Abstract: A process for the manufacture of symmetrical dialkylureas by reacting monoalkylamines with CO.sub.2 at an elevated temperature and under superatmospheric pressure, in which the unconverted starting materials, water and the by-products formed in the reaction zone, as well as alkylamine alkylcarbamate, after thermal decomposition into monoalkylamine, CO.sub.2 and water, are separated from the dialkylurea formed, and thereafter a part of the unconverted starting materials plus by-products, with or without water, may or may not be recycled to the reaction zone, before isolating an aqueous solution, containing monoalkylamines, CO.sub.2 and other by-products, which solution is treated with alkali metal hydroxide solution in a column, the monoalkylamine, after separation from carbon dioxide and water, being recycled to the reaction zone. The dialkylureas obtained contain not more than 1% of monoalkylurea and 1% of trialkylurea, and may be used as starting materials for various syntheses.

Abstract: A process for separating, by means of a selective solvent, a mixture of C.sub.

Abstract: 1,3-Butadiene is recovered with the aid of a selective solvent from a C.sub.4 -hydocarbon mixture containing 1,3-butadiene, hydrocarbons which are more soluble in said selective solvent than 1,3-butadiene, including acetylenes and possibly 1,2-butadiene and C.sub.5 -hydrocarbons, and hydrocarbons which are less soluble in said selective solvent than 1,3-butadiene. The C.sub.4 -hydrocarbon mixture is separated by the use of one or more extractive distilling zones into a distillate containing the less soluble hydrocarbons, a stream consisting of 1,3-butadiene and a stream containing the more soluble hydrocarbons including the higher acetylenes and 1,3-butadiene, the latter stream being subjected to catalytic hydrogenation.