(153a) Techno-Economic Analysis and Life Cycle Analysis of a Modular Carbon-Neutral Methanol Synthesis Process Using Direct Air Capture and Green Hydrogen

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. It has traditionally been produced from natural gas by first converting methane to syn gas and then converting syn gas to methanol. 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 conceptual design of an integrated process for producing green methanol is presented. The proposed process includes: (i) a novel building-based direct air capture (DAC) process that eliminates large amount of capital and operating costs of air handling equipment items in typical DAC processes, (ii) a functionalized solid sorbent offering high equilibrium loading and very low pressure drop thus enabling use of HVAC systems, (iii) solid oxide electrolysis cells (SOECs) that produce green hydrogen at about 30% lower power than polymer electrolyte membrane (PEM) electrolyzers, (iv) a novel structured catalyst coated into metallic monolith substrate resulting in high heat transfer rate and high reaction rate (iv) a highly integrated process that utilizes building hot air return and heat recovery from reactor effluent for regeneration heat for the DAC sorbent, utilizes steam generated in the reactor, and utilizes eletrolyzer product streams for superheating of the steam generated in the reactor thus generating the entire amount of superheated steam for SOEC. The process produces 5000 metric tons of 99.7 wt% green methanol per year by using CO₂ through building-based DAC and green H₂ produced through electrolysis of water by a SOEC. Required heating, cooling, and electric utilities for operating the process are computed by simulating an ASPEN Plus model. Both carbon dioxide and hydrogen are compressed to about 75 bars by separate 4-stage compressors with interstage coolers. Then the gases are heated to around 210 degrees C by using the reactor effluent and sent to the reactor. An embedded heat exchanger is considered in the reactor where steam is produced. The reactor effluent exchanges heat with the reactor feed and then goes to a low pressure/temperature steam generator (around 1100 degrees C) before it goes to a water cooler followed by a flash separator. About 1.5% of the off-gas from the flash separator is purged while the remaining gas is recycled back before the preheater by using a single stage compressor. The bottom of the flash separator is sent to a low-pressure flash separator that operates at 1.5 bars. A small portion of the gas is purged from the flash separator while the remaining portion is recycled through a multi-stage compressor with interstage cooling. The bottom of the flash separator is sent to a distillation column producing about 99.7 wt% pure methanol from the top. An economic analysis is developed, where conventional equipment items are costed using Aspen Process Economic Analyzer while electrolyzer, DAC and methanol synthesis catalysts costs, are estimated by using in-house and literature data. A thorough evaluation of the impacts of uncertainties in the capital cost of components, especially SOEC and DAC sorbent, are undertaken. A cradle-to-gate life cycle analysis (LCA) is undertaken to evaluate the economic, energy, and environmental benefits of the proposed process.

Acknowledgment

This study was supported by the United States Department of Energy