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Module 1: Petroleum Products

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Conversion of Intermediate Products

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Hi friends now we will discuss on the topic conversion of intermediate products.So, in the previous class we have discussed on the petroleum crude its properties andcharacteristics then how we can produce different liquid products from the petroleum crude ina refinery and we have seen that different liquid products like naphtha, gasoline, kerosene,ATF and diesel or vacuum residue or atmospheric residue we get.So, these products have different applications and requirement of these products may changefrom time to time.So, to meet the requirement in the market the refinery needs to convert these productsfrom one form to other form as per the requirement of the market as well as to maintain the qualityof the product and environmental requirement also.So, this conversion processes we will discuss in this class and the contents are need ofconversion of intermediate products then major conversion routes there are basically twomajor routes one is carbon rejection and another hydrogen addition.And other routes are also we will discuss that is reforming, isomerisation, alkylation,polymerization and blending.The need of the conversion already we have discussed that we need to meet the marketrequirement so one product to other product conversion is necessary.And also to improve the product quality I will give some examples that how the somespecific property of that particular fuel oil or that particular liquid oil can be improvedby these conversion methods.And already have discussed meet the market requirement of different products and thenachieve environmental standards.Now we will discuss the carbon rejection routes that is basically cracking it takes placein presence of catalyst or in absence of catalyst.So, the cracking means the application of heat to crack the bigger molecules of hydrocarbonsinto the smaller part smaller ones.So, the liquid fractions or we can get more amounts of liquid lighter liquids and thatis the main objective of the cracking.And if we apply catalyst then the requirement, the process requirements the high temperatureis reduced to some extent.So, we have two types of cracking one is thermal cracking another is catalytic cracking andthe thermal cracking temperature is around say 500 to 700 degree centigrade and pressureis around 70 atmosphere.However if we use catalyst then the temperature may be 475 to 530 degree centigrade and pressurerequirement is also less that is 20 atmosphere.If we apply this cracking process may be in thermal or may be in catalytic path.So, the higher hydrocarbons will be converted to lower one.And the two processes having different mechanism of this conversion so one the thermal routethat follows the free radical mechanism where as the catalytic route follows the carbo-cation,productions are carbenium and and carbonium ion productions so there are two CR5+ or CR3+that is carbonium and carbenium ion respectively.So, the mechanism is different and requirement of energy is also less for the catalytic routethat is why it can take place at lower temperature.Now we will see the catalytic route that is fluidized fluid catalytic cracking.So, when catalyst is used in a fluidised bed and then feed is fed through this reactor.So, this is the riser part of the reactor and this reactor here the catalyst is comingas a recycle.So, this catalyst and the feed is reacting here and then we are getting the product therethat side.And this catalyst after use in the reactor is coming to the regeneration part.And then after regeneration it is again recycle so this is a closed circuit and where thecatalyst and fuel is coming in contact and giving us the required product.So, this is our one fuel say which is having less requirement in market.So, you want to convert into other fuel where will be having more requirements.So, this is the concept of the process or this is the descriptions of the FCC processand now what can be the feedstock we can use.In this process different types of feedstocks have been used like say a vacuum gas oil,hydro treated VGO or vacuum gas oil, hydro cracker bottom then coker gas oil De-asphaltedoil, reduced crude oil and vacuum residue so any one of these feedstocks can be processedthrough this so that we can achieve more valuable products from this.So, what are some examples of these products are say dry gas, we can have LPG, we can havelight cracked naphtha.We can have heavy cracked naphtha we can have light cycle oil and clarified oil.So, this naphtha when the naphtha requirement and LPG requirement is high in that case wecan explain the conversion in terms of this that feed how much feed you have taken minusthis part.Then remaining part is here so divided into 100 divided by feed.So, this is the