Abstract: A process for working up alkaline process wastewater from the nitration of aromatic compounds to mono-, di- and trinitroaromatics with a pH of 7.5 to 13 or a mixture W with a pH of 6 to 10 of alkaline process wastewater and the aqueous distillate of the sulfuric acid concentration, comprising the steps of a) acidifying the alkaline process wastewater or the mixture W by adding concentrated sulfuric acid which originates from the workup of the aqueous, sulfuric acid-containing phase obtained in the nitration to a pH below 2, which forms a mixture A consisting of organic phase which separates out and acidic aqueous phase, and b) extracting the mixture A with an aromatic extractant.

Abstract: The invention relates to polyphenylenepolymethylene polyisocyanates (B) comprising (B1) the 2-ring product of polyphenylenepolymethylene polyisocyanate (B2) the 3-ring product of polyphenylenepolymethylene polyisocyanate (B3) the 4-ring product of polyphenylenepolymethylene polyisocyanate (B4) the 5-ring product of polyphenylenepolymethylene polyisocyanate, wherein the constituents (B2), (B3) and (B4) are, at a content of (B1) of up to 55% by weight, based on the weight of (B), present in a weight ratio of (B2):(B3):(B4) of 8±4:3.5±1.8:1.2±0.9 and the component (B) comprises at least 85% by weight, based on the weight of the component (B), of the constituents (B1), (B2), (B3) and (B4).