Removal of Aromatic Compounds from Mineral Naphthenic Oil by

Ind. Eng. Chem. Res. 2008, 47, 3207-3212

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Removal of Aromatic Compounds from Mineral Naphthenic Oil by Adsorption F. Murilo T. Luna, Antonio A. Pontes-Filho, Eduardo D. Trindade,† Ivanildo J. Silva, Jr., Diana C. S. Azevedo, and Ce´ lio L. Cavalcante, Jr.* UniVersidade Federal do Ceara´ , Departamento de Engenharia Quı´mica, Grupo de Pesquisa em Separac¸ o˜ es por Adsorc¸ a˜ o - GPSA, Campus do Pici, 709, Fortaleza, CE, 60.455-900, Brazil, and PETROBRAS/CENPES, Ilha do Funda˜ o, Rio de Janeiro, RJ, 21.949-900, Brazil

The removal of aromatics from mineral naphthenic oil (MNO) by adsorption was studied. Commercial adsorbents were evaluated using batch experiments. The equilibrium data were fitted using the Langmuir equation. Batch experiments were used to estimate pore-diffusion coefficients. Column experiments were performed for two activated carbon samples that presented the best batch adsorption properties. A simulation model was used to predict the breakthrough curves for adsorption and desorption runs. After three cycles of adsorption/desorption, using n-hexane as eluent, only a slight decrease in aromatics capacity was observed. Activated carbon seemed to be adequate for aromatics removal in this system. 1. Introduction Because of widespread use of aromatic compounds as ingredients and solvents in various manufacturing industries, these compounds are common water and soil contaminants. Polycyclic aromatic hydrocarbons (PAHs), which are made up of only carbon and hydrogen, are ubiquitous contaminants and are well-known for their toxic, carcinogenic, and mutagenic effects.1,2 This has led to an upsurge of interest in developing and implementing methods for their removal from commercial products using adsorption. Because of the dimensions of the typical PAH molecules (e.g., naphthalene, anthracene, pyrene), mesoporous materials seem to be adequate for this purpose. Several studies have reported the usage of ordered structures such as MCM-413,4 or DAY zeolite.5 Also, PAH adsorption in nonordered activated carbons have been reported.6-8 It is wellknown that the uptakes of gaseous, vapor, or liquid adsorbates by different carbon adsorbents can vary over a remarkably wide range. Several of these variations are due to differences in the physical surface properties, that is, surface area effects, as well as to different degrees of molecular sieving because of their widely varying pore-size distributions.8,9 Extensive research has been carried out on the adsorption of organic compounds from dilute aqueous solutions by activated carbons. In particular, the adsorption of phenol and related compounds is one of the most studied systems in liquid-phase applications of carbon adsorbents, due to their industrial and environmental importance.10,11 Despite this, the relationship between the active sites on the adsorbent and their adsorptive capacities for organic compounds in aqueous media is still relatively unknown. Moreover, most of the research into pollution by PAH has been performed using gas-phase experiments,12 whereas investigations on liquid systems are still relatively scarce. Just recently, Namane and Hellal13 investigated the dynamics of adsorption in liquid phase for the removal of phenol from water using granular activated carbon. They evaluated the operating conditions (height of the bed, flow, and concentration of effluent) on the characteristics of the mass transfer zone and the mechanism of adsorption. It was concluded that hydrodynamic, equilibrium, and kinetics of adsorption are * To whom correspondence should be addressed.Tel.: +55-85-33669611. Fax: +55-85-3366-9601. E-mail: [email protected]. † PETROBRAS/CENPES.

