U.S. patent application number 09/798600 was filed with the patent office on 2001-11-22 for process for the branching of saturated and/or unsaturated fatty acids and/or alkyl esters thereof.
Invention is credited to Connor, Daniel Stedman, Kenneally, Corey James.
Application Number | 20010044550 09/798600 |
Document ID | / |
Family ID | 22686852 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010044550 |
Kind Code |
A1 |
Kenneally, Corey James ; et
al. |
November 22, 2001 |
Process for the branching of saturated and/or unsaturated fatty
acids and/or alkyl esters thereof
Abstract
A process for the branching of saturated and/or unsaturated
fatty acids and/or alkyl esters thereof comprises subjecting the
fatty acids and/or alkyl esters to a skeletal isomerization
reaction using a catalyst comprising a crystalline porous structure
having incorporated therein a metal to form metal sites on said
catalyst and isolating branched fatty acids, alkyl esters thereof,
or mixtures thereof, from a reaction mixture obtained by said
skeletal isomerization reaction. The catalyst used in the
isomerization reaction is preferably a zeolite catalyst containing
metal sites of a Group VIII metal. The process produces a mixture
of fatty acids and/or alkyl esters that contain significant
quantities of branched molecules.
Inventors: |
Kenneally, Corey James;
(Mason, OH) ; Connor, Daniel Stedman; (Cincinnati,
OH) |
Correspondence
Address: |
THE PROCTER & GAMBLE COMPANY
PATENT DIVISION
IVORYDALE TECHNICAL CENTER - BOX 474
5299 SPRING GROVE AVENUE
CINCINNATI
OH
45217
US
|
Family ID: |
22686852 |
Appl. No.: |
09/798600 |
Filed: |
March 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60186924 |
Mar 3, 2000 |
|
|
|
Current U.S.
Class: |
554/125 ;
554/124 |
Current CPC
Class: |
C07C 51/353 20130101;
C07C 51/353 20130101; C07C 51/353 20130101; C07C 57/02 20130101;
C07C 69/24 20130101; C07C 53/126 20130101; C07C 67/333 20130101;
C07C 67/333 20130101 |
Class at
Publication: |
554/125 ;
554/124 |
International
Class: |
C11C 003/14 |
Claims
What is claimed is:
1. A process for branching saturated and/or unsaturated fatty acids
and/or alkyl esters thereof comprising the steps of: (a) subjecting
a feedstock comprising saturated and/or unsaturated fatty acids
having from 3 to 25 carbon atoms, alkyl esters thereof, or mixtures
thereof, to a skeletal isomerization reaction using a catalyst
comprising a crystalline porous structure having incorporated
therein a metal to form metal sites on said catalyst; and (b)
isolating branched fatty acids, alkyl esters thereof, or mixtures
thereof, from a reaction mixture obtained by said skeletal
isomerization reaction.
2. The process of claim 1 wherein said crystalline porous structure
is a crystalline microporous structure.
3. The process of claim 2 wherein said crystalline microporous
structure is a zeolite.
4. The process of claim 3 wherein said zeolite is selected from the
group consisting of pentacyl zeolite, beta zeolite, mordenite, and
mixtures thereof.
5. The process of claim 4 wherein said zeolite has a median pore
diameter of from about 4 angstroms to about 9 angstroms.
6. The process of claim 1 wherein said metal to form metal sites is
a Group VIII metal.
7. The process of claim 6 wherein said metal sites are located
within pores of said crystalline porous structure.
8. The process of claim 6 wherein said Group VIII metal is selected
from the group consisting of platinum, nickel, palladium, and
mixtures thereof.
9. The process of claim 8 wherein said metal to form metal sites is
platinum.
10. The process of claim 1 wherein said skeletal isomerization
reaction is carried out in the presence of a hydrogen gas.
11. The process of claim 10 wherein said skeletal isomerization
reaction is carried out in the presence of an additional gas
selected from the group consisting of nitrogen, carbon dioxide,
argon, and mixtures thereof, and wherein a concentration of said
hydrogen gas is at least about 1% of the total headspace.
12. The process of claim 10 wherein said skeletal isomerization
reaction is further carried out in the presence of a supercritical
fluid selected from the group consisting of carbon dioxide, ethene,
ethane, propane, and mixtures thereof.
13. The process of claim 10 wherein said skeletal isomerization
reaction is carried out at a pressure of less than 1000 pounds per
square inch gauge (psig).
14. The process of claim 1 wherein said skeletal isomerization
reaction is carried out at a temperature of from about 240.degree.
C. to about 380.degree. C.
15. The process of claim 1 wherein said feedstock comprises less
than about 50%, by weight of said feedstock, of unsaturated fatty
acids, alkyl esters thereof, or mixtures thereof.
16. The process of claim 15 wherein said feedstock comprises
saturated fatty acids, alkyl esters thereof, or mixtures thereof
and is essentially free of unsaturated fatty acids, alkyl esters
thereof, or mixtures thereof.
17. The process of claim 1 wherein a ratio of said saturated and/or
unsaturated fatty acids, alkyl esters thereof, or mixtures thereof,
to said catalyst is from about 5:1 to about 1000:1, by weight.
