Density and Partial Mo lar Volumes of Binary Mixtures for the Dimethyl Ether of a Glycol + Eth a nol from T = K to T = 318.

Transcription

1 Jour nal of the Chi nese Chem i cal So ci ety, 00, 49, Density and Partial Mo lar Volumes of Binary Mixtures for the Dimethyl Ether of a Glycol + Eth a nol from T = 88.5 K to T = 38.5 K Su-Chen Ku ( ) and Chein-Hsiun Tu* ( ) De part ment of Ap plied Chem is try, Prov i dence Uni ver sity, Shalu, Taiwan 433, R.O.C. Den sities of {xch 3(OCH CH ) OCH 3 + ( - x)c H 5OH} for = - 4 at T = (88.5, 98.5, 308.5, and 38.5) K have been mea sured over the en tire mole-fraction range. The mea sure ments were made by means of a vi brat ing-tube densimeter. From these den si ties, some de rived quan ti ties, such as par tial mo lar vol umes and par tial ex cess mo lar vol umes have been ob tained. Values of the lim it ing par tial mo lar vol umes and thence of the lim it ing par tial ex cess mo lar vol umes of the com po nents have been de rived. The den si ties can be ex - pressed in terms of fourth-degree poly no mi als with re spect to the mole frac tion of the gly col. The tem per a ture has no sig nif i cant ef fect on the par tial mo lar vol umes of the glycols with = 3 and 4 in eth a nol. These vol u - met ric prop er ties are dis cussed in terms of mo lec u lar in ter ac tions be tween the gly col and eth a nol. IN TRO DUC TION Mixing prop er ties, such as ex cess mo lar vol ume and ex cess mo lar enthalpy have been used as a qual i ta tive and quan ti ta tive guide to un der stand the mo lec u lar in ter ac tions be tween the com po nents of the mix ture, to de velop new the o - ret i cal mod els, and also in car ry ing out en gi neer ing ap pli ca - tions in the pro cess in dus try. Data of these prop er ties can be ob tained ex per i men tally or by us ing gen er al ized meth ods that per mit the cal cu la tion of the prop er ties of mix tures. The de vel op ment of a cal cu la tion method re quires that an ad e - quate da ta base should be avail able. Al though many tab u lated val ues of the above prop er ties are gen er ally avail able for the pure sol vents, lit er a ture data rel a tive to var i ous bi nary mix - tures are of ten lack ing. The pres ent work was ori ented to ward ob tain ing an ac - cu rate set of mea sure ments of the den si ties of (the dimethyl ether of a gly col + eth a nol): {xch 3(OCH CH ) OCH 3 + ( - x)c H 5 OH} for = - 4 at four tem per a tures (88.5, 98.5, 308.5, and 38.5) K over the en tire mole-fraction range. Ac cord ingly, some de rived quan ti ties (par tial mo lar vol umes V, par tial ex cess mo lar vol umes V E, lim it ing par tial mo lar vol ume V, and lim it ing par tial ex cess mo lar vol ume V E, ) have been ob tained. These sys tems were cho sen in or der to study the mo lec u lar in ter ac tions be tween the etheric ox y gen (-O-) and the hydroxyl (-OH) groups un der the in flu ence of the changes of the -OCH CH - unit for spe cies with a com - mon alkyl chain and their sen si tiv i ties to vari a tions in com po - si tion and tem per a ture un der at mo spheric pres sure. EX PER I MEN TAL SEC TION Ma te rials The chem i cals used were of an a lyt i cal grade and ob - tained from Aldrich, Tedia, and SHOWA. The gas chro mato - graphic anal y sis of pure com po nents showed that the ma jor peak area ex ceeded 99.9 per cent for eth a nol and eth yl ene gly - col dimethyl ether, 99.6 per cent for di- and tetraethylene gly - col dimethyl ether and 99.3 per cent for triethylene gly col dimethyl ether. All chem i cals were used with out fur ther pu ri - fi ca tion. The pu rity of the fi nal sam ple was also checked by mea sur ing the den si ties and re frac tive in di ces at T = 98.5 K, which agreed rea son ably well with the cor re spond ing lit - er a ture val ues -8 as shown in Ta ble. Re frac tive in di ces, n D, of pure chem i cals were mea sured with a dig i tal refractometer RX-5000 (ATAGO, To kyo, Ja pan), with an un cer tainty of units. Procedure Liq uids were dried over ac ti vated mo lec u lar sieves type 0.4 nm from Aldrich. All dried liq uids were boiled to re - move dis solved air. Sam ples were pre pared by mass in a 50-cm 3 Erlenmeyer flask pro vided with a joint stop per, us ing a Precisa 6SMA bal ance with an ac cu racy of g. The un cer tainty of the mole frac tion in com po si tion was be - lieved to be less than -4. Den sities were mea sured with an Anton Paar DMA-58 vi brat ing-tube densimeter ther mo - stat i cally con trolled to within 0.0 K. Cal i bra tion was per - formed at at mo spheric pres sure pe ri od i cally, in ac cor dance Ded i cated to the cel e bra tion of the sev en ti eth an ni ver sary of Chem i cal So ci ety the lo cated in Tai pei.

