Equilibrium partial vapor pressures over solutions ofthe diethylene triamine--sulphur dioxide--water system

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Authors Roberson, Alva Harold, 1900-

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EQUILIBRIUM PARTIAL VAPOR PRESSURES OVER SOLUTIONS OF THE DIETHYLENE TRIAMINE— SULPHUR DIOXIDE— WATER

SYSTEM

"• - - . "by

. : r Alva Harold Roberson

- : - a Thesis - > ̂ - , -,submitted to the faculty of the

Department of Mining Engineering and Metallurgy

in partial fulfillment of the requirements for the degree of

Master of Science

in the Graduate College University of Arizona

1937

Approved: / :Major Professor

Date

C 0 N T E N T S

Chapter pageI. Introduction..................................... i,

II • Apparatus and Methods.. ...... 5III. Data^......... 12IV. Capacity of Diethylene Triamine Solutions for

Sulphur Dioxide....... ...... 15V. Partial;Vapor Pressure of Water............. .. 19VI. :: Estimation of Vapor Pressure of ailphur Dioxide.. 20VII• Conclusions.and Suggestions...................... 27

ACKNOVfLEDGMEHTS

■V U..: ■. i" : : ■ , . , . ' : ' :The writer wishes to acknowledge the help and super

vision of Mr. ?. s. Wartman, Associate Mettalurgist, U. S. Bureau of Mines, in all phases of this work, and to ex­press his appreciation for the cooperation he has shown.

To Dr. T. G. Chapman, head of the department of Metal lurgy, whose friendly interest has been so helpful; and to- - " ' v - ; .Dr. R. S. Dean, Chief Engineer, Metallurgical Division, U. S. Bureau of Mines,, for permitting this work to be publish7 ..7 77.7 , 7 7 7.777 7 -7:7 1 7 7 . , ■ ' .. ' .7 . ” '"

ed, the writer also, extends his thanks.

-1'

EQUILIBRIUM PARTIAL YAPOR PRESSURES OVER SOLUTIONS OF THE DIETHYLENE TRIAMINE— SULPHUR DIOXIDE— WATER

SYSTEM/ : CHAPTER I.--INTRODUCTIONElimination of sulphur dioxide from waste gases of metal­

lurgical reduction works and the subsequent recovery of the sulphur is one of the major problems faced by the smelting in­dustry today. Recovery of the sulphur would make available a great natural resource; moreover, the damage caused by sulphur dioxide in agricultural and heavily forested regions, and the

1resulting;bitter and expensive litigation would be eliminated. At the Washoe smelter at Anaconda, Montana, where about three hundred tons of copper are produced daily, sulphur dioxide is discharged in the smelter smoke at the rate of 2090 tons per day.1 2 If all of this sulphur dioxide could be converted into elemental sulphur it would yield 1045 tons of sulphur per day and have a value of $18,800 at the current price of sulphur. This example represents only a small proportion of the sulphur lost daily, as this smelter is one of about twenty, in the west­ern states.

The litigation between the farmers of the Deer Lodge Val­ley and the Anaconda Copper Mining Company is one example. of the many controversies arising from the damage by sulphur di-

1Thum, Ernest E •, Smoke Litigation in the Salt Lake Val­ley, Chem. and Met. Engineering, vol. 82, pp. li.45-50, June 23, 1920.

2Pulton, Charles H., Metallurgical Smoke, U. s. Bureau of Mines Bulletin 84, p. 9.

