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The Systems of Sulphur Dioxide and Ortho, Meta and Para Xylenes Martin, K.W. 1932

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!Ehe Systems of Sulphur Dioxide and Ortho, Meta and Para Xylenes by K.W. Martin A thesis submitted to the Department of Chemistry f o r the Degree of Master of Applied Science. fhe University of B r i t i s h Columbia A p r i l - 1938. Table of Contents page. Introduction. 1 Materials. 2 Procedure. 2 - 7 Results. 7 Conclusion. 7 - 8 fable I. 9 Table I I . 10 Table I I I . 11 Diagrams 1 and 2. 12 Diagram 3. Diagram. 4. ) THE SYSTEMS 0 1 SULPHUR DIOXIDE AND ORTHO, META AND PARA XYLENES. INTRODUCTION. The increasing uses of l i q u i d Sulphur Dioxide as a r e f i n i n g agent i n the Petroleum Industry has led to a great deal of research on the subject of the systems of Sulphur Dioxide and the various compounds composing the crude petroleum. In the aetual extraction processes the Sulphur Dioxide i s i n solution with such a mixture of compounds that no d e f i n i t e r e s u l t s as to the chemical relat i o n s are obtain-able. I t has been found necessary to work with pure compounds separately and for several years studies have been ca r r i e d out along t h i s l i n e i n t h i s laboratory and r e s u l t s are recorded of work done by Miss Dunbar, E. Todd and E.&. King. The objeet of t h i s research i s to continue these observations by determining the Phase relationships of l i q u i d Sulphur Dioxide with the three Xylenes, Ortho, Meta and Para. From these relationships we can determine whether the combination of each one of the Xylenes with Sulphur Dioxide gave a simple binary solution or whether de f i n i t e compounds were formed. MATERIALS. The materials used, Qrtho, Meta and Para Xylene were obtained from Kohlbaum's, Germany, and were further p u r i f i e d by d i s t i l l a t i o n over metallic Sodium i n an in e r t atmosphere. The small bulbs to hold the Xylene were made by blowing a f a i r l y thick-walled glass bulb about one half inch i n diameter on the end of an eight inch piece of glass tubing. When made these bulbs were given a thorough cleaning with hot Chromic aeid washed with d i s t i l l e d water, dried and put i n a dessicator. The l i q u i d Sulphur Dioxide was obtained i n a small tank and was further p u r i f i e d by passing i t through Sulphuric Aeid to remove any Sulphur Trioxide which might be present. PROCEDURE. The dry bulbs were now weighed together with small rubber caps made to seal off the open end of the tube. Then a small quantity of one of the Xylenes was inserted into the bulb by means of a long, thin-stemmed t h i s t l e tube. The bulb was sealed with the rubber cap and weighed again to give the amount of Xylene which had been put i n . Fifteen bulbs were f i l l e d i n t h i s manner f o r each of the three Xylenes and each of the bulbs i d e n t i f i e d with a small s t i c k e r and number. Two methods f o r i n t r o d u c i n g the Sulphur Dioxide were used. I n the case of the Para Xylene which was the f i r s t to he done, the apparatus shown i n Diagram I was used. Bulbs A and B are la r g e containers i n t o which Sulphur Dioxide was passed from a r e s e r v o i r , a small tank of l i q u i d Sulphur Dioxide. These bulbs were shut o f f from the r e s t of the apparatus by stopcocks. The apparatus at G i s a manometer and the s i x small bulbs at D c o n t a i n the Para Xylene. These were sealed on by f i r s t f r e e z i n g the Para Xylene i n l i q u i d a i r and then by use of a t o r c h were fastened to the tube extending down from the stopcock. A small c o n s t r i c t i o n was l e f t a t the j o i n t to enable easy removal of the bulb. The system, w i t h the bulbs A and B shut o f f , was evacuated by a Mercury D i s t i l l a t i o n Pump u n t i l a l l the a i r had been removed. The Para Xylene was kept f r o z e n during t h i s exhaustion to prevent a p p r e c i a b l e l o s s by v a p o r i z a t i o n . When the evacuation was complete the pump was shut o f f and e i t h e r A or B was opened to the c i r c u i t u n t i l Sulphur Dioxide had f i l l e d the system. This was r e g i s t e r e d on the Manometer. Sulphur Dioxide