angelhair
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What size column for my flask?
Can some one suggest an appropiate size column, width and height for a 12L RBF, because the largest that I can find is only a B24, about 600mm height
and 25mm width.
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not_important
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What are you separating, how many theoretical plates does that take?
knowing that and the HETP for a given column type, you'll be able to calculate the column length.
The flask volume has little to do with the question, except for rather small volumes; size is more important for the head source rating. It does play
an important role determine how many hours of days you'll spend fractionally distilling.
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angelhair
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yes I understand what you're saying. I don't have anything specific to separate, just general solvent purifications, acetone IPA, benzene toluene
xylene' etc.
I have a book called chemical separations but the section about columns and plates is writen very badly, there are lots of formulas but no
explanations. The only thing useful to me is a table listing deg C of separation and the coresponding number of plates needed.
Since my question is too vague, can you suggest a book that explains it in simple terms. I have a copy Perry's chemical engineering but the section on
fraction columns is way too complex for me.
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not_important
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That table is likely your best guideline, although a proper one would list low and high boiling points rather than just the difference. Figure out
what your closest separation is likely to be and use that number of plates.
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angelhair
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Where can I find information that tells me how many milimeters equals number of plates. I haven't found that in my books. Also I am assuming that
speed of distillation, still with good separation, is a factor of width.
Basicly, if I have say 6L of toluene and xylene or something with closer bp I don't want it to take more than 8-10 hrs.
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watson.fawkes
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| Quote: | Originally posted by angelhair
Where can I find information that tells me how many milimeters equals number of plates. I haven't found that in my books. |
That's because it depends on how your column is packed. A theoretical plate is a measure (roughly) of the intimacy of contact
between solid and liquid phases. Since this is how heat is transferred between a condensing vapor phase and an evaporating liquid phase, it's the
rate-determining step. The specification for your column (not a reference book) should give this figure.
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chemrox
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If it's separations your doing the flask size is irrelevant. The column length will be a function of column design and the boiling point differences
in the materials you're separating. There's a decent discussion in Vogels 3rd edition. Snyder columns are good basic fractionating columns. I have
a six cell one I use for separating liquids that boil 40 deg or more apart. An important part of the setup is reflux ratio. You need a partial
takeoff head to control that. There are some nice solvent heads made... there's quite a bit to fractional distillation particularly when the
materials boil closely.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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