Patent ID: 7495129

Claim:
A process for purification of an acidic monomer having a double bond, comprising the steps of: (a) providing a starting mixture, containing as starting mixture components, respectively based on the starting mixture, (a1) at least about 5 wt.% of the acidic monomer and either (a2) at least about 0.01 wt.% water, or (a3) at least about 0.01 wt.% of at least one starting mixture component comprising impurities which are different to the acidic monomers with the exception of water, or (a2) and (a3) wherein the sum of the wt.% proportions of the starting mixture components gives respectively 100 wt.%; (b) adding a phase former or a salt of this phase former or a mixture of both to obtain a purification mixture, from which (c) at least one first phase and an at least one further phase distinguished from the first phase by means of a phase boundary form a phase system; (d) lowering of the temperature of the phase system; wherein (e) in one of the phases of the phase system a product crystal containing at least about 50 wt.% of one of the starting mixture components is formed in addition to another starting mixture component as a crystal system; (f) isolating the product crystals wherein the acidic monomer is (meth) acrylic acid.