Ind. Eng. Chem. Res. 1998, 37, 4783-4791
4783
Recovery of Nicotine from Aqueous Extracts of Tobacco Wastes by an H+-Form Strong-Acid Ion Exchanger Antonio de Lucas, Pablo Can ˜ izares, Miguel A. Garcı´a,† Julia´ n Go´ mez, and Juan F. Rodrı´guez* Department of Chemical Engineering, University of Castilla-La Mancha, Avda. de Camilo Jose Cela s/n, 13004 Ciudad Real, Spain
Equilibrium ion exchange isotherms of nicotine on an H+-form strong-acid resin, Amberlite IR120, have been determined in order to assess the possibility of using such a system to recover nicotine from aqueous nicotine extracts. The effect of pH on the experimental equilibrium isotherms has been explained by taking into account that the nicotine can be removed by two different mechanisms: a conventional exchange in ionic form and an acid/base reaction between the neutral amino group of the nicotine and the fixed acid groups of the cation exchanger. Theoretical equations for equilibrium isotherms including the different ways in which the nicotine can be adsorbed by the resin were derived. The proposed model accounts for the influence of pH on the equilibrium isotherms by means of an empirical equation. The theoretical equilibrium isotherms for any constant pH were determined from the theoretical equations. An additional equilibrium isotherm for nicotine-NH3 was also obtained. Adsorption, elution, and regeneration experiments have also been reported. Intraparticle diffusivity of nicotine was determined from the breakthrough curves. Theoretical breakthrough and elution curves were calculated by using the analytical solution for a rectangular isotherm in a single-component system. Introduction Tobacco dust is a waste byproduct of cigarette manufacture. A way to increase the value of this waste is the recovery of nicotine present in the dust for use as an insecticide. Nicotine is the principal alkaloid of tobacco, along with small amounts of 12 other alkaloids. It is a water-soluble compound and exhibits a relatively high volatility. Nicotine sulfate has been used as an aphicide on fruit, vegetables, and ornamentals because it is less volatile than nicotine and safer to handle. Nicotine, together with other water-soluble compounds present in tobacco leaves, can be easily extracted from tobacco dust using only pure water as solvent, with an acceptable yield. After that, nicotine must be recovered and concentrated from the leached solution in a second step.1 The isolation of nicotine from extracts of tobacco wastes, such residual powder from cigarette manufacture and low-grade leaves, using ion-exchange resins was explored by Kingsbury.2 More recently Narasimha Rao and Chakraborty3 and Bhat and Sindhi4 reported aqueous extraction and capture of nicotine by strongacid ion-exchange resins. Although a considerable amount of papers have been presented on the ion exchange separation of amino acids5-7 and amines,8,9 there is a lack of information in the literature about the application of ion exchange to the purification of alkaloids such as nicotine. Ion-exchange resins are particularly effective for the selective removal of amphoteric and weak bases or acid substances (and therefore for alkaloids) from aqueous solutions. The net charge of these molecules may vary * To whom correspondence should be addressed. † On leave from the ICIDA (Cuban Research Institute for Sugar Cane Derivatives), University of La Habana, Via Blanca 804, Ciudad de La Habana 4026, Cuba.
in magnitude and sign when the pH of the solution changes. So it is important to study the uptake equilibria of such molecules on ion-exchange resins as a function of solution composition. Dye et al.10 investigated the equilibria for adsorption of amino acids on a strong-acid ion-exchange resin. These authors showed that the uptake of an amino acid by the hydrogen form of the resin took place primarily as the stoichiometric exchange of amino acids for hydrogen ions. On the other hand, alkaloids can be considered as organic amines, and according to Yoshida et al.11 the amine species (R-NH2) can be immobilized on the resin (R′-H) by the acid-base neutralization reaction
R′-H + R-NH2 S R′-NH3-R
(1)
An H+-form strong-acid ion exchanger adsorbs amine and ammonia almost irreversibly,8,12 and the amines can be desorbed almost irreversibly by using an aqueous solution of caustic soda.9,13 On the other hand, the elution of amino acid can be also accomplished using ammonia or simply a strong acid.8 The expressions for the breakthrough and the elution curves for a rectangular isotherm system in which the mass transfer rate is controlled by the combined effects of external film and internal homogeneous resistance have been given by Yoshida et al.14 and Yoshida and Kataoka,13 respectively. They were successfully applied to simulate the behavior of an ion exchange fixed bed for the removal and elution of ammonia and amines,9,11 and therefore they should be suitable for the simulation of the breakthrough curves of nicotine. Equilibrium isotherms were measured for different initial pHs on the strong-acid ion-exchange resin Amberlite IR-120. Theoretical equations to simulate the equilibrium isotherms, accounting for the effect of pH on the equilibria are derived by assuming five different kinds of interactions between the nicotine and the fixed
10.1021/ie9801958 CCC: $15.00 © 1998 American Chemical Society Published on Web 10/28/1998
4784 Ind. Eng. Chem. Res., Vol. 37, No. 12, 1998
