Removal of some 4-pyrazolone dyes from aqueous solutions by adsorption onto different types of carbon

Removal of some 4-pyrazolone dyes from aqueous solutions by adsorption onto different types of carbon

Desalination 186 (2005) 129–153 Removal of some 4-pyrazolone dyes from aqueous solutions by adsorption onto different types of carbon A. Al-Sarawya, ...

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Desalination 186 (2005) 129–153

Removal of some 4-pyrazolone dyes from aqueous solutions by adsorption onto different types of carbon A. Al-Sarawya, I.G. Rasheda, M.A. Hannab, F.K.M. Walia* a

Mathematical and Physical Science Department, Faculty of Engineering, Mansoura University, Egypt Tel. +20 (10) 5659204; Fax +20 (50) 2244690; email: [email protected] b Chemistry Department, Faculty of Science (Damietta), Mansoura University, Egypt

Received 19 August 2003; accepted 18 April 2005

Abstract A novel group of 4-pyrazolone based dyestuffs, considered as a group of tartrazine dye analogous, was synthesized by the authors [1]. In view of the current interest in utilizing the arylazo-4-pyrazolone dyestuffs for dyeing different types of fibers, this article describes the possibility of using carbon for their removal as organic pollutants from aqueous solutions. The removal of these dyestuffs from their aqueous solutions was carried out by using different adsorbents such materials as granular carbon, carbon soot, and powdered activated carbon (PAC) at different temperatures ranging from room temperature (25°C) to 60°C. Kinetics and mass transfer studies were studied by applying different models such as Lagergren, Weber-Morris, Langmuir, Freundlich and Burnaur Emmette and Teller (BET). Different kinetic parameters (Kad, Kp, a, b, RL, n, K, A, Xm) were calculated from these models. The thermodynamic parameters (∆H, ∆S and ∆G) were calculated for the interpretation of the adsorption process. Keywords: Adsorption; Adsorption dynamics; Thermodynamic functions of adsorption; Langmuir, Freundlich and Burnaur Emmette and Teller (BET); Isotherms; 4-pyrazolone dyestuffs

1. Introduction In Egypt, the problem of color removal from textile wastewater has been considered in recent years to be of great importance because of the need to satisfy the increasing demand for water. For this reason, a national effort has been launched to deal with this problem using natural, local adsorbents. Investigations have been undertaken *Corresponding author.

to determine whether cheap commercially available materials hold promise in the treatment of wastewater. In spite of the presence of a huge number of dyestuffs which are widely used in dyeing processes, little data is available about the removal of these dyes from textile effluents. Adsorption is used in industrial wastewater treatment to remove organic materials such as color, phenols, detergents, other toxic or non biodegradables. The most important component of

0011-9164/06/$– See front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.desal.2005.04.059

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the cost of using powdered activated carbon (PAC) is the cost of PAC itself; therefore, searching for inexpensive sources or substitutes for PAC is a must. Recently many investigators tried to search for some materials as adsorbents to be utilized in water and wastewater treatment. Ahmed et al. [2], Sen [3], Gupta et al. [4] and Kashi Banerjef et al. [5] used coal fly ash which is a solid waste of thermal power plants as adsorbent. Asfour et al. [6,7] used hardwood sawdust for the adsorption of basic dyes. Mckay et al. [8,9] studied the ability of using bagasse pith (a byproduct of the sugar industry remaining after the extraction of juice) as adsorbent for the adsorption of two basic dyes (Basic-blue 69 and Basic-red 22) and two acid dyes (Acid-blue 25 and acid-red 114). El-Gundi [10–11] tested the ability of maize cobe (an agricultural solid waste) to adsorb two basic dyestuffs (Astrazene-blue and Maxilon-red) and two acid dyestuffs (Teflon-blue and Erionyl-red). Korshin et al. [12] studied the adsorption of natural organic matter (NOM) onto iron-oxide-coated sand (IOCS). Rashed et al. [13–15] reported that carbon soot which is a byproduct resulting from partial oxidation of natural gas in Talkha Fertilizers and Chemical Plants (SEMADCO Egypt now named as Delta for Fertilizers Production) is a promising material for various industrial applications as a substitute for commercial powdered activated carbon. Al-Sarawy [16] studied the using of carbon soot as a good adsorbent for the removal of colors of some dyes from their solutions. Jain and Daya Ram [17] studied the removal of lead and zinc on bed sediments collected from the river Kali (in western Uttar Pradesh, India). Attia [18] used carbon soot, powdered activated carbon, and bentonite as adsorbent for the removal of some heavy metals from water. Cheung et al. [19] studied the kinetic analysis for removal of cadmium ions from effluents using bone charcoal; they found that bone charcoal is a suitable adsorbent for the removal of cadmium from wastewater. Since the adsorption capacity is relatively

