattice strain is accompanied by an
increase in surface oxygen vacancies that results in enhanced
catalytic activity. This (inverse) size dependent activity provides
not only for more efficient fuel cells, but better oxidative
properties when used in the combustion of petroleum fuels.
[0085] Henly, U.S. Patent Appl. Publ. No. 2005/0005506, the
disclosure of which is incorporated herein by reference, has
described a distillate fuel additive composition, including calcium
sulfonate detergent, a succinimide dispersant, and an
organomanganese compound. The organic manganese compound, along
with other compounds, acts to improve the cleanliness of the fuel
system.
[0086] Rim, U.S. Pat. No. 6,892,531, the disclosure of which is
incorporated herein by reference, describes an engine lubricating
oil composition for a diesel engine that includes a lubricating oil
and 0.05-10 wt. % of a catalyst additive comprising cerium
carboxylate.
[0087] As described above, currently available fuel additives have
improved the performance of diesel engines; however further
improvements are still needed. It would be desirable to formulate a
fuel additive for diesel engines that provides: improved fuel
combustion while maintaining engine power while simultaneously
reducing, reduced PM emissions. In addition, protection of engines
from wear, reduced engine friction, greater lubricity, with
improved fuel efficiency would be tremendously beneficial. It would
also be desirable to provide one or more of these features without
requiring a long conditioning period.
SUMMARY OF THE INVENTION
[0088] The present invention is directed to a method of improving
the efficiency of a diesel engine provided with a source of diesel
fuel, wherein the method comprises the steps of: a) adding to the
diesel fuel a reverse micellar composition comprising an aqueous
first disperse phase that includes a free radical initiator and a
first continuous phase that includes a first hydrocarbon liquid, a
first surfactant, and optionally a co-surfactant, thereby producing
a modified diesel fuel; and b) operating the engine, thereby
combusting the modified diesel fuel.
[0089] The present invention is further directed to a method of
improving the efficiency of a diesel engine provided with a source
of diesel fuel and a source of lubricating oil, wherein the method
comprises the steps of: a) adding to the diesel fuel a reverse
micellar composition comprising an aqueous first disperse phase
that includes a free radical initiator and a first continuous phase
that includes a first hydrocarbon liquid and a first surfactant,
thereby producing a modified diesel fuel; b) adding to the
lubricating oil a stabilized nanoparticulate composition of cerium
dioxide, thereby producing a modified lubricating oil; and c)
operating the engine, thereby combusting the modified diesel fuel
and lubricating the engine with the modified lubricating oil.
[0090] The present invention is also directed to a method of
improving the efficiency of a diesel engine provided with a source
of diesel fuel, wherein the method comprises the steps of: a)
adding to the diesel fuel a first reverse micellar composition that
includes an aqueous first disperse phase comprising boric acid or a
borate salt and a first continuous phase that includes a first
hydrocarbon liquid, a first surfactant, and optionally a
co-surfactant; and b) operating the engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0091] FIG. 1 shows a schematic representation of a conventional
batch reactor for forming cerium dioxide nanoparticles.
[0092] FIG. 2A shows a schematic exploded view of a colloid mill
reactor that may be used in the invention.
[0093] FIG. 2B shows a partial view of a colloid mill reactor that
may be used in the invention.
[0094] FIG. 2C shows a schematic exploded view of another type of
colloid mill reactor that may be used in the invention.
[0095] FIG. 3 shows a schematic representation of a continuous
reactor for forming very small cerium nanoparticles.
[0096] FIG. 4 shows the size distribution of the cerium dioxide
particles prepared in Example 1.
[0097] FIG. 5 shows a transmission electron micrograph of a
dried-down sample of the cerium dioxide particles of Example 1.
[0098] FIG. 6 shows an X-ray powder diffraction spectrum of cerium
dioxide nanoparticles prepared in Example 1.
DETAILED DESCRIPTION OF THE INVENTION
[0099] The preparation of cerium dioxide nanoparticles is described
in co-pending, commonly assigned application Ser. No. ______,
METHOD OF PREPARING CERIUM DIOXIDE NANOPARTICLES, filed September
______, 2007, the disclosure of which is incorporated herein by
reference.
[0100] Cerous ion reacts, in the presence of hydroxide ion, to form
cerium hydroxide. The reaction vessel is then heated to convert
cerium hydroxide to cerium dioxide. The temperature in the reaction
vessel is maintained between about 50.degree. C. and about
100.degree. C., more preferably about 65-75.degree. C., most
preferably about 70.degree. C. Time and temperature can be traded
off, higher temperatures typically reducing the time required for
conversion of the hydroxide to the oxide. After a period at these
elevated temperatures, on the order of about 1 hour or less and
suitably about 0.5 hour, the cerium hydroxide is converted to
cerium dioxide and the temperature of the reaction vessel is
lowered to about 15-25.degree. C. Subsequently, the cerium dioxide
nanoparticles are concentrated, and the unreacted cerium and waste
by-products such as ammonium nitrate are removed, most conveniently
for example, by diafiltration.
[0101] In one aspect of the present invention, a method of making
cerium dioxide nanoparticles includes providing an aqueous reaction
mixture comprising cerous ion, hydroxide ion, a stabilizer, and an
oxidant at a temperature effective to generate small nuclei size,
and achieve subsequent oxidation of cerous ion to ceric ion so that
these particles can be grown into nanometric cerium dioxide. The
reaction mixture is subjected to mechanical shearing, preferably by
causing it to pass through a perforated screen, thereby forming a
suspension of cerium dioxide nanoparticles having a mean
hydrodynamic diameter in the range of about 2 nm to about 15 nm.
While the particle diameter can be controlled within the range of 2
nm to 15 nm, preferably the cerium dioxide nanoparticles have a
mean hydrodynamic diameter of about 10 nm or less, more preferably
about 8 nm or less, most preferably, about 6 nm. Desirably, the
nanoparticles comprise one or at most two primary crystallites per
particle edge, each crystallite being on average 2.5 nm
(approximately 5 unit cells). Thus, the resulting nanoparticle size
frequency in substantially monodisperse, i.e., having a coefficient
of variation (COV) less than 15%, where the COV is defined as the
standard deviation divided by the mean.
[0102] Mechanical shearing includes the motion of fluids upon
surfaces such as those of a rotor, which results in the generation
of shear stress. Particularly, the laminar flux on a surface has a
zero velocity, and shear stress occurs between the zero-velocity
surface and the higher-velocity flow away from the surface.
[0103] In one embodiment, the current invention employs a colloid
mill, which is normally used for milling micro emulsions or
colloids, as a chemical reactor to produce cerium dioxide
nanoparticles. Examples of useful colloid mills include those
described by Korstvedt, U.S. Pat. No. 6,745,961 and U.S. Pat. No.
6,305,626, the disclosures of which are incorporated herein by
reference.
[0104] A colloid mill, referred to as a Silverson mill, is depicted
in U.S. Pat. No. 5,552,133, the disclosure of which is incorporated
herein by reference. FIG. 2A schematically represents a colloid
mill reactor, according to the present invention, that includes
reactant inlet jets 34 and 35. The depicted colloid mill reactor
has a rotating shaft 30 that is connected to a paddle blade rotor
31. The rotor is received in a cup-shaped screen stator 32, which
has perforations 36 and encloses the reaction chamber 37. The
stator is mounted on a housing, 33, fitted with inlet jets 34 and
35. The inlet jets 34 and 35 extend into the housing 33 to the
bottom of the perforated screen stator 32 into the reaction chamber
37. A plate (not shown) forms a top to the screen stator 32. The
reactants are introduced via jets 34 and 35 into the reaction
chamber. The colloidal mill reactor is enclosed in a reaction
vessel 38, which may be submerged in a constant temperature bath
(not shown).
[0105] During the stirring of the reaction mixture by rotation of
the rotor shaft, the shaft rotation causes mechanical shearing of
the reaction mixture between the flat faces (35) of the paddle
rotor and the inner cylindrical surface of the stator. Cerium
hydroxide particles initially formed in the reaction chamber are
forced through the perforations in the screen and into the
surrounding reaction vessel.
[0106] Various factors influence the mean diameter size and yield
of the product cerium dioxide particles. Factors include reactant
ratios, the rotor speed, the "gap" of the mill, which can be
defined as the space between the rotor 31 and stator 32, and the
size of the perforations 36 of the stator.
[0107] Typical rotor speeds are 5000 to 7500 rpm; however, at very
high reagent concentrations (about 1 Molal or greater) rotor speeds
of greater than 7500 rpm, such as 10,000 rpm, are preferred. It is
desirable to keep the gap spacing as small as possible, typically
about 1 mm to about 3 mm, consistent with a low back pressure in
the colloid chamber, which allows a facile passage of the particles
through the perforations of the stator. In one embodiment, the
perforations of the screen have a mean diameter of preferably about
0.5 mm to about 5 mm.
[0108] FIG. 2B shows a partial view of the reactor, including the
inlet jets 34 and 35 and the base of the reaction chamber 33A. In
one embodiment, the inlet jets 34 and 35 are substantially flush
with the bottom of the reaction chamber 33A.
[0109] FIG. 2C shows a schematic representation of a modification
of the device described above, wherein the inlet jets, 34 and 35,
extend into the reaction chamber from the top of the mill, instead
of the bottom of the mill. Reactants are introduced into the
reaction chamber by means of the reaction inlet(s) and the reaction
mixture is stirred. Desirably, the reactants include an aqueous
solution of cerous ion, for example cerous nitrate; an oxidant such
as hydrogen peroxide or molecular oxygen; and a stabilizer, such as
2-[2-(2-methoxyethoxy)ethoxy]acetic acid. Typically, a two-electron
oxidant, such as peroxide, is present, preferably in at least
one-half the molar concentration of the cerium ion. The hydroxide
ion concentration is preferably at least twice, more preferably
three times, the molar cerium concentration.
[0110] Initially, the reaction chamber is maintained at a
temperature sufficiently low to generate small cerous hydroxide
nuclei size, which can be grown into nanometric cerium dioxide
particles after a subsequent shift to higher temperatures,
resulting in conversion of the cerous ion into the eerie ion state.
Initially, the temperature is suitably about 25.degree. C. or less,
preferably about 20.degree. C., more preferably about 15.degree. C.
In one embodiment, the temperature is about 10-20.degree. C.
[0111] In one embodiment, a source of cerous ion, a nanoparticle
stabilizer, and an oxidant is placed in the reactor and a source of
hydroxide ion, such as ammonium hydroxide, is rapidly added with
stirring, preferably over a time period of about 90 seconds or
less, more preferably about 20 seconds or less, even more
preferably about 15 seconds or less. In an alternative embodiment,
a source of hydroxide ion and an oxidant is placed in the reactor,
and a source of cerous ion is added over a period of about seconds.
In a third and preferred embodiment, the stabilizers are placed in
the reaction vessel, and the cerous nitrate is simultaneously
introduced into the reaction chamber with a separate jet of
ammonium hydroxide at the optimum molar stoichiometric ratio of 2:1
or 3:1 OH:Ce.
[0112] Cerous ion reacts in the presence of hydroxide ion to form
cerium hydroxide, which can be converted by heating to cerium
dioxide. The temperature in the reaction vessel is maintained
between about 50.degree. C. and about 100.degree. C., preferably
about 65-90.degree. C., more preferably about 80.degree. C. After a
period of time at these elevated temperatures, preferably about 1
hour or less, more preferably about 0.5 hour, the cerium hydroxide
has been substantially converted to cerium dioxide, and the
temperature of the reaction vessel is lowered to about
15-25.degree. C. The time and temperature variables may be traded
off, higher temperatures generally requiring shorter reaction
times. The suspension of cerium dioxide nanoparticles is
concentrated, and the unreacted cerium and waste by-products such
as ammonium nitrate are removed, which may be conveniently
accomplished by diafiltration.
