Molecular sieve abstract
Alpha, beta-unsaturated esters are prepared by reaction between
dimethylformal and carboxylic acid compounds of the formula RCH.sub.2
COOR' wherein R is a member of the class consisting of --H, -alkyl,
-aryl, -aralky, -cycloalkyl, and -alkylaryl radicals, and R' is
selected from the group consisting of --H and --CH.sub.3 radicals
in the presence of AMS-1B borosilicate crystalline molecular sieve
catalyst under reaction conditions.
Molecular sieve claims
What is claimed is:
1. A process for the preparation of alpha, beta-unsaturated methyl
esters by reaction between dimethylformal and carboxylic acid compounds
of the formula RCH.sub.2 COOR' wherein R is a member of the class
consisting of --H, -alkyl, -aryl, -aralkyl, -cycloalkyl, and -alkylaryl
radicals and R' is selected from the group consisting of --H radicals
and -CH.sub.3 radicals, in the presence of AMS-1B borosilicate crystalline
molecular sieve catalyst under reaction conditions wherein the acid
compound:dimethylformal mole ratio is from about 0.5:1 to 20:1 at
a temperature within the range of from about 250.degree. C. to about
430.degree. C.
2. The process of claim 1 wherein said AMS-1B is the hydrogen form
AMS-1B.
3. The process of claim 2 wherein hydrogen of hydrogen form AMS-1B
is replaced by a member of the group consisting of rare earth metals,
lanthanum and sodium.
4. The process of claim 1 wherein R is selected from the group
consisting of -alkyl, -aryl, -aralkyl, -cycloalkyl, and -alkylaryl
radicals and contains from 1 to 18 carbon atoms.
5. The process of claim 1 wherein R' is --H and said acid compound
is propionic acid.
6. The process of claim 1 wherein R' is --H, said acid compound
is propionic acid and said alpha, beta-unsaturated methyl ester
is methyl -methacrylate.
7. The process of claim 1 wherein R' is --H and said acid compound
is acetic acid.
8. The process of claim 1 wherein R' is --H, said acid compound
is acetic acid and said alpha, beta-unsaturated methyl ester is
methyl acrylate.
9. The process of claim 1 wherein R' is --H and said acid compound:dimethylformal
mole ratio is 1:1.
10. The process of claim 1 wherein R' is --CH.sub.3 said acid
compound is methyl propionate and said alpha, beta-unsaturated methyl
ester is methyl -methacrylate.
11. The process of claim 1 wherein R' is --CH.sub.3 said acid
compound is methyl acetate and said alpha, beta-unsaturated methyl
ester is methyl acrylate.
12. The process of claim 1 wherein R' is --CH.sub.3 and said acid
compound:dimethylformal mole ratio is 10:1.
13. The process of claim 1 wherein said carboxylic acid compounds
of the formula RCH.sub.2 COOR' are recycled and comprise carboxylic
acids of the formula RCH.sub.2 COOH, methyl esters of the formula
RCH.sub.2 COOCH.sub.3 and mixtures thereof wherein the acid:dimethylformal
mole ratio is from about 0.5:1 to about 20:1 and the methyl ester
RCH.sub.2 COOCH.sub.3 :dimethylformal mole ratio is within the range
of from about 20:1 to about 1:1.
14. The process of claim 13 wherein said acid:dimethylformal mole
ratio is 1:1 said methyl ester RCH.sub.2 COOCH.sub.3 :dimethylformal
mole ratio is 10:1 and said carboxylic acid ester:acid:dimethylformal
mole ratio is 10:1:2.
15. The process of claim 1 wherein said temperature is within the
range of from about 250.degree. C. to about 330.degree. C.
16. The process of claim 1 wherein water content of said acid compound
and said dimethylformal is no greater than 8% by weight.
17. The process of claim 1 wherein water content of said acid compound
and said dimethylformal is no greater than 4% by weight.
18. The process of claim 1 wherein said AMS-1B borosilicate crystalline
molecular sieve composition is incorporated within an alumina or
silica-alumina matrix.
19. The process of claim 1 wherein said AMS-1B borosilicate crystalline
content in said matrix ranges from about 10 to 80 wt. %.
