Depletion in fossil fuel sources and growing issues regarding environmental problems accelerated the development of technology to substitute petroleum-derived chemicals. As an alternative, ethanol is considered critical alternative energy for automotive engines and chemical feedstocks [1]. Acetic acid is an important product that can be utilized as an intermediate for various products such as vinyl acetate monomer and acetic anhydride or as a solvent for the production of purified terephthalic acid [2]. Methyl acetate (MA) can be an effective intermediate for the synthesis of both ethanol and acetic acid via hydrogenation and hydrolysis, respectively. As carbonylation of dimethyl ether (DME) has been introduced as a synthetic route for MA, many studies were conducted to increase its efficiency [3]. In this work, experiments regarding DME carbonylation were performed over a ferrierite zeolite catalyst at various operating temperatures, pressures, GHSV, and CO/DME ratios. Based on the reaction mechanism for DME carbonylation [4], the rate equation for MA synthesis was calculated and the kinetic parameters were estimated by “lsqcurvefit†subroutine in MATLAB (MathWorks, Inc.), in which the Levenberg-Marquardt method is applied. The mean of the absolute relative errors and the relative standard deviation of individual errors were calculated to be 14.75 % and 8.21 % respectively, indicating that the model is validatory. Results show that the conversion of DME was influenced by only three variables: CO/DME ratio, pressure, and temperature. The developed kinetic model was integrated into a reactor module in a process simulator (Unisim Design Suite, Honeywell Inc.) to design an industrial scale process that generates ethanol or acetic acid selectively from syngas. The process model includes three consecutive reactors; The first reactor converts syngas into DME over hybrid Cu/ZnO/Al2O3/ferrierite catalyst whose kinetic model was reported in our previous work [5]. Detailed kinetics developed in this work for DME carbonylation takes place in the second reactor to obtain MA, and the third reactor considers hydrogenation or hydrolysis of MA to selectively synthesize ethanol or acetic acid. The composition of syngas was determined to be 21.88 mol% CO, 9.37 mol% CO2, and 68.75 mol% H2, assuming that it is available as a byproduct from coke oven gas in steel manufacturing plants. Also, this composition corresponds to the stoichiometric H2 concentration, which indicates that the molar ratio H2/(2CO + 3CO2) is 0.96 for COx hydrogenation [6]. Based on the integrated process model, total of six cases were considered in this study; Case 1 to 3 and Case 4 to 6 corresponds to the open-loop and recycle-loop cases respectively, while different CO/DME ratios (10, 20, and 30) were considered in the second reactor. As recycle loop was added to fully consume unreacted CO resulting from its excess supply over DME, conversion, carbon molar yield, annual production, and energy consumptions were evaluated. The results showed that recycle loop can enhance carbon molar yield to more than 40 %, which is approximately 20 times higher than open-loop cases owing to high overall DME conversion in the second reactor (91 % ~ 97 %). An increase in the CO/DME ratio caused higher annual production at the expense of energy consumption in the separation process, mainly composed of the condenser duty to separate CO. Consequently, the kinetic model and process model developed in this study can contribute to the design of a strategy for the production of valuable products based on the tradeoff between energy efficiency and production rate.
[1] Subramani, V., & Gangwal, S. K. (2008). A review of recent literature to search for an efficient catalytic process for the conversion of syngas to ethanol. Energy & fuels, 22(2), 814-839.
[2] Yoneda, N., Kusano, S., Yasui, M., Pujado, P., & Wilcher, S. (2001). Recent advances in processes and catalysts for the production of acetic acid. Applied Catalysis A: General, 221(1-2), 253-265.
[3] Zhou, H., Zhu, W., Shi, L., Liu, H., Liu, S., Ni, Y., ... & Liu, Z. (2016). In situ DRIFT study of dimethyl ether carbonylation to methyl acetate on H-mordenite. Journal of Molecular Catalysis A: Chemical, 417, 1-9.
[4] Cheung, P., Bhan, A., Sunley, G. J., Law, D. J., & Iglesia, E. (2007). Site requirements and elementary steps in dimethyl ether carbonylation catalyzed by acidic zeolites. Journal of Catalysis, 245(1), 110-123.
[5] Park, J., Woo, Y., Jung, H. S., Yang, H., Lee, W. B., Bae, J. W., & Park, M. J. (2020). Kinetic modeling for direct synthesis of dimethyl ether from syngas over a hybrid Cu/ZnO/Al2O3/Ferrierite catalyst. Catalysis Today.
[6] Jung, H. S., Zafar, F., Wang, X., Nguyen, T. X., Hong, C. H., Hur, Y. G., ... & Bae, J. W. (2021). Morphology Effects of Ferrierite on Bifunctional Cu–ZnO–Al2O3/Ferrierite for Direct Syngas Conversion to Dimethyl Ether. ACS Catalysis, 11(22), 14210-14223.