[0113] The nanoparticle stabilizer is a critical component of the
reaction mixture. Desirably, the nanoparticle stabilizer is water
soluble and forms weak bonds with cerium ion. K.sub.BC represents
the binding constant of the nanoparticle stabilizer to cerium ion
in water. Log K.sub.BC for the nitrate ion is 1 and for hydroxide
ion is 14. Most desirably, log (K.sub.BC) lies within this range,
preferably towards the bottom of this range. Useful nanoparticle
stabilizers include alkoxysubstituted carboxylic acids,
.alpha.-hydroxyl carboxylic acids, pyruvic acid and small organic
polyacids such as tartaric acid and citric acid. Examples of
ethoxylated carboxylic acids include 2-(methoxy)ethoxy acetic acid
and 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEA). Among the
.alpha.-hydroxy carboxylic acids, examples include lactic acid,
gluconic acid and 2-hydroxybutanoic acid. Polyacids include
ethylenediaminetetraacetic acid (EDTA), tartaric acid, and citric
acid. Combinations of compounds with large K.sub.BC such as EDTA
with weak K.sub.B C stabilizers such as lactic acid are also useful
at particular ratios. Large K.sub.BC stabilizers such as gluconic
acid may be used at a low level or with weak K.sub.BC stabilizers
such as lactic acid.
[0114] In one desirable embodiment, the nanoparticle stabilizer
includes a compound of formula (Ia). In formula (Ia), R represents
hydrogen, or a substituted or unsubstituted alkyl group or aromatic
group such as, for example, a methyl group, an ethyl group or a
phenyl group. More preferably, R represents a lower alkyl group
such as a methyl group. R.sup.1 represents hydrogen or a
substituent group such as an alkyl group. In formula (Ia), n
represents an integer of 0-5, preferably 2. In formula (Ia), Y
represents H or a counterion, such as an alkali metal, for example
Na.sup.+ or K.sup.+. The stabilizer binds to the nanoparticles and
prevents agglomeration of the particles and the subsequent
formation of large clumps of particles.
R--O--(CH.sub.2CH.sub.2O).sub.nCHR.sup.1CO.sub.2Y (Ia)
[0115] In another embodiment, the nanoparticle stabilizer is
represented by formula (Ib), wherein each R.sup.2 independently
represents a substituted or unsubstituted alkyl group or a
substituted or unsubstituted aromatic group. X and Z independently
represent H or a counterion such as Na.sup.+ or K.sup.+ and p is 1
or 2.
XO.sub.2C(CR.sup.2).sub.pCO.sub.2Z (Ib)
[0116] Useful nanoparticle stabilizers are also found among
.alpha.-hydroxysubstituted carboxylic acids such as lactic acid or
even the polyhydroxysubstituted acids such as gluconic acid.
[0117] Preferably, the nanoparticle stabilizer does not include the
element sulfur, since sulfur-containing materials may be
undesirable for certain applications. For example, if the cerium
dioxide particles are included in a fuel additive composition, the
use of s sulfur-containing stabilizer such as AOT may result in the
undesirable emission of oxides of sulfur after combustion.
[0118] The size of the resulting cerium dioxide particles can be
determined by dynamic light scattering, a measurement technique for
the determination of a particle's hydrodynamic diameter. The
hydrodynamic diameter (cf. B. J. Berne and R. Pecora, "Dynamic
Light Scattering: With Applications to Chemistry, Biology and
Physics", John Wiley and Sons, NY 1976 and "Interactions of Photons
and Neutrons with Matter", S. H. Chen and M. Kotlarchyk, World
Scientific Publishing, Singapore, 1997), which is slightly larger
than the geometric diameter of the particle, includes both the
native particle size and the solvation shell surrounding the
particle. When a beam of light passes through a colloidal
dispersion, the particles or droplets scatter some of the light in
all directions. When the particles are very small compared with the
wavelength of the light, the intensity of the scattered light is
uniform in all directions (Rayleigh scattering). If the light is
coherent and monochromatic as, for example, from a laser, it is
possible to observe time-dependent fluctuations in the scattered
intensity, using a suitable detector such as a photomultiplier
capable of operating in photon counting mode. These fluctuations
arise from the fact that the particles are small enough to undergo
random thermal (Brownian) motion, and the distance between them is
therefore constantly varying. Constructive and destructive
interference of light scattered by neighboring particles within the
illuminated zone gives rise to the intensity fluctuation at the
detector plane which, because it arises from particle motion,
contains information about this motion. Analysis of the time
dependence of the intensity fluctuation can therefore yield the
diffusion coefficient of the particles from which, via the Stokes
Einstein equation and the known viscosity of the medium, the
hydrodynamic radius or diameter of the particles can be
calculated.
[0119] In another aspect of the invention, a continuous process for
producing small cerium dioxide nanoparticles, that is, particles
having a mean diameter of less than about nm, includes combining
cerous ion, an oxidant, a nanoparticle stabilizer, and hydroxide
ion within a continuous reactor, into which reactants and other
ingredients are continuously introduced, and from which product is
continuously removed. Continuous processes are described, for
example, in Ozawa, et al., U.S. Pat. No. 6,897,270; Nickel, et al.,
U.S. Pat. No. 6,723,138; Campbell, et al., U.S. Pat. No. 6,627,720;
Beck, U.S. Pat. No. 5,097,090; and Byrd, et al., U.S. Pat. No.
4,661,321; the disclosures of which are incorporated herein by
reference.
[0120] A solvent such as water is often employed in the process.
The solvent dissolves the reactants, and the flow of the solvent
can be adjusted to control the process. Advantageously, mixers can
be used to agitate and mix the reactants.
[0121] Any reactor that is capable of receiving a continuous flow
of reactants and delivering a continuous flow of product can be
employed. These reactors may include continuous-stirred-tank
reactors, plug-flow reactors, and the like. The reactants required
to carry out the nanoparticle synthesis are preferably charged to
the reactor in streams; i.e., they are preferably introduced as
liquids or solutions. The reactants can be charged in separate
streams, or certain reactants can be combined before charging the
reactor.
[0122] Reactants are introduced into the reaction chamber provided
with a stirrer through one or more inlets. Typically, the reactants
include an aqueous solution of cerous ion, for example, cerous
nitrate; an oxidant such as hydrogen peroxide or molecular oxygen,
including ambient air; and a stabilizer, such as
2-[2-(2-methoxyethoxy)ethoxy]acetic acid. A two-electron oxidant
such as hydrogen peroxide is present, preferably in at least
one-half the molar concentration of the cerium ion. Alternatively,
molecular oxygen can be bubbled through the mixture. The hydroxide
ion concentration is preferably at least twice the molar cerium
concentration.
[0123] In one embodiment of the present invention, a method of
forming small cerium dioxide nanoparticles includes the step of
forming a first aqueous reactant stream that includes cerous ion,
for example, as cerium(III) nitrate, and an oxidant. Suitable
oxidants capable of oxidizing Ce(III) to Ce(IV) include, for
example, hydrogen peroxide or molecular oxygen. Optionally, the
first reactant stream also includes a nanoparticle stabilizer that
binds to cerium dioxide nanoparticles, thereby preventing
agglomeration of the particles. Examples of useful nanoparticle
stabilizers were mentioned above.
[0124] The method further includes a step of forming a second
aqueous reactant stream that includes a hydroxide ion source, for
example, ammonium hydroxide or potassium hydroxide. Optionally, the
second reactant stream further includes a stabilizer, examples of
which were described previously. At least one of the first or
second reactant streams, however, must contain a stabilizer.
[0125] The first and second reactant streams are combined to form a
reaction stream. Initially, the temperature of the reaction stream
is maintained sufficiently low to form small cerous hydroxide
nuclei. Subsequently the temperature is raised so that oxidation of
Ce(III) to Ce(IV) occurs in the presence of the oxidant, and the
hydroxide is converted to the oxide, thereby producing a product
stream that includes cerium dioxide. The temperature for conversion
from the hydroxide to the oxide is preferably in the range of about
50-100.degree. C., more preferably about 60-90.degree. C. In one
embodiment, the first and second reactant streams are combined at a
temperature of about 10-20.degree. C., and the temperature is
subsequently increased to about 60-90.degree. C.
[0126] Desirably, cerium dioxide nanoparticles in the product
stream are concentrated, for example, by diafiltration techniques
using one or more semi-porous membranes. In one embodiment, the
product stream includes an aqueous suspension of cerium dioxide
nanoparticles that is reduced to a conductivity of about 3 mS/cm or
less by one or more semi-porous membranes.
[0127] A schematic representation of a continuous reactor suitable
for the practice of the invention is depicted in FIG. 3. The
reactor 40 includes a first reactant stream 41 containing aqueous
cerium nitrate. An oxidant such as hydrogen peroxide is added to
the reactant stream by means of inlet 42, and the reactants are
mixed by mixer 43a. To the resulting mixture is added stabilizer
via inlet 45, followed by mixing by mixer 43b. The mixture from
mixer 43b then enters mixer 43c, where it is combined with a second
reactant stream containing ammonium hydroxide from inlet 44. The
first and second reactant streams are mixed using a mixer 43c to
form a reaction stream that may be subjected to mechanical shearing
by passing it through a perforated screen. In a further embodiment,
mixer 43c comprises a colloid mill reactor, as described
previously, that is provided with inlet ports for receiving the
reactant streams and an outlet port 45. In a further embodiment,
the temperature of the mixer 43c is maintained at a temperature in
the range of about 10.degree. C. to about 25.degree. C.
[0128] The mixture from 43c enters a reactor tube 45 that is
contained in a constant temperature bath 46 that maintains tube 45
at a temperature of about 60-90.degree. C. Cerium nanoparticles are
formed in the reactor tube 45, which may include a coil 50. The
product stream then enters one or more diafiltration units 47,
wherein the cerium nanoparticles are concentrated using one or more
semi-porous membranes. One or more diafiltration units may be
connected in series to achieve a single pass concentration of
product, or the units may placed in parallel for very high
volumetric throughput. The diafiltration units may be disposed both
in series and parallel to achieve both high volume and rapid
throughput. Concentrated cerium nanoparticles exit the
diafiltration unit via exit port 49, and excess reactants and water
are removed from the diafiltration unit 47 via exit port 48. In an
alternative embodiment, stabilizer may be added to the second
reactant stream via port 51 rather than to the first reactant
stream via port 45.
[0129] In one embodiment of the invention, the product stream of
concentrated cerium nanoparticles exiting the diafiltration unit 47
is combined with a stream that includes a nonpolar solvent and at
least one surfactant, wherein the surfactant is chosen so that a
reverse micelle is formed in the emulsion, as described below.
[0130] The use of a continuous process for producing cerium dioxide
nanoparticles allows better control of the production of particle
nuclei and their growth relative to that afforded by batch
reactors. The nuclei size can be controlled by the initial reagent
concentration, temperature, and the ratio of nanoparticle
stabilizer to reagent concentrations. Small nuclei are favored by
low temperatures, less than about 20.degree. C., and high ratios of
nanoparticle stabilizer to reagent concentrations. In this way,
very small cerium dioxide nanoparticles having a mean hydrodynamic
diameter of less than about 10 nm can be produced in an economical
manner.
[0131] It may be possible to use some of the aqueous precipitation
medium in which cerium dioxide particles are typically formed to
subsequently enhance the activity of the nanoparticles. When a
mixture, including cerium nanoparticles and a small amount of
water, undergoes combustion in the presence of air and fuel in a
diesel engine, flame temperatures may reach levels as high as
900.degree. C. (1652.degree. F.). At these high temperatures,
reduction of cerium and production of oxygen according to equation
1 is very efficient. Additionally, at these elevated temperatures
superheated steam can be generated from the water. This not only
will increase the compression ratio, resulting in higher engine
efficiency, but will also result in the separation of the fuel wave
front into many, very small, high surface area droplets. This
allows better mixing of the air-fuel regions, which enables the
cerium dioxide particles to provide oxygen to the fuel more
readily, resulting in more complete fuel combustion. This in turn
increases engine performance while simultaneously reducing
particulate matter emissions. If sufficient water is present, the
combustion temperature will be lowered somewhat, and may also
reduce levels of nitrogen oxide (NO.sub.x) production, which is
greatest at higher temperatures. However at sufficiently high
levels of water, the combustion temperature can be lowered to the
point at which engine power is reduced. This phenomenon can be
offset by replacing some of the water in the aqueous phase with a
water-soluble cetane improver such as hydrogen peroxide or t-butyl
hydroperoxide. Thus, it would be beneficial to provide a
homogeneous mixture of stable nanoparticles of cerium dioxide and
water in a nonpolar medium such as, for example, diesel fuel.
[0132] The invention provides a method for formulating a
homogeneous mixture that includes cerium dioxide nanoparticles, a
nanoparticle stabilizer, a surfactant, water, and a nonpolar
solvent. Preferably, the nanoparticles have a mean diameter of less
than about nm, more preferably less than about 8 nm, most
preferably about 6 nm.
