Researchers at Tianjin University in China have developed an energy-efficient two-step synthesis pathway for the conversion of CO2 to methanol and ethylene glycol, paving the way for greener industrial production of methanol, and the establishment of an artificial carbon cycle.
Methanol is produced in vast quantities globally as an industrial chemical feedstock for the production of everything from plastics and paints to car parts and construction materials. It is also used as a fuel and is a stable and efficient hydrogen carrier that could form a critical part of the future hydrogen economy.
Green conversion of CO2 and hydrogen to methanol is considered to be an important technological route to achieving a large-scale artificial carbon cycle. Xinbin Ma, a professor of chemistry engineering at Tianjin University, has been leading a team looking for ways to optimize the conversion process with a focus on efficient use of captured CO2.
“Methanol is an important raw material accounting for about 30% of global industrial feedstock, and also a liquid fuel with the highest hydrogen content per unit volume,” says Ma. In 2005, George Olah proposed the idea of a ‘methanol economy’ based on a CO2 cycle, where the conversion of CO2 to methanol is the entry point. “It’s one of the key technologies to reduce carbon emissions and achieve hydrogen and carbon resource storage at the same time.”
Based on their expertise in one-carbon (C1) resource conversion, Ma’s team is now making important breakthroughs in CO2 hydrogenation ― a chemical reaction with the addition of hydrogen― to methanol technology.
“Direct hydrogenation of CO2 to methanol is limited by the thermodynamic equilibrium, resulting in low conversion rates,” says Ma. “Our idea was to break the reaction equilibrium by changing the reaction path, that is, to use an efficient reaction to first activate and fix CO2 into an intermediate product, and then hydrogenate and get the final products.”
In the team’s most recent research1, they have achieved this by reacting CO2 with ethylene oxide to synthesize ethylene carbonate (EC) as the first step, and then hydrogenating EC over a nickel-modified copper catalyst to produce methanol as well as ethylene glycol – another versatile and important chemical feedstock.
“This non-homogeneous copper-based catalyst has been successfully applied in a 1,000-tonne pilot test, achieving stable operation with the highest methanol selectivity reported to date for this synthesis, at more than 93%2,” says Ma.
According to Ma, the co-production of ethylene glycol also makes this approach highly feasible in terms of full life-cycle economics, with the cost of pilot production already comparable to the current market price for the methanol and ethylene glycol products.
“The development of efficient CO2 conversion technology like our two-step methanol synthesis will both reduce energy consumption for methanol synthesis and contribute to the achievement of carbon neutrality as a key carbon capture and use technology,” Ma says.
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