Ind. Eng. Chem. Res. 2008, 47, 5629–5635
5629
Multicomponent Sorptive Removal of Toxics Pyridine, 2-Picoline, and 4-Picoline from Aqueous Solution by Bagasse Fly Ash: Optimization of Process Parameters D. H. Lataye,† I. M. Mishra,*,‡ and I. D. Mall‡ Department of CiVil Engineering, VisVesVaraya National Institute of Technology, Nagpur 440010, India, and Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee 247667, India
The present paper deals with the simultaneous removal of Pyridine (Py) and its derivatives 2-picoline (2Pi) and 4-picoline (4Pi) by adsorption from aqueous solutions using bagasse fly ash (BFA) as an adsorbent. The effect of various parameters, such as adsorbent dose (m), initial pH (pH0), contact time (t), initial concentrations (C0,i), and temperature (T), on the simultaneous adsorption of Py, 2Pi, and 4Pi have been studied using Taguchi’s design of experimental methodology. Each parameter has been tested at three levels to see their effect on the selected response characteristic, i.e., the total sorptive uptake of Py, 2Pi, and 4Pi, by BFA (qtot, mg g-1), and the optimal level of each parameter for maximizing qtot has been determined. The analysis of variance (ANOVA) shows that the adsorbent dose, m, is the most significant parameter with 35.65% and 10.50% contribution to the qtot and signal-to-noise (S/N) ratio data, respectively. The contribution of interactions between initial concentrations and other parameters is also significant. Confirmation adsorption experiments carried out at the optimal values of the parameters validated the effectiveness of the Taguchi’s design of experimental methodology for multicomponent adsorption of organics from aqueous solution. The percent removal (and the sorptive uptake) of Py, 2Pi, and 4Pi was found to be ∼50% (∼12.38 mg g-1), ∼68% (∼17 mg g-1), and ∼69% (∼17.01 mg g-1), respectively, with a total uptake of all the components at optimal conditions being 46.39 mg g-1. 1. Introduction Pyridine (Py) and picolines [2-picoline (2Pi) and 4-picoline (4Pi)] are volatile and toxic organics and are flammable with a pungent and unpleasant odor. Industries manufacturing and/or using Py and its derivatives are easily identified because of the malodorous and pungent smell emanating from the vents of the factory premises and evaporation from wastewaters. Py, 2Pi, and 4Pi are soluble in water, and the wastewater contaminated with these components is toxic to aquatic life.1–10 Such wastewaters have Py and its associated compounds, generally, in the range of 20-300 mg dm-3, which, however, may rise to a high level of 600-1000 mg dm-3 during emergency spills. Py odor is detectable at a Py concentration of 0.82 µg dm-3 in wastewaters and at a vapor concentration of 7 µg dm-3. The threshold odor concentration can be as low as ∼0.3 µg dm-3.11 Although, the environmental regulating agencies in India do not prescribe effluent standards for Py, the wastewater should have less than 1 mg dm-3 of Py and its derivatives, so as to minimize the toxicity of the wastewater and the odor emanating from it. These compounds are biorefractories, and therefore, the wastewater containing these compounds is generally incinerated in an incinerator after its concentration in multiple-effect evaporators. Adsorption can also be used to remove such recalcitrant compounds. Activated carbons, various clays, zeolites, resins, oil shales, etc., and agricultural wastes such as bagasse fly ash (BFA) and rice husk ash (RHA) have been used by several investigators for the sorptive removal of Py and its derivatives.6–10,12–20 However, all these studies were concerned with the removal of single component, either Py or any of its derivatives. Industrial wastewaters generally have several compounds dissolved which may have synergistic or antagonistic impact on their removal from wastewaters. * To whom correspondence should be addressed. Tel: +91-1332285715. Fax: +91-1332-273560. E-mail:
[email protected]. † Visvesvaraya National Institute of Technology. ‡ Indian Institute of Technology Roorkee.