conversion of this process.Now we will see the typical conditions under which this FCC reaction takes place.So, here if we consider here, so obviously catalyst and feed is coming in contact withit so what is the ratio of catalyst and feed I am giving that is important.What is the temperature we are maintaining here so here again riser is there so at whattemperature the regeneration of the catalyst is taking place that will also influence thedegree of regeneration of the catalyst as a whole the performance of the process, whattype of feed we are using that will also influence this one.So, we will see catalyst to oil ratio there are Indian and foreign units FCC units arethere typical properties are shown here that is catalyst to oil ratio 7 to 9 for foreignunit and 5 to 9 Indian unit say reactor riser temperature that is 540 and is a 490 to 510reactor contact time there is also very important there is 1 to 8 second here 1.5 to 3 second.Feed-end point then that means what type of heat we are using it is 600 to 621 here 540to 560.Regeneration temperature that is related with the catalyst here it is 700 to 750 here 640to 730 and then carbon on regenerated catalyst.So, what is the extent of the regeneration of the catalyst that is the indicator of thecarbon deposited on it and then this is for foreign units this 0.05 to 0.1 and this is.3 to .6 or .01 to .02 regeneration regenerated pressure that is 1.75 kg per centimetre squarehere it is 3 kg per centimetre square.So, these are the comparison of two FCC units which is in India and in foreign.Now we will see the reaction mechanism and how the cracking takes place when we choosethe FCC process.So, in this case there are number of steps the first is initiation the first initiationtakes place then is propagation then it is cracking and then we go for isomerisationand cyclization.So, we will see how the cracking reaction initiates.So, we have one hydrocarbon say and then we have catalyst so protonation can take placewith this hydrocarbon so 1 H+ from this is coming here and being added to this CH sothis CH+.So then another process may be possible this may be catalyst so that will take 1 hydrogenfrom this so R 1 CH 2 CH+ and then we are getting here R2, so this way hydrogen thatis protonation or hydrogen abstraction takes place that is the initiation.So, we are getting now the carbocation so that carbocation will react with another hydrocarbonand then there will be some hydride transfer.So, this is called propagation step.So here we had plus charge and another hydrocarbon so this charge has shifted here and now weare getting this one n-R 2 another hydrocarbon and this charge is shifted to this one sothat is why this is called hydride transfer.So, 1 hydrocarbon to other hydrocarbon it is transferred.And then cracking step so we are getting this one, this carbocation there will be some crackingin this chain so beta scission it is called.So, beta position see if we have a positive charge here so these positions will be crackedso we are getting R 3+ and then CH 2 CH and R 4 so this will be there some double bondand then R 3 will be separated as R 3+ and then we are getting this other product.So, this is called a cracking step so we are getting a smaller hydrocarbon now from a biggerone.So, that is desirable to improve the quality.And now the carbocations which is produced here what type of carbocation so we are discussinghere that this hydrogen transfer takes place from one to other hydrocarbon.So if it is more stable the carbocation is more stable, so this one and this one outof these two which one is more stable? this one or this one this one we have to decideand if you can decide then we can we can predict that this conversion will take place or maynot take place.So, it has been seen that if this carbocation is tertiary in nature it may be in secondaryor maybe in primary in nature.So, it is shown that the tertiary has more stability than secondary and then primary.So, that way product nature will also change.Then isomerisation may also take place so we have on secondary carbenium ion in thiscase.So, there may be some isomerisation so this H + some you see so R CH 2 and C+ CH 3 CH3 so this can also take place that is called tertiary carbonium ion, so secondary to tertiaryformation can also take place and then cyclisation, some cyclization reactions can also take placein this process so as shown here this is our hydrocarbon so this is converted to cyclicform.This is also 2 hydrocarbons they can make this one okay so that way the cyclizationreaction can takes place and alkylation, condensation, polymerization can also take place alkylationmay take place condensation may take place and polymerization may take place.So, these are the different type of reactions which can take place during FCC process.Now what are the factors that influence the FCC performance?Already we have mentioned some of those that is a feed rate, those