Good afternoon, Digeronimo.
Yes, the humidity will affect the capacity available for H2O2.
What follows is a simplified physics / chemistry lesson in vapor
pressure that provides the basis for answering your question.
Briefly, the vapor pressure of a substance is the gas pressure which
results when the substance is placed inside a sealed evacuated
container and allowed to reach equilibrium. Consider a container with
only water inside (no air). At the surface of the water there are
water molecules bouncing around amongst themselves with some average
energy (varies with temperature). If a water molecule is very lucky
and gets hit by other water molecules in just the right way, it will
fly off the surface of the water and begin to bounce around the
container. If the molecule then hits the surface of the water again,
it may become trapped as a liquid once again. If all the water exists
in liquid form, the only change that can happen is that molecules
escape to the vapor phase. As more and more vapor collects above the
liquid water, the rate at which vapor is recaptured by the liquid
water increases. Eventually the rate of evaporation and the rate of
condensation will reach equilibrium, and the vapor bouncing about the
container will exert pressure on the walls - this is the vapor
pressure of the liquid (or solid, though liquids tend to have much
higher vapor pressures because they evaporate more easily).
When considering multiple vapors (water vapor and hydrogen peroxide
vapor, as in your question) we have something called the partial vapor
pressure, which is the fraction of the total vapor pressure due to
each of the vapors present. When only peroxide vapor is present, we
have a given vapor pressure. When we add water vapor, the total vapor
pressure increases, but does not increase by the vapor pressure of
water - that is, the presence of water vapor in the air forces some of
the hydrogen peroxide back into liquid form.
Thus, as the humidity increases, less and less peroxide will vaporize.
Here are a few links about vapor pressure and the effect of multiple
vapors:
Vapor Pressure (University of Idaho)
http://www.chem.uidaho.edu/~honors/vapress.html
Vapor Pressure of a Solution (University of Arizona)
http://quiz2.chem.arizona.edu/preproom/Demo%20Files/vapor_pressure_of_a_solution.htm
Search strategy:
vapor pressure
vapor pressure "two liquids"
vapor pressure humidity
If you would like more explanation, please ask and I will be happy to
provide a clarification for you.
-Haversian |
Request for Answer Clarification by
digeronimo-ga
on
24 Oct 2002 13:09 PDT
But what if you are in a temperature controlled room. In a temperature
contolled room will the weather outside affect the relative humidity.
And I thought that there can be an infinate amount of water or H2O2
present in vapor state.
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Clarification of Answer by
haversian-ga
on
24 Oct 2002 13:52 PDT
Express the H2O2 capacity of the air in terms of a unit volume of air
(otherwise the number is meaningless - you can always increase the
capacity by adding more air). As the temperature rises, the H2O2 will
evaporate faster, and condense more slowly, increasing the vapor
pressure (and the amount in the air). As the amount of water vapor in
the air increases, the H2O2 will evaporate more slowly and condense
more quickly, reducing the vapor pressure (and the amount in the air).
During the summer, the temperature rises and while the humidity tends
to be greater, the temperature more than compensates for this - during
the winter, the temperature decreases and the ability of the air to
contain either water vapor or peroxide also decreases.
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Request for Answer Clarification by
digeronimo-ga
on
24 Oct 2002 13:58 PDT
Can you show me this mathamatically.
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Clarification of Answer by
haversian-ga
on
24 Oct 2002 14:06 PDT
What do you want me to show mathematically? Are you looking for a
formula giving the vapor pressure of H2O2 as a function of water vapor
pressure at STP?
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Request for Answer Clarification by
digeronimo-ga
on
25 Oct 2002 07:09 PDT
You say that humidity will affect the capacity available for H2O2.
Can you show me that using equations. Because I feel that at a 130C
in a tube that the humidity will not affect the capacity of air to
carry H2O2 Vapor. If it will that i have to show it mathamatically.
And yes also answer it the way you mentioned.
I really appriciate the time and effort that you have put into this
question.
I have a fax number if you need to write it down. Please be as
explisit as possible and as much detail as possible.
|
Request for Answer Clarification by
digeronimo-ga
on
25 Oct 2002 07:14 PDT
We have 18M^3/hour of air flowing in a pipe at a temp of 55C with .2
bar of pressure. The Vapor Peroxide is flowing at 53 milliLiters /
min at a temperature of 130C.
Will the humidity affect the capacity of air to carry the peroxide.
Can you show it mathamatically
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Request for Answer Clarification by
digeronimo-ga
on
25 Oct 2002 07:18 PDT
Also this is all done in a closed system except for the air that is
flowing into the piping. The air and peroxide are mixed together in a
vapor generator that is 130C.
