162 ELL IS & TH W A I TES-NI TRIC A CI D- W A TE R-SUL PH U RI C A CI D

VAPOUR-LIQUID EQUILIBRIA OF NITRIC ACID-WATER- SULPHURIC ACID MIXTURES By S. R. M. ELLIS and J. M. THWAITES*

New vapour-liquid equilibrium data have been obtained for the systems nitric acid-water and nitric acid-sulphuric acid-water and have been applied to the design of a column for the concen- tration of nitric acid by extractive distillation with sulphuric acid. The new data require an increasc in the number of theoretical plates, and thus explain in part the present use of larger quantities of sulphuric acid than should be necessary in a column designed according to previously published data.

Introduction In recent years it has become common practice to employ mixtures of nitric and sulphuric

acids as nitration agents in the explosives, dyestuffs and other industries. The development of the manufacture of nitric acid by ammonia oxidation and by arc processes using atmospheric nitrogen has resulted in the production of large quantities of dilute (50 to 65%) acid. The concentration of this acid has normally been carried out by extractive distillation using sulphuric acid as a non-volatile solvent.

An accurate knowledge of the vapour-liquid equilibrium relationships for the ternary system nitric acid-sulphuric acid-water is necessary for the design of equipment for the concentration of nitric acid. The equilibrium data which have normally been used are those obtained by Pascal & Garnier,l Berl & Samtleben,21 and Carpenter & Babor4 in about 1920. I t has been found, however, that the actual performance of equipment designed from these results does not match that calculated from the equilibrium data; in particular more than the theoretical amount of sulphuric acid is necessary to obtain a given separation, and this suggested the likelihood that the published equilibrium data were unreliable.

The primary object of this paper is the presentation of accurate ternary vapour-liquid equilibrium data for the system nitric acid-sulphuric acid-water, and accurate binary data for the system nitric acid-water.

. Experimental

Design of apparatus In the early stages of tllis work, published equilibrium data for the binary system nitric

acid-water were correlated thermodynamically and it was shown that, whereas the data of Pascal & Gamier, etc. are inaccurate, the recent data of J. Potier,'j determined with a new type of continuous equilibrium still'* are reasonably correct. It was thought desirable, however, in view of the difficulties of operating a still of this type, to use a still of the recirculation type for the present study as the design and operation of stills of this kind are already familiar.

Preliminary studies of the binary system nitric acid-water were carried out using a number of different stills of the recirculation types-l1 and, although initially difficulty was experienced in obtaining smooth boiling conditions, showed that it would be possible to use a recirculation still for the determination of data for the nitric acid-water system and probably also for the ternary system nitric acid-sulphuric acid-water. Accordingly a recirculation equilibrium still was designed especially for use with these systems. It was based on a design by Ellis,O with provision being made for an increased heating surface to avoid ' bumping '. A mixing chamber was also introduced to avoid the difficulty of a low-boiling condensate ' flashing ' as it entered the main bulk of the higher-boiling Liquid in the still. The modified equilibrium still is shown in Fig. 1. The main features of the apparatus are as follows :

The clearancc between the walls in this unit is as small as can be practicably made, about 1.5 mm. After a considerable amount of trial and error this type of heater was found to give the smoothest boiling conditions, provided that the clearance between the walls was kept very small. A spiral baffle is embodied in the heating unit and was constructed by sealing the two walls together along a spiral path. This means that the boiling mixture has to follow a spiral path through the

The mixture is boiled in the bayonet-type double-walled heating unit A.

* Present address: Ministry of Supply, E.R.D.E., Walthain Abbey, Essex

J. appl. Chem., 7, April, 1957

ELLIS C THWAITES-NITRIC ACID-WATER-SULPHURIC ACID 153

boiler and therefore better circulation is obtained. The main heat input is provided by an electric heater inserted into the centre of the boiling unit.

