Prof. Rangaiah,

 I think PSA is a more common option. I have read some literature on pervaporation (PV) being an option but I don’t think it is common yet in industry despite its theoretical advantage (I think, this is mainly due to the relatively low selectivity of the current PV membranes in this context). Feel free to share if you have any further thoughts on this.

 Regards

Murthy.

Many thanks, Murthy, for your prompt comments. We found the following statement in a conference paper published in the year 2010. We would like to know whether this is still valid and/or recent trends.

In Brazil and United States, the two largest producers of ethanol in the world, azeotropic

distillation with cyclohexane, extractive distillation with ethylene glycol and adsorption

with molecular sieves are used.

Molecular sieves 4a and sometimes 3a are commonly used in packed beds with switching valves and regeneration cycles. Manufacturers have become unwilling to specify their sieves for food grade ethanol. Activated alumina was used in the past.

Pervaporation is used in some applications and is improving in reliability, but still not the dominant technology. The one I saw looked like pipes made of papier-mâché  and operated with hot ethanol vapor under pressure inside a containment vessel.

In principle two distillation columns operating at different pressures could break the azeotrope, but in at least one of the columns a fairly strong vacuum would be preferred, raising the cost of equipment.

On a small scale adding a third component like mineral oil can break the azeotrope but with additional material handling. 

Adsorption is usually preferred because the azeotrope vapor pressure is almost the same as pure ethanol.

Cellulose powder can break the azeotrope by selectively adsorbing water, the same principle that makes sherry out of wine In wooden barrels. Then there is the wet cellulose to dehydrate.

The intended use of the ethanol should be considered and what impurity if any is allowed.

firstly the ethanol should be concentrated and then subjected to separation. azeotropic distillation is the common route.

In my opinion, extractive distillation (ED) using ethylene glycol (EG) as solvent, despite the fact of an older, classical procedure is the most economic and most controllable process.

Many thanks, Jerry Decker, Yadollah Tavan and Alexandru woinaroschy, for all your comments. They will be useful in our study.

A typical method that is used for bringing Ethanol concentration beyond its azeotropic point -in (Ethanol-Water) mixture- is by adding a dehydration unit, which is just some kind of fixed bed adsorber, backed with Zeolite.

Many thanks, Ahmed Elnour, for your inputs. Does 'a typical method' in your comment mean the common method in industry? If possible, please provide references for this.

I agree with Ahmed Elnour's comment. An Ethanol Producing Factory i have visited is using zeolite for dehydration to separate ethanol at azeotropic point.  But the factory is currently facing efficiency problems in this unit.

Many thanks for your inputs. My question arose in revising our manuscript on bioethanol separations. Based on literature and your inputs, we included the following paragraph in our revised manuscript, which will soon be published in Industrial & Engineering Chemistry Research (IECR). I will inform you once it is published. Then, you can find the details of references (numbers) in the following paragraph. Hope this information will be useful to you.

In Brazil and United States, the two largest producers of ethanol in the world, distillation continues to be dominant in industries for the recovery section, as evident from Wooley et al.19, Humbird et al.20, Haelssig et al.21, Batista et al.22, Bessa et al.23, Ponce et al.24, Palcios-Bereche et al.25, and Batista and Meirelles26. For the dehydration section in Brazilian and United States industries, azeotropic distillation with cyclohexane, extractive distillation with ethylene glycol and adsorption with molecular sieves are used.27 According to reports by Wooley et al.19 and Humbird et al.20, pressure swing adsorption (PSA) with molecular sieves is used in the dehydration section. Also, Tavares et al.28 stated that most of current ethanol dehydration facilities in the United States rely on hydrophilic zeolite molecular sieves.

Glad to inform you that our paper entitled "Review of Technological Advances in Bioethanol Recovery and Dehydration" is now published in Industrial and Engineering Chemistry Research (IECR). Interested readers can download a soft copy (limited to 50 downloads) using the following link. You may need to register for an ACS ID. 

http://pubs.acs.org/articlesonrequest/AOR-BSeC66EDvt9zQQI5s64R 

Hope you will find the review useful in your work.

very nice and exhaustive review article.. thanks for sharing with us..

I was wondering if you have any good book in which the mass balances for heterogeneous azeotropic distillation are described analytically.

Thank you in advance!

Hope you are all doing well. Our latest paper entitled "Heat-pump assisted distillation versus double-effect distillation for bioethanol recovery followed by pressure swing adsorption for bioethanol dehydration" is just published in Separation and Purification Technology, Volume 210, Pages 574-586 (2019). If this is of interest, you can download a copy from the following link (free until Oct. 19).

https://authors.elsevier.com/a/1XecD4wbrSvg1d

Hope you are all doing well. You may be interested in our following latest study.

Singh A. and Rangaiah G.P., Development and Optimization of a Novel Process of Double-Effect Distillation with Vapor Recompression for Bioethanol Recovery and Vapor Permeation for Bioethanol Dehydration, Journal of Chemical Technology & Biotechnology, in press (2018).

Dear Prof. Rangaiah, have you tried using salts instead of liquid solvents? Best regards.

Many thanks, Jesus Rafel Alcantara-Avila, for your query. We have not tried using salts instead of solvents for ethanol dehydration in extractive distillation. One major issue with using salts is the recovery of salts for re-using. In this connection, the following paper may be of interest to you. Feel free to contact me directly ([email protected]) for further discussion.

Hussain, M. A. M.; Pfromm, P. H. Reducing the Energy Demand of Cellulosic Ethanol through Salt Extractive Distillation Enabled by Electrodialysis. Sep. Sci. Technol. 2013, 48 (10), 1518−1528.