Synergistic effect of hydrochloric-leaching pretreatments and hematite catalysis on chili straw pyrolysis to produce liquid oil and pyrolysis gas

A novel pathway to clean production of rich-phenol and ketone liquid oil and rich-methane and hydrogen gas by hematite catalytic pyrolysis of pretreated chili straw (CS) was investigated for the first time. The process integrated hydrochloric acid-leaching pretreatment and hematite catalysis. The results indicated that alkali and alkaline earth metals can be dissolved by hydrochloric acid-leaching to reduce the ash content. Moreover, HCl-leaching could improve the yield of the liquid oil generally that increased nearly 8 % after 0.5 mol/L HCl-leaching and the relative content of phenol and ketone in the liquid oil effectually increased. In addition, the presence of hematite increased the content of CH4 and H2, and the yield of liquid oil was improved by 10.39 %. The results of three catalytic pyrolysis experiments with different mass ratios were dearly divergent. Compared with R-1:1 group, the acid content of 0.5 H-1:1 group was significantly reduced, the ketone content was increased by 18.38 %, and only 2.84 % of phenol was decreased which was still 70.59 %. The relative CO2 content of 0.5H-2:1, 0.5H-1:1, and 0.5H-1:2 groups was reduced by 6.81–21.65 % compared to the 0.5HCl group without catalyst and the total content of combustible gas (CH4 and H2) was also increased by 23.39–37.03 %. This work provided a promising strategy for the high-value utilization of CS and hematite with high yield and quality. •0.5 mol/l HCl has the best removal effect on ash which is only 1.37 %.•The β-1, 4-glucoside bond of cellulose is hydrolyzed under acid leaching.•Acid leaching increased the content of phenol in liquid oil and CO2 in gas.•The addition amount of hematite greatly affects the composition of liquid oil.•The group 0.5H-1:1 was the most effective in increasing CH4 and H2 in gas.