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Module 1: Biomass and Waste

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Energy from Biomass and Waste - Chemical Route

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Hi friends, now we will start discussing on the topic energy production from biomass andwaste part 2 and that is chemical route based processes. So in the part 1, we have discussedhow the biomass and waste can be converted to energy component through biological routes,basically anaerobic digestion, and some specific type of waste we have seen that are most suitablefor that route. Similarly for the chemical route, we will also see that some specifictype of waste and biomass components will be more suitable for the energy production.Some example say some used oil or waste grease or say some oil seeds can also be used forthis process. So what we will see some of the biomass can be directly used for chemicalconversion in which the glycerol or say lipid content is higher or some feedstock can beused to produce the oil or lipid first then to it can be converted to biodiesel. So basicallythe chemical route converts the feedstock, particularly the bio-oil or the lipids tobiodiesel through transesterification.Now we will discuss on this contents that is the chemical route transesterificationwhat is this, then organic waste for transesterification that is what type of waste can be used fortransesterification process and oil seeds to oil production, then need of bio-oil upgradationvia biodiesel production, why we can’t use bio-oil directly that part we will discuss,then biodiesel production from bio-oil through transesterification sort of the routes andthe flow sheets and different prospects and concerns we will discuss,And flow sheet for biodiesel production from various feedstock, and then comparison ofbiodiesel and different bio-oil to justify the need of the biodiesel production.So now we will see what the transesterification process is. We see the term indicates transesterification,so there will be some esters and the alkyl groups of the esters will be changed in thisreaction and one example is the glycerol if we have that is the major component of oil,in the plant oil maybe, say edible and non-edible oil if we have, so it is our oil if we have,this oil we have here CH2OH and CH2H that is the glycerol back bone and this OH is replacedby some organic acids.So 3 different organic acids so that is giving us triglyceride. So this triglyceride is availablein the oil and then that has to be converted to this fatty acid methyl ester that is calledbiodiesel and we will get the glycerol here. So we are getting the glycerol. So triglyceridewill be converted to fatty acid methyl esters and glycerol. So this process is called transesterification.So these R1COOCH2 this group, we are getting this separated R1COO and CH3.So we are getting here R1COOCH3, similarly R2COOCH3, similarly R3COOCH3. So, these arethe different compounds which we are getting, those are the composition of biodiesel, thatis called fatty acid methyl ester and this process is called transesterification process.So, this process will not take place at any condition. So some specific requirement isthere for this reaction. So that is we need some catalyst and we need to add methyl alcohol,so methyl alcohol will give us the methyl group and that will be added with R1COOCH3like this type of esters.So, one esters we had here, we are getting another ester, so that is transesterificationand in this case, during the processes of transesterification, an alcohol such as methanolreacts with the triglyceride oils contained in plant oil, animal fats or recycled greasesto form fatty acid alkyl esters that is biodiesel and glycerin. The reaction requires heat anda strong base catalyst such as sodium hydroxide or potassium hydroxide and the simplifiedchemical reaction is as follows as i have explained.Now, what type of feedstocks will be more suitable for this type of conversion processesthat part we will see. So, we have some organic waste which can go through this transesterificationprocess, may be of waste oil seed, it may have waster oil or cooking oil or we may haverecycled grease. So these 3 major components of the waste which can be processed throughthis route, and if it is waste oil seed, then we have to get the oil first from the oilseeds, then we will get bio oil by oil extraction.Then bio oil or this waste oil or cooking oil and recycled grease, all those intermediateproducts or all the inputs will be converted to biodiesel through the transesterificationand this process is called upgradation of the oil. So, these are the different feedstockswhich can be used or can be upgraded to biodiesel.Now, we will see how this bio oil can be produced from the waste oil seeds. So waste oil seedscan be converted to bio oil through different routes. One is your conventional methods thatis expeller. Expeller that is based on the pressing on the oil seed and extract the oilfrom it and then solvent extractions, so you can use some solvent also, the solvent willtake the oil part and then the residual part will be as a solid and then also will getthe bio oil or some advanced method are there, they are ultrasonic assisted extractions andthen supercritical fluid extractions.So in this solvent extraction, we can use some solvent and then there