U.S. patent application number 13/756971 was filed with the patent office on 2013-08-01 for rapid method for production of cerium-containing oxide organic colloids.
This patent application is currently assigned to Cerion Technology, Inc.. The applicant listed for this patent is Cerion Technology, Inc.. Invention is credited to Gary Robert Prok, Stephen Charles Williams.
Application Number | 20130192122 13/756971 |
Document ID | / |
Family ID | 48869005 |
Filed Date | 2013-08-01 |
United States Patent
Application |
20130192122 |
Kind Code |
A1 |
Prok; Gary Robert ; et
al. |
August 1, 2013 |
RAPID METHOD FOR PRODUCTION OF CERIUM-CONTAINING OXIDE ORGANIC
COLLOIDS
Abstract
Improved methods for producing colloidal dispersions of
cerium-containing oxide nanoparticles in substantially non-polar
solvents is disclosed. The cerium-containing oxide nanoparticles of
an aqueous colloid are transferred to a substantially non-polar
liquid comprising one or more amphiphilic materials, one or more
low-polarity solvents, and, optionally, one or more glycol ether
promoter materials. The transfer is achieved by mixing the aqueous
and substantially non-polar materials, forming an emulsion,
followed by a phase separation into a remnant polar solution phase
and a substantially non-polar organic colloid phase. The organic
colloid phase is then collected. The promoter functions to speed
the transfer of nanoparticles to the low-polarity phase. The
promoter accelerates the phase separation, and also provides
improved colloidal stability of the final substantially non-polar
colloidal dispersion. The glycol ether promoter reduces the
temperature necessary to achieve the phase separation, while
providing high extraction yield of nanoparticles into the
low-polarity organic phase. In addition, use of particular
amphiphilic materials, such as heptanoic acid or octanoic acid,
enable efficient extractions at ambient temperatures without the
use of a glycol ether promoter.
Inventors: |
Prok; Gary Robert; (Rush,
NY) ; Williams; Stephen Charles; (Rochester,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cerion Technology, Inc.; |
Rochester |
NY |
US |
|
|
Assignee: |
Cerion Technology, Inc.
Rochester
NY
|
Family ID: |
48869005 |
Appl. No.: |
13/756971 |
Filed: |
February 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13753992 |
Jan 30, 2013 |
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13756971 |
|
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61632778 |
Jan 30, 2012 |
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61632881 |
Feb 1, 2012 |
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Current U.S.
Class: |
44/280 |
Current CPC
Class: |
C10M 129/16 20130101;
C10L 1/1233 20130101; C10L 1/10 20130101; C10L 2290/24 20130101;
C10M 129/40 20130101; C01P 2004/04 20130101; C10L 2200/0245
20130101; C10L 1/1852 20130101; C10L 10/00 20130101; C10L 2200/0254
20130101; C10M 125/10 20130101; C01P 2002/85 20130101; C10L 1/18
20130101; C10L 1/1826 20130101; C10L 10/02 20130101; C01P 2004/64
20130101; C01G 49/0054 20130101; C10L 1/1881 20130101 |
Class at
Publication: |
44/280 |
International
Class: |
C10L 10/00 20060101
C10L010/00 |
Claims
1. A process for preparing a colloidal dispersion, comprising: (a)
preparing an aqueous colloidal dispersion of cerium-containing
oxide nanoparticles; (b) adding a substantially non-polar solvent,
an amphiphilic material, and, optionally, a glycol ether; (c)
mixing the liquid mixture of step (b) to form an emulsion; (d)
heating the emulsion to a predetermined temperature for a
predetermined time, whereafter the emulsion separates into a
substantially non-polar colloidal phase and a remnant aqueous
phase; and, (e) collecting the separated substantially non-polar
colloidal dispersion of cerium-containing oxide nanoparticles.
2. The process of claim 1, wherein said temperature ranges from
about 20.degree. C. to less than 60.degree. C.
3. The process of claim 1, wherein said time ranges from 0 to 8
hours.
4. The process of claim 1, wherein said glycol ether is added in
its entirety during step (d).
5. The process of claim 4, wherein said glycol ether is added 0 to
4 hours after the end of step (c).
6. The process of claim 1, wherein said glycol ether is selected
from the group consisting of diethylene glycol monomethyl ether,
propylene glycol monomethyl ether, diethylene glycol monoethyl
ether, diethylene glycol monobutyl ether, dipropylene glycol methyl
ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl
ether, ethylene glycol monopropyl ether, and combinations
thereof.
7. The process of claim 6, wherein said glycol ether is selected
from the group consisting of diethylene glycol monomethyl ether,
propylene glycol monomethyl ether, and a mixture thereof.
8. The process of claim 6, wherein said glycol ether comprises
about 5-25 wt. % of the total materials added during step (b).
9. The process of claim 1, wherein said amphiphilic material is a
monocarboxylic acid having from 6 to 22 carbon atoms.
10. The process of claim 9, wherein said monocarboxylic acid is
2-ethylhexanoic acid, heptanoic acid or octanoic acid.
11. The process of claim 10, wherein said monocarboxylic acid is
heptanoic acid or octanoic acid, and said temperature is ambient
temperature.
12. The process of claim 9, wherein said monocarboxylic acid is
oleic acid.
13. The process of claim 9, wherein the amount of said carboxylic
acid comprises about 25-33 wt. % of the total amount of
substantially nonpolar solvent, amphiphilic material, and glycol
ether added during steps (a) through (e).
14. The process of claim 1, wherein said substantially nonpolar
solvent is added in its entirety during step (d).
15. The process of claim 14, wherein said substantially nonpolar
solvent is added 0 to 1 hour after the end of step (c).
16. The process of claim 1, wherein the amount of said
substantially nonpolar solvent comprises about 50-63 wt. % of the
total amount of substantially nonpolar solvent, amphiphilic
material, and glycol ether added during steps (a) through (e).
17. The process of claim 1, wherein said cerium-contain oxide
nanoparticles have a nominal composition of
Ce.sub.(1-x)Fe.sub.xO.sub.(2-.delta.), wherein x ranges from about
0.01 to 0.8.
18. The process of claim 1, wherein said aqueous colloidal
dispersion of cerium-containing oxide nanoparticles is prepared
without a conventional nanoparticle isolation step, thereby
directly using the aqueous colloid resulting from the nanoparticle
synthesis reaction mixture in step (a).
