RESUMEN
Biomass conversion to fuels and chemicals is crucial to decarbonization, but choosing an advantageous upgrading pathway out of many options is challenging. Rigorously evaluating all candidate pathways (process simulation, product property testing) requires a prohibitive amount of research effort; even simple upgrading schemes have hundreds of possible permutations. We present a method enabling high-throughput screening by approximating upgrading unit operations and drop-in compatibility of products (e.g., fuel properties) and apply it to volatile fatty acid (VFA) conversion to liquid transportation fuels via a MATLAB script, VFA Upgrading to Liquid Transportation fUels Refinery Estimation (VULTURE). VULTURE selects upgrading configurations that maximize fuel blend bio-derived content. We validate VULTURE's approximations through surrogate fuel property testing and process simulation. Techno-economic and life cycle analyses suggest that VFA upgrading processes down-selected by VULTURE are profitable and have low carbon intensities, demonstrating the potential for the strategy to accelerate process development timelines at decreased costs.
RESUMEN
Lignocellulosic biomass offers a renewable carbon source which can be anaerobically digested to produce short-chain carboxylic acids. Here, we assess fuel properties of oxygenates accessible from catalytic upgrading of these acids a priori for their potential to serve as diesel bioblendstocks. Ethers derived from C2 and C4 carboxylic acids are identified as advantaged fuel candidates with significantly improved ignition quality (>56% cetane number increase) and reduced sooting (>86% yield sooting index reduction) when compared to commercial petrodiesel. The prescreening process informed conversion pathway selection toward a C11 branched ether, 4-butoxyheptane, which showed promise for fuel performance and health- and safety-related attributes. A continuous, solvent-free production process was then developed using metal oxide acidic catalysts to provide improved thermal stability, water tolerance, and yields. Liter-scale production of 4-butoxyheptane enabled fuel property testing to confirm predicted fuel properties, while incorporation into petrodiesel at 20 vol % demonstrated 10% improvement in ignition quality and 20% reduction in intrinsic sooting tendency. Storage stability of the pure bioblendstock and 20 vol % blend was confirmed with a common fuel antioxidant, as was compatibility with elastomeric components within existing engine and fueling infrastructure. Technoeconomic analysis of the conversion process identified major cost drivers to guide further research and development. Life-cycle analysis determined the potential to reduce greenhouse gas emissions by 50 to 271% relative to petrodiesel, depending on treatment of coproducts.
RESUMEN
The objective of this study was to begin to quantify the benefits of a smoke opacity-based (SAE J1667 test) inspection and maintenance program. Twenty-six vehicles exhibiting visible smoke emissions were recruited: 14 pre-1991 vehicles and 12 1991 and later model year vehicles. Smoke opacity and regulated pollutant emissions via chassis dynamometer were measured, with testing conducted at 1609 m above sea level. Twenty of the vehicles were then repaired with the goal of lowering visible smoke emission, and the smoke opacity testing and pollutant emissions measurements were repeated. For the pre-1991 vehicles actually repaired, pre-repair smoke opacity averaged 39% and PM averaged 5.6 g/mi. NOx emissions averaged 22.1 g/mi. After repair, the average smoke opacity had declined to 26% and PM declined to 3.3 g/mi, while NOx emissions increased to 30.9 g/mi. For the 1991 and newer vehicles repaired, pre-repair smoke opacity averaged 59% and PM averaged 2.2 g/mi. NOx emissions averaged 12.1 g/mi. After repair, the average opacity had declined to 30% and PM declined to 1.3 g/mi, while NOx increased slightly to 14.4 g/mi. For vehicles failing the California opacity test at >55% for pre-1991 and >40% for 1991 and later model years, the changes in emissions exhibited a high degree of statistical significance. The average cost of repairs was 1088 dollars, and the average is very similar for both the pre-1991 and 1991+ model year groups. Smoke opacity was shown to be a relatively poor predictor of driving cycle PM emissions. Peak CO or peak CO and THC as measured during a snap-acceleration were much better predictors of driving cycle PM emissions.