METHOD FOR PREPARING 1,4-DIACYLOXY-2-BUTENES

Abstract: Crude butadiene can be used for making 1,4-diacyloxy-2-butenes by acyloxylation over palladium-containing catalyst by hydrogenating the crude butadiene sufficient to enhance at least one of catalyst activity and catalyst life for acyloxylation.

Description: METHOD FOR PREPARING 1.4-DIACYLOXY-2-BUTENES This invention pertains to processes for the preparation of l,4-diacyloxy-2-butenes from crude butadiene streams. Background to the Invention Heretofore, the reaction of butenes and/or butadiene with oxygen and carboxylic acid (acyloxylation) has been proposed to make, among other compounds, l,4-diacyloxy-2-butene (DAOB) . DAOB can be used as an intermediate to, e.g., 1,4-butanediol and tetrahydrofuran. Exemplary of the processes for making DAOB include that disclosed in United States Patent No. 3,872,163 (Shimizu, et al.). According to the patent, at least one unsaturated compound selected from the group consisting of butene-1, cis-butene-2, trans-butene-2, l-acyloxy-2-butene, l-acyloxy-l,3-butadiene and 1,3-butadiene is reacted with a carboxylic acid and oxygen in the presence of an effective amount of a catalyst containing palladium. The carboxylic acid is a monocarboxylic acid of the general formula RCOOH wherein R is a hydrocarbon radical of 1 to 18 carbons, and the ratio of starting-unsaturated compound to carboxylic acid is in the range of from 10:0.1 to 10:100. The amount of oxygen in the gas mixture is preferably 2 to 10 percent by volume and the reaction is carried out at temperatures preferably in the range of 80° to 200° C and a pressure of 20 atmospheres or less. The palladium catalyst preferably contains a promoter which is an alkali metal salt of a carboxylic acid. The examples show various butenes, mixtures of butenes, and butadiene as feed reactants. Example XXIX discloses the use of "BB-fraction" in the feed. The BB-fraction is said to contain butane, 1-butene, 2-butene, isobutene, butadiene and hydrocarbons having more than five carbon atoms at a volume ratio of respectively 4, 11, 6, 19, 56 and 4 percent. Onoda, et al., in United States Patent No. 3,755,423 disclose the preparation of unsaturated glycol diesters by reacting a conjugated diene, a carboxylic acid and oxygen in the presence of a catalyst composed of a mixture of palladium and at least one component of antimony, bismuth, selenium or tellurium. This catalyst is said by Onoda, et al., to be improved in their United States Patent No. 3,922,300 in which an activated carbon support is used and the catalyst has been treated by sequential oxidation and reduction steps. In the latter patent, the patentees state that butadiene and isoprene are the preferred conjugated dienes. "The conjugated diene need not be in purified form and may contain inert gases, such as nitrogen; or the like, or a saturated hydrocarbon such as methane, ethane, butane and others." (Column 2, lines 45 to 48) The carboxylic aςid are said to include any aliphatic, alicyclic or aromatic acids with lower aliphatic carboxylic acids being industrially desirable, and the acid is provided in an amount preferably above 50 weight percent of the reaction medium. The oxygen iε provided in an amount of 1 to 60 mole percent of the feed gases. The reaction is preferably conducted at 60° to 180° C at atmospheric or superatmospheric pressure. Japanese patent 84022692 discusses the preparation of acetic acid esters by reacting butenes with oxygen and acetic acid over palladium and lead-containing catalyst. 1-Butene is said to provide butyl acetate, sec-butyl acetate and 1,4-diacetoxybutane. Tanabe in United States Patent No. 4,075,413 addresses a problem of catalyst deactivation in the preparation of DAOB by the reaction of butadiene, acetic acid and oxygen over palladium-containing catalyst. Tanabe states that vinyleyelohexene can have a deleterious effect on catalyst life and therefore states that the vinylcyclohexene content of the feed should be 1 to 5000 parts per million by weight of butadiene and at least one polymerization inhibitor be present. At column 2 , lines 53 ei seq.. the patentee states: "A small amount of impurities such as carbonyl compounds, acetylenes, etc., are