groups of the resin. Although the primary objective was to demonstrate the feasibility of the proposed process and to obtain sufficient data to permit a preliminary evaluation of the economics, the data obtained were in fact sufficiently accurate and extensive to allow a somewhat more detailed kinetic analysis. The breakthrough and elution curves for the nicotine-water system on Amberlite IR120 resin were obtained. The mathematical models proposed by Yoshida et al.14 and Yoshida and Kataoka13 considering homogeneous particles and irreversible reactions were adopted in order to simulate the breakthrough and elution curves, and the intraparticle effective diffusion coefficient of nicotine was calculated. Experimental Procedures Amberlite IR 120 (Rohm and Haas) is a gel-type strongly acid cation-exchange resin. It is a sulfonated cross-linked styrene/divinylbencene copolymer with 12% DVB and a density of 0.619 g of wet resin/cm3. The total exchange capacity and the average particle radius of the resin have been reported in a previous work,15 being Q ) 5.05 mequiv/g of dry resin and Rp ) 0.0275 cm, respectively. Before its utilization, the resin was saturated and regenerated in successive cycles by using HCl and NaOH solution, 0.1 M, to obtain normalized conditions of capacity and ionic form. After that, the resin was dried under a controlled atmosphere until reaching a constant humidity content, about 20%. Furthermore, before each equilibrium experiment, the water content of the resin was measured in order to ensure that the resin weight used for calculations was correct. Equilibria. Equilibria were measured by the batch method at four different initial pHs. The pH was adjusted by using 0.1 M HCl. Experiments were carried out in 100 mL flasks, hermetically sealed and magnetically agitated. The flasks were submerged in a temperature-controlled thermostatic bath at 25 ( 0.2 °C. All the experiments were carried out at the same initial nicotine concentration (2 g/L, 12.34 mmol/L). This value is greater than the maximum concentration of nicotine that can be reached in a solution from the lixiviation of tobacco dust. Equilibrium was achieved in 10 h. After equilibration (at least 24 h), resin and solution were separated by filtration and the pH and nicotine content of the solution were measured. The nicotine concentration in water solution was measured according to the traditional method proposed by Willits and Swain,16 using a Perkin-Elmer UV/vis model Lambda 3B. The equilibrium resin phase concentration of nicotine was calculated by mass balance according to eq 2, where
n/a )
V (C - C/a) W 0
(2)
C0 and C/a are the initial concentration and equilibrium “analytical” concentration of nicotine in the liquid phase (mmol/L of solution), respectively. n/a denotes the resin phase equilibrium concentration of nicotine (mmol/g of dry resin), V is the solution volume (L), and W is the dry resin weight (g). Breakthrough and Elution Experiments. Breakthrough and elution experiments were carried out in a glass column of 10.5 mm i.d. and 174 mm length. Feed solution pH was always adjusted to 7. The column was filled with 22.5 g of dry resin, and a bed void fraction
Figure 1. Equilibrium isotherms for nicotine on H+-form Amberlite IR120. Stirring speed ) 430 rpm, C0 ) 12.34 mmol/L, and T ) 25 °C. Solid lines: Langmuir curves.
equal to 0.36 was measured by filling the swelled resin bed with water, blowing the water off the bed, and finally weighing the amount of water displaced. The nicotine solution was pumped to the resin bed at different flow rates and concentrations. After the breakthrough run, nicotine was eluted from the resin with ammonia, and after that, the resin was regenerated to its H-form by using 1 M HCl. The analysis of nicotine in the liquid phase was conducted as described in a previous section. The concentration of ammonia in the effluent was measured by using a CRISON ammonia ionic electrode detector. Results and Discussion Equilibria. Figure 1 shows the effect of initial pH on the experimental equilibrium isotherms for adsorption of nicotine on an H+-form Amberlite IR-120 resin. The experiments were carried with a fixed value of the initial concentration of nicotine (2 g/L, 12.34 mmol/L), at 25 °C. As can be seen, equilibrium is very favorable for nicotine resin uptake under any conditions, and the isotherms can be considered nearly irreversible. The experimental equilibrium isotherms for the different initial pHs were correlated by the Langmuir equation
n/a )
KLQC/a 1 + KLC/a
(3)
The solid lines in Figure 1 are the Langmuir isotherms calculated from the experimental data obtained at each initial pH, showing that the data correlated reasonably well. Figure 2 shows that the total capacity Q and the parameter KL obtained from Langmuir plots depend on the pH value significantly. It was not possible to maintain pH constant during an equilibrium experiment, but it could be carefully measured at the end of the experiment. The largest amount of nicotine adsorbed is found when the initial pH is 9 (the maximum pH that can be reached without base addition) and decreases as the initial pH decreases. The increase of
Ind. Eng. Chem. Res., Vol. 37, No. 12, 1998 4785
total resin capacity with pH cannot be explained on a conventional ion exchange basis. Nicotine is an alkaloid, namely a moderately weak base in aqueous solution, and dissociates as follows:
(4)
With ideal behavior assumed for the aqueous phase, the dissociation constants for eq 4 are respectively given by the following equations
Ka1 )
CN+CH+ CN2+
(5.1)
Ka2 )
CNCH+ CN+
(5.2)
Figure 2. Effect of pH on KL and on the resin capacity for the system nicotine/H+-form Amberlite IR120. Stirring speed ) 430 rpm, C0 ) 12.34 mmol/L, and T ) 25 °C.
where CN, CN+, and CN2+ represent the concentrations of the different forms of the generic nicotine (neutral, monocations, and dicationic). The total “analytical” concentration of the nicotine in solution, Ca, is given by
Ca ) CN2+ + CN+ + CN
(6)
By combination of eqs 5 and 6, the following expressions for the concentration of the different ionic forms can be obtained as a function of the hydrogen ion concentration, CH+, and the analytical concentration Ca:
CN2+ )
Ca Ka1 Ka1Ka2 1+ + CH+ C +2
(7.1) Figure 3. Theoretical concentration distribution of nicotine species in the liquid phase at 25 °C.
