GB2274106A

GB2274106A - Process for the simultaneous production of acetic acid, methyl acetate and acetic anhydride

Info

Publication number: GB2274106A
Application number: GB9326127A
Authority: GB
Inventors: Sung Jin Uhm; Sung Hwan Han
Original assignee: Korea Advanced Institute of Science and Technology KAIST; Korea Institute of Science and Technology KIST
Current assignee: Korea Advanced Institute of Science and Technology KAIST; Korea Institute of Science and Technology KIST
Priority date: 1992-12-23
Filing date: 1993-12-22
Publication date: 1994-07-13
Anticipated expiration: 2013-12-22
Also published as: KR940013604A; KR960003797B1; GB2274106B; GB9326127D0

Abstract

A process for the simultaneous production of acetic acid, methyl acetate and acetic anhydride or the selective production of any one of the same products, comprises the steps of carbonylating methanol with carbon monoxide, optionally in admixture of hydrogen, in the presence of a rhodium catalyst and a halide co-catalyst in a first gas phase carbonylation reactor for gas phase carbonylation of methanol to produce acetic acid and methyl acetate; separating the resulting methyl acetate and the co-catalyst from the reaction mixture, respectively, while recovering acetic acid; recovering part of the separated methyl acetate by distillation while introducing the remaining parts thereof and the co-catalyst to a second carbonylation reactor together with carbon monoxide; carbonylating the methyl acetate with carbon monoxide, optionally in admixture of hydrogen, in the presence of the co-catalyst to produce acetic anhydride; and finally separating the co-catalyst from the acetic anhydride thus produced while recovering the acetic anhydride and recycling the co-catalyst to the first gas phase carbonylation reactor.

Description

PROCESS FOR ThE SIMULTANEOUS PRODUCTION OF ACETIC ACID, METHYL ACETATE AND ASCETIC ANHYDRIDE BACKGROUN'D OF TBE INVENTION 1. Field of the Invention The invention relates to a process for the simultaneous production of acetic acid, methyl acetate and acetic anhydride or the selective production of any one of the same products.

2. Description of the Prior Art Acetic acid and acetic anhydride have long been employed as useful chemicals for industrial purposes. Acetic anhydride has hitherto been employed as a second source of acetic acid, particularly, as a starting material mainly for the production of cellulose acetate and cellulose ester. Recently, alkyl acetates which are derivatives of acetic acid, are being employed as solvents. In particular, lower alkyl acetates such as methyl acetate, ethyl acetate, and the like are in wide use because they can easily be converted into ethanol by hydrogenation.

Acetic acid has before now been produced noneconomically by the oxidation of residuum fractions from a petroleum refining process, despite its low yields. However, according to an increase in the additional value of petroleum residuum fractions recently, various advanced processes for producing acetic acid have been developed. For example, a process for preparing acetic acid by the carbonylation of methanol using a rhodium catalyst is promising as a new catalytic process. Particularly, acetic anhydride can be produced by the reaction of a ketene intermediate obtained by pyrolysis of acetic acid from the above catalytic process with acetic acid in a ratio of 1:1; however, this suffers from a high cost of manufacture.On the other hand, alkyl acetates can be produced by the esterification of acetic acid thus obtained with corresponding alcohols, followed by dehydration; this reaction requires a long period of procedural steps and a high cost of manufacture.

Hitherto, various proposals have been made to economically provide a process for producing acetic acid. For example, a commercially feasible liquid phase process for producing acetic acid by carbonylation of methanol, as disclosed in U.S. Patent No.

3,769,329 to Paulik, has recently been developed; this has stimulated intensive research in this field of art. To cite an example, a process for producing acetic acids employing Fe, Ni, Co, and the like as a reaction catalyst has been proposed by Reppe ESee, Justus Liebig's Ann, Chem., 582 1(1953)]. Since this proposal, various metals have been employed as catalysts, but rhodium is still considered to be commercially beneficial.

Although U.S. Patent No. 4,482,497 granted to Rizkalla discloses that the use of a nickel carbonyl compound or a nickel compound in lieu of rhodium together with a cocatalyst in a liquid phase process for the preparation of acetic acid from an alcohol results in a high reactivity under relatively mild conditions, this method has still not been commercialized. Further, in German DE A 33 35 595, there is proposed a process for preparing acetic acid from an alcohol in a high yield, wherein a molybdenum/nickel/lithium iodide/iodide catalyst system is employed at 83 atm of CO atmosphere.

U.K. Patent Publication No. 2 089 803 A discloses a process for preparing acetic acid by carbonylation of methanol, wherein molybdenum and tungsten promotes the effect of a nickel catalyst and wherein various organic or inorganic iodide compounds render the yield of the resulting acetic acid highly increased; however, this method does not reveal any commercial difference in productivity.

As mentioned above, commercial liquid phase processes for the production of acetic acid have suffered from various practical problems, and thus many efforts have been concentrated to solve the problems, particularly to eliminate problems due to the corrosion of the apparatus which is unavoidable in a liquid phase. A gas phase process for producing acetic acid has thus been suggested in an attempt to resolve the above problems encountered in a liquid phase process.

