Preparation of cyclohexanedimethanol with a particular ratio

A continuous process for the production of 1,4-cyclohexanedimethanol having a desired or predetermined trans-:cis- isomer ratio of from about 2.0:1 to about 3.84:1 by catalytic hydrogenation of dimethyl 1,4-cyclohexanedicarboxylate in the presence of an ester hydrogenation catalyst, which process is capable of being operated for an extended period of time during which the hydrogenation catalyst declines in catalytic activity, said process comprising:

• (a) providing a hydrogenation zone containing a charge of a granular hydrogenation catalyst selected from reduced copper chromite catalysts wherein the Cu:Cr weight ratio is from about 0.1:1 to about 4:1;
• reduced, copper chromite catalysts wherein the Cu:Cr weight ratio is from about 0.1:1 to about 4:1 promoted with from about 0.1% by weight up to 15% by weight of barium, manganese or a mixture of barium and manganese;
• or reduced manganese promoted copper catalysts wherein the Cu:Mn weight ratio is from about 2:1 to about 10:1 capable of catalysing the hydrogenation of esters;
• (b) determining a Reference Activity (RA) of the granular hydrogenation catalyst by measuring the extent of conversion of the dimethyl 1,4-cyclohexanedicarboxylate to 1,4-cyclohexanedimethanol in passage of a reaction mixture comprising dimethyl 1,4-cyclohexanedicarboxylate and a hydrogen-containing gas through the granular hydrogenation catalyst at a preselected feed temperature, feed pressure, dimethyl 1,4-cyclohexanedicarboxylate feed rate, and hydrogen-containing gas:dimethyl 1,4-cyclohexanedicarboxylate molar ratio;
• (c) determining an Effective Residence Time (ERT) for contact of the reaction mixture at the preselected feed temperature and feed pressure with the granular hydrogenation catalyst at the reference activity thereof which produces 1,4-cyclohexanedimethanol having the desired trans-:cis- isomer ratio of from about 2.0:1 to about 3.84:1;
• (d) forming a vaporous feed stream comprising dimethyl 1,4-cyclohexanedicarboxylate and a hydrogen-containing gas having a preselected hydrogen-containing gas:dimethyl 1,4-cyclohexanedicarboxylate molar ratio;
• (e) feeding the vaporous feed stream to the hydrogenation zone at a constant temperature of from about 150.degree. C. to about 300.degree. C. and which is above the dew point of the feed stream and at a constant pressure in the range of from about 450 psia (about 31.03 bar) to about 1000 psia (about 68.95 bar) at a rate which corresponds to an Actual Residence Time (ART) of the feed stream in contact with the catalyst which yields 1,4-cyclohexanedimethanol of the desired trans-:cis- isomer ratio of from about 2.0:1 to about 3.84:1;
• (f) recovering from the hydrogenation zone a product stream containing 1,4-cyclohexanedimethanol;
• (g) monitoring the Actual Activity (AA) of the granular hydrogenation catalyst with passage of time by measuring the extent of conversion of the dimethyl 1,4-cyclohexanedicarboxylate to 1,4-cyclohexanedimethanol under the actual operating conditions of feed temperature, feed pressure, dimethyl 1,4-cyclohexanedicarboxylate feed rate, and hydrogen-containing gas:dimethyl 1,4-cyclohexanedicarboxylate molar ratio;
• and
• (h) adjusting at least one feed condition of the vaporous feed stream to the hydrogenation zone selected from
• (i) the dimethyl 1,4-cyclohexanedicarboxylate feed rate and
• (ii) the hydrogen-containing gas:dialkyl 1,4-cyclohexanedicarboxylate molar-ratio while maintaining the feed stream above its dew point to provide an Actual Residence Time (ART) of the vaporous feed stream in contact with the catalyst which corresponds to the Effective Residence Time (ERT) required to provide 1,4-cyclohexanedimethanol having the desired trans-:cis- isomer ratio in accordance with the relationship:
• ##EQU4##