流化床光催化臭氧氧化苯酚动力学模型

Kinetics modeling on heterogeneous photocatalytic ozonation of phenol in a fluidized bed

摘要:

为了检验O3对光催化氧化苯酚效率提高能力,采用试验与数学模型联合方法量化O3的贡献.以球形活性炭(AC)作为载体,采用溶胶-凝胶法制作负载型二氧化钛光催化剂(TiO2-AC).原始活性炭与催化剂对苯酚的等温吸附研究表明,两种颗粒的吸附是可逆的,并且在稀溶液条件下符合Freundlich方程.在流化床中分别采用O3、UV/O3、UV/O3/AC、TiO2-AC/UV/O2和TiO2-AC/UV/O3等5种工艺对苯酚的氧化效率进行了对比,发现液相臭氧氧化、多相臭氧氧化与多相光催化的综合作用导致光催化臭氧氧化效率比光臭氧氧化高34.5%.建立了流化床中多相光臭氧氧化与多相光催化臭氧氧化苯酚动力学模型.模型结果表明,溶液中臭氧质量浓度为0.02mg/L时,二氧化钛光催化氧化苯酚速度提高了14.8倍,在光催化氧化有机物过程中,臭氧比氧更适合作为电子的捕获剂.

Abstract:

Experimental data and model prediction was combined to quantify the enhancing effiecency of O3 on the photocatalytic oxidation of phenol.Titanium dioxide was immobilized onto spherical activated carbon (AC) particles via the sol-gel coating method.The isotherms of original AC and photocatalysts (TiO2-AC) annealed at 500 ℃ for phenol were measured.The results showed a reversible adsorption of phenol onto both kinds of particles at 25 ℃,which agrees well with the Freundlich adsorption isotherm in the dilute solution.Five oxidation processes,namely O3,UV/O3,UV/O3 /AC,TiO2-AC/UV/O2 and TiO2-AC/UV/O3,for phenol degradation in fluidized bed were compared and the photocatalytic ozonation was found to give the highest phenol conversion because of the combined actions of homogenous ozonation in the liquid phase,heterogeneous ozonation on the surface of catalyst support,and heterogeneous photocatlytic oxidation on the TiO2 catalyst surface.The experimental data of UV/O3 /AC process were used to determine the heterogeneous photolytic ozonation reaction rate constant.Predictions of the proposed model were compared with experimental results for the photocatalytic ozonation of phenol in the fluidized bed.The global photocatalytic oxidation constant was found to be enhanced by 14.8 times in photocatlytic ozonation process with ozone as the scavenger compared with the photocatalytic oxidation process with oxygen as the scavenger.