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Re: Vapour Management Head

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  • mr_ethanol2003
    ... management still head. What are its advantages/disadvantages over the nixon-stone type? ... but have yet to find a description of how they work. ... to
    Message 1 of 17 , Jul 2, 2003
      --- In Distillers@yahoogroups.com, "Mike Nixon" <mike@s...> wrote:
      > From: mr_ethanol2003
      > Subject: [Distillers] Vapour Management Head
      >
      > Hi,
      >
      > Can anyone please explain the working principle of a vapour
      management still head. What are its advantages/disadvantages over
      the nixon-stone type?
      >
      > I've seen pictures of this type of head on www.homedistiller.org
      but have yet to find a description of how they work.
      >
      > Thanks folks,
      > Andy.
      > =======================
      > Hi Andy,
      > It is getting late here in the Antipodes, but I will post a reply
      to your query tomorrow morning.
      > Mike Nixon


      Thanks Mike,

      I look forward to it.


      Andy.
    • Mike Nixon
      mr_ethanol2003 wrote: Subject: [Distillers] Vapour Management Head Can anyone please explain the working principle of a vapour management still head. What are
      Message 2 of 17 , Jul 2, 2003
        mr_ethanol2003 wrote:
        Subject: [Distillers] Vapour Management Head

        Can anyone please explain the working principle of a vapour management still head. What are its advantages/disadvantages over
        the nixon-stone type?

        I've seen pictures of this type of head on www.homedistiller.org but have yet to find a description of how they work.
        =====================
        Hokay Andy, here we go.  I'll try and make it as short as possible.
         
        If you feed vapour to the middle point of a horizontal tube, then it will split into two streams. 
        If the cross-sectional area of one arm of the tube is A and the other is B, then the vapour will divide in that ratio, A/B.
        You can control that cross-sectional area by means of gate valves, and this is useful for some applications.
         
        If you feed vapour into the middle point of a vertical tube, density now becomes a factor and this can be used to control the behaviour of a distilling column depending on the composition of the vapour inside.
        First thing to note is that vapour rises in a distillation column not because if convection, as some think, but because it is pushed by vapour generated in the boiler.  All vapour in a distillation column therefore rises at the same rate no matter what its density, and at a rate determined by the power pumped into the boiler.
        When vapour meets the middle point of the vertical tube, some will be driven further up the column and some will enter the tube.  In practise, this middle feed point is sealed off by a gate valve in a side arm during stabilisation of the column, and the vertical tube comprises the path up to the top condenser and the path down to the product condenser.  It is a 'kinked' vertical tube fed with vapor at its middle point.  When the gate valve is opened, vapour enters the side arm and, if it is less dense than air, will try to rise.  If it is denser than air then it falls.  It cannot rise in the side arm as that arm only goes down, but can fall as it points down to the product condenser and collecting vessel.  The gate valve controls amount that can enter the side arm.
        The relative densities of steam at 100C, air at room temperature, and ethanol vapor at 78C are 0.6/1.0/1.6
        If the vapour in the column is ethanol, then it will fall down through the product arm, and if it is steam then it will continue up to the top condenser.  The changeover point, when the vapor in the column is the same density as air, if when the vapour comprises 45.5% ethanol and 54.5% steam.  The volume of vapour falling down through the side arm therefore tails off and finally stops as the vapour mix in the column approaches and then reaches this point.  As this represents the onset of tails, the side arm being at the top of the column, a vapour management still automatically stops delivering product before it is contaminated with a significant amount of tails.  It is also the reason why you cannot test the operation of such a still using steam alone.  Subsequent collection of tails can be done by turning off the top condenser, blocking that path with a rag in the top vent, and fully opening the gate valve.  A rag is recommended for blocking the top vent as a gate valve would present the possibility that both gate valves could be closed together, sealing the whole still.
         
        Sorry if that still seems long winded.  I would seriously welcome any summary that manages to cover everything more concisely.
         
        Mike N
         
         
         
      • mr_ethanol2003
        Wow, thanks for such a detailed answer Mike :) I think I ll have to read it a few times before I understand it though... Best regards, Andy. ... management
        Message 3 of 17 , Jul 2, 2003
          Wow, thanks for such a detailed answer Mike :)


          I think I'll have to read it a few times before I understand it
          though...

          Best regards,

          Andy.


