PREPARATION OF UNSATURATED ACIDS AND ESTERS BY OXIDATIVE CONDENSATION

Abstract: A process for the production of unsaturated acids and esters comprises reacting in the vapor phase at a tempera­ ture of 200°C to 500°C a first reactant selected from saturated monocarboxylic acids, esters and anhydrides, a second reactant selected from primary and secondary alcohols and di-alkyl ethers, and oxgyen, in the presence of an oxidation catalyst, said catalyst having at least two elements, at least one element being a multi-valent metallic element. The process obviates the need for formaldehyde as a starting material. The starting materials are easily available from synthesis gas.

Description: Title: PREPARATION OF UNSATURATED ACIDS AND ESTERS BY OXIDATIVE CONDENSATION. This invention relates to a novel vapor phase process for the production of unsaturated acids and esters, such as acrylic acid and methyl acrylate. Preparation of unsaturated acid derivatives from corresponding saturated compounds by condensation with formaldehyde is known. For example, U.S. Patent No. 3,701,798 discloses the production of unsaturated acid derivatives through condensation with formaldehyde over catalysts containing rare earth oxides. U.S.Patent No. 3,014,958 discloses an improvement for making unsaturated- esters from formaldehyde and other esters wherein the feed contains more than 7% of the desired unsaturated ester. Catalysts used in this reference are phosphates and mixed oxides. U.S. Patent No. 3,933,888, U.S. 3,578,702 and U.S. 4,165,438 all disclose reactions using formaldehyde over various cxide catalysts such as vanadium-phosphorus, metals of the lanthanide series, or metals found in Groups llA and Group lllA of the Periodic Table. It has now been discovered that derivatives of unsaturated acids can be obtained by the reaction of a saturated derivative with methanol and oxygen, over a suitable catalyst, thus eliminating the need for the use of formaldehyde. Since methanol can be made directly from carbon monoxide and hydrogen (synthesis gas), the invention significantly increases the economic incentive for the production of important monomers, such as methyl acrylate, from starting materials easily available from synthesis gas, e.g. methanol, acetic acid, methyl acetate, providing a viable alternative.to processes based on petroleum hydrocarbons. The invention provides therefore a process for the production of unsaturated acids and esters which comprises reacting in the vapor phase a first reactant selected from the group consisting of saturated monocarboxylic acids, esters and anhydrides, a second reactant selected from the group consisting of primary and secondary alcohols, and oxygen, in the presence of an oxidation catalyst, said catalyst having at least two elements, wherein at least one is a multi-valent metallic element. The first reactant feed for the process of the present invention may be a saturated monocarboxyric acid, ester, or anhydride having two to fourteen carbon atoms. It is preferred to utilize acids and esters. The preferred acids and esters are acetic acid and acetates, and propionic acid and propionates. While these compounds are preferred, esters of other aiiphatic acids may also be used. The alcohol in the second reactant is a primary or secondary alcohol, of which ethanol, n-propanol, nbutanol, and isobutanol are preferred. The particularly preferred alcohol is methanol. It may be advantageous to use an ether such as dimethyl ether as feed instead of methanol. Both compounds are easily and selectively interconvertible over a variety of dehydration/hydration catalysts, e.g. gamma-alumina. Thus, if desired, dimethyl ether or its mixtures with the methanol may serve as an alternate feed equivalent to methanol alone. The oxygen necessary for the oxidative condensat ion may be supplied as oxygen or an oxygen-containing gas such as air. The oxidative condensation is conveniently carried out by mixing the alcohol such as methanol, with the appropriate acid derivative such as methyl propionate, in the desired ratio, vaporizing the mixture, and passing the vapors along with oxygen over suitable catalyst. If dimethyl ether is used as feed, it may be introduced together with the oxygen and any gaseous