Mass Transfer And Kinetics Of Phenol Degradation By Heterogeneous Catalyzed Ozone In High Gravity Field

In the production process of coal chemical production,a large amount of phenol-containing wastewater is produced,especially phenol.Because phenol has certain toxicity and corrosiveness and it is difficult to be biodegraded,the treatment of phenol in wastewater is a very difficult task,which is of great significance to human health and ecological environment protection.Heterogeneous catalytic ozonation technology has been widely concerned due to its advantages of easy separation of solid catalysts,high treatment efficiency,low cost,and no secondary pollution to the environment.However,ozone is an insoluble gas,resulting in low utilization and high cost in actual wastewater treatment.However,ozone is a kind of insoluble gas,which leads to low degradation rate of organic matter and high cost in actual wastewater treatment.The high-gravity technology is a technology which can intensify the chemical process.and it has broad application prospects in industry.In the Rotating Packed Bed（RPB）,three phases of gas,liquid and solid are contacted fully.The liquid is shear into liquid elements by centrifugal force formed by the high-speed rotation of the rotor.The contact area between phases is increased,and the gas-liquid mass transfer coefficient is improved.It can also promote the adsorption of liquid phase ozone on the active site of catalyst surface,generate more·OH,thus improving the degradation effect of organic matter in water and reducing the treatment cost.In addition,RPB can pack the solid catalyst in the rotor,realizing the functionalization of the packing and facilitating separation after the reaction to save the cost.At present,the heterogeneous catalytic ozone oxidation technology in high-gravity field mainly focuses on optimizing the process parameters to improve the degradation rate of organic matter,but the mass transfer and kinetics of this system are rarely reported.In this paper,using phenol as the target pollutant,RPB as the reactor and Fe-Mn-Cu O_X/γ-Al₂O₃ catalyst as the packing,the mass transfer and kinetics of phenol degradation by heterogeneous catalytic ozone in high-gravity field were systematically studied.It mainly includes mass transfer and decomposition behavior of heterogeneous catalytic ozone in high-gravity field,direct reaction apparent kinetics of ozone and phenol,indirect reaction apparent kinetics of·OH and phenol,and the degradation pathways of the two different reactions.The research results are as follows:（1）The mass transfer behavior of heterogeneous catalytic ozone was studied in the high-gravity field,and which was compared in the Bubbling Reactor（BR）.using the concentration of ozone in the liquid phase as the measurement standard.Taking liquid phase ozone concentration as the comparison standard,when the gas-phase ozone concentration was 50mg·L^-1,the liquid-phase ozone concentration first increased and then decreased with the increase ofβand V_L,and decreased with the increase of p H and T.Under the similar conditions,the liquid-phase ozone concentration was 3.76 mg·L^-1 in the presence of the catalyst in RPB,while it was only 2.31 mg·L^-1 in BR,which indicated that the high-gravity technology can significantly improve the turbulence of the liquid,increase the mass transfer driving force from the gas phase to the liquid phase,increase the ozone concentration in the liquid phase,and provide a guarantee for the efficient degradation process of organic matter.The decomposition behavior of heterogeneously catalyzed ozone was studied in the high-gravity field,and took the ozone decomposition rate constant（k_c）as the comparison measure.When the gas phase ozone concentration was 50 mg·L^-1,k_c increased first and then decreased with the increase ofβ,p H and V_L,and increases with the increase of T.Under the similar experimental conditions,the k_cis 5.8×10^-3 s^-1 in the presence of catalyst in RPB,which is 1.76 times that of BR.Compared with the literature,the k_c in RPB under the catalytic system is 4.20 times higher than that without catalyst.The results showed that k_c was improved by the strong turbulent characteristics of RPB,and the content of·OH per unit time was increased,which provided favorable conditions for the advanced treatment of organic compounds in wastewater.The proportion of·OH produced by the self-decomposition of O₃ and the catalytic decomposition of Fe-Mn-Cu O_X/γ-Al₂O₃ was clarified:under the catalytic system in RPB,the content of·OH produced by the self-decomposition of O₃ was about 37.2%,and the content of·OH produced by Fe-Mn-Cu O_X/γ-Al₂O₃ is about 62.8%.（2）Using phenol as the pollutant,the indirect reaction of·OH was inhibited by the free radical scavenger tert-butanol（TBA）in the high-gravity field,and the apparent kinetics of direct reaction of ozone was studied by the solute depletion method;·OH probe compound 4-Chlorobenzoic Acid（p CBA）was added to study the indirect reaction apparent kinetics of·OH,and the apparent reaction rate constants of O₃ and·OH with phenol in the high-gravity field were determined,and the kinetic model was established.The results showed that the contribution rate of direct reaction of O₃（88%）was greater than that of indirect reaction of·OH（12%）in the degradation process of phenol.In the 20 min reaction time of mineralization,direct reaction of O₃ accounted for 41%of the total reaction,·OH indirect reaction was 59%.In the direct reaction,the apparent reaction rate constant of O₃ and phenol was between8.17×10~4～8.80×10~5 L·mol^-1·s^-1.In the indirect reaction,the apparent reaction rate constant of·OH and phenol was between 1.54×10¹⁰～1.83×10¹⁰ L·mol^-1·s^-1.The empirical model of indirect reaction kinetics showed thatβhas the greatest influence among the influencing factors.Compared with BR,the strong turbulence and high shear effect of RPB can significantly increase the apparent reaction rate constant.（3）Main intermediates in the degradation process of phenol by direct reaction of O₃ and indirect reaction of·OH were analyzed by GC-MS,and the degradation process was speculated.The results showed that the direct reaction process of O₃ is mainly the electrophilic substitution reaction of ozone,which degraded phenol into catechol,hydroquinone and other substances with larger molecular weight.And the indirect reaction of·OH was mainly electrophilic addition reaction,rapid and non-selective attack phenol,the main intermediate products were maleic acid,ethylene acid,malonic acid and other small molecule compounds.Through the comparison of the two reaction degradation pathways,it can be concluded that:the indirect reaction of·OH can degrade phenol more quickly and thoroughly.