[0133] As described above, cerium dioxide nanoparticles can be
prepared by various procedures. Typical synthetic routes utilize
water as a solvent and yield an aqueous mixture of nanoparticles
and one or more salts. For example, cerium dioxide particles can be
prepared by reacting the hydrate of cerium(III) nitrate with
hydroxide ion from, for example, aqueous ammonium hydroxide,
thereby forming cerium (III) hydroxide, as shown in equation (2a).
Cerium hydroxide can be oxidized to cerium (IV) dioxide with an
oxidant such as hydrogen peroxide, as shown in equation (2b). The
analogous tris hydroxide stoichiometry is shown in equations (3a)
and (3b).
Ce(NO.sub.3).sub.3(6H.sub.2O)+2NH.sub.4OH.fwdarw.Ce(OH).sub.2NO.sub.3+2N-
H.sub.4NO.sub.3+6H.sub.2O (2a)
2Ce(OH).sub.2NO.sub.3+H.sub.2O.sub.2.fwdarw.2CeO.sub.2+2HNO.sub.3+2H.sub-
.2O (2b)
Ce(NO.sub.3).sub.3(6H.sub.2O)+3NH.sub.4OH.fwdarw.Ce(OH).sub.3+3NH.sub.4N-
O.sub.3+6H.sub.2O (3a)
2Ce(OH).sub.3+H.sub.2O.sub.2.fwdarw.2CeO.sub.2+4H.sub.2O (3b)
Complexes formed with very high base levels, e.g., 5:1 OH:Ce, also
provide a route to cerium dioxide
[0134] In some cases, especially where ammonium hydroxide is not
present in excess relative to cerous ion, the species
Ce(OH).sub.2(NO.sub.3) or (NH.sub.4).sub.2Ce(NO.sub.3).sub.5 may
initially be present, subsequently undergoing oxidation to cerium
dioxide.
[0135] The cerium dioxide particles are formed in an aqueous
environment and combined with one or more nanoparticle stabilizers.
Desirably, the cerium dioxide nanoparticles are either formed in
the presence of the stabilizer(s), or a stabilizer(s) is added
shortly after their formation. Useful nanoparticle stabilizers
include alkoxysubstituted carboxylic acids,
.alpha.-hydroxylcarboxylic acids, pyruvic acid, and small organic
polycarboxylic acids. Examples of alkoxysubstituted carboxylic
acids include 2-(methoxy)ethoxy acetic acid and
2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEA). Examples of
.alpha.-hydroxy carboxylic acids include lactic acid, gluconic acid
and 2-hydroxybutanoic acid. Polycarboxylic acids include
ethylenediaminetetraacetic acid (EDTA), tartaric acid, and citric
acid. In desirable embodiments, the nanoparticle stabilizer
includes a compound of formula (Ia) or formula (Ib), as described
above.
[0136] The reaction mixture includes, in addition to cerium dioxide
nanoparticles, one or more salts, for example, ammonium nitrate and
unreacted cerium nitrate. The stabilized particles can be separated
from these materials and salts by washing with 18 Mohm water in an
ultrafiltration or diafiltration apparatus. Low ionic strength
(<3 mS/cm) is highly desirable for the formation and
stabilization of retained water in a micellar state. The washed,
stabilized cerium dioxide nanoparticles may be concentrated, if
desired, using a semi-porous membrane, for example, to form an
aqueous concentrate of the nanoparticles. The particles may be
concentrated by other means as well, for example, by
centrifugation.
[0137] In one preferred embodiment, the cerium dioxide
nanoparticles are concentrated by diafiltration. The diafiltration
technique utilizes ultrafiltration membranes, which can be used to
completely remove, replace, or lower the concentration of salts in
the nanoparticle-containing mixture. The process selectively
utilizes semi-permeable (semi-porous) membrane filters to separate
the components of the reaction mixture on the basis of their
molecular size. Thus, a suitable ultrafiltration membrane would be
sufficiently porous so as to retain the majority of the formed
nanoparticles, while allowing smaller molecules such as salts and
water to pass through the membrane. In this way, the nanoparticles
and the associated bound stabilizer can be concentrated. The
materials retained by the filter, including the stabilized
nanoparticles, are referred to as the concentrate or retentate, the
discarded salts and unreacted materials as the filtrate.
[0138] Pressure may be applied to the mixture to accelerate the
rate at which small molecules passes through the membrane (flow
rate) and to speed the concentration process. Other means of
increasing the flow rate include using a large membrane having a
high surface area, and increasing the pore size of the membrane,
but without an unacceptable loss of nanoparticles.
[0139] In one embodiment, the membrane is selected so that the
average pore size of the membrane is about 30% or less, 20% or
less, 10% or less, or even 5% or less than that of the mean
diameter of the nanoparticles. However, the pore diameter must be
sufficient to allow passage of water and salt molecules. For
example, ammonium nitrate and unreacted cerium nitrate should be
completely or partially removed from the reaction mixture. In one
preferred embodiment, the average membrane pore size is
sufficiently small to retain particles of 3 nm diameter or greater
in the retentate. This would correspond to a protein size of
approximately 3 kilodaltons.
[0140] Desirably, the concentrate includes stabilized nanoparticles
and residue water. In one embodiment, the concentration of cerium
dioxide nanoparticles is preferably greater than about 0.5 molal,
more preferably greater than about 1.0 molal, even more preferably
greater than about 2.0 molal.
[0141] Once the concentrate is formed, it is combined with one or
more surfactants and a nonpolar solvent to form a homogeneous
mixture. The surfactant is chosen so that a reverse micelle
consisting of an aqueous, stabilized cerium dioxide nanoparticles
dispersed in a nonpolar medium is formed. Reverse micellar
solutions consisting of particles in an aqueous environment
dispersed in a nonpolar solvent, have been described previously in,
for example, Ying, et al., in U.S. Pat. No. 6,869,584 and U.S.
Patent Appl. Publ. No. 2005/0152832, the disclosures of which are
incorporated herein by reference.
[0142] Depending upon the relative sizes of the cerium dioxide
nanoparticles and the reverse micelle particles, the former may be
incorporated into the structure of the latter to varying extents.
In one embodiment, the stabilized cerium dioxide nanoparticles are
added, with mixing, to a solution of the surfactant and a
co-surfactant and a nonpolar solvent at a temperature in the range
of about 25.degree. C. to about 0.degree. C. Suitable nonpolar
solvents include, for example, hydrocarbons containing about 6 to
20 carbon atoms, for example, pentane, heptane, octane, decane and
toluene, and hydrocarbon fuels such as gasoline, biodiesel, and
diesel fuels.
[0143] Useful surfactants include nonylphenyl ethoxylates having
the formula,
C.sub.9H.sub.19C.sub.6H.sub.4(OCH.sub.2CH.sub.2).sub.nOH, wherein n
is 4-6. Other surfactants that contain both an ether group and an
alcohol group includes compounds of formula (Ic), in which R.sup.3
represents a substituted or unsubstituted alkyl group, and m is an
integer of 1-8.
R.sup.3--(OCH.sub.2CH.sub.2).sub.m--OH (Ic)
[0144] In certain embodiments, carboxylate surfactants such as the
salts of stearic acid, palmitic acid, and oleic acid may be useful
as surfactants.
[0145] Another type of useful surfactant is represented by formula
(Ib), wherein each R.sup.2 independently represents a substituted
or unsubstituted alkyl group or a substituted or unsubstituted
aromatic group, X and Z independently represent H or a counterion
such as Na.sup.+, or K.sup.+, and p is 1 or 2.
XO.sub.2C(CR.sup.2).sub.pCO.sub.2Z (Ib)
[0146] In another embodiment, the reverse-micelle forming agent
includes an anionic surfactant and a nonionic co-surfactant. Useful
co-surfactants include aliphatic alcohols, for example, pentanol
and hexanol and their geometric isomers.
[0147] Formulating cerium dioxide nanoparticle dispersions using a
reverse micelle formation allows the aqueous nanoparticle
stabilizing agent(s) to be independently optimized from that of the
surfactant(s).
[0148] A desirable reverse-micellar composition is effective for
lowering the cold pour cloud point of diesel fuel, that is, the
temperature at which wax crystals begin to form and the diesel fuel
begins to gel. For a discussion of the cold pour cloud point, see
Langer et al., U.S. Pat. No. 6,368,366 and U.S. Pat. No. 6,383,237,
the disclosures of which are incorporated herein by reference.
[0149] A desirable reverse-micellar composition is extremely stable
and capable of very high dilution ratios; a dilution of 500:1
fuel:micellar composition or greater is, highly advantageous. To
optimize the stability of the reverse-micellar composition, the
cerium dioxide nanoparticle concentrate preferably includes high
resistivity water, that is, water having a resistivity of about
1-18 mega ohm per cm, preferably about 18 mega ohm per cm. Pure
water has a resistivity of 18.3 mega ohm per cm.
[0150] Resistivity is the reciprocal of conductivity, which is the
ability of a material to conduct electric current. Conductivity
instruments can measure conductivity by including two plates that
are placed in the sample, applying a potential across the plates
(normally a sine wave voltage), and measuring the current.
Conductivity (G), the inverse of resistivity (R), is determined
from the voltage and current values according to Ohm's law,
G=1/R=I/E, where I is the current in amps and E is the voltage in
volts. Since the charge on ions in solution facilitates the
conductance of electrical current, the conductivity of a solution
is proportional to its ion concentration. The basic unit of
conductivity is the siemens (S), or milli-Siemens (mS). Since cell
geometry affects conductivity values, standardized measurements are
expressed in specific conductivity units (mS/cm) to compensate for
variations in electrode dimensions.
[0151] In an optimal micellar composition, it is desirable that
very few ions be present in the cerium dioxide concentrate to
conduct electricity. This situation can be achieved by
concentrating the cerium dioxide particles through diafiltration to
a conductivity level of less than 5 mS/cm, preferably to 3 mS/cm or
less.
[0152] The present invention is further directed to a method for
formulating a homogeneous mixture including cerium dioxide
nanoparticles, at least one nanoparticle stabilizer and at least
one surfactant, water, and a nonpolar solvent. A first step
provides an aqueous mixture including stabilized cerium dioxide
nanoparticles, wherein molecules of the nanoparticle stabilizer are
closely associated with the nanoparticles. A second step includes
concentrating the stabilized cerium dioxide nanoparticles while
minimizing the ionic strength of the suspension to form an aqueous
concentrate that is relatively free of anions and cations. A third
step includes combining the concentrate with a nonpolar solvent,
containing a surfactant, thereby forming a substantially
homogeneous mixture that is a thermodynamically stable,
multicomponent, single phase, reverse ("water in oil") micellar
solution.
[0153] The substantially homogeneous mixture contains water at a
level of preferably about 0.5 wt. % to about 20 wt. %, more
preferably, about 5 wt. % to about 15 wt. %. The cerium dioxide
nanoparticles have a mean hydrodynamic diameter of preferably less
than about 10 nm, more preferably less than about 8 nm, most
preferably about 6 nm. Desirably, the cerium dioxide nanoparticles
have a primary crystallite size of about 2.5 nm.+-.0.5 nm and
comprise one or at most two crystallites per particle edge
length.
[0154] The aqueous mixture is advantageously formed in a colloid
mill reactor, and the nanoparticle stabilizer may comprise an ionic
surfactant, preferably a compound that includes a carboxylic acid
group and an ether group. The nanoparticle stabilizer may comprise
a surfactant of formula (Ia),
R--O--(CH.sub.2CH.sub.2O).sub.nCHR.sup.1CO.sub.2Y (Ia)
wherein:
[0155] R represents hydrogen or a substituted or unsubstituted
alkyl group or a substituted or unsubstituted aromatic group;
[0156] R.sup.1 represents hydrogen or an alkyl group;
[0157] Y represents H or a counterion; and
[0158] n is 0-5.
Preferably, R represents a substituted or unsubstituted alkyl
group, R.sup.1 represents hydrogen, Y represents hydrogen, and n is
2.
[0159] Another suitable nanoparticle stabilizer comprises a
compound of formula (Ib),
XO.sub.2C(CR.sup.2).sub.pCO.sub.2Z (Ib)
wherein:
[0160] each R.sup.2 independently represents hydrogen, a
substituted or unsubstituted alkyl group or a substituted or
unsubstituted aromatic group;
[0161] X and Z independently represent H or a counterion; and
[0162] p is 1 or 2.
Other useful nanoparticle stabilizers are included in the group
consisting of lactic acid, gluconic acid enantiomers, EDTA,
tartaric acid, citric acid, and combinations thereof.
