An answer—perhaps not the only one—may be that these alcohols can undergo chemical reactions if kept at high temperatures for a long time.

Another reason could be that their behavior is wet (according to T-s diagram), and therefore are not advantageous (they would need superheating).

And may be these fluids are corrosive at some pressure or temperature. but being corrosive is not a thermodynamic property. Maria's answer is closer to be correct.

I would like to thank you all for your responses.

Indeed, Methanol and Ethanol are wet fluids and they would need superheating. But of course it also the case of water.

They also have a quite low temperature limit of stability (roughly 350 Celsius degrees) but as far as ORC are mostly used at low to medium grade, I thought that it would not necessarily be a hurdle.

Other reason might be that they are corrosive, dangerous for health and flammable. But a Dutch company uses Toluene, which also not very nice for health and flammable. I have also heard about Ammonia too (whereas it is dangerous and wet).

Regards

Margot, just for curiosity, did you find any publication in which they clearly state that ethanol and methanol must be excluded from fluid scans? In some papers they do consider them, but of course, results for them don't look so promising. Have a look at these references!

Victor, R.A., Kim, J.-K., Smith, R.

Composition optimisation of working fluids for organic rankine cycles and kalina cycles

(2013) Energy, 55, pp. 114-126.

Bertrand Fankam Tchanche*, George Papadakis, Gregory Lambrinos, Antonios Frangoudakis

Fluid selection for a low-temperature solar organic Rankine cycle

Applied Thermal Engineering 29 (2009) 2468–2476

Hi Maria,

The autors of the following article do not considerate Methanol and Ethanol as potential ORC working fluids (see p.311)

Junjiang Bao, Li Zhao, A review of working fluid and expander selections for organic Rankine cycle, Renewable and Sustainable Energy Reviews 24 (2013) 325-342

Besides, I feel that during my researches I rarely find out articles that included alcohol in the fluid scans.

Hi, a recent paper use ethanol as working fluids to do some experiment, i hopt it should be useful for you:

Experimental and thermodynamic analysis of a bottoming Organic Rankine Cycle (ORC) of gasoline engine using swash-plate expander. Volume 103, October 2015, Pages 519–532