18 Search Results

As we work to transition the modern society that is based on non-renewable chemical feedstocks to a post-modern society built around renewable sources of energy, fuels, and chemicals, there is a need to identify the renewable resources and processes for converting them to platform chemicals. Herein, we explore a strategy for utilizing the p-hydroxybenzoate in biomass feedstocks (e.g., poplar and palm trees) and converting it into a portfolio of commodity chemicals. The targeted bio-derived product in the first processing stage is p-hydroxybenzamide produced from p-hydroxybenzoate esters found in the plant. In the second stage a continuous reaction process converts the p-hydroxybenzamide to p-aminophenol via the Hofmann rearrangement and recovers the unreacted p-hydroxybenzamide. In the third stage the p-aminophenol can be acetylated to form paracetamol, which is readily isolated by liquid/liquid extraction at >95 % purity and an overall p-hydroxybenzamide-to-paracetamol process yield of ~90 %. We explore how utilization of protecting groups alters the challenges in this process and expands the portfolio of possible products to include p-(methoxymethoxy)aniline and N-acetyl-p-(methoxymethoxy)aniline. These target compounds could become value-added renewably-sourced platform chemicals that could be used to produce biodegradable plastics, pigments, and pharmaceuticals.

The economic and environmental sustainability of lignocellulosic biomass biorefineries is predicated on generating biofuels and bioproducts from cell-wall polysaccharide and lignin polymers. Historical efforts in plant genetic engineering have focused on the development of strategies that facilitate biomass deconstruction, with more recently efforts including the synthesis of high-value chemicals in planta . One such genetic modification is the expression of the bacterial quinate and shikimate utilization B ( qsuB ) gene that increases the accumulation of protocatechuic acid in lignocellulosic biomass. Herein, we evaluated the effectiveness of an alkaline pretreatment process to extract phenolics directly from wild-type and QsuB-transgenic lines of Arabidopsis, poplar, and sorghum, and then upgrade them to the polyester precursor 2-pyrone-4,6-dicarboxylic acid (PDC) with an engineered strain of Novosphingobium aromaticivorans . Protocatechuic acid extracted from all QsuB transgenic lines was found to be mostly in the glycosylated form. Glycosylated protocatechuic acid and other plant-derived phenolics were effectively metabolized by N. aromaticivorans, and PDC production was greatest using extracts from an Arabidopsis QsuB transgenic line (∼5% w/w), followed by QsuB sorghum (∼1.1% w/w), and QsuB poplar (∼0.4% w/w) lines. The comparison of PDC production from wild-type and QsuB transgenic lines of Arabidopsis, poplar, and sorghum demonstrates the utility of a mild alkaline pretreatment to liberate phenolics from plant biomass that are either naturally present or that accumulate as a consequence of genetic engineering strategies. All QsuB transgenic lines outperformed their wild-type counterparts with respect to observed PDC yields. In addition, microbial funneling to PDC was effective even when most of the protocatechuic acid extracted was in glycosylated form, clearly demonstrating that this bacterium can metabolize these aromatic conjugates. These findings illustrate the benefits of combining plant and microbial engineering for bioproduct formation from phenolics in lignocellulosic biorefineries.

The economic feasibility of the lignocellulosic biomass refinery requires the valorization of lignin in addition to its polysaccharide fraction. One promising approach is the combination of chemical methods for lignin fractionation and depolymerization with microbial funneling of the resulting phenolic monomers into valuable chemicals. In this work, we explored the integration of γ-valerolactone (GVL) for biomass pretreatment, catalytic hydrogenolysis for lignin depolymerization, and microbial funneling to 2-pyrone-4,6-dicarboxylic acid (PDC) by the engineered bacterium Novosphingobium aromaticivorans strain PDC. We first investigated the microbial PDC production feasibility from common phenolic compounds previously identified in lignin hydrogenolysis products. Next, we studied the PDC production potential from maple, poplar, sorghum, and switchgrass using the proposed integrated pipeline and, finally, we performed a technoeconomic analysis (TEA) of the system to identify parameters that affect its economic feasibility. We found that N. aromaticivorans strain PDC is able to produce PDC from phenolic compounds with propanol, methyl, or methyl ester sidechains. Using Pd/C as a catalyst for hydrogenolysis to favor the production of these phenolics from lignin extracted with the GVL process, we obtained microbial PDC production yields of 88, 139, 103, and 79 g PDC per kg lignin from maple, poplar, sorghum, and switchgrass, respectively. Using these yields, we estimated a baseline minimum selling price of $$\$$12.10$ per kg of purified PDC, and identified options to further improve the integrated pipeline.

Following biomass fractionation of corn stover using γ-valerolactone (GVL) pretreatment, the resulting lignin stream was subjected to base hydrolysis reactions to achieve the isolation of pcoumaric acid (pCA) from p-coumarate esters present as pendent groups on the lignin. pCA was produced from 5-g-scale experiments in crude yields of 8.3 wt % with 95% purity and, following a straightforward purification using liquid–liquid extraction and crystallization from water, yielded crystalline pCA in 4.8 wt % yield with 97% purity; a methodology to realize 99.5% purity is demonstrated. Because of the mild saponification, the remaining lignin residue retains its value as a feedstock for oxidative or hydrogenolytic deconstruction or as a fuel for energy production in the biorefinery.

