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Ind. Eng. Chem. Res. 1996, 35, 2856-2859
A Reversible Extraction Process of Phenethyl Alcohol, A Fragrance Stig E. Friberg,* Jiang Yang, and Tian Huang Center for Advanced Materials Processing and Department of Chemistry, Clarkson University, Potsdam, New York 13699-5814
An extraction/separation process for phenethyl alcohol is described. The extraction takes place into a solution of common hydrotrope, sodium xylene sulfonate, and the separation is achieved by addition of water to the water hydrotrope/phenethyl alcohol solution. The system was optimized for the ratio of the amount amount extracted fragrance to amount of water that needs to be evaporated for each extraction/separation cycle. Introduction Extraction of fragrances from natural materials is an important industrial process (Bauer et al., 1990). The early processes of this kind focused on organic solvents as the extraction medium, because most fragrance molecules are hydrophobic in nature with only insignificant solubility in water. However, environmental concerns brought forward alternative methods and the introduction of the extraction of fruit and juice aromas by liquid carbon dioxide in 1970 (Schultz and Randall, 1970) meant a new approach. It was soon discovered that the supercritical state was a significantly more efficient medium for extraction (Bott, 1980; McHugh and Ksukonics, 1986; Vallbrecht, 1982), and although hydrodistillation remains the extraction method of preference, supercritical extraction plays a role (Gerbault and Robic, 1994) in today’s fragrance industry. With this paper we would like to draw attention to hydrotropes (Friberg and Chiu, 1988; Balusubramanian and Friberg, 1993; Friberg et al., 1994) as an extraction agent for fragrances. Their aqueous solutions display the most pronounced solubilization capacity, and the separation of the fragrance from the hydrotrope solution is obtained by simple dilution with water. Evaporation of water restores the hydrotropic solution, and the repeated process is reversible. Experimental Section Materials: sodium xylenesulfonate (SXS) and phenethyl alcohol (PEA), 99+%, Aldrich Chemical Co., Inc., Milwaukee, WI; water, doubly distilled. Phase Diagram. The phase diagram was determined by visual and microscopic observation of samples after titration with one liquid component. Results and Discussion The phase diagram of water, sodium xylenesulfonate, and phenethyl alcohol is shown in Figure 1. The hydrotrope was soluble in water to 55% by weight, while the solubility of the phenethyl alcohol was limited to 2%. The phenethyl alcohol dissolved water to 7.5%; a molar ratio of 0.5. The phenethyl alcohol solution dissolved only insignificant amounts of sodium xylenesulfonate. The diagram is characterized by a large isotropic liquid solution L1; the aqueous solution of the hydrotrope, which solubilizes up to 60% by weight of phenethyl alcohol. The solubilization is initiated by 4% of sodium xylenesulfonate in water and increases suddenly when the hydrotrope concentration exceeds 9%. S0888-5885(95)00661-0 CCC: $12.00
Figure 1. Phase diagram of phenethyl alcohol-water-sodium xylenesulfonate.
The limitation for solubility of the hydrotrope corresponds to a water/hydrotrope weight ratio of 0.82; a mole ratio of 9.5. The entire range of the phenethyl alcohol solution was in equilibrium with crystalline hydrotrope, leaving its composition with maximum water in equilibrium with the aqueous solution of phenethyl alcohol. This latter factor facilitates the treatment of the extraction. The entire extraction/separation process is built on the specific shape of the solubilization by a hydrotrope (Friberg and Rydhag, 1970) with the large concentration of hydrotrope to initiate the solubilization and the extremely high solubilization maximum. Such a shape means that dilution by water leads to separation of the solubilized substance with high yield. The extraction process is modeled by addition of phenethyl alcohol to composition A (Figure 2). The maximum solubilization for this composition is at B (Figure 2). Dilution of the composition at B with water means that the total composition follows a straight line from B toward the water corner, line BCD (Figure 2). The process leads to phase separation indicated at C. Further dilution to composition D results in the separation of a phenethyl alcohol solution with maximum water content, P (Figure 2). The latter composition stays constant with added water, but the composition of the aqueous phase, L1, follows the line C to E, reaching the latter point when the added water gives a total composition at D. The weight ratio of separated phenethyl alcohol of composition P to the aqueous phase at E is proportional to the length ratio of the ED/DP. © 1996 American Chemical Society
Ind. Eng. Chem. Res., Vol. 35, No. 9, 1996 2857
Figure 2. Paths during extraction and separation of phenethyl alcohol.
