Solventless dimeric cyclic ester distillation process

Claim 3

The process of claim 1 wherein the depolymerizable oligomer is an oligomer of L-lactic acid and the lactide product is L-lactide.

Claim 4

The process of claim 2 wherein the distillation temperature is below about 200° C.

Claim 5

The process of claim 2 wherein the distillation is conducted below about 180° C.

Claim 6

A process for the separation and recovery of a dimeric cyclic ester from a vapor product stream containing said ester and minor amounts of one or more hydroxylic impurities including an alpha-hydroxycarboxylic acid more volatile than the cyclic ester, water and oligomeric hydroxycarboxylic acid higher-boiling than the cyclic ester, which process comprises condensing the vapor stream to form a dimeric cyclic ester condensate, fractionally distilling the resulting condensate and recovering a dimeric cyclic ester fraction having a substantially lowered content of water alpha-hydroxy acid, and oligomeric acid wherein the fractional distillation is conducted continuously and comprises the steps of: (a) providing a multi-stage distillation column having a feed inlet at a midpoint of the column, an overhead vapor takeoff at the upper end of the column, a vapor sidestream takeoff at a point below the midpoint feed inlet and a high-boiler take off at the lower end of the column; (b) feeding the cyclic ester condensate to the midpoint of the column; (c) establishing in the column (i) an overhead vapor fraction consisting essentially of water, when present, alpha-hydoxycarboxylic acid more volatile than the cyclic ester and little or no cyclic ester, (ii) a cyclic ester fraction below the midpoint feed inlet that is substantially free of water, lower-boiling acid and higher-boiling acid and (iii) a high-boiling fraction consisting largely of cyclic ester and higher-boiling oligomeric acids at the lower end of the column; (d) removing the overhead fraction from the upper end of the column; (e) removing the cyclic ester vapor fraction through the vapor sidestream takeoff; and (f) removing the higher-boiling fraction at the lower end of the column.

Claim 7

A process for the separation and recovery of a dimeric cyclic ester from a vapor product stream containing said ester and minor amounts of one or more hydroxylic impurities including an alpha-hydroxycarboxylic acid more volatile than the cyclic ester, water and oligomeric hydroxycarboxylic acid higher-boiling than the cyclic ester, which process comprises condensing the vapor stream to form a dimeric cyclic ester condensate, fractionally distilling the resulting condensate and recovering a dimeric cyclic ester fraction having a substantially lowered content of water alpha-hydroxy acid, and oligomeric acid wherein the fractional distillation is conducted continuously and comprises the steps of: (a) providing a multi-stage distillation column having a feed inlet at a midpoint of the column, an overhead vapor takeoff at the upper end of the column, a vapor sidestream takeoff at a point below the midpoint feed inlet and a high-boiler take off at the lower end of the column; (b) feeding the cyclic ester condensate to the midpoint of the column; (c) establishing in the column (i) an overhead vapor fraction consisting essentially of water, when present, alpha-hydoxycarboxylic acid more volatile than the cyclic ester and little or no cyclic ester, (ii) a cyclic ester fraction below the midpoint feed inlet that is substantially free of water, lower-boiling acid and higher-boiling acid and (iii) a high-boiling fraction consisting largely of cyclic ester and higher-boiling oligomeric acids at the lower end of the column; (d) removing the overhead fraction from the upper end of the column; (e) removing the cyclic ester vapor fraction through the vapor sidestream takeoff; and (f) removing the higher-boiling fraction at the lower end of the column.

Claim 8

The process of claim 5 wherein the feed rate of the condensate to the column, the removal rate of the vapor overhead from the column, the removal rate of the cyclic ester fraction from the column and the removal rate of the high boiling fraction from the column are coordinated so as to establish a substantially steady state in the column.

Claim 9

The process of claim 5 wherein the cyclic ester is a lactide, the hydroxycarboxylic acid is lactic acid and the oligomeric hydroxy acid is an oligomer of lactic acid.