Abstract: Isocyanates are prepared by a process in which a product stream from the isocyanate synthesis is purified.

Abstract: The invention relates to a process for the partial or complete separation of a mixture comprising hydrogen chloride and phosgene, possibly solvents and possibly low boilers and inerts as are typically obtained in the preparation of isocyanates by reaction of amines with phosgene, which comprises firstly carrying out a partial or complete condensation of phosgene, then a distillation or stripping step in a column to remove the hydrogen chloride from the bottom product phosgene and subsequently a scrub of the top product hydrogen chloride by means of the process solvent to absorb the phosgene in the process solvent. An after-purification by means of adsorption on activated carbon or by another suitable method can subsequently be carried out to remove solvent residues.

Abstract: The present invention relates to a process for preparing sulfur-containing compounds of the general formula I in which Q, R1 and R2 are each independently defined as follows: Q: —S— or —S—S—, R1: hydrogen or saturated or unsaturated, linear or branched C1-C30-alkyl radical, R2: hydrogen or saturated or unsaturated, linear or branched C1-C30-alkyl radical, where R1 and R2 are not simultaneously hydrogen, by reacting a mixed gas stream comprising hydrogen sulfide, with or without oxygen, with linear or branched C1-C30-olefins, which comprises carrying out the reaction in the presence of water and carbon dioxide at a pressure of from 2 to 325 bar.

Abstract: The invention provides a process for preparing isocyanates by reacting amines with phosgene, wherein the phosgene-containing feed stream has a hydrogen chloride content of more than 0.8% by mass.

Abstract: Process for preparing chlorine from hydrochloric acid, which comprises the steps: a) providing a hydrochloric acid feed stream I; b) providing a hydrochloric acid recycle stream II; c) separating off a hydrogen chloride stream IV from the hydrochloric acid feed stream I and the hydrochloric acid recycle stream II in a distillation step; d) feeding the hydrogen chloride stream IV, an oxygen-containing steam V and, if desired, an oxygen-containing recycle stream Va into an oxidation zone and oxidizing hydrogen chloride to chlorine in the presence of a catalyst to give a product gas stream VI comprising chlorine, unreacted oxygen, unreacted hydrogen chloride and water vapor; e) separating off hydrogen chloride and water from the product gas stream VI in an absorption step to give a gas stream VII and the hydrochloric acid recycle stream II; f) if desired, drying the gas stream VII; g) separating off an oxygen-containing stream from the gas stream VII and, if desired, recirculating at least part of this as oxygen

Abstract: The present invention relates to a process for preparing isocyanates by reaction of amines with phosgene in a reactor and subsequent separation of the isocyanate from the reaction mixture leaving the reactor and purification of the isocyanate, wherein the separation and purification of the isocyanate is carried out in a column having a pressure at the top of 1-950 mbar, preferably 5-50 mbar, particularly preferably 10-20 mbar, and a temperature at the bottom of 90-250° C., preferably 120-170° C., particularly preferably 130-150° C., and the pure isocyanate stream is preferably taken off in liquid or gaseous form at a side offtake of the column.

Abstract: The invention relates to a method for producing a highly pure, aqueous hydroxylamine solution by distilling an aqueous solution, devoid of salt, of a hydroxyl ammonium salt in a plate column comprising at least two mechanical plates. Said method is characterised in that packing bodies are arranged between at least two plates of the plate column over the cross-section of said column.

Abstract: The invention relates to a process for preparing isocyanates by reaction of amines with phosgene in the presence of inert organic solvents in a reactor and subsequent work-up of the reaction mixture leaving the reactor, wherein the solvent is separated off in a two-stage or multistage, preferably two-stage, distillation process in which the solvent is separated off at a pressure of 0.1-15 bar in a first apparatus and at 1-900 mbar in a second apparatus or further apparatuses, with the heat of condensation of the solvent vapor from the first apparatus being used for partial or complete vaporization of solvent in the second apparatus.

Abstract: A process for preparing chlorine by catalytic gas-phase oxidation of hydrogen chloride over a fixed catalyst bed is disclosed that includes: making available a feed gas stream I with hydrogen chloride and an oxygen-containing feed gas stream II, feeding the feed gas stream I, the feed gas stream II, and, if desired, a recycled stream Ia with hydrogen chloride, an oxygen-containing recycle stream IIa, and a recycled stream III into an oxidation zone and oxidizing hydrogen chloride to chlorine in the presence of a catalyst present in a fixed bed to give product gas stream IV having chlorine, unreacted oxygen, unreacted hydrogen chloride and water vapor, and taking the recycled stream III from the product gas stream IV, without further treatment, and recirculating it to the oxidation zone, leaving a product gas stream IVa.

Abstract: A process for preparing a salt-free aqueous hydroxylamine solution by distilling an aqueous solution of a hydroxylammonium salt and a base in a tray column having at least two mechanical trays, wherein random or structured packings are located above at least one tray of the tray column over the cross section of the column.

