Recyclable Aqueous Two-phase Systems Extraction And Membrane Vapor Extraction For Recovering Biosolute

Global interest in sources of renewable energy has encouraged a significant number of recent investigations into the production of bioproducts by fermentation from biomass.However removal of bioproducts from fermenter broths is a major challenge to recover solutes economically and environmental-friendly.Here we propose two new processes,recyclable aqueous two-phase systems extraction and membrane vapor extraction for recovering bioproducts(citric acid and butanol).The recyclable aqueous two-phase systems extraction is a green technology that can be used for bioproducts separation.It has advantages of mild operation condition,low pollution,simple manipulation and scale-up potential.Two recyclable pH-responsive aqueous two-phase systems have been used for purification of citric acid.The influences of species of the system,pH and salts on the partition were investigated.In ATPS of PADB/PADBA.the optimal partition coefficient of citric acid is 0.18 with adding 40mM KBr,where the citric acid concentrated in bottom phase(PADBA).In ATPS of PMDB/PADBA.the optimal partition coefficient of citric acid is 3.04 with adding 80mM NaNO3,where the citric acid concentrated in top phase(PADBA)In order to obtain a better separation of citric acid,pH responsive polymers have been used to form two phases with citric acid fermentation broth for extraction of citric acid based on that citrate could form two-phase with some polymers.Four water soluble pH-responsive polymers PADB are synthesized by using acrylic acid,dimethylamine-ethyl methacrylate,and butyl methacrylate as monomers with different ratios.These polymers,which yield high recoveries(over than 97.0%),can be easily precipitated and recovered by changing pH to their isoelectric points(2.8,4.2,6.3 and 6.8,respectively).The polymers were characterized by infrared equipment,gel permeation chromatography and transmission electron microscopy.The Low field NMR was applied in phase separation mechanism investigation.It validated the phase formation possibility.Four ATPS composed of polymers and citrate have been conducted.The phase diagrams were determined and three empirical equations were used to correlate the binodal data.The increasing temperature caused the expansion of two-phase area.Measurements of the physicochemical properties(viscosity,density and interfacial tension)of the phases provide insight into the mechanisms responsible for the phase separation behavior.The kinetic of phase separation has been studied as a function of the physical properties of the system.A correlation describes the rate of phase separation with function of these properties.The effect of ATPS species,tie line length and ionic strengths in ATPSs were investigated to optimize separation behavior of citrate.PADB6.8/citrate had the best separation of citrate among these four ATPS.The influences of temperature,pH and additional salt ionic in the system on the separation factor have been studied.Increasing temperature raised the separation factor.The result shows the optimal separation cofficience of citrate is 30.3 and the recovery efficient of citrate from bottom phase is 98.1%in ATPS that composed of PADB6.s and citrate at pH=6.3,T=318K.Furthermore,potential difference between two phases was found to be positive dependent with the separation factor.Citric fermenter broth from lignocellulose has been used for forming two phases with PADB6.8 and it showed a good separation potential.A novel,nearly isothermal,nonselective-membrane separation process,membrane vapor extraction(MVE),efficiently recovers butanol from a dilute aqueous solution,for example,from a fermentation broth.In MVE,feed and solvent liquids are not in contact;they are separated by vapor.Therefore,compared to conventional extraction,MVE avoids formation of difficult-to-separate emulsions.In MVE,a semi-volatile aqueous solute(e.g.,butanol)vaporizes at the upstream side of a membrane,diffuses as a vapor through the membrane pores,and subsequently condenses and dissolves into a high-boiling nonpolar solvent,favorable to the solute but not to water.Design analysis of a 1.5-m long,30-m2 membrane-area countercurrent MVE unit for processing 2-wt%aqueous butanol by dodecane solvent at 40℃ indicates over 90%recovery of the feed butanol with essentially no water loss and with very low energy requirement.The separation factor is over 1500.Here,we present experimental data to validate the MVE process.We use an omniphobic，0.2-μm pore-diameter Versapor(?)200R membrane housed in a 6-cm wide by 10-cm long plate-and-frame channeled flow cell with 0.8-cm gap thickness.Membrane transfer area is 28 cm2.The membrane flow cell is designed for minimal axial concentration change and is operated between recirculating flow loops.2-wt%aqueous butanol is extracted into dodecane or mesitylene at 25 or 40℃.Since vapor transport across the membrane contributes minimal resistance,MVE performance is governed by mass transfer through feed and solvent boundary layers.Mass-transfer coefficients are determined from the Graetz-Leveque analysis of laminar thin-slit flow.Predicted extraction performance agrees well with experiment using no adjustable parameters.Consistent with our initial multistage-design analysis,experimental results here confirm that MVE is a viable separation process to recover dilute semi-volatile biosolutes from water with minimal energy requirement.Preliminary analysis of downstream solute recovery from the extract via distillation is more efficient than that for pervaporation because of insignificant water carry over through the MVE membrane.