high, they also found that the adsorption process was considered as a first order process. Feng-Chin Wu et al. [20] studied the kinetic modeling of liquid phase adsorption of reactive dyes (RR222, RY 145 and RB222) and metal ions (such as Cu++) on chitosan (chitosan is a partially acetylated glucosamine bipolymer existing in the cell wall of some fungi such as the Mucorales strains); they found that chitosan is a suitable adsorbent for the removal of these reactive dyes and Cu++ from their aqueous solutions at 30°C. Shawwa et al. [21] studied the removal of color and chlorinated organics from pulp mills wastewater using activated petroleum coke. They found that the removal efficiency was over 90% and the utilization of petroleum coke for the production of activated carbon can provide an excellent disposal option for oil sand industry and at the same time would provide a cheap and valuable activated carbon. 2. Materials and methods All chemicals and solvents used in this study were of the highest grade of purity (spectral grade). Sodium salts of five dyes of the hitherto synthesized dyestuffs (listed in Table 1) and considered as 4-pyrazolone dyestuffs or tartrazine dye analogues; their chemical structure shown in Fig. 1 which were previously synthesized by the authors [1] was chosen for studying their adsorption behavior on different types of carbon at different temperatures. Powdered activated carbon and granulated carbon were obtained from El-Nasr pharmaceutical chemical company. Carbon soot, was produced as a result of partial oxidation of natural gas at SEMADCO (El-Delta for Fertilizers Co.); the existing method of collecting carbon soot in the factory is performed by precipitation using lime, Ca(OH)2, as coagulant agent. Experimental procedures were carried out to study the adsorption of this dyestuff from their aqueous solutions by using a shaker with water bath controlling temperature. The remaining con-

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centration was measured using a spectrophotometer (Qualen kamp visi-spec SPR-590-010-W). The separation of adsorbants from solutions was performed by centrifugation using a bench top centrifuge model T-54. 3. Results and discussion 3.1. Effect of contact time and temperature on adsorption Effect of contact time and temperature on adsorption of dyes was studied by plotting remaining concentration against time for granular carbon, carbon soot and powdered activated carbon as shown in Figs. 2–16. Results indicate that the remaining concentration of all dyes decrease with increasing time till equilibrium time is attained and the remaining concentration would be constant after a time specific for each dye. The effect of temperature is clear from these plots since the equilibrium time decreases with increasing temperature due to the fact that by increasing temperature the rate of adsorption increases and equilibrium time decreases [5]. Table 1 indicates the equilibrium time and structure for the tested dye at different temperatures on the different types of carbon used. It is noted that the equilibrium time depends only on temperature and is specific for each dye, adsorbate and adsorbent. Also it was learned that the removal efficiency for color of dyes was reduced with a very good efficiency (over 95% in case of carbon soot and PAC at higher temperatures). 3.2. Adsorption dynamics The rate constant for adsorption of the tested dyes on carbon soot, granulated carbon and powdered activated carbon (PAC) was determined using the Lagergren equation by plotting log (Ce – C) against T at different temperatures [16,22]. Fig. 1. Chemical structure of the five 4-pyrazolone dyestuffs.

log ( Ce − C ) = log Ce − ( K ad / 2.303) t

(1)

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Table 1 Equilibrium time for adsorption of dyes on carbon at different temperatures Type of carbon Temperature, °C Dye No. and color 1. Orange 2. Scarlet red 3. Blue 4. Dark blue 5. Dark blue

Carbon soot, critical dose = 0.1 gm/10 ml

GAC, critical dose = 0.50 gm/10 ml

PAC, critical dose = 0.05 gm/10 ml

25

40

50

60

25

40

50

60

25

40

50

60

70 150 70 180 180

65 140 65 160 170

60 135 55 145 180

40 115 40 125 135

190 145 130 50 85

180 125 125 45 80

165 110 115 40 75

145 100 100 35 55

90 140 190 210 120

80 130 155 170 105

65 120 135 160 90

50 105 120 135 70

Table 2 Adsorption kinetic parameters of different dyes on carbon soot, granular carbon and PAC Dye

Temperature, °C Carbon soot

Granular carbon

PAC

Kad

Kp

Kad

Kp

Kad

Kp

1

25 40 50 60

0.019 0.035 0.046 0.058

0.564 0.657 0.777 0.938

0.012 0.023 0.024 0.025

0.036 0.038 0.046 0.049

0.029 0.053 0.058 0.064

0.060 0.713 0.910 0.969

2

25 40 50 60

0.028 0.029 0.031 0.032

0.149 0.181 0.198 0.213

0.026 0.029 0.030 0.031

0.041 0.057 0.058 0.061

0.037 0.038 0.039 0.042

0.212 0.222 0.436 0.493

3

25 40 50 60

0.015 0.021 0.030 0.320

0.225 0.243 0.247 0.326

0.010 0.017 0.019 0.020

0.038 0.049 0.052 0.065

0.071 0.073 0.075 0.076

0.356 0.574 0.590 0.742

4

25 40 50 60

0.027 0.035 0.037 0.039

0.314 0.315 0.333 0.345

0.016 0.017 0.018 0.023

0.037 0.070 0.082 0.083

0.027 0.038 0.040 0.042

0.333 0.338 0.357 0.476

5

25 40 50 60

0.020 0.021 0.022 0.023

0.043 0.053 0.073 0.111

0.017 0.020 0.021 0.022

0.020 0.041 0.047 0.064

0.030 0.031 0.034 0.038

0.459 0.508 0.542 0.580

The value of Kad for the five dyes on different adsorbents was calculated from the slopes of the respective linear plots of log (Ce – C) against t as shown in Figs. 17–31 and Kad is found as the slope of the straight line and listed in Table 2. From these values of Kad, it may be concluded that the

reaction taking place is a first order one as the relation between log (Ce – C) against time (t) was found to be linear [16,22]. It is found also from the values that the rate constant for adsorption of the five dyes on the three types of carbon (K ad) increases with

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Fig. 2. Plot of equilibrium time for the absorption of dye 1 at different temperatures on GAC.

