Wei Chen

Oxygen Transport Membranes:

A material science and process engineering approach

Promotion date: May 16.

Promotor: Prof.dr.ir. Arian Nijmeijer

Assistant Promotor: Prof.dr. Louis Winnubst

The integration of oxygen transport membranes in the oxy-fuel combustion process can be applied in two ways: the 3-end mode (where air is used as feed gas, nitrogen is retained and pure oxygen is pumped out), or in the 4-end mode (where a sweep gas is used to carry away the permeated oxygen). The work is focused on the 4-end operation because it is more energy efficient than the 3-end mode.

The feasibility of integrating mixed ion-electron conducting (MIEC) membranes into the oxy-fuel combustion processes for CO2 capture is investigated. This includes the fabrication of MIEC membranes and the design of a membrane-integrated oxy-fuel combustion process.

The membrane material research reveals that the composition of the membrane, the operating temperature, the ambient oxygen partial pressure and the CO2 partial pressure jointly determine the stability of the membrane in a CO2 containing atmosphere.

The process design and simulation studies suggest that the integration of oxygen transport membranes decreases the energy demand for CO2 capture, if compared to the oxy-fuel combustion process based on cryogenic distillation from air.

It is further recommended that more research should be done to study the influence of SO2 and water vapor on the membrane performance. In addition, processes based on a 3-end mode should be investigated as well.

Was your research application oriented?

Yes, it was. The idea of using MIEC membranes in a big fossil fuel fired power plant was suggested around ten years ago. The research for more efficient membranes has continued ever since, with some nice results.

My research objective was quite unique, combining more fundamental material science aspects with process design parameters. Taking into account both aspects leads to a creative approach, coming up with realistic results.

In studying the process aspects, like transport details, I also was interested in the material properties of the membranes to be used, all the way through. Sometimes a membrane is good enough - one could say - by looking to the process as a whole. Increasing the flux by some percentage points for example, is not always worthwhile if material costs rise disproportionately.

Did you experience some special moments during your PhD period?

In studying the process parameters a lot of simulation runs were involved, whereas material analyzing aspects involved small scale experiments. Solving mathematical programming difficulties gave rise to some fulfilling moments, both of relief and of joy.

Being an experimentalist, I learned a lot in executing process simulations, using up-to-date commercial software in which I now posses a vast set of new skills. It was a privilege to make use of them because of the good licensing policy provided by the University of Twente. Correct licensing was needed for publishing the results in leading journals. I can imagine more PhD students, and also staff members, may benefit from these facilities more, if proper introduction courses are offered more regularly.

The collaboration with dr. Louis van der Ham from the Sustainable Process Technology (SPT) group was memorable as well. As an expert he contributed a lot on process engineering topics which I came across during my PhD work.

Did you succeed in publishing some nice articles?

Two papers appeared in Solid State Ionics and one in the Journal of Membrane Science. The fourth one has been submitted, and the fifth one is ready for submission. I expect at least five publications will result from my PhD work in the end.

What are your future plans?

I prefer to stay in an academic research environment in the research field of membranes, at a university or a knowledge institute in China. Working in an industrial company, as a researcher, is an opportunity which I would be happy to grasp as well, though working there might be a different story, I suppose.

My topic of research will be of interest in China the years to come, as CO2 emission is a major topic. The air quality is very poor in many parts of China at the moment already.

In what way did you develop as a researcher and scientist in this PhD period?

I have grown considerably, in many respects. Perhaps I am not an expert but I consider myself a professional, both in the field of material analyses as well as in process engineering. I enjoyed being part of MESA+ though I did not make much use of the nanolab facilities, apart from some analyses methods. The MESA+ days were a success, especially the time I was offered to give a presentation being able to explain my work to a broader audience within MESA+. Expert meetings and international conferences were really interesting as well.