20. The process of claim 1 wherein said AMS-1B borosilicate crystalline
content in said matrix ranges from about 30 to 65 wt. %.
21. The process of claim 1 wherein said AMS-1B crystalline molecular
sieve composition is unsupported.
Molecular sieve description
BACKGROUND OF THE INVENTION
This invention relates to the production of alpha, beta-unsaturated
methyl esters by reaction between dimethylformal and carboxylic
acid compounds of the formula RCH.sub.2 COOR' wherein R is a member
of the class consisting of --H, -alkyl, -aryl, -aralkyl, -cycloalkyl,
and -alkylaryl radicals. Where R is not hydrogen, the number of
carbon atoms in R is preferably from 1 to 18. R' is selected from
the group consisting of --H and --CH.sub.3 radicals.
It is well-known that methyl alpha-methacrylate and methyl acrylate
can be prepared by reacting formaldehyde with a suitable reactant,
i.e., methyl propionate and methyl acetate, in the presence of a
suitable catalyst. This invention is directed to an in situ process
for synthesis of alpha, beta-unsaturated methyl esters, e.g., methyl
alpha-methacrylate (and methyl acrylate) from propionic acid (or
acetic acid) and methyl esters of such acids dimethylformal, i.e.,
formaldehyde in the form of its dimethyl acetal of the formula CH.sub.3
OCH.sub.2 OCH.sub.3. The process requires the presence of a catalyst
comprising a borosilicate crystalline molecular sieve, designated
as AMS-1B, having the following composition in terms of mole ratios
of oxides:
wherein M is at least one cation, n is the valence of the cation,
Y is a value within the range of 4 to about 600 and Z is a value
within the range of 0 to about 160 and providing a specific X-ray
diffraction pattern.
Unsaturated acids, such as methacrylic and acrylic acids, acrylonitrile
and the esters of such acids, such as methyl alpha-methacrylate,
are widely used for the production of corresponding polymers, resins
and the like. Various process and catalysts have been proposed for
the conversion of alkanoic acids, such as propionic acid, and various
forms of formaldehyde to the corresponding unsaturated monocarboxylic
acids, e.g., methacrylic acid, by an aldol-type reaction. Generally,
the reaction of the acid and formaldehyde takes place in the vapor
or gas phase while in the presence of a basic or acidic catalyst.
Various catalysts have been proposed for such reactions. For example,
Vitcha, et al., I&EC Product Research and Development, 5 No.
1 (March, 1966) pp. 50-53 propose a vapor phase reaction of acetic
acid and fomaldehyde employing catalysts comprising alkali and alkaline
earth metal aluminosilicates, silica gel, alumina and the like.
U.S. Pat. No. 2734074 teaches the preparation of acrylic ester
by formaldehyde condensation with a lower alkyl ester in the presence
of a dehydration catalyst comprising lead acetate suspended on silica
gel. U.S. Pat. No. 2821543 teaches a similar preparation using
basic metal compounds such as basic reacting salts or oxides of
metals, i.e., manganese oxide, deposited upon a suitable carrier
such as activated alumina or activated silica. U.S. Pat. No. 3051747
describes the preparation of acrylic acids by reacting an alkanoic
acid and formaldehyde in the presence of a catalyst comprising an
alkali metal salt of the alkanoic acid supported on alumina. The
same reaction is also promoted by catalysts which include alkali
metal or alkaline earth metal aluminosilicates, silica gel or alumina.
Catalysts of this kind are described in U.S. Pat. No. 3247248
which teaches a process for the reaction of formaldehyde and acetic
acid or propionic acid in the presence of a natural or synthetic
aluminosilicate catalyst that may include alkali or alkaline earth
metals, such as the aluminosilicates of sodium, potassium, rubidium,
magnesium, calcium, strontium or barium. In addition, the use of
silica gel in combination with an alkali metal or alkaline earth
metal hydroxide as a catalyst for the reaction is described. U.S.
