Process for preparing a zinc-containing solid catalyst and process for preparing polyalkylene carbonate

Abstract: A zinc-containing solid catalyst is prepared by contacting zinc oxide with an organic dicarboxylic acid in the presence or absence of an organic solvent under a mechanical pulverization treatment. The catalyst exhibits high catalytic activity in the copolymerization of carbon dioxide with an epoxide to provide a polyalkylene carbonate.

Description: This invention relates to a process for preparing a zinc-containing solid catalyst and to a process for preparing a polyalkylene carbonate using the catalyst. Large quantities of carbon dioxide are evolved on earth by commercial productive activities and respiration of animals. Although carbon dioxide is readily available as a raw material, because of its low reactivity it has not been effectively utilized as an industrial resource. It is important to make use of this readily available industrial resource. Several processes for the production of synthetic resins in which carbon dioxide is used as a raw material have heretofore been proposed. Among others, Journal of Chemical Society of Japan (1982) No. 2, page 295, discloses such a process in which a reaction product of zinc acetate with an aliphatic dicarboxylic acid or a reaction product of an alkyl zinc with water is used as a catalyst. Further, a process disclosed by Polymer Journal, Vol. 13 (1981) page 407, use is made of as a catalyst reaction products of zinc hydroxide with various organic carboxylic acids. The invention seeks to provide a process for the preparation of a zinc-containing solid catalyst having high catalytic activity which can be used to prepare a polyalkylene carbonate having a high transparency in good yield. According to the invention there is provided a process for preparing a zinc-containing solid catalyst which comprises contacting zinc oxide with an organic dicarboxylic acid under a mechanical pulverization treatment without adding water. Preferably the reaction is carried out in the presence of an organic solvent. The invention also provides a process which comprises the further step of preparing a polyalkylene carbonate by copolymerizing carbon dioxide with an epoxide in the presence of said zinc-containing solid catalyst. The catalyst prepared by the process of the invention is in a good pulverized state and exhibits high polymerization catalytic activity. Zinc Oxide Zinc oxide which can be used herein for the preparation of the catalyst is not restricted by its preparation processes. It may be prepared by a variety of known processes including, for example, a process wherein zinc oxalate is pyrolyzed at a temperature of at least 400 °C., a process wherein hydroxyzinc carbonate is dehydrated under heat, a process wherein metallic zinc is burnt or a process wherein zinc ores are roasted together with a reducing agent and the generated zinc dust is oxidized by air. Organic Dicarboxylic Acids The organic dicarboxylic acids which can be used herein for the preparation of the catalyst include, for example, aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, 1,5-pentane dicarboxylic acid, 1,6-hexane dicarboxylic acid, 1,8-octane dicarboxylic acid and 1,10-decane dicarboxylic acid; and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1,2-naphthalene dicarboxylic acid, 1,3-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 1,6-naphthalene dicarboxylic acid, 1,7-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 2,3-naphthalene dicarboxylic acid, 2,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid and 2,7-naphthalene dicarboxylic acid. Of these acids, glutaric acid and adipic acid are particularly preferred. These organic dicarboxylic acids may be used alone or as mixtures. Organic Solvents Organic solvents can be used herein as a pulverising assistant for the preparation of the catalyst. Such organic solvents include, for example, aliphatic hydrocarbons or their halogenated derivatives, e.g. pentane, hexane, heptane, octane, decane and kerosine; aromatic hydrocarbons or their halogenated derivatives, e.g. benzene, toluene and xylene; phenols or their ether or ester derivatives, e.g. phenol, cresol and xylenol; ethers or their alkyl or aryl derivatives, e.g. diethyl ether, dibutyl ether, methyl butyl ether, ethyleneglycol dimethyl ether, diethyleneglycol dimethyl ether, ethylene oxide, propylene oxide, isobutylene oxide, stylene oxide, cyclohexene oxide, tetrahydropyran, tetrahydrofuran, oxetane, oxirane, dioxane and trioxan; alcohols or their derivatives, e.g. methanol, ethanol, propanol, isopropanol, butanol, isobutanol, hexanol, ethylene