The Application Of Catalytic Active Membrane Reactor On Condensation Of N-butyraldehyde With 1,2-propanediol

The n-butyraldehyde 1,2-propanediol acetal is synthesized from n-butyraldehyde and 1,2-propanediol under the action of an acidic catalyst.That is a novel perfume having a high added value and a wide range of uses.However,since the reaction is a typical reversible reaction,the conversion of the reactants is at a lower level.As a means of process strengthening,the reaction separation coupling technique can remove the by-product water generated during the reaction,thereby breaking the reaction equilibrium and promoting the reaction to move in the direction of product formation.At present,the commonly technology adopts reactive distillation or reaction-azeotropic.This technology can improve the reaction efficiency by coupling the reaction process with the separation process.However,these methods have some problems,such as complicated operation,high energy consumption and high production cost.Moreover,it is necessary to introduce a water-carrying agent when using reaction-azeotropic technology for production.However,the water-carrying agent is generally toxic,so this technology will seriously affect the quality of acetal products.In order to overcome the above problems,this paper proposes to introduce a pervaporation catalytic active membrane reactor into the synthesis of n-butyraldehyde 1,2-propanediol acetal to achieve high-efficiency synthesis of acetal,this technology is low energy consumption and simple operation.Based on the previous research of our group,the PVA/Zr(SO4)2·4H2O pervaporation catalytic membrane was prepared and applied to the membrane reactor.The pervaporation catalytic active membrane reactor was studied for n-butyraldehyde 1,2-propanediol acetal synthesis.Polyvinyl alcohol(PVA)was used as a membrane-forming material,Zr(SO4)2·4H2O was used as a catalyst,and anhydrous ethanol was used as a coagulation bath.A pervaporation catalytic membrane with a porous structure was prepared by immersion precipitation phase transformation.The physicochemical properties of the prepared pervaporation catalytic membrane(SEM,XPS,TGA,porosity)were characterized.The separation performance of the pervaporation catalytic membrane for 1,2-propanediol/water and n-butyraldehyde/water was investigated.The acetal reaction was carried out using different types of reactors,and the reaction-separation coupling properties were investigated.The operating conditions of the pervaporation catalytic membrane reactor are optimized.The experimental results show that the combination of the layers of the pervaporation catalytic membrane is good,no peeling phenomenon.The thermal stability is good when the temperature is lower than 350℃.The separation performance of the pervaporation catalytic membrane is good.When the separation temperature is 30℃,the water flux can reach 120 g·m-2·h-1 for 7 wt.%of the 1,2-propanediol/water binary system.The factor has reached more than 3,000.The catalytic performance of the pervaporation catalytic membrane is well.When the catalyst loading is 5 wt.%,the catalytic performance of acetal reaction can be satisfied.When the reaction temperature is 30℃,n-butyraldehyde as a reactants can reach equilibrium conversion rate(about 47%)in a short time.The acetal reaction-separation coupling experiment was carried out using an pervaporation catalytic active membrane reactor.The thermodynamic equilibrium of the reaction can be broken,and the conversion of n-butyraldehyde reached 70%within 12 h.Compared with the equilibrium conversion rate,the conversion increased by more than 20%.In addition,the effects of different operating conditions were investigated.The suitable temperature for the reaction was 50℃,and the suitable V/A ratio was 0.8 mm.The conversion of n-butyraldehyde was carried out under the condition of V/A of 0.8 mm and temperature of 50℃.The conversion of n-butyraldehyde is above 93%,which is about 46%higher than the equilibrium conversion.