In our earlier publications, we have focused on the single component sorption of Py and 2Pi from aqueous solution by using BFA as a sorbent.7,8,10 No information is available in literature on the simultaneous sorptive removal of Py, 2Pi, and 4Pi from aqueous solutions. It is, therefore, important and necessary to study the simultaneous adsorption of Py and picolines and also to quantify the impact of one compound on the sorption of the others. Since the adsorption of any component from an aqueous solution is affected by several parameters such as the adsorbent dosage (m), initial pH (pH0), contact time (t), temperature (T), and initial adsorbate concentration (C0), therefore, the effect of these parameters on the sorptive removal of Py and Pi should be studied. Such a study, however, may not take into account the effect of interactions of different parameters on the sorption process. Several designs of experiments are available which optimize the number of experiments to be carried out based on the number of parameters and the range of values of these parameters. Taguchi’s design of experiments has been used extensively in product quality assessment and several other studies.21–27 Recently, Srivastava et al.27,28 have used Taguchi’s experimental methodology for multicomponent metal sorption by adsorbents.27,28 The present paper deals with the simultaneous adsorptive removal of Py, 2Pi, and 4Pi from aqueous solution by using BFA as an adsorbent. Taguchi’s fractional factorial design of experiments has been used to examine the effects of significant parameters and their interactions on the multicomponent adsorption. The selected response characteristic, i.e., the total adsorption capacity (qtot) of BFA for Py, 2Pi, and 4Pi, is maximized by optimizing the parametric values affecting the sorption process. The average values and the signal-to-noise (S/N) ratio of the quality response characteristic for each parameter at three levels of their values have been calculated from the experimental data. The response curves have been graphically represented to reflect any change in the quality characteristic and S/N ratio with the variation in process parameters. These response curves are used to study
10.1021/ie0716161 CCC: $40.75 2008 American Chemical Society Published on Web 07/02/2008
3 poison by intraperitorial route, moderately toxic by ingestion, skin contact, intravenous and subcutaneous routes; mildly toxic by inhalation, skin and severe eye irritant can cause CNS depression, gastrointestinal upset, and liver and kidney damage
TWA 2 (8 h exposure) 5 (STEL, 15 min) TWA 2 (8 h exposure) 5 (STEL, 15 min)
UN hazard class safety profile
health effects
13 14
15
11 12
5 6 7 8 9 10
density (g cm-3) boiling point (°C) freezing point (°C) flash point (°C) soluble in IDLH (immediately dangerous to life or health), mg dm-3 OSHA PEL (mg dm-3) ACGIH TLV (mg dm-3)
TWA 5 TWA 5 (proposed: TWA 1 mg dm-3 confirmed animal carcinogen) 3 poison by intraperitorial route, moderately toxic by ingestion, skin contact, intravenous and subcutaneous routes; mildly toxic by inhalation, skin and severe eye irritant can cause CNS depression, gastrointestinal upset, and liver and kidney damage
0.95 145 3.6 134 water, alcohol, ether not known 0.94 129 -70 102 water, alcohol, ether not known
R-picoline, R-methylpyridine C6H7N 93.14 colorless liquid, strong unpleasant odor
azabenzene, azine, piridina, etc. C5H5N 79.11 colorless liquid, sharp penetrating empyeumatic odor, burning taste 0.98 115.3 -42 68 water, alcohol, ether 1000 synonyms chemical formula molecular weight physical properties 1 2 3 4
2-picoline pyridine property S. no.
Table 1. Properties of Pyridine (Py), 2-Picoline (2Pi), and 4-Picoline (4Pi)4,5,31
2.1. Adsorbent and Adsorbates. Bagasse fly ash (BFA) was collected from the particulate collection equipment attached downstream of bagasse-fired boilers of Deoband Sugar Mills, Deoband, U.P. (India). The collected BFA was washed with hot water (70 °C), dried, and sieved using IS sieves (IS 4371979). The mass fraction between -600 and +180 µm size was used in the sorption studies. Detailed physicochemical characteristics of the BFA have been presented elsewhere.8 All the chemicals used in the study were of analytical reagent grade. The adsorbate pyridine (synonym: azabenzene, azine, chemical formula ) C5H5N, formula weight ) 79.1) was procured from E. Merck (India), and adsorbates 2-picoline (synonym: 2-methylpyridine, chemical formula ) C6H7N, formula weight ) 93.13) and 4-picoline (synonym: 4-methylpyridine, chemical formula ) C6H7N, formula weight ) 93.13) were procured from Acros Organics. The physical and toxicological properties of the three adsorbates are shown in Table 1. The stock solution of 1000 mg dm-3 concentration of each adsorbate was prepared in doubledistilled water (DDW). The mixed solution of all the three adsorbates was made by mixing precalculated volume of each stock solution and making its volume to a predetermined value by adding DDW and mixing it. 2.2. Analytical Measurements. The aqueous solution of Py, 2Pi, and 4Pi are stable over the concentration range used in the study. No change in the Py, 2Pi, and 4Pi concentration was observed over a time period of 12 h. The experiments were carried out in glass containers with glass stoppers, and no loss of adsorbates due to vaporization was observed during the experiments and the analysis. The concentrations of Py, 2Pi, and 4Pi in the aqueous solutions were determined by using a NETEL (NETEL Ind. Ltd., Mumbai) gas chromatograph having a flame ionization detector (FID) and using Netwin software. 2.3. Taguchi’s Design of Experimental Methodology. Taguchi’s design strategy, as detailed in our earlier papers,27,28 was used in the present study. The critical parameters affecting the simultaneous adsorptive removal of Py and picolines, the range of values, and their levels are shown in Table 2. The interactive influence of the three components in the ternary system was studied by having binary concentration interactions, i.e., C0,Py × C0,2Pi, C0,2Pi × C0,4Pi, and C0,Py × C0,4Pi, in the design. As shown in Table 3, seven parameters, each at three levels, and three second-order initial concentration interactions were used in the Taguchi’s L27 (313) orthogonal array (OA) matrix and the 27 experiments were carried out in triplet under the same conditions. The total adsorbates uptake, qtot, by BFA is also given in Table 3. The L27 OA matrix is the optimized procedure to run only 27 experiments in different combinations of parameters at three levels and the binary concentration interactions to elucidate the sorption phenomenon. 2.3.1. Batch Adsorption Studies. For each experimental run the aqueous solutions of known concentrations of the three adsorbates, Py, 2Pi, and 4Pi, were mixed as per the desired total concentration, and 50 mL of this mixed aqueous solution was taken in a 250 mL conical glass flask with a glass stopper containing a known amount of BFA (m). The initial pH (pH0) of the adsorbate solution was adjusted using 0.1 N H2SO4 or 0.1 N NaOH aqueous solution. As shown in our earlier publications,7–9 the adsorption of Py and its derivatives is pHdependent, and the solution pH changes with contact time,
4-picoline
2. Materials and Methods
γ-picoline, 4-methylpyridine C6H7N 93.14 colorless liquid, disagreeable odor
the effects of various parameters on the response characteristic. Significant parameters have been identified by using the analysis of variance (ANOVA) on the experimental data.
