samples coated with polyurethane. Three temperatures were used, and the data for both water and a 0.15 M saline solution as the source for diffusion are shown. The calculated values shown are those calculated for the water source and were computed by using the diffusivity and saturation concentration at the appropriate temperature, but the adsorption equilibrium isotherm a t 25 "C-the only moderate temperature for which Young's (1968) data were available-was used.
I O = surface leakage current at reference condition (30% relative humidity a t 26 "C), A a = constant of proportionality e = limiting surface concentration of water, g/cm* u = surface conductivity, (ohm/square)-' uo = surface conductivity at reference condition (30% relative humidity at 26 " C ) , (ohm/square)-l t = time, h x = distance,cm Literature Cited
Conclusions The results show that the postulated mechanism for surface conductance is supported by the experimental results and that the simple governing equations lead to the prediction of a surface conductivity which is compatible with that which is measured. Only the value of the fraction of surface sites which remain open to adsorb water after the dielectric surface is coated need be determined from data. All other parameters can be measured by independent means. Nomenclature a = constant in eq 4, cm3/g c = concentration, g/cm3 Ci = concentration of water at the dielectric polymer interface, g/cm3 Co = initial concentration, g/cm3 C, = surface concentration (of adsorbed water), g/cm2 ( C s ) o = surface concentration at reference condition (30% relative humidity a t 26 "C), g/cm2 C, = saturation concentration, g/cm3 or g/g I = surface leakage current, A
Barrie. J. A., Machin, D., J. Macromol. Sci.-Phys., 83 (4), 645-672 (Dec 1969a). Barrie, J. A.. Machin, D., J. Macromoi. Sci.-Phys., 83 (4), 673-692 (Dec 1969b). Barrie, J. A,, "Water in Polymers," chapter in "Diffusion in Polymers," J. Crank and G. S.Park, Ed., Academic Press, New York. N.Y., 1968. Crank, J., "The Mathematics of Diffusion," Oxford University Press, England, 1956. Crank, J., Park, G. S., "Methods of Measurement," Chapter in "Diffusion in Polymers," J. Crank and G. S. Park, Ed., Academic Press, New York, N.Y., 1968. Kawasaki, K., "Water Vapor Adsorption and Wettability of Organic High Polymers and Glasses," Researches of the ElectrotechnicalLaboratory, No. 690, Tokyo, Japan (in Japanese), Nov 1968. LaDidus. L.. Diaitai ComDutation for Chemical Enaineers." McGraw-Hill, New 'York, N.Y., 1562. ' Richman, D., Long, F. A,, J. Am. Chem. SOC.,82,509-513 (1960). Schneider, N. S., Dusablon, L. V., Snell, E. W., Prosser, R . A,, J. Macromoi. Sci.-Phys., 83 (4), 623-644 (Dec 1969). Schneider, N. S.,Dusablon, L. V., Spano, L. A., Hopfenberg, H. B., J. Appi. Poly. Sci., 12, 527-532 (1968). White, M. L., Roc. I€€€, 57, No. 9 (Sept 1969). Yang, H. W., M.S. Thesis, University of Utah, 1974. Yasuda, H., Stannett, V., J. Poly. Sci., 57,907-923 (1962). Young, G. J., J. Colloid Sci., 13,67-85 (1958).
Receiued for reuieu, August Accepted M a r c h
16, 1976 18, 1977
Adsorption of Flavor Components from Aqueous Orange Peel Aroma Solutions William L. Bryan, Eric D. Lund, and Charles J. Wagner, Jr." Citrus and Subtropical Products Laboratory, Winter Haven, Fiorida 33880'
The usefulness of porous polymers and activated carbon as adsorbents for Concentration of aqueous solutions of orange peel aroma was evaluated. The adsorbents were saturated by batch processing, and their capacity to adsorb various aroma components was determined. Of the porous polymers, cross-linked polystyrene resin (Amberlite XAD-4) had the highest capacity, about 20% of the resin dry weight. Activated carbon, by comparison, adsorbed about 30%. Compounds with less than six carbons were adsorbed much less efficiently than those with higher molecular weights. Elution of the saturated adsorbents with 5 bed volumes of ethanol removed all adsorbed material from the resins, but only 70% from carbon. Flavor of the resin eluate was similar to that of a highly concentrated orange peel oil. Amberlite XAD-4 appeared most suitable for fixed-bed applications for recovery of desirable flavor components from orange peel aroma solutions.
