<p>A polyisocyanate production process uses the steps:
(a) C1 2 + CO †’ COCl 2 ; (b) COCl 2 (from (a)) + polyamine †’ polyisocyanate + HCl; (c) HCl (from (b)) is oxidised to Cl 2 which is used in (a). In a start-up operation, the steps (a), (b) and (c) are started. In a load-up operation, the amount of product produced in one of the steps (a) to (c) is selectively increased, then the amounts produced in the other two steps are increased. This is repeated.</p>
