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Due to challenges related to weight and travel distance, the medium to long-haul aviation sector is expected to remain reliant on liquid hydrocarbon fuels into the foreseeable future, representing a persistent source of CO2 emissions within the anthropogenic carbon cycle. As the world grapples with the environmental fallout from rising CO2 emissions, a prevailing strategy to mitigate the impact of air travel is through the utilization of sustainable aviation fuels (SAF) produced from biogenic carbon sources such as fats, oils, greases, and biomass. However, with the demand for SAF expected to grow substantially in the coming decades, there is concernmore » around the availability of these feedstocks at scale. Recent studies have proposed that this potential gap in supply could be closed by utilizing CO2 as a complementary source of carbon combined with renewable electricity to drive the chemical transformation. In this study, a crosscutting comparison of an emerging CO2-to-SAF pathway with existing routes to SAF is performed, revealing the potential for CO2-derived SAF to be competitive both in terms of costs and carbon intensity, further diversifying future options for SAF and providing a complementary option for the conversion of CO2-to-SAF beyond the decades old methanol to olefins (MTO) and Fischer–Tropsch (FT) technologies. In addition, we discuss potential technical, market, and systems integration risks for the ultimate scale-up and commercialization of the pathway identified herein.« less

It is well documented that the enzymatic hydrolysis of cellulose follows a reaction pattern where an initial phase of relatively high activity is followed by a gradual slow-down over the entire course of the reaction. This phenomenon is not readily explained by conventional factors like substrate depletion, product inhibition or enzyme instability. It has been suggested that the underlying reason for the loss of enzyme activity is connected to the heterogeneous structure of cellulose, but so far attempts to establish quantitative measures of such a correlation remain speculative. Here, we have carried out an extensive microscopy study of Avicel particlesmore » during extended hydrolysis with Hypocrea jecorina cellobiohydrolase 1 (CBH1) and endoglucanase 1 and 3 (EG1 and EG3) alone and in mixtures. We have used differential interference contrast microscopy and transmission electron microscopy to observe and quantify structural features at um and nm resolution, respectively. We implemented a semi-automatic image analysis protocol, which allowed us to analyze almost 3000 individual micrographs comprising a total of more than 300,000 particles. From this analysis we estimated the temporal development of the accessible surface area throughout the reaction. We found that the number of particles and their size as well as the surface roughness contributed to surface area, and that within the investigated degree of conversion (<30 %) this measure correlated linearly with the rate of reaction. Lastly, based on this observation we argue that cellulose structure, specifically surface area and roughness, plays a major role in the ubiquitous rate loss observed for cellulases.« less