U.S. patent application number 13/681548 was filed with the patent office on 2013-07-11 for microwave process for preparing stable metal oxide dispersions.
This patent application is currently assigned to Chemtura Corporation. The applicant listed for this patent is Chemtura Corporation. Invention is credited to Kenneth Lassen, Qinggao Ma, Venkatramanan K. Madabusi, Kirk A. Schlup.
Application Number | 20130178404 13/681548 |
Document ID | / |
Family ID | 48744320 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130178404 |
Kind Code |
A1 |
Ma; Qinggao ; et
al. |
July 11, 2013 |
Microwave Process for Preparing Stable Metal Oxide Dispersions
Abstract
Microwave irradiation is used to prepare stable dispersions of
small particle metal oxides, such as magnesium oxide and calcium
oxide, from a composition prepared from a mixture comprising an
oxide, hydroxide or carbonate of the metal, a carrier, a sulfonic
or carboxylic acid dispersant, and typically a low MW carboxylic
acid and water. Dispersions with an average particle size of one
micron or less, often from 1-100 nm, are typically obtained.
Inventors: |
Ma; Qinggao; (Naugatuck,
CT) ; Lassen; Kenneth; (Cheshire, CT) ;
Madabusi; Venkatramanan K.; (Naugatuck, CT) ; Schlup;
Kirk A.; (Woodbury, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Chemtura Corporation; |
Middlebury |
CT |
US |
|
|
Assignee: |
Chemtura Corporation
Middlebury
CT
|
Family ID: |
48744320 |
Appl. No.: |
13/681548 |
Filed: |
November 20, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61583749 |
Jan 6, 2012 |
|
|
|
Current U.S.
Class: |
508/390 ;
508/534 |
Current CPC
Class: |
C10N 2020/06 20130101;
C10L 1/12 20130101; C10L 1/1233 20130101; C10N 2070/00 20130101;
C10L 1/2437 20130101; C10M 141/02 20130101; C10M 2201/062 20130101;
C10M 163/00 20130101; C10L 1/188 20130101; C10N 2030/52 20200501;
C10N 2050/015 20200501; C10M 2219/046 20130101; C10M 141/08
20130101 |
Class at
Publication: |
508/390 ;
508/534 |
International
Class: |
C10M 141/08 20060101
C10M141/08; C10M 141/02 20060101 C10M141/02 |
Claims
1. A process for preparing a stable, free flowing overbased metal
oxide dispersion, wherein a) 5-80% of a metal hydroxide, metal
oxide or metal carbonate b) 2-15% of a sulfonate or carboxylate
dispersant c) 10-70% of a high boiling hydrocarbon carrier selected
from mineral oils, alkylated benzenes, oligomers or polymers of
alpha olefins, polycyclic aromatics, alkylated derivatives of
polycyclic aromatics and waxes, d) 0-10% of a C.sub.1-5 carboxylic
acid, e) 0%-30% water and f) 0-60% of an organic solvent having a
boiling point of less than 280.degree. C., wherein the percentages
are by weight based on the total weight of the mixture, are
combined to form a preliminary dispersion, which is subjected to
microwave irradiation to yield after irradiation a metal oxide
dispersion with average particle size of less than 1 micron.
2. The process according to claim 1 wherein the metal of the
hydroxide, oxide or carbonate is selected from Li, Na, K, Cs, Mg,
Ca, and Ba.
3. The process according to claim 2 wherein the metal of the
hydroxide, oxide or carbonate is selected from Mg, Ca, and Ba.
4. The process according to claim 3 wherein the metal of the
hydroxide, oxide or carbonate is Mg.
5. The process according to claim 1, 2, 3, 4 or 5 wherein the
sulfonate or carboxylate dispersant is an alkylarylsulfonate or
alkylaryl carboxylate dispersant.
