Preparation method of hexamethylene diisocyanate

The invention provides a preparation method of hexamethylene diisocyanate. The method comprises the following steps: carrying out desolventizing treatment on an HDI (hexamethylene diisocyanate) synthetic solution to obtain a first recovered solvent and an HDI desolventizing residual material; carrying out light component removal treatment on the HDI desolventizing excess material to obtain a light component and a light component removed excess material; carrying out alkali washing layering on the light component to obtain a second recovery solvent; rectifying the light component removal excess material to obtain an HDI product and a chlorine-containing HDI material; hDI, a phenol dechlorinating agent and an antioxidant are mixed to obtain a composite dechlorinating agent solution, then the composite dechlorinating agent solution is mixed with a chlorine-containing HDI material for dechlorination treatment, and the obtained dechlorinated HDI material is returned to light component removal treatment. By using t