correlation with different models for adsorption ...

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption ISSN 0126-2807 Isotherms of m-Xylene and Toluene on Zeolites. Volume 2, Number 2: 43-56, May-August, 2007 © T2007 Department of Environmental Engineering Sepuluh Nopember Institute of Technology, Surabaya & Indonesian Society of Sanitary and Environmental Engineers, Jakarta Open Access http://www.trisanita.org

Research Paper

CORRELATION WITH DIFFERENT MODELS FOR ADSORPTION ISOTHERMS OF M-XYLENE AND TOLUENE ON ZEOLITES ZOUBIR BENMAAMAR1* and ABDELKHADER BENGUEDDACH2 1Laboratoire 2Laboratoire

de Chimie, Département de Chimie, Université de Blida, B.P. 192 Douera 16103 Alger Algerie. de Chimie des Matériaux, Département de Chimie, Université d’ Oran Es-sénia, Oran, Algerie. *Corresponding Author: E-mail: [email protected] Received: 9th May 2007; Revised: 22nd May 2007; Accepted: 30th May 2007

Abstract: The ability of NaY, KY, BaY, BaX and NaX zeolites to adsorb m-xylene and toluene was studied experimentally. Thus, the adsorption isotherms of two volatile organic compounds, toluene and m-xylene, on NaY, KY, BaY, BaX and NaX were measured at 298, 308, 318, and 333 K using a vacuum microbalance system. The toluene and the m-xylene were chosen because they belong to the same chemical family. The experimental data obtained were correlated with different existing adsorption isotherm models such as the Langmuir model, the Freundlich model, the FowlerGuggenheim model, the Hill-De Boer model and the Sips model. The Langmuir model is well adapted to the description of m-xylene and toluene adsorption on NaY, KY, BaY, BaX and NaX zeolites at all four temperature. The Sips model is also found to be well adapted to describe the adsorption of toluene on to NaY, KY, BaY, BaX and NaX zeolites at all four temperature. The Freundlich model, the Fowler-Guggenheim model, and the Hill-De Boer model were not satisfactory. The adsorption affinity of m-xylene on NaY, KY, BaY, BaX and NaX zeolites is sufficiently greater than the affinity of toluene. The adsorption affinity of m-xylene and toluene decreased in the following order NaY>NaX>BaX>KY>BaY. These results demonstrate the high capacity of NaY, KY, BaY, BaX and NaX zeolites to remove vapors of m-xylene and toluene at very low concentrations. However, in the volumetric method, the accuracy of the data depends on the precision with which the equilibrium pressure is measured. Besides, the existence of dead volume, the value of which is never known with high precision, is a source of error. That is why, the gravimetric method remains the most accurate method for measuring gas-solid equilibrium data for pure gases. Keywords: Existing models, gas-solid equilibrium, gravimetric method, volatile organic compounds

INTRODUCTION Volatile organic compounds (VOCs) are pollutants of great interest because they are very harmful for both human health and the environment, even at very low concentrations. The 43 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

abatement of VOCs present in gas streams at very low concentrations is very difficult and requires an extremely optimized process. Environmental protection regulations of volatile organic compounds’ emission, introduced under the Clean Air Act amendments, have accelerated the development of VOCs’ abatement systems. Add on control techniques are broadly classified into two types: destruction (biofiltration, thermal oxidation, catalytic oxidation, reverse flow reactor) and recovery (adsorption, condensation, membrane separation) [1]. Adsorption of these pollutants in zeolites could be one of the best solutions for the treatment of these streams. In this study, the considered zeolites are NaY, KY, BaY, NaX and BaX. These zeolites are a FAU (faujasite) structure. A comparison of the properties of this material with those of the activated carbon, which is common commercial adsorbent, was given by Otten [2]. The advantages of this and in general those of the faujasites are essentially its incombustibility, its great stability, its hydrophobic character, and its regenerability at low temperature [3, 4]. In comparison, the activated carbon shows some inconveniences [2], it is a flammable material, it does not desorb efficiently high boiling solvents, and it is a hygroscopic material requiring relative humidity control. Moreover, zeolite systems offer improved safety, simplicity of operation, and easy maintenance, explaining why the adsorption on hydrophobic zeolite is one effective solution for removal of VOCs [2, 3]. However, the application of zeolite for removal of VOCs has only recently gained attention [5, 6]. There are relativety limited studies done on hydrophobic zeolites as adsorbents for VOCs. Sakuth [7] have shown the influence of the surface polarity on the adsorbate phase composition containing a polar and a nonpolar component, toluene and 1 propanol, respectively. They have used a flow type apparatus for vapor adsorption experiments. Ryu [8] measured the adsorption equilibrium of toluene and gasoline vapors on DaY zeolite F 20 by a static volumetric method. Bathen [9] measured isotherms for the system zeolites DaY/ethanol/air by using the desorptive method. In this work, the vapor adsorption properties of toluene and m-xylene were studied in NaY, KY, BaY, NaX and BaX zeolites. The objectives of the present research were: to show the effectiveness of adsorbent to reduce the concentration of VOC and lower the cost of regenerated adsorbent, to compare adsorption isotherms of m-xylene and toluene belonging to the same family, to evaluate the influence of the temperature on VOC’s adsorption, to correlate the experimental data with different existing adsorption isotherms models, to determine the adsorption affinity of VOC’s, and to validate a gravimetric method. Adsorption isotherms were measured at four different temperatures using a vacuum microbalance system: 298, 308, 318, and 333 K. The experimental data obtained were correlated with the following adsorption isotherms: Langmuir model, Freundlich model, Fowler-Guggenheim model, Hill-De Boer model, Sips model. MATERIALS AND METHODS The VOCs selected in this study were toluene (mass fraction 0.99 purity) and m-xylene (mass fraction 0.98 purity). They were respectively purchased from Carlo Erba and Aldrich. The physical properties of these VOCs are listed in Table 1. NaY (KÖSTROLITH UY8 Type Y, Ball) and NaX (KÖSTROLITH 13X K1 Type 13X, Ball) were in the form of solid extrudates (diameter respectively 1.0-1.6mm and 1.0-1.8mm). These zeolites allow the adsorption of VOCs from polluted air without exhausting the capacity by adsorbing water vapor. Ionic exchange was carried out at room temperature by stirring 2 g of parent zeolite in 100 ml of aqueous solution containing 5 x 10-3 mol L-1 of the metal nitrate for 24 hours. The sample was washed until free of nitrate, dried overnight at 353 K. 44 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

