Hydrothermal Dehydration of Monosaccharides Promoted by Seawater: Fundamentals on the Catalytic Role of Inorganic Salts

The key role of pretreatment for the one-step and multi-step conversions of European lignocellulosic materials into furan compounds

Nowadays, an increased interest from the chemical industry towards the furanic compounds production, renewable molecules alternatives to fossil molecules, which can be transformed into a wide range of chemicals and biopolymers. These molecules are produced following hexose and pentose dehydration. In this context, lignocellulosic biomass, owing to its richness in carbohydrates, notably cellulose and hemicellulose, can be the starting material for monosaccharide supply to be converted into bio-based products. Nevertheless, processing biomass is essential to overcome the recalcitrance of biomass, cellulose crystallinity, and lignin crosslinked structure. The previous reports describe only the furanic compound production from monosaccharides, without considering the starting raw material from which they would be extracted, and without paying attention to raw material pretreatment for the furan production pathway, nor the mass balance of the whole process. Taking account of these shortcomings, this review focuses, firstly, on the conversion potential of different European abundant lignocellulosic matrices into 5-hydroxymethyl furfural and 2-furfural based on their chemical composition. The second line of discussion is focused on the many technological approaches reported so far for the conversion of feedstocks into furan intermediates for polymer technology but highlighting those adopting the minimum possible steps and with the lowest possible environmental impact. The focus of this review is to providing an updated discussion of the important issues relevant to bringing chemically furan derivatives into a market context within a green European context.

Catalytic Hydroconversion of 5-HMF to Value-Added Chemicals: Insights into the Role of Catalyst Properties and Feedstock Purity

5-hydroxymethylfurfural (HMF) is an important bio-derived platform molecule that is generally obtained from hexoses via acid-catalyzed dehydration. It can be effectively transformed into a variety of value-added derivatives, thus being an ideal candidate for fossil replacement. Both HMF oxidation and hydrogenation processes enable the synthesis of numerous chemicals, monomers for polymerization, and biofuel precursors. This Review summarizes the most recent advances in heterogeneous catalytic hydroconversion of HMF into valuable chemicals with strong focus on 2,5-bishydroxymethyl furan (BHMF), 2,5-bishydroxymethyltetrahydrofuran (BHMTHF), and 2,5-dimethyltetrahydrofuran (DMTHF). In addition, multifunctional catalytic systems that enable a tunable production of various HMF derived intermediates are discussed. Within this chemistry, the surprising impact of HMF purity on the catalytic performance, such as selectivity and activity, during its upgrading is highlighted. Lastly, the remaining challenges in the field of HMF hydroconversion to the mentioned chemicals are summarized and discussed, taking into account the knowledge gain of catalyst properties and feedstock purity.

Inorganic Salt Catalysed Hydrothermal Carbonisation (HTC) of Cellulose

The presence of inorganic salts either as part of the substrate or added to the reaction medium are known to significantly affect the reaction pathways during hydrothermal carbonisation (HTC) of biomass. This work aims to understand the influence of salts on hydrothermal carbonisation by processing cellulose in the presence of one or more inorganic salts with different valency. Batch experiments and Differential Scanning Calorimetry were used to investigate the change in reaction pathways during hydrothermal conversion. The effect of salts on the rate of HTC of cellulose can be correlated with the Lewis acidity of the cation and the basicity of the anion. The effect of the anion was more pH-dependent than the cation because it can protonate during the HTC process as organic acids are produced. The introduction of salts with Lewis acidity increases the concentration of low molecular weight compounds in the process water. The addition of a second salt can influence the catalytic effect of the first salt resulting in greater levulinic acid yields at the expense of hydrochar formation. Salts also play an important role in cellulose dissolution and can be used to modify the yield and composition of the hydrochars.