3 poison by intraperitorial route, moderately toxic by ingestion, skin contact, intravenous and subcutaneous routes; mildly toxic by inhalation, skin and severe eye irritant can cause CNS depression, gastrointestinal upset, and liver and kidney damage
5630 Ind. Eng. Chem. Res., Vol. 47, No. 15, 2008
Ind. Eng. Chem. Res., Vol. 47, No. 15, 2008 5631
experimental data. The details of the analysis procedure are explained in our earlier works.27,28 The plot of response curves, analysis of variance (ANOVA) for raw data, and S/N ratios data were used for the analysis of results and to predict the sorption performance. The mean of the response characteristic (µ) at the optimal condition was estimated as
Table 2. Process Parameters for Multicomponent Adsorption Study of Py, 2Pi, and 4Pi onto BFA Using Taguchi’s OA levels parameters A B C D E F G
units
initial concentration of pyridine initial concentration of 2-picoline initial concentration of 4-picoline temperature initial pH of solution BFA dose contact time
C0,Py C0,2Pi C0,4Pi T pH0 m t
-3
mg dm mg dm-3 mg dm-3 K (-) mg dm-3 min
1
2
3
0 0 0 293 4 4 30
50 50 50 303 6 8 60
100 100 100 313 8 12 90
¯
µ ) T + (A2 - T) + (B2 - T) ) A2 + B2 - T
j 2 and B j2 where Tj is the overall mean of the response and A represent average values of response at the second levels of parameters A and B, respectively. The estimation of µ is only a point estimate based on the average of results obtained from the experiments. The statistical range defined as the confidence interval (CI) of the statistical parameter is a maximum and minimum value between which the true mean, µ, should fall at some stated level of confidence. The confidence interval is of two types: CIPOP, which is for the entire population, and CICE, which is for only a sample group of experiments carried out under specified conditions. These confidence intervals are defined as
ultimately reaching its equilibrium value; however, no matter what the pH0 of the sorbate solution is, the final equilibrium pH of sorbate-sorbate (BFA) mixture remains constant at ∼10.7. Therefore, all the experiments have been carried out at the three levels of pH0 without any control. These samples were then agitated at a constant shaking speed of 150 ( 5 rpm in a temperature-controlled orbital shaker (Remi Instruments, Mumbai, India) at the desired temperature (293, 303, or 313 K). The samples were withdrawn at appropriate time intervals and centrifuged using a research centrifuge (Remi Instruments, Mumbai, India), and the supernatant solutions were analyzed for the residual concentrations of Py, 2Pi, and 4Pi. The total adsorption uptake of the adsorbates in the solid adsorbent phase, qtot (mg g-1), was calculated using the following relationship:
CIPOP ) CICE )
3
qtot )
∑ (C
0 - Ce,i)V/W
(2)
(1)
FR(1, fe)Ve neff
FR(1, fe)Ve
[
(3)
1 1 + neff R
]
(4)
where FR(1, fe) ) the F ratio at a confidence level of (1 - R) against DOF 1 and error DOF fe, Ve ) error variance (from ANOVA),
i)1
where C0,i and Ce,i are the initial and the equilibrium concentrations in mg dm-3 of Py, 2Pi, or 4Pi, V is the volume (dm3), and W is the weight (g) of the adsorbent. 2.3.2. Analysis of Experimental Data. The “higher-isbetter” quality characteristic was used in the analysis of
neff )
N 1 + [total DOF associated in estimate of mean] (5) 13
Table 3. Column Assignment for the Various Factors and Three Interactions in the Taguchi’s L27 (3 ) Orthogonal Array and Experimental qtot Values for Multicomponent Py and Its Derivatives Adsorption onto BFA experimental qtot values expt no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 total mean
1 A
2 B
3 A×B
4 A×B
5 C
6 A×C
7 A×C
8 B×C
9 D
10 E
11 B×C
12 F
13 G
1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3
1 1 1 2 2 2 3 3 3 1 1 1 2 2 2 3 3 3 1 1 1 2 2 2 3 3 3
1 1 1 2 2 2 3 3 3 2 2 2 3 3 3 1 1 1 3 3 3 1 1 1 2 2 2
1 1 1 2 2 2 3 3 3 3 3 3 1 1 1 2 2 2 2 2 2 3 3 3 1 1 1
1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3
1 2 3 1 2 3 1 2 3 2 3 1 2 3 1 2 3 1 3 1 2 3 1 2 3 1 2
1 2 3 1 2 3 1 2 3 3 1 2 3 1 2 3 1 2 2 3 1 2 3 1 2 3 1
1 2 3 2 3 1 3 1 2 1 2 3 2 3 1 3 1 2 1 2 3 2 3 1 3 1 2
1 2 3 2 3 1 3 1 2 2 3 1 3 1 2 1 2 3 3 1 2 1 2 3 2 3 1
1 2 3 2 3 1 3 1 2 3 1 2 1 2 3 2 3 1 2 3 1 3 1 2 1 2 3
1 2 3 3 1 2 2 3 1 1 2 3 3 1 2 2 3 1 1 2 3 3 1 2 2 3 1
1 2 3 3 1 2 2 3 1 2 3 1 1 2 3 3 1 2 3 1 2 2 3 1 1 2 3
1 2 3 3 1 2 2 3 1 3 1 2 2 3 1 1 2 3 2 3 1 1 2 3 3 1 2
R1
R2
R3
S/N ratio (dB)