For example, European Patent Publication No. 0 069 514 A2 assigned to Toyo Engineering Corporation, German DE 33 23 654, and Ind. Chem. Prod, Res. Dev., 22, 436(1983) and Chemistry Letters, 895(1987) disclose gas phase processes for the nickelcatalyzed carbonylation of methanol, but these processes have many problems from the point of view of practical use. European Patent Publication 0 335 625 A2 discloses a process for producing acetic acid which is carried out under the conditions that a nickel/rhodium active carbon supported catalyst is employed at 188"C. In this process, the CO/H2 (1:2) gas is introduced at 9 atm, the ratio of methanol to methyl iodide is 100: 19.1, the LHSV of the gas is 1. However, this process results in a low yield of 9.7 %.In particular, nickel is apt to be volatilized from the catalyst beds during the reaction, thereby resulting in the shelflife of the catalyst being considerably shortened. It has been found that, in a gas phase process like the liquid phase process, rhodium is superior to nickel in view of its reactivity and stability.

U.S. Patent Nos. 3,717,670 to Schultz and 3,689,533 to Schultz disclose a process for producing acetic acid in a heterogenous gas phase using a rhodium catalyst. These patents teach that the conversion of methanol and the yield of acetic acid are increased by mixing a Rh catalyst with a metal component. However, according to these patents, the methanol conversion, the selectivity to acetic acid, and the yield of acetic acid are no more than 78.5 %, 58 % and 45.5 %, respectively, under the most preferred reaction conditions including a reaction temperature of 285"C and a pressure of 200 psi, and a molar ratio of introduced reactants, CH3I:CH3OH:CO of 1:12.3:26.2.

Japanese Laid-Open Patent Publication No. (Sho) 48-80511 discloses a gas phase process in which cobalt-, nickel- or iron-containing rhodium is employed as a catalyst and a small amount of aluminum, copper, titanium, mercury and/or lithium are added as a cocatalyst or co-catalysts. The yield of acetic acid is 71 S; under the most preferred reaction conditions for this prior art, wherein using the catalyst prepared by supporting 0.43g of RhC13-4H2O, 0.43g of Nix12, 0.44g of AlCl3 and 0.43g LiCl on 25g of active carbon, methanol, carbon monoxide and methyl iodide are introduced at a rate of 169 g/hr, 224 g/hr and 27 g/hr, respectively, and the reaction is carried out at 2300C under 220 psi. This process gives a yield of only 71 %.

U.S. Patent No. 4,918,218 to Mueller, et al. and German Patent No. 36 06 169 also disclose a gas phase process using a nickel/palladium complex catalyst system and a process using a zeolite supported cobalt catalyst, respectively. Toyo Engineering Corporation, a Japanese company, has developed a process using a nickel-based catalyst system. However, all of these catalyst systems are still commercially impractical in terms of their reactivity, conversion and selectivity.

Recent research has focused on the processes for the simultaneous production of acetic anhydride having a lower corrosion of the reactors, U.K. Patent No. 1 468 940 discloses a liquid phase carbonylation process for preparing acetic anhydride from an alkyl ester of monocarboxylic acid and an alkyl iodide under anhydrous conditions. In this process a catalyst selected from noble metals of Group VIII, i.e., iridium, osmium, platinum, palladium, rhodium, ruthenium, etc. and a promoter selected from lithium, magnesium, calcium, titanium, chromium, iron, nickel, aluminum, and so forth, are employed. However, since this process must be carried out in anhydrous conditions, it has the drawback that the reactants have to be stored under anhydrous conditions.

U.K.. Patent No. 1 523 346 teaches a process for preparing acetic anhydride from methyl acetate and carbon monoxide in a liquid phase reaction in the presence of a metal catalyst which may be ruthenium, rhodium, palladium, osmium, iridium, or platinum.

According to this process, starting materials are preferably used in anhydrous form as much as possible, but they may contain up to 25% of methanol and below 5% of H2O. In this case, acetic acid is produced simultaneously with acetic anhydride due to the presence of methanol and water.

It is important to remove water from the reactants to obtain acetic anhydride, which has always been a critical problem. Methyl acetate is conventionally prepared by esterification between acetic acid and methanol; the esterification resulting in simultaneous formation of much water.

U.K. Patent Publication No. 2 033 385 A discloses a process for preparing pure methyl acetate by reacting acetic anhydride with methyl acetate containing much water. In this process, the resulting methyl acetate containing much water reacts further with acetic anhydride obtained in the step of carbonylation to produce acetic acid and dehydrated methyl acetate, and finally to produce simultaneously acetic acid and acetic anhydride after being passed through a carbonylation reactor.