Table 1: Physical Properties of m-Xylene and Toluene m-xylene -1 Molecular weight MW (g mol ) 106.7 Normal boiling point Teb (°C) 139.1 Vapor pressure Ps (Pa) 1122 298 K 308 K 1954 318 K 3265 6588 333 K -1 -3 0.836 liquid density at 20°C (ρ g cm )

Toluene 92.14 110.6 3783 6219 9850 18465 0.867

A SARTORIUS 4201 electromagnetic suspension microbalance was installed for the measurement of the adsorbed quantities of vapors in zeolites. It has a ± 0.01 mg resolution and a ± 0.02 mg precision, for measuring full scale of 100.00 mg. The temperatures of the VOC vapor, of the sorption chamber, and of the magnet chamber were separately controlled. In a typical experiment, about 15 mg of NaY, KY, BaY, NaX and BaX zeolites were evacuated at 60°C under 0.01 Pa during 2 days. This procedure was previously published by Otten [2], who explained that the DaY zeolite could be completely regenerated in such conditions. Then, the VOC vapor source was connected to the sorption chamber. The mass was digitized and monitored as a function of time by a computer. The mass was obtained by averaging five mass values acquired at 0.2 s intervals around the time point (one point every 1 s). The background noise, averaged by means of statistical function in the assistance software, was subtracted from the measured values. This way, smooth, reproducible sorption curves were obtained. The sorption experiments were carried out below atmospheric pressure, and the sample mass was measured over a large range of vapor pressures. To avoid any condensation of VOC in the gas phase, the pressure of the VOC (PVOC ) was kept lower than the VOC saturated vapor pressure (PS) at the sorption chamber temperature. Attention was paid to maintain PVOC < 0.8 PS. The VOC saturated vapor pressure, listed in Table 1, were calculated using the following equation [10]: B (1) Log10 ( PS ) = A + + C log10 (T ) + DT + ET 2 T where A, B, C, D, and E are compound dependent parameters and Ps (expressed in Pa) RESULTS AND DISCUSSION Adsorption isotherms The adsorbed amount is expressed in moles per kg. The adsorption isotherms were measured at 298, 308, 318, and 333 K. To correlate our experimental VOC adsorption data, the Langmuir, Fowler- Guggenheim, Hill De Boer, Sips and the Freundlich equations were used. The Langmuir equation The simplest and still the most useful isotherm, for both physical and chemical adsorption, is the Langmuir isotherm [11] which is usually written as: q bp = (2) qs 1 + bp where q is the adsorbed quantity (moles of m-xylene or toluene per kg of zeolites) and p is the pressure of the adsorbate in the bulk gas phase. 45 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

The two parameters qs is the saturation limit (mole/kg) and b is the Langmuir constant (Pa-1). This parameter depends on the temperature: it decreases with increase of temperature, according to a relation of the type. b = A exp( TB ) (3) where A and B are constants and T is the absolute temperature. The Langmuir isotherm verifies Henry’s law for the low pressures. Indeed, the limiting slope of this isotherm at low pressures is qsb dq lim = lim =q b (4) p → 0 dp p →0 (1 − bp )2 s In this study, linear plots are obtained in coordinates p/q = f(p), if this equation is verified. The parameters obtained, the regression coefficient (R2), the corresponding average relative error (∆q(%)) and mean average relative error (∆qm(%)) are summarized for each temperature in Table 2 and Table 3. Such average relative error was calculated by N 100 exp q exp − q cal ∆ q (% ) = (5) ∑ q N exp 0 exp where qexp is the experimental amount of adsorbate, qcal that calculated with the model, and Nexp the number of experimental data. Table 2: Parameters of linearization of the Langmuir model for m-xylene adsorption Isotherm equation qs(mol/kg) b(Pa-1) Adsorbent T(K) R2 NaY 298 0.999 Y = 0.285 X + 1.925 3.510 1.823 NaY 308 0.999 Y = 0.332 X + 0.832 3.009 3.615 NaY 318 0.999 Y = 0.357 X + 1.260 2.799 2.222 NaY 333 0.999 Y = 0.367 X + 1.3 60 2.726 2.004 ∆qm(%) BaY 298 0.999 Y = 0.371 X + 3.466 0.778 2.697 BaY 308 0.999 Y = 0.448 X + 1.584 1.407 2.230 BaY 318 0.999 Y = 0.493 X + 2.201 0.922 2.029 BaY 333 0.999 Y = 0.508 X + 2.627 0.748 1.966 ∆qm(%) KY 298 0.999 Y = 0.444 X + 4.113 0.547 2.252 KY 308 0.999 Y = 0.535 X + 1.774 1.052 1.867 KY 318 0.999 Y = 0.582X + 2.782 0.617 1.718 KY 333 0.999 Y = 0.603 X + 2.905 0.570 1.657 ∆qm(%) BaX 298 0.999 Y = 0.338 X + 2.804 1.054 2.957 BaX 308 0.999 Y = 0.403 X + 1.177 2.105 2.479 1.194 BaX 318 0.999 Y = 0.437 X + 1.917 2.289 1.103 BaX 333 0.999 Y = 0.451 X + 2.008 2.216 ∆qm(%) 1.358 NaX 298 0.999 Y = 0.310 X + 2.376 3.227 NaX 308 0.999 2.632 Y = 0.366 X + 1.037 2.730 NaX 318 0.999 1.698 Y = 0.397 X + 1.483 2.520 NaX 333 0.999 1.492 Y = 0.409 X + 1.639 2.445 ∆qm(%) 46 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

