Electrolytic Synthesis Of Organic Compounds Applicable To Food Industry Through Glyoxylate By Using Inorganic Carbon

The target of this study was to synthesize formate and oxalate by electrochemical reduction of inorganic carbon in different water solvent and non-water solvent systems using high hydrogen over-potential metal or graphite electrodes. The effects of voltage, electrolyte, temperature and time on the electrochemical reduction of inorganic carbon were studied. Experimental results showed the feasibility of producing oxalate from formate under high temperature, and the optimal conditions for making oxalate from formate were established by experimentation. Further study was undertaken to make glyoxylate from oxalate, and the best conditions of achieving this were found.The first chapter introduced the background of electrochemical reduction techniques and present research status of transforming CO₂ into formic acid or oxalic acid based on literature review.The second chapter mainly studied on electrochemical reduction of CO₂ to produce formic acid in the aqueous solvent system by using various electrodes. Experimental results showed that the formate was found in electrolyte choosing platinum as the anode electrode, calomel as the parallel electrode, plumbum or graphite as the cathode electrode. The experimental results showed that, when the voltages were controlled in the range of 2.9 - 3.8 V, formate was produced and the best reaction chamber voltage was 3.2 V [the electrode voltage was -0.63 V (vs.SCE)]. Na₂CO₃, NaHCO₃, K₂CO₃ or KHCO₃ electrolyte showed good Faraday efficiency of the electrochemical reduction of CO₂ to produce formate, respectively. Temperature did not affect the production of formic acid a lot. Different reaction times resulted in different amounts of formic acid formed. Formic acid was generated when the electrochemical reduction of CO₂ was carried out for one hour and maximum yield was achieved after three hours. Experimental results showed that the maximum rate of transforming formate into oxalate was obtained at 400 - 420℃for 30 - 50 min.The third chapter mainly studied on the production of oxalate in aqueous or non- aqueous solvent system by the electrochemical reduction of CO₂. Among C-C, Pt-C, C-Pb, Pt-Pb, C-Cu, Pt-Cu electrode systems, graphite electrode showed the best capability of producing oxalate and it was able to produce 0.54×10^-4mol oxalate by electrolysis for 4 h. No oxalate was detected when copper was used as the electrode. The experimental results also showed that, when the voltage was controlled at 23.8 V, it was able to produce 0.63×10^-4mol oxalate in 0.1 M NaOH solution with 1 g carbon powder added. It was found that bicarbonate ion facilitated the production of oxalate, but oxalate could not be found in ammonium solution. In sodium hydroxide solution with some carbon powder added, the amount of oxalate produced was higher compared with other electrolytes (for example, TEABF₄, in which about 0.46×10^-4mol oxalate can be produced). Temperature did not affect the production of oxalate a lot since it was nearly the same at 0℃, 25℃or 40℃. The production of oxalate in non-aqueous solvent system, for example, in DMSO, by electrochemical reduction of CO₂ using different electrolytes was studied. Experimental results showed that when the electrode voltage was between -0.9 - -1.5 V (vs.SCE) oxalate could be produced by using Pb electrode. There was the maximal oxalate output (0.18×10^-4 mol) at -1.2 V (vs.SCE). The finding also told that Cl^- is more conducive to the production of oxalate than Br^- and (?), for example, TEACl is better than TEABF₄, in which 0.20×10^-4mol oxalate was produced.The fourth chapter studied on the effects of electrode, current density and cationic exchange membrane set on the efficiency of transforming oxalate into glyoxylate by electrochemical reduction. Experimental results showed that in comparison with aluminium and graphite electrodes, the anti-eroding property of plumbum electrode is better as a cathode.Current density affected the conversion rate a lot. The results also showed that the maximum amount of glyoxylate was achieved by electrolysis at 100 mA·cm^-2 for 2h. Cation exchange membrane set could also make an impact on glyoxylate output. The optimal conditions for transforming oxalate into glyoxylate are as follows: electrolysis at 100 mA·cm^-2 for 2h using plumbum electrode. By this way, 42.35 % oxalate could be transformed into glyoxylate.