In order to effectively solve the problem of the presence of water encountered in the preparation of acetic anhydride, European Patent Publication 0 087 870 A2 proposes a method wherein the steps of esterifying the produced acetic acid and methanol, dehydrating, carbonylating and separating the resulting product are effected in that order.The process comprises six steps of esterifying methanol with cycled acetic acid to obtain a mixture of methyl acetate, methanol and water; removing part of the water from the esterification product; reacting the resulting methyl acetate thus dehydrated with CO in a liquid phase carbonylation step to produce simultaneously acetic anhydride and acetic acid depending on the contents of water and methanol in the reactants; separating a lower boiling fraction containing halide promoters, acetic acid and acetic anhydride and a higher boiling fraction containing catalyst components from the reaction mixture; collecting the lower and the higher boiling fractions independently and recycling the lower boiling fraction to a carbonylation reactor; and recycling the separated acetic acid to an esterification reactor.The production ratio of acetic acid and acetic anhydride is determined by controlling the amount of the water to be removed, which is produced in the esterification step. However, this process has many problems, in particular, it is difficult and complicated to remove water after the esterification step. For example, when the esterification is carried out using methanol and acetic acid in a ratio of 2:1, 57.5 % by weight of methyl acetate, 27.9 % by weight of methanol, only 13.6 % by weight of water is yielded. The resulting water must be removed by azeotropic distillation of water and methanol. In addition, another step is required to separate methanol from water.

In this process for the preparation of acetic anhydride mentioned above, the starting material employed is one of the important factors. According to this process, methyl acetate is used as a starting material, which is prepared by esterification between acetic acid and methanol. The process can simultaneously produce acetic acid and acetic anhydride in a batch system; however, ultimately, the process must involve a carbonylation step of methyl acetate which is an expensive starting material. Thus, if the starting material, i.e., methyl acetate, is directly produced, the production costs of methyl acetate as well as acetic anhydride could be reduced. A variety of derivatives, in addition to acetic anhydride, particularly, absolute ethanol, vinyl acetate monomers, alkyl esters, propionic acid, and the like can be produced from the methyl acetate.

The inventors of the present invention have intensively investigated the foregoing conventional processes for the simultaneous production of acetic acid and acetic anhydride in order to provide a process for economically producing acetic acid, methyl acetate and acetic anhydride. As a result, the inventors have discovered that the problems associated with the corrosion of reactors can be solved by employing a gas phase reaction catalyst system having a high productivity, which can properly reduce the number of steps in the conventional multi-step processes and the production costs. The present invention has been developed based on such a discovery.

SUMMARY OF THE INWENTION It is therefore an object of the invention to provide a process for the simultaneous production of acetic acid, methyl acetate and acetic anhydride on a large scale by reduced procedural steps.

It is another object of the invention to provide a process for selectively producing acetic acid, methyl acetate or acetic anhydride by controlling the catalyst system employed and the reaction conditions involved so that the production ratio may optionally be varied.

These and other objects of the invention can be accomplished by a process for simultaneously producing acetic acid, methyl acetate and acetic anhydride which comprises the steps of carbonylating methanol with carbon monoxide, optionally in admixture of hydrogen, in the presence of a rhodium catalyst and a halide co-catalyst in a first gas phase carbonylation reactor for gas phase carbonylation of methanol to produce acetic acid and methyl acetate; separating the resulting methyl acetate and the co-catalyst from the reaction mixture, respectively, while recovering acetic acid; recovering part of the separated methyl acetate by distillation while introducing the remaining parts thereof and the co-catalyst to a second carbonylation reactor together with carbon monoxide; carbonylating the methyl acetate with carbon monoxide, optionally in admixture of hydrogen, in the presence of the co-catalyst to produce acetic anhydride; and finally separating the co-catalyst from the acetic anhydride thus produced while recovering the acetic anhydride and recycling the co-catalyst to the first gas phase carbonylation reactor.

According to the present invention, the conditions for the first carbonylation of methanol with carbon monoxide can easily be controlled and the ratio of the methyl acetate to the acetic acid to be produced is also optionally controllable. Thus, the productivity of the desired methyl acetate can be increased in a more simple manner than the conventional processes for the preparation of methyl acetate, and the conventional problems caused by the containment of water may also readily be resolved.

In order to selectively produce acetic acid only, a total amount of the methyl acetate to be produced should be recycled to the first carbonylation reactor. In this case, it is possible to maintain the selectivity to acetic acid at 99% or higher. Also, hydrogen may be added in a small amount to carbon monoxide, which is a stock gas, to enhance the selectivity to acetic acid.

In addition, a carbonylation catalyst according to the present invention is prepared by adding more than one transition metal, alkali metal, and alkaline earth metal compounds such as CoCl2, RuCl3, PdCl2, PtCl2, OsCl3, IrCl3, Nisi2, MnCl2, ReCi5, CrCl3, MoCI3, We16, Vac13, NbCl5, Tact5, Tic3, ZrCl4, HfCl4, LiI, NaI, KI, RbCl, BeCl2, MgCI2, CaCl2, SrCl2, BaCl2, and the like to a rhodium catalyst.Since the catalyst system according to the present invention maintains high conversion and high selectivity to methyl acetate, the problem related to the selectivity to methyl acetate, which was encountered in the conventional heterogenous gas phase process catalysts, can easily be solved. Consequently, acetic acid and methyl acetate can be effectively co-produced using the catalyst system under appropriate reaction conditions.

The invention will be described hereinbelow in greater detail.

