3066
Ind. Eng. Chem. Res. 1993,32, 3056-3060
Countercurrent Extraction of Nicotine from Tobacco Juice D. Leslie C. Millen' and W. Raymond Murphy Department of Chemical Engineering, The Queen's University of Belfast, Belfast, Northern Ireland
The countercurrent extraction of nicotine from aqueous solution and tobacco juice, using kerosene and hexane as solvents, was investigated. A 57-mm-diameter column was operated in three modes: as a spray tower, packed with Raschig rings, and packed with Multifil high-efficiency packing. Volume-based mass-transfer coefficients and HTU (height of a transfer unit) values were evaluated for various solvent/liquid ratios and various p H values. The HTU values were found to vary between 10.1 and 0.7 m depending on the operating parameters selected.
Introduction In the industrial recovery of nicotine from tobacco, one possible process results in an aqueous tobacco juice containing nicotine together with other soluble plant matter and coloring. The nicotine can be recovered from this juice by solvent extraction. Traditionally kerosene has been used as the solvent in the first stage of the operation, the liquid-liquid extraction. The second stage consisted of stripping the nicotine-rich kerosene with 22% w/w sulfuric acid. This caused the formation of nicotine sulfate, which is insoluble in the kerosene, and permitted the solvent to be decanted off and recycled. Anumber of workers have reported studies of the water/ nicotine/kerosene system while some actually used tobacco juice in their work. Norton (1940) reported the distribution coefficients of nicotine between water and kerosene at 25 "C over a concentration range of 0.5-530 g/L. He also investigated the effects of acids and alkalis on the distribution coefficient. Claffey et al. (1950) determined the distribution coefficients of the system for concentrations ranging from 1 to 794 g/L over the temperature range 5-98 "C. They then carried out extraction trials using a 1.875-in.-diameter column packed to a height of 39 in. with either Raschig rings or Berl saddles. They investigated the effect of various sizes,of both types of packing, over the temperature range 21-84 "C. They used watednicotine solutions with a concentration of 0.1-0.5% nicotine but did not study tobacco juice. Griffin et al. (1952) studied the extraction of tobacco juice with kerosene. They reported a complete process for the production of nicotine sulfate from Nicotiana FUS~~CU This . process involved a water leaching followed by an energy-intensive clarification stage. The clarified juice was then solvent extracted using kerosene in a 4-in. column which was packed to a height of 12 f t with Raschig rings. This pilot plant scale unit was constructed using the data published by Claffey et al. (1950)and was actually a continuation of their work applied to the juice. As in the previous paper, the extraction was carried out at elevated temperatures, in this case mostly around 65 "C. The clarification stage in the above work seemed undesirable from two aspects. Firstly, from an economic viewpoint the heating of large volumes of water to almost boiling was unacceptable, and secondly, from a process aspect the heat might cause thermal degradation of the
* To whom correspondence should be addressed. Present address: Du Pont (UK)Ltd., Maydown Works, P.O. Box 15, Londonderry, BT47 lTU, Northern Ireland. 0888-5885/93/2632-3056$04.00/0
1 SOLVENT
IRAFFINATE
I
Figure 1. Extraction equipment.
nicotine. The latter point is not too valid considering the comment of Jarboe and Rosene (1961)concerning thermal stability, nevertheless it was taken into account in the present work. The object of the work described in this paper was to compare the effectiveness, at ambient temperature, of kerosene and hexane in extracting nicotine from aqueous tobacco juice which had not been clarified in any way.