was condensed i n t o the small bulbs by f r e e z i n g them i n l i q u i d a i r . D e f i n i t e amounts could be introduced because the volume of the system was known. With the corr e c t amount of Sulphur Dioxide i n the small bulb the stopcock connecting i t to the c i r c u i t was cl o s e d and the bulb sealed o f f at the c o n s t r i c t i o n . F i f t e e n bulbs, f i l l e d with Para Xylene, were treated i n t h i s manner. I t was found that the above procedure was slow, laborious and p a r t l y unnecessary and f o r the introduction of Sulphur Dioxide into the bulbs containing the Ortho and Meta Xylenes apparatus represented by Diagram I I was used. In t h i s process, instead of evacuating the bulb, Sulphur Dioxide was passed through by means of a long t h i n tube u n t i l a l l the a i r had been displaced. Then the bulb was closed off by the stopcock and Sulphur Dioxide condensed into i t by using l i q u i d a i r as before. The care f u l removal of the a i r was very necessary as i t was found that when Sulphur Dioxide was condensed into the Xylene when a i f was present, the solution on attaining room temperature changed from colorless to various shades of brown. This was probably due to oxidation. However, by careful manipulation t h i s apparatus proved to be more convenient and just as accurate as the f i r s t and gave solutions whieh, when allowed to warm up to room temperature, were clear and c o l o r l e s s . When the Sulphur Dioxide was put i n values ranging from f i v e to ninety-five percent by weight of Sulphur Dioxide were obtained i n order to give a good range of values for each system. The next step was to determine the freezing point of the solution i n each bulb. A bath containing ninety-five percent Alcohol and a l i t t l e Ether was set up i n a Dewar fl a s k and connected to a container from which l i q u i d a i r was 5 blown to cool the bath. A pentane thermometer, a Platinum Resistance thermometer standardized by the Bureau of Standards j Washington B.C., and one of the bulbs to be treated were placed i n the bath. The temperature was slowly lowered by the l i q u i d a i r u n t i l c r y s t a l s appeared i n the solution i n the bulb. The temperatures of the Platinum Resistance and the Pentane thermometers were recorded and the bath allowed to warm very slowly u n t i l only one or two small crystals remained. The temperature was kept at t h i s l e v e l f o r several minutes and as long as there was no apparent increase or decrease i n the siz e or number of the c r y s t a l s then the bath was allowed to warm very s l i g h t l y u n t i l the c r y s t a l s slowly disappeared. This temperature was taken as the freezing point of the solution and was accurately given by the Resistance thermometer. The remaining bulbs were treated i n the same manner and t h e i r freezing points obtained. The amount of Sulphur Dioxide i n each bulb was determined i n tow ways, f i r s t by weight and seeond by t i t r a t i o n of the Sulphur Dioxide with a standard Sodium Hydroxide solution. For the t i t r a t i o n two standard solutions were prepared, one of approximately 1 Normal Sodium Hydroxide and the other of .5 Normal Hydrochloric Acid. The determination by weight was done by weighing r the sealed bulb. Then the contents were frozen, the top of the tube was snapped off and the bulb was inserted through a rubber stopper into an erlenmeyer f l a s k containing 50 c.c. of standard Sodium Hydroxide. The open neck of the bulb was 6 below the surface of the Hydroxide and the f l a s k was t i g h t l y stoppered. As the solution i n the bulb melted the Sulphur Dioxide bubbled into the Hydroxide solution and was neutral-ized. When the reaction was over the bulb was removed, cleaned, dried and weighed together with the top piece. The difference i n weight of the bulb when f u l l and when empty gave the weight of Xylene and Sulphur Dioxide. The weight of the Xylene was known and therefore the weight of Sulphur Dioxide was obtained. The so l u t i o n of Sodium Hydroxide whieh was p a r t l y neutralized by the Sulphur Dioxide was completely neutralized by the standard Hydrochloric Aeid. From these values the weight of Sulphur Dioxide was obtained and these