Study On Paired Electrocatalytic Synthesis Of Ethylene And Oxalic Acid From Acetylene

Ethylene and oxalic acid are all very important basic organic chemical raw materials.But most of existing synthesis processes need higher temperature and higher pressure,some of them need higher requirements for production equipment and raw materials,some of their processes are more complex,some are backward in technology,some lead to higher energy consumption and more serious pollution,some sources of raw materials are too difficult to obtain.Paired electrocatalytic synthesis of ethylene and oxalic acid from acetylene by the route of "Coal→Calcium carbide→Acetylene→Ethylene and Oxalic acid" is a new idea and a new way for maximizing efficient and clean use of coal.In this study,the clean and efficient electrochemical synthesis method with characteristics of room temperature and atmospheric pressure has been used to paired electrocatalytically synthesize ethylene and oxalic acid from acetylene.The influence factors in the reaction process have been investigated and optimized.Ethylene and oxalic acid have been electrochemically synthesized successfully catalyzed by palladium and platinum,respectively.At the same time,FTIR（UV-Vis spectrophotometry）,UV-Vis.（UV-Vis spectrophotometry）,NMR（Superconducting nuclear magnetic resonance spectroscopy）and GC（Gas chromatography）have been adopted to characterize the products of oxalic acid and ethylene.The electrode polarization curves and kinetic parameters have been determined,the rate-determining step of the reaction processes and the reaction mechanism have been discussed,the essence of electrocatalytic oxidation and electrocatalytic reduction processes of acetylene has been revealed.The first-principles calculation method based on DFT（Density functional theory）has been used to the reaction process of paired electrocatalytically synthesize ethylene and oxalic acid from acetylene to discuss the relevant basic scientific questions,and it provides solid experimental foundation and theoretical basis for the optimization of the reaction process.The main research works and results are as follows:1.Study on solubility of acetyleneAccording to the basic principle that purple copper acetylide can be produced from acetylene and cuprous,the concentration of dissolved acetylene has been determined accurately and dissolving properties of acetylene in different solvents such as acetone,TEG（triethylene glycol）,DMSO（dimethyl sulfoxide）and DMF（N,N-dimethyl formamide）have been investigated systematically by UV-Vis.The experimental results show that the solubility order of acetylene in different solvents is DMF>DMSO>TEG>acetone.2.Electrocatalytic hydrogenation of acetylene to ethylene（1）Study on electrochemical behavior of electrocatalytic synthesis of ethylene from acetyleneElectrochemical experiments were performed in a three-electrode cell.The electrochemical behavior of electroatalytic synthesis of ethylene from acetylene has been examined in H₂SO₄ solution by CV.The influence factors on the cathode electrode process of electrode materials（Pd,Ni,Ag,Cu and Nb,et al）,concentration of electrolyte,type and volume fraction of cosolvents（acetone,TEG,DMSO and DMF）,temperature and scan rate have been investigated.The results show that Pd shows good electrocatalytic effect in the process of electrocatalytic hydrogenation of acetylene,the cosolvent of acetone can increase the solubility of acetylene in H₂SO₄ solution significantly,resulting in accelerated reaction rate,0.8 mol·L^-1 H₂SO₄ solution with acetone（8%,by volume）is the most appropriate electrolyte,the electrocatalytic hydrogenation process of acetylene in H₂SO₄ solution on Pd electrode is irreversible and under adsorption control.（2）Electrocatalytic hydrogenation of acetylene to ethyleneElectrocatalytic synthesis of ethylene was performed in an H shaped devided glass cell.A Pt electrode and a Pd electrode were used as anode and cathode,respectively.All the experiments were carried out in 0.8 mol·L^-1 H₂SO₄ solution with acetone（8%,by volume）as the catholyte.The current density on the cathode was 106.2 mA·cm-2.Acetylene（20 mL·min-2）must be piped into the catholyte for 10 min before carrying out the experiments.The synthesized ethylene was characterized by GC.All the results show that ethylene can be electrocatalytically synthesized successfully,the yield and current efficiency are 68%and 55%,respectively.