Scaling up of ethanol production from sugar molasses using yeast immobilized with alginate-based MCM-41 mesoporous zeolite composite carrier

Microporous and mesoporous zeolites, including ZSM-5, H-β, H-Y, and MCM-41, were modified with 3-aminopropyl-triethoxysilane (APTES), then inorganic fillers, such as abovementioned zeolites or mesoporous materials, (α-AlOOH or γ-Al2O3), were mixed with alginate embedded with yeast; and finally these carriers were cross-linked through the double oxirane. The alginate-based immobilized yeast with MCM-41 exhibited much shorter fermentation time and higher ethanol concentration than pure alginate and other composite carriers with the highest cell concentration of 4.8 × 109 cells/mL. The composite carrier maintains the highest ethanol productivity of 6.55 g/L/h for 60 days in continuous fermentation process, implying good operational durability for commercial applications. The reason for the higher bio-catalytical function of the immobilized yeast might lay in the uniformly yeast distribution in the bio-reactor and high yeast cell concentration, which contributed by the improved transmission of fermentation media and combined effects of yeast adsorption by MCM-41 and embedment by alginate.

To increase the ethanol productivity of fermentation bioprocess as biofuel and provide a solution to the environmental issue arising from the disposal of sugar molasses, facile alginate-based micro- and mesoporous composite materials, such as zeolites (including ZSM-5, H-β, H-Y, and MCM-41), α-AlOOH and γ-Al2O3, as carriers of yeast cells were successfully synthesized and evaluated for ethanol fermentation of sugar molasses in laboratory- and pilot-scale. Results indicate that the alginate-based MCM-41 immobilized yeast exhibited much shorter fermentation time and higher ethanol concentration than pure MCM-41 zeolites or alginate with the highest concentration of 4.8 × 10 9 cells/mL and shortest batch fermentation time of 12 h after repeated use across 60 days. The reason for the higher bio-catalytical function of the alginate-based MCM-41 immobilized yeast might lay in the uniformly yeast distribution in the bio-reactor and high yeast cell concentration, which contributed by the improved transmission of fermentation media and combined effects of yeast adsorption by MCM-41 and embedment by alginate. For the performance and durability of ethanol production showed during the fermentation process, this unique synthetic method is extremely valuable and suitable for economical and enhanced fermentation of ethanol as biofuel at pilot-scale. The studies may also have general implications in other cell immobilization process.Figure optionsDownload as PowerPoint slideHighlights
► Alginate-based mesoporous materials as immobilization carriers of yeast cells.
► Ethanol fermenting performance of composite carriers was better than pure carriers.
► Improved transmission between immobilization carriers and fermentation medium.
► Combined effects of yeast adsorption by MCM-41 and embedment by alginate.
► Stable fermentation results with uniformly yeast distribution in the bio-reactor.