diluent, added dissolved in the liquid feed, or introduced both ways. Fixed or fluid bed operation is possible, and inert diluents such as steam or nitrogen may be added. The reaction temperature may range from 200 to about 5000C, preferably from 300 to 4500C; the average residence time may be from 2 to about 60 seconds, preferably trom 5 to 20 seconds. The molar ratio of the acid derivative to the alcohol may range from 1:10 to 10:1; the molar ratio of oxygen to the alcohol is suitably from 0.2:1 to 10:1. A wide variety of catalysts are suitable for the oxidative condensation reaction of this invention. The main requirement of the catalyst is to have an oxidation or dehydrogenaticn function and a condensation/ dehydraticn function. Thus, many oxidation and dehydrogenation catalysts, both acidic and basic, can be used. In one aspect of the invention, excellent results have been obtained with mixed phosphates having the general formula AaBbCCPOX where A = alkali metal, alkaline earth metal, T1, or mixtures thereof B = Fe, Co, Ni, V, Cr, Mn, Cu, Ag, Pt, Pd, Rh, Ru, or mixtures thereof C = Sc, Y, La, rare earth metal, Th, U, Ti, Nb, Si, Ge, Ta, Mo, W, Bi, Sb, Te or mixtures thereof where a = 0-1.5; b = 0.01-3.0; c = 0-2.0; x = the number of oxygensrequired to satisfy the valence requirements of the other elements present. Preferably the values of a, b and c should be such that the value of an a + bnb + cnc is 1 to 5, where na is the valency of the ion or ions from Group A, nb is the valency of the ion (or ions) from Group B, and n c is the valency of the ion or ions from Group C. The catalysts are prepared by methods known in the art; some typical methods of preparation are shown in the examples. In another aspect of the invention, catalysts containing antimony and vanadium have proved very useful. They have the general formula: A B C VSBm0x where A = alkali metal, alkaline earth metal, T1, La, rare earth metal, Th, or mixtures thereof; B = Cu, Ag, Fe, Co, Ni, Mn, Cr, Nb, Ta, Ti, P, As, Sn, B, U, or mixtures thereof; C = Mo, W, Te, Bi, or mixtures thereof; a = 0-1; b -- 0-1; c = 0-1; m = 0.5 - 40, preferably 3-15; x = the number of oxygens required to satisfy the valence requirements of the other elements present. Preferably, the value of a + b + c should be equal to or smaller than 2 but less than m. The catalysts containing V and Sb, as shown above, are conveniently prepared by a redox reaction such as EMI5.1 in which pentavalent vanadium is reduced, while the trivalent antimony of Sb203 is oxidized to the pentavalent state. The V205 can be replaced by ammonium metavanadate or other compounds of pentavalent vanadium. Where excess Sb203 used, such that m > l, such excess will, during the calcination of the catalyst at a high temperature in air, be oxidized to Sb204, Sb603, and/or Sb205, or the like. Alternatively, the excess antimony in compositions with m > 1 can be supplied as a compound of pentavelent antimony, e.g. Sb2O5. In such a case the excess antimony is preferably added after the redox reaction shown above had been completed. Thus, the catalytic compositions contain all or part of the vanadium in an oxidation state of less than 5+, and most of the antimony in the oxidation states of 4+ and 5+. The preparative methods include, for example, heating an intimate mixture of the dry reactants or, preferably, using an aqueous slurry method as illustrated in the examples. Alternatively, the catalysts may be prepared by reducing the pentavalent vanadium (e.g. V205) separately followed by reaction with a compound of pentavalent antimony e.g. SbCl5 or Sb205. In all methods, supports and additicnal promoting and modifying elements may be added at different stages of the preparation. Other suitable catalysts include the following: molybdates, tungstates, vanadates and chromates of various transition elements, optionally promoted with alkaliand alkaline earth metals; heteropolyacids of molybdenum and/or tungsten and their salts; Mixtures of molybdates with the phosphates and V Sb catalysts described above; Crystalline aluminosilicates include zeolites X, Y, mordenites, ZSM-series, and the like, suitably exchanged and/or impregnated with alkali metals, preferably K, Rb and Cs, alkaline earth metals, and