Diffusion Coefficients of Ethane in the Liquid Phase of the Ethane-White Oil System.

Abstract

INVESTIGATION of the molecular transport of the lighter paraffins in the liquid phase of hydrocarbon mixtures was initiated by Lacey in collaboration with Pomeroy, Scudder, Stapp, Hill, and Bertram ( 1 , 3 , 4, 7), with primary emphasis upon the transport of methane. These early studies have been supplemented by further investigations over a wider range of pressures and temperatures. The data indicate a systematic but large variation in the Fick diffusion coefficient of methane with variations in the concentration and molecular weight of the less volatile component.The extensive background of molecular transport investigations of substances other than hydrocarbons has not been reviewed. The resistance to diffusion at the interface (15) between gas and liquid phases is not important for the range of pressures involved in this investigation.As a result of the marked variation in the Fick diffusion coefficient for methane with the nature of less volatile component in binary systems, the molecular transport of ethane in the liquid phase of the ethane-white oil system was studied at pressures up to 1000 p.s.i. in the temperature interval between 40" and 400" F. METHODS AND EQUIPMENTThe experimental approach involved the introduction of ethane into an isochoric chamber which contained a heterogeneous mixture of ethane and white oil. Initially, the mixture was brought to physical equilibrium by mechanical agitation. The pressure was then raised a predetermined amount by addition of ethane, and the quantity of ethane required to maintain the system a t a higher pressure under isobaric conditions was determined as a function of time.Some revisions of the original equipment (8) were made, including introduction of a number of vertical tubes within the isochoric vessel (II), to decrease the influence of local accelerations upon the molecular transport.The temperature was determined by a strain-free, platinum resistance thermometer (6), recently compared to the indications of a similar instrument calibrated by the National Bureau of Standards. The temperature of the isochoric vessel was known relative to the international platinum scale within O.0Zo F. Change in local temperature with time during a single measurement was less than 0.003" F.The quantity of white oil introduced into the apparatus was determined gravimetrically. The volume of the liquid phase was adjusted so that the gas-liquid interface was always below the top of the vertical stainless steel tubes. The surface tension resulted in somewhat larger interfacial areas of contact between the gas and liquid phases than the net free cross-sectional area between and within the tubes. The composition of the fluid adjacent to the meniscus near the tube walls was nearly constant. As a result, increase in interfacial area had no influence on the molecular transport process associated with the migration of ethane into the liquid phase.The quantity of ethane introduced was determined by an automatically controlled injector (8) driven by a direct current motor a t such a rat...

Diffusion Coefficients in Systems Related to Reservoir Fluids: Available Data and Evaluation of Correlations

“…Overall, we can expect reasonable accuracy from HM for relatively light oils; the predictions became more uncertain for heavier oils, which is not surprising, considering HM was developed using paraffins with viscosities orders of magnitude smaller than those of heavy oils and bitumen. [197] 2 60.8 C 1 + white oil [191] 5 25.0 C 2 + white oil [193] 4 55.6 C 3 + kerosene [194] 19 60.3 C 3 + spray oil [194] 12 31.1 Average 45.0…”