B Caroteno M. Johannsen

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Solubilities of the Fat-Soluble Vitamins A, D, E, and K inSupercritical Carbon Dioxide

Monika J ohannsen*, and Gerd Brunner

Arbeitsbereich Verfahrenstechnik II, Technical University Hamburg-Harburg, Eissendorfer Strasse 38,D-21073 H am burg, G ermany

Solubilit ies of eight different species of the fat-soluble vitamins A, D, E, and K in supercritical carbond i ox id e w e r e m e a s ur e d a t (31 3, 3 33 , a n d 3 53 ) K a n d o ve r a p r es s ur e r a n g e o f 2 0 M P a t o 3 5 M P a .Solubilit ies ha ve been det ermined by a n a na lyt ica l met hod us ing t he direct coupling of a n equilibriumcell to a supercritical fluid chromatogra phic system wit h U V detection. The solubilit ies of all fa t-solublevita mins in supercritical car bon dioxide under t he conditions investiga ted a re in t he ra nge of 10 g/kg,except for -ca rot ene (provit a min A), w hich is 3 orders of ma gnit ude les s s oluble. Wit h increa s ingmolecula r ma s s of t he vit a min, i t s s olubili t y in s upercrit ica l ca rbon dioxide decrea s es . At cons t a ntt empera t ure, t he s olubili t y of a l l s ubs t a nces increa s es w it h increa s ing dens it y. At cons t a nt dens it y, arise of temperat ure results in an in crease in solubility. This is caused by t he increasing vapor pressureof the solid.

Introduction

During t he last 30 years the interest in th e technical useof supercritical fluids has increased. There are importan tapplications in the field of extraction, chromatography, andreactions using supercritical fluids.

Supercrit ica l f luid ext ra ct ion (SFE) ma kes pos s ible as elect ive a nd mild is ola t ion of s ubs t a nces from na t ura lma t eria l . Some of t he mos t w ell-know n a pplica t ions oftechnical gas extraction are the decaffeination of coffee andtea, and the extraction of hops, spices, drugs, and naturalcolors w it h s upercrit ica l ca rbon dioxide. There ha s a ls obeen a growing interest in preparative supercritical fluidchromatography (SFC), which shows the same advantagesas technical SFE (B runn er, 1994). In a ddition the selectiv-

it y of a chroma t ogra phic s epa ra t ion could be inf luenceds u bs t a n t i a l l y b y c hoos i ng t h e m os t s u it a b l e s t a t i on a r yphase ad sorbent mat erial. The use of supercritical fluidsas solvents leads to a reduction or elimination of organica nd pa rt ly chlorina t ed s olvent s in a l l t hes e a rea s .

The knowledge of the characteristic phase equilibriumis of considerable economic interest for optimal calculationof separation processes controlled by phase equilibrium.S e pa r a t i on c os t s m a y c om p r is e u p t o 8 0% o f t h e t o t a linvestment and running costs of a production process.

I n t h i s w or k , t h e s ol u bi li t y d a t a of t h e f a t -s ol u bl ev it a m i n s A, D , E , a n d K a r e p r es en t e d . P r e s en t l y f a t -soluble vitam ins are mainly produced synthetically. How-ever, their isolation from natural sources is of increasing

interest. Only a few solubility da ta of tocopherols (vitam inE ) a n d -carotene (provitamin A) in supercritical fluidshave been published. These data ar e listed in Tables 1 and2.

Experimental Section

A p p a r a t u s a n d P r o ced u r e. An a p pa r a t u s f or t h equasi-static measurement of equilibrium solubilit ies withon-line coupling to a supercritical fluid chromatographics ys t em w a s us ed. This a ppa ra t us a nd t he procedure ha vebeen described before (J ohannsen and Brunner, 1994a,b,1996).

M a t e r i a l s . Ca rbon dioxide of 99.95 ma ss %purity w asfrom KWD, Kohlensa urew erke Deut schlan d, B a d H on nin-gen, G erma ny. Ca rbon dioxide wa s fed to the system from

the vapor phase of a carbon dioxide tank, further dried bya m oisture tra p conta ining a molecular sieve, and liquefiedin the cylinder. The vitamins w ere obta ined from varioussources, as shown in Table 3.

