TERTIARY ALKYL ESTER PREPARATION

Abstract: A tertiary olefin such as isobutylene is reacted with a lower carboxylic acid to produce the ester in the presence of a large pore zeolite catalyst such as Zeolite Y, Zeolite beta or Zeolite X.

Description: TERTIARY ALKYL ESTER PREPARATION Background of the Invention Field of the Invention The present invention provides an improved method for the preparation of esters such as t-butyl acetate by reaction of a tertiary olefin with acetic acid in the presence of a large pore zeolite catalyst such as Zeolite Y, Zeolite X or Zeolite beta. Description of the Prior Art It is known to produce esters by the reaction of an olefin such as isobutylene with a lower carboxylic acid over a sulfonate group-containing cation exchange resin. See U.S. Patent 3,678,099 and the references disclosed therein including U.S. Patents 2,678,332, 3,031,495, 3,172,905 and 3,173,943. A problem which is encountered in such prior procedures has been the tendency for polymerization of the olefin to occur during the esterification which results both in significant yield losses and in the formation of products such as olefin dimer which are difficult to separate from the product ester. For example, isobutylene dimer forms an azeotrope with t-butyl acetate thus making separation exceedingly difficult. Problems of diisobutylene formation can be substantially overcome through the use of a selectivity enhancing modifier such as tertiary butanol. However, although the use of such a modifier has striking advantages, its use entails additional processing costs and purification procedures. Other processes are described. For example, U.S. Patent 3,492,341 describes the reaction of isobutylene with acetic acid to form ester using a mordenite aluminosilicate catalyst. U.S. Patent 4,365,084 describes ester production by reaction of a linear or slightly branched olefin with acetic acid using a catalyst such as HZSM-5. The use of olefins having unsaturation at the number 2 carbon atom is excluded. U.S. Patent 4,461,729 is similar to 4,365,084 and contains the additional step of hydrolyzing the ester to form secondary alcohol. U.S. Patent 4,465,852 relates to ester preparation by reaction of olefin with acetic acid. Although a great number of olefins are mentioned, including isobutylene, and a great number of catalysts are mentioned, including ZSM-5, the olefins exemplified are ethylene and propylene and the claims are limited to ethylene, propylene and butylene. Copending patent application Serial Number 09/022183 filed February 11, 1998 describes ester preparation by reaction of an olefin such as isobutylene with acetic acid using a ZSM-5 catalyst. Data are presented indicating that at the reported conditions of the testing, poor results were achieved with large pore zeolite catalyst, Zeolite beta. Brief Description of the Invention In accordance with the invention, olefin and lower carboxylic acid are reacted in the presence of a large pore acidic zeolite such as Zeolite Y, Zeolite X, or Zeolite beta at conditions where ester is formed at high rates and selectivity, and whereby the formation of olefin polymerization products is maintained at a very low level. Detailed Description The present invention is applicable to the formation of esters having the formula O // R - C-O-R ! wherein R n is a C 4 or C 5 tertiary alkyi group and R is hydrogen or a C C 2 alkyl group. T-butyl acetate is an especially preferred product. In accordance with the invention, olefin and organic carboxylic acid are reacted in the liquid phase to form ester over a solid acidic large pore size zeolite catalyst. The large pore zeolites used in accordance with the invention are those having twelve-ring pores as described, for example, at page 19 of "Introduction to Zeolite Science and Practice", van Bekkum et al. Elsevier (1991). Zeolite Y is especially useful as is Zeolite beta and Zeolite