pervaporation 1

Bioethanol production by a coupled fermentation/pervaporation process using silicalite membranes coated with silicone rubbers T. Ikegami a*# , D. Kitamoto b , H. Negishi c , T. Imura d , H. Yanagishita e Green Processes Group, Research Institute for Green Technology, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8565, Japan a Tel. +81 (29) 861-2677; Fax +8 1 (29) 861-4660; email:[email protected] b Tel. +81 (29)861-4664; Fax +81 (29) 861-4660; email:[email protected] c Tel. +81 (29) 861-4666; Fax +81 (29) 861-4674; email:[email protected] d Tel. +81 (29) 861-4666; Fax +81 (29) 861-4674; email:[email protected] e Tel. +81 (29) 861-4659; Fax +81 (29) 861-4674; email: [email protected] Abstract In order to stably produce highly concentrated bioethanol, a coupled fermentation/pervaporation process was studied using ethanol-selective silicalite membranes coated with two types of silicone rubber,KE-45 and KE-108, as a hydrophobic material. Ethanol recovery was greatly improved by using a membrane coated with KE-45 silicone rubber. The recovered ethanol concentration in the permeate was 67% (w/w), and the amount of recovered ethanol from the broth was more than 10 times higher than th at using a non-coated silicalite membrane. Succinic acid and glycerol created during fermentation, and glucose as the carbon source greatly interfered with the pervaporation performance of the coated membrane when used to separate an ethanol/water solution. 1. Introduction It is very important to efficiently produce bioethanol as an energy source by yeast fermentation employing renewable biomass resources, from viewpoints of not only getting ready for exhaustion of fossil energy resources in future, but also decreasing greenhouse gas emission, CO 2 , which causes global warming today. Bioethanol must be conc entrated before use. Distillation process used ge nerally for this purpose, howe ver, is not cos t effective. On the other ha nd, it is poss ible to conce ntrate bioethanol by a membrane separation technique, pervaporation which can accomplish selective remov al of ethanol. By using a pervaporation s eparation proce ss with ethan ol- selective membranes, which are required to be hydrophobic, it is possible to concentrate low- concentration bioethanol from fermentation broths, which contain many compounds such as inorganic salts, by-products, and microorganisms, in a single step. It is reported that silicalite membrane, a polycrystalline zeolite with a negligible aluminum content, exhibits a very high pervapotarion performance in the separation of an ethanol/water mixture [1]. By a coupled ferme ntation/pervaporation process employing a silicalite membrane, we have reported that an enriched ethanol solution, 85% (v/v) at maximum, could be o btained [2]. However, the pe rmeate flux and the e thanol concentration in the permeate decreased with time during fermen tation. Considering that ac etic acid is adsorbed onto silicalite membranes [3], it is assumed that the acidic by-products during ethanol fermentation change the properties of the silicalte membrane surface from their originally hydrophobic characteristics to hydrophilic characteristics, resulting in a decrease in ethanol permselectivity. In this study, using silicalite membranes coated with silicone rubber as a hydrophobic material to keep the membrane surface hydrophobic, the fermentation/pervaporation process was examined for concentration of bioethanol. *Corresponding author # Presenting author

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