Ultrafiltration of Beechwood Hydrolysate for Concentrating Hemicellulose Sugars and Removal of Lignin : Parameter Estimation Using Statistical Methods and Multiobjective Optimization

Hemicellulose sugars have the potential to replace fossil-based materials in various high-value-added products. Ultrafiltration (UF) of beechwood hydrolysate for concentrating hemicellulose sugars with simultaneous removal of lignin was investigated. For the estimation of process parameters, statistical methods and multiobjective optimization were used. Atomic force microscopy and pure water flux measurements were applied to characterize the UF membranes UA60 and UH004. By means of response surface methodology, the multidimensional correlation of the parameters transmembrane pressure (TMP), temperature, and pH value with the performance parameters permeate flux, hemicellulose sugar retention, and lignin retention was determined. The response models were statistically validated, showing high values for the coefficient of determination (R2 > 0.92). Using the model equations, multiobjective optimization by the determination of Pareto frontiers was applied to identify the optimal conditions for high permeate flux and hemicellulose sugar retention as well as low lignin retention. The estimated optimum parameters for UA60 and UH004 were found to be TMPs of 0.98 and 1.0 MPa, temperature of 55 °C, and pH values of 2.5 and 4.1, respectively. Under these conditions, the permeate fluxes were 49.2 and 45.2 L/(m2 h), hemicellulose sugar retentions 84.7 and 70.9%, and lignin retentions 40.9 and 20.7%, respectively.