Pat. No. 3933888 teaches the preparation of unsaturated acids,
the esters and nitriles of such unsaturated acids wherein alkanoic
acids, esters of such acids and alkyl nitriles are reacted with
formaldehyde in the presence of a basic catalyst comprising pyrogenic
silica. The pyrogenic silica is taught as especially effective when
treated with activating agents which provide basic sites on the
pyrogenic silica catalyst support, such as organic bases, inorganic
bases of Groups IA, IIA and IIIB of the Periodic Table, particularly
the alkali metal hydroxides such as potassium hydroxide and cesium
hydroxide. The addition of a compound of a metal as an activating
agent is taught as increasing the effectiveness of the catalyst.
Other processes and catalysts have been proposed for the preparation
of methacrylic acid and esters. U.S. Pat. No. 3089898 teaches
a process and catalyst for preparation of methyl acrylate which
comprises contacting vapor mixtures of methyl acetate and formaldehyde
with aluminosilicate catalysts, particularly alkaline earth metal
zeolites, alkali metal zeolites and zeolites of certain heavy metals
such as manganese, cobalt, zinc, cadmium and lead. Aqueous and alcoholic
sources of formaldehyde are taught as useful. U.S. Pat. No. 3089899
teaches preparation of methyl methacrylate which comprises contacting
vapor mixtures of methyl propionate and formaldehyde with zeolite
catalysts, particularly certain synthetic zeolites, especially the
aluminosilicates of Group IIA of the Periodic Table, such as magnesium,
calcium, strontium and barium aluminosilicates, and manganous aluminosilicates.
Aqueous of alcoholic formaldehyde or anhydrous paraformaldehyde
can be used. U.S. Pat. No. 3089900 teaches preparation of methyl
methacrylate using a catalyst consisting of potassium hydroxide
impregnated on silica gel. G.B. Pat. No. 1107234 teaches a similar
process using potassium, rubidium or cesium hydroxide on silica
gel as catalyst. U.S. Pat. No. 3089901 teaches use of alkali metal
metaborates on silica gel and alkali metal tetraborates on silica
gel as catalysts. U.S. Pat. No. 3089902 teaches alkali metal silicate
on silica gel as catalyst.
Accordingly, a number of processes using basic metal catalysts
have been taught heretofore. Other process using basic metal compounds
on silica gel catalysts are taught in U.S. Pat. Nos. 3100795;
3247248; 3534087; 3670016; 3840587; 3840588. But, although
an alkali-treated silica gel improves the activity of the formaldehyde
with regard to the desired reaction, at the same time, as is well-known,
formaldehyde has a tendency to undergo undesirable side reactions
owing to its high reactivity in alkaline media.
Processes to minimize or to avoid the aforesaid undesirable side
reactions which formaldehyde undergoes in alkaline media have been
taught. U.S. Pat. No. 3535371 teaches use of a niobium oxide catalyst
on alumina. U.S. Pat. No. 3845106 teaches use of an unmodified
silica gel. G.B. Pat. No. 1491183 teaches use of methylal instead
of formaldehyde with a metal oxide catalyst, preferably Al.sub.2
O.sub.3. U.S. Pat. No. 4085143 teaches use of a catalyst comprising
silica gel and a salt or an oxide of a metal selected from the group
consisting of tantalum, titanium, niobium, and zirconium with an
acid anhydride and formaldehyde. Boric acid deposited an alumina
is also taught as a catalyst. U.S. Pat. No. 4118588 teaches a
process and catalyst for preparing methacrylic acid and methyl methacrylate
which comprises reacting, respectively, propionic acid and methyl
propionate with dimethoxymethane in the presence of catalysts based
on phosphates and/or silicates of magnesium, aluminum, zirconium,
thorium and/or titanium and in the presence of water. Boric acid
and/or urea can also be present. Preferably, the catalysts are modified
with alkali metal and/or alkaline earth metal carboxylates and/or
alkali metal compounds and/or alkaline earth metal compounds which
yield carboxylates under the reaction conditions. Suitable modifiers
are the carboxylates, oxides and hydroxides of lithium, sodium,
potassium, magnesium and calcium as well as those of beryllium,
strontium, rubidium, cesium and barium.