contained in industrial grade butadiene. Among such impurities, vinylcyclohexene, if contained in excess, may give rise to a side reaction and cause excessive deactivation of the acetoxylation reaction catalyst." Industrial grade.butadiene was not defined by Tanabe. Although there are few general specifications for butadiene, industrial grade butadiene is conventionally considered to be a refined butadiene stream from which impurities have been removed. Generally, industrial grade butadiene has less than 1000 parts per million by weight (ppmw) of acetylenes (and sometimes less than 50 ppmw of acetylene and less than 25 ppmw carbonylε). The majority of the butenes and butanes have also been separated from the butadiene. Vinyl cyclo- hexene is an impurity that is generated upon storage of butadiene and therefore may not be present in significant amounts in a freshly refined butadiene stream. Mitsubishi Kasei Corporation has implemented a commercial process for making 1,4-butanediol and tetrahydrofuran involving producing l,4-diacetyloxy-2-butene from 1,3-butadiene by reaction with acetic acid and oxygen in the presence of palladium-containing catalyst. See, for instance, Tanabe, "New Route to 14BG and THF," Hydrocarbon Processing, September, 1981, pages 187 to 190, and "1,4-Butanediol/Tetrahydrofuran Production Technology," ghemtech. December 1988, pages 759 to 763. While l,4-diacetyloxy-2-butene has been effectively produced on a commercial scale using a refined butadiene feed which has a relatively low content of vinylcyclohexene, refining these crude butadiene streams to obtain a refined butadiene can be relatively expensive. Generally, these refining processes involve one or more extractive distillation steps and two or more distillation operations. The ability to effectively use crude butadiene feedstreams could offer additional economic advantages. Crude butadiene streams, e.g., from thermally cracking ethane, other lower alkanes, naphthas or gas oils to ethylene, contain butane, various butenes (1-butene, cis-2-butene, trans-2-butene and isobutene), various acetylenes (e.g., methyl acetylene, dimethylacetylene and vinyl acetylene), carbonyls and heavier hydrocarbons, especially those containing five or more carbon atoms. Processes are therefore sought to effectively use these crude butadiene streams to produce l,4-diacyloxy-2-butene. Summary of the Invention In accordance with this invention, crude butadiene streams which have been subjected to mild hydrogenation to reduce the content of acetylenic components, are reacted (acyloxylated) with carboxylic acid and oxygen in the presence of an effective amount of palladium-containing catalyst to produce l,4-diacyloxy-2-butene (DAOB). Preferably, the total acetylene components in the hydrogenated crude butadiene stream are less than about 0.5, most preferably less than about 0.05, weight percent based on the total weight of the crude butadiene stream. Often, the mild hydrogenation conditions comprise a temperature of about 20°C to 70°C, a pressure of 6 to 11 atmospheres absolute, the presence of a catalytically-effective amount of palladium hydrogenation catalyst and a mole ratio of hydrogen to acetylenic components of about 0.5:1 to 5:1 or 10:1 or more. By the processes of this invention, crude butadiene streams can effectively be used to produce DAOB without undue deactivation of the palladium-containing catalysts. Detailed Discussion In the processes of this invention, treated, crude butadiene streams are reacted with carboxylic acid and oxygen to produce DAOB. Crude butadiene streams typically contain: Typical Amounts, Component weight percent Methyl acetylene 0.01 to 1.5 Isobutane 0.01 to 20 n-Butane 1 to 20 Isobutylene 0.02 to 40 1-Butene 4 to 25 Trans-2-Butene 1 to 10 Cis-2-Butene 1 to 10 1,3-Butadiene 25 to 90 C Acetylenes 0.1 to 5 C5Ε up to 1.0 Vinylcyclohexene 0.01 to 0.5 Crude butadiene streams may be obtained as a co-product from the thermal pyrolysis of hydrocarbon feedstocks to ethylene. The crude butadiene is typically the distillation fraction from the ethylene unit refining train which has predominately four carbons in the hydrocarbon chain, and boils in the range of about -11.6°C to about 10.9°C at atmospheric pressure. The crude butadiene is typically recovered as the overhead from the debutanizer tower in the ethylene unit. See for instance, Albright, Lyle F.; Crynes, Billy L. and Corcoran, William H., Pyrolysis Theory and Industrial Practice, pp. 41, 285-291 and 402-406, herein incorporated by reference. Alternatively, if the ethylene unit feedstock is predominately ethane, which produces only small quantities of C 5 and heavier hydrocarbons, the refining train may be configured such that a rough C 3 /C 5 fractionation is made first, with the C.'s recovered later from the lower boiling cut as a tails from the depropanizer column. The composition of the crude butadiene stream can vary greatly, depending on the type of hydrocarbon feedstock and cracking severity used in the pyrolysis section in the ethylene unit. In general, higher severity produces higher concentrations of 1,3-butadiene and C . acetylenes, and results in lower concentrations of butanes and butenes, in the crude butadiene for a given feedstock. The 1,3-butadiene and C. acetylenes concentrations are highest for high severity ethane cracking, and lowest for n-butane cracking at moderate severity. Isobutylene concentrations from ethane or propane cracking are generally low, with higher concentrations from naphtha or gas oil cracking. (See, for instance, Schulze, J., and Humann, M. , C^-Hvdrocarbons and Derivatives: Resources. Production. Marketing (1989), pp. 19-22.) Because the crude butadiene is recovered from the ethylene unit as a distillation fraction, the concentration of vinylcyclohexene, which boils at a much higher temperature (126°C at atmospheric pressure), is extremely low in the crude butadiene as it leaves the'olefins unit. Generally, the concentration of 4-vinylcyclohexene in the crude butadiene is less than 0.04 weight percent as the material leaves the ethylene unit. However, because the 1,3-butadiene can dimerize slowly to 4-vinylcyclohexene, even at ambient temperatures. the concentration of 4-vinylcyclohexene may increase to as high as 0.4 weight percent (or more) in the crude butadiene aε the material sits in storage, or during shipment to a butadiene refining facility. By feeding the crude butadiene from the olefins unit directly to the acyloxylation process, only minimal amounts of vinylcyclohexene have time to form. Usually, the amount of vinylcyclohexene in the feedstream for reaction with the carboxylic acid is less than 5000, preferably, less than about 2000, parts per million by weight based on the weight of butadiene. To the extent that vinylcyclohexene iε present in deleterious amounts, it may be removed by distillation or adsorption such as disclosed in United States Patent No. 4,075,413, herein incorporated by reference. As stated above, the crude butadiene stream contains acetylenic components. In accordance with this invention, sufficient amounts of the acetylenic components are hydrogenated to enhance at least one of catalyst activity and catalyst life. The hydrogenation is preferably conducted under conditions such that relatively little, if any, of the butenes and butadienes are hydrogenated. Exemplary of the hydrogenation processes includes Desiderio, et al:, in United States Patent No. 3,898,298; Frevel, et al., in United States Patent 3,897,511; and Gross, et al., in United States Patent 3,859,377, all herein incorporated by reference. According to Desiderio, et al., which is practiced commercially, a preferred process for selectively hydrogenating the vinyl acetylene and ethyl acetylene with relatively low conversion of butadiene uses a catalyst of about 0.05 to 0.2 percent palladium supported on alumina under hydrogenation conditions including a temperature within a range of about 20°C to about 70°C, preferably about 35 β C. Selectivity is achieved by maintaining the pressure within a range of about 6 to 11 atmospheres absolute, e.g., near 7, to achieve mixed (liquid and vapor) phase operation. The crude butadiene stream is passed through two reactors in series, with the hydrogen to acetylenes ratio set at about one in the first reactor and not more than about five in the second reactor. In a given example, the first