Experimental Section The equipment arrangement is shown schematically in Figure 1. The complete apparatus consisted of the extraction column, inlet and exit lines, rotameters, storage and receiving vessels, and centrifugal pumps. The column was constructed from 57-mm-i.d. Perspex tubing 1.92 m long with 6-mm-i.d. inlet and outlet tubes. The dispersed liquid distributor consisted of a 40-mmdiameter flat plate drilled with 42 holes, each 2.5-mm diameter. The distributor was mounted on a piece of 34mm-id., 16-cm-long tube to form an internal settling chamber at the continuous-phase exit. In all the experiments the water or the tobacco juice was the continuous phase and the solvent was dispersed so the interface always occurred at the top of the column. This was maintained at approximately 15cm from the top of the column; thus the effective extraction height was 1.61 m. 0 1993 American Chemical Society
Ind. Eng. Chem. Res., Vol. 32, No. 12,1993 3057 The inlet and outlet lines used were suitably sized plastic tubing. Rotameters were used to regulate the flows, but volumetric measurements were made on the exit streams. The height of the interface was regulated by a pinch clamp on the continuous-phase exit line. Each pump was equipped with a bypass system to return fluid to the storage vessels. The storage vessels for the continuous and dispersed phases were of 50- and 25-L capacity, respectively. Experimental conditions were such that during certain runs the dispersed-phase vessel had to be refilled. The temperature was measured at three points on the column: 6 cm above the interface, halfway up the column, and 6 cm below the distributor. This was carried out using a digital thermometer, and the thermocouple wires were taped to the column wall. During the investigations the temperature varied from top to bottom of the column by a maximum of 2 "C. The column was operated in three modes: as a spray tower, packed with glass Raschig rings, and packed with Multifil high-efficiency packing. The glass Raschig rings used in this work were 6-mm diameter and were packed onto layers of 14-mm-diameter ceramic Raschig rings which in turn were placed on the distributor, which provided a suitable base. The packing was taken to 4 cm below the continuous-phase inlet pipe which gave an overall packed height of 1.55 m. The Multifil packing is a multifilament knitted mesh packing which is manufactured by Knitmesh Ltd. and supplied in 100-mm lengths. I t has a contact surface of 1600 m2/m3, a free volume of 94.592, and a density of 450 kg/m3. Fifteen sections of packing were used, with every third roll being Variknit. Variknit is a special form of Multifil with a lower density of mesh at the top of the roll than at the bottom. This variation in density of the mesh tends to change the liquid flow pattern in the mesh, resulting in a redistribution of the liquid within the column. The packing, which was a tight fit inside the column, was commenced 3 cm above the distributor, which meant that it ended 6 cm below the continuous-phase inlet pipe.
Materials The kerosene used in this work was commercial "pink" paraffin which had a measured specific gravity of 0.789 at 20 "C. The hexane used was described as a 60-80 "C fraction from petroleum; it had a specific gravity of 0.675 at 20 "C. Tap water was used to make up the solutions and juices, the juice being produced by leaching tobacco leaf waste for 24 h using a liquid/solid mass ratio of 101. To obtain the actual nicotine concentration required (1, 3, and 5 g/L), each batch of juice was analyzed and then spiked with purified distilled nicotine.
Analysis In the course of this work the nicotine content of water, tobacco juice, and hexane had to be estimated. For the nicotine/water/juice mixtures the method used was ultraviolet spectrophotometry as proposed by Willits et al. (1950). Their method was modified with reference to Harvey et al. (1967) and Bangarayya et al. (1971). The modification permitted the deletion of a time-consuming steam distillation and ita replacement with an activated carbon, Darco G60, clean-up stage to remove impurities which interfered with the analysis. The absorbance was measured, using a Perkin-Elmer which UV-vis Model 550S,at three wavelengths: at ,A,
was 259 nm and at 23 nm on either side of the maximum, i.e., 236 and 282 nm. The relationship between the absorption values was given by Willits et al. (1950) as A'259 = 1.059(A259- 0-5(A2,,
+482))
(1)
where A'259 is the corrected absorbance contributed by the nicotine in the solution. A calibration line of absorbance versus nicotine concentration was produced and used to read off the concentration of nicotine in the samples. The nicotine content of the kerosene and hexane was estimated using a nonaqueous titration detailed by Aktiebolaget Leo (1987). In this method the solvent (containing nicotine) was dissolved in acetic acid and titrated with a standard solution of perchloric acid in acetic acid, using crystal violet as an indicator.