Results and Discussion

The solubilities of eight different species of th e fat -solublevit a mins A , D, E, a nd K in s upercrit ica l ca rbon dioxidewere measured at temperatures of (313, 333, and 353) Ka n d ov er a p re ss ur e r a n g e of (20 t o 35) M P a . Th eexperiment a l res ult s a re report ed in Ta bles 4-11. Thepres s ure w a s mea s ured t o a n a ccura cy of (0 .1 M P a , a n dt he t empera t ure regula t ion w a s w it hin ( 1 K . D e n s it i esof pure CO 2 w ere ca lcula t ed w it h t he B ender equa t ion ofsta te (Bender, 1970). All solubility values represent meanva lues of a t lea s t f ive s a mplings . St a nda rd devia t ions ofthe measurement s were within 5%. In wh at follows someselected results ar e considered.

In F igure 1, the solubilit ies of R- a nd -tocopher ol (2) insupercritical carbon dioxide (1) are presented as a functionof the CO2 density in a semiloga rithm ic scale. The solubili-ties of tocopherols mea sured und er th ese conditions a re inthe ra nge of (5 to 40) g/kg, corresponding to x2 ) (0.5 10-3 to 4.6 10-3). There are no rema rkable differencesbetween the solubilit ies of R- a nd -tocopherol. For bothis omers t he low es t s olubili t y w a s found a t a t empera t ureof 353 K an d a pressure of 20 MPa (density a bout 590 kg/m 3) a nd t he highes t one a t a t empera t ure of 333 K a nd apressure of 35 MP a (density a bout 860 kg/m 3).

Actua l ad dress: F. H offmann-La Roche AG, VFH, B ldg 214/218, CH-4070 Basel, Sw itzerland. E -ma il: monika.joha [email protected].

Table 1. Synopsis of Solubility Measurements ofTocopherols in Supercritical CO2 in the Literature

tocopherol P/MP a T/K a ut h or (s)

R 8-20 313-3 53 C hra st i l (1 98 2)R 10-1 8 2 98 , 3 13 O hg aki e t al . (1 98 9)R 15-35 327-353 Zehnder (1992)R 10-35 303-353 Meier (1992); Meier et al. (1994)R 9-26 292-333 P ereira et al . (1993)R, 9-26 3 13 P e r ei r a e t a l . (19 94); P e r e ir a (1 99 5)R 7-35 313-3 53 Bi rt i g h et al . (1 99 5)R 10-20 313-333 Scha ffner an d Trepp (1995)

106 J . C h e m . E n g . D a t a 1997, 42 , 106-111

S0021-9568(96)00219-1 CCC : $14.00 1997 American C hemical Society


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There are tw o effects observed: At consta nt tempera tur et he s olubilit y increa s es w it h increa s ing dens it y. This isproba bly due t o t he increa s ing s olvent pow er of ca rbondioxide a t higher dens it y. A nea rly l inea r r ela t ions hipbet w een t he dens it y of ca rbon dioxide a nd t he loga rit hmof the solubility w as found for both tocopherols in the regionof pres s ure a nd t empera t ure inves t iga t ed. At const a ntden sit y (e.g. a t 750 kg/m 3) a rise of temperatur e results inan increase in solubility. This results from the increasing

vapor pressure of the solid.

Figure 2 illustrat es the solubility va lues of R-tocopheroli n c a r b on d i ox id e p r e se n t ed i n t h i s w or k a t 33 3 K i ncom p a r i so n w i t h d a t a f r om l it e r a t u r e. Th e d a t a f r omChra stil (1982) correspond t o this w ork. Also the valuesfrom Zehnder (1992) at 327 K and 336 K fit to this work,especially if their deviation range is taken into consider-at ion. The da ta of Pereira et a l. (1993) are generally lowert h a n t h i s w o r k . H ow e v er , t h e i r d a t a s h ow v a r i a t i on a tcons t a nt dens it y up t o 10%. M eier (1992) mea s ureds ol u bi li t ie s a t 34 3 K . As e xp ect e d , t h e s e v a l u e s a r es omew ha t higher t ha n t his w ork.

