Innovative reactor set to harvest alternative fuel
As isobutanol is created, it can be lethal to the bacterium producing it. Microwell plates (above) are used to periodically collect samples to see how the bacterium is faring.Take proven biochemical engineering practices and add innovation. The result is a reactor that will be able to produce the next generation of alternative fuels.
MSU AgBioResearch chemical engineer R. Mark Worden is part of a research team that received $1.7 million from the U.S. Department of Energy Advanced Research Projects Agency-Energy to build a reactor system for Ralstonia eutropha, a bacterium that scientists are engineering to metabolize hydrogen and carbon dioxide to produce isobutanol, a fuel that can be used as a replacement for gasoline.
Anthony Sinskey, professor of biology at Massachusetts Institute of Technology, leads the genetic engineering team.
“Sinskey is a leader in metabolic engineering,” said Worden, a professor in the MSU Department of Chemical Engineering and Materials Science. “His research group is focused on the biology of the bacterium and engineering it to produce isobutanol. To make the bacterium produce the biofuel we are working on, Sinskey and his research team have successfully altered the genetics of the bacterium, also called a microbe, by adding new DNA that allows the cell to produce isobutanol.”
Worden’s role in this project is to build a reactor system for the fermentation system. A prototype reactor has been designed and built, and it is currently being tested. Getting to this point, however, was not easy.
“Developing the reactor is a complex project,” said Worden, who had had experience designing reactors. “This one is different from a normal bioreactor because the food the microbe eats is hydrogen gas, oxygen gas and carbon dioxide gas. With other fermentations, the food the microbes eat dissolves easily in water. In this case, the hydrogen and oxygen don’t like to dissolve in water. They are sparingly soluble, meaning that it is difficult to dissolve the hydrogen and oxygen as fast as the microbes can eat them.”
Worden points out that this problem of getting gases into water is the same problem that started the biochemical engineering discipline back in the 1940s.
“There was a need back then to produce penicillin from a fungus,” he explained. “Scientists could produce it on Petri dishes, but that is not a good way to make a lot of the product. They learned to grow the fungus in a tank of water but then were initially not able to get oxygen into the water fast enough so that the fungus could produce the penicillin at a high rate. The biochemical industry field was formed to solve that mass transfer problem, so this idea of designing reactors to enhance gas mass transfer in water is a pioneering problem of our industry, and we are well-equipped to deal with it.”
The typical way to get these gases into the water faster is to use smaller bubbles because the smaller the bubbles, the more surface area they have.
“We took this approach to an extreme by making micro-bubbles, which helps to dissolve the gas fast enough to meet the need,” Worden said.
This project, however, presented several new challenges.“The gas which is consumed the most -- measured in moles -- is hydrogen gas, and hydrogen is less soluble than oxygen,” Worden said. “That is part of the problem —high demand for a gas that is not very soluble.”
Another major problem is that hydrogen and oxygen cannot be bubbled together in the same liquid because, when these gases mix, they are explosive. This created a huge safety issue that was a challenge in designing the reactor.
The result of Worden’s work is a new reactor design called Bioreactor for Incompatible Gases, for which MSU Technologies submitted and received a provisional patent.
“The way it works is that the hydrogen and oxygen gases are kept separate,” Worden said. “You never have to mix the two gases, so that helps with the safety issue. And the design incorporates micro-bubbles, so we have two innovations combined in the bioreactor.”
The reactor also overcomes another challenge in the project. Isobutanol is an inhibitor to the cells that make it. Cells can produce only a certain amount, and then the product kills the cells.
“To prevent the cells from being killed, our idea is to operate in a manner where we continuously remove the product as the fermentation continues,” Worden explained.
Worden and his research team are considering two ways to remove the isobutanol during the fermentation process.
“In the first, we have the isobutanol stick to little plastic spheres and then later release the isobutanol and recover it,” Worden said. “Our other strategy is using a gas such as hot air to evaporate the isobutanol out of the water. Isobutanol is more volatile than water, so it comes out faster and we can selectively remove it from the water during fermentation.”
The prototype reactor is now being tested.
“We recently put all of the components together and developed a complicated control process to automate the reactor so that it can detect what’s needed and take corrective action without an operator having to be there to do it manually,” Worden said. “The control system has been a challenge because different pieces of equipment talk different languages. We have had to use electronic translators to get the signals from different instruments into a compatible format so that all the data and signals can be analyzed at the same time.”
Worden recently received a new strain of the microbe from the Massachusetts Institute of Technology and is working on a test run with the actual microbe.
One of the big advantages of isobutanol is that it is a direct substitute for gasoline. Ethanol, another alternative fuel, can only be added to gasoline in low concentrations. That’s one of the reasons for the emerging interest in isobutanol as an alternative fuel, Worden said.
This project has spawned an initiative with the Michigan Biotechnology Institute (MBI).
“MBI realizes that this kind of fermentation, where hydrogen is fed to microorganisms, could be a growing area of research,” Worden said. “MBI can scale up a reactor that is bigger than the one we can make at MSU. Ultimately, we want to be the focal point for the development of these gas-intensive fermentations. MBI is the perfect partner because scaling up fermentations is what they do.”
For Worden, the project has other ultimate rewards.
“As an educator, we tell the students that if they apply the engineering principles we teach, they can deal with systems,” he said. “This is a great example of that. We integrated well-established principles in a creative new way to address challenges in a novel fermentation process. ”