Introduction The dilute aqueous solutions of aromatic orange flavoring materials (orange peel aroma) that are steam distilled from orange peel (Veldhuis et al., 1972) require concentration for 1 One of t h e laboratories of t h e Southern Region, US.D e p a r t m e n t of Agriculture, A g r i c u l t u r a l Research Service. M e n t i o n of a b r a n d name is for identification only and does n o t imply endorsement of the product by the US.Department of Agriculture over others which m a y
also b e suitable.
use in certain products. Such solutions have been characterized (Lund et al., 1972) and are available as by-products of the production of distilled orange oil. Although aroma solutions have been concentrated by fractional distillation (Wagner and Berry, 1976) and solvent extraction with some success a t this laboratory, their concentration by adsorption would reduce heat damage and preclude the use of large quantities of solvents. A number of different types of porous polymers, organic adsorbents of high surface area, are available. One such commercial cross-linked Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No.
3, 1977
257
Table I. Composition of Aroma Solutionsa Concentration, mg/L Valencia Synthetic Methanol Acetaldehyde Ethanol Ethyl vinyl ketone n-Hexanal 1-Penten-3-01 Unid. A b d-Limonene trans -2-Hexenal Unid B Unid C n -0ctanal Unid D 1-Hexanol cis- 3-Hexen-1-01 Linalool I-Octanol Terpinen-4-01 Neral a-Terpineol Geranial trans-Carveol 1,8-p-Menthadien79-01
530 78 890 4.2
3.0 9.7 1.4 1.9 7.3 3.4 3.3 5.0
4.3 4.6 18.6 33.4 4.1
1.8 1.2
... 174 3.27 2.34 2.43 2.62 2.37
...
2.33 3.36 17.03 1.67 2.31
10.5 2.0
8.32
1.5
2.09
0.7
a Listed in order of retention time on Carbowax 20M. Unidentified compounds.
polystyrene resin suitable for adsorbing substances from aqueous solution (Gustafson et al., 1968),has recently become available. Use of these resins in the concentration of dilute aqueous solutions of organic flavoring materials and elution with methylene chloride has been demonstrated (Naipawer e t al., 1971). We surveyed various types of resins, determined their capacity for adsorbing components from orange peel aroma solution, and found that these compounds were readily eluted in a concentrated form with ethanol. Activated carbon was also used for comparison.