In Figure 3, the solubility of retinol (2) (vitamin A) insupercritical carbon dioxide (1) is shown as a function of

t he CO2 density on a semilogarithm ic scale. The solubilityof retinol measured und er these conditions is in the ra ngeof (9.2 to 28) g/kg, w it h r espect t o x2 ) (1.4 10-3 to 4.3 10-3). The solubility increases wit h increasing density atcons t a nt t empera t ure a nd w it h increa s ing t empera t ure a tcons t a nt dens it y.

A similar behavior occurs for the solubility of vitaminD 3 in Figure 4. The s olubili t ies of vit a min D 3 (2) are inth e ra nge fr om (4.0 to 44) g/kg, corresponding to x2 ) (0.46 10-3 to 5.2 10-3).

I n Figure 5, t he s olubili t y of vit a min K 1 (2) in super-critical ca rbon dioxide (1) at tempera tur es of (313, 333, a nd353) K is shown as a function of pressure. The solubilityof vit a min K 1 is in t he ra nge of 3.0 g/kg a t 353 K a nd a

Table 2. Synopsis of Solubility Measurements of-Carotene in Supercritical Fluids in the Li terature

solvent P/MP a T/K a ut h or (s)

C O2 20-50 313-343 C y gn a r ow icz et a l. (1990)C O2, N2O 9.6-30 308-323 S a ka ki (1992)C O2, N2O, C 2H 4, Xe, SF 6, C 3H 8, et c. 0.15-50 (sin gle da ta ) 288-3 29 (s in g le d a t a ) J a y a n d S t e yt l er (1 99 2)C O2 10-30 298-313 S ker get et a l. (1995)

Table 3. Purities and Manufacturer of the TestCompounds

compoun d pur it y/%manufac ture r

(al l i n Ge rman y )product

n o.

t r a n s -re t i nol (vi tami n A) approx 7 0 Si g ma, De i senhofen R 7 63 2t r a n s --ca r ot en e a p pr ox 95 S ig ma , D eis en h of en C 9750vi tami n E

(DL -R-tocopherol)>98 F luka , Neu-U lm 95240

-t ocoph er ol a ppr ox 90 S ig ma , D eis en hof en T 2028vi tami n D 2 (ergocalciferol) 97-100 M er ck , D a r ms t a dt 8533vi tami n D 3

(cholecalciferol)97-100 M er ck , D a r ms t a dt 8523

vi tami n K 1 >99 Mer ck, D a rm st a dt 8355vi tami n K 3 (menadione) >98 S ig ma , D eis en h of en M 5625

Table 4. Solubility S (in Grams per K ilogram of Solvent)and Mole Fraction Solubility x2 ofr-Tocopherol (2) inSupercritical C arbon Dioxide (1)

T/K P/MP a F/kg m-3 S/gkg-1 x2/10-3

313 19.9 839.3 13.7 1.4221.9 856.8 16.3 1.6923.9 872.3 18.1 1.8825.9 886.1 20.2 2.1027.9 898.5 23.6 2.4629.9 909.9 25.5 2.6731.9 920.5 25.7 2.6934.9 935.0 27.7 2.90

333 19.9 721.6 10.6 1.0921.9 750.8 13.6 1.4123.9 774.9 17.1 1.7725.9 795.4 19.8 2.0627.9 813.3 22.9 2.3929.9 829.2 25.1 2.6231.9 843.5 29.4 3.0934.9 862.7 33.9 3.57

353 19.9 591.6 6.2 0.6421.9 634.9 10.1 1.0423.9 669.7 14.4 1.4925.9 698.6 17.3 1.8027.9 723.2 19.9 2.0729.9 744.5 23.1 2.4131.9 763.4 28.4 2.9834.9 788.2 33.2 3.50

Table 5. Solubility S (in Grams per K ilogram of Solvent)and Mole Fraction Solubility x2 of-Tocopherol (2) inSupercritical Carbon Dioxide (1)


313 19.9 840.2 9.7 1.0821.9 857.7 10.4 1.1523.9 873.0 11.7 1.3025.9 886.7 15.1 1.6827.9 899.1 21.2 2.3729.9 911.0 25.0 2.7931.9 921.0 27.3 3.0634.9 935.9 30.8 3.46

333 19.9 723.2 7.9 0.8721.9 753.4 11.7 1.2923.9 778.2 17.5 1.9525.9 798.3 20.8 2.3227.9 816.7 25.7 2.8829.9 831.5 31.7 3.5631.9 844.2 37.1 4.2034.9 863.9 40.2 4.56