interdependent and cannot be neglected in the process design. Guilarduci et al.14 also reported the liquid-phase adsorption of phenol from alkaline solutions with water using commercial activated carbon. It was shown that the adsorption capacity decreased with increasing temperature. Moreover, the authors concluded that the high presence of mesopores in the functionalized adsorbent surface lead to favorable adsorption behavior. The correlation between the textural and chemical features of chemically modified activated carbons with the adsorption capacity of naphthalene from aqueous solution has been more recently reported by Ania et al.10 The adsorption capacity of naphthalene in different carbon materials strongly depends on the pore-size distribution, particularly microporosity, and the functionalities in activated carbons with higher nonpolar nature. Gas-phase adsorption of pure PAHs (naphthalene, acenaphthene, phenanthrene, anthracene, fluoranthene, and pyrene) on activated carbons was studied by Mastral et al.12 They found that the microporosity size distribution was the main factor controlling the adsorption process in these systems. In a later study, the binary adsorption of naphthalene and phenanthrene on activated carbons was also reported.15 There are few reports in the literature for the removal of PAHs from a complex mixture. Recently, Gong et al.8 investigated the effectiveness of using activated carbon as an adsorbent to remove PAHs from vegetable oil, using batch and fixed-bed experiments. However, for naphthenic based mineral oils, which have different properties and composition from vegetable oil, there are no studies reported so far. Therefore it shall be interesting to evaluate the behavior of commercial adsorbents for the removal of aromatics from mineral naphthenic oil (MNO). Batch experiments were used for studies on particle kinetics and equilibrium. Dynamic frontal adsorption capacities were also evaluated in a fixed bed. A general rate model was used to validate the kinetic and equilibrium parameters. Cycles of adsorption/desorption were performed to evaluate the regeneration capacity of each system and the reduction in total adsorption capacity of the system after more than one cycle of adsorption and desorption. 2. Experimental and Modeling 2.1. Materials. Mineral naphthenic oil (MNO) from distilled Brazilian petroleum was kindly supplied by PETROBRAS. The MNO that we used is typically used in the fibers industry,

10.1021/ie071476v CCC: $40.75 © 2008 American Chemical Society Published on Web 03/21/2008

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Ind. Eng. Chem. Res., Vol. 47, No. 9, 2008 Table 1. Properties of Mineral Naphthenic Oil method density at 20/4 °C sulfur content, FRX, wt % refractive-index at 20 °C kinematic viscosity, cSt

0.916 0.569 1.511 31.68 (40 °C) 4.524 (100 °C) 328

molecular weight (g/gmol)

Figure 1. Experimental system for fixed-bed operation: (1) column, (2) temperature controller, (3) valve, (4) pump, (5) solvent storage, (6) feed storage, (7) sample collection, and (8) waste.

because of its good stability and low flash point, to improve fiber handling and to prevent microorganisms’ growth in the fibers. Two commercial granulated activated carbons were provided by Norit (Netherland) and Sutcliffe (United Kingdom), called ADS1 and ADS2, respectively. A commercial activated clay (Filtrol-24 from Engelhard, coined as ADS3) was also evaluated. All adsorbents were used as received. Naphthalene (Acros Organics 99%, USA) and HPLC grade n-hexane (J.T. Baker, USA) were used as reference PAH and mobile phase in our fixed-bed experiments, respectively. 2.2. Oil and Adsorbents Properties. The oil characterization was performed according to ASTM methods16 and is presented in Table 1. The density analysis was done at 20 °C using DMA 4500 (Anton Paar). Sulfur contents were determined using Horiba-SLFA-11OOH. Refraction index was obtained using Quimis-Q109B. The kinematic viscosity was measured using a viscosimeter 7305 (Koehler). Detailed quantification of organic compounds was carried out by high-resolution mass spectrometry (group type) using a high-resolution gas chromatograph (HP 5890II). The adsorbents were previously treated at 110 °C for at least 24 h for water removal and an Autosorb-1 MP (Quantachrome, USA) was used to measure N2 isotherms at 77 K for the determination of textural properties such as surface area, total pore volume, micropore volume, and mean pore diameter. The specific surface area was calculated using the BET methodology, and micropore volume was determined using the DubininRadushkevich (DR) equation. The average pore width was estimated by the Horvath-Kawazoe (HK) method, according to the procedure described by Rouquerol et al.17 2.3. Batch Experiments. Liquid-phase batch experiments were performed for equilibrium and kinetic measurements at 25 °C and under constant agitation. All of the measurements were made in duplicate, and the experimental error on the calculated value of the solid-phase concentration was limited to 5%. For our study, we used the average values of the duplicate experiments. For the equilibrium measurements, oil samples (ca. 5 g each) were put in contact with varying amounts of adsorbent (0.1, 0.25, 0.5, 0.75, 1.0, 1.25, and 1.5 g). After reaching equilibrium (appxroximately 12 h), the oil was separated from the adsorbent by vacuum filtration and analyzed using a FTIR