Experimental Section Preparation of Aroma Solution. Aroma solution (42 L) was prepared in five distillation runs from Valencia orange peel emulsion according to Veldhuis et al. (1972). Emulsion containing about 2.3% peel oil (Scott and Veldhuis, 1966) was obtained from a local citrus processing plant, cooled immediately to 5 "C, and processed within 24 h. The emulsion was preheated to 100 OC and steam stripped a t a rate of 1500g/min with about 12% vaporization. Stripped emulsion retained about 0.4%residual oil (Scott and Veldhuis, 1966). Vapor from the steam stripper, containing the volatile flavoring components was fed (185 g/min) to the center of a fractional distillation column (3-in. i.d. X 60-in. height) packed with 5/,-in. diameter stainless steel Pall rings, with condenser water temperature a t 10 "C. The reboiler rate of the distillation column was about 10% of the vapor feed rate to the column midpoint. Distillate rate was about 85 g/min, and the distillate consisted of aqueous aroma solution and distilled peel oil in a weight ratio of about 2:l. The distillate was stored at 2 "C for a t least 1week for complete separation of the two phases. The aqueous aroma phase was carefully removed by siphoning, blended, and stored a t 2 "C for experimental evaluations. Identification of Aroma Components. Aroma solutions were qualitatively analyzed by the method of Wolford et al. (1962). Aroma solution (300 mL) was saturated with sodium sulfate and extracted successively three times with distilled methylene chloride (100 mL in each extraction). Most of the 258
Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 3, 1977
solvent was removed from the combined extracts by fractional distillation a t atmospheric pressure through a Vigreux column. Concentrated extract was separated into components by a Hewlett-Packard Model 7620A gas chromatograph equipped with a flame ionization detector in conjunction with a 30:l effluent splitter. A 300-& sample was injected into a %-in. diameter by 9-ft stainless steel column packed with 20% Carbowax 20M on 60/80 Gas Chrom-P (Applied Science Laboratories Inc., State College, Pa.). Helium carrier gas flow was 200 mL/min and the temperature was programmed from 80 to 200 "C a t 1 "C/min. Temperature of the injection port, exit port, and detector was 220 "C. As the larger peaks were detected, samples from the effluent splitter were collected in traps immersed in liquid nitrogen. These were identified by use of a Perkin-Elmer Model 137 infrared spectrometer and a Dupont Model 21-490 mass spectrometer. Quantitative Analyses of Aroma Solutions. Aroma solutions were analyzed directly for methanol, acetaldehyde, and ethanol with a Hewlett-Packard Model 7620A gas chromatograph with flame ionization detector. Samples (2 FL) were injected into a ?&in. diameter X 5-ft stainless steel column packed with 50/80 Porapak Q (Waters Associates, Inc., Framingham, Mass.) and maintained a t 120 "C. Helium gas flow was 35 mL/min, and temperature of injection port and detector was 220 "C. The instrument was calibrated by injection of known concentrations of methanol, acetaldehyde, and ethanol in water. Aroma solutions were quantitatively analyzed for higher molecular weight components by a modification of the precolumn separation procedure of Moshonas and Lund (1971). The instrument used was a Hewlett-Packard Model 7620A gas chromatograph with flame ionization detector. Aroma ) injected into a pre-column (Ih-in. disamples (400 ~ L Lwere ameter X 5-ft stainless steel packed with 50/80 Porapak Q) maintained a t 120 "C. After the lower molecular weight compounds had passed through the pre-column, it was heated to 160 "C and purged by back-flushing with helium. The compounds purged from the pre-column were condensed in a liquid nitrogen trap (Dravnieks and O'Donnell, 1971).These were then injected into an analytical GC column by rapid heating of the trap to 240 "C in a bath of heated air. The analytical column (l/s-in. X 5-ft stainless steel) was packed with 5% Carbowax 20M on 70/80 Anakrom ABS, (Analabs, Inc., North Haven, Conn.). Temperature was programmed from 80 to 200 OC a t 2 "C/min. Injection port and detector block temperature was 220 "C, and helium gas flow was 33 mL/min. The detector response was calibrated with a synthetic aroma