353 19.9 594.2 4.9 0.5421.9 634.9 6.7 0.7423.9 671.3 11.9 1.3125.9 699.9 13.8 1.5327.9 723.2 18.6 2.0729.9 746.5 19.4 2.1631.9 766.1 25.5 2.8534.9 788.9 32.6 3.67

Table 6. Solubility S (in Grams per K ilogram of Solvent)and Mole Fraction Solubility x2 of Retinol (2) inSupercritical Carbon Dioxide (1)


313 20.0 840.2 10.3 1.6022.0 857.7 12.5 1.9524.0 873.0 15.1 2.3526.0 886.7 18.5 2.88

28.0 899.1 19.8 3.1030.0 910.5 21.8 3.4232.0 921.0 22.4 3.5035.0 935.4 23.8 3.73

333 20.0 723.2 10.0 1.5522.0 752.1 11.7 1.8224.0 776.0 16.0 2.5026.0 796.4 19.0 2.96

353 20.0 594.2 9.2 1.4222.0 636.8 9.4 1.4624.0 671.3 11.0 1.7026.0 699.9 13.9 2.1628.0 724.3 18.0 2.8030.0 745.5 22.3 3.4932.0 764.3 25.2 3.9635.0 788.9 27.6 4.34

J o u r n a l of C h e m i c al a n d E n g i n eer i n g D a t a , V o l . 4 2 , N o . 1 , 19 9 7 107


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pressure of 20 MPa up to 35 g/kg a t 313 K a nd 333 K a nd

a pressure of 35 MPa . The solubility of vita min K 1 is in a

ra nge s imila r t o t hose of t he ot her compounds dis cus s ed

before.

The 313 K isotherm is h igher th an the 333 K isotherm.The 353 K isotherm is t he lowest. For all pressures in the

range investigated, the solubility decreases with increasing

temperat ure. Two effects influence the behavior: First is

the decrea se of the solvent power of car bon dioxide because

of t he decrea s ing dens it y a nd s econd is t he increa s e of

solubility due to the increasing vapor pressure of vitamin

K 1. I n t his ca s e t he decrea s e in t he s olvent pow er pre-

dominates over the increase in vapor pressure.

In Figure 6, the solubility of vitamin D 2 is presented as

a fun ction of pressure. The solubilit ies of vita min D 2 (2)

under t hes e condit ions a re in t he ra nge from (2.7 t o 9.3)

g/kg or x2 ) (0.3 10-3 to 1.04 10-3). The solubility of

vit a min D 2 is ma rgina lly low er t ha n t ha t of vit a min D 3.

At a pressure of 20 MPa the tendency of the isotherms

is similar to tha t seen in Figure 5. The 313 K isotherm is

higher t ha n t he 333 K is ot herm, a nd t he 353 K is ot herm

is t he low es t . The decrea s e of s olvent pow er of ca rbon

dioxide due to the decreasing density predominates over

the increasing va por pressure of vitam in D 2. B u t b et w e e n

21 MP a a nd 22 MP a a crossover pressure wa s found. Thus,

in t he pres s ure ra nge higher t ha n 22 M P a t he s olubili t y

a t a t empera t ure of 313 K is low er t ha n t he one a t 333 K

a n d t h e s ol ub il it y a t 353 K i s t h e h i g he st . H e re t h e

reversed case occurs an d th e increasing va por pressure of

Table 7. Solubility S (in Grams per K ilogram of Solvent)and Mole Fraction Solubility x2 of-Carotene (2) inSupercritical C arbon Dioxide (1)


313 20.0 840.2 0.11 0.0922.0 857.7 0.12 0.1024.0 873.0 0.13 0.1126.0 886.7 0.16 0.1328.0 899.1 0.17 0.1430.0 910.5 0.19 0.1632.0 921.0 0.29 0.2435.0 935.4 0.34 0.28

333 20.0 723.2 0.34 0.2822.0 752.1 0.43 0.3524.0 776.0 0.64 0.5226.0 796.4 0.72 0.5928.0 814.2 1.05 0.8630.0 830.0 1.26 1.0332.0 844.2 1.46 1.1935.0 863.3 1.44 1.18

