Equilibrium partial vapor pressures over solutions ofthe diethylene triamine--sulphur dioxide--water system
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Authors Roberson, Alva Harold, 1900-
Publisher The University of Arizona.
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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