The Hitac-process (high Temperature Adsorption on Activated Charcoal) New Possibilities in Autohydrolysate Treatment

Water prehydrolysis of wood is an interesting process for the recovery of xylooligosaccharides and derivatives thereof, while at the same time cellulose is preserved to a large extent for subsequent dissolving pulp production. The recovery of value-added products out of autohydrolysates is frequently hindered by extensive lignin precipitation, especially at high temperatures. In this study, a new high temperature adsorption process (HiTAC process) was developed, where lignin is removed directly after the autohydrolysis, which enables further processing of the autohydrolysates. The suitability of activated charcoals as a selective adsorbent for lignin under process relevant conditions (150 and 170 °C) has not been considered up to now, because former experiments showed decreasing efficiency of the adsorption of lignin onto activated charcoals with increasing temperature in the range of 20 – 80 °C. In contrast to these results, we demonstrated that the adsorption of lignin at 170 °C directly after autohydrolysis is even more efficient than after cooling the hydrolysate to room temperature. The formation of lignin precipitation and incrustations can thus be efficiently prevented by the HiTAC process. The carbohydrates in the autohydrolysis liquor remain unaffected over a wide charcoal concentration range and can be further processed to yield valuable products.