(90d) Concentrating Solar Power Based Conversion of Carbon Dioxide to Fuels

We are employing a range of in-house developed technologies to address conversion of impure CO₂-rich waste streams into products that will function as drop-in replacements for petroleum or petroleum fractions. Advantages of PCI’s approach include energy efficiencies and improved reactor performances, in terms of both yields and energy efficiencies that are inherent to our reactor designs. The underlying improvements are due to use of Microlith^®-based catalyst substrates; use of which enables the demonstrated improved performances as well as enabling reactor designs effective over a wide range of thermal inputs from low kW to high MW scales. This reactor technology enables meeting DOE performance goals of CO₂ conversion, energy efficiencies, and product yields. Additionally, the use of PCI’s processes enables the conversion of waste CO₂, without the need for further purification, into value-added saleable products or serves as a drop-in replacement to petroleum or crude oil. We also address the impact of solar or wind variabilities on the operability of our process.

Our approach to upgrading CO₂-rich streams containing CO, CH₄, H₂ and N₂ is to use high-temperature reforming, with the addition of supplemental CH₄ and process recycle, to form syngas. This can be followed by water-gas shift, if needed to adjust the CO/H₂ ratio, then Fischer-Tropsch synthesis to produce liquid-range hydrocarbons for sales or as alternative refinery feedstocks. This process makes use of concentrating solar power (CSP) to provide the high temperatures needed for the reforming reaction, ~850-925 °C. We have demonstrated moderate durability with no evidence of catalyst deactivation or carbon formation, achieving close to equilibrium CO₂ and CH₄ conversions. Our reactor design also minimizes the impact of the significant endotherm that other approaches to CO₂/CH₄ reforming suffer from; our ability to maintain near-optimum temperature through the reactor enables the noted equilibrium conversions while preventing carbon deposition.

Concentrating Solar Power (CSP) technologies, either cone or mirror-illuminate receivers, depending on the required power levels ranging from 250 kW to over 10MW per solar receiver, are used to drive the highly endothermic CO₂/CH₄ reforming process. We estimated that over 50% of solar energy can be converted into fuel energy, exceeding the DOE target of 40% thermal efficiency and at a cost competitive basis with current pump-diesel value.

Microlith mesh is a catalyst substrate consisting of thin catalytically-coated high-alloy metal mesh screens with very small channel diameters. Reactors employing this coated mesh have excellent fluid mixing, elimination of internal thermal gradients, high volumetric concentrations of catalysts, and low pressure drops, which together enable the CO₂ conversion efficiencies observed experimentally. Additionally, the resulting high heat and mass transfers on the Microlith-based reactor allows for compact reactor sizes needed for tight integration with CSP. The open structure leads to extremely low pressure drops, as compared to pellet packed beds, and less of a pressure drop as compared to structured substrates such as honeycomb monoliths. The same structure is also useful for supporting sorbents for capture of CO₂ from flue gas and other sources in addition to use in reactors conducting highly exothermic or endothermic reactions.