Irina Delidovich

Cellulose and hemicellulose valorisation: an integrated challenge of catalysis and reaction engineering

Platform molecules have recently been in the focus of numerous investigations as intermediates for transformation of lignocellulosic biomass into fuels and chemicals. Herein we focus on challenges associated with technical implementation of the production of selected platform molecules. 5-(Hydroxymethyl)-furfural, furfural and levulinic acid were chosen to illustrate pitfalls and limitations of currently available catalytic reaction systems. Owing to the prominent reactivity, high polarity and high boiling points of most biomass-derived platform chemicals, the design of efficient, economic and environmentally benign chemical processes offers a number of difficulties. Challenges include not only a selective synthesis of such platform chemicals and their further transformation into potential products but also methods to allow an energy efficient product separation and sufficient catalyst stability under the applied reaction conditions. In this review we discuss three approaches to tackle the integration of catalytic transformations, reaction engineering and product separation. First, extraction-assisted synthesis methods are discussed. In the next step the integration of such extraction-assisted approaches into reaction cascades is considered. Finally, one-pot transformations of lignocellulose-derived carbohydrates into value-added products without isolation of the intermediate platform chemicals are outlined. The present status of predictive tools facilitating the selection of suitable solvent systems for extraction systems is discussed to outline current opportunities and constraints of a theoretical process design and optimization. In summary, this review provides an overview of recent progress with regard to strategies for process integration of chemo-catalytic biomass valorisation and highlights challenges associated with such approaches.

Catalytic Isomerization of Biomass-Derived Aldoses: A Review

Abstract Selected aldohexoses (d‐glucose, d‐mannose, and d‐galactose) and aldopentoses (d‐xylose, l‐arabinose, and d‐ribose) are readily available components of biopolymers. Isomerization reactions of these substances are very attractive as carbon‐efficient processes to broaden the portfolio of abundant monosaccharides. This review focuses on the chemocatalytic isomerization of aldoses into the corresponding ketoses as well as epimerization of aldoses at C2. Recent advances in the fields of catalysis by bases and Lewis acids are considered. The emphasis is laid on newly uncovered catalytic systems and mechanisms of carbohydrate transformations.

Catalytic activity and stability of hydrophobic Mg–Al hydrotalcites in the continuous aqueous-phase isomerization of glucose into fructose

The aqueous-phase isomerization of glucose into fructose, catalyzed by Mg–Al hydrotalcites, has been investigated under batch and continuous conditions. A commercial hydrotalcite with a hydrophobic surface modification and two hydrophilic hydrotalcites in carbonate form, or with OH− anions in the interlayer space, served as catalysts. With the hydrophobic hydrotalcite a lower conversion but superior selectivity to fructose could be demonstrated, reaching above 92% selectivity at 30% conversion. The observed by-products confirm retroaldolization of glucose and fructose as the main side reactions causing catalyst deactivation via adsorption. Additionally, acidic degradation products such as lactic acid cause neutralization of the hydrotalcites facilitating leaching of the Mg2+ ions. Fructose contributes a greater extent to by-product formation. Applying continuous operation conditions, fructose is removed from the reaction mixture. Therefore, by-product formation is notably suppressed and catalyst stability increases. During 70 to 100 h time-on-stream a slow deactivation of the hydrophobic hydrotalcite occurs. Regeneration can be achieved via calcination and treatment in an aqueous sodium n-dodecyl sulfate solution to introduce dodecyl sulfate anions to the interlayer space of the hydrotalcite, restoring the hydrophobic material properties.

A heteropoly acid ionic crystal containing Cr as an active catalyst for dehydration of monosaccharides to produce 5-HMF in water

Cs2[Cr3O(OOCC2H5)6(H2O)3]2[α-SiW12O40], a chromium-based heteropoly acid (HPA) ionic crystal, was demonstrated to be an active heterogeneous catalyst for production of 5-hydroxymethylfurfural (HMF) from fructose or glucose. The dependencies of catalytic activity on reaction parameters such as solvent, temperature and reaction time were investigated and the reaction conditions were optimized. Based on fructose, the yield of HMF reaches 86% and 56% when using DMSO and water as solvents, respectively. Starting from glucose, a yield of HMF up to 48% can be achieved for both aqueous and DMSO media. The catalyst was successfully recycled 5 times.

Catalytic formation of monosaccharides: from the formose reaction towards selective synthesis.

The formose reaction (FR) has been long the focus of intensive investigations as a simple method for synthesis of complex biologically important monosaccharides and other sugar-like molecules from the simplest organic substrate-formaldehyde. The fundamental importance of the FR is predominantly connected with the ascertainment of plausible scenarios of chemical evolution which could have occurred on the prebiotic Earth to produce the very first molecules of carbohydrates, amino- and nucleic acids, as well as other vitally important substances. The practical importance of studies on the FR is the elaboration of catalytic methods for the synthesis of rare and non-natural monosaccharides and polyols. This Minireview considers the FR from the point of view of chemists working in the field of catalysis with emphasis on the mechanisms of numerous parallel and consequent catalytic transformations that take place during the FR. Based on its kinetics, the FR may be considered as a non-radical chain process with degenerate branching. The Minireview also considers different approaches to the control of selectivity of carbohydrate synthesis from formaldehyde and lower monosaccharides.

