WO2000058248A1

WO2000058248A1 - Process for producing 1,4-cyclohexanedimethanol with enhanced cis-isomer content

Info

Publication number: WO2000058248A1
Application number: PCT/US2000/005817
Authority: WO
Inventors: Paul Randolph Worsham; Bruce Leroy Gustafson; Yeong-Jen Kuo
Original assignee: Eastman Chemical Company
Priority date: 1999-03-25
Filing date: 2000-03-06
Publication date: 2000-10-05

Abstract

In a process for the preparation of 1,4-cyclohexanedimethanol (CHDM), a dialkyl 1,4-cyclohexanedicarboxylate (DACD) is contacted with hydrogen in the presence of a copper hydrogenation catalyst essentially devoid of barium under hydrogenolysis conditions of temperature and pressure. The CHDM thus produced contains a significant amount of the cis-isomer of CHDM, e.g., CHDM having a cis:trans ratio of at least 0.7:1.

Description

PROCESS FOR PRODUCING 1,4-CYCLOHEXANEDIMETHANOL WITH ENHANCED C/S-ISOMER CONTENT

TECHNICAL FIELD OF THE INVENTION This invention pertains to processes for the preparation of

1 ,4-cyclohexanedimethanol (CHDM), and more particularly to processes for the preparation of CHDM consisting of a significant amount of the cis- isomer.

BACKGROUND OF THE INVENTION

CHDM is an important intermediate for producing a variety of polyester and poly(ester-amides) for use in fibers, molding plastics, packaging materials, and the like. CHDM presently is manufactured by the hydrogenolysis of a dialkyl 1 ,4-cyclohexanedicarboxylate (DACD), especially dimethyl 1 ,4-cyclohexanedicarboxylate, in the presence of a barium- promoted, copper chromite catalyst. This hydrogenolysis produces a mixture of cis- and trans- isomers of CHDM. The composition of the mixture, which tends toward the thermodynamic equilibrium mixture, contains about 75-80% of the trans- isomer at the usual hydrogenolysis temperature of around 230°C regardless of the isomer content of the starting DACD. Although

DACD may be enhanced in either isomer by simply cooling to separate the trans- isomer, the two isomers of CHDM are difficult and expensive to separate. The isomer ratio of CHDM may be varied to some extent by changing the hydrogenolysis conditions. Most technology development in this area has been directed almost exclusively to the production of CHDM with an enhanced content of -frans-CHDM, which is preferred for the manufacture of most polyester plastics.

The effectiveness of copper chromite for the hydrogenation of a variety of organic compounds was first reported by Adkins and Connor, J. Am. Chem. Soc. 53_* 1091 (1931). The use of barium-promoted copper chromite in one stage of a two-stage process for the preparation of CHDM starting with dimethyl terephthalate was described by Akin, Lewis, and Reid in U.S. Patent 3,334,149. This patent does not mention isomer content.

Thakur et al., U.S. Patent No. 5,345,005, describes catalysts comprising the oxides of copper, zinc, and aluminum which are said to be useful for hydrogenating a number of organic compounds including dimethyl 1 ,4-cyclohexanedicarboxylate (DMCD). The '005 patent does not mention the isomer content of the product.

U. S. Patent Nos. 5,243,095 and 5,418,201 to Roberts et al. describe catalysts comprising the oxides of copper, iron, aluminum, and manganese which are claimed to be useful for ester hydrogenolysis. The examples in these patents concern the hydrogenolysis of fatty acid esters and no reference is made to isomer ratio control or to CHDM.

Thakur et al., U. S. Patent No. 5,134,108, describes catalysts based upon the oxides of a first metal selected from copper or zinc, and a second metal selected from chromium, molybdenum, tungsten, and vanadium, optionally with a promoter metal selected from the group consisting of manganese, barium, zinc, nickel, cobalt, cadmium, iron, and any combination thereof. The '108 patent refers to dimethyl ester of terephthalic acid but does not mention any products obtained therefrom. Recently, a series of U.S. patents has been issued which deal specifically with the hydrogenolysis of DMCD to CHDM. These patents describe apparatus and processes for carrying out the reaction in the vapor phase.