Fig. 3. Plot of equilibrium time for the absorption of dye 1 at different temperatures on soot.

Fig. 4. Plot of equilibrium time for the absorption of dye 1 at different temperatures on PAC.

Fig. 5. Plot of equilibrium time for the absorption of dye 2 at different temperatures on GAC.

Fig. 6. Plot of equilibrium time for the absorption of dye 2 at different temperatures on soot.

Fig. 7. Plot of equilibrium time for the absorption of dye 2 at different temperatures on PAC.

Fig. 8. Plot of equilibrium time for the absorption of dye 3 at different temperatures on GAC.

Fig. 9. Plot of equilibrium time for the absorption of dye 3 at different temperatures on soot.

134

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Fig. 10. Plot of equilibrium time for the absorption of dye 3 at different temperatures on PAC.

Fig. 11. Plot of equilibrium time for the absorption of dye 4 at different temperatures on GAC.

Fig. 12. Plot of equilibrium time for the absorption of dye 4 at different temperatures on soot.

Fig. 13. Plot of equilibrium time for the absorption of dye 4 at different temperatures on PAC.

Fig. 14. Plot of equilibrium time for the absorption of dye 5 at different temperatures on GAC.

Fig. 15. Plot of equilibrium time for the absorption of dye 5 at different temperatures on soot.

Fig. 16. Plot of equilibrium time for the absorption of dye 5 at different temperatures on PAC.

Fig. 17. Plot of Lagergren equation of dye 1 at different temperatures on GAC.

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135

Fig. 18. Plot of Lagergren equation of dye 1 at different temperatures on carbon soot.

Fig. 19. Plot of Lagergren equation of dye 1 at different temperatures on PAC.

Fig. 20. Plot of Lagergren equation of dye 2 at different temperatures on GAC.

Fig. 21. Plot of Lagergren equation of dye 2 at different temperatures on carbon soot.

Fig. 22. Plot of Lagergren equation of dye 2 at different temperatures on PAC.

Fig. 23. Plot of Lagergren equation of dye 3 at different temperatures on GAC.

Fig. 24. Plot of Lagergren equation of dye 3 at different temperatures on carbon soot.

Fig. 25. Plot of Lagergren equation of dye 3 at different temperatures on PAC.

136

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Fig. 26. Plot of Lagergren equation of dye 4 at different temperatures on GAC.

Fig. 27. Plot of Lagergren equation of dye 4 at different temperatures on carbon soot.

Fig. 28. Plot of Lagergren equation of dye 4 at different temperatures on PAC.

Fig. 29. Plot of Lagergren equation of dye 5 at different temperatures on GAC.

Fig. 30. Plot of Lagergren equation of dye 5 at different temperatures on carbon soot.

Fig. 31. Plot of Lagergren equation of dye 5 at different temperatures on PAC.

increasing temperature. These results are in agreement with findings in the literature [16,18,22]. The rate constant can be found from a plot of dye adsorbed x/m against t 0.5 at different temperatures as shown in Figs. 32–46. The double nature of these plots (Weber Morris) may be explained as: the initial curved portions are attributed to boundary layer diffusion effects, while the final linear portions are due to intra-particle diffusion effects [16,18,23].

The rate constant for intra-particle diffusion (Kp) for different dyes adsorbed on carbon soot, granular carbon and powdered activated carbon was determined from the slopes of the linear portions of the respective plots and are given in Table 2. Results obtained indicate that the rate constant for intraparticle diffusion (Kp) of the five dyes on the three types of carbon increases with increasing temperature; These results are in agreement with finding in the literature [16,18]. Both of the values

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137

Fig. 32. Plot of Weber Morris of dye 1 at different temperatures on GAC.

Fig. 33. Plot of Weber Morris of dye 1 at different temperatures on carbon soot.

Fig. 34. Plot of Weber Morris of dye 1 at different temperatures on PAC.

Fig. 35. Plot of Weber Morris of dye 2 at different temperatures on GAC.

Fig. 36. Plot of Weber Morris of dye 2 at different temperatures on carbon soot.

Fig. 37. Plot of Weber Morris of dye 2 at different temperatures on PAC.

Fig. 38. Plot of Weber Morris of dye 3 at different temperatures on GAC.

Fig. 39. Plot of Weber Morris of dye 3 at different temperatures on carbon soot.

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Fig. 40. Plot of Weber Morris of dye 3 at different temperatures on PAC.

Fig. 41. Plot of Weber Morris of dye 4 at different temperatures on GAC.