H
CN+ )
Ca Ka2 CH+ 1+ + CH+ Ka1 Ca
CN )
2
1+
CH+ CH+ + Ka2 Ka1Ka2
(7.2)
following acid-base neutralization reactions:
R-H + N(R1R2R3)(R′1R′2R′3)N S (7.3)
Figure 3 shows theoretical concentration distributions of N, N+, and N2+ in the liquid-phase calculated from eqs 7 by using Ka1 ) 7.59 × 10-4 and Ka2 ) 9.55 × 10-9 (from ref 17). The distribution curve shows that the predominant species at each pH changes from N2+ at pH ) 3.8 to N at pH ) 9. As shown in Figure 3, for pH greater than 8, the concentrations of N+ and N2+ are almost negligible. If the adsorption process of nicotine on a strong-acid ion exchanger is only considered as a conventional ion exchange process, at pH ) 9 the concentration of exchangeable cations would be very low in the aqueous phase and the nicotine adsorption might be negligible. According to Yoshida et al.,8 if we consider nicotine as an amine with two tertiary amine groups, it can be also adsorbed in its neutral form by the
R-NH-(R1R2R3)(R′1R′2R′3)N (8.1) 2R-H + N(R1R2R3)(R′1R′2R′3)N S R-NH-(R1R2R3)(R′1R′2R′3)-NH-R (8.2) where R h refers to the resin polymeric matrix and R1, R2, R3, R′1, R′2, R′3 denote the groups linked to the nitrogen atoms in the nicotine molecule. In this way, N+ and N can be adsorbed in the resin phase occupying one or two active centers, with the exchange of one or zero hydrogen ions of the resin matrix. Therefore, the total solute concentration in the resin calculated by means of eq 2 is equal to: / n/a ) nN + +
/ nN 2+ 2
(9)
/ / where nN + and nN2+ are the concentrations of monoand divalent nicotine inside the resin in mequiv/g.
4786 Ind. Eng. Chem. Res., Vol. 37, No. 12, 1998
Note in this regard that if there is no physical adsorption of nicotine and if all the nicotine in the resin phase could be considered as monovalent species, the maximum exchange capacity of the resin should be 5.05 mequiv/g. At the other limit, if nicotine could be merely considered as a divalent species, the observed capacity should be half of the mentioned value. In practice, the observed values never exceed the upper capacity limit and approximate the lower limit for pH ) 3.8. This fact would indicate that there is probably no physical adsorption of nicotine (the upper limit is never exceeded), and the observed capacity is merely the result of a different distribution (depending on pH) of the two species of nicotine inside the resin. Therefore, five different equilibrium equations can be postulated, corresponding to the five possible kinds of interactions between nicotine species and the active centers of the resins. On a conventional ion exchange basis, the equilibrium of each ionic form of nicotine with the ion exchanger can be written as
N2+ + 2R-H S R2-N + 2H+
KN2+ )
/ /2 nN 2+ CH+ / /2 (2CN 2+)nH
/ nN 2+ )
2n/a 1+p
(11.1)
/ nN + )
pn/a 1+p
(11.2)
In the same way, n* and n/H (mequiv/g) can be obtained from the previous relations:
(2 + p)n/a 1+p
n* )
n/H ) Q -
N+ + R-H S R-N + H+
K1N+ )
K1N )
N + R-H S R-N
N + 2R-H S R2-N
K2N )
/ nN + / CN n/H
(
K1N+ )
/ nN 2+
(2C/N)n/2 H
(10.3)
(10.4)
Finally, the possibility that N+ can be also adsorbed occupying two active centers should also be considered:
N+ + 2R-H S R2-N + H+
K2N+ )
/ / nN 2+ CH+ / /2 (2CN +)nH (10.5)
To evaluate this complex equilibrium behavior, the amount of nicotine in each ionic form in the resin has to be estimated. It is due to the fact that the individual concentrations of the different ionic forms of the nicotine can be neither independently measured nor calculated from the pH values by material balance because of the buffer effect of nicotine. Taking into account the influence of the pH on the final capacity, it seems evident that there is some kind of relation between the nicotine species ratio in the resin / / p ) nN +/nN2+ and the pH of the external solution. The concentration of the individual species in the resin can be related to the concentration of nicotine n/a (calculated with eq 2) using the following relations:
(11.4)
2n/a /2 C 1 + p H+ KN2+ ) (2 + p)n/a / (2CN ) Q 2+ 1+p
/ CN +
(10.2)
Taking into account eqs 8 and the fact that at pH ) 9 the final resin capacity is between the maximum and the minimum attainable values, the nonionic form of nicotine will be in the resin in its mono and divalent forms:
(2 + p)n/a 1+p
Substituting the above expressions into the equilibrium equations (10.1) and (10.2) leads to eqs 12.1-12.5.