Results and Discussion The investigations were conducted at three pH values: 9, 11, and 13. The pH of 9 was obtained without the addition of any alkali to the tobacco juice and was actually between 8.6 and 9.1 depending on the batch of tobacco used. Sodium hydroxide was added to produce a pH of 11. The pH of 13 was obtained by making the tobacco juice a 0.5 M solution of sodium hydroxide, i.e., 20 g/L. During each investigation the pH of the solution did not change appreciably as extraction progressed. Three solvent to liquid ratios, 1:1, 1.51,and 2:1, were used to obtain a quantitative appreciation of extraction efficiency with increasing quantity of solvent. The flooding capacities of the column were measured before the extraction commenced. This was done by maintaining a constant flow of continuous phase and then increasing the dispersed-phase flow until droplets had just started to leave in the exit stream. The values obtained were approximate only since the column became unstable as flooding approached. Precise values were not required since the results were only used to select appropriate flow rates of the two phases for the extraction operation. Before any samples were taken the column was operated at steady-state conditions until the continuous phase had been replenished three times. As the run neared completion, samples of the raffinate and extract were withdrawn every few minutes and then a final quantity of approximately 3 L of both outlet streams were collected as average equilibrium samples. The samples collected during the run provided information as to how well the system had approached equilibrium. In fact the results were invariably very close to the final samples, proving that equilibrium had been attained. Actually, equilibrium appeared to be attained after only a few mintues operation. The experimental data obtained were treated by the application of an equation taken from Coulson and Richardson (1983). Although widely used to calculate mass-transfer coefficients from experimental results, this equation does not consider axial mixing but is based on the assumption of plug flow. Differential extractors are subject to axial mixing, and the real (axial mixing) concentration profiles show a smaller concentration driving force than those for plug flow. In particular spray towers have so much back mixing that they approximate to stirred tanks. The equation can be written as NIB = K,aV log mean AC,
The log mean ACw is defined as
(2)
Ind. Eng. Chem. Res., Vol. 32, No. 12, 1993
I
Initial Nicotine Concentration 3g/l Temperature 20 OC pH 11
SOLVENTLIQUID RATIO 1 5 1
10
-
5-
1 .o
0.5
0.0
Water flowrate (litreshinUte) Figure 2. Volume-based mass-transfer coefficient versus water flow rate for the spray tower using kerosene and aqueous solutions. Table I. Scope of Work Using Kerosene aq nicotine soln at solvent/soln ratio for feed concn (g/L)
1 PH 9 pH 11 pH 13
1:l 3 X
5
1
1.51 3
5
1
X
2:1 3 X
5
tobacco juice at solvent/juice ratio for feed concn (g/L) 1:l 1.51 2:l 1 3 5 1 3 5 1 3 5 x x x x x x x x x x x x x x x X
WWl - ACw2)/ln~ACw1/ACw2),
(3) where ACWland ACw2are the concentration driving forces at either end of the column. AC,, = C,, - BC,,
(4)
AC,, = C,, - BC,,
(5)
The volume-based mass-transfer coefficient, K 4 , can then be used to calculate the overall height of a transfer unit, HTU, based on the raffinate (w) phase, by applying a further equation from Coulson and Richardson (1983) as follows: HTU = L,/K,a (6) Concentration differences were taken as the differences between the observed water concentration and that which would be in equilibrium with the observed kerosene concentration. The latter was calculated using distribution coefficientareported by Norton (1940),Claffey et al. (1950), and Millen (1988).