6. The process according to claim 5 wherein a) 5-50% of a metal
hydroxide, metal oxide or metal carbonate b) 2-15% of a sulfonate
or carboxylate dispersant c) 10-70% of a high boiling hydrocarbon
carrier selected from mineral oils, alkylated benzenes, oligomers
or polymers of alpha olefins, polycyclic aromatics, alkylated
derivatives of polycyclic aromatics and waxes, d) 0-10% of a
C.sub.1-5 carboxylic acid, e) 0%-30% water and f) 0-60% of an
organic solvent, are combined and heated to temperatures of from
about 85.degree. C. to about 220.degree. C. for from about 0.25 to
about 5 hours, and volatiles are removed by distillation to form
the preliminary dispersion which is then subjected to microwave
irradiation.
7. The process according to claim 6 wherein a) 5-40%, typically a
metal hydroxide, metal oxide or metal carbonate b) 3-7% of an
alkylbenzene sulfonic acid dispersant, c) 10-70% of a high boiling
hydrocarbon carrier, d) 1-7% of a C.sub.1-5 carboxylic acid, e)
8%-30% water and f) 10-60%, of an organic solvent with a boiling
point of from about 80.degree. C. to about 210.degree. C., are
combined, heated and distilled to remove volatiles to form the
preliminary dispersion.
8. The process according to claim 7 wherein the metal hydroxide,
metal oxide or metal carbonate is magnesium oxide or magnesium
hydroxide, the C.sub.1-5 carboxylic acid is acetic acid, and the
organic solvent is xylene or mesitylene and the metal oxide
dispersion formed is a magnesium oxide dispersion with an average
particle size of less than 1 micron.
9. The process according to claim 8 wherein the metal oxide
dispersion formed is a magnesium oxide dispersion with an average
particle size of from about 1 nm to about 100 nm.
10. A magnesium oxide dispersion obtained by the process according
to claim 1.
11. A lubricant or fuel composition comprising the magnesium oxide
dispersion according to any of claims 1 to 10.
12. The composition according to claim 11 wherein the lubricant or
fuel is petroleum based.
Description
[0001] This application claims the benefit of the filing date of
U.S. Provisional Application No. 61/583,749, filed Jan. 6, 2012,
the entire contents of which are incorporated herein by reference.
This invention relates to stable dispersions of small particle
metal oxides, such as magnesium oxide and calcium oxide, with an
average particle size of one micron or less, often from 1-100 nm,
are prepared by microwave irradiation of a composition prepared
from a mixture comprising an oxide, hydroxide or carbonate of the
metal, a carrier, a sulfonic or carboxylic acid dispersant, and
typically a low MW carboxylic acid and water.
BACKGROUND OF THE INVENTION
[0002] Fine particle metal oxides have a variety of commercial
uses. For example, overbased detergents, e.g., compositions
comprising overbased alkaline metal or alkaline-earth metal
compounds such as metal oxides and often complexed with an organic
dispersant, are well known additives for lubricating oil
compositions and petroleum fuels. In such cases, the metal oxide is
most conveniently added and used as a dispersion in a carrier.
[0003] Petroleum fuels such as residual fuel oils contain large
amounts of impurities which result in corrosive deposits in the
equipment. For example, crude oil usually contains 1- 500 ppm of
vanadium in the form of a porphyrin complex depending on the
source. Because of its origin as a concentrate from the refining
process, residual oil contains several times more vanadium than the
crude from which it was derived. The combustion of these
vanadium-containing fuels produces very corrosive deposits which
can destroy a metal part, such as a gas turbine blade, in a matter
of hours.
[0004] The presence of sodium in fuel can also have catastrophic
consequences. For example, in maritime use the sodium level can be
increased because of the introduction of sodium chloride through
the air intake and contamination of the fuel by sea water. During
combustion, the sodium can react with sulfur in the fuel to form a
sulfate which is deposited in turbine parts.
[0005] Overbased detergents, perform a variety of functions
including anti-corrosion, deposit control, acid scavenger functions
For example, overbased magnesium compounds complexed with sulfonate
and carboxylate dispersants, have long been used as anti-corrosion
and acid neutralization additives for lubricating oils and greases,
anti-corrosion and acidic neutralization additives during the
combustion of fuels such as residual fuel, pulverized
sulfur-containing coal, corrosion inhibitors in fuels containing
vanadium etc. The addition of overbased magnesium detergents to,
for example, boiler fuels or gas turbine fuels, is known to reduce
corrosion, presumably by forming magnesium complexes with the
vanadium or sodium.