DETAILED DESCRIPTION OF ThE INVENTION A process for the simultaneous production of acetic acid, methyl acetate and acetic anhydride according to the present invention comprises the following five steps: Step 1: Acetic acid and methyl acetate are produced by a gas phase carbonylation of methanol with carbon monoxide, optionally in admixture of hydrogen, in the presence of a halide co-catalyst. In this step, the selectivity to acetic acid is increased under severe conditions, whereas the selectivity to methyl acetate is increased under mild conditions.In order to selectively obtain acetic acid only, the selectivity to acetic acid may be enhanced by employing a catalyst having a high selectivity to acetic acid, such as a rhodium/lithium catalyst system, and separating the resulting methyl acetate from the reaction mixture together with methyl iodide followed by recycling to the first carbonylation reactor. In this step, the selectivity to acetic acid may be maintained at 99% or more.Also, hydrogen may be added in a small amount to the stock gas, i.e., carbon monoxide, in order to improve the selectivity to acetic acid; Step 2: Acetic acid is isolated and recovered at the bottom of the reactor and the lower boiling fractions, i.e., the co-catalyst and methyl acetate are separated at the top of the same reactor; Step 3: A predetermined amount of the methyl acetate separated in Step 2 is distilled in order to recover the methyl acetate as an end product, and the remainder of the methyl acetate is charged into the second carbonylation reactor together with a co-catalyst in order to obtain acetic anhydride; Step 4:In this step, a second carbonylation occurs, wherein acetic anhydride is prepared by carbonylation of the methyl acetate introduced into the second reactor in Step 3 with carbon monoxide, optionally in admixture of hydrogen, in the presence of a Co- catalyst; and Step 5: The co-catalyst is separated from the acetic anhydride produced and the Co- catalyst thus separated is recycled to the first carbonylation reactor for reuse.

Although the overall process is carried out in a gas phase, the second carbonylation may be carried out in either a gas phase or a liquid phase, preferably in a gas phase.

The first gas phase carbonylation of methanol is conducted in the presence of a rhodium catalyst under the reaction conditions as described in detail in copending Korean Patent Application Nos. 92-11524 and 92-20188 filed in the name of the same assignee as that of an application for patent for the present invention on June 30, 1992.

A catalyst for the gas phase carbonylation of methanol according to the present invention may be prepared by supporting a solution of a rhodium compound in water or an organic solvent on an inert vehicle together with an alkali metal, alkaline earth metal or transition metal compound, sintering the resulting mixture at 200 to 5000C. The inert vehicle includes active carbon, clay, alumina, silica and silica-alumina.

All of the rhodium compounds, which are soluble in water or an organic solvent and can be sintered at 200 to 500 C to form rhodium oxide, may preferably be used. A variety of rhodium compounds, such as RhX3 (X=Cl, Br, I), RhX33H2O (X=Cl, Br, I), Rh2(CO)4X2 (X=Cl, Br, I), FRh(CO)X4]Y (X=Cl, Br, I; Y=Na, Li, K), Rh2(CO)S, Rh(NO3)3, [Rh(CO)2XY (X=C1, Br, I;Y=Li, Na, K), Rh2O3, [Rh(C2H4)2Xj2 (X=Cl, Br, I), Rh((CJ?5)3 P (CO)X (X=Cl, Br, I), Rh metal, RhX [(CJI5)3P12(CH3Y)2 (X,Y=C1, Br, I), Rh(SnC13)[(CJ15)P (X=C1, Br, I), RhX(CO)[(C6H5)3n2 (X=CI, Br, I; Y=As, P, Sb), [R4Y][Rh(CO)2X]2(X=Cl, Br, I; R=C1-C12 alkyl; Y=N, As, P), [R4Y]2[Rh(CO)X4] (X=CI, Br, I; R=C1-C12 alkyl; Y=N, As, P), RhX((C6H5)3P]3 (X=Cl, Br, I), RhXF(CEH5)3PJH2 (X=Cl, Br, I), [(C6H5)3P]3Rh(CO)H, Y4Rh2X2(SnX3)4 (X=Cl, Br, I; Y=Li, Na, K), and the like may be used.Preferably, RhCl3-3H20 or Rh(N03)3, inter alia is used.

Such rhodium compounds may be added so as to produce 0.1 to 20 % by weight, preferably 0.6 to 5 % by weight, of Rh based on the amount of an inert vehicle. The transition metal compound may be added in 1 to 1000 mol%, preferably 30 to 300 mol %, based on the amount of rhodium. The alkali metal or alkaline earth metal compound may be added in 1 to 1000 mol%, preferably 200 to 800 mol %, based on the amount of rhodium.

A gas phase process for producing acetic acid, methyl acetate and acetic anhydride according to the present invention comprises reacting methanol or methyl acetate with carbon monoxide using a halide as a co-catalyst in the presence of the catalyst prepared by the present invention.

The halide catalysts which are employed as co-catalysts for use in the present invention may include CH3I, CH3Br, CH3Cl, 12, Br2, Cl2, KI, HBr, HCl, and the like.

Preferably, CH3I is employed.

According to the present invention, by controlling the reaction conditions of the first carbonylation, it is possible to adjust the production ratio of methyl acetate to acetic acid.

