Study On The Subcritical Water Oxidation Of Guaiacol And Potassium Hydrogen Phthalate With Raman Spectroscopy And Fused-Silica Capillary Reactor

Supercritical/subcritical water oxidation is a kind of organic wastewater treatment technology which has characteristics of high efficient, clean and thoroughness. In the supercritical/subcritical water,reaction medium, organics are readily degraded to smaller inorganic molecules such as H2O, CO2or other small molecule compounds.This topic used optically transparent fused silica capillary reactors (FSCR), to investigate the oxidative decomposition of guaiacol and potassium hydrogen phthalate in subcritical water. We used a Raman spectroscopic system for qualitative and quantitative analyses of the gaseous product CO2and GC-MS for the species of liquid phase intermediate products. The effects of operating parameters, including the stoichiometric ratio of the oxidizer (100-300%), temperature (guaiacol:160-300℃; KHP:180-320℃), and reaction time (2-10min), on conversion rate of target compounds and CO2yield were investigated. We used a polarization microscope recorder system for visual observations of phase changes of guaiacol during heating and cooling with H2O2and deionized water as the the reaction medium. The concrete results are as follows:(1) During the oxidative degradation of guaiacol, its conversion yield increased as the stoichiometric ratio of the oxidizer was changed from100to150%, but was relatively constant over the range of150to300%. Guaiacol conversion yield and CO2yield were increased with increasing temperature and reaction time. We found that complete conversion of guaiacol was achieved with a150%stoichiometric ratio of oxidizer after10min at the temperature of200℃. When the temperature was300℃, the Raman peak area of molecular CO2was almost no change after10min, indicating that the amount of CO2has reached the maximum at the temperature of300℃and time of10min. We found that the yield based on guaiacol conversion is always higher than the CO2yield under the identical experimental conditions, which indicates that the degradation of the reaction was more than one step. Several intermediate byproducts of incomplete oxidation in the liquid phase were identified by GC-MS, including toluene, benzene,3-hexen-2-one and 4-hydroxy-4-methyl-2-pentanone. During the oxidative degradation of KHP, its conversion yield increased as the stoichiometric ratio of the oxidizer was changed from100to200%, but was relatively constant over the range of200to300%. Potassium hydrogen phthalate conversion yield and CO2yield were increased with increasing temperature and reaction time. We found that complete conversion of potassium hydrogen phthalate was achieved with a200%stoichiometric ratio of oxidizer after10min at the temperature of260℃. When the temperature was320℃, the Raman peak area of molecular CO2was almost no change after10min, indicating that the amount of CO2has reached the maximum. The yield based on guaiacol conversion is always higher than the CO2yield under the identical experimental conditions, which implies that degradation of the reaction was more than one step, too.(2)The phase changes of guaiacol in the FSCRs, using either deionized water or hydrogen peroxide solution (30wt%), were observed in this study. When the medium was deionized water, guaiacol’s main behavior was dissolution. Guaiacol was dissolved completely at188.8℃. During the cooling process, guaiacol in an oil phase occurred at122.7℃. After cooling to room temperature, we found that the total amount of the oily liquid was roughly unchanged, indicating that no obvious oxidation reaction happened on guaiacol. When the medium was hydrogen peroxide solution, some yellow intermediate byproducts appeared and then became darker and eventually turned black during heating process. With continued heating, the color of the aqueous phase became lighter and some particulates appeared. It is noteworthy that the particulates and the yellow color eventually disappeared completely, resulting in a homogeneous, colorless liquid solution in the high compressed H2O-H2O2system at320.0℃. As the temperature decreased to ambient no oil droplets were observed, indicating that the guaiacol had completely decomposed during this process.(3) In this research, kinetics analysis of the degradation of guaiacol/potassium hydrogen phthalate and the generation of CO2were studied. The result showed that CO2formation by the decomposition of guaiacol through subcritical water oxidation follows first order kinetics. Through the association of Arrhenius equation, the activation energy of degradation of guaiacol/potassium hydrogen phthalate are19.024kJ-mol"1and8.123kJ-mol"1, respectively, the activation energy of CO2formation are18.62kJ-mol"1and11.092kJ-mol"1, respectively.