hello everybody we're talking in this video about the liquid liquid extraction so it's a new topic and as we usually do we are gonna talk first about the basics of the topic the main points that we need to be aware of this is the theoretical background and then we will move to Microsoft Excel and see how we can use Microsoft Excel as a software that can help us do the calculation easier or get more accurate results and so on so the liquid liquid extraction is mass transfer operation that we use to separate two components from each other and in this case we depend on the solubility of one of the components in another component so we use a solvent and and and with the solvent is mixed with that mixture that contains the component of interest and another component and it has high affinity to this component so it extracts as it dissolves it and then we get the component instead of being in a mixture with the first component to be in a mixture with the solvent so we see here that this is it's not a final stage of separation because the product of this process is a mixture still another mixture of the component of interest with the solvent instead of the component with the initial mixture so that's why we do not usually think of the liquid liquid extraction as a first separation procedure we usually think of distillation because they are - totosai of distillation is usually a pure component or close to pure component because it separates the components in one step or in one process but here we will we will need another separation step to separate the solvent from the component of interest and to recover the solvent that we want and we use I'm sorry and to get the output of our already the component that we are interested in as pure component so we usually think of this process when the distillation is not possible and there are many reasons that makes the distillation not possible first of them if we have dissolved or complex inorganic substance in organic or eco solution in some cases you will have the two components that you want to separate from each other are making a complex which means that they're kind of making a bond that is attaching them together in in this case it's it's not possible to separate them based on the difference in boiling point because they usually behave like a single component with respect to the solution of course in some cases you have a component that is present in a small concentration in this case the distillation would be very very difficult as you all remember in the distillation at the very far end of the e of the mikepsilve diagram you have the operating and equilibrium curves very very close together and in this case you will need a lot of stages to do the separation and to get the component that's present in very small concentrations so the solution is not gonna be economically feasible in this case in some cases you would have higher boiling component that is present in a small quantities and in this case you need to do the the the distillation at very high temperature so you can get that component in enough purity or or good purity that you're looking for if you have a heat sensitive material which is decomposed or break down into small smaller components by heat in this case you need to do the distillation under high vacuum which is very very expensive to do the vacuum and to make the the distillation column from a material with a thick or high enough thickness that withstand this this vacuum which is which is gonna be very very costly process or design if you have clothes melting or close boiling liquids which is not very good to do with the distillation and similarly if you haven't as a trope which is gonna be not possible to do the separation with the distillation so in these cases you would find that it's Laish isn't gonna be either it's not gonna be possible or cannot do the job or it it's gonna be very very expensive so you you go to the other option which is the liquid liquid extract and the liquid liquid extraction goes in two steps the first step is a mixing step so you put your solvent with the mixture that includes the solute that you're interested in and you do the mixing well enough to enable the mass transfer to take take part and in this case you need to make sure that the mixing is good enough so that you get most of the process you get almost all the solid if you can from this liquid mixture to go to this solvent and then you would end up with mixture of two phases which are not actually separated here so you need to go to or remove this mixture into a separating stage in the separation stage you just let these two comport to phases to separate and then you can get this top product it doesn't necessarily need to go to the top but it depends on the the difference in densities but the the solvent with the solute is called extract and then the feed after getting this solute out of it it's called raffinate so these are two terminal or two terms that are very very famous in this process we didn't talk about the solvent and previously so it's it's important to know how to pick a solvent was a very critical point in the in the process the solvent needs to have some properties which are very very essential to make the process successful the first is that the solvent need to be selective meaning that it has to be able or to dissolve the solute and not the other component otherwise it's not gonna be useful because you'll have two components here and then you'll have another component that is miscible with them so you didn't do anything useful now so you have to make sure first that it is selective and it is high it has high affinity to the solute meaning that it dissolves a lot of solvent or solute otherwise you need to use a lot of solvent very very big amount of solvent to dissolve the amount of solute that you are interested in so to be economically feasible you need to have the solvent having high affinity to the solid one other important parameter is that the solvent needs to be it's not cheap but it's not not expensive expensive solvents is not good to use because you pay a lot of money to get this solvent and of course you will have some losses in each run and even after you separate these two together from each other you'll need to recover this solvent and then you need to do some makeup to compensate that loss so getting very expensive solvent is not a sometimes will not make the process even feasible so it's not gonna be worth it and the solvent needs to be safe to work with so it's doesn't it's prefer preferable to be not corrosive not explosive not flammable as much as we can of course sometimes you'll be forced to use a solvent that doesn't match all these criteria but it has to be the very critical criteria is the ease all the the selectivity and the solubility which are very very important and of course the solvent needs to be easily to separate from the solid because this is very very important as well if these two are not easy to separate then the process is all together it is not of any use to us you're just wasting time and instead of having this solute soluble or dissolve it in another component you're dissolving it in a solvent and you're not able to separate them so it's it's not gonna be useful so you need to make sure that these two components have very highly difference in boiling points or any other things that would make the separation easier in the future so let's see how the equipment that do the liquid liquid extraction work so one of them is the mixer settler X attractors and it's used for batch separation you put the feed here which is the feed mixture plus the solvent and you put them in this tank just a very normal mixing tank with an agitator with buffers to increase the turbulence and the Reynolds number and then the mass transfer coefficient increases then the rate of mass transfer increases and then you get an efficient separation and then this is followed by a separation stage that is just an empty tank that lets the two phases separate and then you get their subtract and raffinate from here and this is a similar process it just combines them in one place you have here the mixer and the separator in just one tank but it's exactly the same process with different arrangement for steady state or continuous process you use or reuse other equipment which is for instance the subtraction towers one of them is similar to the distillation column is strake Tower and you have the two components one flow from flowing from up to down through the downcomers and the other is going through the holes of the trace is going from down to up and it's like distillation the flow is as going based on the difference in densities it might be difficult to imagine because in the solution you have liquid and and and gas and in vapor and in this case it's very easy to imagine that the paper is going from down to up and the liquid is going from top to down or from up to down but here it's kind of not very easy to imagine and and here you would see that the the mass transfer actually occurs below the tray it's not above the tray as we do in distillation because of this difference in nature of the two fluids flowing in the distillation in the separation column one other thing is the agitated tower and agitated tower is simply a tower that has a lot of mixers and you force the flow to go here and in this large area it stays here for some time for that it agitators work and do the mixing and the mass transfer takes place and then it goes here down through this narrow flowing area to the second stage and that's what is called the calming section you want to make sure that the fluid will take enough time or the two liquids will take enough time in the baffles or in the agitated area so that it must answer takes place otherwise of this these sections are not put and the flow will go from up to or from top to bottom and from bottom to top without having enough residence time to do the restaurant so this is mainly the the main idea of the liquid liquid extraction we will see in the next video how we do the calculations and how the phase diagram is is used and which phase diagrams to use and how to deal with them so I'll stop here and I'll see you in the next video ciao