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The critical temperature of solution of normal paraffin hydrocarbons and sulphur-dioxide Todd, Eric Edward 1930

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- '-' * "t )' ' 'l " -U . B . C . L t B R A R Y i I CAT. ^ a Acc. Mo!, SmxMaanMtKac: The Cr i t i ca l Temperature of Solution of Normal Para f f in Hydrocarbons and Sulphur-Dioxide. by Eric Fdward Todd 0O0 A Thesis Submitted f o r the Degree of Master of Applied Science in the Department of Chemistry 0O0 The Univers i ty of Br i t i sh Columbis Apr i l 1930 Contents Introduction Page 1 Preparation of the Hydrocarbons Page 2 Method f o r Determination of Cr i t ica l Solution Temperatures Page 3 Procedure for f i l l i n g bulbs with Hexane Page 4 Procedure for Butane Page 5 Determination of Miscible Points Page 7 Tables for Miscible Temperatures o f : Butane; Hexane* Octane* Decane* Dodecane and Tetradecane Page 8 Conclusion . Page 12 Graph of the Cr i t ica l Solution Temperature of The Hydrocarbons with Sulphur-Dioxide Graph of the Maximum Cr i t ica l Solution Temperatures plotted against Molecular Weight . . The Cr i t ica l Temperature of Solution of Normal Paraf f in Hydrocarbons and Sulphur-Dioxide. By far the majority of l iquids are only par t ia l l y soluble in one another. When two such l iquids are heated in a closed bulb one phase disappears above a certain temperature. This temperature of disappearance of one of the phases i s known as the c r i t i c a l solution temperature! since above i t ; the two phases are miscible in a l l proportions. The c r i t i c a l solution temperatures of many hydrocarbons with l iquid sulphur-dioxide have been measured, among them have been octane, hexane and cyclohegane. The object of this investigation has been twofold. First to find a relationship between molecular weight and c r i t i ca l solution so that the c r i t i c a l solution temperature of any saturated hydrocarbon might be calculated. Such an equation is of inestimable value to the o i l industry where the use of l iquid sulphur-dioxide as a purifying agent i s being used more and more. Secondly i t was hoped some simple relationship might be discovered between molecular volume, surface tension (a measure of the internal pressure) and c r i t i c a l solution temperature in the case of binary mixtures. Up to the present only the hydrocarbons with an even number of carbon atoms have been measured because of the d i f f i c u l t y in securing pure odd number hydrocarbons. As i t i s , most of the hydrocarbons investigated have had to be synthesized by various methods. This investigation covers the c r i t i c a l solution temperatures for ethane, butane, hexane, decane. dodecane and tetradecane. Octane which has been investigated previously by A. T. Gallaugher f i t t e d in with the above determinations but hexane appeared incorrect on the l e f t side of the curve representing high percentages of hexane. A re-investigation of hexane disclosed the fact that considerabls quantities of hexane were removed when passing in sulphur-dioxide (as w i l l be explained l a t e r ) . By correcting this error in procedure the curve was found to agree with the others. Prepara- Ethane was prepared by the e lectro lys is of potassium tion of Hydro- acetate and col lected over water, carbons ' v- / yo// ^ I t was puri f ied by bubbling through strong potassium hydroxide solutions* concentrated sulphuric acid and over phosphorus pentoxide then l ique f i ed by l iquid air and red is t i l l ed to g ive a pure product. In the case of butane* which is also a gas* ethyl bromide and sodium were used with methyl cyanide as a catalyst . A con-denser attached to the top of the