[0163] The surfactant may also comprise a nonionic surfactant,
preferably a compound comprising an alcohol group and an ether
group, in particular, a compound of formula (Ic),
R.sup.3--(OCH.sub.2CH.sub.2).sub.m--OH (Ic)
wherein:
[0164] R.sup.3 represents a substituted or unsubstituted alkyl
group; and m is an integer from 1 to 8.
[0165] The nonionic surfactant may also comprise a compound of
formula (Id),
R.sup.3-.phi.-(OCH.sub.2CH.sub.2).sub.m--OH (Id)
wherein:
[0166] R.sup.3 represents a substituted or unsubstituted alkyl
group; and
[0167] .phi. is an aromatic group
[0168] m is an integer from 4 to 6.
[0169] The surfactant may also comprise an anionic surfactant,
preferably a compound containing a sulfonate group or a phosphonate
group. A useful anionic surfactant is sodium
bis(2-ethyl-1-hexyl)sulfosuccinate (AOT).
[0170] The aqueous reaction mixture may further include a
co-surfactant, preferably an alcohol.
[0171] Concentrating the aqueous mixture is preferably carried out
using diafiltration, which results in the reduction in conductivity
of said concentrated aqueous mixture to about 3 mS/cm or less.
[0172] The nonpolar solvent included in the substantially
homogeneous solution is advantageously selected from among
hydrocarbons containing about 6-20 carbon atoms, for example,
octane, decane, toluene, diesel fuel, biodiesel, and mixtures
thereof. When used as a fuel additive, one part of the homogeneous
mixture is with at least about 100 parts of the fuel.
[0173] Further in accordance with the present invention is a method
for preparing cerium dioxide nanoparticles comprising a core and a
shell, wherein the shell comprises a material selected from the
group consisting of a transition metal, a lanthanide, a
sulfur-containing compound that may include a mercaptide group, and
combinations thereof. Preferably, the core comprises about 90% or
less of the nanoparticle by volume, and the shell comprises about
5% or more of the nanoparticle by volume. The shell comprises
lattice sites, and up to about 30% of the lattice sites include a
material selected from the group consisting of a transition metal,
a lanthanide, a sulfur-containing compound, and combinations
thereof.
[0174] The transition metal is preferably selected from the group
consisting of Fe, Mn, Cr, Ni, W, Co, V, Cu, Mo, and Zr, or from the
lanthanide series, and combinations thereof. Desirably, the
transition metal is capable of binding to iron. It is also
desirable that the transition metal be capable of reacting with an
oxide of sulfur. In a further embodiment, the transition metal is
associated with at least one ligand that comprises sulfur.
[0175] A composition comprising aqueously suspended cerium dioxide
nanoparticles that comprise a core and a shell, wherein the shell
includes at least one transition metal, may be subsequently solvent
shifted into a non polar medium in which the particles are
essentially water free and are incorporable into a lubrication oil.
The nanoparticles in the oil act as an adjuvant to further reduce
friction of contacting moving engine parts.
[0176] It would be beneficial to form a ceramic oxide coating on
the surface of diesel engine cylinders in situ. The potential
benefits of the coating include added protection of the engine from
thermal stress; for example, CeO.sub.2 melts at 2600.degree. C.,
whereas cast iron, a common material used in the manufacture of
diesel engines, melts at about 1200-1450.degree. C. Even 5 nm ceria
particles have demonstrated the ability to protect steel from
oxidation for 24 hours at 1000.degree. C., so the phenomenon of
size dependent melting would not be expected to lower the melting
point of the cerium dioxide nanoparticles of the invention below
the combustion temperatures encountered in the engine. See, for
example, Patil et al., Journal of Nanoparticle Research, vol. 4, pp
433-438 (2002). An engine so protected may be able to operate at
higher temperatures and compression ratios, resulting in greater
thermodynamic efficiency. A diesel engine having cylinder walls
coated with cerium dioxide would be resistant to further oxidation
(CeO.sub.2 being already fully oxidized), thereby preventing the
engine from "rusting." This is important because certain additives
used to reduce carbon emissions or improve fuel economy such as,
for example, the oxygenates MTBE, ethanol and other cetane
improvers such as peroxides, also increase corrosion when
introduced into the combustion chamber, which may result in the
formation of rust and degradation of the engine lifetime and
performance. The coating should not be so thick as to impede the
cooling of the engine walls by the water recirculation cooling
system. In one embodiment, the current invention provides cerium
dioxide nanoparticles having a mean hydrodynamic diameter of less
than about 10 nm, preferably less than about 8 nm, more preferably
6 nm or even less, that are useful as a fuel additive for diesel
engines. The surfaces of the cerium dioxide nanoparticles may be
modified to facilitate their binding to an iron surface, and
desirably would, when included in a fuel additive composition,
rapidly form a ceramic oxide coating on the surface of diesel
engine cylinders.
[0177] In one embodiment, a transition or lanthanide metal having a
binding affinity for iron is incorporated onto the surface of the
cerium dioxide nanoparticles. Examples of iron surfaces include
those that exist in many internal parts of engines. Suitable
transition metals include Mn, Fe, Ni, Cr, W, Co, V, Cu, and Zr.
[0178] The transition or lanthanide metal ion, which is
incorporated into the cerium dioxide nanoparticles by occupying a
cerium ion lattice site in the crystal, may be introduced as a
dopant during the latter stages of the precipitation of cerium
dioxide. The dopant can be added in combination with cerous ion,
for example, in a single jet manner in which both cerous ion and
transition metal ion are introduced together into a reactor
containing ammonium hydroxide. Alternatively, the dopant and cerous
ion can be added together with the simultaneous addition of
hydroxide ion. The doped particles can also be formed in a double
jet reaction of cerous ion with dissolved transition metal ion
titrated against an ammonium hydroxide steam simultaneously
introduced by a second jet. In any event, it is understood that
sufficient nanoparticle stabilizer is present to prevent
agglomeration of the nascent particles.
[0179] In a further embodiment, cerium dioxide nanoparticles are
prepared having a core-shell structure. The core of the particle
preferably includes at least about 75% more preferably, about 95%
or greater of the bulk particle, and may be optionally doped with a
metal. The shell, including the outer portion and surface of the
particle, preferably comprises about 25% or less, more preferably
about 10% or less, most preferably about 5% or less, of the
particle, and includes a transition or lanthanide metal. Up to
about 30% of the Ce.sup.+4 lattice sites of the shell may occupied
by one or more transition or lanthanide metals. Suitable transition
metals include Mn, Fe, Ni, Cr, W, Co, V, Cu, Zr, and Mo, and
combinations thereof.
[0180] In a further embodiment, the cerium dioxide nanoparticles
have a core-shell structure, wherein the shell includes at least
one compound comprising sulfur.
[0181] Preferably, the sulfur is present so that it is capable of
forming a bond with iron. When used as a fuel additive for a diesel
engine, the sulfur contained in the shell of the cerium dioxide
particles binds to the iron surface of the combustion chamber of
the engine, thereby accelerating the deposition of cerium dioxide
on the surface of the combustion chamber. Suitable sulfur compounds
include ZnS, MnS, FeS, Fe.sub.2S.sub.3, CoS, NiS, and CuS. The
sulfur may be part of a transition metal ligand, wherein the metal
and its associated ligand are incorporated into the surface of the
cerium dioxide nanoparticles. For example, ligands that include a
mercaptide group can form sulfur-iron bonds.
[0182] Sulfur can be incorporated into the cerium dioxide
nanoparticles during the aqueous precipitation of CeO.sub.2, for
example, by incorporating with the cerium nitrate hexahydrate
reactant the appropriate water soluble transition metal salt
(nitrate, sulfate or chloride), together with a labile source of
sulfur such as thiosulfate (alternatively, the thiosulfate salt of
a transition metal may be used). During the thermal conversion of
the cerium hydroxide to the oxide at elevated temperatures, for
example, about 70-90.degree. C., the corresponding transition metal
sulfide will also form.
[0183] In another embodiment, a transition metal is incorporated
into the surface of the cerium dioxide nanoparticles. Desirably,
this metal is chosen so that it is capable of reacting with sulfur
and forming a bond to sulfur. The transition metal is present in
the reaction mixture during the shell formation of the CeO.sub.2
precursor (cerium hydroxide). Suitable metals include Mn and Fe as
well as W, Co, V, Cu, and Mo. Typical aqueous soluble transition
metal salts include sulfates, nitrates, and chlorides of these
metals.
[0184] When used as a fuel additive, the transition
metal-containing nanoparticles can bind sulfur that may be present
in the fuel. Iron, for example, can react with sulfur dioxide to
form Fe.sub.2S.sub.3. This reduces the level of reactive sulfur,
for example, sulfur oxides, present in gases emitted from the fuel
combustion chamber. Removal of sulfur after fuel combustion is very
desirable, since many vehicle exhaust systems include particulate
traps containing a platinum catalyst that can be poisoned by
sulfur. Hence removal of sulfur before it reaches the catalyst can
prolong the life of the catalyst. Useful metals for the reduction
of sulfur dioxide are also described by Yamashita, et al., U.S.
Pat. No. 5,910,466, the disclosure of which is incorporated herein
by reference.
[0185] It is known in the art that small particles can be made
within the isolated phase of an emulsion, which is a stable mixture
of at least two immiscible liquids. Although immiscible liquids
tend to separate into two distinct phases, an emulsion can be
stabilized by the addition of a surfactant that functions to reduce
surface tension between the liquid phases. An emulsion comprises a
continuous phase and a disperse phase that is stabilized by a
surfactant. A water-in-oil (w/o) emulsion having a disperse aqueous
phase and an organic continuous phase, typically comprising a
hydrocarbon, is often referred to as a "reverse-micellar
composition."
[0186] Further in accordance with the invention, a reverse-micellar
composition comprises a disperse phase comprising a cerium (IV)
nanoparticle-containing aqueous composition, together with a
continuous phase comprising a hydrocarbon liquid and at least one
surfactant. A fuel additive composition of the invention comprises
a reverse-micellar composition whose aqueous disperse phase
includes in situ-formed nanoparticles comprising a cerium (IV)
oxidic compound, and whose continuous phase includes a hydrocarbon
liquid and a surfactant/stabilizer mixture. The
surfactant/stabilizer mixture is effective to restrict the size of
the nanoparticles thus formed, preventing their agglomeration and
enhancing the yield of the nanoparticles.
[0187] In another embodiment, a reverse-micellar composition
comprises: an aqueous disperse phase that includes a free radical
initiator, and a continuous phase that includes a hydrocarbon
liquid and at least one surfactant. Optionally, the
reverse-micellar composition may include cerium-containing
nanoparticles.
[0188] In a further embodiment, a fuel additive composition
comprises: a continuous phase comprising a hydrocarbon liquid, a
surfactant, and optionally a cosurfactant; and forming a
reverse-micellar composition comprising an aqueous disperse phase
that includes a cetane improver effective for improving engine
power during combustion of the fuel. The fuel additive composition
optionally further comprises cerium-containing nanoparticles, which
may be included in either a separate dispersion or a separate
reverse-micellar composition.
[0189] In one embodiment of the present invention, a water-in-oil
emulsion has a small micellar disperse size, and the particulate
material is formed within the aqueous disperse phase. The
appropriate choice of surfactants and reaction conditions provides
for the formation of stable emulsions, the control of particle size
distribution and growth, and the prevention of particle
agglomeration. The oil phase preferably comprises a hydrocarbon,
which may further include oxygen-containing compounds. In the
micelle, the disperse aqueous phase is encompassed by a surfactant
boundary that isolates and stabilizes the aqueous phase from the
organic continuous phase.
[0190] A surfactant included in the emulsion preferably in the
continuous phase to stabilize the reverse micelles can be an ionic
surfactant, a non-ionic surfactant, or a combination thereof.
Suitable surfactants include, for example, nonylphenyl ethoxylates,
monoalkyl and dialkyl carboxylates, and combinations thereof.
[0191] The difficulties of using two distinct reverse micelles for
the cerium-containing reactant and a precipitating agent such as
ammonium hydroxide are avoided by the present invention, which
provides for the combination of both reactants into a single
reverse micelle using a homogeneous precipitation method, wherein a
first reactant is homogeneously mixed with a precursor of a second
reactant. A suitable first reactant is a Ce.sup.+4-containing
compound, which may be obtained by oxidation using H.sub.2O.sub.2
for example, of a Ce.sup.-3-containing compound such as, for
example, Ce(NO.sub.3).sub.3.6H.sub.2O.
