PROCESS FOR HYDROGENATING ACETIC ANHYDRIDE USING A CATALYST CONTAINING A NOBLE METAL

Abstract: Process for hydrogenating acetic anhydride by contacting hydrogen gas with the acetic anhydride in liquid phase in the presence of a homogeneous catalyst. The homogeneous catalyst is a rhodium or ruthenium catalyst combination of (1) a rhodium or ruthenium compound with methyl iodide and lithium iodide or (2) a ruthenium compound with methyl iodide. The process is capable of forming ethylidene diacetate, ethyl acetate and mixtures thereof, depending upon the appropriate selection of catalyst and reaction conditions.

Description: -1- PROCESS FOR HYDROGENATING ACETIC ANHYDRIDE USING A CATALYST CONTAINING A NOBLE METAL This invention relates to the hydrogenation of acetic anhydride in the presence of a catalyst containing rhodium or ruthenium. More specifically, this invention relates to contacting hydrogen gas with acetic anhydride in liquid phase in the presence of a homogeneous catalyst combination containing rhodium or ruthenium to obtain ethylidene diacetate and/or ethyl acetate. Ethylidene diacetate and ethyl acetate. are _ known chemical compounds of significant interest to the chemical industry. Ethylidene diacetate is a valuable chemical intermediate and is used, for example, in the preparation of vinyl acetate. Ethyl acetate is a well known solvent for many materials including, for example, cellulose esters. In recent years, interest has increased in developing new and commercially feasible processes for preparing ethylidene diacetate and ethyl acetate. One reason for such interest is that these chemicals are presently derived principally from petroleum which is relatively expensive and frequently in short supply. It is known that ethylidene diacetate and ethyl acetate can be prepared by the hydrogenation of acetic anhydride in the presence of noble metal containing homogeneous catalysts. However, very little prior art pertaining to such processes exists and the few processes described in the art have significant disadvantages. For example, U.S. Patent 3,579,566, issued .May 18, 1971 describes the ' hydrogenation of acetic anhydride to predominantly form ethylidene diacetate using a noble metal containing homogeneous catalyst comprising a complex of a Group VIII noble metal and a biphyllic ligand of phosphorous, arsenic or antimony and U.S. Patent -2- 3,957,827, issued May 18- 1976 describes the hydrogenation of acetic anhydride to form ethyl acetate using a ruthenium containing homogeneous catalyst having the formula: SΛ_X (ER^- -- — where X is hydrogen, halogen or lower alkyl, n is 0-2, R is alkyl, cycloalkyl, aryl or a bidentate ligand, x is 1-3, L is a neutral ligand and y is 2 or 3. Unfortunately slow reaction rates are obtained using the catalysts disclosed in U.S. Patents 3,579,566 and 3,957,827. Furthermore, it is known that organic catalyst components such as the organic phosphines employed in the aforementioned U.S. patents are subject, to degradation upon prolonged exposure to the temperatures and other reaction conditions normally employed in the hydrogenation of acetic anhydride. This results.particularly in continuous operations, in the build-up of unwanted by-products known as "soot" or "tar" which cannot be easily separated from the catalyst present in the reaction medium. This makes it very difficult to achieve efficient catalyst recovery which is necessary as the noble metal containing, catalysts are very expensive. This invention provides a process for hydrogenating acetic anhydride which comprises contacting hydrogen gas with acetic anhydride in liquid phase in the presence of a homogeneous catalyst that is a combination of (1) a rhodium or ruthenium compound with methyl iodide and lithium iodide or (2) a ruthenium compound with methyl iodide. It will be evident from the following ' description that the process of this invention provides a means for obtaining ethylidene diacetate and/or ethyl acetate in reasonable quantities at good to excellent reaction rates. . Furthermore, this process is quite flexible in that the composition of -3- the reaction product can be varied to meet the desires of the operator. Thus, as described more fully hereinafter, the appropriate selection of the