will be some extractionprocess with maintaining certain condition, and in this case, if we use ultrasonicator,then that will help the release of oil from the oil seeds. So, if we have oil seed say,inside the oil is there. So these oil molecules has to come out. So that can come out if thesurface is dissolved with the solvent or through the pores it made. So then these moleculeswill come out.Now if we use ultrasonification, then helps the extractions of this oil and it will comeeasily, so the extractions becomes easier, that is its called advanced method. Supercriticalextraction is also possible by using some carbon dioxide in supercritical phase thatcan be used to extract the liquid from the outer part of the oil seed to the solvent,that is the supercritical solvent. So, these are different methods, which have been reportedto use for the extraction of the oil from the oil seeds.Now, these are the oil press how it looks like various lab scale and this is your labscale solvent extraction unit, where the oil is extracted from the oil seeds.What are the factors that influence the extraction of the oil from oil seeds are mentioned here,that is type of solvent, what type of solvent we are using, that solvent has to be goodinteraction with the or the mixing capacity with the lipid part or that is the oil partor the oil seed. Then we have to biomass to solvent ratio, obviously, we have to use moresolvent, more will be gradient for the transfer of mass, so more extraction we will get. Thentemperature also influence, the temperature should not be very high.If it is very high, then the solvent can be vaporized, or if it is very less, then alsothe extraction may not be that efficient. Then extraction method, what type of extractionmethod we are using, whether it is mechanical method like expeller or chemical or we aregoing for a extraction method using some solvent. So all those things will influence the efficiency.The extraction time, how much time we are allowing that also influence what amount ofoil is coming, more we get the time, it expected that more oil will come out, and then moisturecontent and there may be some optimum value for the extraction time also.The moisture content that also influences the oil extraction method. The particularsize and shape, obviously that will also provide the surface area for the oil molecules tocome out from it. So, smaller the particles, obviously more will be the extraction. So,these are the factors which influences the overall extraction processes.So now we will compare the different extraction process, which have been used for the productionof bio oil from the oil seeds. So we have oil press, then solvent extraction, then supercriticalfluid extraction, and then ultrasonic assisted extraction. So, all these have some advantageand disadvantage as given here. Then it is very simple to use and no solvent is required,that is the great advantage, but what is the disadvantage large biomass requirements, slow,that means its complete recovery may not be possible, some amount of oil can still beavailable and it is a slow process.Then solvent extraction process, solvent is required which may be expensive, let us sayhexanes, as we have mentioned here the hexanes, n-heptane, etc., so those are expensive solventcan be required. Solvent is recoverable and reproducible, although we are using the expensivesolvent we can recover it, but disadvantage is that large volume of solvent is requiredand expensive solvent recovery. If we want to recover the solvent, then that recoveryalso require some amount of money.So, that is also flammable and toxics, we have to be careful for handling of the solvent.Then is supercritical, then solvent is nontoxic and non flammable, and operation in simple.So that way we are getting advantage replacing the solvent like hexane, n-heptane by thesupercritical carbon dioxide. This also has a limitation that is the extraction of polarcompounds from biomass is difficult and the limited interaction between supercriticalcarbon dioxide and biomass. So, these are the disadvantage of this process.The next is ultrasonic assisted. So then less extraction time as it helps to rupture thewall of the seeds and helps to release the oil molecules from the inner side to the outerside and to the solvent. So less solvent requirement for that reason and good penetration of solventinto cell and more release of cell contents. So, these are the advantage when we use theultrasonic assisted extraction method. This has some difficulty, that they scale up isnot very easy and power requirement is also very high. So these are the advantage anddisadvantage of different types of oil extraction methods from the oil seed.After this extraction of oil, what oil we are getting that contains different typesof lipids as mentioned here, the different types of say lauric acid, myristic acid, palmiticacid, stearic acid, folic acid, linoleic acid, linolenic acid, and arachidonic acid. So,these are the seeds which are normally available in the bio oil, which is produced from theoil seeds and these are the elementary formula and from these formula if we see, most structureof this compound, so that it C12H24O2, so CH3(CH2)10COOH, so there is no unsaturation.For the second myristic also there is no unsaturation, here also no unsaturation, here also no unsaturation.So if we go for these fatty acids, then