U.S. Patent No. 5,387, 752 is directed to a process for the production of CHDM and, particularly, to a process for the production of a mixture containing a major amount of the trans- isomer. A variety of catalysts is described.

U.S. Patent No. 5.395,991 describes a two-zone hydrogenation process for the vapor phase hydrogenation of esters such as DMCD. One zone is used for catalyst regeneration (U. S. Patent No. 5,387,753) while the hydrogenation is carried out in the other.

U.S. Patent No. 5,395,986 relates to "...a process for the production of a mixture containing a major amount of the trans- isomer of CHDM and a minor amount of the corresponding cis- isomer". The process produces CHDM with a trans.cis ratio greater than 1:1.

U.S. Patent No. 5,395,987 describes a continuous, vapor-phase process for the production of CHDM having a desired or predetermined ratio. A specific object of the invention is the production of CHDM with a higher trans:cis ratio than is achievable by conventional hydrogenolysis processes. The trans:cis ratio may be varied from 1 :1 to approx. 3.84:1.

U.S. Patent No. 5,395,990 pertains to the use of catalysts of specific pore size in the manufacture of alcohols from esters. No data is given on the isomer ratio of the products. U.S. Patent No. 5,406,004 describes a vapor phase process for the hydrogenolysis of esters including a process for the production of CHDM having a higher trans.cis ratio than is achievable by conventional methods.

U.S. Patent No. 5,414,159 also describes a vapor-phase, hydrogenolysis process for the production of CHDM having a higher trans:cis ratio than is achievable by conventional methods.

As the above patents suggest, a mixture of CHDM isomers high in the trans- isomer is preferred for most applications, particularly for use in the manufacture of polyester molding plastics. In an early attempt to modify the cis:trans ratio of CHDM, U. S. Patent No. 2,917,549 to Hasek et al. describes a method for attaining the equilibrium high trans- isomer mixture by heating the isomers to elevated temperatures in the presence of such strong bases as metal alkoxides. The composition of the product in every case approached 75-80% trans- isomer.

CHDM is widely used as one of the glycol components of polyesters used in molding plastics, particularly those used for making bottles. U.S. Patent No. 5,552,512 to Sublett reports that polyesters based upon terephthalic acid, 2,6-naphthalenedicarboxylic acid, and CHDM exhibit a substantially higher barrier to oxygen transmission if the CHDM contains a relatively high concentration of the cis- isomer.

Thus, a need in the art exists for a process for the hydrogenolysis of DACD that yields a product whose isomer content can be controlled to give either high c/s-CHDM for barrier polymer applications, or high trans-CHDM for molding plastics. Accordingly, it is to the provision of such that the present invention is directed.

SUMMARY OF THE INVENTION In a process for the production of CHDM having a cis.trans ratio of at least 0.7:1 , a dialkyl 1,4-cyclohexanedicarboxylate (DACD) is contacted with hydrogen in the liquid phase in the presence of a copper hydrogenation catalyst essentially devoid of barium under hydrogenolysis conditions of temperature and pressure.

DETAILED DESCRIPTION OF THE INVENTION DACD isomerization, which occurs in barium- promoted, copper chromite hydrogenolysis, has been observed to be minimized by limiting the conversion of the DACD to CHDM either by reducing the contact time with the catalyst or by reducing the temperature and/or pressure. Operation of the process at low conversion, however, is not economical and, at lower temperatures and pressures, tends to increase the production of by-products. Further study of DACD hydrogenolysis has led to the discovery that the presence of barium in the hydrogenolysis catalyst is responsible for the isomerization of DACD high in cis- isomer to CHDM high in trans- isomer and that elimination of the barium or substitution of another metal, e.g., manganese, for the barium permits operation of the process at economical rates and conversions. The process provided by the present invention, therefore, involves the production of CHDM having a cisdrans ratio of at least 0.7:1 and as high as about 6:1, preferably a cis:trans ratio in the range of about 1:1 to 1.5:1, by contacting DACD having a cis.trans ratio of at least 2:1 with hydrogen in the liquid phase in the presence of a copper hydrogenation catalyst essentially devoid of barium under hydrogenolysis conditions of temperature and pressure. The process of this invention provides for the hydrogenolysis of DACD which minimizes or entirely eliminates interconversion of the cis- and trans- isomers and thus permits the production of CHDM having an isomer composition which more nearly approximates the isomer composition of the DACD feedstock than it does the equilibrium composition. This invention provides a method for minimizing, if not entirely eliminating, the isomerization which occurs during the hydrogenolysis of DACD.

