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Re: [Distillers] Vapour Management Head

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  • 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 1 of 17 , Jul 2, 2003
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      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 2 of 17 , Jul 2, 2003
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        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 3 of 17 , Jul 2, 2003
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          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 4 of 17 , Jul 2, 2003
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            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 5 of 17 , Jul 2, 2003
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              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 6 of 17 , Jul 2, 2003
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                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


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              • 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 7 of 17 , Jul 2, 2003
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                  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 8 of 17 , Jul 2, 2003
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                    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 9 of 17 , Jul 2, 2003
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                      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 10 of 17 , Jul 4, 2003
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                        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 11 of 17 , Jul 4, 2003
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                          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 12 of 17 , Jul 5, 2003
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                            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 13 of 17 , Jul 5, 2003
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                              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 14 of 17 , Jul 6, 2003
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                                --- 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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