[0192] A suitable second reactant is ammonia, NH.sub.3, which can
be obtained by the heat- and/or light activated hydrolysis of
hexamethylenetetramine, C.sub.6H.sub.12N.sub.4, (HMT), as shown in
equation (4):
C.sub.6H.sub.12N.sub.4+12H.sub.2O.fwdarw.4NH.sub.3+6CH.sub.2O
(4)
The homogeneous precipitation of cerium dioxide using HMT has been
reported by Zhang, F., Chan Siu-Wai et al., Applied Physics, 80, 1
(2002), pp 127-129, and in the previously discussed Chan, U.S.
Patent Appl. Publ. No. 2005/0031517. In the absence of a
stabilizer, the size of the cerium dioxide particles produced by
the procedure described in these references continues to increase
with time. Furthermore, the procedure utilizes very dilute
solutions and long reaction times, and produces low product
yield.
[0193] In an example of the process of the present invention, which
beneficially combines reverse micelle with homogeneous
precipitation techniques, Ce(NO.sub.3).sub.3(6H.sub.2O) is combined
with H.sub.2O.sub.2 to generate a Ce.sup.+4-containing solution.
Preferably, the solution further includes a stabilizer for
controlling the size of the cerium-containing nanoparticles. A
preferred stabilizer is 2-[2-(2-methoxyethoxy)ethoxy]acetic acid
(MEEA). The resulting solution is added to a cold HMT solution at a
temperature sufficiently low, less than about 15.degree. C., to
inhibit premature reaction. The resulting mixture is then slowly
added to an oil phase comprising a surfactant and an organic
solvent such as, for example, toluene, octane, decane, gasoline, D2
diesel fuel, ULSD, biodiesel, or combinations thereof. The new
mixture is heated to a temperature just sufficient to effect
substantially complete formation of the Ce-containing
nanoparticles. The precise temperature required depends on the
choice of reverse-micelle surfactant and the concentration of the
first reactant and second reactant precursor but is desirably
maintained below about 47.degree. C. The reverse-micelle surfactant
may also serve to stabilize the Ce-containing nanoparticles.
Alternatively, the aqueous Ce.sup.+4-HMT mixture may be premixed
with another surfactant different from that used to form the
reverse-micellar composition. The aqueous composition may
optionally further include a cetane improving agent generally
recognized to be a free radical forming species at elevated
temperatures.
[0194] Depending on the reaction conditions, the individual
micelles may be small enough to encompass a single
cerium-containing nanoparticle or large enough to contain a
plurality of the nanoparticles. Thus, the micelles have a diameter
of preferably about 5 nm to about 50 nm, more preferably about 20
nm. The cerium-containing nanoparticles have a diameter of
preferably about 1 nm to about 15 nm, more preferably about 2 nm to
about 10 nm.
[0195] The CH.sub.2O generated in the aqueous phase by the
hydrolysis of HMT may be utilized in a subsequent fuel combustion
process. Alternatively, if the reverse micelle contains some
cross-linkable groups, the CH.sub.2O can effect cross-linking
within the micelle, strengthening it or increasing its
heat-resistance.
[0196] A fuel additive emulsion formed by the reverse micelle
process of the present invention includes water used in the
preparation of the cerium-containing nanoparticles. Excess water
introduced into a fuel with the cerium-containing emulsion can lead
to a loss of engine power. To overcome this problem and thereby
improve fuel performance, water can be removed from the
cerium-containing aqueous phase and replaced by a cetane improver.
Water removed by, for example, diafiltration may be replaced by a
water-soluble cetane improving compound. Compounds suitable for
this purpose include, for example, 30-50 wt. % aqueous
H.sub.2O.sub.2, t-butyl hydroperoxide, nitromethane, and low
molecular weight alkyl ethers such as dimethyl ether and diethyl
ether.
[0197] Free radical initiators such as, for example, H.sub.2O.sub.2
are known to be effective cetane improvers for diesel fuel,
resulting in reductions in soot and hydrocarbon emission. Cetane
number is an indicator of the ignition delay time after injection
of fuel into the combustion chamber; alternatively, it can be
regarded as being related to the inverse of the ignition time,
i.e., the time between the injection of the diesel fuel into the
compressed superheated air in the combustion chamber and the actual
ignition of the injected fuel stream. The higher the cetane number,
the more completely combusted the fuel and the less soot
production, as ignition delay gives rise to the formation of soot.
An additional consideration is the desire for this ignition to
occur as closely as possible in time to when the piston reaches
top-dead-center (TDC), since too short an ignition time would
result in the combusted gases working against the compressive
stroke of the piston. For 12-liter diesel and smaller engines, fuel
injection usually occurs at a crank angle of 5 or 6 degrees before
TDC. Thus, cetane improvement would have a very small effect on the
crank angle and minimal adverse effect on engine power. On the
other hand, substantial cetane improvement with diesel locomotive
engines, which have a 25 degree crank angle, would be problematic
for engine power without prior adjustment of the crank angle.
[0198] Utilization of a free radical mechanism for enhanced
combustion efficiency is a very attractive alternative to simply
increasing the O.sub.2 stoichiometry in the combustion chamber,
since free radical chemistry involving O atoms or OH species is
roughly two orders of magnitude faster than direct oxidation by
O.sub.2, as represented in equation (5):
C.sub.14H.sub.30+22O.sub.2.fwdarw.15H.sub.2O+14CO.sub.2 (5)
This is partly a consequence of the need to initially rupture a 0=0
bond (bond dissociation energy delta H of 119.2 Kcal/mole) and the
high reactivity of OH radicals, which are one of the most
chemically reactive species that can be generated (on an
electromotive force scale or free energy scale), just slightly less
reactive than fluorine radicals.
[0199] Oxidation of hydrocarbons and soot by free radical chemical
chemistry, on the other hand, can involve breaking a relatively
weak 0-0 single bond (delta H=47 kcal/mole for hydrogen peroxide)
and then proceed via direct C--H bond scission to give water and a
"hot," i.e., chemically reactive, hydrocarbon radical, as shown in
equation (7):
H.sub.2O.sub.2.fwdarw.2.OH (6)
H.sub.3C--C.sub.13H.sub.27+.OH.fwdarw.H.sub.2O+.CH.sub.2--C.sub.13H.sub.-
27 (7)
H.sub.2O.sub.2.fwdarw.H.sub.2O+1/2O.sub.2 (8)
[0200] This highly reactive hydrocarbon radical can subsequently
readily undergo oxidation. According to Born and Peters in
"Reduction of Soot Emission in a DI Diesel Engine of Hydrogen
Peroxide during Combustion," S.A.E. Technical Paper 982676 (1998),
equation (7) represents the dominant reaction path for the
decomposition of peroxide at temperatures above 727.degree. C., not
the thermolytic reaction generating water and oxygen, as shown in
equation (8).
[0201] Maganas et al., U.S. Pat. No. 6,962,681, the disclosure of
which is incorporated herein by reference, describes a system
wherein catalytically reactive particles of silica or alumina
interact with the moisture in combustion exhaust gases to generate
hydroxyl radicals, which are returned to the site of combustion and
increases the efficiency of combustion, resulting in reduced soot
formation.
[0202] Hashimoto et al., U.S. Patent Application Serial No.
2006/0185644, the disclosure of which is incorporated herein by
reference, describes a fuel composition that includes 95-99.5 wt. %
of a base fuel and 0.1-5 wt. % of an additive compound selected
from the group consisting of an organic peroxide such as di-t-butyl
peroxide, a nitrate ester such as n-pentyl nitrate, a nitrite ester
such as n-pentyl nitrite, and an azo compound such as
2,2-azobis(2,4-dimethylvaleronitrile).
[0203] The inclusion of a free radical initiator in a fuel additive
composition of the present invention provides multiple
advantages:
[0204] When incorporated in a separate reverse-micellar composition
or co-incorporated with a CeO.sub.2 fuel borne additive in a
reverse micelle, it provides a mechanism by which the internal
engine components are "cleaned" or scrubbed of residual soot,
thereby providing a fresh surface. This greatly accelerates the
rate at which the cerium dioxide nanoparticles can be incorporated
into the cast iron matrix of the engine, thereby reducing the time
it takes to "condition" the engine, i.e., provide it with a coating
of catalytic nanoparticles that results in an increase in mpg
economy. Additionally, the preferred stabilizers for CeO.sub.2
nanoparticles, for example, hydroxycarboxylic acids such as lactic
and gluconic acids, are themselves potent free radical generators
at high temperatures.
[0205] Even in a fully conditioned diesel engine in which the
interior surfaces are rendered into a ceramic catalyst, the free
radical mechanism would still account for most of the observed
increase in fuel efficiency, owing to the fact that only 25% of the
injected fuel actually comes in contact with the cylinder walls and
thus becomes available for catalytic combustion; the majority of
the fuel being combusted in the space over the piston head. Thus a
fuel-borne additive that contains a water-soluble free radical
initiator such as H.sub.2O.sub.2 within a reverse micelle would be
very useful.
[0206] Additionally, a fuel-borne additive in which the reverse
micelle contains only a free radical precursor could be used to
great advantage with a nanoparticulate lubricity enhancing agent
introduced as a component of the lubrication oil.
[0207] Generally, reverse micellar compositions having very small
disperse particle diameters, preferably about 5 nm to about 50 nm,
more preferably about 10 nm to about nm, are very effective, as
their disintegration and attendant release of superheated steam
helps to mix the additive-containing diesel fuel with air in the
combustion chamber, resulting in more complete fuel combustion.
[0208] Preferably, the free radical initiators included in the
reverse micelle in accordance with the present invention have
substantial water-solubility. The following patents, the
disclosures of which are incorporated herein by reference, teach
the use of water-soluble free radical initiators:
[0209] U.S. Pat. No. 3,951,934 discloses azo-bis compounds, as well
as combinations of water-soluble peroxides with tertiary amines,
sulfites, and bromates.
[0210] U.S. Pat. No. 5,248,744 teaches azo-bis compounds as well as
peroxydisulfates and organic peroxides.
[0211] U.S. Pat. No. 6,391,995 discloses the use of water-soluble
azo initiators, including four compounds commercially available
from Wako Chemicals, Dallas Tex. Oak Ridge National Laboratory
document TM-11248 by W. V. Griffith and A. L. Compere includes an
extensive list of cetane improvers for increasing engine power that
may be included in the reverse-micellar compositions of the present
invention. Useful compounds for this purpose include alkyl
nitrates, esters, azoles, azides, ethers, and hydroperoxides such
as cumene hydroperoxide.
[0212] Puchin et al., USSR patents 236,987 and 214,710 (1970),
discloses that poly(dimethyl(vinylethynyl)methyl) t-butyl peroxide
at a 0.01% level, i.e. 100 ppm, gives a .DELTA. cetane % additive
ratio of 1000, corresponding to a cetane improvement of 10. The
references also disclose "other additives" that may be small mono
esters incorporated into aqueous micelles, or even long chain fatty
acid mono esters (high cetane rating) that would not require
incorporation as a reverse micelle but might act as a surfactant
for a reverse micelle emulsion.
[0213] Hicks et al., U.S. Patent Appl. Publ. No. 2002/0095859, the
disclosure of which is incorporated herein by reference, states
that high surfactant to water ratios on the order of 2.5:1 in a
concentrated micro-emulsion forming fuel additive produces improved
hydrocarbon fuel combustion at only 5 to 95 ppm of additional
water.
[0214] A fuel additive composition of the present invention may
comprise more than one type of reverse micelle. For example, one
type of reverse micelle may include a cetane improver, and a second
type reverse micelle may include cerium-containing nanoparticles
together with associated reverse micellar phase water that may be
at least partially replaced by a free radical initiator such as
hydrogen peroxide or, more preferably, a stabilized hydrogen
peroxide.
[0215] In accordance with the present invention, a
cerium-containing fuel additive composition includes a
surfactant/stabilizer mixture that preferably includes a
combination of at least one non-ionic surfactant with at least one
anionic surfactant, or a combination of a single-charged anionic
surfactant and a multiple-charged anionic surfactant. The effect of
the combination of surfactant/stabilizer compounds is to restrain
the size of the nanoparticles, prevent their agglomeration, and
enable an increase in the concentration of reactants, thereby
producing a higher yield of nanoparticles.