reactor was operated with an inlet temperature of 41°C and outlet temperature of 52 β C, and the second reactor with an inlet temperature of 30°C and outlet of 60°C. A 93% conversion of vinylacetylene and 78% conversion of ethylacetylene was obtained with a 1% net loss of 1,3-butadiene to n-butenes. According to Gross, et al., a preferred process for selectively hydrogenating C. acetylenes in crude butadiene uses a catalyst of 0.01 to 1.0 weight percent palladium impregnated to a depth of at least 0.012 inch on a kieselguhr support having macropores of greater than 700A , constituting at least 75 percent of the total pore volume thereof. The reaction is carried out in the liquid phase at temperatures of 10°C to 80°C, preferably from 21°C to 66°C and pressures of about 40 psig to about 300 psig, preferably 80 to 200 psig. The weight hourly space velocity of the liquid C . hydrocarbons is less than about 50 and preferably within the range of 2 to 35. The hydrogen stream is diluted by at least 50 percent with an inert gas, preferably contains from 4 to about 35 mole percent hydrogen, and is present in a ratio of hydrogen to total C. hydrocarbons of 0.005 to 0.08 mole ratio, preferably at about 0.008 to 0.06 mole ratio. At these conditions about 94 to 99.5 percent of the vinylacetylene is converted and 48 to 77 percent of the ethylacetylene is converted, with a net 1,3-butadiene loss as low as one percent. Frevel, et al., which has also been commercialized, disclose a process which selectively reacts the alpha acetylenes from hydrocarbon streams using a finely divided metal catalyst, consisting of copper plus at least one polyvalent activator metal supported on a high surface area gamma-alumina containing a defined amount of Na_0. Suitable activator metals include silver, platinum, palladium, manganese, nickel, cobalt, chromium and molybdenum. The hydrocarbon stream, such as crude butadiene, is fed as a vapor over the catalyst at temperatures of about 40°C to about 250°C, preferably 50 to*100°C. Pressure is stated tόliavφ little effect on catalyst performance. In one example, the crude butadiene was fed at 64 gas hourly space velocity at 49-59 β C catalyst temperature and ambient pressure to give greater than 96 percent conversion of acetylenes. No data were given on net losses of 1,3-butadiene. Vinylacetylene and other acetylenes from the crude butadiene would be hydrogenated in the liquid phase, according to the processes disclosed by Desiderio, et al., or Groεε, et al. Crude butadiene iε generally available from the ethylene unit aε a liquid. Therefore, by performing the hydrogenation in the liquid phase, the costly vaporization and recondensation of the hydrogenated crude butadiene can be avoided. Although acetylenes can be removed from crude butadiene to low levels according to any number of absorption processes, e.g., see United States Patent Nos. 3,436,438; 3,772,158; 3,798,132; 4,024,028; 4,038,156; 4,054,613 and 4,076,595, in accordance with this invention the acetylenes are selectively hydrogenated. Thus, the energy and capital intensive distillation and refining stages required in the absorption processes are avoided. Moreover, by this invention, the hydrogenated crude butadiene is proven to be an advantageous feed for acyloxylation. Advantageously, the hydrogenated crude butadiene stream can be directly used to make DAOB without further treatment. Preferably, the crude butadiene stream is used within about 50, preferably within about 30, hours of the cracking operation which generates the C. stream. The carboxylic acid used in making DAOB may be any suitable aliphatic, alicyclic or aromatic carboxylic acid, e.g., of 2 to 18 or more carbon atoms. Preferably, the carboxylic acid is monofunctional. The commercially preferred carboxylic acids are acetic acid and propionic acid with acetic acid being most frequently desired. The carboxylic acid is usually provided in a molar amount of at least about 1:1 preferably about 2:1 to 20:1, to the unsaturated components in the feedstream. The source and amount of oxygen provided for the reaction may also vary widely. Often oxygen or air is used as the source of oxygen due to their ready availability. Preferably, the