equilibrium data - water and acetic acid, water and methanol, and water and ethanol

7/25/2019 Equilibrium data - water and acetic acid, water and methanol, and water and ethanol

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December. 1933 I N D U S T R I A L A N D E X G I N E E R I N G C H E M I S T R Y 1331

(14) In te rna t iona l Cr i t i ca l Tab les , Vol. I11 a n d V, McGraw-Hill,

(15) Ki rk br ide and hfoCabe, IKD. SG. C H E M . , 3 , 625 (1931).(16) Kraussold, Forsch . Geb ie fe Inoen ieu rw . , d 3 , 21 (1932).(17) Landolt-Biirnstein, Phys. Chem. Tabe l l en , Spr inger, 1912 .(18) Lawrence and Sherwood, ISD. ESG. CHEM., 3, 301 (1931).(19) R lcAdams and Frost, I h i d . , 14 , 13 (1922) .(2 0) h le r ke l, D ie G r u n dl a ge n d e r ~ ~ ~ i r m e ~ ~ b e r t r a g l i n g , . 140,

(21) h lonrad , I X D . ESG. CHEX, 24, 505 (1932).(22) Monrad and Badger, I b i d . , 22, 1103 (1930).

1927.

Theodor Steinkoyff, Dresden and Leipzig, 1927.

(23) Morris a n d W h i t m a n , I b i d . , 20, 234 (1928).(24) Kusselt , 2 . Ver. deut . I n g . , 54, 1154 (1910).(25) I b i d . , 60, 541 (1916).(26) Othmer, IKD. ESQ. C H E Y. , 1, 576 (1929).(27) Sherwood , Ki ley, and Mang sen , I h id . , 24, 273 (1932).(28) Webster, Tr a n s . I n s t . Engr. Sh ipSu i lde r s , Scot., 57, 5 8 (1913).

R E C & V E DM a y 13,1933. Presented before the Division of Petroleum Chem-iatry a t the 85th Meeting of the American Chemical Society, Warrhington,D. C. , March 26 t o 31, 1933.

Studies in Distillation11. Liquid-Vapor Equilibria in t h e Systems Ethanol -Water, M ethanol -

Wat,er, and Acetic Acid-Water'

L. V LL L CE CORNELL ND RALPHE. fiIONTONNA University of Minnesota, h'hneapolis, Minn.

STHE course of an experi- The nieihod of Rosanoff, Bacon, and White t h e i n d i c a t e d leve l i n a s u it -menta l s tudy o f the plate has been used for the determination, at atmos- able l ig h t o il , held a t a tem-

p e r a t u r e h i g h e n o u g h t oefficiencies Of a pheric pressure, of the liquid-vapor equilibriump r e v e n t condensation of theolumn for different binary mix-

tures, i t was found th at values Of systems ethanol-water, mefkanol- v a p o r s . T h e oil b a t h w a sconsiderably Over 100 per writ water, and acetic acid-water. T h is method is heated electrically, the tem-were obtained for ethanol-water shown to be consistent and reliable. Th e equilib- perature being controlled towhen the most reliable equi- rium data obtained y t are *0.5 c . b y t h e m e r c u r y

bulb, M, through a relay. T h eibrium data were used* The cally wit h all other data fou nd in the literature. t e m p e r a t u r e w a s varied b yethod of calculation was thatproposed hy McCabe a nd Thiele raising or lowering the contact12) and gave the plate require ments for theoretically perfect wire in th e capillary tub e,C.

operation; hence, it was indicated tha t the equilibrium data Th e heater,H , in th e still, S, was of KO 4 nichrome wirewere not accurate. It was decided, therefore,t o determine in the work on th e alcohols, bu t for acetic acid-water it wasthe eauilibrium curve for ethanol-n-aterby a reLable metho d, necessary to changeto KO 0 platinum wire. This heater

Igraphi-

and later also those for methanol-water and acetic acid-mater.

