 Now, I am talking about azeotrop ok. Suppose your formation of azeotrop will the residue curve map change. Now, in macaphthyl method ok, in macaphthyl method y versus x really is this right no azeotrop for ideal system or non azeotropic system for that matter. So, this is the region in which I can move right depending on the reflux ratio and I can go from x B to x D right that means, from pure component B to pure component A right. So, that movement is possible there is no restriction ok, there is no boundary whereas, when I have formation of azeotrop minimum boiling azeotrop can be maximum also. What happens? I cannot move from x B to x D or I can go from pure component B to pure component A right my movement is restricted. So, I have this as my feasible region if I want to move in this part of the composition space or this right I cannot go from this to this. So, there is a boundary ok. Now, in ternary system there is no azeotrop there is no azeotrop I can go from this point to this point ok. So, I have residue curves going from the most volatile component to the least volatile component no boundary right there is no boundary. Suppose, your formation of azeotrop now let us consider only one azeotrop one binary azeotrop this is your A, this is your B, this is your C right. A is the most volatile B is the intermediate boiling C is the least volatile ok. Now, I say I have one azeotrop here a binary azeotrop between B and C ok. Now, suppose A boils at 30 degree centigrade, B boils at 50 degree centigrade, C boils at 70 degree centigrade ok and these are the boiling points of these components ok. Now, I say I have azeotrop between B and C which is a minimum boiling azeotrop ok which boils at say 40 degree centigrade because the boiling point should be less than these two right a minimum boiling azeotrop and its composition is here say 50-50 percent ok, but this boiling point is greater than this right. Now, I want to plot a residue curve map for this particular system and this map is going to be different from the ideal system because we will see that it may not be possible to go everywhere in the triangle in the composition space if I start from any point. See here there is no restriction you can move anywhere. Now, let us see what happens ok, how will the residue curve map behave in this case ok. For example, suppose I start with this composition say mixture of B and C and just boil it residue curve I want to plot residue curve. In which direction will I move? Suppose I start from this point I will go up or down. Down. Down because see the temperature see the residue temperature is going to increase with respect to time right. Here you have a temperature 40 do not look at this temperature ok this point the temperature is 40. So, with respect to time ok the temperature is going to increase. So, I will move up right I will move towards B ok right slightly unusual right you starting with mixture of B and C ok B and C C is the less volatile component high boiling ok and B is more volatile component, but then when I start boiling I am starting with this composition what happens? At the end I will be left with B and not C even if C is the less volatile component right why? Right let us write let us write ok. So, it means that C even if C as such is less volatile as such in pure form it is less volatile as per its boiling point in the presence of B it becomes volatile its excrept tendency increases because of as your drop ok and goes out. If you do material balance since you are starting with large amount of B compared to C all C goes away and in the residue you have pure B right ok. What if I start with this particular point in which direction will I go towards B or C? C. C why again follow temperature right because now even if I start with BC mixture C goes away, but initially itself I have large amount of C present. So, I will be left with C material balance right. This is your behavior start with binary system ok. What about this mixture where will I go? C right what about this B ok. Now I just start started with binaries now let us look at what happens if I am starting with a ternary mixture ok. I am starting with a ternary mixture. Suppose you are here right you will have a residue curve which will go to the stable point C right. If you extend it in backward direction it will go to the unstable point A right ok. Now suppose you are here where will you go? Will you go to C? See you are very close to this binary edge. This binary edge tells me this binary edge tells me that I should move towards B. Look at these two arrows they both are pointing towards B. So, B is going to be a stable point now. B is going to be a stable point compare it with this. Here these arrows one arrow was going towards B and one arrow was moving away from B right. So, B was not stable B was saddle. Here both the arrows are going towards B. B is going to be stable. Now what happens to this particular point like if I start with this as starting mixture ok start boiling it residue composition ok which direction will it go? It will move in B direction. So, you have a residue curve like this it will go and stop there because I started with very small amount of C present. See here right I have large amount of B present. So, I am going towards B here. So, what does that mean? It means that if I start with this composition the stable point is C. If I start with this composition stable point is B right. That means unlike this particular case