Preparation Of Zeolite Membrane Microreactor And Its Catalytic Performance

Miniaturization is the trend of chemical engineering. It can incorporate reaction andseparation together. To some extent, it can simplify the equipments. The advantages of themicroreactor are: Excellent temperature control that is able to prevent hot-spot formation,higher selectivity and conversion compared to conventional reactors, intrinsic safety andeasier scale up, especially the production of hazardous and explosive materials.Zeolites, with the supercages and channels of defined sizes, are important catalysts inmany chemical and petrochemical processes because of their high specificity in adsorptionand catalysis. Recently, it has been successfully shown that zeolite and molecular sievesmaterials could be incorporated as catalyst, membrane and structural material in miniaturechemical devices such as microreactors and microseparators. Miniaturization benefits bothreaction and separation by improving mass and heat transfer rates through increasedinterfacial area and shorten diffusion path length.In this paper, the method of using colvalent linkers to introduce zeolites on stainless steelwas studied. Three kinds of siloxane colvalent linkers, such as3-aminopropyltrimethoxysilane(AP-TMS), 3-chloropropyltrimethoxysilane(CP-TMS) and3-mercaptopropyltrimethoxysilane(SP-TMS), were used. The two different kinds of NaA andSilicalite-1 zeolite seeds were introduced onto stainless steel, respectively. The results showedthat NaA seeds can be successfully deposited on stainless steel using CP-TMS and AP-TMScolvent linkers, respectively. As for Silicalite-1 seeds, CP-TMS and SP-TMS worked well.NaX zeolites were introduced onto stainless steel multichannel microreactors usingAP-TMS covalent linker prior to regrowth. Membrane was regrown in the channel onassembled reactor on-site by a novel flow method. The cesium ion exchange was takenon-site by the similar flow method, too. The performance of the synthesized CsNaXmembrane was tested by the Knoevenagel condensation reaction of benzaldehyde andcyanoacetate. The product yield reached around 40ï¼…at a residence time of 50 min. However,in conventional reactor, the yield only reached 10ï¼…or so.In order to incorporate reaction and separation together, the NaX/NaA compositemembrane was synthesized into multichannel microreactor. First, the NaA zeolite particleswere introduced onto the surface of the stainless steel multi-channel plate via AP-TMS colvalent liker to form densely packed seed layers which can serve as good seeds for zeolitemembrane growth. Then, the NaA membrane was synthesized by secondary regrowthmethods in autoclave. After the NaA membrane NaX zeolites were coated on the synthesizedNaA membrane. The NaX membrane was regrowth by the flow method.The performance of the membrane was tested by pervaporation of the mixture ofbenzaldehyde and water. The results showed that the highest separation factor 17036 can beobtained when the feed concentration is 1wtï¼…water in benzaldehyde. The reaction resultsshowed that the product yield can be enhanced 10ï¼…with separation layer compared to thatwithout separation layer.At last, the higher activity catalyst CsNaX-NH₂ was used to catalyze Claisen-Schmidtcondensation of benzaldehyde and acetophenone which required more highly active catalyst.The performances of three kinds of reactors were studied, such as batch reactor, macro reactor(packed bed reactor) and microreactor. The highest product yield (65.3ï¼…) was obtained frommicroreaction, while the lower was from batch reaction and the lowest was frommacroreaction. The product yield was only 13.1ï¼…in macroreactor.