(551g) Crude Methanol from Alternative Energy Source As Low-Cost, Low-Carbon Hydrogen Carrier

Methane emissions from stranded associated gas, biomass digesters, and municipal wastes can be avoided and instead converted to methanol from a gas-to-methanol plant on an easily deployable commercial trailer [1]. This methanol from otherwise flared or emitted methane can be a safer hydrogen medium than ammonia, and a more economic hydrogen medium for mid-to-long-range transportation relative to hydrogen in the form of compressed gas, cryogenic liquid, and metal hydrides [2]. Moreover, methanol synthesized from these unconventional sources can be used as a low-carbon hydrogen carrier, which can be electrolyzed to form hydrogen at the point of use. The high-purity CO₂ byproduct stream can be captured to further decrease the carbon intensity (CI).

Compared to conventional methanol from pipelined natural gas, alternative methanol, as a hydrogen carrier, is attractive due to its decentralized production, which lends access to cheap gas and energy independence for regional networks. The decreasing cost of renewable electricity further provides an incentive for electrolysis. Such a process, however, is more economically viable if crude methanol can be directly fed to electrolyzers, bypassing any requisite upgrading through costly distillation processes at more centralized facilities. From our estimation, methanol upgrading steps account for more than 10% of the overall cost of decentralized methanol; direct use of crude methanol thus avoids these costs and further decreases the CI of this alternative methanol by more than 10%. The tradeoff involves the energy penalty associated with the loss in electrolysis efficiency resulting from the presence of trace impurities within crude methanol. While inorganic impurities, such as chloride and sulfur species, can be managed or removed by upstream cleaning processes, organic impurities that persist as natural byproducts of methanol synthesis reactions are challenging to avoid [3]. The removal of ethanol, the most common organic reaction byproduct, is particularly energy intensive because of its similar volatility to methanol. These higher alcohols are known to poison catalysts for methanol electrolysis and lower the efficiency of hydrogen production.[4] Feeding crude methanol into a point-of-use electrolyzer makes economic sense when the electrochemical energy penalty associated with the presence of these organic impurities is lower than the cost of transport and distillation of crude methanol to grade methanol.

In this work, sensitivity tests are performed by bench-scale electrochemical reactions to quantify the impact of trace (0 to 5000 ppm) mixed C₂-C₄ alcohols on methanol electrolysis simulating the composition of actual crude methanol produced from alternative resources. The experiment data is then used in techno-economic assessment and the learning can be used as a decision-making tool to determine the conditions and scenarios under which direct electrolysis of crude methanol is economically feasible.

Reference

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