Enhanced hydrocracking Car-Calk bridged bonds in the extraction residue from Piliqing subbituminous coal over a recyclable and active magnetic solid superacid

A novel and highly active magnetic solid superacid (MSSA) with extraordinary separable and recyclable properties was facilely developed by impregnating trifluoromethanesulfonic acid onto mesoporous zirconia coated ferroferric oxide nanoparticles. The extraction residue (ER) from Piliqing subbituminous coal was subjected to non-catalytic hydrocracking (NCHC) and catalytic hydrocracking (CHC) in cyclohexane over MSSA at 300 °C. Detailed molecular compositions of the soluble portions from NCHC (SPNCHC) and CHC (SPCHC) were characterized with a Fourier transform infrared spectrometer and gas chromatograph/mass spectrometer (GC/MS). As a result, the yield of SPCHC is remarkably higher than that of SPNCHC and most of the GC/MS-detectable compounds in SPCHC are arenes, while SPNCHC contains alkanes, arenes, arenols, and ketones, indicating that MSSA effectively catalyzed the cleavage of Car-Calk bridged bonds connecting some aromatic rings (ARs) and side chains on some ARs in the ER. Di(1-naphthyl)methane (DNM) and 9-benzylphenanthrene (9-BP) were used as coal-related model compounds (CRMCs) and their CHCs were investigated to further probe the catalysis of MSSA in the CHC of the ER. The result suggests that MSSA is highly active for cleaving the Car-Calk bond in the CRMCs and generating naphthalene and phenanthrene under mild conditions. Based on the exploration of controlling reactions, the catalytic mechanism was discussed. MSSA could be easily separated and still active for the CHC of DNM after 3-times recycle.