Process options for the recovery of a pentosan-enriched fraction from wheat-based bioethanol thin stillage

Stillage, the main residue from cereal-based bioethanol production, offers a great potential for the recovery of pentosan-type carbohydrates. Therefore, potential process options for the recovery of pentosans from bioethanol thin stillage are investigated and their basic feasibility is demonstrated on a laboratory scale.

The main result of this work is the development of a three-stage process for pentosan recovery, including solid-liquid separation, pentosan solubilisation and purification. The pentosan content of the thin stillage used here was determined to be about 14% related to dry matter (DM). By means of solid-liquid separation, these pentosans accumulate in the liquid phase (up to 80%), while the remainder (about 20%) is found in the solid phase. Solubilisation of these insoluble pentosans was achieved by using either a hydrothermal, an alkaline or an enzymatic treatment. Here, the results indicate a maximum solubilisation yield of 90% with a hydrothermal treatment using liquid hot water at 180 °C. Ultrafiltration and precipitation are investigated for purification. The most promising process option in this study is solid-liquid separation followed by ultrafiltration. In this case, the total pentosan yield is assessed to be about 48% (based on thin stillage) with a final pentosan concentration of about 30%DM.