(10.1) / / nN + CH+ / / CN + nH
(11.3)
)
2
2n/a / C 1 + p H+ (2 + p)n/a Q1+p
(
)
(12.2)
2n/a 1+p K1N ) (2 + p)n/a / CN Q 1+p
(
)
(12.3)
2n/a 1+p K2N ) (2 + p)n/a (2C/N) Q 1+p
(
)
(12.4)
2
2n/a / C 1 + p H+ K2N+ ) (2 + p)n/a / (2CN+) Q 1+p
(
(12.1)
)
2
(12.5)
By combination of eqs 12.1, 12.4, 12.5, and 6, the following expression that directly relates the “analytical” concentration of nicotine C/a in solution and the concentration of nicotine in the resin n/a can be obtained, as a function of the hydrogen ion concentration, the p function, and the three equilibrium constants:
C/a )
(
)
/2 / CH n/a CH + + 1 + + 1 + p KN2+ K2N+ K2N
(
)
(2 + p)n/a Q1+p
2
(13)
This expression includes four unknown parameters: three equilibrium constants and the ratio p that is a function of pH. Initially, a global fit of all the experimental points to eq 13 was attempted using different functions to relate p with pH (eqs 14-17 in Table 1)
Ind. Eng. Chem. Res., Vol. 37, No. 12, 1998 4787 Table 1. Different Functions and Parameters Relating p with pH equation
eq no.
a
b
av dev (%)
p ) a + b pH p ) a pHb p ) a + b log pH p ) a + b exp(pH)
14 15 16 17
-0.1 × 10-5 1.078 × 10-3 -1 × 10-10 0.1545
0.2733 3.34 3.208 3.82 × 10-3
24.29 6.15 35.97 7.34
and a nonlinear regression method based on Marquardt’s algorithm.18 Results of the fittings (not shown here) were not satisfactory since the large number of parameters of eq 13 made the convergence difficult when possible. Elsewhere, very different values of the parameters with no physical sense were obtained depending on the function of p initially proposed. Therefore, a more intuitive and easier step by step method was used in order to obtain these parameters. As indicated above, the capacity of the resin, in mmol/ g, for the equilibrium isotherm carried out at an initial pH of 3.8 approaches half of the total resin capacity, indicating that p is very low and that the major part of the nicotine species in the resin are occupying two active centers. By assuming that this is true for pH ≈ 3.8, we estimated the experimental equilibrium coefficient KN2+ by fitting the experimental values to the theoretical equation (12.1), using the mentioned nonlinear regression method based on Marquard’s algorithm. A value of KN2+ equal to 2.9 g/L (% av dev ) 6.2) was obtained. The same procedure could be applied to obtain the value of K2N+ from the equilibrium isotherm of initial pH ) 3.8. In this case, a value of K2N+ ) 3.0 g/mequiv (% av dev ) 6.2) was obtained. As the concentration of neutral nicotine N at pH < 3.8 is extremely low, the same procedure could not be applied to calculate K2N. Since the concentration of neutral nicotine is only appreciably high at pH > 7, the third equilibrium constant was obtained by fitting the experimental equilibrium data points from initial pH ) 9 to eq 12.5, assuming a constant value of p. The best fitting was obtained for a value of p equal to 1.4 and K2N equal to 6.3 g L/mequiv2 (% av dev ) 1.8). In the following step, a global fitting of all the experimental points was carried out by employing the mentioned nonlinear regression method and different empirical functions relating p to pH (linear, potential, exponential, and logarithmic). The values of the equilibrium relations used were the previously obtained by the step by step method. The experimental results are shown in Table 1. Equation 15 with the lower average standard deviation describes better the dependence of the ratio between the species inside the resin p on pH. Figure 4 shows the excellent fit between all the experimental points and the theoretical ones. Using eqs 13 and 15 and the values of the parameters previously calculated, the equilibrium ion exchange isotherms were obtained at different final pHs. Such iso-pH curves are shown in Figure 5. Finally, the value of K1N+ was calculated by fitting / all the experimental values of CN + using eqs 12.2 and 15. A value of K1N+ equal to 0.17 with an average standard deviation of 10.5% was obtained. The value of K1N was calculated by fitting the experimental values with a concentration of neutral nicotine C/N higher than 10-4 mmol/L using eqs 12.5 and 15. This value is equal to 971 L/mequiv with an average standard deviation of 7.5%. In summary, the following values for the
Figure 4. Experimental and theoretical equilibrium data points for the system nicotine/H+-form Amberlite IR120, showing comparison between measured and calculated values. Stirring speed ) 430 rpm, C0 ) 12.34 mmol/L, and T ) 25 °C.
