Separation Of Isobutaonol From An Aqueous Solution By Salt/Solvent Extraction

With the decreasing of fossil energy,bio-based isobutanol has attracted people's attention due to its extensive application and excellent fuel performance.Isobutanol is a raw material for synthesizing several high value-added compounds and is also a compound with excellent fuel properties.It has higher energy density,lower oxygen content and hygroscopicity than ethanol,thus can be used as an ideal gasoline additive or alternative.However,the production of bio-based isobutanol still exists several problems,including low concentration and many impurities in the fermentation broth,high downstream purification cost and so on.Therefore,developing a highly efficient and low cost downstream separation process is the key to the industrial production of bio-based isobutanol.This research used solvent extraction,salt/solvent extraction and salting-out methods respectively to separate isobutanol from its dilute aqueous solution.The types and concentration of salt and organic solvent as well as temperature were explored to acquire the phase equilibrium data and define the optimum extraction conditions.The simulation process of extractive distillation,salt/solvent extractive distillation and salting-out distillation were built by Aspen Plus,the energy analysis of those processes was calculated to determine the best extraction process.The solvent extraction experiment showed that with the increase of extractant concentration,the recovery of isobutanol increased significantly,but the dehydration rate decreased.When the amount of extractant was equal to or lower than 1:2?mass ratio of dilute aqueous solution to extractant?,the recovery of isobutanol in different extraction systems was ordered in the following sequence:R?cyclopentanol?<R?2-methyl-2-butanol?<R?valeraldehyde?<R?2-ethyl-1-hexanol?,2-ethyl-1-hexanol was verified to be the most effective extractant by its the highest recovery.When the mass ratio was 1:3,the recovery of isobutanol in the?water+isobutanol+2-ethyl-1-hexanol?system was 99.20%.Thermodynamic study showed that the higher the extraction temperature,the better the separation effect when used cyclopentanol,2-methyl-2-butanol and 2-ethyl-1-hexanol as extractants,and the lower the separation efficiency of valeraldehyde.Nine salts and four organic solvents were introduced in salt/solvent extraction process.The result showed that the separation of isobutanol was greatly affected by the types and concentration of salt and extractant.The salting-out effects of different anions in nine salts were ordered to simplify the selection of suitable salting-out agent.The distribution behavior of isobutanol between two conjugated phases can be evaluated by Othmer-Tobias equation,Bancroft equation and solubility equation.Four kinds of salting-out agents,including K₄P₂O₇,K₃PO₄,K₂HPO₄ and K₂CO₃,were used in salting-out experiment.With the increase of initial molar salt concentration,the recovery and dehydration ratio of isobutanol increased.K₄P₂O₇ can produce the best salting-out effect.The following sequence was ordered according to the solubility equation:??K₄P₂O₇?<??K₃PO₄?<??K₂CO₃?<??K₂HPO₄?,which means the value of?can be used to evaluate the salting-out effect of different salts.The simulations of extractive distillation,salt/solvent extractive distillation and salting-out distillation were built by Aspen Plus and the result showed the final mass fractions of isobutanol were 99.99%,100%and 100%,the energy consumption of the reboilers of those processes were5.59,3.76 and 2.34 MJ/kg isobutanol,respectively.The salting-out distillation process had the advantages of good separation effect,simple process and low energy consumption,therefore it was beneficial to realize the high-efficiency and low-cost separation of isobutanol.