0.00 5.81 8.32 4.16 22.01 18.44 12.26 12.41 38.80 6.17 8.23 28.07 22.11 17.75 16.32 12.22 35.38 28.06 8.16 26.63 23.38 17.43 16.32 36.55 34.64 25.70 22.61 507.94
0.00 5.87 8.32 4.16 22.06 18.43 12.26 12.40 38.81 6.17 8.23 28.12 22.23 17.81 16.34 12.21 35.13 28.04 8.16 26.51 23.38 17.44 16.30 36.43 34.58 25.67 22.63 507.67 18.82
0.00 5.76 8.31 4.16 22.16 18.42 12.27 12.43 38.69 6.20 8.24 27.97 22.12 17.78 16.32 12.22 35.38 28.06 8.17 26.64 23.41 17.43 16.32 36.56 34.64 26.30 22.59 508.54
0.00 15.29 18.40 12.39 26.88 25.31 21.77 21.88 31.77 15.82 18.31 28.96 26.91 25.00 24.26 21.74 30.95 28.96 18.24 28.50 27.38 24.83 24.25 31.25 30.79 28.26 27.08
5632 Ind. Eng. Chem. Res., Vol. 47, No. 15, 2008 Table 4. Average and Main Effects of qtot Values for BFA - Raw and S/N Data raw data, average value
A B C D E F G AxB AxC BxC
L1
L2
L3
13.58 12.75 13.02 17.28 18.18 27.12 18.26 17.41 17.66 17.73
19.37 19.02 18.93 20.10 19.71 17.25 18.79 19.37 18.68 19.16
23.50 24.68 24.49 19.07 18.57 12.08 19.40 19.67 20.11 19.56
main effects (raw data) L2 5.78 6.27 5.91 2.81 1.53 -9.87 0.53 1.95 1.02 1.43
-L1
L3
-L2
4.14 5.66 5.56 -1.02 -1.14 -5.16 0.62 0.30 1.42 0.41
N ) total number of results, and R ) sample size for confirmation experiment. It can be seen from eq 4 that as R approaches infinity, i.e., the entire population, the value 1/R approaches zero and CICE ) CIPOP. As R approaches 1, the CICE becomes wider. In order to confirm that the optimal parametric values determined by using Taguchi’s methodology are valid, a selected number of confirmatory sorption experiments are carried out under optimal conditions. The average of the results of the confirmation experiments is then compared with the anticipated average based on the optimal parameters and levels tested by Taguchi’s methodology. If the deviation between actual and determined qtot by Taguchi’s methodology is within 5%, it can be confirmed that the optimal parametric values determined by Taguchi’s design are valid. 3. Results and Discussion In accordance with the parametric values set by L27 OA (Table 3) the adsorption experiments were conducted in triplet, and the mean values of qtot and S/N ratio for each parameter at levels 1, 2, and 3 are calculated in Table 3. 3.1. Effect of Process Parameters. Table 4 provides the raw data for the average value of qtot and S/N ratio for each parameter at levels 1, 2, and 3 along with interactions at the assigned levels for Py, 2Pi, and 4Pi adsorption onto BFA. The effect of various parameters (m, pH, t, C0, and T) and initial concentration interactions of the three adsorbates on qtot values are also shown in this table. The adsorbent dosage m (parameter F) at level 1, the solution pH (parameter E) at level 2, and the initial concentration C0,4Pi (parameter C) at level 3 have the
S/N data, average value L1
L2
L3
19.30 18.99 19.16 22.59 22.64 26.22 22.60 21.76 21.75 21.89
24.55 24.56 24.37 23.65 23.65 23.62 24.31 24.12 24.13 23.96
26.73 27.02 27.04 24.33 24.28 20.73 23.66 24.70 24.70 24.73
main effects (S/N data) L2
-L1
5.25 5.58 5.20 1.07 1.01 -2.60 1.70 2.36 2.38 2.07
L3
-L2
2.18 2.46 2.67 0.68 0.62 -2.90 -0.64 0.58 0.57 0.77
highest influence on qtot. The difference between influence at level 2 and level 1 (L2 - L1) of each parameter indicates that C0,i has the largest influence on qtot in comparison to other parameters. The qtot increased with an increase in the C0,i because of a decrease in the mass transfer resistance to the uptake as the mass transfer driving force increased. Figure 1 shows the response curves for the individual effects of sorption parameters of different sorbates on the average value of qtot and the respective S/N ratio. An increase in the levels of C0,i and T from 1 to 2 and from level 2 to 3 has resulted in an increase in the qtot values. An increase in m from level 1 to 2 and subsequently to level 3 led to a decrease in the value of qtot. An increase in the sorption uptake with m is because of the availability of larger number of adsorption sites and greater contact surface area. Although the unit adsorption decreases with an increase in m, the sorbate removal or sorbate uptake increases. An increase in the pH0 resulted in an increase in the adsorption up to level 2 and the subsequent increase to level 3 resulted in the decrease in qtot. The removal of Py, 2Pi, and 4Pi is found to increase with an increase in the pH0 from 4 to 6. The maximum uptake was obtained at about pH0 6, and the qtot value decreased at pH0 > 6. The transition of Py and its derivatives, Py to PyH+, is pH-dependent, with a maximum amount of PyH+ occurring in the pH0 range of 4.5-6.0 (around the pKa value).7–9 The solution pH affects the surface charge of the adsorbents and, therefore, the adsorption process through dissociation of functional groups, viz. surface oxygen complexes of acid character such as carboxyl and phenolic groups or of basic character such as pyrones or chromens, on the active sites
