Recovery of Oligosaccharides from Prehydrolysis Liquors of Poplar by Microfiltration/Ultrafiltration Membranes and Anion Exchange Resin

The recovery of oligosaccharides (OS) from prehydrolysis liquor (PHL) is of great economic significance, along with having environmental benefits. In the present study, a novel and environmentally friendly process using microfiltration/ultrafiltration membranes (MM/UM) and anion exchange resin was investigated to separate and purify OS from the PHL of poplar. The results showed that the addition of NaOH prior to filtration improved the filtration capacity and reduced fouling for MM (pore size 0.45 mu m), and the removal rate of lignin was as high as 31%. On this basis, 36.8% of the remaining lignin was further removed by an ultrafiltration process using UM, while 39% of the remaining OS was recovered by ethanol or acid precipitation. The crude OS in the filtrate was then purified with anion exchange resin, and its purity was 96.4%. The current process recovered a total of 41.7% of the OS in the PHL, and the obtained OS exhibited relatively stable molecular weight, which was characterized by gel permeation chromatography (GPC).