—2—

oxide. In all over $1,000,000 was spent from 1903 to 1911. Before the suits started about $400,000 was paid to the far­mers for claimed damages. Later the company spent about $500,000 and the farmers $100,000 gathering evidence for a law suit, the testimony of which covered 32,000 pages and required a year and-a half to present. -/l; ^

Similar proceedings have taken place at nearly every : smelter in the Y/est which is located near an agricultural region. " : - ': : ;

One of the proposed methods for the recovery of sulphurdioxide from smelter smoke is based on the absorption of this gas in aqueous solutions of diethylene triamine * * and the subsequent regeneration of the diethylene triamine with re­lease of the dissolved gas by heating, either with or with­out reduced pressure. :

Diethylene triamine is one of a series of aminoethy derivitives of ethylene diamine. It has the structural form­ula DH 0 H NEC H NH and adds directly to acids to form, tri- 2. 2 4 2 4 2basic salts and soaps. If the acid is weak the salts are de­composed by heating, particularly in aqueous solutions. * l

3l Mathewson, E. P., Personal communication.Marks, G. W.,, and Ambrose, P. M., Diethylene Triamine

and Other Amines as Agents for the Recovery of Sulphur Di­oxide... Unpublished, report, u. S. Bureau of Mines, 1936.

Wilson, A. L., New Aliphatic Amines, Industrial and Engineering Chemis try, vol. 27, p . 869, Aug. 1935.

Bottoms, Robert Roger, U. S. Patent 1,783,901. Dec.2, 1930.

Titration of the amine with a strong acid results in complete neutralization at the methyl orange end point. The series is described by Wilson7 as follows:

nThese compounds, of a straight chain structure and pos­sessed of a multiplicity of reactive amino groups, offer un­usual possibilities in the synthesis of complex molecules as might be of value for rubber accelerators, pickling inhibitors resins, etc. They are strongly alkaline high boiling liquids, can be substituted for ethylene diamine in many of its uses, and form well-defined polybasic salts and, under certain con­ditions, monoamides• A mixture of these amines is found to possess most of the characteristics of an ideal gas absorbent. They absorb large quantities of hydrogen sulfide, carbon di­oxide, and other acid vapors at a high rate, and regenerate these gases on boiling their aqueous solution. In commercial operation the aqueous solution of these amines is cycled through an absorption tower in countercurrent contact with an acid-containing gasi The inert gas is thereby purified, and the amine solution, on boiling, evolves the acid gas in substantially free form and is itself revivified. The pro­cess is particularly applicable to the removal of sulphur compounds from natural and manufactured gases and to the re­moval or recovery of carbon dioxide from waste or artificial gases.”

The absence of quantitative data on the equilibrium partial vapor pressures of sulphur dioxide and water over aqueous diethylene triamine solutions containing sulphur di­oxide, and the importance of these data in determining the optimum concentration of absorbing solution and in the de­sign of both the absorber and regenerator have made it nec­essary to obtain a series of vapor pressure,^measurements on the diethylene triamine—sulphur dioxide—water system.

' In this paper the vapor pressure data are given over the entire range of concentration of diethylene triamine and rel­

7Work cited, p, 2.

4-

ative concentrations of sulphur dioxide usually encountered in the cycle of absorption and desorption, and also over the temperature range likely to be encountered in such a process.

—5—

CHAPTER II.— APPARATUS AND METHODS The equilihrixm partial vapor pressures were measured

by the dynamic method, nitrogen being used as the carrier gas. The apparatus described is shown in figure 1.

*V-

DHoHofCcHo»nitrr Tybf

FIGURE 1. DIAGRAM OF APPARATUS A steady stream of nitrogen was passed from the cyclinder

MA" through the saturator "Bn, which consisted of two glass tubes designed to give the maximum time of contact between the solution and the carrier gas. These tubes were designed

and constructed by F. 8. Wartman, Associate Metallurgist,TJ. S. Bureau of Mines, Tucson, Arizona. The gas, after be­ing saturated with sulphur dioxide and water vapor, was first passed through a filter tube (figure 1) containing a small piece of cotton to remove any mist or spray carried over from the saturator. The ground glass seal eliminated any chance of the rubber stopper being attacked by the sulphur dioxide, and at the same time provided a convenient method for replac­ing the cotton, which was changed after each set of determi­nations. Cork stoppers were not used since the wax seals necessary to make them waterproof softened and caused leaks at the higher temperatures employed. This filter was follow­ed by a weighed Vanier absorption bulb containing a solution of sodium hydroxide in the outer part and anhydrone in the inner tube. After leaving this absorption bulb the nitrogen ' was passed through a protective anhydrone tube followed by a humidifier, and finally into the large aspirator bottle nCM.