Fig. 42. Plot of Weber Morris of dye 4 at different temperatures on carbon soot.

Fig. 43. Plot of Weber Morris of dye 4 at different temperatures on PAC.

Fig. 44. Plot of Weber Morris of dye 5 at different temperatures on GAC.

Fig. 45. Plot of Weber Morris of dye 5 at different temperatures on carbon soot.

Fig. 46. Plot of Weber Morris of dye 5 at different temperatures on PAC.

Kad and Kp are the highest in case of using PAC as adsorbent; the lowest values of Kad and Kp are in case of using granular carbon as adsorbent while in the case of carbon soot their values (Kad and Kp) are in between. It could be concluded that the efficiency of adsorption of the five dyes on the PAC, carbon soot and granular carbon may be arranged in the order PAC > carbon soot > granular carbon.

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3.3. Adsorption isotherms Analysis of equilibrium data for the adsorption of the five dyes on the three types of carbon have been done in light of the Langmuir [16], Freundlich [24] and Burnauer, Emmett, and Teller models [25]. All adsorption studies were carried out at four different temperatures: room temperature 25°C, 40°C, 50°C and 60°C.

The plots of the reciprocal of the amount of adsorbed dye x/m (mg dye/mg carbon) against the reciprocal of equilibrium concentration (1/C) for the studied dyes gave straight lines. This indicates that the adsorption process conforms with the Langmuir adsorption isotherm and the Langmuir equation is applicable [24]: x / m = abC / (1 + aC )

(2)

The slope of the best fit (1/ab) and the intercept (1/b) of linear plots of Langmuir isotherm for the five dyes was obtained as shown in Figs. 47–61 and Langmuir parameters a and b for adsorption of the five dyes on carbon soot, granular carbon and powdered activated carbon are calculated at the previously mentioned temperatures and listed in Table 3. From these results, it was found that b values (the indication of monolayer coverage) for PAC are higher than that of the carbon soot and that for carbon soot is higher than that of granulated carbon. This is in agreement with the findings in the literature concerning the increase in b value with the decrease in particle size of adsorbent [16, 18,23]. The monolayer coverage parameter b generally increases with increasing temperature. Table 3 contains the equilibrium parameter (RL) which is defined from the relation [17,19,24]:

RL = [1 + aCo ]

−1

0–1 showing a favorable adsorption for the tested dyes on carbon soot, granular carbon and PAC [16,24]. 3.3.2. Freundlich isotherm Test of validity of Freundlich adsorption isotherm for adsorption process was followed according to the equation [24]: log ( x / m ) = log K + (1/ n −1 ) log C

3.3.1. Langmuir isotherm

(3)

The values of RL (dimensionless separation factor) for the studied systems were found to be

139

(4)

Plotting log (x/m) against log C as shown in Fig. 62–76 gave rise to a group of straight lines corresponding to adsorption of the tested dyes on different types of carbon at different temperatures. From slope and intercept n and K (adsorption capacity) values were calculated respectively and delineated in Table 4. The delineated data reveals that adsorption capacity value (K) increases as the pore size of carbon changes from PAC to carbon soot and finally to granular carbon. This may be explained in view of Freundlich equation which implies the two important parameters K and n–1 which are related to the capacity of adsorbent for the adsorbate and the strength of adsorption process respectively [16,24]. It is found that n values are in the range that indicates a good adsorption since n values are higher than unity [16,25]. Moreover these data revealed that there is a direct relation of adsorption capacity with temperatures. Generally the capacity of the three used types of carbon for adsorption of the chosen dyes could be arranged in the order of PAC > carbon soot > granular carbon. 3.3.3. Brunauer, Emmett and Teller (BET) isotherm Brunauer, Emmett and Teller [25] derived an adsorption isotherm based on the assumption that molecules could be adsorbed more than one layer thick on the surface of the adsorbent. This equation, like the Langmuir equation assumes that the adsorbent surface is composed of uniform,

