Preparation Of Supported Superacid And Its Catalytic Hydrocracking Of Coals

Direct coal liquefaction is one of the effective ways to realize the efficient utilization of coal resources. The preparation of highly active catalysts is the key technology in coal liquefaction. In this study, three supported solid acid catalysts(TFMSA/MSZO, TFMSA/AP and TFMSA/MPZCA) were prepared by impregnating trifluoromethanesulfonic acid(TFMSA) into mesostructured zirconium oxide(MSZO), purified attapulgite powder(AP) and mesoporous zirconia coated attapulgite(MPZCA). A series of characterizations for the above three kinds of catalysts were performed, i.e., Fourier transform infrared(FTIR) spectroscopy, scanning electron microscopy(SEM), transmission electron microscopy(TEM), energy dispersive spectroscopy(EDS), X-ray photoelectron spectroscopy(XPS), X-ray diffraction(XRD), N2 adsorption and NH3 temperature programmed desorption(NH3-TPD) analyses. The characterization results showed that TFMSA was effectively loaded on the surface and pores of three kinds of carriers, and there exists interaction between the carrier and the active component. Compared with TFMSA/MSZO and TFMSA/AP, TFMSA/MPZCA possesses larger specific surface area, regular mesoporous structure and stronger acidity. Hydrocracking of di(1-naphthyl)methane(DNM), benzyloxybenzene(BOB) and dibenzyl ether(DBE) were used as probe reactions to investigate the activities of three kinds of catalysts under the same reaction conditions. The results show that TFMSA/MPZCA is much more active for hydrocracking DNM, BOB and DBE than TFMSA/MSZO and TFMSA/AP.Huozhou lignite(HL) and its extraction residue(HER), Shaerhu subbituminous coal(SSBC) and its extraction residue(SER) and Xigou bituminous coal(XBC) were selected as the coal samples in the catalytic hydrocracking(CHC) over TFMSA/MPZCA. The non-catalytic hydrocracking(NCHC) were used as contrast experiments. The soluble portions(SPs) from CHC and NCHC were analyzed with a gas chromatograph/mass spectrometer(GC/MS) qualitatively and quantitatively to investigate the catalysis of TFMSA/MPZCA on the hydrocracking of coal samples. The SPs of the coal samples from CHC and NCHC mainly consisted of aliphatic hydrocarbons, arenes, phenols, ketones, esters, and small amounts of compounds containing N and S elements. The yields of products from CHC were significant higher than that from NCHC, and the yields of arenes and phenols of SPs from CHC were also significant higher than that from NCHC, suggesting that TFMSA/MPZCA can highly promote the arenes and phenols to release from coals and their extraction residues. The content of arenes is the highest among the SPs from CHC of coals and their extraction residues, and the homologs of benzene accounted for the largest proportion in arenes. The product yields of HER and SER from CHC were significant higher than that of the corresponding raw coals. The yields of aliphatic hydrocarbons, arenes, phenols and ketones among SPs from extraction residue CHC is higher than that from raw coals, and the yields of arenes increased the most, suggesting that the catalysis of TFMSA/MPZCA for extraction residue hydrocracking was more significant, especially for the formation of arenes. The results provides a new way for the directional depolymerization and subsequent efficient utilization of coals.Based on the characteristics of large molecular structure of coals, alkyl aromatics containing Car–Calk bond and aryl ethers containing C–O bond were selected as coal-related model compounds to investigate the CHC mechanism of TFMSA/MPZCA. The results showed that among alkyl aromatics, DNM, diphenylmethane and 9-benzylphenanthrene can be hydrocracked over TFMSA/MPZCA except bibenzyl. The reactivity is related to the resonance energy(RE) and resonance stabilization energy(RSE) of the intermediates from CHC in addition to the super delocalization energy(Sr); BOB and DBE can be hydrocracked over TFMSA/MPZCA except oxydibenzene among the aryl ethers. The stability of the intermediates from CHC is the decisive factor in the cracking reaction. The protons released from TFMSA/MPZCA attack selectively on the ipso-position of aromatic ring, leading to the cleavage of Car–Calk bond, which could be the crucial step for alkyl aromatic hydrocracking; The proton transfer to the oxygen atom of the ether bridge bond leads to the cleavage of C–O bond, which is a precondition for aryl ether hydrocracking. Based on the hydrocracking mechanism of the two kinds of model compounds containing Car–Calk and C–O bonds and the group distributions of SPs from CHC and NCHC of coal samples, the formation mechanisms of arenes and phenols from CHC were revealed, providing a reference for the directional depolymerization mechanisms of coals.