Regeneration of Spent Activated Charcoals Used for Lignin Removal from Prehydrolysis-Kraft Prehydrolyzates

Abstract

Lignin in prehydrolysis-kraft prehydrolyzates leads to incrustations and impedes the utilization of the hemicellulosic fraction as a product. The adsorption of the lignin on activated charcoal directly after prehydrolysis at prehydrolysis temperatures prevents the formation of these incrustations efficiently. However, reutilization of the charcoal is necessary to ensure an economic process. To develop adequate recycling strategies for the spent activated charcoal, solvent extraction and thermal regeneration were investigated with respect to the recycling performance of the regenerated charcoals. Solvent extraction of the spent charcoals showed only limited efficiency, while the adsorption capacity of the activated charcoal was quantitatively restored by a thermal treatment at 950 °C. This was demonstrated by a pore size distribution and a lignin adsorption behavior of the recycled activated charcoal comparable to that of a fresh one which allows the reutilization of the charcoal in the adsorption process.