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SOLUBILITIES OF GASES IN AQUEOUS SOLUTIONS OF EAK *

Eizo SADA, Shigeharu KITO and Yoshitaka ITO

W Department of Chemical Engineering, Nagoya University, Nagoya

Solubility data of gases in aqueous solutions are very Solubilities of and in important to engineers in practical uses such as gas- pure at 25 °C were0.7597 and 0.5512, respective- contact operation. Hence, many experimental ly, as the Bunsen absorption coefficients. The accuracy data have been reported for various gas solubility of these values has been discussed elsewhere3'6). systems in aqueous solutions. For the solubilities of The systems studied in this work are as follows: gases in aqueous electrolyte solutions in particular carbon dioxide-formic , , , there are plentiful data, and also some empirical corre- oxalicacid, citric acid andphosphoric acid, and nitrous lations have been presented by Markham and Kobe1'2) , oxide-formicacid, acetic acid^propionic acid and oxal- van Krevelen and Hoftijzer7), and Onda et al.s>A). For other gas- systems, however, few Results and Discussion experimental data have been presented and no quanti- ic acid. ative correlation has yet been proposed. The results of the solubility determinations are For aqueous solutions of weak electrolytes such as shown in Table 2 for carbon dioxide and in Table 3 the organic acids and amines, it should be emphasized for nitrous oxide. Thepe results are also shown in that there are no experimental data. Considering these, graphical form in Figs. 1, 2 and 3. Inthese figures, the dependence of log(a/aw), which means the negative t the authors have recently observed the solubilities of nitrous oxide and in aqueous solutions of logarithm of the activity coefficient of the gas species, monoethanolamine and discussed the possibility ofpre- on the of weak acid is represented. As diction6). can be seen from these figures, these plots cannot be In the present work, in order to build up gas solu- correlated by straight lines as in the case of aqueous bility data for these systems, solubilities of carbon di- solutions. Furthermore, these curves are all concave oxide and nitrous oxide in aqueous solutions of the in contrast to those for the aqueous solutions of mono- weak acids were measured by a volumetric method at ethanolamine. 1 atm and 25°C, and the results studied. In general, solubility of gas is discussedbased on the thermodynamic behavior of the solution. However, for Experimental aqueous solution of weak acid, this seems to be very Experimental apparatus and procedures adopted in complicated since the of the weak acid dis- this work were the same as those in the previous sociate partially into in the aqueous solution, and papers3'4'6). As shown in that work, the reliabilities of the fraction of dissociated species cannot be neglected the apparatus and procedures have been confirmed. in some cases. Therefore, in the present work, an em- grade weak acids of guaranteed purity irical correlation of solubility data was attempted.

were used without further purification, and distilled p As previously mentioned, the Setchenow equation is water was used. In Table 1, thedensities and refractive not applicable to such cases, so the authors tried to indices of water, , acetic acidand propionic correlate the experimental results by the following acid at 25°C are shown to comparewith the values in hyperbolic equation.

the literature5). For gases, on the other hand, carbon a dioxide was supplied from a commercial cylinder, and =aC+- 1+bC nitrous oxide of high purity was supplied by Showa DenkoCo., Ltd., in Tokyo, and the purities were veri- This equation was proposed by Markham and Kobe1'2) fied by gas chromatographic analyses as more than 9.8% for both. Table 1 Physical properties of water and organic acids The concentration of weak acid was determined by volumetric with to a phe- 9

Substanceobs.å å tf2S lit.5> nolphthalein end-point. obs. Water Formic acid Received on October 3, 1973 Acetic acid T464 £-£MTfr=HI K^BT * Propionic acid

VOL7 NO.1 1974 57

1.19981.04400.98830.997041.214051.043660.98801.33251.36881.37181.38451.369381.36981.3843(1)1lit.5) 0|W^