353 20.0 594.2 0.42 0.3522.0 671.3 1.07 0.8824.0 699.9 1.17 0.9626.0 724.3 2.05 1.6828.0 745.5 2.45 2.0130.0 764.3 2.64 2.1732.0 788.9 3.95 3.24

Table 8. Solubility S (in Grams per K ilogram of Solvent)and Mole Fraction Solubility x2 of Vitamin D3 (2) inSupercritical C arbon Dioxide (1)


313 20.0 840.2 5.0 0.5722.0 857.7 5.2 0.6024.0 873.0 5.0 0.5726.0 886.7 5.5 0.6428.0 899.1 6.3 0.7230.0 910.5 6.4 0.7335.0 935.4 6.9 0.79

333 20.0 723.2 4.0 0.4622.0 752.1 5.1 0.5824.0 776.0 5.8 0.6726.0 796.4 7.3 0.8428.0 814.2 9.0 1.0430.0 830.0 11.8 1.3632.0 844.2 26.4 3.0935.0 863.3 43.8 5.21

353 20.0 594.2 4.0 0.4622.0 636.8 4.1 0.4724.0 671.3 5.9 0.6826.0 699.9 6.4 0.7328.0 724.3 6.9 0.7930.0 745.5 9.3 1.0832.0 764.3 11.7 1.3635.0 788.9 25.0 2.92

Table 9. Solubility S (in Grams per K ilogram of Solvent)and Mole Fraction Solubility x2 of Vitamin D2 (2) inSupercritical Carbon Dioxide (1)


313 20.0 840.2 3.2 0.3522.0 857.7 3.4 0.3824.0 873.0 3.8 0.4226.0 886.7 4.2 0.4628.0 899.1 4.0 0.4530.0 910.5 4.3 0.4832.0 921.0 4.6 0.51

333 20.0 723.2 2.7 0.3022.0 752.1 3.3 0.3724.0 776.0 4.3 0.4826.0 796.4 5.2 0.5828.0 814.2 5.7 0.6430.0 830.0 6.3 0.70

353 20.0 594.2 2.6 0.2922.0 636.8 4.9 0.5424.0 671.3 5.8 0.6425.0 686.2 6.9 0.7726.0 699.9 7.4 0.8328.0 745.5 9.3 1.04

Table 10. Solubility S (in Grams per K ilogram ofSolvent) and Mole Fraction Solubili ty x2 of Vitamin K1(2) in Supercritical Carbon Dioxide (1)


313 20.0 840.2 13.4 1.3222.0 857.7 15.2 1.5124.0 873.0 17.0 1.6926.0 886.7 20.0 1.9928.0 899.1 22.4 2.2330.0 910.5 27.8 2.7832.0 921.0 32.3 3.2535.0 935.4 35.3 3.56

333 20.0 723.2 7.2 0.7122.0 752.1 11.2 1.1124.0 776.0 15.3 1.5126.0 796.4 17.2 1.7028.0 814.2 20.5 2.0430.0 830.0 22.6 2.2532.0 844.2 28.1 2.8135.0 863.3 34.8 3.51

353 20.0 594.2 3.0 0.2922.0 636.8 5.7 0.5624.0 671.3 9.1 0.8926.0 699.9 11.6 1.1428.0 724.3 16.4 1.6230.0 745.5 20.1 2.0032.0 764.3 24.8 2.4835.0 788.9 29.8 2.99

Table 11. Solubility S (in Grams per K ilogram ofSolvent) and Mole Fraction Solubili ty x2 of Vitamin K3(2) in Supercritical Carbon Dioxide (1)


313 22.0 857.7 23.6 6.1424.0 873.0 23.9 6.2126.0 886.7 23.0 5.9928.0 899.1 25.6 6.68

30.0 910.5 23.5 6.1232.0 921.0 23.3 6.07

108 J o u r n a l of C h e m i c al a n d E n g i n e er i n g D a t a , V o l . 4 2 , N o . 1, 1 9 9 7


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vitamin D 2 predomina tes over the decrease of solvent powerof carbon dioxide due to the decreasing density.

Thes e t w o cont ra s t ing ef fect s a re a ls o decis ive i f t heinfluence of the t emperatur e on solubility is discussed. InFigure 7, the result of experimental measurements of the

solubility of -tocopherol in supercritical carbon dioxide iss how n a s a funct ion of t empera t ure.