Levoglucosanol (LGOL) is a critical intermediate for the bio-based production of hexane-1,2,5,6-tetrol, 1,2,6-hexanetriol, and 1,6-hexanediol. Here we report on the aqueous-phase hydrogenation of cellulose-derived dihydrolevoglucosenone (Cyrene™) to LGOL using a calcined and reduced heterogeneous copper/hydrotalcite/mixed oxide catalyst, denoted as Cu8/MgAlO_x-HP. The turnover frequency for LGOL conversion over this copper-containing catalyst is equal to 0.013 s^–1 at 353 K as measured in a flow reactor which is half the one obtained using 0.4 wt% Pd/Al₂O₃. Moreover, while Cu8/MgAlO_x-HP shows a stable activity, the activity of 0.4 wt% Pd/Al₂O₃ decreases with time-on-stream. Neither Cu- nor Al-leaching is observed (resp. <1 ppb and <1 ppm) but Mg leaching can be seen (5.5 ppm). The latter leaching relates to the acidity of the Cyrene/H₂O mixture (pH 3.5–4.5 range), which is due to the occurrence of the geminal diol moiety of Cyrene, an acidic species. In contrast, additional and consecutive oxidation and reduction of the catalyst leads to a gradual decrease in activity over time. Applying still further oxidation/reduction cycles to this catalyst tends to decrease its activity with some overall stabilization being observed from the fourth run onwards. Mg-leaching is shown to change the relative meso-to-macro pore content, but leaves the total pore volume unchanged between the fresh and the spent catalyst. In spite of the high copper loading (8 wt%), small Cu-nanoparticles (2–3 nm) are present over the hydrotalcite/mixed oxide surface of the Cu8/MgAlO_x-HP material, and these particles do not aggregate during the hydrogenation reaction.

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Abstract High yields of furfural (>90 %) were achieved from xylose dehydration in a sustainable solvent system composed of γ‐valerolactone (GVL), a biomass derived solvent, and water. It is identified that high reaction temperatures (e.g., 498 K) are required to achieve high furfural yield. Additionally, it is shown that the furfural yield at these temperatures is independent of the initial xylose concentration, and high furfural yield is obtained for industrially relevant xylose concentrations (10 wt %). A reaction kinetics model is developed to describe the experimental data obtained with solvent system composed of 80 wt % GVL and 20 wt % water across the range of reaction conditions studied (473–523 K, 1–10 m m acid catalyst, 66–660 m m xylose concentration). The kinetic model demonstrates that furfural loss owing to bimolecular condensation of xylose and furfural is minimized at elevated temperature, whereas carbon loss owing to xylose degradation increases with increasing temperature. Accordingly, the optimal temperature range for xylose dehydration to furfural in the GVL/H ₂ O solvent system is identified to be from 480 to 500 K. Under these reaction conditions, furfural yield of 93 % is achieved at 97 % xylan conversion from lignocellulosic biomass (maple wood).

Elucidation of active sites in supported bimetallic catalysts is complicated by the high level of dispersity in the nanoparticle size and composition that is inherent in conventional methods of catalyst preparation. We present a synthesis strategy that leads to highly dispersed, bimetallic nanoparticles with uniform particle size and composition by means of controlled surface reactions. We demonstrate the synthesis of three systems, RhMo, PtMo, and RhRe, consisting of a highly reducible metal with an oxophilic promoter. These catalysts are characterized by FTIR, CO chemisorption, STEM/EDS, TPR, and XAS analysis. The catalytic properties of these bimetallic nanoparticles were probed for the selective CO hydrogenolysis of (hydroxymethyl)tetrahydropyran to produce 1,6 hexanediol. Based on the characterization results and reactivity trends, the active sites in the hydrogenolysis reaction are identified to be small ensembles of the more noble metal (Rh, Pt) adjacent to highly reduced moieties of the more oxophilic metal (Mo, Re).

We report a process for converting fructose, at a high concentration (15 weight %), to 2,5-furandicarboxylic acid (FDCA), a monomer used in the production of polyethylene furanoate, a renewable plastic. In our process, fructose is dehydrated to hydroxymethylfurfural (HMF) at high yields (70%) using a γ-valerolactone (GVL)/H₂O solvent system. HMF is subsequently oxidized to FDCA over a Pt/C catalyst with 93% yield. The advantage of our system is the higher solubility of FDCA in GVL/H₂O, which allows oxidation at high concentrations using a heterogeneous catalyst that eliminates the need for a homogeneous base. In addition, FDCA can be separated from the GVL/H₂O solvent system by crystallization to obtain >99% pure FDCA. Our process eliminates the use of corrosive acids, because FDCA is an effective catalyst for fructose dehydration, leading to improved economic and environmental impact of the process. Our techno-economic model indicates that the overall process is economically competitive with current terephthalic acid processes.