O HCOOH j / O(o_ OCH3COOH O C2H5COOH / OHCOOH -0.05- \ *\^ OCH3COOH OC2H6C00H e C2H204 //? ^,0.05a - // - Jy5.0.10 - °C2HA X. o c6hto7 X^ O H3P04 ^\

-0.15I 1 1 I 2 3 4 0 1 2 3 4 5 0 I 2 C (mole/l) C (mole/1) C (mole/I) Fig. 1 Solubilities of carbon dioxide Fig. 2 Solubilities of carbon dioxide Fig. 3 Solubilities of nitrous oxide in aqueous solutions of weak acids at in aqueous solutions of weak acids at in aqueous solutions of weak acids l atmand25 C(l) 1 atm and 25°C (2) at1atmand25 C

Table 2 Solubilities of carbon dioxide in aqueous Table 3 Solubilities of nitrous oxide in aqueous weak acid solutions at 1 atm and 25 C weak acid solutions at 1 atm and 25 C Weak acid C a Weak acid C a

Formic acid 0.3607 0.7480 Formic acid 0.6234 0.5481 0.7014 0.7422 1.3125 0.5529 1.2525 0.7432 1.4033 0.5542 1.4028 0.7472 2.4451 0.5579 2.7204 0.7632 2.8999 0.5653 3.5120 0.7790 Acetic acid 0.3096 0.5476 Acetic acid 0.4282 0.7667 0.5012 0.5472 0.9155 0.7712 0.5466 0.5458 1.7973 0.7887 0.6188 0.5472 2.5150 0.8108 1.1204 0.5610 2.7928 0.8212 1.8731 0.5742 3.7938 0.8561 2.2123 0.5814 3.8939 0.8591 2.2750 0.5815 4.2993 0.8844 2.6174 0.5897 Propionic acid 0.5405 0.7655 2.6975 0.5899 1.1414 0.7769 3.2019 0.6071 1.9819 0.7924 3.5392 0.6193 215727 0.8164 3.7865 0.6227 2.6379 0.8140 Propionic acid 0.4319 0.5583 3.0330 0.8358 0.8473 0.5612 4.0922 0.9127 1.3523 0.5711 4.7848 0.9971 2.3654 0.5985 0.1774 0.7512 3.2994 0,648 1 0.3861 0.7447 Oxalic acid 0.2091 0.5471 0.5110 0.7418 0.2433 0.5468 0.7776 0.7357 0.5227 0.5418 0.9013 0.7374 0.8434 0.5380 Citric acid 0. 1867 0.7381 0.8567 0.5353 0.3874 0.7179 0.7365 0.6966 Table4 Values ofa and b 1.0477 0.6741 Gas Weak acid a b 1.2662 0.6648 1.3524 0.6611 CO2 Formic acid 0.1018 0.1399 Phosphoric acid 0.701 3 0.6714 Acetic acid 0. 1066 0.0997 1.0923 0.6405 Propionic acid -0.0838 - 0.0867 1.6024 0.6076 Oxalic acid 0.1460 0.2147 1.7412 0.5958 Citric acid 0.0861 0.2412 2.0573 0.5731 Phosphoric acid 0.0382 0.2280 N2O Formic acid 0.0716 0.0776 to correlate the solubilities of carbon dioxide and Acetic acid 0.1231 0.1298 nitrous oxide in aqueous salt solutions. In this work, Propionic acid 0.1529 0.1523 however, the Bunsen absorption coefficient and molari- Oxalic acid 0.0335 0.0683