where irrespective of where I start I get C at the end. Whereas in this case if you start in this region you get C, you start in this region you get B right. That means there is a boundary that two different regions ok. If I join this line right any point above this line right any point above this line if I start with that composition I get B as a stable point any point below this line. If I start with that composition I get C as a stable point. So, at two different distillation regions ok and because of that you have this particular behavior ok where I cannot cross the boundary right. Now, I have just drawn a straight line it need not be a straight line it all depends on how the residue curves moves here. But most of the times most of the times the boundary is linear ok. This is no basic condition why it should be linear, but it is observed that most of the systems the boundary is linear. But some systems may be a curve right. So, if you are in this region stable point is B you are in this region stable point is C. That means I have got two different regions and because of this is because of the aziotraw right. What is the difference between this system and this system? Just the formation of aziotraw between B and C that has that is responsible for creating boundary in the distillation region or other composition space ok. And I have two different regions I hope it is clear ok. So, let us go ahead what is its significance? How does it affect or influence my methodology as far as conceptual design is concerned? So, I have a residue curve map and in this case I have a boundary right. This boundary is similar to this ok. Here since it was binary system I was plotting y versus x right. But then the meaning is saying I am not able to cross. In this case also I am not able to cross this boundary. A residue curve map starting from a point in this region or residue curve starting from point in this region cannot cross this boundary and go here right ok. If the residue curve this is very important. If the residue curve cannot cross then the column profile cannot cross why? Because residue curve is the behavior obtained under extreme conditions the best possible conditions at infinite reflux ratio large number of stages. If the residue curve cannot cross then even column cannot take you from this region to this region right. See that is a reason I spent some time correlating residue curve with column profiles right. Residue curve is something that is obtained under best possible conditions inside a column right as far as this diagram is concerned x a versus x b right. And suppose you have boundary where residue curve is not able to go from one region to another region a column also cannot take you from one region to another region right. That means that means I cannot have my x d here in this region and I cannot have my x b here or other way round I cannot have my x d here and I cannot have my x b here at a time. So, this is not possible this is not possible is that clear? The end compositions of a distillation column should not be sitting in two different regions of residue curve map. This is a very important information vital information that helps us do further analysis and it is quite similar to what we have learned here. Here two regions I cannot have my x d here and x b here at a time right. Similarly I cannot have my x d here and x b here or other way round at a time. So, if I have my x d here my x b should be in this region somewhere right. You have your x d here then you should have x b here somewhere depending on where your x f is should be on the straight line ok. Suppose my x f is here and if I join this this is my straight line this is my x b this is my x f alright. My x b will be can I have my x b here? I cannot have my x b there because distillation is not able to cross the boundary even in the material balance is valid ok. So, my x b can be only in this particular region before the line crosses the boundary right. So, this can be my x b right that is the meaning of it. If it is a maximum boiling as your drop how will the residue curve map behave or how will it look? Can you do it ok because we have done it for minimum boiling ok. The same procedure we can follow it ok. Just draw the arrows on the binary edges first ok. This is your maximum boiling as your drop 30 degree centigrade 50 70 and maximum say you have 90 degree centigrade which should be higher than these two right. So, if you start with this point instead of going in this direction I will go in this direction towards the higher temperature right. Similarly, if I start with this point instead of going to this point now I will move to this point right ok. Now, this point becomes as far as this binary edge is concerned this point becomes a stable point right ok. So, let us see for this binary edge I will move in this direction right 30 and 70 towards the higher temperature then on this binary edge 30 and 50 I will move in this direction ok. Now, look at these points in the earlier case these two points were stable points because both the arrows were going towards this point right, but now in this case look at what is happening at first this point is concerned one arrow is going towards it one is going away from it what does it mean it is saddle, one arrow is going towards it and one is going away right that is saddle both the arrows are going towards it it is stable point right. So, this is a saddle now see stability is changed earlier it