Production of Biomass-Derived p-Hydroxybenzamide: Synthesis of p-Aminophenol and Paracetamol.

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.

Enhanced Furfural Yields from Xylose Dehydration in the γ-Valerolactone/Water Solvent System at Elevated Temperatures.

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 mm acid catalyst, 66-660 mm 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/H2 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).

Toward biomass-derived renewable plastics: Production of 2,5-furandicarboxylic acid from fructose.

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.

Solvent effects in acid-catalyzed biomass conversion reactions.

Reaction kinetics were studied to quantify the effects of polar aprotic organic solvents on the acid-catalyzed conversion of xylose into furfural. A solvent of particular importance is γ-valerolactone (GVL), which leads to significant increases in reaction rates compared to water in addition to increased product selectivity. GVL has similar effects on the kinetics for the dehydration of 1,2-propanediol to propanal and for the hydrolysis of cellobiose to glucose. Based on results obtained for homogeneous Brønsted acid catalysts that span a range of pKa values, we suggest that an aprotic organic solvent affects the reaction kinetics by changing the stabilization of the acidic proton relative to the protonated transition state. This same behavior is displayed by strong solid Brønsted acid catalysts, such as H-mordenite and H-beta.

Control of thickness and chemical properties of atomic layer deposition overcoats for stabilizing Cu/γ-Al2 O3 catalysts.

Whereas sintering and leaching of copper nanoparticles during liquid-phase catalytic processing can be prevented by using atomic layer deposition (ALD) to overcoat the nanoparticles with AlOx , this acidic overcoat leads to reversible deactivation of the catalyst by resinification and blocking of the pores within the overcoat during hydrogenation of furfural. We demonstrate that decreasing the overcoat thickness from 45 to 5 ALD cycles is an effective method to increase the rate per gram of catalyst and to decrease the rate of deactivation for catalysts pretreated at 673 K, and a fully regenerable copper catalyst can be produced with only five ALD cycles of AlOx . Moreover, although an overcoat of MgOx does not lead to stabilization of copper nanoparticles against sintering and leaching during liquid-phase hydrogenation reactions, the AlOx overcoat can be chemically modified to decrease acidity and deactivation through the addition of MgOx , while maintaining stability of the copper nanoparticles.