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Solvent Volatility

03/30/2011 10:42 AM

Dear friends,

Most organic solvents are flammable or highly flammable, depending on their volatility? Why the volatility will affect to solvent flammability?

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#1

Re: Solvent Volatility

03/30/2011 3:52 PM

It's the vapour that burns not the liquid.
If you drop a lit cigarrette into a dish of petrol (gasoline) the petrol will exinguish it, unless of course it lights the vapour before it hits the liquid, in which case run like hell.
Del

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#4
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Re: Solvent Volatility

03/31/2011 8:28 AM

Run like hell...

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#2

Re: Solvent Volatility

03/30/2011 5:33 PM

Del is correct. You need oxygen for ignition, just like a candle wick burns by melting and vaporizing paraffin to burn.

Volatility has to do with the boiling point of the substance. The lower the boiling point the lower the flashpoint for ignition.

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#11
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Re: Solvent Volatility

04/01/2011 1:15 PM

The problem with making a flat statement w/o qualifications.... Take for example carbon tetrachloride. It's BP is around 77 C. Butyl ether has a BP around 143 C. Which would you think would be the most flammable? Also, water will burn in Fluorine. Where's the oxygen? Then there are hypergolic mixtures, such as hydrazine and dinitrogen tetoxide that don't require an ignition source. Caution!! Don't play with these things unless you are thoroughly familiar with them!!

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#12
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Re: Solvent Volatility

04/01/2011 2:08 PM

I think the argument circles around the definition of flash point, which I think is correctly used in my post.

From my link above, "The flash point of a volatile liquid is the lowest temperature at which it can vaporize to form an ignitable mixture in air."

Also, autoignition is a different phenomena than flash point. One requires no ignition source, the other does not preclude ignition, as defined above.

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#13
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Re: Solvent Volatility

04/01/2011 2:14 PM

Agreed. I was extending the concept to include other avenues like ignition and the requirement for oxygen. In science, "oxidation" does not necessarily mean "reaction with oxygen", as you well know. We're on the same page.

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#3

Re: Solvent Volatility

03/30/2011 6:36 PM

Volitility may be common among substances that are highly flammable, but it is not vital. There are a number of highly flammable solids and highly flammable low volatility liquids.

Even some organic solvents that are highly volatile are nonflammable, for example carbon tetrachloride.

Since volitility is not requirement for high flammability and high volatility does not confer flammability, the 'effect' of volatility on flammability is not something that lends itself easily to a useful rule of thumb.

'Volatility is common in many highly flammable organic solvents, but low volatility and high flammability are not mutually exclusive, neither are high volitility and nonflammability' doesn't grab me as particularly useful.

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#5

Re: Solvent Volatility

03/31/2011 8:39 AM

There is flash point attached to every solvent. Flash point is auto sustainable ignition point. Based on ability of atmosphere to dilute a particular type of solvent and its easy to auto ignite under a flash ignition it will start burning.

All solvent will have flash point. High the molecular weight high carbon content and lower oxygen content will generally have higher flash point. Low carbon atom containing solvent will have lower flash point. Acetone will catch fire at lower vapor pressure than Isopropyl alcohol and examples are full in literature.

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#6
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Re: Solvent Volatility

03/31/2011 10:01 AM

Masyood:

I dont quite understand about flash point. Do you mean it as "auto-ignition ability" of material (here is solvent). Does it have any connection with oxygen concentration?

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#7
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Re: Solvent Volatility

03/31/2011 10:40 AM

Flash point is concentration of solvent vapor needed to produce flame but not have ability to have sustained burning of solvent. If you get above that concentration you will have sustainable burning of the solvent.

You can test out using equiopment which is available or develop your own test method if you are like me

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#8
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Re: Solvent Volatility

03/31/2011 5:08 PM

Masywood:

Some corrections of your comments are needed. You wrote:

'Flash point is auto sustainable ignition point.'

Flash point and Auto ignition temperature are not the same. While, in rare cases, these might occur at the same temperature, they describe distinct qualities of a substance. Flash Point is the lowest temperature at which ignition can be initiated, while Auto Ignition Temperature is the lowest temperature at which ignition will occur without an obvious initiating event, (such as a spark).

'All solvent will have flash point.'

'Flash point' is a term used almost exclusively relating to flammable or combustible materials. The flashpoint of combustible materials generally does not exceed 200F. 100F is generally the limit for flammable.

Carbon tetrachloride is a solvent that has also been used to extinguish fires, describing a flashpoint of this non-flammable non-combustible material liquid seems a misuse of the concept.

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#9
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Re: Solvent Volatility

03/31/2011 5:21 PM

My mistake and you are correct. This is typo. Flash point is nonsustained flame . Thanks you for correcting me

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#10
In reply to #9

Re: Solvent Volatility

03/31/2011 9:04 PM

Chemical mistake could kill.

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