was stable point now it is a saddle similarly here ok one arrow is going towards it one is going away from it right. So, this again is saddle right ok inside see then I have to just follow this I will just go close to this it is going to follow see it will be one residue curve like this and so on right. Similarly, you will have one residue curve going this way ok. So, best way to plot residue curve map using just boiling point information is first do it for binaries and slowly go inside a triangle and just follow the binaries ok. How many stable points you have here in this diagram two stable points there is only one stable point no because all the residue curves are meeting this point right. So, this maximum boiling as your top is the stable point in the earlier case I had two stable points right in this case I have just one stable point. How many unstable points you have here only one unstable I am not asking saddle then unstable only one unstable point in earlier case you had how many unstable points. One unstable points. Yeah right one side yeah in earlier case you had one unstable and two stable points in this case you have one unstable and one stable right ok. Shall I take the earlier case and I will just draw the earlier case again here. In earlier case this is case one this is case two in earlier case I had this as unstable point in this case also had this as unstable point in earlier case since you had two regions at this as a stable point this has a stable point here two stable points. So, one unstable node two stable nodes in this case I have one unstable node how many stable one stable node right see the difference saddles in this case how many saddles you had one where is that as your draw right. So, this is the saddle look at this you have one arrow going towards it and two going away from it right. So, this is saddle right this is a saddle. So, one saddle ok what is happening here how many saddles two saddles total should be four why total should be four always in this case why three pure components how many nodes see terminal system minimum three nodes pure components and depending on how many azeotropes you have the additional nodes right in this case both the cases rather you have only one azeotrop. So, the total is four, but stability is changing depending on whether the azeotropes maximum boiling or minimum boiling right whether the azeotropes maximum boiling or minimum boiling in the cap field you have ideal system how many stable how many unstable how many unstable. One stable or unstable that is right see two pure components two components pure components two nodes ideal system or non azeotropic system you have one unstable one stable right azeotropic system how many nodes total three right three how many stable how many unstable is a minimum boiling azeotrop is a minimum boiling azeotrop how many unstable two unstable yeah one unstable which is a minimum boiling okay the minimum boiling unstable and two stable what does it mean stable node in a column where will you realize a stable node in the bottom or top yeah in this case unstable node is this and stable are these two okay these are stable nodes oh sorry down is one unstable and one stable sorry one stable one unstable okay there are two nodes one stable one unstable here the three nodes okay one unstable and two stable you have unstable node and stable node okay now in the column will you realize stable node in the top or will you realize a stable node composition in the top can you get C in the top C is stable node in ideal system C is stable can you realize at the top no right distillate composition will be close to unstable node right okay the bottom composition will be close to stable node right so in this case this is my unstable node if I start distillation here with this feed I will realize this at the top the minimum boiling azeotrop will always come at the top but if I start with this composition what is the top composition okay azeotrop only okay because it is unstable node if you are in this region the top composition is this and not this okay because you really curve is opposite okay the volatility is changing right okay so unstable node would be always at the top and stable will be at the bottom now based on this information can you say how many regions are there if I tell you that I have these many stable nodes these many unstable nodes and these many saddles okay I give this information for a given system I tell you about the nodes how many nodes I have and their stability okay how many say saddles how many unstable nodes how many stable nodes if I give you this information can you tell me how many regions are there how many regions are there I don't need to really plot a residue curve map see all the examples that we have considered here okay based on this I can come up with some rule right saying how many regions are there if I know the number of nodes and their stability look at this case one stable sorry one unstable one stable how many region how many regions just one just one you have one unstable two stable that means there are two regions what is so particular about this if I look at number of pairs available of stable and unstable okay how many pairs two pairs right two pairs one unstable node is common okay in two pairs so that two pairs right there are two pairs so two zones okay two zones in ideal ternary how many unstable one unstable one stable one saddle right how many pairs of stable and unstable