catalyst composition and reaction conditions makes it possible to obtain ethylidene diacetate to the substantial exclusion of ethyl acetate, ethyl acetate to the substantial exclusion of ethylidene diacetate or mixture of such compound ' s in good to excellent space-time yields. Space-time yield is the yield of desired product in a unit of time per unit of liquid volume. It is conveniently expressed in grams (of product)/per liter (of liquid volume)/hour (of reaction) . In addition, methyl iodide which is employed as an organic component of the homogeneous catalysts used in the process of this invention, is much less susceptible to degradation than organic ' phosphine components of the type disclosed in U.S. Patents 3,579,566 and 3,957,827. This results in the formation of less "soot" or "tar" and simplifies the catalyst recovery problem previously discussed. Also, as illustrated by Example 3 which follows, the ruthenium containing catalysts can be used in the process of this invention to effectively hydrogenate mixtures of acetic anhydride and ethylidene diacetate to form ethyl acetate. Such mixtures are conveniently obtained from the carbonylation of methyl acetate in the presence of hydrogen. The reactions involved in the process of this invention can be represented as follows: -4- 2 βthylidene H 2 ^ Ethyl Acetic Diacetate * Acetate Acid In hydrogenating the acetic anhydride, as represented above, the rhodium containing homogeneous catalysts direct the reaction to the formation of ethylidene diacetate and only very small amounts of ethyl acetate are formed. In contrast, the ruthenium containing homogeneous catalysts, with varying amounts of methyl iodide and lithixna iodide, are used iα. this invention to prepare ethylidene diacetate with little or no ethyl acetate, ethyl acetate with. little or no ethylidene diacetate or mixtures of ethylidene diacetate with, ethyl acetate. The acetic acid obtained as a co-product in the reaction can, of course, be readily recovered, dehydrated and recycled &s acetic anhydride to- avoid the loss of starting material. The rhodium and ruthenium catalysts employed in this invention are "homogeneous catalysts". Such catalysts are known in the art and identified as "homogeneous" because they are soluble in the liquid ' reaction phase. This is in contrast to noble metal containing heterogeneous catalysts which are insoluble in such phase. The homogeneous catalysts are typically formed by mixing a noble metal compound, e.g., an inorganic compound such as -5- RhCl 3 .xH 2 0 or uCl^. ^O with an iodine component or components, e.g., methyl iodide and/or lithium iodide, as illustrated by U.S. Patent 4,046,807, issued September 6, 1977, European Published Patent Application No. 0008396, published March 5, 1980 and Japanese Published Patent Application No. 75-47922, published April 28, 1977. Examples of suitable rhodium compounds include rhodium halides such as RhCl-, Rl-Br- and Rhl-, 10 rhodium carbonyl halides such as h^CO ^ Br £ > oxides such as O?. Examples of suitable ruthenium compounds include ruthenium halides such as UCI-.3H2O, ruthenium oxides such as 0 2 a∑-d 15 ruthenium salts of organic acids such as ruthenium acetate. An effective catalyst that can be employed in the practice of this invention is a homogeneous rhodium catalyst which is formed by contacting the 20 rhodium compound such as a rhodium halide or oxide with the iodine compounds in the presence of carbon monoxide. The carbon monoxide can conveniently be supplied in a gas stream fed to the hydrogenation zone or it can be derived as a decomposition product 5 from the acetic anhydride present in the zone. A carbon monoxide pressure of 10 to 500 psig (170.3 to 3,548.9 kPa) can be maintained during the hydrogenation reaction to supply the carbon monoxide to the catalyst, although a carbon monoxide partial 0 pressure can inhibit the hydrogenation reaction rate when very high total pressures are employed in —-_ ' -practicing this invention. The concentration of the rhodium or ruthenium employed in the process of this invention 5 can vary substantially depending upon such factors as the temperature, pressure and the desired space-time -6- yield. However, when catalysts that contain rhodium are used at appropriate