Catalytic reforming of lignite pyrolysis volatiles over metal oxide and zeolite tandem catalysts for light aromatics production

Pyrolysis is an important approach for achieving graded conversion of low-rank coal. However, the volatiles generated during this process are rich in oxygenated compounds and heavy components, which lead to low efficiency in direct utilization. Selecting appropriate catalysts for catalytic reforming of large molecules in volatiles can facilitate the upgrading of tar into lighter fractions, thereby simplifying the tar processing flow. This study proposes a tandem catalytic system combining metal oxides and zeolites. Through synergistic catalysis between the two catalysts, the pyrolysis volatiles of lignite are efficiently and selectively converted into light aromatics (such as benzene, toluene, ethylbenzene, xylene, naphthalene, methylnaphthalene, etc.). Simultaneously, pre-cracking effectively removes oxygenated components, reducing carbon deposition on the zeolite and extending the catalyst’s lifespan. Research demonstrates that MgO, a metal oxide with strong alkalinity, significantly enhances the cracking and deoxygenation of volatiles; compared to using ZSM-5 alone, the addition of MgO in the upper layer significantly increases the yield of light aromatics while maintaining the original proportion of liquid products. The total yield of light aromatics rose by approximately 20%, reaching 21.5 mg/g. Furthermore, the incorporation of metal oxides effectively reduces carbon deposition on the zeolite, prolonging the catalyst's lifespan.