When the carbonylation is carried out under more severe reaction conditions, for example, under an elevated temperature, the production ratio of acetic acid is increased. However, the production ratio of methyl acetate is increased under mild reaction conditions. Therefore, according to the present invention, the production ratio of the desired product can readily be controlled.

Meanwhile, in conventional liquid phase reactions, when hydrogen is contained as an impurity in carbon monoxide, which is a stock gas, various side reactions occur, resulting in lowering the efficiency of the catalytic reaction system. However, in the heterogeneous gas phase catalytic reaction system according to the present invention, even if hydrogen is contained in carbon monoxide in an amount of 1-50%, the carbon monoxide does not substantially affect the reaction system. Rather, the selectivity to acetic acid is considerably increased owing to the presence of hydrogen. Also, the use of hydrogen containing carbon monoxide eliminates the necessity of separation of hydrogen from carbon monoxide, and therefore is beneficial from an economic point of view.

The type of the product from the first carbonylation depends on the reaction conditions involved. Preferably, the product is composed of about 60% of methyl acetate, about 20 to 30% of acetic acid, and about 10 to 20% of unreacted methanol. The product having the above composition can easily be obtained on the first carbonylation catalyst beds.

As will be described hereinafter by way of the examples of the present invention, the product having the above composition is obtained under very mild conditions. Therefore, the space velocity of the inlet stream becomes rapid, resulting in a significant enhancement of productivity.

Separation of the first carbonylation products may be conducted by distillation.

Acetic acid is separated at the bottom of the reactor, while a desired amount of methyl acetate is separated and recovered from the middle of the reactor by distillation. Then, methyl acetate and the co-catalyst from the top of the reactor by distillation are charged into the second carbonylation reactor to prepare acetic anhydride. At this time, the reaction is accelerated by introduction of water or methanol. However, since an excess amount of water results in increasing the production ratio of acetic acid; the water content should be maintained at as relatively low a concentration as possible to inhibit the formation of acetic acid.

The second carbonylation is carried out at a temperature of 100 to 300"C, preferably 240 to 260"C at GHSV of 100 to 700her'. The molar ratio of methyl acetate to a halide cocatalyst, in particular CH3I, to be introduced into the reactor, is preferably 10:1.

The introducing pressure of carbon monoxide, which participates in the second carbonylation with methyl acetate, is in the range of from atmospheric pressure to 1000 psi, preferably 150 to 300 psi, more preferably 200 psi. A reaction mixture from the second carbonylation may be separated by distillation. The co-catalyst thus separated is recycled to the first carbonylation reactor as described hereinabove.

The present invention has the important advantages that mass-production of methyl acetate is possible in a single step; that problems involved in the removal of water are resolved; that separation of the product is very simply performed; that it is possible to selectively produce acetic acid only and control easily the production ratio of acetic acid/methyl acetate/acetic anhydride in their simultaneous production; that since the reaction is carried out in a gas phase, the corrosion resistance of all the reactors is improved; that there is no need to recover and recycle the catalyst used; and that since it is possible to massproduce methyl acetate, various types of alkyl acetates may be produced by isolating pure methyl acetate and then subjecting it to trans-esterification, and also an ethanol may be produced by a hydrogenation as described in connection with the above prior art.

DESCRIPTION OF ThE PREFERRED EMBODIMENTS The present invention will be illustrated in greater detail by way of the following examples. The examples are presented for illustration purpose only and should not be construed as limiting the invention which is properly delineated in the claims.

EXAMPLE 1 RhCl3 and LiI were supported on an active carbon by impregnating the carbon in a solution of RhCl3 and LiI such that 0.6% by weight of Rh based on the amount of the active carbon and 400 mol% of LiI based on the amount of Rh were supported thereon. The resulting material was then sintered at 300 C to prepare a catalyst. A reaction tube having a diameter of 1.27 cm (0.5 inch) and a length of 40 cm was charged with 5g of the catalyst.

Glass fibers were filled in the top end of 15 cm in height and the bottom end of 15 cm in height of the reaction tube, respectively, and the catalyst beds of 10 cm in height were formed between the top and the bottom glass fiber ends. Thereafter, a tube having a diameter of 0.64 cm (0.25 inch) was inserted into the center of the tube, and a thermocouple was equipped therewith. The outside of the reaction tube was oil jacketed so as to heat the reaction tube with a heating medium. Methanol and carbon monoxide in a molar ratio of 1:2.3 were introduced into the reaction tube, and they were allowed to react with one another in the presence of 10 mol% of a co-catalyst, CH3I, based on the amount of methanol at an internal temperature of above 240 C under a pressure of 200 psi.

The conversion of methanol, and the yields of acetic acid and methyl acetate depending on the GHSV under the above conditions are shown in Table 1 below.

Table 1

GHSV1)(hr-1) 660 887 1130 1379 1810 2168 2536 3333 3841 5598 Methanol 100 100 100 100 100 100 99 99 99 97 conversion Yield Yield of 92 90.5 89.6 83.9 89.3 87.4 85.2 76.0 74.0 66 acetic acid2) Yield of methyl 4.3 3.0 3.4 6.9 9.2 9.8 12.0 19.0 25.5 27.0 acetate3} " GHSV = Gas Hourly Space Velocity (hr-1):This is a measure demonstrating the methanol reactant in a gas phase passed through the catalyst per hour. The higher the GHSV, the shorter the contacting time of the catalyst with the reactants, and the more the amount of the reactants to be treated per hour.