glycol, diethylene glycol and glycerine; ester derivatives of aliphatic carboxylic acids, e.g. ester derivatives of acetic acid, propionic acid, butyric acid, oxalic acid, malonic acid, succinic acid, glutaric acid or adipic acid , e.g. methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butylate and ethyl butylate; esters of aromatic carboxylic acids, e.g. esters of benzoic acid, phthalic acid, naphthoic acid and naphthalene dicarboxylic acids; nitriles or their derivatives, e.g. acetonitrile, propionitrile and butyronitrile; and amides or their derivatives e.g. N,N-dimethylformamide(DMF) and hexamethylphosphorous triamide (HMPT). When zinc oxide is contacted with the organic dicarboxylic acids in the presence of the pulverising assistant under a mechanical pulverization treatment, the resulting zinc-containing solid catalysts are in a good pulverized condition such as maintaining finely divided and uniform particle size without occurrence of aggregation and coagulation and also they exhibit a very high polymerization catalytic activity. Of those organic solvents, there are preferably used benzene, toluene, xylene, dioxane, tetrahydrofuran, ethyleneglycol dimethyl ether, diethyleneglycol dimethyl ether, oxetane, epoxide, methanol, ethanol, propanol, isobutanol, ethyl acetate, butyl acetate, methyl propionate, acetonitrile, propionitrile and dimethylformamide. Such organic solvents are preferable, since they are ordinarily liquid at the temperature at which zinc oxides and organic dicarboxylic acids undergo mechanical pulverization, resulting in penetration into the particles of the zinc-containing solid catalyst to prevent effectively aggregation and coagulation, thus maintaining a finely divided state of the catalyst in good condition. Further, such pulverising assistants accelerate the formation of the catalyst and also prevent the catalyst particles from aggregating and coagulating, since water by-produced from the reaction of zinc oxide with the organic dicarboxylic acids under a mechanical pulverization treatment will become incorporated into the pulverising assistant. The pulverising assistants may be used alone or in combination. Preparation of the Catalyst The zinc-containing solid catalyst is prepared by bringing zinc oxide into intimate contact with an organic dicarboxylic acid under a mechanical pulverization treatment and reacting them. The mechanical pulverization treatment is performed using a mill such as a ball mill, vibration mill or shock mill. The organic dicarboxylic acids are used in the amount of usually 0.1 to 10 moles, preferably 0.5 to 2 moles, per mole of zinc oxide. When the organic solvents are used, the amount of organic solvent added is 1 to 5000 parts by weight, preferably 5 to 1000 parts, by weight per 100 parts of the total weight of zinc oxide and the organic dicarboxylic acids. Particular milling conditions may be chosen depending upon the kind and quantity of the materials to be milled and the particular mill used. For example, in a case wherein from 20 to 40 grams of the materials in sum are milled in a rotating ball mill whose stainless steel cylinder has an inner volume of 800 ml and an inner diameter of 100 mm and contains 100 stainless steel balls of a diameter of 15mm, milling the materials over a period of from 10 minutes to 30 days, preferably from 20 minutes to 7 days, with a rate of 125 rpm will by suitable. In a case wherein from 20 to 40 grams of the materials in sum are milled in a vibration mill whose stainless steel cylinder has an inner volume of 800 ml and an inner diameter of 100 mm and contains 2.8 kg of stainless steel balls of a diameter of 15 mm, milling the materials over a period of from 1 minute to 10 days, preferably from 5 minutes to 4 days, with a shock acceleration of 7 G will be suitable. While the milling may be carried out under ambient conditions, if excess heat is generated it is preferred to control the temperature within the range between 0 o and 150 o C. In the present invention, the zinc-containing solid catalyst as synthesized may be used, as it is, for the polymerization of carbon dioxide and an epoxide to produce a polyalkylene carbonate. It is usually preferable to deaerate and dry the zinc-containing solid catalyst prior to the polymerization, since water by-produced during the reaction of zinc oxide with the organic dicarboxylic acid as well as alcohols and amines of the organic solvents used in the preparation of the zinc-containing solid catalyst will act as a polymerization inhibitor. In the zinc-containing solid catalyst so prepared, it is believed that the organic dicarboxylic acid has reacted with zinc