2017 Annual Meeting
(586b) Adsorption Desulfurization Performance of B2O3 Modified Ag-CeOx/TiO2-SiO2 and Adsorption Diffusion Study
Meiqin Zheng1, Xiaohui Chen1*
1National Engineering Research Center of Chemical Fertilizer Catalyst, School of Chemical Engineering, Fuzhou University
* Correspondence author E-mail: chenxhfzu@fzu.edu.cn.
In this word, the effect of B2O3 modified Ag-CeOx/TiO2-SiO2 adsorbent on adsorption desulfurization and adsorption diffusion behaviour was investigated. The adsorption desulfurization performance was studied by static batch and fixed bed test through CN-IV diesel (sulfur content 32.78 mg/L). The pore diffusion model (PDM) and homogeneous surface diffusion model (HSDM)1were employed to investigate the adsorption diffusion behaviour of 4,6-dimethyldibenzothiophene (4,6-DMDBT) on model diesel. Simultaneously, a 2D porous media CFD model is developed for a fixed bed adsorber to remove the 4,6-dimethyldibenzothiophene (4,6-DMDBT) from diesel. The batch tests proved that the sulfur concentration after desulfurization was less than 10 mg/L, which can meet the CN-IV standard.
The B2O3 modified CeOx/TiO2-SiO2 support was prepared by co-impregnation method with 1:1:2:44.3 molar ratio of B:Ce:Ti:Si. Silver was dispersed onto the B2O3 modified CeOx/TiO2-SiO2 support through typical incipient wetness method2. The adsorbents were characterized by means of X-ray diffraction, N2-adsorption specific surface area measurements (BET), images of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) etc. The results proved that B species was dispersed evenly on the supports, and didnât change the pore structure of adsorbents. It was found that B2O3 species exhibited a great enhancement for the adsorption desulfurization activity because of a significant enhancement for the amounts of weak acid sites generated from more BO4 species on surface of the adsorbent3,4.
The batch equilibrium and kinetics of adsorption desulfurization of model diesel fuel were also investigated. The proposed HSDM model and PDM model can successfully describe the adsorption of 4,6-DMDBT for different operating conditions studied. The adsorbate was absorbed rapidly initially because the adsorption rate at the beginning was dominated only by external diffusion. The Biot numbers proved that the predominant rate controlling step was intraparticle diffusion. Simultaneously, the adsorption rate was mainly controlled by surface diffusion at lower initial bulk phase concentration and less adsorbent dosage, while pore diffusion played a significant role at higher initial bulk phase concentration and more adsorbent dosage.
The CFD simulation results demonstrated that porous media CFD model can describe successfully the adsorption mass transfer process for removal of 4,6-DMDBT from diesel. The mass transfer rate increased with increasing feed concentration at the beginning due to the higher driving force at higher feed concentration, conversely, the lower mass transfer rate was obtained at higher feed concentration after a period of adsorption time because of the decrease in the saturation time at the fixed bed column entrance gradually at higher feed concentration.
Key words: adsorption desulfurization; B2O3; HSDM; PDM; CFD.
REFERENCES
1. Zheng M, Xu C, Hu H, Ye Z, Chen X. A modified homogeneous surface diffusion model for the fixed-bed adsorption of 4,6-DMDBT on AgâCeOx/TiO2âSiO2. RSC Adv. 2016;6:112899-112907.
2. Xu CZ, Zheng MQ, Chen K, Hu H, Chen XH. CeOx Doping on a TiO2-SiO2 Supporter Enhances Ag Based Adsorptive Desulfurization for Diesel. J. Fuel. Chem. Techno. 2016;44(8):943-953.
3. Li-Da LI, Cheng-Zhi XU, Zheng MQ, Chen XH. Effect of B2O3 modified Ag/TiO2 -Al2O3 adsorbents on the adsorption desulfurization of diesel. J. Fuel. Chem. Techno. 2015;43(8):990-997.
4. Peil KP, Galya LG, Marcelin G. Acid and Catalytic Properties of Nonstoichiometric Aluminum Borates. J. Catal. 1989;115(2):441-451.