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Module 1: Petroleum Products

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Characteristics of Crude Oil and Petroleum Products

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Hi friends, now we will discuss on the topic characteristics of crude oil and petroleumproducts. In the last class, we have discussed on petroleum, we have seen that what petroleumis? How it is produced? And how did how it is different from crude oil? And we have alsoseen some types of this and some issues for its utilisation. In this class we will discusson the characteristics of petroleum both crude as well as its different products.So, content is, crude oil properties, then impurities in crude oil and methods for estimation,how we will estimate that we will also cover in this class. Now we will see the propertiesof petroleum, so, petroleum has some properties which are interesting for us as we are dealingwith its utilisations as energy feedstock. Like coal it also has some properties. Butunlike coal, this petroleum is mostly use to produce transportation fuel.So, the properties which are most important are density and API gravity, REID vapour pressure,Pour point, viscosity, flash point, cloud point, wax content, asphaltenes contents,carbon residue, ash content, distillation characteristics, distillation characteristicsis important for this, because, if for a pure compound we get a specific boiling point.But petroleum is a mixture of compounds; large numbers of organic compounds, hydrocarbonsare present in it.So, each will be having different boiling points. So, when it is going for distillationso, then different components will be vaporised at different temperature. So, we will notget a specific temperature for this petroleum crude as a boiling point so, we will be havingsome initial boiling point and one will be end boiling point for a particular part orparticular sample.Then we have base of crude oil, that is also one important parameters and then carbon andhydrogen ratio and octane number, cetane number, diesel index, smoke point and flash pointare also related with the application point of view for some petroleum crude, petroleumproducts like for example smoke point is used for kerosene. Octane number is used for gasolineand cetane number is used for diesel. And over all heating values is very, very importantas we are dealing with the energy from the feedstock and different types of impuritiesare also present.The one is water content, then salt content, then basic sediment and water, sulphur, nitrogen,inorganic acid and trace metals. So these are the different properties of the crudeoil. And we will discuss the importance of these and how to measure these properties.First we will see density and degree API or API gravity. As you know density is nothingbut mass by volume of any substance and specific gravity is also used M by V divided by M dashby V dash that means with respect to water, so, it is the density of any material anddensity of water at 4 degrees centigrade that is specific gravity. So, similar way API gravityhas been defined by American Petroleum Institute that is 141.5 by specific gravity at 60 degreeFahrenheit -131.5. So, this is the definition of API gravity as for American Petroleum Institute.And this is used to clearly understand the difference between fractions of petroleumcrude. For one example, if say, if we consider the water then specific gravity, API gravitywill be 141.5 – 131.5, almost 10. But if it is lower; it is lighter than water thenspecific gravity will be less, so, this minus this will be more than 10. So, for kerosene,we get 45 API, for moter gasoline, we can get 58 API and for natural gasoline we canget 75 API. So, higher the API, lighter the fractions of the product we are considering.Now, we will see some example of density and API and total distillate upto 370 degreescentigrade. So, these are the source of different crude, so, if we see the maximum API is here,say 47.08. So here we see maximum distillate. So, more the API lighter, more will be thelighter that is why more the value of, here of the distillate product operate at 370 degreecentigrade.And another properties REID vapour pressure, so REID vapour pressure that is the indicativeor what are the extent of volatiles present in the crude. So, it is determined under specifica condition that is 37.8 degrees centigrade and as for ASTM-D-323 this method it is measured.So, more the vapour pressure more will be the lighter fractions in the crude. If wetake some example, say in petroleum crude we get C2 to C8 or more than that. So, C1is very less in this case, so, C2, C3, C4, C5, n-C5 these fractions produces the LPG.So, how much LPG we can get from that crude that we indicated by the REID vapour pressure.So, these vapour pressure if we consider for propane it is 14.1 kg per centimetre square,butane it is 6.6 kg per centimetre square whereas for crude oil it is 0.01 to 0.05 kgper centimetre square. Another property is pour point and ash content. So, pour pointindicates the solubility of this that means, it is that temperature at which the fuel ceasesits flow.So, it is related with the wax content also, more wax, more easy to get, to cease the flowof it and it alongside the viscosity this is also used for pumping design and then waxcontent as you know that paraffins of having carbon more than 16 is solid. So, this solidifiedparaffins are considered as the wax in it and this is determined