oxide. This is because when compared with an infrared spectrum of the starting organic dicarboxylic acid and that of the catalyst reveals that an assymmetric/symmetric vibration absorption band of the carbonyl group has been shifted to a side of lower wave number, and also because a thermal decomposition temperature of the catalyst differs from that of the organic dicarboxylic acid. Production of Polyalkylene Carbonate According to the invention, polyalkylene carbonates are produced by reacting carbon dioxide with epoxides in the presence of the zinc-containing solid catalysts as prepared above. Epoxides The epoxides which can be used herein include a variety of known epoxides such as monoepoxides or diepoxides, the monoepoxides being preferred. Such monoepoxides include, for example, ethylene oxide, propylene oxide, 1-butene oxide, 2-butene oxide, isobutylene oxide, 1-pentene oxide, 2-pentene oxide, 1-hexene oxide, 1-octene oxide, 1-decene oxide, cyclopentene oxide, cyclohexene oxide, styrene oxide, vinylcyclohexene oxide, 3-phenylpropylene oxide, 3,3,3-trifluoropropylene oxide, 3-naphthylpropylene oxide, 3-phenoxypropylene oxide, 3-naphthoxypropylene oxide, butadiene monoxide, 3-vinyloxypropylene oxide, 3-trimethylsilyloxypropylene oxide, methyl glycidylcarbonate, ethyl glycidylcarbonate and cholesteryl glycidylcarbonate. Of these epoxides, propylene oxide, ethylene oxide and cyclohexene oxide are particularly preferred. These epoxides may be used alone or in combination. Polymerization The reaction of carbon dioxide with an epoxide is carried out usually using a solvent. Such solvents include, for example, aliphatic hydrocarbons such as pentane, hexane, octane, decane and cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylenes; and halogenated hydrocarbons such as chloromethane, methylene dichloride, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, ethyl chloride, trichloroethane, 1-chloropropane, 2-chloropropane, 1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane, chlorobenzene and bromobenzene. These solvents may be used alone or in combination. In some cases the monomer (epoxide) in itself serves as a polymerization medium. Further, the process of the invention may be carried out in a gaseous phase or in a fluidized bed. The order of addition of the monomer (epoxide), carbon dioxide and the catalyst to the polymerization medium is not particularly restricted. The ratio by volume of the solvent used to the monomer (epoxide) is generally from 0:100 to 99:1, and preferably from 0:100 to 90:10. The pressure of carbon dioxide in the reaction system is not particularly restricted but is generally from 0 to 19.6 MPa gauge (0 to 200 kg/cm 2 G), preferably from 0.3 to 9.81 MPa gauge (3 to 100 kg/cm 2 G), and more preferably from 0.49 to 4.9 MPa gauge (5 to 50 kg/cm 2 G). The polymerization temperature is generally from 0 to 200 °C., preferably from 50 to 150 °C. In this reaction, longer polymerization time can provide more increased yield of the polyalkylene carbonate polymer. Thus, the polymerization time is not particularly restricted, but is usually from 30 minutes to 240 hours, preferably from 1 to 80 hours, and more preferably from 1 to 10 hours. The polymerization can be performed in a batchwise, semi-continous or continuous operation. Further, the polymerization may be carried out in two or more steps using different reaction conditions. After completion of the polymerization, catalyst residues may be removed by filtration or by washing with a diluted aqueous acid or alkali. The polymer can be recovered by flush drying or evaporation to dryness of the reaction product to remove the polymerization solvent or by charging a solution of the reaction product in a good solvent into a poor solvent such as hexane or methanol to precipitate the polymer dissolved therein. The zinc-containing solid catalysts prepared in accordance with the invention by a mechanical pulverization treatment especially in the presence of organic solvents are in such good pulverized condition that the catalyst particles are finely divided and have a uniform particle size. Furthermore, they exhibit a very high polymerization catalytic activity. By use of such catalysts, polyalkylene carbonates can be produced in good efficiency starting from carbon dioxide which has not been utilized for a commercial production of polymers. The polymers produced by the process of the invention have a good transparency and can be completely decomposed by heating. For these properties, they find applications as materials for the production of optical fibers, optical discs, ceramic binders, and lost form castings in addition