ASTM D-1298 ASTM D-2622 ASTM D-1218 ASTM D-445 ASTM D-2502-92

spectrometer (BIO-RAD, resolution of 8 cm-1) using a KBr cell of 32 mm with an optical path of 0.015 mm. The concentrations of the samples were evaluated through the area of the band between 1615 and 1580 cm-1 of the infrared spectrum, which corresponds to the aromatics band. The values of the area were calibrated using the concentration of pure naphthalene as a reference. The same procedure was followed for the kinetic experiments (5 g of oil and 1.5 g of adsorbent), sampling the liquid phase every 10 min (only 100 µL was sampled each time, quickly analyzed in the FTIR spectrometer, and returned to the experimental batch system). Equilibrium adsorption pseudoisotherms (assuming that the aromatic compounds are more strongly adsorbed and thus neglecting any adsorption of paraffinic and naphthenic compounds) were fit using the Langmuir equation (eq 1),

q* )

qmbC 1 + bC

(1)

where C (mg/g of solution) and q* (mg/g of adsorbent) are the total aromatics concentrations in equilibrium in the liquid phase and in the adsorbed phase, respectively; and qm and b are Langmuir equation parameters. This will obviously be an empirical isotherm that characterizes the lumped behavior of all aromatics in this type of system (MNO). We believe that this simplification will not be harmful for the latter purpose of modeling the system dynamics for aromatics removal in fixedbed systems. To investigate the contribution of mass transfer parameters in the kinetics of adsorption of MNO in these adsorbents, a pore-diffusion model was employed for the solid phase (eqs 2-5),18 with liquid film mass transfer resistance around the adsorbent particle (eqs 6-7).

(

)

Solid-Phase Balance: ∂Cp ∂Cp ∂q* ∂ 2C p +2 + Fap ) pDp p 2 ∂t ∂t r∂r ∂r

Initial Conditions: t ) 0, Cp ) C0, Cp ) 0, q ) 0

(2) (3)

Boundary Conditions: r ) 0, r ) R, pDp

∂Cp )0 ∂r

∂Cp ) kf,b(C - Cp) ∂r

Liquid-Phase Balance: 3kf,b(1 - ) dC r ) R, )(C - Cp) dt R Initial Condition: t ) 0, C ) C0

(4) (5)

(6) (7)

In the above equations, C and Cp are the bulk liquid phase and intra-particle liquid-phase concentrations, respectively, p the particle porosity,  the bed porosity, Dp the pore-diffusion

Ind. Eng. Chem. Res., Vol. 47, No. 9, 2008 3209 Table 2. Composition of the Mineral Naphthenic Oil by High-Resolution Mass Spectrometry

Table 3. Adsorbents Properties adsorbents

% v/v saturated compounds parafinics naphthenics aromatic compounds monoaromatics diaromatics triaromatics tetraromatics sulfur compounds

(m2/g)

BET surface area average pore width, HK (Å) total pore volume (cm3/g) micropore volume, DR (cm3/g) average particle diameter (cm) particle porosity

