Selective arabinose extraction from Pinus sp sawdust by two-step soft acid hydrolysis

Acid hydrolysis of Pinus sp. sawdust is optimized in this work in order to selectively recover arabinose from the hemicellulose fraction by an environmental-friendly process (reactions at atmospheric pressure and mild conditions and using dilute HCl as catalyst). The influence of temperature, HCl concentration and reaction time was studied in the first experiments considering one step hydrolysis. One step hydrolysis was studied at different conditions, being the best results obtained at 65 C-omicron for 18 h with 3% of HCl, with more than 3.8 g/L of arabinose in the liquid phase. This value corresponds to more than 47.5% of recovery of the arabinose present in the original sawdust and a selectivity of a 52% in the liquid phase (hydrolysis of other hemicellulosic sugars). In a second approach, a two steps process was considered in order to maximize the arabinose recovery. The optimum results were obtained combining a first cycle at 65 C-omicron with a second one at 80 C-omicron. More than 54% of the initial arabinose was recovered in the liquid phase as monomers. This percentage increases to 100% if the oligomers are also considering (no arabinose detected in the solid phase after the treatment). At these conditions, more than 56% of the global hemicellulose sugars were removed from the solid phase, without having a relevant degradation of glucose (pentose selectivity in liquid phase is higher than 88%, corresponding the resto mainly to hemicellulosic glucose).