solution of known composition (Table I). For preparation of that solution, a weighed quantity of each chemically pure component was dissolved in 2 mL of ethanol, and this mixture was then dissolved in 9 L of distilled water. Concentrations of compounds not present in the synthetic aroma solution were determined from the peak areas of those compounds and a peak area correction factor (Dal Nogare and Juvet, 1962) equal to the molecular weight divided by 12 X the number of non-oxygen bonded carbon atoms (MWI12C). Precision of the analytical procedure was f 5 % (std. dev.) based on repeated injections of aroma solutions. Adsorbent Selectivity and Capacity. Adsorbent samples for testing were rinsed repeatedly with ethanol until all soluble contaminants had been removed, as determined by GC analyses of washings. A total of 10 volumes of alcohol was required. The adsorbent, placed in a Buchner funnel, was then rinsed successively with water for removal of the ethanol. Adsorbent samples were pressed damp-dry and stored in closed containers. Weight was determined for samples dried to constant weight a t 40 "C and 3 mmHg pressure. We tested the relative capacity of the adsorbents for aroma components by shaking 1-mL samples with 400 mL of aroma
Table 11. Relative Adsorbent CaDacitv for Linalool Linalool removed, Adsorbent
%=
Activated carbon (CAL 2 0 ~ 4 0 ) ~ Cross-linked polystyrene, (Amberlite XAD-4)C Cross-linked polystyrene (Amberlite XAD-2) Cross-linked polystyrene with hydroxyl and keto groups (Poragel PT) Cross-linked polyacrylic ester (Amberlite XAD-7)C Cross-linked Dextran alkylated to form hydrophobic derivative (Sephadex LH-20)e Polar resin containing N-0 groups (Amberlite XAD-
99 91
L
2o
t
1
I
81 47
29 6 5
12)C
Cr&+linked Dextran (Sephadex G-lO)e Polyacrylamide (Biogel P-2)f
2 0
Linalool adsorbed from 400 mL of aroma solution by 1 mL of adsorbent, 16 h at 2 "C. Pittsburgh Activated Carbon Div., Calgon Corp., Pittsburgh, Pa. Rohm & Haas Co., Philadelphia, Pa. Waters Associates, Inc., Framingham, Mass. e Pharmacia Fine Chemicals Co., Uppsala, Sweden. /' Bio-Rad Laboratories, Richmond, Calif. solution for 16 h a t 2 "C. Amount adsorbed was determined from the change in composition of the aroma solution, as determined by the GC methods previously described. Prolonging the contact period beyond 16 h had no effect on the composition of the supernatant solution; this indicated that equilibrium between phases had been reached. Saturation capacity of selected adsorbents was determined by ten equilibrations of 1mL absorbent (0.3-0.5 g) with fresh aroma solution (1.5 L/g absorbent). After each equilibration (16 h a t 2 "C), the supernatant solution was removed through a sintered glass filter stick and the adsorbent reequilibrated with fresh aroma solution. Amount of each aroma component adsorbed was determined after each equilibration by GC analysis of the supernatant. Adsorbed aroma components were eluted with ethanol a t 2 mL/h from the saturated adsorbent, placed in a 0.4-mm i.d. column (8-cm bed height). Successive 0.5-mL eluates were analyzed by GC, and the relative amounts of compounds recovered were determined. Flavor Evaluation. Eluate recovered from Amberlite XAD-2 which had been saturated with aroma solution was compared in flavor tests with a folded Valencia orange oil prepared as described below. Folded oil a t a concentration of 1 x IO-% in reconstituted orange juice concentrate was used as control. Flavor of control was compared in triangle taste tests (24-member trained panel) with Amberlite XAD-2 eluate a t several concentrations in reconstituted juice. Preparation of Folded Valencia Orange Oil. A 180-fold Valencia peel oil was prepared by a distillation-extraction procedure for comparison of its flavor with that of the eluate recovered from Amberlite XAD-2 resin. Cold-pressed Valencia peel oil (1830 g) was distilled a t 70 "C head temperature and 16 mmHg pressure in a spinning band column (15-mm i.d. X 30-cm length) to leave 83 g of pot residue. This was extracted with 2 L of 60% ethanol, the extract was concentrated to 700 mL in a rotary vacuum evaporator a t 55 "C and 100 mmHg, and the residue was mixed with 200 mL of saturated NaCl. The oil phase (27 g) that separated was removed and steam distilled to yield 10 g of folded oil distillate.