EXPCRIMEKTAL ROCEDURE

The re are a number of differentmethods for the determination ofequilibriuni c urves of bi nar y liquidm i x t u r e s . d careful review ofthe l i te ra ture ind ica ted tha t themethods of Rosanoff and his co-w o rk er s a r e r e l i a b l e . T h ey a r er e c o m m e n d e d by Y o u n g (23).Rosanoff , Lam b, and Br eithut 19)a n d R o s a n o f f a r id E as le y 1 8 )ha v e de ve lo ped a n a c c u r a t e bu t

i n v o l v e d m e t h o d . R osa noff,Bacon, and White ( 1 7 )have workedout a less involved method basedon an entirely different principle.Young ( 2 2 ) s ta tes tha t these twomethods have been found to giver es ul ts in good a g r e e m e n t , a n dfor this reason the simpler methodof Rosanoff, Baco n, and W hite wasselected for this work.

A diagram of the a ppar atus isshown in Figure 1. The still, ofP yre x g l a s s , w a s i m m e r s e d t o

The first paper in this series wasp u b l i e h e d b y L. H. Shirk and R. E.

Montonna, IND. ENQ. C H E M . , 9 907-11(1927).

.AY

uT0 AC

31L LEV - -11_ - - -

IN CENTIMETERS GLASS WORM

CONDENSER

ALL DIMENSIONS

FIGURE . APPARATUSOR DETERMINATIONFCOMPOSITIONF VAPORSROM BOILING INARYSOLUTIONS

was a small coil wound in th e fo rmof a spiral as indicated in Figure1,and the le n g t h s of wire were asf o l l o w s : KO. 4 n i c h r o m e , 36inches (91.4 cm .); No. 30 plat inum,38 inches (96.5 cm.). Con tact wasmade w ith the mercury in the lead-in tubes by means of loops of N o .24 platinum wire sealed throughthe glass.

I n t h e work with th e alcohols, thecorks which were in contact withhot vapors were covered with leadfo il, b u t t h i s w a s r e m o v e d f o racetic acid-water.

The oil bath was heated to a tem-p e r a t u r e 2 to 5 C. above theinitial boiling point of the liquidmixture to be tested. The appara-tus was dried before eachrun bydrawing air through i t for 10 to 15m i n u t e s . T h en t h e t em p er at ur einside the still was allowed to riseto 4 t o 5 C. below tha t of th e oilb ath , a n d a b o u t 130 ml. of t h ebinary mixture were run into theinner boiling vessel, S, through A .The composition of this liquid hadbeen determined previously. Theaddition of the liquid lowered the

tem pera ture shown by the still ther-mometer, and , as soon as this had


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Vol. 25, No. 12332 I N D U T R I A L A N D E I\ G I I\ E E R I N G C H E M I T R Y

risen to a value 2 t o 3 C. below th e initial boiling point ofthe binary mixture, the electric heater,H , was turned on, thedistillation commencing in a bou t5 minutes. Enough heat wassupplied to distill over 60 t o 70 grams in 30 t o 45 minutes.

During th e distillationthe o il b i th tempera turewas main ta ined 2 t o

4 C. above tha t in thes t i l l . T h i s d iff er en cewas so small tha t therecould hardly have beenany superheating of theinner chamber, and yet ,as will be shown later,there was evidently noc o n d e n s a t i o n . F o ra c et i c acid-water andf o r t h e r u n s a t t h ehigher concentrations ofthe alcohols, four frac-t i o n s O f l 3 to l 5 ml*were collected, but for

t he o the r a l coho l r unsfive were taken. Th e fraction s were collected i n small vials(20 t o 25 ml.) connected to t he bottom of t he condenser b yacork with only a small opening to the air. Since the con-densed distillate was qu ite cold (about15 C.), no other pre-caution was needed to preve nt loss by evaporation.