At a cons t a nt press ure in t h e ra nge of 313 K t o 333 Kthe solubility increases with increasing temperat ure. Thevapor pressure effect predominates over the density effect,a s s ee n i n t h e u p pe r f i gu r e. H o w e ve r , i n t h i s c a s e, as olubili t y ma ximum occurs a nd a t t empera t ures grea t ert ha n 333 K t he s olubili t y decrea s es w it h increa s ing t em-p er a t u r e . I n t h a t c a s e t h e e f fe ct of d e cr e a s in g d e n s it ypredominates over the vapor pressure effect.

Figure 8 i l lus t ra t es t he s olubili t y of -carotene (2) incarbon dioxide (1) at different pressures as a function of

Figure 1. Solubility S (in gra ms per kilogram of solvent) oftocopherols (2) in carbon dioxide (1) as a function of density.

Figure 2. Solubility S (in gra ms per kilogram of solvent) of

R-tocopherol (2) in carbon dioxide (1) (all data a t 327 t o 343 Kf r om l i t er a t u r e : () t h is w or k, 3 3 3 K ; (9) Pereira et al. (1993),

333 K; (1) Zehnder (1992), 327 K; (2) Zehnder (1992), 336 K; (b)

Meier (1992), 343 K; (() Ch ra stil (1982), 333 K ).

Figure3. Solubility S (in gra ms per kilogram of solvent) of retinol(2) in carbon dioxide (1) as a function of density.

Figure 4. Solubility S (in gra ms per kilogram of solvent) ofv i t a m in D 3 (2) in carbon dioxide (1) as a function of density.

Figure 5. Solubility S (in gra ms per kilogram of solvent) ofv i t a m in K 1 (2) in carbon dioxide (1) as a function of pressure.

Figure 6. Solubility S (in gra ms per kilogram of solvent) of

v i t a m in D 2 (2) in carbon dioxide (1) as a function of pressure.



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temperat ure. The solubility of -carotene is in the rangeof (1 10-3 g/kg up t o 4 10-2) g/kg, corresponding to x2) (0.09 10-6 to 3.2 10-6). The solubility is 3 orders of

ma gnit ude low er t ha n t hos e of t he ot her fa t -s oluble vit a -mins.

At a ll pressures the solubility increases with increasingtemperature a lthough the car bon dioxide density decreasesa t t h e s a m e t i m e. O b vi ou s ly , t h e i n cr e a s e of t h e v a p orpressure of -carotene exerts a great er influence on solubil-ity t ha n th e decrease of the density of carbon dioxide here.

In F igure 9, the solubility va lues of -carotene in carbondioxide pres ent ed in t his w ork a t a t empera t ure bet w een313 K a n d 353 K a r e com pa r ed w i th t h e d a t a f romliterat ure. The values from Cygna rowicz et a l. (1990) ar elow er t ha n t his w ork. Their da t a a t a t empera t ure of 343K a r e o nl y a l it t le h i gh er t h a n o ur s a t 333 K . Th ediscrepan cies between the data from Saka ki (1992) an d thiswork are smaller. However, their results indicate a highersolubility. Also a higher solubility of -carotene in carbondioxide wa s found by S kerget et a l. (1995). These irregula rdevia t ions could be ca us ed by dif ferent ma t eria ls or dif-f er e n t m e t h od s u s ed f or t h e s ol u bi li t y m e a s u r em e n t s.Sa mpling is dif ficult a t low -concent ra t ion s a mples. Ourmet hod ha s been proved s uit a ble for low s olubili t y m ea -surement s (J ohan nsen and B runn er, 1994a ). Additiona lly,-carotene is sensitive to oxygen and light.

In F igure 10, all experimenta lly determined solubilit iesof t he vit a m ins a re s how n. The s olubili t y of vit a min K 3has been determined only at the temperature of 313 K. Thes olubili t y beha viors of a l l fa t -s oluble vit a mins except-ca rot ene a re q uit e s imila r . U n der t hes e condit ions t hesolubilities of these vita mins in su percritical ca rbon dioxide

a re in th e ra nge of 3 g /kg u p to 40 g/kg. -Ca rotene is about3 orders of magnit ude less soluble than the other vita mins.This extremely low solubility of -carotene first of all seemst o be unus ua l beca us e -carotene is a nonpolar hydrocar-b on . B u t t h e h i gh m ol a r m a s s s h ou ld b e t a k en i nt o

Figure 7. Solubility S (in gra ms per kilogram of solvent) of-tocopherol (2) in carbon dioxide (1) as a function of temperature.

