Hydrogenation Of Maleic Acid By Hydrogen Pump Reactor With Electrospun PAN-based CNFs As Cathode Diffusion Layer

The Polymer electrolyte membrane hydrogen pump hydrogenation reactor (HPHR) is a kind of electrochemical in-situ hydrogenation device, which can realize the liquid-phase hydrogenation reaction at room temperature and atmospheric pressure. Compared with the traditional catalytic hydrogenation technology, it shows great advantages for the mild reaction condition, low energy consumption and high safety coefficient. Cathode diffusion layer in PHPR is one of the key factors that influence the reactant diffusion and the reaction rate. Therefore it needs good conductivity, high gas-liquid diffusion efficiency and strong corrosion resistance. The general gas diffusion layers (GDLs) used in fuel cells are hydrophobic and have large liquid infiltration resistance, as a result they are unsuitable for the HPHR dealing with aqueous solution reaction systems. So the cathode diffusion layer of HPHR need to be re-designed.Here we prepared the polyacrylonitrile (PAN) based carbon nanofibers (CNFs) by electrospinning and subsequent heat treatment process, which owns three-dimensional porous structure, with large void ratio, excellent gas/liquid permeability, high conductivity and chemical stability. After surface acidification treatment with sulphuric acid, the CNFs was used as the HPHR cathode liquid diffusion layer during the electrochemical hydrogenation of the bio-oil aqueous compound.Firstly, PAN/DMF solutions of different concentrations were used to prepare nanofiber mats by electrospinning method, and the influence of solution concentration, spinning distance, spinning voltage on the morphology of nanofibers were investigated. It was found that PAN/DMF shows the best spinnability with a solution concentration of8wt.%, a voltage range of14kV-20kV and a spinning distance range of8cm-20cm.Then we converted the PAN nanofibers into carbon nanofibers (CNFs) by procedure of pre-oxidation and carbonization. The temperature of peroxidation in the rage of250℃～280℃ and carbonization of700℃～1100℃were studied. It was found that a pre-oxidation process of250℃/2h bring PAN nanofibers the best oxidation degree, and consequently the final CNFs show good compressive strength, which could meet the demands of the HPHR diffusion layer. Moreover, the thickness-direction conductivity of CNFs reached3.4S/m, equal to the levels of commercial carbon paper.Maleic acid (bp:355℃,1mol/L) solution used as a model compound of the high boiling point fractions of bio-oil, was hydrogenated in a HPHR. H2SO4-acidized CNFs with different hydrophilicity were used as cathode diffusion layer of HPHR. For comparison, the performance of commercial diffusion layers such as GDL, Carbon Paper and Metal Mesh were also studied. It was found that the hydrogenation reach the highest conversion (7%) with the diffusion layer of CNFs which was acidized by H2SO4(98%) with condition of90℃/3h, better than all other commercial diffusion layers, illustrating that CNFs has good gas-liquid phase diffusion properties, and shows good application future in HPHR cathode liquid diffusion layers.