The Process Research Of The P-xylene Oxidation To Terephthalic Acid Using The Combination Of Ozone And UV

The production of purified terephthalic acid(PTA)plays a leading role in the polyester chemical fiber industry and the liquid-phase oxidation technology of p-xylene(PX)is the core of the whole PTA production process.At present,the traditional oxidation process of PX has many shortcomings,such as environmental pollution and high energy consumption.With the continuous improvement of global environmental protection requirements,it is urgently needed to develop a green alternative process for the large scale production of PTA.In this thesis,the green selective oxidation process from PX to terephthalic acid(TPA)was realized by using ozone as oxidant and the ultraviolet field enhancement technology.The process conditions including stirring rate,solvent ratio,ozone flux,ultraviolet wavelength,pH value and temperature were optimized through oxidation experiments.The results showed that under the optimal conditions of acetonitrile-water volume ratio of 1.5,pH=6.0,UV light 305 nm,reaction time 20 h,and temperature 45?,the yield of TPA can reach 80%.After repeated washing with acetonitrile-water solvent,the purity of the main product TPA can reach 98.1 wt%,and the content of the main impurities p-TA and 4-CBA were 1.9 wt%and 20 ppm,respectively.Secondly,the free radical quenching experiments showed that ·OH in the ozone-UV co-oxidation reaction process can be completely quenched by a certain concentration of quenching agent TBA,but the direct ozone oxidation still exists after ·OH quenched.Through the free radical capture experiment and EPR detection,the existence of·OH with strong oxidation ability in the reaction process was directly proved.Then,based on the experimental results and the mechanism of hydrocarbon oxidation,the oxidation reaction mechanism of PX with and without water was proposed.Under the condition of no water,O(1D)was successively embedded with methyl C-H bond on the benzene ring to obtain the products of alcohols,aldehydes,and acids.In the presence of water,the methyl groups on the benzene ring followed the classical free radical chain reaction mechanism and were oxidized to aldehyde and carboxyl groups in turn.Finally,the effect of hydrogen peroxide on the ozone-UV co-oxidation of PX was studied,and found that when the amount of hydrogen peroxide was 24 wt%,the time of TPA yield reached 80%can be reduced by 6 h.The related research results of this thesis can provide a theoretical reference for the development of the new oxidation process of PX to PTA.