The mixture of boiling liquid and vapour leaves the boiling unit and passes along the tube B. It then passes through a coiled Cottrell device and impinges directly on to the thermometer pocket C. The liquid and vapour phases then separate, the liquid falling into the main bulk of the liquid below, and the vapour passing to the condenser. The main body of the still includes a separating device, D, which prevents entrainment by ensuring that the vapour rises to the top of the still before passing to the condenser. The thermometer in pocket N gives the temperature of this vapour. From the condenser E the condensate falls into the receiver F and recirculates through the drop-counter G to the mixing chamber T through tube R. The mixing chamber is packed with glass rings to assist mixing of the two phases. The mixture leaves the chamber though a central tube U, the inlet

Y

to which is just below the liquidievel. FIG. 1, Equilibrium still Samples of liquid and vapour are taken from taps P and Q respectively. The inlet to tap P is situated just below the surface of the liquid and immediately below the thermometer pocket in order to obtain a sample which is as nearly as possible the liquid which has just impinged on the thermometer pocket.

The whole still was lagged before use with a layer of magnesia asbestos on top of a thin layer of asbestos paper. Before lagging, an external heater was wound round the upper part of the still to maintain the vapour at a slightly higher temperature than the observed boiling point in order to prevent any fractionation of the vapour before it reaches the condenser.

In operating the still approximately 350 C.C. of the mixture are charged, and boiled so that the rate of distillation is from 20 to 60 drops per minute. The rate for each mixture was as high as could be maintained without ' bumping '. Mixture compositions are given in the tables of experimental results. The still is allowed to recycle steadily for 1* to 3 hours according to the rate of distillation.

Boiling points are read on mercury-in-glass thermometers which permit temperatures to be read to within f 0.05". A correction is applied to compensate for the effect of changes in atmospheric pressure.

Materials used

nitric acid was distilled when necessary to remove decomposition products. The nitric acid and sulphuric acid used were free from all impurities other than water. The

Methods of analysis All the analyses of nitric acid-water and nitric acid-sulphuric acid-water mixtures were

carried out volumetrically using standard caustic soda solution, the nature of the components making other methods impracticable. In the case of ternary mixtures two separate determina- tions were carried out-for total acidity and for sulphuric acid concentration-the strength of nitric acid being obtained by difference. In the determination of the sulphuric acid concentration the nitric acid contained in the sample was driven off by boiling over a water bath.

Results Binary system nitric ncid-water

The experimental results and activity coefficient data calculated for the system nitric acid-water are presented in Table I. The results are plotted in Figs. 2-4 as temperature vs. composition, activity coefficient vs. composition, and as a Li-Coull plot. la

Where there is a difference between the boiling points of the components in a system i t is necessary to take into account the resulting deviation of the vapour pressure from the ideal

J. appl. Chem.,-7, April, 1957

154 ELLIS & TH W A I TES-NI TRIC A CI D-IVA T E R-S UL PH U RI C A CI D

Table I Experimental results for system nitvic acid-water

t , O C X N Y N log ' YN log YW ( log ' yN)-0*5 XW

104.0 6.1 0.36 106.4 9.6 0.95 107.8 11.7 1.5

' 109.4 13.9 2.11 111.8 17.5 4.23 112.3 18.3 5.1 114.8 22.5 8.85 116.85 26.6 13.6 117.5 27.7 15.99 119.4 34.1 25.9 119.9 37.4 36.5 120.05 38.32 37.45 116.1 48.5 73.0 113.4 52.1 81.08 110.8 54.7 85.0 102.9 65.1 94.2 96.1 71.9 97.2 92.0 76.5 98.75 88.4 81.6 99.3 83.4 100.0 100.0

-1.4895 - 1 -31 16 - 1 '1986 - I .1530 - 0 '9796 - 0.9165 -0.7991 - 0.7089 -0.6674 -0.5751 -0.4647 - 0.4660 -0.2426 -0.1943 -0.1510 -0.0740 -0.0257 - - -