2 65 J. Chin. Chem. Soc., Vol. 49, No. 5, 00 Ku and Tu Table. Comparison of Measured Densities and Refractive Indices of Pure Components with Literature Values at 98.5 K Compound /g cm -3 n D This study Literature This study Literature Ethanol Ethylene glycol dimethyl ether Diethylene glycol dimethyl ether Triethylene glycol dimethyl ether Tetraethylene glycol dimethyl ether with spec i fi ca tions, us ing deionized wa ter and dry air. Pre - cau tions were taken in or der to avoid evap o ra tion losses and air dis solved dur ing the ex per i men tal work. An av er age of at least three mea sure ments was taken for each com po si tion. The un cer tainty of the den sity mea sure ments was es ti mated to be less than 0-4 g cm -3. The ex cess mo lar vol umes and par tial mo lar vol umes were cal cu lated from den sity data and the un cer tain ties were es ti mated to be within 0 - cm 3 mol - and cm 3 mol -, re spec tively. RE SULTS AND DIS CUS SION The ex per i men tal den si ties for all of the bi nary mix - tures are pre sented in Ta bles to 5. The mea sured den si ties are ex pressed as a poly no mial in the mole frac tion of gly col, x, 4 i 0 to es ti mate the ad just able co ef fi cients a i by a mul ti ple re gres - sion anal y sis based on the least-squares method. The stan - dard de vi a tion ( ) was de fined as: N i i a x [ ( ) /( N 4)] i expt calc / i i where N is the num ber of points. expt and calc are ex per i men - tal den si ties and cal cu lated den si ties, re spec tively. The val - ues of co ef fi cients a i of equa tion () along with the stan dard de vi a tions be tween the ex per i men tal and fit ted val ues and are sum ma rized in Ta ble 6. The val ues for lie be tween 4 () () 0-5 g cm -3 and g cm -3 and the larg est value cor - re sponds to tetraethylene gly col dimethyl ether + eth a nol mix tures at 88.5 K. From a the o ret i cal point view, a deeper ex am i na tion of the par tial de riv a tive prop er ties ap pears to be of par tic u lar in - ter est. The par tial mo lar vol umes can be cal cu lated from equa tion () for gly col (V ), V M x M x M d dx ( x ) and the cor re spond ing equa tion for eth a nol (V ), V M x M x M d dx ( x ) based on the der i va tions in Glasstone. 9 is the den sity of the mix ture and x,, M, x,, and M are the mole frac tions, den si ties, and mo lec u lar weights of pure com po nents (glycols) and (eth a nol), re spec tively. Values of the V and V are given in Ta bles 7 to 0. The par tial ex cess mo lar vol ume ( V E i ) of the ith com po nent in a bi nary mix ture can be de ter - mined from par tial mo lar vol ume data by equa tions (3) and (4): E V i Vi Vi where V i is the mo lar vol ume of pure com po nent i. Figs. to 4 show the trends of V i E with the cor re spond - ing mole frac tion for each of the four glycols + eth a nol mix - tures at T = (88.5 and 38.5) K. The be hav ior is quite sim - i lar to that re ported for wa ter-ethylene gly col mix tures. 0 Large and pos i tive val ues of par tial ex cess mo lar vol umes (3) (4) (5)

3 Thermophysical Data of Mixing Property J. Chin. Chem. Soc., Vol. 49, No. 5, Table. Experimental Densities ( ) for Binary Mixtures of Ethylene Glycol Dimethyl Ether () (88.5 to 38.5) K Ethanol () from T x /g cm -3 x /g cm -3 x /g cm -3 x /g cm -3 T 88.5 K T 98.5 K T K T 38.5 K Table 3. Experimental Densities ( ) for Binary Mixtures of Diethylene Glycol Dimethyl Ether () (88.5 to 38.5) K Ethanol () from T x /g cm -3 x /g cm -3 x /g cm -3 x /g cm -3 T 88.5 K T 98.5 K T K T 38.5 K