Hetropolyacid-Catalyzed Oxidation of Glycerol into Lactic Acid under Mild Base-Free Conditions.

Lactic acid (LA) is a versatile platform molecule owing to the opportunity to transform this compound into useful chemicals and materials. Therefore, efficient production of LA based on inexpensive renewable feedstocks is of utmost importance for insuring its market availability. Herein, we report the efficient conversion of glycerol into LA catalyzed by heteropolyacids (HPAs) under mild base-free conditions. The catalytic performance of molecular HPAs appears to correlate with their redox potential and Brønsted acidity. Namely, H3 PMo(12)O(40) (HPMo) exhibits the best selectivity towards LA (90 %) with 88 % conversion of glycerol. Loading of HPMo onto a carbon support (HPMo/C) further improves LA productivity resulting in 94 % selectivity at 98 % conversion under optimized reaction conditions. The reaction takes place through the formation of dihydroxyacetone/glyceraldehyde and pyruvaldehyde as intermediates. No leaching of HPMo was observed under the applied reaction conditions and HPMo/C could be recycled 5 times without significant loss of activity.

Fructose production via extraction-assisted isomerization of glucose catalyzed by phosphates

Fructose presents a highly attractive substrate for future biorefineries for production of biofuels as well as bulk and fine chemicals. Starting from cellulose, fructose is available via hydrolysis to glucose followed by isomerization. Despite commercial production of high-fructose corn syrup, efficient strategies for a combined chemo-catalytic isomerization and fructose separation are missing. This contribution describes a three-step approach combining the isomerization of glucose into fructose with recovery of the product. The first step covers isomerization of glucose into fructose using water as a solvent and soluble Na2HPO4 + NaH2PO4 as a catalyst. Na2HPO4 + NaH2PO4 exhibits catalytic activity under mild reaction conditions at pH 7.5. The specific-base-catalyzed isomerization proceeds via the formation of an enediol anion. The yield of fructose obtained using phosphates under batch conditions reaches 30%. The second step relates to recovery of fructose by selective anionic extraction due to complexation with ortho-hydroxymethyl phenylboronic acid (HMPBA). Under optimized conditions, up to 72% of fructose can be extracted from a glucose–fructose mixture with 76% selectivity. Fructose is extracted as a mixture of complexes with HMPBA exhibiting 1-to-1 stoichiometry. Formulae of two complexes were proposed, namely β-fructofuranoside esterified at C2 and C3 positions and an ester of β-fructopyranoside at C1 and C2. After extraction, the aqueous phase containing phosphate and the remaining glucose can be recycled. In the third step, fructose can be back-extracted from the organic phase with an acidic solution. This extraction-assisted isomerization strategy significantly improves the yield of fructose reaching up to 51%.

Catalytic versus stoichiometric reagents as a key concept for Green Chemistry

25 years ago catalysis was highlighted as a main principle of Green Chemistry. Selective catalysis enables an efficient utilisation of resources and the design of benign processes. Waste formation caused by stoichiometric reagents, for instance in reduction or oxidation reactions, can be overcome using suitable catalysts and benign reductants and oxidants, respectively. Solid acidic and basic catalysts prevent prevalent salt formation associated with the use of molecular acids and bases. Catalysts allow us to decrease the activation energy of chemical transformations, enhance the reaction rate, facilitate high selectivity and are crucial to reduce the number of process steps.

Anionic Extraction for Efficient Recovery of Biobased 2,3-Butanediol-A Platform for Bulk and Fine Chemicals

2,3-Butanediol (BDO) presents a promising platform molecule for the synthesis of basic and fine chemicals. Biotechnological production of BDO from renewable resources with living microbes enables high concentrations in the fermentation broth. The recovery of high-boiling BDO from an aqueous fermentation broth presents a subsequent challenge. A method is proposed for BDO isolation based on reversible complexation with phenylboronate in an anionic complex. BDO can be recovered by back-extraction into an acidic solution. The composition of the extracted species was determined by NMR spectroscopy, MS, and GC-MS methods. The conditions of extraction and back-extraction were optimized by using commercial BDO and finally applied to different fermentation broths. Up to 72-93 % BDO can be extracted and up to 80-90 % can be back-extracted under the optimized conditions. Purified bio-BDO was used in the presence of sulfuric acid for the synthesis of methyl ethyl ketone, an established organic solvent and discussed tailor-made biofuel.

Nickel phosphate molecular sieves VSB-5 as heterogeneous catalysts for synthesis of monosaccharides from formaldehyde and dihydroxyacetone

Condensation of dihydroxyacetone with formaldehyde was found to be effectively catalyzed by nickel phosphate molecular sieves (VSB-5 and Fe–VSB-5) in neutral aqueous medium. In the presence of VSB-5 the main products are erythrulose and 3-pentulose, while Fe–VSB-5 favours the formation of only erythrulose.