to as general purpose shaped structures including films and fibers. Further since the polymers produced by the process of the invention are decomposable in a living body, they will also find applications as medical materials which are required to be biodegradable. Moreover, we have found that vibration dampers made of the polymers produced by the process of the invention exhibit excellent performances. The invention is further illustrated by the following non-limitative examples. Example 1 <Preparation of Catalyst> A cylinder of a stainless steel ball mill having an inner volume of 800 ml and an inner diameter of 100 mm and containing 100 stainless steel balls of a diameter of 15 mm, was charged with 10.0 grams of commercially available zinc oxide and 16.2 grams of glutaric acid and rotated at a rate of 25 rpm for about one hour. The solid product so treated was dried at a temperature of 150 o C under a reduced pressure and dispersed in hexane to provide a slurry of the catalyst in hexane. <Polymerization> A 2 liter-autoclave was charged with 200 ml of propylene oxide and the slurry of catalyst in hexane consisting of 700 ml of hexane and 5.4 grams of the catalyst. Carbon dioxide was fed to the autoclave, and the reaction system was heated to a temperature of 80 o C and a pressure of 1.96 MPa gauge (20 kg/cm 2 G). While supplying amounts of carbon dioxide to the reaction system sufficient to maintain the pressure, the polymerization was carried out for a period of 2 hours. At the end of the period the autoclave was cooled and depressurized. From the hexane slurry of a polymer, which was white due to the presence of the catalyst, the polymer was recovered by filtration After drying 45.4 g of the polymer was obtained. The yield of the polymer was 8.4 g per gram of the catalyst. Examples 2 to 4 Catalysts were prepared as described in Example 1 except that the zinc oxide was brought in contact with the glutaric acid for various periods of time as indicated in Table 1. Using each of the catalysts so prepared, the polymerization was carried out as described in Example 1. The results are shown in Table 1. Example Contact time (min.) Activity of catalyst (g/g of cat.) 2 30 8.4 3 180 11.9 4 360 8.1 Example 5 <Preparation of Catalyst> A cylinder of a stainless steel ball mill having an inner volume of 800 ml and an inner diameter of 100 mm and contalning 2.8 kg of stainless steel balls of a diameter of 15 mm, was charged with 10.0 grams of commercially available zinc oxide and 16.2 grams of glutaric acid and milling was carried out with a shock acceleration of 7G for a period of 15 minutes. The solid product so treated was dried at a temperature of 150 o C under a reduced pressure and dispersed in hexane to provide a slurry of the catalyst in hexane. <Polymerization> Using 5 grams of the catalyst so prepared, the polymerization was carried out as described in Example 1. The polymer obtained weighed 34.3 grams after drying. The yield of the polymer was 6.9 g per gram of the catalyst. Examples 6 and 7 Catalysts were prepared as described in Example 5 except that the zinc oxide was brought in contact with the glutaric acid for various periods of time as indicated in Table 2. Using each of the catalysts so prepared. the polymerization was carried out as described in Example 1. The results are shown in Table 2. Example Contact time (min.) Activity of catalyst (g/g of cat.) 6 30 8.3 7 60 6.5 Comparative Example 1 <Preparation of Catalyst> A solution of 12 grams of glutaric acid in 150 ml of methanol was dropwise added to a solution of 20 grams of a commercially available zinc acetate in 200 ml of methanol over a period of 30 minutes under stirring at ambient temperature. Stirring was further continued for 2 hours at ambient temperature. The white precipitate so formed was recovered by filtration, washed with methanol, dried at a temperature of 150 °C under a reduced pressure and used for the polymerization in the form of a slurry in hexane. <Polymerization> Using 5 grams of the catalyst so prepared the polymerization was carried out as described in Example 1. The polymer obtained weighed 5.1 grams after drying. The yield of the polymer was 1 g per gram of the catalyst. Comparative Example 2 Comparative Example 1 was repeated except that the catalyst was prepared by dropwise addition of the solution of zinc acetate in methanol to the solution of glutaric acid in methanol. The yield of the polymer was 1.7 g per gram of the catalyst. Example 8 <Preparation of Catalyst> 10.0 grams of commercially available zinc oxide, 16.2 grams of glutaric acid and 20 ml of n-decane were charged into a cylinder of a stainless