72.2 4.6 67.6 21.4 11.3 7.2 2.4 0.5 6.4

coefficient, kf,b the film mass transfer in the batch adsorption system, t the time, and r the radial coordinate. 2.4. Column Experiments. The breakthrough behavior of MNO in a fixed-bed system was investigated by frontal adsorption experiments. An adsorption column containing the adsorbent was connected to a HPLC pumping system from Varian ProStar 210 (Figure 1). Initially, the pumping system delivered pure n-hexane as solvent to establish the flow rates through the column. After that, the MNO was pumped through the column at the same flow rate, and samples were taken periodically at the outlet and analyzed for aromatics content. After saturation was reached (constant concentration of aromatics at the column outlet), the MNO was eluted from the column using pure n-hexane at the same flow rate and temperature. Two different flow rates were used (0.1 and 0.2 mL/min). The aromatics concentrations were obtained using FTIR spectroscopy as done previously with the batch experiments. All of the experiments were carried out at 25 °C. We used a general rate model18 (eqs 8-14) to predict the breakthrough curves using parameters obtained in the batch experiments (Dp) or from literature (kf, DL): Differential mass balance in liquid phase:



3kf ∂C ∂2C ∂C +u ) DL 2 - (1 - ) (C - Cp|r ) Rp) ∂t ∂z R ∂z

Initial: t ) 0 and z ) L, C ) 0, q ) 0

[

Boundary 1: z ) 0, uC - DL Boundary 2: z ) L,

(8) (9)

dC ) uC0 dz z ) 0

]

dC )0 | dz z ) L

(10) (11)

where DL is the axial dispersion coefficient, kf is the liquid film mass transfer coefficient, u is the superficial fluid velocity, R is the particle radium, and z is the spatial coordinate. Differential mass balance in solid phase:

p

( )

∂Cp 1 ∂ 2 ∂Cp ∂q + (1 - p) Fap ) Dp 2 r ∂t ∂t ∂r r ∂r

(12)

∂Cp )0 dz

(13)

CC 2: r ) R, Cp ) C

(14)

CC 1: r ) 0,

The pore-diffusion coefficients (Dp) estimated in batch experiments were used in the fixed-bed simulations. The axial dispersion coefficients were estimated from the correlation:19



DL ) 0.2 + 0.011Re0.48 udp

(15)

ADS 1

ADS 2

ADS 3

688 16.8 0.422 0.314 0.058 0.39

1218 21.0 1.041 0.781 0.056 0.43

262 20.4 0.275 0.076 0.062 0.28

Because MNO is a complex mixture of organic compounds including aromatics, we calculated an average external mass transfer coefficient from the individual external mass transfer calculated for the most representative aromatic compounds (benzene, naphthalene, anthracene, and pyrene), using the Wilson and Geankoplis correlation,20

Sh ≡

dpkf 1.09 (Sc)1/3(Re)1/3 ) Dm 

(16)

where Sh, Sc, and Re are the Sherwood, Schmidt and Reynolds numbers, respectively. Dm is the molecular diffusion coefficient, estimated using the Wilke-Chang equation,21

Dm ) 7.4 × 10-8

(φM)1/2T ηVb0.6

(17)

where M is the molecular weight, η the solution viscosity, T the absolute temperature, Vb the molar volume at normal boiling point, and φ is an association coefficient, taken as 1.0 for the aromatics compounds of our MNO sample. 2.5. Numerical Procedures. Both models (batch and column) were numerically solved using the gPROMS commercial simulator. The mathematical systems are composed by systems of partial differential and algebraic equations. The axial and radial domains are discretised using a third-order orthogonal collocation method in finite elements. The estimation of the mass transfer parameters of the batch system (Dp and kf,b) was performed by an optimization package using the heterocedastic method.22 All of the simulations were carried out on a personal computer Pentium IV 2300 MHz processor with 1 GB of RAM memory. 3. Results and Discussion 3.1. Characterization of the Oil and Adsorbents. The physical properties of MNO are presented in Table 1. The composition of MNO obtained from the high-resolution mass spectroscopy is presented in Table 2. As can be seen, the total aromatics content was found to be 21.4% (v/v); 52.8% of total aromatic compounds are monoaromatics, 33.6% are diaromatics, 11.2% are triaromatics, and 2.3% are tetraromatics. The textural characterization of the adsorbents from the N2 adsorption isotherms at 77 K is presented in Table 3. It can be seen that both activated carbon samples (ADS1 and ADS2) present better porous properties (higher surface area and pore volumes) than the commercial clay (ADS3). 3.2. Batch Experiments. Batch adsorption isotherms of MNO with the three different adsorbents are presented in Figure 2. Lines represent the Langmuir fit of the data, with parameters listed in Table 4. As summarized in Table 5, ADS1 has the largest adsorption capacity (181 mg/g), followed by ADS2 (168 mg/g) and, finally ADS3 with the lowest adsorption capacity (113 mg/g). The higher adsorption capacity of the activated carbons may be due to different functionalized structures of the samples that we studied. We also present in Table 5 several