. The total quantity of carrier gas used was measured by the weight of water flowing from the aspirator bottle, with .. suitable corrections for temperature and pressure. The flow of water was adjusted so that, the rate of inflowing gas and outflowing water were the same and was maintained at about 1800 cc. per hour. A slight pressure was maintained on the saturators due to the resistance in the Vanier bulb, anhydrone tube, and humidifier.

Temperatures in the saturator and aspirator bottle, and

7

pressures of the carrier gas at the Intake and outlet of the • saturators were read at frequent intervals.

The partial pressures of sulphur dioxide and water were determined "by substituting appropriate experimental values in one of the following typical equations:

PSO2 M + M SO H O2 2

+ M.P or

x'-.

p.h2°

' mh ?o

h * v * \

.P

where M. — moles of the substance designated by the subscript, p "ss corrected barometric pressureThe weights of sulphur dioxide and water were found as

follows: sulphur dioxide was determined by oxidizing the ab­sorbed sulphur dioxide in the sodium hydroxide solution tosulphur trioxide with hydrogen peroxide, acidifying with hy­drochloric acid, and heating to boiling. The resulting sul­phate was precipitated with barium chloride and weighed as :

. . - Qbarium sulphate. Water was determined as the difference

Scott, w. W•, Standard Methods of Chemical Analysis, vole 1, 3rd. Edition, p. 511: D. Van Nostrand Co., New York, 1922.

8-

between the increase in weight of the Vanier bulh and the weight of the sulphur dioxide absorbed by the sodium hydrox­ide. Since there are no data available for the partial pres­sures of diethylene triamine there is no direct method of knowing when the carrier gas is completely saturated with the amine and water. Two indirect methods were used for de- terming when the saturators were operating satisfactorily.One method consisted in measuring the partial pressure of pure water. If the value obtained agreed, within the limits of error, with accepted values the assumption was made that the correct values would also be obtained for the amine solu­tions. The other method used was to make several determina­tions with varying rates of flow of the carrier gas and it was assumed that saturation was accomplished if the results were unchanged by decreasing the rate.

Usually two determinations were made at each concen­tration and temperature and the results were accepted if they agreed within three millimeters of mercury. On the lower concentrations and higher saturations, where the par­tial pressures were high, three or four determinations were made and the results plotted, the final value being obtained by extrapolating back to the vapor pressure ordinate.

QWilson determined the vapor pressures of pure diethy- .

lene triamine over a wide range of temperatures and his re­sults are plotted in figure 2, except that the curve has

-§ 1 — :— :------ ---- --------:— :--------- -----------Work cited, p. 2.

been extrapolated down to 0*1 nm# Wilson* s measurements ex­tend from 10 to 1000 mm. while this extrapolation is only over a range of 0.1 to 10 ram. It is abserved that at 85°C• the vapor pressure is about 10 mm. If Raoult* s law is as­sumed to hold, the partial pressures of diethylene triamine at about 85°c. over the 10, 20j 30, and 40 percent solutions .are approximately 0.16, 0.35, 0.60, and 0.94 mm. respectively

iVo 190 iio;o 30 40 50 60miPBiATURS, IBGRBS COfTICRAI*

FIGURE 2. VAPOR PRESSURE OF DIETHYLEHE TRIAIIENE

10-

10Examination of boiling point-composition curves for diethylene triamine show that there is not more than one percent of diethylene triamine in the vapor phase when aque­ous solutions containing 40 percent amine are boiled.

In this work on the partial vapor pressures of aqueous diethylene triamine solutions partially saturated with sul­phur dioxide the partial pressure of the amine was not measured as the above data indicated that it was low over the t empe rature- rang e studled.

