EPFL Research Post # 2

In this post, I am going to go into the rolling and testing portion of the project and the results we received. 

To roll the SW we follow specific instructions that were made by the researcher who created the experiment. Essentially, you had to put a permeate spacer down, apply epoxy glue, put the membrane on top, apply glue, put a feed spacer on top, apply glue, fold the membrane down, apply glue, and roll the aluminum rod down it, creating a circle, then roll some aluminum foil on top and seal it using glue and tape. By using too much glue, no air would be able to pass through and it would be a failure. By using too little glue, there could be leaks or the glue could break, so it would be a failure. We had to apply just the right amount of glue to seal the membrane, but not so much as to prevent any air flow.

To test a SW, you need to put it in a module from which pressurized air will flow through. Connect the module to a sensor to measure the flow rate, or permeance, in liters per minute (LPM). Our goal was to get a flow rate of less than 1 LPM. In this post I am only going to go into the results of house gas (I will mention the CO2 and N2 later in this post).

The first few cores we tested on house gas resulted in flow rates of over 70 LPM which was far from our target. The reason this was happening was because the core was not properly inside the metal module – air was flowing through the gaps. To combat this issue, we put larger rubber rings around the ends of the rod of the SW to insulate the air and prevent leakage. This solved the issue and the module was able to properly pressurize and give us a flow rate of around 30 LPM.

This was still far from our target so we continued to troubleshoot. The only thing causing such a high flow rate would be leaks. These leaks can originate from a variety of places, such as, the PDMS itself, the PES membrane, loose screws in the module, or leaks in the epoxy (when rolling the membrane).

In order to test if the epoxy was the issue, we took old SWs and took them apart to see how strong the glue held the materials together. We found that the materials were hard to pull apart, suggesting that the glue was not the issue. However, it was relatively easy to pull the aluminum foil off the aluminum rod, which suggests that a stronger glue may be needed for that portion of the rolling.

The PDMS was supposed to have a positive effect on the membrane and decrease the flow rate, but based on the results we were getting, we were unsure if that was the case. To test the effect of PDMS, we rolled a new SW and also rolled a PES membrane (without PDMS) and compared the results. We found that the PES membrane had a flow rate of around 38 LPM, while the PES membrane with PDMS had a flow rate of around 18 LPM, which suggests that PDMS had a positive effect on the permeance.

Next, we decided to try new methods of rolling to ensure that the SW was as tight as it could be. The way we achieved this was by having one person hold the membrane down, applying tension, while the other rolled it as tight as possible. Ultimately, this method gave us a SW that was much tighter than any of the previous ones.

By doing a combination of experimenting with the amount of glue and the rolling method, we achieved a SW that had a flow rate of 0 LPM. In reality, the flow rate was likely less than 1 but greater than 0, our sensor was just not able to detect a flow rate of that precision. So, our project turned out to be a success and this PDMS coating had never been done before.

Going back to the N2 and CO2 tests - our tests were primarily done on house gas, which is why I have not mentioned those tests in detail. The reason for conducting N2 and CO2 gas tests is to find the selectivity of the membrane. The optimal membrane would have a high flow rate of CO2 and a low flow rate of N2, because it would be highly selective then. Since our results were not that good with house gas, we did not move on to the selectivity tests, but since the house gas results are better, the project can move to being tested on N2 and CO2.

So, those are the results of the project and what I did during my internship at EPFL. Spiral wounding is a novel technique for carbon capture membranes and the ultimate goal of this project is to implement these SWs in an industrial setting. SWs are good for industrial scaling because they are very small and ideally would have high selectivity. They are still in the research process, but the ultimate goal is to get them scaled out to companies.

EPFL Research Post # 1

Hi everyone, I just finished a two week internship at the Swiss Federal Institute of Technology Lausanne (EPFL) in the Laboratory of Advanced Separations (LAS). Here, my project was to experimentally develop a carbon capture membrane from a polymer. The methods being used were novel and had not been tried before.

The goal of this project was to develop a spiral-wound (SW) module and test it on house gas, N2, and CO2. Essentially, an SW is a carbon capture membrane wrapped around an aluminum rod several times. By layering the carbon capture membrane on itself over and over, it allows the whole SW to have a much lower permeability. Permeability is the ability for a membrane to have air pass through it – high permeance means more air passes through, and low permeance means less air passes through – measured in liters per minute (LPM). Our goal was to get a permeance, or flow rate, of less than 1 LPM.

In the past, this project had been done with a membrane of only polyethersulfone (PES). The new step that we were introducing was coating a polymer called polydimethylsiloxane (PDMS) onto the PES with the goal of decreasing permeability.

The first step was to develop the PDMS coating. Based on previous results, we decided to use a 30% ratio of monomer to solvent. This ratio proved to likely be the best option for industrially scaling. We aimed to measure 1.04 g of monomer in 8 vials. We used the actual measurements of the monomer to find the amount of heptane (solvent) to put in the vials. After the heptane was put in the vials, we applied parafilm on each one and put them in the sonic bath. Monomer is a gel-like substance and heptane is liquid, so the sonic bath applied sonic waves to the vial to combine the monomer and heptane. Once the samples are no longer viscous, we remove them from the sonic bath and put them on the magnetic agitator for 5 minutes. Magnetic pills are put in each vial and the magnetic agitator creates a magnetic field around it, spinning the pill. This serves the purpose of agitating the mixture and mixing the monomer and heptane. After they are removed from the magnetic agitator, they go back in the sonic bath for 5 minutes to ensure that the solution is homogeneous. Then, we add the catalyst. The amount of catalyst is simply 0.1 multiplied by the amount of monomer. After the catalyst is added, the reaction immediately starts happening. Once the catalyst is added, the samples need to be parafilmed and put in another bath which is heated to about 65 degrees C. This bath also has a magnetic agitator in it, so the samples will be agitated throughout. The vials are put in this bath for 1 hour and 15 minutes. Once the time is up, the PDMS coating is finished.

The next step is plating the PES membrane. During the time the PDMS is cooking, we prepare the plates with the PES membrane. We take aluminum plates and tape some PES membrane to them. The method of taping is very specific as it prevents bubbles from forming. We first take a small piece of tape and place it in the middle of the smaller side. Then, using a rod to flatten the membrane, we take small pieces of tape and apply them to the longer sides and finally put a piece of tape on the other small side. Then, we apply long pieces of tape on all the sides to prevent any liquid from getting underneath the membrane. Once the samples are done, we take them to the spin coater. The aluminum plate is placed on the spin coater and is run at 2500 rpm to ensure it does not fall. Then, we pour all the samples of PDMS on the membrane, covering as much area as possible. Then, the spin coater is run on 2500 rpm for 1 minute. After this, the membrane is done and is put in the oven at 140 degrees C for 24 hours.

That is all we did in the first week. I will write another post about making the spiral wounds and the results as well as next steps for the project.