Patent ID: 8841480

Claim:
A process for preparing a polyphenylene-polymethylene polyisocyanate (PMDI), the process comprising (a) separating an amount of chlorine, having an original amount of bromine and iodine, to obtain a first chlorine fraction having a content of free and bound bromine and iodine of less than 50 ppm and a second chlorine fraction having an increased content of free and bound bromine and iodine that depends on the original amount of bromine and iodine and a separation split, (b) reacting carbon monoxide with at least a portion of the first chlorine fraction to form a first phosgene fraction, (c) reacting carbon monoxide with at least a portion of the second chlorine fraction to form a second phosgene fraction, (d) reacting at least a portion of the first phosgene fraction with at least one amine of a diphenylmethane diamine (MDA) to form a polyphenylene-polymethylene polyisocyanate (PMDI), and (e) reacting at least a portion of the second phosgene fraction with at least one primary amine to form an isocyanate, wherein the primary amine is selected from the group consisting of 1,3-polyphenylenediamine, 1,4-butylenediamine, 1,5-pentamethylenediamine, 1,6-hexamethylenediamine, a methylenediamine homologue of 1,7-heptamethylene diamine or higher, isophoronediamine (IPDA), cyclohexyldiamine, cyclohexylamine, aniline, phenylenediamine, para-toluidine, 1,5-naphthylenediamine, 2,4-toluenediamine, and 2,6-toluenediamine, provided that mono-and polyphenylene polymethylene poly-amines are excluded.