temperatures and pressures as indicated herein, rhodium concentrations (as rhodium metal) in the range of 50 to 5000 ppm, preferably 50O to 2500 ppm, based upon the acetic anhydride to be hydrogenated^are employed in practicing this invention. Where the catalyst contains ruthenium, -\) concentrations of ruthenium (as ruthenium metal) in the range of 100 to 2500 ppm, preferably 500 to 1000 ppm. based upon the material to be hydrogenated, (acetic anhydride or mixture of acetic anhydride with ethylidene diacetate, e.g.) generally give satisfactory results. The specific rhodium or ruthenium compound that is introduced into the hydrogenation zone is not particularly critical so long as it is soluble in the liquid phase (the reaction medium) o_r provides a soluble catalyst containing rhodium or ruthenium, i.e., a homogeneous catalys . Th amount of methyl iodide used- in the catalyst is also subject to variation and depends upon several factors including, the specific hydrogenation product or- products desired, whether the noble metal in the catalyst is. rhodium or ruthenium, the presence or absence of lithium iodide, the temperature, and to a lesser degree, the pressure employed in the hydrogenation process. Vith catalysts that contain rhodium, the amount of methyl iodide employed can be in the range of 5 to 35, preferably 10 to 20, weight percent, based on the weight of acetic .anhydride to be hydrogenated. The absence of lithium iodide from the catalyst results in the formation of very large (and unacceptable) amounts of acetic acid. Accordingly, when the catalyst contains rhodium, the concentration of lithium iodide is in the range of 0.1 to 5, -7- preferably 0.3 to 3 weight percent, based on the weight of material to be hydrogenated. The mole ratio of lithium iodide to rhodium is normally in the range of 4 to 300 and preferably in the range of 5 to 100. When the catalyst employed in this invention contains ruthenium, the amount of methyl iodide used can be in the range of 0.25 to 15 weight percent, based on material to be hydrogenated. However, depending upon the particular hydrogenation product desired, the amount of methyl iodide is subject to variation within that range. For example, where it is desired to hydrogenate acetic anhydride to ethylidene diacetate and essentially no ethyl acetate, the amount of methyl iodide employed is in the range of 3 to 15 weight percent based on the acetic anhydride. . The use of methyl iodide without lithium iodide in the lower part of the range generally requires the use of temperatures of 200°C. or above. Lithium iodide in a concentration of 0.3 to 2, preferably 0.5 to 1.5, weight percent, based on the weight of the acetic anhydride, increases the rate of ethylidene diacetate formation at a given temperature. The lithium'iodide can be added to the hydrogenation zone as such or it can be generated in the reaction mixture from suitable lithium compounds such as lithium hydroxide, lithium carbonate or lithium acetate. Where it is desired to hydrogenate acetic anhydride or a mixture of acetic anhydride and ethylidene diacetate to ethyl acetate, the amount of methyl iodide used in the catalyst is less than 5 ' weight percent, often less than 1.5 and preferably less than 1 weight percent, based on the weight of the reactant(s), i.e., acetic anhydride and, when present, ethylidene diacetate. Good reaction rates for the production of ethyl acetate are obtained when -8- the catalyst contains less than 0.1 weight percent, lithium iodide, and preferably no lithium iodide. When it is desired to produce significant amounts of ethylidene diacetate with the ethyl acetate, e.g., 5 weight ratios of 2:1 to 1:2, the amount of methyl iodide normally used is 7.5 to 25 weight percent, while the amount of lithium iodide is in the range of 0.5 to 1.5 weight percent. The process of this invention is carried out •tn with, the acetic anhydride in liquid phase. A solvent or diluent which is inert to the reactants can be used if desired. If a solvent or diluent is used, the conventional solvents or diluents normally used with noble metal containing homogeneous catalysts ■ y e give satisfactory results. Acetic acid is an example of such a solvent, or diluent and it can be added to the. hydrogenation