The DACD reactant employed in the process may be any dialkyl 1 ,4-cyclohexanedicarboxylate diester wherein each alkyl group contains up to about 4 carbon atoms. However, the DACD reactant preferably is the dimethyl diester (DMCD), which is obtained by the partial hydrogenation of dimethyl terephthalate, an aromatic diester used extensively in the manufacture of polyesters. The DACD reactant normally should have a cis.trans isomer ratio of at least 2:1, preferably about 2: 1 to 10: 1. The process may be carried out in the presence of an inert solvent such as lower alkanols, ethers and hydrocarbons commonly used in hydrogenation processes. The process of the present invention preferably is carried out in the absence of an extraneous solvent. A wide variety of copper-based catalysts may be used in the process of this invention, provided that they are devoid or essentially devoid of barium, i.e., contain less than 500 parts per million by weight (ppm) barium, preferably less than 100 ppm barium. Examples of suitable catalyst include unpromoted copper chromite, as well as copper chromite which contains promoters other than barium, for example manganese- promoted copper chromite. Other copper-based catalysts such as copper oxide/zinc oxide deposited on a catalyst support material such as alumina, magnesium oxide and titania also may be used. It is only essential that the catalyst be reasonably active, and that its activity for catalyzing isomerization be relatively much lower than its activity for catalyzing the hydrogenolysis reaction. Preferred catalysts comprise, in their reduced/active form, about 25 to 60 weight percent copper and about 10 to 35 weight percent chromium, manganese or a combination thereof.

Examples of suitable copper-containing catalyst include copper on alumina catalysts, reduced copper oxide/zinc oxide catalysts, with or without a promoter, manganese-promoted copper catalysts, and reduced copper chromite catalysts, with or without a promoter. Suitable copper oxide/zinc oxide catalyst precursors include CuO/ZnO mixtures wherein the Cu:Zn weight ratio ranges from about 0.4:1 to about 2:1. Promoted copper oxide/zinc oxide precursors include CuO/ZnO mixtures wherein the Cu:Zn weight ratio ranges from about 0.4:1 to about 2:1 which are promoted with from about 0.1% by weight up to about 15% by weight manganese. Suitable copper chromite catalyst precursors include those wherein the Cu:Cr weight ratio ranges from about 0.1 to about 4:1 , preferably from about 0.5:1 to about 4:1. Promoted copper chromite precursors include copper chromite catalyst precursors wherein the Cu:Cr weight ratio ranges from about 0.1 to about 4:1 , preferably from about 0.5:1 to about 4:1 , which are promoted with from about 0.1% by weight up to about 15% by weight manganese. Manganese- promoted copper catalyst precursors typically have a Cu:Mn weight ratio of from about 2:1 to about 10:1 and can include an alumina support, in which case the Cu:AI weight ratio typically is from about 2:1 to about 4:1.

The physical form of the catalyst is not critical and normally is determined by the mode in which the process is operated. For example, pellets having an average diameter of 2 to 6 mm and a length of 4 to 12 mm may be employed in the process wherein the DACD reactant is passed over and through one or more fixed beds of catalyst in a mode of operation referred to as trickle bed operation. The reaction may be run either continuously as in the examples contained herein or batchwise using, for example, a copper catalyst in the form of a powder. Operation of the process in the vapor phase is also within the scope of the invention.

