Process for continuously preparing ethylene glycol

A process for continuously preparing ethylene glycol, which comprises

• (1) a first step of contacting a gas containing carbon monoxide and an ester of nitrous acid with a solid catalyst of platinum group metal series in the gaseous phase at a temperature of from 50.degree. to 200.degree. C. and a pressure of from ambient pressure to 10 kg/cm.sup.2 (guage) thereby to obtain a product containing a diester of oxalic acid, and said ester of nitrous acid is an ester of a saturated monohydric aliphatic or alicyclic alcohol having 1 to 8 carbon atoms with nitrous acid,
• (2) a second step of condensing the product of the first step thereby to separate a non-condensed gas containing nitrogen monoxide formed by the catalytic reaction of the first step from a condensed liquid containing the diester of oxalic acid, and then evaporating the thus condensed liquid to distil out the alcohol containing the diester of carbonic acid by-produced in the catalytic reaction of the first step and to obtain the diester of oxalic acid as a distillation residue,
• (3) a third step of contacting in a regeneration column the non-condensed gas of the second step with a gas containing molecular oxygen and an alcohol to produce a gas mixture containing (i) an ester of nitrous acid and (ii) nitrogen monoxide and controlling the concentration of said nitrogen monoxide within the range of from 2 to 7% by volume, and recycling the resulting gas containing an ester of nitrous acid to the first step,
• (4) a fourth step of contacting the distillation residue of the second step containing the diester of oxalic acid and hydrogen with a catalyst for hydrogenation in the gaseous phase thereby to obtain a product containing ethylene glycol,
• (5) a fifth step of distilling the product of the fourth step thereby to distil out the alcohol and to obtain ethylene glycol, and
• (6) a sixth step of recycling the alcohol of the fifth step as an alcohol source for the third step.

A process for continuously preparing ethylene glycol, which comprises

• (1) a first step of contacting a gas containing carbon monoxide and an ester of nitrous acid with a solid catalyst of platinum group metal series in the gaseous phase at a temperature of from 50.degree. to 200.degree. C. and a pressure of from ambient pressure to 10 kg/cm.sup.2 (guage) thereby to obtain a product containing a diester of oxalic acid, and said ester of nitrous acid is an ester of a saturated monohydric aliphatic or alicyclic alcohol having 1 to 8 carbon atoms with nitrous acid,
• (2) a second step of condensing the product of the first step thereby to separate a non-condensed gas containing nitrogen monoxide formed by the catalytic reaction of the first step from a condensed liquid containing the diester of oxalic acid,
• (3) a third step of contacting in a regeneration column the non-condensed gas of the second step with a gas containing molecular oxygen and an alcohol to produce a gas mixture containing (i) an ester of nitrous acid and (ii) nitrogen monoxide and controlling the concentration of said nitrogen monoxide within the range of from 2 to 7% by volume, and recycling the resulting gas containing an ester of nitrous acid to the first step,
• (4) a fourth step of contacting the condensed liquid of the second step containing the diester of oxalic acid and hydrogen with a catalyst for hydrogenation in the gaseous phase thereby to obtain a product containing ethylene glycol, ester of glycolic acid and the alcohol,
• (5) a fifth step of distilling the product of the fourth step thereby to distil out the alcohol and the glycolic acid formed in the fourth step and to obtain ethylene glycol, and then recycling the glycolic acid to the fourth step, and
• (6) a sixth step of recycling the alcohol of the fifth step as an alcohol source for the third step.