[LaylaLee]

Referring to pfd in attached file, fresh acetic acid is combined with an acetic acid recycle stream and fed into a vaporizer along with a gas stream, which is the fresh ethylene feed. The vaporizer operates at 6.6 atm and 423 K/ 150 C. The vapor stream is then combined with fresh oxygen and enters the cooled tubular reactor at 421 K.

My doubts is regarding on:
1) Why is the vaporizer operated at 6.6 atm instead of a lower pressure? Isn't a lower pressure such as 1 atm would allow the components to have lower boiling points? So less heat are required to boil them into vapour? My guess would be that if the vaporizer is operated at lower pressure, then a compressor would be needed to compressed all the gas to the reactor which operate at 6.5 atm.

2) Why is ethylene mixed with acetic acid? Assuming that feed of ethylene is at room temperature, then it would be in gas form, wouldnt it make the vaporizer bigger? Why not just heat up the acetic acid alone? Or is the ethylene somehow helping in vaporizing the acetic acid by increasing pressure? But at 6.6 atm, from what i calculated using antoine equation, the boiling point temperature of acetic acid would be at 190 C. Which seems that acetic acid is in in liquid form. Or i'm interpreting this wrongly??

3) There are addition of oxygen after into the reactor, somehow it would affect the temperature of the stream, why arent it considered? The reactor is operating at a higher temperature, and inlet temperature would be lower than 150C.

Hmmm..

[curiouscat]

Compressors are best avoided. They are expensive finicky machines. Especially when liquid droplets are likely.

Medium pressure steam is cheaper.

Regarding ethylene feed point, maybe preheat is needed? Easier to preheat together. Could also have to do with flamability limits. You don't want to mix oxygen with hot ethylene directly. Pre-diluting with AcOH might make it safer.

I'm speculating though. What's the source of the flowsheet? Is it authoritative?

Vaporiser is at 423K. Reactor inlet is at 421K. Oxygen feed rate is 2% of molar feed of (AcOH + Ethylene). There won't be much cooling.

[LaylaLee]

The pfd is from a journal (http://pubs.acs.org/doi/pdf/10.1021/ie201131m).

Ahh, thanks for helping.

One more thing is the boiling point at 6.6 atm. I used antoine equation to calculate that at 7atm the boiling point temperature would be 190++ C. But vaporizer and reactor both at 150 C. Acetic acid would be in liquid form? From the journal it said its vapour phase process.

[curiouscat]

The pfd is from a journal (http://pubs.acs.org/doi/pdf/10.1021/ie201131m).

Ahh, thanks for helping.

One more thing is the boiling point at 6.6 atm. I used antoine equation to calculate that at 7atm the boiling point temperature would be 190++ C. But vaporizer and reactor both at 150 C. Acetic acid would be in liquid form? From the journal it said its vapour phase process.

Sorry I can't read that paper. A subscription is needed. Mail me a link to a copy & I can try to see.

In vaporizer there's two components: ethylene + acetic acid. So strictly speaking, there's a bubble point and a dew point not a boiling point. At 6.6 atm the BP of pure components are ~-60 & 190 so  I'd assume at 150 C this is a two phase situation between bubble & dew points. I could be wrong.