Patent ID: 8569517

Claim:
A method for producing a biodegradable, intermolecular cyclic diester of an alpha-hydroxycarboxylic acid of formula I by at least partial separation from material mixtures comprising the diester of formula I and also the alpha-hydroxycarboxylic acid, corresponding thereto, of formula II and also linear dimers and oligomers of the corresponding a-hydroxycarboxylic acids and water, the method comprising: a) feeding the material mixture into a cleaning device which has a dividing wall column, the cleaning device comprising at least the following components which are arranged from top to bottom in the following sequence: aa) at the top, at least one dephlegmator and also at least one outlet, bb) at least one mass transfer packing which fills the diameter of the device at least partially, cc) a dividing wall column which is divided into two zones by a vertical dividing wall, each zone comprising at least two mass transfer packings which are separated from each other respectively by a gap, the first zone comprising a prefractionation zone comprising at least one inlet for supplying the material mixture and the second zone comprising a main fractionation zone comprising at least one side outlet for removing the cleaned product, and the at least one inlet and also the at least one side outlet being located respectively in the region of the at least one gap, dd) at least one further mass transfer packing which fills the diameter of the device at least partially, ee) on a sump side, at least one evaporator and at least one outlet, a length ratio of the dividing wall column to a total length of the cleaning device comprising approximately 0.5 to 0.9, b) separating the material mixture, the acid of formula II leaving the column in a vaporous aggregate state and c) removing the cleaned diester of formula I via the at least one side outlet.