Process intensification for the valorization of lignocellulosic biomass-derived feedstocks
Date
2023
Authors
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Publisher
University of Delaware
Abstract
Research into alternative renewable carbon sources and their effective valorization to fuels and high-value chemicals has been intensified due to the concerns about their environmental impact. Non-edible lignocellulosic biomass is a promising carbon source due to its abundance, high chemical functionality, and its potential to stimulate carbon sequestration. Despite extensive research in biomass valorization, significant challenges remain. Among potential biomass valorization pathways, sugars dehydration to furans (5-hydroxymethylfurfural (HMF) and furfural), their hydrodeoxygenation (HDO) to 2,5-dimethylfuran (DMF) and 2-methylfuran (MF), and DMF’s subsequent cycloaddition and dehydration to form para-xylene (pX) shows promise. This dissertation utilizes computational and experimental tools toward process intensification of this valorization route. ☐ In Chapter 2, we introduce a conceptual framework for selecting solvents for reactive extraction in biphasic organic-water systems and demonstrate it for the separation of HMF. We perform in silico screening of ~2,500 solvents, from a database using the COSMO-RS model. We then determine experimentally the partition coefficients for HMF, fructose, and products of HMF rehydration (levulinic acid (LA), and formic acid (FA)), the mutual water-organic solvent solubilities, and the separation factors in >50 select solvents spanning multiple homologous series at room temperature and a typical reaction temperature with in-situ sampling. We find that COSMO-RS is excellent for screening (typical error in most cases is within a factor of ~2). Increased temperatures lead to significant reduction in partitioning, and room temperature measurements are clearly inadequate for solvent selection. Upon down-selecting classes of solvents based on separation performance, we assess the thermal stability and reaction compatibility s of a small set of solvents at relevant reactive-extraction temperatures. We discover that many substituted phenols exhibit order-of-magnitude increased partitioning compared to conventional solvents. ☐ The above framework was extended to the C-5 platform chemical, furfural, and mixtures of furfural and HMF in Chapter 3. We predict the liquid-liquid equilibria and furfural/HMF partition coefficients and measure experimentally the single-component (furfural) and mixture partition coefficients at room and dehydration reaction-relevant temperatures in 28 solvents. We find the experimental data to be within a factor of 2 from the COSMO-RS predictions. Even though furfural and HMF have chemical similarity, furfural can be separated by more solvents with higher partition coefficient. We leverage the molecular difference to demonstrate selective extraction of furfural from furfural-HMF mixtures and rationalize it using COSMO-RS sigma-profile analysis. ☐ In Chapter 4, we combine HMF HDO experiments in 2-pentanol over the Ru/C catalyst with Aspen Plus process flowsheet design and simulation using experimental conditions, yields, and separation specifications. The experiments and techno-economic analysis (TEA) are guided using the active learning-based experimental design toolkit NEXTorch focusing on the impact of water. Our experimental investigations lead to DMF yields of 80% at 100% HMF conversion before any catalyst optimization. The formation of furan-solvent ethers is significant at higher water loadings and lower reaction temperatures in 2-pentanol and shorter reaction times, while for experiments in 2-propanol, water suppresses ether formation. We then conduct Bayesian optimization on process simulation to search for reaction conditions that minimize production costs and greenhouse gas emissions. The optimal HDO reaction conditions have high conversion and selectivity and occur at relatively high reaction temperatures, zero water content, high hydrogen pressures, and medium HMF loading. Moreover, a slight water content in the reaction inlet stream more significantly impacts the greenhouse gas emissions than the cost. ☐ In Chapter 5, we demonstrate highly selective production of pX from ethylene and DMF in a packed bed microreactor with phosphorous-decorated zeolite beta (P-BEA), with pX selectivity up to 97% at 80% DMF conversion. We map the operation regime of the reactor in temperature, space velocities, concentration, gas:liquid ratio, and process pressure. Time-on-stream (TOS) data and in situ regeneration show no sign of reduced productivity over ~5 h and full restoration of productivity upon regeneration for multiple cycles. Initial nonselective reactions are attributed to the trace remaining Al bridge site. The flow setup reveals most of the non-selective Brønsted acidity occurs at short time-on-stream. External mass transfer limitations are revealed at low space velocities. Reactions using mesoporous P-BEA further illustrate the extent of internal mass transfer limitations, although long-time performance of mesoporous P-BEA is worse than P-BEA without mesopore addition. We combine TOS on P-BEA with NMR, XRD, and Raman spectroscopy to explore the structural-activity insights into the catalyst behavior.
Description
Keywords
Process intensification, Valorization, Biomass-derived feedstocks, Renewable carbon sources, Reactive extraction