High-temperature pH measuring during hot-water extraction of hemicelluloses from wood

•pH is important during hot-water extraction of hemicelluloses from wood.•An in-line high-temperature pH measuring system for wood extractions was developed.•Phthalate and phosphate buffers at 160, 170, and 180 °C were used for calibration.•Water with different ion concentrations wereused to study the system response.•In-line pH during wood extraction was 0.35 pH units higher than at room temperature.

A high-temperature pH measuring system was developed, calibrated, and validated for measuring pH during hot-water extraction of hemicelluloses from wood. The aim was to measure in-line pH during extraction in order to control the extraction pH. An yttria-stabilized Zr/ZrO2 electrode was used for measuring the potential. Phthalate and phosphate buffers were used to calibrate the system at 160, 170, and 180 °C. Also, different buffer concentrations were tested for stability. Tap water and different salt solutions were tested to investigate the system response to pure water and water solutions. Calibration curves were acquired from the calibration results and Nernst equation was used to calculate the in-line pH during wood extractions. The setup showed stable and reliable potential readings during both calibration tests and wood extractions. The in-line pH was found to be 0.35 pH units higher than when measured at room temperature with a conventional pH meter.