[0216] The surfactant/stabilizer combination may have the added
benefit of aiding in the solvent shift process from the aqueous
polar medium to the non-polar oil medium. In a combination of
charged and uncharged surfactants, the charged surfactant compound
plays a dominant role in the aqueous environment. However, as
solvent shifting occurs, the charged compound is likely to be
solubilized into the aqueous phase and washed out, and the
uncharged compound becomes more important in stabilizing the
reverse micelle emulsion.
[0217] Dicarboxylic acids and their derivatives, so called "gemini
carboxylates", where the carboxylic groups are separated by at most
two methylene groups, are also useful cerium dioxide nanoparticle
stabilizers. Additionally, C.sub.2-C.sub.8 alkyl, alkoxy and
polyalkoxy substituted dicarboxylic acids are advantageous
stabilizers.
[0218] In accordance with the invention, nanoparticle stabilizer
compounds preferably comprise organic carboxylic acids such as, for
example, 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEA) and
ethylenediaminetetraacetic acid (EDTA), lactic acid, gluconic acid,
tartaric acid, citric acid, and mixtures thereof.
[0219] A reverse-micellar composition in accordance with the
present invention comprises an aqueous disperse phase that includes
a free radical initiator, preferably water-soluble, and a
continuous phase that includes a surfactant, an optional
co-surfactant, and a hydrocarbon liquid, preferably selected from
among toluene, octane, decane, D2 diesel fuel, ULSD, biodiesel, and
mixtures thereof. In general, hydrocarbons containing about 6-20
carbon atoms are useful. The aqueous disperse phase of the
composition comprises micelles having a mean diameter of preferably
about 5 nm to about 50 nm, more preferably about 3 nm to about 10
nm.
[0220] Free radical initiators suitable for inclusion in the
aqueous dispersed phase may be selected from the group consisting
of: hydrogen peroxide, organic hydroperoxides, organic peroxides,
organic peracids, organic peresters, organic nitrates, organic
nitrites, azobis compounds, persulfate compounds, peroxydisulfate
compounds, and mixtures thereof. Preferred azobis compounds are
selected from the group consisting of
2-2'-azobis(2-methylpropionamidine)dihydrochloride;
4-4'-azobis(4-cyanovaleric) acid;
2-2'azobis[2-methyl-N-(2-hydroxyethyl)propionamide];
2-2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, and
mixtures thereof.
[0221] In a preferred embodiment, the free radical initiator in the
aqueous dispersed phase comprises stabilized hydrogen peroxide or
t-butyl hydroperoxide. The aqueous disperse phase may further
comprise, in addition to the aforementioned peroxides, a compound
selected from the group consisting of a tertiary amine compound, a
sulfite compound, a bromate compound, and mixtures thereof.
[0222] The reverse-micellar composition may further comprise boric
acid or a borate salt in the aqueous disperse phase, and the
hydrocarbon liquid preferably comprises diesel fuel. In a further
embodiment of the invention, a lubricating oil that optionally
contains cerium-containing nanoparticles may be used in conjunction
with a fuel containing the reverse-micelle fuel additive.
[0223] The reverse micellar composition of the invention preferably
includes as a radical initiator stabilized hydrogen peroxide or
t-butyl hydroperoxide in the aqueous phase at a level of 30%, 40%,
or even 50% or greater by weight. In another embodiment, within the
reverse micellar composition the ratio of water to hydrocarbon by
weight is greater than or equal to about 5%, about 10%, or
preferably, greater than or equal to about 15% by weight. In a
further embodiment, the reverse micellar composition includes an
alcohol such as hexanol, and/or an alkoxylate surfactant such as
Triton N-57.
[0224] A method for improving the performance of a diesel engine
includes adding to diesel fuel, for example, D2 diesel or
biodiesel, a reverse micellar composition comprising an aqueous
first disperse phase that includes a free radical initiator and a
first continuous phase that includes a first hydrocarbon liquid and
at least one first surfactant. Suitable free radical initiators
such as hydrogen peroxide or t-butyl hydroperoxide, suitable
hydrocarbon solvents preferably containing about 6 to about 20
carbon atoms, and suitable surfactants were described above.
Preferred surfactants include only the elements C, H, and O.
Preferably the aqueous disperse phase includes about 20 wt. %, or
wt. %, or more preferably 40 wt. % or more of the radical
initiator.
Operating the engine and combusting the modified diesel fuel
provides improved engine efficiency relative to unmodified diesel
fuel. Preferably, the modified diesel fuel includes less than 500
ppm water unless accompanied by an equal amount of free radical
initiator.
[0225] A useful reverse micellar composition for use as a diesel
fuel additive includes an aqueous disperse phase that includes a
boric acid or a borate salt, and a continuous phase that includes a
surfactant and a hydrocarbon liquid. Examples of useful borate
salts include, for example, sodium borate and potassium borate.
Examples of useful hydrocarbon liquids include toluene, octane,
decane, D2 diesel fuel, biodiesel, and mixtures thereof. In
general, hydrocarbons containing about 6-20 carbon atoms are
useful. Suitable surfactants include Aerosol AOT; however, as
already mentioned, preferred surfactants include only the elements
C, H, and O. Desirably, the aqueous disperse phase of the
composition comprises micelles having a mean diameter of,
preferably, about 5 nm to about 50 nm, more preferably, about 10 nm
to about 30 nm.
[0226] A method for improving diesel engine performance includes
the addition of an additive as described above to diesel fuel to
obtain modified diesel fuel. Such an additive, when used in
combination with diesel fuel, may provide improved diesel fuel
mileage, reduced diesel engine wear, or reduced pollution or a
combination of these features.
[0227] Motor oil is used as a lubricant in various kinds of
internal combustion engines in automobiles and other vehicles,
boats, lawn mowers, trains, airplanes, etc. In engines there are
contacting parts that move against each other at high speeds, often
for prolonged periods of time. Such rubbing motion causes friction,
forming a temporary weld, which absorbs otherwise useful power
produced by the motor and converting the energy to useless heat.
Friction also wears away the contacting surfaces of those parts,
which may lead to increased fuel consumption and lower efficiency
and degradation of the motor. In one aspect of the invention, a
motor oil includes a lubricating oil, cerium dioxide nanoparticles,
desirably having a mean diameter of less than about 10 nm more
preferably 5 nm, and optionally, a surface adsorbed stabilizing
agent.
[0228] Diesel lubricating oil is essentially free of water,
preferably less than 300 ppm, but may be desirably modified by the
addition of a cerium dioxide-containing reverse-micellar
composition in which the cerium dioxide has been solvent shifted
from its aqueous environment to that of an organic or non-polar
environment. The cerium dioxide compositions include nanoparticles
having a mean diameter of less than about 10 nm more preferably
about 6 nm, as already described. A diesel engine operated with
modified diesel fuel and modified lubricating oil provides greater
efficiency and may, in particular, provide improved fuel mileage,
reduced engine wear or reduced pollution, or a combination of these
features.
[0229] Metal polishing, also termed buffing, is the process of
smoothing metals and alloys and polishing to a bright, smooth
mirror-like finish. Metal polishing is often used to enhance cars,
motorbikes, antiques, etc. Many medical instruments are also
polished to prevent contamination in marks in the metals. Polishing
agents are also used to polish optical elements such as lenses and
mirrors to a surface smoothness within a fraction of the wavelength
of the light they are to manage. Smooth, round, uniform cerium
dioxide particles of the present invention may be advantageously
employed as polishing agents, and may further be used for
planarization (rendering the surface smooth at the atomic level) of
semiconductor substrates for subsequent processing of integrated
circuits.
[0230] Nanoparticles, or quantum dots, are being considered for
many potential applications. Because of their small size, on the
order of 1-20 nm, these nanoparticles have properties different
from their bulk versions, 100 nm and larger. They exhibit novel
electronic, magnetic, optical, chemical, and mechanical properties
that make them attractive for many technological applications.
Those nanoparticles that fall into the semiconductor material
category are being considered for biological labeling and
diagnostics, light emitting diodes, solid-state lighting,
photovoltaic devices, and lasers.
[0231] Cerium dioxide nanoparticles are wide-gap semiconductors
that are potentially useful in such applications. Furthermore,
suitably doped versions of cerium dioxide nanoparticles could
extend the range of applications.
[0232] There are two critical properties of nanoparticulate ceria
that make it uniquely suited for medical applications.
[0233] First and perhaps most critically, is ceria's very low to
non existent toxicity to humans, a conclusion based upon human cell
culture and other data, (Evaluation of Human Health Risk from
Cerium Added to Diesel Fuel: Communication 9, 2001 Health Effects
Institute, Boston Mass. and Development of Reference Concentrations
for Lanthanide, Toxicology Excellence for Risk Assessment, The
bureau of Land Management, National Applied Resource Sciences
Center, Amended Stage 2, November 1999).
[0234] The second property involves the utility of the
Ce.sup.3+/Ce.sup.4+ redox couple. Reactive free radical species
such as the hydroxyl radical (.OH) that can cause cellular damage
in the body can be chemically reduced to the relatively harmless
hydroxyl anion (OH.sup.-) by Ce.sup.3+. Conversely, another
cellular damaging radical species, the oxygen radical anion
(O2..sup.-) can be oxidized to molecular oxygen by Ce.sup.4+, There
have appeared a number of reports that describe the exploitation of
these properties of nanoparticulate ceria, for example, to prevent
retinal damage induced by intracellular peroxides (Chen, et. al.
Nature Nanotechnology, 1, p 142, November 2006) and tumor studies
in which ceria confers radioprotection upon healthy but not
cancerous cells (Tarnuzzer, et, al., NanoLetters 5, 12, p 2573,
2005).
[0235] Suitably engineered nanoparticulate ceria, along with other
nanomaterials, may be used as a biotag exploiting surface enhanced
Raman spectroscopy for fields such as immunodiagnostics, molecular
diagnostics and proteomics.
[0236] The invention is further illustrated by the following
examples. These examples are not intended to limit the invention in
any manner.
Example 1
Preparation of Cerium Dioxide Nanoparticles: Single Jet
Addition
[0237] To a 3 liter round bottom stainless steel reactor vessel was
added 1.267 liters of distilled water, followed by 100 ml of
Ce(NO.sub.3).sub.3.6H.sub.2O solution (600 gm/liter
Ce(NO.sub.3).sub.3.6H.sub.2O). The solution was clear and has a pH
of 4.2 at 20.degree. C. Subsequently, 30.5 gm of
2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEA) was added to the
reactor vessel. The solution remained clear, and the pH was 2.8 at
20.degree. C. A high sheer mixer was lowered into the reactor
vessel, and the mixer head was positioned slightly above the bottom
of the reactor vessel. The mixer was a colloid mill manufactured by
Silverson Machines, Inc., modified to enable reactants to be
introduced directly into the mixer blades by way of a peristaltic
tubing pump. The mixer was set to 5,000 rpm, and 8.0 gm of 30%
H.sub.2O.sub.2 was added to the reactor vessel. Then 16 ml of
28%-30% NH.sub.4OH, diluted to 40 ml, was pumped into the reactor
vessel by way of the mixer head in about 12 seconds. The initially
clear solution turned an orange/brown in color. The reactor vessel
was moved to a temperature controlled water jacket, and a mixer
with an R-100 propeller was used to stir the solution at 450 rpm.
The pH was 3.9 at 25.degree. C. at 3 minutes after pumping the
NH.sub.4OH into the reactor. The temperature of the reactor vessel
was raised to 70.degree. C. over the next 25 minutes, at which time
the pH was 3.9. The solution temperature was held at 70.degree. C.
for 20 minutes, during which time the solution color changed from
orange brown to a clear dark yellow. The pH was 3.6 at 70.degree.
C. The temperature was lowered to 25.degree. C. over the next 25
minutes, at which time, the pH was 4.2 at 25.degree. C. Particle
size analysis by dynamic light scattering indicated a cerium
dioxide intensity weighted hydrodynamic diameter of 6 nm. The
dispersion was then diafiltered to a conductivity of 3 mS/cm and
concentrated, by a factor of about 10, to a nominal 1 Molar in
CeO.sub.2 particles.
[0238] The cerium dioxide particles were collected, the excess
solvent evaporated off, and the gravimetric yield, corrected for
the weight of MEEA, was determined to be 26%. The size distribution
of the cerium dioxide particles (plotted in FIG. 4), determined by
dynamic light scattering, indicated a particle size having a mean
intensity weighted hydrodynamic diameter of about 6 nm. Over two
dozen replicated precipitations and independent measurements of
these precipitations gave a mean intensity weighted size of 5.8
nm.+-./-0.4 nm (one standard deviation). Thus, the reaction
precipitation scheme is robust. Additionally, the size distribution
is substantially monomodal, i.e., only one maximum, with most of
the particles falling in the range 5.2 nm to 6.4 nm. Feature 55 of
the size distribution is a binning artifact.