A t the end of the r un th e waste l iquor was siphoned fromthe st i l l, a nd a sample was bottled and analyzed if desired.Th e fractions of distillate were weighed and thei r compositionsdetermined. From these data were calculated the percentagecompositions for different tot al weights of distillate , assumingth at th e fractions were combined successively. By plottingthese values, it was possible to extrapolate back to zeroweight of distillate and obtain the composition of the firstinfinitesimal fraction of vap or evolved from th e liquid, which

was the desired vapor composition (curveA , Figure 2 ) . Bysimilar calculation th e composition of th e last infinitesimalfraction of vapor evolved from th e residual Iiquid in the stillcould be found (curveB, Figure 2) . For a more detailed de-scription of t he m eth od of calculation, the reader is referredt o the original article of Rosanoff, Bacon, and White 17).

FIGURE . DATA ROM APPARATUSOF ROSANOFF, ACON, ND WHITE

ON ETHANOL-WATER

MATERIALS.Absolute alcohol was prepared fromc. P. 95 per cent unde-

natured ethanol by treatment with lime followed by careful dis-tillation . The finished product was a frac tion distilling within0.1 C., and contained 99.8 to 99.9 per cent ethanol by weight(specific gravi ty, 0.7898 a t 20 C.).

General Chemical Companyc. P. methanol was fractionated ina 12-inch column sled with short glass tubes, the middle frac-tion (distilling over within 0.1 C . ) being used in this work.This fraction gave negative testsfor acetone, ethanol, aldehydes,and reducing substances when tested by the methods given byMurray f3 ) , and contained about 99.8 per cent methanol byweight (specific gravit y, 0.7923 a t20 C.),

Grasselli's reagent grade acetic acid was distilled through ashort column from chromic oxide to remove any formic acid, thefirst and last fractio ns being discarded. The middle fractionanalyzed 99.5 per cent acetic acid according to th e freezing point(data of Worden, 8 f ) and by titration with sodium hydroxide(freezing point, 15.64 C.).

METHODS F ANALYSIS. For both ethanol and methanol thecompositions of the samples were determined a t20' C. by meansof a 10-ml. pycnometer, using the specific gra vity da ta of theU. . Bureau of S tanda rds as given in the H andbook of Chemistryand Physics 4 ) or ethanol, and those from International CriticalTables IO) or methanol. The thermometer in the pycnometerstopper was checked against a Bureauof Stand ards thermometer.The compositionsof the original and residual liquids were deter-

mined in duplicate, w hile thoseof the various fractions were ob-taine d from one carefully made specific gra vity determination, acheck being run only when there was indication that this wasnecessary.

In several runs with ethanol and with methanol, determinationswere made with the AbbB refractometer, for reasons which willbe given later. Immersion refractometer scale readings weretaken from the Handbook of Chem istry and Physics( 5 ) , nd thesereadings were converted into refractive indices by means of atable published by Zeiss ( 2 4 ) .

Th e compositions of the acetic acid samples were determinedby titration with 0.5 N sodium hydroxide solution with phenol-phthalein as indicator, the solution being boiled to removecarbon dioxide. Duplicate determinations w ere made on theoriginal liquid and t he first two fractions, t he others being checkedonly when it seemed necessary to doso. Th e samples for analysiswere weighed out in small stoppered vials.

Redistilled water was used in all runs.

PRELIMINARY ESTS N THE APPARBTCS. Eight prelimi-nar y runs were made with ethanol-water to te st the reliabilityof the appara tus . With theexception of runsE and F, in which the conditions were themost abnormal, the apparatus gave consistent results overa wide range of operating conditions.

The da ta a re g iven in TableI.

FIGURE . ETHANOL-WATER QUILIBRIUM IAGRAM FIGURE . METHANOL-WATER QUILIBRIUMIAGRAM


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December, 1933 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I T R Y 1333

TABLE . PRELIMINARY TESTS ON APPARATUSO F ROSANOFF,B WON, AXD WHITE 1 7 )

(Ethanol-water)LENQTH V O L . TEMP. F VA P O R E t O H

OF o r F R I C - OIL VE- INR U N R U N CHARQE I O N S BATH L O C I T V b VA P O R

Mzn. M 1 . C . Cm./soc. Wt. %B 1E

CGADHF

12090603035353521

130130130100130130130100

92-101100-101

92-101100-101

92-101100-101

94-101100-101

2 . 32 . 84 .67 . 07 . 58 . 08 . 79 . 5

54 .053.754 .354.254 .55 4 . 354.554 .9

Composition of liquid charged to still = 10.75 per vent ethanol b y

b Average velocity, f o r the entire run, up the inside of the 3-cm. tubeweight; the initial boiling point was about 90' C.