steel having an internal volume of 800 ml and an inner diameter of 100 mm and containing 2.8 kg of stainless steel balls having a diameter of 15 mm and the mixture was pulverized with a shock acceleration of 7 G for 30 minutes. The solid product so treated was dried by heating under reduced pressure to prepare a zinc-containing solid catalyst of the invention. <Polymerization> Into a 2 liter autoclave was charged a slurry consisting of 700 ml of hexane and 4.6 grams of the zinc-containing solid catalyst, 200 ml of propylene oxide and carbon dioxide and the system was maintained at 80 o C and 1.96 MPa gauge (20 kg/cm 2 G). The polymerization was carried out for 2 hours while supplying amounts of carbon dioxide consumed. After completion of the polymerization, the autoclave was cooled and depressurized. From the hexane slurry of a polymer which was white due to the presence of the catalyst, the polymer was recovered by filtration. The yield of the polymer was 44.9 grams and the activity of the catalyst was 9.8 g/g-cat. Examples 9 to 12 Catalysts were prepared in a similar manner as in Example 8 but replacing n-decane used therein by ethyl acetate, toluene, dioxane, and isobutanol, respectively as shown in Table 3. Using each of the catalysts thus prepared, the polymerization was carried out similarly to the method of Example 8. The results are shown in Table 3. Example Organic solvent Yield (g) Activity of catalyst (g/g of cat) 8 n-decane 44.9 9.8 9 ethyl acetate 62.6 13.6 10 toluene 61.2 13.3 11 dioxane 79.6 17.3 12 isobutanol 74.5 16.2 Examples 13 to 17 Catalysts were prepared in a similar manner as in Example 8 but using various times of the pulverization as indicated in Table 4. Using each of the catalysts thus prepared, the polymerization was carried out similarly to the method of Example 8. The results are shown in Table 4. Example Pulverization time (min.) Yield (g) Activity of catalyst (g/g of cat) 13 5 48.3 10.5 14 15 53.4 11.6 15 60 60.7 13.2 16 180 60.3 13.1 17 360 57.0 12.4 Examples 18 to 22 Catalysts were prepared in a similar manner as in Example 11 but using various times of the pulverization as indicated in Table 5. Using each of the catalysts thus prepared, the polymerization was carried out similarly to the method of Example 8. The results are shown in Table 5. Example Pulverization time (min.) Yield(g) Activity of catalyst (g/g of cat) 18 15 68.5 14.9 19 60 115.0 25.0 20 180 121.9 26.5 21 360 157.3 34.2 22 720 131.1 28.5 Examples 23 to 26 Catalysts were prepared in a similar manner as in Example 10 but using various molar ratios of zinc oxide(ZnO) to glutaric acid(GA) as indicated in Table 6. Using each of the catalysts thus prepared, the polymerization was carried out similarly to the method of Example 8. The results are shown in Table 6. Example Molar ratio ZnO/GA Yield (g) Activity of catalyst (g/g of cat) 23 1/0.95 47.8 10.4 24 1/0.9 55.2 12.0 25 1/0.8 47.4 10.3 26 1/0.6 38.6 8.4 Comparative Example 3 <Preparation of Catalyst> Catalysts were prepared in a similar manner as in Example 8 but using water (pulverizing assistant) as indicated in Table 7. Using the catalysts thus prepared, the polymerization was carried out similarly to the method of Example 8. The results are shown in Table 7. Comparative Example Pulverizing Assistant Yield (g) Activity of catalyst (g/g of cat) 3 water (20ml) 33.6 7.3

Claims: A process for preparing a zinc-containing solid catalyst which comprises contacting zinc oxide with an organic dicarboxylic acid under a mechanical pulverization treatment without adding water. A process according to claim 1 which is carried out in the presence of an organic solvent. A process according to claim 2 wherein the organic solvent is at least one aliphatic hydrocarbon, aromatic hydrocarbon, phenol, ether, alcohol, ester, nitrile or amide. A process according to claim 1, 2 or 3 which comprises the further step of preparing a polyalkylene carbonate by copolymerizing carbon dioxide with an epoxide in the presence of said zinc-containing solid catalyst. A process according to claim 4 wherein the epoxide is propylene oxide, ethylene oxide or cyclohexene oxide. A process according to claim 4 or 5 wherein the pressure of carbon dioxide is from 0 to 19.6 MPa gauge (0 to 200 kg/cm 2 G). A process according to claim 4, 5 or 6 wherein the polymerization temperature is from 0 to 200°C.

Inventors: ARMOR JOHN N, KAWACHI HIDESHI, MINAMI SHUJI, ROKICKI ANDRZEJ, STEIN BEATRICE K, ARMOR, JOHN N., KAWACHI, HIDESHI, MINAMI, SHUJI, ROKICKI, ANDRZEJ, STEIN, BEATRICE K.
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1989
Main classification: C08G64
IPC codes: C08G64, B01J31