In-line high-temperature pH control during hot-water extraction of wood

An in-line pH control system for hot-water extraction of wood was developed and tested for optimalextraction of high-molar-mass hemicelluloses from spruce wood. Automated alkali addition was achievedby combining a controller and HPLC pump with a solid ZrO2-based high-temperature and high-pressurepH electrode and a high-temperature and high-pressure Ag/AgCl reference electrode. Three different setpoints were tested; 600 mV, 575 mV and 550 mV corresponding to a pH at 170°C of 4.3, 4.6, and 4.85,respectively. An extraction with no pH control was conducted for reference. The extracts were analyzedfor total dissolved solids, non-cellulosic carbohydrates, monomeric sugars, average weight molar massof the hemicelluloses and free acetic acid. The results show that higher extraction pH increases the molarmass but decreases the total yield of dissolved hemicelluloses and also inhibit sugar monomer formation.