reaction f lask condensed the highly v o l a t i l e ethyl bromide and allowed butane to pass over to a gas tank* where i t col lected over water. The gas was then care fu l ly washed and red is t i l l ed as in the case of ethane. Hexane was prepared by allowing propyl chloride to react with sodium for several days unti l a blue powder formed. The general equation for alkyl halides with sodium i s : J The hydrocarbon was then care ful ly d i s t i l l ed by an o i l bath from the mixture and purif ied by washing and repeated d i s t i l l -ation unti l f r ee of a l l impurities. The decane used had been previously prepared by A. T* Gallaugher from very pure amy! alcohol converted into the iodide and treated with sodium. Dodecane was s imi lar ly prepared from hexyl alcohol, while tetradecane was used as supplied by the Eastman Kodak Company. The freezing point of each hydrocarbon was determined by a standard platinum resistance thermometer as a test for purity as well as f o r use on the graph. Method The bulb method was used to determine the mutual so lub i l i t i es used fo r Determin- of each hydrocarbon with l iquid sulphur-dioxide. The method ations consists of introducing various amounts of the hydrocarbon into weighed glass bulbs holding two or three cubic centimeters. The amounts were adjusted so that the f i na l mixture with sulphur-dioxide would occupy about two thirds of the bulb. The bulbs were weighed to g ive the amount of hydrocarbon added and then immersed in a bath of solid carbon dioxide and ether to f reeze the hydrocarbon. A slow current of sulphur-dioxide was then allowed to f low into each bulb where i t condensed as a clear colorless l i qu id . J A <?/-t7/r Procedure with Hexane Bulbs The sulphur-dioxide was puri f ied by passing through a train of concentrated sulphuric acid wash bottles and phosphorus pentoxide tubes. The rate of bubbling through the wash bott les was kept constant so that d i f f e rent times gave varying amounts of sulphur-dioxide in each bulb, which were then sealed o f f and weighed to g ive the amount'of sulphur-dioxide added. In this manner about twelve tubes were f i n a l l y obtained containing percentages of sulphur-dioxide varying from 0 - 100%. The above method was sat is factory in the case of high boi l ing hydrocarbons l i ke tetradecane; however in the case of hexane! which is very vo la t i l e * a considerable error was intro-duced by evaporation of the hexane* when passing in sulphur-dioxide. This necessitated a change of procedure. A bulb was weighed then cooled in the carbon-dioxide bath and sulphur-dioxide allowed to condense in i t . Meanwhile a bulb containing hexane sealed with a dropper and rubber tube had been weighed. The hexane was drawn up into the dropper which was then detached and a quantity of hexane quickly transferred into the bulb con-taining the l iquid sulphur-dioxide. The dropper was then re-placed in the bulb of hexane and weighed to g ive the amount of hexane introduced into the other bulb. The bulb of sulphur-dioxide and hexane was then sealed o f f and weighed thus allowing the amount of sulphur-dioxide present to be computed. Procedure Butane being a gas, required a more elaborate mode of f o r Butane f i l l i n g the bulbs. Two, f i v e l i t r e pyrex f lasks were accurately calibrated by weighing empty and then f u l l of d i s t i l l ed water at a known temperature. These were connected with a row of bulbs in the manner i l lus t ra ted . /or A mercury manometer and high vacuum pump were also connected with the f lasks . Stopcocks allowed each f lask to be shut o f f from the system, while the other communicated with the bulbs. The whole system was evacuated by a combined mercury vapor pump