19. The process of claim 1, wherein said aqueous colloidal
dispersion of cerium-containing oxide nanoparticles has a pH less
than or equal to seven.
20. The process of claim 1, wherein said substantially nonpolar
colloidal dispersion of cerium-containing oxide nanoparticles is
used as a component of a fuel additive.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 13/753,992, IMPROVED METHOD FOR PRODUCTION OF
STABLE CERIUM OXIDE ORGANIC COLLOIDS, filed Jan. 30, 2013, which
claims priority to U.S. Provisional Application No. 61/632,778,
filed Jan. 30, 2012, the disclosures of which are incorporated
herein by reference in its entirety. This application also claims
the benefit of priority to Provisional Application Ser. No.
61/632,881, METHOD FOR PRODUCTION OF STABLE CERIUM OXIDE ORGANIC
COLLOIDS, filed Feb. 1, 2012, the disclosure of which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to colloidal
nanoparticle dispersions and more specifically to improved
processes for the manufacture of doped and un-doped cerium oxide
colloidal dispersions in solvents having low-polarity.
BACKGROUND OF THE INVENTION
[0003] Cerium-containing oxide nanoparticles have many current
industrial uses, along with many emerging technical applications.
They are well known as important components, for example, in
three-way automotive exhaust catalysts, automotive fuel borne
catalysts, water gas shift reaction catalysts, polishing and
planarization agents, solid oxide fuel cells, hybrid solar cells
and ultra-violet sun blockers. There are many synthetic processes
for the production of metal oxides, including aqueous and
hydrothermal precipitation, spray precipitation, combustion, plasma
deposition and electrochemical techniques, among others. While a
variety of solvents may be used in these synthetic processes,
aqueous reaction chemistries are particularly favored in
manufacturing processes where high material through-put is desired.
However, conventional aqueous processes--precipitation in
particular--are costly as they involve multiple steps that are
often time and energy consuming, as well as equipment
intensive.
[0004] Conventional large-scale metal oxide manufacturing processes
can typically be divided into three stages: aqueous precipitation
of precursor compounds, calcination to promote chemical reaction
and to enhance crystallinity, followed by final particle size
adjustment. In more detail, aqueous precipitation includes the
initial steps of reactant delivery, reactant dispersal, particle
precipitation, isolation, washing, drying, and optional
impregnation with other metal ions; calcination involves heating to
400-1000.degree. C. for several hours; followed by grinding,
milling or classification to adjust the final particle size, among
other steps.
[0005] One approach to reduce the number of steps in the aqueous
preparation is to employ methods that produce a stable aqueous
dispersion (suspension, colloid, sol) of the final particles
directly from the initial reactants, thereby avoiding the time,
cost and potential contamination inherent in the particle
precipitation, isolation, and drying steps. Moreover, if the
particles produced in such a direct method are sufficiently pure,
wherein the chemical composition of the particles is as desired,
and the particles are sufficiently crystalline, then the
calcination step may also be eliminated. In addition, if the
particle size and size distribution produced by such a direct
method are substantially as desired, then the grinding, milling and
classification steps may also be eliminated. Direct methods to
produce aqueous dispersions (suspensions, colloids, sols) of
crystalline cerium-containing oxide nanoparticles without the use
of precipitation, isolation, drying, calcination, grinding, milling
or classification steps, and the like, are described in commonly
assigned U.S. patent application Ser. No. 12/779,602, now
Publication US 2010/0242342 A1, by A. G. DiFrancesco et al. The
'342 reference discloses stable aqueous dispersions of crystalline
cerium-containing nanoparticles in a size range, for example, of
1-5 nanometers.
[0006] While substantial progress has been made in eliminating
manufacturing steps from the synthetic process by which stable
aqueous dispersions of metal oxide nanoparticles are prepared, use
of these nanoparticles in applications such as fuel-borne
combustion catalysts requires that dispersions of these
nanoparticles also exhibit colloidal stability in the fuel. Such
stability would also be required for a fuel additive, miscible in
the fuel. Thus, these particles, although readily formed and
suspended in a highly polar aqueous phase, must then be transferred
to a substantially non-polar phase, a process known as solvent
shifting. This problem is conventionally addressed by the use of
particle stabilizers. However, most particle stabilizers used to
prevent particle agglomeration in an aqueous environment are
ill-suited to the task of stabilization in a non-polar environment.
When placed in a non-polar solvent, such particles tend to
immediately agglomerate and, consequently, lose some, if not all,
of their desirable particulate properties. Changing stabilizers can
involve a difficult displacement reaction or separate, tedious
isolation and re-dispersal methods such as, for example,
precipitation and subsequent re-dispersal with a new stabilizer
using, for instance, a ball milling process. which can take several
days and tends to produce polydisperse size frequency
distributions.
[0007] One approach to simplifying the solvent shifting process
employs diafiltration methods and glycol ether solvents having a
polarity intermediate between that of water and those of non-polar
hydrocarbons. The intermediate polarity colloid is then further
shifted to reduce the polarity of the cerium-containing
nanoparticle dispersion, as disclosed in commonly assigned U.S.
patent application Ser. No. 12/549,776, now Publication US
2010/0152077A1 to Alston et al. Diafiltration, sometimes referred
to as cross-flow microfiltration, is a tangential flow filtration
method that employs a bulk solvent flow that is tangential to a
semi-permeable membrane. However, drawbacks of diafiltration
methods include the following: relatively slow filtration rates,
substantial financial investment in equipment (e.g. pumps and
microfilters), and production of a relatively large amount (e.g.
several turnover volumes) of waste solvent.
[0008] Use of promoter agents to accelerate transfer of iron oxide
nanoparticles from aqueous to non-polar solvents is known in the
art. U.S. Pat. No. 7,459,484 to Blanchard et al. discloses use of
promoter materials having alcohol functionality and having 6 to 12
carbon atoms to promote transfer, and to improve stability of the
organic colloid so formed. US Patent Application Publication
2006/0005465 A1 to Blanchard et al. discloses contact of basic
aqueous colloids of rare earth or mixed rare earth/other oxide
nanoparticles with an acid and a diluent to form an organic colloid
dispersion. U.S. Pat. No. 6,271,269 to Chane-Ching et al. discloses
direct transfer of cerium oxide or doped cerium oxide colloidal
particles from a counterpart aqueous dispersion. Use of
alcohol-based promoters is disclosed as well. However, high process
temperatures and times for the transfer of the colloidal
particulates represent a significant limitation of the prior art
process. It is also apparent that concern over the presence of
ionic constituents, and other materials needed to bring about the
formation of the colloidal particulate material in the aqueous
reaction mixture, affects the viability of the direct process.