Figure 5. Equilibrium isotherms (25 °C) at various pH values as calculated with eqs 13 and 15 for the system nicotine/H+-form Amberlite IR120.
experimental equilibrium constants were obtained: KN2+ ) 2.9 g/L; K1N+ ) 0.17; K1N ) 971 L/mequiv; K2N ) 12.5 g L/meq2; K2N+ ) 3.0 g/mequiv. An additional equilibrium isotherm for the nicotineNH3 system was also obtained at 25 °C and an initial NH3 concentration of 0.1 M. Figure 6 shows that the isotherm is very favorable for ammonia adsorption. This fact is very important in the elution process when nicotine has been obtained from tobacco extracts because nicotine will be selectively displaced before the rest of the cations present in the resin. Breakthrough Curves. Experimental breakthrough curves obtained using nicotine concentrations ranging between 3.1 and 9.2 mmol/L and three different flow rates (3.6, 6.6, and 9.6 L/h) are shown in Figure 7. When the flow rate or the concentration increases, the breakthrough time decreases as expected. The expression for the breakthrough curve for a rectangular isotherm system in which the mass transfer rate is controlled by the combined effects of external film
4788 Ind. Eng. Chem. Res., Vol. 37, No. 12, 1998
Figure 6. Equilibrium isotherm for ammonia on nicotine/H+-form Amberlite IR120. Stirring speed ) 430 rpm, C0 ) 100 mmol/L, and T ) 25 °C.
and internal homogeneous diffusional resistance has been given by Yoshida et al.14 For simplicity, axial dispersion was neglected and the intraparticle mass transfer was represented by a linear driving force. The general analytical solution used for the prediction of the breakthrough curves is shown in Table 2. τ, δ, and ξ are dimensionless parameters with respect to contact time, bed height, and the ratio of external to intraparticle mass transfer resistance, respectively. The time dimensionless variable τ and the parameters ξ and δ are defined as
τ)
(
C0kf t -
z ν
)
n0
ξ)
(1 - )kf z ν
δ)
kfC0 kpn0
where kf (s-1) and kp ) 15Deff/Rp2 (s-1) are mass transfer coefficients in the external film and inside the solid phase, respectively. The experimental equilibrium isotherms are sufficiently favorable to justify the assumption of a rectangular isotherm. First of all, the external masstransfer coefficient kf (s-1) was estimated from the following correlation:19 2/3 1 - 1/3k′f Sc ) 1.85Re-2/3 ν
(19)
Figure 7. Breakthrough curves of nicotine on H+-form Amberlite IR120. Theoretical curves were calculated from the analytical solution for a rectangular isotherm in a single-component system. (a) C0 ) 3.1 mmol/L; (b) C0 ) 6.2 mmol/L; (c) C0 ) 9.2 mmol/L. H ) 0.174 m, W ) 22.5 g of dry resin, and T ) 25 °C.
The free diffusivity of nicotine in the solution was estimated from the Wilke-Chang equation.20 The value obtained was equal to 2.44 × 10-6 cm2/s. The values of τ and ξ can be calculated according to the definitions and the estimated values of kf. The value of the intraparticle effective diffusivity of nicotine, Deff (cm2/ s), was unknown. It was therefore obtained by matching the experimental data with the analytical solution of the breakthrough curve. A value of Deff equal to 2 × 10-7 cm2/s provided the best fitting. This value is in good agreement with the values obtained by Yoshida and Kataoka8 for the adsorption of amines on a quite similar gel type ion exchanger. The empirical correlation proposed in the mentioned work provides values
of the effective diffusion coefficients for nicotine (assuming a maximum molecule length of 1.152 nm) at concentrations of 3.1, 6.2, and 9.2 mmol/L ranging between 1.57 × 10-11 and 2.31 × 10-11 cm2/s. Experimental behavior was well predicted by theoretical curves, as can be seen in Figure 7. Thus the effective interdiffusion coefficients and the proposed model are sufficiently accurate to describe the behavior of the system for its industrial application. Although the diffusivity values were derived from the WilkeChang equation, they may be considered acceptable for practical purposes, taking into account the good fitting of the model to the experimental curves. It is also remarkable that the final capacity reached in the equilibrium experiments coincides with the value
(
)
kf )
6k′f 2Rp
(18)
Ind. Eng. Chem. Res., Vol. 37, No. 12, 1998 4789 Table 2. Summary of the Analytical Solution of the Breakthrough Curve for a Rectangular Isotherm and a Single-Component System in the Homogeneous Model ranges of τ and ξ
general solution δg1
x)1-
ξ exp(-τ/δ), δ
yj ) 1 - exp(-τ/δ)
τ g 0,
0eξeδ-1
1 x ) exp(δ - 1 - ξ), yj ) τ exp(δ - 1 - ξ) δ 1 1 - 1 /δ x ) yj ) 1 - 1 - exp(δ - 1 - ξ) exp δ δ 1 1 x ) yj ) exp τ - ξ + δ - 1 δ δ δ+1 δ 1 x ) yj ) 1 /δ exp -τ + ξ - δ + 1 + - ln δ+1 δ δ
1 0eτe , ξgδ-1 δ 1 δ+1 τ g , δ - 1 e ξ e δ - 1 + ln δ δ 1 δ+1 δ+1 1 e τ e ξ - δ + 1 + - ln , ξ g δ - 1 + ln δ δ δ δ δ+1 δ+1 1 τ g ξ - δ + 1 - - ln , ξ g δ - 1 + ln δ δ δ
