Study On The Chemical Behavior Of Linear Alkanes In Nitric Acid System

Spent fuel reprocessing is essential for the economic use of uranium and plutonium in nuclear energy production.The PUREX process is always the first choice for spent fuel reprocessing which is a liquid-liquid extraction method using tributyl phosphate(TBP)and linear alkanes as solvents.Since the solvent is in contact with nitric acid during the post-treatment and is exposed to high temperature and radiation for a long time,it will cause a chemical reaction between TBP or linear alkane,and the reaction product will lower the solvent performance and the extraction separation effect will be worse,which may produce“Red-oil" and cause the "Red-oil" explosion accident.In this paper,a comprehensive qualitative analysis of the reaction products of n-hexane and n-dodecane linear alkanes in nitric acid heating system was carried out by infrared spectroscopy,gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy,and the type of nitrification product under this system was determined.At the same time,the products were quantitatively analyzed by gas chromatography and nuclear magnetic resonance spectroscopy.The effects of reaction temperature,nitric acid concentration,reaction time,material ratio,metal nitrate and free radical initiator on the nitration of n-hexane and n-dodecane were studied.In addition,we designed an orthogonal experiment on the reaction conditions.According to the results of orthogonal experiments,the reaction of n-hexane with nitric acid reached the highest yield at a temperature of 150 °C,a nitric acid concentration of 10 mol/L,a reaction time of 12 h,and a material ratio of 1:1.5.When the temperature is 110 °C,the concentration of nitric acid is 6 mol/L or 10 mol/L,the reaction time is 8 h,and the material ratio is 1:1.5,the ratio of the two products is the largest.According to the orthogonal experimental results of the liquid phase nitration conditions of n-dodecane and nitric acid,when the reaction of n-dodecane with nitric acid is at a temperature of 150 °C,a nitric acid concentration of 8 mol/L,a reaction time of 12 h,and a material ratio of 1:1.5,the total yield of nitrododecane is the highest.In order to investigate the temperature and pressure changes during the reaction between alkane and nitric acid,a 500 mL intelligent reactor was designed to carry out the amplification experiment,and the time-temperature and time-pressure curves of the system were obtained.The results showed that the change of the temperature of the material during the reaction and the pressure change caused by the reaction system are related to the concentration of nitric acid,the ratio of materials and the length of the carbon chain.Among them,the maximum pressure generated by the n-hexane-nitric acid system at a material ratio of 1:1 is 29 bar,and the maximum pressure generated by the n-hexane-nitric acid system at a material ratio of 1:2is 34.4 bar.The maximum pressure generated by the n-dodecane-nitric acid system at a material ratio of 1:1 is 8.4 bar,and the maximum pressure produced by the n-dodecane-nitric acid system at a material ratio of 1:2 is 15.8 bar.This paper explored the thermal hazard of the reaction using an adiabatic accelerated calorimeter(ARC).The temperature,pressure data and autothermal rate during the exothermic reaction provided by adiabatic accelerated calorimetry(ARC)experiments provide a basis for studying chemical kinetic parameters.The results showed that in the alkane-nitric acid system,as the material ratio increases from 1:1 to 1:2,the activation energy of the reaction decreases,that is,the larger the proportion of nitric acid,the smaller the activation energy,the easier the reaction occurs.