[0009] Thus, progress has been achieved in reducing the cost of
producing and solvent shifting aqueous dispersions of
cerium-containing nanoparticles. However, further improvements in
manufacturing efficiency are desired, particularly in the case of
nanoparticle dispersions used as fuel-borne combustion catalysts
that require dispersion stability in both a low-polarity solvent
carrier of a fuel additive or in the fuel itself.
[0010] It would be very desirable to transfer oxide nanoparticles
directly from the aqueous reaction mixture in which the
nanoparticles are formed, to a substantially non-polar phase, at
low temperatures, to reduce manufacturing hazards in dealing with
combustible liquids. At the same time it is desirable that the
nanoparticle colloidal dispersions that are the fuel additives
exhibit excellent colloidal stability and good fluid flow
properties at low ambient temperatures.
SUMMARY OF THE INVENTION
[0011] The present invention has various embodiments that provide
simple, rapid, low temperature processes for the production of
stable doped or un-doped cerium oxide nanoparticle dispersions in
solvent systems having low-polarity.
[0012] In a first aspect, the invention is directed to an improved
process that uses conventional cerium-containing oxide aqueous
nanoparticle dispersions. The nanoparticles of the aqueous
dispersion are transferred to a substantially non-polar liquid
comprising one or more amphiphilic materials, one or more
low-polarity solvents, and, optionally, a glycol ether promoter
material. The transfer is achieved by mixing the aqueous dispersion
and substantially non-polar liquid, wherein an emulsion is formed,
followed by a phase separation into a remnant polar solution phase
and a substantially non-polar dispersion phase, and then a
collection of the substantially non-polar (low-polarity) dispersion
phase. The promoter may function to speed the transfer of
nanoparticles to the low-polarity phase. The promoter may
accelerate the phase separation, and may also provide improved
dispersion stability of the final substantially non-polar
dispersion phase. In particular embodiments, the glycol ether
promoters reduce the temperature necessary to achieve the phase
separation while providing high extraction yield of nanoparticles
into the low-polarity phase. Low temperatures and reduced time at
temperature during the processing have benefits of lower process
energy costs and, moreover, reduced risk of hazard in managing the
often combustible organic low-polarity solvents during processing,
as well as simplifying equipment and facility requirements.
[0013] In at least one embodiment, a process for preparing a
colloidal dispersion, comprises: [0014] (a) preparing an aqueous
colloidal dispersion of cerium-containing oxide nanoparticles;
[0015] (b) adding a substantially non-polar solvent, an amphiphilic
material, and, optionally, at least one glycol ether; [0016] (c)
mixing the liquid mixture of step (b) to form an emulsion; [0017]
(d) heating the emulsion to a predetermined temperature for a
predetermined time, thereafter the emulsion separates into a
substantially non-polar colloidal phase and a remnant aqueous
phase; and, [0018] (e) collecting the separated substantially
non-polar colloidal dispersion of cerium-containing oxide
nanoparticles.
[0019] In a second aspect, the invention is directed to an improved
process wherein conventional cerium-containing oxide nanoparticle
precipitates are collected from an aqueous reaction mixture in
which they were formed. Collection can be by filtration,
centrifugation, and the like, and may include washing to remove
unwanted constituents from the aqueous reaction mixture. The washed
nanoparticulates may then be in the form of a powder or a paste.
The nanoparticles are then re-dispersed into an aqueous phase. The
nanoparticles of the aqueous dispersion are transferred to a
substantially non-polar liquid comprising one or more amphiphilic
materials, one or more low-polarity solvents, and a glycol ether
promoter material. The transfer may be achieved by mixing the
aqueous dispersion and substantially non-polar liquid, wherein an
emulsion is formed, followed by a phase separation into a remnant
polar solution phase and a substantially non-polar dispersion
phase, and then a collection of the substantially non-polar
(low-polarity) dispersion phase. The promoter may function to speed
the transfer of nanoparticles to the low-polarity phase. The
promoter may accelerate the phase separation, and may also provide
improved dispersion stability of the final substantially non-polar
dispersion phase. In particular embodiments, the glycol ether
promoters reduce the temperature necessary to achieve the phase
separation while providing high extraction yield of nanoparticles
into the low-polarity phase. Low temperatures and reduced time at
temperature during the processing may provide benefits of lower
process energy costs and, moreover, reduced risk of hazard in
managing the often combustible organic low-polarity solvents during
processing, as well as simplifying equipment and facility
requirements.
[0020] In a third aspect, the invention provides an improved
process wherein conventional steps of aqueous nanoparticle
isolation and washing may be eliminated, dramatically simplifying
prior art processes, the inventive process reduces the process
temperatures while reducing process waste, to significant economic
advantage. Process simplification may be achieved by directly using
the aqueous colloid resulting from the nanoparticle synthesis
reaction mixture for extraction of nanoparticles to form the
substantially non-polar dispersion. The aqueous colloid may be
mixed with a substantially non-polar solvent or mix of solvents,
along with one or more amphiphilic materials and a glycol ether
promoter material, to form an emulsion. The emulsion separates
rapidly at low process temperatures into a low-polarity colloid
phase and a remnant aqueous solution phase. The substantially
non-polar colloid may be collected, thereby achieving a stable
substantially non-polar dispersion, nearly entirely free of
contaminants present in the aqueous phase. The promoter material
may function to accelerate the separation of the emulsion while
lowering the process temperature, to stabilize the low-polarity
dispersion, and, in some embodiments, to achieve desired low
temperature flow characteristics for the low-polarity
dispersion.
[0021] In another aspect, the invention relates to a variant of the
first aspect, wherein the addition of the glycol ether promoter
follows an aging (i.e. holding) period for the emulsion formed from
mixing the aqueous dispersion phase, the substantially non-polar
solvent, and the amphiphilic material.
[0022] In another aspect, the inventive transfer process of
cerium-containing oxide nanoparticles from an aqueous dispersion
phase to a substantially non-polar dispersion phase may be
accomplished at low process temperatures and/or with substantially
complete transfer of nanoparticles to the substantially non-polar
dispersion phase.