Figure 1. Effect of process parameters on qtot and S/N ratio for multicomponent adsorption of Py, 2Pi, and 4Pi onto BFA.
Ind. Eng. Chem. Res., Vol. 47, No. 15, 2008 5633
of the adsorbent. pH may affect the structural stability of Py and its derivatives. BFA contains oxides of aluminum, calcium, and silicon on its surface. The presence of these metal oxides in contact with water leads to the development of surface charge according to the pH of the solution as explained in our earlier publications.7–9 It has been found that if the pH of the solution is not controlled, it will ultimately reach its equilibrium value of ∼10.7 at the end of the equilibrium sorption. As Niu and Conway29 have shown, the mol % of PyH+ in the solution would be 6. Since Py contains nitrogen atom, which is more electronegative than an sp2-hybridized C, Py gets preferentially adsorbed on a positively charged surface.29 At low pH (pH e (pKa ) 5.2)), the Py is converted to PyH+ through protonation, resulting in the low adsorption of protonated Py on the positively charged BFA surface. At higher pH (pH g (pKa), π-π dispersion interactions along with electrostatic interactions become important, and Py molecules are sorbed onto BFA. It may, however, be noted that BFA has a maximum affinity to Py and PyH+ at pH0 ∼ 6 and that Py adsorption predominates over that of PyH+. The mechanistic details of Py sorption are given in our earlier publications.7,8 An increase in contact time, t, from level 1 to 2 results in an increase in the qtot, but qtot remains invariant with further increase in t from level 2 to 3. The sorption of Py and its derivatives increases with t until equilibrium is reached between the solution phase and the solid phase. Initially, maximum number of vacant surface sites are available for adsorption, which, however, decreases with the progress in sorption. The Py and its derivatives are adsorbed into the mesopores that get almost saturated during the early stage of adsorption. Thereafter, the sorbate molecules have to traverse farther and deeper into the pores, encountering much larger mass transfer resistance. This results in the slowing down of the adsorption during the later period of adsorption. Generally, sorption is an exothermic process. Therefore, it is expected that an increase in T would result in a decrease in qtot. However, if the diffusion process controls the sorption process, the qtot value will increase with an increase in T due to endothermicity of the diffusion process. An increase in T results in an increased mobility of the molecules and a decrease in the retarding forces acting on the diffusing molecules, resulting in the enhancement in the sorptive capacity qtot. However, the pore diffusion is not the only rate-controlling step30 in the overall sorption process, and the diffusion resistance can be ignored with adequate contact time. Therefore, the increase in sorptive uptake “qtot” of Py and its derivatives with an increase in temperature can be attributed to chemisorption. Table 4 (and Figure 2) shows the significance of the interactions between initial concentrations of Py, 2Pi, and 4Pi [(A × B), (A × C), or (B × C)] affecting the average value of qtot. It can be seen from Figure 2 that the difference in the slopes of the lines is greater when the level of the parameters is lower. Hence, it may be concluded that the effect of initial concentration of Py and its derivatives on qtot values is more pronounced when C0 is increased from the lowest level to the middle level as compared to that when C0 is increased from the middle level to the highest level. The sorption of Py, 2Pi, and 4Pi seems to be antagonistic in nature. It appears that the components share the binding sites on the surface, and therefore, the adsorption of one species reduces the number of binding sites available for adsorption of other species. The screening effect may also be playing its role in the sorption antagonism. The antagonistic behavior is more
Figure 2. Interaction between parameters A, B, and C at three levels on qtot and S/N ratio for multicomponent adsorption of Py, 2Pi, and 4Pi onto BFA.