by Engler holde methodand under this method is based on the solvent extraction method.So, as shown here, the two solvents that is absolute ether and absolute alcohol solventsystem is used. And then paraffin wax is precipitated at -20 degree centigrade. So, this is a methodof determination of the wax. Now, we will see asphaltenes, carbon residue and ash content.They are also important parameter of the crude oil, asphaltenes basically is related withthe residual part, more the asphaltene we will be having more vacuum residue.And this is nothing but the poly nuclear condensed aromatic compounds and its solubility is alsodifferent in different solvents, and we can take advantage of it for its determinationwhere it is insoluble in heptane and soluble in benzene/toluene solvent. Next is your carbonresidue, so, carbon residue it is a carbonaceous material. So, it is if we evaporate it andfinalise it at specific conditions, then it will be remaining some residue so that residueis called carbon residue.And conradson method is used and ash content we can measure from the proximate analysisand just like coal here also ash content is related to mineral matters present in it.Metals which are present that also contribute to ash and you can convert the ash into drybasis and wet basis also as provided here.And Conradson carbon residue we can determine under specific condition we will take theweight certain amount of material, we place it in a crucible and subject to destructivedistillation during a fixed period by some severe heating, after that we will collectthe residue and how much is left that is considered as Conradson carbon ratio and is expressedin terms of percentage with the original sample.Salt content is also one parameter of the crude oil. So, when the crude oil is takenout from the underground, then it forms it contains different type of material includingwater and salt.These salts are basically sodium, potassium, calcium and magnisium chloride and the saltcan be present as crystallised solid or maybe dissolved in water, which water can form anemulsion with the organic phase in the oil in the crude oil. As shown here so one Brinedroplets, salt in water Brine droplet, so this droplet size is maintained by the formationof a layer and resins, asphaltenes, waxy agglomerates, carboxyhlates and naphthenates or alkyl benezeneall those things helps to get the stability of this brine droplet.And some brines may also b, some salts may also be available in terms of particulates,so or solid particles. So, this is a salt and this salt if present in crude that willcreate lot of problem and above certain limit it is not desirable in the refinery, it willcreate pollution, it will give the irregular behaviour in distillation, it will be foulingthe heat exchanger and it will also cause equipment corrosion.So, these are the disadvantage of the salt and if we think about different type of salts,mostly sodium is used at 70 to 75% typically, magnesium at 15 to 20%, calcium is around10% and magnesium salt mostly gives a HCL so, that is corrosive in nature.Then for the determination of this salt, some methods are available, that is here, silvernitrate and KCNS method by titration or by conductivity measurement based on the standardsodium calcium and magnesium chlorides and standard solutions in mixed alcohol. So, theseare methods which are used for its determination. Then metals which are available metals, whichare available in crude oils, are mainly lead, nickel, vanadium and copper.So, it will also contribute on ash when it will be burn then soot will be formed andparticulates will be formed and it poisons the catalyst. So, the lesser the metals morewe will get the quality of the crude or of the derived product from it.Now, this can be measured by using atomic absorption spectroscopy and another propertysediment and water. So, as I told that, when crude oil is taking out, then it containssalt, different types of sediments which are basically sand clay, volcanic ash, drillingmust, rust iron and sulphide and metals and different types of scales. So, these contributesthe sediment and water is already available in the crude oil.So, the presence of these affects the process of refining and it damages that is the pluggingabrasion and residual product contamination. So, these are the important effect of thesecontaminants on the crude oil. And water causes irregular behaviour in the distillation andfor the measurement of this there are a number of methods that is Base sediment and watermeasurement is ASTM D 96, Sediment by extraction is ASTM D 4007 and Water content Dean andStark or ASTM D 4006 methods.Now we will be discussing some property of the refined products that is your octane number.Octane number is the property of the gasoline and it is related with the knocking propertyof it. Now what is the resistance of a motor fuel to knock, this indicates.So, more the octane number more the quality of the gasoline and this is also called octanerating and octane number are based on a scale on which the isoocatane is 100 and heptaneis 0. So if we have a fuel, which burns in the similar way, which are having the similarknocking property with a blend of isooctane and heptanes in that blend, what is the percentageof isooctane that will be the octane number of this fuel.And for the determination of octane number, some standard machine is used in laboratory.So, in that case, what number octane number we get that is called research octane numberand it