Results and Discussion Composition of Aroma Solution. Methanol, acetaldehyde, and ethanol were the major components of Valencia aroma solutions (Table I). Other more oil-soluble components were present a t much lower concentration; of these, linalool was the
v)
n a
NO. OF S U C C E S S I V E E Q U I L I B R A T I O N S
Figure 1. Cumulative adsorption of Valencia orange peel aroma solution components on Amberlite XAD-4 during batch equilibration
tests. most prevalent. Limonene, the only hydrocarbon identified, was present in very low concentration, as expected from the distribution coefficients of components found in citrus oils and aroma solutions (Lund and Bryan, 1976). Several components were not identified and are listed in Table I as "Unid." Relative Capacity of Adsorbents. Eight porous polymers and a sample of activated carbon were screened for relative capacity (Table 11). Degree of adsorption of linalool from aroma solution in a single equilibration was the basis for our selection of adsorbents for further testing. Activated carbon had the highest capacity for linalool in this test, followed by Amberlite XAD-4 and XAD-2. Other adsorbents removed less than 50% of the linalool from 400 mL of aroma solution. Affinity for linalool appeared to correlate negatively with polarity of the porous polymers. Saturation Capacity and Selectivity. The three adsorbents with highest relative capacity for linalool were evaluated for saturation capacity and selectivity for specific aroma components in successive equilibration tests with fresh aroma solution. The amount of each component adsorbed was expressed in grams per 100 g of dry adsorbent, as determined by GC analysis from the change in liquid composition after each equilibration, and the cumulative amounts of components adsorbed on Amberlite XAD-4 were graphed as shown in Figure 1.All components were adsorbed to some degree during the first equilibration of adsorbent with aroma solution. In succeeding equilibrations, a few components continued to be adsorbed, but most reached maximum concentration as shown in Figure 1. Most compounds with six or fewer carbon atoms were quickly displaced from the adsorbents by compounds with higher affinity. The general nature of the affinities followed the expected lipophylic-hydrophylic properties of the compounds. Capacity curves of most components were similar in shape for the three adsorbents; this indicated that the components had about the same relative affinity for the adsorbents. Terpinen-4-01 was an exception and was retained to a larger degree by activated carbon. The maximum adsorptive capacity of the adsorbents for total aroma components was established by the multipleequilibration technique. For the Amberlites, the maximum capacity declined slightly with repeated equilibration (Figure 11,probably caused by displacement of less readily adsorbed Ind. Eng. Chem., Prod. Res. Dev.. Vol. 16, No. 3, 1977
259
Table 111. Maximum Adsorbent Capacity for All Components in Equilibration Tests Capacity, % bv w t Carbon, CAL 12x40 Amberlite XAD-4 Amberlite XAD-2
Aroma solution volume L/e adsorbent
29.9 20.5 9.9
-
5
10 8
5
i
0 3
. x
P
Table IV. Langmuir Equation Quasi Constants for Linalool Carbon CAL 12x40
K , L/mol X b, mol/g X lo4 Surface area, m2/ga blarea, mol/m2 X lo7 a
7.8 10.1 1050 9.6
" 2
Amberlite Amberlite XAD-4 XAD-2 3.0 6.8 750 9.1
3.2 3.1 330 9.4
I
-
1
'
2
OO
3
c x'104 ( r n o l e / i i t e r )
Figure 2. Quasi-Langmuir isotherms for adsorption of linalool on
activated carbon and Amberlites XAD-2 and XAD-4.
Manufacturer's specifications.