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Figure 2. Equilibrium adsorption isotherms of total aromatics compounds present in MNO at 25 °C on different adsorbents. (0) ADS1, (O) ADS2, (1) ADS3. Full lines are calculated from the Langmuir equation. Table 4. Langmuir Parameters of MNO on Different Adsorbents adsorbents

b (g/mg)

qm (mg/g of adsorbent)

ADS1 ADS2 ADS3

4.48 2.05 1.15

181 168 113

Figure 3. Kinetic adsorption experiments of MNO at 25 °C on different adsorbents. (0) ADS1, (O) ADS2, (3) ADS3. Full lines are calculated from the pore-diffusion model.

Table 5. Aromatics Adsorption Capacities of Different Adsorbents adsorbent

sorbate

capacity (mg/g)

reference

ADS1 ADS2 ADS3 activated carbons organoclays MCM 41 MCM 41

MNO MNO MNO naphthalene phenanthrene naphthalene pyrene

181 168 113 185 to 563 40 88 265

this study this study this study (10) (23) (4) (4)

Figure 4. Experimental and theoretical breakthrough curves of MNO on ADS 1. (O) Q ) 0.1 mL/min, (0) Q ) 0.2 mL/min. Full line is model representation.

Table 6. Mass Transfer Parameters Estimated by Pore Diffusion Model from Batch Experiments adsorbents ADS1 ADS2 ADS3

kf,b (cm/s)

pDp (cm2/s)

10-2

10-7

1.6 × 1.6 × 10-2 8.6 × 10-3

1.56 × 6.07 × 10-8 1.27 × 10-9

tortuosity 3.8 9.7 462

Table 7. Input Parameters for the Column Simulation Model

b (g/mg) qm (mg/g) Dp (cm2/s) DL (cm2/s) kf (cm/s)  P C0 (mg/g) R (cm) L (cm) D (cm)

ADS1

ADS2

4.48 181 1.56 × 10-7 3.25 × 10-2 2.52 × 10-3 0.49 0.38 216 0.029 25.0 0.46

2.05 168 6.07 × 10-8 3.34 × 10-2 2.53 × 10-3 0.60 0.43 216 0.028 25.0 0.46

aromatics adsorption capacities reported in the literature, for the sake of comparison. Figure 3 shows the kinetics of adsorption for MNO in the three different adsorbents. Lines represent the best estimate from the pore-diffusion model used to represent the experimental data (eqs 2-7). The pore-diffusion coefficient (Dp) and the external film mass transfer (kf,b) were the fitted parameters of the model. The theoretical solutions are in good agreement with the experimental data. Table 6 presents the estimated parameters. It may be observed that the pore-diffusion values are higher for ADS1 and ADS2 (activated carbons) and lower for ADS3 (activated clay). These values for Dp here obtained will later be used to try to correlate the column experiments. To evaluate the proper physical adequacy of our model, we calculated the tortuosity values obtained for these systems. For this, we used the Dp values that were estimated from the porediffusion model. Assuming that all of the aromatics present in

Figure 5. Experimental and theoretical breakthrough curves of MNO on ADS 2. (O) Q ) 0.1 mL/min, (0) Q ) 0.2 mL/min. Full line is model representation.