pronounced when the initial concentration is increased from level 2 to 3 than from level 1 to 2. The contribution of the individual parameters is weighted to enforce control on sorptive uptake of various compounds. ANOVA results for raw and S/N ratio data with desired response characteristics (qtot) are given in Table 5 for multicomponent Py, 2Pi, and 4Pi adsorption onto BFA. The F ratios obtained from ANOVA for raw and S/N ratio data show that all parameters and concentration interactions of the three components are statistically significant at 95% confidence limit for qtot as desired response characteristic. Figure 3 shows the contribution of each of the parameters for qtot. Table 5 shows that m (parameter F) is the most significant parameter with 35.65% and 10.50% contribution to the raw and S/N ratio data, respectively, qtot as the desired characteristic within the assigned levels for each factor. Table 5 and Figure 3 also revealed that the sorbate initial concentration interactions also contribute significantly to both raw and S/N ratio data for simultaneous removal of the three components by BFA. 3.2. Selection of Optimal Levels and Estimation of Optimum Response Characteristics. Using qtot as the “higher the better” type quality characteristic, the optimal level of various parameters obtained after examining the response curves (Figure 1) of the average value of qtot and S/N ratios are summarized in Table 6. This table indicates that the level 3 of parameters A, B, C (C0,i), level 2 of parameter D (temperature) and parameter E (pH0), level 1 of parameter F (m), and level 3 of parameter G (t) results in higher average value of qtot. Since the aim of the work is to remove maximum amount of Py and its derivatives with highest possible initial concentrations of Py, 2Pi, and 4Pi present together in the wastewater, level 3 of
5634 Ind. Eng. Chem. Res., Vol. 47, No. 15, 2008 Table 5. ANOVA of qtot and S/N Ratio Data for Multicomponent Adsorption of Adsorption of Py, 2Pi, and 4Pi onto BFA raw data parameter A B C D E F G A×B A×C B×C residual model total
S/N data
S
DOF
mean square
% contribution
F value
sum of squares
DOF
mean square
1340.39 1923.59 1777.73 109.62 34.05 3151.89 17.73 180.21 203.88 102.16 0.32 8841.26 8841.63
2 2 2 2 2 2 2 4 4 4 54 26 80
670.20 961.80 888.86 54.81 17.03 1575.95 8.86 45.05 50.97 25.54 0.01 4299.07 4299.07
15.16 21.76 20.11 1.24 0.39 35.65 0.20 2.04 2.31 1.16 0.20 99.80 100.00
97548.39 139991.05 129375.84 7977.60 2478.20 229381.86 1290.16 6557.59 7418.93 3717.37
262.62 305.15 288.82 13.89 12.24 136.04 (13.33) 92.24 90.88 80.07 0.00 1295.26 1295.26
2 2 2 2 2 2 (2) 4 4 4 2 26 26
131.31 152.58 144.41 6.94 6.12 68.02 (6.66) 23.06 22.72 20.02 6.12 575.72 587.95
625736.00
Table 6. Predicted Optimal qtot Values, Confidence Intervals, and Results of Confirmation Experiments
adsorbent BFA
optimal levels of process parameters
predicted optimal value (mg g-1)
A3, B3, C3, D2, E2, F1, G3
46.1
confidence i ntervals (95%) CIPOP: 45.44 < µBFA < 46.76 CICE: 45.41 < µBFA < 46.80
av of confirmation experiments (mg g-1) 46.39
parameters A, B, and C (C0,Py, C0,2Pi, and C0,4Pi) are used for further calculations. The significant process parameters affecting the removal of these organics by BFA and their optimal levels (as already selected) are A3, B3, C3, D2, E2, F1, and G3. The average value (from Table 3) of qtot at: 3rd level of j 3) ) 23.5, 3rd level of concentration of concentration of Py (A j 3) ) 24.68, 3rd level of concentration of 4Pi (C j 3) ) 24.49, 2Pi (B j 2) ) 20.10, 2nd level of pH0 (E j 2) 2nd level of temperature (D j ) 19.71, 1st level of adsorbent dosage (F1) ) 27.12, and 3rd j 3) ) 19.4. level of contact time (G j BFA) ) 18.82(from Table 3). The overall mean of qtot(T The predicted optimum value of qtot for BFA (µBFA) has been calculated as ¯
µBFA ) TBFA + (A3 - TBFA) + (B3 - TBFA) + (C3 - TBFA) + ¯
(D2 - TBFA) + (E2 - TBFA) + (F1 - TBFA) + (G3 - TBFA)
% contribution 20.28 23.56 22.30 1.07 0.94 10.50 pooled 7.12 7.02 6.18 0.94 99.06 100.00
F value 21.46 24.94 23.60 1.13 1.00 11.12 3.77 3.71 3.27 94.09
3.3. Confirmation Experiments. Three confirmation experiments have been carried out for simultaneous adsorption of Py, 2Pi, and 4Pi onto BFA at selected optimal levels (A3, B3, C3, D2, E2, F1, G3). The average value of qtot from the three experiments and that predicted by Taguchi’s method are compared in Table 6. The experimental value of the optimum individual sorptive uptake of Py, 2Pi, and 4Pi is respectively 12.38, 17, and 17.01 mg g-1, giving a total qtot of 46.39 mg g-1. It is found that the qtot from confirmatory experiments is within 95% of CI. It may, however, be noted that the optimal parametric values are valid within the specified range of process parameters only and that any extrapolation/interpolation must be verified through additional experiments. 3.4. Use of Taguchi’s Design in Fixed Bed Sorption. Our recent publications27,28 and the present work show the efficacy of Taguchi’s experimental design methodology in optimizing process parameters and to understand the interactive effects of these parameters for maximizing the total adsorptive uptake of all the sorbate components by the adsorbent. Having optimized these parameters, it becomes easy to extend the methodology for fixed bed sorption studies. The parameters to be optimized are the flow rate, diameter and height of the column, and the sorbent particle size. The optimized values of pH, initial concentration, and temperature from the batch experiments can be used as such.
