(320f) Decarbonization of Natural Gas to Methanol Conversion Process Using Microwave-Assisted Dry Reforming

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. These chemicals are used in the production of plastics, paints, textiles, and other products. Methanol is used as a solvent in many industrial applications, including the production of resins, varnishes, and dyes. It is also used as an antifreeze in automotive applications because of its low freezing point and high boiling point. Methanol can be used as a means of energy storage, either by using it as a fuel or by converting it to hydrogen for use in fuel cells. The global methanol market size was valued at $28.78 billion in 2020 and is projected to reach $41.91 billion by 2026¹.

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 decarbonization strategy is developed for Natgasoline's existing process plant that currently converts natural gas to methanol. To achieve this goal, the following specific objectives are pursued: (1) Investigate the impact of replacing the conventional syngas reactor with a microwave reactor for dry reforming of methane³, (2) Develop a heat integration approach for the entire process to minimize utility costs and improve process efficiency⁴, (3) Conduct a techno-economic analysis to assess the cost-effectiveness of implementing the microwave reactor compared to the conventional syngas reactor, (4) Investigate the environmental impact of the new decarbonization strategy and quantify the reduction in carbon emissions achieved.

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. The feed to the process is natural gas that goes through a desulfurization step to remove sulfur and the resulting methane stream 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. Additional hydrogen 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 only 36% 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 or 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 1°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.

Acknowledgment

This study was supported by the United States Department of Energy.

References

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