Chemical looping gasification with potassium-catalyzed petroleum coke for enhanced production of H2 and H2S

Abstract

A large amount of petroleum coke (petcoke) is considered as waste with low gasification rate and urgently needs to be exploited in an environmentally friendly, efficient and economic method. As potassium plays an important role in the gasification reactivity enhancement, the effects of potassium on the carbon conversion, gas product distribution and the sulfur conversion were investigated in the chemical looping gasification (CLG) process via a batch fluidized bed. H2 yield produced by 10%KNO3-petcoke increased to 2.1 times and 2.9 times for K-catalyzed steam gasification and CLG processes respectively, in comparison with the non-catalyzed processes. The results demonstrated that K promoted char gasification and water-shift reaction in K-catalyzed processes. The optimal amount of KNO3 was 10% taking the syngas quality and the gasification rate into account. When petcoke was modified by K2CO3 instead of KNO3, the yields of H2 and CO2 increased dramatically, but the gas distributions were similar (about 10% CO, 30% CO2 and 60% H2). For K2CO3-petcoke, a long time for high conversion rate was obtained, and the carbon conversion efficiency reached 91.58%. The increase in the gasification rate was ascribed to the inhibition of graphitization after adding K. And sulfur released mainly in the form of H2S in the K-catalyzed CLG, indicating that K facilitated sulfur recovery to get the maximum possible value-addition. Besides, K had less enhancement in sulfur conversion than carbon conversion with the increasing additive amount of K. With respect of sulfur fate, the fraction of mercaptan decreased while the inorganic sulfur became dominant composition at the presence of K. In conclusion, K-catalyzed CLG provided a novel approach to effectively solve the problem of utilizing petcoke of low gasification reactivity and high sulfur emission.