X. The zeolites employed are suitably made with conventional binders, eg. alumina, silica, and the like. The conditions at which the esterification reaction is carried out are exceedingly important. The large pore acidic zeolites are extremely active catalysts and unless certain reaction conditions are employed, excessive amounts of olefin polymer are obtained. The esterification reaction is carried out at pressures sufficient to maintain the liquid phase, usually 50 psig or higher. The upper pressure limit is governed largely by practical considerations , little is to be gained by operating at pressures in excess of 800 psig. Operation at 250-500 psig is generally preferred. Reaction temperature is important, temperatures of about 20 to 80 °C are suitable, temperatures of about 35 to 50 °C are preferred. Excessive contact times, especially at the higher temperature ranges are to be avoided. Reactant liquid weight hourly space velocities (WHSV) of about 10-100 hr 1 , preferably 25 to 50 hr 1 are employed. These figures are based on the large pore zeolite content of the catalyst contact solid. The mol ratio of olefin to carboxylic acid can vary widely, ratios of 0.1- 10 mols olefin per mol carboxylic acid are generally useful, ratios of 0.125 to 0.5 mols olefin per mol carboxylic acid are especially useful. The higher amounts of acid relative to olefin improve reaction selectivity and further aid in suppressing dimer make. Where a selectivity enhancing modifying agent such as described in copending application Serial No. 08/816,704 filed March 13, 1997 is used, reaction conditions outside the above ranges can be used. For example, higher temperatures and longer contact times can be employed as can higher olefin to carboxylic acid ratios where the modifier is used. For example, reaction temperatures in the upper part of the 20-80°C range can be used and liquid hourly space velocities below 10 hr 1 , eg. as low as 4 hr 1 can be used where a selectivity enhancing modifier is used. Especially preferred selectivity enhancing modifiers, where one is used, are t-butyl alcohol, t-amyl alcohol and the lower (0^ 3 ) alkyl ethers thereof such as methyl tertiary butyl ether, methyl tertiary amyl ether, and the like. Where used, at least 1 wt % of modifier based on the feed is used up to about 50 wt %. The following examples illustrate the invention: A series of esterification runs were carried out using large pore zeolite catalysts and reacting isobutylene and acetic acid to form t-butyl acetate, the runs were carried out at 500 psig. The following table shows the catalyst employed, the feed reactant composition, and the results obtained: Table 1 *- OS Run Catalyst Reaction WHSV Molar % i-C 4 % Sel. % Sel. % Sel. % Sel. Temp., °C hr. "1 AcOH: Conversion TBAC DIB TIB OTHERS i-C 4 1 21.0g A 75 5.5 2.0:1 85 17.4 42.6 26.7 13.3 2 21.0g A 60 5.3 1.7:1 62 77.2 21.5 1.2 0.2 3 21.0g A 50 5.6 1.9:1 61.6 89.6 10.0 0.3 0.1 4 21.0g A 40 5.6 1.8:1 56.9 93.5 6.3 0.2 5 20.0g B 80 2.88 7.4:1 5.8 96.3 3.7 — — "0 O H W SO v© VO Table 1 continued Run Catalyst Reaction WHSV, Molar % i-C 4 % Sel. % Sel. % Sel. % Sel. Temp., °C hr. "1 AcOH: Conversion TBAC DIB TIB OTHERS i-C 4 6 5.0gA 60 11.5 8.2:1 81.0 55.6 34.8 8.2 1.4 15.0g B 7 5.0gA 60 23.2 8.2:1 79.1 76.2 21.0 2.6 0.3 15.0gB σ\ 8 5.0gA 50 23.7 8.4:1 82.4 94.1 5.6 0.3 — 15.0g B 9 5.0gA 40 23.4 8.6:1 86.2 97.8 2.1 0.1 — 15.0gB 10 5.0gA 40 36.0 8.2:1 73.5 97.9 2.0 0.1 — 15.0 gB O H 4-. "-- Table 1 continued 4-. ^1 Run Catalyst Reaction WHSV, Molar % i-C 4 % Sel. % Sel. % Sel. % Sel. Temp., °C hr.., AcOH: Conversion TBAC DIB TIB OTHERS i-C 4 11 5.0gA 35 23.7 8.4:1 81.0 98.3 1.6 0.1 — 15.0gB 12 5.0gA 35 35.4 8.1:1 69.6 98.4 1.6 — — 15.0gB 13 5.0gA 50 35.8 8.2:1 73.7 95.7 4.1 0.2 — 15.0gB 14 5.0gA 60 23.4 8.4:1 88.4 8.8 13.9 72.5 4.7 15.0gB 15 5.0gA 40 23.7 8.4:1 85.1 69.7 16.1 13.5 0.7 15.0gB O H W SO SO SO 5 *-i Table 1 continued Run Catalyst