18. The process of claim 1 wherein said process further comprises a
recycle step, wherein said recycle step comprises the steps of: (a)
subjecting said reaction mixture, wherein said reaction mixture is
substantially free of branched fatty acids, alkyl esters thereof,
or mixtures thereof, to a recycle skeletal isomerization reaction
using said catalyst; and (b) isolating branched fatty acids, alkyl
esters thereof, or mixtures thereof, from a recycle reaction
mixture obtained by said recycle skeletal isomerization reaction.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/186,924, filed Mar. 3, 2000.
TECHNICAL FIELD
[0002] The present invention relates to a process for the branching
of saturated and/or unsaturated linear fatty acids and/or alkyl
esters thereof utilizing a crystalline, porous solid acid catalyst,
such as a zeolite, which also contains metal sites.
BACKGROUND OF THE INVENTION
[0003] Branched alkyl fatty acids and alkyl esters are useful in a
number of consumer products, including surfactants, fabric
conditioners, cosmetics, and lubricants. Branched fatty acids and
alkyl esters which are saturated offer a number useful features,
including lubricity/surfactancy due to their chain length and
random branching, oxidative stability due to little or no
carbon--carbon double bonds present, and low crystallinity over a
wide range of temperatures due to a significantly lower melt point
compared to their linear counterparts.
[0004] A number of various processes for making branched fatty
acids and esters have been previously disclosed. One approach
involves the exclusive use of unsaturated fatty acids or alkyl
ester feedstocks using a microporous catalyst. For example, U.S.
Pat. No. 5,856,539, issued Jan. 5, 1999 to Hodgson et al.,
discloses a process for converting unsaturated fatty acids into
branched fatty acids by using catalysts having a microporous
structure, such as zeolites. In addition, U.S. Pat. No. 5,677,473,
issued Oct. 14, 1997 to Tomifuji et al., discloses a process for
preparing branched chain fatty acids or alkyl esters by subjecting
unsaturated fatty acids or esters having 10 to 25 carbon atoms to a
skeletal isomerization reaction in the presence of water or a lower
alcohol using a zeolite catalyst having a linear pore structure
that is small enough to minimize dimerization and large enough to
allow diffusion of the branched molecules. Both of these patents
have numerous disadvantages, including high feedstock costs (i.e.
oleic acid), relatively high yields of by-products such as
oligomers, and high equipment capital costs due to the need for
custom separation processes (i.e. molecular distillation to recover
dimers and trimers).
[0005] A second approach involves the use of saturated fatty acids
and non-microporous catalysts. For example, U.S. Pat. No.
3,090,807, issued May 21, 1963 to Illing, describes the branching
of saturated aliphatic carboxylic acids by heating with carbon
monoxide in the presence of (a) a metal carbonyl, (b) a halogen,
such as chlorine, bromine, or iodine, (c) an activator, such as
compounds of bismuth, antimony, titanium, boron, iron, or tin, and
(d) water. In addition, WO 98/07680 published Feb. 26, 1998 by
Roberts et al., describes the branching of saturated or unsaturated
fatty acids or their derivitives using a binary ionic liquid
catalyst, such as a metal chloride and/or an organic or inorganic
halide salt. Both of these patents have numerous disadvantages,
including high operating costs associated with using the types of
catalysts described above, high equipment capital costs associated
with corrosion prevention when using halogens or ionic liquids, and
also the environmental issues associated with disposal of these
materials.
[0006] A third approach is a totally synthetic based route to
making branched fatty acids or alkyl esters. Ullman's Encyclopedia
of Industrial Chemistry (Volume A5, 5.sup.th Ed., 1986, pp.
239-240) describes four different approaches to making synthetic
fatty acids, including carbonylation of olefins, carboxylation of
olefins, oxidation of alkanes, and alkali fusion of alcohols. The
first two approaches result in significant quantities of branched
molecules. Carbonylation of olefins is currently the principal
method for the commercial production of C.sub.4-C.sub.13 carboxylic
acids. Because of the complex nature of the olefinic raw materials,
the higher carboxylic acids obtained in this process (C.sub.8 and
higher) are usually mixtures of branched chain products. The
disadvantages of these types of approaches to making branched acids
and/or alkyl esters include the high capital cost and yield losses
associated with a multi-step synthetic route (i.e. linear olefin
synthesis, olefin branching, hyroformulation, and oxidation for the
carbonylation process) vs. that of the natural route (i.e
hydrolysis of triglycerides, followed by branching of the fatty
acid), as well as the undesirability of using non-renewable,
petroleum based feedstocks as opposed to using renewable, natural
based fatty acid or methyl ester feedstocks.
[0007] Crystalline, microporous solid acid catalysts, containing
metal sites have also been disclosed. For example, U.S. Pat. No.
4,882,307, issued Nov. 21, 1989 to Tsao discloses a process for
preparing noble metal-containing zeolites having high metal
dispersion. The catalysts are used in processes such as
hydrogenation, dehydrogenation, dehydrocyclization, isomerization,
hydrocracking, dewaxing, and reforming of materials such as
hydrocarbons. However, these types of catalysts have not heretofor
been used to catalyze isomerization reactions to branch saturated
and/or unsaturated fatty acids and/or alkyl esters thereof.
[0008] It is the object of the present invention to create an
efficient process for branching saturated or unsaturated fatty
acids and/or alkyl esters thereof to achieve significant quantities
of branched molecules using a crystalline, microporous solid acid
catalyst, such as a zeolite, with metal sites present.
[0009] It is a further object of the present invention to create a
process that uses renewable, natural-based feedstocks such as
linear fatty acids derived from vegetable or animal sources, which
is also environmentally friendly from the standpoint of waste
disposal of catalysts or other process aids.
