Effect of sulfur additives on coke formation during steam cracking of naphtha

Sulfur compounds are widely used as additives in commercial cracking processes as they play an important role in coke inhibition, CO formation and light olefins yield. It is important to understand the thermal decomposition of sulfur additives and their impact on coke formation to enable the effective utilization of the additives. Thermal decomposition of dimethyl disulfide (DMDS) and diethyl disulfide (DEDS) is studied experimentally in a bench-scale cracker over a temperature range of 200-800 °C at two concentrations of the additives. The studies indicated that decomposition of DEDS leads to the formation of more ethylene as compared to DMDS at cracking conditions. Hence, both the additives were further evaluated for ethylene and propylene yield, coke formation and CO reduction in steam cracking of naphtha at coil outlet temperature (COT) 810 °C, steam dilution ratio 0.5 and residence time of around 0.4 s. It was observed that DEDS gives 1.28%wt/wt more ethylene compared to DMDS. Graphical abstract Thermal decomposition of dimethyl disulfide (DMDS) and diethyl disulfide (DEDS) is studied experimentally in a bench-scale cracker over a temperature range of 200-800 °C at two concentrations of the additives.