one pair right one pair so how many regions just one region what about this how many pairs let's look at this first how many pairs two pairs because one unstable node is common okay so two pairs okay right so two zones two zones in this case you have two zones in this case how many zones if you go by pairs then how many zones just one zone one pair so one zone of course a very peculiar residue curve map where if you just look at this I tend to think that this is a boundary okay because there is no residue curve going from this region to this region right okay a very peculiar RCM or residue curve map where I tend to believe or tend to think that there is a boundary there okay but then this is not a real boundary I can break this boundary we will come to that later okay as per this analysis there is only one pair okay that means that there is only one zone okay that means I can have a distillation column okay which can of which the profile can cross this boundary okay we will come to that later but in this case since I have two regions okay or two zones right I have a boundary present right I can't cross this let's look at another case let's look at another case where I have a B C okay and I have a minimum boiling as your drop between A and C okay I have a minimum boiling as your drop between A and C a minimum boiling as your drop so say 30 50 70 and minimum boiling okay 25 okay 25 alright can you draw RCM for this just look at a binary edges first okay you will get the answer how many stable nodes how many unstable nodes okay so I have one answer which says one unstable one saddle and two stable and one answer saying two unstable one saddle and one stable is any other answer okay I will look at a binary edges where should I draw the arrow towards A or as your drop A here C here towards B to C here A to A to B right okay so look at the points no pure points one arrow is going towards it one is going away from it saddle or stable unstable unstable one is going towards it no and one is going away from it saddle right okay so this is saddle right one saddle I have identified what about this one arrow is going towards it one is going away from it okay second saddle what about this stable both the arrows are going towards it okay so one stable I have identified what about this point yeah so both the arrows are going away from it so so two saddles one stable node and one unstable node okay two saddles one unstable and one stable can I draw the RCM see I will just follow this look at this I am going in this direction then here then here and then right and I have to just do this this is my RCM this is my residue curve map okay for this system how many zones or how many regions is there boundary simple no let first look at the pairs only one pair no boundary there is no boundary I hope this is correct or this is clear rather you can formulate your own problem okay like I say I have azeotrope here okay I can have minimum boiling azeotrope at the center okay ternary azeotrope okay you can you can do it on your own okay like for example okay I will go fast I have azeotropes like they have four azeotropes okay all are minimum boiling all are minimum boiling okay now let us not spend time in this I will draw RCM for you okay minimum boiling this is the minimum of minimum okay right alright so this is 30 this is 50 this is 70 now this is 25 this is 20 this is 40 and this is 10 okay right a residue curve map for this would be like this the point in the center is unstable so how many unstable point one okay these are all saddles now three saddles and three three stable points three stable points okay so how many regions now how many pairs one unstable three stable so three pairs so three zones one two and three right they are all minimum boiling what if this is maximum two are minimum again our same will change okay what if two are maximum one is minimum okay what if this is maximum and rest all are minimum there are many possibilities accordingly RCM will change and we do not have any control over VLE okay basically the compounds they decide how to interact and off right depending on their structures so we have to just accept it and design our system accordingly okay so there are many such possibilities okay in fact most of them have we have seen this is the one that we looked at in the last diagram okay see you have a boundary you have one stable you have one unstable this is sorry two stables and one unstable right the one that we looked at now this is something that we are not seen okay you may have azeotrop between A and B which is a minimum boiling azeotrop okay so this becomes unstable point and you have this residue curve map now in this case in this case again probably the convention is different see A is the stable point but it is quite similar to what we have seen just now the formation of azeotrop between A and C which is a minimum boiling azeotrop okay A is highest boiling so it goes this way exactly opposite to what we have seen just now okay because in that case C is the stable point in this case A becomes a stable point depending on its boiling point okay so I am just not following our regular convention here okay so there are many possibilities I have just shown some representative RCMs okay or the RCMs which we come across most of the times right and there are some features of every RCM so if you just look at RCM you should be able to know what kind of system is this okay and later on depending on RCM