-0.0321

-0.0659 -0.0514

- 0.0748 -0'0934 -0.1235 -0.1500 -0 1588 -0.1906 -0 2278 - 0 2669

-0.5071 -0.5991 -0,6349

-0 9382

- 0.2698

- 0 4236

- - -

0.0424 0.0448 0.0467 0.0477 0.051 5 (1.0531 0.0568 0.0601 0.0621 0.0672 0.0741 0.0741 0.1018 0.1154 0.1170 0.1893 0.3246 - - -

FIG. 2. Xitric acid-wateu system: tempera- ture-composition diagram

0.065 0.106 0.1325 0.160 0.212 0.224

0.362 0.3825 0.517 0.596 0.621 0.94 1.08 1 *21 1.87 2.56

0.290

- - _-

0.127 2.759 0.1159 2.62 0.1081 1.935 0.0900 1.68 0.0945 1 a61 0.0713 1.06 0.0657 0.91 0.0641 0.828 0.0568 0.535 0.0537 0.391 - -

- -

FIG. 3. Nitric acid-wateu syAlem: acfivity coefficreni-coniposiiioii diayram

F I G . 4. Nktt'ic acithJatev systent: Li-coull plot

0 0 5 10 1 5 2.0 3 0,- xW xN

vapour prcssure in the evaluation of thc activity coefficicnts, so that

where Z is the correction factor for gas-law and liquid pressure deviations.* For systems where there is a small temperature range this correction may be neglected, but in the case of nitric

* .I list of symbols with definitions is given at the elid of the paper

J. appl. Chem., 7, April, 1957

ELLIS & TH WAI TES-"TI TRIC ACID-WA TER-SUL PH URIC A CID 155

acid-water the difference in temperatures is about 37" and in this paper Z correction factors have been used throughout. These were determined using the nomograph proposed by Scheibel13 which has been shown to give almost as accurate results as the much more lengthy equations proposed by Wohl I4 and is much more convenient.

The activity coefficient plot given in Fig. 3 shows that the scatter of the experimental points is slight and smooth curves may be drawn. This indicates the general consistency of the results. For high concentrations of nitric acid where the vapour compositions approach lOOyo nitric acid, the activity coefficients are very sensitive to smal1,variations in concentration and the accuracy of the analysis becomes less reliable for concentrations very near to lOOyo. There- fore points corresponding to vapour concentrations greater than 99% have been neglected.

For azeotropic systems a convenient method of checking the accuracy of experimental equilibrium data consists of comparing the values of A and B (the logarithms of the end values of the activity coefficients) calculated from the azeotropic data by means of the van Laar equations with the values of A and B obtained from the experimental activity coefficient plot.

The experimental azeotropic data give compositions of XN = YN = 38.65% and xw = yw = 61*35y0 and the values of A and B calculated from these data are A = -1.752 and B = - 1 * 149. This value of A compares well with the value obtained from the experimental activity coefficient plot of A = -1.77. For the other end value, B, comparison of the experi- mental and predicted values is of little value since some extrapolation of the log y vs. x curve was necessary in this region, and the curve was therefore extrapolated to the predicted value of

When values of ( T log 2 Y ) - O ' ~ are plotted against the ratio of the liquid compositions, the experimental points fall reasonably closely on straight lines as shown in Fig. 4. This is a method of correlation proposed by Li & Cou1112 which gives straight line plots for accurate data. Further- more the ratio of the mean values of (T log Zy)-Oe5 at composition ratios of unity and zero is 2.07, comparing well with the value of 2.0 suggested by Garner & Ha1116 for accurate data.

Decomposition of nitric acid-water mixtures was found to occur in mixtures of above about 65% with the formation of oxides of nitrogen. Above about 75% some of these decomposition products remained in the boiling liquid and, although their presence did not apparently affect the equilibrium relationships, it did cause a reduction in the boiling point of the liquid. A relationship between the extent of decomposition and the effect on the boiling point was obtained and a correction was applied to boiling points where decomposition occurred.