[0023] In a further aspect, the invention provides
cerium-containing oxide nanoparticles in a stable, substantially
non-polar dispersion at low process temperatures, and having
desired low temperature flow and other characteristics, by further
addition of a glycol ether compound, or a mix of such compounds, to
the separated substantially non-polar dispersion.
[0024] In yet another aspect, the inventive transfer process
provides a substantially non-polar dispersion of cerium-containing
oxide nanoparticles by a rapid, complete transfer of nanoparticles,
with excellent dispersion stability over the useful operating
temperature range of the dispersion.
[0025] In still another aspect, with the use of particular
amphiphilic materials, such as heptanoic acid or octanoic acid,
extraction of nanoparticles from the aqueous colloid phase, and
separation of the aqueous and substantially non-polar colloidal
phases, occur at room temperature in seconds, with no need for the
additional cost or complexity of promoter materials. In addition,
use of these particular amphiphilic materials (e.g. heptanoic acid
and octanoic acid) also provide high extraction yield of
nanoparticles into the low polarity organic phase.
[0026] In a still further aspect, the invention is directed to the
processes set forth above, wherein the substantially non-polar
dispersion of nanoparticles comprising cerium and iron oxides, is a
fuel additive. The fuel additive produced by the inventive process
is characterized as having reduced contamination from ionic
constituents, aqueous stabilizer material, and free water, wherein
such components originate in the aqueous synthetic reaction
mixture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a ternary phase diagram representing combinations
of a set of exemplary non-polar solvent, amphiphilic agent, and
glycol ether promoter, of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] For effectiveness in many end-use applications, nanoparticle
size distributions with mean diameters ranging from below about 100
nm to below about 3 nm are useful.
[0029] As used herein, the terms dispersion, colloid, suspension,
sol, colloid dispersion, and colloidal dispersion are used
interchangeably to mean a stable biphasic mixture of a
discontinuous phase (e.g., nanoparticles) within a continuous phase
(e.g., liquid or other solvent medium).
[0030] As used herein, the term cerium-containing oxide includes
doped and un-doped cerium oxides. Doped cerium oxide compounds
include those with the formula Ce.sub.(1-x)M.sub.xO.sub.(2-.delta.)
where M is a divalent or trivalent metal and .delta. is indicative
of oxygen vacancies. It should be recognized by one skilled in the
chemical art that dopant metal M, in addition to being either
substitutionally or interstitially doped into the cerium oxide
crystal structure, could be present as oxides of metal M, either as
separate nanoparticles or nanocrystals, or as nanoparticles or
nanocrystals in agglomeration (composite) with other doped or
un-doped cerium oxide nanocrystals. In various embodiments,
nanoparticles comprised of crystalline substitutionally doped or
un-doped cerium oxide phases, are present. In other embodiments,
nanoparticles comprised of non-crystalline metal oxide phases, such
as amorphous iron oxide phases, are present. In various
embodiments, dopant metal M is Fe, Zr, Pd, Pt, Ag, Co, Cu, and Ni.
In particular embodiments, nanoparticles of a nominal composition
of Ce.sub.(1-x)Fe.sub.xO.sub.(2-.delta.) wherein x ranges from
about 0.01 to 0.8, or from about 0.5 to 0.7, and .delta. ranges
from about 1 to 2, such as, for example, from about 1.5 to 2, are
employed in the inventive process.
[0031] The invention relies in part, on the discovery of the
effectiveness of certain glycol ethers in aiding the extraction or
transfer of doped or un-doped cerium oxide nanoparticles or
mixtures thereof from aqueous to substantially non-polar solvents,
at low process temperatures. In particular, the choice of a glycol
ether, such as diethylene glycol monomethyl ether (DEGME), has been
discovered by the inventors to accelerate the phase separation of
aqueous and substantially non-polar colloid phases formed by the
mixing of aqueous colloidal solutions with substantially non-polar
materials (liquids) including a low-polarity solvent or mix of
low-polarity solvents, one or more amphiphilic materials, and one
or more specific glycol ethers. The mixing of the aqueous colloid
and the substantially non-polar materials (liquids) provides an
emulsion. In the presence of certain particular glycol ethers, the
emulsion separates at room temperature or modestly elevated
temperatures into an aqueous solution phase and a substantially
non-polar colloid containing substantially all of the nanoparticles
from the aqueous colloid, the amphiphilic material, and a portion
of the glycol ether. In particular embodiments, wherein the
nanoparticles exhibit substantial coloration, the efficiency or
degree of transfer of the nanoparticles from the aqueous phase to
the non-polar phase, may be qualitatively assessed by visual
observation.
[0032] In particular embodiments, additional glycol ether materials
may be added to the substantially non-polar colloid to enhance
colloidal stability, to enhance low temperature flow properties,
and/or to raise the flashpoint temperature of the substantially
non-polar colloid. In other embodiments, materials useful for
modifying the low temperature flow characteristics and flash points
the substantially non-polar colloid include low molecular weight
organic liquids such as alcohols and diols.
[0033] In particular embodiments, the glycol ether promoter may
reduce the temperature necessary to achieve phase separation while
providing high extraction yield of nanoparticles to the organic
phase. Low temperatures and lower time at temperature during the
processing have benefits of lower process energy costs and,
moreover, reduced risk of hazard in managing the organic
combustible materials during processing, as well as simplifying
equipment and facility requirements.
[0034] The invention also relies in part, on the discovery of the
effectiveness of heptanoic acid or octanoic acid in aiding the
extraction or transfer of cerium-containing oxide nanoparticles or
mixtures thereof from aqueous to substantially non-polar solvents,
at low process temperatures, and at comparatively very high rates.
Use of heptanoic acid or octanoic acid has been shown by the
inventors to accelerate the phase separation of aqueous and
substantially non-polar colloid phases formed by the mixing of
aqueous colloidal dispersions with heptanoic acid or octanoic acid
and the substantially non-polar materials including a solvent or
combination of solvents. With the use of heptanoic acid or octanoic
acid, extraction of nanoparticles from the aqueous colloid phase
can occur at room temperature in seconds, with no need for the
additional cost or complexity of promoter materials. The mixing of
the aqueous colloid and heptanoic acid or octanoic acid, alone or
in combination with the substantially non-polar solvents, provides
an emulsion. In the presence of heptanoic acid or octanoic acid,
the emulsion separates at room temperature or modestly elevated
temperatures into an aqueous solution phase and an organic colloid
containing substantially all of the nanoparticles from the aqueous
colloid, and the heptanoic acid or octanoic acid. With the addition
of at least one substantially non-polar solvent, the substantially
non-polar colloids so-formed, exhibit excellent colloidal
stability. To the substantially non-polar colloid, other materials
may be added to enhance colloidal stability, to enhance low
temperature flow properties, and to raise the flashpoint
temperature of the substantially non-polar colloid and to provide
other advantages as set forth below.