Reaction WHSV, Molar % i-C 4 % Sel. % Sel. % Sel. % Sel. Temp., °C hr. "1 AcOH: Conversion TBAC DIB TIB OTHERS i-C 4 16 5.0gA 40 36.0 7.7:1 79.6 79.2 12.9 7.5 0.4 15.0gB 17 2.5gC 40 48.3 8.6:1 84.7 83.4 11.3 5.0 0.3 17.5g B 18 2.5gC 40 71.1 8.1:1 75.9 86.1 10.1 3.5 0.2 17.5g B 19 5.0gC 40 23.8 8.1:1 83.6 71.6 14.4 13.2 0.8 15.0gB n H M \© so SO 4-- o SO SO Di Table 1 continued *- Run Catalyst Reaction WHSV Molar % i-C 4 % Sel. % Sel. % Sel. % Sel. Temp., °C hr. '1 AcOH: Conversion TBAC DIB TIB OTHERS i-C 4 20 5.0g C 40 35.8 8.2:1 85.0 82.1 10.9 6.6 0.4 15.0g B 21 5.0g C 40 34.9 8.0:1 82.9 93.5 5.5 0.9 0.1 15.0g B 22 2.5g C 40 69.8 8.0:1 65.1 95.3 4.6 0.1 — SO 17.5g B O H M -a SO so SO 4-> 10 In the above tables, AcOH is acetic acid i-C 4 is isobutylene TBAC is t-butyl acetate DIB is diisobutylene TIB is triisobutylene Space velocity is based on zeolite content of contact solid Catalyst A is Zeolite Y Contact solid B is inert alumina Catalyst C is Zeolite beta In the above, Run 1 is comparative showing the high production of isobutylene polymers at high temperatures and low space velocity. In Runs 2-4, 10 wt % tertiary butyl alcohol was added to the feed as a selectivity enhancing modifier. As a result of the use of the modifier, selectivity to the ester was greatly improved at the conditions employed, i.e. low space velocities. The data also show the pronounced effect on selectivity of reduction of the reaction temperature. Run 5 was carried out without the large pore zeolite, only inert solid alumina was used. Only minimal conversion was achieved. Runs 6-13 were carried out with a mixture of Zeolite Y and inert alumina as contact solid. The data show the excellent results achieved without modifier, and indicate the beneficial effects of reducing reaction temperature and decreasing contact time on ester production. Runs 14-22 were carried out using a mixture of Zeolite beta and inert alumina as the contact solid. Run 14 illustrates the relatively poor results obtained at higher temperatures (60 °C) as compared with operation at lower temperature (40 °C) in Run 15. A comparison of Runs 15 and 16 shows the effect of lowering contact time on ester selectivity. 11 In Runs 21 and 22, the feed contained 2 wt % tertiary butyl alcohol as selectivity enhancing modifier. A comparison of results obtained in these runs with the results in Run 20 and 18 shows the substantial effect of the modifier on ester selectivity.

Claims: 12 CLAIMS 1. A process for the production of a carboxylic ester, which process comprises reacting a C 4 or C 5 olefin with a lower carboxylic acid in the presence of a large pore acidic zeolite. 2. A process according to claim 1 which is effected at a temperature from 20 to 80°C. 3. A process according to claim 1 or 2 which is effected at a WHSV from 10 to 100 hr "1 . 4. A process according to any preceding claim which is effected at an olefin: acid feed molar ratio from 0.1: 1 to 10: 1. 5. A process according to any preceding claim effected at a pressure sufficient to maintain the reactants in the liquid phase. 6. A process according to any preceding claim wherein the olefin comprises isobutylene. 7. A process according to any preceding claim where the carboxylic acid comprises acetic acid. 8. A process according to any preceding claim wherein the catalyst comprises zeolite beta, zeolite X or zeolite Y. 9. A process according to any preceding claim wherein a selectivity enhancing modifier is used and wherein the WHSV is from 4 to 100 hr 1 . 10. Use of a large pore acidic zeolite as catalyst in the production of carboxylic ester, especially butyl acetate, from olefins and carboxylic acids.

Inventors: KARAS LAWRENCE J, KARAS, LAWRENCE, J.
Applicants: ARCO CHEM TECH, LYONDELL CHEMIE TECHNOLOGIE NE, ARCO CHEMICAL TECHNOLOGY, L.P., LYONDELL CHEMIE TECHNOLOGIE NEDERLAND B.V.
Application year: 1999
Main classification: C07C67
IPC codes: C07B61, C07C67, C07C69