THERMAL DECOMPOSITION OF SULFUR COMPOUNDS AND THEIR ROLE IN COKE FORMATION DURING STEAM CRACKING OF HYDROCARBONS

摘要

Sulfur-containing compounds play a key role in many industrial processes. Particularly for the steam cracking process, they have been linked with increased olefin selectivity, CO formation, and coke inhibition. This makes it imperative to quantify sulfur containing compounds to ppm and even ppb levels. On-line sulfur detection is a difficult task because of the adsorption of sulfur containing compounds on metal surfaces (tubings), as well as due to absorption and destruction in the GC system and capillary columns. In this work the influence of four different sulfur-containing additives, methanedithione (CS2), (methyldisulfanyl)methane (DMDS), (methylsulfanyl)methane (DMS), and dimethyl sulfoxide (DMSO), on product selectivity, coke deposition, and CO production during steam cracking of hydrocarbons. The use of online comprehensive two-dimensional gas chromatography with sulfur chemiluminescence detection (GC × GC-SCD) is the key enabling technology to characterize the sulfur compounds. In addition to the GC × GC-SCD, the low molecular weight sulfur containing compounds such as hydrogen sulfide (H2S) are analyzed using a thermal conductivity detector of a so-called refinery gas analyzer (RGA). Steam cracking in a pilot-plant unit revealed that all studied sulfur compounds are efficient in reducing the CO yield. Simultaneously, they strongly promote coke.