Catalytic Distillation For Esterification Of Cyclohexene/ethanol With Acetic Acid: Nafion And ZSM-5 Structured Catalysts And Experimental Optimization Via Response Surface Methodology

In recent years,the chemical industry is moving in a compact,safe,efficient and environmentally sustainable development.As been a leading role in the chemical industry,catalyst research has played a significant role in improving the efficiency of catalytic process,reducing energy consumption,simplifying the production process and protecting environment.From the view point of green chemistry,catalytic reaction essentially involves the surface/interface process.The preparation of an efficiently new catalyst should not only consider the active sites,porosity,shape,microstructure and composition of catalyst in molecular level,but also consider the effects on catalytic reaction engineering such as the reactants diffusion,multiphase contact,fluid distribution,mass/heat transfer and pressure drop.With the development of traditional coating technology,the structured catalyst has been a hot intersectional topic between catalysis and chemical engineering due to the enhanced heat/mass transfer and improved hydrodynamics.The structured catalyst is widely used in the field of chemical reaction engineering because of its properties which combine both catalyst and reactor.For these reactions which affected by the limitation of diffusion and strongly exothermic process,structured catalysts and reactors?SCRs?overcome the shortcomings of conventional reactors such as slurry bed or fixed bed reactor to uniform the fluid distribution and temperature of catalyst bed,eliminate diffusional limitation,and decrease the pressure drop.Therefore,it is of great significance to design a new structured catalyst for the catalysis and reaction engineering.The carboxylic ester?for example ethyl acetate?is an important organic chemical material and solvent and widely used as an environmentally friendly replacement solvent for traditional aromatic compounds such as toluene,xylenes and ketones in the fields of coatings,spices,adhesive and organic synthesis.Industrially,carboxylic ester is commonly produced via direct esterification of acetic acid with alcohol in the presence of homogeneous inorganic mineral acids.However,this industrial process would generate chemically reactive waste streams with highly corrosive media,making both purification and waste disposal difficult and hazardous,and high heating effect and mass transfer limitation.In this dissertation,based on the“Top-Down”design philosophy,namely reactor?Top,hydrodynamics and transfer?-catalyst?Down,surface/interface reaction?,we developed microfiber structured catalysts via dip-coating and in-situ hydrothermal growth method to make the solid acid directly supported on the surface of stainless steel microfiber supports with the unique three-dimensional?3D?network structure,and coupled with enhanced heat/mass transfer and improved hydrodynamics properties.These soild acid catalysts exhibited good catalytic activity and stability,which realized the collaborative coupling between reactor?hydrodynamics and transfer?and catalyst?surface/interface reaction?.Such a microfibrous-structured catalyst was used in the catalytic distillation route as a chemical process intensification and unique combination of high catalytic efficiency and instantaneous distillation within a single column.The catalytic distillation process can restrain the formation of azeotrope and removal of products to promote the efficiency of catalytic reaction and distillation separation.The reaction heat can be utilized efficiently for the catalytic distillation to lower energy consumption and capital investment as a green chemistry process.The content and main results of this dissertation consisted of three parts as following:?1?Catalytic distillation for ethyl acetate synthesis using stainless steel fiber?SS-fiber?structured Nafion-SiO2 soild acid catalystsIn this study,we presented a sinter-locked 3D network consisting of stainless steel microfibers?SS-fiber?as the structured matrix and shaped into?-ring analogues.As an active component,Nafion was then firmly locked into the SiO₂ layer that was anchored onto the SS-fiber surface by a dip-coating method using self-crosslinking Nafion-SiO₂ sol-gel prepared by Nafion-catalyzed hydrolysis of tetraethylorthosilicate.High acidity?denoted by ion exchange capacity,IEC?and excellent durability of the structured catalyst were obtained by regulating the Nafion polymer dispersion concentration and the weight ratio of Nafion to TEOS.A high ethyl acetate actual yield of 91.6%and purity of 96.2%were obtained under the optimal conditions which including the reboiler duty of 220°C,molar feed ratio of acetic acid to ethanol of1.2:1,WHSV of 0.5 h^-1,catalyst dosage of 10.5 mmol of H⁺,reflux ratio of 2 and molar ratio of acetic acid to ethanol in the flask of 1:1.2.Moreover,the microfibrous-structured catalysts were stable for at least 40 h with not only well-preserved structures but also chemical stability,which were evidenced by SEM,FTIR and TGA.?2?Catalytic distillation for ethyl acetate synthesis using microfibrous-structured SS-fiber@HZSM-5 catalystsA thin-sheet?1 mm thick?sinter-locked 3-dimensional?3D?network consisting of 15 vol%20?m SS-fiber and 85 vol%voidage was employed as the structured matrix and the microfibrous-structured SS-fiber@HZSM-5 solid acid catalyst had been successfully developed using a hydrothermal synthesis method to make the uniform and dense zeolite shell growing continuously along with the SS-fiber to form a hierarchical 3D porous fiber@zeolite structure.As-obtained SS-fiber@HZSM-5catalysts engineered from micro-to macro-scales have a high zeolite loading,adjustable SiO₂/Al₂O₃ molar ratio and excellent structure robustness.The suitable acid strength of catalyst and its distribution on catalyst with stability of catalyst were optimized by tuning the SiO₂/Al₂O₃ molar ratio.The response surface software for statistical analysis and model fitting was employed to investigate the effects of the five independent reaction parameters on the catalytic distillation and to determine the optimal conditions,with the aim of maximizing the catalytic effieiency?yield of ethyl acetate?and distillation effieiency?purity of ethyl acetate?.The high total yield?95.9%?and actual yield?90.9%?of ethyl acetate with a high STY of 1.25 g g^-1_zeoliteeolite h^-1 could be achievable in catalytic distillation process under the optimum reaction conditions obtained by response surface analysis,while the high CD efficiency was well-preserved after at least 240 h.The SS-fiber@HZSM-5 catalyst possesses a thin shell?6?m?,large void volume?70 vol%?,high surface-to-volume ratio and a low pressure drop,which could intensify the mass transfer,eliminate the diffusion limitation and enhance the heat transfer.?3?Catalytic distillation for one-step cyclohexyl acetate production and cyclohexene-cyclohexane separation over microfibrous-structured Nafion-SiO2/SS-fiber soild acid catalystsTo remove contaminations,as-obtained?-ring-like analogues?3 mm in dia.?of SS-fiber were soaked in an aqueous 0.1 mol L^-1 NaOH solution and then washed with acetone.A dip-coating method using 10 wt%Nafion solution and Nafion/TEOS weight ratio of 2.5:1 was used to firmly embedded Nafion-SiO₂ film onto the SS-fiber support.The well-preserved structure and excellent acidity and chemical stability of the structured catalyst were characterized by SEM,FTIR and TGA.Catalytic distillation can be used for one-step cyclohexyl acetate production and cyclohexene-cyclohexane separation via esterification of cyclohexene with acetic acid.The response surface software was applied to develop an experimental design and empirical process model,followed by the effects of the independent reaction parameters on the synthesis of cyclohexyl acetate as well as the separation of cyclohexane and the optimization of reaction parameters.High actual yield of cyclohexyl acetate?78.1%?and high recovery of cyclohexane?93.0%?with 94.3%of cyclohexane purity were achievable in catalytic distillation process under the optimum reaction conditions obtained by response surface analysis,while the high CD efficiency of such microfibrous-structured Nafion catalyst was well-preserved after at least 200 h over these consecutive batch runs of response surface.