1. Petroleum Refining Process

2. Overview of petroleum refining process
Process name
Action
Method
Purpose
Feedstock(s)
Product(s)
FRACTIONATION PROCESSES
Atmospheric distillation
Separation
Thermal
Separate fractions
Desalted crude oil
Gas, gas oil, distillate, residual
CONVERSION PROCESSED--DECOMPOSITION
Catalytic cracking
Alteration
Catalytic
Upgrade gasoline
Gas oil, coke distillate
Gasoline, petrochemical feedstock
Coking
Polymerize
Convert vacuum residuals
Hydro-cracking
Hydrogenate
Convert to lighter HC's
Gas oil, cracked oil, residual
Lighter, higher-quality products
Visbreaking
Decompose
reduce viscosity
Atmospheric tower residual
Distillate, tar
CONVERSION PROCESSES--UNIFICATION
Alkylation
Combining
Unite olefins & isoparaffins
Tower isobutane/ cracker olefin
Iso-octane (alkylate)
Polymerizing
Unite 2 or more olefins
Cracker olefins
High-octane naphtha, petrochemical stocks

3. Overview of petroleum refining process
Process name
Action
Method
Purpose
Feedstock(s)
Product(s)
FRACTIONATION PROCESSES
CONVERSION PROCESSES--ALTERATION OR REARRANGEMENT
Catalytic reforming
Alteration/ dehydration
Catalytic
Upgrade low-octane naphtha
Coker/ hydro-cracker naphtha
High oct. Reformate/ aromatic
Isomerization
Rearrange
Convert straight chain to branch
Butane, pentane, hexane
Isobutane/ pentane/ hexane
TREATMENT PROCESSES
Desalting
Dehydration
Absorption
Remove contaminants
Crude oil
Desalted crude oil
Hydrotreating
Hydrogenation
Remove impurities, saturate HC's
Residuals, cracked HC's
Cracker feed, distillate, lube

4. 1. UNIFICATION (Alkylation)
Alkylation is basically the INTRODUCTION of one hydrocarbon group into another hydrocarbon molecule. It is inverse of cracking process, because it increases the chain length
In oil refining, ISOBUTANE is alkylated with the low molecular weight olefins (propene/butene,..), (means isobutane is combined with olefin) in the presence of strong catalyst, low temperature and high pressure.

5. Alkylate is mixture of HIGH octane number, branched chain paraffin hydrocarbons. It is premium blending stock because it has exceptionally good antiknock properties.
Since crude oil contains only upto 40% of the hydrocarbon constituents in the gasoline range, refiners use FCC process to convert high molecular weight olefins into smaller and more volatile compounds. While Alkylation process transforms low molecular-weight alkenes and iso-paraffins molecules into large iso-paraffins with high octane number.

6. Reaction Mechanism of Acid catalyzed alkylation
Step I:
 Reaction of olefin (here we use example of Propene) with an acid to form carbo-cation named here propyl cation. In this reaction addition of H+ ion to the double bond of alkene takes place. Means the double bond breaks up and one of the carbon atoms picks up the H+ ion;
The cation of carbon atom is named as “carbo-cation”.

7. Reaction of carbo-cation with isobutene to form
Step II:
 It takes place in two further steps:
Reaction of carbo-cation with isobutene to form
higher carbon atom carbo-cation:
This Carbo-cation now is more reactive and has
3carbon atoms directly attached to it and known as
tertiary carbo-cation. (Intermolecular Hydride transfer).

8. (b) Reaction of butyl cation with propene to form long chain cation
(b) Reaction of butyl cation with propene to form long chain cation. Means double bond break up and cation adds to one of the carbon atom to form a long chain cation.