I should be able to come up or work out a column sequence for azeotropic distillation extractive distillation and all that that is the purpose okay that is the purpose now let us read these comments of nodes rather node okay only case one that is this case out of these three has distillation boundary and two regions you know the reason okay because the two pairs okay I have I see the distillation boundary number of regions is equal to number of pairs of unstable and stable nodes okay in case two and three two and three azeotrop can be broken by synthesizing a proper column sequence and we are going to see that now okay now for example see what is the typical problem in industry I have azeotrop you look at that particular experiment okay ethanol water azeotrop okay I want to break that azeotrop and get both components in pure form can I use the RCM to design or synthesize the column sequence okay to get pure A and pure B which are forming azeotrop right we will see this okay so RCMs can be used to break the azeotrop for example I have this azeotrop can I break this azeotrop and get pure A and C by using B as entrainer okay because when I use B as entrainer okay I have a terminal system so any azeotropic or extractive distillation most of the times there is very special cases where you have binary azeotropic distillation but most of the times since you add the third component okay minimum you have three components in the system okay so it becomes multi component system so problem is like this I have azeotrop between A and C this is my azeotrop can I use B as entrainer to break this azeotrop and get pure A and pure C okay now when I say can I use B means what when I select B the RCM gets fixed automatically okay because it is the characteristic of the components okay right it is it depends on the thermodynamics of the system so A and B are given to you for example say ethanol water okay can I add B now B is such that the RCM of the ternary system is like this so can I add B to break this azeotrop that is the answer I want and we are going to see whether I can add B and get a separation okay similarly here I have this azeotrop A and B can I add C okay so that you have the RCM for the ternary system like this which breaks this azeotrop and gives you A and B and read this particular note the case 3 that means this particular RCM okay is a very typical case okay of traditional extractive distillation okay the entrainer C is the least volatile okay you remember extractive distillation what do you do in extractive distillation you have mixture right you add third component now third component may not form azeotrop that is what I told you okay when we define very first lecture the third component that I add in extractive distillation may not form azeotrop with either A or B same is happening here I am adding the third component C it is not forming azeotrop with B it is not forming azeotrop with A but the third component changes your vapour equilibrium favorably in such a way that it helps the separation or breakage of this azeotrop okay an example is again ethanol water and C is ethylene glycol extractive distillation to break the azeotrop of ethanol water okay using ethylene glycol as entrainer okay most of the times this is the least volatile you can see this is stable point highest boiling C right so what do you do you add it at the top you have mixture azeotrop going in the ball in the column the bottom you get one of these components in pure form and next column you separate other component okay you are going to see the sequence right okay so basically now these RCMs are used to design or synthesize a sequence for azeotropic distillation or extractive distillation okay so I am slowly coming to the feasibility aspect or designing sequence for or synthesizing the sequence for azeotropic and extractive distillation okay right now let us consider this particular case right we go back to this problem I have this mixture A and C formation of azeotrop this is my feed this is my feed and can I use B to separate or break this azeotrop and get pure A and B okay so let us solve this problem this is my azeotrop right the minimum boiling azeotrop and I will go back to my old convention where C is the least volatile and we have it earlier RCM okay instead of going in this direction I am just going in the direction of C because C is the least volatile component the problem is you have this as a feed this mixture is given to you and you you are supposed to get pure A and B now B is not in picture see the B is not in picture initially the mixture given to you is azeotrop okay azeotrop now I want to break that azeotrop and get A and B now suppose I just give this azeotrop to a distillation column A C azeotrop what will happen what will happen nothing will happen azeotrop okay you will get azeotrop at the top you will get azeotrop at the bottom right so I cannot cannot help it okay I cannot really do simple distillation to break the azeotrop right that is why I use third component so the question now is can I use B which gives me this RCM right to break this azeotrop okay so that is the question now that means I am going to add B in the system I have this as a feed okay I have this as a feed there are no boundaries in RCM I am going to use this RCM to synthesize the column sequence separate A and C from from the feed which is azeotropic composition right if I add B in the system the overall composition would be now I have A C