Patent ID: 7041776

Claim:
A method of producing polyisocyanates of the diphenylmethane series comprising: a) reacting aniline and formaldehyde in the presence of HCl to provide a product mixture containing polyamines of the diphenylmethane series, HCl, aniline and water; b) removing excess aniline and water by distillation to provide a product mixture comprising polyamines of the diphenylmethane series, HCl, no more than 10 wt. % aniline based on the polyamines, and no more than 5 wt. % water based on the polyamines; and c) phosgenating the product mixture from (b) which comprises polyamines of the diphenylmethane series, HCl, no more than 10 wt. % aniline based on the polyamines, and no more than 5 wt% water based on the polyamines; wherein the acidic HCl catalyst is not neutralized.