and magnovac rotary pump capable of giving a .000001 mn vacuum. After care fu l ly testing f o r leakage sulphur-dioxide was l e t into one f lask until a pressure of about one atmosphere registered on the manometer. This f lask was then shut o f f and* a l l sulphur-dioxide pumped from the rest of the system. A bulb of butane frozen in l iquid a i r was then sealed to a tube connected with the second f lask and the butane allowed to d i s t i l into i t unti l a pressure of about one atmosphere was recorded. The butane bulb was again cooled and sealed o f f leaving the apparatus ready fo r use. The mercury manometer was then very care ful ly read by a cathetometer and the pressure of the butane found from the di f ference in leve ls of the mercury. One bulb was then immersed in l iquid air and butane condensed in i t . The pressure was again read and from the di f ference in pressure with the previous reading the amount of butane condensed could be calculated. Several bulbs were f i l l e d with butane* sealed o f f and weighed: The di f ference between the calculated and observed weights gave the volume of the tubing connecting f lasks with bulbs and manometer. The diameter of the manometer was also computed so that allowance f o r change in volume of the system could be made f o r the d i f f e rent l e ve l s of the mercury. When the true volume of the system had been found in the above manner, varying amounts of butane were condensed in the other bulbs which were then closed o f f by their stopcocks and the f lask of butane closed. The butane remaining in the system was then evacuated completely. When the stopcock leading to the vacuum pump had been closed the sulphur-dioxide f lask was opened and the pressure recorded. A bulb immersed in l iquid air to f reeze the butane was then opened and sulphur-dioxide condensed in i t . The decrease in pressure was noted and the bulb sealed o f f at a str icture in the Btem, which prevented collapse due to the vacuum and subsequent cracking of thick g lass . When a l l the bulbs had been sealed and removed^ others were sealed on and the process repeated until a suf f ic ient ^ number had been obtained. The important advantage of this methdd was that the percentages of the components in each bulb could be controlled very accurately and time wasted f i l l i n g duplicate bulbs, as in the other cases* eliminated. Determin- When the bulbs had been f i l l e d as described, their miscible ation of Miscible points were determined. In the case of decane, dodecane and Points tetradecane the l iquid sulphur-dioxide and hydrocarbon divided into two layers at room temperature so that the bulbs required heating in order to determine the miscible temperature. A water bath was used with a standardized thermometer immersed in i t . A bulb was taken and held in the bath while the temperature was gradually raised unti l the two layers disappeared. This temper-ature was recorded and the bath then allowed to cool until the contents of the bulb turned milky. The two temperatures thus obtained agreed within one tenth of a degree f o r mixtures between twenty and ninety percent sulphur-dioxide. However, in the case of small percentages of either component supersaturation became evident and much d i f f i c u l t y was experienced in obtaining the correct miscible temperatures. Each bulb treated in this manner gave the composition of a mixture that was miscible above a certain temperature. The lower hydrocarbons in many cases are miscible with l iquid sulphur-dioxide;at room temperature so these were cooled to obtain the c r i t i c a l solution temperature. A cooling bath of sol id carbon-dioxide dissolved in alcohol was used with a pentane thermometer standardized