MNO can be represented by a mixture of only the four most representative aromatic compounds for each number of aromatic rings (benzene for mono-, naphthalene for di-, anthracene for tri-, and pyrene for tetra-aromatics), an aVerage molecular diffusivity (based on the aromatics distribution presented in Table 2) can be calculated. The value thus estimated (Dm ) 5.87 × 10-7 cm2/s) was then used to calculate the tortuosity (τ ) Dm /pDp) of our adsorbents from the batch experiments presented in Table 6. 3.3. Column Experiments. Column experiments were performed using activated carbons (ADS1 and ADS2) because of their higher adsorption capacity and faster mass transfer kinetics, when compared to clay (ADS3). To study the dynamic adsorption of the selected adsorbents, breakthrough curves with fixed initial concentration of aromatics in MNO were obtained at 25 °C at two different flow rates (0.1 and 0.2 mL/min), as shown in Figures 4 and 5. Lines represent the general rate model (eqs 8-17) without any fitted parameters. All of the input values (see Table 7) were either measured or estimated from correlations available in the open literature. It should be highlighted that the value of the pore-diffusion coefficient (Dp) used for

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Figure 6. Adsorption/desorption steps of MNO on ADS1 at 25 °C. (0) First cycle, (4) second cycle, (×) third cycle. Full line is model representation for the first cycle.

Figure 7. Adsorption/Desorption steps of MNO on ADS2 at 25 °C. (0) First cycle, (4) second cycle, (×) third cycle. Full line is model representation for the first cycle.

these simulations was obtained in the batch experiments reported in the previous section. Also, for the calculation of kf using the Wilson and Geankoplis correlation (eq 16) we had to assume pure component properties of representative aromatics (for each number of aromatic rings mainly present in the mixture) to estimate the molecular diffusivity (Dm) used in the correlation. So, as done for the batch experiments calculations, we used data of benzene to represent the monoaromatics, of naphthalene to represent the diaromatics, of anthracene for triaromatics, and of pyrene for tetraromatics. Again, an aVerage molecular diffusivity (based on the aromatics distribution presented in Table 2) was then used to calculate the kf used in the simulation model (eq 8). A remarkable agreement between the experimental data and the model representation is observed in Figures 4 and 5, especially considering the complex nature of the mixture used in the experiments (MNO) and the simplifications that were adopted. The breakthrough times could be very well predicted in all cases, showing agreement with the flow rates that were used. Some small deviations in the upper C/Co region of the curves for the lower flow rate experiments (Q ) 0.1 mL/min) can be attributed to heavier compounds (higher than tetraromatics) eventually present in MNO being more slowly retained throughout the column than predicted by the model. However, in general we could predict very well the behavior of our adsorption column used to remove aromatics from naphthenic mineral oil straight from simple batch experiments. Cycles of adsorption/desorption were performed to verify if any amount of total aromatic compounds present in naphthenic oil remains adsorbed in the column during the desorption step. It is expected that a portion of polyaromatic compounds eventually not desorbed in the desorption step would decrease the adsorption capacity of the adsorbent and consequently the efficiency of the aromatics removal with increasing number of cycles. Adsorption/desorption breakthrough curves (with n-hexane at 25 °C as desorption solvent) are presented in Figures 6 and 7 for adsorbents ADS1 and ADS2, respectively, along with a model simulation with the same data already used for the adsorption step. Both ADS1 and ADS2 show a slight decrease in adsorption capacity between the first and third cycles. This might indicate that some heavier compounds could probably not be totally desorbed in the desorption step and could have eventually built up in the adsorbent column after the first cycle. It should be noted also from Figures 6 and 7 the excellent reproducibility of the adsorption/desorption cycle behavior, more notably for the second and third cycles.