          --- In Distillers@yahoogroups.com, "Mike Nixon" <mike@s...> wrote:
          > mr_ethanol2003 wrote:
          > Subject: [Distillers] Vapour Management Head
          >
          > Can anyone please explain the working principle of a vapour
          management still head. What are its advantages/disadvantages over
          > the nixon-stone type?
          >
          > I've seen pictures of this type of head on www.homedistiller.org
          but have yet to find a description of how they work.
          > =====================
          > Hokay Andy, here we go. I'll try and make it as short as possible.
          >
          > If you feed vapour to the middle point of a horizontal tube, then
          it will split into two streams.
          > If the cross-sectional area of one arm of the tube is A and the
          other is B, then the vapour will divide in that ratio, A/B.
          > You can control that cross-sectional area by means of gate valves,
          and this is useful for some applications.
          >
          > If you feed vapour into the middle point of a vertical tube,
          density now becomes a factor and this can be used to control the
          behaviour of a distilling column depending on the composition of the
          vapour inside.
          > First thing to note is that vapour rises in a distillation column
          not because if convection, as some think, but because it is pushed
          by vapour generated in the boiler. All vapour in a distillation
          column therefore rises at the same rate no matter what its density,
          and at a rate determined by the power pumped into the boiler.
          > When vapour meets the middle point of the vertical tube, some will
          be driven further up the column and some will enter the tube. In
          practise, this middle feed point is sealed off by a gate valve in a
          side arm during stabilisation of the column, and the vertical tube
          comprises the path up to the top condenser and the path down to the
          product condenser. It is a 'kinked' vertical tube fed with vapor at
          its middle point. When the gate valve is opened, vapour enters the
          side arm and, if it is less dense than air, will try to rise. If it
          is denser than air then it falls. It cannot rise in the side arm as
          that arm only goes down, but can fall as it points down to the
          product condenser and collecting vessel. The gate valve controls
          amount that can enter the side arm.
          > The relative densities of steam at 100C, air at room temperature,
          and ethanol vapor at 78C are 0.6/1.0/1.6
          > If the vapour in the column is ethanol, then it will fall down
          through the product arm, and if it is steam then it will continue up
          to the top condenser. The changeover point, when the vapor in the
          column is the same density as air, if when the vapour comprises
          45.5% ethanol and 54.5% steam. The volume of vapour falling down
          through the side arm therefore tails off and finally stops as the
          vapour mix in the column approaches and then reaches this point. As
          this represents the onset of tails, the side arm being at the top of
          the column, a vapour management still automatically stops delivering
          product before it is contaminated with a significant amount of
          tails. It is also the reason why you cannot test the operation of
          such a still using steam alone. Subsequent collection of tails can
          be done by turning off the top condenser, blocking that path with a
          rag in the top vent, and fully opening the gate valve. A rag is
          recommended for blocking the top vent as a gate valve would present
          the possibility that both gate valves could be closed together,
          sealing the whole still.
          >
          > Sorry if that still seems long winded. I would seriously welcome
          any summary that manages to cover everything more concisely.
          >
          > Mike N
        • Mike Nixon
          mr_ethanol2003 wrote: Subject: [Distillers] Re: Vapour Management Head Wow, thanks for such a detailed answer Mike :) I think I ll have to read it a few times
          Message 4 of 17 , Jul 2, 2003
            mr_ethanol2003 wrote:
            Subject: [Distillers] Re: Vapour Management Head

            Wow, thanks for such a detailed answer Mike :)

            I think I'll have to read it a few times before I understand it though...
            ========================
            Me too!    :-)
             
            Mike N
             
          • abbababbaccc
            So this basically means that VM head closes at 94C vapor temp? I looked this figure from a graph at Tony s site. How about methanol, propanol and butanol? Are
            Message 5 of 17 , Jul 2, 2003
              So this basically means that VM head closes at 94C vapor temp? I
              looked this figure from a graph at Tony's site. How about methanol,
              propanol and butanol? Are they heavier than air as well and if so
              what are their changeover points?

