Abstract: The present invention relates to an improved process for the preparation of polyisocyanates with a biuret structure by continuous reaction of excess amounts of organic diisocyanates having exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups with organic diamines having exclusively aliphatically and/or cycloaliphatically bonded primary amino groups at elevated temperatures by 2-stage addition of the isocyanate component.

Abstract: A circulation evaporator for separating mixtures having more volatile and less volatile components. The circulation evaporator contains an evaporator, a discharge container connected to the evaporator by a connecting piece, a condenser, a vacuum pump, a recirculating line, a feed line and an outflow line. The discharge container contains a chamber for feed and a chamber for outflow. The invention further relates to a process for the separation by distillation of a mixture having more volatile and less volatile components by employing the circulation evaporator.

Abstract: The invention relates to a circulation evaporator for separating mixtures consisting of more volatile and less volatile components, which comprises a discharge container that consists of at least a chamber for the feed and of a chamber for the outflow. The invention further relates to a process for the separation by distillation of a mixture consisting of more volatile and less volatile components by employing the circulation evaporator.

Abstract: The process for producing crystallisation products with an average particle diameter of <1 .mu.m is based on the atomisation of a solution and the simultaneous evaporation of the solvent. The atomised solution A crystallises in a gas atmosphere, in which it is simultaneously contacted with a cloud of drops 4 of a surfactant-containing liquid B, thus forming an aerosol mixture A, B which is then deposited in the form of a colloidal crystal suspension in which the surfactant-containing liquid B forms the continuous phase. The cloud of drops 4 of the surfactant-containing liquid can also be produced by atomisation.