SUMMARY OF THE INVENTION
[0010] The present invention encompasses a process for branching
saturated and/or unsaturated fatty acids and/or alkyl esters
thereof comprising the steps of:
[0011] (a) subjecting a feedstock comprising saturated and/or
unsaturated fatty acids having from 3 to 25 carbon atoms, alkyl
esters thereof, or mixtures thereof, to a skeletal isomerization
reaction using a catalyst comprising a crystalline porous structure
having incorporated therein a metal to form metal sites on said
catalyst; and
[0012] (b) isolating branched fatty acids, alkyl esters thereof, or
mixtures thereof, from a reaction mixture obtained by said skeletal
isomerization reaction.
[0013] The catalyst utilized in the present process is preferably a
zeolite catalyst containing metal sites of Group VIII metal. The
process is carried out in the presence of hydrogen gas, or a
mixture of gases including hydrogen gas, under pressure.
[0014] The present invention further encompasses the present
process further comprising a recycle step in which higher yields of
branched molecules can be obtained.
DETAILED DESCRIPTION OF THE INVENTION
[0015] It has now been found that it is possible to convert (by
isomerization) a feed of fatty acids and/or alkyl esters comprising
saturated and/or unsaturated fatty acids and/or alkyl esters
thereof (e.g. oleic, stearic, palmitic, myristic) into a mixture
which has a significant content of branched fatty acids and/or
alkyl esters. In the present process, a fatty acid and/or alkyl
ester feed comprising either saturated and/or unsaturated fatty
acids and/or alkyl esters is contacted with a catalyst, wherein the
catalyst comprises a material having a crystalline microporous
structure containing metal sites, preferably a zeolite catalyst
containing metal sites, particularly Group VIII metal sites. The
reaction which is the subject of this invention can be seen as an
isomerization reaction (involving both skeletal and positional
isomerization). The branching reaction is herein included.
[0016] The process of the present invention is to prepare branched
chain fatty acids and/or alkyl esters thereof from either saturated
and/or unsaturated fatty acids and/or alkyl esters having a total
carbon number of from about 3 to about 25, comprising at least a
step wherein skeletal isomerization is carried out at a temperature
of from about 240.degree. C. to 380.degree. C., preferably in the
presence of a gas selected from the group consisting of hydrogen,
nitrogen, carbon dioxide, argon, and mixtures thereof, using a
zeolite catalyst having a linear pore structure with a pore size
small enough to retard oligomerization and aromatization, and large
enough to allow diffusion of branched chain saturated fatty acids
and/or alkyl esters thereof.
[0017] When a starting material mixture contains both fatty acids
and alkyl esters thereof, both branched chain fatty acids and alkyl
esters, thereof can be produced, because both can be isomerized
simultaneously. Such cases are also included in the technical scope
of the present invention.
[0018] The saturated and/or unsaturated fatty acid and/or alkyl
ester used as the starting material are fatty acids and/or alkyl
esters having a total carbon number of from about 3 to 25,
preferably from about 10 to about 25, and more preferably from
about 12 to about 24. Considering industrial applications, it is
further preferable that a major component of the starting material
has a total carbon number of about 18, such as stearic acid.
Branched fatty acids having a total carbon number of this range are
useful as starting materials for the synthesis of fabric
conditioners, cosmetic bases, lubricating oil additives, and the
like.
[0019] In the processes of the present invention, the starting
material can be a saturated and/or unsaturated fatty acid and/or
alkyl ester, and mixtures thereof. In a preferred process wherein
the reaction is carried out in the presence of hydrogen gas, or a
mixture of gases including hydrogen gas, any unsaturated molecules
present tend to be quickly hydrogenated into saturated fatty acids
and/or alkyl esters in the process described. It is preferable that
the content of the unsaturated molecules in the starting material
be kept below 50%, more preferably below 10%, most preferably below
1%, in order to minimize formation of by-products such as oligomers
in the process. In a preferred embodiment, the starting material
(i.e. the feedstock) in the present process comprises saturated
fatty acids and/or alkyl esters and is essentially free of
unsaturated fatty acids and/or alkyl esters. Catalytic
hydrogenation can also be used to convert all or some of the
unsaturated molecules present in the feedstock into the
corresponding saturated molecules prior to using the branching
process described herein.
[0020] Suitable fatty acids include oleic acid, stearic acid,
palmitic acid, and myristic acid, which can be produced by
hydrolysis of triglycerides of vegetable or animal origin,
including beef tallow, palm oil, palm kernal oil, coconut oil, tall
oil, canola oil, and soybean oil. Synthetic fatty acids produced
from petrochemical feedstocks which are substantially linear can
also be used. The starting material can be a mixture containing one
or more of these saturated or unsaturated fatty acids, or alkyl
esters thereof
[0021] From the viewpoint of minimizing cost of the branched fatty
acids and/or alkyl esters, it is preferable that the
above-described starting material be derived from low cost
feedstocks such as tallow or soybean oil, which are typically rich
in stearic and palmitic acids.
