Acetone Production

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acetone productionSeparations and Reaction Engineering Spring 2000 Design Project Production of Acetone Process Objective Function We would like to complete our investigation of the economic feasibility of producing 15,000 metric tons per year of 99.9 mol% acetone from isopropyl alcohol. It is unlikely that this process will appear profitable because most acetone is made as a byproduct of phenol manufacture. However, we expect to be able to charge a premium for our acetone since it will be free of aromatics. Therefore, your objective function should be the break-even price (BEP) for acetone, defined as follows: (Acetone Produced per Year)(CB) = Annuity Value of Total Installed Cost + Annual Cost of Raw Materials + Annual Utility Cost Annual Revenue from By-products - Annual Credit from Fuel Gas and Steam where CB is the break-even price for acetone The above equation for estimating the cost of acetone is based on the minimum price for which acetone could be sold to cover our operating expenses. A 10-year plant lifetime (n = 10) and an interest rate of 15% (i = 0.15) should be used. The annuity value of the total installed cost is calculated by  i (1 + i ) n  annuity va lue = capital cost   n  (1 + i ) − 1    In your final analysis, please compare your BEP for acetone to the current market price for acetone. A process flow diagram (PFD) is not presented in this problem statement. You should be in a position to synthesize your own PFD based on your previous experience with this project. Reaction Kinetics The main reaction for producing acetone is (CH 3 ) 2 CHOH → (CH3 ) 2 CHO + H 2 isopropano l acetone and the kinetics for this reaction are given below:


− rIPA = k1CIPA where

mol IPA m3 catalyst ⋅ s m 3 gas m 3 catalyst ⋅ s

 60,000  k1 = 1.76 × 10 exp  − RT    mol IPA CIPA = m 3 gas 5

These kinetics are only valid if the actual conversion does not exceed 85% of the equilibrium conversion at reactor conditions. Although, several side reactions are possible, none of them take place to any considerable extent. The activation energy in the kinetic expression above is in units of kJ/kmol.

Catalyst Information
Catalyst physical properties are given below: density of the inert catalyst, ρci = 2500 kg/m3 density of solid catalyst, ρc = 2500 kg/m3 packed bed voidage of the cylindrical pellets = 0.5 void fraction of the spherical particles at minimum fluidizing conditions = 0.55 particle diameter, dp = 100 µm

Chemcad Hints
For heat exchangers with multiple zones, it is recommended that you simulate each zone with a separate heat exchanger. Actual equipment may include several zones, so costing should be based on the actual equipment specifications. On your PFD, only the actual equipment should appear. For the distillation columns, you should use the shortcut method (SHOR) to get estimates for the rigorous distillation simulation (TOWR or SCDS). The shortcut method may be used until an optimum case is near. It is then expected that everyone will obtain a final design using rigorous simulation of the columns. For an absorber, shortcut calculations are not possible. When simulating a process using “fake” streams and equipment, it is absolutely necessary that the process flow sheet that you present not included any “fake” streams and equipment. It must represent the actual process.


Specific Assignments
General Optimize the process using decision variables of your choosing. You should choose as decision variables the design variables most strongly affecting the objective function. ChE 112 – Separations Determine the number of distillation columns required, their location, and enough information for each distillation column to cost it. The distillation column that provides the acetone product should be designed in detail. Additionally, if you choose to recover acetone from the flash vaporizer vapor stream by scrubbing with water (must be deionized) or any other solvent, that absorber must be...
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