This study adopted the fundamentals of the catalytic dechlorination of p-chlorophenol in a MSFB column, technology developed by Graham (1). A CFD-DPM approach is used to simulate the catalytic process. The code is validated by comparison with the experimental results, considering the p-chlorophenol removal and the particle catalyst deactivation

Cruz-Fierro, Carlos F.

Martínez-Prado, Adriana

Pinto-Espinoza, Joaquín

Reyes-Jaquez, Damian

English

Engineering Conferences International

Refereed ProceedingsThe 12th International Conference onFluidization - New Horizons in FluidizationEngineeringEngineering Conferences International Year 20072-D Simulation of the CatalyticDechlorination of P-Chlorophenol in aMagnetically Stabilized Fluidized BedJoaqu´ın Pinto-Espinoza∗ Damian Reyes-Jaquez†Adriana Mart´ınez-Prado‡ Carlos F. Cruz-Fierro∗∗∗Instituto Tecnolo´gico de Durango, pintoejo@yahoo.com†Instituto Tecnolo´gico de Durango‡Instituto Tecnolo´gico de Durango∗∗Instituto Tecnolo´gico de Durango, cfcruz@orst.eduThis paper is posted at ECI Digital Archives.http://dc.engconfintl.org/fluidization xii/74FLUIDIZATION XII 609    2-D SIMULATION OF THE CATALYTIC DECHLORINATION OF P-CHLOROPHENOL IN A MAGNETICALLY STABILIZED FLUIDIZED BED  Joaquín Pinto-Espinoza*, Damian Reyes-Jaquez, Adriana Martínez-Prado, and Carlos F. Cruz-Fierro Chemical Engineering Department at Instituto Tecnológico de Durango; Blvd. Felipe Pescador 1830 Ote., C.P. 34080, Durango, Dgo., México. Phone (618) 829-0918. Fax (618) 818-4813. Email: pintoejo@yahoo.com.   ABSTRACT  This study adopted the fundamentals of the catalytic dechlorination of p-chlorophenol in a MSFB column, technology developed by Graham (3). A CFD-DPM approach is used to simulate the catalytic process (7). The code is validated by comparison with the experimental results, considering the p-chlorophenol removal and the particle catalyst deactivation.   INTRODUCTION  The rate at which we are increasing pollution is greater than the rate of recovery. The actual world is responsible for cleaning up polluted waters and soils of the past while preventing further pollution and environmental deterioration. Chlorinated organics in the form of pesticides, pharmaceutics, solvents, and dielectric fluids have been released from industrial, commercial, and agricultural activities. Unfortunately, most of them end up in soils and underground waters that we use for crops and as drinking water, (5).  This research, start with the basic study at lab scale, of the clean up of a p-chlorophenol contaminated soil using a Magnetically Stabilized Fluidization Bed (MSFB) as a catalytic reactor. An illustration of the reaction mechanism proposed for this process is shown in Figure 1. On the catalyst surface, chlorine is replaced by hydrogen, producing two products phenol and chlorine, (3)   Figure 2 shows a schematic representation of the experimental apparatus used at laboratory scale. Experimental data from a MSFB reactor, were obtained under the following conditions: ferromagnetic particles (nominal diameter: ~2 [mm]) were composite particles prepared with sodium alginate and Pd/Fe catalyst powder. In average, the alginate beads consist of 88% alginate (1.5% algin, 98.5% dionized water) and 12% catalyst with 0.188 Pd/Fe [w/w%]. Magnetic susceptibility: 0.2548. Particle average density: 1.173 [kg/m3]. Minimum fluidization velocity: 0.0104 [m/s]. The experimental samples were collected from the slurry phase and analyzed in a 1Pinto-Espinoza et al.: 2-D Simulation of the Catalytic Dechlorination of P-ChlorophenolPublished by ECI Digital Archives, 2007PINTO-ESPINOZA et al. 610HPLC, (3).   