9. There are 3 types of carbocations depending upon the number of carbon atoms directly attached to the carbon atom having positive charge.
(i) Primary carbocation (p-carbocation): having single carbon atom attached
(ii) secondary carbocation (sec-carbocation): having two carbon atoms attached, e.g.: propyl cation
(iii) tertiay carbocation (ter-carbocation): having three carbon atoms attached
The order of their reactivity is:
Ter-carbocation > sec-carbocation > p-carbocation

10. Step III:
 It takes place in two further steps:
(a) Picks up H- ion to form ALKYLATE or Rearranges to form a new carbocation for further chain reaction.

11. Reaction Mechanism of Acid catalyzed alkylation
Overall reaction:   
Acid sulfuric acid (H2SO4) or hydrofluoric acid (HF) is represented as symbol “H+X-” where H+ = H+
X- = F-/ HSO4-

12. Refinery Process for Alkylation
Alkylation plant uses catalyst hydrofluoric acid HF, known as HF-plant, or sulfuric acid H2SO4: known as sulfuric plant.
The HF is very volatile, and difficult to use, so this plant is not commonly used while mostly common is sulfuric plant.
The sulfuric plant consist of 7 main parts: the chillers, the reactor, the acid separator, the caustic wash and three distilling plants as shown in figure 2.

13. Figure 2 Alkylation unit flow diagram

14. Refinery Process for Alkylation
The chillers: are used to reduce the working temperature and to maintain high pressure. Since acid is very strong, highly reactive, it releases heat, which may cause explosion. So temperature must be controlled to be low 10-30oC. High pressure is maintained in order to keep the reaction mixture in liquid form.

15. The reactors: mixture is then pumped into the reactor
The reactors: mixture is then pumped into the reactor. The reaction time for the alkylation process is relatively long, so the reactors used here are very large. The residence time for the reaction is minutes to assure that olefins are in good contact with isobutane and acid, to promote the reaction.
The acid separators: also called acid Settler. The mixture then moves to this chamber, where hydrocarbon mixture gets completely separated from the acid like water and oil. Hydrocarbons are drawn off from the top, the acid is drawn off the bottom and then recycled back to the feed stock (raw material Or crude oil).

16. The caustic wash: the Hydrocarbons (HC) from the acid separators have some traces of acid in it, which must be removed. This mixture is then washed with caustic soda (NaOH), which neutralize the acid and removes from the mixture.
Fractionators: 3 fractionators separate the alkylate and saturated gases. Any unreacted isobutene is recycled back to the feed stock.
During the alkylation some reactions also takesplace. Because there are lot of molecules forming and reacting, so there are small amount of propane, butane also forms.

17. 2. Polymerization- UNIFICATION
It is the process in which light olefins, e.g., ethene, propene, butene are induced to combine/polymerize with itself to produce a single branched molecule of two/three times their original molecular weight having same elements in the same proportion as the original molecule.
The reaction takes place in the presence of catalyst: phosphoric acid, high pressure and temperature in the range of 300° and 450° F. 17

18. The product of polymerization is known as DIMATE.
For example: Propene polymerizes to form isohexene
This process is similar to Alkylation. Here the reaction plant is named as POLY PLANT or DIMER plant.

19. Description
Polymerization in the petroleum industry is the process of converting light olefin gases including ethene, propene, and butene into hydrocarbons of higher molecular weight and higher octane number that can be used as gasoline blending stocks. It is similar to the Alkylation process.
Polymerization combines two or more identical olefin molecules to form a single molecule with the same elements in the same proportions as the original molecules. Polymerization may be accomplished thermally or in the presence of a catalyst at lower temperatures.

20. Polymerization
The reaction can takes place through various types of mechanisms, such as free-radical type (involve free-radical formation), cationic mechanism (involve carbo-cation formation), Anionic mechanism (involve carbo-anion formation). And the final product in Termination step can either have double bond in it (by rearrangement of carbon chain) or with the single bond (like in alkylation process).

21. Polymerization Reactions
The simplest way to catalyze the polymerization reaction that leads to an addition polymer is to add a source of a free radical to the monomer.
The free radical is reactive, short-lived components that contain one or more unpaired electrons.
Free radical mechanism involves chain-initiation, chain-propagation, and chain- termination steps.

