Patent ID: 7897805

Claim:
A polyisocyanate production method comprising, a carbonyl chloride production process of producing carbonyl chloride by allowing chlorine to react with carbon monoxide, a polyisocyanate production process of producing polyisocyanate by allowing the carbonyl chloride produced in the carbonyl chloride production process to react with polyamine, a chlorine production process of producing chlorine by oxidizing hydrogen chloride produced secondarily in the polyisocyanate production process, and a hydrochloric acid production process of producing hydrochloric acid by allowing at least a part of the hydrogen chloride produced secondarily in the polyisocyanate production process and unoxidized hydrogen chloride in the chlorine production process to be absorbed or mixed in water, wherein the carbonyl chloride is produced by allowing the chlorine produced in the chlorine production process to react with carbon monoxide in the carbonyl chloride production process.