Study On The Reinforcement Of Esterification Of N-butyl Acetate And The Removal Of Trace Phenol From Water By Pervaporation

Pervaporation utilizes the adsorption and diffusion difference of the components in the membrane to separate liquid mixtures.The separation is carried out with the ocncentration difference or pressure difference as the driving force.Compared with traditional separation methods,pervaporation is superior in terms of simple operation and is suitable to priority selection separate low content group in the mixtures.Pervaporation is widely used in dehydration of organic solvent or removal of trace organic compounds in wastewater in petrochemical industry,environmental chemical industry and other related industries.Esterification reaction is one of the most typical reversible reactions.If the products are removed from the reaction system,the reaction equilibrium can be broken and enhance the forward direction.Water,generated from esterification reaction,is the only inorganic substance in the reaction mixtures and it owns the simplest molecular structure and the smallest molecular weight.So removal water from the reaction system it is the most commonly used method to strengthen the esterificatioii reaction.Phenolic effluent has a wide resource and great environmental harmfulness.Because it is difficult to be biodegraded at higher phenol concentration,phenol wast water should be treated by some other methods.The traditional separation methods to treat the phenol wastewater may cause secondary pollution and high-energy consumption.From an energy saving prospective,pervaporation is especially suitable for separating and recovery phenol from wast waters.Therefore,main content of this paper is to use the PVA-CS blend membrane for pervaporation coupling esterification process and application of pervaporation technology in the treatment of phenolic wastewater.Specific research contents are as follows:1.Preparation and characterization of PVA-CS blend membranes.FTIR,DSC,XRD and other characterization methods were used to investigate the effect of CS content on intermolecular interaction,miscibility,crystallization and mechanical properties of PVA-CS blend membranes.Swelling properties of PVA-CS blend membrane were carried out in pure solvents.The group contribution method was used to calculate the solubility parameters of pure PVA,pure CS,water,butyl acetate,n-butyl alcohol and acetic acid.Solubility parameters of PVA-CS blends were calculated through a simple mixing rule,the blending compatibility between PVA and CS was also predicted.The characterization results illustrated hydrogen bonds existing between CS(-NH2,-OH)and PVA(-OH),which ensured good compatibility between PVA and CS.Tensile strength increased and flexibility decreased of the blend membrane as the wt.%CS increased.The degree of swelling decreased remarkably upon the addition of CS and increased with elevation of temperature.The swelling test results were in good agreement with the solubility parameters.The affinity of the PVA-CS blend membrane to water was higher than that of n-butyl acetate,n-butyl alcohol and acetic acid.PVA-CS blend membrane is suitable for pervaporation dehydration of esterification of acetic acid with n-butanol.2.Study on pervaporation dehydration of three kinds of binary mixtures(n-butyl acetate/water,n-butanol/water,acetic acid/water)and one ternary mixtures of n-butyl acetate/n-butanol/waterThe effects of PVA-CS blending ratio,operating temperature and water content in feed solutions on the permeation flux and separation factor were investigated.Both the total and partial flux linearly increased with the increase of temperature and permeation activation energy of each component can be regressed from Arrhenius equation.The results showed that permeate flux of water was much higher than the other three kinds of organic compounds,while the blending ratio shows little effect on the total flux for the binary mixtures.For the ternary system,maximum permeate flux is abttained at PCA-CS50 membrane.The PVA-CS25 shows best separation performance for all three binary system while PVA-CS75 for ternary system.3.Study on the pervaporation-aided esterification of n-butyl acetate(1)DA340 strong acidic ion exchange resin was used as catalyst for esterification of acetic acid with n-butanol.The pseudo homogeneous second order reaction kinetics model was established.Kinetic parameters were determined from the experimental data after eliminating internal and external diffusion.The calculated values from kinetics model are in good agreement with the experimental data.(2)The esterification reaction was intensified by pervaporation through PVA-CS/PVDF blend membrane and the PVA-CS75 film showed the best strengthening effects.Selective behavior of PVA-CS/PVDF film on reaction mixtures follows the sequence as:water>acetic acid>n-butanol>n-butyl actate,which agrees well with the PV dehydration of the binary and ternary mixtures.The effects of operating parameters on the process were investigated.The reaction rate and PV dehydration rate both increase with temperature increase.When the initial molar ratio of alcohol to acid was increased,the permeation flux of water decreased,which would weaken the effect of strengthening while increasing of S/V could effectively enhance the esterification.4.Preparation of ?-cyclodextrin filled PEBA membranes and the pervaporation separation of phenol from dilute solution.?-cyclodextrin(?-CD)filled poly(ether block amide)(PEBA)membranes(??CD-f-PEBA)were prepared by solution casting method to recover phenol from dilute solution by pervaporation.The physicochemical structure of the membrane was studied by SEM,FTIR and tensile test.The results showed that the p-CDs were dispersed uniformly within the polymer phase and a good adherence was obtained between the P-CD and PEBA just by physical crosslinking.Tensile and breaking strength of ?-CD-f-PEBA membranes decreased initially and then increased with the increase of ?-CD dosages in the membranes.The swelling experiments showed that the degree of swelling increased significantly both with the phenol concentration in feed solutions and the ?-CD dosage in PEBA base membranes.The solubility parameters of PEBA,phenol and water were calculated by the group-contribution method.The solubility parameter difference between PEBA and phenol are smaller than the difference between PEBA and water,which means the PEBA owned high phenol selectivity than water.The adsorption and diffusion separation factor of the ?-CD-f-PEBA membrane were used to conform the controlling step of the PV process.The PV performance of P-CD-f-PEBA membrane was investigated at different operating conditions.With the increase of P-CD content,the(3-CD-f-PEBA membranes displayed significantly improvement of the permeation flux and the separation factor.The?-CD-f-PEBA membrane containing 0.5 wt.%?-CD showed the best separation performance with a total flux and separation factor of 3062.9 g·m-2·h-1 and 43.3,respectively.With temperature increasing,both the total flux and separation factor increased.The activity energies of phenol and water flux were calculated according to Arrhenius equation with values of 97.19 kJ·mol-1 and 52.12 kJ·mol-1,respectively.The long term stability of(3-CD-f-PEBA membrane was tested by repeated experiment.