Figure 8. Solubility S (in gra ms per kilogram of solvent) of-carotene (2) in carbon dioxide (1) as a function of temperature.

Figure 9. Solubility S (in gra ms per kilogram of solvent) of-carotene (2) in carbon dioxide (1) (all dat a at 313 to 353 K fromliterature: this work (b) 353 K, (1) 333 K, (9) 313 K; Cygna rowitz

et al. (1990) (4) 343 K, (3) 333 K, (0) 313 K; Sakaki (1992) ()

323 K, (+) 313 K; Skerget et al. (1995) ()) 313 K).

Figure 10. Solubility S (in grams per kilogram of solvent) of fat-soluble vitamins (2) in carbon dioxide (1).

Figure 11. Mole fraction solubility x2 of fat-soluble vitamins (2)in car bon dioxide (1) at P) 2 6 M P a a n d T ) 333 K a s a function

of molecular ma ss M.

110 J o u r n a l of C h e m i c al a n d E n g i n e er i n g D a t a , V o l . 4 2 , N o . 1, 1 9 9 7


6/6

considerat ion. Also, the shape of the -car otene m oleculecould have a negative effect on the solubility.

I n F i g u r e 1 1, t h e m ol e f r a ct i on s ol u bi li t i es o f t h evitamins in carbon dioxide at a temperature of 333 K anda p re ss u re o f 2 6 M P a a r e s h ow n a s a f un ct i on of t h emolecula r ma s s . I t is found t ha t for a l l pa irs of vit a mins ,the one wit h th e higher molecular ma ss is less soluble. Thist rend is a ls o s een in t he da t a overa ll .

Conclusion

Experimental solubilit ies of eight different fat-solublevit a mins A , D, E, a nd K in s upercrit ica l ca rbon dioxidewere mea sured from 313 K to 353 K a nd a t pressures from20 M P a t o 3 5 M P a . Th e i n f lu en ce o f t e m pe r a t u r e a n ddens it y on t he s olubili t y w a s s how n. At cons t a nt t emper-a t u r e , t h e s ol u bi li t y of a l l s u bs t a n c es i n cr e a s es w i t hi n cr e a s in g d e ns i t y . At co ns t a n t d e n si t y a n i n cr e a s e i ntemperat ure results in an increase in solubility. This is aresult of increasing vapor pressure of the solid.

The solubilities of all fa t-soluble vitam ins in supercriticalcarbon dioxide under the conditions investigat ed ar e in th era nge of 10 g/kg, except for -carotene, which is 3 ordersof magnitude less soluble.

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P ereira, P. J .; Ferreira, L. E.; Nunes da P onte, M. P ha se equilibria forsy ste ms wi th C O2 an d tocopherol containing mixtures. Pr oceedin gsof the 3rd International Symposium on Supercrit ical Fluids, S t r a s -bourg 17-1 9, O ctober 1 99 4; I nst i tut Nat i onal Pol y te chni q ue deLorra ine (INP L), Vand oeuvre-Les-Nan cy Cedex, F ra nce, 1994; Tome1, pp 89-94.

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Skerget, M.; Knez, Z.; Habulin, M. Solubility of -carotene a nd oleicac i d i n de nse C O2 and data c orre l at i on by a de nsity ba se d mode l.F l u i d Ph a s e Eq u i l i b . 1995, 10 9, 131-138.

Z eh n d er , B . H . D e t er m i na t i on o f m a s s t r a n s f er c oe ff ic ie n t s a n dequilibrium solubilities in fluid-fluid systems at supercritical condi-tions by means of NIR spectroscopy. D issertat ion ETH Zurich/Schweiz, 1992 (in G erman ).

Received for review J une 27, 1996. Accepted October 9, 1996.X

F in a n ci a l s u pp or t of t h is w or k b y t h e D e ut s ch e F or s ch u n gs -gemeinschaft (Gra nt Br 846/9-2) is gra tefully a cknowledged.

J E960219M

X Abstract published in Advance ACS Abstracts, November 15, 1996.


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