zone with the acetic anhydride. However, since acetic acid is formed as a co-product during the process it is generally not necessary to n add acetic acid to the hydrogenation zone' from an external source. The temperature and pressure employed in the process of this invention are interrelated, with respect to the reaction rate and also depend, to a 25 large extent, upon the nature of the catalyst. In general, the process is run at relatively mild, but somewhat elevated temperatures and pressures. With the " catalysts containing rhodium, satisfactory results are usually obtained with temperatures in the 30 range of 100 to 225°C, preferably 150° to 190°C. and pressures (total reaction pressures) in the range of 100 to 500 psig (790.9 to 34,576.4 kPa) , preferably 500 to 3000 psig (3,548.9 to 20,786.4 kPa). With catalysts containing ruthenium, the temperatures are 35 in the range of 125° to 250°C, preferably 160° to 210°C, or even 185° to 210°C. and the pressures (total reaction pressures) are in the range of 500 to 2200 psig (3548.9 to 15,270.5 kPa) , preferably 1000 to 2000 psig (6996.4 to 13891.4 kPa) . The pressures can be maintained by the hydrogen gas or a mixture of 5 hydrogen gas with another gas, e.g., carbon monoxide, that is added to the hydrogenation zone. The hydrogenation process of this invention is performed as a batch operation or, more suitably, - as a continuous operation wherein acetic anhydride 10 alone or with ethylidene diacetate is continuously fed to a hydrogenation zone and reaction mixture containing the desired product or products is continuously removed. Unreacted materials and the co-product acetic acid resulting from hydrogenation 15 can be removed from the reaction zone, separated in a distillation unit, and recycled along with any catalyst and iodides present, back to the reaction zone. The process of the invention is further 20 illustrated by the following examples. Example 1 Acetic anhydride can be effectively hydrogenated to form ethylidene diacetate in the presence of a catalytic amount of a homogeneous 25 catalyst combination of a rhodium compound, methyl iodide and lithium iodide using varying reaction conditions and amounts of catalyst components. Also, as previously indicated herein, carbon monoxide can be added to the reaction zone with hydrogen but, as 30 illustrated by Run 3, this is an optional feature of the invention. " --- To illustrate, acetic anhydride (800 g) was hydrogenated for 2 hours in the presence of a catalyst combination of a rhodium compound added as 35 Cl 3 .xH 2 0, with methyl iodide and lithium iodide, and acetic acid (100 g) using the _OMPI -10- temperatures and total pressures shown in Table I. The acetic anhydride, acetic acid, rhodium chloride, methyl iodide and lithium iodide were put into a 1.8 liter autoclave fitted with a stirrer. The autoclave was purged with carbon monoxide and then carbon monoxide was added to provide the pressure indicated in Table I (Initial CO, psig (kPa)). The autoclave was sealed, heated and the contents stirred until the reaction temperature was reached, at which time hydrogen gas was added to increase the autoclave internal pressure to a predetermined value. The time at which the autoclave internal pressure reached the predetermined value was taken as the start of the 2 hour reaction time. The pressure in the autoclave was maintained at the preset value during each run by adding hydrogen gas at the same rate at which it was consumed. When the reaction time elapsed the autoclave was cooled using a stream of cold air. Gas was vented from the autoclave and the reaction product was analyzed by gas chromatographic- methods. Table I shows the temperature (°C.) and pressure (Initial CO and Total, psig (kPa)) used, the amounts of RhCl-.xH 2 0 (g) and methyl and lithium iodides (CH-I, Lil, g.) added to the autoclave in each run, the amounts (in moles) of acetic acid (HOAc) and ethylidene diacetate (EDA) produced, the amount of acetic anhydride (Ac ^ O, in moles) recovered, and the percent yield of ethylidene diacetate (EDA). The percent yield EDA was determined by measuring, by the gas chromatographic method, the amount of Ac«0 present in the autoclave at the start of the reaction when the reaction temperature was