(Figure 1 .

TABLE I. EXPERIMENTAL IQUID-VAPORQ U I L I B R I C X DATA

R C N

5350545548

346

444

520

678

11211243141542173318521922232 425262734282930313235363738394041

IFOR ETHANOL-WATER(730 to 750 mm. of mercury)

EtOH I N LIQUID E t O H IN VA P O RWt M o l e Wt. M o l e% frac tzon % f r a c t i o n

0.6 0.003 6.2 0.0251 . 1 0 . 0 0 5 1 0 . 9 0.0462.0 0,008 20.0 0.0892 . 1 0 , 0 0 9 1 9 . 9 0.0883 . 0 0 . 0 1 2 26.2 0.1223 .44 0 .014 29 .0 0.1384 . 9 0 ,020 37 .4 0.1906 . 1 5 0.025 42.3 0.2236 . 8 0.028 44.8 0.2418 . 5 0.035 49.3 0.275

10.14 0 ,042 53 .1 0.30713 .6 0 ,058 58 .9 0.35915.14 0 .065 61 .1 0.38017.14 0 .075 63 .0 0.40019.04 0 .084 64 .7 0.41719 .4 0.086 65.1 0.42220.9 0.094 66 .3 0 .43522 .7 0.103 67.8 0.45125.35 0.117 69 .1 0 ,46626.85 0.126 69.7 0.47329.932.953 3 . 336.638.041.2445 .148 .953 .057.0

0.1430.1610.1630.1840.1940.2150.2430.2720 .3050 .341

71 .372 .37 2 . 973 .774 .07 4 . 875 .97 6 . 877 .678 .7

0.4930 ,5050.5130.5230.5270.5370.5620.5640.5760 , 5 9 0

61 .3 0.382 79 .9 0 .60865.6 0.427 80.9 0.62368 .6 0.460 81 .7 0 .63670 .9 0.488 82.6 0.65074 .8 0.537 83.9 0.67178 .0 0 .581 85.0 0.6908 1 . 5 0.633 86.5 0.7158 3 . 9 0.672 87 .7 0 .7358 6 . 0 0.706 88 .8 0 .75688 .0 0 .741 90.0 0.77890 .1 0 .780 91 .3 0.8039 2 . 8 0.834 93 .3 0 .84494.20 0.864 94.31 0.86696.28 0 .910 96.16 0.90798.07 0.952 97 .88 0 ,948

When the weight distilled-per cent composition da ta forany of the runs in Table I were plotted, the curve producedhad an S-shape,as shown by curveC in Figure 2 . For liquidsof lower alcohol content t he curves were similar to curveD inFigure 2 . As may be seen, it was difficult to determine justwhere th e curve should cross they axis with only five pointsas a guide. I n order to overcome this difficulty, for ethanol-water an d methanol-water, the A bbe refractometer was usedto dete rmine the compositions of t he distillates from liquidsbelow 10 per cent by weight. Since the refractometer wasnot as accurate as the pycnometer, two runs were made onliquids of identical composition, one in the usual way usingthe pyc nometer, and the other w ith fract ions of3 to 5 gramsfor the first 20 to 25 grams distilled, using the refractometer.The refractometer points gavea reasonably accurate indica-tion of the exact shape of the curve near they axis , and th epycnometer curve was drawn with as nearly the same shapeas possible, as shown by curves D and E in Figure 2 . They intercept of the pycnometer curve was takenas the vapor

TABLE 11. EXPERIMENTAL IQUID-VAPOR QUILIBRIUM ATAF O R E T H b N O L - WAT E R , BASEDO N RESIDUAL IQCID 3 STILL

(730 t o 750 mm. of mercury)RUN EtOH IN LIQUID EtOH IN VA P O R

Wt. M o l e W1 M o l e% fractaon % frac tzon

2425262734282930313235363739

TABLE V.

