lecture no.3

PETROCHEMICAL & REFINING TECHNOLOGY

LECTURE NO. 3

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Crude Assay

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Ta

Tb

Te

Cut points

{

EP

IBP

0% 20% 40% 60% 80% 100%

naphthakerosene light gas

oil

heavy gasoil

vacuum gasoil

How is D-86 important ?

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• 86D is used to ooooooooo ooo

l vol ati l i ty ac ross the enti re

boi l i ngrange of fuel.• A = Front End (0–20% evaporated)• B = Mid-range (20-90% evaporated)• C = Tail End (90-100% evaporated)

True boiling point

• ASTM D-2892 is used for samples with a wide boiling range such as crude petroleum up to a final cut temperature of 400°C (752°F) atmospheric equivalent temperature (AET).

• Theoretical plate = 14-18 (15)

• Distillation pot, volume = 15 L

• Volumetric of feed 5 – 10 L

• Reflux ratio = 5:1

• Temperature of distillation ≤ 350C (AET)

• Weight loss ≤ 4%

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True boiling point• It is often useful to extend the boiling point data to higher t

emperatures than are possible in the fractionating distillation method and for this purpose a vacuum distillation in a simple still with no fractionating column (ASTM D-1160) can

be carried out. • This distillation, which is done under fractionating conditio

ns equivalent to one theoretical plate, allows the boiling point data to be extended to about 600°C (1112°F) with ma

ny crude oils. • This method gives useful comparative and reproducible res

ults that are often accurate enough for refinery purposes, provided significant cracking does not occur.

• Usually seven fractions provide the basis for a reasonably thorough evaluation of the distillation properties of the fee

dstock:

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True boiling point

• 1. Gas, boiling range: <15.5°C (60°F)• 2. Gasoline (light naphtha), boiling range: 27–149°C

(80–300°F)• 3. Kerosene (medium naphtha), boiling range: 149–

232°C (300–450°F)• 4. Gas oil, boiling range: 232–343°C (450–650°F)• 5. Atmospheric gas oil, boiling range: 343–371°C (6

50–700°F)• 6. Vacuum gas oil, boiling range: 371–566°C (700–1

050°F)• 7. Residuum, boiling range: >566°C (1050°F)

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Typical Refinery Products

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Product Boiling RangeDeg. C

Boiling RangeDeg. F

LPG -40 - 0 -40 - 31

Gasoline 30 - 200 80 - 400

Kerosene, Jet Fuel, #1 Diesel 170 - 270 340 - 515

#2 Diesel, Furnace Oil 180 - 340 350 - 650

Lube Oils 340 - 540 650 - 1000

Residual Oil 340 - 650 650 - 1200

Asphalt 540 + 1000 +

Petroleum Coke Solid

From: Schmidt, G.K. and Forster, E.J., “Modern Refining for Today’s Fuels and Lubricants,” SAE Paper 861176, 1986.

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For vacuum residues a typical true boiling point (TBP) cut point is 538C, but it may be lower or higher depending on the crude. The TBP cut point will define the concentration of Conradson

carbon residue (CCR), sulfur, and metals in the feed and thereby affect yields and product quality.

TYPES OF REFINERY

Hydroskimming Refinery

Cracking Refinery

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HYDROSKIMMING REFINERY

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HYDROSKIMMING REFINERY• Hydro skimming refinery is suitable where the demand for gasoline is

low and close to that produced from single stage distillation. • When demand for gasoline or middle distillates is high, conversion

processes are required.• The minimum conversion processes are:

– Atmospheric and vacuum distillation– Catalytic gas oil cracking– Reforming– Light ends recovery– Treating and blending

• The vacuum tower enables to cut deeper into the crude and also avoid temp. above 750 F/399 C which can cause cracking of crude

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CRACKING REFINERY

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BOTTOM CONVERSION REFINERY

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HIGH CONVERSION REFINERY PROCESSES

Gasoline maximization: Alkylation: converts olefins(propylene, butylenes, amylenes) to high octane gasoline by reacting them with isobutane. PolymerizationReaction of propylene/butylene to unsaturated hydrocarbon mixture in the gasoline range. FCCConverts vacuum gas oils to LPG and gasoline. Catalytic ReformingConverts straight naphtha to high octane gasoline and petrochemical aromatic feed stock.

IsomerizationConverts straight run naphthas to branched chain compounds to improve octane of gasolines.

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• Quality improvement– Hydro processing: A variety of petroleum fractions

can be treated at elevated temperatures & pressure and in presence of a catalyst to:

• Reduce sulfur content• Improve stability• Remove odor• Improve combustion characteristics• Improve appearance• Convert heavy fractions to light valuable products

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• Three types– Hydro fining: Desulfurization and denitrification of a wide range of

feeds – naphtha, light & heavy distillates, residues. Brings about minor molecular changes, and hydrogen consumption is about 100-1000 cft/bbl.

– Hydrotreating: Carried out at higher pressures, and upgrades combustion quality of petroleum fractions. Typically, low grade straight run diesel is hydrotreated to produce high grade diesel. FCC feed is hydrotreated to remove sulfur, nitrogen, aromatic rings and metals. Lubricating oil feedstocks are hydrotreated to change paraffing wax structures to produce lower pour point.

– Hydrocracking: Converts a wide range of feedstocks to light hydrocarbons, gasoline, kerosine, diesel, fuel oil with very low sulfur content and rich in paraffins. Carried out at about 200 atmos pressure.

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BOTTOM CONVERSION PROCESSES

• The vacuum distillation residue is converted to useful fuel products like LPG, gasoline, kerosine, gas oil– Delayed coking/fluid coking: the residue is thermally

cracked to produce light hydrocarbons, gasoline, kerosine, gas oil.