∆q(%) 0.118 0.072 0.095 0.161 0.111 0.039 0.124 0.028 0.117 0.077 0.052 0.038 0.070 0.036 0.049 0.034 0.137 0.148 0.137 0.114 0.077 0.132 0.135 0.115 0.115

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

Table 3: Parameters of linearization of the Langmuir model for toluene adsorption Isotherm equation qs(mol/kg) b(Pa-1) Adsorbent T(K) R2 NaY 3.191 0.130 298 0.999 Y = 0.313 X + 24.503 NaY 2.994 308 0.080 0.999 Y = 0.334 X + 37.487 NaY 2.923 0.071 318 0.999 Y = 0.342 X + 41.284 NaY 2.836 0.066 333 0.999 Y = 0.352 X + 43.093 ∆qm(%) BaY 2.403 0.049 298 0.999 Y = 0.416 X + 48.447 BaY 2.230 0.031 308 0.999 Y = 0.448 X + 71.519 BaY 2.164 0.026 318 0.999 Y = 0.462 X + 81.064 BaY Y = 0.480 X + 85.584 2.084 0.024 333 0.999 ∆qm(%) Y = 0.498 X + 49.749 0.040 2.008 KY 298 0.999 Y = 0.536 X + 78.362 0.024 1.864 KY 308 0.999 Y = 0.551 X + 89.152 0.020 KY 1.814 318 0.999 Y = 0.572 X + 93.870 0.018 1.748 KY 333 0.999 ∆qm(%) Y = 0.376 X + 35.302 2.660 0.075 BaX 298 0.999 Y = 0.403 X + 55.368 2.478 0.044 BaX 308 0.999 Y = 0.415 X + 61.255 2.406 0.039 BaX 318 0.999 Y = 0.430 X + 64.589 2.327 0.036 BaX 333 0.999 ∆qm(%) Y = 0.343 X + 30.152 0.096 2.913 NaX 298 0.999 Y = 0.367 X + 46.516 0.058 2.720 NaX 308 0.999 Y = 0.377 X + 51.827 0.051 2.649 NaX 318 0.999 Y = 0.388 X + 62.124 0.041 2.578 NaX 333 0.999 ∆qm(%)

∆q(%) 0.008 0.041 0.107 0.103 0.065 0.091 0.084 0.084 0.886 0.065 0.027 0.004 0.004 0.115 0.038 0.041 0.067 0.096 0.166 0.093 0.019 0.128 0.023 0.171 0.085

The regression coefficient (R2) is higher than 0.970, the average relative error (∆q(%)) and mean average relative error (∆qm(%)) are quite low (lower than 1%). It is possible here to conclude that the Langmuir model is well adapted to the description of m-xylene and toluene adsorption on NaY, KY, BaY, BaX and NaX zeolites at all four temperatures. The determination of parameters qs and b, by linear regression, makes possible the calculation of theoretical isotherms and their comparison with the experimental data. For example the Langmuir equation provides a very satisfactory description of both VOC adsorption on NaY zeolite (Fig. 1). Similar results were found for KY, BaY, BaX and NaX zeolites. The mechanism of VOC adsorption is by volume filling of zeolite micropores by physical adsorption [12]. The VOC isotherms are of type I according to the IUPAC classification [13]. The toluene and the m-xylene belong to the same chemical family, so the toluene saturation amount adsorbed is close to that of the m-xylene. The slope of these isotherms, at low adsorptive pressures and at low temperature, is very steep. Indeed, the values of experimental adsorbed quantities at p/ps = 0.1, listed in Table 4, for the both VOCs are close to those obtained at saturation. So, the first molecules are adsorbed at low pressures and it was difficult to obtain data at very low pressure. That is why the values of the parameters b are not very precise. Nevertheless, the m-xylene parameter b is higher than that of toluene, which indicates that the affinity of NaY, KY, BaY, BaX and NaX zeolites for m-xylene is stronger than that for toluene. Good agreement between the experimental isotherms and the model of Langmuir was also found, in the case of systems m-Xylene-Actived Carbon [14], Quinine bichlorhydrate-Actived Carbon [15], Dyes-Clay [16], and Oleate-Bentonite and Biomasse [17]. 47 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

Fig. 1:

m-Xylene adsorption isotherms according to Langmuir model (solid lines) and experimental data for NaY with: ‘+’ T=298K, ‘∗’ 308K, ‘×’ 318K, and ‘∆’ 333K

Table 4: Adsorption data for pure m-Xylene and Toluene on NaY, KY, BaY, BaX and NaX zeolites Adsorption capacity at p/ps m-xylene toluene Adsorbent T(K) q0.1(mole/kg) q0.1/qs (%) q0.1(mole/kg) q0.1/qs (%) NaY 298 3.310 94.30 2.614 81.92 NaY 308 2.962 98.44 2.547 85.07 NaY 318 2.759 98.57 2.529 86.52 NaY 333 2.702 99.11 2.501 88.19 BaY BaY BaY BaY