4. Conclusions We studied the removal of aromatic compounds from mineral naphthenic oil using adsorption on two samples of commercial activated carbons and a sample of commercial activated clay. Using only physical properties of the oil and the adsorbents and batch experiments, the breakthrough behavior in a fixedbed column could be well predicted. The complex nature of the oil mixture, containing ca. 21% total aromatics, distributed from one to four ring compounds, was simplified using four representative compounds of each ring number present in the mixture (benzene, naphthalene, anthracene, and pyrene). Activated carbon, according to our results, seemed to be adequate for aromatics removal in this system. It was also observed that the performance of this removal in column experiments was not severely affected with continuous runs up to three adsorption/desorption cycles, using n-hexane as a desorption solvent. Finally, we may conclude from this study that a reliable scaleup may be performed from simple laboratory batch experiments for an adsorption process for aromatics removal from mineral naphthenic oil using activated carbon as adsorbent. Acknowledgment PETROBRAS, FUNCAP, CNPq, and FINEP are gratefully acknowledged for financial support to this study. List of Symbols b ) Langmuir equation parameter (g‚mg-1) C ) Bulk liquid-phase concentration (mg‚g-1) Cp ) Intra-particle liquid-phase concentration (mg‚g-1) C0 ) Initial concentration (mg‚g-1) dp ) Average particle diameter (cm) D ) Column diameter (cm) Dm ) Molecular diffusion coefficient (cm2‚s-1) Dp ) Pore diffusion coefficient (cm2‚s-1) DL ) Axial dispersion coefficient (cm2‚s-1) kf ) Film mass transfer coefficient (cm‚s-1) kf,b ) Film mass transfer in the batch adsorption system (cm‚s-1) L ) Column length (cm) M ) Molecular weight Q ) Flow-rate (mL‚min-1) q ) Solid-phase concentration (mg‚g-1) q* ) Solid phase average concentration (mg‚g-1) qm ) Langmuir equation parameter, saturation capacity (mg‚g-1) r ) Radial coordinate R ) Particle radius (cm) Re ) Dimensionless Reynolds number Sh ) Dimensionless Sherwood number Sc ) Dimensionless Schmidt number

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t ) Time (min) T ) Absolute temperature (K) u ) Superficial velocity (cm‚min-1) Vb ) Molar volume at normal boiling point (cm3‚gmol-1) z ) Axial coordinate Greek Symbols  ) Bed porosity p ) Particle void fraction Fap ) Particle apparent density (g‚cm-3) φ ) Association coefficient, eq 17 η ) Viscosity of the solution (cP) Literature Cited (1) Harvey, R. G. Polycyclic Aromatic Hydrocarbons: Chemistry and Carcinogenicity; Cambridge University Press: Cambridge, U.K., 1991. (2) Mackerer, C. R.; Griffis, L. C.; Grabowski, J. S.; Reitman, F. A. Petroleum Mineral Oil Refining and Evaluation of Cancer Hazard. Appl. Occup. EnViron. Hyg. 2003, 18, 890. (3) Choudhary, V. R.; Mantri, K. Temperature Programmed Desorption Of Toluene, P-Xylene, Mesitylene and Naphthalene on Mesoporous High Silica MCM-41 for Characterizing its Surface Properties and Measuring Heats of Adsorption. Microporous Mesoporous Mater. 2000, 40, 127. (4) Arau´jo, R. S.; Azevedo, D. C. S.; Cavalcante, C. L., Jr.; Jime´nezLo´pez, A.; Rodrı´guez-Castello´n, E. Adsorption of Polycyclic Aromatic Hydrocarbons (PAHs) from Isooctane Solutions by Mesoporous Molecular Sieves: Influence of the Surface Acidity. Microporous Mesoporous Mater. 2008, 108, 213. (5) Chang, C.; Chen, K.; Tsai, W.-T. Adsorption of Naphthalene on Zeolite from Aqueous Solution. J. Colloid Interface Sci. 2004, 277, 29. (6) Mastral, A. M.; Garcia, T.; Callen, M. S.; Murillo, R.; Navarro, M. V.; Lopez, J. M. Sorbent Characteristics Influence on the Adsorption of PAC: I. PAH Adsorption with the Same Number of Rings. Fuel Process. Technol. 2001, 77-78, 373. (7) Garcia, T.; Murillo, R.; Cazorla-Amoros, D.; Mastral, A. M.; LinaresSolano, A. Role of the Activated Carbon Surface Chemistry in the Adsorption of Phenanthrene. Carbon 2004, 42, 1683. (8) Gong, Z.; Alef, K.; Wilke, B.; Li, P. Activated Carbon Adsorption of PAHs from Vegetable Oil Used in Soil Remediation, J. Hazard. Mater. 2006, 143, 372. (9) Nouri, S.; Haghseresht, F. Estimation of Adsorption Capacity for Dissociating and Non Dissociating Aromatic Compounds on Activated Carbon with Different Models. Adsorption 2005, 11, 77.

