Synthesis Of Composite Imprinted Membrane And Application In Selective Separation And Recovery Of Salicylic Acid Compounds

Salicylic acid series products including salicylic acid, methyl salicylate, salicylamide and acetyl salicylic acid and so on, are widely used in the field of chemical, pharmaceutical, food, cosmetic and so on. On account of the incomplete conversion of raw materials and poor technology of separation and purification during the production process of salicylic acid series products, it will inevitably create a lot of by-products in the aim products as well as large number of the liquid waste rich in salicylic acid substance. Because most of the application of salicylic acid is closely related to people, the by-products concentration exceeded standard will directly affect human life and health safety issues. Moreover, it seems impossible to effectively recycle of salicylic acid series material in the waste liquid and turn "waste" into wealth with the traditional separation/enrichment technology. These waste liquid with high recycling value are often treated as industrial wastewater, causing serious waste of resources and economic losses. Additionally, the general sewage treatment technology is difficult to dispose of the high concentration of salicylic acid series material in the waste liquid. If released into the environment of water and soil, it will cause varying degrees of damage, and affect the ecological balance and ultimately endanger human life. Therefore, the effective separation and purification of the waste liquid during the production process of salicylic acid series products will, on the one hand, can recycle high value of salicylic acid series material, then it can prevent the formation of the industrial waste water. It is of great significance For the green production of salicylic acid products and environmental protection.At present, the main methods for the separation and enrichment of salicylic acid products are recrystallization, extraction, chromatography method, molecular distillation and membrane separation, etc. These methods have their own unique advantages, but also has its limitations. The rise of membrane separation technology with its high efficiency, energy conservation, convenient operation, molecular filtration, environment friendly advantages in the production process has been widely used in enterprises. But the membrane separation technology in traditional still exist some restrict factors of its development, such as the current commercially available membrane can realize the separation of a substance but can not achieve the separation of a single material, especially for organic compounds with similar structure. The traditional film can not show a single, highly selective separation of a substance. Therefore, it is significant to research and develop a high efficiency, low energy consumption, green and convenient purification method of salicylic acid series products. Molecularly imprinted polymers (MIPs) prepared via molecular imprinting technology (MIT) is a polymer materials with molecular recognition ability, there are many imprinted cavities on its surface which have specific affinity and recognition ability to the target molecule. Molecularly imprinted composite membrane is compounded of a optimized porous support layer structure and selective layer, which unite molecular imprinting technology and membrane separation technology. This composite membrane possesses the advantages of specific recognition excellent performance of flux, it is an ideal imprinted membrane materials. On the one hand, the technique is convenient for continuous operation, easy amplification, low energy consumption, high energy utilization rate, it is the typical "green chemistry". On the other hand, it overcomes the defect that the present commercial membrane materials such as ultrafiltration, microfiltration and reverse osmosis membrane cannot realize single substance separation. It provides a feasible and effective way to separate the specific molecular from the structure similar mixture.In this paper, using a variety of surface modification technology, on the surface of different substrate membrane (polyvinylidene fluoride microfiltration membrane, polypropylene microfiltration membrane and inorganic ceramic membrane), prepared of compound molecularly imprinted membrane which is used in the study of selective purification of salicylic acid products. Through the system analytical measurements to character the surface morphology, structural composition, hydrophobic and membrane flux of the prepared composite membranes. Studying the adsorption capacity, permeability, and the dynamic separation performance of various molecularly imprinted composite membranes for selectively recognizing salicylic acid products, and discusses the recognition mechanism in detail. The main study results of this thesis are as follows:1. The preparation of salicylic acid composite imprinted membrane by the photo-init iation polymerization method for selective separation and enrichmentThree kinds of imprinted membranes for salicylic acid:MAA-MIM, AM-MIM and4-VP-MIM, were prepared via photopolymerization based on polyvinylidene fluoride membrane (PVDF) with methacrylic acid (MAA), acrylamide (AM) or4-vinylpyridine (4-VP) as the functional monomer, respectively, and N.N’-methylene-bis-acrylamide (MBAA) as crosslinking agent, benzophenone as photoinitiator. The structure, morphology of three imprinted membrane was characterized by UV, SEM, FT-IR and Raman spectra. The static kinetics experiment indicates that adsorption equilibrium time for three imprinted membranes were all10min. The isothermal adsorption curve indicates that the membrane prepared with4-VP as functional monomer had good adsorption effect. Moreover, the adsorption capacity of4-VP-MIM for SA increases with the increase of the concentration of functional monomer. Selectivity study shows that4-VP-MIM has better selectivity