Removal and transformation mechanisms of nitrogen and sulfur in petcoke supercritical water gasification via ReaxFF simulation

Abstract

ABSTRACT High-sulfur petroleum coke (petcoke) is generally used as fuel in industries, but the S and N in petcoke will damage the environment during the combustion process. Gasification of petcoke could reduce pollution from S/N-containing compounds. Supercritical water gasification (SCWG) is a new direction with good potential because of its high activity and accelerated reaction characteristics. This work used the reactive molecular dynamics (ReaxFF) simulation to explore the removal and conversion mechanisms of S and N during the SCWG of petcoke. The simulation results showed increasing the pressure and temperature could improve the desulfurization speed. S removal began with the conversion of thiophene-S into C1–4S (mainly C2S) or COS, followed by the conversion into H1–2S in the presence of a large number of hydrogen atoms. The removal of N began with the conversion of pyrrole/pyridine-N into C1–3N(mainly CN). Then, CHON and CON were successively formed. The behaviour of S/N in SCWG could be summarised as follows: thiophene-S → CxS + H → HS + H → H2S, thiophene-S → CxOS + H → CHOS, pyrrole/pyridine-N → CxN/HCxN → CN → CHON → CON, H2N → HON.