[0239] A transmission electron microscope (TEM) was also used to
analyze the cerium dioxide particles. A 9 microliter solution
(0.26M) was dried onto a grid and imaged to produce the image 60,
shown in FIG. 5. The dark circular features 61 are the imaged
particles. The particles show no signs of agglomeration, even in
this dried-down state. In solution, the particles would be expected
to show even less propensity to agglomerate. The gradicule (61)
represents 20 nm; it is clear from FIG. 5 that the mean particle
size is quite small, less than 10 nm. From several micrographs such
as these, particles were individually sized and the mean was
calculated to be 6.7.+-.1.6 nm. This independently corroborates the
sizing data measured by dynamic light scattering.
[0240] FIG. 6 shows an X-Ray powder diffraction pattern 70 of a
sample of the dried cerium dioxide nanoparticles, together with a
reference spectrum 71 of cerium dioxide, provided by the NIST
(National Institute of Standards and Technology) library. The line
positions in the sample spectrum match those of the standard
spectrum. The two theta peak widths were very wide in the sample
spectrum, which is consistent with a very small primary crystallite
size and particle size. From the X-Ray data (Cu K alpha line at
about 8047 ev) and the Scherrer formula
(d=0.9*lambda/delta*cos(theta), where lambda is the x-ray
wavelength, delta the full width half maximum, and theta the
scattering angle corresponding to the x ray peak), the primary
crystallite size is calculated to be 2.5.+-.0.5 nm (95% confidence
of 5 replicas)
Examples 1a-f
Evaluation of Alternative Stabilizers to MEEA
[0241] Example 1 was repeated, except that in Example 1a an
equivalent molar amount of succinic acid was substituted for the
MEEA stabilizer. A brown precipitate that readily settled was
obtained, which is an indication of very large particles (several
tens of microns). The same experiment was repeated each time
substituting an alternative stabilizer (malonic acid--Example 1b,
glycerol--Example 1c, ethyl acetoacetate--Example 1d). In each
case, a readily settling brown precipitate was obtained, indicating
the failure to obtain nanoparticles. For Example 1e, lactic acid at
twice the molar concentration was substituted for the MEEA
stabilizer. Quasi-inelastic dynamic light scattering measurements
revealed a mean hydrodynamic diameter particle size of 5.4 nm when
the hydroxide was doubled, and 5.7 nm when the hydroxide was
increased by 75%. Mixtures of EDTA (which by itself produces no
particles) and lactic acid at a ratio of about 20%/80% also gave
particles of CeO.sub.2 with a hydrodynamic diameter of 6 nm. In
Example 1f, the optimal EDTA:lactic acid ratio of 1:4 was used, but
at twice the overall concentration of this stabilizer mixture,
which resulted in a decrease in the mean particle size to 3.3 nm.
At a three times level (same ratio) there were no particles formed
(the stabilizer effectively complexed all the free cerium ion,
preventing the formation of the hydroxide). It is therefore
possible to control the particle size by adjusting the stabilizer
component ratios and overall stabilizer concentration levels.
Example 2
CeO.sub.2 Precipitation with EDTA/Lactic Acid Stabilizer--Effect of
Mixing
[0242] To a 3 liter round bottom stainless steel reactor vessel was
added 76.44 gm EDTA disodium salt in distilled water to a total
weight of 1000 gm, 74.04 gm of DL-lactic Acid (85%), 240.0 gm of
Ce(NO.sub.3).sub.3.6H.sub.2O in 220 gm of distilled water and 19.2
gm of 50% H.sub.2O.sub.2 aqueous solution. As in Example 1, the
mixer speed was set to 5000 rpm, and the contents of the reactor
were brought to a temperature of 22.degree. C. Separately, a
solution of 128.0 gm NH.sub.4OH (28-30%) was prepared. This
quantity of hydroxide is equivalent to twice the number of moles of
cerium solution, so the initially nucleated precipitate was
presumably the bis-hydroxyl intermediate. In one experiment, the
ammonium hydroxide solution was single jetted into the reactor in
the reaction zone defined by the mixer blades and perforated
screen. In another experiment, the hydroxide was added via a single
jet just subsurface into the reactor in a position remote from the
active mixing zone of the colloid mixer. After the usual heat
treatment and filtration, the intensity weighted diameter of the
CeO.sub.2 particles produced at the actively mixed zone was 6.1 nm,
with a polydispersity of 0.129. The diameter of the particles
produced via the second method, i.e., sub-surface introduction of
the of the ammonium hydroxide at a position remote from the
reaction zone, was essentially the same, 6.2 nm, but the
polydispersity was much greater, 0.149. Thus, the size frequency
distribution can be narrowed by mixing in the high shear region of
the colloid mill.
Example 3
CeO.sub.2 Particle Size Dependence upon Hydroxide Stoichiometry
[0243] The conditions of this experiment follow that of Example 2,
except that the cerium ion was not in the reactor but was
separately introduced via a jet into the reaction zone
simultaneously with the jetting of the ammonium hydroxide solution.
Three molar stoichiometric ratios of hydroxide ion to cerium ion
were explored: 2:1, 3:1 and 5:1. The following table summarizes the
intensity weighted particle size diameters and polydispersities
obtained by the quasi-inelastic dynamic light scattering
technique.
TABLE-US-00001 Gravimetric Yield OH:Ce CeO.sub.2 CeO.sub.2
(1000.degree. C. muffle mole ratio diameter (nm) Polydispersity
furnace) 2:1 5.8 0.110 51.7% 3:1 10.2 0.158 57.2% 5:1 12.5 0.156
49.9%
[0244] It is clear from the data that the smallest, most uniformly
distributed particles can be obtained in good yield by this double
jet procedure when the molar ratio of hydroxide to cerium is 2:1.
The size of the particles obtained in higher yield under 3:1
stoichiometry conditions may be reduced by a suitable increase in
the stabilizer level, as was demonstrated in Example 1f.
Example 4
CeO.sub.2 Precipitation Temperature Effects
[0245] The effect of low temperature nucleation at 20.degree. C.,
followed hydroxide conversion to the oxide at 70.degree. C., versus
an isothermal precipitation in which both nucleation and conversion
were conducted at 70.degree. C. was investigated using the reagent
conditions specified in Example 2. The preferred double jet method
was employed (separate jets for cerium ion and hydroxide ion, both
introduced into the reactive mixing zone of the colloid mixer). The
ammonium hydroxide concentration was at the 128 gm, i.e., 2.times.
level or a OH:Ce molar stoichiometric ratio of 2:1. Quasi-inelastic
dynamic light scattering measurements revealed that the particles
made at the lower temperature precipitation had an intensity
weighted hydrodynamic diameter of 5.8 nm, with a polydispersity of
0.117, and a yield of 54.6%, while the isothermal precipitation
gave larger particles, 8.1 nm, that were more widely distributed,
with a polydispersity of 0.143, in comparable yield. Thus, if a
more uniform particle size frequency distribution is desired, it is
preferable to nucleate at lower temperature before carrying out the
higher temperature conversion of the hydroxide to the oxide.
Example 5
Preparation of Cerium Oxide-Containing Additive Formulations of
Varying Batch Size
[0246] Formulations with volumes of 207 ml, 1.5 liters, and 9.5
liters were prepared according to procedures summarized in the
following table:
TABLE-US-00002 Approximate Batch Volume 207 ml 1.5 liters 9.5
liters Reactor 250-ml S.S, 3-liter S.S. 11-liter S.S. beaker w/
round-bottomed round-bottomed magnetic stirring vessel vessel bar
Solution Preparation Components Distilled water in reactor 127 g
1.267 kg 8.2355 liters Ce(NO.sub.3).sub.3.cndot.6H.sub.2O 8.52 g in
distilled 60 g in H.sub.2O to 390 g in H.sub.2O to H.sub.2O to 25
ml 100 ml 500 ml Stabilizer--MEEA 4.36 g in distilled 30.5 g 198.25
g H.sub.2O to 25 ml Oxidant--50% H.sub.2O.sub.2 0.69 g in 4.8 g
31.2 g deionized H.sub.2O to 25 ml Base--NH.sub.4OH (28-30%
NH.sub.3) 2.29 g in 16 ml in 104 ml in distilled H.sub.2O to
distilled H.sub.2O to distilled H.sub.2O to 3.4 g 40 ml 260 ml
Distilled water rinse 2 ml 20 ml 100 ml Precipitation Process 1.
Stabilize water at 15-25.degree. C. 2. With mild stirring, add
solutions in the following order: Ce(NO.sub.3).sub.3, MEEA,
H.sub.2O.sub.2 3. Insert a Silverson mixer with appropriate 3/4-in
tubular Standard mixer Standard mixer mixing head and jets mixer
head head w/ fine head w/ medium w/ fine screen- screen-5,000
screen-8,100 7,000 rpm rpm rpm 4. Pump NH.sub.4OH solution at flow
rate of 17 ml/min 200 ml/min 650 ml/min 5. Rinse water purge at
flow rate of 17 ml/min 200 ml/min 650 ml/min 6. Heat the mixture to
70.degree. C. by Placing beaker in Ramping Ramping preheated
70.degree. C. temperature temperature bath over 25 min over 25 min
7. Hold at 70.degree. C. for 50 min 8. Cool mixture to
20-25.degree. C. 9. Filter via diafiltration to less than 3 mS/cm,
and concentrate by 20.times.
[0247] Particle sizes were determined for 19 of the large
(9.5-liter) batches prepared as described above. The average
particle hydrodynamic diameter was 5.8 nm, with a standard
deviation of 0.40. Average particle sizes measured for 207-ml and
1.5-liter batches have generally fallen in the range of 5.2-6.4 nm,
well within +/- two standard deviations of 5.8 nm (95% confidence
level). Therefore it is reasonable to conclude that the particles
from the two smaller batches are of essentially the same size as
those of the large batches.
Example 6
Preparation of Fuel Concentrate
[0248] A portion of cerium dioxide dispersion, prepared as
described in Example 1, was added slowly to a mixture of D2 diesel
fuel, surfactant Aerosol AOT, and 1-hexanol co-surfactant,
resulting in a clear reddish brown colored solution that can be
employed as a fuel concentrate. The concentrate is 14% by volume
cerium dioxide dispersion; the remaining volume is 1.72% 1-hexanol
co-surfactant, 18.92% surfactant Aerosol AOT, and 65.36% diesel D2
diluents.
Example 7
Preparation of Additivized Diesel Fuel Containing Fuel Additive
[0249] A portion of the fuel concentrate, prepared in Example 6,
was diluted 1 part to 600 parts of diesel fuel by volume. Thus the
final additivized D2 fuel has nominally a concentration of 42 ppm
(by weight) of CeO.sub.2 and 258 ppm water and 361 ppm Aerosol
AOT.
Example 8
Evaluation of Additivized Diesel Fuel
[0250] The additivized diesel fuel was evaluated in an Element
Power Systems model #HDY5000LXB diesel generator operating at a
Frequency of 60 Hz and a Power Factor of cos .phi.=1.0 rated at 5
KVA (AC power output). The diesel engine is a model #DH186FGED
forced air cooled 4 stroke with a rated maximum power output of 10
HP.
[0251] A portion of the exhaust is drawn through a porous filter
medium by the action of a downstream in-line vacuum pump. Diesel
particulate matter is collected on the filter media for 150
seconds, after which time its percent grey scale is measured (Adobe
Photoshop). The percent grey scale is taken as a measure of the
amount of soot collected. The grey scale level increases as the
amount of soot present on the filter media increases.
