Abstract: The invention relates to a method for purifying mixtures comprising 4,4?-methylenediphenyl diisocyanate, which comprises purifying by distillation a mixture I comprising 4,4?-methylenediphenyl diisocyanate having a hydrolyzable chlorine content as specified in ASTM D4663-10 of greater than 100 ppm by means of a column K1, wherein the gaseous stream comprising the mixture I is brought into contact in the column K1 with at least one liquid compound A which has the same or higher boiling point than 4,4?-methylenediphenyl diisocyanate and which has a hydrolyzable chlorine content as specified in ASTM D4663-10 of a maximum of 100 ppm, and wherein the gaseous stream O obtained at the top of the column comprises 4,4?-methylenediphenyl diisocyanate has a hydrolyzable chlorine content as specified in ASTM D4663-10 of a maximum of 100 ppm.

Abstract: A process for preparing aromatic amines by hydrogenation of nitroaromatics in the presence of catalysts, forming a fluid, amine-comprising reaction mixture in a reactor, wherein chromatographic analysis of the reaction mixture is carried out to determine the concentration of nitro and nitroso compounds in the reaction mixture.

Abstract: A process for working up alkaline process wastewater from the nitration of aromatic compounds to mono-, di- and trinitroaromatics, said alkaline process wastewater having a pH of 7.5 to 13, comprising the steps of a) acidifying the alkaline process wastewater 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 5, which forms a mixture A consisting of organic phase which separates out and acidic aqueous phase, b) contacting the mixture A with fresh sewage sludge, and c) removing the sewage sludge.

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: A process for working up alkaline process wastewater from the nitration of aromatic compounds to mono-, di- and trinitroaromatics, said alkaline process wastewater having a pH of 7.5 to 13, comprising the steps of a) acidifying the alkaline process wastewater 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 5, which forms a mixture A consisting of organic phase which separates out and acidic aqueous phase, b) contacting the mixture A with fresh sewage sludge, and c) removing the sewage sludge.

Abstract: A process for preparing aromatic amines by hydrogenation of nitroaromatics in the presence of catalysts, forming a fluid, amine-comprising reaction mixture in a reactor, wherein chromatographic analysis of the reaction mixture is carried out to determine the concentration of nitro and nitroso compounds in the reaction mixture.

Abstract: The invention relates to a method for purifying mixtures comprising 4,4?-methylenediphenyl diisocyanate, which comprises purifying by distillation a mixture I comprising 4,4?-methylenediphenyl diisocyanate having a hydrolyzable chlorine content as specified in ASTM D4663-10 of greater than 100 ppm by means of a column K1, wherein the gaseous stream comprising the mixture I is brought into contact in the column K1 with at least one liquid compound A which has the same or higher boiling point than 4,4?-methylenediphenyl diisocyanate and which has a hydrolyzable chlorine content as specified in ASTM D4663-10 of a maximum of 100 ppm, and wherein the gaseous stream O obtained at the top of the column comprises 4,4?-methylenediphenyl diisocyanate has a hydrolyzable chlorine content as specified in ASTM D4663-10 of a maximum of 100 ppm.

Abstract: The present invention relates to a process for preparing polyetherols in the presence of basic catalysts, wherein propylene oxide (PO) and/or ethylene oxide (EO) whose summated contents of aldehydes, expressed by the contents determined by gas chromatography or titrimetrically using the bisulfite method and calculated for propionaldehyde, do not exceed the value of 300 ppm and of allyl alcohol determined by gas chromatography do not exceed the value of 2500 ppm and of water determined by Karl-Fischer titration do not exceed the value of 1700 ppm and of acid, expressed by the contents determined by acid-base titration and calculated for acetic acid, do not exceed the value of 100 ppm and of carbon dioxide determined by KOH titration do not exceed the value of 500 ppm are used.

Abstract: A process is proposed for distillatively removing dinitrotoluene from process wastewater from the preparation of dinitrotoluene by nitrating toluene with nitrating acid, which comprises basifying the process wastewater to a pH of >8.5, feeding it to a stripping column in the upper region thereof and stripping it with steam in countercurrent to obtain a vapor stream laden with dinitrotoluene and a bottom stream depleted in dinitrotoluene compared to the process wastewater used.

Abstract: A process is proposed for distillatively removing dinitrotoluene from process wastewater from the preparation of dinitrotoluene by nitrating toluene with nitrating acid, which comprises basifying the process wastewater to a pH of >8.5, feeding it to a stripping column in the upper region thereof and stripping it with steam in countercurrent to obtain a vapor stream laden with dinitrotoluene and a bottom stream depleted in dinitrotoluene compared to the process wastewater used.

Abstract: The present invention relates to thermal insulation gas mixtures comprising cyclopentane and argon for filling cavities.