4 654 J. Chin. Chem. Soc., Vol. 49, No. 5, 00 Ku and Tu Table 4. Experimental Densities ( ) for Binary Mixtures of Triethylene Glycol Dimethyl Ether () + Ethanol () T = (88.5 to 38.5) K x /g cm -3 x /g cm -3 x /g cm -3 x /g cm -3 T = 88.5 K T = 98.5 K T = K T = 38.5 K Table 5. Experimental Densities ( ) for Binary Mixtures of Tetraethylene Glycol Dimethyl Ether () + Ethanol () from T = (88.5 to 38.5) K x /g cm -3 x /g cm -3 x /g cm -3 x /g cm -3 T = 88.5 K T = 98.5 K T = K T = 38.5 K

5 Thermophysical Data of Mixing Property J. Chin. Chem. Soc., Vol. 49, No. 5, Table 6. Coefficients and Standard Deviations of /g cm -3 of Equation () for the Binary Mixtures from T (88.5 to 38.5) K T/K a 0 0 a 0 a 0 a 3 0 a Ethylene glycol dimethyl ether Ethanol Diethylene glycol dimethyl ether Ethanol Eriethylene glycol dimethyl ether Ethanol Tetraethylene glycol dimethyl ether Ethanol may in di cate a rup ture of or der, whereas small pos i tive or neg a tive val ues may in di cate the ex is tence of spe cific in ter - ac tion be tween com po nents. It can be seen from Figs. to 4 that di-, tri-, and tetraethylene gly col dimethyl ether in eth a - nol have a clear min i mum in V E (oc curred at x 0.0) and the po si tion of the min i mum is af fected only slightly by tem - Fig.. Par tial ex cess mo lar vol umes of eth yl ene gly col dimethyl ether () and eth a nol () in bi nary mix tures at T = 88.5 K (full lines) and T = 38.5 K (dashed lines). Fig.. Par tial ex cess mo lar vol umes of diethylene gly - col dimethyl ether () and eth a nol () in bi nary mix tures at T = 88.5 K (full lines) and T = 38.5 K (dashed lines).

6 656 J. Chin. Chem. Soc., Vol. 49, No. 5, 00 Ku and Tu Table 7. Partial Molar Volumes V and V for Binary Mixtures of Ethylene Glycol Dimethyl Ether () Ethanol () from T (88.5 to 38.5) K x V / V / V / V / cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - T 88.5 K T 98.5 K T K T 38.5 K per a ture changes. The step wise ad di tion of -OCH CH - groups to the gly col mol e cules leads to a pro gres sive deep en - ing of the min i mum. The monotonic in crease in V E is ob - served in the con cen tra tion range x 0.0 to x 0.50 and a nearly con stant value is found af ter x The sharp changes in V E at low mole frac tions of CH 3(OCH CH ) OCH 3 would im ply the rapid changes in or der and hence struc ture or clus ter ing in the eth a nol en vi ron ment. A slightly dif fer ent per spec tive of the same sit u a tion is ob tained from look ing at the eth a nol-rich par tial ex cess mo -

7 Thermophysical Data of Mixing Property J. Chin. Chem. Soc., Vol. 49, No. 5, Table 8. Partial Molar Volumes V and V for Binary Mixtures of Diethylene Glycol Dimethyl Ether () Ethanol () from T (88.5 to 38.5) K x V / V / V / V / cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - T 88.5 K T 98.5 K T K T 38.5 K lar vol umes of eth a nol (V E ). That the val ues should be come more pos i tive as the num ber of -OCH CH - groups in creases has been at trib uted to a struc ture mak ing ef fect be ing pro - moted in the aggregative char ac ter of the eth a nol mol e cules that are in di rect con tact with the -OCH CH - groups. There is seen to be a fairly steady de crease to neg a tive val ues in V E as the -OCH CH - groups are in creased in the gly col-rich mix tures. A nearly hor i zon tal stretch of the V E curve or even