other elements such as Fe, Cu, V, Sb, Pt, Pd, Ag, Mo or W. The catalysts described herein may be used unsupported, but the use of a suitable carrier, such as silica, alumina, amorphous silica-alumina, mixtures of silica and alumina, crystalline aluminosilicates, titania, zirconia, BPO4, SbPO4 natural clays, and similar materials is often preferred. Good results have been obtained using alumina with the mixed phosphates, and mixtures of alumina and silica with the catalysts containing vanadium and antimony described above. The concentration of the active catalyst on the support may range from about 5 to about 95% by weight. The following Examples illustrate the invention: Example 1 A catalyst having the composition 50% K0.4Th0.48- CuO 48POx + 50% A1203 was prepared as follows. A slurry of 44.lg hydrated alumina (Catapal SB, 85% A1203) in 170 ml H20 was heated to 700C and a solution of 19.4g (NH4)211P04 in 50 ml H20 was added with stirring, followed by the addition of a warm solution of 39.lg (Th(N03)4.4 H20 and 17.1 g Cu(N03)2.3H20 in 65 ml H20, and a solution of 5.9g KN03 in 10 ml H20. The slurry was evaporated to a low volume at about 900C. then dried at 120-1250C. The dry material was treated 3 hours at 2900C, 3 hours at 3500C, ground and screened to 20/35 mesh size, and finally calcined 5 hours at 5000C. Examples 2 - 10 Following the procedure of Example, various promoted copper-phosphate catalysts were prepared as shown in Table 1. The catalysts were charged to a fixed-bed microreactor equipped with a preheat leg, serving as a vaporizer, and immersed in a temperature-controlled salt bath at 3300C. Liquid feed consisting of a mixture of methyl acetate and methanol in a molar ratio of 10:1 was injected by a syringe pump into the reactor, through the preheat leg over a period of 100 minutes. A mixture of 10 viol, oxygen and 90 vol.% nitrogen was introduced into the reactor through the preheat leg at the same time. The respective flow rates of the liquid and the gaseous feed were such that a reactant ratio methyl acetate/methanol/02/N2 = 10/1/0.8/7.2 was obtained, and the average residence time in the reactor was 10 seconds. The reactor effluent was condensed, weighed, and analyzed by gas chromatography. The results of these experiments are shown in Table 1. Examples 11 - 16 In the same manner as Example 1, catalysts containing phosphorus promoted with iron, chromium, cobalt, silver and molybdenum were prepared and run as per Examples 2-10 at 3300C with a contact time of 10 seconds. The results of these experiments are shown in Table II. Example 17 A catalyst having the composition 42% VSbOx, 42% Al 203, and 16% SiO2 was prepared as follows. A slurry of 25.9g Sb203 in 100 ml H20 was heated to 750C, and a hot solution of 2.8 g NH4V03 in 300 ml H20 was added with stirring. The mixtutewas boiled under reflux overnight. The resulting dark-green liquid was mixed with 49.4g hydrated alumina, and with 40. or 40% silica sol. The mixture was stirred in an open beaker, evaporated at 85 90or, and dried at 120-1250C. The dried material was treated 5 hours at 3500C, ground and screened to 20/35 mesh size, and calcined 5 hours at 5500C. Examples 18 - 25 In the same manner as Example 17, catalysts containing vanadium-antimony and promoted by potassium, copper, silver, iron, molybdenum and uranium were prepared. Catalysts of these examples were calcined at 550 C, except for Example 19 which was calcined at 6500C. The catalysts of Examples 17-25 were tested according to the procedure of Examples 2-10 at a temperature of 3300C and a contact time of 10 seconds. The results are shown in Table III. Examples 26-29 in the manner previously disclosed, catalysts of the invention were prepared having the composition set forth in Table IV. Examples 26 and 29 had a support of 50% A1203, while Examples 27 and 28 had a support of 42% A103, 16% SiO2. A feed of methyl propionate, methanol and oxygen was passed over the catalyst at a ratio of methylpropionate/methanol of 10/1, and a ratio of oxygen/methanol as shown in the Table. The reaction temperature was 3300C, with a contact time as shown. The results are presented in Table IV. The following example illustrates the use of dimethyl ether as the second reactant in the oxidative