THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CVII. FRIDAY, MAY 22, 1914. No. 2786. Separation of the Gaseous Paraffins by Fractional Distillation at Low Temperatures. From a paper presented before the Spring Meeting of the American Chemical Society, April 7-10, 1914, by permission of the Director of the United States Bureau of Mines, U.S.A. By GEORGE A. BURRELL and FRANK M. SEIBERT. This paper describes experiments that resulted in the separation of a natural gas sample into the individual paraffin hydrocarbons present. This had not been accomplished hitherto. The natural gas used in Pittsburg is a complex mix- ture, and is typical of gas that is supplied to many cities to the extent of billions of cubic feet per year. The exact composition of this gas is of importance to the Bureau of Mines, because it is used in testing explosives, safety lamps, electrical mining machiuery, and other mining appliances. By the scheme sh >wn herein it is also possible to determine more closely the quantity of the vapours of the liquid paraffins in a natural gas mix- ture than has been possible heretofore. I In the experiments reported herein (natural gas was first liquefied by means of liquid air, Ind the different paraffin hydrocarbons separated by ploperly adjusting temperatures and removing the varioul fractions with a mercury pump. These fractions wer<| analysed by the ordinary slow combustion methods. I Advantage was taken of the work of P. Lebeau and A. Damiens, * who prepared various mixtures of the gaseous paraffins, liquefied them, and partially separated them. This work is an advance over their work, In that the separa- tion was made into single constitueds. The important part of this paper, however, is thaapplication of the work to the determination of the constituents of natural gas. Such a separation is possibh, because in the liquid condition the boiling poiits of the gaseous paraffins are rather widely separatd. These boiling points follow: Methane, —160° Cent.; ethane, —93° Cent.; propane, —45° Cent.; n butpe, + 1° Cent.; and iso butane, —10° Cent. The Mo butanes were not separated. In order to finish tha work with fractions large enough for accurate analyses Ithe experiment given herein was started with about I7 lires of gas (1531 c.c.). Other experiments were performel with various natural gases, in which smaller quantites were used. The sample as analysed by ordinty slow combustion methods contained the followingponstituents :— I Per cent. Methane ............1....... 79’2 Ethane .............1....... 19'6 Nitrogen ...........|........ 1’2 Total .............. 100’0 There is also about 0'03 per cent. of carbon dioxide in the gas mixture. Carbon monoxide, hydrogen, and olefine hydrocarbons are not present. Methods of Experiment. The experimental procedure follows :— Fig. 1 shows the general arrangement of the appar- atus. The Topler pump is on the left of the photo- graph. A is a small glass vessel used for holding the liquefied gases. It could be enclosed in the Dewar flask B. Surrounding this Dewar flask is shown another and larger one. This arrangement was adopted in order to provide better insulation than was afforded by only one flask. The gas sample prior to liquefaction «as measured in the glass vessel C, then transferred to the gas burette D, and from there passed into the lique- fying bulb A. At E is shown a mercury manometer for registering pressures in the! pump. At the base of the Topler pump are shown tine glass vessels for trapping the different gas fractions! over mercury as they were removed. The entire sample was! first liquefied by means of liquid air or liquid oxygen, j With the gas in the liquid condition, connection was Wade between it and the mer- * Comp. Rend,., 156, 4, 19131 page 325. cury pump, and as much of the gas removed with the pump as possible. This process divided the original quantity into two portions : first, a gaseous portion; and second, a liquid residue. In other words the vapour pressure of liquid ethane (boiling point, —93° Cent.) is so small at the temperature of liquid air, that none cguld be detected in the distillate within the experimental error of making the analysis. It was found that when liquid air was used that had stood for some time so that its boiling point had risen to a point near to the boiling point of liquid oxygen ( — 183° Cent.), the methane and nitrogen were removed from the original mixture more quickly than when newly-made liquid air was used. This is to be expected. The residue from this first fractionation was allowed to volatilise, was Fig. 1. I measured, and again liquefied at the temperature of