Associate Professor LEE Yuan Kun
Microbiology
Yong Loo Lin School of Medicine

The bottleneck in the productivity of outdoors mass algae cultivation, and the way forward

Abstract:
To date, photosynthesis remains a major means for solar energy and CO2 capture and conversion. Microalgae have a higher growth rate than land plants and their photosynthetic yields are up to 100 times that of the higher plants. Microalgae can store in their cells up to 75% oil of the biomass, they represent a most promising means for biofuel production. However, the potential of microalgae has not been fully realized. Naturally occurring microalgae possess a photosynthetic system that is saturated at a relatively low light intensity, thus unable to take advantage of high solar irradiance in most part of the day in sunlit region. Moreover, self-shading and their relatively slow rate of dark reaction compared to the light harvesting process lead to low light energy utilization efficiency (2 - 5% of photosynthetic available radiance), low volumetric productivity, low cell density and high harvesting and dewatering cost. The productivity and cost would need to be improved by 10 folds for algal biomass to be an economically feasible source of biodiesel feedstock. The light harvesting and photosynthetic efficiency could be improve through reduction of the photosynthetic antenna cross section, allowing each microalgal cells to capture only light irradiance that it could process. The light that passes through it could be capture and process by cells in the lower level, and the light path is thus extended. Biochemically, the rate-limiting step in photosynthetic CO2 fixation is the turnover of carbon reduction cycle in the dark reaction. The sedoheptulose 1,7-bisphosphatase (SBPase) is the rate-limiting enzyme in the carbon reduction cycle. The bottleneck could be overcome by over-expression of SBPase in selected microalgae. These manipulations may bring the economy of microalgal CO2 capture closer to CO2 sequestration by physical and chemical means, and microalgae an economically feasible source of biofuels.

“Efficient utilization of solar irradiance is not a survival criterion of photosynthetic cells. Much like persuading the mold Penicillium to produce the antibiotic penicillin, the photosynthetic cells would need to be genetically modified to maximize the capturing of carbon dioxide using sunlight energy for conversion to biomolecules of industrial important.”

Assistant Professor YAN Ning
Chemical & Biomolecular Engineering
Faculty of Engineering

Lignocellulosic biomass into fuels via hydrodeoxygenation

Abstract:
Although various catalytic transformations for biomass utilization are known, the catalysis of biorenewable conversion is still in its infancy. In recent years, we developed a novel strategy for the C-O cleavage of cellubiose, leading to the successful degradation of cellulose into polyois, the latter of which is an ideal platform for H2, alkane fuels and chemical production. Meanwhile, we developed a related, two-step strategy for lignin degradation into fuels. The first step involves the hydrogenolysis of C-O bond linkage of C9 monomer units to obtain C6-C15 aromatic compounds and the second step involves upgrading of these chemicals into hydrocarbons and methanol. Upgrading of phenolic compounds in bio-oil to alkane fuels were also achieved, through tandem dehydration-hydrogenation reactions catalyzed by combined Bronsted acidic ionic liquid and metal nanoparticle catalysts. Based on these results, we propose a one-pot transformation of woody biomass into fuels and commodity chemicals. Some preliminary results will be discussed.

"At NUS,Dr. Yan's team is devoted to the development of cheap metal based catalyst for biomass transformation into fuels and chemicals."