[0006] Overbased metal detergents are also added to lubricating
oils to prevent or remove deposits of oil-insoluble sludge,
varnish, carbon and lead compounds which otherwise form on internal
combustion engine parts and for combating severe rust conditions
which may be encountered during shipping or storage of machinery or
exposure to out-door weather. Detergent additives for automotive
and diesel engine oils also chemically react with the highly acidic
by-products of combustion that find their way into the lubricating
oil system.
[0007] Obviously a useful dispersion of metal oxide must be stable
during storage and the overbased metal must stay well dispersed in
the lubricant or fuel. A variety of parameters will affect the
stability and activity of these dispersions such as the dispersants
and carriers employed, particle size of the solid components, and
the relationship between metal and dispersant. The process by which
the overbased metal compounds and complexes are prepared will
greatly influence the actual physical make up and properties of the
overbased metal dispersion, impacting particle size and
distribution of the metal compound throughout the dispersion, the
viscosity and stability of the dispersion, the amount of the metal
within the dispersion etc.
[0008] Overbased metal additives, for example, overbased MgO
dispersions are often added as a dispersion in a high boiling
liquid hydrocarbon. Part of the rationale for supplying MgO
dispersions in high boiling carriers, i.e., carriers with boiling
points over 200.degree. C., often greater than 250.degree. C. or
280.degree. C., and even much greater than 300.degree. C. is due to
the manner in which the dispersions are made. For example,
overbased stable MgO dispersions with fine particle sizes and good
flowcharacteristics are typically produced, even when starting with
MgO as a starting material, through thermal decomposition of
Mg(OH).sub.2 or Mg(OH).sub.2 derived intermediates which require
high temperature (300-350.degree. C.). Thus, the use of high
boiling point solvents as carriers is dictated by practical
processing considerations.
[0009] U.S. Pat. No. 4,163,728, discloses magnesium-containing
dispersions prepared by high temperature decomposition of magnesium
salts of carboxylic acids to MgO in a dispersant-containing fluid.
In the process, Mg(OH).sub.2, an organic carboxylic acid or
sulfonic acid surfactant such as naphthenic acid, acetic acid and
water are heated in a high boiling hydrocarbon to temperatures up
to 350.degree. C., which is above the decomposition point of
magnesium acetate, 323.degree. C. It is believed that magnesium
acetate is formed in situ and decomposes at the high temperatures
used. Water is also removed at the elevated temperatures.
[0010] U.S. Pat. No. 4,293,429, discloses a variation of U.S. Pat.
No. 4,163,728 which begins with MgO instead of Mg(OH).sub.2. In the
process, the bulk MgO is converted to magnesium acetate which forms
suspended MgO particles of less than 5 microns, and preferably less
that 1 micron. Thus, the coarse MgO particles are converted into a
dispersion of stabilized MgO microparticulates. Lower temperatures
fail to provide the fine particle size MgO.
[0011] U.S. Pat. No. 4,129,589, discloses a process for preparing
an over-based oil-soluble magnesium salt of a sulfonic acid by
contacting carbon dioxide gas with a mixture comprising an
oil-soluble magnesium salt of a sulfonic acid, magnesium oxide,
water, and a promoter system comprising a carboxylic acid of 1 to 5
carbons in an inert solvent for lowering the viscosity of said
mixture to facilitate mixing. The products of U.S. Pat. No.
4,129,589 had acceptably low viscosity but the magnesium content
was typically 9-10% and no more than 14%.