However, the processes and catalysts taught heretofore suffer from
disadvantages which are greatly minimized in the process of the
present invention. For example, the processes as described in Vitcha,
I&EC, op. cit. p. 50 are inferior to the present invented process
in that conversion of formaldehyde is low when acid concentration
is low. Vitcha indicates that as the ratio of acetic to formaldehyde
decreases, the competitive reaction of formaldehyde with itself
to form polymers predominates, to result in lower conversion and
yield. Other examples can be cited. U.S. Pat. No. 3051747 indicates
that the major product of the process is not an unsaturated compound
but a symmetric ketone. The process described in U.S. Pat. No. 3247248
is also inferior to the process of the present invention. Yield
percent based on formaldehyde taught by U.S. Pat. No. 3247248
with 5:1 ratios of acid to formaldehyde is between 20 and 40 percent.
Quite unexpectedly, it has been found that a catalyst comprising
AMS-1B borosilicate crystalline molecular sieve having the following
composition in terms of mole ratios of oxides:
wherein M is at least one cation, n is the valence of the cation,
Y is a value within the range of 4 to about 600 and Z is a value
within the range of 0 to about 160 and providing a specific X-ray
diffraction pattern, performs in a much superior manner for the
present process with respect to conversion and selectivity relative
to conventional catalysts. Whereas previously taught catalyst formulations
require a basic metal on silica or alumina substrates, the catalyst
of the instant invented process is a borosilicate crystalline molecular
sieve catalyst. Yield and selectivity are also improved over previously
taught catalysts. The improved process has several unexpected results.
Whereas previously taught processes result in low formaldehyde-based
yields of methyl alpha-methacrylate or methyl acrylate when the
ratio of acid to formaldehyde is low, such as 1:1 the preferred
acid:dimethylformal ratio for the process of the present invention
is 0.5:1 to 20:1 preferably 1:1 with consequent economic advantage.
Also, in previously taught processes, substantial amounts of acid
often are formed from the ester from ester-cleavage side reactions.
Even when the reaction is carried out in the presence of excess
alcohol, the formation of acid via cleavage is not easily suppressed.
The process and catalyst of the instant invention circumvent the
ester-cleavage mechanism by utilizing an acid:dimethylformal mechanism.
In preparation of methyl alpha-methacrylate, the major products
of the reaction, methyl propionate and methyl methacrylate, are
easily separated by conventional methods. The methyl propionate
can be reached with formaldehyde under suitable process conditions
to prepare methyl alpha-methacrylate, and, alternatively, along
with unesterified propionic acid, is recycled to the reactor. In
this way, methyl alpha-methacrylate is conveniently synthesized
in situ directly from propionic acid and without the need for a
separate esterification section within the overall process. In addition,
the present invention is with the use of a dry derivative of formaldehyde,
dimethylformal.
An object of the present invention is to provide a process for
making unsaturated methyl esters from saturated carboxylic acids
and dimethylformal. A further object is to provide a process for
making methyl acrylate. A further object is to provide a process
for making methyl alpha-methacrylate. Other objects will appear
hereinafter.
SUMMARY OF THE INVENTION
Disclosed is a process for production of alpha, beta-unsaturated
methyl esters by reaction between the acetal of formaldehyde, dimethylformal,
and carboxylic acid compounds of the formula RCH.sub.2 COOR', wherein
R is a member of the class consisting of --H, -alkyl, -aryl, -aralkyl,
-cycloalkyl, and -alkylaryl radicals, the number of carbon atoms
in R being preferably from 1 to 18 when R is not hydrogen, R' being
selected from the group consisting of --H and --CH.sub.3 radicals,
in the presence of AMS-1B borosilicate crystalline molecular sieve
catalyst under reaction conditions wherein the acid compound:acetal
mole ratio is from about 0.5:1 to 20:1 at a temperature within the
range of from about 250.degree. C. to about 430.degree. C.