The experimental equilibrium results for the system nitric acid-water have been shown to be consistent. These results agree closely with the published data of Potier5 and show that accurate experimental data for this system can be obtained with a recirculation equilibrium still.

B = -1,149.

Ternary system nitric acid-sulphuric acid-water The experimental results for the ternary system nitric acid-sulphuric acid-water are

presented in Table I1 which includes about a quarter of the actual number of determinations carried out. The experimental data are plotted on a triangular vapour-liquid composition diagram as shown in Fig. 5, and Fig. 6 shows a plot of relative volatility against composition. The relative

volatility of nitric acid to water in the ternary mixture is defined as the ratio - YNeXw and XWYW

provides a convenient measure of the ease of separation of the components. Large values of the relative volatility indicate mixtures which are readily separated. The experimental results were plotted on a binary sulphuric-acid-free basis in Fig. 7, values of the nitric acid concentration in

the liquid phase being calculated as the ratio xN . The published data of Carpenter & XN + xw

Babor4 are also plotted on the same diagram showing the appreciable discrepancy between the two sets of data. Although the most marked difference is in the upper part of the curves, the most significant is in the lower part where the relative volatilities given by the new data are less than those for corresponding compositions from the published results. It is in this part of the curves, corresponding to the stripping section of a distillation column, that any difference in the data will have the greatest effect on column design.

