Re: 2-phase flow.


"Ron Jones" <ron@xxxxxxxxxxxxxxx> wrote in
message
news:g84vvo$1rqa$1@xxxxxxxxxxxxxxxxxxxx
Peter Jason wrote:
Thanks for all replies.

I have the azeotropic details from Horsley
and the purpose of the exercise is to
remove
a product from the other reactants to
drive
the reaction to the right.

I am using two possible methods, the first
assembly is a modified heavy-entrainer
Dean &
Stark head with the addition of a tap at
the
bottom of its collection tube. I hoped by
this method to have infinite reflux with
the
light (desired) component collecting in
the
tube and any excess, together with the
water,
passing back into the column to supply
reflux. Of course this is a semi-batch
distillation in that the liquid in the
tube
will represent a collection at infinite
reflux. Alas, the levels in the D&S
device
are never constant and the liquid
(2-phase)
therein surges back & forth upsetting the
column equilibrium shown by a cycling
top-of-column temperature.

The other method I mentioned uses a
standard
Quickfit reflux offtake set, with the same
type of problem.

Clearly I will have to get the glassblower
to
set up a two-valve head, one for each
phase.
Or perhaps a small metering pump to
deliver
2-phase liquid.

If I understand correctly - you want to
remove the top layer and let the lower one
flow back? If so it is possible, but the
apparatus looks nothing like a standard
dean and starke!
I could probably sketch a drawing if you
need one - or look up page 2 of US Patent -
US5210339 on http://gb.espacenet.com or
http://patft.uspto.gov/netahtml/PTO/srchnum.htm
(NB - espacenet won't work with IE7 on my
machine - use Firefox, or if you use Uspto
it needs a tiff viewer installed). Patents
are free on those sites. Anyway back to
drawing - just add a tap near the top of
the sidearm about where HNO3 is marked. A
good glassblower can also add a condenser
section below the tap - that can help
separation as the liquid flows through.


Thank you. I have checked out this patent
and the drawing (fig1) is the same as the one
I am using, except I had the glassblower
attach a small tap at the very bottom.

This is called a D&S for the collection of
light liquids because it allows a heavy
entrainer (eg water) flow back into the
fractionating column.

My way of using this device was to allow the
distillation to continue at infinite reflux
so allowing a collection of the light liquid
in the left-hand tube. The light organic
liquid in this tube then would be that at
infinite reflux. Then I would empty the
left-side tube via the installed valve and
simply wait for another lot to collect. In
this way I would collect numerous fractions
*automatically* and I could walk away from
the apparatus and do other things.

The problem seems to be having each phase
flow back into the fractionating column
separately to avoid any two-phase flow
problems, though this will mean holding the
interface at some constant level. I will
have to figure this out.



.

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