[0035] As mentioned previously, U.S. Pat. No. 6,271,269 to
Chane-Ching et al. discloses direct transfer of cerium oxide or
doped cerium oxide colloidal particles from a counterpart aqueous
dispersion. The range of temperatures disclosed for the transfer
reaction is from higher than 60.degree. C. to 150.degree. C., with
a preferred range of from 80-100.degree. C. Disclosed examples were
carried out at 90.degree. C.
[0036] In particular embodiments, substantially non-polar
(low-polarity) solvents include, alone or in combination, aliphatic
hydrocarbons and mixtures thereof, and alicyclic hydrocarbons and
their mixtures. In other embodiments, non-polar solvents include
diesel fuel, biodiesel fuel, naphtha, kerosene, gasoline, and
commercially available petroleum derivatives such as isoparafin
distillates (e.g., Isopar.RTM.), hydrotreated petroleum distillates
(e.g., Kensol.RTM. 48H and Kensol.RTM. 50H available from American
Refining Group, Ltd of Bradford, Pa. (USA); or Calumet 420-460
available from Calumet Lubricants Co. of Cotton Valley, La. (USA)).
Kensol.RTM. 48H and 50H are used in particular embodiments as
components of fuel-additive applications of the invention because
of their low sulfur content, high flashpoint, and low concentration
of components having unsaturated bonds. Solvents having some
concentration of aromatics, for example, Solvesso.RTM. type
solvents, may be useful for the purposes of the invention. Low cost
may be another driver for the choice of a particularly preferred
substantially non-polar solvent. In various embodiments, the
substantially non-polar solvent comprises from about 50-65 wt. % of
the total substantially non-polar liquid used to form the emulsion
mixture.
[0037] In particular embodiments, amphiphilic materials include
monocarboxylic acids having from 6 to 22 carbon atoms, dicarboxylic
acids, polycarboxylic acids, and combinations thereof. In
particular embodiments, monocarboxylic acid materials include, for
example, oleic acid, stearic acid, linoleic acid, linolenic acid,
and isomers thereof alone or in combination. In other particular
embodiments, monocarboxylic acids having from 7 to 9 carbon atoms,
for example, heptanoic acid, octanoic acid, nonanoic acid and
mixtures thereof, are employed. In particular embodiments,
dicarboxylic acids include, for example, derivatives of succinic
acid, such as polyisobutylene succinic acid (PIBSA), and anhydrides
thereof. The amphiphilic materials may also characterized in that
they are soluble in non-polar hydrocarbon diluents, such as
kerosene, isoparafin and hydrotreated petroleum distillates, which
in turn are compatible with most hydrocarbon fuels, such as
gasoline, diesel and biodiesel, and lubricating oils. In various
embodiments, the amphiphilic materials comprise from about 25-33
wt. % of the total substantially non-polar liquid used to form the
emulsion mixture.
[0038] In particular embodiments, glycol ether promoters include,
for example, diethylene glycol monomethyl ether (DEGME), propylene
glycol monomethyl ether (PGME), diethylene glycol monoethyl ether,
diethylene glycol monobutyl ether, dipropylene glycol methyl ether,
ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,
ethylene glycol monopropyl ether, and mixtures thereof. Choice of
particular glycol ether promoters may be based in part on efficacy
of low temperature acceleration of extraction of nanoparticles from
aqueous to a substantially non-polar phase. It has been found that
the level of glycol ether present may be sensitive, there being a
threshold for the beneficial acceleration of the separation of the
emulsion to give a stable high yield substantially non-polar
colloid. Consideration of the miscibility and stability, as will be
discussed further below, of the ternary combination of non-polar
solvent, amphiphilic agent, and the glycol ether may also be a
factor in the determination of the appropriate level of glycol
ether in the process and in the final product. Other considerations
for the specific choice of and relative amount of glycol ether
include satisfying product requirements regarding cost, low
temperature flow, flashpoint, and health/environmental
considerations. In various embodiments, the glycol ether promoters
comprise from about 5-25 wt. % of the total substantially non-polar
liquid used to form the emulsion mixture.
[0039] The aqueous doped or un-doped cerium oxide colloid that is
to be directly transferred or extracted into a non-polar phase
could be formed according to a number of known approaches. For
example those described in copending U.S. application Ser. No.
12/779,602 now published as US2010/0242342, to Reed et al.,
incorporated herein by reference, are applicable. In some
embodiments of the invention, such an aqueous colloid as formed in
its reaction vessel is directly useful for transfer to
substantially non-polar colloid phase, even though the aqueous
colloids have constituent components comprising reactant remnants
and addenda. In other embodiments, nanoparticles formed as aqueous
colloids using other well-known processes can be isolated and
washed and then re-dispersed in water to form another aqueous
colloid that can be used as a starting material for the inventive
transfer process discussed herein.
[0040] In particular embodiments, the temperature range for the
formation of the emulsion, transfer of the nanoparticles between
aqueous and substantially non-polar phases, and separation of the
emulsion, may range from about 20.degree. C. to 60.degree. C. In a
particular embodiment, a temperature of about 40.degree. C. is used
because an aqueous colloid in which the nanoparticles are formed
directly, will often be substantially above 40.degree. C. at the
conclusion of the aqueous nanoparticle synthesis in order to impart
high yield and crystallinity in a short amount of time. An aqueous
colloid so formed, when combined with the other materials that
comprise the non-polar constituents, conveniently at room
temperature, will yield an emulsion with a temperature near
40.degree. C. Such low temperatures compared to prior art process
temperatures are a significant advantage afforded by the inventive
approach. And near this temperature, in particular embodiments, the
presence of glycol ether promoters of the invention cause the
emulsion to separate into two phases within about 1 to 4 hours,
with substantially complete extraction of the nanoparticles from
the aqueous phase into the non-polar phase. In still other
embodiments, wherein, for example, heptanoic acid or octanoic acid
are employed, the emulsion can separate into two phases within
about 5 seconds to 10 minutes with substantially complete
extraction of nanoparticles from the aqueous phase. It is
understood by those skilled in the chemical engineering art, that
the time required to complete phase separations will increase as
the total volume of the emulsion increases.