components by d-limonene. Percent adsorptive capacity, based on weight of dry adsorbent, was maximal when the adsorbents had equilibrated with the volumes of aroma solution shown in Table 111. Mathematical Correlations. The Langmuir isotherm equation satisfactorily correlated concentrations of linalool in the liquid and solid phases, before saturation was reached in the equilibration tests (Figure 2). In the Langmuir equation, c / q = ( l / K b ) ( c / b ) (eq I), c is the concentration of solute in mol/L, q is the concentration of sorbate in mol/g of dry adsorbent, b is a constant theoretically representing the amount of sorbate in the form of a monomolecular layer on the adsorbent surface (mol/g of dry adsorbent), and K is the equilibrium constant for the resin-sorbate interaction (Gustafson e t al., 1968). The quasi constants, K and b, calculated for linalool from Figure 2, are shown in Table IV. The K values for the Amberlites were not significantly different but lower than for
+
activated carbon, indicating a larger binding force for linalool to carbon. The b values for linalool varied approximately in proportion to the manufacturer's specifications of adsorbent surface areas, m2/g of dry adsorbent (determined by the BET method), which are also listed in Table IV. The ratio, b/surface area, was about the same, 9.4 f 0.3 X mol/m2 for the three adsorbents. The Langmuir equation is usually applied to systems with a single component in solution. In its application for multicomponent adsorption the magnitude of the quasi constants probably have no theoretical significance, but the K and b values in Table IV did enable us to compare the adsorbents. Linalool was three times more concentrated in aroma solution than other adsorbed components and its concentration would probably be most representative for characterization of adsorbents. Data for the other adsorbed compounds were also correlated by the Langmuir equation, and the results suggest that adsorption of most aroma components a t low concentrations probably occurs without interaction between ad-
Table V. Composition of Original Aroma Solution and Eluates (%, Solvent-Free Basis) Aroma solution
Carbon CAL 12x40
27 4
25
Amberlite XAD-4
Amberlite XAD-2
Enrichment Linalool n -0ctanal 1-Octanol d-Limonene Terpinen-4-ola Geranial Unid A Neral 1-8-p-Menthadiene-9-01
3 2 2 2
1 1 1
11 10 17
39 15
31 16
7
8 11
10
1
1 9 3 3 3 7
1 7 2 2
8 4 3 1
3 No change
a-Terpineol Unid C trans -Carve01
9 3
9 4
8
3
3
1
1
1
2
15
0 0 2 0 0 1 0 0
0 0 2 1 0 1 0 0
0 0
Depletion cis-3-Hexen-1-01 1-Penten-3-01 trans-2-Hexenal 1-Hexanol Ethyl vinyl ketone Unid B Unid D n-Hexanal a
260
8 6
4 3 3 3 2
Terpinen-4-01 was enriched in eluate from activated carbon and depleted in eluates from the Amberlites. Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 3,1977
1 0 0
1 0 0
sorbed molecules and without change of binding energy with increasing amount adsorbed (Gustafson, 1968). Elution of Adsorbents. Essentially all components were recovered in 5 mL of ethanolic eluate (five bed volumes) from Amberlite XAD-2 and XAD-4. Adsorbate was less readily eluted from activated carbon, and about 30% of the adsorbed compounds remained on carbon after elution with five bed volumes of ethanol. After elution of activated carbon with another five bed volumes, less than 1Wo of adsorbed compounds remained on carbon. In Table V, compositions of the eluates from each adsorbent are compared with the composition of the original aroma solution, all on a solvent-free basis. The compounds are listed in groups by relative change in concentration as compared to aroma solution. Many compounds present in higher concentration in eluant than in aroma solution (enrichment group) are essential for typical orange flavoring (linalool, n-octanal, cl-limonene, geranial and neral) (Ahmed, 1975). Of the compounds with unchanged relative concentration, a-terpineol is known to contribute off-flavor (Tatum et al., 1975). The lower molecular weight compounds were less concentrated in eluant than aroma solution, and some would be undesirable in an orange flavoring concentrate. cis-3-Hexen-1-01 (leaf alcohol) has an odor similar to green leaves. trans- 2-Hexenal and n-hexanal impart a characteristic immature or "greenish" flavor (Ahmed, 1975).Thus, the eluates were enriched in some desirable orange flavoring components and depleted in some undesirable components. The compositions of the eluates resemble the composition of a terpene-free orange oil (Shaw and Coleman, 1974). Flavor Comparison. When Amberlite XAD-2 eluate was compared in triangle taste tests at twice the concentration of the folded oil, panelists could not find a significant difference. This indicated eluates were approximately equivalent to a 90-fold orange oil.
