PhD project title: Stable polyelectrolyte multilayer based membranes for water treatment under... (# of pos: 14)

Topic background
Complex oil/water/solids mixtures are found in many industrial processes and water treatment facilities. One key example, so called “produced water”, makes up one of the largest aqueous waste streams in the world, generated by oil and gas (enhanced) recovery operations. Produced water is a complex mixture of organic and inorganic compounds, that are present in both a dispersed and a dissolved state. But rather than viewing this as a problematic waste stream, one can also see this as a promising resource that can be treated for re-use, helping to alleviate the world-wide shortage of clean water. Unfortunately, the stream can have very harsh conditions, including very high salinities, extreme pH values and the presence of dissolved solvents organics and problematic chemicals such as hydrogen sulfide. Clearly, a high stability against these harsh chemicals will be required for any approach to treat produced water.     

Research challenges
Many technologies are available to treat produced water, including gas flotation, hydrocyclones, adsorption, media filtration and membrane technology. Typically, multiple of these techniques need to be incorporated in the treatment process to give the required result, becoming part of a larger process layout. Here, membrane technology is especially interesting as it is one of the few approaches that can successfully remove the smallest (< 10 µm) and most stable oil droplets. For this purpose, microfiltration and especially ultrafiltration (UF) have been shown to be very suitable techniques. Moreover, denser membranes such as nanofiltration (NF) and Reverse Osmosis (RO) membranes can remove heavy metals, multivalent ions and for RO also the monovalent ions. Essential steps to make produced water ready for re-use. But especially these dense NF and RO membranes often lack the stability to be used under the required harsh conditions.

Objectives and methodology
For treatment of complex oil/water/solids mixtures, such as produced water, nanofiltration is very interesting, due to the ability to de-oil and to have control over the ionic composition of the permeate at acceptable fluxes. In this project we will develop NF membranes that are stable under harsh conditions on the basis of so called polyelectrolyte multilayers (PEMs). These PEM coatings have the potential to provide such membranes with excellent characteristics, in the form of selectivity, water flux and resistance to fouling. In this project we will further their development to push them towards excellent stability under the harsh conditions that can be found in produced water treatment. This will be achieved by innovative combinations of ionic and covalent crosslinking.  In collaboration with the involved companies we will then translate obtained insights into relevant process designs for the treatment of specific produced water streams for re-use.