R U N

2220181615241 4132512112610

230

927

8736

2854

29

TABLE .

R U N

111012

913

814

715

6

25 .533 .741.750 .653 .158 .6

0 . 07 6 . 079.38 2 . 686 .78 9 . 394.05

G4.7

0.1180 .1660 ,2180 ,2860.3060.3560.4170.4770.5530 .6000.6510.7180 .7650.861

6 9 . 872 .275.277 .177.77 9 . 08 0 . 682 .384.28 5 . 787 .189 .290 .794.22

0.4750.5040.5430.5680.5770.5950.6190.6460.6770.7010.7250.7630 ,7920 .865

EXPERIMENTAL IQUID-VAPORQUILIBRIUMATAFOR METHANOL-WATER

(730 to 750 mm. of mercury)MeOH I N LIQEID MeOH I N \-.APOR

W t . M o l e W t . M o l e% f rac taon % frac tzon

1 . 3 0.007 9 . 5 0 . 0 5 63 . 0 0 . 0 1 7 18.5 0.1135 .06 0 .029 27.8 0.1787 . 0 0 041 35 .0 0 .233

10 .2 0.060 44.0 0.30715 .0 0 ,090 53 .5 0 .3931 5 . 1 0 .091 53 .1 0 .38920 .2 0.124 61.5 0.47322.4 0.140 63.8 0.49825 .1 0 .159 66 .8 0 .53030.2 0.196 70.5 0.5733 5 . 1 0.233 73.8 0.61339 .6 0 ,269 76.3 0.6444 9 . 3 0 .354 81 .0 0 .70549 .55 0 .356 81 .0 0 .70549.7 0 .357 81 .1 0 .70659.5 0,452 84.6 0.75560.0 0 ,457 84 .7 0 .75669.9 0.566 88 .4 0 .81078.9 0.677 91.6 0.86081 .3 0 .710 92.5 0.87489.4 0.825 95.7 0.9259 0 . 4 0.841 96.4 0.93894 .9 0.913 98.1 0.96695.1 0.916 98. 1 0.966

EXPERIMENTAL IQUID-VAPORQUILIBRIUMATAF O R ACETICACID-m'ATER(730 to 750 mm. of mercury)

Hz0 I N VA P O RzO IN LIQUIDwt. M o l e Wt. M o l e% f r a c t i o n % fraction9 . 9 0 , 2 6 8 16.0 0.388

10 .4 0 .278 16.9 0.40415 .0 0 ,370 23 .1 0 .50019.6 0.449 29.1 0.57824 .2 0 .515 34 .8 0 .64030 .3 0.592 42.1 0.70834 .3 0.636 46.8 0.74539 .6 0 .686 52 .4 0.78544 .1 0 .724 56 .6 0 .81349 .5 0 .765 61.6 0.842

20183

195

21

74 .975 .48 0 . 084.789 .990 .3

0.9090 ,9110.9300.9490.9670.969

81.281.48 5 . 08 8 . 593 .692.8

0 .9350.9360 ,9500.9620.9760.977

composition in equilibrium with liquid of the compositionof the initial charge.

EXPERTMEUTALATA. The experimental results given inTables 11, IV, and V are based on the liquid originallycharged to the still, while those in TableI11 are based onthe residual liquid. The results in Table111, with the excep-tion of runs 24 and 25 , are in excellent agreement with thosein Table 11. The writers feel that this isa further indicationof the reliability of the method.

The system ethanol-water was investigated more thor-oughly th an the other two, for two reasons-the wide disagree-me nt between th e previously published resultsfor this system,


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1334 I hT D U S T R I A L A N D E N G I N E E R I D; G C H E %I I S T R Y Vol. 2 5 , No. 12

The experimental results were carefully plotted, both inmole fraction and in weight per cent, and the coordinates ofpoints read from these curves are given in TableTI.