Mole of acetic acid produced 2) Yield of acetic acid = - x 100 Mole of methanol introduced into the reactants Mole of methyl acetate produced x 2 3) Yield of methyl acetate = x 100 Mole of methanol introduced into the reactants Example 2 This example was carried out by employing the same catalyst and the same conditions as described in Example 1, except that the reaction temperature and pressure were changed to 233"C and 150 psi, respectively. The results are shown in Table 2 below.

Table 2

GHSV r1 | 1207 | 1568 1735 | 2133 3293 3652 4149 Methanol 96.4 93.7 88.9 84.3 71.6 68.8 62.2 conversion Yield of acetic 33.0 22.3 20.0 15.5 10.7 8.6 7.5 acid Yield of methyl 63.0 64.8 64.8 63.6 60.1 54.5 49.5 acetate As can be seen from Tables 1 and 2, even if an identical catalyst is used, the production ratio of methyl acetate to acetic acid can easily be adjusted under different reaction conditions. That is, the results from Example 2 show that methyl acetate is massproduced under relatively mild conditions.

Example 3 This example was carried out as described in Example 1, except that a catalyst prepared by supporting 800 mol% of LiI on active carbon was employed. The results are shown in Table 3 below.

Table 3

GHSV (hr.1) ) 600 900 1200 1500 1800 2100 2400 2700 Methanol 100 100 100 100 100 100 > 99 > 99 conversion Yield of acetic 91.5 92.1 93.6 92.7 92.2 92.6 78.5 78.9 acid Yield of methyl 6.5 6.3 5.1 6.0 5.6 6.1 19.2 19.8 acetate Example 4 This example was carried out as described in Example 1, except that an active carbon supported catalyst that supports thereon 1.8% by weight of Rh and 400 mol% of LiI based on the amount of Rh was employed and that the reaction temperature and the CO partial pressure were changed to 270"C and 150 psi, respectively. The results are shown in Table 4 below.

Table 4

GHSV (hr-" 1000 2000 3500 4800 Methanol 100 100 100 100 conversion Yield of 95 83 75 68 acetic acid Yield of 5 16 22 30 methyl acetate Example 5 This example was carried out as described in Example 1, except that an active carbon supported catalyst that supports thereon 0.6% by weight of Rh based on the amount of the active carbon and 200 mol% of NaI based on the amount of Rh was employed and that the reaction temperature and pressure were changed to 240 C and 200 psi, respectively. The results are shown in Table 5 below.

Table 5

GHSV (hr-1) 1000 1568 1735 2133 Methanol 100 100 100 100 conversion Yield of 83 58 40 31 acetic acid Yield of methyl 17 42 60 69 acetate Example 6 This example was carried out in the same manner as described in Example 1, except that an active carbon supported catalyst that supports thereon 0.6% by weight of Rh and 200 mol% of KI based on the amount of Rh was employed. The results are shown in Table 6 below.

Table 6

GHSV 1039 1795 2997 4017 Methanol conversion 100 I 100 I 100 96 Selectivity to acetic acid 95 80 50 33 Selectivity to methyl acetate 5 20 50 63 Example 7 This example was carried out as described in Example 1, except that an active carbon supported catalyst that supports thereon 0.6% by weight of Rh and 50 mol% of MgCl2 based on the amount of Rh was employed. The results are shown in Table 7 below.

Table 7

GHSV (hrl) 2068 | 3417 4855 5754 Methanol 100 98.8 94.6 84.9 conversion Yield of acetic 89.9 66.6 43.1 30.0 acid Yield of methyl 8.8 30.6 49.6 52.3 acetate Example 8 This example was carried out as described in Example 1, except that an active carbon supported catalyst that supports thereon RhCl3 and frCl3 in a molar ratio of 1:0.5 was employed and that the reaction temperature was changed to 255"C. The results are shown in Table 8 below.

Table 8

GHSV (hr-1) 800 1200 1500 2000 2500 Methanol 100 100 100 100 100 conversion Yield of acetic 74 54 40 28 18 acid Yield of methyl 26 46 60 72 82 acetate Example 9 This example was carried out as described in Example 1, except that an active carbon supported catalyst that supports thereon 0.6% by weight of Rh and 200 mol% of Pd Cl2 based on the amount of Rh was employed and that the reaction temperature and the CO partial pressure were changed to 2550C and 150 psi, respectively. The results are shown in Table 9 below.

Table 9

GHSV (hurt) 1000 2000 3000 4000 Methanol 99 95 85 78 conversion Selectivity to 55 30 19 17 acetic acid Selectivity to 45 70 81 83 methyl acetate Example 10 This example was carried out as described in Example 1, except that an active carbon supported catalyst that supports thereon RhCl3 and RuCl3 in a molar ratio of 1:0.5 was employed and that the reaction temperature was changed to 255"C. The results are shown in Table 10 below.

