A process for preparing an aromatic polyamine mixture including 4,4-methylenedi(phenylamine) and higher homologues of MDA is provided. The process includes steps of (i) reaction of aniline with formaldehyde by means of an acid catalyst to form a crude product mixture (I), (ii) neutralization of the crude product mixture (I) and removal of the salts formed; (iii) isolation of aniline; (iv) distillation of the resulting crude product mixture so as to separate off (iv-1) a mixture (II) of MDA isomers (II-1) containing from 8 to 20% by weight of 4,4-methylenedi(phenylamine) and not more than 0.3% by weight of secondary components (II-2) and (iv-2) a low boiler mixture of at least 55% by weight of secondary components (II-2) and MDA isomers (II-1); and (v) recirculation of the mixture (II).

A process for preparing an aromatic polyamine mixture including 4,4-methylenedi(phenylamine) and higher homologues of MDA is provided. The process includes steps of (i) reaction of aniline with formaldehyde by means of an acid catalyst to form a crude product mixture (I), (ii) neutralization of the crude product mixture (I) and removal of the salts formed; (iii) isolation of aniline; (iv) distillation of the resulting crude product mixture so as to separate off (iv-1) a mixture (II) of MDA isomers (II-1) containing from 8 to 20% by weight of 4,4-methylenedi(phenylamine) and not more than 0.3% by weight of secondary components (II-2) and (iv-2) a low boiler mixture of at least 55% by weight of secondary components (II-2) and MDA isomers (II-1); and (v) recirculation of the mixture (II).

The invention relates to a process for the preparation of di- and polyamines of the diphenylmethane series (MDA), in which firstly crude MDA is prepared and is then subjected to a distillation process, wherein the distillation process comprises the following: in a distillation column, separating off a stream containing aniline and water as head product so as to obtain the first product stream as sump product, in said distillation column or in an apparatus arranged downstream of said distillation column, performing a stripping with steam so as to obtain a gaseous stream containing aniline, water and MMDA, partially condensing this gaseous stream containing aniline, water and MMDA so as to obtain a liquid stream containing MMDA and water (and optionally aniline) and a gaseous stream containing aniline and water (and optionally MMDA), drying the liquid stream containing MMDA and water (and optionally aniline) obtained by the partial condensation so as to obtain the second product stream.

The invention relates to a process for the preparation of di- and polyamines of the diphenylmethane series (MDA), in which firstly crude MDA is prepared and is then subjected to a distillation process, wherein the distillation process comprises the following: in a distillation column, separating off a stream containing aniline and water as head product so as to obtain the first product stream as sump product, in said distillation column or in an apparatus arranged downstream of said distillation column, performing a stripping with steam so as to obtain a gaseous stream containing aniline, water and MMDA, partially condensing this gaseous stream containing aniline, water and MMDA so as to obtain a liquid stream containing MMDA and water (and optionally aniline) and a gaseous stream containing aniline and water (and optionally MMDA), drying the liquid stream containing MMDA and water (and optionally aniline) obtained by the partial condensation so as to obtain the second product stream.

The invention relates to a process for the preparation of di- and polyamines of the diphenylmethane series (MDA), in which firstly crude MDA is prepared and is then subjected to a distillation process, wherein the distillation process comprises the following: in a distillation column, separating off a stream containing aniline and water as head product so as to obtain the first product stream as sump product, in said distillation column or in an apparatus arranged downstream of said distillation column, performing a stripping with steam so as to obtain a gaseous stream containing aniline, water and MMDA, partially condensing this gaseous stream containing aniline, water and MMDA so as to obtain a liquid stream containing MMDA and water (and optionally aniline) and a gaseous stream containing aniline and water (and optionally MMDA), drying the liquid stream containing MMDA and water (and optionally aniline) obtained by the partial condensation so as to obtain the second product stream.

The invention relates to a method for producing aniline or products that are obtained by further chemical reaction of aniline (aniline derivatives), involving decarboxylation of aminobenzoic acid, particularly ortho-aminobenzoic acid, in which one portion of the previously formed crude aniline is recirculated in the decarboxylation step. The aminobenzoic acid is obtained enzymatically or chemically, preferably enzymatically.

The invention relates to a method for producing aniline or products that are obtained by further chemical reaction of aniline (aniline derivatives), involving decarboxylation of aminobenzoic acid, particularly ortho-aminobenzoic acid, in which one portion of the previously formed crude aniline is recirculated in the decarboxylation step. The aminobenzoic acid is obtained enzymatically or chemically, preferably enzymatically.

The present invention relates to a process for preparing di- and polyamines of the diphenylmethane series (MDA), a system for producing MDA and a process for operating a system for preparing MDA. The invention enables optimization of production standstills during operation of the MDA process with respect to time expenditure and optionally also with respect to energy and material consumption by means of a so-called recirculation mode for individual system components. During interruption of the process or interruption of the operation of individual system components, formaldehyde is not introduced into the reaction and the system components that are not affected by a revision, repair, or cleaning measure are operated in so-called recirculation mode. This enables, among other things, that only the affected system component can be put in standstill during the time period of the measure, which is advantageous in terms of productivity and economy of the process as well as in terms of the quality of the products produced.

The present invention relates to a process for preparing di- and polyamines of the diphenylmethane series (MDA), a system for producing MDA and a process for operating a system for preparing MDA. The invention enables optimization of production standstills during operation of the MDA process with respect to time expenditure and optionally also with respect to energy and material consumption by means of a so-called recirculation mode for individual system components. During interruption of the process or interruption of the operation of individual system components, formaldehyde is not introduced into the reaction and the system components that are not affected by a revision, repair, or cleaning measure are operated in so-called recirculation mode. This enables, among other things, that only the affected system component can be put in standstill during the time period of the measure, which is advantageous in terms of productivity and economy of the process as well as in terms of the quality of the products produced.

The present invention relates to a process for preparing di- and polyamines of the diphenylmethane series (MDA), a system for producing MDA and a process for operating a system for preparing MDA. The invention enables optimization of production standstills during operation of the MDA process with respect to time expenditure and optionally also with respect to energy and material consumption by means of a so-called recirculation mode for individual system components. During interruption of the process or interruption of the operation of individual system components, formaldehyde is not introduced into the reaction and the system components that are not affected by a revision, repair, or cleaning measure are operated in so-called recirculation mode. This enables, among other things, that only the affected system component can be put in standstill during the time period of the measure, which is advantageous in terms of productivity and economy of the process as well as in terms of the quality of the products produced.