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Hydrolysis of oligosaccharides over solid acid catalysts: a review

Publication . Vilcocq, Léa; Castilho, Paula C.; Carvalheiro, Florbela; Duarte, Luís C.

Mild fractionation/pretreatment processes are becoming the most preferred choices for biomass processing within the biorefinery framework. To further explore their advantages, new developments are needed, especially to increase the extent of the hydrolysis of poly- and oligosaccharides. A possible way forward is the use of solid acid catalysts that may overcome many current drawbacks of other common methods. In this Review, the advantages and limitations of the use of heterogeneous catalysis for the main groups of solid acid catalysts (zeolites, resins, carbon materials, clays, silicas, and other oxides) and their relation to the hydrolysis of model soluble disaccharides and soluble poly- and oligosaccharides are presented and discussed. Special attention is given to the hydrolysis of hemicelluloses and hemicellulose-derived saccharides into monosaccharides, the impact on process performance of potential catalyst poisons originating from biomass and biomass hydrolysates (e.g., proteins, mineral ions, etc.). The data clearly point out the need for studying hemicelluloses in natura rather than in model compound solutions that do not retain the relevant factors influencing process performance. Furthermore, the desirable traits that solid acid catalysts must possess for the efficient hemicellulose hydrolysis are also presented and discussed with regard to the design of new catalysts.

2014Journal article

Open access

Acid-modified clays as green catalysts for the hydrolysis of hemicellulosic oligosaccharides

Publication . Vilcocq, Léa; Spínola, Vítor; Moniz, Patrícia; Duarte, Luís C.; Carvalheiro, Florbela; Fernandes, César; Castilho, Paula

The hydrolysis of hemicellulosic oligosaccharides (OS) was investigated using acid-activated clays (prepared from natural Porto Santo montmorillonite clay) as catalysts. Acid activation was performed in HCl solution or with aluminium exchange. The clay catalysts were characterized by XRD, N2 adsorption isotherms, CEC, FTIR, titration of acid sites in water and adsorption of sugars and disaccharides. They were tested for the hydrolysis of a model compound, maltose, and of OS-rich liquor from rice straw fractionation. The HCl-activated clays were the most efficient catalysts for maltose hydrolysis. It was demonstrated that the hydrolysis of OS into monomer sugars over a clay catalyst is technically feasible and that this reaction leads to the selective removal of glucose, arabinose and acetic acid side groups from the OS structure, thus yielding simpler xylo-oligosaccharide chains. Furthermore, no significant conversion of monomer sugars into furans was observed.

2015Journal article

Open access

Autohydrolysis of Annona cherimola Mill. seeds: optimization, modeling and products characterization

Publication . Branco, P. C.; Dionísio, A.M.; Torrado, I.; Carvalheiro, F.; Castilho, P. C.; Duarte, L.C.

Annona cherimola Mill. seeds are a residue of the industrial processing of this fruit, for which, presently, there is no industrial application. They have a considerable amount of oil, which can be converted into biodiesel, but the remaining lignocellulosic fraction still needs relevant added-value valorization routes. Inthis work,the selectivehemicelluloses removal by autohydrolysis was optimizedaiming tomaximize the yield of oligosaccharides with potential applications in food, pharmaceutical and cosmetic industries. A maximum of 10.4 g L−1 of oligosaccharides was obtained, for a severity factor of 3.6, where 74.5% of the original hemicellulose was solubilized. The process kinetics is presented, modeled (based on the Arrhenius equation) and its scale-up is dis cussed. The hydrolyzate shelf-life was evaluated and the produced oligosaccharides are stable at room temperature for, at least, 3 weeks. Furthermore, all oligosaccharides are also stable at 100 ◦C for 1 h, in pH values between 1 and 11, enabling their industrial processing, and at 37 ◦C for 3 h, in pH values between 1 and 3, thus indicating its potential classification as non-digestible oligosaccharides. The remaining cel lulose enriched solids presented an increased enzymatic digestibility (as a function of the autohydrolysis severity) that assures its efficient use in subsequent processes (e.g., bioethanol production). The upgrade route developed in this work in combination to the previously reported use of A. cherimola seed oil for biodiesel production can lead to an integrated zero-waste valorization strategy within the biorefinery framework.

2015Journal article

Open access