Preparation of SolutionsThe stock solutions of diethylene triamine were made up

by volume from ordinary commercial grade material, its speci­fic gravity at 25°C, being practically the same as that of water. Thus a 30 percent solution contained 30 percent by volume of commercial diethylene triamine. These stock solu­tions were standardized by titration with normal sulphuric acid, and the assumption made that all the amino nitrogen present was in the form of diethylene triamine.

The solutions for the measurements of vapor pressure were prepared by adding accurately measured volumes of a given solution of definite diethylene triamine concentra­tion to carefully measured volumes of the same solutions saturated with sulphur dioxide; the sulphur dioxide being obtained from cylinders of commercial grade liquid gas.

10 ' --------------------------—Furnished by Carbide and Carbon Chemicals Corp.

-11-

The ratio of the volume of saturated solution to the sum of the volumes of the solutions, after multiplying by 100 gave the "Saturation Percent",

Since considerable heat is evolved when such solutions are mixed, which may cause appreciable losses of sulphur di­oxide one solution was slowly added to the other and mixed in a flask surrounded by a bath of cold water. A cotton plug was used for closing the part of the flask not occupied by the tip of the delivery burette.

-12-

CHAPTER III.— DATAPour series of solutions representing four different

strengths of diethylene triamine were used, namely 10, 20,30, and 40 percent by volume. Partial pressures of sulphurdioxide and water over these solutions containing varyingamounts of sulphur dioxide at temperatures of 33°, 50°, 75 ,

oand 90 0. are shown in tables I and II.The partial pressure jof sulphur dioxide over the 10

percent solution 90 percent saturated with the gas was tooohigh to be accurately measured at 33 0. A measurement made

at 20 0# on this solution gave the value of 307 millimeters.

Table 1.— Partial Pressures of Sulphur Dioxide

Percent 1 Saturation** SOr, Partial Pressures$ Diethylene

Triamine 1 Percent 1 millimeters of mercury -# by volume f t 1’ euro e nature G.$ f * 33 I 50 * 75 dtiit 10

11 $ it 0.8t* 2.90 7.0t 20 * 50 t 0.8t 30 t t * 0.17 0.5#* 40 ft f tt i 0.6

* # t tt 10 * 0,16 t 1.9 » 12.1 39.2t 20 * 80 t 0.7 * 6.72 15.8i 30 t 0.6 ♦ 3.63 9.02tt 40 t » tY