[0041] In various embodiments, once active mixing of the emulsion
is stopped, the emulsion will separate into two phases within about
60 minutes, within about 50 minutes, within about 40 minutes,
within about 30 minutes, within about 20 minutes, within about 10
minutes, within about 5 minutes, within about 1 minute, within
about 30 seconds, within about 10 seconds, within about 5
seconds.
[0042] In a particular embodiment, it has been found that it may be
beneficial to age (hold) for a predetermined period of time, the
emulsion formed from the mixing of the aqueous cerium-containing
oxide colloid, the substantially non-polar solvent, and the
amphiphilic material (e.g. organic acid), prior to the addition of
the glycol ether promoter. In various embodiments, the aging
(holding) temperature is in the range of 20-60.degree. C., and the
aging (holding) time is in the range of 0 to 8 hours, 0 to 4 hours,
or 0 to 2 hours.
[0043] The inventors have explored the ternary phase diagram of a
combination liquid comprising a non-polar solvent--Kensol.RTM. 50H,
an amphiphilic material--oleic acid, and the promoter--DEGME. FIG.
1 depicts the ternary phase diagram for the ternary system at room
temperature. Note that there are 2 regions: Region A is
characterized by a single-phase liquid in which all three of the
components are miscible. Region 13 is characterized by a separation
into 2 liquid phases. It may be preferable to choose the ratio of
the 3 constituents to be in the single-phase region, while at the
same time optimizing other desirable characteristics of the
product, for example, long-term colloidal stability of the organic
colloid (sol) product. Colloidal stability over the manufacturing
process temperatures and product exposure temperatures, both high
and low, may need to be considered. Product characteristics of
concern may include flow-ability at low operating temperatures
(cold outdoor ambient temperatures) and flash-point at higher
potential exposure temperatures. Conveniently and unexpectedly, in
some embodiments, product ratios of the three materials of the
ternary diagram also provide for an ideal composition for the
extraction of nanoparticles from the aqueous colloid to the
substantially non-polar colloid.
[0044] In some embodiments, it has been found that the low
temperature extraction of nanoparticles from the aqueous phase to
the substantially non-polar phase is accelerated by forming the
emulsion with high shear mixing.
[0045] In some embodiments, analysis of the final organic colloid
material produced by the inventive process reveals that it is
substantially free of constituents of the aqueous reaction mixture
in which the nanoparticles were initially formed. Levels of water,
nitrates, and nanoparticle stabilizer (e.g. methoxyacetic acid)
were all lower than in the comparative process disclosed in the
commonly assigned U.S. application Ser. No. 12/549,776 now US
Publication 2010/0152077 A1 to Alston et al. Analysis also revealed
that a portion of the glycol ether promoter material or materials
may be retained in the aqueous phase after phase separation.
Optionally, an additional amount of glycol ether is added to the
separated substantially non-polar colloid, according to
considerations previously stated.
[0046] It is well known in the art that extraction of metal oxide
nanoparticles for fuel additives from aqueous colloid form to
organic colloid form can be accomplished using amphiphilic
materials together with non-polar solvents. For example, Blanchard
et al. in US 2006/0005465 A1 disclose carboxylic acids having from
10 to 50 carbon atoms, and, in particular, 2-ethylhexnoic acid, as
preferred amphiphilic agents. However, in this earlier work the pH
of the aqueous metal oxide nanoparticle dispersions remained basic.
More specifically, the pH of the reaction mixture (i.e. aqueous
metal oxide nanoparticle dispersion) is described therein as being
kept to a value of at least 7, more particularly at least 7.5,
still more particularly in the range 7.5 to 10.5.
[0047] In contrast to the disclosures of US 2006/0005465 A1,
embodiments of the invention employ aqueous cerium-containing oxide
nanoparticle dispersions that remain acidic. In particular
embodiments the pH of the aqueous cerium-containing oxide
nanoparticle dispersions are less than 7, less than 6, and less
than 5. In a specific embodiment the pH of the aqueous
cerium-containing oxide nanoparticle dispersion is about 4.5.
[0048] Hexanoic acid (C.sub.7H.sub.16O.sub.2) and octanoic acid
(C.sub.8H.sub.18O.sub.2) are particular carboxylic acids that give
the very surprising result of substantially complete extraction of
cerium-containing oxide nanoparticles from an acidic aqueous phase
into a substantially non-polar phase, do so at room temperature,
and without the use of a promoter (e.g. alcohol or glycol ether).
Even more surprising, 2-ethyl hexanoic acid
(C.sub.8H.sub.18O.sub.2), a closely related isomer of octanoic
acid, does not function nearly as well as an amphiphilic agent in
regard to the rate of extraction of cerium-containing oxide
nanoparticles from an acidic aqueous phase to an organic phase,
particularly so at room temperature. 2-Ethylhexanoic acid is widely
used to prepare metal compounds that are soluble in non-polar
organic solvents.
[0049] To further illustrate the invention and its advantages, the
following examples are given, it being understood that the specific
examples are not limiting.
Experimental Section
Preparation of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) Aqueous
Nanoparticle Dispersion
[0050] To an 11 liter round bottom Type-316 stainless steel kettle
or reactor with 3 mixing baffles, was added distilled water (Kettle
Water), which was maintained at 70.degree. C. Using an impeller,
the water was stirred at sufficient speed to provide good mixing.
Then 98% methoxyacetic acid was added to the reactor. Two solution
introduction jets directed to the impeller blades were put into the
reactor and secured. An ammonium hydroxide solution was pumped
through one jet at a rate of 69.3 ml /minute. A cerium-iron
containing solution (334.5 gram of Ce(NO.sub.3).sub.3.6H.sub.2O and
207.5 gram of Fe(NO.sub.3).sub.3.9H2O with distilled water to make
625 ml) was pumped through the other jet at a delivery rate of 125
ml/minute. The cerium-iron solution was purged from the delivery
line with a 15 ml distilled water chase. Then a 50% H.sub.2O.sub.2
solution was pumped into the reactor at 9.38 ml/minute using a
third jet and was followed by a brief distilled water flush. The
reaction mixture was held at 70.degree. C. for an additional sixty
minutes, after which time it was cooled to 20.degree. C., providing
a stable Ce.sub.0.6Fe.sub.0.4O.sub.2-.delta. aqueous nanoparticle
colloidal dispersion, wherein .delta. is between about 1.5 to 2.