[0012] U.S. Pat. No. 6,197,075, discloses an overbased magnesium
sulfonate, carboxylate or phenate product containing at least 14%
and up to about 18% by weight of magnesium, useful as a deposit
control additive for residual fuel oils and turbine fuels prepared
by contacting a mixture of i) a sulfonic acid, phenol or carboxylic
acid or salt thereof, ii) a magnesium oxide, iii) a co-promoter
comprising a lower carboxylic acid, a lower alcohol, a succinic
anhydride and water, and iv) a solvent and/or oil, with an acidic
gas such as carbon dioxide at 50.degree. F. up to the reflux
temperature of the mixture to overbase the reaction mixture.
[0013] The overbased metal compositions described above and
elsewhere are best described as products by process as there is
typically no simple chemical formula which adequately correlates to
the essential material makeup and the physical properties of the
product. Often, the molecular structures of the metal complexes are
not fully known and are not a critical aspect of the invention. For
example, two compositions containing compounds with the same
chemical formula in the same amounts and differing only by the
manner in which they were prepared can have very different physical
properties.
[0014] While the use of high boiling solvents or carriers in the
above processes can provide useful dispersions, there is the need
for improved products and methods. For example, MgO dispersions
with a higher magnesium content are desirable. However simple
modification of known procedures to prepare overbased detergents
with high metal content can lead to unforeseen drawbacks including
unacceptably high viscosities and gelling. Also, attempts to
concentrate the dispersion by distillation to get higher Mg content
must be carried out at very high temperatures or reduced
pressure.
[0015] Co-pending application U.S. Ser. No. 13/167,127,
incorporated herein by reference, describes a method of obtaining
free flowing MgO dispersions with high Mg content in high boiling
carriers using a mixture of solvents and defined quantities of
lower carboxylic acid and water. Co-pending provisional application
U.S. 61/502,914, incorporated herein by reference, discloses a
process for preparing similar MgO dispersions in lower boiling
solvents by performing some of the processing steps under increased
pressure.
[0016] Along with heat, light etc, microwave radiation is a source
of energy that can be used to promote chemical reactions. In some
cases, the products produced from a microwave induced reaction are
different than those produced by thermal or UV initiated reactions;
in some cases the products are the same but the chemical conversion
is more efficient. Makhluf, et. al, "Microwave-Assisted Synthesis
of Nanocrystalline MgO and Its Use as a Bacteriocide" Advanced
Functional Materials 2005, 15, 1708-1715; Sugiyama, et. al,
Matsuda, T. "Synthesis of Magnesium oxide catalyst in a Microwave
plasma reactor" 9th Int. Symp. Plasma Chem. 1989, 2, 820-824; and
Nakano, et. al, "Surface Characterization of Metal Oxide fine
Powders Prepared by Microwave Cold Plasma: AFM Observations of
Silica Surface" 11th Int. Symp. Plasma Chem. 1993, 1, 1422-1427
disclose the use of microwave radiation in the production of
inorganic particles.
[0017] It has been discovered that microwave irradiation can be
used to advantage in the preparation of stable, small particle size
metal oxide dispersions, such as those used as overbased metal
oxide lubricant and fuel additives. Stable dispersions of
sub-micron particles are obtained, typically while avoiding the
very high temperatures that are otherwise required.
SUMMARY OF THE INVENTION
[0018] The present invention provides a method for preparing stable
dispersions of small particle size metal oxides, for example,
overbased metal oxide dispersions, said method comprising
subjecting a preliminary composition or preliminary dispersion
formed from a mixture comprising a metal hydroxide, oxide or
carbonate, a sulfonic or carboxylic acid dispersant, and an organic
carrier, e.g., a high boiling hydrocarbon carrier to microwave
irradiation resulting in a dispersion of metal oxide particles
having an average particle size of one 1 micron or less, often
having an average particle size of from 1-100 nm.
[0019] In one embodiment, the preliminary composition which is
subjected to microwave irradiation is a preliminary dispersion
formed by heating to a temperature of 85.degree. C., typically
higher, e.g., from 100 to 220.degree. C., a mixture comprising a
metal hydroxide, oxide or carbonate, a sulfonic or carboxylic acid
dispersant, a high boiling hydrocarbon carrier, a low MW carboxylic
acid, i.e., a C.sub.1-5 carboxylic acid and water, optionally in
the presence of an organic solvent. Often, water and other
volatiles are removed, e.g., by distillation, before subjecting the
resulting preliminary dispersion to microwave irradiation.
