Phase Behavior in the Methane-propane-n-pentane System
- R.T. Carter (Standard Oil Company) | B.H. Sage (Institute of Technology) | W.N. Lacey (Institute of Technology)
- Document ID
- Society of Petroleum Engineers
- Transactions of the AIME
- Publication Date
- December 1941
- Document Type
- Journal Paper
- 170 - 178
- 1941. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 4.6 Natural Gas, 4.3.4 Scale, 5.2.1 Phase Behavior and PVT Measurements
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The phase behavior of a number of binary systems consisting of paraffinhydrocarbons has been determined in recent years. In addition, the compositionof the coexisting phases of mixtures of crude oil and natural gas has beeninvestigated. However, the latter study did not include information concerningthe influence of the concentration of a component upon its distribution betweentwo coexisting phases. Owing to the paucity of such information it wasconsidered desirable to investigate in some detail the composition of thecoexisting phases in the methane-propane-n-pentane system throughout thegreater part of the two-phase region at a temperature of 100?F. Information ofthis nature also permits the establishment of the critical behavior of thisternary system.
The compositions of the coexisting phases in this ternary system at 100?F weredetermined by withdrawing samples from a pressure vessel containing aheterogeneous mixture of the three components that had been brought toequilibrium by mechanical agitation at the desired pressure and temperature.The samples were withdrawn under such conditions that the equilibrium was notdisturbed and the composition of each of the phases was ascertained by means ofthe conventional low-temperature fractionation procedure.
The apparatus employed in this investigation was nearly the same as thatutilized in an earlier study of the methane-n-pentane system. Several minormodifications in the arrangement of the apparatus were made in the interest ofsimplifying the procedure and avoiding the possibility of condensation in thetubing connecting the equilibrium apparatus with the analytical equipment. Thepressures were measured by means of a pressure balance with a precision of 0.5lb. per sq. in. It is believed that the equilibrium pressure was ascertainedwith an uncertainty of not more than 2 lb. per sq. in., even though smallvariations in pressure obtained during the withdrawal of the samples. Thetemperature of the equilibrium equipment was maintained by use of anautomatically controlled oil bath. The bath temperature was determined by meansof a copperconstantan thermocouple, the electromotive force being determined bymeans of a potentiometric circuit of such a nature as to reduce the uncertaintyof the temperature to less than 0.1?F.
The fractionating column employed in the determination of the composition ofthe gas phase had a diameter of 0.12 in. and was approximately 4 ft. long,while the column employed in the analysis of the liquid phase was 0.18 in. indiameter and about 5 ft. long. Each column was equipped with the conventionalconstant-volume receivers, which were maintained at a constant temperature bymeans of an automatically controlled oil bath.
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