Production technology of p-xylene production by toluene methylation with selective carbon dioxide hydrogenation
YANG Yong1,2, ZHANG Zhao1, WANG Dongliang1,2, WEN Zhuoyu1, ZHOU Huairong1,2, ZHANG Dongqiang1,2
1. School of Petrochemical Engineering, Lanzhou University of Technology, Lanzhou 730050, China; 2. Key Laboratory of Low Carbon Energy and Chemical Engineering of Gansu Province, Lanzhou 730050, China
Abstract：[Objective] p-Xylene (PX) is an important aromatic product with the highest consumption among xylene isomers. It is widely used as a raw material for upstream production of several important chemical products. Carbon dioxide (CO2) is a major gas responsible for the greenhouse effect. Furthermore, in addition to methanol, CO2 and syngas also show great technical potential as methylation agent. The direct synthesis of PX by CO2 hydrogenation coupled with toluene methylation over a bifunctional catalyst has the advantages of atomic economy, green hydrogen storage, and CO2 utilization, but a complete techno-economic evaluation of process design and optimization strategy has not been performed. [Methods] Based on the selective catalytic results of CO2 hydrogenation coupled with toluene methylation, three toluene methylation catalysts with high conversion, high xylene selectivity, and high PX selectivity and their experimental results were chosen, and the process flow of PX production by CO2 hydrogenation coupled with toluene methylation was designed and simulated by software. The following was the process flow: the raw materials of the reaction were pretreated and compressed into the reactor, the reaction products were flashed four times to separate the gas from the liquid, some raw materials were circulated, and the liquid products were sequentially separated or purified to yield benzene, PX, o-xylene, and heavy aromatic hydrocarbons. Moreover, because of the various catalysts, RStoic, a stoichiometric reactor module, was employed to model the methylation reaction unit. Based on the characteristics of different catalysts, the conversion rate of each reactant was specified. Furthermore, based on controlling the same PX output, the raw material feed ratio of the reactor was also specified, and the xylene isomer was separated by reactive distillation. [Results] Analysis of the raw material cost, equipment cost, and energy consumption of the process flow corresponding to the three catalysts was conducted, and the results showed that the raw material of the unit PX product of the high-PX-selectivity catalyst process was only 72.6% and 58.9% of those of the other two catalyst processes and the CO2 consumption of the unit PX product was 27.3% and 44.7% of that of the other two catalyst processes. However, the high-xylene-selectivity catalyst process could yield more PX production through isomerization technology, and its energy consumption was also the lowest. Because reactive distillation was employed as the post-separation of xylene isomerization products, the high-xylene-selectivity catalyst process had a high raw material consumption rate and the highest energy consumption, but by isomerization technology, it had the highest PX production potential and showed the best economy through economic accounting of different PX production processes. [Conclusions] CO2 hydrogenation coupled with toluene methylation technology can enhance the conversion rate of raw materials, reduce the energy consumption of material circulation, and enhance the xylene and PX selectivities, which will greatly improve its technical economy. Furthermore, the production process with high PX selectivity is a green chemical process with broad development prospects for reducing carbon emissions in the environment, achieving carbon cycle, energy conservation, and emission reduction.
杨勇, 张钊, 王东亮, 汶卓宇, 周怀荣, 张栋强. 基于CO2加氢耦合甲苯甲基化选择催化的PX生产工艺对比[J]. 清华大学学报（自然科学版）, 2024, 64(3): 538-544.
YANG Yong, ZHANG Zhao, WANG Dongliang, WEN Zhuoyu, ZHOU Huairong, ZHANG Dongqiang. Production technology of p-xylene production by toluene methylation with selective carbon dioxide hydrogenation. Journal of Tsinghua University(Science and Technology), 2024, 64(3): 538-544.