reached. The amount of c 2 O was — again measured at the end of the two hour reaction period (amount c 2 0 recovered). The di ference in these two measured values was divided by two in order -11- to account for the stoichiometry of the reaction and determine the value for a 100% theoretical EDA yield under the conditions of reaction. The value for the amount of EDA recovered was then divided by the value of the 100% theoretical EDA yield and converted to percent. Table I Initial CO Total Temp Pressure, Preasure Run βlg (kPa) palft (kPa) 1 175 100 (790.9) 1500 (10,443.8) 2 175 100 (790,9) 2500 (17,338,9) 3 175 0 1500 (10,443.8) 4 175 100 (790.9) 1500 (10,443.8) 5 130 100 (790.9) 2500 (17,338.9) Table I Cont 'd. EDA HoAc, Ac?0, 0/0 Yield Run RhClyxH^O.g . Lil,g. CH3I1J molea moleβ molea EDA 1 0.62 3.18 100 0,72 0.84 0.78 92 2 0.62 3.18 100 1.12 1.22 1.32 85 3 0.62 3.18 100 0.76 0.93 .98 77 4 0.62 3.18 50 0.41 0.45 0.41 100 5 2.48 12.70 100 0.81 0,81 0.84 97 <_υ -14- Exa ple 2 Acetic anhydride can be effectively hydrogenated to form ethylidene diacetate, ethyl acetate and mixtures of these compounds using a homogeneous catalyst combination of a ruthenium compound with methyl iodide alone or methyl iodide plus lithium iodide. Depending upon the reaction conditions, catalyst components and concentration, the reduction or hydrogenolysis of acetic anhydride is favored. To illustrate, acetic anhydride (100 g.) was hydrogenated for 30 minutes in the presence of a catalyst combination of ruthenium added as rutheniu chloride (0.25 g) with methyl iodide and lithium iodide in the amounts 7 shown in Table II. For comparison, a control run was made with a catalyst containing no iodide compounds. .The temperatures and total pressures employed in the reaction are shown in Table II. The acetic anhydride and the catalyst were placed into a 300 ml. autoclave designed to operate in a rocking mode. The autoclave was purged with 100 psig (790.9 kPa) hydrogen gas at 25°C and then the gas was vented. The autoclave internal pressure was increasd to 10 psig (170.3 kPa) by adding hydrogen gas at 25°C. The autoclave was sealed, heated and rocked until the reaction temperature was reached, at which time additional hydrogen gas was added to increase the autoclave internal pressure to a predetermined value. The time at which the autoclave internal pressure reached the predetermined value was ~ taken as the start of the 30 minute reaction time. The pressure was maintained at the predetermined value during each run by adding hydrogen gas at the same rate at which it was consumed. When the reaction time elapsed, the autoclave was cooled using a stream of cold air. Gas was vented from the -15- autoclave and the reaction product was analyzed by gas chromatographic methods. Table II shows the temperature (°C.) and pressure (psig (kPa)) used, the amounts of methyl and lithium iodide (CH3I, Lil, g.) added, the amounts (in moles) of ethyl acetate (EA), acetic acid (HOAc) and ethylidene diacetate (EDA) produced, the amount of acetic anhydride (Ac 2 0, in moles) recovered and the space-time yields (STY, in grams/liter/hour) for ethylidene diacetate (EDA) and ethyl acetate (EA) . * Table II 'emp., Preβsure EA, HOAc, AcoO, EDA, EDA, Run °C. ' pβig.(kPa) UI, g. Mel ι 8? moleβ moleβ moleβ moleβ STY Control 200 500 (3,548.9) - 0.344 0.718 0.031 91 1 200 500 1 (3,549.9) - 0.35 0.259 1.020 - - — 2 200 500 (3,548.9) m 0.50 0,375 1,20 0,032 0.003 9 3 160 2000 (13,891.4) - 0.50 0.388 1.26 - 0.01 29 4 200 2000 (13,891.4) *_m 0.50 0.443 1,10 - wm mm 5 210 1000 (6.996.4) em 1,0 0.390 1.21 0.034 - - 6 210 2000 (13,891.4) 1.0 0.340 1.17 0.037 - - 7 170 1000 (6,996.4) . 