than MAA-MIM and AM-MIM on SA and high functional monomer concentration affect the selectivity of MIM. The different performance among MAA-MIM, AM-MIM and4-VP-MIM was investigated by UV spectra and1HNMR. It was drawn that the ionic bonding between SA and4-VP stronger than the hydrogen bond between SA and MAA or AM may the main recognition mechanism of imprinted membrane. Permeation experiment shows that transport mechanism for permeation of the ASA and SA towards4-VP-MIM was accordance with the facilitated mechanism.2. The preparation of composite imprinted membrane by the the sol-gel method for selective separation and enrichment(1) Two kinds of composite imprinted membranes (CIAM) for p-hydroxybenzonic acid (p-HB) was prepared via hydrolytic sol-gel method based on alumina membrane by using p-HB as the template molecule,(3-isocyanatopropyl) triethoxysilane (ICPTES) or aminopropyltriethoxysilane (APTES) as the functional monomer, the tetraethoxysilane (TEOS) as the cross-linker, and hydrochloric acid as the catalyst. The structure, morphology of CIAM was characterized by FT-IR and SEM. Flux test shows that the imprinted polymer layer on the membrane is helpful to increase the membrane flux. Binary selective experiments shows CIAM can selective rebind the p-HB, moreover, Compared with composite imprinted membrane via non-covalent imprinting approach (NCIM), the SCIM exhibited higher selective separation factor (3.120), showing excellent selectivity for p-HB. Permeation experiment show that transport mechanism for permeation of the p-HB and SA towards SCIM or NCIM was accordance with the facilitated mechanism. Response surface methodology of a three level, three variable Box-Behnken design (BBD) was applied to determine the best dynamic separation parameters for optimizing the separation process including the the concentration of p-HB (mg/L), the temperature (℃) and the flow rates (mL/min). The optimal conditions for the separation of p-HB from SA were as follows:the p-HB concentration of5.0mg/L, the temperature of10℃and the flow rate of1.0mL/min.(2) Three kinds of composite imprinted membranes (CIAM) for gentisic acid (GA) was prepared via room temperature ionic liquid (RTIL)-mediated nonhydrolytic sol-gel (NHSG) methodology based on alumina membrane by using GA as the template molecule, acrylic acid (AA), cinnamic acid (CA), and methacrylic acid (MAA) as three functional monomers, RTIL as pore template, methacryloxypropyltrimethoxysilane (MPS) as the crosslinker,2,2’-azobis(2-isobutyronitrile)(AIBN) as an initiator. The structure, morphology of CIAM was studied by UV、FTIR、SEMA、AFM. Flux test shows that the CIAM have good porosity and the structure of the imprinted polymer on the membrane was stable. Static adsorption study show that the CIAM prepared with CA as functional monomer has higher adsorbing capacity. Additional, it is obvious that the crosslinker amount can affect the performance of the membrane. Permeation experiment show that the ionic liquid play an important role in the separation effect of CIAM. The higher SA permeability coefficients (5.146×10-3cm/s) and lower GA permeability coefficients (1.233x10-3cm/s) for CIAM2show the optimal separation effect. Additionally, a three-level Box-Behnken experimental design with three factors combining the response surface modeling was used to optimize dynamic separation process and the optimal conditions were as follows:the GA concentration of5.0mg/L, the temperature of15℃and the flow rate of1.0mL/min.3. The preparation of composite imprinted membrane by the emulsion polymerization method for selective separation and enrichment(1) The submicrosized imprinted polypropylene microfiltration membrane (SIPM) for salicylic acid (SA) was prepared via common water-in-oil emulsion polymerization method based on polypropylene microfiltration membrane by using salicylic acid as template molecule,4-vinyl pyridine as functional monomer, Span80as emulsifier, toluene as the oil phase, ethyleneglycol dimethacrylate as cross-linking agent,2,2’-azobis (2-methylpropionitrile) as initiator. The structure, morphology and surface wettability of SIPM was characterized by Raman spectra, SEM, AFM and contact angle test. Flux test shows that the submicrosized Imprinted Spheres on the membrane is helpful to increase the membrane flux. Static adsorption experiment indicates that SIPM had a selective rebinding for SA. Moreover, it will increase the adsorption amount of SA with properly increasing the amount of imprinted spheres. Permeation experiment show that transport mechanism for permeation of the SA and ASA towards SIPM was accordance with the facilitated mechanism.(2) The molecularly imprinted composite membrane (CIAM) for phenol was prepared via oil-in-water microemulsion polymerization method based on alumina membrane by using phenol as template molecule,4-vinyl pyridine as functional monomer, styrene as the monomer, N,N,N-trimethyl-l-dodecanaminium bromide as the emulsifier, deionized water as the continuous phase, divinylbenzene as cross-linking agent and potassium persulfate as initiator. The structure, morphology of CIAM was characterized by UV, Raman spectra, SEM, TEM and XPS. The amount of surfactant and the mixed mode of oil and water phase can affect the particle size of imprinted nano-spheres in the membrane. Flux test shows that CIAM possessed good porosity. The nano-spheres with different size affect the adsorption capacity and selective performance of the CIAM. In the permeation experiment, the selective separation factor of CIAM5for SA and phenol was18.2, indicating that smaller nano-spheres benefited selective separation to some extent. However, it will be bad for selective separation if the nano-spheres is too small because of their reunion. Last, simulating dynamic separation of salicylic acid and phenol as well as the detection of phenol in salicylic acid industrial products through standard addition recovery method were investigated.