Table 10

GHSV(hr-1) 1800 3000 4200 Methanol 93 84 73 conversion Selectivity to 24 13 11 acetic acid Selectivity to 75 85 86 methyl acetate Example 11 This example was carried out as described in Example 1, except that an active carbon supported catalyst that supports thereon RhCl3 and CoCl2 in a molar ratio of 1:0.5 was employed and that the reaction temperature was changed to 210 C. The results are shown in Table 11 below.

Table 11

GHSV (hr-1) 1000 2000 3000 4000 Methanol 100 98 91 82 conversion Selectivity to 45 33 23 15 acetic acid Selectivity to 55 67 77 l 85 methyl acetate Example 12 This example was carried out as described in Example 1, except that an active carbon supported catalyst that supports thereon RhCl3 and NiCl2 in a molar ratio of 1:0.5 was employed and that the reaction temperature was changed to 210 C. The results are shown in Table 12 below.

Table 12

GHSV r1 1000 2000 3000 4000 Methanol 100 95 90 79 conversion Selectivity to 50 39 29 18 acetic acid Selectivity to SO 61 71 82 methyl acetate Example 13 This example was carried out employing the same catalyst as described in Example 1, except that a certain amount of hydrogen was mixed with the carbon monoxide stock gas.

While changing the ratio of carbon monoxide to hydrogen, the mixed gas was introduced with methanol into the reactor under a pressure of 14.1 kg/cm2 (200 psi). At this time, the molar ratio of methanol to carbon monoxide was in the range of 1:1.6, the GHSV of methanol was maintained at 1500 at the reaction temperature of 250 C. The results are shown in Table 13 below.

Table 13

CO 100% Addition Addition Addition Addition of H2 7% of H2 14% ofH2 20% of H2 25% Methanol Methanol 100% 100% 100% 100% 100% conversion Yield of 83% 97% 95% 93% 92% Acetic acid Example 14 RhCI3-3H2O and LiI were supported on an active carbon in an aqueous phase in such a manner that 0.6% by weight of Rh and 200 mol% of LiI based on the amount of Rh were contained thereon.The resulting mixture was then sintered at 300 C to prepare a catalyst.

Using the catalyst thus obtained, this example was carried out as described in Example 13 except that the GHSV of methanol was maintained at 3000. The results are shown in Table 14 below.

Table 14

CO cho 100% Addition of H2 7% Methanol 86.2% 100% conversion Yield of 21.6% 65.9% acetic acid Yield of 64.4% 31.0% methyl acetate Example 15 This example was carried out as described in Example 13, except that an active carbon supported catalyst that supports thereon 0.6% by weight of Rh and 200 mol% of KCl based on the amount of rhodium was employed and that the GHSV of methanol was maintained at 2000. The results are shown in Table 15 below.

Table 15

CO 100% Addition of H, 7% Methanol 86.9% 100% conversion Yield of 22.5% 46.1% acetic acid Yield of 50.4% 50.1% methvl acetate Example 16 Rh Cl3 3H2O and PdCl2 were supported on an active carbon in an aqueous phase in such a manner that 0.6% by weight of Rh and 50 mol% of PdCi based on the amount of rhodium were contained thereon. The resulting mixture was then sintered at 300"C to prepare a catalyst.

Using the catalyst thus obtained, this example was carried out as described in Example 13 except that the GHSV of methanol was maintained at 1000. The results are shown in Table 16 below.

Table 16

CO 100% Addition of H? 7% Methanol 100% 100% conversion Yield of 55.6% 7s.2 acetic acid Yield of 40.6% 21.9% methyl acetate Example 17 This example was carried out as described in Example 13, except for employing an active carbon supported catalyst on which RhCl3 was supported so that 0.6% by weight of rhodium and 50 mol % of RuCl3 were contained thereon and that the GHSV of methanol was maintained at 2,000. The results are shown in Table 17 below.

Table 17

CO 100% Addition of H1 7% Methanol 93.9% 100% conversion Yield of 25.6% 73% acetic acid Yield of 60.1% 22% methyl acetate Example 18 Employing the same reactor and the same catalyst as in Example 1, methyl acetate and CH3I in a molar ratio of 10:1 were introduced into a reactor. Thereafter, carbon monoxide was introduced into the reactor followed by allowing the reaction mixture to undergo the gas phase second carbonylation at 250"C at 200 psi. The results are shown in Table 18 below.

Table 18

GHSV t1) 150 300 500 650 Methyl acetate conversion 32 1 28 25 20 Selectivity to 98 98 98 98 acetic anhydride Example 19 This example was carried out in the same manner as described in Example 18 except for employing the same catalyst in Example 8. The results are shown in Table 19 below.

Table 19

GHSV (hr-1) 150 330 500 1 670 Methyl acetate 32 26 24 22 conversion Selectivity to 99 98 98 98 acetic anhydride Example 20 This example was carried out in the same manner as described in Example 18 except for employing the same catalyst in Example 4 and maintaining the GHSV at 500 with varying the reaction temperature. The results are shown in Table 20 below.

