Chemical Kinetics of the Alkylation of Xylenol for the Separation of Their Close-Boiling Isomers from Coal Tar
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mical Kinetics of the Alkylation of Xylenol for the Separation of Their Close-Boiling Isomers from Coal Tar Cong-Yu Kea, Guo-Min Lua, Ying-Lin Weia, Xiao-Xia Zhanga, Wu-Juan Suna, Xuan Tanga, Qun-Zheng Zhanga, and Xun-Li Zhanga, * aCollege
of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an, 710065 China *e-mail: [email protected] Received January 29, 2020; revised May 18, 2020; accepted July 10, 2020
Abstract—To support the industrial design and process development for the separation of xylenol isomers from coal tar, the present work was focused on 2,4/2,5-xylenol mixture as 2,4-xylenol and 2,5-xylenol have very close boiling points. Specifically, the kinetics of the alkylation of 2,4/2,5-xylenol mixture was investigated that formed the first step of the alkylation-distillation-dealkylation separation strategy. By quantifying the influence of various key factors on the reaction rate, the rate equations of 2,4-xylenol and 2,5-xylenol −39360 RT
−32241 RT
0.8 0.7 1.0 0.4 alkylation were determined as r2,4 = 1538e c1.1 c1.0 2,4 PPIBcPTSA and r2,5 = 516e 2,5 PPIBcPTSA , respectively. The alkylation rate of 2,4-xylenol was notably higher than that of 2,5-xylenol. The influence of temperature, xylenol concentration and isobutylene partial pressure on the reaction rate of 2,4-xylenol was also greater than that of 2,5-xylenol, whilst the influence of catalyst dosage on the alkylation rate of 2,5-xylenol was found to be greater than that of 2,4-xylenol. The results can be potentially used for reactor design and process development for the separation of 2,4/2,5-xylenol mixture from coal tar.
Keywords: 2,4-xylenol, 2,5-xylenol, alkylation, reaction kinetics, separation DOI: 10.1134/S0965544120110031
INTRODUCTION Xylenol (or hydroxyxylene) generally refers to any of the six isomers of dimethylphenol [(CH3)2C6H3OH] or to combinations thereof. Xylenols are naturally-occurring phenolic compounds, which are present in various sources such as coal, petroleum and tobacco [1, 2]. Individual xylenol isomers may be produced through separation, and/or synthetic processes. When extracted from coal tar, the products are typically in the form of mixtures of more than one isomers, which normally need further separation if pure xylenol isomers are required [3, 4]. Owing to their unique reactivity and solvency properties, xylenols are regarded as key raw materials in many products manufacturing, e.g. resins and polymers, antioxidants in fuels and plastics, and reactive solvents in applying insulation to electrical wires/cables [5, 6]. Overall, the technological development trend with time in the production of xylenols has followed that in the general chemical industry, showing heavy dependence on sources of raw materials [2, 7]. The interest in using coal tar as raw materials for xylenols production dates back to the 1930s [8–10], that was largely replaced by the natural gas- and oil-based resources for chemical synthesis of xylenols [11–13]. However, with the growing challenges faced by the petroleum-
based chemical
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