              Greetz, Riku

              > If the vapour in the column is ethanol, then it will fall down
              through the product arm, and if it is steam then it will continue up
              to the top condenser. The changeover point, when the vapor in the
              column is the same density as air, if when the vapour comprises 45.5%
              ethanol and 54.5% steam. The volume of vapour falling down through
              the side arm therefore tails off and finally stops as the vapour mix
              in the column approaches and then reaches this point. As this
              represents the onset of tails, the side arm being at the top of the
              column, a vapour management still automatically stops delivering
              product before it is contaminated with a significant amount of
              tails. >
              > Mike N
            • BOKAKOB
              Thanks from me, MIke, too... I have a question if you dont mind educating me and many more of us here. If I understood correctly it is crucial to where exactly
              Message 6 of 17 , Jul 2, 2003
                Thanks from me, MIke, too... I have a question if you dont mind educating me and many more of us here. If I understood correctly it is crucial to where exactly this horizontal appendix is located, its size and slope as well. Is this correct?
                And the second question, is this scheme works the same way with foreshots or the density of foreshot vapors is different?


                I can be wrong I must say
                Cheers, Alex...
                A


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              • BOKAKOB
                When I very slowly distill, the temperature is never above 80~80.5C however I do get the full blast of tails if I am not careful. In practice I worked out a
                Message 7 of 17 , Jul 2, 2003
                  When I very slowly distill, the temperature is never above 80~80.5C however I do get the full blast of tails if I am not careful.
                   
                  In practice I worked out a rule to separate my 19L@14% batch in three stages:
                  Heads_30%(20%-80%) + Collection_40%+Tails_30% of the theoretical amount of alcohol in it. The first 20% of heads get tossed out (about 180mL), the remaining 85% heads and 30% of tails get re-distilled with the next 1st distillation batch.
                   
                  How to explain that?

                  abbababbaccc <abbababbaccc@...> wrote:
                  So this basically means that VM head closes at 94C vapor temp? I looked this figure from a graph at Tony's site. How about methanol, propanol and butanol? Are they heavier than air as well and if so what are their changeover points?


                  I can be wrong I must say
                  Cheers, Alex...
                  A


                  Do you Yahoo!?
                  SBC Yahoo! DSL - Now only $29.95 per month!
                • Mike Nixon
                  abbababbaccc Subject: [Distillers] Re: Vapour Management Head So this basically means that VM head closes at 94C vapor temp? I looked this figure from a graph
                  Message 8 of 17 , Jul 2, 2003
                    abbababbaccc
                    Subject: [Distillers] Re: Vapour Management Head

                    So this basically means that VM head closes at 94C vapor temp? I looked this figure from a graph at Tony's site. How about methanol, propanol and butanol? Are they heavier than air as well and if so what are their changeover points?

                    Greetz, Riku
                    ===========================
                    Hi Riku,
                     
                    Methanol vapor is 1.1 times as dense as air, and the generally accepted values for propanol and butanol are 2.1 and 2.5 respectively (depends which isomer you are talking about).  However, as far as we are concerned, those last two can be ignored as they both have boiling points higher than ethanol and so will only get near the top if there is very little ethanol in the column.  In contrast, methanol with a BP of 65C would get there before ethanol (BP 78.3C) and, being slightly denser than air, would be extracted via the downward-going collection path as part of the heads.  As the density difference is slight, it pays to take this stage slowly. The other likely heads component is ethyl acetate (BP 77C) which would also take the downward collection path as its relative density is 3.0
                     
                    The 'changover' points (assuming you are referring to the 45.5% I mentioned in respect of ethanol) are really irrelevant. The heads will be extracted before the bulk of the ethanol comes along, so it will be 100% for them, then you will have a mix of just steam and ethanol vapor at the top during the main run.  The relative density of this falls to 1.0 when the mix is 45.5% ethanol and so output falls to zero down the collection path at that stage.  This mix then 'sits' there in dynamic equilibrium and prevents the higher BP components from rising up the column.  For academic interest, if you had a mix of just water and propanol in the boiler, then the VM system would merrily collect propanol until its percentage in the vapor mix fell to 37%, and if you did the same with butanol then it would run until the mix fell to 32.3%
                     
                    Mike N
                     
                  • Mike Nixon
                    BOKAKOB wrote: Subject: Re: [Distillers] Re: Vapour Management Head Thanks from me, MIke, too... I have a question if you dont mind educating me and many more
                    Message 9 of 17 , Jul 2, 2003
                      BOKAKOB wrote:
                      Subject: Re: [Distillers] Re: Vapour Management Head

                      Thanks from me, MIke, too... I have a question if you dont mind educating me and many more of us here. If I understood correctly it is crucial to where exactly this horizontal appendix is located, its size and slope as well. Is this correct?
                      And the second question, is this scheme works the same way with foreshots or the density of foreshot vapors is different?
                      =======================
                      Hi Alex,
                       