The hydrogenolysis conditions of temperature and pressure are, in general, critical and can be varied over a wide range. Normally, the process will be operated at temperatures in the range of about 200 to 300°C. As would be expected, lower temperatures result in lower reaction rates, while temperatures which are excessively high increase the amount of undesirable by-products. The preferred temperature range is between 225 and 240°C. These temperatures refer to the mean temperature of the catalyst bed, when the reaction is conducted in a continuous trickle-bed reactor. The hydrogenolysis pressure may be varied between about 140 and 415 bar gauge (barg). The preferred pressure is between 310 and 380 barg. Lower pressures generally lead to lower conversion, while higher pressures increase both the energy and equipment cost of the operation.

The process of the present invention is further illustrated by the following examples. The examples were carried out in a continuous mode of operation utilizing a vertical pressure vessel having a length of 1.88 meters (74 inches) and an inside diameter of 2.54 cm (1 inch) as the reactor. Temperature measurements in the reactor were made with a series of 10 thermocouples inserted through the wall of the reactor at 20.6 cm (8.1 inch) intervals starting 1.27 cm (0.5 inch) below the top. The reactor was loaded with 772 mL of one of the following catalysts:

Catalyst I Manganese-promoted copper chromite on alumina spheres about 1.6 mm (1/16 inch) in diameter. Catalyst II Manganese-promoted copper chromite pellets about 3.2 mm (1/8 inch) in diameter containing no binder. Catalyst III Manganese-promoted copper chromite pellets about 3.2 mm (1/8 inch) in diameter containing an inert binder comprised of 30% copper, 26% chromium, 2.5% manganese, 4.3% silicon and 2.8% carbon. Catalyst IV Barium-promoted copper chromite pellets about 3.2 mm

(1/8 inch) in diameter. The catalyst was positioned above and supported by 90 mL of Penn State packing and an additional 90 mL of packing was placed on top of the catalyst. These volumes provided a bed of catalyst 5 feet long with 7 inches of inert packing material at each end of the catalyst bed..

The feed reservoir was a jacketed, 4-L, graduated vessel with a bottom take-off valve. The DMCD feed was pumped with a high-pressure diaphragm pump into a recycle stream and then through a preheater to raise the feed temperature to the approximate reactor temperature. The reservoir, pump head, and feed lines were steam heated to prevent the DMCD from freezing. Three zone heaters on the reactor were used to establish an approximate isothermal temperature profile during each experiment. Heat losses in the tubing between the preheater and reactor generally required that the preheater exit temperature be significantly higher than the desired reactor inlet temperature. However, the combination of preheater and reactor heaters usually allowed an even temperature profile to be obtained at different rates of feed flow and different temperatures.

The DMCD/recycle mixture was fed at the top of the reactor vessel along with hydrogen. Crude product was removed from the bottom of the reactor and fed to a level pot wherein hydrogen was separated from the crude product. A portion, e.g., from about 3 to 15 weight percent, of the crude product was removed from the CHDM production system and the remainder was recycled.

The liquid hold-up in the reactor system was approximately 1 L. For each experiment/example, the system was allowed to stabilize and then approximately 3 L of DMCD was fed before sampling was begun. Although the recycle rates were somewhat variable, the estimated recycle rate was 12 to 14 L per hour.

The product and feed samples were analyzed by capillary GLC analyses using a gas chromatograph with a thermal conductivity detector and the total conversion and the cis:trans ratio of the CHDM product were determined. Samples (0.1 microliter) were injected without dilution.