J. appl. Chem., 7, April, 1957

166 ELLIS d TH W A I TES-N I T RI C A CI D- W A TE R-S UL PH U RI C A CI 1)

t , O C

114.3 115.5 120.2 120.0 110.0

109.9 112.8 115.8 118.7 121.25 122.2 117.4

115.3 116.9 118.5 121.3 123.1 125.1 125.7 125.25 112.5

124.1 124.95 129.5 132.3 131.2 130.1 123.0 115.9

140.5 138.0 141.5 142.2 141 -35 137.6 134.4 129.4

161.4 163.0 165.0 165.8 164.6 162.0 152.2 144.5 137.5

198.3 196.6 197.9 196.6 193.9 195.6

Table IS Experimental results for system nitric acid-sulphuric acid-water

Weight-%

Liquid

H2SO4

7.45 7.38 7.51 6.8 6.9

19.7 20.1 20.1 20.5 19.8 19.5 19.8

38.2 37.5 37.0 37.6 37-7 37.0 38.1 37.2 37.6

49.8 48.75 50.1 49.75 50.0 50.0 50.6 51 * O

59.8 59.0 60.5 60-4 60.0 59.95 59.1 60.0

70-1 69.25 70.43 70-0 69.9 69.8 69.4 68.8 70.0

80.5 79.25 80.4 81 -0 80.2 80.7

HNO,

40.8 43.4 59.5 64-0 74.0

15.81 22.6 29.5 35.5 41 -3 46.7 53.2

6.74 9.53

12.6 16.4 21.6 24.9 29.25 33.3 41.2

2.38 4.5 9.12

13.55 15.9 18.4 26.2 30.15

0.812 1 a67 2.59 3.94 6.04 9.18

11.72 14.72

0.285 0 * 676 0.925 1.3 2.02 3.05 4.28 7.2 8.46

0.19 0.44 0.645 0.95 1.15 1.312

Vapour

HNO,

20.95 25.2 65.7 75.0 95.6

4.86 10.1 20.9 37.7 55.9 73.7 91 * 2

6.33 10.8 16.25 27.6 46.7 55.9 76.7 85.95 97.8

6.45 12.28 35.3 59.5 72.5 82-3 98.0 99.4

6.95 14.4 23.26 34.9 54.2 74 * 02 83.55 95.0

8.5 17.91 26.81 35.0 48.2 65.0 79.8 92.3 98.7

14.8 28.0 46.25 59.5 65.0 80.3

Mol.-%

Liquid

H W , 2.1 2.16 2-7 2.5 3.0

5.0 5.47 5.9 6.52 6.69 7.06 7.93

10.96 11.0 11.2 11.97 12.86 13.1 14.57 14.9 17.4

15.9 15.7 17.5 18.37 18-15 20.0 23.4 24.9

21.7 21.39 22.8 23.35 23.7 25.0 25.1 27.2

30.2 29.6 30.91 30.7 31.0 31.38 32.8 32.7 34.9

43-3 41 * 6 43.6 44.8 43.5 44.6

HNO,

18.2 19.6 33.1 37.5 51 * O

6.22 9.57

13.5 17.5 21.71 26.3 33.16

3.01 4.35 5.93 8.13

11.47 13.5 17.41 20.75 29.4

1.17 2.26 4.96 7.79 7.2

11.4 18.8 22.8

0.45 0-94 1.51 2.37 3.7 5.94 7.72

10.38

0.19 0.45 0.62 0.87 1.39 2-13 3.1 5 .3 6.6

0.15 0.32 0.54 0.81 0.96 1.12

Vapour

HNO,

7.0 8.75

35.2 46.5 85.6

____

0.15 3.11 7.03

14.7 26-58 44.5 74.74

1 *89 3.36 5.26 9.8

20.02 26.2 48.46 63.61 92.5

1 *93 3-84

13.5 29.5 42.96 57.5 93.7 97.7

2.08 4-58 7.9

13.3 25.2 45.1 59.3 84.45

2.58 5.86 9.47

13.3 21 .o 34.66 53.0 77.3 95.6

4.7 10.0 19-73 29.55 34.6 53.8

Relative volatility

0.329 0.381 1.055 1 a 3 8 8 5.36

0.02 0.285 0.451 0-748 1.19 2.03 5.25

0.551 0.676 0.777 1 *07 1.65 1.935 3.67 5.42

22.3

1 *396 1 -45 2.45 3-99 7.8 8.11

45.9 97.7

3.64 3.99 4.29 4.81 6.54 9.58

12.69 32-65

9.78 9.82

11.52 11.93 12.89 14.38 23.39 39.97

193.4

18.21 20.09 25.63 27.92 30.59 56.19

The various ways in which the ternary equilibrium data have been plotted show clearly the marked effect on the vapour-liquid relationships for mixtures of nitric acid and water produced by increasing amounts of sulphuric acid. This is shown particularly by the relative volatility-composition diagram (Fig. 6).

J. appl. Chem., 7, April, 1957

ELLIS G THWAITES-NITRIC ACID-WATER-SULPHURIC ACID 157

SULPHURIC ACID. wt.-O/o

FIG. 5 . Nitric acid-sulphuric acid-water system: vapour-liquid composition diagram

FIG. 6. Nitric acid-sulphuric acid-water system: relative volatility-comfiositaon diagram

Discussion The experimental data have been correlated in two ways. The first method is that proposed

by Heringtonls which involves the comparison of binary and ternary relative volatility and vapour pressure data for various concentrations of sulphuric acid in the ternary system.

The vapour pressure data for nitric acid are those of Egan" which have been obtained by calculation from thermodynamic data on the assumption that fugacity and vapour pressure are equal. Vapour pressure data for water are derived from Callendar's Steam Tables. Equili- brium data for the system nitric acid-sulphuric acid were not available owing to the impossi- bility of obtaining pure anhydrous sulphuric acid under normal conditions. It has therefore been necessary to use assumed relative volatility data for this sytem in the application of the

J. appl. Chem., 7, April, 1957

168 ELLIS G TH WAI TES-NI TRIC A CI D-WA T E R-SUL PH URI C A C I D

FIG. 7 . Nitric acid-sulphuric acid- water system: vapour-liquid compo- sitran diagram on binary basis - - - Published data of Carpenter

- Experimental results & Babor

Herington correlation. I t has been found that when these assumptions are made so that the data agree with the correlation for one concentration of sulphuric acid, then the data for all other sulphuric acid concentrations also agree. This suggests that the experimental data are likely to be internally consistent, but the absence of complete binary data makes it impossible to assess conclusively the accuracy of the results of this method.

