Hydrolysis of Arabinoxylans From Wheat Bran into Monomeric Sugars Over Heterogeneous Catalysts

The aim of this work is to study the conversion of arabinoxylans from wheat bran into monomeric sugars, namely xylose and arabinose, using RuCl3-based catalysts. Arabinoxylans (AX), which are the major components of wheat bran, can be converted into arabinose and xylose by a hydrolysis process (Fig. 1). These two sugars are very interesting platform chemicals, as they can be transformed into different high added­value products. For example, arabitol and xylitol are produced by hydrogenation reactions of arabinose and xylose, respectively, using ruthenium catalysts. Arabitol and xylitol are considered two of the top value added chemicals to be produced from biomass defined by the U.S. Department of Energy.

Figure 1. Conversion of arabinoxylans from wheat bran to arabinose + xylose
Figure 1. Conversion of arabinoxylans from wheat bran to arabinose + xylose

In the first step, the AX contained in wheat bran are solubilized and partly hydrolyzed into oligomers by pressurized hot water and the acid sites of RuCl3 supported catalysts. 80% of the total AX are obtained using RuCl3/Al-MCM-48. However, only 20% of the total AX solubilized are in monomeric form. Due to this low yield in monomeric sugars, the AX previously solubilized in water are further hydrolyzed into arabinose and xylose in a second step. Hydrolysis of arabinose and xylose oligomers reaches 96% and 94%, respectively, using the same RuCl3 catalysts as in the first step. When no catalyst is used, only a hydrolysis yield of 51% and 6% in arabinose and xylose, respectively, is achieved (Fig. 2).

Figure 2. Effect of RuCl3 catalysts on the AX hydrolysis into monomeric sugars
Figure 2. Effect of RuCl3 catalysts on the AX hydrolysis into monomeric sugars

This study reveals the possibility of an integrated process from real biomass to monomeric sugars using heterogeneous catalysts.

Nuria Sánchez, Esther Alonso

Project: BIOFRAHYNERY CTQ2015-64892-R (MINECO/FEDER) 

Scholarship: FPU14/00812

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