Table 20

Temperature 240 l 250 260 Methyl acetate 28 26 21 conversion Selectivity to 98 98 98 acetic anhydride

Claims

CLAIMS 1. A process for the simultaneous production of acetic acid, methyl acetate and acetic anhydride which comprises the steps of: (a) preparing acetic acid and methyl acetate by gas phase carbonylation of methanol with carbon monoxide, optionally in admixture with hydrogen, in the presence of a rhodium catalyst and a halide co-catalyst in a first carbonylation reactor; (b) separating the resulting product and the co-catalyst from the reaction mixture while recovering the acetic acid; (c) recovering a certain amount of the separated methyl acetate by distillation while introducing the remainder of the separated methyl acetate with the co-catalyst into a second carbonylation reactor;; (d) preparing acetic anydride by carbonylation of the methyl acetate introduced into the second carbonylation reactor with carbon monoxide, optionally in admixture with hydrogen, in the presence of a co-catalyst; and (e) separating the co-catalyst from the resulting acetic anhydride, followed by recovering the acetic anhydride while recycling the co-catalyst to the first carbonylation reactor.
2. A process according to Claim 1, wherein step (a) is carried out using methanol and carbon monoxide in a molar ratio of 1:0.1 to 1:100 at a temperature of 100 to 4000C at a carbon monoxide partial pressure ranging from atmospheric pressure to 1,000 psi.
3. A process according to Claim 1, wherein step (a) is carried out using methanol and carbon monoxide in a molar ratio of 1:0.5 to 1:2.3 at a temperature of 150 to 3000C at a carbon monoxide partial pressure ranging from 150 to 300 psi.
4. A process according to Claim 1, wherein step (a) is carried out at moderate conditions of a temperature of below 3000C at a carbon monoxide partial pressure of below 200 psi.
5. A process according to any one of the preceding claims, wherein step (d) is carried out at a GHSV of 50 to 10,000 hr 1 and a temperature of 100 to 4000C.
6. A process according to any one of the preceding claims, wherein the carbon monoxide used in steps (a) and (d) is mixed with 1 to 50% of hydrogen.
7. A process according to any one of the preceding claims, wherein the rhodium catalyst is prepared by dissolving a rhodium compound in water or an organic solvent so that 0.1 to 20% by weight of rhodium based on the amount of an inert vehicle to be used is contained; supporting the resulting mixture on an inert vehicle together with 0.1 to 1,000 mol% of an alkali or alkaline earth metal or transition metal based on the amount of the rhodium; and then sintering the resulting mixture at 100 to 5000C.
s. A process according to Claim 7, wherein the rhodium compound is selected from the group consisting of RhX3 (X=Cl, Br, I), RhX3-3H20 (X=C1, Br, I), Rh2(CO)4X2 (X=Cl, Br, I), [Rh(CO)X4]Y (X=Cl, Br, I; Y=Na, Li, K), Rh2(CO)8, Rh(NO3)3 [Rh(CO)2X2]Y (X=Cl, Br, I; Y=Li, Na, K), Rh203, [Rh(C2H4)2X]2 (X=Cl, Br, I), Rh[(C6H5)3P2](CO)X (X=Cl, Br, I), Rh metal, RhX [(C6H5)3P]2(CH3Y)2 (X,Y=Cl, Br, I), Rh(SnCl3)[(C6H5)P]3 (X=Cl, Br, I), RhX(CO)[(C6H5)3Y32 (X=Cl, Br, I; Y=As, P, Sb), [R4Y] [Rh(CO)2X]2 (X=Cl, Br, I; R=Cl-C,2 alkyl; Y=N, As, P), [R4n2Rh(CO)X4] (X=C1, Br, I; R=C,-Cl2 alkyl;Y=N, As, P), RhXt(C6H5)3P]3 (X=C1, Br, 1), RhX[(C6H5)3P]H2 (X=Cl, Br, I), [(C6Hs)3P]3Rh(CO)H, and Y4Rh2X2(SnX3)4 (X=Cl, Br, I; Y=Li, Na, K).
9. A process according to Claim 7 or 8, wherein the inert vehicle is selected from an active carbon, clay, alumina, silica and silica-alumina.
10. A process according to any one of Claims 7 to 9, wherein the rhodium compound is used such that 0.6 ~ 5% by weight of rhodium based on the amount of the inert vehicle is present in the first carbonylation reactor.
11. A process according to any one of Claims 7 to 10, wherein the alkali metal or alkaline earth metal is used in an amount of 200 800 mol% based on the amount of rhodium.
12. A process according to any one of Claims 7 to 10, wherein the transition metal is used in an amount of 10- 500 mol% based on the amount of rhodium.
13. A process according to any one of the preceding claims, wherein the halide co-catalyst is selected from CH3I, CH3Br, CH3Cl, I2, Br2, C12, HI, HBr and HCl.
14. A process according to Claim 13, wherein the molar ratio of the CH3 I co-catalyst to methanol or methyl acetate which is introduced into each of the first and second carbonylation reactors is in the range of 0.01:1 to 1:10.
15. A process for the simultaneous production of acetic acid, methyl acetate and acetic anhydride substantially as described in any one of the foregoing Examples 1 to 20.
16. Acetic acid, methyl acetate or acetic anhydride whenever produced by a process according to any one of the preceding claims
17. A catalyst for carbonylation of methanol prepared by the method according to Claim 7.