Abstract: Crude polyisocyanates are purified by extraction at a temperature from 80.degree. to 180.degree. C. to form a two-phase system. The phases are separated and the phase made up of purified polyisocyanate and solvent is cooled to a temperature which is at least 50.degree. C. below the extraction temperature. Upon cooling, a second two-phase system forms. Purified polyisocyanate containing residual solvent is recovered upon separation of these phases. Solvent in which polyisocyanate is present that is reclaimed during this process may be reused in subsequent extractions. The purified polyisocyanates have a viscosity which is lower than that of crude polyisocyanates having substantially the same isocyanate content and average functionality. These purified polyisocyanates are useful in the production of polyurethane foams and moldings as well as adhesives and coatings.

Abstract: Polyisocyanates are produced by reacting a polyamide solution with a phosgene solution. After the product polyisocyanate has been recovered, the solvent or a portion of the solvent employed is treated with crosslinked polymers insoluble in the solvent which polymers contain primary and/or secondary alcoholic hydroxyl groups and/or primary and/or secondary amino groups. After treatment, the polymer and any reaction products are removed. The solvent may then be reused. Preferred solvents are chlorobenzene and o-dichlorobenzene. The preferred polymers are bead polymers or bead copolymers of (meth)acrylic acid or styrene/divinyl benzene copolymer.

Abstract: The present invention is directed to a process for the production of polyamines of the diphenylmethane series having a high diamine content and a low 2,2'-diamino-diphenylmethane content by condensing aniline with formaldehyde in the presence of hydrochloric acid as catalyst, neutralizing the acid catalyst at the end of the condensation reaction and working up the polyamine mixture thus obtained by distillation, characterized in that(a) in a first reaction stage, from 2.0 to 3.5 moles of aniline are reacted with 1 mole of formaldehyde in the presence of hydrochloric acid or a condensation product produced from 2.0 to 3.5 moles of aniline and 1 mole of formaldehyde in the absence of acid catalyst is reacted in the presence of hydrochloric acid at a degree of protonation maintained at 40 to 60% at temperatures below 50.degree. C.

Abstract: A new process for the production of very pure 4,4'-diisocyanatodiphenylmethane is disclosed, in which diisocyanatodiphenylmethane isomers which are obtained by distillation from the phosgenation products of aniline/formaldehyde condensates are initially freed from 2,2'- and 2,4'-isomers under certain distillation conditions and are then further worked-up by distillation, in that in a first final stage, from 50 to 90%, by weight of the diisocyanate freed from 2,2'- and 2,4'-isomers is isolated as the head product in the form of pure 4,4'-diisocyanatodiphenylmethane and in a second final stage, another quantity of pure 4,4'-diisocyanatodiphenylmethane is separated as the head product from the distillation of the sump of the first final stage.

Abstract: Polyisocyanates are prepared by reacting a polyamine solution with a phosgene solution. Excess phosgene and hydrogen chloride formed during the reaction are removed from the reaction mixture. The solvent is subsequently removed from the reaction mixture (e.g., by evaporation and condensation) and treated with a compound containing isocyanate reactive hydrogen atoms to convert any isocyanates present into urethanes and/or ureas. The thus-treated solvent may then be reused, preferably after any urethanes and/or ureas present in the solvent have been removed.

Abstract: Plaques for rapid retrospective recognition of an overdose of noxious gases are of great importance for industrial protection in the chemical industry. These plaques carry an indicator which undergoes a color change on exposure to the gas. Visual assessment of the indicator is considerably facilitated by subdivision of the indicator surface into a plurality of measuring fields with graded sensitivity by means of different covering membranes. Rapid allocation to a given range of dose is possible by separate or combined visual observation of the individual fields of the indicator.

Abstract: The instant invention is directed to a process for the production of diisocyanatodiphenyl methane isomers having an adjusted content of chlorine compounds comprising:(a) separating diisocyanatodiphenyl methane isomers from a polyisocyanate mixture of the diphenyl methane series in a first distillation stage,(b) subjecting said separated isomers to a second distillation stage using a recycle ratio of from 0.1 to 10 and wherein from 0.5 to 10% by weight of the feed into said second distillation stage is run off as the sump product,(c) subjecting the head product of said second distillation stage to a third distillation stage whereby readily volatile impurities are freed therefrom, and(d) working up the sump product of said third distillation stage to obtain purified 4,4'-diisocyanatodiphenyl methane and, optionally, purified 2,4'-diisocyanatodiphenyl methane.

Abstract: This invention relates to a new and improved process for the preparation of polyamines based on diphenylmethane by acid condensation of aromatic amines with formaldehyde followed by processing of the condensation mixture. Compared with similar processes known in the art, the process according to the invention combines the advantage of requiring less distillation for processing the reaction mixture with the advantage of a wide scope for variation of the composition of the product finally obtained, particularly with regard to its concentration of 2,4'-isomers and greatly reduced concentration of 2,2'-isomers.

Abstract: The instant invention is directed to a process for the preparation of multinuclear aromatic polyamines by condensation of aromatic amines with formaldehyde in the presence of aqueous acid catalysts followed by neutralization of the catalyst and processing of the resulting reaction mixture in known manner, characterized in that free amine is removed from the reaction mixture leaving the last condensation stage by means of a hydrophobic solvent, optionally after partial neutralization of the catalyst but before neutralization of the total quantity of catalyst put into the process, and the amine thus removed is returned to the catalyst-containing aqueous phase by return of the resulting amine-containing solvent phase into said aqueous, catalyst-containing phase at any point before the last condensation stage.

Abstract: The instant invention is directed to a novel process for the production of aromatic polyamines.

Abstract: The instant invention is directed to a process for the preparation of multinuclear aromatic polyamines by the condensation of aniline with formaldehyde in the presence of water and acid catalysts, in which the completely reacted aqueous condensation mixture is extracted with a hydrophobic solvent in extraction stage (I), optionally with the addition of aniline, the resulting solvent phase is worked-up in known manner to isolate the polyamine and the aqueous phase is recycled to the beginning of the process, the improvement characterised in that before the aqueous phase is returned to the beginning of the process, it is extracted in one or more separate extractors (II) with a hydrophobic solvent which may contain aniline and/or aniline/formaldehyde condensates with an increased proportion of ortho-isomers, the resulting solvent phase or phases is or are extracted with the aqueous acid condensation mixture in one or more separate extractors (III) at any one or more points after the first condensation stage and

Abstract: The instant invention is directed to a novel process for the production of aromatic polyamines. The process of the invention comprisesA. condensing an aromatic amine with formaldehyde in the presence of a hydrophobic solvent and in the absence of an acid catalyst to produce a pre-condensate mixture containing the corresponding N,N'-disubstituted aminals,B. removing substantially all the water from said pre-condensate mixture to produce a first organic phase,C. extracting said first organic phase with an aqueous solution containing an acid catalyst thereby producing a second organic phase and an aqueous pre-condensate phase which contains said aminals,D. subjecting said aqueous pre-condensate phase to a rearrangement reaction thereby producing an aqueous condensation mixture containing said aromatic polyamines,E.