298 308 318 333

2.500 2.180 1.997 1.940

92.69 97.75 98.42 98.68

1.910 1.790 1.770 1.760

79.49 80.26 81.77 84.46

KY KY KY KY

298 308 318 333

2.090 1.820 1.688 1.645

92.80 97.43 98.25 99.27

1.620 1.580 1.560 1.530

80.68 84.75 85.99 87.52

BaX BaX BaX BaX

298 308 318 333

2.760 2.400 2.230 2.200

93.34 96.79 97.41 99.28

2.200 2.100 2.090 2.060

82.69 84.73 86.86 88.51

NaX NaX NaX NaX

298 308 318 333

3.020 2.650 2.480 2.430

93.59 97.07 98.41 99.36

2.400 2.331 2.323 2.300

82.39 85.69 87.69 89.19

The Freundlich isotherm The Freundlich isotherm [18] is an empirical expression used to describe adsorption isotherms. It is represented as: (6) q = K P 1/n 48 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

The k and m are empirical constants which were determined with a classic non-linear curve fitting routine. The parameters are summarized in Table 5 and Table 6. Table 5: Parameters of linearization of the Freundlich model for m-xylene adsorption Adsorbent T(K) R2 Isotherm equation 1/n 298 0.848 Y = 0.069 X + 0.832 NaY 0.069 Y = 0.030 X + 0.916 308 0.825 NaY 0.030 0.835 Y = 0.029 X + 0.843 NaY 318 0.029 Y = 0.034 X + 0.785 333 0.882 NaY 0.034

K 2.300 2.499 2.323 2.193

BaY BaY BaY BaY

298 308 318 333

0.829 0.806 0.815 0.859

Y = 0.089 X + 0.446 Y = 0.040 X + 0.554 Y = 0.039 X + 0.463 Y = 0.046 X + 0.383

0.089 0.040 0.039 0.046

1.562 1.741 1.589 1.466

KY KY KY KY

298 308 318 333

0.833 0.798 0.819 0.867

Y = 0.086 X + 0.281 Y = 0.038 X + 0.393 Y = 0.037 X + 0.302 Y = 0.043 X + 0.227

0.086 0.038 0.037 0.043

1.325 1.481 1.352 1.255

BaX BaX BaX BaX

298 308 318 333

0.834 0.799 0.838 0.863

Y = 0.080 X + 0.590 Y = 0.035 X + 0.691 Y = 0.035 X + 0.606 Y = 0.040 X + 0.540

0.080 0.035 0.035 0.040

1.804 1.996 1.832 1.716

NaX NaX NaX NaX

298 308 318 333

0.841 0.814 0.833 0.868

Y = 0.076 X + 0.703 Y = 0.033 X + 0.798 Y = 0.032 X + 0.718 Y = 0.037 X + 0.658

0.076 0.033 0.032 0.037

2.020 2.222 2.051 1.930

Table 6: Parameters of linearization of the Freundlich model for toluene adsorption Adsorbent T(K) R2 Isotherm equation 1/n Y = 0.107 X + 0.310 0.843 298 NaY 0.107 Y = 0.136 X + 0.012 0.899 308 NaY 0.136 Y = 0.154 X - 0.154 0.933 318 NaY 0.154 Y = 0.150 X – 0.162 0.955 333 0.150 NaY