                      The location should be as near the top of the column as possible simply because that is where the greatest separation is to be found, and that is what we want to collect.  The size and shape don't matter very much if you are feeding a vertical path down to the collector, so long as it's not ridiculously small like a pinhole :-)  The role of the gate valve in this case will be to control the aperture and rate of collection.  Size does matter with the horizontal configuration as this is the only thing controlling flow ... and this is what misled me when I did the first experiments as my rig was set up in that way.  In that case, the flow in each horizontal direction depends on the relative sizes of the apertures and I took that to be the only factor that mattered as I hadn't considered the vertical path case ... sighhhh.  The slope of the collection path is also not critical, so long as it is going down.  Obviously, vertical is most efficient.  Incidentally, ignore any short horizontal section (the take-off point) in the vertical case as this makes no difference whatsoever.
                       
                      Foreshots behave exactly the same way as heads.  However, take it slowly to ensure they come off cleanly.  I noted in a post to Riku this morning that methanol vapor is only a bit denser than air, so it needs to be 'persuaded'.  No different to what you would do with LM really, but for slightly different reasons.
                       
                      Cheers!
                      Mike N
                       
                    • abbababbaccc
                      Thanks Mike, this is good to know. Greetz, Riku ... looked this figure from a graph at Tony s site. How about methanol, propanol and butanol? Are they heavier
                      Message 10 of 17 , Jul 2, 2003
                        Thanks Mike, this is good to know.

                        Greetz, Riku

                        --- In Distillers@yahoogroups.com, "Mike Nixon" <mike@s...> wrote:
                        > abbababbaccc
                        > Subject: [Distillers] Re: Vapour Management Head
                        >
                        > So this basically means that VM head closes at 94C vapor temp? I
                        looked this figure from a graph at Tony's site. How about methanol,
                        propanol and butanol? Are they heavier than air as well and if so
                        what are their changeover points?
                        >
                        > Greetz, Riku
                        > ===========================
                        > Hi Riku,
                        >
                        > Methanol vapor is 1.1 times as dense as air, and the generally
                        accepted values for propanol and butanol are 2.1 and 2.5 respectively
                        (depends which isomer you are talking about). However, as far as we
                        are concerned, those last two can be ignored as they both have
                        boiling points higher than ethanol and so will only get near the top
                        if there is very little ethanol in the column. In contrast, methanol
                        with a BP of 65C would get there before ethanol (BP 78.3C) and, being
                        slightly denser than air, would be extracted via the downward-going
                        collection path as part of the heads. As the density difference is
                        slight, it pays to take this stage slowly. The other likely heads
                        component is ethyl acetate (BP 77C) which would also take the
                        downward collection path as its relative density is 3.0
                        >
                        > The 'changover' points (assuming you are referring to the 45.5% I
                        mentioned in respect of ethanol) are really irrelevant. The heads
                        will be extracted before the bulk of the ethanol comes along, so it
                        will be 100% for them, then you will have a mix of just steam and
                        ethanol vapor at the top during the main run. The relative density
                        of this falls to 1.0 when the mix is 45.5% ethanol and so output
                        falls to zero down the collection path at that stage. This mix
                        then 'sits' there in dynamic equilibrium and prevents the higher BP
                        components from rising up the column. For academic interest, if you
                        had a mix of just water and propanol in the boiler, then the VM
                        system would merrily collect propanol until its percentage in the
                        vapor mix fell to 37%, and if you did the same with butanol then it
                        would run until the mix fell to 32.3%
                        >
                        > Mike N
                      • abbababbaccc
                        Thinking about this a bit more. Is following assumption correct? When vapor is condensed in the vertical liebig it creates low pressure area which draws more
                        Message 11 of 17 , Jul 4, 2003
                          Thinking about this a bit more. Is following assumption correct? When
                          vapor is condensed in the vertical liebig it creates low pressure
                          area which draws more vapor from the horizontal part and column. The
                          thing that control vapor flow is the gate valve, which acts as
                          throttle blades on carburetor. So basically the relational areas of
                          column and takeoff pipe (vertical) do not have much effect as the
                          vapor velocity through the horizontal pipe could be much greater than
                          vaporspeed in the column.