0.6 * 2.40t 7.1$t 10

#t t» 3.53

YY 88.8

t*315

20 * 75 « 1.65 Y 9.4 » 51.5 129t 30 t ' 0.11 Y 0.4 * 29.8 93.4i

i40 i

t* 0.24t

YY

0.04 * 21.9t

59.2$

10*

«*307YY ___

Y

i 20 ' 90 ' 59.5 *231t 30 t * 13.5 *167 *230i

«40 t

f• 3.18*t t

21.0 *174t

14-

Table 2,— Partial Pressures of Water

* Percent1 Dlethylene 1 Triamine* by volume

SaturationPercent

*ttt

EgO Partial Pressuresmillimeters of mergury

Temperature 0.i 33 « 50 Y 75 T 60* 10

$t

t86.5

IY 291

t

Y 522* 20 50 Y 89.9 Y 1 504* 30 32.3 * 87.4 Y 265 Y 481« 40 f

t 26.5 *t 75.1 YY

215 YY

430

» 10Yt 32.4 ! 86.8 288 Y 522

* 20 60 t 31.4 * 90.2 Y 264 Y 504* 30 t 30.0 * 84.5 Y 252 Y 470* 40 t

t 25.0 *t 78.5 YY

217 YY

410

* 10t1

t30.4 » 86.5

tY 290

YY

* 20 75 t 29.4 » 89.3 Y 264 Y 510• 30 I 29.6 * 86.0 Y 258 Y 457' 40 ,*

tt

26.1 * t 72.3 YY

223 YY

412

• 1 Af t 1 T

1 JLU» 20 90 t 24.0 * 84.8 Y

YY

* 30 Y 22.8 * 78.5 Y 238 «

* 40 YY

26.3 «t

73.5 YY

211Y

CHAPTER IV.--CAPACITY OF DIETHYLENE TRIAMINE SOLUTIONS FOR SULPHUR DIOXIDE

Assuming that each, amino group of diethylene triamine will hold one molecule of sulphur dioxide it follows that one molecule of the amine will hold three molecules of sul­phur dioxide, or one gram of the amine will absorb 1.86 grams of the gas.

The amount of sulphur dioxide that will be held by a given diethylene triamine solution at a definite temperature may be determined if the density before and after saturation,and the volume change of the solution on saturation are known.

!_"LThese values have been determined and are shown in figures 3, and 4.

Since the density of the diethylene triamine is practi­cally unity and an impure grade of the amine was used the den­sity was taken as unity, in the calculations presented in table3.

Marks,'G-, We, and Roberson, A. H., Unpublished Report, U« S. Bureau of Mines, 1936*

FIGURE 5. VOLUME CHANGE OF ORIGINAL DIETHYLENE TRIAMINESOLUTION IN CC. PER CO., AFTER PARTIAL SATURATION WITH SULPHUR DIOXIDE

Ten»MR*rtM* *C

FIGURE 4. DENSITIES OVER A TEMPERATURE RANGE OF 20°C. TO 70°C.AqUEOUS DIETHILENE THIAMINE-SOLUTIONS SATURATED : IYITE SULPHUR DIOXIDE

Table 3.— Concentration of Constituents In Solutions for Vapor Pressure Measurements

fPercent 1 'Amine in » Solution * before * Saturation* with SO *

99

Percent * Moles per 1so2 ;Saturation

* Water *i t

t. ' t100 grams of Solution*

Diethylene* sulphur * Triamine » Dioxide *

Total » No. of * Moles *

Molefractionso2

9u9

9999

Mole *Fraction*h 2° ;

f 0 * 5.071 0.084 * 0 5.155 r 0 9 0.984 *t 25 * 4.831 0.080 » 0.074 4.985 * 0.0148 0.969 *10 f 50 * 4.599 0.076 » 0.145 9 4.820 * 0.0300 9 0.954 *1 60 » 4.512 0.075 » 0.172 9 4.759 * 0.0361 9 0.948 »t 75 » 4.385 0.073 » 0.207 9 4.665 » 0.0437 9 0.940 *1 90 » 4.263 0.071 » 0.249 4.583 * 0.0543 9 0.930 *f 0 1 4.61? 0.163 f 6 9 4.760 * 0 9 0.966 »f 25 * 4.22 0.149 » 0.134 4.503 * 0.0298 9 0.937 *20 I 50 * 3.86 0.136 * 0.254 9 4.250 * 0.0598 9 0.908 »f 60 ♦ 3.73 0.131 * 0.299 9 4.160 * 0.0719 9 0.896 *t 75 » 3.54 0.125 * 0.362 9 4.027 * 0.0898 9 0.880 *t 90 * 3.38 0.119 * 0.421 : 9 3.920 » 0.1078 9 0.862 *1 0 1 4.062 0.66O * di i 4.322 f 0 9 5.940 *1 25 * 3.580 0.229 » 0.185 ‘3.994 * 0.0463 9 0.897 *30 t 50 » 3.171 0.203 » 0.342 3.716 * 0.0920 9 0.853 *f 60 » 3.025 0.193 » 0.339 f 3.617 * 0.1103 9 0.836 *t 75 » 2.821 0.180 * 0.477 9 3.478 * 0.1371 9 0.811 »• 90 * 2.634 0.169 » 0.549 9 3.352 * 0.1638 0.786 *I 0 1 3.473 0.363 * 6 9 3.836 * d. 9 5.9554*