The DMCD used in the experiments/examples was commercial production material and had the following GLC analysis: DMCD = 93%, methyl 4-methylcyclohexanecarboxylate = 2.5%, methyl 4-carboxycyclo- hexanecarboxylate = 2.0%, and methanol = 2.3%. Titration analysis for acid and water gave 3% acid (as methyl 4-carboxycyclohexanecarboxylate) and 0.2% water. The DMCD consisted of approximately 67% cis- isomer and 33% trans- isomer. In each of Examples 1 - 13 and Comparative Examples C-1 - C-6

DMCD was contacted with hydrogen in the presence of Catalyst I, II, III, or IV at a pressure of 344.6 barg (5000 pounds per square inch gauge) according to the above-described procedure. The results obtained are shown in Table I wherein Temp is the average temperature (°C) measured by the 10 thermocouples, Conv is conversion of DMCD to CHDM calculated from:

Conv = Moles Ester Converted to Alcohol X 100 Moles Ester Fed

Cis:Trans is the molar ratio of c/s-CHDM:fra/7s-CHDM in the CHDM product, and LHSV is the liquid hourly space velocity and is liters of DMCD fed to the reactor per liter of catalyst per hour. The results reported in Table

I are arranged according to increasing conversion to CHDM. TABLE I

Example Catalyst Temp Conv Cis:Trans LHSV

1 II 230 49.1 1.33 1.74

C-1 IV 230 57.0 0.61 1.21

2 I 228 57.5 1.21 1.13

3 II 240 67.4 0.88 1.77

C-2 IV 230 70.6 0.64 1.89

4 III 230 71.6 1.08 1.72

5 II 230 73.6 1.00 1.22

6 II 230 73.7 1.03 1.16

7 III 228 84.6 0.91 1.23

8 III 230 85.2 0.85 1.24

9 III 222 85.2 1.11 1.18

10 III 219 91.0 0.93 0.67

11 III 240 91.2 0.65 1.25

C-3 IV 243 91.9 0.42 1.12

C-4 IV 230 92.1 0.53 1.22

C-5 IV 220 93.5 0.47 0.60

12 II 233 95.9 0.81 1.72

C-6 IV 230 98.0 0.41 0.53

The procedure described above for Examples 1-12 was repeated using a copper oxide/zinc oxide on alumina catalyst (Catalyst V) and a barium-free, copper chromite catalyst (Catalyst VI). The results obtained are shown in Table II wherein Temp, Conv, Cis:Trans and LHSV have the meaning given above. TABLE II

Example Catalyst Temp Conv Cis:Trans LHSV

13 V 228 78.7 0.95 1.16

14 V 230 78.2 0.98 1.15

15 VI 230 86 0.73 1.42

16 VI 230 74 1.09 1.87

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

CLAIMS We claim:

1. A process for the preparation of 1 ,4-cyclohexanedimethanol (CHDM) having a cis:trans ratio of at least 0.7:1 comprising the step of contacting a dialkyl 1 ,4-cyclohexanedicarboxylate (DACD) having a cis:trans ratio of at least 2:1 with hydrogen in the liquid phase in the presence of a copper hydrogenation catalyst essentially devoid of barium under hydrogenolysis conditions of temperature and pressure.

2. The process according to Claim 1 wherein the step of contacting is at a temperature of about 200 to about 300°C and at a pressure of about 140 to about 415 bar gauge.

3. The process according to Claim 1 wherein the step of contacting is at a temperature of about 225 to about 240°C and at a pressure of about 310 to about 380 bar gauge.

4. A process for the preparation of 1 ,4-cyclohexanedimethanol (CHDM) having a cis trans ratio in the range of about 1:1 to 1.5:1 comprising the step of contacting dimethyl 1 ,4-cyclohexanedicarboxylate (DMCD) having a cis.trans ratio of 2:1 to 10:1 with hydrogen in the liquid phase in the presence of a copper hydrogenation catalyst essentially devoid of barium selected from copper chromite, manganese-promoted copper chromite, and copper oxide/zinc oxide deposited on an alumina, magnesium oxide or titania catalyst support material at a temperature of about 200 to about 300°C and at a pressure of about 140 to about 415 bar gauge.

5. The process according to Claim 4 wherein the temperature is in the range of about 225 to about 240°C and at a pressure is in the range of about 310 to about 380 bar gauge.

6. The process according to Claim 5 wherein the catalyst contains about 25 to 60 weight percent copper and about 10 to 35 weight percent chromium, manganese or a combination thereof.