Formation of an Efficient Sol-gel Capsule to Encapsulate Yeast for the Production of Ethanol
Camille Warner
Department of Chemistry and Bio-molecular Science, ClarksonUniversity
NSF REU Fellowship
Abstract
June 13, 2008
The rising prices of gasoline, the shortage of fossil fuels, and the negative environmental impacts caused from the removal of these fuels, call for an alterative energy source that is cheaper, abundant and environmentally friendly. Extracting ethanol by fermenting plant matter is analternative energy source. Encapsulating biological materials (i.e. yeast and enzymes) needed for fermentation decreases the costs need and increases the production of ethanol. The capsule created must be able to withstand the low pH needed for fermentation and porous enough to allow nutrient to diffuse easily through the membrane. The objective of this project is to microencapsulate yeast in a sol gel material that will provide functionality in the hydrolyte mixture.
Using sol gel capsules as the outer shell is advantageous because the silica glass structure provide chemical resistance and added support to the biological materials. The core materials, sol-gel precursors, pH and temperature were varied to form and optimize the sol gel capsules. Several materials (i.e. alginate, derived from seaweed,chitosan, taken from crab shells and agar) are tested to form the core. Other chemicals like poly (sodium 4-styrene sulfonate) andsodium poly(allylamine hydrochloride) were also tested but they formed flimsy beads or the beads dissolved in the sol gel precursor. Chitosan has been found to have a greater affinity to the sol gel because of the amino and alcohol functional groups. Chitosan, in comparison with alginate is thicker, stronger and lasts longer. Figure 1 shows basic alginate beads and chitosan beads in their respective hardening solutions. Sodium triphosphate pentabasic (NaTTP) is used to remove the core materials after coating the beads with sol gel to leave a hollow core.
Figure 1: Chitosan beads on the left in NaTTP with alginate beads
on the right in CaCl2.
Agar has alcohol functional groups allowing it to mix well with the chitosan helping the formation of the sol gel. Beads made with agar as the core would eliminate the need to extract the core after sol gel formation because the yeast can grow in it. To form the sol gel layer methyltrimethoxy silane (MTMOS) and tetramethyl orthosilicate (TMOS) were the best sol gel precursors. The pH and temperature were optimized to create the strongest capsule that is able to yield ethanol more efficiently. Theformation of sol-gel requires acidic conditions for hydrolysis and basic for condensation each at a specific temperature. Both the pH and the temperature are specifically chosen in the optimal range for the yeast to survive. The beads were stained and dissected to confirm sol gel formation under the microscope. UV spectroscopyhelps determine the percent of ethanol and the ethanol yield in the beads after optimization studies. Pore size will be analyzed using a Scanning Electron Microscope. These results demonstrated that the sol gel capsules have improved strength and longevity as compared to the polymeric capsules as well as an increase in ethanol production. The sol gel capsules were able to have a 3.74 ethanol yield. Using these capsules will make the production of ethanol more feasible and decrease our dependence on oil.