Education

Courses

The Membrane Surface Science group participates actively in the teaching of the Chemical Engineering curriculum, both in the BSc and the MSc phase. The following are the courses offered and their details:

BSc and MSc projects

Many different BSc and MSc project are possible within the MSuS group. Projects can involve making or coating membranes (Material Science), but can also be more focused on characterizing membranes and optimizing their performance for a specific application (Process Technology). For a most up-to-date overview of possible projects please contact w.m.devos@utwente.nl.

Some examples of possible projects are given below:

1. RESPONSIVE MEMBRANES BY AQUEOUS PHASE SEPARATION

Joshua Willott  (1), Wiebe M. de Vos (1)

(1) Membrane Surface Science (MSuS)

Project Outline

Membranes are vitally important in the production of safe drinking water, the processing of food, dairy and beverages, CO2 capture, and the treatment of human waste streams. As a consequence, membranes are produced on mass each year allowing for sales worth many billions of Euros. However, their fabrication nearly always makes use of harmful and environmentally unfriendly aprotic solvents such as N-methyl-4-pyrrolidone (NMP). This project will investigate a highly novel approach allowing the production of sustainable, advanced membranes without the need for toxic organic solvents. Here, stimuli-responsive polyelectrolytes will be used as the basis for the preparation of membranes where water is the only solvent required. The major focus in this investigation will be on controlling the pH and salt responsive properties of the fabricated membranes by tuning the crosslink density inside the membrane. Crosslink density can be adjusted by varying the type and amount of crosslinking agent as well as the crosslinking reaction time.

By joining MSuS you have the opportunity to become a part of a larger team of collaborative researchers all working towards the production and characterization of new and sustainable membranes.

Project Description

In this project, you work to tune the stimuli-responsive permeability of membranes made from weak polyelectrolytes using aqueous phase separation (APS) methodology (see Figure 1). Weak polyelectrolytes are composed of monomers that are ionizable; meaning that their charge and hence water solubility varies with environmental pH and ionic strength. This behavior can be exploited to prepare membranes, where rapidly changing the environmental pH/ionic strength results in precipitation of the polymer into membrane-like structures. By controlling the kinetics of the precipitation process many diverse internal membrane structures can be formed. Several crosslinking routes exist to improve the mechanical strength of the membranes. Moreover, for these class of polymers, the crosslinking reaction allows for control over the stimuli-responsive behavior of the membranes. Internal membrane structure will be scrutinized using scanning electron microscopy (SEM), while membrane performance and stimuli-response will be studied through solvent permeability measurements.

Figure 1. Schematic representation of membrane formation via aqueous phase separation using a weak polyelectrolyte.

2. EXPLORATION OF SUITABLE MEMBRANE STRUCTURES FOR GREEN-ENERGY WATER PURIFICATION

Mehrdad Mohammadifakhr (1)

(1) Advanced Membranes for Aqueous Applications (AMAA)

Project Outline and description

In this project, we have a close cooperation with a membrane company in Denmark (Aquaporin A/S) to fabricate forward osmosis (FO) membranes. Membrane technology is the most applied method for water purification. Recently increasing attention is being paid to the FO technology. FO technology is a green technique which can solve unique challenges where other techniques such as RO, NF and UF struggle [1]. Fabrication of biomimetic membranes based on aquaporins has attracted a lot of attention in recent years. Aquaporins are cell proteins which act as small water channels to allow fast transport of only water molecules, meanwhile blocking all other types of molecules [2]. FO membranes consist of a thin, selective separating layer on top of a porous support. Both layers are important for the properties of the membrane such as its water flux, reverse salt flux, and salt rejection. So far, RO-type supports have been mostly used for FO membranes which however result in high internal concentration polarization (ICP) and low water flux due to their dense and thick layer. These pressure resistant supports are unnecessary due to the low pressure applied in FO. Therefore, it seems essential to fabricate an ideal and custom-made support for FO. However, there is an uncertainty about the suitable support structure in literature. Some claim that a finger-like is the best structure while in others sponge-like structures are assumed as the most suitable [Figure 1].

The degree of ICP is determined by its S-factor (eq.1), in which A (water permeation) and B (salt permeation) are measured in a low-pressure RO experiment, including the water flux (Jw) as determined in an FO experiment. In order to measure the S-factor, application of the active layer is pre-requisite. The application of the active layer is performed by so-called interfacial polymerization technique.