[0020] No additional solubilizing or dispersing agents, promoters
or reactants such as carbon dioxide, amines, alcohols etc are
needed to obtain the desired metal oxide dispersions and metal
content of up to 40 or 50 weight %, and in certain embodiments
higher, based on the total weight of the dispersion can be
prepared. For example, metal contents of 10%, 15%, 20%, 30%, 35%,
40% and higher can be prepared.
[0021] A specific chemical formula for the composition of the
dispersion is not fully descriptive of the product, and the
molecular structures of the metal oxide complexes of the invention
are not fully known, however, the product obtained is a free
flowing dispersion of predominately submicron metal oxide particles
engulfed by and complexed to a sulfonate or carboxylate dispersant.
Other metal compounds such as traces of metal hydroxide are also
believed to be present.
[0022] The dispersions of the invention can be used as formed or
may be further modified and are effective additives in fuels,
lubricating oils, such as petroleum based fuels and lubricants,
anti corrosive paints, and as part of any formulation containing
similar materials. For example, the stable metal oxide dispersion
of the invention is added to fuels and lubricants used in gas
turbine, boiler, cracking and engine operations etc.
DESCRIPTION OF THE INVENTION
[0023] According to the invention, a preliminary composition, e.g.,
a preliminary dispersion is prepared from a mixture comprising
[0024] a) 5-80%, e.g., 5-50%, of a metal hydroxide, metal oxide or
metal carbonate
[0025] b) 2-15% of a sulfonate or carboxylate dispersant
[0026] c) 10-70% of a high boiling hydrocarbon carrier selected
from mineral oils, alkylated benzenes, oligomers or polymers of
alpha olefins, polycyclic aromatics, alkylated derivatives of
polycyclic aromatics and waxes,
[0027] d) 0-10% of a C.sub.1-5 carboxylic acid,
[0028] e) 0%-30% water
and
[0029] f) 0-60% of an organic solvent,
wherein the percentages are by weight based on the total weight of
the mixture, and then subjected to microwave irradiation to yield a
metal oxide dispersion with average particle size of less than 1
micron.
[0030] The microwave irradiation may be performed with or without
external heating, however it is likely that even without additional
heating the temperature of the reaction mixture will increase.
There is no specific limitation on the type of reaction vessel
used, however, if a sealed vessel is used, common provisions must
be made to account for the build up in pressure, whereas if the
vessel is "open", either exposed to the atmosphere or under an
inert atmosphere at ambient pressure, common provisions must be
made to account for any byproducts, starting materials or solvents
that may evaporate.
[0031] In one embodiment, the preliminary dispersion is prepared by
subjecting the mixture of a) through f) to a preliminary heating
step. In another embodiment, the mixture of a) through f) is
subjected to a preliminary heating step and distillation to remove
volatiles. The distillation may be a separate from the preliminary
heating step, may occur during the preliminary heating step, or
partial distillation may occur during preliminary heating followed
by a second step to complete distillation, for example, a separate
vacuum distillation step or distillation under higher temperatures
or while using certain distillation equipment such as a thin film
evaporator, distillation column etc may be used.
[0032] For example, a mixture comprising a), b), c) and any
optional d), e) and f) above is heated, to temperatures of from
about 85.degree. C. to about 220.degree. C., for example from about
85.degree. C. to about 180.degree. C., often from about 90.degree.
C. to about 150.degree. C., typically the mixture is heated at
reflux, with stirring or other agitation for about 0.25 to 5 hours,
generally 0.5 to 4 hours, for example 1 to 3 hours, during which
time volatiles may be distilled and collected;
[0033] the mixture is then distilled, or further distilled, at a
temperature of from about 125.degree. C. to about 240.degree. C.,
for example from about 150.degree. C. to about 220.degree. C., or
from about 165.degree. C. to about 240.degree. C., optionally under
vacuum; cooled and then subjected to microwave irradiation.