9 25 » 2.958 0.309 * 0.230 3.497 * 0.0742 9 0.846 *40 9 50 * 2.542 0.266 » 0.419 9 3.227 * 0.1298 9 0.788 *

9 60 * 2.395 0.250 * 0.486 9 3.131 * 0.1552 9 0.765 *9 75 * 2.195 0.229 * 0.575 9 2.999 * 0.1917 9 0.732 *9 90 * 2.013 I 0.210 * 0.656 9 2.897 * 0.2280 9 0.699 *

CHAPTER V . — PARTIAL VAPOR PRESSURE OF WATERA few slight variations in the partial pressures of water

may be observed in table 2. Since.these deviations are not great, and since the partial pressures of water were finally considered relatively unimportant in this problem the experi­mental work along this line was discontinued.

Reductions in the partial pressures of water considerably greater than -those which would have been obtained if-Raquit's law had held were observed when the concentrations of diethy­lene triamine and sulphur dioxide were increased.

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CHAPTER 71.— ESTIMATION OF VAPOR PRESSURE OF SULPHUR DIOXIDEThe vapor pressures over a solution depend on several

variables, some of which are concentration, pressure, and temperature, and the estimation of these vapor pressures is difficult if some simple relationship does not exist. The vapor pressure rises rapidly with increasing temperature, and it is difficult to interpolate values between the tem­perature-vapor pressure curves. These curves are all slmi-

12lar in form, however and the application of Duhrlng* s Rule ' 13, 14

provides a method of obtaining straight line curves of the various vapor pressures. If, instead of plotting the tem­peratures of diethylene triamine solution as ordinates against the partial pressures of sulphur dioxide as abscissas, one plots as abscissas the temperatures at which a suitable stan­dard reference liquid, in this case water, exerts the same pressures, the experimental points will fall on a straight line, any variation being presumably due to experimental error. This general agreement of the experimental values with DuhringTs rule is striking. In other words, these vapor

22 ; — ;Neue Grundgsetze sur nationelle Physik und Chemie (erste

folde); Leipzig, 1878.13Baker, E. M., and Waite, H. V., Boiling Point of Salt

Solutions under Varying Pressures. Chemical and Metallurgical Engineering, vol. 25, No. 25, pp. 1137-40, Dec. 21, 1921.

14Walker, Win. H., Lewis, W. K., McAdams, Win. H., Princi­ples of Chemical Engineering, pp. 429-432, Second Edition-Mc- Graw Hill, New York, 1927.

pressures obey the relationship

t + tK = 1 2v e2

where K is a constant, t and t are the temperatures at which1 2the sulphur dioxide partial pressures are p and p » and ©

1 ^ t.and © are the temperatures at which the vapor pressures or 2water are p and p •1 2

The application of this rule is shown in figures 5, 6, 7, and 8, each concentration of diethylene triamine being plotted separately. *

From the proceeding facts it will be seen that it is nec­essary to know only two points in order to draw a curve from which any desired vapor pressure may be read. While only two points are necessary it is desirable to have more to serve as checks on the accuracy.of the results, since a discrepancy that was hardly noticeable in the conventional method of plotting was very evident when the erroneous result was plotted accord­ing to Duhring's rule.

The use of the curve should do much to eliminate a great deal of tedious effort in obtaining the many points necessary to construct an accurate temperature-pressure curve of the usual type.