METHODOLOGY  To perform the dechlorination simulation, it is necessary to modify the AZTECA® code, (7),(2),(6). Besides of the Navier-Stokes equations and Newton second law of motion, which describes momentum of fluid and particles respectively, the heterogeneous catalytic reaction should be considered as follows, (5):  The pseudo-first order rate with respect to the chlorinated hydrocarbon (p-Figure 2. MSFB Experimental Apparatus Figure 1. Multistep Dechlorination Reaction on the Pd/FeCatalyst Surface 2The 12th International Conference on Fluidization - New Horizons in Fluidization Engineering, Art. 74 [2007]http://dc.engconfintl.org/fluidization_xii/74FLUIDIZATION XII 611chlorophenol) concentration was found to be the most appropriate kinetic model; these equations describe the mass transfer phenomena of the process, (1). aCkaCkWdtVCdAAA *)()( ==−      (1) nd akdtda =−        (2) To account for the passivation effects on the FePd / surface, an activity term, a, is integrated into the reaction kinetics as shown above. This term accounts for the decrease in catalyst activity caused by the loss of active sites. Numerical solution of the partial differential equations for p-chlorophenol diffusion trough alginate beads with entrapped FePd /  catalyst and the respective boundary conditions implemented are described below, (3). nlllel atrCVkrtrCrrtrCDttrC ))(,(),(2),(),(*22−∂∂+∂∂=∂∂  (3)   −−=blblbKtRCtCaVkdttdCV),()()( εε     (4) Initial conditions:     0,)0,( ll CtrC ==        (5)    0.)0( bb CtC ==        (6)  Boundary conditions:    0),(0=∂∂=rlrtrC        (7)  RrblblRrle KtrCtCkrtrCD== −=∂∂ ),()(),(     (8)         Calculation of p-chlorophenol aqueous diffusivity will be made by an approximation considering a DAB of a known compound with molecular weight of similar structure; this approximation is represented by Schwarzenbach et al (8).   5.0olchlorophen-pPhenolPhenol,olchlorophen-p,__=weightmolecularweightmolecularDDABAB    (9)   3Pinto-Espinoza et al.: 2-D Simulation of the Catalytic Dechlorination of P-ChlorophenolPublished by ECI Digital Archives, 2007PINTO-ESPINOZA et al. 612RESULTS  In Figure 3, it is shown the magnetic field applied to the MSFB reactor used during the dechlorination process, (4).    Table 1 shows a comparison of experimental and simulated constants used in dechlorination process. Such constants were evaluated at similar conditions  used during the experimental run, (3).   Table 1. Comparison of determined constants Constants Experimental data Calculated data De [m²/s] 10.876E-10 8.2E-10 k [m³/s-kg(catalyst)] 0.021 0.021 kd [1/s] 2.292E-04 2.3E-04 k* [m³/s] 1.386E-04 1.386E-04 Kd [moles/kg(soil)/ moles/L(solution)] 1.08792 1.12 kl [m/s] 1.215475E-04 1.3E-05  51015202530356 7 8 9 10 11 12 13Magnetic field strength (mT)Bed height (cm)Figure 3. Magnetic Field Applied to MSFB dechlorination process 4The 12th International Conference on Fluidization - New Horizons in Fluidization Engineering, Art. 74 [2007]http://dc.engconfintl.org/fluidization_xii/74FLUIDIZATION XII 613In Figure 4, the simulated results are compared with the experimental. Quantitatively, the simulated result shows an excellent agreement with the experimental ones. The p-Chorophenol concentration drops approximately 58 %, in the experimental data and about 50 % with simulation; which is a reasonable approximation.   The modified AZTECA® code allows tracking the p-chlorophenol consumption, the average fluid velocity, particle position, particle activity decaying, average voidage and column pressure drop. The simulated data is storages in a binary file and then opened using a Visual Basic interface code named BOLITAS®, (7). The AZTECA® code was developed following the SAFIRE code procedure in a 2-D environment, (6).   