摘要:
Condensation products are prepared from carboxamides, formaldehyde, dicyandiamide and ammonium and/or amine salts in a single process step. After the end of the exothermic reaction the reaction mixture is heated for from 30 minutes to 5 hours at a temperature of from 70.degree. to 100.degree. C.
摘要:
Maleic anhydride is recovered by evaporating the effluent from the production of phthalic anhydride at from 40.degree. to 150.degree.C and from 50 to 760 mm to a water content of less than 10% by weight, heating the concentrate in a thin-film or falling-film evaporator at from 100 to 600 mm at from 120.degree. to 180.degree.C and distilling it in a column. The pure maleic anhydride is withdrawn laterally and the aqueous condensate is recycled to the offgas scrubber.