/oo

FIGURE 5, DUHRIITG*S RULE APPLIED TO VAPOR PRESSURE OF SULPHUR

DIOXIDE OVER 10 PERCENT DIETHYLENE TRIAMINE SOLUTIONS

35-

FIGURE 6. DUHRING*S RULE APPLIED TO VAPOR PRESSURES OF SULPHUR

DIOXIDE OVER 20 PERCENT DIETHYLENE TRIAMINE SOLUTIONS

JOJt ̂OLi/r/dn

Tgmperaturv ofVJoten DefC

FIGURE 7. DUHRING’S RULE APPLIED TO VAPOR PRESSURES OF SULPHUR

DIOXIDE OVER 30 PERCENT DIETHYLENE TRIAMINE SOLUTIONS

Temperature o f Water. Def .C

FIGURE 8. DUHRING’S RULE APPLIED TO VAPOR PRESSURES OF SULPHUR

DIOXIDE OVER 40 PERCENT DIETHYLENE TRIAMINE SOLUTIONS

—26—

By using the group of curves corresponding to the approx­imate amine concentration of a given diethylene triamine-sul- phur dioxide solution the partial pressure of sulphur dioxide over a solution of definite sulphur dioxide saturation can be readily obtained. This method is especially valuable in cal­culating partial pressures that are too high to be accurately measured. Pressures of about 300 mm. were considered the max­imum which could be accurately measured with the apparatus used in this work. One example will illustrate the use of these graphs. Suppose it is desired to know the partial pressure of sulphur dioxide over a 20 percent diethylene triamine solution 90 percent saturated with the gas at any given temperature, say 92°C. referring to figure 5, a point on the ordinate cor­responding to 92° is projected horizontally to the right un­till it intersects the 90 percent saturation line. Prom this point a perpendicular is dropped to the abscissa which corres­ponds to the temperature of 141°. By referring to a vapor pressure table of water it is observed that at 141°Ce the vapor pressure is 2788.4 mm.

These graphs are not only valuable for estimating vapor pressures above the range of these experimental results; they also permit the estimation"of vapor pressures at reduced tem­peratures, thus making it possible to estimate the efficiency of solutions of various degrees of saturation to absorb sulphur dioxide.

-27-

CHAPTER VII.— CONCLUSIONS AND SUGGESTIONSCapacity of absorbing solution and rate of absorptionIt is desirable that the solutions have an appreciable

Capacity for sulphur dioxide, and at the same time have a partial pressure low enough to permit a substantial degree of saturation. According to Henry's Law sulphur dioxide will be more rapidly absorbed by solutions whose partial pressures of the gas at the absorption temperature are low; the absorp­tion becoming less rapid as the solutions become nearly satu­rated, with a resulting increase in the partial pressure. The capacity of the absorbing solution for sulphur dioxide in­creases as the concentration of the diethylene triamine in­creases. (See Table 3)

If one assumes a smelter smoke containing two percent of sulphur dioxide at an atmospheric pressure of 700 mm. the par­tial pressure of the sulphur dioxide would be 14 mm. This pres sure corresponds to the vapor pressure of water at 14°C. on the abscissa of figures 4, 5, 6, and 7. It will be impossible for any solution to absorb sulphur dioxide after the partial pres­sure of the gas over the absorbing solution reaches the above value, namely 14 mm. and the rate of absorption will become in­creasingly slower as the partial pressure over the solution approaches this value.

Suggested coraiter-currentProbably the most efficient method of absorbing the gas

from smelter smoke would b@ to eool the latter to at least 40°C. and use the more nearly saturated solution as the first spray, thereby allowing the solution with the least absorbing power to take up as much gas as possible before being sent to the re­generators. By using successively less saturated absorbing so­lutions for succeeding sprays or washes the smoke could be..more thoroughly stripped of all its sulphur dioxide content, and at the same time permit the maximm concentration of the sulphur dioxide gas in the absorbing solution.

Strength of Absorbing SolutionWhile it is obvious that the capacity of diethylone tri-

mine solutions for sulphur dioxide varies directly as the amine concentration of the solutions the final choice of a suitable absorbent cannot be made on this basis alone. Other factors, such as viscosity of the saturated solutions, the cost of cool­ing the smelter smoke, the rate of absorption, and other physi­cal properties of the solutions, none of which were considered in this investigation, would have to be known before the design­ing engineer could make any choice of a suitable absorbant.

The data presented in this paper provides some of this nec­essary information and should be of value in the design of a process for the removal of sulphur dioxide from waste industrial