condensation with methyl acetate. Example 30 The reactor was charged with a catalyst having the composition 508 K0.4 Ce0.58Cu0.58PO+5O% A1203 (see Example 7). The testing procedure was essentially the same as that of Examples 2-10, except that the liquid feed consisted of methyl acetate alone, while the gaseous feed consisted of oxygen, nitrogen, and dimethyl ether. The composition of the gaseous feed and the respective flow rates of the liquid and the gaseous feeds were such that a reactant ratio methyl acetate/dimethyl ether/02/N2=10/ 0.5/0.8/7.2 was obtained, and the average residence time in the reactor was 10 seconds. At the reaction temperature of 3300C, 45.2% ppc of methyl acrylate and 4.6% ppc acrylic acid were obtained, resulting in 49.8% ppc to total product. At 3500C the yields were 82.1% ppc to methyl acrylate and 13.68 ppc to acrylic acid, resulting in 95.7% ppc to total product. The following example illustrates the use of a molybdate as oxidation catalyst. Example 31 A catalyst having the composition 50% Fe2Mo5.4Ox and 508 A1203 was prepared as follows. To a warm slurry of 59g Catapal SB in 230 ml H20 there was added a solution of 50.9 g ammonium heptamolybdate in 90 ml H20, and a solution of 43.1 g Fe(N03)3.9H20 in 30 ml H20. The slurry was stirred and evaporated at 900C, dried at 1250C, treated 3 hours at 2900C, 3 hours at 3500C, ground and screened, then calcined 5 hours at 4300C. When tested according to Examples 2-10, with Me-acetate and methanol in the feed, 24.2% ppc to methyl acrylate and 12.4% ppc to acrylic acid were obtained, resulting in 36.6% ppc to total product. The following example illustrates the use of a zeolite exchanged with alkali metal and other elements as oxidation catalyst, Example 32 A sample of commercial Zeolite 13X (sodium form) was exchanged with cesium by conventional treatment with an excess of Cs2CO3 solution, washing and drying. The dried material was impregnated with Fe and Mo to a total of approximately 8 wt.% by treatment with aqueous solutions of ammonium heptamolybdate and ferric nitrate, evaporating, drying at 1259C and treated 3 hours at 2900C. This material (l2.6g) was then mixed with lo.5g 40% silica sol (4.2 g Si02), dried, ground and screened, then calcined 5 hours at 4500C. This catalyst, when tested according to the procedure of Examples 2-10 gave a yield of 7.3% ppc to methyl acrylate, and 0.2% ppc to acrylic acid. TABLE I Reaction of Methyl Acetate With Methanol and Oxygen Over Promoted Phosphate Catalysis Per Pass Conversion % Example Catalyst Methyl Acrylate Acrylic Acid Total 1 K0.4Th0.48Cu0.48 POx 74.9 10.9 85.8 2 K0.4Th0.6Cu0.24 POx 64.5 6.5 71.0 3 K0.4Th0.48Cu0.48V0.1 POx 61.7 4.1 65.8 4 K0.4Th0.48Cu0.48Te0.1 POx 10.4 -0- 10.4 5 K0.4Cu1.45 Pox. 22.5 1.5 24.0 6 K0.4La0.58Cu0.58 Pox 66.9 3.8 70.7 7 K0.4Ce0.58Cu0.58 POx 89.9 12.9 102.8 8 K0.4Cr0.58Cu0.58 POx 41.2 11.6 52.8 9 K0.4U0.725Cu0.725 POx 27.0 4.3 31.3 10 K0.4Bi0.58Cu0.58 POx 10.8 2.1 12.9 TABLE II Reaction of Methyl Acetate With Methanol and Oxygen Over Promoted Phosphate Catalysis Per Pass Conversion % Example Catalyst Methyl Acrylate Acrylic Acid Total 11 K0.4Fe0.57POx 22.4 2.1 24.5 12 Th0.11Fe0.54POx 19.8 2.7 22.5 13 K0.4Cr0.57POx 15.8 1.0 16.8 14 K0.4Th0.58Co0.48POx 7.5 0.0 7.5 15 K0.4Th0.58Ag0.58POx 53.3 1.6 54.9 16 K0.4Th0.09Fe0.45Mo0.1POx 39.5 8.5 48.0 TABLE III Reaction of Methyl Acetate With Methanol and Oxygen Over Vanadium-Antimony Catalysis Per Pass Conversion % Example Catalyst Methyl Acrylate Acrylic Acid Total 17 VSbOx 35.4 9.6 45.0 18 VSb5 Ox 36.6 10.8 47.4 19 VSb5 Ox 42.8 11.3 54.1 20 K0.4 VSb5 Ox 39.3 5.5 44.8 21 K0.4 Cu0.5 VSb5 Ox 20.3 6.0 26.3 22 K0.4 Ag0.5 VSb5 Ox 33.5 7.7 41.2 23 K0.4 Fe0.5 VSb5 Ox 33.5 6.5 39.8 24 K0.4 Mo0.5 VSb5 Ox 32.5 8.5 41.0 25 U0.5 VSb5 Ox 35.8 9.1 44.9 TABLE IV Reaction of Methyl Propionate With Methanol and Oxygen Over Various Catalysts Contact O2 Per Pass Conversion % Catalyst Time Sec. MeOH Methyl Methacrylate Methacrylic Acid Total VSbOx 6 0.4 17.5 3.0 20.5 VSb5Ox 6 0.4 22.0 2.3 24.3 K0.4VSb5Ox 10 0.8 23.3 2.5 25.8 K0.4Fe0.5Ce0.47POx 10 0.8 7.9 0.5 8.4