values gave a good cheek with those of the f i r s t determination. The moi percent of Sulphur Dioxide i n each solution was next calculated and together with the weight of Sulphur Dioxide, the weight of Xylene, the weight percent of Sulphur Dioxide and the temperature are show*, i n Tables I, I I and I I I . Table I represents the values for Ortho Xylene, Table I I n " " Meta Xylene, Table I I I * " n Para Xylene. From these tables diagrams were drawn showing the freezing point curves f o r Sulphur Dioxide and each of the Xylenes. Two curves were drawn f o r each system, one representing the weight percent of Sulphur Dioxide i n solution and the other 7 representing the moi percent of Sulphur Dioxide i n solution. Diagram I I I shows the three curves for the weight percent values and Diagram 17 shows the three curves for the moi pereent values. RESULTS. The r e s u l t s as shown "by these freezing point curves are as follows. In each ease we have a simple binary solution represented. The two components form a normal system showing a d i s t i n c t euteetic at the point A. By means of the Phase Rule we can determine the degrees of freedom i n each case. The number of components i s two, the number of phases i s two. Therefore since F=C + 2 - P, then F=2. This shows we have two degrees of freedom which, i n our case, are represented by temperature and composition since the pressure i s n e g l i g i b l e . From B to A on the graphs we have the Xylene c r y s t a l l i z i n g out of the solution. From C to A only Sulphur Dioxide c r y s t a l l i z e s out. At the point A we have a d e f i n i t e euteetic forming c r y s t a l s of Sulphur Dioxide and the Xylene. CONCLUSION. It i s i n t e r e s t i n g to note that the eutCctics a l l f a l l near the same composition value and range between 95 and 99 percent Sulphur Dioxide. In the case of Benzene which i s the same type of compound as the three Xylenes the euteetic f a l l s i n nearly the same position. However i n the case of 8 Hydrogenated Benzine compounds, which were s t u d i e d by E.G. King during the past two y e a r s , the e u t e c t i c i s on the opposite side of the curve and ranges between 1 and 5 percent Sulphur Dioxide. The study of the chemical r e l a t i o n s h i p s between Sulphur Dioxide and the three Xylenes i n s o l u t i o n has shown that no compounds are formed. The system i s a simple b i n a r y s o l u t i o n and t h e r e f o r e the e x t r a c t i o n of Ortho, Meta -and Para Xylenes from crude petroleums by means of Sulphur Dioxide i s a p r a c t i c a l process. TABLE I. Bulb Grains Ortho Xylene Grams Sulphur Dioxide Weight Moi % Temp. 1 1.7S61 .2005 10.41 16.06 -34.42 2 2.6440 .1362 4.90 7.88 -31.00 3 .8756 .3756 30.02 41.42 -42.90 - 4 .8109 .6969 46.22 58.69 -51.40 5 .6172 .5927 48.99 61.33 -54.00 6 .2099 .4853 61.03 72.11 -60.51 7 .2714 1.4259 84.01 89.87 -72.50 8 .0894 .2537 73.94 82.58 -66.13 9 .4684 3.0402 86.65 91.50 -72.73 10 .0398 .6235 94.00 97.00 -77.08 11 .0524 1.2478 95.97 97.70 -78.10 IE .0318 1.5661 98.01 98.82 -78.76 Ortho Xylene 100$ Sulphur Dioxide 100$ -28.00 -76.10 i a TABLE I I . Xb Grams Meta Xylene Grams Sulphtir Dioxide 1 1.8307 .3257 2 1.2469 .39 37 3 1.0973 .8057 4 1.1060 .9064 5 .8079 1.2128 6 .4032 .8916 7 .4172 1.9854 8 .2213 1.7839 9 .1949 1.9730 10 .3205 4.2385 11 .1032 6.1136 Weight Moi $ Temp. 15.11 22.52 -57.45 24.00 34.26 -60.00 42.34 54.82 -64.07 45.04 57.55 -64.74 60.02 71.32 •68.10 68.86 78.62 -70.70 82.64 88.89 -73.50 88.96 93.07 -75.52 91.01 94.78 -76.48 92.97 95.65 -76.60 98.34 98.99 -76.98 Meta Xylene 100$ Sulphur Dioxide 100$ -54.00 -76. fO TABLE III. Julb Grams Para lylene G-rams Sulphur Dioxide Weight Moi $ Temp. 1 .7152 .3503 32.85 44.75 -12.93 2 .5409 .6001 48.95 64.80 -29.30 3 .8552 .9192 51.70 64.00 -34.10 4 .3963 1.0023 71.80 80.70 -51.20 5 1.2749 .4935 27 .90 39.00 -10.56 6 2.4287 .2435 9.11 14 .20 4.87 7 2.3583 .2767 10.50 16.40 4.27 8 1.1742 .2325 16.51 24.65 .77 9 1.8424 .0740 3*86 6.23 8.73 10 . 2668 .8867 76.90 84.70 -57.60 11 .1087 .5693 84.00 89.90 -65.20 12 .1596 8.0000 98.00 98.90 -76.77 Para Xylene 100$ Sulphur Dioxide 100$ 15.00 -76.10 T To Pu mp DIAGRAM I Rubber Sea/s T Reservoir Outlet DIAGRAM Z. 


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