oxygen concentration in the reactor is maintained below explosive limits, and the mole ratio of oxygen to total unsaturates is about 0.5:1 to 20:1 or more, and the mole ratio of oxygen to carboxylic acid is often about 5:1 to 20:1. The oxygen may be diluted with gases such as nitrogen and carbon dioxide. The palladium-containing catalyst iε provided in a catalytically-effective amount. In batch processes, the catalyst is uεually present in an amount of about 0.001 to 5 weight percent based on the weight of the feed; however, the processes are preferably conducted in a continuous mode, and the space velocity (based on the volume of carboxylic acid and crude butadiene fed to the volume occupied by the catalyst) is about 0.5 to 100 or more reciprocal hours. The catalyst may be unsupported or supported on a suitable carrier, e.g., activated carbon, silica gel, silica-alumina, molecular sieves, alumina, clay, magnesia, magnesium aluminates, diatomaceous earth and pumice. When supported, the catalyst comprises about 0.1 to 40, preferably 2 to 30, weight percent palladium. The catalyst may contain co-catalysts such as bismuth. selenium, antimony and tellurium, e.g., in amounts of 0.05 to 25 percent by weight as well as promoters such as halide ions and alkali metal salts of carboxylic acids, especially of the carboxylic acid used in the formation of DAOB. United States Patents Nos. 3,755,423; 3,872,163; 3,922,300 and 4,075,413 which disclose catalysts and their preparation are herein incorporated by reference. The reaction is frequently conducted at an elevated temperature, e.g., between about 50° and 200° C, say, 80° and 160° C, and at reduced, atmospheric or superatmospheric pressure, for instance, between about 0.1 to 200, more often about 10 to 100, atmospheres absolute. The reaction may be conducted with the carboxylic acid and crude butadiene in the vapor, liquid or mixed vapor and liquid phases. Generally, the pressure and temperature are such that at least a portion of the carboxylic acid and crude butadiene stream is maintained in the liquid phase during the reaction. When a liquid phase reaction is sought, solvents may be used; however, excess carboxylic acid reactant may conveniently provide suitable liquid phases. The catalytic reaction may be conducted in any suitable reactor, e.g., fixed bed, moving bed, fluidized bed, ebulating bed, or rising bed reactors. Often, fixed bed reactors prove to ' e . adequate. The reactants may be introduced into the reactor in any suitable manner, e.g., as separate or multiple streams or as premixed streams. When at least a portion of the carboxylic acid and crude butadiene stream are in the liquid phase, the oxygen-containing gas may be introduced countercurrently or, preferably, cocurrently. The reaction mixture, when a liquid phase is to be present in the reactor, may contain polymerization inhibitor such as disclosed in United States Patent No. 4,075,413. Exemplary of polymerization inhibitors are phenolε and quinones and derivatives thereof such as hydroquinone, 2,5-di-t-butylhydroquinone, 2,5-di-t-amylhydroquinone, t-butylcatechol, di-t-butylphenols, di-t-butyl-p-cresol, 4,4'-butylidene bis (3-methyl-6-t-butylphenol) , 2,2 • -methylene bis (4-methyl-6-t-butylphenol) , quinone, anthraquinone, elemental sulfur and the like. The amount of polymerization inhibitor used will vary by the type of inhibitor used. In general, when employed, the polymerization inhibitor is present in an amount of between about 2 and 5000 parts per million by weight based on the weight of the total crude butadiene stream and carboxylic acid. Optionally, a portion of the liquid product from the acyloxylation reactor may be recycled to the feed of the reactor to help moderate the exotherm of the reaction to less than about 30°C. See United States Patent No. 4,235,729, herein incorporated by reference. Alternatively, the heat may be removed by any other conventional means, such as heat exchange with the reactor tubes. The temperature is preferably kept low to limit the reaction of butadiene to vinylcyclohexene. The unreacted C. hydrocarbons from the reactor effluent may be flashed from the reaction productε, and be recovered from the