0.034 0.108 0.162 0.086

0.006 0.035 0.053 0.079

0.099 0.098 0.084 0.110

0.052 0.037 0.015 0.113

0.212 0.148 0.171 0.158

25 40 50 60

25 40 50 60

25 40 50 60

25 40 50 60

25 40 50 60

1

2

3

4

5

0.00033 0.00049 0.00061 0.00066

0.00032 0.00050 0.00061 0.00078

0.00046 0.00089 0.00101 0.00114

0.00650 0.00140 0.00140 0.00143

0.00065 0.00140 0.00160 0.00260

Dye Temperature, Granular carbon o C A b

0.059 0.083 0.072 0.078

0.204 0.266 0.474 0.105

0.092 0.093 0.106 0.083

0.645 0.222 0.159 0.113

0.129 0.044 0.030 0.056

RL

0.966 0992 0.995 0.961

0.989 0.988 0.902 0.866

0.790 0.833 0.918 0.969

0.893 0.954 0.930 0.929

0.836 0.799 0.901 0.955

r

0.159 0.940 11.34 16.89

0.014 0.017 0.115 0.715

0.050 0.140 0.017 0.093

0.095 0.201 0.196 0.327

0.001 0.034 0.121 0.019

a

Soot

0.007 0.008 0.007 0.008

0.037 0.125 0.008 0.014

0.011 0.012 0.017 0.019

0.014 0.013 0.013 0.011

0.027 0.012 0.011 0.052

b

0.078 0.014 0.001 0.001

0.486 0.437 0.012 0.018

0.166 0.067 0.189 0.098

0.095 0.047 0.049 0.030

0.510 0.127 0.039 0.208

RL

0.956 0.967 0.923 0.961

0.960 0.984 0.975 0.987

0.958 0.971 0.967 0.981

0.988 0.990 0.996 0.992

0.919 0.860 0.928 0.870

R

Table 3 Analysis of Langmuir parameters of different dyes on different adsorbents at different temperatures

0.039 0.040 0.062 0.061

0.045 0.332 2.054 1.677

0.040 0.144 0.160 0.357

0.033 0.030 0.041 0.047

0.083 0.080 0.085 0.109

a

PAC

0.010 0.018 0.038 0.043

0.012 0.025 022..0 0.018

0.035 0.049 0.048 0.040

0.033 0.033 0.041 0.038

0.041 0.058 0.058 0.056

b

0.166 0.250 0.177 0.178

0.026 0.039 0.070 0.0.90

0.199 0.075 0.059 0.027

0.233 0.170 0.100 0.045

0.037 0.068 0.055 0.029

RL

0.835 0.865 0.969 0.963

0.789 0.916 0.912 0.864

0.902 0.980 0.972 0.964

0.890 0.965 0.996 0.957

0.886 0.971 0.981 0.953

r

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A. Al-Sarawy et al. / Desalination 186 (2005) 129–153

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Fig. 47. Plot of Langmuir equation of dye 1 at different temperatures on GAC.

Fig. 48. Plot of Langmuir equation of dye 1 at different temperatures on carbon soot.

Fig. 49. Plot of Langmuir equation of dye 1 at different temperatures on PAC.

Fig. 50. Plot of Langmuir equation of dye 2 at different temperatures on GAC.

Fig. 51. Plot of Langmuir equation of dye 2 at different temperatures on carbon soot.

Fig. 52. Plot of Langmuir equation of dye 2 at different temperatures on PAC.

Fig. 53. Plot of Langmuir equation of dye 3 at different temperatures on GAC.

Fig. 54. Plot of Langmuir equation of dye 3 at different temperatures on carbon soot.

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Fig. 55. Plot of Langmuir equation of dye 3 at different temperatures on PAC.

Fig. 56. Plot of Langmuir equation of dye 4 at different temperatures on GAC.

Fig. 57. Plot of Langmuir equation of dye 4 at different temperatures on carbon soot.

Fig. 58. Plot of Langmuir equation of dye 4 at different temperatures on PAC.

Fig. 59. Plot of Langmuir equation of dye 5 at different temperatures on GAC.

Fig. 60. Plot of Langmuir equation of dye 5 at different temperatures on carbon soot.

Fig. 61. Plot of Langmuir equation of dye 5 at different temperatures on PAC.

Fig. 62. Plot of Freundlich equation of dye 1 at different temperatures on GAC.

A. Al-Sarawy et al. / Desalination 186 (2005) 129–153

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Fig. 63. Plot of Freundlich equation of dye 1 at different temperatures on carbon soot.

Fig. 64. Plot of Freundlich equation of dye 1 at different temperatures on PAC.

Fig. 65. Plot of Freundlich equation of dye 2 at different temperatures on GAC.

Fig. 66. Plot of Freundlich equation of dye 2 at different temperatures on carbon soot.

Fig. 67. Plot of Freundlich equation of dye 2 at different temperatures on PAC.

Fig. 68. Plot of Freundlich equation of dye 3 at different temperatures on GAC.

Fig. 69. Plot of Freundlich equation of dye 3 at different temperatures on carbon soot.

Fig. 70. Plot of Freundlich equation of dye 3 at different temperatures on PAC.

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Fig. 71. Plot of Freundlich equation of dye 4 at different temperatures on GAC.

Fig. 72. Plot of Freundlich equation of dye 4 at different temperatures on carbon soot.

Fig. 73. Plot of Freundlich equation of dye 4 at different temperatures on PAC.

Fig. 74. Plot of Freundlich equation of dye 5 at different temperatures on GAC.

Fig. 75. Plot of Freundlich equation of dye 5 at different temperatures on carbon soot.

