Summer Research

This summer I've been in Singapore, doing chemical engineering research, and I've been enjoying it a lot!

 I'm working on clathrate hydrate research at the National University of Singapore. Clathrate or gas hydrates are crystalline solids formed from water and a gas. The water forms cages that enclose the gas molecules. Different guest gas molecules result in different hydrate structure, the most common of which are structure I (sI), structure II (sII), and structure H (sH) hydrates. For example, carbon dioxide generally forms structure I hydrates, which have six small dodecahedral cages and two large tetradodecahedral cages. Hydrate formation tends to occur at low temperatures and high pressures, the kinds of conditions that you would find in permafrost or subsea regions.

Why do we care about hydrates? The biggest reason is related to the oil and gas industry. The majority of the earth's methane is in the form of methane hydrates, and we'd like to extract it. We also need to be able to prevent the formation of natural gas hydrates in pipes.

The other main application, the one to which my work is more related, is gas separation and storage, particularly of carbon dioxide. Carbon dioxide emissions make up around 60% of greenhouse gas emissions, but if we could capture and sequester carbon dioxide, then it wouldn't be released into the atmosphere. One solution is hydrate based gas separation. Industrial applications generally involve a mixture of gases including carbon dioxide. If we're clever about the temperatures and pressures we use, we can form hydrates in a way that is very selective for carbon dioxide. For example, fuel gas is 60 percent carbon dioxide and 40 percent hydrogen, but we can form hydrates from fuel gas in which 80 or 90 percent of the guest gas molecules are carbon dioxide. If we do a couple of cycles of forming and dissociating the hydrates, we end up with a gas that is almost entirely carbon dioxide. The hydrogen can then be combusted.

The carbon dioxide can also be stored in hydrate form in the earth; if it's injected into parts of the earth's crust with the right conditions, then the carbon dioxide will form hydrates and not be released to the atmosphere. In fact, researchers have been doing experiments on methane/carbon dioxide hydrate exchange, working on how we could replace the methane in methane hydrates with carbon dioxide so that we can use the methane gas and store the carbon dioxide in hydrate form.

There are basically three general areas that you can study when thinking about gas hydrates: thermodynamics, kinetics, and morphology. They're all pretty closely linked, and I've had the opportunity to do at least a little bit of work on each while I've been in the lab.

Morphology focuses on crystal growth, where and in what shape the crystals are growing. Kinetics is about times and rates. How long does formation take, what amount of gas is consumed at what rate, and how can we speed up the process? By thermodynamics, here I really mean equilibrium -- essentially constructing phase diagrams for hydrate formation. This is important knowledge going into any other kind of experiment because you have to know your equilibrium values in order to form hydrates reasonably quickly (or at all). We also look at how adding other substances impacts the equilibrium values. If we add this compound to our system, do hydrates form at lower pressures (always nice for industrial applications)?

We do hydrate experiments in the lab in crystallizers. Here's a diagram of the set-up I used for kinetics experiments:

The external refrigerator/chiller cools the water bath, which then cools the liquid and gas in the crystallizer. The crystallizer contains porous material (such as silica sand) saturated with water and then is filled with a gas when the system is pressurized. This crystallizer consists of a transparent column with a stainless steel base and lid. There is also a thermocouple in the crystallizer to measure temperature.

There are a couple of kinds of crystallizers. For thermodynamics and morphology experiments I'm using one that just contains water, CO2, and whatever additive I'm studying, as well as a magnetic stirrer. Some experiments are done without stirring. The other kind of crystallizer, the one in the diagram, is used for fixed bed experiments. Basically, you fill part of a column with a porous material, such as silica sand, saturate the silica sand with water + additives, and then add the gas. Using a fixed bed reactor lets you experiment with porous material, which generally has more contact area between the gas and water, and is also a better model of the earth (which is relevant since hydrates form in the earth's crust).

The diagram doesn't really give a sense of scale. The crystallizer is half a foot or so tall, with a three or four inch outer diameter. The water bath is pretty close to cubical, about a foot on each side. The gas cylinders vary in size, but they're all over five feet tall. The carbon dioxide one, with which I've done the most work, is maybe half an inch shorter than I am.

The lab is pretty safe. The biggest danger in general would be dropping something (particularly a gas cylinder), so we're careful when we move things, and I have steel-toed shoes. I wear a lab coat around my set-up, but it would be really strange if I got anything worse than water on me. When I weigh out silica sand or some of the additives, I wear gloves, but that's basically it for PPE.

The experiments take a while and involve a lot of waiting: waiting for the system to cool, waiting for hydrates to form, waiting for the pressure to stabilize, waiting for the hydrates to dissociate. Despite that, I've been surprised at how much I enjoy and how comfortable I am with experimental work. Most of my research prior to this had been theoretical, and even a lot of the engineering experience from my Olin classes has been modeling and simulation work. I loved chemistry in high school, but I was always really uncomfortable in lab, so I was nervous about doing chemE experiments, for all that I really wanted experience doing non-theoretical work, so this has been a pleasant surprise. After a couple of weeks, I was comfortable doing pretty much anything in the lab. The fact that I'm enjoying chemE research has complicated my thoughts about what I want to do after Olin, though not in a bad way. Fluid dynamics, heat transfer, and thermodynamics are my favorite fields in mechanical engineering, and they're all important in chemical engineering as well. I've been looking at fluid dynamics grad programs, and the researchers are regularly a mix of mechanical engineers, chemical engineers, and applied mathematicians.

I'm here for about two more weeks, so I'll be finishing up experiments soon and then working on writing up my results for my final report. The opportunity to be here this summer came a little bit out of nowhere, and the application process was really rushed, but I'm so glad I chose to come.