gaε phase by absorption into acetic acid as described by Tanabe, et al., in United States Patent No. 4,152,525, herein incorporated by reference. Alternatively, the untreated C.'s may be recovered by absorption into another suitable solvent, by distillation, or by other suitable means. The recovered C.'s may then be recycled to the reactor. See also, United States Patent No. 4,057,472. Generally, a portion of the unreacted C. hydrocarbons are purged from the reactor system to remove the butanes and other unreactive species. Because the butenes are less reactive than 1,3-butadiene in the acyloxylation reaction, the unreacted C. hydrocarbons purge typically contains butenes and butanes. In fact, this unreacted C. hydrocarbon stream may be similar in composition to the butenes/butanes co-product stream typically recovered from refining crude butadiene to rubber grade 1,3-butadiene. In this manner, the 1,3-butadiene from the original crude butadiene can be reacted out of the stream, eliminating the need to separate the crude butadiene into refined 1,3-butadiene and butenes/butanes in several separate expensive absorption and distillation steps before the acyloxylation reactors. By way Of example, a crude butadiene feedstream, available as a liquid co-product from an ethylene unit, contains: Pounds Per Hour and is fed at a rate of 11,416 pounds per hour to a hydrogenation reactor. The hydrogenation reactor feed is pumped directly to the first stage hydrogenation reactor as a liquid at 35°C and 150 psig. The reactor is a series of two fixed beds, packed with a 0.1% palladium on alpha alumina catalyst, such as disclosed in Example 1 of Desiderio, et al., United Stateε Patent No. 3,898,298. The two beds contain a total of 900 lbs. of catalyst, giving a WHSV of 12.7 pound feed/pound catalyst/hr. A mixture of hydrogen and methane is fed co-currently with the crude butadiene stream to the bottom of the first catalyst bed at a hydrogen to total acetylenes ratio of 1.0. This is equal to 17.8 pounds per hour hydrogen and 7.5 pounds per hour methane. The product from the first catalyst bed is fed to the bottom of the second catalyst bed along with an additional 11.1 pounds per hour hydrogen and 4.6 pounds per hour methane. The product from the reactors iε then flashed to remove the residual 1.4 pounds per hour hydrogen and 12.1 pounds per hour methane. The hydrogenated stream contains approximately the same amount of butanes, 1,3-butadiene, isobutylene and C 5 'ε aε in the feedεtream. The methylacetylene iε reduced to 17 poundε per hour and the C. acetyleneε are reduced to about 2.4 poundε per hour. Propylene is present in the amount of 161 pounds per hour, and the 1-butene and 2-butene contents are increased to 985 per hour and 1278 pounds per hour, respectively. The hydrogenated crude stream is admixed with an acetic acid feed stream which contains some unreacted C *s scrubbed from the flashed vapors from the acetoxylation reactor: Pounds Per Hour The reεulting crude butadiene/acetic acid mixture is blended with 423,467 pounds per hour of liquid recycle from the reactor, which haε the following compoεition: Pounds Per Hour Water 8868 Nitrogen 5244 Oxygen 61 Argon 88 Carbon dioxide 9 Propylene 172 Isobutane 3503 n-Butane 3998 By material balance, the sum of the three feed streams to the reactor is: Methylallyl acetate 14 3-Acetoxy-l-butene 382 Crotyl acetate 595 tert-Butyl acetate 191 3,4-Diacetoxy-l-butene 4417 l,4-Diacetoxy-2-butene 46251 1,4-Diacetoxybutane 16 Other 2751 Total 626517 Thiε liquid reactor feed stream is introduced into the bottom of the acetoxylation reactor at about 870 psia and 80°C. The reactor containε 38000 poundε of palladium-tellurium on activated carbon catalyεt, such as discloεed in Example 3 in Onoda, et al., U.S. Patent No. 3,922,300. Sparged into the bottom of the reactor is a compressed air/nitrogen stream containing: Pounds Per Hour Water 3 Nitrogen 46939 Oxygen 3592 Argon 787 Carbon dioxide 24 Propylene 23 Isobutane 180 n-Butane 197 Isobutylene 67 1-Butene 53 2-Butene 64 1,3-Butadiene 163 C5 Hydrocarbons 3 Acetic Acid 75 TOTAL 52170 Withdrawn from the top of the reactor at 102 β C is the product stream containing: Pounds Per Hour Total 