Alchohol in low atmospheric pressure/vacuum

Discussion in 'Chemistry' started by domesticated om, Jul 16, 2007.

  1. domesticated om Interplanetary homesteader Valued Senior Member

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    How does alchohol (we'll use ethanol for this example) behave in lower atmospheric pressures? Would it become volatile, or would it be less volatile and simply evaporate?
     
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  3. Facial Valued Senior Member

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    By volatile, we shall mean the tendency for a liquid substance to evaporate. It becomes more volatile, because of lower atmospheric pressure that counteracts the vapor pressure of ethanol.
     
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  5. mikal Registered Member

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    fire paste

    Hi I was looking at the posts on fire paste in this forum ,that's the stuff invented by Troy Hurtubise that has very good heat insulating properties..I believe it is a geopolymer...with some organic components in it which causes holes in the ceramic during the curing process.Troy mentions that this material is made from diet coke and some low cost material that costs about 5 dollars per 45 gallon drum and that it would make people laugh if they knew what this material was.This material is I believe Fullers earth which is often used and sold as a kitty litter material because of it's absorbent properties.So two ingredients are diet coke and kitty litter (Fullers earth) the other ingredient which would make a geopolymer from the above two ingredients would then be either sodium bicarbonate or caustic soda.If bicarbonate of soda is used then the ceramic would cure at a relatively high temp.maybe around 400 to 600 deg C. If caustic soda is used the curing temp. would be considerably lower around 200 to 300 deg C.I made a really tough, light ceramic geopolymer from fullers earth, citric acid(diet coke ingredient) and bicarbonate of soda..I mixed the dry ingredients first and then added some water and pounded the stuff in a mortar and pestal till it was like a clay...the stuff fizzed first and then absorbed the water to become clay like..I formed the material into a little cube which I then cooked into ceramic on my gas stove top...the right combinations of fullers earth, citric acid powder and bicarbonate of soda powder will produce a good ceramic geopolymer without cracks that is light and tough and with very good heat insulating properties.

    Mikal
     
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  7. guthrie paradox generator Registered Senior Member

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    And this has what to do with alcohol?
     
  8. mikal Registered Member

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    Fire paste

    Nothing to with alcohol other than I had a beer after making a geopolymer on my kitchen stove from cheap ingredients I found in my local supermarket.I tried to start a new thread by putting 'fire paste' in the title but nothing came through for some reason.

    Mikal
     
  9. domesticated om Interplanetary homesteader Valued Senior Member

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    Actually, 'volatile' was a poor choice of words on my part.
    What I meant to ask was if it would lower the temperature required to cause it to ignite, or would it simply evaporate.
     
  10. Chatha big brown was screwed up Registered Senior Member

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    Pressurized volatile compounds like alchohol would never evaporate under low pressure, remember higher pressure equals lower boiling point, and lower pressure equals higher boiling boint. Combustible compounds for instance like gasoline can explode if over pressurized in an engine. You can do this experiment yourself by putting alchohol in a pressure cooker and heat the mixture, most likely it will explode or evaporate at a low temperature, but it will never evaporate at low pressure or in a vacuum. Significantly, water boils easily at high pressures (low altitude), and takes forever to boil at low pressures(high attidudes). I'm not really sure about the alchohol, so look it up.
     
  11. andbna Registered Senior Member

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    You have that backwards, something will boil when its vapour pressure is above the atmosphearic pressure. That is, if I have water, and I take it to a sufficiantly high altitude it will 'spontaniously' boil. if I take it to a lower altitude (high preassure) it will take longer to boil. Boiling point increases with atmosphearic preasure.
    Thus, if you want alchohol to not evapourate, increase the atmosphearic pressure.

    This is correct, and is how diesel engines operate, however the reason is that, under higher preassures the molecules are forced closer together, and thus more likely to react. The fact that tempurature increases with preassure also contributes.

    -Andrew
     
  12. guthrie paradox generator Registered Senior Member

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    The ideal gas law: PV=nRT.
    Pressure times volume = number of moles times constant R times temperature.
    I hope I've remembered tha correctly, I havn't used it since uni, and that was a few years ago.
     
  13. Chatha big brown was screwed up Registered Senior Member

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    andbna,
    Here's the fact. Alchohol is volatile, and volatility is directly proportional to pressure. Therefore low pressure will result to nothing happening or more than likely a near freezing point since low pressure almost always equals low energy. A high pressure will result in quadropling the pressure in the system and possible ,though unlikely, explosion. You are mistaken with the altitude thing. A high altitude equals low pressure, and low pressure means the molecules are less tightly packed, which is why it takes longer to boil water. A low altitude means higher pressure(think deep sea) and a higher pressure means it takes shorter time to boil water (which is why using pressurized cooker to cook takes half the time).
     
  14. Nasor Valued Senior Member

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    No, boiling point increases as pressure increases and decreases as pressure decreases. You can cook things faster in a pressure cooker because the high pressure raises the boiling point, which means that the water is hotter (and therefore the food cooks fasters).
     