δe1 x ) exp(-ξ), yj ) τ exp(-ξ) x ) yj ) 1 - {1 - exp(δ - 1 - ξ)} exp{(1 - τ)/δ} x ) yj ) exp(τ - ξ - 1)
0 e τ e 1, ξ g 0 τ g 1, 0 e ξ e ln(1 + δ) 1 e τ e ξ + 1 - ln(1 + δ),
{
} {(
(
)}
)
[{
)} ]
(
δ exp[{-τ + ξ + 1 - ln(δ + 1)}/δ] x ) yj ) 1 δ+1
(
(
(
τ g ξ + 1 - ln(1 + δ),
)
)
)
(
(
)
)
ξ g ln(1 + δ)
ξ g ln(1 + δ)
Table 3. Summary of Experimental Conditions and Parameters in Breakthrough Runs flow rate (mL/min)
C0 (mmol/L)
Re
Kf (s-1)
n0 (mmol/g)
δ
60 60 60
3.1 6.2 9.2
2.068 2.068 2.068
0.492 0.492 0.492
3.01 3.04 3.11
0.194 0.387 0.581
110 110 110
3.1 6.2 9.2
3.791 3.791 3.791
0.602 0.602 0.602
2.92 2.82 2.95
0.237 0.474 0.711
160 160 160
3.1 6.2 9.2
5.514 5.514 5.514
0.682 0.682 0.682
2.92 3.13 3.03
0.269 0.537 0.806
calculated from the isotherm of pH ) 7 for each concentration, as shown in Table 3. Elution Curves. For the elution of nicotine, there are two possibilities: (i) the direct regeneration with a strong acid; (ii) the elution with an adequate alkaline solution and then regeneration with a strong acid. The first alternative seems to be easier and less expensive, but taking into account the equilibrium behavior of nicotine, the second one will be necessarily more selective when different cations are adsorbed in the resin phase. For this reason, the elution of nicotine with an aqueous solution of NH3 was attempted. A first elution run was performed using a 0.147 M ammonia solution. The concentrations of nicotine and NH3 were measured. The effluent concentrations of both species are shown in Figure 8. Theoretical elution curves for nicotine in Figures 8 and 9 have been calculated from the analytical solution for a rectangular isotherm in a single-component system.13 Their analytical equations are summarized in Table 4. The theoretical curve for ammonia breakthrough has been obtained from the previously described model using Dw ) 1.96 × 10-5 cm2/s (from ref 21) for the ammonia free solution diffusivity and Deff ) 2.1 × 10-6 cm2/s (from ref 8) for its effective diffusivity. The fit between the experimental curves and the theoretical ones is not very good because the plateau zone of the elution curve, with the present column length (175 mm), is small and the final effects are of considerable importance. The concentration of nicotine, reached in the plateau zone, is about half of the concentration of ammonia in the feed solution; that is, each nicotine mole in the resin is approximately exchanged by two ammonia moles.
Figure 8. Elution curve of nicotine and breakthrough curve of ammonia on H+-form Amberlite IR120. Theoretical curves were calculated from the analytical solutions for a rectangular isotherm in a single-component system. F ) 60 mL/min, H ) 0.174 m, W ) 22.5 g of dry resin, and T ) 25 °C.
The maximum value of nicotine concentration in the effluent can be enlarged, but the efficiency in molar terms decreases, as can be seen in Figure 10, for ammonia concentrations of 1.17 and 3 M. For large ammonia concentrations, the plateau of the elution curves disappears as predicted by the theoretical model. Finally, Figure 10 shows the breakthrough curves of nicotine using as feed an aqueous extract from tobacco wastes (1 g/L of nicotine). This extract also contains an important amount of potassium (2.7 g/L) and small amounts of calcium and sodium. The breakthrough curves for sodium and potassium and the pH are also presented in Figure 10; that for calcium is not presented. Breakthrough curves of potassium and sodium show a peak due to the greater affinity of the resin for nicotine, which progressively displaces both cations from the resin. The concentration of nicotine in the effluent does not reach the inlet value until a period of time later meanwhile the rest of the cations in the resins are being eluted. The elution curves using 1.17 M ammonia for the experiment with a tobacco extract are shown in Figure 11. The nicotine peak appears first but, with the present column length, is not being very selectively eluted. Potassium is released a bit later, reflecting the
4790 Ind. Eng. Chem. Res., Vol. 37, No. 12, 1998
Figure 9. Influence of ammonia concentration on the elution of nicotine from Amberlite IR120. Theoretical curves were calculated from the analytical solution for a rectangular isotherm in a singlecomponent system. F ) 60 mL/min, H ) 0.174 m, W ) 22.5 g of dry resin, and T ) 25 °C.
Figure 10. Breakthrough curves of a tobacco extract (nicotine, potassium, sodium, and pH) on H+-form Amberlite IR120. F ) 60 mL/min, H ) 0.174 m, W ) 22.5 g of dry resin, and T ) 25 °C.
order of relative affinity for the resin. Although separation under the present conditions is not achieved, the general trend of the elution process seems to be clear.
