The Equation of State for Methane Gas Phase

Frederick G Keyes, Leighton B Smith, David B Joubert
1922 Journal of Mathematics and Physics  
The 1sotherms for gaseous methane have been measured by Amagat 1 The absolute volumes are not gwen, but merely the volumes relatwe to the capaClty of a certalll manometric tube The data extend from 147 0 to 1001 0 and over a pressure range of 40 to 300 atms AS1de from the relattve pressure-volume products of Amagat there are no data from Wh1Ch the constants of the equatlOn of state for the gas phase can be evaluated Moreover, the questlOp of punty 1S of tmportance, and Amagat at the ttme (1880)
more » ... at the ttme (1880) d1d not have the faClhttes for lllsunng the punty of a hydrocarbon such as methane In the present lllvestIgatton the attempt has been made to measure the 1sometncs of methane between 0 0 and 200 0 and over a pressure range from about 36 to 300 atms There are advantages expenmental and theorettcal in choosing the "lsometnc method" of investtgatlllg the pressure-volumetemperature relation for a fiUld Of the three quantities the volume 1S the most dtfficult to measure and control and III the attempt to keep the volume constant attention 1S parttcularly focused upon the cond1tions necessary accurately to mallltalll a chosen volume The theorettcal work III connectlOn Wlth the equatlOn of statell,s, 4, Ii, 6, has made it seem h1ghly probable that in * This work IS pubhshed by penrusslOn of the Director of the Bureau of Mmes The present paper together With the other papers of this number are some of the mvesttgattons required by the Bureau of Mmes m perfectmg the processes for the extractlOn of hehum from natural gas This mvesttgatton was undertaken by the Massachusetts Instttute of Technology at the request of the Bureau of Mmes, workmg m cooperatIOn wlth the War and Navy Departments The Bureau of Mmes as well as the Massachusetts Institute of Technology contnbuted hberally m funds needed to carry forward the work The funds of the Bureau of Mmes were allotted from Army and Navy appropnattons made available for research work connected With extractmg hehum from natural gas 1 Amagat, Annales de Chlmle et de PhYSique 22,367, 1881. 192 KEYES, SMITH AND JOUBERT the case of a flUld composed of molecules of mvanable type,' the pressure should vary hnearly Wlth the temperature at constant volume The attempt to test thIS lmeanty of pressure mcrease directly makes It further desirable to employ the Isometnc method In fact, the investIgatIOn of the sources of error m the methods used to carry out measurements at constant volume has led by successive approXImatIOns to consIderable Improvements m the apparatus The relatIVely slffiple form of the equatIOn of state for a fluid composed of mvanable molecular speCIes requmng the pressure to be hnear m the pressure-temperature relatIOn makes It, moreover, comparatIvely easy to determme the constants of the equation of state In the mvestigatIOn here presented It was hoped to Improve materially the accuracy Wlth WhICh a gwen volume could be mamtamed and reproduced The pressure measurements also have been improved from the point of VIeW of accuracy and senSI-tIveness The temperature measurements made by means of the platinum reSIstance thermometer were found at the conclUSIOn of the measurements not to be as rehable as was at first thought ThIs cIrcumstance was due to defects m the reSIstance bndge whIch, however. after haVIng been dIscovered. proved not to invahdate the temperatures by more than probably 0 1 0 at most Of course temperatures are deSIred on the absolute temperature scale. and the compansons of the platmum thermometer WIth the gas scale leave uncertamtIes at present whIch may amount to 010 at 200 0 The present data on methane are the most nearly linear of any pressure-temperature data thus far examined and verify the partIcular form of the equatIOn of state ConsIderable improvement m the apparatus doubtless can be reahzed m future work, however, and a stIll more accurate test made of this most important relatIOn Preparation of Pure Methane The methane was prepared by heatmg a mIXture of dry SOdIum acetate and soda-lime The dIagram, Fig 1, Illustrates the apparatus employed for generatmg and purifying the gas The dry powdered sodium acetate and soda-hme were contained in EQUATION OF STATE FOR METHANE GAS PHASE 193 Fig1 194 KEYES, SMITH AND JOUBERT the pyrex tube A about 2 5 cm III diameter and 50 cm III length The salt m1xture could be heated regularly and the gas evolutlOn controlled by the movable electnc furnace B A safety valve was provided by the barometnc mercury column D, whlle a Bunsen type valve, cons1stlllg of a band of rubber covenng a small hole III the glass reentrant portlOn at E, prevented surges m the hqUld punfymg tubes EvacuatlOn of the salt m1xture tube was secured through C, wh1le F contamed 20 per cent fummg sulphunc aC1d employed to retam acetone or unsaturated hydrocarbons QUlte a proportion of acetone 1S formed m the acetate soda-hme reactlOn The tube G contamed 98 per cent concentrated sulphunc aC1d to absorb 80 3 fumes and H 20 per cent caustlc soda solutlOn followed by sohd caustlc I for the removal of CO 2 The tube J contammg P 2 06 served finally to dry the gas wh1ch was condensed by means of hqUld alr m the recelVer K, whence 1t could be d1stllled back and forth from K to L to remove hydrogen and other gases The tube L was doublewalled and SlIvered, but arranged so that the double-walled portlon could be exhausted or made conductmg by adm1ttmg hydrogen The thermocouple M sufficed to observe the constancy of melting of the solid methane Wlthin L The frozen methane was pumped at 0 The punfied matenal was finally allowed to expand through 0 mto a five-hter giobe wh1ch pre-vlOusly had been exhausted hot to remove adsorbed mOlsture and other gases A special analysis apparatus was a part of the system and .wlll be presented m a later paper dealmg wlth the lsometncs of mtrogen-methane m1xtures The analytlcal apparatus md1cated that foreign gases were not m excess of one part m 500, wh1ch was the hm1t of acc~racy attainable from the apparatus at the tlme From the precautlOns taken m the preparatlOn the punty of the methane would have been greater than the analys1s mdicated
doi:10.1002/sapm192214191 fatcat:7mhl5ml4irdkjfpjfxdnfbys3a