Method for continuously producing a dialkyl carbonate and a diol

A method for continuously producing a dialkyl carbonate and a diol from a cyclic carbonate and an aliphatic monohydric alcohol, comprising:

• (1) continuously feeding a cyclic carbonate represented by the following formula (A):
• ##STR5## wherein R.sup.1 is a divalent group represented by the formula --(CH.sub.2).sub.m --, wherein m is an integer of from 2 to 6, which is unsubstituted or substituted with at least one substituent selected from the group consisting of a C.sub.1 -C.sub.10 alkyl group and a C.sub.6 -C.sub.10 aryl group,
• and an aliphatic monohydric alcohol represented by the following formula (B):
• R.sup.2 OH (B)
• wherein R.sup.2 is a monovalent aliphatic C.sub.1 -C.sub.12 hydrocarbon group which is unsubstituted or substituted with at least one substituent selected from the group consisting of a C.sub.1 -C.sub.10 alkyl group and a C.sub.6 -C.sub.10 aryl group, to a continuous multi-stage distillation column, wherein said aliphatic monohydric alcohol contains a concomitant dialkyl carbonate in an amount of from 0 to 40% by weight, based on the total weight of said aliphatic monohydric alcohol and said concomitant dialkyl carbonate, and continuously effecting a transesterification between said cyclic carbonate and said aliphatic monohydric alcohol in the presence of a transesterification catalyst in at least one reaction zone selected from the group consisting of
• (a) said multi-stage distillation column, and
• (b) at least one transesterification reactor which is disposed outside of said multi-stage distillation column and which has an inlet and an outlet, each fluid-tightly communicating with said multi-stage distillation column,
• thereby continuously producing a dialkyl carbonate and a diol,
• while continuously withdrawing a low boiling point mixture containing the produced dialkyl carbonate in a gaseous form from an upper portion of said multi-stage distillation column and continuously withdrawing a high boiling point mixture containing the produced diol and unreacted cyclic carbonate in a liquid form from a lower portion of said multi-stage distillation column,
• wherein when said transesterification is conducted in said transesterification reactor, a liquid flowing-down inside said multi-stage distillation column is continuously withdrawn through at least one withdrawal port provided in a side wall of the multi-stage distillation column at a position or positions thereof corresponding to a stage or stages selected from the group consisting of intermediate stages and a lowermost stage of said multi-stage distillation column, and said withdrawn liquid is continuously introduced to said transesterification reactor through said inlet thereof to thereby contact the cyclic carbonate and aliphatic monohydric alcohol contained in said withdrawn liquid with said transesterification catalyst and effect a transesterification between said cyclic carbonate and said aliphatic monohydric alcohol, whereupon the resultant reaction mixture is continuously withdrawn from said at least one transesterification reactor through said outlet thereof and recycled to said multi-stage distillation column through an introduction port provided in the side wall of the multi-stage distillation column at a position above the or each withdrawal port;
• and
• (2) continuously feeding water and said high boiling point mixture withdrawn from the lower portion of said multi-stage distillation column in step (1) to a continuous hydrolysis reactor, to thereby effect a continuous hydrolysis of said unreacted cyclic carbonate and produce a diol and carbon dioxide, while continuously withdrawing the resultant hydrolysis reaction mixture containing the produced diol from said continuous hydrolysis reactor.