Figure 3. Fractions of phenethyl alcohol (PEA) versus water fractions in the left boundary region L1 in Figure 1. Experimental points (×) and calculated values, eq 5 (s).
Figure 2 makes it obvious that extraction starting at A′ will be more efficient for the separation part than starting at composition A. The amount of separated phenylethyl alcohol solution versus the amount of added water may be obtained manually, but for optimization, in practice, computerization is necessary and the different lines must be described algebraically. In the following equations the weight fractions of the three components are given as w, h, and p, with initial conditions indicated by a subscript zero.
Line AB p ) 1 - w/wo;
p+w+h)1
(1)
Line BCD p ) pB(w - 1)/(wB - 1)
(2)
pD ) pB(wD - 1)/(wB - 1)
(3)
Figure 4. Percentage of separated 92.5% PEA solution versus weight of added water, with the initial weight of extract equal to 1.0 g. The initial extraction along line AB, wo ) 0.60 (Figure 2), having different fractions of PEA: (O) p ) 0.600; (2) p ) 0.500; (0) p ) 0.400; (b) p ) 0.300.
Point D
Line PD p - 0.925 ) (pD - 0.925)(w - 0.075)/(wD - 0.075) (4) Line C′E was found to follow a simple polynomial
p ) 0.6252 + 0.3897w - 2.3368w2 + 1.3057w3
(5)
with an R value of 0.999 98 as shown in Figure 3. Point E is found from a combination of line PD and line C′E.
1.3057w3 - 2.3368w2 + {0.3897 - (pD - 0.925)/(wD - 0.075)}w 0.2998 + 0.075(pD - 0.925)/(wD - 0.075) ) 0 (6) The total weight in any initial point of separation is assumed at 1.0 g. Two series of points, wo ) 0.60 and 0.80 for point A and point A′ (Figure 2), were chosen with varied amounts of PEA dissolved. Adding water meant the compositions moving along the lines BCD and B′C′D′. The amount of the solution 92.5% PEA as a percentage
Figure 5. Percentage of separated solution containing 92.5% PEA versus weight of added water, with the initial weight of extract equal to 1.0 g. The initial extraction along line A′B′, wo ) 0.80, having different fractions of PEA: (O) p ) 0.473; (2) p ) 0.350; (0) p ) 0.250; (b) p ) 0.150.
of the total sample weight is plotted against the ratio of water added to the amount before separation (Figures 4 and 5). The results gave a distinct maximum of the alcohol solution versus weight ratio. Furthermore, the maximum was reduced with reduced p, and, in addition,
2858 Ind. Eng. Chem. Res., Vol. 35, No. 9, 1996
Figure 6. Maximum extract containing 92.5% PEA versus different fractions of water, wo.
Figure 7. Ratio of BF/EF at maximum extract containing 92.5% PEA versus different fractions of water, wo.
Table 1. Effect of Different wo on Maximum Extract along the Boundary ECB
Table 2. Effect of Different wo on the Ratio of BF/EF along the Boundry ECB
maximum mp/mtotal, %
wo
wB
pB
wF
addition of water (g)
20.41 22.97 24.14 24.33 24.22 23.20 21.22 18.53 15.49 12.39 9.50 4.92
0.603 0.693 0.747 0.778 0.786 0.812 0.832 0.846 0.857 0.866 0.875 0.899
0.240 0.300 0.350 0.390 0.400 0.450 0.500 0.550 0.600 0.650 0.700 0.800
0.602 0.567 0.531 0.499 0.491 0.446 0.399 0.350 0.300 0.250 0.200 0.110
0.428 0.517 0.583 0.625 0.633 0.674 0.709 0.737 0.763 0.787 0.813 0.866
1.341 0.992 0.789 0.671 0.644 0.559 0.501 0.482 0.490 0.527 0.610 0.705
