Effect of acidification treatment on the extraction performance of coking coal

In order to study the influence mechanism of minerals removal from coal on solvent extraction behavior, different concentrations of tetrahydrofuran (THF) solvents were used to extract coking coal before and after acidification with hydrochloric acid (HCl) and hydrofluoric acid (HF). With the help of conventional coal quality analysis and GC-MS test methods, the differences of THF extraction rate and extract composition before and after demineralization of coal samples were analyzed, and the influence mechanism of solvent concentration, extraction time, temperature and minerals was discussed. The results show that: ①After acidification, the ash yield of coal sample reaches 97.3%, the content decreases significantly, the fixed carbon content increases by 21%, the volatile content increases relatively, but the moisture content remains basically unchanged; The contents of C and H decrease, while the contents of O, N and S increase, among which the contents of C and O change significantly. ②The extraction rate of coal samples after acidification increase significantly, but with the increase of THF concentration, the increase of extraction rate show a decreasing trend. The same extraction effect is achieved under the same conditions, and the extraction time of acidified coal is 1.25~5 times faster than that of raw coal; Acidification treatment enlarges the effect of temperature on extraction rate, which makes the extraction advantage at 35 ℃ more obvious. ③The relative content of heteroatom compounds in raw coal extracts is the highest, while aliphatic hydrocarbons are the main components in acidified coal extracts, among which the content of straight chain hydrocarbons increases with the increase of THF concentration, accounting for 91.92% of the total content. The number of carbon atoms is mainly concentrated in C₁₅~C₂₂, but the number of extracted species is significantly less than that of raw coal. Generally speaking, acidification treatment can effectively improve the extraction capacity of THF, greatly shorten the extraction time, and improve the extraction capacity of high carbon alkanes in coal. In addition, although water does not dominate the extraction process, it will also affect the extraction ability of THF to a certain extent, making the extraction ability of low concentration THF solvent better than that of pure THF solvent.