[0034] The time required for microwave irradiation is subject to
various parameters including the intensity and wavelength of
irradiation.
[0035] The metal of the hydroxide, oxide or carbonate is an
alkaline metal or alkaline-earth metal, i.e., Li, Na, K, Rb, Cs,
Fr, Be, Mg, Ca, Sr, Ba or Ra, typically selected from Li, Na, K,
Rb, Cs, Mg, Ca, Sr and Ba. In many embodiments the metal is an
alkaline-earth metal selected from Mg, Ca and Ba, for example,
Mg.
[0036] Excellent results are achieved when the sulfonate or
carboxylate dispersant is an alkylarylsulfonate or alkylaryl
carboxylate dispersant, for example, an alkyl benzene sulfonate. In
the process, there is less than a molar equivalent of the
dispersant present relative to metal hydroxide, oxide or
carbonate.
[0037] In most embodiments of the invention both water and a
C.sub.1-5 carboxlic acid are added to the mixture from which the
preliminary composition is formed. Less than a molar equivalent of
the C.sub.1-5 carboxlic acid is added, relative to metal hydroxide,
oxide or carbonate, often much less than a molar equivalent, but
there can be significantly more than a molar equivalent of water
added. Typically, when water and C.sub.1-5 carboxlic acid are
added, the mixture is subjected to the preliminary heating step
above and volatile distillates are removed, i.e., distilled, prior
to microwave irradiation. Reaction, or complex formation, involving
water, C.sub.1-5 carboxylic acetic acid, metal compound and/or
dispersant may occur during this heating step and volatiles,
including water, may be removed.
[0038] Even if a distillation is performed prior to microwave
irradiation, it may still be necessary to remove water upon
microwave irradiation as it is possible to form water during the
this part of the process. Of course it is desirable to remove most
or all of any added or generated water at some point as the final
product dispersion will contain significantly less than 8% water,
in many cases the final product dispersion will contain less than
2% water, for example, less than 1% water.
[0039] The organic solvent f) is optional and in general is removed
or greatly reduced by distillation before microwave irradiation.
The organic solvent is described in more detail below, has a with a
boiling point below 280.degree. C., generally has a with a boiling
point below 220.degree. C., for example a boiling point ranging
from about 80.degree. C. to about 210.degree. C., and is not the
same as the high boiling hydrocarbon carrier.
[0040] For example, a mixture comprising
[0041] a) 5-50% of a metal hydroxide, metal oxide or metal
carbonate
[0042] b) 2-15% of a sulfonate or carboxylate dispersant
[0043] c) 10-70% of a high boiling hydrocarbon carrier selected
from mineral oils, alkylated benzenes, oligomers or polymers of
alpha olefins, polycyclic aromatics, alkylated derivatives of
polycyclic aromatics and waxes,
[0044] d) 1-10% of a C.sub.1-5 carboxylic acid,
[0045] e) 8%-30% water
and
[0046] f) 0-60% of an organic solvent with a boiling point below
220.degree. C., for example a boiling point ranging from about
80.degree. C. to about 210.degree. C., for example xylene or
mesitylene,
is stirred and heated under reflux for about 0.5 to about 4 hours,
for example from about 0.5 to about 2 hours, for example about 1
hour, and then heated from about 165.degree. C. to about
240.degree. C. to distill off volatiles, resulting in a reaction
mixture which is cooled to below 100.degree. C., for example cooled
to approximately room temperature, and subjected to microwave
irradiation in a commercial microwave (e.g., 2.45 GHz) to a yield
MgO oxide nanoparticle dispersion in excellent yield, with average
particle size expected to be from about 1 to about 100 nm.