                          Mike, if I'm wrong please correct me. I plan on building a 2.5 inch
                          column which has 1 inch pipe to the gate valve and VM condenser (much
                          smaller area than column). I'd like to be able to run it with low
                          reflux levels as well. If the assumption above is correct it should
                          work that way.

                          Greetz, Riku

                          --- In Distillers@yahoogroups.com, "Mike Nixon" <mike@s...> wrote:
                          > BOKAKOB wrote:
                          > Subject: Re: [Distillers] Re: Vapour Management Head
                          >
                          > Thanks from me, MIke, too... I have a question if you dont mind
                          educating me and many more of us here. If I understood correctly it
                          is crucial to where exactly this horizontal appendix is located, its
                          size and slope as well. Is this correct?
                          > And the second question, is this scheme works the same way with
                          foreshots or the density of foreshot vapors is different?
                          > =======================
                          > Hi Alex,
                          >
                          > The location should be as near the top of the column as possible
                          simply because that is where the greatest separation is to be found,
                          and that is what we want to collect. The size and shape don't matter
                          very much if you are feeding a vertical path down to the collector,
                          so long as it's not ridiculously small like a pinhole :-) The role
                          of the gate valve in this case will be to control the aperture and
                          rate of collection. Size does matter with the horizontal
                          configuration as this is the only thing controlling flow ... and this
                          is what misled me when I did the first experiments as my rig was set
                          up in that way. In that case, the flow in each horizontal direction
                          depends on the relative sizes of the apertures and I took that to be
                          the only factor that mattered as I hadn't considered the vertical
                          path case ... sighhhh. The slope of the collection path is also not
                          critical, so long as it is going down. Obviously, vertical is most
                          efficient. Incidentally, ignore any short horizontal section (the
                          take-off point) in the vertical case as this makes no difference
                          whatsoever.
                          >
                          > Foreshots behave exactly the same way as heads. However, take it
                          slowly to ensure they come off cleanly. I noted in a post to Riku
                          this morning that methanol vapor is only a bit denser than air, so it
                          needs to be 'persuaded'. No different to what you would do with LM
                          really, but for slightly different reasons.
                          >
                          > Cheers!
                          > Mike N
                        • Mike Nixon
                          abbababbaccc wrote: Subject: [Distillers] Re: Vapour Management Head Thinking about this a bit more. Is following assumption correct? When vapor is condensed
                          Message 12 of 17 , Jul 4, 2003
                            abbababbaccc wrote:
                            Subject: [Distillers] Re: Vapour Management Head

                            Thinking about this a bit more. Is following assumption correct? When vapor is condensed in the vertical liebig it creates low pressure area which draws more vapor from the horizontal part and column. The thing that control vapor flow is the gate valve, which acts as throttle blades on carburetor. So basically the relational areas of column and takeoff pipe (vertical) do not have much effect as the vapor velocity through the horizontal pipe could be much greater than vaporspeed in the column.

                            Mike, if I'm wrong please correct me. I plan on building a 2.5 inch column which has 1 inch pipe to the gate valve and VM condenser (much smaller area than column). I'd like to be able to run it with low reflux levels as well. If the assumption above is correct it should work that way.

                            Greetz, Riku
                            ========================
                            Hi Riku,
                             
                            Not quite correct I'm afraid.  When a vapor condenses then it certainly occupies less volume, and in a closed container this would result in lower overall pressure.  However, when the vapor condenses in a tube that is open to the air, then the localised lowering of pressure is almost immediately compensated for by both air and uncondensed vapor entering the tube from either end to take its place.  Exactly how much of each will depend on the local dynamics of the sytem, but it certainly won't lean heavily on either one option or the other.  The flow of vapor into the side collection arm is not driven forcibly like air in a carburettor, but is simply the flow you would expect from the difference in density inside the tube system (from top condenser down through the side arm/gate valve to the outlet of the collection arm) compared with the density of the surrounding air.  This will be very slow compared to the speed at which vapor is moving up the column as that vapor is being pushed by new vapor generated all the time in the boiler. To give some idea of the speeds,  vapor in a 2.5 inch diameter column fed by a 1500W boiler will be moving at just over 14 inches/sec (0.8 mph puts that in better perspective ... it's a long way from the air speed in a carburettor).  I've no idea what the speed of the vapor will be when it moves into the side arm under the influence of its greater density than air ... that depends on all sorts of factors, the opening in the gate valve being one ... but it will be like a tortoise compared with the hare of the vapor in the column.  Certainly not faster as you suggest.
                             