22. Free Radical Chain Initiation
A source of free radicals is needed to initiate the chain reaction. In the presence of either heat or light (uv), these peroxides decompose to form a pair of free radicals that contain an unpaired electron.

23. Free Radical Chain Propagation
The free radical produced in the chain-initiation step adds to an alkene to form a new free radical.
The product of this reaction can then add additional monomers in a chain reaction.

24. Free Radical Chain Termination
Whenever pairs of radicals combine to form a covalent bond, the chain reactions carried by these radicals are terminated.

25. Anionic Polymerization
Addition polymers can also be made by chain reactions that proceed through intermediates that carry either a negative or positive charge.
When the chain reaction is initiated and carried by negatively charged intermediates, the reaction is known as anionic polymerization.
Like free-radical polymerization these chain reactions take place via chain-initiation, chain-propagation, and chain-termination steps.
The reaction is initiated by a Grignard reagent or alkyllithium reagent, which can be thought of a source of a negatively charged CH3- or CH3CH2- ion.

26. Anionic Polymerization
Continue….
The CH3- or CH3CH2- ion from one of these metal alkyls can attack an alkene to form a carbon-carbon bond.

27. Anionic Polymerization
Continue….
The product of this chain-initiation reaction is a new carbanion that can attack another alkene in a chain-propagation step.
The chain reaction is terminated when the carbanion reacts with traces of water in the solvent in which the reaction is run.

28. Polymerization Reaction (cationic)
 Step I(Initiation)
 Reaction starts with the addition of acid (H+) to the butene. The double bond breaks up and picks up the H+ ion to form butyl cation.

29. Mechanism of Reaction Step II
Addition of propyl cation to the propene: double bond breaks up and adds to the carbon centre with positive charge and forms long chain carbo-cation

30. Mechanism of Reaction H- Step III (termination)
The unstable iso-hexyl cation picks up H- ion to terminate the reaction and forms stable iso-hexane molecule. H-

31. Details for the Refinery process of polymerization
The olefin feedstock is pretreated to remove sulfur and other undesirable compounds.
In the catalytic process the feedstock is either passed over a solid phosphoric acid catalyst or comes in contact with liquid phosphoric acid, where an exothermic polymeric reaction occurs. This reaction requires cooling water and the injection of cold feedstock into the reactor to control temperatures between 300° and 450° F at pressures from 200 psi to 1,200 psi (pound per square inch).
The reaction products leaving the reactor are sent to stabilization and/or fractionator systems to separate saturated and unreacted gases from the polymer gasoline product.

32. Details for the Refinery process of polymerization
In the petroleum industry, polymerization is used to indicate the production of gasoline components, hence the term "polymer" gasoline.
Furthermore, it is not essential that only one type of monomer be involved. If unlike olefin molecules are combined, the process is referred to as "copolymerization." Polymerization in the true sense of the word is normally prevented, and all attempts are made to terminate the reaction at the dimer or trimer (three monomers joined together) stage.

33. Refinery process
However, in the petrochemical section of a refinery, polymerization, which results in the production of, for instance, polyethylene, is allowed to proceed until materials of the required high molecular weight have been produced

34. 3. Catalytic Reforming (alteration)
What is Reforming?
Reforming takes the straight-chain hydrocarbons in the range of C6 to C8 from the gasoline/naphtha fractions and rearranges them into aromatic (cyclic double bond) compounds.
Catalytic reforming is an important process used to convert low-octane naphthas into high-octane gasoline blending components called reformates. For example: 34

36. Description
Catalytic reforming is an important process used to convert low-octane naphthas into high-octane gasoline blending components called reformates.
Reforming represents the total effect of numerous reactions such as cracking, polymerization, dehydrogenation, and isomerization taking place simultaneously.

