Modeling transport phenomena with COMSOL Multiphysics - Adsorptive membrane fouling in lignocellulosic biorefineries and lessons learned from it

Abstract: The separation of hemicelluloses, like glactoglucomannans, from lignocellulosic process streams is an important step in building profitable lignocellulosic biorefineries. The most common method for the separation is membrane filtration, however, it has the draw-back of being sensitive to membrane fouling. To better understand the fouling process, it is desirable to be able to model the adsorption of hemicelluloses onto the membrane surface, since adsorption is a contributing mechanism in fouling. In this project a model was developed in COMSOL Multiphysics®v.5.3. to simulate the adsorption of glucose, dextran and GGM as model compounds onto a model membrane surface of polysulfone and one of gold, respectively. The model in COMSOL considered bulk fluid dynamics and adsorption kinetics. The adsorption kinetics was investigated using Quartz crystal microbalance with dissipation monitoring (QCM-D). Glucose and dextran had too weak adsorption kinetics to develop a suitable adsorption model. The adsorption of GGM was best described with pseudo-second-order model, compared with a pseudo-first-order model and the Langmuir adsorption model. The pseudo-second-order model was unsuccessfully integrated with the COMSOL model as it lacked a direct connection to the bulk concentration. A reference model based on literature data for Langmuir kinetics failed to produce results comparable with the literature data. Further investigations into the adsorption kinetics for adsorption of hemicelluloses are needed to build a computer model for membrane fouling. These investigations need to consider the validity of the adsorption kinetic models applied as well as the underlying assumptions of the experimental methods.