FIGURE . ACETICACID-WATER QUILIBRIUM IAGRAM

and a desire to test the consistency of the apparatus. Nospecial attempt was made to determine the composition ofthe constant-boiling mixture of ethanol and water.

DISCUSSIONF RESULTSETEL~soL-WATER.Equil ibrium curves for th i s sys tem a t

atmospheric pressure have been determined by Evans S ) ,Blacher, as given by Hausbrand 9) , Lewis and Carey I I ) ,Rayleigh I @ , Bergstrom as quoted by Hausbrand 6 ) , andSorel 60). Blacher s data were obtained by interpolat ionfrom a graph reported by Hausbrand, and are not thereforeextremely accurate. The da ta of Sorel were taken fromElliott 6). A comparison of the various setsof equilibriumdata is given in Figure3. The curve is tha t drawn throughthe points determined experimentally in the presentwork,only the d a ta f rom Table I1 being plotted.

The da ta of Len+ and Carey did not appear in the l itera-ture unti l af ter th e completionof the present work, and theirresults are in excellent agreement with the latter, being onlya little low in the middle portion of the curve. It is obviousth at the d ata of Eva ns and of Sorel are seriously in error,while those of Rayleigh are evidently low. Blacher andBergstrom agree fairly well with the r esults of the presentwork.

WEIGHT PERCENT O F M O R E VOL TILE C O U P O M h T N LIQUID

FIGURE . EQUILIBRIUM IAGRAMS

TABLE VI. COORDINATES OF CCRV E DR AW N THROUGH EX-PERIMESTAL PO IST S FOR ETHANOL-KATER

IN I NLIQUID VAPOR

0.010 0.1040 . 0 2 0 0 , 1 9 00.030 0.2500.040 0.2970.050 0.3320 .060 0 .3640 .080 0 .4100.100 0.4420.120 0.4680.140 0.4880 .160 0 .5050.180 0.51Q0.200 0 .531

1 . 0 1 0 . 32 . 0 1 9 . 23 . 0 2 6 . 34 . 0 3 2 . 55 . 0 37 .76 . 0 41.9

8 . 0 4 8 . 110 .0 52 .712 .0 56 .514 .0 59 .516 .0 61 .918 .0 63 .920 .0 65 .6

(730 to 750 mm. of mercury)

LIQCID VAPOR LIQUIDVAPOR

0.220 0.541 0.480 0.6460 .240 0 .551 0.500 0.6540 .260 0 ,560 0 .520 0 .6630.280 0 . 5 6 8 0.540 0.6720 .300 0 .576 0 5 6 0 0 . 6 8 10 .320 0 ,584 0 . 5 8 0 0 .6900 .340 0 .591 0 . 6 0 0 0.6990 .360 0 .599 0 . 6 2 0 0.7090.380 0.607 0.640 0.7190.400 0.614 0.660 0.7300.420 0 .621 0 . 6 8 0 0.7410.440 0.629 0.700 0.7530.460 0.637 0.720 0.765

I N I N I N I N

MOLE FRACTION O F ETHANOL

WEIQHT PER CENT ETHANOL

22.024 .026.028.03 0 . 032 .0

34.036 .038 .040.042 .044.046 .0

67.268.469 .470.471.372.0

7 2 . 87 3 . 474.074.675 .175 .676 .1

48 .050.052.054 .05 6 . 058.0

6 0 . 062 .06 4 . 06 6 . 06 8 . 07 0 . 072 .0

76.677 .177.578 .078 .47 8 . 9

7 9 . 479.980 .581 .181.782.282.9

I N I NLIQUID VAPOR

0.740 0.7770.760 0.7900 .780 0 .8040.800 0.8180.820 0.8330.840 0.8480 .860 0 .8640 .880 0 .8810 .900 0 ,8980 .920 0 .9170.940 0.9380.960 0.9560.980 0.978