is determined by running the fuel in a test engine with a variable compressionratio under control condition and the comparing the results with those for mixture of isooctaneand n-heptane as it to what is the percentage of isooctane in this mixture, that will bethe having the similar knocking barrier that will be the octane number.So, that is called your research octane number and when the vehicle will be on road withactual loading, then it will be consuming some amount of more energy so motor octanenumber is also used in this case higher RPM is used a whereas that is equal to 900 RPM,but for RON it is 600 RPM. Another property that is Anti knock index is also used in somecountry to get the knocking behaviour of the gasoline.And this is defined by R+M by 2, research octane number plus motor octane number dividedby 2 then we come to cetane number. So, cetane number is the property of diesel.So, it is a relative measure of the interval between the beginning of injection and autoignition. So, how much time it is late that is the indication of the cetane number andagain like octane number there are two compounds here the cetane which is having 100 and 100number and then for one methylnaphthalene it is zero. And isocetane is also 15 so 0and 100 will be blending with different ratio and used in the specified machine and youwill get the delay period and then that will be and the percentage of cetane will be thecetane number.So, catane number is measured by burning the fuel in a cooperative fuel research engineunder standard test conditions a wheel is their, hand wheel is used to increase thecompression ratio and then this compression ratio is increased until the time betweenthe fuel injections and ignition is 2.407 millisecond. So, then this cetane and 1-methylnaphthalenemixture is also used in the similar way on the same compression ratio, then time requirementis considered and then for the composition which is having the same time, in that mixture,the percentage of cetane will be the cetane number.And another Aniline point and diesel index; So, for diesel cetane number is measured forother fuels like say lubricating oil etcetera for these diesel index is measured and dieselindex is defined as aniline point in degree Fahrenheit into API gravity divided by 100.So aniline point is measured first then diesel index is measured. So, what is aniline point?It is a temperature at which equal volume of aniline and the lubricant oil will be mixed.See if we get that temperature we will put it here. If we have the degree API of thefuel, then we will multiply it by it and divide by 100 will get the diesel index. So, nextis acid value. So, crude also have some acids organic and inorganic acids may be availablein it and total acid content we can measure by its titration with base solution. And itis defined as total acid number TAN that is equal to mgKOH required to neutralise allthe free acids per one gram of crude.So, this is our total acid number. Similarly, total base number is also determined by thetitration using perchloric acid.Viscosity is another property of the crude oil, which is very important for its transportationand for pumping purpose. As you know, the viscosity indicates the resistance and so,in one form layer flows on the other layer that is the fluid one fluid layer is flowingon the another layer that experienced resistance and that is related to the viscosity. So,it also represents the thickness of the oil and is determined by measuring the amountof time taken for a given measure of oil to pass through an orifice of a specified size.So, for the determination of viscosity, what happens for a simple arrangement we can make,we can pass the fluid through orifice and know what time it is taking we can measureit because this is a flow through a porous channel we can consider and in this case,we can use the Poiseuilles’s equation that is Eta is equal to Pi R to the power 4 p intot divided by 8 into V into L and we get eta is viscosity coefficient.And P is the hydraulic pressure and t is the time of falling and V is the volume of liquidcollected an L is the distance travelled by the liquid during time t and r is the radiusof the tube. So, in this formula, we can see the Pi, radius of that tube is fixed, V volumehow much liquid you are collecting, that can also be targeted and fixed and then L is thelength of the distance travelled by the fluid. So that L is also fixed for the system.So we can get Eta equal to k into P into t. This P is nothing but related to P, the hydrostaticpressure it is proportional to Kmt we can get, because P proportional to m. Now, ifwe have 2 fuels one is standard known viscosity and another viscosity is not known, we aregetting what is the time to fall certain distance through the orifice for both oil samples.Then we will get the viscosity coefficient ratio by this m t by mr tr where mr is thereference mass of the reference fuel and t is the time required to travel the same distanceby the reference oil and this is for our which I want to determine t the time required bythe oil which we are interested to get the viscosity and mass is the mass of that oilfor which we are interested to get the viscosity. So, now we can get the value of viscositycoefficient.So this viscosity can be measured by different ways. As mentioned here, viscometer are thereOstwald viscometer, Falling sphere viscometer, falling piston viscometer, oscillating pistonviscometer, vibrational viscometer, rotational viscometer, bubble