Effect of P sources on the phosphorus modified MCM-22 for n -hexane catalytic cracking
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Effect of P sources on the phosphorus modified MCM‑22 for n‑hexane catalytic cracking Shuhao Bao1,2 · Mengting Guo1,2 · Bo Liu2 · Bing Feng2 · Dongguang Yin1 · Biao Jiang2 · Hong Zhao2 Received: 8 June 2020 / Accepted: 13 November 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract In this study, phosphoric acid (PA), tributylphosphine (TBP) and phenylphosphonic acid (PPA) were chosen as the P sources to modify MCM-22 through incipient impregnation followed by calcination. The acidity, Al distribution and structure of modified samples were characterized by XRD, N2 physical adsorption, NH3-TPD, 31 P MAS NMR, 27Al MAS NMR and XPS. Their catalytic performance upon cracking of n-hexane was also examined. The experimental results demonstrated that all the phosphorus modified samples showed a better catalytic life than that of the parent MCM-22, which can be attributed to acidity reduction and changes in Al distribution. However, the destruction of structure during modification will make the extension of lifetime insignificant. Among all the P sources, TBP/MCM-22, with the lowest acid and the smallest amount of Al content in the T2 sites but the least destruction of zeolite structure, exhibited the best stability and over 70% conversion with time on stream of 35 h. Keywords Phosphorus modification · MCM-22 · Lifetime · Cracking
Introduction Light olefins, especially propylene, play a leading role in the petrochemical industry, due to they are directly related to the development of plastics, rubber, textile, packaging materials, chemical machinery manufacturing, building materials, etc., which make a huge contribution to the social life [1, 2]. In the past decades, steam cracking of hydrocarbons had been the major source of light olefins. But the high energy consumption, CO2 emission, low light olefin yield and undesirable P/E (propylene/ethylene) ratio * Hong Zhao [email protected] 1
School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, China
2
Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China
13
Vol.:(0123456789)
Reaction Kinetics, Mechanisms and Catalysis
make it not suitable for the demand of green chemistry [2–4]. To date, the most effective way to produce olefins is catalytic cracking which mainly uses the zeolite ZSM-5 as a catalyst [5]. When zeolite like ZSM-5 was used as catalyst, the reaction temperature could be reduced to 600 °C, and the yield of olefins was enhanced. As a new type of zeolite developed by Mobile in 1992 [6], the MCM-22 zeolite possesses a unique two-dimensional pore system consist of a 10-ring sinusoidal inter-layer channel system and a 12-ring super cages accessible through 10-ring windows [7–9]. Theoretically, MCM-22 cracking would yield less dry gas, higher alkane/alkene ratio and even a higher selectivity of propylene [8–10]. However, because of the strong acidity that comes from the low Si/Al ratio produced during the direct hydrothermal synthesis, MCM-22 has a relatively short lifetime due to
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