The method of linear interpolation proposed by Carlson and Colburnls involves plotting the log activity coefficient-composition data for each component in a ternary mixture on the same diagram as the plots for the same component in the two binary systems in which it occurs. For accurate data the activity coefficients for the ternary data should fall between the two binary plots in linear proportion to the ratio of the other two components present.

Activity coefficient curves for the water component in the system nitric acid-water and sulphuric acid-water are plotted together with the ternary activity coefficient data for the water component in Fig. 8. The parameters are values of the ratio HZSO4/(H,SO4 + HNO,), and it can be seen that most of the points lie reasonably proportionately between the binary curves. Curves for several ratios of H,SO,/(H,SO, + HNO,) have been interpolated linearly between the binary

FIG. ' 8. Nitric acid-szdphuric acid-water system: liiaear interpolation plot Tevnarv activitv coefficient data for zcater component in HN0,-H,SO,-HpO

J. appl. Chem., 7, April, 1057

ELLIS C THWAITES-NITRIC ACID-WATER-SULPHURIC ACID 159

curves and are shown as dotted lines in Fig. 8 so that a comparison can rea l ly be made between the experimental and interpolated curves. It can be seen that the experimental points compare quite well with the interpolated curves. Data corresponding to temperature ranges greater than about 30" do not agree with the correlation but this is to be expected since the method is based on assumptions involving isothermal conditions.

The correlations which have been applied have indicated that the ternary data are likely to be accurate, but it would appear that it is not possible to predict the ternary data for this system from binary results by any of the normal methods. Firstly, insufficient binary data are available; in particular no results are available for the system nitric acid-sulphuric acid. Secondly, the large temperature differences involved in some of the binary and ternary mixtures introduce inaccuracies into the use of the normal theoretical methods of prediction and correla- tion of ternai-y data.

The equilibrium data for the system nitric acid-sulphuric acid-water have been applied to the design of a typical column for the concentration of nitric acid using sulphuric acid as the extractive agent. The experimental results and the published data of Carpenter & Babor4 have both been used in order to show the comparison between the results obtained from these two sets of data. A design quoted by Robinson & Gilliland19 was used as a basis for this calculation and the number of theoretical plates required to obtain a given separation for a number of different feed conditions was obtained using a McCabe-Thiele lagram. In each case i t was found that more theoretical plates were required when the new experimental results were used than when the published data were used, and this difference was entirely accounted for by the stripping section. I t is known that in existing columns used for the concentration of nitric acid by this process the actual amount of sulphuric acid which has to be used to obtain the desired separation is considerably greater than the amount calculated from previously published vapour- liquid equilibrium data.

Conclusions Experimental vapour-liquid equilibrium data for the ternary system nitric acid-sulphuric

acid-water are different from previously published data for this system. The experimental data have been correlated by the Herington method and by the method of linear interpolation, although the application of these is restricted by the absence of complete binary data and by the large temperature differences involved. I t is concluded that the results are likely to be accurate although it appears that it would not be possible to predict the ternary data from binary results by any of the normal theoretical methods.

The application of the ternary results to the design of an extractive distillation column for nitric acid concentration has shown that there is a considerable difference between the results obtained from the experimental and previously published equilibrium data. More theoretical plates are required when the new experimental data are used than when the published data are employed.

Equilibrium data presented for the system nitric acid-water are in close agreement with the published data of Potier, showing that a suitably designed recirculation still can give accurate results for this system. In the determination of data for this system the effect of decomposition on the boiling points must be taken into account.