1 4 . 0 8 3 . 66 . 0 8 4 . 3

7 8 . 0 8 5 . 08 0 . 0 85.882 .0 86 .884 .0 87 .7

86 .0 88 .888 .0 90.090.0 91.292.0 92.69 4 . 0 9 4 . 29 6 . 0 9 5 . 998 .0 97 .8

METHANOL-WATER.nly three equilibrium curves forthis system at atmospheric pressure could be found in theli terature. These were determined by Bergstrom, as quotedby Hausbrand 7 ) , Bredig and Bayer I ) , and Blacher asgiven by Hausbrand 9). A graphic comparison of th e vari-ous sets of data is given in Figure4. Bergstroms curve isquite a l i tt le higher than that found in the present work. Thedata of Bredig and Bayer are high also, but their data arebadly sca t te red . The da ta of Blacher were obtained in the

same way as for ethanol-water, and,u hile the reading of thepoints from the graph ma y not have been extremely accurate,every one of them checks the present curve almost exactly.

Th e coo rdinates of points re ad from smooth plots of the ex-perimental da ta a re given in TableVII.

TABLE VII . COORDINATES OF CURVE DRANN H R O U G H Ex-PERIYESTAL POINTS OR METHANOL-WATER

(730 t o 750 m m . of mercury)

LIQUID VAPOR LIQUID VAPOR LIQUID VAPOR LIQUID VAPORI N I N I N I N I N IN I N I N

MOLE FRACTION OF METHANOL

0.1400.1600.1800.200

1 . 02 .03 . 04 . 05 . 06 . 08 . 0

10 .01 2 . 014.016 .018 .020.0

0.420 0.7390.440 0.7490.460 0.759

0.480 0.7680.500 0.7780.520 0.7870.540 0.7970.560 0.8060.580 0.8150.600 0.8250.620 0.8340.640 0.8430.660 0.8520.680 0.8620 .700 0 .8710.720 0.880

WEIQ HT PER CENT METHANOL

22 .024.026.028.030.03 2 . 03 4 . 036.038 .040 .042.044.046 .0

48.050.05 2 . 054.056 .058.06 0 . 06 2 . 06 4 . 066 .06 8 . 070.072.0

87.688 .38 9 . 1

74 .07 6 . 078.080.08 2 . 08 4 . 08 6 . 08 8 . 09 0 . 09 2 . 094 .09 6 . 098.0

ACETICACID-WATER. Equilibrium curves for this system

a t atmospheric pressure hav e been determined by Ray leighIf?), Blacher as quoted by Hausbrand 8), Bergstrom as


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6/6

Effect of Addition Agents upon the CorrosionRate of Aluminum by Alkalies

Effect of Various SubstancesF. H. RHODESND F. W. BERKER, ornel1 University, Ithaca, N . Y.

N THE pickling of stee l with acid it is well known th atth e action of th e acid upon th e metal m ay be minimizedb y adding to the ac id cer ta in inh ib i tors tha t re ta rd the

corrosion of the metal without at the same t ime seriouslyinterfering with the solution of th e scale. I n the presentinvestigation t he effects of various inorganic salts and organiccompounds upon t he ra teof corrosion of a luminu m by alkalieshas been determined, witha view to th e possibility of findingsome substance tha t would minimize or preven t th e corrosionof t he m eta l by alkaline solutions.

Some work o n the effects of addit ion agents on th e rateofcorrosion of a luminu m b y alkalies has alread y been published,Rohrig 5) ound th at th e addition of sodium silicate toa solu-tion of sodium ca rbona te decreases th e ra te of action of th esolution on aluminum , al though t he si l icate increases th e rat eof a t tac k of t he me tal by sodium hydroxide in moderately

F

FIGURE . APPARATUSOR DETERMINATIONOF CORROSIONATE

E, F. Control stopcocksM , Reaction bulbS. Capillary spiral2. Inlet tube for hydrogenX Hydrogen inlet controlY . Inlet for alkaline solution

conce ntrated solutions. Seligman an d Williams (6) alsoinvestigated th e effects of sodium silicate as an additionagen t in the cleaning of aluminum by alkalies. Th e use ofsilicate as a re ta rder in th i s process was pa ten ted b y Lea 3 ) .Rohrig ( 5 ) found that certain colloidal substances, such asglue, agar agar, and gelatin, exhibited inhibiting action.Othe r substances for which similar act ion has been claimedinclude am monium compounds, dichromates, sodium molyb-date, permanganates, a nd sa l ts of th e noble met.als1, 2 , 4) .