Figure 11. Elution curves using NH3 (1.17 M) for nicotine and potassium recovered from a tobacco extract on H+-form Amberlite IR120. F ) 3.6 L/h, H ) 0.174 m, W ) 22.5 g of dry resin, and T ) 25 °C.
New experimental work and a computer program to simulate the behavior of the adsorption and elution of nicotine from tobacco extracts (a multicomponent system) will be developed in continuing studies. Conclusions To develop a method to separate and purify nicotine from extracts of tobacco wastes, the possibility of using an H+-form strong-acid ion exchanger for adsorption of nicotine and also the desorption method using mainly aqueous ammonia solutions have been investigated. The following conclusions were drawn: 1. The recovery of nicotine from dilute aqueous solutions (extracts of waste tobacco leaves) by ion exchange on an H+-form ion exchange resin appears technically and economically feasible. 2. Nicotine is strongly adsorbed on an H+-form acidic ion exchanger. Equilibrium isotherms are affected by the pH of the external solutions. Five possible kinds of interactions between the different nicotine ionic forms and the resin active sites have been proposed to explain the equilibrium behavior. 3. Theoretical equations for equilibrium isotherms accounting for the dependence on pH have been developed. The five equilibrium constants that describe the behavior of the system and an empirical equation
Table 4. Summary of the Analytical Solution of the Elution Curve for Irreversible Desorption in the Homogeneous Model ranges of τ and ξ
general solution δe1
ξ exp(-τ/δ), yj ) exp(-τ/δ) δ 1 x ) 1 - exp(δ - 1 - ξ), yj ) 1 - τ exp(δ - 1 - ξ) δ 1 1 - τ /δ x ) yj ) 1 - 1 - exp(δ - 1 - ξ) exp δ δ 1 1 x ) yj ) 1 - exp τ - ξ + δ - 1 δ δ δ+1 δ 1 exp -τ + ξ - δ + 1 + - ln x ) yj ) /δ δ+1 δ δ
1 0eτe , ξgδ-1 δ 1 δ+1 τ g , δ - 1 e ξ e δ - 1 + ln δ δ 1 δ+1 δ+1 1 e τ e ξ - δ + 1 + - ln , ξ g δ - 1 + ln δ δ δ δ δ+1 δ+1 1 τ g ξ - δ + 1 - - ln , ξ g δ - 1 + ln δ δ δ
δe1 x ) 1 - exp(-ξ), yj ) 1 - τ exp(-ξ) x ) yj ) {1 - exp(δ - 1 - ξ)} exp{(1 - τ)/δ} x ) yj ) 1- exp(τ - ξ - 1)
0 e τ e 1, ξ g 0 τ g 1, 0 e ξ e ln(1 + δ) 1 e τ e ξ + 1 - ln(1 + δ),
x)
{
( [{
} {( )
)}
(
δ x ) yj ) exp[{-τ + ξ + 1 - ln(δ + 1)}/δ] δ+1
)} ]
τ g 0,
0eξeδ-1
(
(
(
τ g ξ + 1 - ln(1 + δ),
)
)
)
ξ g ln(1 + δ)
ξ g ln(1 + δ)
(
(
)
)
Ind. Eng. Chem. Res., Vol. 37, No. 12, 1998 4791
relating the ratio between the different ionic forms of nicotine inside the resin and the pH have been obtained. 4. The equilibrium isotherm for the nicotine-ammonia system on Amberlite IR-120 has been obtained. The ion exchanger exhibits a very large affinity for ammonia. 5. The experimentally observed breakthrough curves for pure nicotine are well predicted from the analytical solution for a rectangular isotherm system with external mass transfer and intraparticle homogeneous diffusion. 6. The values of the final capacity reached in the breakthrough runs agreed fairly well with those expected from the equilibrium experiments. Nicotine can be eluted with an ammonia solution. 7. The experimental behavior when nicotine is recovered from a tobacco extract agreed with that expected by taking into account the relative affinity of the different components of the extract for the resin phase. Acknowledgment We gratefully acknowledge a fellowship awarded to M.A.G. by the AECI (Spanish Agency for Iberoamerican Cooperation). Insightful discussions with Prof. Alirio Rodrigues (University of Porto) are also acknowledged. Nomenclature a: first parameter of eqs 14-17 b: second parameter of eq 14-17 Ca: analytical liquid-phase concentration of nicotine, mmol/L CN: concentration of different species of nicotine in the liquid phase, mmol/L CH: concentration of hydrogen ions in the liquid phase, mmol/L C0: initial bulk liquid-phase concentration, mmol/L C*: equilibrium liquid-phase concentration, mequiv/L Deff: effective intraparticle interdiffusion coefficient, cm2/s Dw: free diffusion coefficient of nicotine estimated, cm2/s F: volumetric flow, mL/min Ka1: first acidity constant of nicotine Ka2: second acidity