[0022] Alkyl esters of saturated and/or unsaturated fatty acids
having a total carbon number of from about 3 to about 25,
preferably from about 10 to about 25, and more preferably from
about 12 to about 24, used as a starting material are those
corresponding to the above-described saturated fatty acids. That
is, alkyl esters of the saturated and/or unsaturated fatty acids
exemplified above can be used. Although the alkyl moiety is not
subject to limitation as to carbon number, its carbon number is
normally 1 to 4, preferably 1. Specific examples of alkyl esters
include methyl esters, ethyl esters and propyl esters of the
above-mentioned saturated and/or unsaturated fatty acids, with
preference given to methyl esters.
[0023] Catalysts used in the processes of the present invention are
generally crystalline porous structures containing metal sites.
Suitable crystalline porous structures useful in the present
processes include both mesoporous and microporous structures. As
used herein, the term "mesoporous" refers to structures containing
pores having diameters of from about 10 to about 100 angstroms, and
the term "microporous" refers to structures containing pores having
diameters of less than about 10 angstroms. Preferably, the catalyst
has a crystalline microporous structure. The catalysts herein
typically have an acidic crystalline porous structure.
[0024] Crystalline microporous structures generally encompass two
broad classes of materials, zeolites and non-zeolites. Zeolites are
three dimensional networks built up of TO.sub.4 tetrahedra
(T.dbd.Si or other heteroatom) such that each of the four oxygen
atoms is shared with another tetrahedron. The most common forms are
aluminosilicates, although structures containing boron, gallium, or
iron in place of aluminum and germanium in place of silicon have
been reported. See, e.g., L. L. Hegedus, CATALYST DESIGN, PROGRESS
AND PERSPECTIVES, p. 165 (Wiley, 1987), which is incorporated by
reference herein. Non-zeolitic microporous structures typically
contain AlO.sub.2 and PO.sub.2 oxide units. They can contain
silicon and/or one or more metals other than aluminum which will
form oxide linkages in tetrahedral coordinates with aluminum and
phosphorous in a crystalline network. Common forms are
aluminophosphates (AlPO's) and silicoaluminophosphates (SAPO's),
the latter with tetrahedrally coordinated AlO.sub.2, PO.sub.2 and
SiO.sub.2 units. Other forms in this category include MO.sub.2,
AlO.sub.2 and PO.sub.2 tetrahedrally bound structural oxide units,
wherein M is selected from the group consisting of arsenic,
beryllium, boron, chromium, cobalt, gallium, vanadium, and zinc.
See, e.g., U.S. Pat. No. 5,741,759 issued Apr. 21, 1998 to Gee et
al., which is incorporated by reference herein.
[0025] Preferably, the crystalline microporous catalyst used in the
present process is a zeolite possessing a unidimensional pore
topology. A preferred zeolite of this type is mordenite. As
previously discussed, zeolites typically consist of a microporous
network of SiO.sub.4 and AlO.sub.4 tetrahedra linked together via
shared oxygen atoms. Aluminum has a (3+) valency resulting in an
excess negative charge on the AlO.sub.4 tetrahedra, which can be
compensated by H.sup.+ or other cations (Na.sup.+, NH.sup.4+,
Ca.sup.2+). When M is hydrogen the materials are Bronsted acidic,
when M is for example Cs the materials are basic. Upon heating,
Bronsted acidic hydroxyls condense creating coordinately
unsaturated Al, which acts as a Lewis acid site. The acid strength,
acid site density and Bronsted versus Lewis acidity are determined
by the level of framework aluminium. The ratio of silica/alumina
can be varied for a given class of zeolites either by controlled
calcination, with or without the presence of steam, optionally
followed by extraction of the resulting extraframework aluminium or
by chemical treatment employing for example ammonium
hexafluorosilicate. It has been found that when a zeolite
containing metal sites is used as a catalyst for achieving a high
selectivity of branched fatty acid and/or alkyl esters, the
catalyst preferably comprises a 10 member ring or a 12 member
ring.
[0026] The pore topology of the preferred zeolite catalysts herein
can impact the efficiency and the shape selectivity of the
catalyst. Shape selectivity refers to the size and shape of the
molecules that are allowed to enter and leave the pores of the
catalyst. Examples of shape selectivity in the present invention
include the size and number of branched chains which are isomerized
within the parent molecule and the size and concentration of
by-products such as substituted aromatics and oligomers which are,
generated during the course of the reaction. The zeolite catalysts
preferred herein typically have the following characteristics: a
median pore diameter of from about 4 angstroms to about 9
angstroms, more preferably from about 5 angstroms to about 6
angstroms; and a Langmuir surface area of from about 50 m.sup.2/g
to about 900 m.sup.2/g, more preferably from about 400 m.sup.2/g to
about 750 m.sup.2. In order to maximize Bronsted acidity, the
Na.sub.2O content of the zeolite is preferably minimized in that
the preferred zeolites contain less than about 20% Na.sub.2O,
preferably less than about 10% Na.sub.2O, and more preferably less
than about 0.1% Na.sub.2O.
[0027] The silica/alumina molar ratio (SiO.sub.2/Al.sub.2O.sub.3
ratio) of the present zeolite catalysts, which can be determined by
atomic absorption photometry, is preferably from about 3 to about
300, and more preferably from about 20 to about 100.