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Request for Answer Clarification by
digeronimo-ga
on
25 Oct 2002 07:24 PDT
Maybe this website will help you
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/relhum.html
or go to www.google.com and type in "relative humidity"
take the 3rd link I think
|
Request for Answer Clarification by
digeronimo-ga
on
25 Oct 2002 07:27 PDT
I need to now at what point will the amount of peroxide vapor in the
is 54.75 grams /min be less than that based on humidity
|
Clarification of Answer by
haversian-ga
on
25 Oct 2002 07:27 PDT
Quick question:
If you are injecting vaporous H2O2 into a stream of air, you don't
care about whether the air can "carry" it or not - you'll end up with
a mix of the two gases that will flow through your pipe just fine.
I'm not sure what the boiling point of H2O2 is to know whether you
have to worry about condensation or not. If you intend this question
to be related to the previous clarification you made, could you try to
explain how?
I'm running off to class - I'll give this more than 5 minutes' thought
when I get back.
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Clarification of Answer by
haversian-ga
on
25 Oct 2002 10:22 PDT
This started out as a theoretical question and now it seems that you
have a specific application in mind yet you haven't described it
fully. I need to know the following:
You are mixing air and H2O2 and water vapor, correct?
Where is the air coming from?
Where is the H2O2 coming from?
How are they mixing?
What temperature is the resulting mixture at?
Why do you think the air's ability to absorb H2O2 is important?
How is this aparatus powered? (what causes the vapors and gases to
flow?)
Please describe the aparatus in addition to answering these specific
questions. As your previous clarifications seem to me to be
contradictory in some respects, I will disregard them to the greatest
extent possible and will concentrate on the answers you provide to
this message so please try to be complete. Unless I understand your
specific setup, I can only answer in the general sense.
Thank you.
-Haversian
|
Request for Answer Clarification by
digeronimo-ga
on
25 Oct 2002 11:15 PDT
Question 1 :We are mixing just air and H2O2.
Question 2 : The air is coming from a blower and is piped into the
H2O2 vapor generator.
Question 3 : It is being vaporized in the vapor generator.
Question 4 : The air and H2O2 are being mixed in the Vapor Generator
for the peroxide mixture.
Question 5 : The temperaure can be between 100 and 130C.
Question 6 : The reason why it is important because there needs to be
a minimum amount of peroxide in the mixture and if the humidity will
dilute this then that will affect the ability of the peroxide to kill
the micro-organisms. This is why in this evironment in a controlled
room the humidity of the outside will not affect the ability of air to
carry H2O2.
Your insight and research has been outstanding. I really appriciate
your work and hopefully we can solve this issue.
|
Clarification of Answer by
haversian-ga
on
25 Oct 2002 15:22 PDT
If your application is hydrogen peroxide vapor sterilization, you may
be interested in the following:
US5445792: Optimum hydrogen peroxide vapor sterlization method
http://www.delphion.com/details?pn10=US05445792
US4169123: Hydrogen peroxide vapor sterilization method
http://www.delphion.com/details?pn10=US04169123
And other patents at http://www.delphion.com/details?pn10=US05445792
Only parts of the patents are available without giving them money, but
if any look promising, you can get patent applications for free
elsewhere.
Offhand, I'd say you'd need to be pretty close to 100% relative
humidity before it would become a problem - you're trying to shoehorn
just over 3 liters of vapor in 18,000 liters of air - no sweat.
I'm still working on the math / chemistry for you. I'll get back to
you on that tonight or tomorrow morning.
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Clarification of Answer by
haversian-ga
on
26 Oct 2002 09:30 PDT
If the pressure (.2 bar) is less than the vapor pressure of H2O2 at
100-130C, we don't need to worry about any complicated formulae with
partial pressure and whatnot because any peroxide that condenses will
evaporate. From this page (
http://ekachem.com/paper/bleaching/1.2.5.asp - scroll way down), we
know the vapor pressure of H2O2 at 120C is about 30kPa, or .3bar.
Bingo! Looking at the 120C line, we could even dilute the H2O2 to
about 80% and still have it spontaneously evaporate.
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Request for Answer Clarification by
digeronimo-ga
on
28 Oct 2002 12:46 PST
If we have only air and H2O2 in the mixture. Will there still be the
same amount of H2O2 in the mixture as before with the introduction of
Relative Humidity. Can we have a formula that will show this.
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Clarification of Answer by
haversian-ga
on
29 Oct 2002 18:51 PST
I'm not sure what formula you're looking for. At that high
temperature and low pressure, you won't have a vapor, but a gas. It
doesn't matter whether you're using air (with or without water in it),
or nitrogen gas, or what have you - the H2O2 is going to remain a gas.
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