18 ANALYTICAL EDITION Vol. 6, No. 1 to 40 per cent graphs corresponding to all possible pentane-hexane ratios. corrections presented are based on an average boiling point of -3.2” C. for the butane fraction of the stabilizer bottoms. Accordingly, it is desirable to determine the average boiling ACCURACY OF METHOD point of the butane fraction of the stabilizer bottoms to be The accuracy of this method is limited by that of the micro- analyzed and to alter the 10 to 40 per cent correction curves fractionation column used to analyze the materials required accordingly. It is believed that under ordinary operating in making up the synthetic mixtures. However the analyses conditions the average boiling point of the butane fraction would not change appreciably from day to day. 80
ADVANTAGES O F SHORT-CUT METHOD The short-cut method for control purposes offers several advantages over fractional distillation. The time required for a short-cut analysis is about 1.5 hours, including calculations, while a similar analysis by fractionation would take 30 about 3.5 hours for a gas sample and 6 hours for a liquid 40 08 sample. The operation is simple and does not require as great 50 I 60 expertness for good results as microfractionation; further70 more the operation, being largely automatic, is less sub2 ject to the human element, which often leads to widely 3 divergent results in I microfractionation , c especially in routine -L L c analysis. Rosen and Robertson (7) describe the analysis of stabilizer reflux by the shortcut method without the use of l i q u i d nitrogen and it is known t h a t such FIGURE16. COXPARISON OF CALCUa n a l y s i s may be LATED AND SYNTHETIC DISTILLATION used to calculate the CURVES amount of butane A and C calculated, B synthetic run in the stabilizer gas. COMPOSITION WEIQRTPIR CENT Since the analysis of Butylene A B C . . 26.5 stabilizer bottoms Butane 50 50 23.5 33.3 33.3 33.3 by the s h o r t - c u t 16.7 16.7 method does not reHexane .. 1617 ,. FIGURE15. NOMOGRAPH FOR CALCULATING LIQUID-VAPOR quire liquid air, the EQUILIBRIA FOR SMALL AMOUNTS VAPORIZED short-cut apparatus, using solid carbon dioxide as the cooling agent, permits complete analytical control over the operawere carefully carried out by an experienced operator and tion of the stabilizer. are believed to be of a high order of accuracy. The short-cut runs, both synthetic and routine, are highly reproducible. ACKNOWLEDGMENT A comparisoii of short-cut and microfractionation analyses The authors are indebted to J. B. Maxwell, of the Enon several routine samples is given in Table 11. gineering Department of this company, for the preparation of the nomographic chart used in calculating the distillation TABLE11. COMPARATIVE ANALYSES curves. ~
..
2 : : +
MICROFRACTIONATION WEIQHT SHORT-CUT WEIQETPBR CENT PERCBNT SAMPLE Propane Butane Pentane Hexane Propane Butane Pentane Hexane 0.9 25.4 31.2 42.6 1 1.0 25.8 31.8 41.4 0.9 26.3 26.4 46.4 2 0.7 26.3 27.0 46.0 1.1 27.1 29.5 42.3 3 1.4 27.5 29.6 41.5 0.0 26.6 31.0 42.4 4 0.0 26.3 30.6 43.1 3.2 22.4 24.5 49.9 6 3.6 22.0 25.6 48.8 0.0 25.6 29.2 46.2 6 0.0 25.5 28.7 45.8 1.7 43.6 34.7 20.0 7 1.9 44.4 33.6 20.1
LITERATURE CITED (1) Blair, NI. G., and Alden, R. C., IND.ENG.CHEIM., 25, 559 (1933). (2) Cerini, W.F.,Petroleum Eng., 2, No. 5, 84 (1931). (3) Coats, H.B., and Brown, G. G., Univ. of Mioh., Dept. Eng. Research, Cir. Series, NO. 2 (1928). (4) Colman, H.G.,and Yoeman, E. W., J. SOC.Chem. Ind., 38, 57T (1 91 9). \-_ -_ ,-
(5) Murray, W., IND. ENQ.CHDM.,21,917 (1929).
These data show that this method checks the microfractionation column within 0.5 per cent on the propane fraction, 1 per cent on the butane fraction, and 2 per cent on the pentane and hexane fractions. In the preparation of these graphs, every effort was made to avoid complications whenever possible. It would be possible to reconstruct the graphs in Figures 6, 7, 8, 9, and 10 so that the corrections in Figure 11 would be automatically applied, as was done in the case of Figure 5, but it was felt that the 70 per cent correction would probably be fairly constant for all sorts of samples whereas the 10 and 40 per cent corrections wouldprobably not be constant. The 10 to 40 per cent
(6) Pocock, L. A., and Blair, M. G., Nut. Petroleum News, 24, No.20, 37 (1932).
(7) Rosen, R., and Robertson, A. E., IND.ENG.CHEM.,Anal. Ed., 3,284 (1931). (8) Smith, S. S., Oil and Gus J.,28, No.4, 38 (1930). RECEIYED August 17. 1933.
In the article entitled “Asbestos in PermanCORRECTION. ganate Titrations” by Curtis and Finkelstein [IND.ENQ.CHEM., Anal. Ed., 5,318 (1933)l the second line in the second column on page 318 should read “in a typical limestone carrying 54 per cent of calcium as calcium oxide.”