The final dispersion was a clear, dark brown aqueous liquid that
was washed and concentrated by diafiltration to an ionic
conductivity of less than about 12 mS/cm and a pH of about 4.5.
[0051] Transmission electron microscopy (TEM) grain sizing revealed
a particle size of 2.5.+-.0.5 nm. Electron diffraction revealed a
distinct CeO.sub.2 cubic fluorite electron diffraction pattern. No
electron diffraction peaks characteristic of a crystalline iron
oxide phase were detected. Ultra-high resolution TEM and electron
energy loss spectroscopy revealed a plurality of composite
nanoparticles comprised of crystalline cerium oxide rich regions
and amorphous iron oxide rich regions.
EXAMPLE 1
Extraction of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) with Oleic Acid
and DEGME
[0052] A 100 ml aliquot of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.)
aqueous nanoparticle dispersion prepared as described above, was
added to a 500 ml reaction vessel and heated to a temperature of
about 60.degree. C. A 74.0 ml aliquot of Kensol.RTM. 50H and 37.6 g
of oleic acid were then added, these two materials being at room
temperature at the time of addition. The mixture was stirred by
manual shaking of the vessel for a period of 1 minute, forming an
emulsion. The emulsion mixture was then held at 40.degree. C. to
age for 2 hours. Then, 30 ml of DEGME was added to the emulsion and
it separated in about 4 hours to yield a stable dark brown
non-turbid substantially non-polar colloid phase, above a nearly
colorless aqueous phase. The non-polar colloid phase was separated
out by pipette.
[0053] To 100 ml of the separated organic colloid phase were added
13.9 ml of DEGME and 7.2 ml of PGME. Long-term stability
observations of samples of the above non-polar colloid were carried
out while samples were held in separate 10 ml vials. One was held
at room temperature (about 20.degree. C.) and the other at
40.degree. C. At the conclusion of 6 months, the non-polar
colloids, remained essentially non-turbid and free of settled
precipitates.
EXAMPLE 2
Extraction of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) with Oleic Acid
and DEGME
[0054] A 100 ml aliquot of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.)
aqueous nanoparticle dispersion prepared as described above, was
added to a 500 ml reaction vessel and heated to a temperature of
about 60.degree. C. A 75.0 ml aliquot Kensol.RTM. 50H and 35.9 g of
oleic acid were then added, these two materials being at room
temperature at the time of addition. The mixture was stirred by
manual shaking of the vessel for a period of 1 minute. The emulsion
mixture was then held at 40.degree. C. to age for 2 hours. Then, 30
ml of DEGME was added to the emulsion and it was returned to
40.degree. C., thereafter it completely separated in about 4 hours
to yield a stable dark brown non-turbid substantially non-polar
colloid phase, above a nearly colorless aqueous phase. The
non-polar colloid phase was separated out by pipette. To 100 ml of
the separated organic colloid phase were added 12.2 ml of DEGME and
9.1 ml of PGME.
[0055] Long-term stability observations of samples of the above
non-polar colloid were carried out while samples were held in
separate 10 ml vials, one at room temperature (about 20.degree. C.)
and the other at 40.degree. C. At the conclusion of 6 months, the
non-polar colloids, remained essentially non-turbid and free of
settled precipitates. Cold temperature stability was also checked
at -17.degree. C. and it was found that the sample remained a
non-turbid liquid, free of precipitates.
EXAMPLE 3
Extraction of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) with Oleic Acid
and DEGME
[0056] A 500 ml aliquot of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.)
aqueous nanoparticle dispersion prepared as described above, was
heated to a temperature of about 60.degree. C. and transferred to a
2 L reaction vessel. The liquid was stirred with a 1 9/16'' R100
(Rushton) impeller that was lowered into the reactor vessel. The
mixer head was positioned slightly above the bottom of the reactor
vessel. The mixer was set to 1690 rpm. A mixture of 370 ml of
Kensol.RTM. 50H and 188 g of oleic acid, at room temperature, was
added to the vessel over a 30 second period. The whole mix was then
stirred at 1750 rpm for 2 minutes resulting in the formation of an
emulsion. The reaction vessel was then moved to hot plate with
magnetic stirrer and stirred using a 21/2'' magnetic bar at high
speed setting. 50 ml of DEGME was then added over 15 seconds. The
vessel was then held without stirring at a temperature of about
45.degree. C. After about 4 hours, the emulsion separated
completely to yield about 600 ml of dark brown non-turbid organic
colloid above an aqueous remnant phase.
[0057] Analysis of the organic colloid by Gas Chromatography Mass
Spectrometry revealed no detectable amount of methoxyacetic acid,
the nanoparticle stabilizer present in the
Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) aqueous nanoparticle
dispersion prepared as described above. This reduction in
methoxyacetic acid in the final organic colloid was accompanied by
an improvement in long-term stability relative to organic
dispersions of similar nanoparticles prepared by the solvent
shifting process described by Alston et al. in US Pat. Publication
2010/0152077.
EXAMPLE 4
Ambient Temperature Extraction of
Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) with Heptanoic Acid
[0058] A 20 ml aliquot of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.)
aqueous nanoparticle dispersion prepared as described above, was
added to a 40 ml glass vial at room temperature. To that was added
7.3 ml of heptanoic acid, the contents were shaken by hand for 30
sec, forming an emulsion. Then 13.2 ml of Kensol.RTM. 50H solvent
was added, and the mixture was shaken again by hand for 30 sec,
forming an emulsion. Upon standing for 5 minutes, the emulsion
mixture was observed to separate into a dark brown upper layer and
a clear light yellow lower layer. All of the materials used in this
example were at an ambient temperature of about 20.degree. C.
EXAMPLE 5
Ambient Temperature Extraction of
Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) with a Heptanoic Acid and
Kensol.RTM. 50H Mixture
[0059] A 10 ml aliquot of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.)
aqueous nanoparticle dispersion prepared as described above, was
added to a 40 ml glass vial at room temperature. A mixture of 6.6
ml of Kensol.RTM. 50H and 3.7 ml of heptanoic acid was added to the
vial, the contents were shaken by hand for 30 sec, forming an
emulsion. The emulsion mixture was allowed to separate over night.