678682 The overhead may be separated by distillation to provide a bottoms stream rich in l,4-diacetoxy-2-butene which may be, e.g., hydrogenated and hydrolyzed to form 1,4-butanediol and tetrahydrofuran. The overhead from this separation may be treated to recover and recycle acetic acid and butenes and butanes. Esamples 1 to 8 The following examples are provided in illustration and are not in limitation of the invention. All parts and percentages are by weight unlesε otherwise stated. The following examples illustrate through the use of synthesized feed streams, that hydrogenated, crude butadiene streams can effectively be used in acyloxylation proceεses. A synthetic mixture of C. hydrocarbons is prepared to simulate a crude butadiene stream that has been hydrogenated as above and haε the compoεition set forth in Table I. TABLE I Component wt. % Methylacetylene leεs than 500 ppmw n-Butane 14.2 Isobutylene 6.3 1-Butene 15.3 2-Butene 6.7 1,3-Butadiene 57.1 C4 Acetylenes leεε than 200 ppmw 4-vinylcyclohexene 0.4 Total 100.0 The catalyst for the acetoxylation reaction is prepared as follows: Approximately 2400 milliliters of 15% by weight nitric acid aqueous solution are charged to a glass still. About 150 grams of 20-40 mesh activated carbon are added to the solution and refluxed for an hour at approximately 100°C and atmospheric pressure. The liquid is then poured off, and the activated carbon is washed with distilled water. The activated carbon is then dried in a vacuum oven overnight at about 90°C and 250 mmHg absolute preεsure. Palladium nitrate is also dried in the oven at 90°C and about 250 mmHg abεolute preεsure for about 4 hours. A 600 milliliter solution iε then made of 30% by weight nitric acid, 6.749 gramε of the palladium (II) nitrate and 1.132 grams tellurium powder, 60 mesh. The 150 grams of the washed, activated carbon are then added to the solution, with gentle stirring for about 5 minutes. The mixture is then dried slowly for about 36 hours in the vacuum oven at 250 mmHg abεolute pressure and 90°C. After the catalyst drying is complete the catalyst is purged for at leaεt 30 minuteε with flowing nitrogen. About 56.35 gramε of the catalyst are then charged to a 16 inch reactor with a 3/4 inch inner diameter. The top inch and bottom inch of the reactor are packed with quartz beads, held in place with quartz wool, so that approximately 14 inches of catalyst are present in the heated reactor zone. The catalyst is then heated to 150°C under 3 liters per minute nitrogen flow for 2 hours. The catalyεt is then reduced by passing 3 liters per minute hydrogen over the bed at 200°C for 2 hours, followed by reduction at 300°C for another hour. The reactor is then purged with 3 liters per minute nitrogen at 300°C for 30 minutes and then left overnight at 300°C under 3 liters per minute nitrogen flow and up to 315 cubic centimeters per minute air. Initially, care is taken to control the air flow at 50 to 100 cubic centimeters per minute so as to keep the exotherm in the catalyst bed below 400°C, and then the air flow rate is gradually increased to the 315 cubic centimeter per minute rate. After oxidation overnight (about 12 hours), the air flow is discontinued, and the nitrogen flow continued for 30 minutes while cooling to 200°C. The catalyst is then further reduced with 3 liters per minute hydrogen at 200°C for 4 hours, then heated to 400°C and reduced for another 4 hours under the same hydrogen flow rate. After completing the final reduction cycle, the catalyst is purged with 600 cubic centimeters per minute of nitrogen, while cooling to ambient temperature. The reactor is then left under positive nitrogen pressure until the acyloxylation runs are started. The synthetic C. hydrocarbon stream is blended with acetic acid in the ratios given in Table II. The resulting mixture iε introduced aε a liquid into the bottom of a reactor vessel at the conditions given in Table II. To obtain the 0.45 to 8.96 weight hourly space velocitieε in the catalyεt bed requireε the liquid mixture to be fed at 25 milliliters per hour to 500 milliliters per hour. The oxygen for the reaction is supplied in an air and nitrogen mixture, such that the oxygen content iε present