Adsorption of lignin and wood extractives on activated carbon (AC) at high temperature prior to ultrafiltration (UF) was shown to significantly improve filtration capacity about 1.5 fold in recovery of hemicelluloses from wood extracts. Furthermore, adsorption pretreatment enabled the production of purer concentrated high-molecular-mass hemicellulose fractions. For instance, purity of the produced concentrated spruce fraction was more than 20% units higher when the AC treatment was used prior to UF compared to the fraction produced without the pretreatment. AC adsorbed lignin and wood extractives. In addition, AC treatment caused some hemicellulose losses. The results indicated that at least part of the hemicelluloses was adsorbed onto the AC in ligninhemicellulose complexes. It seemed that also xylans containing 4-O-Me-glucuronic acid might have been removed by adsorption. However, AC was nonetheless clearly selective to lignin over hemicelluloses. Adsorption on activated carbon removed from the wood extract more high-molecular-mass compounds than smaller ones. The decrease in molecular mass was compensated to some extent in UF, since concentration filtration increased molecular mass significantly.
- lignin removal
- membrane filtration