we are getting unsaturation here. Here so maybeone unsaturation in this case, somewhere it maybe 2 unsaturation also. So that way saturatedand unsaturated both type of acids are available in the bio oil. So these type of fatty acidswill also influence the quality of bio diesel.So then what is the need of this bio oil? Bio oil we are getting just simply extractingthe oil part or lipid part from the oil seed, but what is the need of its upgradation, becauseof its inferior quality. If we see the viscosity of this bio oil is higher, and we need toreduce it for its applications in the engine and the plant oil is much more viscous thanits conventional diesel fuel that is 11 to 17 times thicker than the conventional dieseloil. So, we have to break the viscosity, we have to reduce the viscosity of this.Then plant oil has also very different chemical properties and combustion characteristicsto those of the conventional diesel fuel, so we have to change those properties by theconversion. Then if the fuel is too thick, it will not automize properly. So it willbe difficult to use in the engine or the injectors may get coked up and leading to poor performance,higher exhaust emissions and reduced engine life.In the waste oil or cooking oil or recycle grease, those waste materials lose their fuelproperties basically and we require the recycling and reuse and then conversation is required.Transesterification process basically improves all those qualities and gives an improvedquality to the upgraded product that is called biodiesel. So that is the need of the upgradationof the bio oil and that is done through the transesterification process.Now depending upon the feedstocks also, the process maybe to some extent different, sothat part we are going to discuss and here are the generalized flow sheet for biodieselproduction from various feedstocks. So generalized process if we see, we have some plant oilor so that is vegetable oil we have say or we have say recycle grease. So what is thebasic difference between these 2. So if we think about the vegetable oils, then freefatty acids in these case is less, but we think about the recycle grease, we are havinghigher free fatty acid.So when free fatty acid is available in the feedstock, then if we go for transesterificationprocess, then free fatty acid, they will help to the production of soap, so we have to removethe free fatty acid first. So how will do, we will have to use some alcohol and thenthat will be the H2SO4 will be consumed by that process and then we will go for the transesterificationreaction. So if we take the vegetable oils first, then vegetable oil that is containingtriglycerides, we need one catalyst and we need some alcohol.So alcohol and catalyst, methanol plus KOH or NaOH that is mixed with this vegetableoils. So then maybe vegetable oil or maybe say recycled oil, if recycled oil, then wehave to separate this acid free fatty acids we have to get it free from the free fattyacids in the free state and then that is called dilute acid esterification step, then theproduct from this dilute acid esterification step will come to the transesterificationreaction and then this is after that it is very common to both type of feedstock, butup to this, these two processes are different.When free fatty acids is less, we do not need any dilute acid esterification, but when thefree fatty acid is high, then we need this process. Then when starting from this transesterificationreaction, then we will be getting the product of it, then those products will be havingobviously glycerol, unconverted alcohol, and water also, separation has to be done. So,we will get biodiesel part and another we will get glycerin part, so biodiesel and glycerinpart will separate and biodiesel will also contain alcohol, so will be biodiesel refining.So what alcohol we are getting, it is going back to this and then refined biodiesel willget. Similarly what glycerin we are getting here that crude glycerin. So crude glycerinwill also contain some soap, some alcohol, water, etc., so that refining of the crudeglycerin is also required. So after refining we will get refined glycerin and alcohol partwhich is being recovered that will go to this alcohol recovery sections and will be recycledback, can be used in the transesterification reaction.So, this is the overall flow sheet for the transesterification of vegetable oils or recycledgrease.Now, from this flow sheet, it is very clear to us that it had basic 5 steps. One is acidesterification, then transesterification, methanol recovery, biodiesel refining, andglycerin refining. This acid esterification is also called as pretreatment and this isrequired basically when the free acid content in the feedstock is higher.Then what is the acid esterification and how we will do it. So, free fatty acids in biodieselfeedstock react with alkali catalyst like a NaOH and KOH and from soaps, so which reducethe oil properties of the biodiesel. So, that is the major disadvantage. If free fatty acidis available, then free fatty acid will react with NaOH and it will form soap, which isnot desirable in the biodiesel product. So, triglyceride + free fatty acids + alcoholif we take base catalyst, we will get sodium plus potassium salt or free fatty acids +triglycerides.So, this will be the initial step because the free fatty acids reacts earlier quicklythen the