Alcohol-promoted methanol synthesis uses heterogeneous methanol synthesis catalysts in alcoholic solvents where the alcohols act as a co-catalyst. In the presence of alcohol, the reaction proceeds through alcohol formate ester as an intermediate, allowing methanol synthesis at lower temperatures than conventional gas-phase synthesis. In the present work, alcohol-promoted CO2 hydrogenation to methanol was studied experimentally using a Cu/ZnO catalyst with 1-butanol and 2-butanol as solvents. As water is known to inhibit methanol synthesis on Cu/ZnO catalysts, the alcohol-promoted process was further developed by in-situ adsorption of water using a 3Å molecular sieve. The methanol productivity significantly improved as a result of the lowered concentration of water.The concentration of water was thus identified as a key factor affecting the overall methanol productivity. As the alcohol-promoted methanol synthesis process is characterized by two separate reaction steps, the use of separate catalysts optimized for each step offers an interesting approach for the development of this process. Such a dualcatalysis concept was tested using a copper chromite catalyst together with Cu/ZnO. Promising results were obtained, as methanol productivity increased with the addition of copper chromite. Catalyst characterization was carried out using XRD and SEM-EDS and potential effects of observed changes in catalyst structure during reaction are discussed.

Synthesis of methanol from recirculated CO2 and H2 produced by water electrolysis allows sustainable production of fuels and chemical storage of energy. Production of renewable methanol has, however, not achieved commercial breakthrough, and novel methods to improve economic feasibility are needed. One possibility is to alter the reaction route to methanol using catalytic alcoholic solvents, which makes the process possible at lower reaction temperatures. To estimate the techno-economic potential of this approach, the feasibilities of the conventional gas-phase process and an alternative liquid-phase process employing 2-butanol or 1-butanol solvents were compared by means of flowsheet modelling and economic analysis. As a result, it was found that despite improved methanol yield, the presence of solvent adds complexity to the process and increases separation costs due to the high volatility of the alcohols and formation of azeotropes. Hydrogen, produced from wind electricity, was the major cost in all processes. The higher cost of the present, non-optimized liquid-phase process is largely explained by the heat required in separation. If this heat could be provided by heat integration, the resulting production costs approach the costs of the gas-phase process. It is concluded that the novel reaction route provides promising possibilities, but new breakthroughs in process synthesis, integration, optimization, and catalysis are needed before the alcoholic solvent approach surpasses the traditional gas-phase process.

A continuously operated CO2 capture unit, based on absorption in a membrane contactor and lowtemperature vacuum desorption, is demonstrated. The major advantage of membrane contactors is their high specific interfacial area per unit volume. The unit is designed to be modular to allow different absorption membrane modules and stripping units to be tested, with the aim of capturing CO2 from simulated flue gases at concentrations down to the ambient concentration. In addition, desorption can be performed under vacuum to improve the desorption efficiency. The experimental unit incorporates comprehensive measurements and a high level of automation, with heat integration and continuous measurement of electricity consumption providing real-time estimates of the energy consumed in the capture process.In preliminary tests, the results of which are described herein, a 3M Liqui-Cel™ polypropylene hollow-fiber membrane module and a glass vacuum chamber were used for absorption and desorption, respectively, along with a potassium glycinate amino acid salt absorbent solution. This solution has high surface tension and is fully compatible with the polypropylene membrane unit used. In preliminary tests, the highest observed CO2 flux was 0.82 mol m -2 h -1 , with a CO2 product purity of above 80%. The calculated overall mass transfer coefficient was comparable to reference systems. The performance of the unit in its current setup was found to be limited by the desorption efficiency. Due to the low desorption rates, the measured specific energy consumption was exceedingly high, at 4.6 MJ/mol CO2 (29.0 MWh/t) and 0.8 MJ/mol CO2 (5.0 MWh/t) of heat and electricity, respectively. Higher desorption temperatures and lower vacuum pressures enhanced the desorption efficiency and reduced the specific energy consumption. The energy efficiency could be improved via several methods in the future, e.g., by applying ultrasound radiation or by replacing the current vacuum chamber stripping unit with a membrane module or some other type of desorption unit.

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