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Cellulose membranes via alkaline hydrolysis of cellullose acetate membranes and their application in organic solvents

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2019
İmir, Zeyne
Cellulose, the most abundant polymer in nature, is an attractive membrane material. Hydroxyl groups in the polymer chain make it hydrophilic, which makes cellulose membranes fouling resistant. Intra and intermolecular hydrogen bonding due to these groups on the other hand gives cellulose solvent resistance which is an attractive property for membrane filtration in organic solvents. Although cellulose is insoluble in many solvents, ionic liquids dissolve cellulose so that cellulose membranes can be prepared by phase separation. Molten salts which are in liquid form below 100 ºC are called as ionic liquids. In this study, 1-ethyl-3-methyl-imidazolium acetate (EMIMAc) is used as ionic liquid. Alternatively, by deacetylation of cellulose acetate membranes in alkaline media, regenerated cellulose membranes are obtained without any necessity of ionic liquids. Sodium hydroxide solution serves as regenerating agent due to its hydroxide groups. Effect of deacetylation duration and solution concentration on the regeneration efficiency is examined by FTIR spectra. Increasing NaOH concentration and time until 24 hours increased the degree of deacetylation. Firstly, cellulose and regenerated cellulose membranes are fabricated in flat sheet geometry. Drying medium effect on membrane morphology and separation performance of flat sheet cellulose membranes was evaluated and drying from ethanol was chosen as best method. In order to find out deacetylation and annealing effects on separation performance of cellulose acetate membranes, filtration tests were performed with Bromothymol Blue (624 Da)-ethanol solution. Annealed cellulose acetate membranes showed >80% dye rejection while this value decreased after deacetylation. Membrane modules which are made of hollow fiber membranes have much higher surface area comparing with flat sheet membrane modules. In the view of limited sources, producing and characterizing cellulose hollow fiber membranes for OSN applications is very important for the chemical industry. In this study, cellulose and regenerated cellulose hollow fiber membranes for OSN applications are produced. Polymer solution, bore liquid and coagulation bath temperatures were varied to arrange skin layer of hollow fibers. Separation performances are evaluated with Bromothymol Blue (624 Da) retention. As an application of cellulose membranes in solvent recovery, annealed and regenerated membranes were used to recover aprotic solvents from their 1 g/L and 10 g/L PES solutions. Experiments were performed in DMSO, NMP and DMF at 10 bar and 40 bar. Annealed and regenerated cellulose membranes have over 99% PES rejections approximately in all solvents. Also these membranes were stable in DMSO for over 10 days, in NMP and DMF for over 25 days.