Interpretation of interactions between low rank coal and polyethylene during co-pyrolysis from the bond cleavage perspective

Abstract

Co-pyrolysis of low rank coal and plastic to extract oil is one of effective methods for solving the white pollution. The interactions between coal and plastic during the co-pyrolysis process significantly improve the yield and quality of tar. However, the understanding of the interactions during co-pyrolysis from microscopic perspective is still scarce. The effect of polyethylene on the cleavage of covalent bonds during Hami coal pyrolysis was investigated by combining TG-MS, Py-TOF-MS and ReaxFF MD simulations. The results showed that derivative DTG curves can be decoupled into 6 sets of covalent bonds. The addition of PE had no effect on the breakage of Cal-O bonds in HM from the chemical perspective, but it promoted the breakage of Cal-Cal bonds in both HM and PE. Furthermore, after the addition of PE, the breakage peak temperature of Car-Cal in HM to shift towards a higher temperature (from 532 to 545 °C), and the peak area decreased from 13.12 % to 9.22 %. According to in-situ Py-TOF-MS analysis, the addition of PE can promote the breaking of Cal-Cal bonds, resulting in the increase of alkene products and radicals such as alkene, alkadienes and alkane radicals. Meantime, the long-chain alkenes produced by PE cracking coats on the surface of HM during co-pyrolysis, which hinders the pyrolysis of the broken Cal-Car bonds in its structure and leads to the reduction of aromatics. Moreover, the results of ReaxFF MD simulations further confirmed that the results of experimental.