are the independentparameters on which it depends the feed rate then recycle ratio, feed preheat, riser toptemperature, reactor pressure and press catalyst activity that what is the extent of regenerationof the catalyst and then fresh catalyst selectivity also the how selectivity so that we can geta particular product in higher extent.And some dependent variables are also there that is regenerated temperature then catalystcirculation rate then regenerator airflow, coke on regenerated catalyst and product yield.Now we will see other type of cracking in which hydrogen is added so if we add hydrogenthen we will be getting more liquid and at the same time we will be able to remove somesulphur nitrogen etcetera.So, that is the advantage of this hydro cracking reactions and we see different types of feedsare also used for this process and different products can also be achieved.So, some examples are straight run gas oil.So, gas oil which is produced directly through the fractionation in atmospheric distillationso that is that can be used vacuum gas oil which is obtained from the vacuum distillationcolumn that can also be used cycle oil, coker gas oil, thermally cracked stocks and solventdeasphalted residual oils.So, after solvent is deasphalted then what liquid we get that can also be used for hydrocracking and then straight run naphthas and cracked naphthas.So those are the feedstocks for this hydrocracking process and some products are liquefied petroleumgas LPG, motor gasoline, reformer feeds, ATF, diesel fuels, heating oil solvent and thinners,lube oils and petrochemical feedstocks.So, once we are getting naphtha will be the naphtha is converted to petrochemical feedstocksso that is the use of this.And we will see the chemistry of this hydrocracking process so like FCC process here also differenttypes of reactions can take place.And obviously hydrogen addition is taking place here so we will get we will get somehydrogen analysis.So, we will be adding hydrogen that hydrogen will break the structure here say benzothiopheneso due to the addition of hydrogen this structure will be converted this is broken here so lysesis taking place.So that is hydrogenolysis due to the addition of hydrogen we are getting some lyses is inthe structure the organic compound and then similarly quinoline and this one then hydrogenationsay poly aromatics hydrogenation so we have one naphthalene.So, if we add hydrogen so this unsaturation will be removed so in one ring it is shownand in this second step again the both the rings unsaturation is removed.So that way hydrogenation can takes place or hydro dealkylation can take place hydrodealkylation can take place here say this is your one aromatic hydrocarbon we are addinghydrogen so then we are getting hydrogen addition here plus dealkylation.Alkylation dealkylation also taking place alkyl group is removed from this ring so thattype of reaction can also place.Another example is here only dealkylation has take place.And then hydro decyclisation see if we have this type of compound if we add hydrogen thende cyclization this is a cyclic compound due to this there will be some cracking and thenhydrogen addition.So, these two different compounds we are getting here which is not having cyclic structureso here decalin, hydrogen it gives this type.So, these are some typical examples and numbers of reactions are may be possible during thereaction conditions.And then hydro cracking can take place so this is a cracking bigger molecule so it isconverted to smaller one.Hydro isomerisation some isomerisation can also take place so this is one hydrocarbonthis can be converted to this one so isomeric form of it.So different types of reactions can take place during the hydrocracking process or in thehydro crackers.So, if we think about the catalyst and their properties then the catalysts will be havingsome dual functions one is cracking we have to crack it and another is hydrogenation anddehydrogenation.So, one is cracking another is hydrogenation and dehydrogenation these are the basic processwhich is available during the whole process that is why the catalyst should have two sides.One will favour the cracking another will favour the hydrogenation dehydrogenation reactions.So, for the cracking reactions the active sites is acidic in nature and say some examplesis silica alumina or say crystalline zeolite modified zeolite along with binder so theseare the some examples of acidic sites in a catalyst.And there will be some other sites for hydrogenation and dehydrogenation and these sites are basicallycontaining a metal that is noble metals maybe platinum, palladium or non noble metals likemolybdenum and tungsten or nickel cobalt has also been used to increase this hydrogenationand dehydrogenation capacity of the catalyst.And noble metals less than 1% non noble metals 2 to 8% see if we use noble metal the catalystwill be costly but obviously noble metal in