triglyceride. So free fatty acids reacts quickly than the triglycerides, thatis also formations will take place very easily. Then low levels of free fatty acids if available,then this can be managed, say around 4% can be managed. How it can be managed, initiallywe will add some additional NaOH, additional NaOH if it is added, then these reactionswill take fast and the soap formation will not be that very high as the free fatty acidsis less.So that can be manageable to some extent. What will be the alkali content in case ofthree fatty acids, there are some formula. So, these catalyst concentration we have toadd in excess amount and that excess amount is presented here. If we use NaOH, then thatwill be percentage of free fatty acids x 0.144 + 1%. If it is KOH, then it will be percentageof free fatty acids x 0.197/0.86 + 1%. If it is sodium methoxide, then percent of freefatty acid x 0.190 + 0.25%.So, these are the some formula which are available and that can be used for the removal of thosefree fatty acids by these catalyst itself. But when it will be higher than 4%, then wehave to remove the free fatty acids first as the pretreatment state and basically incase of animal fats and recycle grease, we get more than 4% free fatty acids and it requirespretreatment. So the sulfuric acid is dissolved in methanol and then mixed with the pretreatedoil.The mixer is heated and stirred and the free fatty acids are converted to biodiesel. Thatmeans, fatty acid is converted to biodiesel first through the acid catalysis reactions.So, fatty acid is not available as free fatty acids, it is now into glyceride form. So,once the reaction is complete, it is dewatered and fed to the transesterification process,then it is going for the transesterification process as shown in this step.So, what are the alternative methods to remove the free fatty acids or manage the free fattyacids. One we have discussed that we can use some more amount of alkali if it is less than4%, free fatty acid is les s than 4%. Otherwise you can use some enzymatic method okay, enzymaticmethod can convert the free fatty acids into glyceride and then but this is very costlyand not popular choice.So glycerolysis, in this process, glycerol is added, some amount of glycerol is addedand then free fatty acid and glycerol reacts in presence of ZnCl2 catalyst and it is converted,FFA is converted to monoglyceride and diglycerides plus water. So, this is one method which canbe followed to convert the free fatty acids to monoglyceride or diglycerides and thenwater is vented off and it requires high temperature and it is also slow process. Then acid catalysisfollowed by base catalysis.So, if we can use some acid catalyst, then if we use base catalytic reactions for transesterification,then also it can be very good solution. If we use sulfuric acid, then it catalyzes bothesterification and transesterification reactions and esterification of free fatty acid thatis within 1 hour this reaction takes place, but for transesterification it takes 2 daysat 60 degrees centigrade. So, this property we can exploit it. So, within 1 hour the FFAis converted to esters whereas the triglyceride is converted to esters with 2 days of reactions.So, if we have free fatty acids, at the initial stage you can add acid sulfuric acid, so thefree fatty acid should be converted to esters. So when we will be going for transesterificationprocess and use alkali catalyst, then the production of soap will be reduced, the chanceof the soap production will be reduced. So, that is the concept.Then how we know that free fatty acid is available or not or what would be conversion of freefatty acids, how we will determine. So, conversion of free fatty acid is your obviously the initialminus final, so initial - final acid value/initial acid value, so that we can measure. If wecan measure avid value, then you can get the conversion of free fatty acids. So acid valuewe have to measure. So, how we can measure acid value, that can be measured by this expression.So, what we have to do, known amount of sample is added to some amount of neutralized ethanoland is fully dissolved by heating. Then phenolphthalein is used as indicator and the sample is titratedwith standard alkali solution, then how much alkali solution is taking and what is thestrength of the alkali solution that will be used to calculate the acid value as perthis expressions.So S = 56.1 x V x c/m where V is the volume of KOH employed for the titration in mL andthen c is concentration of any solution which we have used in mole/L unit and then S whichwe are getting here that is the mg KOH per gram waste cooking oil. So that way we candetermine the free fatty acids.Then we are coming to transesterification. So after free fatty acids removal or withconversion into esters, we are going for the transesterification reaction, and transesterificationreactions we have explained what reaction is and we see we need some catalyst and basecatalyst is used. So if homogeneous catalyst is used like NaOH or KOH, then it will convertthe triglyceride to methyl esters and then the glycerol, and at the same time if we havesome additional catalyst and even in the stoichiometric ratio also some amount of soap formation willalso take place.So, soap, what is soap, sodium and potassium salt of fatty acids, so, fatty acids whichwill be generated during the process can also react