[0028] Preferred zeolite catalysts for use herein include pentacyl
zeolite (i.e. zeolite ZSM-5), beta zeolite, and/or mordenite. In
the present invention, any zeolite can be used, however, the
zeolites described above are preferred from the viewpoint of pore
size, heat resistance, acid resistance and acid properties. Beta
zeolite and pentacyl zeolites are available only as a synthetic
substance; while mordenite is available both as a natural substance
and as a synthetic substance. The term "pentacyl type zeolite" as
used herein, also referred to as ZSM-5 type, is a zeolite composed
of oxygen 10-membered ring wherein zigzag pore pathways intersect
tunnel-like pore pathways at right angles to form pores. Beta type
zeolite is composed of oxygen 12-membered rings, where two of the
pore dimensions are elliptical and the third is nearly circular.
The mordenite type zeolite, the highest in silicon content among
naturally-occurring zeolites, is a zeolite composed of 12-membered
rings wherein the pores are formed mainly by tunnel-like pore
pathways [Shokubai Koza, Vol. 10, edited by the Catalysis Society
of Japan, Kodansha Ltd. (1986)]. Although these zeolites can be
synthesized by hydrothermal synthesis [J.C.S., 2158 (1948)], they
are also commercially available. For example, commercial products
of the pentacyl type include CBV 3024 (having a
SiO.sub.2/Al.sub.2O.sub.3 ratio of 30), CBV 8014 (having a
SiO.sub.2/Al.sub.2O.sub.3 ratio of 80), and CBV 28014 (having a
SiO.sub.2/Al.sub.2O.sub.3 ratio of 280) available from Zeolyst
International of Valley Forge, Pa. Commercial products of the
mordenite type include CBV 20A (having a SiO.sub.2/Al.sub.2O.sub.3
ratio of 20) and CBV 90A (having a SiO.sub.2/Al.sub.2O.sub.3 ratio
of 90) available from Zeolyst International. Commercial beta
zeolite products include CP814E (having a SiO.sub.2/Al.sub.2O.sub.3
ratio of 25) available from Zeolyst International.
[0029] Other suitable classes of zeolites for performing the
reaction according to the present invention are the zeolites
belonging to the classes of zeolites L and zeolite omega. Zeolites
L (including their preparation) have been described in WO 91/06367.
Zeolites omega have been described in GB 1,178,186.
[0030] It has been found that incorporating metal sites into the
zeolite catalyst will effectively isomerize saturated and/or
unsaturated fatty acids and/or alkyl esters into branched
molecules. While not wishing to be bound by theory, it is believed
that the reaction mechanism consists of the following steps. First,
any unsaturated fatty acids and/or alkyl esters present are rapidly
hydrogenated to their corresponding saturated forms over the metal
sites of the catalyst. Second, the saturated fatty acids and/or
alkyl esters are randomly dehydrogenated over the metal sites to
form low concentrations of unsaturated molecules. Third, the
unsaturated fatty acid and/or methyl ester thus formed is
skeletally and positionally isomerized over the acid sites of the
catalyst. Fourth, the unsaturated, isomerized molecule is
rehydrogenated over the metal sites to form the saturated, branched
molecule. The preferred zeolite catalysts, previously described,
are doped with a metal to form metal sites on the catalyst.
Preferably, the zeolite catalyst is doped with a Group VIII metal
such as iron, cobalt, nickel, ruthenium, rhodium, palladium,
osmium, iridium, and/or platinum. The metal incorporated in the
zeolite catalyst is preferably selected from the group consisting
of platinum, palladium, nickel, and mixtures thereof. In a more
preferred embodiment, the zeolite catalyst is doped with platinum
to form platinum sites on the catalyst.
[0031] Metal sites are incorporated in the present zeolite
catalysts via a number of processes known in the art including
incipient wetness impregnation, ion exchange, vapor deposition, and
the like. Suitable processes for preparing zeolite catalysts
containing metal sites are described in Romero et al., IND. ENG.
CHEM. RES. 36, 3533-3540 (1997), 37, 3846-3852 (1998); Canizares et
al., IND. ENG. CHEM. RES. 36, 4797-4808 (1997); Girgis et al., IND.
ENG. CHEM. RES. 35, 386-396 (1996); which are all hereby
incorporated by reference herein. The amount of metal incorporated
in the catalyst is typically from about 0.1% to about 10%, by
weight of the catalyst. If platinum and/or palladium is
incorporated in the catalyst, it is typically at a level of from
about 0.1% to about 2%, preferably from about 0.5% to about 1.5%,
by weight of the catalyst. If nickel is incorporated in the
catalyst, it is typically at a level of from about 1% to about 10%,
preferably from about 3% to about 7%, by weight of the
catalyst.
[0032] The metal sites can be incorporated either on the surface of
the catalyst or within the pores of the catalyst, or both. In a
preferred embodiment, the metal sites are incorporated within the
pores of the zeolite catalyst. It is believed that incorporating
the metal within the pores of the zeolite catalyst is more
effective in isomerizing saturated fatty acids and/or alkyl esters
into branched molecules as opposed to other types of molecules such
as alkanes, substituted aromatics, or oligomers. The percent metal
dispersion, as measured by CO chemisorption, is typically from
about 0.5% to about 100% and preferably at least about 50%.
[0033] The isomerization reaction step in the present invention is
carried out using the above-described starting material, catalyst
containing metal sites, as described hereinbefore. As for specific
reaction conditions, it is preferable that the reaction be carried
out at a temperature of from about 240.degree. C. to about
380.degree. C., preferably from about 280.degree. C. to about
350.degree. C., and more preferably from about 320.degree. C. to
about 340.degree. C. The amount of catalyst, preferably a zeolite
catalyst containing metal sites as described hereinbefore, used in
the present reaction is typically from about 0.1% to about 20%,
preferably from about 0.5% to about 10%, and more preferably from
about 1% to about 6%, by weight of the reaction mixture.