In th e present work t he ra te of ac tion of t he alkaline solu-t ions on the a luminum was de termined by measur ing thera te of evolution of th e hydrogen formed b y th e reaction.Th e construction of the a ppar atus used is shown in Figure1.

Into the reaction tube,M , was placed sufficientof the solu-ton to be tested to cover thetest strip of aluminum. Gaseoushydrogen was passed through the solutionfor about 3 minutesin order to satura teit with hydrogen and th us eliminateany errordue t o the solubilityof the gas in the solution. The reaction tubewvas then immersed in a bath of water maintained ata constanttemperatureof 30 C. and allowedt o stand until the solution hadattained the temperatureof the bath. A cleaned and weighedstrip of aluminum, 5 cm. long, 1 cm. wide, and 0.0635 cm. thickwas introduced, and the reaction vesselwas connected immedi-ately with a Hempel buret in which the volumeof evolved hydro-gen was measured. Readings were taken every minutefor 20minutes. At the endof this period, the aluminum was removed,rinsed, and again weighed. The loss in weightof the metalserved as a check upon the amountof hydrogen evolved as ameasure of the total extent of the corrosion. The aluminumused was commercial sheet aluminum,99.3 per cent pure.

EFFECTSF ADDITION GENTSN CORROSIONALKALIESALONE. I n th e f irst series of experiments th e

ra te of corrosion of a luminu m in sodium hydroxide solutionsof various concentrat ions was measured. Th e pH of eachsolution was determined, usinga standa rd hydrogen electrodebalanced against a satura ted calomel electrode. Th e re-su l t s a re shown in F igure2, in which th e va lues for p H andfor rates of corrosion are plotted against th e concentrations,and in F igure 3 , in which is shown th e variat ion in the rateof corrosion with the change in pH. Th e rates of act ionofmolar and 0.5 molar solutions of potassium hydroxide werealso measured:

ALKALI CONCENTRATION RATIO

Sodium hydroxide 1 2.50Potassium hydroxide 1 2.13Sodium hydroxide 0.5 1.60Potassium hydroxide 0.5 1.42

Molar Cc. Hn/min.

Although potassium hyd roxide is more nearly completely dis-sociated th an is sodium hydro xide in solutions of the se con-centrat,ions, there is a distinct and consistent difference inthe ra te a t which they a t tack a luminum.

I n t he ne xt series of experiments th e effects ofsal ts were investigated. I n each experiment th e sal t , in theconcentration indicated, was dissolved ina 0.5 molar solution

of sodium hydroxid e.

SALTS.

SALT CONCN. RATE SALT COXCN. RATEMolar Cc. Hl/min. M o l a r Cc. Hdmin

None ... 1.6 KCl 0.5 1.66NaCl 0 . 5 1.96 NazSOo 0.5 1.98NaCl 1.0 1.93 KnSO, 0.5 1.83NaCl 1 . 5 1.89 NrtsPO4 0.5 3.98

Th e addition of sodium chloride increases th e activity ofthe hydroxyl ions from the sodium hydroxide and markedlyaccelerates th e corrosion. Th e accelerat ion is most markedin solutions of 0.5 molar concentrat ion and decreasesas t h econcentration rises above this value. -4 imilar effect isobserved with solutionsof sodium chloride in molar alkali.Sodium sulfate shows an effect s imilar to th atof sodium chlo-ride bu t even more pronounced. Th e addition of sodium phos-phate increases the ra teof corrosion very greatly, th e increasebeing due in pa r t at least to the hydrolysis of th e sal t and th eresulting increase in concentrationof hydroxyl ions.

1336

equilibrium data - water and acetic acid, water and methanol, and water and ethanol

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