9.0 0.014 0.563 0.408 0.161 470 8 170 2000 (13,891.4) 9.0 «_» 0.308 0.498 0.205 600 9 190 2000 (13,891.4) 1.0 9.0 0 * 002 0.268 0.614 0.169 493 10 205 2000 (13,891.4) 0.5 5.0 0.018 0.457 0.250 0.294 858 11 175 2000 (13,891.4) 1.5 13.0 0.007 0.175 0.641 0.126 368 12 205 2000 (13,891.4) 0.5 13.0 0.018 0.643 0.022 0.365 1066 13 205 2000 (13,891.4) 1.5 5.0 0.016 0.301 0.502 0.174 508 14 205 2000 (13,891.4) 1.5 13.0 0.006 0.432 0.347 0.255 745 NOTE. A daβh (-) in thlβ and the following Table -17- Example 3 A mixture of acetic anhydride with ethylidene diacetate can be effectively hydrogenated to ethyl acetate using a homogeneous catalyst combination of a ruthenium compound with methyl iodide under varying reaction conditions. To illustrate, a mixture of acetic anhydride with ethylidene diacetate (50 g. of each) was hydrogenated in the presence of a catalyst combination of 0 ruthenium added as ruthenium chloride (0.25 g) , with methyl iodide in the amounts shown in Table III and at the temperatures and pressures indicated. No lithium iodide was used in these runs. The acetic anhydride, ethylidene diacetate, ruthenium chloride 5 and methyl iodide were placed in a 300 ml. autoclave designed to operate in a rocking mode. The autoclave was purged with hydrogen at 25°C. and then a predetermined amount of hydrogen gas was added. The autoclave was sealed, heated and rocked until a predetermined temperature was reached and then held at that temperature for 30 minutes. No additional hydrogen gas was added during the reaction period. When the 30 minute reaction time had elapsed the autoclave was cooled by a stream of cold air. Gas was vented from the autoclave and the reaction product was analyzed by gas chromotographic methods. Table III shows the temperature (°C.) used, the ' amounts of hydrogen (H * * moles) and methyl iodide (CH^I, g.) added, the amounts (in moles) of ethyl acetate (EA) and acetic acid (HOAc) produced, _ ^ the amount, (in moles) of acetic anhydride (Ac^O) " and ethylidene diacetate (EDA) recovered and the percent yield and space-time yield (STY, in grams/ liter/hour) for ethyl acetate produced. Table III Tgmp., ,H2ι EA, HOAc, Ac2θ t EDA EA EA un moleβ CH 3 I t B- moleβ moles moleβ moleβ Yield STY 1 175 1.0 1.0 0.256 0.763 0.091 0.095 57.3 451 2 160 1.5 0.25 0.137 0.340 0.176 0.303 81,1 241 3 190 0.5 0.25 0.123 0.367 0.137 0.301 56.4 216 4 160 1.5 1.75 0.265 1.210 0.055 0.017 48.8 466 5 190 1.5 1.75 0.323 1.320 0.016 - 55.8 568

Claims: -19- Clai s : 1. A process for hydrogenating acetic anhydride which comprises contacting hydrogen gas with acetic anhydride in liquid phase in the presence of a homogeneous catalyst that is a combination of (1) a rhodium or ruthenium compound with methyl iodide and lithium iodide or (2) a ruthenium compound with methyl iodide. 2. The process according to claim 1 wherein the catalyst contains rhodium. 3. The process according to claim 1 wherein the catalyst contains ruthenium. 4. The process according to claim 2 wherein the amount of methyl iodide is 5 to 35 weight percent, and the amount of lithium iodide is 0.1 to 5 weight percent, based on the weight of acetic anhydride» 5. The process according to claim 2 wherein the hydrogen gas is contacted with acetic anhydride a t. a temperature of 100° to 225°C. and a 'pressure of 790.9 to 34,576.4 kPa, the amount of methyl iodide is 5 to 35 weight percent, and the amount of lithium iodide is up to 0.1 weight percent, based on the weight of acidic anhydride. 6. The process according to claim 2 wherein . the acetic anhydride is contacted with a mixture of hydrogen and carbon monoxide gases. 7. The process according to claim 3 wherein the hydrogen is contacted with acetic anhydride at a temperature of 160° to 210° C. and a pressure of - 3,548.9 to 15,270.5 kPa, the amount of methyl iodide is 3 to 15 weight percent, and the amount of lithium iodide is 0.3 to 2 weight percent, based on the weight of acetic anhydride. 8. The process according to claim 3 wherein the hydrogen is contacted with acetic anhydride at a -20- temperature of 160° to 210°C. and a pressure of 3,543.9 to 15,270.5 kPa, the amount of methyl iodide is 0.25 to 1.5 weight percent, and the amount of lithium iodide is up to 0.1 weight percent, based on the weight of acetic anhydride. 9. The process according to claim 3 wherein the hydrogen gas is contacted with a mixture of acetic anhydride and ethylidene diacetate at a temperature of 160° to 210°C. and a pressure of 3,548.9 to 15,270.5 kPa, the amount of methyl iodide is 7.5 to 25 weight percent, and the amount of lithium iodide is 0.5 to 1.5 weight percent, based on the weight of acetic anhydride and ethylidene acetate.

Inventors: LARKINS THOMAS HASSELL JR, POLICHNOWSKI STANLEY WHITMORE
Applicants: EASTMAN KODAK CO
Application year: 1981
Main classification: C07C67
IPC codes: B01J31, C07B61, C07C51, C07C69