[0034] The reaction is carried out in the presence of hydrogen gas,
or in a mixture of gases including hydrogen gas, such as nitrogen,
carbon dioxide, argon, and mixtures thereof. Hydrogen gas is both
generated and consumed in the course of the present reaction, and
as such is required to be present in the headspace of the reactor.
It is preferable to have a net input of hydrogen gas into the
present process during the reaction step in order to bring the
reaction to completion. Hydrogen is generated during
dehydrogenation of the alkyl chain prior to the isomerization step,
then consumed during rehydrogenation of the alkyl chain after the
isomerization step is completed. Hydrogen is also consumed if there
are any significant levels of unsaturated carbon bonds in the
starting feedstock, which are hereby converted into saturates in
the course of the isomerization reaction.
[0035] The present process can further include carrying out the
reaction in the presence of a supercritical fluid selected from the
group consisting of carbon dioxide, ethene, ethane, propane, and
mixtures thereof. The supercritical fluid can speed the overall
rate of reaction by greatly increasing the solubility of hydrogen
gas into the liquid phase of the reaction.
[0036] Also, the reaction is preferably carried out in a closed
system, e.g. utilizing an autoclave, where the reaction pressure is
normally less than about 1000 pounds per square inch gauge (psig),
preferably from about 10 to about 300 psig, and more preferably
from about 50 to about 100 psig. Low pressure is recommended is to
prevent vaporization of low boiling substances in the system
including those substances contained in the catalyst. Higher
pressures are less desirable, in that they are associated with more
side reactions, e.g. cracking to alkanes.
[0037] The process of the present invention typically takes from
about 0.1 to about 24 hours, preferably from about 0.5 to about 12
hours, and more preferably from about 1 to about 6 hours. Since the
catalyst tends to be poisoned by coke during the reaction, the
reaction normally takes from about 1 to about 10 hours. If this
problem is overcome, the reaction time can be shortened to several
minutes or even several seconds. Also, continuous reaction becomes
possible. Excessively long reaction time tends to cause thermal
decomposition, resulting in decreased yield.
[0038] The reaction apparatus used is preferably an autoclave,
because a pressurized reaction system is preferred, but the
reaction can also be carried out in a reactor such as a stirred
tank or fixed bed reactor. The atmosphere in the apparatus (i.e.
headspace) is at least about 1% hydrogen, preferably from about 1%
to about 100% hydrogen, more preferably from about 50% to about
100% hydrogen, and still more preferably from about 90% to about
100% hydrogen.
[0039] The product obtained by the above-described isomerization
reaction contains branched chain saturated fatty acids or esters
thereof, when the starting material is a corresponding linear fatty
acid or ester, with a high selectivity. The selectivity of branched
molecules in the product resulting from the present process is
typically from about 1% to about 99%, preferably from about 50% to
about 99%, and more preferably from about 75% to about 99%. The
branched chain fatty acids, etc. thus obtained normally have alkyl
side chains of 1 to 4 carbon atoms. They are normally obtained as a
mixture of many isomers with different branching positions. Other
components can include alkanes, substituted aromatics, oligomers,
and any unreacted linear fatty acid and/or alkyl ester.
[0040] The unreacted linear fatty acid and/or alkyl ester in the
product mixture can often be converted further into branched
molecules by further reaction with catalyst and hydrogen gas. This
can be achieved by subjecting the entire product mixture to further
reaction, or more preferably, by separating the unreacted linear
molecules from the rest of the product mixture and reacting further
only this portion of the product stream. This can be efficiently
done in a continuous process by recycling the unreacted linear
molecules and mixing them with fresh material entering the reaction
zone. The reactor preferably converts at least 10% of the linear
fatty acid or alkyl ester fed into the reaction zone, more
preferably at least 50%.
[0041] As mentioned previously, the catalyst tends to be subject to
coking, either with unsaturated molecules or with carbon. It is
possible to regenerate the catalyst by treatment with an
appropriate solvent, such as hexane or octane, followed by drying,
calcination, and reduction of the catalyst, the latter being done
typically in the presence of hydrogen gas in a muffle furnace.
[0042] In order to isolate the branched fatty acid and/or alkyl
ester from the rest of the product mixture, a number of separation
processes can be performed after the reaction step is complete.
Suitable separation processes include, but are not limited to:
filtration to recover catalyst, distillation to remove oligomers,
solvent or non-solvent based crystallization to remove and recycle
the unreacted fatty acid and/or alkyl ester, and/or distillation to
remove alkanes and/or aromatics.
[0043] All of the documents and references referred to herein are
incorporated by reference, unless otherwise specified. All parts,
ratios, and percentages herein, in the Specification, Examples, and
Claims, are by weight and all numerical limits are used with the
normal degree of accuracy afforded by the art, unless otherwise
specified.
[0044] The following are non-limiting examples of the catalysts and
processes of the present invention. The products of the exemplified
processes are analyzed using gas chromatography with a flame
ionization detector to determine the content of linear chains,
branched chains, alkanes, and substituted aromatics in the products
of the processes. The calculated selectivity to branched chains of
a given process is then calculated based upon the following
formula:
(% of branched chains in product)/(% of converted linear
chains).times.100%
EXAMPLE 1
[0045] This example demonstrates the performance of a
platinum-doped beta zeolite in the skeletal isomerization of
stearic acid.
