Increasing efficiency of membrane separation processes

In the food industry, particularly the dairy industry, separation of components is crucial in the value addition process and in provision of proper nutrition to the society. Separation driven processes consume energy and according to the energy consumption data of the Netherlands this amounts to 90PJ. There is therefore a need to reduce this energy to at least 50PJ. This is possible by using membrane technology in separation of dairy protein. Membranes consume less energy compared to other separation processes such as distillation, are environmentally friendly, have scalability advantages and are economically friendly. In this thesis, we evaluate the efficiency of the microfiltration membranes in the separation of casein from serum protein present in bovine skim milk. This separation is possible through selection of membranes with large enough pores to allow serum protein to pass through while retaining casein micelles. Additionally, the separation of proteins is done under low temperature to ensure process stability. Based on temperature conditions and pressure changes, the efficiency of membrane separation is evaluated. This is done by splitting the process into three levels: membrane surface, membrane module and overall filtration process. At the membrane surface level, we describe the role of casein micelles during filtration of skim milk using a simple geometric model. Due to the size of the casein micelles, they are rejected by the membrane and accumulate on the membrane surface forming a deposit layer. The model considers the interstitial pores in between the micelles as the primary conduit for the serum proteins to pass through the deposit layer, towards the membrane. Further increase of the transmembrane pressure causes compression of these micelles, reducing the interstitial pore sizes. This reduction of the pore size increases the filtration resistance further increasing the rejection of serum proteins. The model is validated with experiments using different membrane pore sizes and different temperature conditions. In the module level, we evaluated different membrane configurations namely hollow fiber and spiral wound membranes. When considering key performance indicators such as flux, transmission and yield. Hollow fiber membranes have higher fluxes while transmission and yield of both configurations are comparable. Based on this data we sought to further improve further the separation process by including concentration and diafiltration. We concentrated the proteins in skim milk to known concentrations. Higher concentrations resulted in higher yields. Diafiltration was incorporated to further wash out the serum protein remaining in the concentrated milk. Relations are established between the casein and serum protein retentate concentrations that describe how the retentate concentrations are related to flux and rejections, which are then used to conceptually design and optimize large-scale membrane process systems with both spiral wound and hollow fiber modules. The designs optimized on the required membrane area and required amount of diafiltration water while establishing the required yields and purities. We found that hollow fiber membranes require less membrane area due to their higher fluxes and spiral wound membranes require less diafiltration water. Hybrid systems which include hollow fiber and spiral wound membranes are possible.