DETAILS OF THE INVENTION
The process of the instant invention relates to a process for production
of alpha, beta-unsaturated methyl esters by reaction of dimethylformal
and carboxylic acid compounds of the formula RCH.sub.2 COOR' wherein
R is a member of the class consisting of --H, -alkyl, -aryl, -aralkyl,
-cycloalkyl, and -alkylaryl radicals, the number of carbon atoms
in R being preferably from 1 to 18 when R is not hydrogen, R' is
selected from the group consisting of --H and --CH.sub.3 radicals,
in the presence of AMS-1B borosilicate crystalline molecular sieve
catalyst. In preparation of methyl alpha-methacrylate and methyl
acrylate (from propionic acid and acetic acid), yield is increased
over previously taught process and production of by-products is
minimized. Recycle of the methyl propionate and methyl acetate resulting
from the preparation of methyl alpha-methacrylate and methyl acrylate
further increases yield of the desired products. The general method
requires the presence of AMS-1B borosilicate crystalline molecular
sieve catalyst. Dimethylformal is reacted with propionic acid (or
acetic acid) in the gas phase at a temperature within the range
of from about 250.degree. C. to about 430.degree. C.
The present invention relates to a process using a synthetic crystalline
molecular sieve material, a crystalline borosilicate, as a catalyst.
The family of such crystalline borosilicate materials, which are
identified as AMS-1B borosilicates, and which are taught in commonly-assigned
U.S. Pat. No. 4269813 incorporated herein by reference, has a
particular X-ray diffraction pattern. Such crystalline borosilicate
can generally be characterized, in terms of the mole ratios of oxides,
as follows in Equation I:
wherein M is at least one cation, n is the valence of the cation,
Y is between 4 and about 600 and Z representing the water present
in such material is between 0 and about 160 or more.
In another instance, the claimed crystalline borosilicate can be
represented in terms of mole ratios of oxides for the crystalline
material not yet activated or calcined at high temperatures as follows
in Equation II:
wherein R is an alkylammonium cation, M is at least one cation,
n is the valence of the cation, Y is a value between 4 and 600
Z is a value between 0 and about 160 and W is a value greater than
0 and less than 1.
In Equation I, M can represent an alkali-metal cation, an alkaline-earth-metal
cation, an ammonium cation, an alkylammonium cation, a hydrogen
cation, a catalytically-active-metal cation, or mixtures thereof.
In Equation II, M can represent an alkali-metal cation, an alkaline-earth-metal
cation, an ammonium cation, a hydrogen cation, a catalytically-active-metal
cation, or mixtures thereof.
Advantageously, the value for Y falls within the range of 4 to
about 500. Suitably, Y is 4 to about 300;preferably, about 50 to
about 160; and more preferably, about 80 to about 120.
Suitably, Z is within the range of 0 to about 40.
The original cation M in the above formulations can be replaced
in accordance with techniques well-known in the art, at least in
part by ion exchange with other cations. Preferred replacing cations
include tetraalkylammonium cations, metal ions, ammonium ions, hydrogen
ions, and mixtures of the above. Particularly preferred cations
are those which render the AMS-1B crystalline borosilicate catalytically
active, especially for hydrocarbon conversion. These materials include
hydrogen, natural occurring rare earth metals of Group IIIB, lanthanum,
aluminum, metals of Groups IA, i.e., sodium, potassium, lithium,
etc.; IIA, i.e., calcium, stronium, barium, etc., and VIII, i.e.,
iron, cobalt, nickel, etc. of the Periodic Table of Elements found
in the 46th edition of the Handbook of Chemistry and Physics published
by the Chemical Rubber Company; noble metals, manganese, and other
catalytically active materials and metals known to the art. Rare
earth metals, lanthanum, sodium and hydrogen are considered especially
useful. The catalytically active components, separately or in any
combination, can be present anywhere from about 0.05 to about 25
weight percent of the AMS-1B crystalline borosilicate. The form
wherein hydrogen replaces the original cation M and n is 1 in the
above formulations is designated HAMS-1B. The hydrogen form of the
AMS-1B crystalline borosilicate catalyst imparts an acid character
to the catalyst to improve yields of methyl alpha-methacrylate and
methyl acrylate. Molecular sieves containing divalent and trivalent
cations are generally recognized to impart acidic character to molecular
sieves but the hydrogen ion is considered to impart more acidic
character.