with sodium hydroxide and can be convertedto sodium salt or potassium salt that is called soap. So, efforts are on to replace this homogeneouscatalyst by a heterogeneous one. For example, say if we have sodium hydroxide, so then sodiumhydroxide what it will do, in the immediate it will give sodium plus and OH minus ion.So, this sodium plus is available to be attached with the acid group and then converted tosoap, but if we use calcium oxide as a heterogeneous catalyst, so then it will provide site forthe reaction, but it will not give any calcium two plus ion, it will provide site for thereactions for the conversion of the glyceride to methyl esters, but it will not give Catwo plus, this is not available. So, the salt of fatty acid productions is not possible.So heterogeneous catalyst will be having some advantage that it will not produce soap inthe product which is not desirable, soap is not desirable, it will decrease the qualityof the biodiesel.Now there are many factors which influence the biodiesel production or the performanceof the transesterification process likes the reaction temperature, the reaction time, alcoholto oil mole ratio, how much alcohol we are using that influence it, catalyst concentration,type of catalyst, free fatty acids content, mixing, types of alcohol, water content andcatalyst types. So these are the factors which influence the performance of the transesterificationprocess.Here we will see some example of heterogeneous catalyst. Here we see sunflower, this is yourfeedstock, then solvent methanol used, then we got some catalyst that is strontium oxide,then these are the operating conditions and these are the percentage yield. For soybeanoil, methanol, K2CO3/TiO2 that was the catalyst, and then under these operating conditions,we got this percent of 25.15% of yield, biodiesel yield.Babassu coconut oil, again this is the solvent methanol, for all the cases were having methanolsolvent, and this is another heterogeneous catalyst, again it is having 80% of yield.Waste cooking oil, here also having 92% of yield. So here we see the temperature is different,alcohol to oil ratio is different, catalyst loading is different, and reaction time isdifferent. So all those parameter influence the performance of the process for the yieldof biodiesel production. But in this case, when we use the heterogeneous catalyst, thequality of the biodiesel improves, it does not have any soap in it.Then methanol recovery, so after the transesterification, we are having say one biodiesel stream andanother glycerol stream. So from both the stream, we will be getting methanol, justapplication of heat we will get the methanol early, it will be vaporized fast and by condensationwe will get the methanol recovered. Then biodiesel refining. So once this separated from theglycerin, the biodiesel goes through a series of cleaning up or purification step to removeexcess alcohol, residual catalyst and soaps.These consist of multistage washing with clean water and the product biodiesel is then driedand sent for the storage. It can be further purified through an additional distillationstep to produce a more purified product.Glycerin refining. The glycerin will also have some soap, some catalyst, some waterand some alcohol. So, there will be a series of preparation steps or the cleaning steps.So the water and alcohol are also removed to produce 50 to 80% crude glycerin. The remainingconstituents include untreated fat and oils. In the large biodiesel plants, glycerin canbe further purified through a series of unit operations to produce product of 99% purityand the purified product is suitable for use in pharmaceuticals and cosmetic use and manyother applications also.Now, we will see the comparison of these biodiesel which is produced from the bio oil throughthis transesterification route with some bio oil, so here the properties kinematic viscosity,cetane number, heating value, cloud point, pour point, flash point, density all are fuelproperties. We see here this is the standard diesel, this is the biodiesel from Babassusoil and this is Babassu oil, this is your soybean oil and biodiesel from soybean oil.So, if we have 32.6 millimeter square per second kinematic viscosity, it is reducedto 4.5 for this case, here 30.3 to 3.6, at the diesel is having 3.06. So by this conversion,we are able to make the oil to biodiesel with almost similar viscosity or slightly higherviscosity while the other case in the original bio oil the viscosity was very very high.Similarly, the cetane number is also increased for these biodiesel productions, here 37 to40 and 30 to 63 and these values are very comparable to 50.Heating value also, this is a high but heating values all these biodiesel is not high, becauseyou know we have high content of oxygen in these biodiesel with respect to petrol diesel.So the heating value is less. Other properties are also very comparable. So, here also thedensity also you see, the density of biodiesel this much, so soybean oil is having high density,after this conversions, the density reduced, here also density reduced and this densityand this density are very near to the biodiesel.So that way, the bio oil quality is improved and can be used as a biodiesel. So this isthe chemical route through which waste and biomass can be converted to 2 different fuelcomponents. So thank you very much for patience.