Thermodynamic Insights into Sustainable Aviation Fuel Synthesis via CO/CO2 Hydrogenation

The transformation of CO/CO2 hydrogenation into high-density sustainable aviation fuel (SAF) represents a promising pathway for carbon emission reduction in the aviation industry but also serves as a method for renewable energy assimilation. However, current hydrocarbon products synthesized through CO/CO2 often focus on various catalytic paths with high selectivity and high conversion rates rather than the synthesis of SAFs with complex components. This study undertakes a thermodynamic investigation into the direct or indirect synthesis of SAFs from CO/CO2 hydrogenation. By analyzing the synthesis of seven aviation fuels defined by the American Society for Testing and Materials (ASTM) D7566 standard, our study reveals a temperature-dependent reduction in the reaction driving force for all products. Specifically, for CO, Delta G transitions from approximately -88.6 J/(mol<middle dot>K) at 50 degrees C to 26.7 J/(mol<middle dot>K) at 500 degrees C, with the switch from negative to positive values occurring around 390 degrees C. Similarly, for CO2, Delta G values change from approximately -66.7 J/(mol<middle dot>K) at 50 degrees C to 37.3 J/(mol<middle dot>K) at 500 degrees C, with the transition point around 330 degrees C. The thermodynamic favorability for various hydrocarbon products synthesized is also examined, highlighting a transition at temperatures of around 250 degrees C, beyond which the thermodynamic drive for the synthesis of aromatic compounds increasingly surpasses that of cycloparaffin synthesis. Our findings also underscore that the products with a higher aromatic content yield a lower H-2/CO2 ratio, thus reducing hydrogen consumption. The influence of cycloparaffin and aromatic proportions in the typical SAF products on the Delta G is also explored, revealing that an increase in cycloparaffin content in SAFs slightly elevates the Delta G, whereas an increase in aromatic content significantly reduces Delta G, thereby markedly enhancing the thermodynamic drive of the CO/CO2 hydrogenation reaction. These findings underscore the thermodynamic preference for synthesizing SAF with a higher proportion of aromatic compounds, shedding light on potential pathways for optimizing fuel synthesis to improve efficiency. Finally, the thermodynamic challenges and potential solutions involved in synthesizing SAFs via specific intermediate compounds are discussed, presenting opportunities for more strategic process schemes in industrial scenarios.