FIGURE 3-2 Plugged reactor concept for continuous fuel production.
SOURCE: Image taken from Somerville presentation.
In concluding his talk, Somerville noted two other challenges that require the attention of chemists and chemical engineers. The first is producing optimized depolymerization catalysts, whether they are enzymes or chemical catalysts, in very large quantities at an affordable price. The second is to develop large-scale anaerobic processes that produce gasoline and diesel fuel from sugars.
In response to a question about how much progress was being made on developing a continuous fermentation process, Somerville said that Yong-Su Jin at the University of Illinois would be publishing the results of a study demonstrating efficient continuous fermentation of C12 sugars rather than C6 sugars. Tom Richard asked Somerville to discuss some of his work on developing new enzymes of pretreatment, and Somerville noted that his group has identified enzymes from cow rumen that operate efficiently at high temperature, but that the major limitation in developing those enzymes for industrial use today is the inability to engineer their favorite production hosts to produce them in the necessary quantities. He remarked that this is a fundamental piece of science that needs the attention of the research community.
Somerville then expanded on the need to develop ways of converting sugars into fuels. In his opinion, the most promising long-term strategy is to make short-chain alcohols and then use long-established chemistry to produce mixtures of the longer-chain isoalkanes that are used in jet fuel and diesel. He noted that chemists at his institute are exploring old chemistries that had largely been forgotten because they produce mixtures, but since fuels are mixtures of products, those chemistries may actually be useful today. Getting chemists to change their way of thinking to appreciate reactions that produce mixtures was a real challenge because that idea goes against the paradigm of modern chemical science.
This breakout session was led by Leonard Katz, associate professor at the University of California, Berkeley, and a member of the scientific advisory board of Lygos. The discussion about biological technologies for biomass conversion focused on whether the biological conversion of biomass into chemical and fuel should be conducted in an integrated biorefinery or whether it should be broken into components. The argument was made that preparing biomass for processing should be one component, that deconstruction to produce sugars would be a second component, and that conversion of sugar into fuel or chemicals would be a third process. Developing these three processes together into an integrated biorefinery was considered by many breakout group members to be too risky at this stage of technology and capacity development. However, the discussion also raised the possibility that it might be economically and technologically attractive to combine biomass preprocessing and deconstruction into an integrated process or to combine deconstruction and fermentation in an integrated process. Many breakout group members said that determining the optimal configuration is an area that needs further study and analysis.
One idea that was raised during the discussion was that there may be a market for lignin as a carbon-neutral source of energy and that there may be advantages to removing lignin from biomass at local facilities close to the biomass source. Such an approach might improve the economics of biomass