5 replies to this topic

[runiama]

I'm one of the student in chemical engineering in Malaysia. This year, i were given a final year project named production of ethanol. In my plant design, i use ethylene and water as my raw material. I also use direct hydration as the process involved.

Beginning of my process, the raw material (ethylene+water) fed to the mixer at a temperature of 25 degree celsius of both item. molar flow rate for ethylene is 625 kgmole/hr. and for water is 375 kgmole/hr..

Then, it move to reactor. Before reach the reaction the material flows inside heat exchanger and then the boiler. At the reactor, the vessel temperature is 320 degree celsius and pressure of vessel is 7000 kPa. After that, it will flow at the absorber. i used the pressure of this absorber to be 101.3 kPa with 50 trays. After that, goes the distillation column (T-101) and (T-102), i used 2 distillation column with below 1atm pressure with 50 trays. The percent conversion seems to be only 84.5%.

My questions are; 1) how to increase the percent conversion of this process?

2) do i have to use vacuum distillation column?

3) how to produce an economical plant design with a high conversion of product?

4) how to recycle / demolish the top product from the absorber (T-100)


I will provide the hysis figure if you want it..

(Note: I'm using Aspen Hysis V7.1)

Thanks.. I hope the expert engineers out there can help me...

[Krunal Shah]

Hi
I am a Final Year Chemical Engineering Student,
Here is a solution from my side,

According to me your conversion is higher than 84.5% but as you using your distillation columns under vacuum (below 1 atm), you are losing some amount of ethanol vapor from non-condensate out let of your over head condenser of your distillation columns so you should check it first that how much amount you losing from there.

Regards,
Krunal Shah.
krronaldo@gmail.com

[yeek]

You cannot go beyond 84.5% because water and ethanol form an azeotrope. I also don't think you need two distillation columns. One should be enough and you will still be able to achieve 84.5%

You will need some other method such as using extractive distillation with ethylene glycol to get close to 99% ethanol.

[Krunal Shah]

Hi yeek,

Actually,

At 1 atm, water boils at 100 C and ethanol boils at 78.5 C. There is an azeotrope that boils at 78.2 C that is 0.96 ethanol by mole fraction.
so he should get at least 95.0% ethanol.

[yeek]

I think this 96% is mass fraction and not mole fraction. If you convert the values to mole fraction you will get close to 84.5% which is near to his value.

Extractive distillation with ethylene glycol will get you almost pure ethanol.

[riven]

I think this 96% is mass fraction and not mole fraction. If you convert the values to mole fraction you will get close to 84.5% which is near to his value.

Extractive distillation with ethylene glycol will get you almost pure ethanol.

The state of the art of ethanol dehydration above the azeotrope is molecular sieves. I do not know what ethylene carryover (or other impurities) will do to these.
http://www.grace.com...ences/Zeolites/
Entrainer distillation often using benzene are only done on old or small scale.