Electrochemical Synthesis Of Adipic Acid From Cyclohexanol

The electro-organic synthesis has many advantages of normal temperature and pressure,small environmental pollution.Adipic acid is a basic chemical raw materials,which is mainly used in olefin nylon-66,polyurethane,synthetic resin and so on.Adipic acid was produced from the cyclohexanol or cyclohexanone by the oxidation of nitric acid.But the environment was polluted seriously by N₂O,NO_x and large-tonnage waste acid.Cyclohexene oxidized by 30 percent hydrogen peroxide an environment friendly method,while it has many shortcomings,such as long reaction time,recover catalyst.In order to solve the above problems,adipic acid research has become an important subject in the chemical industry.Adipic acid was synthesized by electro-oxidation of cyclohexanol taking Cr₂O₇^2-/Cr³⁺as indirect oxidant.At present,the use of electrochemical methods in adipic acid production is still a blank area in the country.First,the acid-resisting anode was prepared by the combination technology of thermal decomposition and electrodeposition.Titanium plate was used as substrate,the intermediate layer and the active layer are SnO₂+Sb₂O₃ and PbO₂ respectively.Then,the effects of the concentration of Ag₂SO₄,(NH₄)₂SO₄,H₂SO₄, temperature and the current density on the formation of Cr₂O₇^2-were studied by single-factor method.The optimum conditions were as follows:the concentration of Ag₂SO₄,(NH₄)₂SO₄ and H₂SO₄ were 0.0057 mol·L^-1,0.533 mol·L^-1and 4 mol·L^-1,respectively;the current density and the temperature were 30.3 mA·cm^-2and 35℃.Temperature,the volume of cyclohexanol and the concentration of H₂SO₄ were explored by orthogonal experiment in the synthesis process of adipic acid.The influence of each factor was V_cyclohexanol＞C_H2SO4＞temperature,the temperature,rate of crude material and concentration of H₂SO₄ were 35℃,n_cyclohexanol:n_cr2O72-=0.4:1 and 5 mol·L^-1,respectively.Under these conditions,the conversion rate of Cr³⁺and the current efficiency were 82.52% and 64.29%,respectively.The yield of adipic acid can reach 70.29%.Finally,the effects of Ag⁺ and(NH₄)₂SO₄ to the electro-oxidation of Cr³⁺ and cyclohexanol directly oxidized on Ti/Ni/NiOOH surface were explored by cyclic voltamogramme in acidic and alkaline.The results showed that Ag⁺ can be used as the catalyst for the oxidation of Cr³⁺,and(NH₄)₂SO₄ addition can effectively inhibit oxygen evolution;the mechanism of indirect electrochemical oxidation of adipic acid was obtained,the reaction control step wasAg⁺ -e^-→Ag²⁺;In alkaline condition Ti/Ni/NiOOH electrode had good catalytic effect on the cyclohexanol oxidation,the electro-oxidation mechanism was confirmed in the process.The electrochemical oxidative mechanism of cyclohexanol or cyclohexanone can provide a theoretical foundation for the industrial production of adipic acid.