Abstract: The invention relates to an apparatus provided with heat-exchanging means comprising a housing, in which housing a tube bank is accommodated, having at both sides connecting means for the inlet and outlet of a primary medium stream and a secondary medium stream, wherein the housing comprises a wall that extends in the longitudinal direction of the tube bank wherein the wall is embodied with tubes incorporated therein or mounted thereon, through which a portion of the medium supplied to the tube bank flows.

Abstract: A method for the preparation of urea in a reactor using ammonia and carbon dioxide as starting materials, includes a) bringing the ammonia and carbon dioxide into contact in the reactor under conditions for the formation of carbamate; and b) decomposing the carbamate thus formed to give urea and water. The water formed during step b) is removed from the reaction mixture by a water-selective membrane which is preferably a pervaporation membrane, such as a porous ceramic membrane. Furthermore, a pressure difference is preferably maintained or applied over the selective membrane. The method can in particular be carried out in liquid circulating stream which, in addition to the reactants fed to the circulating stream and the carbamate formed in step a), also contains at least some of the water formed in step b) and also the urea formed in step b), the urea being recovered from the circulating stream and the circulating stream being recycled to the reactor.

Abstract: Mass transfer process, in which, in at least two contact stages, and at least two liquid or gaseous phases are brought into contact with one another, at least one component being transferred between the phases and the phases moving countercurrently. The flow through at least one of the contact stages is batchwise for one phase and continuous for another phase. The phases flow through contact stages which are formed by trays in a column, which trays are opened periodically so that the phase which flows through the column in a batchwise manner flows to the next tray.