[0047] For example, a mixture comprising
[0048] a) 5-40%, typically 10-40%, for example 10-25, of a metal
hydroxide, metal oxide or metal carbonate
[0049] b) 2-10%, for example 3-10%, for example 3-7% of a
dispersant, for example an alkylbenzene sulfonic acid
[0050] c) 10-70%, for example, 10-50%, for example 15-40%, of a
high boiling hydrocarbon carrier,
[0051] d) 1-7%, for example, 1-4% or 2-5% of a C.sub.1-5 carboxylic
acid,
[0052] e) 8%-30%, for example 10%-20%, for example, 12-18%
water
and
[0053] f) 10-60%, for example 20-60%, for example 30-50% of an
organic solvent with a boiling point ranging from about 80.degree.
C. to about 210.degree. C.,
is stirred and heated under reflux for about 0.5 to about 2 hours,
for example about 1 hour, and then heated from about 165.degree. C.
to about 220.degree. C. to distill off volatiles; cooled to
approximately room temperature, and then subjected to microwave
irradiation in a commercial microwave. The dispersion obtained may
be used as is, or further purified, concentrated, diluted or
otherwise modified.
[0054] Most or all of the added water is removed from the
preliminary dispersion by distillation prior to microwave
irradiation, however, the original reaction mixture from which the
preliminary dispersion is prepared typically contains at least 8%,
often at least 10% by weight of water, based on the total weight of
the mixture, and in many embodiments 12% or more. In certain
embodiments, the amount of water is comparable by weight to the
amount of metal hydroxide, oxide or carbonate, and in some
particular embodiments, the weight of water is higher. In terms of
molar equivalents relative to, e.g., metal oxide or metal
carbonate, the reaction mixture contains from about a 5:1 to 1:1
molar ratio of water to metal compound, for example, from about 3:1
to 1:1. Ratios of from 2.5:1 to 1:1, or from 2:1 to 1:1 are common,
such as 1.5, 1.8, 2, 2.2 and 3 molar equivalents of water relative
to metal compound can be employed. The process can also be used to
prepare metal oxide dispersions starting with metal hydroxides, but
in that case, less water is typically added due to the hydroxy
groups present in the starting metal compound.
[0055] The C.sub.1-5 carboxylic acid can be any such acid, for
example, acetic acid, propionic acid, butyric acid, pentanoic acid;
excellent results have been obtained using acetic acid. A small
amount of this acid relative to MgO is generally employed in the
reaction, for example, the molar ratio of MgO to C.sub.1-5
carboxylic acid is from about 100:1 to 2:1, for example, from about
50:1 to about 5:1, or from about 30 to 1 to 10:1, such as a molar
ratio of MgO to C.sub.1-5 carboxylic acid of about 20:1.
[0056] The dispersant is a sulfonic acid or carboxylic acid.
Mixtures of dispersants may be used including mixtures of sulfonic
acids, mixtures of carboxylic acids or mixtures including both
sulfonic and carboxylic acids. Excellent results have been obtained
using sulfonic acid dispersants widely known by those skilled in
the art as oil-soluble sulfonic acids.
[0057] For example, sulfonic acid dispersants be derived from
natural petroleum fractions or various synthetically prepared
sulfonated compounds. Typical oil-soluble sulfonic acids which may
be used include: alkane sulfonic acids, aromatic sulfonic acids,
alkaryl sulfonic acids, aralkyl sulfonic acids, petroleum sulfonic
acids such as mahogany sulfonic acid, petroleum sulfonic acid,
paraffin wax sulfonic acid, petroleum naphthene sulfonic acid,
polyalkylated sulfonic acid, and other types of sulfonic acids
which may be obtained by fuming sulfuric acid treatment of
petroleum fractions. In one embodiment, an alkaryl sulfonic acid,
i.e., an alkylbenzene sulfonic acid, is used as dispersant with
excellent results.
[0058] Carboxylic acid dispersants which may be used are also well
known in the art. The carboxylic acid dispersants are not the same
as the C.sub.1-5 carboxylic acid required for the invention, as the
dispersants have more than 5 carbon atoms, typically much more than
5 carbon atoms. Some examples include, lauric, myristic, palmitic,
stearic, isostearic, archidic, behenic and lignoceric acids;
aromatic acids such as alkyl salicylic acids. Mixtures of
carboxylic acids include commercial grades containing a range of
acids, including both saturated and unsaturated acids. Such
mixtures may be obtained synthetically or may be derived from
natural products, for example, tall, cotton, ground nut, coconut,
linseed, palm kernel, olive, corn, palm, castor, soybean,
sunflower, herring and sardine oils and tallow.