viscometer.Another property is flash point. So, if we heat any fuel, it will produce vapours. So,if we can bring one matchsticks for ignition, immediately the temperature will come at whichsufficient vapour will form and flash will take place at the first time. So, that temperatureis called Flash point if we apply more heat and temperature will increase and more vapourswill form and fire will take place and that time that temperature has a minimum temperatureat which fire takes place that is called fire point.So, Flash point and fire Point are the properties of the liquid fuels which are produced throughrefining of the petroleum crude and it is determined in an Open Cup system and closedcup system. In Open Cup system, the flash point varied with the height of the flameabove the liquid surface and at sufficient time the measured flash point temperaturecoincides with the fire Point, but in case of closed cup, there is a lid and we get the;we bring the ignition source for a moment and we get the flash.So, it has been shown that the value of flash point in case of closed cup is normally lowerthan that obtain through Open Cup and it is typically 5 to 10 degrees centigrade lower.Then asphalt properties, asphalt, which are present in the crude oil that will be availablein the residue, vacuum residue and this is made of some polymeric compounds and it isaromatic rings are present in it as we discussed and it may be directly used.That is the straight run that means starting off vacuum unit or PDA propane deasphalting.So, vacuum residue we are getting that is directly we are using or we are separatingthe lighter part from it by propane deasphalting and using the asphalt. So, that asphalt iscalled straight run asphalt. So, Cut Back; so cut back we are using some solvent here.So rapid cut, a rapid cure RC that may be Naphtha diluent, when we use naphtha thenthat is called rapid cure.We can use kerosene with asphaltene that is called medium cure and slow cure when gasoil is used. Apart from these emulsion asphalt is also available when the water is addedwith these 30 to 50% water plus emulsified chemicals then gives the emulsion asphaltand then industrial or blown asphalt another type of asphalt is also available, which isformed by the air blowing in hot asphalt and these asphalts that is industrial or blownasphalt these have some applications as your waterproofing material and it is harder thanthe asphalt.So, it has some properties that is softening point and hardness these properties are measuredto assess its quality, the softening point is a lowest temperature at which standardisedweight and shape will sink into asphalt that is around say 80 to 340 Fahrenheit and hardnessit is the depth to which a test needle penetrates into asphalt over a time at specified temperatureas a certain condition is maintained and how many what is the depth penetrating needleis going inside that is the hardness related to hardness. Zero pen, 30 to 40 pen millimetreand 250 to 3000 millimetre pen is reported.So, there are some impurities in the crude oil also like say sulphur, nitrogen and oxygen.So, the sulphur is present in elemental form or in case of sulphide or oxide form. Someorganic sulphur is also present and those are called Mercaptans. So, different productshave different types of sulphur as for example present H2S and Mercaptans in LPG, sulphurMercaptans in gasoline kerosene ATFs.And to remove the sulphur we can use some sweetening process that is caustic washing,mercaptan oxidation etc. And nitrogen present in elemental form and also as oxides of nitrogenand it forms acids and causes corrosion. So, removal is necessary to get on grade productsand secondary units feedstock. And oxygen present in the elemental form and also ascompounds of oxygen, it forms naphthenic acid and causes stress corrosion.Sulphur content is may vary, it may be low sulphur up to 0.5% it may be medium 0.5 to0.8% or maybe high greater than 0.8% these are some example of different crude differentcrude oils and different sulphur content. So, you get medium and high as well as low.So, crude oil and their sulphur content.Method of sulphur determination there are a number of methods. So, some important arecolourimetric method or barium sulphate method it is also known as and Wickbond method andthe combustion method this is and then X-ray fluorescence method and ICP-MS. So, theseare the different methods I have mentioned here. These are the number, test number andthese are detection limit and here are some interference which can compounds are elementswhich can interfere on the detection.So, for the nitrogen, so, it is poor colour stability of production, nitrogen gives poorcolour stability of products; it is poor stability in storage and handling also and poor qualityof feedstocks for catalytic processing. So, removal of nitrogen is important and required.So, now, we see the different crude and presence of nitrogen and sulphur in it. And nitrogencan be determined by some methods.There is micro coulometric, chemillumini scence, micro kjedhal and modified kjedhal. So, theseare the methods through which nitrogen is determined and different products are usedfor this purpose and detection limits are also given. Apart from this CHNS or elementalanalysis can be done to measure the carbon, hydrogen, sulphur, nitrogen and oxygen ofthe crude oil sample. Upto this in this class on the characteristics of crude oils and petroleumproducts, thank you very much for your patience.