Enhancing Mass Transfer Of Maleic Acid Hydrogenation Product Through Catalyst Layer In Electrochemical Hydrogen Pump Hydrogenation Reactor

As a circular and environmental friendly renewable energy source,biomass fuel,which is very similar to fossil fuel in composition,is considered as the best alternative power source for fossil fuel.Due to the low heat value and low stability of biomass oil,hydrogenation of biomass oil is a necessary method to convert biomass oil into biomass fuel.Most studies on hydrogenation of biomass derivatives have been done in conventional three-phase reactors.Due to the low solubility of hydrogen in the liquid phase,high temperature and pressure is needed in a conventional three-phase reactor.Electrochemical hydrogen pump reactor(EHPR),with the same structure as proton exchange membrane fuel cell,uses polymer electrolyte(much thinner than electrolyte solution)to fast transport proton to the cathode to create insitu chemisorbed hydrogen(Hads)on the catalyst surface.Therefore,EHPR can be operated under room temperature and atmospheric pressure and reach high reaction rate.Despite the advantage of EHPR,product inhibition is observed in most reported hydrogenation with EHPR,which means hydrogenation rate declines fast with the increase of reaction time or reactant concentration.Product inhibition of C=C,or C=O hydrogenation is more serious in EHPR than in conventional three-phase reactors,which greatly correlates to the microporous flow channels in catalyst and diffusion layers.Maleic acid is chosen as the model compound of biomass derivatives.With the addition of ethanol,it is found that both hydrogenation conversion and rate increase by about 1.46 folds.The effect of ethanol is further investigated with different operating parameters to improve the performance of the EHPR.With ethanol,EHPR is more suitable for high current density.With a current density of 132.3 mA cm-2,addition of ethanol increases the reaction rate,conversion and current density by 83.1 %.By analyzing the construction and property of catalyst layer and the adsorption experiment of amber acid and maleic acid,the strong interaction between amber acid and the surface of carbon carrier is confirmed,which slows down the mass transport of amber acid in the catalyst layer.When ethanol is added into the reaction solution,it tends to take the place of amber acid by competitive adsorption onto the carbon particles.The weaker interactions between ethanol and amber acid release more amber acid molecules into the bulk solution,eventually relieving product inhibition.Assuming Langmiur adsorption and introducing the reverse reaction,a semi-empirical hydrogenation kinetics model considering the product inhibition and ethanol concentration is proposed and fitted with the experiment data well.Based on the analyzation of the parameters,several principles of EHPR catalyst layer design and choice of competitive adsorbent are proposed.