[0059] In many embodiments of the invention, the dispersant is a
naturally occurring or synthetic sulfonic acid. Excellent results
have been obtained using, for example, alkyated arylsulfonic acids,
for example, alkylated benzenesulfonic acids. In general, the
sulfonic acid dispersant will have a MW of 300 or higher, often 350
or higher, for example 400 or higher. Mixtures of sulfonic acids
may be used, for example, alkylated benzene sulfonic acids may be
mono-alkylated, di-alkylated or mixtures of mono- and di-alkylated
compounds may be used and in some embodiments, benzene sulfonic
acid may be alkylated by alkyl chains of varying lengths. In such
cases, the MW is the number average molecular weight. For example,
excellent results have been obtained using alkyated benzene
sulfonic acids with an average MW of from about 350 to 1000.
[0060] In general, a molar ratio of MgO to dispersant of from about
10:1 to 200:1 is employed in the reaction, frequently the ratio is
from about 20:1 to 200:1. In certain embodiments the molar ratio of
MgO to surfactant is from about 20:1 to 100:1 or from about 25:1 to
50:1.
[0061] In many embodiments, the molar ratio of MgO to C.sub.1-5
carboxylic acid, for example acetic acid, is from about 50:1 to
about 5:1 or from 30:1 to10:1 and the molar ratio of MgO to
dispersant, for example, an alkylated sulfonic acid, is from about
20:1 to 100:1 or from about 25:1 to 50:1.
[0062] The high boiling hydrocarbon carrier is a material or
mixture of materials well known in the art with a boiling point of
280.degree. C. or higher, often much higher, for example, mineral
oils, oligomers or polymers of alpha olefins, aromatic systems such
as polycyclic aromatics and alkylated derivatives thereof, long
chain alkanes including waxes and other similar natural or
synthetic materials. Obviously, part of the reasoning for choosing
a high boiling carrier is that part of the process requires
temperatures of 280.degree. C. and higher.
[0063] The optional organic solvent has a boiling point below
280.degree. C., typically 210.degree. C. or lower, and it is
generally desirable to remove it by distillation prior to microwave
irradiation. The solvent can be used to make the initial reaction
mixture more fluid and stirrable during a preliminary heating step,
especially if very low amounts of carrier hydrocarbon are used. The
solvent is chosen so that it does not interfere with the overall
process. For example, well known aliphatic or aromatic hydrocarbons
with boiling points ranging from about 80.degree. C. to about
240.degree. C., for example, boiling points ranging from about
80.degree. C. to about 220.degree. C. and mixtures thereof are
conveniently used, including linear and cycloaliphatic compounds
such as octanes, decanes etc, and aromatic hydrocarbons such as
xylene, mesitylene, ethylbenzene, butyl benzenes, tetralin and the
like. Lower boiling solvents are optional and are readily removed,
if desired, by distillation once the process reactions are
complete.
[0064] The product of the process and the process itself represent
embodiments of the invention.
EXAMPLE
[0065] In a 2000 mL 3-neck round bottom flask, was charged 298
grams of MgO (98%), 120 grams of an alkyl benzene sulfonic acid
dispersant, 500 grams of high boiling hydrocarbon ALCHISOR DE,
1,000 grams of Xylene, 300 grams of water, and 62 grams of glacial
acetic acid under ambient conditions. The mixture was stirred and
heated to reflux for 1 hr. The mixture was further heated to
180.degree. C. to remove all volatiles. The resulting product was
cooled down to room temperature to provide a gray preliminary
dispersion with a small amount of sediment. The preliminary
dispersion was subjected to microwave irradiation in a commercial
microwave (2.45 GHz) to yield MgO oxide nanoparticle dispersion
with average particle size expected to be between 1-100 nm.
* * * * *