Extraction Using Kerosene Table I indicates the work carried out using kerosene as solvent in the column operated as a spray tower. Two further runs were then carried out at a feed concentration of 3 g/L and a pH of 11 with, firstly, the column packed with Raschig rings and, secondly, the column packed with Multifil. The variation of K d with water (continuous phase) flow rate took the form of straight lines which passed
X
X
Table 11. Gradients of Graphs Obtained Using Kerosene and Tobacco Juice in a Spray Column gradient at solvent/liquid ratio
feed concn
WL) 1 3 1 3 5 3
3 3
PH 1:l 1.5:l 9 6.9 8.2 9 6.9 7.9 11 6.0 7.6 11 6.5 7.6 11 6.1 9.4 13 8.7 13.9 Column Packed with Raschig Rings 11 12.8 19.1 Column Packed with Multifil 11 22.5 26.5 ~
~~
2:1 10.8 10.8 11.8 11.8 13.3 17.2 32.9 35.7
through the origin as observed by Claffey et al. (1950). A typical example is presented in Figure 2, and the gradients of the other lines are presented in Table 11.
Extraction Using Hexane Table I11 indicates the work carried out using hexane as solvent with the column operated as a spray tower. This work was continued at a concentration of 3 g/L and pH values of 11and 13in the column packed with Multifil and the same concentrations and a pH of 11in the column packed with Raschig rings. A typical graph is presented in Figure 3, and Table IV lists the gradients of the other graphs. The results for both solvents show that the volumebased mass-transfer coefficient does not vary with con-
Ind. Eng. Chem. Res., Vol. 32, No. 12, 1993 3059 50
Initial nicotine concentration 3g/l Temperature 200C pH 11 40
SOLVENTNQUIDRATIO 1.51
20-
10
-
0.0
1 .o
0.5
1 5
Water Flowrate (litredminute) Figure 3. Volume-based mass-transfer coefficient versus water flow rate for the spray tower using hexane and aqueous solutions. Table 111. Scope of Work Using Hexane aq nicotine soln at solvent/aoln ratio for feed concn (g/L) 1:l 1.51 2:l 1 3 5 1 3 5 1 3 5 pH 11 X X X pH 13 Table IV. Gradients of Graphs Obtained Using Hexane and Tobacco Juice in a Spray Column gradient at feed solvent/liquid ratio concn k."./ L ). DH 1:1 1.5:l 2:1 19.5 11.6 17.2 1 11 21.8 18.6 3 11 11.9 21.3 16.3 5 11 11.2 31.6 27.1 1 13 23.2 29.9 28.0 3 13 16.4 5 13 24.2 27.6 30.6 Column Packed with Raschig Rings 3 11 24.8 40.5 65.4 Column Packed with Multifil 3 11 67.4 77.0 86.2 3 13 77.2 86.8 92.4
centration, over the range investigated. This agrees with the results of Claffey et al. (1950), who found the distribution coefficient to be relatively constant up to 10 g/L. The mass-transfer coefficient increases with pH for both solvents, but only at relatively high concentrations of alkali: 0.5 M solutions. This agrees with the results reported by Norton (19401, who stated that high concentrations of sodium hydroxide reduce the solubility of nicotine in water and thus make extraction by organic solvents easier. The increase with pH is greater for kerosene than for hexane. These observations simplified the next stage of the analysis of the results, calculation of HTU values. The experimental data were reduced to eight different conditions at three solvent/liquid ratios, and the results are presented in Table V. All values were calculated from the experimental data at a concentration of 3 g/L. As found
tobacco juice at solvent/juice ratio for feed concn (g/L) 1:l 1.51 2:l 1 3 5 1 3 5 1 3 5
x x
x x
x x
x x
x x
x x
x x
x x
x x
Table V. HTU Values (in m) for Various Conditions (Based on Plug Flow Assumption) kerosene hexane
E:'
'pray raschig multifil raschig multifil tower solvent/ rings packing - rings packing liquid pH pH pH pH pH pH pH . pH ratio 11 13 11 11 11 13 11 11 1:l 10.1 7.5 5.1 2.9 5.5 3.9 2.6 0.9 1.51 8.6 4.7 3.4 3.5 2.3 2.5 1.6 0.8 2:l 5.5 3.8 1.9 1.8 3.0 2.2 1.0 0.7
by Griffin et al. (19521, HTU values decreased as the solvent ratio was increased. The HTU values show an almost 10-fold increase with hexane and Multifid compared to kerosene in a spray tower. A reduction in flow rate of the continuous phase to onethird of the spray tower value was required, but the benefits outweigh the disadvantage since a much more concentrated lower volume solution will be provided for use in the next processing stage.