An equilibrium still designed for the elimination of uneven boiling conditions incorporates a mixing device for the recirculating liquid and condensate and has given good results for mixtures involving wide differences between the boiling points of the liquid and vapour phases where steady boiling conditions would not be obtained with a still of the normal type.

SYIUbOh A log end value of the activity coefficient of component 1 at infinite dilution in com-

ponent 2 B log end value of the activity coefficient of component 2 at infinite dilution in com-

ponent 1 t = boiling point, O c T = boiling point, K

J. appl. Chem., 7, April, 1957

=

=

160 BLACKMAN et al.-PROMOTING DROPWISE CONDENSATION OF STEAM

Symbols (contd.) x = liquid composition (mo1.-o/) y = vapour composition (mol.-%) 2 = correction factor for gas-law and liquid-pressure deviations y = activity coefficient ?T = total pressure on system p = vapour pressure of component

Subscripts N = nitric acid w = water

Chemical Engineering Department Birmingham University

Received 9 February, 1956; amended manuscript 6 July, 1956

References 1 Pascal, P., & Garnier, C.R. Acad. Sci., Paras, 1917.

165. 589; BuZl.Soc.chim. F Y . , 1919.25,142; 1920, 27, 8; Chem. metall. Engng, 1921, 25, 1103. 1145; Me'mor. Poud., 1923, 20, 39

Berl, E., & Samtleben, O., Chena. metall. Engng, 1922, 27, 1025

Berl. E.. & Samtleben. 0.. Z . aneew. Chem.. , . 1922, 35, 201

"

4 Carpenter, C. D., & Babor, J. A,, Trans. Amer. Inst . chem. Enprs, 1924, 16, 11 1

Potier, J., C.R. 3oc . sav. Paris G. Dip., 1953, 78.

Cathala, J., et al., Bull. Soc. chim. Fr.. 1950, p. 1129 7 Cathala, J . , et al., Publication 54, 1950 (University

457

of Toulouse) Cathala. J., et al., C .R. SOC. sav. Paris G. DLp.,

Ellis, S. R. M., Trans. Ins tn chem. Engrs, 1952, 30, 1953, 78, 441

58

lo Ellis, S. R. M., Bgham Univ. cliem. Engr, 1952, 3.

l 1 Othmer, D. F., Industv. Engng Chem., 1943, 36,

12Li, Y., & Coull, J.. J . Inst . Petrol., 1948, 34, 692 l3 Scheibel, E. G., Industr. Engng Chem., 1949, 41.

1076 l4 Wohl, IC., Trans. Amer . Inst . chem. Engrs, 1946,

42, 215 l6 Garner, F. H., & Hall, R. T. W., J . Ins t . Petrol.,

1955,41, 1 Herington, E. F. G., Research, Land., 1950, 3, 41

l7 Egan, E. P., jun., Industr . Engng Chem., 1945, 37, 303

Carlson. H. C., & Colburn. A. P., Industr. Engng Chem., 1942, 34, 581

l o Robinson, C. S., & Gilliland, E. R., ' Elements of Fractional Distillation ', 1950 (New York: McGraw-Hill Book Co. Inc.)

34

614

AN INVESTIGATION OF COMPOUNDS PROMOTING THE DROPWISE CONDENSATION OF STEAM

By L. C. F. BLACKMAN,* M. J. S . DEWAR and H. HAMPSON

The modes of condensation of steam on a cooled metal surface are discussed, and an apparatus for studying them is described. With this the effect of a number of promoters of dropwise condensation has been studied. Conclusions are drawn concerning the relation between the activity and chemical constitution of promoters. Active promoters have in the molecule an unhindered hydrocarbon chain which confers water-repellency on the compound and an ' anchoring ' group which is usually a divalent sulphur atom.

* Present address: Services Electronic Research Laboratory (Admiralty), Harlow, Essex.

J. appl. Chem., 7, April, 1957