[0252] The diesel engine was operated for over an hour using normal
D2 (low sulfur 500 ppm) fuel to equilibrate it. Towards the end of
this time, diesel particulate matter was collected on a filter
media for 150 seconds. The percent grey scale of the filter, which
correlates with the amount of particulate material present, was
measured at 70%, a figure typical for these operating conditions
and collection times. The engine was turned off; the fuel tank was
drained of regular D2, and then partially filled and drained twice
with additivized diesel fuel. The tank was then filled to the
two-thirds level with additivized diesel fuel. The engine was then
operated with the additivized D2 fuel for over an hour to
equilibrate it to the new fuel. An increase of 3% in the energy
output of the generator was measured (voltage multiplied by current
through a 1.2 KW resistive load). The engine was turned off, the
additivized fuel was drained from the fuel tank, and the tank was
rinsed twice with normal diesel fuel and then filled to the
two-thirds mark with normal diesel fuel. The engine was then
operated for twenty minutes to purge the lines and filters of any
residual additivized fuel. A power measurement indicated that the
engine had returned to the normal operating conditions, that is,
the 3% increase in power obtained when the engine was operated with
additivized fuel was no longer observed, indicating that there is
no residual additivized fuel in the system. Diesel particulate was
collected for 150 seconds, as described previously, and the percent
grey scale was measured as 40%. This represents a 43% reduction in
diesel particulate matter, as determined by the change in the grey
scale of the test filter, even though the fuel no longer contains
additive.
[0253] This example illustrates that the internal working parts of
the engine have been conditioned by the nanoparticulate CeO.sub.2
in a time scale of approximately one hour. Conditioning involves
incorporating CeO.sub.2 into the walls and pistons of the engine.
The CeO.sub.2 is assisting in carbon combustion by providing oxygen
according to the following reaction:
2CeO.sub.2.rarw..fwdarw.Ce.sub.2O.sub.3+1/2O.sub.2.
Improved combustion results in a reduction of particulate matter as
reflected in the diminished grey scale of the test filter.
Example 9
Preparation of a Cerium Dioxide-Containing Fuel Additive by
Reverse-Micelle Formation
[0254] D2 diesel fuel (2320 mL) and co-surfactant, 1-pentanol (200
mL) were placed in a 6 liter Erlenmeyer flask. The surfactant, AOT
(800 g), which was broken into small particles before addition, was
then added in 40 gm portions to the flask with magnetic stirring.
Following addition of the AOT, the resulting clear solution was
allowed to stand for 1 hour. During this time, the solution changed
from a light amber color to an orange color as the microemulsion
formed.
[0255] A 500-mL dispensing burette containing 525 mL of the aqueous
CeO.sub.2 solution (nominal 1.0 M CeO.sub.2 stabilized with 1.5 M
MEEA) was mounted over the flask. The first 400 mL of this solution
was added as a slow steady stream with stirring. As the aqueous
CeO.sub.2 was added, a slime-like cloud surrounded the vortex. The
addition was stopped every 100 mL to allow the solution to clear.
Initially, the solution required about 1 minute to clear between
100-mL additions, but after 200 mL had been added, the solution
cleared more rapidly. A slower addition rate for the last 125 mL
was used; addition was stopped every 50 mL to allow the solution to
clear. Addition of aqueous CeO.sub.2 over a 90 minute period
results in a deep orange-brown solution, that was allowed to
equilibrate for 12 hours, during which time the color had changed
from orange-brown to greenish-brown.
[0256] The procedure described above was used to prepare 1.00
gallons (3.785 L) of a microemulsion containing about a 19700 ppm
CeO.sub.2 in D2 diesel fuel, with a water to surfactant (AOT) mole
ratio of 16.2 and an aqueous volume fraction of 14%. A 1:600
addition of this microemulsion to D2 diesel fuel (density 0.85
g/mL) gives a fuel having 32.8 ppm cerium dioxide (based on 70%
yield of a 10.times. concentrate of CeO.sub.2 prepared from an
initial 0.0945 Ce(NO.sub.3).sub.3 solution) having 30 ppm sulfur
and 265 ppm water.
Example 10
Test Data: Griffith Energy On-Road Tests
[0257] A "cetane improved" formulation that included reverse
micelles containing 220 ppm hydrogen peroxide and 220 ppm water
suspended in ultra low sulfur diesel was run at Griffith Energy
from Oct. 18 to Nov. 17, 2006, using both a control and test
12-liter diesel, class 8 tractors. Once each week, mpg (miles per
gallon) data were downloaded from each of the Volvo truck on board
computers ("Trip Manager") and fit to a linear regression model
that explained 80% of the mpg variation. The data are presented in
the table below. The greatest improvements on day 21 and day 35 are
underestimates of the true potential of the formulation, as
non-treated days were averaged into the weekly results, due either
to beginning the treatment mid-week (day 20) or encountering filter
plugging (day 28). Chemical analysis of the plugged fuel filters
revealed primarily soot particles, from which it can be concluded
that the formulation cleans all of the engine parts, including the
fuel circulation system. No data were collected on day 49, but it
is believed that the treated truck was becoming "dirty" (normal
operation), and that day 49 or subsequent data would have shown
that this truck returned to the baseline of 4.74 mpg.
[0258] Based upon the mpg baseline offset of 1.72%, the cetane
improved formulation demonstrated a maximal effect of 9.44%
improvement in mpg (day 35)
TABLE-US-00003 Control (mpg) Experiment (mpg) Percent Change Day
4.42 4.74 1.72 start 4.75 4.74 1.72 7 4.66 4.84 3.86 14 4.57 5.05
8.37 21 4.76 4.76 2.15 28 4.83 5.18 11.16 35 4.66 5.00 7.30 42
Example 11
Static Engine Test Data
[0259] Test Data: Environmental Energy Technologies (EET) Static
Engine Test-EET diesel generator specifications are as follows:
TABLE-US-00004 Generator: Element Power Systems model # HDY5000LXB
Frequency 60 Hz Power Factor cos .phi. = 1.0 Rated AC Output 5 KVA
Engine: model # DH186FGED Type forced air cooled 4 stroke Max
Output 10 HP Fuel diesel light fuel (BS-AI) Fuel Consumption Rate
210-286 g/kW Oil Temperature <95.degree. C. Exhaust Temperature
<480.degree. C.
[0260] The diesel generator tank was drained and flushed of old
fuel two times before refueling with new D2 diesel fuel. The engine
was brought to a steady state at the beginning of each day's test
by running at 30% load for a warm-up period of approximately 10 to
20 minutes, which allowed drainage of old fuel from the engine
fuel. Following warm-up, testing was performed for the given load
by drawing exhaust at a fixed flow rate through filter papers for a
duration of 150 seconds per sample. An estimate of diesel
particulate matter (soot) and the effect of the fuel formulation
was made by measuring the optical reflectance of the filter paper
that had entrained the soot. Between fuel changes, the engine was
given approximately 5 minutes to reach steady state operating
conditions. For tests requiring the fuel additive, the engine was
turned off, drained and flushed twice with premixed fuel containing
the fuel additive emulsion.
[0261] The data in the table that follows indicate that, at 1500
ppm water, the diesel generator power drops from 1080w to 320 w, a
decrease of 70% for a drop of 5.degree. C. This is accompanied by a
16% reduction in diesel particulate matter, clearly a very poor
power for pollution trade-off.
[0262] Subsequent testing revealed that as much as 300 ppm of water
had very little if any effect on power while reducing diesel
particulate matter by 13%. Finally, as much as 28% of the diesel
particulate matter can be reduced by a very substantial
concentration of water, 960 ppm with only a small 5% power loss
when the formulation contained 540 ppm of hydrogen peroxide. Thus
by balancing the water effect of lowering combustion
temperature/efficiency and soot production by the presence of a
free radical initiator such as hydrogen peroxide it is possible to
simultaneously maintain high engine performance and achieve a
lowering of the DPM thereby avoiding a power for pollution
trade-off.
TABLE-US-00005 Total PM Reduction Exhaust T Comparison water/H2O2
decane AOT Date Load (watts) .degree. C. to Control ppm ppm ppm
Test 1 D2 Control Mar. 6, 2006 1080 w 103 C. 0% 0/0 0 0 Test 2
Emulsified D2 320 w 98 C. 16% 1500/0 5100 3400 Test 1 D2 Control
Mar. 18, 2006 1217 w 106 C. 0% 0/0 0 0 Test 2 1224 w 113 C. 13%
300/0 1020 680 Test 4 1160 w 114 C. 28% 960/540 5100 340
Example 12
Formulation of a Stable Non-Sulfur-Containing Free Radical
Reverse-Micelle Composition
[0263] 130 ml of a 1-hexanol solution is added with low shear
mixing to 440 ml of Ultra Low Sulfur Diesel. Then 310 ml of Triton
N-57 is added to the diesel alcohol mixture. A gestation time of 1
hour is allowed. Finally, 120 ml of a 50% hydrogen peroxide/water
solution is added to the above mixture at a constant flow rate over
a 15 minute period allowing for good uniform volumetric mixing
during this time period. After a 12 hour equilibration period the
micro emulsion has reached a state characterized by particles that
are measured to be in the range of 5 nm to 9 nm (by light
scattering). This concentrate diluted one part per 500 would give a
final concentration of 120 ppm H.sub.2O.sub.2 and 120 ppm
water.
Example 13
Preparation of Reverse-Micelle Free Radical Initiator Using
Stabilized Hydrogen Peroxide
[0264] The following formulation makes 1.0 L of a 12.7 v % of a 50
w % aqueous hydrogen peroxide solution stabilized in a Triton
N57/1-hexanol/diesel microemulsion. This formulation, when diluted
1/500 in ultra low-sulfur diesel, will contain 150 ppm (mg/L)
H.sub.2O.sub.2 active ingredient and 150 ppm (mg/L water).
[0265] To 435 mL ultra low-sulfur diesel fuel in a 1.5 liter vessel
is added 113 mL 1-hexanol, with good volumetric stirring, until a
homogeneous mixture is formed. Then, 325 mL of the non-ionic
surfactant Triton N57 is added, with good mixing. After one hour,
which enables the three-component mixture to stabilize, 127 mL of
50 wt % aqueous hydrogen peroxide is slowly added over a 15 minute
period. The aqueous hydrogen peroxide had been previously
stabilized against catalytic decomposition by free metals with
stannate and metal chelating agents, e.g., phosphonates and/or
etidronic acid.
[0266] A period of twelve hours is allowed for the final emulsion
to reach thermodynamic equilibrium. Samples of this microemulsion,
diluted both 1:250 and 1:500 parts with ULSD, are stable down to
5.degree. C., with no apparent chemical degradation, and stable for
2.5 hours at 100.degree. C. without apparent oxidation (as
determined by UV/visible spectroscopy).
Example 14
Reverse-Micelle Free Radical Initiator Composition Containing
t-Butyl Hydroperoxide and 70% Neutralized Oleic Acid
[0267] The following formulation makes 1.0 L of a 30 v % t-HYDRO
solution (tertiary butyl hydroperoxide) stabilized in a oleic
acid/ethanolamine/1-hexanol/diesel microemulsion. This formulation,
when diluted 1/500 in ultra low-sulfur diesel will contain 390.6
ppm (mg/L) active ingredient (t-butylhydroperoxide).
[0268] To 418.0 mL of ultra low-sulfur diesel fuel in a 1.5 liter
vessel is added 35.0 mL 1-hexanol, with good volumetric stirring,
until a homogeneous mixture is formed. Then, 220.0 mL of technical
grade oleic acid is added, with good mixing, followed by 27 mL of
ethanolamine. After one hour, which enables the four component
mixture to stabilize, 300.0 mL of t-HYDRO (70 v % t-butyl
hydroperoxide in water) is slowly added over a minute period,
preferably at a temperature above 25.degree. C.
[0269] A period of twelve hours is allowed for the final emulsion
to reach thermodynamic equilibrium. Samples of this microemulsion
diluted 1:250 parts with ULSD are stable down to 5.degree. C., with
no apparent chemical degradation, and stable for 2.5 hours at
125.degree. C. without apparent oxidation (as determined by
UV/visible spectroscopy).
Example 15
Improved Lubricity Using Fuel Including Cerium Dioxide
Particles
[0270] Lubricity was determined by measuring wear on a ball bearing
rubbed on a plate coated with fuel containing the respective fuel
additives. Wear was determined by the depth, in mm, of the average
scar imparted by rubbing. Neat fuel, without an additive, gave a
0.35 mm scar. Test results for fuel with a commercial additive,
Platinum Plus.TM.; a comparative fuel additive including 10 nm
particles; and the inventive fuel additive including 5 nm particles
were 0.32, 0.31, and 0.245 mm respectively. Low wear numbers
correlate with greater lubricity. Thus, the inventive small
particles afford a 30% improvement in lubricity.
[0271] While the invention has been described by reference to
various specific embodiments, it should be understood that numerous
changes may be made within the spirit and scope of the inventive
concepts described. Accordingly, it is intended that the invention
not be limited to the described embodiments, but will have full
scope defined by the language of the following claims.
* * * * *