K 1.364 1.012 0.857 0.850

BaY BaY BaY BaY

298 308 318 333

0.826 0.889 0.922 0.951

Y = 0.136 X – 0.218 Y = 0.185 X – 0.671 Y = 0.211 X – 0.913 Y = 0.205 X – 0.909

0.136 0.185 0.211 0.205

0.803 0.511 0.401 0.403

KY KY KY KY

298 308 318 333

0.842 0.889 0.923 0.951

Y = 0.131 X - 0.351 Y = 0.172 X - 0.748 Y = 0.197 X - 0.979 Y = 0.192 X - 0.985

0.131 0.172 0.197 0.192

0.704 0.473 0.375 0.373

BaX BaX BaX BaX

298 308 318 333

0.841 0.892 0.924 0.953

Y = 0.124 X – 0.013 Y = 0.163 X - 0.391 Y = 0.184 X – 0.586 Y = 0.178 X – 0.587

0.124 0.163 0.184 0.178

0.987 0.676 0.556 0.556

NaX NaX NaX NaX

298 308 318 333

0.843 0.893 0.925 0.971

Y = 0.118 X + 0.129 Y = 0.153 X – 0.215 Y = 0.173 X – 0.404 Y = 0.178 X – 0.494

0.118 0.153 0.173 0.178

1.137 0.806 0.667 0.610

49 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

Because such an equation does not reduce to Henry’s law at pressures approaching zero, it is not able to provide a good fit for adsorption data at low pressure. This is particularly evident at high temperature. From the regression coefficient (R2) given in Table (lower than 0.970), it is possible to conclude that the Freundlich model is not good for description of m-xylene and toluene adsorption on NaY, KY, BaY, BaX and NaX zeolites. Good agreement between the experimental isotherms and the model of Freundlich was found, in the case of systems pentachlorophenol/(M)Al-MCM-41 [19], and Toluene/Actived Carbon [20]. The Fowler and Guggenheim Fowler and Guggenheim [21] studied by statistical thermodynamics located adsorption, by introducing the interactions between adsorbed molecules. The Fowler-Guggenheim equation when linearized takes the form: p[1 − θ ] zw q y = ln = − ln k ′ + (7) θ RT q s where θ is the coverage, w is the energy of mutual interactions between two molecules adsorbed on nearby sites, z is the number of sites surrounding a given site, and k' coefficient depending of the temperature. The curve y = f(q/qs) was plotted, and for the isotherms which the Fowler-Guggenheim model applies, the values of the regression coefficient (R2), the isotherm equation were determined, and summarized in Table 7 and Table 8. Table 7: Parameters of linearization of the Fowler-Guggenheim model for m-xylene adsorption Adsorbent T(K) R2 Isotherm equation NaY 298 0.2590 Y = 0.638 X + 1.327 NaY 308 0.1455 Y = - 1.622 X + 2.451 NaY 318 0.2622 Y = 3.283 X – 1.902 NaY 333 0.0052 Y = 0.533 X + 0.756 BaY BaY BaY BaY

298 308 318 333

0.2502 0.2367 0.1977 0.0017

Y = 0.222 X + 2.034 Y = - 1.601 X + 2.764 Y = 1.216 X + 0.338 Y = - 0.231 X + 1.817

KY KY KY KY

298 308 318 333

0.2137 0.1989 0.1473 0.0021

Y = 0.230 X + 2.017 Y = - 2.434 X + 3.476 Y = 1.755 X – 0.117 Y = - 0.171 X + 1.712

BaX BaX BaX BaX

298 308 318 333

0.3896 0.1939 0.1998 0.0001

Y = 0.385 X + 1.767 Y = - 2.833 X + 3.734 Y = 2.356 X - 0.786 Y = - 0.072 X + 1.516

NaX NaX NaX NaX

298 308 318 333

0.3312 0.1390 0.2502 0.0003

Y = 0.438 X + 1.635 Y = - 1.468 X + 2.431 Y = 2.164 X - 0.752 Y = - 0.131 X + 1.459

50 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

From the regression coefficient (R2) given in Table 7 and Table 8 (lower than 0.970), it is possible to assert that the Fowler-Guggenheim model is not suitable to describe the adsorption of m-xylene and toluene on NaY, KY, BaY, BaX and NaX zeolites. Table 8: Parameters of linearization of the Fowler-Guggenheim model for toluene adsorption Adsorbent T(K) R2 Isotherm equation NaY 298 0.0689 Y = - 0.243 X + 4.571 NaY 308 0.0160 Y = - 0.048 X + 4.760 NaY 318 0.0372 Y = - 0.062 X + 4.742 NaY 333 0.0096 Y = - 0.043 X + 4.768 BaY BaY BaY BaY

298 308 318 333

0.0121 0.1994 0.0830 0.0195

Y = - 0.225 X + 4.920 Y = - 0.166 X + 5.204 Y = - 0.087 X + 5.234 Y = - 0.043 X + 5.216

KY KY KY KY

298 308 318 333

0.2851 0.1379 0.0722 0.0229

Y = - 0.285 X + 4.846 Y = - 0.181 X + 5.130 Y = - 0.071 X + 5.141 Y = - 0.027 X + 5.152

BaX BaX BaX BaX

298 308 318 333

0.0732 0.0915 0.0290 0.0001

Y = - 0.249 X + 4.754 Y = - 0.160 X + 5.051 Y = - 0.050 X + 5.033 Y = - 0.004 X + 5.016

NaX NaX NaX NaX

298 308 318 333

0.0814 0.0826 0.0062 0.0015

Y = - 0.248 X + 4.689 Y = - 0.163 X + 4.974 Y = - 0.025 X + 4.942 Y = 0.035 X + 5.039

Good agreement between the experimental isotherms and the model of Fowler-Guggenheim was found, in the case of systems (Chlorobenzene-Carbon Tetrachloride)-Actived Carbon U-02 [22], (Benzene-Hexane)-Carbon Mol Sieve J-1, (Benzene-Pentane)-Carbon Mol Sieve J-1, (Hexane-Pentane)-Carbon Mol Sieve J-1, and (Benzene-Isopropanol)-Actived Carbon B-4 [23]. The Hill-De Boer isotherm Hill [24] and De Boer [25] gave an equation of the isotherm, which takes account of interactions and the mobility of the adsorbed phase. The linearized form of this equation is given by k p[1 − θ ] θ y = ln − = − ln k1 − 2 θ (8) θ 1−θ RT where k1 and k2 represent, respectively, the adsorbate-adsorbent and the adsorbate-adsorbate interactions. The test for the applicability of this equation to the experimental data is a linear plot of y = f (q/qs). The parameters of linearization of this model are given in Table 9 and Table 10. 51 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

Table 9: Parameters of linearization of the Hill-De Boer model for m-xylene adsorption Isotherm equation Adsorbent T(K) R2 NaY 298 0.414 Y = - 321.5 X + 262.3 NaY 308 0.523 Y = - 1943.8 X + 1767.2 NaY 318 0.380 Y = - 1634.7 X + 1489.6 NaY 333 0.290 Y = - 1723.2 X + 1550.2 BaY BaY BaY BaY