58 JOURNALOF CHEMICALENGINEERING OFJAPAN ty are used as solubility and concentration of solute, ná" = at 25:°Q, [-J a =Bunsenabsorption coefficient [-] respectively. The experimental results were fitted to this equation by the nonlinear least aquare method. Literature Cited The calculated values ofa and b are listed in Table 4, 1) Markham, A. E. and K. A. Kobe: J. Am., Chem:Soc, 63, 449 and the fitting curves of Eq.(l) to the experimental (1941) data are also shown in Figs. 1/2 and 3. From these 2) Markham, A. E. and K. A. Kobe: J. Am* Chem. Soc, 63, 1165 (1941) figures, it is found that Eq.(l) can correlate the solu- ) Onda, K.5 E. Sada, T. Kobayashi, S. Kito and K. Ito: J. bility data for these systems well. The standard devi- Chem. Eng. , 3, 18 (1970) ation of this correlation was 0.0140. ) Onda, K., E. Sada, T. Kobayashi, S. Kito and K. Ito: J. Chem. Eng. Japan, 3, 137 (1970) Nomenclature ) Riddick,J. A. and W. B. Bunger: "Organic ", 3rd Ed., Wiley-Interscience, New York (1970) a =constant in Eq.(l) [//mole] 6) Sada, E. and S. Kito: Kagaku Kogaku, 36, 218 (1972) b =constant in Eq.(l) [//mole]

7)3 4 van Krevelen, D. W. and P.J. Hoftijzer: Chim. Ind. XXIeme 5 C =molarity of weak acid [mole//] Congr. Int. Chim. Ind., 168 (1948) «/25 = at 25°C [g/cm3]

REMARKS ON THERMODYNAMIC CONSISTENCY TESTS OF MULTICOMPONENT VAPOR-LIQUID EQUILIBRIUM DATA*

Isamu NAGATA Department of Chemical Engineering, Kanazawa University, Kanazawa

may be possible by use of some analytical functions ex- Introduction pressing the liquid-phase activity coefficient as a Thermodynamic consistency tests of ternary iso- function of composition and . Considerable thermal vapor-liquid equilibrium data based upon the amounts of effort have beenmade to show the applica- direct use of the Gibbs-Duhem equation have been bility of these equations in the calculation of multi- proposed in the literature9'12'13). Herington9> sug- component vapor-liquid equilibrium data. The local gested that graphical integration should be performed composition equations which have built-in temperature either on lines of constant mole ratio of two compo- terms can predict multicomponent equilibrium data nents,-or on lines of constant mole fraction of one of the from only binary parameters without any additional components. The method usually requires that experi- parameter with better accuracy than the Margules and mental data must lie on the selectedlines. Since experi- van Laar equations do20). The present author17) did mental data are not generally observed on the selected extensive studies concerning the prediction accuracy of lines, the interpolation of existing data is unavoidable the Wilson, nonrandom two-liquid (NRTL), and Heil to provide values on the chosen lines. The necessity ofa equations for seventy eight multicomponent systems great number of experimental data and that of inter- and demonstrated that the Wilson equation is the best polation may be the major disadvantages of the in overall performance on the basis of the systems method. To avoid these disadvantages, Li and Lu12) studied. proposed a method that involves numerical inte- In this work the author willshow that the Li-Lu and gration around selected loops of experimental points. McDermott-Ellis tests and the Redlich-Kister equation The method is called the closed or the open test, de- cannot always check experimental errors of particular pending upon whether the first and last points in the forms which the Wilson equation may predict. loops may or may not be linked. Li and Lu placed on asic Equations their test only the limination that the points should not be widely separated so that the error in numerical The condition for consistency described by Li and integration will be minimized. McDermott and B Luis

Ellis13) stated that the open loop only tests the end S S%w [lnri(ii-i) ~W«(»+i)] =0 points and does not test the internal points in the loop, and that the open and closed loop tests on the same where n refers to the n-th point in the loop ofN points. points can give different deviations when random is the number of components. errors are present. They modified the Li-Lu test to M McDermott and Ellis suggested the pair consistency present a pair consistency test. Such consistency tests equation D=ib[xUn)+xUn+i)]DnrUn+i)-]nrUn)'] (2) Received onJuly 6, 1973 T920 &RTMv£32-40-20 * where the absolute value of D lies between 0.00 and

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