[1]于政锡, 徐庶亮, 张涛, 等. 对二甲苯生产技术研究进展及发展趋势[J]. 化工进展, 2020, 39(12):4984-4992. YU Z X, XU S L, ZHANG T, et al. Research progress and development trend in para-xylene production technology[J]. Chemical Industry and Engineering Progress, 2020, 39(12):4984-4992. (in Chinese) [2]CHAKINALA N, CHAKINALA A G. Process design strategies to produce p-xylene via toluene methylation:A review[J]. Industrial & Engineering Chemistry Research, 2021, 60(15):5331-5351. [3]ZHAO Y T, CHENG J J, ZHANG P, et al. Examination of key factors determining the catalytic performance of Zn-Ga/HZSM-5 bifunctional catalysts and establishment of reaction network in alkylation of benzene with carbon dioxide[J]. Applied Catalysis A:General, 2022, 643:118785. [4]BIAN G W, NIU P Y, JIA L T, et al. Alkylation of benzene using CO2 and H2 over ZnZrOx/ZSM-5:The effect of Y doping[J]. New Journal of Chemistry, 2023, 47(2):609-617. [5]BAI Y B, YANG F, LIU X Y, et al. Performance of bifunctional ZnZr/ZSM-5 catalysts in the alkylation of benzene with syngas[J]. Catalysis Letters, 2018, 148(12):3618-3627. [6]LEE S, KIM D, LEE J, et al. An in situ methylation of toluene using syngas over bifunctional mixture of Cr2O3/ZnO and HZSM-5[J]. Applied Catalysis A:General, 2013, 466:90-97. [7]WEN D L, ZUO J C, HAN X Q, et al. Synthesis of durene by methylation of 1,2,4-trimethylbenzene with syngas over bifunctional CuZnZrOx-HZSM-5 catalysts[J]. Catalysis Science & Technology, 2022, 12(8):2555-2565. [8]XU Y B, SHI C M, LIU B, et al. Selective production of aromatics from CO2[J]. Catalysis Science & Technology, 2019, 9(3):593-610. [9]CUI X, GAO P, LI S G, et al. Selective production of aromatics directly from carbon dioxide hydrogenation[J]. ACS Catalysis, 2019, 9(5):3866-3876. [10]ZUO J C, CHEN W K, LIU J, et al. Selective methylation of toluene using CO2 and H2 to para-xylene[J]. Science Advances, 2020, 6(34):eaba5433. [11]MIAO D Y, PAN X L, JIAO F, et al. Selective synthesis of para-xylene and light olefins from CO2/H2 in the presence of toluene[J]. Catalysis Science & Technology, 2021, 11(13):4521-4528. [12]XIAO Z K, HUANG H, CAO C X, et al. Designing a bifunctional ZrCuOx/HZSM-5 catalyst for selective methylation of toluene with carbon dioxide to para-xylene[J]. Fuel, 2022, 319:123848. [13]LIU X Y, PAN Y L, ZHANG P, et al. Alkylation of benzene with carbon dioxide to low-carbon aromatic hydrocarbons over bifunctional Zn-Ti/HZSM-5 catalyst[J]. Frontiers of Chemical Science and Engineering, 2022, 16(3):384-396. [14]SHANG X, LIU G D, SU X, et al. Preferential synthesis of toluene and xylene from CO2 hydrogenation in the presence of benzene through an enhanced coupling reaction[J]. ACS Catalysis, 2022, 12(21):13741-13754. [15]TING K W, KAMAKURA H, POLY S S, et al. Catalytic methylation of aromatic hydrocarbons using CO2/H2 over Re/TiO2 and H-MOR catalysts[J]. ChemCatChem, 2020, 12(8):2215-2220. [16]刘海华, 李艳春, 丁传敏, 等. ZnZr/HZSM-5双功能催化剂在合成气与苯烷基化反应中的催化性能[J]. 化工进展, 2021, 40(12):6696-6704. LIU H H, LI Y C, DING C M, et al. Catalytic performance of ZnZr/HZSM-5 bifunctional catalyst for the alkylation of syngas with benzene[J]. Chemical Industry and Engineering Progress, 2021, 40(12):6696-6704. (in Chinese) [17]HAN X Q, ZUO J C, WEN D L, et al. Toluene methylation with syngas to para-xylene by bifunctional ZnZrOx-HZSM-5 catalysts[J]. Chinese Journal of Catalysis, 2022, 43(4):1156-1164. [18]韩腾飞, 徐红, 葛晖, 等. 苯与合成气烷基化催化剂的研究进展[J]. 化工进展, 2020, 39(8):3057-3065. HAN T F, XU H, GE H, et al. Progress of alkylation catalysts for benzene with syngas[J]. Chemical Industry and Engineering Progress, 2020, 39(8):3057-3065. (in Chinese) [19]ASHRAF M T, CHEBBI R, DARWISH N A. Process of p-xylene production by highly selective methylation of toluene[J]. Industrial & Engineering Chemistry Research, 2013, 52(38):13730-13737. [20]LIU J, YANG Y, WEI S A, et al. Intensified p-xylene production process through toluene and methanol alkylation[J]. Industrial & Engineering Chemistry Research, 2018, 57(38):12829-12841. [21]WANG D L, ZHANG J Q, DONG P, et al. Novel short process for p-xylene production based on the selectivity intensification of toluene methylation with methanol[J]. ACS Omega, 2022, 7(1):1211-1222. [22]KONG L X, WU Y Q, MARAVELIAS C T. Simultaneous utility and heat exchanger area targeting for integrated process synthesis and heat integration[J]. Industrial & Engineering Chemistry Research, 2017, 56(41):11847-11859. [23]IBRAHIM D, JOBSON M, GUILLÉN-GOSÁLBEZ G. Optimization-based design of crude oil distillation units using rigorous simulation models[J]. Industrial & Engineering Chemistry Research, 2017, 56(23):6728-6740.
2024, Vol. 64 