                            However, bottom line is that your system should work just fine   and that is all that really matters :-)
                            If you lower the reflux ratio too much by opening the gate valve too enthusiastically, you will know soon enough when the quality begins to suffer.  So go to that point ... then back off a bit by closing the gate valve a tad.
                             
                            All the best,
                            Mike N
                             
                          • beaui42
                            Mike thank for explanation on the VM head physics. My understanding is that a LM seperation is based (very basically), on temperature. VM contrasts in that
                            Message 13 of 17 , Jul 5, 2003
                              Mike
                              thank for explanation on the VM head physics.

                              My understanding is that a LM seperation is based (very basically),
                              on temperature.
                              VM contrasts in that seperation relies on both temperature and vapour
                              density.

                              With the VM head there is a marked difference in that the densities
                              of ethanol to aethyl-acetate ... 1.6/3.0. Does this density
                              difference make their seperation more evident with VM or does the
                              boiling point spoil this for us ?

                              Grae
                            • Mike Nixon
                              beaui42 wrote: Subject: [Distillers] Vapour Management Head Mike thank for explanation on the VM head physics. My understanding is that a LM seperation is
                              Message 14 of 17 , Jul 5, 2003
                                beaui42 wrote:
                                Subject: [Distillers] Vapour Management Head

                                Mike
                                thank for explanation on the VM head physics.

                                My understanding is that a LM seperation is based (very basically), on temperature.
                                VM contrasts in that seperation relies on both temperature and vapour density.

                                With the VM head there is a marked difference in that the densities of ethanol to aethyl-acetate ... 1.6/3.0. Does this density
                                difference make their seperation more evident with VM or does the boiling point spoil this for us ?

                                Grae
                                ====================
                                Gudday Grae,
                                 
                                Not quite ... both depend on how many cycles of condensation/re-evaporation you get before withdrawing product (I'm talking separation of components now, so may have misread your intent when you use the term 'separation'), the only difference being whether you take liquid that has condensed on the top condenser or tap the vapor stream at the top of the column.  With both LM and VM the temperature at the top of the column will be the same, reflecting the mix you end up with.
                                 
                                I'm afraid that the marked difference in density between ethanol and ethyl acetate doesn't make EA markedly more evident with VM as they both have similar boiling points (1.3C difference).  It is this that matters most in separating EA from eth in the first place, whether you are using LM or VM, and the closeness of the boiling points means you have to go slowly when drawing off heads using either method.

                                Ceers!
                                Mike N
                                 
                              • beaui42
                                ... of ethanol to aethyl-acetate ... 1.6/3.0. Does this density ... boiling point spoil this for us ? ... evaporation you get before withdrawing product (I m
                                Message 15 of 17 , Jul 6, 2003
                                  --- In Distillers@yahoogroups.com, "Mike Nixon" <mike@s...> wrote:
                                  > beaui42 wrote:
                                  > Subject: [Distillers] Vapour Management Head
                                  >
                                  > Mike
                                  > >
                                  > With the VM head there is a marked difference in that the densities
                                  of ethanol to aethyl-acetate ... 1.6/3.0. Does this density
                                  > difference make their seperation more evident with VM or does the
                                  boiling point spoil this for us ?
                                  >
                                  > Grae
                                  > ====================
                                  > Gudday Grae,
                                  >
                                  > Not quite ... both depend on how many cycles of condensation/re-
                                  evaporation you get before withdrawing product (I'm talking
                                  separation of components now, so may have misread your intent when
                                  you use the term 'separation'), the only difference being whether you
                                  take liquid that has condensed on the top condenser or tap the vapor
                                  stream at the top of the column. With both LM and VM the temperature
                                  at the top of the column will be the same, reflecting the mix you end
                                  up with.
                                  >
                                  > I'm afraid that the marked difference in density between ethanol
                                  and ethyl acetate doesn't make EA markedly more evident with VM as
                                  they both have similar boiling points (1.3C difference). It is this
                                  that matters most in separating EA from eth in the first place,
                                  whether you are using LM or VM, and the closeness of the boiling
                                  points means you have to go slowly when drawing off heads using
                                  either method.
                                  >
                                  > Ceers!
                                  > Mike N


                                  Thanks Mike.

                                  Grae
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