Production of diphenylmethanediisocyanate and polyphenylene-polymethylene-polyisocynate mixtures

摘要

Surprisingly, the drawbacks of previous processes for the preparation of mixtures containing diphenylmethanediisocyanate and polyphenylene-polymethylene-polyisocyanate, e.g. high cost, excessive HCl stripping time, can be avoided by a two-stage reaction of corresponding mixtures containing diphenylmethane-diamine and polyphenylene-polymethylene-polyamine with phosgene in the presence of inert organic solvent. Mixtures containing diphenylmethanediisocyanate and polyphenylene-polymethylene-polyisocyanate (PMDI) having a decreased content of chlorinated side product and decreased iodine colour index are obtained by two-stage reaction of corresponding mixtures containing diphenylmethanediamine and polyphenylene-polymethylene-polyamine (PMDA) with phosgene in the presence of at least one inert organic solvent. The weight ratio of phosgene to HCl in the dwell time apparatus of the second phosgenation stage is (10-30):1 in the liquid phase and (1-10):1 in the gas phase. An Independent claim is included for mixtures containing diphenylmethanediisocyanate and PMDI obtainable by the above process.