298 308 318 333

0.415 0.538 0.409 0.285

Y = - 194.3 X + Y = - 1051.2 X + Y = - 950.4 X + Y = - 966.7 X +

151.3 928.4 842.8 841.1

KY KY KY KY

298 308 318 333

0.417 0.555 0.410 0.417

Y = - 205.3 X + 161.2 Y = - 1243.8 X + 1107.8 Y = - 987.0 X + 879.2 Y = - 920.6 X + 805.0

BaX BaX BaX BaX

298 308 318 333

0.407 0.584 0.388 0.276

Y = - 234.4 X + 186.1 Y = - 1469.4 X + 1316.5 Y = - 1196.4 X + 1074.3 Y = - 1287.0 X + 1138.9

NaX NaX NaX NaX

298 308 318 333

0.405 0.533 0.421 0.268

Y = - 264.6 X + 212.0 Y = - 1521.0 X + 1369.2 Y = - 1327.3 X + 1198.2 Y = - 1556.1 X + 1388.4

Table 10: Parameters of linearization of the Hill-De Boer model for toluene adsorption Adsorbent T(K) R2 Isotherm equation NaY 298 0.632 Y = - 117.500 X + 91.416 NaY 308 0.707 Y = - 71.208 X + 54.735 NaY 318 0.735 Y = - 58.100 X + 42.887 NaY 333 0.784 Y = - 61.637 X + 45.718 BaY BaY BaY BaY

298 308 318 333

0.632 0.733 0.773 0.810

Y= Y= Y= Y=

- 72.171 X + 54.123 - 40.021 X + 29.858 - 31.742 X + 22.900 - 33.871 X + 24.506

KY KY KY KY

298 308 318 333

0.651 0.729 0.763 0.812

Y= Y= Y= Y=

- 79.250 X + 59.526 - 46.039 X + 34.479 - 36.072 X + 26.036 - 38.465 X + 27.842

BaX BaX BaX BaX

298 308 318 333

0.640 0.723 0.756 0.799

Y= Y= Y= Y=

- 87.348 X + 4.846 - 51.242 X + 38.545 - 41.489 X + 30.028 - 44.007 X + 32.019

NaX NaX NaX NaX

298 308 318 333

0.640 0.721 0.748 0.846

Y= Y= Y= Y=

- 96.818 X + 74.014 - 58.179 X + 44.043 - 46.597 X + 33.888 - 43.123 X + 31.480

52 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

From the regression coefficient (R2) given in Table (lower than 0.970), the Hill-De Boer model was not satisfactory. Sips isotherm Sips [26] derived an isotherm equation valid for localized adsorption without adsorbateadsorbate interactions. The linearized form of this equation is given by

 θ  log (9)  = log A + c log p 1−θ  where A and c are constants, P is equilibrium pressure, and θ is the coverage. In the low pressure region, this equation reduces to Freundlich isotherm. The difference with the Langmuir model is that it is not any more question of active centre-adsorbate reaction of 1:1 type. The parameters of linearization are given in Table 11 and Table 12. Table 11: Parameters of linearization of the Sips model for m-xylene adsorption Adsorbent T(K) R2 Isotherm equation A Y = 0.974 X – 1.788 0.994 298 0.167 NaY Y = 1.037 X – 1.071 0.985 308 0.343 NaY Y = 0.917 X - 0.837 0.965 318 0.433 NaY Y = 0.998 X – 1.260 0.939 333 0.284 NaY BaY BaY BaY BaY

298 308 318 333

0.999 0.984 0.987 0.940

Y = 0.988 X – 2.177 Y = 1.039 X – 1.438 Y = 0.957 X – 1.282 Y = 1.018 X – 1.692

0.113 0.237 0.277 0.184

KY KY KY KY

298 308 318 333

0.998 0.962 0.971 0.975

Y = 0.989 X – 2.169 Y = 1.051 X – 1.410 Y = 0.937 X – 1.234 Y = 1.009 X – 1.600

0.114 0.244 0.291 0.202

BaX BaX BaX BaX

298 308 318 333

0.998 0.954 0.966 0.936

Y = 0.981 X – 2.022 Y = 1.057 X – 1.306 Y = 0.933 X – 1.124 Y = 1.014 X - 1.520

0.132 0.271 0.325 0.218

NaX NaX NaX NaX

298 308 318 333

0.997 0.983 0.981 0.935

Y = 0.982 X – 1.944 Y = 1.030 X – 1.175 Y = 0.939 X – 1.015 Y = 1.019 X – 1.431

0.143 0.309 0.362 0.239

53 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

c 0.974 1.037 0.917 0.998 ∆qm(%) 0.988 1.039 0.957 1.018 ∆qm(%) 0.989 1.051 0.937 1.009 ∆qm(%) 0.981 1.057 0.933 1.014 ∆qm(%) 0.981 1.030 0.939 1.019 ∆qm(%)

∆q(%) 0.0002 0.0606 0.0170 0.0262 0.0260 0.0739 0.0469 0.0192 0.0724 0.0530 0.0038 0.1040 0.0137 0.0723 0.0480 0.0497 0.0360 0.0883 0.0555 0.0570 0.0078 0.0777 0.1220 0.0201 0.0570

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

Table 12: Parameters of linearization of the Sips model for toluene adsorption Adsorbent T(K) R2 Isotherm equation A NaY 298 0.992 Y = 1.003 X – 4.378 0.012 NaY 308 0.998 Y = 1.005 X - 4.752 0.008 NaY 318 0.998 Y = 0.993 X – 4.747 0.008 NaY 333 0.997 Y = 0.997 X – 4.786 0.008 BaY BaY BaY BaY