azeotrop point is here I am going to add B in this I am going to add B what is the resultant composition where will be in the triangle the resultant composition towards BS fine but towards B means where here here here can you be more specific yeah see I have this as a feed I have gone adding B so I will go in this direction right I will go in this direction but where it will be on the straight line joining right again never rule material balance right I have two different compositions if I mix these two compositions the resultant would be on this line somewhere okay so this resultant composition here would be on the line joining azeotropic composition and B right so you are somewhere here so let us say I add B such that the resultant is here if I add more B resultant will move in this direction right towards B but I add in such a proportion that the resultant feed is here okay right and this feed is going to go to a column right okay now in the column I need to identify the end compositions what will come from the top and what will come from the bottom okay you have choice now you have choice look at the stable loads or unstable loads because I want to identify top and bottom compositions right now in this case which is a stable node this is your stable node this is your unstable node so I cannot really design a column to get unstable node at the top why why should I do that because this is azeotrope in fact I want to break that azeotrope right so I will design a column such that I get stable node at the bottom right stable node at the bottom so C right so I get your C at the bottom is it possible it is possible why why is it possible because there is a residue curve which can take me from this point to C there is no boundary there is no boundary okay if residue curve can take me that means I can design a column okay reflux ratio might be high it doesn't matter okay but at least feasibility is not an issue okay if reflux if your residue curve takes you from this composition to this composition that means okay I don't have problem I can design a column and get pure C there is no boundary in between okay I don't have to really worry about okay so I can get pure C from the bottom now what is the top composition a a b okay a b where on that line joining a b right can you identify a top composition if I have a perfect column with sharp split it is a continuous system okay this is a continuous system if you say that a remains in the column and doesn't have outlet then that is not correct right I am feeding a to the system a should come out so if pure C is coming from the bottom from the top you have mixture of a b look at this diagram and we know okay top bottom compositions and feed composition they are on the same line now for this column this is your feed composition I have already identified the bottom composition the top composition would be where leave a rule I just joined this line and it will be here it can be here it can be here it can be here depending on how many stages I provide in the column how good is my separation okay but I say okay I provide sufficient number of stages I have large reflux ratio the column is good enough to do maximum possible separation a sharp split so I go very close to this particular age right and this is my top composition right so this is a b and not just a b it is with this particular composition right all right so with the help of b I am able to separate C in pure form right that is what I wanted right now I want pure a what will I do next column with the ternary system I need two columns minimum to separate all three components in pure form or at least two next column okay what do you have here this is your feed a binary system what do you get at the bottom and what do you get at the top a will be is that right look at the arrow b stable now on the binary edge stable point is in the bottom and you have a here right okay in order to complete the system now this b and this be the same these compositions are same what will I do I will provide a recycle so what did I do here I have used the residue curve map okay to design or synthesize a column sequence to break the azeotrop ac with the help of b right okay so this is what is very important for azeotropic systems now how many stages your column will have what will be the reflux ratio you can go back to your calculations what did we do there calculate minimum reflux ratio okay we did the same thing can be repeated here okay draw rectifying section profile draw stripping section profile okay see when the feed pinch of one of the sections okay overlaps on the other that is your minimum reflux ratio go by 1.4 or 1.5 times minimum reflux ratio and calculate actual number of stages so that calculation is not going to change okay but formation of azeotrop has helped me in designing or synthesizing the column sequence which is very important there is no other systematic method to do this right for that you need to take help of residue curve map okay where did I use the information of residue curve map what does residue curve map tell me these arrows would tell me what is the bottom composition what is the top composition the arrows have helped me this these arrows were not there this is not possible right the fact that there is no boundary here also lets me another fact that there is no boundary here helps me to design the sequence if there was a boundary here then I shouldn't have said that C is the bottom composition right okay