Effect of liquefaction solvent, catalyst sulfidation method and H2S on mild liquefaction behaviors of Jiangna coal over Fe-based catalysts

Alleviating the harsh liquefaction conditions still remains huge challenge in the process of direct coal liquefaction. To investigate the feasibility of mild coal liquefaction and develop strategies for alleviating reaction conditions, this study adopted a typical low-rank oil-rich coal from Xinjiang as the feedstock, and the effects of initial H 2 pressure, solvent types (9,10-dihydroanthracene (DHA), tetralin (THN), pyrene/tetralin (Py/THN)), catalyst sulfidation method ( in-situ and ex-situ ), and H 2 S atmosphere on liquefaction performances were evaluated under lower H 2 pressure over the Fe-based catalysts. Results show that, at lower initial H 2 pressure (≤5 MPa), the decrease in pressure leads to the decline of coal conversion and oil yield, along with the increase in the yields of asphaltene and preasphaltene. Coal conversion and oil yield under different solvents increased in the order of DHA < Py/THN < THN, indicating that the solvent with good H-donating ability but no H-consumption for itself is vital to improve oil yield. Besides, whether Fe 2 O 3 or FeOOH is used as the iron precursor, in-situ sulfidation of the catalyst contributed to higher oil yield than pre-sulfidation. It is analyzed that the iron precursor undergoes the sulfidation reactions and the produced H 2 S and Fe 1−x S during the process promote H-transfer, thereby improving coal conversion and oil yield. Introducing H 2 S into H 2 atmosphere can remarkably increase coal conversion and oil yield. The oil yield is up to 69.89 wt% under 5%H 2 S/H 2 atmosphere and initial pressure of 5 MPa, close to that under 7 MPa and pure H 2 atmosphere, which is attributed to lower bond energy of the S-H bond. Both the hydrogen free radicals and mercapto free radicals (•HS) generated after the cleavage of H 2 S can stabilize free radicals produced from coal cracking and suppress the polycondensation reaction of the free radicals under low H 2 pressure, thereby increasing oil yield.