Two-Stage Steam Pretreatment of Willow for Increased Pentose Yield

Abstract

A two-stage procedure for pretreatment of fast-growing willow with steam has been investigated. The first stage was performed at temperatures in the range 180°C to 220°C for times between 6 and 10 minutes while the second stage was performed at 220°C for 10 minutes.

The fibrous material was washed between the two stages to remove the pentosans and thus increase the pentose yield. The pretreatment was assessed in terms of glucose yield and xylose yield in the subsequent enzymatic hydrolysis.

The maximum yields, around 70% for both glucose and xylose, were obtained for a pretreatment temperature of 200°C in the first stage. The major part of the xylose was found in the first rinsing water while almost all the glucose was recovered from the final fibrous material.

The glucose yield was increased to above 80% when wet material (30% ODM) was used in the first stage. This required a modification of the steam pretreatment unit, allowing for condensate removal during steaming. The results are very promising but further investigations are needed to optimize the process.