(401j) Recovery of Monosaccharides from Dilute Acid Corncob Hydrolyzate based on Nanofiltration Technology?Modeling and Optimization

Lignocellulosic biomass such as woody materials and agricultural residues is an abundant, environmentally feasible, easily available, and renewable feedstock for the biofuel production. However, utilization of such biomass requires a pre-treatment process, through which polymeric carbohydrates can be decomposed to monosaccharide. Dilute acid pretreatment is the most commonly used method . However, this way produces inhibitors like the furfurals, hydroxymethyl furfural (HMF), phenolic compounds and several other acids such as acetic acid and formic acid . It has been widely conformed that the presence of these by-products during fermentation of sugars may seriously impact the productivity of bio-based products and the growth of bacterial strain. For example, phenolics are lethal to Clostridium which is widely used to produce butanol and butyric acid even at low concentrations. So it is important to remove these inhibitors from hydrolysates.

Nanofiltration is a high-efficiency technology to remove inhibitors and recover monosaccharides from the dilute acid lignocellulose hydrolyzates. In this study, the effect of feed pH, permeate flux and Na₂SO₄ concentration on the rejection of monosaccharides and inhibitors was firstly investigated. The results showed that the separation performance of carboxylic acids and furans from monosaccharides was optimal at pH 3. All the rejection of carboxylic acids and furans decreased with increasing Na₂SO₄ concentration, especially for carboxylic acids. Subsequently, donnan steric pore flow model coupled with mass balance (DSPM-MS model) was successfully applied to predict the rejection of solutes at different permeate flux. Based on the DSPM-MS model a parallel multi-objective optimization strategy was developed to select a reasonable permeate flux j_v and operating time t, in which maximum total inhibitor remove efficiency Prinhibitor, maximum recovery rate of monosaccharides Ysugar and minimum water consumption EC were set as objective functions. The results showed that in the case of maximum Ysugar, more monosaccharides were recovered and less water was consumed as well. The optimal operating condition was consequently verified with the practical hydrolysate solutions. It had consumed about 35 min and 13L water to remove 95% inhibitors, meanwhile, 93.55% glucose, 90.75% xylose and 90.53% arabinose were recovered.In the end of this work, a batch column equipped with strong acid cation-exchange resins Sa-2 were used to recover monosaccharides from the hydrolysate. Using water as eluent, 95.37% of sulfuric acid and 94.87% of monosaccharides was recovered. This work demonstrated that nanofiltration combined with electrolyte exclusion chromatography could be a potential integrated process to recover monosaccharides and inorganic acids in the practical dilute acid corncob hydrolyzate.