against the platinum resistance thermometer. By-plotting the compositions against corresponding miscible temperatures on a graph a curve was obtained showing the variation of so lub i l i t y with temper-ature. The sulphur-dioxide was expressed as the mol. f ract ion percentage: i . e . N, Where N, i s the number of moles of sulphur-dioxide and N^ the number of moles of the hydrocarbon. For small percentages of sulphur-dioxide the mixtures did not have a miscible point. Thus the freezing point of these gave the freezing point of the eutect ic. Butane Amt. Butane Calc. SO^  Calc. Mol. Fraction Misc. Temp, from press. Decrease .9107 gms. .8045 .4500 .6270 .2185 .343 .2870 .1346 .050 .0794 gms. 7.32 -53.8 C ' .0895 9.17 -^4 C ! .2545 33.9 -7.1 C .432 38.4 -&.1 C .^78 ^ 3 . 6 -4.7 (p .488 56.4 -6.8 C .7120 69.3 -5.1 C .9030 8&,.9 C 1.084 95.3 -26 C f ^ -Hexane n l Hexane Molr. Fraction sq. x 100 Misc. Temp. .7640 .0490 17.9 ^ * 1.4590 .4120 27.5 -%3. c ? 1.7730 .5650 30.0 -17 C 1.1300 .9860 54.0 9 C .8190 .8424 58.0 9.9 C .3593 .4643 63.5 10.6 C .4100 .5900 65.0 10 c .3230 .6760 73.7 10.2 C .1850 .8150 85.5 - 9.8 C .2970 2.0290 90 6.5 C .1990 1.6385 91.7 3.8 C .2910 2.6729 92.5 2.5 C .1417 2.8890 96.5 -10 (? .0330 .9670 97.5 -20 C ^ LiJ . i Octane - ^ ' Octane*"; Mol .-Fraction x 100 Ansc-. Temp. .7331 .0279 6.30 -49.8 C 1.4156 .0729 16.5 -21.0 C .6988 .0995 20.2 -18.6 C .6840 .1007 20.8 -16.0 C .7465 .2236 34.8 .7 C .7296 .3630 47.1 16.1 C .7187 .4117 50.5 18.4 C .7175 .4518 52.9 19.9 C .7288 .5729 58.3 23.8 C Tetradecane (continued) Octane Hoi. Fraction SO^  x 100 Misc. Tamp .5110 .5203 64.5 26.0 C .5151 .5945 67.2 26.4 C .5979 .5959 68.4 26.9 C .5330 .7463 71.4 26.5 C .3552 .9047 81.9 25.9 C .6177 2.9628 89.5 24.3 C .6800 4.1994 91.7 22.4 C .1783 5.0762 98.0 -3.6 C .1732 6.9986 98.7 -10.9 C From-- The system Sulphur-Dioxide and Normal Octane by W. F. Seyer and A. T. Gallaugher. - - Transactions Royal Society of Canada. Vol.20 Section 3 1926. ' ' a r * Decane ..V s Decane Mol. Fraction SO? x 100 Misc. Temp. 1.5750 .1088 13.3 -23 C .9428 .1806 29.8 0 C 1.0590 .2530 35.^ 7.5 C 1.0520 .3151 40,t) 14.1 C 1.6960 .7892 50.5 26-^ C 1.5750 .8559 54.6 29 C .9345 1.188 73.8 37 C .6919 1.3588 81.3 37.3 C .5760 1.2400 82.7 37.2 C .4264 2.5120 93 34.4 C Tetradecane (continued) Decane .2290 .2220 .0349 SO^  Mol. Fraction SO? x 100 1.4820 93.5 1.5864 94.<09 1.6600 ^ 99 ^ ^ Dodecane Dodecane Mol. Fraction 1.9477 .253 25.7 1.0582 .2616 39.2 .6656 .7308 .2p70 '.2804 -\Jf4.3 50.6 .8428 .5850 65 ..911 .8206 70.5 1.061 1.2054 75.2 .8189 1.2756 80.4 .3556 .9719 87.8 .4966 2.1279 91.8 .389 2.7217 95 .122 2.114 ^ 97.8 Tetradecane ^ ^—^— Tetradecane 99^ :,iol. Fraction 1.164 .041 9.8 1.0866 .2105 37.4 1.4280 .341 42.5 1.0280 .3900 54 1.1580 .5696 60.4 .7180 .7929 77.4 Misc. Temp. 33.8 C 32.8 C .4 C Misc. Temp c 14.5 C 31.1 C 36 C 40.3 C 41.6 C 44 C 45.3 C 47.3 C 46.4 C 41.8 C 30.2 C Misc. Temp. 2.6 F< P. 16.9 C 26 C 33.7 C 40.5 C 53.4 C Tetradecane (continued) Tetradecane SO^ Nol. Fraction SO^ x 100 Misc. Temp. .7736 1.414 85 55.4 C 1.05 2.044 86 55.5 C .5300 1.515 89.9 55.3 C .779 2.508 91 55.1 C .7985 4.264 94.3 53.7 c .6845 4.122 94.8 52.7 c .2260 2.9440 97.7 44.7 c .0762 3.7100 99.4 21.6 c .0478 4.0850 99.6 11.5 c From the f i r s t graph i t i s seen that the curves are not as equally spaced as might be expected, showing that there are other factors besides molecular weight that influence the so lub i l i t y . The second graph shows that the maximum c r i t i c a l temper-atures are not a l inear function of the molecular weight. The relationship does not appear to answer to any simple formula but tends to resemble a logarithmic function. * * <b 


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