8 658 J. Chin. Chem. Soc., Vol. 49, No. 5, 00 Ku and Tu Table 9. Partial Molar Volumes V and V for Binary Mixtures of Triethylene Glycol Dimethyl Ether () + Ethanol () from T = (88.5 to 38.5) K x V / V / V / V / cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - T = 88.5 K T = 98.5 K T = K T = 38.5 K a slightly max i mum (near x = 0.80 in Figs. to 4) ap pears in the same ap prox i mate con cen tra tion range for di-, tri-, and tetraethylene gly col dimethyl ether + eth a nol mix tures. No ex pla na tion has been found for this phe nom e non. The in - crease in a tem per a ture leads to a higher value in V i E as shown in Figs. to 4, but no sig nif i cant in crease on ei ther V E or V E has been ob served for tri- and tetraethylene gly col dimethyl ether + eth a nol mix tures. The lim it ing par tial mo lar vol umes

9 Thermophysical Data of Mixing Property J. Chin. Chem. Soc., Vol. 49, No. 5, Table 0. Partial Molar Volumes V and V for Binary Mixtures of Tetraethylene Glycol Dimethyl Ether () Ethanol () from T (88.5 to 38.5) K x V / V / V / V / cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - cm 3 mol - T 88.5 K T 98.5 K T K T 38.5 K of the glycols and eth a nol (V and V ) could be ob tained from equa tions (3) and (4) by con sid er ing x and x to be zero, re spec tively. The lim it ing par tial ex cess mo lar vol umes E, (V i ) could then be cal cu lated from equa tion (5) by con sid - er ing x i to be zero for each case. In Ta ble, the val ues of V i E, and V i be tween the tem per a tures 88.5 K and 38.5 K for the bi nary mix tures are en closed. These val ues show that - V of the gly col in eth a nol in creases by about 40 cm 3 mol

10 660 J. Chin. Chem. Soc., Vol. 49, No. 5, 00 Ku and Tu Table. Limiting Values of the Partial Molar Volumes V i and the Partial Excess Molar Volumes E, V of the Binary Mixtures from T (88.5 to 38.5) K i T/K V /cm 3 mol - V /cm 3 mol - E, V /cm 3 mol - E, V /cm 3 mol - Ethylene glycol dimethyl ether () Ethanol () Diethylene glycol dimethyl ether () Ethanol () Triethylene glycol dimethyl ether () Ethanol () Tetraethylene glycol dimethyl ether () Ethanol () Fig. 3. Par tial ex cess mo lar vol umes of triethylene gly - col dimethyl ether () and eth a nol () in bi nary mix tures at T = 88.5 K (full lines) and T = 38.5 K (dashed lines). Fig. 4. Par tial ex cess mo lar vol umes of tetraethylene gly col dimethyl ether () and eth a nol () in bi - nary mix tures at T = 88.5 K (full lines) and T = 38.5 K (dashed lines). for each ad di tional -OCH CH - group. The strong in flu ence of eth a nol in tetraethylene gly col dimethyl ether liq uid phase was ob served for V E, E, and V. AC KNOWL EDGE MENTS The au thors wish to ex tend their deep grat i tude for the

11 Thermophysical Data of Mixing Property J. Chin. Chem. Soc., Vol. 49, No. 5, sup port by the Na tional Sci ence Coun cil of Re pub lic of China. Re ceived April, 00. Key Words Den sity; Par tial vol umes; Gly col ether; Eth a nol. REF ER ENCES. Orge, B.; Iglesias, M.; Ro dri guez, A.; Canosa, J. M.; Tojo, J. Fluid Phase Equilib. 997, 33, Riddick, A.; Bung er, W. B.; Sakano, T. K. Or ganic Sol vents, Phys i cal Prop erties and Method of Pu ri fi ca tion, 4th ed.; Wiley Interscience: New York, Ortega, J.; Matos, J. S. Ma ter. Chem. Phys. 986, 5, Wallace, W. J.; Mathews, A. L. J. Chem. Eng. Data 963, 8, Wallace, W. J.; Shephard, C. S.; Under wood, C. J. Chem. Eng. Data 968, 3, Treszczanowicz, T. Thermochim. Acta 990, 60, Dethlefsen, C.; Hvidt, A. J. Chem. Thermodyn. 985, 7, McGee, R. L.; Wallace, W. J.; Ratalczak, R. D. J. Chem. Eng. Data 983, 8, Glasstone, S. Ther mo dy nam ics for Chem ists; Van Nostrand, New York, N.Y., Ray, A.; Neméthy, G. J. Chem. Eng. Data 973, 8, Domínguez, M.; Gascón, I.; Valén, A.; Royo, F. M.; Urieta, J. S. J. Chem. Ther mo dy nam ics 000, 3,