Study On Separating Ethanol-water System By Sweet Potato Powders

With the increasing shortage of the fossil fuels and growing air pollution, the fuel ethanol becomes the focus in the world at the present as renewable clean resources. Developing fuel ethanol has been listed in the development project of "the tenth five-year-plan" in China. The production of fuel ethanol, particularly gasohol, requires anhydrous ethanol as raw material. Therefore, one key of the fuel ethanol productions is that to make anhydrous ethanol production by separating water from the low concentration of ethanol-water systems.Most of the energy consumption occurs in separating the ethanol from fermentation broths in producing the fuel ethanol process, as there is the azeotropic composition at atmospheric pressure. The biomass raw material as adsorbents can adsorb the water of ethanol-water systems by selective vapor adsorption operation in ethanol dehydration. In addition, the invalid adsorbents needing no regeneration can be used as fermentation raw material. Thus significant energy consumption can be saved and production cost will be reduced. The adsorption performance of sweet potato powders on water and ethanol was studied in this research using inverse gas chromatography. Preparation sweet potato granular adsorbents were studied by optimizing the condition of technique.In addition, the absorption passing curves and throughput of sweet potato granules were investigated using fixed bed. The adsorbents before and after their adsorption were observed using a scanning electron microscope (SEM).The adsorption performance of ethanol and water on to five particle size of sweet potato powders among 60-140 mesh was studied in the temperature range 70-150℃using inverse gas chromatography. From the chromatography retention data it was possible to calculate the separation factors for ethanol and water and to obtain values for thermodynamic parameters such as Gibb's free energy (△GS) and enthalpy of adsorption (△HS). The four factor of theβ-cyclodextrin adding amount, xanthan gum adding amount, water adding amount and wetting agent were studied to orthogonal experiment L9(34) in producing granules with sweet potato powders. The absorption passing curves and throughput of sweet potato granules named No.28 were investigated using fixed bed. All data were processed by using DPS. Main points of the study might be concluded as follows:1. Water was adsorbed more strongly than ethanol on sweet potato powders at 70-150℃. Sweet potato powders as absorber could be used to produce anhydrous ethanol because of its preferential adsorption of water. The separation factors and the absolute values of Gibb's free energy (△GS) decreased with the temperature increasing in the temperature range 70-150℃for sweet potato powders. This indicated that appropriate lower temperatures were favourable for the adsorption of ethanol and water at 70-150℃. In addition, it was founded that sweet potato powders exhibited greater separation capacities at smaller particle sizes.140 mesh fraction exhibited the highest values of 1609 at the temperature 70-90℃. Enthalpies of adsorption for ethanol range between-3.0 and-7.2 kJ/mol. The corresponding values for water were between-23.7 and-38.9kJ/mol, the adsorption of ethanol was the physical adsorption.2 The four factors of theβ-cyclodextrin adding amount, xanthan gum adding amount, water adding amount and wetting agent were studied to orthogonal experiment L9(34) with sweet potato powders. The optimum condition of techniques were as fellows:β-cyclodextrin adding amount was 10g, xanthan gum adding amount was 7.5g, water adding amount was 110g, wetting agent was ethanol of 15%(v/v). Sweet potato granules named No.28 as adsorbent were gained by validated experiments, the hardness was 5948.9g, and the water and ethanol uptake were 38.2mg/g,0.5mg/g respectively. In contrast, the water uptake of raw sweet potato powders was 32.9 mg/g.3 The absorption passing curves of sweet potato granules named No.28 were investigated using fixed bed. The results indicated that sweet potato granules named No.28 could be used as adsorbents producing anhydrous ethanol because of its good adsorption performance. The throughput of sweet potato granular adsorbents named No.28 was 0.332(g 99.5% ethanol/adsorbents g), and it increased by 15.7% compared with that of sweet potato powders. The granular adsorbents before and after their adsorption had little significant change in shape.