CHEN 2650 Assignment
Construct a process flow sheet similar to the one depicted below. In this process, n-butane is pressurized and preheated prior to entry into a “Gibbs” reactor which predicts the equilibrium distribution of the available products based on the minimization of the Gibbs free energy. In this process, n-butane in the presence of a nickel catalyst can lose hydrogen (as H2) to form 1-butene, cis 2-butene, and trans 2-butene. The reactions are:
The Gibbs reactor will determine the amount of reactant actually converted along with the distribution of possible products.
The feed stream is 10 kmole/hour of n-butane at 3 atm pressure and 30 oC. The pump can pressurize this liquid stream up to 10 atm. The heat exchanger is used to heat the feed stream to a vapor at its dew point (vapor fraction of 1.0). The fired heater is used to further heat the vapor to the desired reactor inlet temperature with an upper limit of 1000 oC. The hot feed enters the reactor which operates under adiabatic conditions, that is, no heat is added or removed.
Vary the pump outlet pressure from 4 to 10 atm in increments of 2 atm. Record the outlet temperature of the heat exchanger. For each pump outlet pressure, vary the fired heater temperature from 400 to 1000 oC in 200 oC increments. Record the outlet molar flow rate of each component.
Plot the pump outlet pressure (y-axis) versus temperature of the stream leaving the heat exchanger (x-axis). There is a model which predicts pressure as a function of temperature called Antoine’s equation. The pressure (given in mm Hg) is determined by:
where T is the temperature in oC, and A, B, and C are coefficients for the chemical under consideration. For n-butane, the coefficients are:
A = 6.82485
B = 943.453
C = 239.11
Calculate the pressure using Antoine’s equation for the temperatures determined in the ChemCAD model and determine if this model and the ChemCAD model agree.
Analyze the data for the production of the three products. Using the 1-butene product, show the effects of temperature and pressure on the amount of 1-butene produced. This is best done graphically.
The outlet of the reactor can be cooled to condense some of the material which can be recycled back to the reactor. The following diagram displays the setup:
The outlet temperature of the heat exchanger downstream of the reactor can be adjusted so that some of the reactor product becomes a liquid. Determine the temperature at which the reactor product condenses for the cases run for the non-recycled setup. Gradually decrease the temperature until a maximum of 1000 kg/hour of recycle is attained. Compare the 1-butene product flow leaving the top of the flash tank to that obtained without recycle under the same conditions.
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