Abstract: A kind of coking inhibiter, phosphorothioate, was synthesized using CH3OH, PCl3, and dimethyl sulfone as feed. The anti-coking performance of dimenthyl disulfide (DMDS), phosphodiester and the new self-made coking inhibitor phosphorothioate was investigated, respectively in a tube cracking furnace at the conditions of 800-840 ℃ and atmospheric pressure. The light oil was used as pyrolysis material and steam as inert diluent. The results show that the phosphorothioate，as a new kind of coke inhibitor，has excellent anti-coking performance, better than DMDS and phosphodiester. It is found that the addition of phosphorothioate into light oil can increase the yield of ethylene.

Key words: phosphorothioate, coking inhibitor , light oil , Pyrolysis