<p>A polyisocyanate production method comprises: (a) nitration of an aromatic raw material with H 2 SO 4 /HNO 3 ; (b) reduction of the nitro groups to produce a polyamine; (c) production of COCl 2 from CO and Cl 2 ; (d) reaction of the polyamine and the COCl 2 to produce a polyisocyanate and HCI; (e) oxidation of the HCI to produce Cl 2 and H 2 O; and (f) dehydration of the CL 2 /H 2 O using H 2 SO 4 , which is reused in step (a). The Cl 2 may be used in step (c).</p>
