Heterogeneous Catalysts And Catalytic Process For One-step Preparation Of Adipic Acid From Cyclohexane

Adipic acid is an important chemical raw material,mainly used to make nylon-66 fiber and Polyurethane foam plastics.At present,the main method for industrial synthesis of adipic acid is cyclohexane as a raw material and oxidize molecular oxygen to produce K/A oil?cyclohexanone and cyclohexanol?,and then oxidize K/A oil with50%?60%concentrated nitric acid to obtain the target product.The production of 1 t of adipic acid requires 1.3 t of 68%nitric acid,meanwhile,production of 0.25 t of N₂O,nitric acid steam and waste acid liquid causes great pollution to the environment and high denitration energy consumption,which has been plagued by the development of adipic acid production technology.The development of a chemical process that uses cyclohexane as a raw material to directly produce adipic acid by one-step oxidation with molecular oxygen or hydrogen peroxide is economical,green and sustainable.However,there are multiple C-H bond selective activation and inhibition in the series reaction.Therefore,it is one of the most difficult and challenging research topics in heterogeneous catalytic technology to selectively oxidize the relatively inert cyclohexane C-H bonds and inhibite the deep oxidation of adipic acid to CO₂ and H₂O.It is one of the most difficult and challenging research topics in the research of heterogeneous catalysis technology.Based on this,in this paper,we mainly start by adjusting the active points on the surface of solid catalysts,in order to study the relationship between the microstructure changes on the surface of solid catalysts and the catalytic performance of materials,and deeply to explore the optimization mechanism of surface microstructures.It will lay a solid foundation for the development of a new generation of highly efficient multifunctional catalysts for the oxidation of alkanes.The main research work focuses on the three aspects of sepiolite acid thermal activation regulation,transition metal modification of hollow titanium silicon molecular sieve?HTS?,and HTS deactivation and regeneration of active sites on the surface:?1?The sepiolite is thermally activated by design to regulate the surface properties and catalytic activity of sepiolite.In the absence of any solvents and initiators,molecular oxygen as a green oxygen source,and nitric acid-modified sepiolite?A-Sep-5M7h?one-step oxidation of cyclohexane to adipic acid shows excellent catalytic performance.Through the optimization of experimental conditions,under the optimal conditions?1.4 MPa O₂,140??,the conversion of cyclohexane was18.0%and the selectivity of adipic acid reached 49.6%.Based on the analysis of the catalyst morphology,surface microstructure and condition control experiment,it is proposed that H⁺replaced part of Mg²⁺in the sepiolite framework,and the specific surface area increases.At the same time,the presence of H⁺on the catalyst surface can enhance the adsorption and activation of the intermediate product K/A oil,and then continue to oxidize to the target product of adipic acid.?2?A hollow titanium-silicon molecular sieve?M/HTS?modified with transition metals were prepared for oxidation of cyclohexane to prepare adipic acid and glutaric acid using H₂O₂.By optimizing the experimental conditions,the 1%Cr/HTS catalyst exhibited excellent catalytic performance and achieved 32.5%cyclohexane conversion and57.0%adipic acid and glutaric acid the total selectivity under mild conditions?90?,10 h?.Through the characterization correlation of the catalyst and the catalytic activity point poisoning experiment,the results confirmed that the Cr species dispersed on the surface of the HTS and the Ti species in the carrier were catalytic activity sites of cyclohexane and synergistically promote the one-step conversion of cyclohexane to adipic acid and glutaric acid.?3?HTS is a highly effective catalyst for activating hydrogen peroxide,but it has high preparation cost,easy deactivation and low reutilization rate.Therefore,the study also explored the catalytic performance and structural differences of HTS before and after use.This chapter mainly compared the performance and structural differences of HTS catalysts before and after use.The catalytic performance of fresh and used HTS selective oxidation of cyclohexanol,cyclohexanone and cyclohexanol/cyclohexanone mixture with time was evaluated.The crystal structure,titanium changes and morphology of the catalyst was characterized by FT-IR,UV-vis,XRD,TEM,XPS and other characterization methods.The results confirmed that the skeleton structure of the inactivated titanium-silicon molecular sieve was not destroyed,and the decrease of the tetrahedral Ti⁴⁺content in the skeleton was the key factor leading to catalyst deactivation.