Distillation Isothermal flash

A mixture of ethane and propane is to be separated by distillation at 475 psia. Explain in detail how a series of isothermal flash calculations using the Soave-Redlich-Kwong equation of state can be used to establish y-x and H-y-x diagrams so that the Ponchon-Savarit method can be applied to determine the stage and reflux requirements. 

The reactor system may consist of a number of reactors which can be continuous stirred tank reactors, plug flow reactors, or any representation between the two above extremes, and they may operate isothermally, adiabatically or nonisothermally. The separation system depending on the reactor system effluent may involve only liquid separation, only vapor separation or both liquid and vapor separation schemes. The liquid separation scheme may include flash units, distillation columns or trains of distillation columns, extraction units, or crystallization units. If distillation is employed, then we may have simple sharp columns, nonsharp columns, or even single complex distillation columns and complex column sequences. Also, depending on the reactor effluent characteristics, extractive distillation, azeotropic distillation, or reactive distillation may be employed. The vapor separation scheme may involve absorption columns, adsorption units,... 

This chapter considers the vapor-liquid equilibrium of mixtures, conditions for bubble and dew points of gaseous mixtures, isothermal equilibrium flash calculations, the design of distillation towers with valve trays, packed tower design. Smoker s equation for estimating the number of plates in a binary mixture, and finally, the computation of multi-component recovery and minimum trays in distillation columns. 

For binary flash distillation, the simultaneous procedure can be conveniently carried out on an enthalpy-composition diagram First calculate the feed enthalpy, hp, from Eq. t2-81 or Eq. (2=9b) then plot the feed point as shown on Figure 2-9 (see Problem 2-All. In the flash drum the feed separates into liquid and vapor in equilibrium Thus the isotherm through the feed point, which must be the T nun isotherm, gives the correct values for x and y. The flow rates, L and V, can be determined from the mass balances, Eqs. f2-51 and 2-61. or from a graphical mass balance. 

The reaction of ethylene (C2H4) and hydrogen chloride (HCI) over a copper chloride catalyst supported on silica to produce of ethylene chloride (CjHjCI) is a highly exothermic reaction. In this example, the reaction is assumed to take place in an isothermal conversion reactor. The heat evolved from the reaction is removed from the reactor to keep the reaction at constant temperature. The reactor effluent stream is compressed, cooled, and then separated in a flash unit followed by a distillation column. The flash and distillation top products are collected and then recycled to the reactor after a portion of the stream is purged to avoid accumulation of an inert component (Nj). The recycled stream is depressurized and heated to the fresh feed stream conditions. The liquid from the bottom of the flash enters a distillation column where ethyl chloride is separated from unreacted HCI and ethylene. The entire process is simulated using Hysys/Unisim, PRO/II, Aspen, and SuperPro Designer software packages. 

---