Embodiments of these borosilicates are prepared by the method which
comprises: (1) preparing a mixture containing an oxide of silicon,
an oxide of boron, a hydroxide of an alkali metal or an alkaline
earth metal, an alkylammonium cation or a precursor of an alkylammonium
cation, and water; and (2) maintaining said mixture at suitable
reaction conditions to effect formations of said borosilicate, said
reaction conditions comprising a reaction temperature within the
range of about 25.degree. C. to about 300.degree. C., a pressure
of at least the vapor pressure of water at the reaction temperature,
and a reaction time that is sufficient to effect crystallization.
The hydrogen form can be obtained by ion exchange.
The AMS-1B crystalline borosilicate useful in this invention can
be in an unsupported form for use either in a fixed bed or fluidized
bed reactor. The AMS-1B crystalline borosilicate can be combined
with active or inactive materials, synthetic or naturally-occurring
zeolites, as well as inorganic or organic materials which would
be useful for binding the borosilicate. Well-known materials include
silica, silicaalumina, alumina, magnesia, titania, zirconia, alumina
sols, hydrated aluminas, clays such as bentonite or kaolin, or other
binders well-known in the art. Typically, the borosilicate is incorporated
within a matrix material by blending with a sol of the matrix material
and gelling the resulting mixture. Also, solid particles of the
borosilicate and matrix material can be physically admixed. Typically,
such borosilicate compositions can be pelletized or extruded into
useful shapes. Catalytic compositions can contain about 0.1 wt.
% to about 100 wt. % crystalline borosilicate material and preferably
contain about 10 wt. % to about 80 wt. % of such material and most
preferably contain about 30 wt. % to about 65 wt. % of such material.
Catalytic compositions comprising the crystalline borosilicate
material of this invention and a suitable matrix material can be
formed by adding a finely-divided crystalline borosilicate and a
catalytically active metal compound to an aqueous sol or gel of
the matrix material. The resulting mixture is thoroughly blended
and gelled typically by adding a material such as ammonium hydroxide.
The resulting gel can be dried and calcined to form a composition
in which the crystalline borosilicate and catalytically active metal
compound are distributed throughout the matrix material.
Specific details of catalyst preparations are described in U.S.
Pat. No. 4269813.
It has been found that borosilicate catalysts prepared by the above
method are effective in catalyzing the reaction of carboxylic acids,
particularly propionic acid and acetic acid, and an acetal, i.e.,
dimethylformal, under anhydrous conditions wherein the acid:dimethylformal
ratio is from about 0.5:1 to about 20:1 at a temperature within
the range of from about 250.degree. C. to about 430.degree. C. and
contact time is from about 0.1 to about 20 seconds.
It is essential for the process and catalyst of the instant invention
that water in the acid compound-acetal feed and in the reactor under
operating conditions be maintained at low levels, preferably no
greater than a maximum of 8% by weight of the combined weight of
the acid compound-acetal feed, more preferably no greater than 4%
by weight. Since water is produced as a by-product of the reaction,
the reaction can be self-deactivating to the extent that higher
conversions of the acid compound-dimethylformal reactants cause
higher gas phase concentrations of water in the catalyst bed, thus
requiring an increased operating temperature which in turn decreases
selectivity to the alpha, beta-unsaturated methyl ester.
The alpha carbon of the reactant acid of the formula RCH.sub.2
COOH and its methyl ester is required to possess at least two hydrogen
atoms. When R is not hydrogen suitable carboxylic acids and esters
preferably contain from 1 to 18 carbon atoms in addition to the
--CH.sub.2 COOH or --CH.sub.2 COOCH.sub.3 moiety. Examples of acids
and esters are acetic acid, propionic acid, n-butyric acid, n-valeric
acid, isovaleric acid, n-caproic acid, n-heptanoic acid, capric
and lauric acids, phenylacetic acid, gamma-phenylbutyric acid, 3-methylcyclopentylacetic
acid, and the methyl esters thereof.
In the example, the novel process of the present invention is carried
out to synthesize methyl alpha-methacrylate from propionic acid
and dimethylformal. The instant invented process is useful in synthesis
of methyl acrylate by the vapor phase reaction of acetic acid and
dimethylformal. The instant invented process is also useful in synthesizing
unsaturated monocarboxylic methyl esters from methyl esters of monocarboxylic
acids of the formula RCH.sub.2 COOR' wherein R and R' are as previously
defined.
