Study On Selective Adsorption Mechanism And Energy Efficient Property Of Low Alcohol/Water Separation By Biomass Materials

Dehydration during the production of low alcohols (except for methanol) can beproblematic and energy-intensive owing to the formation of azeotropes. Biosorptionhas distinct advantages over conventional separation processes, as it isenvironmentally friendly, highly selective, cost effective, energy efficient in thetreatment of aqueous organics. We herein investigated the separation of low alcoholsand water on starch based adsorbent from micro mechanisms and macro application,respectively.To investigate the selective adsorption mechanisms of water over alcohols onstarch based adsorbent, inverse gas chromatography (IGC) and fixed-bed adsorptionexperiments were conducted and the results and effects of the dehydration of ethanol,isopropanol and turt-butyl alcohol on starch based adsorbent (CSA) were compared.The IGC and fixed-bed adsorption experimental results all indicate that, under thesame adsorption condition, the separation factor, or effect, of each alcohol-watersystem ranks as: tert-butyl alcohol/water>isopropanol/water>ethanol/water. Theseparation effects for the three systems on the CSA increase with their increasingalcohol carbon atom numbers and the decreasing alcohol polarity. CSA selectivelyfacilitates the separation of the alcohol and water azeotropes, suggesting that theinteractions between water molecules and free-OH groups on the glucose units inCSA are stronger than corresponding interactions with alcohols. CSA is moreeffective at dehydrating alcohols with reduced polarities as the binding betweenalcohols and CSA are weaker for these types of molecules. Besides, as water moleculeis smaller than those of other alcohols, it has faster diffusion rate.Industrial case studies were simulatively done to investigate energy savingpathways to utilize biosorption, three coupling biosorption-distillation processes wereproposed to cut down shortages of biosorption and distillation reciprocally, with theaid of PRO/Ⅱ. Regeneration consumption was also considered based on theregeneration experiment as an indispensable part of manufacturing process withcontributions to total energy cost. Specific energy consumption and exergy analyseswere compared with the commercial counterparts. The results showed that thedistillation-biosorption-distillation process doesn’t have an advantage over extractive distillation. However, the energy consumption of the distillation-biosorption-productprocess is0.54MJ/kg ethanol, which has a distinct advantage over other processes,such as azeotropic distillation, extractive distillation, molecular sieve adsorption, andmembrane separation. Compared with the commercial process, the third process,isopropanol purification process leads to a25.4%reduction in the total energy costand a28.9%reduction in the overall exergy loss.