One of the most promising ways to combat carbon emissions is to transform those emissions into something useful. Recently, Gregory Stephanopoulos, the Willard Henry Dow Professor in Chemical Engineering at MIT; postdoc Amit Kumar PhD ’10, also of the Department of Chemical Engineering; and their team released a paper in the Proceedings of the National Academy of Sciences. Their study focuses on utilizing bacteria to turn waste gases into biofuels. The MIT Energy Initiative talked with Kumar, who is also the energy and environment chair of the MIT Energy Club, and Stephanopoulos to learn more about the research behind the paper, the team’s near-term plans to scale up from a pilot plant to a demonstration plant, and their thoughts on future areas of research.
Q: Tell us a little bit about your research and why it’s significant.
A: We developed a novel bioprocess for converting waste gases containing carbon dioxide and a reducing gas such as hydrogen or carbon monoxide into biofuels. Our process uses bacteria to convert waste gases into acetic acid — vinegar — which is subsequently converted to oil by an engineered yeast. It is a very interesting story of pairing distinct microbes to take advantage of their unique metabolisms in creating a gas-to-liquids process.
In the United Sates, biodiesel — a primary alternative to petroleum-diesel — is the second-most abundant biologically derived transportation fuel. This bio-based diesel is currently produced from vegetable or seed oil (lipids) obtained from crops including canola, palm, or soybean, which are costly and limited in available supply. Similarly sugar-based biofuels are not favored due to high feedstock costs. Our bioprocess paves the way for use of potentially cheaper gaseous feedstocks, which can be obtained from gasification of methane or municipal solid waste, but can also be derived from the exhaust gases of steel manufacturing. As anyone can imagine, availability of these sources is huge.
An important feature of our method is that it utilizes waste as a “resource” allowing a very low or even negative cost for the feedstock. In a broader sense, implementation of these concepts for fuel production may extend to a number of commercially important biological platforms depending on the potential sources of synthesis gas or its conversion products, namely, volatile fatty acids.
Q: What changes did you need to make in your process to scale up from your pilot plant outside Shanghai to the much larger “semi-commercial” demonstration plant that’s set to begin construction?
Scaling up involves many challenges. In a small bioreactor, microorganisms and media are easy to control and well distributed in the system. However, spatial variations arise in a larger system requiring sophisticated models and lots of calculations to generate a design that works well. Another challenge is the logistics and parameters involved in running a bioreactor of several thousand liters, or even bigger, without mixing issues.
An additional issue is the robustness of operation. In the lab, graduate students can adjust the operational parameters at will, as frequently as needed, to provide optimal fermentation conditions for days. In a pilot plant, there is limited capacity to make these adjustments and the continuous system must be kept stable for months. This imposes higher requirement for the robustness of the microbes and the overall process.
Successful operation of a pilot plant for months indicates that the whole gas-to-liquid fuel process is technologically feasible under semi-industrial conditions. But that is only the first step in the developmental process. Cost-effectiveness is another important requirement. Assessment of the economic feasibility of the process is the major goal of operating a pilot plant, and/or semi-commercial demonstration plant. The fixed assets required for pilot construction determine capital costs of a future commercial plant. Additionally, runs at pilot scale better define energy requirements, product quality, and other factors like substrate pre-treatment, heating, and cooling, and product recovery required by a production plant.
Q: What will be some areas of future research for your group?
A: We want to enhance our understanding of the basic physiology of the organisms involved in the process and develop better biological toolkits for their genetic modulation to allow production of various products by metabolic engineering. Additionally, we would like to better understand gasification and other potential supply routes of the gaseous feedstocks in order to maximize the cost effectiveness of the process.
