Catalytic conversion of coal pyrolysis vapors to light aromatics over hierarchical Y-type zeolites. Issue 4 (August 2020) - Lv, Peng
Abstract: A series of hierarchical Y-type zeolites were prepared by a post-treatment method. All the samples were characterized using nitrogen adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and temperature-programmed desorption of ammonia (NH3 -TPD). The results show that hierarchical Y-type zeolites with different porosities can be obtained, and the mesopore size can be controlled by changing the treatment conditions. The acidity of catalysts was also adjusted in this process. The catalysts were evaluated with respect to catalytic conversion of coal pyrolysis vapors to light aromatics online by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Moreover, several model compounds were selected to evaluate the formation pathway of light aromatics during the upgrading of coal pyrolysis vapors over Y-type zeolite. It was found that pore-structure-modified Y-type zeolite has good catalytic performance for the upgrading of coal pyrolysis vapors. After catalytic cracking by EDY zeolites, the total amount of light aromatics such as benzene, toluene, ethyl-benzene, xylene, and naphthalene (BTEXN) in coal pyrolysis vapors increased from 5600 ng/mg (raw coal pyrolysis) to 18, 800 ng/mg. The results of model compound catalytic pyrolysis show that Y-type zeolite is beneficial for the catalytic cracking of polycyclic aromatic hydrocarbons, the breaking of phenolic hydroxyl, and the decomposition of heterocyclic compounds, thus promoting the formation of BTEXN. Hierarchical catalysts with wide pore size and large mesopore volume contribute to the diffusion of bulky reactants and their contact with active sites in channels, further promoting the generation of light aromatics. Graphical abstract: Image 1 Highlights: Coal pyrolysis vapors were upgrading over hierarchical Y-type zeolites. Hierarchical Y-type zeolites can promote the formation of light aromatics. Y-type zeolite can reduce the yield of phenols and heterocyclic compounds.