) 46.10 mg g-1 (6) The 95% confidence interval for the mean of the population and three confirmation experiments (CIPOP and CICE) is calculated by substituting N ) total number of results ) 27 × 3 ) 81; fe(DOF error) ) (80 - 26) ) 54; Ve (error variance) ) 0.32 (recalculated from Table 5) in eqs 7–9. neff ) N )3 1 + [total DOF associated in the estimate of the mean] (7) F0.05(1, 54) ) 4.03 (tabulated F value) CIPOP ) CICE )
FR(1, fe)Ve ) (0.66 neff
FR(1, fe)Ve
[
]
1 1 + ) (0.69 neff R
(8) (9)
The 95% confidence intervals (CIPOP and CICE) of the predicted ranges of qtot for simultaneous adsorption of Py, 2Pi, and 4Pi onto BFA are given in Table 6.
Figure 3. Percent contribution of various parameters for qtot for multicomponent adsorption of Py, 2Pi, and 4Pi onto BFA. A: C0,Py (mg dm-3); B: C0,2Pi (mg dm-3); C: C0,4Pi (mg dm-3); D: T (K); E: pH0; F: m (g dm-3); G: t (min).
Ind. Eng. Chem. Res., Vol. 47, No. 15, 2008 5635
4. Conclusions The following conclusions can be drawn from the present study: • The adsorption process parameters adsorbent dose, pH0, contact time, temperature, and the sorbate initial concentration at three levels with a Taguchi’s design of OA layout of L27 (313) could be optimized with the ‘higher-is-better’ quality characteristic with 27 sets of experiments only. • The interactions between initial concentrations of Py, 2Pi, and 4Pi [(A × B), (A × C), or (B × C)] are significant in influencing the average values of total sorption uptake, qtot. The effect of initial concentration of one compound (C0,Py or C0,2Pi) on qtot values is more pronounced at the lower concentration of the other compounds (C0,2Pi or C0,4Pi) for all possible interactions. • All the factors and the interactions considered in the experimental design with qtot as the desired response characteristic are statistically significant at 95% confidence limit. • The BFA shows a potential for the simultaneous adsorption of Py, 2Pi, and 4Pi at a combined concentration of 100 g dm-3 with a good sorption uptake of ∼46.39 mg g-1 with a percent removal of ∼50%, ∼68%, and ∼69%, respectively, at optimum conditions. • Conditions optimized in the batch study like pH0 and temperature can be used in the fixed bed adsorption study, and Taguchi’s design of experimental methodology can again be used in the fixed bed adsorption study to optimize parameters like flow rate, height and diameter of fixed bed, etc. Acknowledgment The financial assistance provided by the Ministry of Human Resource Development (MHRD), Government of India, and Indian Institute of Technology, Roorkee, to Mr. Dilip H. Lataye is gratefully acknowledged. Dilip H. Lataye also thanks Visvesvaraya National Institute of Technology, Nagpur (India), for allowing him to undertake Ph.D. work under QIP at IIT Roorkee. He also thanks Dr. V. C. Srivastava for useful discussions during the preparation of the manuscript. Literature Cited (1) Yates, F. S. Pyridine and their benzo derivatives: (vi) applications. In Katritzky, A. R., Rees, C. W., Eds.; ComprehensiVe Heterocyclic Chemistry: The Structure, Reaction, Synthesis and uses of Heterocyclic Compounds; Pergamon Press: Oxford, 1984; Vol. 2, Part 2 A, p 511. (2) Gilchrist, T. L. Heterocyclic Chemistry; Pitmax Press: London, 1985. (3) Jori, A.; Calamari, D.; Cattabeni, F.; Domenico, A. D.; Galli, C. L.; Galli, E.; Silano, V. Ecotoxicological profile of pyridine. Working party on ecotoxicological profiles of chemicals. Ecotoxicol. EnViron. Saf. 1983, 7, 251. (4) Kirk, R. E.; Othmer, D. F. Encyclopedia of Chemical Technology, 4th ed.; John Wiley & Sons: New York, 1996; Vol. 20. (5) Lewis, R. J., Sr. Sax’s Dangerous Properties of Industrial Materials, 11th ed.; John Wiley & Sons: Englewood Cliffs, NJ, 2004; p 3106. (6) Kumar, R.; Mishra, I. M.; Mall, I. D. Treatment of pyridine bearing wastewater using activated carbon. Res. Ind. 1995, 40, 33. (7) Lataye, D. H.; Mishra, I. M.; Mall, I. D. Removal of pyridine from aqueous solution by adsorption onto bagasse fly ash. Ind. Eng. Chem. Res. 2006, 45, 3934. (8) Lataye, D. H.; Mishra, I. M.; Mall, I. D. Adsorption of 2-picoline onto bagasse fly ash from aqueous solution. Chem. Eng. J. 2008, 138, 35. (9) Lataye, D. H.; Mishra, I. M.; Mall, I. D. Pyridine Sorption from Aqueous Solution by Rice Husk Ash (RHA) and Granular Activated Carbon