liquid air. Connection was again made to the pump, and more methane removed. In other words, although the residue from the first fraction was treated in exactly the same manner as the original sample, more methane was obtained. Upon volatising the entire residue, however, and again liquefying, a re-arrangement of the solution occurred, and chance for faster evaporation of this last methane portion was afforded. In no case could the last minute portions be recovered, so the attempts at complete recovery were stopped when it was found that only such a small proportion was being left behind as did not sen- sibly affect the results. To this point the first series of fractionations had reached a stage where the larger portion of the methane had been removed by the first fractionation, and where the first residue had been volatilised, re-liquefied, and pumped to obtain another small portion of methane. The residue from the second liquefaction was treated again in the same identical manner, and more methane obtained. A further identical treatment resulted in no additional recovery of methane. No indication of methane was found in the ethane portion within the error of making the analysis. The distillate obtained by the above scheme undoubtedly contained a trace of ethane, but so small that it could not be detected by analysis. The analysis of a portion of the total methane and nitrogen fraction follows :— Table I. Analysis of a Portion of the Total Methane and Nitrogen Fraction. Cubic cm. Cubic cm. Sample taken ...................... 30T0 ... 30'20 O2 added ......................... 95'20 ... 99'30 Total volume ................... 125'30 129'50 Volume after combustion........... 66'30 ... 70'10 Contraction due to combustion .... 59'00 ... 59'40 Volume after CO2 absorption ...... 36'80 ... 40'50 CO2 produced by combustion ....... 29'50 ... 29'60 (a) Methane from contraction ........ 29'44 ... 29'64 (a) Ditto CO3 ....................... 29'59 ... 29'67 Ditto contraction (per cent.) 97'8 ... 98'2 Ditto CO2 ........(percent.) 98'3 ... 98'2 Average per cent, methane ............ 98'1 ... 98'2 (ci) Corrected for the molecular vohune of CO2. Second Series of Fractionations. The next step in the process involved the separation of the ethane from the methane free residue. This necessitated the employment of a temperature such that practically all of the ethane could be separated from the still higher paraffins, propane, the butane, etc. The analysis of a portion of the total ethane fraction follows :— Analysis of a Portion of the Total Ethane Fraction. (1). (2). Cubic cm. Cubic cm. Sample taken ..................... 25'50 ... 20'30 O, added .......................... 96'60 ... 99'40 Total volume .................... 122T0 .. 119'70 Volume after combustion............ 58'30 ... 69'20 Contraction due to combustion ..... 63'80 ... 50'50 Volume after CO2 absorption ........ 7'20 ... 28'70 CO2 produced from combustion 51T0 ... 40'50 Third Series of Fractionations. The final residue from the second series of fractiona- tions then contained propane and higher paraffins. This was treated until there resulted a distillate that con- sisted of propane only. In other words, propane can be separated from the butane at a temperature between -135° and -120° Cent. The analysis of a portion of the total propane fraction follows :— Analysis of a Portion of the Total Propane Fraction. No. 1 No. 2 analyses, analyses. Cubic cm. Cubic cm. Sample taken ...................... 12'60 ... 13'30 O2added ........................... 93'80 ... 97'20 Total volume ..................... 106'40 ...110'50 Volume after combustion............. 67'60 ... 70'00 Contraction due to combustion ...... 38'80 ... 40'50 Volume after CO2 absorption ........ 28'50 ... 29'70 Carbon dioxide produced from com- bustion ...................... 39'10 ... 40'30 The same procedure was followed in the case of the propane separation as in the case of the ethane and methane separations. Distillates and residues were liquefied, and pumped until no propane could be obtained. The analysis of a portion of the final residue fol- lows. This should consist of butane only, providing no vapours of the liquid paraffins are present. Analysis of a Portion of the Total Butane Fraction. Cubic centimetres. Sample taken..................... 9'30 O2 added ...................... 100'00 Total volume .................. 109'30 Volume after combustion ........ 76'30 Contraction due to combustion ... 33'00 Volume after CO2 absorption..... 39'30 CO2 produced by combustion...... 37'00 The above analysis was calculated to butane only, and appears to be almost entirely this gas, but