A Study Of Operating Conditions And Membrane Performances Of Direct Electrolysis For Hydrogen From The Bunsen Reaction Product HI/H₂SO₄/toluene Mixture

Hydrogen energy is the clean energy with the greatest potential for development in the 21st century,and its clean,efficient,and sustainable large-scale production methods attract much attention.H₂S chemical splitting for the production of hydrogen and sulphuric acid system not only provides the feasibility for the conversion of sulfur containing pollutants,including hydrogen sulfide,into high quality and high values of hydrogen and sulfuric acid,but also greatly reduces the energy consumption of the system.Compared with I-S cycle,the novel technical route has sustainable development in energy-saving and emission-reduction,social and economic benefits and other aspects.H₂S chemical splitting cycle consists of the following four steps:hydrogen sulfide oxidation,sulfur oxidation,Bunsen reaction and decomposition of hydroiodic acid.The Bunsen reaction and HI decomposition reaction shared by both the H₂S splitting cycle and the I-S cycle,faced great challenges in the technology development.The toluene was used as a solvent to dissolve iodine and conducted the Bunsen reaction at ambient temperature,in order to mitigate the side reactions,ease the corrosion issues and overcome the deposition of iodine vapor which are difficult to handle when the reaction is conducted at a temperature higher than the melting point of iodine?386.85 K?.This alternative method of Bunsen reaction avoided elevating temperature to melt solid iodine.To replace the acid separation and HI decomposition,our research group proposed the direct electrolysis of the Bunsen reaction product,the mixed hydroiodic acid and sulfuric acid using a proton exchange membrane electrolytic cell.In the membrane electrolysis,iodine was obtained at the anode compartment with the HI/H₂SO₄/H₂O mixture?anolyte?and hydrogen was produced in the cathode compartment with the H₂SO₄ solution?catholyte?.This article aims to increase the conversion rate of I^-as much as possible,increase the amount of organic I₂ extraction of toluene in the anode cell,increase the H⁺migration number of the proton exchange membrane,reduce the electrolytic voltage,reduce the permeability of iodine into the cathode cell,and prolong the service life of the proton exchange membrane.The intermittent electrolysis device was designed for experiment researches to provide guidance for subsequent continuous electrolysis.The research content and main results are described as follows:?1?The Nafion117 membrane with good chemical properties was used as the research object to discuss the electrolysis process of the HI/H₂SO₄/toluene mixture for the Bunsen reaction under electrolytic conditions of anolyte-neutral electrolyte concentration,toluene phase volume ratio in the anolyte,current density and other electrolysis conditions.The results show that increasing initial cathode solution concentration and initial anode solution concentration can promote the formation of I₂.When the initial anolyte concentration is high,the amount of I₂ produced by Nafion 117 membrane electrolysis is greater,and the initial catholyte concentration is high,Nafion212 membrane is generated by electrolysis.When the concentration of H⁺in the catholyte and anolyte is reduced to 0 mol/L,the H⁺needed to generate H₂ in the cathode cell is all from the anode cell solution,which is conducive to maintaining the stability of H₂SO₄concentration in the catholyte.Keeping the anolyte I^-concentration not lower than 0.4 mol/L,increasing the current density is beneficial to the electrolysis reaction.The toluene phase of the anode can promote I^-oxidation by extracting I₂,and the optimal volume ratio of toluene phase aqueous phase is 1:4.?2?Change the proton exchange membrane model and analyze the influence of the membrane's effective acid content and thickness on the electrolysis reaction.The results show that the proton transfer number of the three proton exchange membranes is greater than 0.97 when the catholyte and anolyte H⁺concentration difference is 0 mol/L,which shows good transmission characteristics;and with the decrease of film thickness,the number of protons in the film increases,the film Nafion212 has the best transmission characteristics.Increasing the concentration of H⁺on both sides of the membrane,the number of proton transmissions of the thinner membrane Nafion 212 is greatly affected,and the thicker membrane Nafion 117 is less affected.The electrolytic current efficiency of most of the working conditions under the changed working conditions is greater than 0.8?except for the condition of low initial anolyte concentration?,and the energy conversion performance of the electrolytic process is good.?3?Change the type of the proton exchange membrane and reaction condition conditions,analyze the influence of the effective acid content and thickness of the proton exchange membrane on membrane selectivity.The results show that when the electrolysis current is 0 A/dm²,the selectivity of the membrane is positively correlated with the thickness of the membrane.When the electrolysis current is more than 0 A/dm²,the Nafion212 membrane with high effective acid content has good selectivity;Nafion117 and Nafion115 have the same effective acid content,and the thicker Nafion117 membrane has better selectivity.When the current density is increased to 8 A/dm²,the penetration of iodide into the cathode cell is suppressed,improving the selectivity of the membrane.Low anolyte?HI,H2SO4?concentrations and high toluene content in the anode cell will reduce iodine permeation through the membrane into the cathode cell and improve membrane selectivity.?4?Deposited substances were seen on the membrane surface after the electrolysis by using the scanning electron microscope characterization.The activation process could recover the membrane.The toluene did not change the surface morphology of the membrane.