Conversion of Biomass into Chemicals over Metal Catalysts

The catalytic reduction of carboxylic acid derivatives has witnessed a rapid development in recent years. These reactions, involving molecular hydrogen as the reducing agent, can be promoted by heterogeneous and homogeneous catalysts. The milestone achievements and recent results by both approaches are discussed in this Review. In particular, we focus on the mechanistic aspects of the catalytic hydrogenation and highlight the bifunctional nature of the mechanism that is preferred for supported metal catalysts as well as homogeneous transition metal complexes.

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Heterogeneous and homogeneous catalysis for the hydrogenation of carboxylic acid derivatives: history, advances and future directions

Reaction pathways and kinetics governing the Ru-catalyzed hydrogenation of levulinic acid (LA) in the aqueous phase to form γ-valerolactone (GVL) were considered in a packed bed reactor. GVL can be produced by two distinct hydrogenation pathways; however, over Ru/C at temperatures below 423 K, it forms exclusively via intramolecular esterification of 4-hydroxypentanoic acid (HPA). Over Ru/C, reasonable hydrogenation rates of LA to HPA were observed at near-ambient temperatures (e.g., 0.08 s–1 at 323 K), but GVL selectivities are poor (<5%) under these conditions. Apparent barriers for LA hydrogenation and HPA esterification are 48 and 70 kJ mol–1, respectively, and GVL selectivity improves at higher temperatures alongside increasing mass transfer limitations in 45–90 μm catalyst particles. Reactivity and selectivity trends in LA hydrogenation below 343 K are well-described by an empirical kinetic model capturing sequential hydrogenation and esterification. Coupling stacked beds of Ru/C and Amberlyst-15 de...

Analysis of Kinetics and Reaction Pathways in the Aqueous-Phase Hydrogenation of Levulinic Acid To Form γ-Valerolactone over Ru/C

Catalytic routes from renewables to fine chemicals

The production of chemicals from biomass, a renewable feedstock, is highly desirable in replacing petrochemicals to make biorefineries more economical. The best approach to compete with fossil-based refineries is the upgradation of biomass in integrated biorefineries. The integrated biorefineries employed various biomass feedstocks and conversion technologies to produce biofuels and bio-based chemicals. Bio-based chemicals can help to replace a large fraction of industrial chemicals and materials from fossil resources. Biomass-derived chemicals, such as 5-hydroxymethylfurfural (5-HMF), levulinic acid, furfurals, sugar alcohols, lactic acid, succinic acid, and phenols, are considered platform chemicals. These platform chemicals can be further used for the production of a variety of important chemicals on an industrial scale. However, current industrial production relies on relatively old and inefficient strategies and low production yields, which have decreased their competitiveness with fossil-based alternatives. The aim of the presented review is to provide a survey of past and current strategies used to achieve a sustainable conversion of biomass to platform chemicals. This review provides an overview of the chemicals obtained, based on the major components of lignocellulosic biomass, sugars, and lignin. First, important platform chemicals derived from the catalytic conversion of biomass were outlined. Later, the targeted chemicals that can be potentially manufactured from the starting or platform materials were discussed in detail. Despite significant advances, however, low yields, complex multistep synthesis processes, difficulties in purification, high costs, and the deactivation of catalysts are still hurdles for large-scale competitive biorefineries. These challenges could be overcome by single-step catalytic conversions using highly efficient and selective catalysts and exploring purification and separation technologies.

https://www.mdpi.com/1996-1073/12/2/233/pdf

Bio-Based Chemicals from Renewable Biomass for Integrated Biorefineries

Catalytic Hydrogenation of Arabinonic Acid and Lactones to Arabitol

Catalytic hydrogenation of arabinonic acid and arabinonolactones

Water solutions of glucono-δ-lactone and glucono-γ-lactone in equilibrium with gluconic acid were hydrogenated with molecular hydrogen in the presence of a commercial carbon-supported ruthenium catalyst (5% Ru/C, Engelhard Escat 40). Reactions were conducted batchwise on 20 wt% solutions under 100 bar pressure in the temperature range 80–140°C. Reaction rates were unexpectedly high at moderate temperatures (e.g., 0.58 mol h-1 g
 Ru
 -1
 at 100°C) because lactones were probably the reactive species. The selectivity to sorbitol at total conversion was larger than 99% at temperatures lower than 100°C. Kinetic study was done at different temperatures, pressures and concentrations. Modelling of the reaction kinetics showed that the reaction followed a rate law corresponding either to the Langmuir–Hinshelwood mechanism without H2 dissociation, or to the Horiuti–Polanyi mechanism.

Lionel Fabre

Papers

Catalytic Hydrogenation of Arabinonic Acid and Lactones to Arabitol

Catalytic hydrogenation of arabinonic acid and arabinonolactones

Hydrogenation of gluconolactones in equilibrium with gluconic acid on ruthenium catalyst