at 10 mole percent. The flow rates of air and nitrogen are controlled together, to maintain the desired oxygen to C. hydrocarbons molar ratio. In examples 1 to 8, thiε requireε the air flow rateε to range from 21 to 1250 cubic centimeterε per minute, and the nitrogen flow rates to range from 22 to 1640 cubic centimeters per minute. The effluent from the reactor vessel is flashed (decanted) at 0°C and 1 to 5 psig (1.06 to 1.35 atmospheres absolute) to remove a gaseouε stream for analysis. The liquid from the decanter is also recovered and analyzed. The results are summarized in Table III. TABLE III Conversion of 1,3-Butadiene Conversion of Total C. 's Selectivitieβ (molar) to t-Butyl acetate n-Butyl acetate Isobutyl acetate i t 3-Acetoxy-1-butene I Crotyl acetate Hethylallyl acetate 1-Acetoxy-l,3-butadiene 1,4-Diacetoxy-2-butene 3,4-Diace oxy-1-butene Others/unknowns Heavies Aε seen in Examples 1 to 8, the catalyst gave high conversion of 1,3-butadiene and high selectivity to l,4-diacetoxy-2-butene, even after as much as 216 hours on line. Comparative Example 9 By comparison, when the crude butadiene sample given in Table IV is mixed with acetic acid to provide 5.132 wt. % crude butadiene in acetic acid, and reacted with N,/air with about the ratio of moles 0 2 /N 2 , approximately the same 0 2 / C. hydrocarbons, at about the same reactor temperature (78°C) and pressure (90 psig) aε in Exampleε 1 and 8, the catalyεt activity rapidly declined, possibly due to the high levels of methyl acetylene and vinyl acetylene present in the feed mixture. The conversion of 1,3-butadiene dropped from 81% at 229 hours total catalyst on-stream time and 13 hours with the unhydrotreated crude butadiene feed to 51% at 300 hours total catalyst on-stream (84 hours with the unhydrotreated crude butadiene feed) . The results are summarized in Table V. TABLE V Hours On-Line With Untreated Crude Butadiene 0 13 19 26 45 Conversion of 1,3-Butadiene 97.7 81.0 73.3 66.3 60.1 Conversion of Total C, 's 63.7 49.1 39.1 36.3 34.3 4 Hours On-Line With Untreated Crude Butadiene t I

Claims: IT IS CLAIMED: 1. A process for the production of l,4-diacyloxy-2-butene from crude butadiene containing acetylenic components compriεing contacting the crude butadiene with hydrogen under mild hydrogenation conditions to produce an hydrogenated crude butadiene and then contacting the hydrogenated crude butadiene with carboxylic acid and oxygen under acyloxylation conditions in the preεence of an effective amount of palladium-containing catalyst to produce l,4-diacyloxy-2-butene, wherein the hydrogenation is sufficient to enhance at least one of enhanced catalyst activity and catalyst life for acyloxylation. 2. The process of claim 1 wherein the carboxylic acid comprises acetic acid. 3. The process of claim 2 wherein the total acetylene components in the hydrogenated crude butadiene stream are less than about 0.5 weight percent based on the total weight of the crude butadiene stream. 4. The process of claim 3 wherein the total acetylene components in the hydrogenated crude butadiene stream are less than about 0.05 weight percent based on the total weight of the crude butadiene stream. 5. The process of claim 2 wherein heat is removed during the acyloxylation to mitigate the formation of vinylcyclohexene. 6. The process of claim 5 wherein the acyloxylation is at a temperature of about 80° to 160°C. 7. The process of claim 6 wherein a portion of the product from the acyloxylation is recycled to the acyloxylation to assist in temperature control. 8. The process of claim 2 wherein the crude butadiene stream is the result of thermal pyrolysis of hydrocarbon and the crude butadiene is subjected to acyloxylation within about 50 hours of the thermal pyrolysiε. 9. The process of claim 2 wherein the mild hydrogenation conditions comprise a temperature of about 20°C to 70°C, a pressure of about 6 to 11 atmospheres absolute and a supported palladium hydrogenation catalyst.

Inventors: GARSKA DANIEL CHRISTOPHER, GARSKA, DANIEL, CHRISTOPHER
Applicants: UNION CARBIDE CHEM PLASTIC, UNION CARBIDE CHEMICALS AND PLASTICS COMPANY INC.
Application year: 1991
Main classification: C07C67
IPC codes: B01J27, C07B61, C07C67, C07C69