The instant invented process, as exemplified, is a single step
in situ process for the synthesis of methyl alpha-methacrylate which
is catalyzed effectively by a borosilicate crystalline molecular
sieve catalyst as described herein.
The invented process involves the condensation of dimethylformal
with propionic acid and methyl propionate, separately and in a mixture,
to yield methyl alpha-methacrylate.
The reaction occurs at atmospheric pressure in the gas phase when
the reactants are passed through the catalyst in the presence of
a nitrogen carrier gas at a temperature of 250.degree. C. to about
430.degree. C., preferably 250.degree. C.-330.degree. C. Above 400.degree.
C. significant amounts of 3-pentanone (3-P), a known thermal degradation
product of propionic acid, are formed, as well as some gaseous by-products.
Reactant pressures of from 0.5 to 10 atmospheres can be used. A
broad range of reactant ratios may be successfully used for this
process. For example, when propionic acid and dimethylformal, in
mole ratios varying from 0.5:1 to 20:1 propionic acid:available
dimethylformal, are allowed to react at a temperature of about 300.degree.
C., yields of methyl alpha-methacrylate obtained can be up to about
11%, based on propionic acid. Total yields of methyl alpha-methacrylate
and methyl propionate obtained can be as high as about 75%, based
on propionic acid. Methyl propionate is extractable by suitable
means, such as distillation with use of an inhibitor, and recycled
for additional methyl alpha-methacrylate.
Recycle of the methyl propionate from the reaction of propionic
acid and dimethylformal is preferably wherein the mole ratio of
methyl propionate: dimethylformal is within the range of from about
20:1 to 1:1 but more preferably about 10:1. In operation, the methyl
propionate and unreacted propionic acid are recycled to the reactor
with make-up propionic acid added to obtain a 0.5:1 to 20:1 mole
ratio, preferably a 1:1 ratio, acid:dimethylformal mole ratio. Ratio
of methyl propionate:dimethylformal can vary in a feedstream comprising
propionic acid which results from recycle operation due to process
conditions and the acid:dimethylformal molar ratio.
In recycle operation wherein carboxylic acid compounds of formula
RCH.sub.2 COOR' are reacted with dimethylformal, mole ratio of carboxylic
acids of formula RCH.sub.2 COOH to dimethylformaldehyde can be from
0.5 to 20:1 mole ratio of carboxylic acid ester of formula RCH.sub.2
COOR' to dimethylformal can be from 20:1 to 1:1 and preferred mole
ratio is 10:1:2 carboxylic acid ester:acid:dimethylformal, upon
an additive basis.
Liquid hourly space velocity (LHSV) measured in terms of volume
of liquid per volume of catalyst per hour (V.sub.1 V.sub.c.sup.-1
hr.sup.-1), basis a constant carrier gas rate, is from about 0.05
to 20.0 preferably from about 0.1 to about 10.0. A LHSV less than
about 0.05 results in nonselective decomposition of reactants. A
LHSV above 20 results in low conversion of reactants.
Yield calculations can be based upon propionic acid, methyl propionate
or dimethylformal. For example, propionic acid-based yields are
calculated as follows: ##EQU1## Dimethylformal-based yields are
calculated as follows: ##EQU2## Propionic acid selectivity is calculated
as follows: ##EQU3## Dimethylformal selectivity is calculated similarly.
The instant invention accordingly comprises a process for the preparation
of alpha, beta-unsaturated methyl esters by reaction between dimethylformal
and carboxylic acid compounds of the formula RCH.sub.2 COOR' wherein
R is a member of the class consisting of --H, -alkyl, -aryl, -aralkyl,
-cycloalkyl, and -alkylaryl radicals and R' is selected from the
group consisting of --H radicals and -CH.sub.3 radicals, in the
presence of AMS-1B borosilicate crystalline molecular sieve catalyst
under reaction conditions wherein the acid compound:dimethylformal
mole ratio is from about 0.5:1 to 20:1 at a temperature within the
range of from about 250.degree. C. to about 430.degree. C.
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