298 308 318 333

0.943 0.997 0.998 0.998

Y = 0.975 X – 4.556 Y = 1.015 X – 5.175 Y = 1.006 X – 5.209 Y = 1.005 X – 5.217

0.010 0.005 0.005 0.005

KY KY KY KY

298 308 318 333

0.989 0.996 0.998 0.996

Y = 1.008 X - 4.654 Y = 1.016 X - 5.092 Y = 1.005 X - 5.116 Y = 1.007 X - 5.147

0.009 0.006 0.006 0.006

BaX BaX BaX BaX

298 308 318 333

0.990 0.995 0.998 0.998

Y = 1.004 X – 4.564 Y = 1.015 X - 5.018 Y = 1.002 X – 5.007 Y = 1.001 X – 5.017

0.010 0.006 0.007 0.006

NaX NaX NaX NaX

298 308 318 333

0.992 0.995 0.998 0.983

Y = 1.004 X – 4.503 Y = 1.015 X – 4.937 Y = 1.000 X – 4.921 Y = 0.987 X – 4.981

0.011 0.007 0.007 0.007

C 1.003 1.005 0.993 0.997 ∆qm(%) 0.975 1.015 1.006 1.005 ∆qm(%) 1.008 1.016 1.005 1.007 ∆qm(%) 1.004 1.015 1.002 1.001 ∆qm(%) 1.004 1.015 1.000 0.987 ∆qm(%)

∆q(%) 0.0020 0.2500 0.1230 0.1450 0.1300 0.1770 0.1050 0.1080 0.3260 0.1790 0.2150 0.0930 0.0003 0.0361 0.0860 0.0603 0.0226 0.0970 0.0229 0.0510 0.0495 0.1760 0.0428 0.1470 0.1040

The regression coefficient (R2) for m-xylene vary between 0.93 and 0.99. It is possible here to conclude that the Sips model is not adapted to the description of m-xylene adsorption on NaY, KY, BaY, BaX and NaX zeolites. The regression coefficient (R2) for toluene is higher than 0.970 (except for BaY(298K)), the average relative error (∆q(%)) and mean average relative error (∆qm(%)) are quite low (lower than 1%). It is possible here to conclude that the Sips model is well adapted to the description of toluene adsorption on NaY, KY, BaY, BaX and NaX zeolites at all four temperatures. The determination of parameters A and c, by linear regression, makes possible the calculation of theoretical isotherms and their comparison with the experimental data. For example the Sips equation provides a very satisfactory description of toluene adsorption on NaY (Fig. 2). Similar results were found for KY, BaY, BaX and NaX zeolites. Good agreement between the experimental isotherms and the model of Sips was also found, in the case of systems CO2-NaY, CO2-La(x)Y [27], NH3-Co(x)A, NH3-Y(x)L [28], CO2-MNaX [29], CO2-NaX, CO2-Ni(x)X, CO2Cr(x)X [30] . Constant A could be regarded as being representative of the strength of adsorption. Higher value of A implies a stronger adsorbate-adsorbent interaction, at least at low coverages. For all four temperatures, the parameter A varies according to the sequence: NaY>NaX>BaX>KY>BaY. Except for m-xylene at 298K, the evolution of A is NaY>NaX>BaY>BaX>KY. 54 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

Fig. 2: Toluene adsorption isotherms according to Sips model (solid lines) and experimental data for NaY with: ‘×’ T=298K, ‘∆’ 308K, ‘+’ 318K, and ‘∗’ 333K When the constant c is equal to 1, the Sips equation is reduced to that of Langmuir. Therefore, the deviation of c from unity may be taken as a measure of the deviation from Langmuir isotherm. It is reasonable to admit that this deviation, from phenomenologic point of view, consists of the existence of minority adsorbate-adsorbate interactions. Indeed, considering that the 1:1 correspondence is not valid, more than one molecule of adsorbate may closely surround an adsorptive centre. CONCLUSIONS Adsorption isotherms of toluene and m-xylene on NaY, NaX, BaX, KY and BaY zeolites were determined at 298, 308, 318, and 333 K using a vacuum microbalance system. Zeolites were used because they offer many practical advantages, such as, total regeneration at low temperature. The results were correlated with several models described in literature. From this study, we conclude that the Langmuir model leads to good correlation of data. Sips model also describes satisfactorily the isotherms of toluene adsorption by NaY, KY, BaY, BaX and NaX zeolites at all four temperatures. The Freundlich model, the Fowler-Guggenheim model, and the Hill-De Boer model are not satisfactory. The m-xylene and toluene belong to the same family, but the m-xylene is more strongly adsorbed than the toluene. The adsorption affinity of m-xylene and toluene decrease in this order NaY>NaX>BaX>KY>BaY. The validity of gravimetric mothod is confirmed. These results demonstrate the high capacity of NaY, KY, BaY, BaX and NaX zeolites to remove vapors of m-xylene and toluene at very low concentrations. References 1. Khan, F. I. and A. Kr. Ghoshal, 2000. Removal of Volatile Organic Com-pounds from Polluted Air. Journal of Loss Prevention in the Process Industries, 13: 527- 545. 2. Otten, W., Gail, E. and T. Frey, 1992. Einsatzmo¨glichkeiten Hydrophober Zeolithe in der Adsorptionstechnik. Chemmie Ingenieur Technik, 64: 915-925. 3. Weber, G., Bertrand, O., Fromont, E., Bourg, S., Bouvier, F., Bissinger, D. and M.H. SimmonotGrange, 1996. TCE Adsorption on Hydrophobic Y and MFI Zeolites. Possibilities of Using Materials for Solvents Recovery. Journal de Chimie Physique 93: 1412-1425. 4. Fajula, F. and D. Plee, 1994. Application of Molecular Sieves in View of Cleaner Technology. Gas and Liquid-Phase Separations. Studies in Surface Science and Catalysis 85: 633-651. 5. Gupta, A. and D. Crompton, 1993. Choosing the Right Adsorption Medium for VOC Control. Metal Finishing, 91: 68-72. 6. Blocki, S. W., 1993. Hydrophobic Zeolites Adsorbent: a Proven Advancement in Solvent Separation Technology. Environmental Progress, 12: 226-230.

