Separation And Purfication Of Xylo-oligosaccharide From The Hydrolysate Of Steam-exploded Wheat Straw By Xylanase Using Membrane Technology

Xylo-oligosaccharides (XOs) are new functional oligosacchrides with a degree of polymerization (DP) above 2 and below 7 in which xylobiose is the main effective component. XOs have improving the effects of intestinal flora (stimulation of bifidobacterial). In this study, the flux model, recovery, XOs separation by ceramic microfiltration (MF) membrane and separation performence and purfication of XOs by nanofiltration (NF) membrane were investigated.The equations of membrane fouling resistance and flux model were established based on the experimental data. The flux recovery technology and cleaning formulation of MF were obtained. Separation performence models of NF were built and 95 type XOs produce was obtain by NF membrane technology.To understand the absorption and deposition of fiber, protein and lignin in hydrolysate of steam-exploded wheat straw by xylanase on ceramic membrane surface and the influences on microfiltration flux, the equations of deposition resistance and absorption resistance were established based on the experimental data, and the correlation coefficient between the linear model predicted values and experiment results of deposition resistance was 0.9914. Meanwhile, three kinds of nonlinear absorption resistance model, which were based on saturation model, modificatory pearl growth model and pearl growth model, were established. The correlation coefficient between these nonlinear models predicted values and experiment results of absorption resistance were 0.9931, 0.9980 and 0.9982,respectively. Based on these results, differential equation model of flux was established, the correlation coefficient between predicted values and experiment results of flux was 0.9963, and the correlation coefficient between predicted values and reduplicate results was 0.9838. The results showed that the models'simulation data were good agreement with the experimental data of flux decrement.The separation performance, flux, retention and ratio of concentration polarization of an aqueous solution of XOs by a NF membrane, which was thin-film composite (TFC) HDS-12-2540 supplied by HyfluxTM Co,. Ltd. and of which the molecular weight cut-offs (MWCO) 250 Da, were investigated. The predicted permeate flux based on the irreversible thermodynamic model was significant, and the correlation coefficient between experimental data and simulative data was up to 0.9928. Based on the Speigler–Kedem(SK) equation, concentration polarization model and genetic algorithms program, the observed retention model has been built to significantly simulate rejection of arabinose and xylose, and the correlation coefficient were 0.9695 (arabinose), 0.9865 (xylose) and 0.8268 (xylobiose) respectively. At the concentrations during the experiment, the higher the trans-membrane pressure (TMP) was, the higher the flux, and the flux declines as a function of the concentrations at fixed TMP. The relation between Lp and Cf was linear. The hydraulic permeability Lp is decreased as a function of increasing feed, and can be accounted for by the nonlinear increment of dynamic viscosity as a function of increasing feed. The rejections of arabinose, xylose, xylobiose and xylotriose increase as a function of TMP at the fixed feed concentrations, and the retentions decreased as a function of feed concentrations at fixed TMP.Furthermore, the reflection coefficients,σ(0.97, xylobiose)>σ(0.89, arabinose)>σ(0.78, xylose), the solute permeability, Ps (0.21 L·m-2·h-1, xylobiose) λ(0.85, arabinose)>λ(0.76, xylose) were consistent with experimental projections. The dipole moment of xylose is more than that of arabinose, and the difference of molecular structure and dipole moment may explain the difference of the retentions.Based on those above mentioned separation perfromence models of NF, the mass balance differential equations were built to predict dilfiltration and concentration resluts. The model prediction values of flux and concentrations of arabinose, xylose and xylobiose were good agreement with experimental values. When trans-membrane pressure was set to 26.2 bar, concentration of XOs srupy was 10.2 g/100g, the XOs content of the result solution reached to 93.83% by model predicted and 96.10 % (XOs/ total saccharide) by HPLC result from 83.28 % after the pure water was added 3.73 times volumes as many as the feed volumes.