This SBIR project proposes to develop a novel bioreactor that will contain biocatalytic coatings for the desulfurization of petroleum products. A biodesulfurization microorganism will be immobilized at the interface of a two-phase membrane with a biocatalytic coating. Biodesufurization technology also has the potential to significantly reduce energy consumption and greenhouse gas emissions.
The broader/commercial impact of the proposed project will be a decrease in the levels of sulfur from petroleum products. The petroleum being used is increasingly ?sour,? high sulfur crude. The proposed process can also be used for other industrial processes that rely on mass transfer limited biological reactions.
Petroleum derived fuels tend to contain significant quantities of sulfur, which, upon combustion, produce sulfur oxides which are key air pollutants associated with the formation of acid rain and particulate matter (soot). Increasing awareness of the health and environmental impacts of high sulfur fuel has resulted in more stringent regulation of sulfur content for fuels in developed and emerging economies around the world. The growing demand for ultra-low sulfur fuels has put a strain on refinery hydrodesulfurization (HDS) capacity and opened a major market opportunity for alternative desulfurization processes, such as BioCee's biodesulfurization approach. Biodesulfurization (BDS) is regarded as a particularly promising desulfurization technology. Not only are the microbial catalysts used in BDS particularly successful in removing sulfur from the compounds most difficult to treat with conventional hydrodesulfurization, the technology has the potential to significantly reduce energy consumption and greenhouse gas emissions. Large commercial research efforts have significantly improved the performance of the microbial catalysts. However, their deployment in traditional fermentation systems has proven to be cost-prohibitive due to mass-transfer limitations as well as incomplete catalyst retention. BioCee proposed a radically new reactor design based on its patented process to embed very high concentrations of microorganisms in thin latex coatings, leading to higher reaction rates and significantly improved mass-transfer, while simplifying the overall reactor system. The goal of the work conducted under this SBIR Phase I and Phase IB award was to proof the concept of this novel reactor design by building and testing a prototype reactor and by developing a techno-economic model to assess the conditions under which this technology is economically viable. Based on our results, we conclude that the development of a biocoating reactor using BioCee technology is indeed feasible. Specifically, our model organism, Rhodococcus erythropolis, survives the formulation and film formation processes necessary for making biocatalytic coatings. Using micro reactors for screening, we were able to develop improved coating formulations, which resulted in improved mass transfer to the immobilized cells. In the micro reactors as well as in a larger bench-scale reactor, we could demonstrate reduction rates of the model sulfur compound dibenzothiophene (DBT) in our model petroleum stream comparable to those in a traditional fermentation approach, allowing us to achieve final DBT concentrations below 15ppm (15ppm is the maximum allowable sulfur concentration in Ultra-Low sulfur diesel). Furthermore, we were able to show that the coating reactors are also suitable for the removal of DBT from "real" diesel. Our techno-economic model allowed us to calculate the biodesulfurization process cost on a per gallon basis. Running different process scenarios based on our experimental as a well as literature data, we were able to show that the process can be cost competitive. This research not only proofed the concept of our approach, but also helped us establish the process parameter targets that we will need to focus on in bringing this technology to market. Biocatalytic coatings are not limited to applying biodesulfurization within the refinery. The technology may also be applicable to many crude oil streams. Beyond biodesulfurization, the knowledge gained during our biodesulfurization development effort will also allow us to transform biocatalytic coatings into a true platform technology. This will make energy-efficient and environmentally-sound biocatalysis with living microbial cells much more user-friendly and suitable for many more applications.