55 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.

Zoubir Benmaamar and Abdelkhader Bengueddach, 2007. Correlation with Different Models for Adsorption Isotherms of m-Xylene and Toluene on Zeolites.

7. Sakuth, M., Meyer, J. and J. Gmehling, 1995. Vapor Phase Adsorption Equilibria of Toluene + 1Propanol Mixtures on Y-Zeolites with Different Silicon to Aluminum Ratios. Journal of Chemical and Engineering Data, 40: 895-899. 8. Ryu, Y. K., Chang, J. W., Jung, S. Y. and C.H. Lee, 2002. Adsorption Isotherms of Toluene and Gasoline Vapors on DAY Zeolite. Journal of Chemical and Engineering Data, 47: 363-366. 9. Bathen, D., Schmidt-Traub, H. and M. Simon, 1997. Gas Adsorption Isotherm for Dealuminated Zeolites. Industrial and Engineering Chemistry Research, 36: 3393-3394. 10. Carl, L. Y., 1994. Handbook of Vapor Pressure. Gulf Publishing Company. Houston, TX. 11. Langmuir, I., 1918. The Adsorption of Gases on Plane Surfaces of Glass, Mica and Platinum. Journal of the American Chemical Society, 40: 1361-1402. 12. Rolando, R. M., 2000. Complementary Approach to the Volume Filling Theory of Adsorption in Zeolites. Microporous Mesoporous Materials, 41: 227-240. 13. Donohue, M. D. and G.L. Aranovich, 1998. Classification of Gibbs Adsorption Isotherms. Advances in Colloid and Interface Science, 76 (77): 137-152. 14. Benkhedda, J., Jaubert, J.N. and D. Barth, 2000. Adsorption isotherms of m-Xylene on actived Carbon: Measurements and Correlation with Different Models. The Journal of Chemical Thermodynamics, 32: 401-411. 15. Kifuani Kia Mayeko, Noki Vesituluta, Musibono Eyul’Anki, Ndelo–Di–Phanzu, Nzuzi Panzu and Kunyima Badibanga, 2004. Adsorption sur Charbon Actif Ntola de la Quinine Bichlorhydrate en Solutions Aqueuses ou Chlorhydrique, Revue Conglaise des Sciences Nucleaires, 20 (1/2): 209214. 16. Tahani, A., Smaili, N., Salhi, S., Karroua, M. and F. Bergaya, 2007. Adsorption de Colorants Organiques sur la Bentonite de NADOR et sur ses dérivés pontés, EURODEUR-ECGP’6 FranceMarseille. 17. Abdul Halim, M., 2003. Valorisation Biologique des Résidus Graisseux Urbains par Production de Carbone Bioassimilable (AGV) Utilisable en Traitement Tertiaire des Eaux Usées, Thése de Doctorat, Montpellier. 18. Freundlich, H. 1926. Colloid and Capillary Chemistry, English translation of 3rd German ed.; Methuen: London. 19. Marouf-Khelifa, K., Khelifa, A., Belhakem, A., Marouf, R., Abdelmalek, F. and A. Addou, 2004. The Adsorption of Pentachlorophenol from Aqueuous Solution onto Exchanged Al-MCM-41 Materials. Adsorption Science and Technology, 22 (1): 1-12. 20. Benkhedda, J., Jaubert, J.N. and D. Barth, 2000. Experimental and Modeled Results Describing the Adsorption of Toluene onto actived Carbon. Journal of Chemical and Engineering Data, 45: 650653. 21. Fowler, R.H. and E.A. Guggenheim, 1965. Statistical Thermodynamics, Cambridge University Press, Cambridge. 22. Lavanchy A., Stockli M., Wirz C. and F. Stoeckli, 1996. Binary adsorption of vapors in active carbons described by the Dubinin equation. Adsorption Science and Technology, 13: 537-545. 23. Xie Z., Guo D., Wu J. and C. Yuan, 1998. Adsorption equilibrium of vapor mixture on activated carbon. In Fundamentals of adsorption 6, Meunier F, ed.: 219-224 Elsevier, New York. 24. Hill, T.L., 1964. Journal of Chemical Physics., 14: 1441. 25. De Doer, J.H., 1953. The Dynamical Character of Adsorption, Oxford University Press, Oxford. 26. Sips, R., 1948. Structure of a Catalyst surface The Journal of Chemical Physics, 16: 490-495. 27. Shiralkar, V.P. and S.B. Kulkarni, 1984. Sorption of carbon dioxide in cation exchanged Y type zeolites: sorption isotherme and state of sorbed molecule. Zeolites, 4: 329. 28. Coughlan, B. and P.Larkin, 1977. Proceedings of the Royal Irish Academy Chem. Centenary Issue, 77B: 383. 29. Khelifa, A., Hasnaoui, A., Derriche, Z. and A. Bengueddach, 2001. Adsorption de CO2 par des zéolithes X Echangées par des Cation Bivalents, Annales de chimie science des matériaux, 26 (2): 55-56. 30. Khelifa, A., Benchehida, L. and Z. Derriche, 2004. Adsorption of Carbon Dioxide by X Zeolites Exchanged with Ni2+ and Cr3+: Isotherms and Isosteric Heat. Journal of Colloid and Science, 278: 9-17.

56 Journal of Applied Sciences in Environmental Sanitation, 2 (2): 43-56.