Andersson Alexandra, Persson Tobias, Zacchi Guido, Stålbrand Henrik, Jönsson Ann-Sofi
Department of Biochemistry, Lund University, P.O. Box 124, SE-221 00, Lund, Sweden.
Appl Biochem Biotechnol. 2007 Apr;137-140(1-12):971-83. doi: 10.1007/s12010-007-9112-9.
Hemicelluloses constitute one of the most abundant renewable resources on earth. To increase their utilization, the isolation of hemicelluloses from industrial biomass side-streams would be beneficial. A method was investigated to isolate hemicelluloses from process water from a thermomechanical pulp mill. The method consists of three steps: removal of solids by microfiltration, preconcentration of the hemicelluloses by ultrafiltration, and purification by either size-exclusion chromatography (SEC) or diafiltration. The purpose of the final purification step is to separate hemicelluloses from small oligosaccharides, monosaccharides, and salts. The ratio between galactose, glucose, and mannose in oligo- and polysaccharides after preconcentration was 0.8:1:2.8, which is similar to that found in galactoglucomannan. Continuous diafiltration was performed using a composite fluoro polymer membrane with cutoff of 1000 Da. After diafiltration with four diavolumes the purity of the hemicelluloses was 77% (gram oligo- and polysaccharides/gram total dissolved solids) and the recovery was 87%. Purification by SEC was performed with 5, 20, and 40% sample loadings, respectively and a flow rate of 12 or 25 mL/min (9 or 19 cm/h). The purity of hemicelluloses after SEC was approx 82%, and the recovery was above 99%. The optimal sample load and flow rate were 20% and 25 mL/min, respectively. The process water from thermomechanical pulping of spruce is inexpensive. Thus, the recovery of hemicelluloses is not of main importance. If the purity of 77%, obtained with diafiltration, is sufficient for the utilization of the hemicelluloses, diafiltration probably offers a less expensive alternative in this application.
半纤维素是地球上最丰富的可再生资源之一。为了提高其利用率，从工业生物质侧流中分离半纤维素将是有益的。研究了一种从热机械制浆厂的工艺水中分离半纤维素的方法。该方法包括三个步骤：通过微滤去除固体，通过超滤对半纤维素进行预浓缩，以及通过尺寸排阻色谱法（SEC）或渗滤进行纯化。最后纯化步骤的目的是将半纤维素与小寡糖、单糖和盐分离。预浓缩后寡糖和多糖中半乳糖、葡萄糖和甘露糖的比例为0.8:1:2.8，这与半乳甘露聚糖中的比例相似。使用截留分子量为1000 Da的复合氟聚合物膜进行连续渗滤。用四个透析体积进行渗滤后，半纤维素的纯度为77%（克寡糖和多糖/克总溶解固体），回收率为87%。分别以5%、20%和40%的进样量以及12或25 mL/min（9或19 cm/h）的流速通过SEC进行纯化。SEC后半纤维素的纯度约为82%，回收率高于99%。最佳进样量和流速分别为20%和25 mL/min。云杉热机械制浆产生的工艺水价格低廉。因此，半纤维素的回收不是主要重点。如果渗滤获得的77%的纯度足以满足半纤维素的利用需求，那么在该应用中渗滤可能提供一种成本较低的选择。