– Visbreaking: Mild thermal cracking to reduce viscosity of residue for fuel oil blending

– Solvent deasphalting: Asphaltenes and resins are precipitated from residue by a solvent, and the heavy hydrocarbon separated for use as FCC feed or lube oil manufacture.

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TREATING PROCESSES

• Sweeteing of fuel products: Improves odor of LPG, gasoline and kerosines by removing hydrogen sulfide and mercaptan sulfur. The foul smelling mercaptans are converted to disulfides and separated. Merox process is widely used.

• Solvent extraction: Removes aromatic and cyclic sulfur compounds to improve burning quality of diesel fuels. NMP is the typical solvent.

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LUBE OIL MANUFACTURE

• Vacuum gas oil fractions are also feedstock for lube oil manufacture. Processes are:– Solvent extraction: to remove heavy aromatics

and improve viscosity index of basestocks. NMP and Furfural solvents are commonly used.

– Solvent dewaxing: the waxy components of lube oils are crystallized at low temperatures in presence of solvents like MEK/MIBK/Propane, to improve pour point of lube oil basestocks

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SPECIALITIES

• Grease: Selected lube oil fractions are blended with metallic soaps to produce high viscosity greases.

• Paraffin wax: Waxy distillate cuts or lube oil dewaxing byproduct wax is deoiled to to reduce the oil content, and hydrofined for color improvement. It is fractionated to give desired melting point grades

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SPECIALITIES

• Asphalt : Asphalts are produced from residues of selected crudes. The residue is air blown or oxidized to improve penetration, brittleness, ductility etc. Emulsified asphalts are made for application at relatively low temperatures.

• Chemicals: A wide variety of chemicals and petrochemicals are made from petroleum feed stocks:– Aromatics: benzene, toluene, xylenes

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SPECIALITIES

– Propylene, isobutylene– Alchohols– Resins– Rubber– Additives– White oils– Hexane– Solvents– Paraffin

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LABORATORY TEST METHODS• API gravity: expression of density or weight of crude oil:

API = 141.5 – 131.5 sp gr• Reid vapor pressure (RVP): for measuring vapor pressure of volatile

gasolines & crudes. True vapor pressure is higher by about 10%, but varies.

• ASTM distillation: measures the boiling range of gasoline, naphtha, kerosine, diesel. Initial boiling point (IBP) and end point (EP) are important specifications.

• Flash & fire points: These are temperatures below which oil can be stored without danger of fire. Flash point – temp. at which the oil will momentarily flash when brought in contact with a flame. Fire point – temperature at which vapors are evolved rapidly enough to burn continuously.

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LABORATORY TEST METHODS

• Color: color indicates thoroughness of a refining process. Colored distilled products are an indication of thermal decomposition, entrainment of dark tarry material, inherent color. Measured by Saybolt and ASTM chromometer.

• Viscosity: measure of resistance of oil to flow. Unit – centipoise. Dynamic viscosity used for lubricating oils is centistokes. Viscosity Index for lubricating oils shows change in viscosity with temperature.

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• Cloud & pour point: measure of wax content of oil. The oil is slowly cooled, and the temp. when haziness appears is the cloud point. The temp. at which oil stops flowing is the pour point.

• Octane number: % by vol. of isooctane that must be mixed with n-heptane to give the same knocking characteristic in a standardized engine. – Research octane number (RON): conducted on the engine

at 600 rpm. Indicative of city driving.– Motor octane number (MON): conducted on the engine at

900 rpm. Indicative of highway driving.

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• Sulfur tests: Direct measurement is carried out by combusting a sample, and absorbing the SO2 vapors in an alkaline solution and measured by titration of unused solution. Also measured by noting discoloration of a strip of polished copper when immersed in a heated sample.

• Tests for bituminous material: ductility, penetration, softening point and specific gravity.

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• Gum in gasoline: indicative of gum formation in the engine at high temperatures, and gum formation during storage.

• Freezing point of jet fuel: temp. at which the fuel stops flowing, and important for temperatures encountered during flight.

• Aniline point: Aniline point is defined as the temperature at which equal volumes of aniline and diesel oil are completely miscible. Indicative of aromatic content of diesel oil. The greater the aniline point, the lower the aromatics in diesel oil. A higher aniline point also indicates a higher proportion of paraffin.

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LABORATORY TEST METHODS• Cetane index: An empirical measure of ignition quality of diesel. Defined

as the percentage by volume of cetane in a mixture of cetane and methyl naphthalene which has the same ignition quality when used in an engine as a fuel under test.Another method that fuel-users control quality is by using the Cetane index (CI), which is a calculated number based on the density and distillation range of the fuel. There are various versions of this, depending on whether you use metric or Imperial units, and how many distillation points are used. These days most oil companies use the '4-point method', ASTM D4737, based on density, 10% 50% and 90% recovery temperatures.

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LABORATORY TEST METHODS• Cetane number : is actually a measure of a fuel's ignition delay; the time

period between the start of injection and start of combustion (ignition) of the fuel. In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels. Cetane numbers are only used for the relatively light distillate diesel oils.

• To measure the cetane number properly is rather difficult, as it requires burning the fuel in a special, hard-to-find, diesel engine called a Cooperative Fuel Research (CFR) engine, under standard test conditions. The operator of the CFR engine uses a hand-wheel to increase the compression ratio (and therefore the peak pressure within the cylinder) of the engine until the time between fuel injection and ignition is 2.407ms. The resulting cetane number is then calculated by determining which mixture of cetane (hexadecane) and isocetane (2,2,4,4,6,8,8-heptamethylnonane) will result in the same ignition delay.

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lecture no.3

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