Fig. 76. Plot of Freundlich equation of dye 5 at different temperatures on PAC.

localized sites and that the adsorption at one site does not affect adsorption at neighboring sites. Moreover, it was assumed that the energy of adsorption holds the first monolayer but that the condensation energy of the adsorbate is responsible for adsorption of successive layer. The equation, known as BET equation, is commonly written as follows [16,25]:

x / m = ACX m / ( Cs − C ) ⎡⎣1 + ( A − 1) C / Cs ⎤⎦

(5)

Rearranging the BET equation yields:

C 1 A −1 ⎛ C ⎞ = + ⎜ ⎟ ( Cs − C ) x / m AX m AX m ⎝ Cs ⎠

(6)

Data obtained from adsorption processes, for

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Table 4 Analysis of Freundlish parameters of different dyes on different adsorbents at different temperatures Dye Temperature, Granular carbon °C n K

Soot r

n

PAC K

r

n

K

r

1

25 40 50 60

1.859 3.805 4.934 2.929

0.0575 0.4237 0.6227 0.5526

0.924 0.894 0.974 0.953

1.769 2.348 3.271 1.960

0.649 1.308 2.753 3.060

0.901 0.968 0.938 0.968

7.143 3.220 2.034 2.768

14.318 12.722 13.172 13.569

0.884 0.948 0.965 0.989

2

25 40 50 60

3.766 2.602 2.782 2.882

0.1648 0.1908 0.2424 0.2937

0.896 0.932 0.892 0.920

2.656 2.675 2.440 2.698

2.591 2.840 2.919 3.328

0.959 0.963 0.985 0.992

1.977 1.854 2.170 1.865

2.979 3.181 6.456 7.894

0.961 0.829 0.975 0.990

3

25 40 50 60

2.212 3.178 4.113 3.532

0.0564 0.1737 0.3079 0.3199

0.936 0.800 0.850 0.979

2.039 2.488 2.079 2.202

1.174 2.145 2.288 2.854

0.965 0.958 0.905 0.966

1.632 3.516 2.275 2.437

2.262 2.596 4.130 5.046

0.940 0.957 0.965 0.996

4

25 40 50 60

3.759 4.284 5.509 4.991

0.0803 0.1152 0.2796 0.3029

0.960 0.869 0.964 0.914

17.07 3.974 4.072 5.089

2.289 3.675 4.072 5.090

0.717 0.967 0.974 0.943

2.262 2.596 4.130 5.046

2.504 7.613 12.540 14.316

0.932 0.969 0.981 0.935

5

25 40 50 60

4.610 6.892 4.888 3.438

0.1361 0.2057 0.2178 0.1942

0.996 0.996 0.995 0.960

1.674 2.899 4.127 5.121

1.060 3.569 5.437 7.096

0.953 0.984 0.961 0.943

2.135 2.133 1.582 1.421

1.362 1.933 3.258 3.139

0.914 0.844 0.988 0.944

the tested dyes on different types of carbon are utilized to conform the BET equation when plotting C/(Cs – C)(x/m) against C/Cs as shown in Figs. 77–91. The linear plots obtained from the BET equation have a slope of A – (1/AXm) and intercept of 1/AXm. Values of both A and Xm for the tested dyes on carbon soot, granular carbon and PAC are given in Table 5. It is evident that the amount of solute adsorbed utilized in forming a complete monolayer on PAC is higher than that in the case of carbon soot and that of carbon soot is higher than that in the case of granular carbon. The effect of temperature is clearly obvious, hence the value of Xm increases as the temperature increases from room temperature to 60°C. This may be explained on the basis that increasing temperature increases the rate of adsorption; moreover, increase in temperature

increases the mobility of the large dye ions for further penetration [16,25], consequently the adsorption process becomes more favorable with increasing temperature. 3.3.4. Estimation of thermodynamic parameters The thermodynamic parameters such as enthalpy change ∆Ho and entropy change ∆So for the adsorption of all five dyes on granular carbon, carbon soot and PAC at different temperatures were studied through the following: 3.3.4.1. Effect of temperature on the rate of adsorption The thermodynamic parameters were investigated during this work. Kinetic experiments were

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Table 5 Analysis of BET parameters of different dyes on different adsorbent at different temperatures Dye Temperature, Granular carbon °C A Xm 1 25 –4.564 0.000260 40 –32.801 0.000750 50 –88.162 0.000950 60 47.780 0.001620