Hollow fibers are the best choice for FO supports because of high control on their structure in the fabrication step. Hollow fiber supports are fabricated using a solution containing base-polymer (dissolved in solvent) (dope solution) and a solution of non-solvent (bore solution). These two solutions are used in a spinning machine where they get in contact with each to form the hollow fiber.

Trying different polymers as base-polymer and changing the polymer-to-solvent ratio would lead to different recipes where different morphologies can be obtained (finger-like and sponge-like structures), while the surface properties remain the same. After application of an active layer, these membranes will be tested for their FO performance to obtain the S-factor. Finding the most suitable morphology for FO membranes is the outcome of this project.

For more information, please contact:

Mehrdad Mohammadifakhr (m.mohammadifakhr@utwente.nl): Advanced Membranes for Aqueous Applications (AMAA), Meander 323

References:

[1] Tzahi Y. Cath, Amy E. Childress, Menachem Elimelech; Forward osmosis: Principles, applications, and recent developments; Journal of Membrane Science 281 (2006) 70–87

[2] Lingling Xia, Mads Friis Andersen, Claus Hélix-Nielsen, and Jeffrey R. McCutcheon; Novel Commercial Aquaporin Flat-Sheet Membrane for Forward Osmosis; Ind. Eng. Chem. Res. 2017, 56, 11919-11925


3. SIMULTANEOUS COATING DURING HOLLOW FIBER SUPPORT FABRICATION- AN ATTEMPT FOR FAST FABRICATION

Mehrdad Mohammadifakhr (1)

(1) Advanced Membranes for Aqueous Applications (AMAA)

Project Outline and description

In this project, we are cooperating with a membrane company in Denmark (Aquaporin A/S) to fabricate forward osmosis (FO) membranes. Membrane technology is an often-applied method for water purification. Increasing attention is being paid to the FO technology. FO technology is a less energy consuming technique which can solve unique challenges where other techniques such as RO, NF and UF struggle. FO membranes consist of a thin, selective separating layer on top of a porous support. Both layers are important for the properties of the membrane such as its water flux, reverse salt flux, and salt rejection. The FO supports are fabricated by phase inversion technique and subsequently, an active layer is coated on their surface [1]. Hollow fibers (HF) are the best choice for FO supports because of the excellent control of their structure in the fabrication step and their high surface area. HF supports are being fabricated using a solvent containing a base-polymer (dope) and a non-solvent (bore). These two are brought in contact with each in a spinning machine to form the hollow fiber. These HF supports are then post-treated by either interfacial polymerization (IP) technique or layer-by-layer (LbL) technique to apply the active layer.

Interfacial polymerization (IP) is a reaction between two highly reactive monomers that are dissolved in two immiscible liquids (one dissolved in an aqueous and the other in an organic phase) [Figure 1] [2].

In the Layer-by-Layer (LbL) technique, the film is formed by physically binding alternating layers of oppositely charged materials (polyelectrolytes) with wash steps in between [Figure 2] [3].

So far, the active layers formed by the LbL technique haven’t shown the high salt rejection which is necessary for FO membranes. On the other hand, the IP coated supports showed better results in terms of better FO performance (high salt rejection and high water flux). However, IP coating has its own disadvantages of being a laborious and in some cases, irreproducible technique.

Therefore, a new coating procedure which reduces the coating defects as much as possible seems essential. Alternatively, instead of coating the membrane after support fabrication, the coating reaction can be included in the phase inversion process itself by adding one monomer/polyelectrolyte in the dope solution and the other monomer/polyelectrolyte in the bore solution. This simultaneous coating is going to be tested in this assignment which should lead to a more uniform and suitable active layer for FO.

Several experiments are expected to be carried out in this assignment such as hollow fiber fabrication, pure water permeability, pore size measurements, SEM analysis, FO performance, and low-pressure RO.

For more information, please contact:

Mehrdad Mohammadifakhr (m.mohammadifakhr@utwente.nl): Advanced Membranes for Aqueous Applications (AMAA), Meander 323

References:

[1] Tzahi Y. Cath, Amy E. Childress, Menachem Elimelech; Forward osmosis: Principles, applications, and recent developments; Journal of Membrane Science 281 (2006) 70–87

[2] Michiel J.T. Raaijmakers, Nieck E. Benes; Current trends in interfacial polymerization chemistry; Progress in Polymer Science 63 (2016) 86–142[3] Joseph J. Richardson, Mattias Björnmalm, Frank Caruso; Technology-driven layer-by-layer assembly of nanofilms; Science 348 (6233), aaa2491