Effects of pH Control with Acetic Acid/Sodium Acetate Buffer on the Hot-water Extraction of Polar Wood

摘要

The excessive decline of pH during hot-water extraction of wood chips has become the obstacle and bottleneck for the pre-extraction and high value utilization of hemicellulose.Maintaining appropriate hydronium ion in the hot-water extraction system is very important to make hemicellulose dissolve into the pre-extraction liquor as far as possible in the form of oligosaccharides and to reduce the production of the degradated by-products.In this paper,the poplar wood chips were hot-water extracted using acetic acid/sodium acetate buffer as the reagent under the condition of the maximum temperature(Tmax)of 180 oC,the solid-to-liquid ratio of 1:6,and the isothermal treatment time of 60 min to investigate the effect of pH on the extraction performance of the chemical constituents.The pH value of the buffer was controlled by varying the relative content of sodium acetate and acetic acid in the buffer system.The results showed that the buffer system can promote the dissolution of hemicellulose,obtaining more oligosaccharide and monosaccharide,and also can inhibit the excessive degradation of the monosaccharide.When extracting the poplar in the buffer system of pH 3.6,the yield of oligosaccharide was the highest,while the hydrolysis of acetyl groups was decreased by 32％and the content of furfural was reduced by 30％compared to the plain water system.Moreover,the removal of acid soluble lignin in the buffer system was slightly higher than that of the plain water system.