Impact of prefiltration on membrane performance during isolation of hemicelluloses extracted from wheat bran

Hemicelluloses extracted from wheat bran have to be separated from impurities in order to obtain a valuable product at high concentration and purity. A previous investigation showed that separation by ultrafiltration is possible, but the flux was low due to the high viscosity of the solution and the presence of gel-forming substances in the solution. In this investigation the influence of prefiltration on solution viscosity and ultrafiltration performance was investigated. The viscosity of the hemicellulose solution after extraction was considerably reduced with both prefiltration methods tested, leading to a substantial increase in flux during ultrafiltration. The highest flux achieved without pretreatment was about 75 l/m2 h, and was increased to 225 and 440 l/m2 h after dead-end filtration and microfiltration, respectively. However, the loss of hemicelluloses was considerable during microfiltration, but <5% during dead-end filtration. After prefiltration by dead-end filtration, hemicelluloses could be successfully concentrated and purified by ultrafiltration. Eighty percent of the initial volume was removed during concentration at an average flux of 155 l/m2 h. At the same time, the concentration and purity of the hemicelluloses increased from 7.6 g/l and 15% to 31.6 g/l and 31%, respectively. The results obtained in this investigation indicate that dead-end filtration could be a useful form of pretreatment before ultrafiltration when recovering hemicelluloses extracted from wheat bran.