CONCLUSIONS  The software has been validated by comparing the simulated data with the experimental ones, as shown in Table 1 and Figure 4. The only significant discrepancy found is in the mass transfer coefficient, kl, however it was due to a printing error, (3). The experimental results have proven that the dechlorination process has a promising future. Although, there is not enough experimental data, more evidences will be collected using this software at different operative conditions. The magnetic field generated enhanced a better column stabilization which allows working at higher flow rate without catalyst dragging. Some experiments are on the way, at simulation level, to determine more evidences about the magnetic field contribution in a MSFB reactor on the dechlorination process.     Dechlorination in a MSFB00.020.040.060.080.10.120.140.160 1 2 3 4Time (hours)Concentration (kg/m3)Exp. DataModelFigure 4.  p-Chlorophenol dechlorination in a MSFB reactor 5Pinto-Espinoza et al.: 2-D Simulation of the Catalytic Dechlorination of P-ChlorophenolPublished by ECI Digital Archives, 2007PINTO-ESPINOZA et al. 614ACKNWOLEDGMENTS  ¾ Consejo Nacional de Ciencia y Tecnología (CONACyT) for providing one master science scholarship. ¾ Instituto Tecnológico de Durango (ITD) for funding this research. ¾ Lisa Graham Jean for allow us to use her experimental data.  NOTATION  REFERENCES  1. Al-Mulhim, M., Enhancement of Mass Transfer Coefficient in a Magnetically Stabilized Liquid-Solid Fluidized Bed, M. S. Thesis, Oregon State University.,(1995). 2. Di Felice, R.,The voidage function for fluid particle interaction systems. Int. Journal of Multiphase Flow., (1994) 3. Graham Lisa Jean, Dechlorination of p-chlorophenol on Bimetallic Pd/Fe Catalyst in a Magnetically Stabilized Fluidized Bed; Experiment and Theory, Thesis for the degree of Doctor of Philosophy in Chemical Engineering, Oregon State University, U. S. A., 1999.Jackson, J. D., Classical Electrodynamics, Prentice Hall, Inc., (1999). 5. Levenspiel Octave, Chemical Reaction Engineering, 3rd Ed., John Wiley and Sons, NY., (1999), 6. Mikami, T., Kamiya, H. and Horio, M., SAFIRE model documentation, version 1.2., Tokyo, Japan: 34., (1999). 7. Pinto Espinoza Joaquín, Dynamic Behavior of Ferromagnetic Particles in a Liquid-Solid Magnetically Assisted Fluidized Bed (MAFB): Theory, Experiment, and CFD-DPM Simulation, Thesis for the degree of Doctor of Philosophy in Chemical Engineering, Oregon State University, U. S. A., 2002. 8. Schwarzenbach. R. P., Gschwend, P. M., and Imboden, D. M. Enviromental Organic Chemistry, Wiley-Interscience Publication, John Wiley & Sons Inc., New York., (1993). ε Reactor voidage in magnetically stabilized fluidized bed (H≠0), [-] a Catalyst activity [-] CA Concentration of p-chlorophenol, mol/m3 Cb Bulk concentration, mol/m3 Cl Alginate bead liquid concentration, mol/m3 De Effective diffusion coefficient for p-chlorophenol in alginate beads, m2/s k Reaction rate coefficient for p-chlorophenol dechlorination, m3/kgcatalysts k* Reaction rate coefficient for p-chlorophenol dechlorination, m3/s Kb Gel solid-water distribution ratio, mol/kg bead/(mol/L H2O) kd Deactivation rate coefficient for H2 (g) passivation, 1/s kl Liquid-solid mass transfer coefficient in MSFB (H≠0),m/s n Deactivation order r Bead radius, m t Time, s V Volume of reactor liquid, m3 W Weight of catalyst Pd, kg 6The 12th International Conference on Fluidization - New Horizons in Fluidization Engineering, Art. 74 [2007]http://dc.engconfintl.org/fluidization_xii/74

2-D Simulation of the Catalytic Dechlorination of P-Chlorophenol in a Magnetically Stabilized Fluidized Bed

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2-D Simulation of the Catalytic Dechlorination of P-Chlorophenol in a Magnetically Stabilized Fluidized Bed

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