[0046] A platinum doped beta zeolite catalyst is prepared according
to the following procedure. About 5.6 grams of zeolite
ammonium-beta (Zeolyst, CP 814E) is pre-calcined at 450.degree. C.
for 4 hours in a muffle furnace. A solution of 0.075 grams hydrogen
hexachloroplatinate (IV) hydrate and 5.425 grams of distilled water
is used to impregnate the catalyst. After impregnation, the
catalyst is placed in a muffle furnace and dried at 110.degree. C.
for 14 hours, calcined again at 450.degree. C. for 5 hours, then
reduced at 410.degree. C. for 5 hours in the presence of 500 cc/min
of flowing H.sub.2 gas. The catalyst, prepared according to the
above procedure, has the following properties: surface area of 525
m.sup.2/gr, strong acidity of 0.03 meq/gyr, Pt metal content of
0.4%, and metal dispersion of 20%.
[0047] About 80 grams of stearic acid and 4 grams of Pt/beta
zeolite, prepared as described above, are placed in a 300 ml. batch
autoclave and mixed for 6 hours at a temperature of 340.degree. C.
in the presence of 100 psig hydrogen gas. The product from the
reaction is filtered to remove the catalyst, and then distilled at
180.degree. C. and 3 mm Hg pressure to separate the monomer
fraction from any higher molecular weight components. The yield of
monomer fraction from distillation is 95% and has the following
composition:
1 linear chain fatty acid 80.6% branched chains fatty acid 6%
alkanes 6% substituted aromatics 7.4% The calculated selectivity to
branched chain fatty acid (as a percentage of the material
converted) is 30%.
[0048] The unreacted linear chains are then separated by solvent
crystallization. About 50 grams of the monomer fraction from
distillation is mixed with 100 grams of hexane and chilled to
-15.degree. C. with agitation. The liquid fraction is then filtered
from the solid fraction. The yield of the liquid and solid
fractions from crystallization are 18.5% and 81.5%, respectively.
Both fractions are analyzed by gas chromatography on a solvent free
basis for weight % of each component.
2 liquid fraction linear chain fatty acid 4% branched chain fatty
acid 28% alkanes 28% substituted aromatics 40% solid fraction
linear chain fatty acid 98% branched chain fatty acid 1% alkanes 1%
substituted aromatics not detected
EXAMPLE 2
[0049] This example is similar to Example 1 except that stearic
methyl ester is used instead of stearic acid. Using the same
catalyst, reaction and separation conditions, the composition of
the monomer fraction from distillation is as follows:
3 linear chain methyl ester 91.3% branched chain methyl ester 4.1%
alkanes 1.6% substituted aromatics 3% The calculated selectivity to
branched chain methyl ester is 47%.
[0050] Solvent crystallization with hexane is performed using the
same conditions. The yield of the liquid and solid fractions from
crystallization is 7.5% and 92.5%, respectively, on a solvent-free
basis. Weight % compositions of each fraction are as follows:
4 liquid fraction linear chain methyl ester 23% branched chain
methyl ester 27% alkanes 10% substituted aromatics 40% solid
fraction linear chain methyl ester 97% branched chain methyl ester
2% alkanes 1% substituted aromatics not detected
EXAMPLE 3
[0051] This example demonstrates similar performance between a
fresh and a regenerated platinum-doped, beta zeolite catalyst.
[0052] About 125 grams of stearic acid and 5 grams of Pt/beta
zeolite are placed in a 300 ml. batch autoclave and mixed for 6
hours at a temperature of 340.degree. C. in the presence of 100
psig hydrogen gas. The product from the reaction is filtered to
remove the catalyst, and has the following composition:
5 linear chain fatty acid 97.7% branched chain fatty acid 1.1%
alkanes 1.2% substituted aromatics not detected The calculated
selectivity to branched chain fatty acid is 48%.
[0053] Regeneration is done according to the following procedure.
The catalyst is first washed with hexane solvent at 70.degree. C.,
filtered, and then dried in a muffle furnace at 80.degree. C. for 6
hours. Then it is calcined at 425.degree. C. for 7 hours, and
reduced at 425.degree. C. for 7 hours in the presence of 500 cc/min
of flowing H.sub.2 gas.
[0054] The performance of the regenerated catalyst is demonstrated
with fresh stearic acid. About 80 grams of stearic acid and 4 grams
of regenerated catalyst are reacted using the same conditions as
described above. The product from the reaction is filtered to
remove the catalyst, and has the following composition:
6 linear chain fatty acid 97% branched chain fatty acid 1.4%
alkanes 1.6% substituted aromatics not detected The calculated
selectivity to branched chain fatty acid is 47%.
EXAMPLE 4
[0055] This example demonstrates that the product from reaction can
be recycled and run to a higher conversion using fresh
platinum/beta zeolite catalyst, with consistent reaction
selectivity to branched chains.
[0056] In the first reaction, 125 grams of stearic acid and 5 grams
of Pt/beta zeolite are placed in a 300 ml. batch autoclave and
mixed for 6 hours at a temperature of 340.degree. C. in the
presence of 100 psig hydrogen gas. The product from the reaction is
filtered to remove the catalyst, and has the following
composition:
7 linear chain fatty acid 95% branched chain fatty acid 3% alkanes
2% substituted aromatics not detected The calculated selectivity to
branched chain fatty acid is 60%.
