With Phase Transfer Catalytic Function Of Structural Optimization And Application Of Magnetic Nanoparticles

Liquid-liquid biphase catalytic reaction systems have been developed rapidly. In order to solve the problems related to mass transfer and catalyst recovery in biphase reaction system, many researchers conducted a thorough and meticulous research, such as the development and utilization of thermoregulated phase-transfer catalysts, phase transfer catalyst emulsion system and the immobilized catalyst. Recently, we had reported a novel methodology for creating the broader applicability of catalyst with hydrogel core and amphiphilic phase transfer catalyst shell structure similar to W/O emulsion droplet. The results indicated that the prepared catalysts not only were valuable for deep oxidation desulfurization but also can extract the polar product from system. And the related researches open up new ways for two phase catalysis. However, it was found that the size of composite microreactor is too large to influence the mass transfer. As the continuous part of previous work, we anticipated to explore the preparation of small-size and easy-separated biphase catalytic microreactor for H2O2catalyzed oxidative desulfurization. We constructed three new biphase catalytic microreactors and examined their catalytic properties and expected to open new way for effectively improvement of catalyst performance.Based on the purpose above, two aspects are concluded in the thesis as follow:1. The preparation and performance study of magnetic nanoparticle/hydrogel/phase transfer catalyst microreactorThe magnetic silica nanoparticles (MSN) were prepared via the emulsion system. The obtained MSN surface can be modified with silane coupling agent, led to the formation of terminal C=C bonds on the surface of each MSN core. Finally, in the presence of MPS-modified magnetic silica polymerization of acrylamide (AM, the monomer) and N,N-methylene bis-acrylamide (BA, the cross-linker) was initiated by using potassium persulfate (KPS) as an initiator, resulting in the formation of the magnetic hydrogel nanoparticles MSN/PAM (MHN). Then MHN was impregnated in ethanol solution containing3-(trimethoxysilyl)propyl-N,N-dimethyloctadecyl ammonium chloride (18QAS), followed by ion-exchange between18QAS loaded on the surface of MHN and K2{W(=O)(O2)2(H2O)}2(μ-O)(W2), microreactor MHN/18QAS-W2were obtained. The morphology and components of the composite material were characterized by TEM, EDX, XPS, FT-IR, TGA-DSC and VSM, respectively. Empolyed the oxidation of dibenzothiophene with hydrogen peroxide as the model reaction, the catalytic performances of the microreactor MHN/18QAS-W2and the effects of several factors on desulfurization reactivity were systematically investigated, so that some key factors on the catalytic performances were obtained.The results showed that the microreactor has core-shell structure with nanoscale dimensions. MHN/18QAS-W2not only has high catalytic activity in the oxidation of dibenzothiophene but also can extract the polar product from system. The DBT initial concentration is the key factor related to the catalytic performance. MHN/18QAS-W2can be quickly separated by the external magnetic field due to its superparamagnetic property. However, because of the weak interaction between MHN and18QAS-W2, the reused microreactor MHN/18QAS-W2was less stable.2. The preparation and performance study of magnetic nanoparticle phase transfer catalyst microreactora)MSN/18QAS-PTAIn order to enhance the interaction forces between the phase transfer catalyst and the carrier to prevent catalyst leak, we directly immobilized the phase transfer catalyst on the surface of MSN by the covalently bound. Magnetic silica/18QAS nanospheres were prepared by the condensation between Si-OH groups on surface of MSN and derived from hydrolyzed18QAS in solution. MSN/18QAS-PTA was constructed by ion-exchange between18QAS loaded on the surface of magnetic silica/18QAS and PTA. TEM, EDX, XPS, FT-IR, TGA-DSC, video contact angle analyzer and VSM were used to characterize the structure, composition and special performances of the microreactor MSN/18QAS-PTA. We took the oxidative desulfurization of fuel oil with hydrogen peroxide as an example to verify the feasibility of using the resulting composite microreactor to aqueous/organic biphasic catalysis. The effects of several factors on desulfurization reactivity were systematically investigated.The results showed that the composite nanospheres have core/shell structure with the properties of amphiphilicity and superparamagnetism. The composite nanospheres have high catalytic activity in the oxidation of dibenzothiophene to corresponding sulfones by hydrogen peroxide under mild reaction conditions. The sulfur level could be lowered from487ppm to less than0.8ppm under optimal conditions. The suitable amount of catalysts immobilized on the nanoparticles and hydrogen peroxide used as reactant are necessary for the high efficiency of desulfurization. Additionally, the amphiphilic catalyst and the oxidized product could be simultaneously separated from medium by external magnetism. Compared with the use of magnetic nano-hydrogels (MHN) as a template to construct microreactor in the previous chapter, MSN/18QAS-PTA has a distinct advantage in the recovery and reuse. The recovered composite material could be recycled for four times with almost constant activity,b) MSN/12QAS-PTAIn order to explore the influence of alkyl chain length in the phase transfer catalyst on the microreactor effects, we synthetize3-triethoxysilylpropyl-N,N-dimethyl-dodecylammonium chloride (12QAS) with shorter alkyl chain and immobilized12QAS on the surface of the MSN via hydrolysis and condensation reactions. Then after ion-exchange between12QAS and PTA, the biphase reaction microreactor MSN/12QAS-PTA was prepared.1H NMR,13C NMR and FT-IR were used to character12QAS, then TEM, EDX, XPS, FT-IR, TGA-DSC, video contact angle analyzer and VSM were used to characterize the structure, composition and special performances of the microreactor MSN/12QAS-PTA. The effects of several factors on desulfurization reactivity were systematically investigated.The results showed that the composite nanospheres have core/shell structure with the properties of superparamagnetism and the surface hydrophilic/hydrophobic adjustability. This conception of catalyst design is feasible. The microreactor MSN/12QAS-PTA has a good performance in the catalytic oxidation. The DBT level could be lowered from500-3000ppm to less than5ppm under optimal conditions. The amount of phase transfer catalyst loaded on the surface of MSN/12QAS-PTA and the usage amount of hydrogen peroxide is the critical factors to determine MSN/12QAS-PTA catalytic performance. Additionally, the microreactor can extract the oxidized product and exhibit a stable catalytic performance. Its catalytic efficiency is still high after recycling for five times.In summary, it is feasible to employ MHN or MSN as the template to construct immobilized phase transfer catalyst (the complexes of heteropoly acid quaternary ammonium salt) microreactor. According to the experimental results, the microspheres reactor does have the expected nature and function. Three microreactors mentioned above not only have high specific surface area, good catalytic activity and a certain degree of the product extraction, but also have superparamagnetic property which makes separation process simple. The performances mentioned above are attributed to the specific structure and components of the prepared nanoparticles.Based on the preparation and performance study of biphase catalytic microreactor, this paper not only focused on the improvement of the phase transfer catalyst reaction mass transfer efficiency, but also on the design of effective distribution of the catalyst and reactants in space, in order to achieve the purpose of improving catalytic reaction efficiency. The construction rote of such microreactors may be significant to design multifunctional catalytic materials used in the water/organic diphase systems.