Propane-minus

The de-butanizer works in a similar manner. The upstream tower (depropanizer) determines the maximum vapor pressure of the butane product. If the concentration of propane-minus is too large in the inlet stream, the vapor pressure of the butane overheads will be too high. Similarly, the concentration of pentanes-plus in the butane will depend upon the... 

Half a century later, the work of Carson and Katz (1942) provided a second reason for considering the dissociation condition of the hydrate equilibrium point (see Chapter 3, Figure 3.1b for more details). Their work clearly showed the solid solution behavior of hydrates formed by gas mixtures. This result meant that hydrate preferentially encapsulated propane from a methane + propane gas mixture, so that a closed gas volume was denuded of propane (or enriched in methane) as more hydrates formed. On the other hand, upon hydrate dissociation, when the last crystal melted the initial gas composition was regained, minus a very small amount to account for solubility in the liquid phase. 

Of course, in this binary system, the isobutane compositions are simply 1 minus the propane mole fractions. Therefore, the relative volatility between propane and isobutane on the top tray is... 

In the formulation of the objective function there are two conflicting elements to produce as much valuable product as possible, but using as little energy as possible. For a given feed, the cost function is defined as the amount of propane, butane and pentane from the LP column (at 0.99 mol% or more) multiplied by the relevant product prices, minus the cost of boilup ... 

In propane dewaxing of lubricant fractions, such as cylinder stocks, a typical operation blends three volumes of propane under pressure at 180 F with one volume of stock this solution is cooled to 70 Fand sent to chillers where the pressure is reduced to evaporate propane until the temperature of the remaining propane solution has dropped to, say, minus 40 F. Wax crystallizes out of this solution... 

Refinery and Chemical Plant Gas Recovery. It is becoming increas-in y useful to recover substantially aU of the propane and even ethane (or ethylene). Higher absorber pressures and larger circulations of oil may be used to capture the propane or ethane, but it is also necessary to Use refrigeration if ethane is to be recovered. The Tennessee Gas Trans-mistion Co. cools the entire gas stream (750 MMscf) to minus 96 F with temperatures of minus 121 F at some points. The plant can be operated so that substantially only methane is returned to tiie company pipeline. A somewhat similar operation is shown in the gas recovery part of Figs. 204 and 20-5 under the discussion of Ethylene Plants (Chap. 20). 

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