noble metal using catalyst the requirementof noble metals is less but non noble metal requirement is higher than this for example2 to 8% for nickel cobalt and 12 to 30% for molybdenum tungsten dioxide.So, to reduce the cost of the catalyst the non noble metals have been introduced andthe noble metals have been replaced by this although there are some comparison betweenthe performance obviously the noble metals catalysts are more then the non noble metalcatalysts.Now what type of reactions will take place?What will be the product distribution? that will depend upon the extent of this acidicsite and these your basic sites of these two catalysts.So, accordingly the product pattern will change and depending upon the feedstocks also thiscan be monitored the active sites number of active sites can be monitored.And since and the catalysts can be designed.Some example we will show here so this is our desire reactions we want to hydro cracknaphtha or LPG, naphtha to LPG or gas oil to gasoline so this is our to say desiredreactions we need to do it so our catalyst should have strong acidic site.And then hydrogenation activity is moderate and then surface area high, porosity low tomoderate.But when we go for gas oil to jet fuel and middle distillate conversion as gas oil tohigh viscosity lube oil conversions then we need moderate acidity.Moderate acidity and hydrogenation activity is very strong so we need to add more hydrogenin this case.So, surface area is high.Similarly when we go for hydro conversion of non hydrocarbon sulphur and nitrogen thenobviously we do not need that acidic behaviour because our objective is to remove the sulphurand nitrogen so not to crack the molecules may not be the cracking of the molecules maynot be that important.So, in that case we are using weak acidity and then hydrogenation has to be strong becauseS and N has to react with the hydrogen to give H2S NH3 so that way depending upon thenature of conversions which we are interested to achieve in this process we can design thecatalyst as per our requirement.Now we will see the process how the hydrocracking can take place.So, here we need hydrogen and we need feedstock we have to provide temperature and pressure.So, here we are makeup hydrogen we are providing some pressure and fresh speed so it is cominghere so that way it is going and heated preheat it and it again some heating arrangementsand it is coming to reactor stage 1 so this is one first reactor for hydrocracking.So, after reactions the product is again here cooled down and then it is coming for pressurerelease to high-pressure separator.So, high-pressure separator we are getting some gas so it will be coming and again itwill be recycled with hydrogen.So, it is going to this loop and then the liquid part which we are having here thatis going for lower pressure plus again we are doing reducing the pressure here.So, low pressure flash drum it is coming so again we are getting some gas molecules gasand the remaining part is going there for debutanizer.So, some again some pressure reduction so debutaniser, butane is recovered here thenit is going for different fractionation.So, for fractionation and in the fractionators we get different products light naphtha, heavynaphtha, kerosene, gas oil etc.So, the residual part again it is going and added with makeup hydrogen and it is enteringinto the after preheating it is entering into the reactor 2.So, second stage conversion we are taking the objective is to get more liquid conversionsmore conversions.So, then it is coming and from second reactor again it is cooled out and then high-pressureseparation.So, then high pressure separations we are making a flash so we are getting flash afterflashing temperature pressure reduces.So, then the vapours goes there and it is added with the hydrogen for this recyclingof this and helps for the hydrocracking.And in the bottom part of this it is coming and send to the low pressure flash drum soagain for the recovery of the gases from it so this is a overall flow sheet which is followedto perform the hydrocracking of different products intermediate products.Now we will see the operating conditions these are mainly dependent on feed characteristicsand product pattern which we desired that we have already discussed.And some typical example are given here for a hydrocracker processing VGO’s to producemaximum middle distillates the reaction temperature is around 370 to 450 degree centigrade andreaction pressure is 160 to 200 atmospheric pressure.And LHSV that is 0.6 to 3.0 and what is LHSV? that is the liquid hourly space velocity whichis the ratio of liquid volume flow per hour to catalyst volume.So, fractionating section has operating conditions similar to conventional distillation unit.So these are some operating conditions now we will see the comparison of FCC and hydrocrackingso obviously when we are using hydrogen we need to provide sufficient pressure