Process for preparing aspartic acid from ammonium aspartate, and continuous process for preparing polysuccinimide involving such process

Continuous process for preparing polysuccinimide starting from fumaric or maleic acid and ammonia, characterised by the following process steps:

• reaction of fumaric or maleic acid, or salts thereof, with ammonia to prepare ammonium fumarate or maleate,
• continuous bioconversion of the ammonium fumarate or ammonium maleate respectively into an aqueous ammonium aspartate solution, using immobilised aspartase or fumarate isomerase/aspartase respectively containing micro-organisms,
• concentrating the aqueous solution,
• continuously introducing the concentrated aqueous solution of ammonium aspartate into a diluent in which water has a solubility of less than 2% by weight, which diluent is maintained at a temperature at which ammonium aspartate decomposes into aspartic acid and ammonia,
• continuously removing water and the formed ammonia and aspartic acid at a rate substantially corresponding to the rate of introducing the ammonium aspartate solution into the diluent, whereas the ammonia is recovered for use in the conversion of fumaric or maleic acid into ammonium fumarate or maleate,
• thermal polycondensation of the obtained aspartic acid into polysuccinimide.