[Rishi]

We are quite aware of the azeotropic removal of water by using a solvent like Toluene, Benzene etc for the reaction of an acid and alcohol to covert to esters.
can the reaction be carried out without the use of a solvent. I want to react an organic carboxylic acid and Methanol to get Methyl ester. I am aware of the conventional method but want to avoid the use of solvent.

Looking out for yor advice. Thanks

[cundi]

Try to heat your carboxilic acid in MeOH, with catalytic amounts of a mineral acid. (H2SO4)
I have used this method and it works.

[Rishi]

I did that. After 2-4 hours of reflux two layers form. The upper layer of ester+methanol and lower layer of H₂SO₄, water, soluble carboxylic acid and soluble methanol. But the problem is that the reaction doesnt go beyond 75%.
The second problem is the sulfuric acid effluent. It becomes difficult to neutralise and dispose.

[russellm72]

Rishi your posts suggest you are working on ton scales!

You use a catalytic ammount of H2SO4 how can that be a problem to dispose of?

Is this real work or green chemistry in your head?

Kind Regards

Russell.

[Rishi]

Russell...I am working this out for a large scale production and hence have to keep in consideration the options for pollution treatment.

[russellm72]

Ok how about an acidic resin as catalyst although one would think waste to drain would be cheaper than solid waste.

I don't work on that kind of scale but I am sure the use and disposal of sulfuric acid etc is well documented by large chemical manufacturing companies.

Cheers

R.

[Rishi]

The product for which i want to use is a 1.5$ / kg product and hence not much marjins involved. In these competitive times, i need to take care of the energy costs and hence to economize i distribute the energy by starting multiple batching, hence saving on energy and Fuel costs.
The sulfuric acid needs to be neutralized before being sent to ETP and hence this cost becomes more expensive. Is there any catalyst that can be recylced ?

[Dynamic]

Sulfuric acid can be recycled.  The reason your reaction stops at around 75% conversion is that the water produced in the reaction causes hydrolysis of the nascent methyl ester which competes with the formation reaction.  Remove the acid and replace with fresh concentrated acid to drive it to completion.  What scale are you working?  This process is used in the production of methyl esters on very large scales.

[Rishi]

I use it on tonnes. Well could you guide me through the process. And what is the excess of methanol that i need to take in that case.
From what i understand, definitely the liberated water is going to cause back hydrolysis. But then the layer that separated below will contain sulfuric acid, water, methanol and some soluble acid and ester. So how do you suggest to proceed to get more yield and more importantly recylce the sulfuric acid ?

[gfunk]

I take it a giant Dean-Stark trap wouldn't work ;-).

What about using molecular sieves/zeolites?  You could collect them and dry them to be used again.

[Rishi]

Yes....zeolites are an option. Molecular sieves can be expensive. So am looking toward it.
I also recently came across an article mentioning the "PERVAPORATION" technique. Am looking deeper into it. Right now, I dont even know much about it.

[Rishi]

Can anybody guide me more about the pervaporation technique and whether the membranes are stable to acids ?

[Rishi]

Are pervaporation membranes too expensive ?