A dark brown organic upper layer formed over a light brown aqueous
lower layer. All of the materials used in this example were at an
ambient temperature of about 20.degree. C.
[0060] While some extraction of the cerium-and iron-containing
nanoparticles was achieved, the extraction was much slower and less
efficient compared to the sequential addition method used in
Example 4.
EXAMPLE 6
Ambient Temperature Extraction of
Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) with Octanoic Acid
[0061] An aliquot of 5 ml of aqueous colloid of
Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) prepared as described above,
having a temperature of about 20.degree. C. was added to a 15 ml
vial. To that was added 1.83 ml of octanoic acid. The vial and
contents were shaken by hand for 30 sec, thereby forming an
emulsion. The emulsion then separated within seconds forming a dark
upper organic phase over a nearly colorless yellow aqueous remnant
phase. Next, 3.3 ml of Kensol.RTM. 50H was added to the vial,
followed by 30 seconds of shaking. Again a formed emulsion
separated in seconds to produce a dark upper phase above a light
yellow aqueous remnant.
[0062] Long-term stability observations of samples of the above
non-polar colloid were carried out while samples were held in
separate 10 ml vials. One was held at room temperature (about
20.degree. C.) and the other at 40.degree. C. At the conclusion of
6 months, the non-polar colloids remained essentially non-turbid
and free of settled precipitates.
EXAMPLE 7
Ambient Temperature Extraction of
Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) with Octanoic Acid and Kensol
50H Mixture
[0063] A 10 ml aliquot of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.)
aqueous nanoparticle dispersion prepared as described above, was
added to a 40 ml glass vial at room temperature. A mixture of 6.6
ml of Kensol.RTM. 50H and 3.7 ml of octanoic acid was added to the
vial, the contents were shaken by hand for 30 sec, forming an
emulsion. The emulsion mixture was allowed to separate over night.
A dark brown organic upper layer formed over a translucent brown
aqueous lower layer. All of the materials used in this example were
at an ambient temperature of about 20.degree. C.
[0064] While some extraction of the cerium-and iron-containing
nanoparticles was achieved, the extraction was much slower and less
efficient compared to the sequential addition method used in
Example 6.
EXAMPLE 8
Scale-up Extraction of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) with
Octanoic Acid
[0065] A 12 liter aliquot of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.)
aqueous nanoparticle dispersion prepared as described above, was
heated to a temperature of 60.degree. C. and transferred to a 60
liter stainless steel reaction vessel. The dispersion was stirred
at about 500 to 1000 rpm using a 4'' R100 (Rushton) mixer. Then
4116 ml of octanoic acid was added to the mixing vortex. Next 7944
ml of Kensol.RTM. 50H was added. The mixer speed was increased to
about 1400 rpm and the mixture was stirred for 5 minutes. The
temperature of the reaction mixture dropped as a result of the
additions of room temperature materials, but remained above
40.degree. C. The mixer was turned off and the mixture was held for
5 minutes. The contents were found to separate into a substantially
non-polar colloid phase above a remnant aqueous phase. The
colorless aqueous phase was drained from the reaction vessel and
the substantially non-polar colloidal was collected. A small sample
was taken from the non-polar colloidal and the per cent solids
content was determined.
[0066] The solids content of the non-polar colloidal was then
adjusted to 3.5% solids by the addition of the appropriate amount
of octanoic acid and Kensol.RTM. 50H. The volume ratio of octanoic
acid and Kensol.RTM. 50H was the same as described earlier.
Subsequently, a mixture of 6.0 wt % PIBSA (polyisobutylene succinic
anhydride) and 15 ppm Stadis 450 in Kensol 50H was added to bring
the solids content down to 2.0 wt %.
[0067] Stability of the final non-polar colloid phase was found to
be excellent after a two month period, remaining non-turbid and
free of settled precipitates.
EXAMPLE 9
Use of Glycol Ether Addenda
[0068] A 22.7 ml aliquot Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.)
aqueous nanoparticle dispersion prepared as described above, was
heated to a temperature of 60.degree. C. and transferred to a
reaction vessel. To that was added 10.7 ml of octanoic acid. The
vessel and contents were shaken by hand for 30 sec, forming an
emulsion. The emulsion then separated within seconds forming a dark
upper organic phase over a nearly colorless yellow aqueous remnant
phase. Next, 24.5 ml of Kensol.RTM. 50H was added to the vessel,
followed by 30 seconds of shaking. The formed emulsion separated in
seconds into two phases, a dark upper substantially non-polar
colloidal phase above an aqueous remnant. 36 ml the organic
substantially non-polar colloidal phase was separated out by
pipetting. Next, 2.67 g of propylene glycol monomethyl ether (PGME)
and 1.78 g of diethylene glycol monomethyl ether (DEGME) were added
to the organic substantially non-polar colloid.
[0069] Long-term stability observations of a 10 ml sample of the
above non-polar colloid were carried out. Behavior of the non-polar
colloid at -19.degree. C. was also studied and it was found to
remain a clear single phase liquid under this condition.
EXAMPLE 10
Ambient Temperature Extraction of
Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.) with 2-Ethylhexanoic Acid
[0070] A 20 ml aliquot of Ce.sub.0.6Fe.sub.0.4O.sub.(2-.delta.)
aqueous nanoparticle dispersion prepared as described above, was
added to a 40 ml glass vial at room temperature. To that was added
7.3 ml of 2-ethylhexanoic acid, the contents were shaken by hand
for 30 sec, forming an emulsion. Then 13.2 ml of Kensol.RTM. 50H
solvent was added, and the mixture was shaken again by hand for 30
sec, forming an emulsion. Upon standing for 1-2 hours, the emulsion
mixture was observed to separate into a translucent brown upper
organic layer and a dark muddy brown aqueous lower layer. All of
the materials used in this example were at an ambient temperature
of about 20.degree. C.
[0071] Thus, a substantially incomplete transfer of nanoparticles
from the acidic aqueous phase to the low polarity phase resulted;
and a relatively slow phase separation of the substantially
non-polar colloid phase from the remnant aqueous phase were
achieved at ambient temperature.
[0072] The invention has been described in detail, with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the scope of the invention as described above, by a person of
ordinary skill in the art, without departing from the scope of the
invention.
* * * * *