Date of Award
Doctor of Philosophy (PhD)
Algae and lignocellulosic biomass are viewed as viable renewable energy sources. However, higher cost of production is a major hurdle to make them competitive with fossil fuel sources. In case of algae fuel, the larger material and energy input required for the growth and processing is making algal biofuel both environmentally and economically unsustainable. In case of lignocellulosic biomass, the cost of unit operation steps, including that of enzymatic hydrolysis, to produce monomer sugars is very high. These problems gave us key engineering opportunities to investigate better extraction methods of lipids from algae and continuous enzymatic hydrolysis of lignocellulosic biomass. We performed techno-economic and life-cycle analysis of five probable ‘algae to fuel’ processes and came up with the conclusion that the extraction and dewatering of algae are the major bottlenecks. We hypothesized and tested an extraction method of lipids from wet algae with a ‘novel’ solvent mixture of diesel and isopropanol so that the lipids can be extracted directly from wet algae with a cheaper overall cost without actually killing the algae. We found out that algal lipids can be extracted using this ‘novel’ extraction method and the algae can also regrow in certain extraction conditions. The batch enzymatic hydrolysis is very inefficient method of hydrolysis of lignocellulosic biomass. We hypothesized and tested a membrane based reactor system for continuous hydrolysis of lignocellulosic biomass so that the monomer sugars, inhibitors during the hydrolysis, can remain low in concentration in the reactor and because of that, the reaction rate and overall conversion can go up. Our techno-economic study suggested that the continuous system can be cheaper than the batch mode of production. We learned that the complex nature of the lignocellulosic slurry makes the system difficult to design due to clogging and settling of biomass in the reactor and adjoining tubes. To understand this aspect, a fundamental study of the fluid dynamics of the biomass in a membrane module with the goal of designing a better header that can ‘mitigate’ clogging of the membrane structure (tubes and/or module) was done using OpenFOAM. We found out that certain geometries of membrane arrangement in a membrane module are preferable to some other ones.
Adhikari, Birendra, "Separation challenges and optimizations of sustainable algae and lignocellulose based biofuels" (2015). Mechanical Engineering Graduate Theses & Dissertations. 110.