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Optimization procedures such as experimental designs (DOE) improve pretreatment efficiency, and chemical characterization of the starting material becomes necessary to assess the efficiency. Hydrothermal pretreatment (HTP), also called auto-hydrolysis (AH), is one of the most economically interesting pretreatments since only water work as reactant. AH pretreatment optimization can reach a liquor rich in monosaccharide units at the same time that a low content of toxic compounds to biological processes (i.e., 2-furfuraldefdo (FUR) e 5-hidroximetil-2-furfuraldefdo (HMF). Early, AH pretreatment variables temperature (T), time (t), solid-liquid ratio (SLR) and stirring (RPM) were studied by a 24 factorial design. A new HPLC analytical method for quantifying acids that can be formed during AH (i.e., formic, acetic, glucuronic and levulinic acids) has been developed using Bio-Rad Aminex HPX-37H column in a Shimadzu Prominence HPLC. In general, the most significant factors were T and t; higher levels of T improved hemicellulose depolymerization whereas lower levels of t disfavoured pentoses degradation to FUR. At 220 °C, 60 min, 20 % of SCB and 60 rpm it was possible to achieve a yield of 109.84 g kg-1 of pentoses (i.e., xylose and arabinose) with only 14.42 g kg-1 of FUR. Under these same conditions, the acid content in the liquor was 15.1 g kg-1, 12.2 g kg-1, 39.8 g kg-1 and 55.5 g kg-1 for glucuronic, formic, acetic and levulinic acids, respectively. [ABSTRACT FROM AUTHOR]

The reuse study of niobium phosphate catalyst (NbOPO4.nH2O, abbreviated as NbP) in furfural production from sugarcane bagasse (SCB) in an aqueous medium is the aim of this project. The heterogeneous NbP catalyst was exploited to hydrolize the SCB biopolymers and dehydrate the major released carbohydrate, i.e., xylose, into furfural. The compounds were separated and quantified by high-performance liquid chromatography (HPLC). At the end of each reaction, the catalyst was separated from the SBA by sieving and pre-treated with water (A), 5 ml of acetone (B), 10 ml of acetone (C) or calcined at 550 °C (D). After pretreatment, the catalyst was reused for another cycle. An analysis of variance was performed to compare the difference in productivity between cycles statistically. The catalyst was analyzed for its morphology by SEM images and XEDS. For the release of xylose, at a significance level of 0.01, the pretreatments A, B, and D in the reactions at 150 °C were efficient to reactivate the catalyst's active sites. Cycles 1 and 2 produced about 15 g kg-1 xylose at 110 °C and 80 g kg-1 furfural at 150 °C. The results with pretreatment A at 150 °C are promising from an economic and environmental point of view since the other pretreatments either use a toxic, more costly solvent or consume electricity. [ABSTRACT FROM AUTHOR]

In this work, we report a selective and straightforward process to synthesize glycerol carbonate from urea and glycerol using a simple but commercially unavailable catalyst (Sn(OH)2). This catalyst was generated in situ from the reaction of Sn(ii) halides and urea during the glycerol carbonatation process. Effects of main reaction parameters (i.e., temperature, molar ratio of urea to glycerol, catalyst concentration) were investigated. Different tin halides were assessed as catalytic precursors, with SnCl2 being the most efficient. We found that Sn(OH)2-catalyzed glycerol carbonation reactions with urea achieved high conversion and selectivity (ca. 87 and 85%, respectively). The samples of Sn(OH)2 generated in situ or previously synthesized were equally active and selective catalysts toward glycerol carbonate were successfully reutilized without loss activity. This is a very attractive route based on two inexpensive and readily available feedstocks in a chemical cycle that, overall, results in the chemical fixation of carbon dioxide and, concomitantly, adds value to glycerol, a biodiesel byproduct. [ABSTRACT FROM AUTHOR]