37. Depending on the properties of the naphtha feedstock (as measured by the paraffin, olefin, naphthene, and aromatic content) and catalysts used, reformates can be produced with very high concentrations of toluene, benzene, xylene, and other aromatics useful in gasoline blending and petrochemical processing.
Hydrogen, a significant by-product, is separated from the reformate for recycling and use in other processes.

38. Details for the Cat-reforming refinery Process
There are many different commercial catalytic reforming processes including plat forming, power forming and ultra forming catalytic reforming. But plat forming cat-reforming is the most common.
Platforming catalytic reformer comprises a reactor section, a product-recovery section and feed-preparation section (in which, by combination of hydro treatment and distillation, the feedstock is prepared to specification). 38

39. Catalyst used here is Platinum (Pt) or platinum in combination with a second catalyst (bimetallic catalyst) such as rhenium (Rh) or another noble metal.

40. Details for the Cat-reforming refinery Process
The first step is preparation of the feedstock:
The feedstock is then heated to vaporize and passed through a series of alternating furnace and reactors containing a platinum catalyst.
The effluent from the last reactor is chilled and sent to the separator. The hydrogen-rich gas stream produced is drawn off from the top of the separator for recycling.
The liquid product from the bottom of the separator is sent to a fractionator called a stabilizer. It makes a bottom product called reformate; butanes and lighter gases go overhead and are sent to the saturated gas plant. 40

41. Platforming catalytic reforming unit schematic diagram41

42. 4. Isomerization (alteration)
Isomerization converts n-butane, n-pentane and n-hexane into their respective isoparaffins of substantially higher octane number. The straight-chain paraffins are converted to their branched-chain counterparts whose component atoms are the same but are arranged in a different geometric structure.

43. Isomerization is important for the conversion of n-butane into isobutane, to provide additional feedstock for alkylation units, and the conversion of normal pentanes and hexanes into higher branched isomers for gasoline blending.
Isomerization is similar to catalytic reforming in that the hydrocarbon molecules are rearranged, but unlike catalytic reforming, isomerization just converts normal paraffins to isoparaffins.

44. Details for the Isomerization refining process
There are two distinct isomerization processes, butane (C4) and pentane/hexane (C5/C6).
Butane isomerization produces feedstock for alkylation. Aluminum chloride catalyst plus hydrogen chloride are universally used for the low-temperature processes. Platinum or another metal catalyst is used for the higher-temperature processes.

45. In a typical low-temperature process, the feed to the isomerization plant is n-butane or mixed butanes mixed with hydrogen (to inhibit olefin formation) and passed to the reactor at 230°-340° F and psi. Hydrogen is flashed off in a high-pressure separator and the hydrogen chloride removed in a stripper column. The resultant butane mixture is sent to a fractionators (deisobutanizer) to separate n-butane from the isobutane product.
Pentane/hexane isomerization increases the octane number of the light gasoline components n-pentane and n-hexane, which are found in abundance in straight-run gasoline.

46. 46

47. Treatment process
Treating is a means by which contaminants such as organic compounds containing sulfur, nitrogen, and oxygen; dissolved metals and inorganic salts; and soluble salts dissolved in emulsified water are removed from petroleum fractions or streams.
Petroleum refiners have a choice of several different treating processes, but the primary purpose of the majority of them is the elimination of unwanted sulfur compounds.

48. A variety of intermediate and finished products, including middle distillates, gasoline, kerosene, jet fuel, and sour gases are dried and sweetened. Sweetening, a major refinery treatment of gasoline, treats sulfur compounds (hydrogen sulfide, thiophene and mercaptan) to improve color, odor, and oxidation stability. Sweetening also reduces concentrations of carbon dioxide.

49. Treating can be accomplished at an intermediate stage in the refining process, or just before sending the finished product to storage. Choices of a treating method depend on the nature of the petroleum fractions, amount and type of impurities in the fractions to be treated, the extent to which the process removes the impurities, and end-product specifications. Treating materials include acids, solvents, alkalis, oxidizing, and adsorption agents.