Conclusions Considering the investigation with kerosene in a spray tower, the volume-based mass-transfer coefficient was found to increase with increasing solventlliquid ratio and with increasing tobacco juice flow rate. The mass-transfer coefficient did not vary with concentration over the range studied (1-5 g/L). The value was also unaffected by pH until relatively high concentrations of alkali were used. A 0.5 M solution increased the value by a factor of around 1.6 depending on the solvent ratio used. When the column was packed with Raschig rings, the mass-transfer coefficient increased by a factor of around
3060 Ind. Eng. Chem. Res., Vol. 32, No. 12, 1993
2.4. However, the flow rate of continuous phase had to be reduced to one-third of the spray tower value to prevent flooding. A further increase in the mass-transfer coefficient, by a factor of 3.0, was obtained when the column was packed with Multifil high-efficiency packing, but again the flow rate had to be reduced to prevent flooding. Hexane proved to be a good choice of solvent for the operation. I t is significantly more effective than the kerosene, the common solvent used industrially. Initial valuesobtained with it were just over twice those obtained using kerosene. As with kerosene, the mass-transfer coefficient increased with increasing solvent/liquid ratio and with increasing continuous-phase flow rate but did not depend on concentration over the range investigated. The pH value did not appear to affect the mass-transfer coefficient for hexane as much as it had affected the value for kerosene. In conclusion, the results obtained from this work show that liquid-liquid extraction of nicotine from unclarified tobaccojuice is possible. Kerosene, the traditional solvent, proved to be rather poor in its capability to extract the nicotine, but hexane was identified as a much better solvent, being about twice as good as kerosene.
Acknowledgment The authors thank Mr. J. A. Humphrey, owner and managing director of Nicobrand Ltd., for his assistance and the generous supply of tobacco waste used in the investigations. Nomenclature N / 8 = moles of solute transferred in unit time, mol/s K, = average overall extraction coefficient, m/s
specific surface area coefficient (contact area per unit volume), mVm3 V = effective volume of the equipment, m3 C = actual solute concentration, m0l/m3 C, = actual solute concentration in phase w,mol/m3 C, = actual solute concentration in phase s, m0l/m3 B = distribution coefficient at equilibrium C$C, K& = volume-based mass-transfer coefficient, l/s L, = velocity of the aqueous phase, m/s HTU = height of a transfer unit, m a =
Literature Cited Aktiebolaget Leo Pharmaceutical Company, Sweden. Private communication to Nicobrand Company, Northern Ireland, 1987. Bangarayya, M.; Narasimhamurty, Y. C. H.; Pal, N. L. Tob.Sci. 1971,11,84.
Claffey, J. B.; Badgett, C. 0.;Skalamera, J. J.; Macpherson-Philips, G. W. Ind. Eng. Chem. 1950,42 (l), 166. Coulson, J. M.; Richardson, J. F. Chemical Engineering; Pergamon Press: Oxford, 1983; Vol. 2, pp 610-615. Griffin, E. L.;Macpherson-Philips, G. W.; Claffey, J. B.; Skalamera, J. J.; Strolle, E. 0. Znd. Eng. Chem. 1952, 44 (2), 274. Harvey, W. R.; Badgett, C. E.; Resnik, F. E. Tob.Sci. 1967,11,84. Jarboe, C. H.; Rosene, C. J. J. Chem. SOC. 1961, No. 2,2455. Millen, D. L. C. Ph.D. Thesis, The Queen's University of Belfast, 1988. Norton, L. B. Ind. Eng. Chem. 1940,32 (2), 241. Willits, C. 0.;Swain, M. L.; Connelly, J. A.; Brice, B. A. Anal. Chem. 1950,22 (3), 430. Received for review May 17, 1993 Revised manuscript received August 26, 1993 Accepted September 13, 1993' e
Abstract published in Advance ACS Abstracts, November
1, 1993.
