(182d) Methanol Production By CO2 Hydrogenation in Hybrid Membrane-Nanoparticle Reactors

Methanol presents a range of advantages as a potential future fuel due to its high energy density compared to that of natural gas and hydrogen. In addition, it is a crucial precursor for the production of plastics, fuel additives and adhesives in a range of industries. However, traditional methods of methanol synthesis by natural gas have a significant greenhouse gas footprint as they involve CO₂ release as a byproduct. An alternative approach to methanol production by natural gas, is CO₂ hydrogenation, which is key in mitigating CO₂ emissions. However, several challenges associated with this approach include low reactivity of CO₂ and high selectivity to methanol. So, research interest has focused on the development of new catalysts, such as Cu/ZrO₂ (Kattel et al., 2016), Cu/ZnO/ZrO₂ (Witoon et al., 2018), and Cu/ZnO/Al₂O₃ (Tada et al., 2017), that are both active to CO₂ hydrogenation and selective to methanol.

Here, nanoparticle-membrane nanocomposites are manufactured via direct one-step deposition. CuO/ZrO₂ nanoparticles are produced by flame spray pyrolysis (FSP) at various precursor solution-to-oxygen (P/O) flow rate ratios and are deposited on polymeric membranes that are highly selective to methanol (Figure 1a). Figure 1 shows scanning electron microscopy (SEM) images of flame-made CuO/ZrO₂ catalyst produced at a P/O of (b) 10 mL/min precursor solution to 8 L/min oxygen (10/8, hot flame) and (c) 2/8 (cold flame), deposited on Matrimid®5218 membranes for 2.5 and 9 min, respectively. Increasing the precursor flow rate, leads to higher temperature and longer high-temperature particle residence time, which in turn results in larger CuO and ZrO₂ crystal size and smaller specific surface area. The catalyst is reduced by H₂ at 300 °C for the formation of Cu/ZrO₂ nanocatalysts.

The effect of nanoparticle and film characteristics (crystallinity, crystal size, porosity) on the CO₂ conversion and methanol production rate is quantified. FSP conditions leading to nanocatalysts with highly activity to CO₂ hydrogenation are identified, while the selectivity to methanol, which is enhanced by the presence of polyimide membranes, is also evaluated. Such hybrid membrane-catalytic nanoparticle reactors are a promising technology which enables industries to convert their carbon dioxide wastes into valuable energy products, such as methanol.

Funded by Future Fuels Cooperative Research Centre grant (RP1.3-04) and the University of Melbourne, Australia.

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