(153d) Simulation of a Methanol Conversion Process Using Microwave-Assisted Dry Reforming and Chemical Looping

Methanol is a colorless, flammable liquid that is used as a solvent, fuel, and feedstock in the production of a wide variety of chemicals and materials. Methanol can be used as an alternative fuel for internal combustion engines and can be blended with gasoline to reduce emissions. It is also used as a fuel in fuel cells, which convert chemical energy directly into electrical energy. It is a key raw material to produce formaldehyde, acetic acid, methyl tert-butyl ether (MTBE), and other chemicals. The global methanol market size was valued at $28.78 billion in 2020 and is projected to reach $41.91 billion by 2026 [1]. Methanol has traditionally been produced from natural gas by first converting methane to syn gas and then converting syn gas to methanol². However, this is a very energy intensive process and produces a significant amount of the greenhouse gas carbon dioxide. Hence, there is motivation to look for alternative routes to the manufacture of methanol. In this research a novel microwave reactor is used for simulating the dry reforming process to convert methane to methanol. The objective is to produce 14,200 lbmol/h of methanol, which is the current production rate of methanol at Natgasoline LLC in Beaumont, Texas (USA) using the traditional steam reforming process [2].

Dry reforming requires a stream of carbon dioxide as well as a stream of methane to produce syn gas [3]. Additional hydrogen is required to achieve the necessary carbon to hydrogen ratio to produce methanol from syn gas. These streams of carbon dioxide and hydrogen are generated via chemical looping. A three-reactor chemical looping system is developed that utilizes methane as the feed to produce a pure stream of hydrogen and a pure stream of carbon dioxide. The carbon dioxide stream from the chemical looping reactor system is mixed with a desulfurized natural gas stream and is sent to a novel microwave syngas reactor, which operates at a temperature of 800 °C and pressure of 1 bar to produce a mixture of carbon monoxide and hydrogen. The stream of hydrogen obtained via chemical looping is added to this syngas stream and sent to a methanol reactor train where methanol is produced. These reactors operate at a temperature range of 220-255°C and pressure of 76 bar. The reactor outlet stream is sent to a distillation train where the product methanol is separated from methane, carbon dioxide, hydrogen, and other products. The carbon dioxide is recycled back to the microwave reactor.

This process was simulated in ASPEN Plus. The thermodynamic property method used was RKSoave for the process to convert methane to syn gas and NRTL for the process to convert syn gas to methanol. A base case simulation with no heat integration shows that the feed stream of 5,115 lbmol/h of methane results in a final product stream that consists of 14,200 lbmol/h of methanol that has a purity of 99.99%. This novel process was compared with traditional steam reforming, and it is observed that the microwave process utilizes less than half of the methane as compared to the traditional steam reforming process. Furthermore, there is significant decarbonization potential as this process utilizes 9,401 lbmol/h of carbon dioxide whereas the steam reforming process produces 575 lbmol/h of carbon dioxide. Furthermore, there is significant reduction in hot utility and cold utility usage in the novel microwave process. Heat integration tools are utilized to reduce the hot utility and cold utility usage in this integrated plant that leads to optimal operation. In particular, the use of a heat exchanger network (HEN) is considered in this research. The optimization of HEN is based on the objective function of minimizing the total utility costs and the minimum temperature approach adopted is 5°C. To optimize the heat exchanger units, heat exchange area and loads on each utility a mixed-integer-linear-programming (MILP) approach is used. Several feasible solutions are obtained using the MILP heat integration tool that is built-in ASPEN Energy Analyzer. Simulations are conducted in this heat-integrated plant to study the effect of changing feed conditions on the product quality and quantity. The simulation results from this study demonstrate the significant potential of utilizing a microwave-assisted reactor for dry reforming of methane. There was a noteworthy decrease in the amount of methane utilized, indicating a more efficient and sustainable process. Furthermore, the microwave process demonstrates the potential for substantial decarbonization of the process, contributing to the overall reduction of carbon emissions. The simulation results also revealed the existence of substantial potential for heat integration in the microwave-assisted process. Overall, the findings of this study highlight the importance of utilizing innovative technologies such as microwave-assisted reactors and process integration techniques in the chemical industry to enhance process efficiency and sustainability.

[1] Methanol Market by Feedstock (Natural Gas, Coal, Biomass), Derivative (Formaldehyde, Acetic Acid), End-use Industry (Construction, Automotive, Electronics, Solvents, Packaging), and Region - Global Forecast to 2028, Markets and Markets. (2023). https://www.marketresearch.com/MarketsandMarkets-v3719/Methanol-Feedstoc...

[2] M. E. Haque, N. Tripathi, and S. Palanki,” Development of an Integrated Process Plant for the Conversion of Shale Gas to Propylene Glycol,” Industrial & Engineering Chemistry Research, 60 (1), 399-41 (2021)

[3] G. Aimiuwu, E. Osagie and O. Omoregbe, “Process simulation for the production of methanol via CO2 reforming of methane route,” Chemical Product and Process Modeling, 0049 (2020)

Acknowledgment

This study was supported by the United States Department of Energy