Claims: CLAIMS: 1. A process for the production of unsaturated acids and esters which comprises reacting in the vapor phase at a temperature of 2000C to 5000C a first reactant selected from saturated monocarboxylic acids, esters and anhydrides, a second reactant selected from primary and secondary alcohols and di-alkyl ethers, and oxygen, in the presence of an oxidation catalyst, said catalyst having at least two elements, at least one element being a multi-valent metallic element. 2. A process as claimed in claim 1 wherein the first reactant has 2-14 carbon atoms. 3. A process as claimed in claim 2 characterised in that the first reactant is a saturated mcnocarboxylic acid, or an ester thereof, preferably acetic acid or propionic acid, or ester of such acid. 4. A process as claimed in any of claims 1 to 3 characterised in that the second reactant is an alcohol selected from ethanol, n-propanol, n-butanol, isobutanol and methanol. 5. A process as claimed in claim 4 characterised in that the alcohol is methanol and the first reactant is methylacetate or methylpropionate. 6. A process as claimed in any of claims 1 to 3 characterised in that the second reactant is dimethyl ether. 7. A process as claimed in claim 6 characterised in that the first reactant is methyl acetate or methyl propionate. 8. A process as claimed in any of claims 1 to 7 characterised in that the oxidation catalyst has the empirical formula: A,BbC PO where A = alkali metal, alkaline earth metal, T1, or mixtures thereof B = Fe, Co, Ni, V, Cr, Mn, Cu, Ag, Pt, Pd, Rh, Ru, or mixtures thereof C = Sc, Y, La, rare earth metals, Th, U, Ti, Nb, Si, Ge, Ta, Mo, W, Bi, Sb, Te or mixtures thereof where a = 0-1.5 b = 0.01-3.0 c = 0-2.0 x = the number of oxygens required to satisfy the valence requirements of the other elements present. 9. A process as claimed in claim 8 characterised in that the alkali metal is potassium or cesium. 10. A process as claimed in claim 8 or claim 9 characterised in that member B of the oxidation catalyst is copper, chromium, iron or silver. 11. A process as claimed in any of claims 8 to 10 characterised in that member C of the oxidation catalyst is thorium or cerium. 12. A process as claimed in any of claims 8 to 10 characterised in that member C of the oxidation catalyst is one or more elements selected from cerium, lanthanum, thorium, molybdenum, and tungsten. 13. A process as claimed in claim 8 characterised in that the oxidation catalyst has the empirical formula K0.2-06Ce0.45-0.65Cu0.45-0.65POx or the empirical formula K0.2-0.6Ce0.05-o.2Fe0.4-0.6Mo0.05-0.8POx. 14. A process as claimed in any of claims 1 to 7 characterised in that the oxidation catalyst has the empirical formula: AaBbCcVS bmOx where A = alkali metal, alkaline earth metal, T1, La, rare earth metal, Th, or mixtures thereof; B = Cu, Ag, Fe, Co, Ni, Mn, Cr, Nb, Ta, Ti, P, As, Sn, B, U, or mixtures thereof; C = Mo, W, Te, Bi, or mixtures thereof a = 0-1 b = 0-1 c = 0-1 m = 0.5-40, preferably 3-15; x = the number of oxygen S required to satisfy the valence requirements of the other elements present. 15. A process as claimed in claim 14 characterised in that B of the catalyst is iron or copper. 16. A process as claimed in claim 14 characterised in that the oxidation catalyst has the empirical formula VSb5Ox or the empirical formula VSbloOx. 17. A process as claimed in claim 14 or claim 15 characterised in that the alkali metal is potassium or cesium. 18. A process as claimed in any cf claims 1 to 7 characterised in that the oxidation catalyst comprises a mixture of two or more of the oxides of Mo, W, Fe, Co, Ni, V, Cr, Mn, Cu, Ag, B, P, alkali metal, alkaline earth metal, and rare earth metal. 19. A process as claimed in any of claims 1 to 7 characterised in that the oxidation catalyst is a heteropoly acid of Mo and W, or a salt of such an acid. 20. A process as claimed in any of claims 1 to 7 characterised in that the oxidation catalyst is a zeolite exchanged with one or more of the following elements namely alkali metals, alkaline earth metals, Fe, Cu, V, Sb, Pt, Pd, Ag, Mo, W and B. 21. A process as claimed in claim 20 characterised in that the zeolite is zeolite Y, Zeolite X, ZMS-4, ZMS-5, ZMS-10 or mordenite.

Inventors: GRASSELLI, ROBERT KARL, GUTTMANN, ANDREW TYTUS
Applicants: THE STANDARD OIL COMPANY
Application year: 1982
Main classification: C07C51
IPC codes: B01J23, C07B61, C07C57, C07C67, C07C51, C07C69