50. 1. Catalytic Hydrotreating
Catalytic hydrotreating is a hydrogenation process used to remove about 90% of contaminants such as nitrogen, sulfur, oxygen, and metals from liquid petroleum fractions.
These contaminants, if not removed from the petroleum fractions as they travel through the refinery processing units, can have detrimental effects on the equipment, the catalysts, and the quality of the finished product.

51. Typically, hydrotreating is done prior to processes such as catalytic reforming so that the catalyst is not contaminated by untreated feedstock.
Hydrotreating is also used prior to catalytic cracking to reduce sulfur and improve product yields, and to upgrade middle-distillate petroleum fractions into finished kerosene, diesel fuel, and heating fuel oils. In addition, hydrotreating converts olefins and aromatics to saturated compounds.

52. 2. Blending
Blending is the physical mixture of a number of different liquid hydrocarbons to produce a finished product with certain desired characteristics.
Products can be blended in-line through a manifold system, or batch blended in tanks and vessels. In-line blending of gasoline, distillates, jet fuel, and kerosene is accomplished by injecting proportionate amounts of each component into the main stream where turbulence promotes thorough mixing.

53. Additives including octane enhancers, metal deactivators, anti-oxidants, anti-knock agents, gum and rust inhibitors, detergents, etc. are added during and/or after blending to provide specific properties not inherent in hydrocarbons.

54. Major Refinery Products and their Uses
Gasoline
The most important refinery product is motor gasoline, a blend of hydrocarbons with boiling ranges from ambient temperatures to about 400 °F.
The important qualities for gasoline are octane number (antiknock), volatility (starting and vapor lock), and vapor pressure (environmental control).
Additives are often used to enhance performance and provide protection against oxidation and rust formation.

55. Kerosene
Kerosene is a refined middle-distillate petroleum product that finds considerable use as a jet fuel and around the world in cooking and space heating.
When used as a jet fuel, it shows some of the critical qualities are freezing point, flash point, and smoke point.
Commercial jet fuel has a boiling range of about 375°-525° F, and military jet fuel 130°-550° F.
Kerosene, with less-critical specifications, is used for lighting, heating, solvents, and blending into diesel fuel.

56. Liquified Petroleum Gas (LPG)
LPG, which consists principally of propane and butane, is produced for use as fuel and is an intermediate material in the manufacture of petrochemicals.
The important specifications for proper performance include vapor pressure and control of contaminants.
Distillate Fuels
Diesel fuels and domestic heating oils have boiling ranges of about 400°-700° F.

57. The desirable qualities required for distillate fuels include controlled flash and pour points, clean burning, no deposit formation in storage tanks, and a proper diesel fuel rating for good starting and combustion.
Residual Fuels
Many marine vessels, power plants, commercial buildings and industrial facilities use residual fuels or combinations of residual and distillate fuels for heating and processing.
The two most critical specifications of residual fuels are high viscosity and low sulfur content for environmental control.

58. Coke and Asphalt. Solvents
Coke is almost pure carbon with a variety of uses from electrodes to charcoal briquets.
Asphalt, used for roads and roofing materials, must be inert to most chemicals and weather conditions.
Solvents
A variety of products, whose boiling points and hydrocarbon composition are closely controlled, are produced for use as solvents. These include benzene, toluene, and xylene.

59. Petrochemicals
Many products derived from crude oil refining, such as ethylene, propylene, butylene, and isobutylene, are primarily intended for use as petrochemical feedstock in the production of plastics, synthetic fibers, synthetic rubbers, and other products.

60. Lubricants.
Special refining processes produce lubricating oil base stocks. Additives such as demulsifiers, antioxidants, and viscosity improvers are blended into the base stocks to provide the characteristics required for motor oils, industrial greases, lubricants, and cutting oils.
The most critical quality for lubricating-oil base stock is a high viscosity index, which provides for greater consistency under varying temperatures.

61. THE END