  15. Chatha big brown was screwed up Registered Senior Member

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    You see, you are making a mistake. The boiling point of water is 100 degrees, but at high pressure water boils(evaporates) faster, which means it boils at about 90 degrees. Therefore high pressure lowers boiling point.

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  16. Nasor Valued Senior Member

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    Sorry, you just failed Chemistry 101. You have it exactly backwards. Read a chemistry textbook, or at least google it.
     
  17. Read-Only Valued Senior Member

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    Quite the opposite, Chatha. Lowering the pressure over ANY liquid will cause it to boil/evaporate faster/easier at a lower temperature. The key is something called "vapor pressure." (You might want to look up that term.)

    And the reason for using pressure cookers is right in line with that. The goal of a pressure cooker is to increase the boiling point which allows the cooking water to reach a higher temperature. If you tried to cook a piece of meat on, say, the top of Pike's Peak, it not only would take forever but the meat would be undercooked. The pressure cooker is needed so that a high enough temperature can be achieved. (It's easy to see that you've never lived in Denver, Colorado.)

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  18. Chatha big brown was screwed up Registered Senior Member

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    I know what your problem is, I will help you understand. First you need to know that boiling point is the same as evaporating point. You see, the whole reason why things evaporate (escape) is because its too crowded inside the system, so when you increase the pressure of the system you will obviously increase the tendency of the molecules to evaporate. Water boils faster in a pressurized system because there is no way for the energy of the system to escape, it conserves energy, which is why it is able to evaporate or boil easily at temperatures around 95 degrees. The temperature of a pressurized system after 5 minutes will obviously be higher than an open system after the same time, but that does not mean that evaporation did not start at a lower temperature in a closed system. You are right, the goal of a pressure cooker is to increase the temperature by conserving energy, but that doeasn't mean water boils at 120 degrees in a pressure cooker, in fact water boils at about 95 degrees in a pressure cooker. Hence pressure decreases the boiling point of water and all other substances. Take a balloon and fill it with air then pierce it with a tiny pin, you will feel a lot of air escaping(evaporating) from the ballon. That means that you don't even need heat energy to make things escape when you have enough pressure. Thus pressure lowers boiling point, not increasing it. Low pressure cools things down, increasing the boiling point, thats why water boils at about 105 degrees in the mountains.
     
  19. Chatha big brown was screwed up Registered Senior Member

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    Vapor pressure is the pressure exerted by a liquid when being heated, which when added with atmospheric pressure equals the total pressure. Lowering the pressure of a system will not cause it to boil faster, otherwise cooking with an opened pot will be faster than cooking with a closed one.

    The goal of a pressure cooker is not to increase the boiling point as you say, but to conserve energy and increase the temperature in the system. Increasing the temp of the system is NOT the same as increasing the boiling point, otherwise water will boil at 150 degrees in a pressure cooker, which would be scientifically silly. Water will always boil around 100 degree regardless of the circumstance, but it will start to evaporate easily with increased pressure at constant temperature.
     
  20. domesticated om Interplanetary homesteader Valued Senior Member

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    Last edited: Jul 31, 2007
  21. Read-Only Valued Senior Member

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    Certainly. Ethanol stills are as old as bootleggers and Prohibition. (Much older than that, actually.)

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    Ethanol has a higher vapor pressure than water and boils out of a mixture quite readily. Reducing the pressure in the receiver (condenser) allows the process to work at greatly reduced temperatures.

    Vacuum distillation has many applications in the food industry and several others.
     
  22. andbna Registered Senior Member

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    -http://en.wikipedia.org/wiki/Vapor_pressure

    Not quite, if I only increased the preassure of the water, then perhaps that would happen, but I can't do that. The corresponding increase in atmospheric preassure keeps the molecules in place as a liquid.

    I don't understand what you mean by 'conserving energy'?
    Water does not boil at 95 degrees in a preassure cooker. If it did, the food would be sitting in a 95 degree liquid and cook more slowly than my stovetop which boils at 100 degrees.


    -http://en.wikipedia.org/wiki/Boiling

    -Andrew
     
  23. Chatha big brown was screwed up Registered Senior Member

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    Actually you can, all you have to do is put a lid on the container, the weight of the lid is a function of the total pressure. Remember atmospheric pressure is nothing but the weight of the atmosphere.

    If you don't understand, just ask. A closed or pressurized system conserves energy because heat is not lost, but that's not the reason why water evaporates earlier, its because the molecules are packed too tightly together. When we say water boils at 100 degrees, thats just a general evaluation because water can and does boil at lower temperatures depending on the efficiency of the system. Water never boils at a higher temperature because there is no further heat loss or gain during phase transition (the process where water changes state). If you want water to have a higher boiling point, you have to mix it with something that has a higher boiling point, sort of like the same way adding salt to ice decreases its freezing point. Boiling point is the instant when one molecule of liquid water escapes as water vapor or gas, and the temperature always varies, just ask any scientist, but it never goes above 100 degrees.
     

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