[0057] In the second reaction, 80 grams of the product from the
first reaction and 3.65 grams of fresh Pt/Beta zeolite are placed
in the autoclave and run under similar conditions to that reported
above. The product from the second reaction is filtered, and has
the following composition:
8 linear chain fatty acid 90.7% branched chain fatty acid 5.4%
alkanes 3.9% substituted aromatics not detected The calculated
selectivity to branched chain fatty acid is 58%.
COMPARATIVE EXAMPLE 1
[0058] This example shows that both a platinum-doped alumina
catalyst and a platinum/chloride doped alumina catalyst have little
or no activity for the skeletal isomerization of stearic acid.
These catalysts have historically been used in the skeletal
isomerization of short chain alkanes such as pentane or hexane
(Belloum et al., Revue do L'Institut Francais Du Petrole 46, 92-93,
1991).
[0059] The 5% platinum on alumina catalyst is available from
Aldrich Chemical Co. (#31,132-4). The platinum/chloride doped
alumina catalyst is prepared using the following procedure, as
described in detail in U.S. Pat. No. 3,242,228, issued Mar. 22,
1966 to Riordan et al. About 7.5 grams of 1% Pt on alumina catalyst
is obtained from Alfa Aesar (#11797). About 1.0 grams of methylene
chloride solvent is impregnated onto the catalyst. The catalyst is
placed in the muffle furnace and treated at 260.degree. C. for 4
hours.
[0060] About 100 grams of stearic acid and 5 grams of
platinum/alumina catalyst are placed in a 300 ml. batch autoclave
and mixed for 6 hours, at a temperature of 340.degree. C. in the
presence of 100 psig hydrogen gas. The product from the reaction is
filtered to remove the catalyst, and has the following
composition:
9 linear chain fatty acid 98.7% branched chain fatty acid 0%
alkanes: 1.3% substituted aromatics not detected The calculated
selectivity to branched chain fatty acid is 0%.
[0061] Likewise, 150 grams of stearic acid and 7.5 grams of
platinum/chloride doped alumina catalyst are placed in the
autoclave and mixed for 6 hours at a temperature of 320.degree. C.
in the presence of 200 psig hydrogen gas. The filtered product has
the following composition:
10 linear chain fatty acid 89.7% branched chain fatty acid 0.3%
alkanes 10% substituted aromatics not detected The calculated
selectivity to branched chain fatty acid is 3%.
COMPARATIVE EXAMPLE 2
[0062] This example shows that a non-crystalline, silica-alumina
catalyst doped with platinum has little activity for the skeletal
isomerization of stearic acid.
[0063] An amorphous silica-alumina catalyst (Grace-Davison, 70-90%
SiO.sub.2 by weight) is impregnated with platinum using the same
procedure described in Example 1 above for the Pt/beta zeolite
catalyst.
[0064] About 85 grams of stearic acid and 5 grams of
Pt/silica-alumina catalyst are placed in the autoclave and reacted
under the same conditions described in Example 1. The product from
the reaction is filtered to remove the catalyst, and has the
following composition:
11 linear chain fatty acid 98.4% branched chain fatty acid 0.2%
alkanes 1.4% substituted aromatics not detected The calculated
selectivity to branched chain fatty acid is 12.5%.
COMPARATIVE EXAMPLE 3
[0065] This example shows that a sulfated zirconium oxide catalyst
doped with platinum has little activity for the skeletal
isomerization of stearic acid. This catalyst has been shown to be
effective in isomerization of both short chain (n-heptane) and long
chain (n-hexadecane) hydrocarbons (Wen et al., Energy and Fuels,
4,372-379, 1990).
[0066] A platinum-doped, sulfated zirconium oxide catalyst is
prepared according to the following procedure. About 9.004 grams of
sulfated zirconium hydroxide is obtained from Magnesium Elektron
(X20682/01). A solution of 0.119 grams hydrogen hexachloroplatinate
(IV) hydrate and 2.898 grams of distilled water are used to
impregnate the catalyst. After impregnation, the catalyst is placed
in the muffle furnace and dried at 110.degree. C. for 4 hours,
calcined at 600.degree. C. for 5 hours, then held at 110.degree. C.
for 4 hours. The catalyst, prepared according to the above
procedures has the following properties: surface area of 80 m2/gr,
pore volume of 0.3 cc/gr, sulfate content of 3.4%, % Pt metal of
0.5%.
[0067] About 101 grams of stearic acid and 5.2 grams of platinum
doped sulfated zirconium oxide catalyst are placed in a 300 ml.
batch autoclave and mixed for 6 hours at a temperature of
320.degree. C. in the presence of 200 psig hydrogen gas. The
product from the reaction is filtered to remove the catalyst, and
has the following composition:
12 linear chain fatty acid 97% branched chain fatty acid 0.5%
alkanes 2.0% substituted aromatics 0.5% The calculated selectivity
to branched chain fatty acid is 17%.
[0068] Solvent crystallization with hexane is done using the
conditions similar to that of Example 1. The yield of the liquid
and solid fractions from crystallization is 6% and 93%,
respectively. Weight % compositions of each fraction are as
follows:
13 liquid fraction linear chain fatty acid 46.5% branched chain
fatty acid 8.5% alkanes 35% substituted aromatics 10% solid
fraction linear chain fatty acid 99% branched chain fatty acid 0%
alkanes 1%
* * * * *