(10) Ania, C. O.; Cabal, B.; Pevida, C.; Arenillas, A.; Parra, J. B.; Rubiera, F.; Pis, J. J. Removal of Naphthalene from Aqueous Solution on Chemically Modified Activated Carbons. Water Res. 2007, 41, 333. (11) Terzyk, A. P. Further Insights into the Role of Carbon Surface Functionalities in the Mechanism of Phenol Adsorption. J. Colloid Interface Sci. 2003, 268, 301. (12) Mastral, A. M.; Garcia, T.; Callen, M. S.; Murillo, R.; Lopez, J. M.; Navarro, M. V. PAH Mixture Removal from Hot Gas by Porous Carbons from Model Compounds to Real Conditions. Ind. Eng. Chem. Res. 2003, 42, 5280. (13) Namane, A.; Hellal, A. The Dynamic Characteristics of Phenol by Granular Activated Carbon. J. Hazard. Mater. 2006, 137, 618. (14) Guilarduci, V. V. S.; Mesquita, J. P.; Martelli, P. B.; Gorgulho, H. F. Adsorc¸ a˜o de Fenol sobre Carva˜o Ativado em Meio Alcalino. Quim. NoVa, 2006, 29, 1226. (15) Mastral, A. M.; Garcia, T.; Callen, M. S.; Murillo, R.; Lopez, J. M.; Navarro, M. V. Measurements of Polycyclic Aromatic Hydrocarbon Adsorption on Activated Carbon at Very Low Concentrations. Ind. Eng. Chem. Res. 2003, 42, 155. (16) Annual Book of ASTM Standards, Section 5 - Petroleum Products, Lubricants and Fossil Fuels, American Society for Testing and Materials, ASTM: Philadelphia, PA, 2001. (17) Rouquerol, F.; Rouquerol, J.; Sing, K. Adsorption by Powders & Porous Solids; Academic Press: San Diego, CA, 1999. (18) Ruthven, D. M. Principles of Adsorption and Adsorption Processes; John Wiley & Sons: New York, 1984. (19) Butt, J. B. Reaction Kinetics and Reactor Design; Prentice Hall: Englewood Cliffs, NJ, 1980. (20) Wilson, E. J.; Geankoplis, C. J. Liquid Mass Transfer at very low Reynolds Numbers in Packed Beds. Ind. Eng. Chem. Fundam. 1966, 5, 9. (21) Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 4th ed.; McGraw-Hill Book Company: New York, 1987. (22) gPROMS, ver. 2.3.1, User Guide; 2004. (23) Safi, J. M.; El-Nahhal, Y. Z. Adsorption of Phenanthrene on Organoclays from Distilled and Saline Water. J. Colloid Interface Sci. 2004, 269, 265.

ReceiVed for reView October 31, 2007 ReVised manuscript receiVed February 19, 2008 Accepted February 19, 2008 IE071476V