Abstract: In a process for the preparation of isocyanates from carbamic esters, (i) a mixture containing a monofunctional or polyfunctional carbamic ester is passed continuously into a cleavage reactor or a cascade of two or more cleavage reactors, (ii) the carbamic ester is subjected to a thermal cleavage to give isocyanate and alcohol, (iii) the cleavage gas escaping from the cleavage reactor or reactors and containing the isocyanate, the alcohol, any uncleaved and/or partly cleaved carbamic ester and byproducts is brought into contact with a liquid coolant and condensing agent, cooled and at least partly condensed and (iv) the isocyanate and the alcohol are obtained from the cooled cleavage gas and the condensate in a rectification column, a part-stream of the alcohol obtained being used as liquid coolant and condensing agent for cooling and condensing the cleavage gas.

Abstract: Process for preparing organic isocyanates, which comprises the steps (a) making available a first partial amount of chlorine, with the chlorine of this first partial amount having a content of free and bound bromine and iodine of <400 ppm; (b) making available a second partial amount of chlorine; (c) reacting the first and second partial amounts of chlorine with carbon monoxide to form phosgene; (d) reacting the phosgene from step (c) with one or more primary amines to form the corresponding isocyanates and hydrogen chloride; (e) separating off and, if necessary, purifying the isocyanates formed in step (d); (f) separating off and, if necessary, purifying the hydrogen chloride formed in step (d); (g) catalytically oxidizing at least part of the hydrogen chloride separated off in step (e) by means of oxygen to form chlorine; (h) separating off the chlorine formed in step (g) and using at least a partial amount of the chlorine which has been separated off as second partial amount of chlorine in step (b).

Abstract: The invention relates to a method for producing isocyanates by reacting primary amines with phosgene in the gaseous phase. Said method is characterized in that the reaction of amine and phosgene occurs in a reaction channel, the internal dimensions of which have a width/height ratio of at least 2/1.

Abstract: The invention relates to a process for the production of isocyanates by reaction of primary amines with phosgene, in which isocyanate is used as solvent, wherein some or all of isocyanate used as solvent is added to the reaction mixture only after the amine and phosgene have been physically combined.

Abstract: A process for preparing methylenedianiline by reacting aniline with formaldehyde in the presence of acid catalysts comprising, in a semicontinuous process, introducing aniline with or without acid catalyst, feeding formaldehyde with or without acid catalyst through a mixing element into a circuit in which aniline with or without acid catalyst and with or without previously added formaldehyde is circulated and, after feeding in at least 50% of the total amount of formaldehyde to be fed in, heating the reaction mixture to a temperature above 75° C. In addition, the invention relates to a process for preparing polyisocyanates by phosgenation of amines obtainable in this manner and to the polyisocyanates obtainable by this process.

Abstract: The invention relates to a process for the production of isocyanates by reaction of primary amines with phosgene, in which isocyanate is used as solvent, wherein some or all of isocyanate used as solvent is added to the reaction mixture only after the amine and phosgene have been physically combined.

Abstract: Hydroxylamine solutions stabilized using tri(4-(2,3-dihydroxyphenyl)-4-oxabutyl)amine, tri(4-(2,3-dihydroxyphenyl)-4-keto-3-azabutyl)amine or salts thereof, and methods of stabilizing hydroxylamine solutions using these compounds.

Abstract: A process for working up distillation residues from the synthesis of tolylene diisocyanate by reaction of the distillation residues with water comprises reacting the TDI distillation residues with water in a continuous or semicontinuous process in a backmixed reactor in the presence of hydrolysate.

Abstract: A method of reacting a solution comprising a mixture of chemical compounds which are in chemical equilibrium with one another with at least one further chemical compound (9) is provided. The method comprises the following steps: fractionation of the solution by means of a separation method to give at least two fractions (5, 6) which are enriched in different chemical compounds of the mixture; and reaction of a fraction (5) with the further chemical compound or compounds (9). The fractionation is advantageously carried out using a film evaporator (1). Unreacted fractions (6) can be recirculated via a residence time vessel (3) back to the fractionation step. The method is particularly suitable for reactions of an aqueous formaldehyde solution in which various components of the solution (formaldehyde, methylene glycol, polyoxymethylene glycols) react in different ways.

Abstract: In a process for preparing mixtures of diphenylmethane diisocyanates and polyphenylpolymethylene polyisocyanates having a reduced content of chlorinated by-products and a reduced iodine color number by two-stage reaction of the corresponding mixtures of diphenylmethanediamines and polyphenylpolymethylenepolyamines with phosgene in the presence of at least one inert organic solvent at elevated temperature, separation of the excess phosgene and solvent after the phosgenation is complete and thermal treatment of the reaction product, the mass ratios of phosgene to hydrogen chloride in the residence time apparatus of the second stage of the phosgenation are at the same time 10-30:1 in the liquid phase and 1-10:1 in the gas phase.