Selective Hydrogenation of Polycyclic Aromatics to Monocyclic Aromatics over NiMoC/Hβ Catalysts in a Methane and Hydrogen Environment
Shen Zhibing, Fu Rao, Zhang Shangli, Wang Shunmei, Zhang Wu, Tang Ruiyuan, Liang Shengrong, Zhang Juntao, Yuan Shibao, Jiang Haiyan
2023, 25(2):
92-100.
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To obtain higher yields of monocyclic aromatic hydrocarbons with methyl side chains, such as toluene and xylene, methane(CH4) can be introduced into the hydrocracking of polycyclic aromatic hydrocarbons. CH4 can participate in the reaction, supply methyl side chains to the product, and improve product distribution. In this study, the hydrogenation reaction of polycyclic aromatic hydrocarbons over a carbonized NiMo/Hβ catalyst in a CH4 and hydrogen (H2) environment was investigated to study the promotional effect of CH4 on the hydrocracking of polycyclic aromatics.Under conditions of 3.5 MPa, 380 ℃, volume air velocity of 4 h-1, gas-oil volume ratio of 800, and H2:CH4 ratio of 1:1, the conversion rate of naphthalene was 99.97%, the liquid phase yield was 93.62%, and the selectivity’s of BTX were 17.76%, 25.17%, and 20.47%, respectively. In comparison to the use of a H2 atmosphere, the selectivity of benzene was significantly decreased, whereas the selectivity’s of toluene and xylene were increased. It was shown that CH4 can participate in the hydrocracking of naphthalene and improve the selectivity of toluene and xylene in the liquid product. The carbonized NiMo/Hβ catalyst was characterized by a range of analytical methods (such as X-ray diffraction (XRD), ammonia-temperatureprogrammed desorption (NH3-TPD), hydrogen-temperature-programmed reduction (H2-TPR), and X-ray photoelectron
spectroscopy (XPS)). The results indicated that Ni and Mo carbides were the major species in the carbonized NiMo/Hβ catalyst and were considered to be active sites for the activation of CH4 and H2. After loading the metal components, the catalyst displayed prominent weak acidic sites, which may be suitable locations for cracking, alkylation, and other related reactions. Therefore, the carbonized NiMo/Hβ catalyst displayed multiple functions during the hydrocracking of polycyclic aromatic hydrocarbons in a CH4 and H2 environment. These results could be used to develop a new way to efficiently utilize polycyclic aromatic hydrocarbons and natural gas resources.