Soot

PAC

r

A

Xm

r

A

Xm

r

0.967 0.984 0.865 0.984

–16.143 –26.570 –20.802 16.311

0.0037 0.0041 0.0045 0.0209

0.970 0.974 0.985 0.976

–19.741 –39.847 –62.812 –81.783

0.0135 0.0222 0.0246 0.0394

0.994 0.985 0.991 0.997

2

25 40 50 60

–2.344 –4.470 –6.796 –14.339

0.000099 0.000197 0.000298 0.000449

0.994 0.885 0.949 0.965

–81.901 –297.020 –46.121 –63.788

0.0043 0.0058 0.0077 0.0078

0.995 0.996 0.999 0.999

–37.673 16.690 41.699 17.274

0.0094 0.0162 0.0212 0.0388

0.990 0.991 0.996 0.998

3

25 40 50 60

–1.787 –10.487 –25.128 105.230

0.000083 0.000351 0.000431 0.000612

0.974 0.978 0.903 0.968

316.524 24.701 81.176 41.538

0.0043 0.0058 0.0077 0.0087

0.980 0.988 0.983 0.995

17.188 44.508 39.041 43.448

0.0148 0.0215 0.0245 0.0313

0.901 0.969 0.999 0.999

4

25 40 50 60

–2.596 –13.540 –13.690 –19.340

0.000055 0.000087 0.000144 0.000178

0.925 0.989 0.906 0.970

–32.937 159.010 151.370 56.778

0.0018 0.0060 0.0065 0.0089

0.996 0.995 0.999 0.989

–20.818 33.346 102.830 70.179

0.0055 0.0179 0.0196 0.0227

0.989 0.998 0.999 0.994

5

25 40 50 60

–5.510 –6.460 –27.810 44.060

0.000093 0.000122 0.000244 0.000276

0.942 0.941 0.989 0.987

7.139 58.625 352.480 782.190

0.0073 0.0074 0.0084 0.0092

0.951 0.998 0.999 0.999

–3.554 –9.806 53.720 7.693

0.0023 0.0042 0.0139 0.0259

0.988 0.995 0.959 0.995

conducted at various temperatures starting from room temperature 25°C including 40°C, 50°C and 60°C. The results indicate that the adsorption rate increases with increasing temperature. The increase in rate of adsorption with increasing temperature is described by Arrhenius equation [5,18]: K = A′e − E / RT

(7)

where A′ is a temperature dependent factor called “frequency factor”, K is a specific rate constant, E is the activation energy, representing the minimum energy that the reacting system must have for the reaction to proceed, R is the universal gas constant (1.98 cal/K mol) and T is the absolute temperature. Eq. (8) can be written as: log K p = log A′ − ( E / RT )

(8)

The apparent activation energies (E) for the external mass transfer region for the used dyes were calculated by plotting log Kp values against 1/T as shown in Figs. 92–96; a group of straight lines was obtained illustrating a linear relationship. The apparent activation energy (E) has been determined from the slopes of these lines (slope = –E/R) and listed in Table 6. The values of apparent activation energy (E) obtained are relatively small values indicating a diffusion controlled process [5,18]. 3.3.4.2. Determination of thermodynamic functions (∆Ho, ∆So and ∆Go) The thermodynamic functions such as enthalpy change (∆Ho) and entropy change (∆So), were determined using Eq. (9) [5,18]:

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Table 6 Apparent activation energy values for the adsorption process of dyes on different types of carbon

Dye

Apparent activation energy, Kcal/mole Carbon soot

Granular carbon

PAC

1 2 3 4 5

4.56 2.133 1.510 0.912 1.604

1.330 2.221 3.560 2.645 8.067

0.513 4.560 0.775 1.350 1.179

Fig. 78. Plot of BET equation of dye 1 at different temperatures on carbon soot.

Fig. 77. Plot of BET equation of dye 1 at different temperatures on GAC.

Fig. 79. Plot of BET equation of dye 1 at different temperatures on PAC.

Fig. 80. Plot of BET equation of dye 2 at different temperatures on GAC.

Fig. 81. Plot of BET equation of dye 2 at different temperatures on carbon soot.

Fig. 82. Plot of BET equation of dye 2 at different temperatures on PAC.

Fig. 83. Plot of BET equation of dye 3 at different temperatures on GAC.

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Fig. 84. Plot of BET equation of dye 3 at different temperatures on carbon soot.

Fig. 85. Plot of BET equation of dye 3 at different temperatures on PAC.

Fig. 86. Plot of BET equation of dye 4 at different temperatures on GAC.

Fig. 87. Plot of BET equation of dye 4 at different temperatures on carbon soot.

Fig. 88. Plot of BET equation of dye 4 at different temperatures on PAC.

Fig. 89. Plot of BET equation of dye 5 at different temperatures on GAC.

Fig. 90. Plot of BET equation of dye 5 at different temperatures on carbon soot.

Fig. 91. Plot of BET equation of dye 5 at different temperatures on PAC.

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Fig. 92. Plot of Arrhenious equation for the adsorption of dye 1 on granular carbon, carbon soot and PAC.

Fig. 93. Plot of Arrhenious equation for the adsorption of dye 2 on granular carbon, carbon soot and PAC.

Fig. 94. Plot of Arrhenious equation for the adsorption of dye 3 on granular carbon, carbon soot and PAC.

Fig. 95. Plot of Arrhenious equation for the adsorption of dye 4 on granular carbon, carbon soot and PAC.

constant (Kc) at different temperatures were calculated using the following equation [5,18]:

Kc =

K1 ( CBo + C Ao X Ae ) = K 2 ( C Ao + C Ao X Ae )

(10)

The free energy change (∆Go) parameter was calculated using Eq. (11) [5,18]: Fig. 96. Plot of Arrhenious equation for the adsorption of dye 5 on granular carbon, carbon soot and PAC.

ln K c = ∆S o / R − ( ∆H o / R )1/ T

(9)

Eq. (9) represents a straight line with two variables, Kc and 1/T, as shown in Figs. 97–101. By plotting ln Kc vs. 1/T the values of ∆Ho can be calculated from the slope (slope = ∆Ho/R) and ∆So can be calculated from the intercept of that line (intercept = ∆So/R). The values of equilibrium

∆G 0 = ∆H o − T ∆S o

(11)

From these plots the values of ∆Ho, ∆So from slopes and intercepts respectively as well as the calculated values of ∆Go are listed in Table 7. Investigation of the values of the thermodynamic parameters shown in Table 7 reveals that the adsorption process of the hitherto selected dyestuffs on the three types of carbon are endothermic and nonspontaneous, especially at higher temperatures. The trend of ∆Go values with the increase in temperature supports strongly this conclusion [5,18].