constant of nicotine KiN: equilibrium constants of eqs 10 kf: liquid-phase mass-transfer coefficient, s-1 k′f: liquid-phase mass-transfer coefficient, cm/s KL: parameter of eq 2, mmol2/(g L) kp: resin-phase mass-transfer coefficient (kp ) 15Deff/Rp2), s-1 n/a: equilibrium solid-phase concentration of nicotine, mmol/g n/N: equilibrium solid-phase concentration of the nicotine species, mequiv/g n/H: equilibrium solid-phase concentration of hydrogen ions, mequiv/g n0: resin-phase concentration in equilibrium with the feed, mmol/g p: ratio between the species of nicotine in the resin phase Q: resin capacity, mmol/g Rp: radius of resin particle, cm Re: 2RpνF/µ(1 - ) t: time, s v: interstitial fluid velocity, cm/s V: volume of bulk solution, L W: weight of resin particles, g
x: y: z: :
molar fraction of the species in solution (x ) C/C0) molar fraction of the species in the resin phase (y ) n/n0) distance through the bed, cm bed void fraction
Literature Cited (1) Millen, C. L.; Murphy, R. W. Countercurrent Extraction of Nicotine from Tobacco Juice. Ind. Eng. Chem. Res. 1993, 32, 3056. (2) Kingsbury, A. W. Recovery of nicotine by ion exchange. Chem. Eng. Prog. 1948, 44, 497. (3) Narasimha Rao, N. C.; Chakraborty, L. Preliminary Studies with Ion Exchange Resins for Recovery of Nicotine from Tobacco Waste. Res. Ind. 1992, 37, 115. (4) Bhat, C. V.; Sindhi, P. C. Ion exchange column studies with nicotine choice of solvent and flow rate. Orient. J. Chem. 1993, 9, 246. (5) Jones, I. L.; Carta, G. Ion Exchange of Amino Acids and Dipeptides on Cation Resins with Varying Degrees of CrossLinking. 1. Equilibrium. Ind. Eng. Chem. Res. 1993, 32, 107. (6) Yoshida, H.; Kishimoto, N. Adsorption of Glutamic Acid on a Weakly Basic Ion Exchanger: Equilibria. Chem. Eng. Sci. 1995, 50, 2203. (7) Melis, S.; Markos, J.; Cao, G.; Morbidelli, M. Ion-Exchange Equilibria of Amino Acids on a Strong Acid Resin. Ind. Eng. Chem. Res. 1996, 35, 1912. (8) Yoshida, H.; Kataoka, T. Adsorption of Amine and Ammonia on an H+-Form Ion Exchanger. AIChE J. 1987, 42, 1805. (9) Yoshida, H.; Shimizu, K.; Kataoka, T. Recovery of Amine and Paints from Electrodeposition Wastewater by an H-Form Ion Exchanger: Desorption Process. Ind. Eng. Chem. Res. 1992, 31, 934. (10) Dye, S. R.; De Carli, J. P., II; Carta, G. Equilibrium Sorption of Amino Acids by a Cation Exchange Resin. Ind. Eng. Chem. Res. 1990, 29, 849. (11) Yoshida, H.; Shimizu, K.; Kataoka, T. Adsorption of Amine and Paints on an H-Form Resin from Electrodeposition Wastewater. AIChE J. 1990, 36, 1815. (12) Yoshida, H.; Kataoka, T. Recovery of Amine and Ammonia by Ion Exchange Method: Comparison of Ligand Sorption and Ion Exchange Accompanied by Neutralization Reaction. Solvent Extr. Ion Exch. 1986, 4, 1171. (13) Yoshida, H.; Kataoka, T. Irreversible Desorption of AmineH+-Type Resins by NaOH Aqueous Solution. Chem. Eng. J. 1989, 41, 117. (14) Yoshida, H.; Kataoka, T.; Ruthven, D. M. Analytical Solution of the Breakthrough Curve for a Rectangular Isotherm System. Chem Eng. Sci. 1984, 39, 1489. (15) Rodriguez, J. F.; Valverde, J. L.; Rodrigues, A. E. Measurements of Effective Self-Diffusion Coefficients in a Gel-Type Cation Exchanger by the ZLC Method. Ind. Eng. Chem. Res. 1998, 37, 2020. (16) Willits, C. O.; Swain, M. L. Nicotine Determination by the UV-Vis Method. Anal. Chem. 1950, 22, 430. (17) CRC Handbook of Chemistry and Physics, 70th ed.; Weast, R. C., Ed.; CRC Press: Boca Raton, FL, 1987. (18) Marquardt, D. W. An algorithm for least squares estimation of nonlinear parameters. J. Soc. Ind. Appl. Math. 1963, 2, 431. (19) Kataoka, T.; Yoshida, H.; Yamada, T. Liquid-Phase Mass Transfer in Ion Exchange Based on the Hydraulic Radius Model. J. Chem. Eng. Jpn. 1973, 2, 172. (20) Reid, C. R.; Prausnitz, J. M.; Poling, E. B. The Properties of Gases and Liquids, 4th ed.; McGraw-Hill: New York, 1987. (21) Slater, M. J. The Principles of Ion Exchange Technology; Butterworth-Heinemann, Oxford, U.K., 1991.
Received for review March 31, 1998 Revised manuscript received July 20, 1998 Accepted August 4, 1998 IE9801958