it should be observed that more water was required to obtain the maximum. Variation of the initial hydrotrope concentrations A, A′, etc. (Figure 2) leads to a most pronounced difference in the extracted and separated amounts. As an example, the maximum percentage at wo ) 0.8 in Figure 5 (23.94%) was higher than that at wo ) 0.6 in Figure 4 (20.04%). Hence, in order to find the maximum extract, the initial composition of the aqueous solution of hydrotrope was varied from 0.24 to 0.80 weight fraction of water, wB. A BASIC computer program was written to determine the maximum extraction for each point with a 0.01 interval in water weight fraction along the boundary line BCE (Figure 2). Each value of the water content gave a maximum similar to those in Figures 4 and 5. These maxima are plotted in Figure 6, and the maximum extract, 24.3% containing 92.5% PEA, was found at composition wB ) 0.390 and pB ) 0.499 with 0.671 g of water added. This point corresponded to starting point A, wo ) 0.778, and Table 1 shows the numerical values of other corresponding points. However, the conditions giving maximum phenethyl alcohol solution separated may not necessarily be optimal from an economic point of view. Instead, the ratio of the amounts BF to EF, with Figure 2 showing the ratio of the amount phenethyl alcohol solution separated to the amount of water to be evaporated for each cycle, is the optimum. In order to find this optimum, a series of points along the boundary line of BCE were chosen associated with wo and the latter varied from 0.60 to 0.90 with 0.01 intervals. Again, a BASIC program was written and used for the calculation. A maximum value of BF/EF,
BF/EF
wo
wB
pB
wF
addition of watera (g)
0.783 0.916 1.091 1.405 1.791 2.117 2.196 2.087 1.641 1.285
0.600 0.652 0.700 0.756 0.800 0.830 0.850 0.860 0.880 0.900
0.238 0.270 0.306 0.360 0.424 0.494 0.567 0.616 0.720 0.804
0.603 0.586 0.563 0.524 0.469 0.405 0.333 0.284 0.181 0.106
0.427 0.475 0.528 0.594 0.655 0.705 0.746 0.771 0.825 0.869
1.357 1.148 0.965 0.756 0.596 0.507 0.481 0.502 0.633 0.688
a
Corresponding to the maximum value of extract, mp/mtotal.
2.196, was found at wB ) 0.567 and pB ) 0.333 with 0.481 g of water added; this point corresponded to starting point A, wo ) 0.850. A plot of the mass ratio BF/EF (Figure 2) against water fraction wo is shown in Figure 7, and Table 2 shows the numerical values of other corresponding points. The results demonstrate that a reversible extraction separation method using a hydrotrope is readily optimized, and the results in Figure 7 demonstrate the optimization to be an essential preparation for the process. A simple determination of the phase diagram and a few hours of labor, combined with a suitable computer program, leave sufficient information to find the most economical initial concentration of hydrotrope in the aqueous solution. Acknowledgment This material is based upon work supported in part by the New York State Science and Technology Foundation and by Bristol Myers, Hillside, NJ. Literature Cited Balusubramanian, D.; Friberg, S. E. HydrotropessRecent Developments. Surf. Colloid Sci. 1993, 15, 197. Bauer, K.; Garbe, D.; Surburg, H. Common Fragrance and Flavor Materials, 2nd ed.; VCH Publishers: New York, 1990. Bott, T. R. Supercritical Gas Extraction. Chem. Ind. 1980, 228. Friberg, S. E.; Rydhag, L. Lo¨slichkeit and Assoziatiionsverha¨ltnisse Hydrotroper. Tenside 1970, 7, 80.
Ind. Eng. Chem. Res., Vol. 35, No. 9, 1996 2859 Friberg, S. E.; Chiu, M. Hydrotropes. J. Dispersion Sci. Technol. 1988, 9, 443. Friberg, S. E.; Brancewicz, C.; Morrison, D. O/W Microemulsions and Hydrotropes: The Coupling Action of a Hydrotrope. Langmuir 1994, 10, 2945. Gerbault, P.; Robic, Y. Supercritical Carbon Dioxide Extraction of Vanilla. Parfums, Cosmet., Aromes 1994, 117, 81. McHugh, M.; Ksukonics, V. Supercritical Fluid Extraction: Principles and Practice; Butterworths: London, 1986. Schultz, W. G.; Randall, J. M. Liquid Carbon Dioxide for Selective Aroma Extraction. Food Technol. 1970, 24, 1282.
Vallbrecht, R. Extraction of Hops with Supercritical CO2. Chem. Ind. 1982, 397.
Received for review November 2, 1995 Revised manuscript received February 9, 1996 Accepted February 21, 1996X IE950661I X Abstract published in Advance ACS Abstracts, August 15, 1996.