1 2 3 4 5

4.462 4.749 6.22 3.438 3.125

3.25 11.85 1.42 3.45 3.78

4.23 8.35 9.49 5.65 4.11

–6.659 –6.096 –8.183 –4.479 –4.398

–5.17 –19.1 –5.95 –7.47 –7.59

–6.93 –13.6 –15.5 –9.55 –7.90

1.99 1.82 2.45 1.34 1.31

2.09 1.91 2.57 1.41 1.38

2.16 1.97 2.65 1.45 1.42

2.22 2.04 2.71 1.49 1.47

60°C 1.54 5.71 1.77 2.23 2.27

1.62 5.99 1.86 2.34 2.38

40°C

25°C

50°C

25°C

40°C

Soot

Granular carbon

PAC

Granular Soot carbon

Granular Soot carbon

PAC

∆Go (at different temperatures in Kcal/mol)

∆So (Kcal/mol)

Dye ∆Ho (Kcal/mol)

Table 7 Thermodynamic parameters for adsorption of different dyes on carbon soot, granular carbon and PAC

1.67 6.18 1.92 2.42 2.46

50°C

1.72 6.38 1.98 2.48 2.53

60°C

2.06 4.07 4.61 2.85 2.36

25°C

PAC 2.07 4.28 4.85 2.99 2.48

40°C

2.24 4.42 4.99 3.09 2.56

50°C

2.31 4.55 5.15 3.18 2.64

60°C

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Fig. 97. Plot of Van’t Hoff equation for the adsorption of dye 1 on granular carbon, carbon soot and PAC.

Fig. 98. Plot of Van’t Hoff equation for the adsorption of dye 2 on granular carbon, carbon soot and PAC.

Fig. 99. Plot of Van’t Hoff equation for the adsorption of dye 3 on granular carbon, carbon soot and PAC.

Fig. 100. Plot of Van’t Hoff equation for the adsorption of dye 4 on granular carbon, carbon soot and PAC.

Fig. 101. Plot of Van’t Hoff equation for the adsorption of dye 5 on granular carbon, carbon soot and PAC.

4. Conclusions This article studied aims to identify the ability of soot produced as a byproduct from the partial oxidation of a natural gas as adsorbent material (for some of newly synthesized dyestuffs) against conventional carbon adsorbents (powdered activated carbon and granular carbon). The study reveals that:

• Carbon soot is a good adsorbent for removal of these prepared dyestuffs from their aqueous solutions at 60°C, the color of dye is reduced with a very good efficiency over 95% as shown in Figs. 2–16. • The data of all parameters obtained in the adsorption study are explained through several adsorption models; all the calculated parameters were found to be in agreement with the finding in literature as indicated from the following: – Values of Kad indicate that the adsorption process is first order. – Fitting the Langmuir model to the experimental data at different temperatures suggests that the monolayer coverage of the adsorbed dyes at the outer surface of the adsorbent increases with increasing temperature. – Fitting the Freundlich model to the experi-

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mental data at different temperatures show that the adsorption of tested dyes on PAC is slightly higher than carbon soot and much greater than granular carbon. – Fitting the of Burnaur Emmett and Teller (BET) model to the experimental data at different temperatures show that the amount of dye adsorbed in forming a complete monolayer (Xm) on PAC is slightly higher than carbon soot and highly greater than granular carbon. It is found also that the amount of dye adsorbed in forming a complete monolayer (Xm) increase with increasing temperature. – Thermodynamic parameter indicates that all adsorption processes are endothermic (since their enthalpy of adsorption have positive values) and non-spontaneous, especially at higher temperatures (since their entropy of adsorption have negative values). The trend of free energy values with the increase in temperature strongly supports this conclusion. 5. Symbols A A′ a b C Co CAo CBo Cs D E

— Constant describing the energy of interaction between the solute and the adsorbent surface — Temperature independent factor called “frequency factor” — Langmuir isotherm constant — Monolayer coverage constant — Concentration of solute in solution at equilibrium, mg/l — Initial dye concentration — Initial concentration of solute in solution at time t = 0 — Initial concentration of solute in the sorbent at time t = 0 — Saturation concentration of solute, mg/l — Slope of saturation vapour pressure curve, Pa/ºC — Activation energy

K Kad Kc Kp

— — — —

m n R RL

— — — —

T t x x/m XAo

— — — — —

Xm



Adsorption capacity, Freundlich The rate constant for adsorption of dye Equilibrium constant The rate constant for intra-particle diffusion Weight of adsorbent, mg Freundlich adsorption constant Universal gas constant, 1.98 cal/Kmol Dimensionless seperation factor, Langmuir Absolute temperature Adsorption time Amount of solute adsorbed, mg Amount of dye adsorbed per adsorbent Fraction of solute adsorbed at equilibrium condition Amount of solute adsorbed used in forming a complete monolayer, mg/mg

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