probably be useful as adsorbents in a fixed-bed operation to recover a flavor concentrate from an aqueous solution of orange peel aroma. The mixture of orange flavoring components eluted by ethanol was similiar in flavor to a folded orange oil. The fact that components were readily eluted with ethanol suggests that a fixed bed could probably be cycled many times without deterioration of adsorbent properties, but this was not tested. A fixed-bed adsorption process would be superior to fractional distillation in several ways. Desirable flavor compounds would be adsorbed preferentially to some of the lower molecular weight components detrimental to orange flavor, heat damage would be minimized, and the product would be in a generally useful anhydrous form. Although Amberlites XAD-2 and XAD-4 are not yet approved for food use by the FDA, their similarity to presently approved ionexchange resins suggests they will be approved.
Literature Cited Ahmed. E. M., U.S. Dept. of Agriculture, Contract No. 12-14-100-10337, (1975). Dal Nogare, S.,Juvet, R . S.,Jr., "Gas-Liquid Chromatography", Interscience. p 220, New York, N.Y., 1962. Dravnieks, A., O'Donnell. A,, J. Agric. Food Chem., 19, 1049 (1971). Gustafson, R. L., Albright, R. L., Heisler, J., Lirio, J. A., Reid, 0. T., Jr., lnd. Eng. Chem.. Prod. Res. Dev., 7, 108 (1968). Lund, E. D., Berry, R. E., Wagner, C. J., Jr., Veldhuis. M. K., J. Agric. FoodChem., 20, 685 (1972). Lund, E. D., Bryan, W. L., J. Food Sci., 41, 1194 (1976). Moshonas, M. G., Lund, E. D., J. FoodSci., 36, 105 (1971). Naipawer, R. E., Potter, R.. Vallon. P., Erickson, R . E., Flavour lnd., 465 (1971). Scott, W. C., Veldhuis, M. K., J. Assoc. Offic. Anal. Chem., 49, 628 (1966). Shaw, P. E., Coleman, R. L., J. Agric. FoodChem., 22, 785 (1974). Tatum, J. H.,Nagy, S..Berry, R . E., J. FoodSci., 40, 707 (1975). Veldhuis, M. K., Berry, R. E., Wagner, C. J.. Jr., Lund, E. D., Bryan, W. L., J. Food Sci., 37, 108 (1972). Wagner, C. J., Jr., Berry, R. E.. FoodProd. Dev., 10, 55 (1976). Wolford, R. W., Alberding, G. E., Attaway, J. A., J. Agric. FoodChem., 10, 297 (1962).
Conclusions Our study showed that Amberlites XAD-2 or XAD-4 would
Receiued for reuieu, December 23, 1976 Accepted April 26,1977
Catalytic Amination of Long Chain Aliphatic Alcohols Alfons Baiker and Werner Richarz" Swiss Federal lnstitute of Technology (ETH), Deparfment of lndustrial and Engineering Chemistry, 8092 Zurich, Switzerland
The activity and selectivity of several types of catalysts have been examined for the amination of dodecanol with dimethylamine. The experiments showed that copper oxide or copper oxide/chromium oxide catalysts are very effective for this type of reaction. A global scheme for the reaction path is proposed. The most important reaction parameters were optimized for both batch (stirred autoclave) and continuous (fixed bed) reactors. On the basis of these studies a continuous process has been developed which gives at almost quantitative conversion a selectivity of over 0.96 with respect to dimethyldodecylamine.
Introduction The synthesis of long chain aliphatic amines is of particular interest since they are widely used as corrosion inhibitors, epoxy hardeners, textile additives (Shinzo Otsuka, 1966; Yakushkin, 1966) etc. Several processes are known starting from olefins (Kraiman et al., 1968) fatty acids or from the
corresponding alcohols. Some known processes utilizing aliphatic alcohols are given in Table I from which it can be seen that catalysts of very different chemical composition are reported to be effective for the amination reaction. In order to obtain more specific information on the applicability of the different types of catalysts for the amination reaction, several Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 3, 1977
261