（3）Study on reaction mechanism of the electrocatalytic hydrogenation of acetylene to ethyleneTafel curves of polarization on the anode and cathode have been measured.The rate-determining step of the reaction process and the reaction mechanism have been discussed.The first-principles calculation method was carried out to examine the adsorption of acetylene over the Pd（111）surface and the rate-determining step is（CH ≡ CH）ads+Hads→（CH2=CH）ads.3.Electrocatalytic oxidation of acetylene to oxalic acid（1）Study on electrochemical behavior of electrocatalytic synthesis of oxalic acid from acetyleneElectrochemical experiments were performed in a three-electrode cell.The electrochemical behavior of electroatalytic synthesis of oxalic acid from acetylene has been examined in Na₂SO₄ solution by CV.The influence factors on the anode electrode process of electrode materials（Pt,Ni,Ag,Ti/SnO2+Sb2Ox/PbO2 electrode,Ti/Cu+Ag electrode,Ti/Mn0.2Cr0.8O3/2 electrode,et al）,concentration of electrolyte,type and volume fraction of cosolvents（acetone,TEG,DMSO and DMF）,temperature and scan rate have been investigated.The results show that Pt shows good electrocatalytic effect in the process of electrocatalytic oxidation of acetylene,the cosolvent of acetone and TEG can increase the solubility of acetylene in Na₂SO₄ solution significantly and reduce the Ea(reaction activation energy,14.42 kJ·mol^-1 and 13.20 kJ·mol^-1),resulting in accelerated reaction rate,0.5 mol·L^-1 solution with acetone（2%,by volume）is the most appropriate electrolyte,the electrocatalytic oxidation process of acetylene in Na₂SO₄ solution at Pt electrode is irreversible and under adsorption control.（2）Electrocatalytic oxidation of acetylene to oxalic acidElectrocatalytic synthesis of oxalic acid was performed in an H shaped devided glass cell.A Pt electrode and a Pd electrode were used as anode and cathode respectively for the experiment.All the experiments were carried out in 0.5 mol·L^-1 Na₂SO₄ solution with acetone（2%,by volume）as the anolyte.The current density on the anode was 159.2 mA·cm-2.Acetylene（20 mL·min-1）must be piped into the anolyte for 10 min before carrying out the experiments.The synthesized oxalic acid was characterized by FTIR,UV-Vis.and NMR.All the results show that oxalic acid can be electrocatalytically synthesized successfully,the yield and current efficiency are 75%and 14%,respectively.（3）Study on reaction mechanism of the electrocatalytic oxidation of acetylene to oxalic acidTafel curves of polarization on the anode and cathode have been measured.The rate-determining step of the reaction process and the reaction mechanism have been discussed.The first-principles calculation method was carried out to examine the adsorption of acetylene over the Pt（111）surface and the rate-determining step is CH ≡ CH+（OH·）ads→HOCH=CHOH.4、Paired electrocatalytic synthesis of ethylene and oxalic acid from acetylenePaired electrocatalytic synthesis of ethylene and oxalic acid from acetylene was performed in an H shaped devided glass cell.A Pt electrode and a Pd electrode were used as anode and cathode respectively for the experiment.All the experiments were carried out in 0.5 mol·L^-1 Na₂SO₄ solution with acetone（2%,by volume）as the anolyte and 0.8 mol·L^-1 H₂SO₄ solution with acetone（8%,by volume）as the catholyte respectively.The current density on the anode was 159.2 mA·cm-2 and the current density on the cathode was 106.2 mA·cm-2.Acetylene（20 mL·min-1）must be piped into the anolyte for 10 min before carrying out the experiments.The synthesized ethylene and oxalic acid was characterized by GC,FTIR,UV-Vis.and NMR.All the results show that ethylene and oxalic acid can be electrocatalytically synthesized successfully,the yield and current efficiency are 64%and 68%,53%and 19%,respectively.