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I aim to decrease boiling point of water that will be used to generate steam. I wonder maybe there is an opportunity to add a substance that will help to decrease boiling point of water without harming environment with toxic byproducts. Do you know any solutes or substances?

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  • $\begingroup$ No, that can't be done. $\endgroup$ – Ivan Neretin Sep 23 '18 at 11:10
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    $\begingroup$ Why do you want steam? If it is about driving an energy source or for cooking then the temperature matters (both depend on the amount of energy which depends on the temperature so won't work as well if the temperature is lower even if you can achieve that goal chemically). You can get lower temperature boiling with lower pressure, but the same issues apply. $\endgroup$ – matt_black Sep 23 '18 at 22:24
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If you add another low-boiling chemical that forms an azeotrope, e.g. ethanol, the b.p. is lowered... however, you are no longer boiling water but a mixture. In this example, it would be 95.6% ethanol and 4.4% water. Ethanol is comparatively inexpensive and environmentally "friendly", but would need to replace most of the water. Check a table of azeotropic mixtures for other compounds that could be used.

Perhaps an ammonia-water working fluid would be more suitable for your use, or just pure $\ce{NH3}$. Ocean thermal energy conversion (OTEC) often uses ammonia as the working fluid. Ammonia-water is also used in absorption refrigerators, the converse of a motor. Ammonia is also inexpensive, and safe if fully dispersed into the environment (i.e. it's biodegradable), but is quite toxic in close quarters.

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