(GAC): Parametric, Kinetic, Equilibrium and Thermodynamic Aspects. J. Hazard. Mater. 2008, 154, 858. (10) Mall, I. D.; Tewari, S.; Singh, N.; Mishra, I. M. Utilisation of bagasse fly ash and carbon waste from fertiliser plant for treatment of Py and 3-picoline bearing wastewater. Proceeding of the 18th International Conference on Solid Waste Technology and Management held at Philadelphia, PA, March 23-26, 2003. (11) Baker, R. A. Threshold odors of organic chemicals. J. Am. Water Works. Assoc. 1963, 55, 913. (12) Zhu, S.; Bell, P. R. F.; Greenfield, P. F. Adsorption of pyridine onto spent Rundle oil shale in dilute aqueous solution. Water Res. 1988, 22, 1331. (13) Baker, R. A.; Luh, M. D. Pyridine sorption from aqueous solution by montmorillonite and kaolinite. Water Res. 1971, 5, 839. (14) Ardizzone, S.; Hoiland, H.; Lagioni, C.; Sivieri, E. Pyridine and abiline adsorption from an apolar solvent: the role of the solid adsorbent. J. Electroanal. Chem. 1998, 447, 17. (15) Bludau, H.; Karge, H. G.; Niessen, W. Sorption, sorption kinetics and diffusion of pyridine in zeolites. Microporous Mesoporous Mater. 1998, 22, 297. (16) Sabah, E.; Celik, M. S. Interaction of pyridine derivatives with sepiolite. J. Colloid Interface Sci. 2002, 251, 33. (17) Mohan, D.; Singh, K. P.; Sinha, S.; Ghosh, D. Removal of pyridine from aqueous solution using low cost activated carbons derived from agricultural waste materials. Carbon 2004, 42, 2409. (18) Mohan, D.; Singh, K. P.; Sinha, S.; Ghosh, D. Removal of pyridine derivatives from aqueous solution by activated carbon developed from agricultural waste materials. Carbon 2005, 43, 1680. (19) Mohan, D.; Singh, K. P.; Sinha, S.; Ghosh, D. Removal of R-picoline, β-picoline and γ-picoline from synthetic wastewater using low cost activated carbons derived from coconut shell fibers. EnViron. Sci. Technol. 2005, 39, 5076. (20) Akita, S.; Takeuchi, H. Sorption equilibria of pyridine derivatives in aqueous solution on porous resins and ion exchange resins. J. Chem. Eng. Jpn. 1993, 26, 237. (21) Taguchi, G. Introduction to Quality Engineering; Quality Resources: New York, 1986. (22) Taguchi, G.; Wu, Yu-in. Off-line Quality Control; Central Japan Quality Control Association: Nagoya, Japan, 1979. (23) Byrne, D. M.; Taguchi, S. The Taguchi Approach to Parameter Design; Quality Progress: 1987. (24) Ross, P. J. Taguchi Techniques for Quality Engineering; McGraw Hill Book Co.: New York, 1996. (25) Barker, T. B. Engineering Quality by Design; Marcel Dekker: New York, 1990. (26) Roy, R. K. A Primer on the Taguchi Method; Society of Manufacturing Engineers: Dearborn, MI, 1990. (27) Srivastava, V. C.; Mall, I. D.; Mishra, I. M. Multicomponent Adsorption Study of Metal Ions onto Bagasse Fly Ash Using Taguchi’s Design of Experimental Methodology. Ind. Eng. Chem. Res. 2007, 46, 5697– 5706. (28) Srivastava, V. C.; Mall, I. D.; Mishra, I. M. Optimization of parameters for adsorption of metal ions onto rice husk ash using Taguchi’s experimental design methodology. Chem. Eng. J. 2008, doi: 10.1016/ j.cej.2007.09.030. (29) Niu, J.; Conway, B. E. Development of techniques for purification of wastewaters: removal of pyridine from aqueous solution by adsorption at high-area C-cloth electrodes using in situ optical spectrometry. J. Electroanal. Chem. 2002, 521, 16. (30) Srivastava, V. C.; Mall, I. D.; Mishra, I. M. Adsorption thermodynamics and isosteric heat of adsorption of toxic metal ions onto bagasse fly ash (BFA) and rice husk ash (RHA). Chem. Eng. J. 2007, 132, 267– 278. (31) Web reference: www.jubl.net/msds.
ReceiVed for reView November 27, 2007 ReVised manuscript receiVed May 2, 2008 Accepted May 19, 2008 IE0716161