for thereaction of hydrogen with the liquid part.So, gas phase and liquid phase reaction so we need to increase the high pressure so pressureis high here for FCC we do not need that high pressure.Operating temperature here it is high but in this case temperature is relatively lessbecause hydrogen is present there.So, construction cost is moderate for FCC, hydrocracker is high because it requires highpressures so cost is also higher, products olefins is high here, here it is nil.So, olefin will not be available because we are providing hydrogen so olefin unsaturationswill be removed.And then light naphtha octane number it is greater than 100 but here we get 78 to 81,so unsaturation is not there so octane number is not much with respect 100 where we getin FCC.But heavy naphtha octane we get in 95 to 100 where 40 to 64 and then they distillate cetaneindex so cetane index here it is low and we have 56 to 60 and distillate sulphur contentobviously in this case will be having moderate to high because sulphur removal does not takeplace in this case but here hydrocracking sulphur removal takes place.So, will be very low sulphur will be bottom sulphur content is also very low in this caseof hydrocracking.So, that way we can compare the FCC and hydrocracking process.Now we will see the reforming and isomerisation process so reforming means reforming willreform some products to other one.So, basically in this case it helps to produce high octane number reforming so it helps toproduce high octane number reformate octane number reformate and different type of reactionswhich we get here that is naphthene dehydrogen and then paraffin’s dehydrocyclisation andthe linear paraffin’s isomerization and Nephthene's isomerisation.So, dehydrogenation and isomerization are desired product desired reactions.Whereas adverse reactions which can take place here that is hydrocracking, hydrogenolysishydrodealkylation and alkylation, transalkylation and coking.So, these are not desired for the reforming.And isomerisation is required to produce branch say C5-C6 hydrocarbons that is gasoline product.So, when we need more gasoline to improve the quality of gasoline this reactions ispreferred.Here also this is also reforming is also preferred to increase the octane number.Then we can add some blending so blending is possible so that can help to improve thequality of the product as well as to meet the requirement of a specific fraction.So, some example will show here.So, typical motor gasolines that may consist of straight run naphtha from distillationatmospheric distillation so a straight run naphtha which we are getting, that plus crackatefrom FCC crackers which gasoline we are getting.We can make some proper blend we may get reformate, reforming is also giving us gasoline thatpart can be blend.Alkylate, isomerate and polymerate so different reactions can give us some gasoline type productso if we can mix it then ultimately gasoline blend will get.And that may have higher octane number than the straight run gasoline.So, in most cases the components blend non linearly for a given property that means ifwe mix these different gasoline from different sources.So, after the mixing what will be the property normally it is not that linear it is non linearand some correlations are developed to predict what will with the properties of this.Then polymerization and alkylation another type of reactions which are also used forthe conversion of one intermediate product to other form that is polymerization and alkylation.The in polymerization the light olefins are introduced to combine or polymerize into moleculesof 2 to 3 times their original molecular weight so, smaller molecules are converted to higherone.So, the catalysts employed are acidic that is phosphoric acids on pellets of Kieselguhr.So, that is used and we see here it requires high pressure in the order of 30 to 75 barsand temperature is 175 to 230 degree centigrade.And this polymerization derived gasoline may have higher quality some example is shownhere polymer gasoline derived from propylene and butylenes have octane numbers above 90.This alkylation reactions also achieves long-chain molecules by combination of two smaller moleculesso one being an olefin and the other as Isoparaffin.So, sulphuric acid can also be used or hydrofluoric acid can also be used for this reactions.This alkylation when sulphuric acid is used that is 98% concentration and say and thetemperature is 2 to 7 degree centigrade.The octane number of these alkaloids may be 85 to 95 so this so polymerizations alkylation’sall these processes helps to increase the octane number and to give better quality gasoline.So, we have discussed different type of reactions which can take place or which you can useto convert one form of liquid to other one to meet the market requirement as well asto improve the quality of that particular liquid fraction, thank you very much for yourpatience.