Hi all,

I am currently doing an exercise of a process to make styrene from ethylbenzene and benzene. First task is to analyze the degrees of freedom to see if they are saturated. And then saturate the degrees of freedom for both distillate columns. The flowsheet is the following:

**flowsheet_process.png** **108.01KB**
0 downloads

The reactions taking place in the gas-phase reactor at a pressure Ptot of 1.3 bar are the following:

- C_{8}H_{10} -> C_{8}H_{8} + H_{2}

- C_{6}H_{6} + 3 H_{2} -> C_{6}H_{12}

We know both reaction conversion (X_{A} and X_{B}). The feed is only ethylbenzene and benzene (molar ration X_{f} known).

We remove H_{2} as soon as possible as it is dangerous. Both distillations columns contain a partial reboiler and total condenser. Styrene is removed by the first column at low pressure and low temperature. The second distillation column is working at atmospheric pressure.

What I've done for the degrees of freedom (in order of the flowsheet):

- Mixer : d = 4 . Saturate with both inlet streams (u_{0 }and u_{5.2}) as well as P_{Mix} and T_{Mix}.

- RXN : d = 3 . Saturate with inlet stream (u_{1 }) as well as P_{Rxn} and T_{Rxn}.

- Flash : d = 3 . Saturate with inlet stream (u_{2 }) as well as T_{Flash }and the recovery of one key component (eg: we suppose that this is Hydrogen and recovery of 1% (to be realistic) since we want to take it off).

- Dist 1 : d = (P+Q) +5 (from my notes...). Saturate with inlet stream (u_{3.2 }) as well as P_{dist1} , receovery of light key component and also the one of the heavy key component. The two remaining we can fix reflux ratio to infinite at the top and the bottom if we assume Fenske conditions. (Q denotes thermal behaviour that we fix at 0 except from reboiler and condenser because of adiabatic conditions).

- Dist 2 : Same as Dist 1 except inlet stream and pressure are different.

I was first wondering if all of this was correct. Moreover, I will need to guess some parameters before doing my shortcut model I suppose. How could I guess the temperature of the Flash if I don't know the temperature of the reaction? I suppose it will be around the cooling water temperature (so maybe 37°C ??). I guess the choice needs to be done according to hydrogen to avoid any explosion.

Thanks in advance for your help.

**Edited by chemical_teo, 10 October 2018 - 01:11 PM.**