Petroleum, Its constituents and method of separation

Petroleum, Its constituents and method of separation

   The word petroleum means literally rock oil. It was thought to be completely different oil than that which comes from vegetables sources such as olive, but modern researched has traced its origin to the lipids (oils) of planktonic (free floating) plant and animals which live in brackish water such as blue-green algaes and for a minifera. The brackishness is essential because aerobic bacteria do not live in brackish water. Aerobic bacteria would decompose all of the organic matter of the planktonic plants and animals sinks to the bottom and is incorporated in clay sediments which ultimately become sedimentary rocks.

This is the organic of the oil shales

Under high pressure and temperature the oil of the clay shales can be squeezed out and into porous rock. In porous rock the oil can travel until it reaches an impervious barrier such as a salt dome.

The evidence for the organic origin of petroleum is overwhelming petroleum is found only in association with sedimentary rocks. There is no petroleum associated with igneous or metamorphic rocks. Polarized light passing through all petroleum undergoes a rotation that is the same as for the organic oils.

Chlorophyll and hemin are found in petroleum

During the past 600 million years incompletely decayed plant and animals have become buried under buried thick layers of rock. It is believed that petroleum consists of the remain that are largely responsible for the relatively high organic carbon content of the fine grained sediments like the Chattanooga shale which are the principle source rocks for petroleum. Among the leading producers of petroleum are Saudi Arabia, Russia, the United States, (chiefly Texas, North Dakota, Alaska, and California) China, Iran, Canada, The United Arab Emirate, Mexico, Brazil, Iraq, Nigeria, Venezuela, and Norway. The largest proven reserves are in the middle east.

The following are the types of crude oil: The petroleum industry often uses references to geographical locations “in order to descriptively classify crude oils. 

This is due to the fact that oil from different geographical locations will naturally have its own very unique properties. These oils vary dramatically from one when it comes to their viscosity, viscosity and toxicity. The term viscosity relate to the oils resistance to flow. Higher viscosity crude oil is crude oil is much more difficult to pump from ground transport and refine.

The term volatility describes how quickly the oil evaporates into the air. Oils that are naturally volatile need additional effort to ensure that temperature regulation and sealin procedures loose as little as oil as possible.

-         Crude oil is classified as light, medium or heavy according to its measured API gravity.

Light crude oil has an API gravity higher than 31.1⁰ API.

-         Medium crude oil has an API gravity between 2.3 ⁰API and 31.1 ⁰API

-         Heavy crude oil has an API gravity below 22.3 ⁰API

API gravity is a measure of how heavy or how light a petroleum liquid is compared to water. If its API gravity is greater than 10. it is higher and floats on water. If less than 10, it is heavier and sinks. Most values fall between 10 and 70 API gravity degrees.

There are five primary types of crude oil

-         West Texas intermediate (WTI) oil, a.k.a. Texas sweet light, it is a type of crude oil used as a bench mark in oil pricing and the underlying commodity of New York mercantile exchange’s  oil futures contracts. WTI and Brent crude are usually referenced in western news report about its properties and production site make it ideal to be refined in the U.S. typical price difference per barrel is about $1 more than Brent, and $2 more than Opec basket.

-         Light crude oil is a crude oil with a low wax content.

-         Sour crude has a hydrogen sulfide level greater than 1%. It also contain carbon dioxide. It is usually processed into heavy oil such as diesel instead of gasoline top reduce processing costs. Venezuela is the world’s major producer of crude oil.

-         Sweet crude contains less than 0.5 suphur and contains trace amounts of hydrogen sulphide and carbon dioxide it is commonly used for processing to gasoline.

-         Brent crude oil consists of Brent crude, Brent sweet light crude, Osberg and Forties Brent crude is sourced from the north sea. The name “Brent” comes from the formation layers Broom, Rannoch, Etieve, Ness and Tarbat. Oil production from Europe, Africa and middle east tends to be priced relative to this oil. Bent is ideal production for gasoline and is typically refined in northwest Europe. Typical price difference per barrel is about $1 less than WTI and is $ more than Opce Basket. Brent crude has an API gravity of about 38.

Crude oil and natural gas are called hydrocarbons because both are composed of carbon and hydrogen atoms. Natural gas molecules are generally shorter; four carbon atoms o lees. Crude oil molecules contain five or more carbon atoms per molecule.

Crude oil is described as “crude” for a simple reason: it contains many different hydrocarbon compounds. An oil refinery in simples term does three things:

-         Separate the multiples of compounds within the crude oil into individual chemical unit.

-         Removal of contaminants

-         Convert units into as much gasoline as possible.

The constituents of crude oil; crude oil is essentially a mixture of many different hydrocarbons, all of varying lengths and complexities. In order to separate the individual components that make up the raw natural resource, the crude oil must be fractionally distillated so that chemical components can be removed at a time according to their boiling points.

a.     Light Distillates

b.     Naptha – made into gasoline/petrochemicals

c.      Kerosene

-         Middle distillates

·        Light gas oil – made into jet/diesel furnace fuels

·        Heavy gas oil – Further processing to produce Naptha and other products. The constituent of crude oil are petrol, tar, oil dissolved gases and kerosene also known as petroleum.

·        Residue – Further processed into refinery fuels, heavy fuel oil, waxes, greases, asphalts (the lighter the stuff the higher the price).

      Each refinery is uniquely designed to process specific crude oils into selected products. In order to meet the business objectives of the refinery, the process designer selects from an array basic processing units, in general these units perform one of three functions

-         Separating the many types of hydrocarbon present in crude oils into fractions of more closely related properties.

-         Chemically converting the separated hydrocarbon into more desirable reaction products.

-         Purifying the products of unwanted elements and compounds.

FRACTIONAL DISTILLATION: The primary process of separating the hydrocarbon components of crude oil is fractional distillation, crude oil distillers separate crude oil into fractions for subsequent processing in such units as catalyistic reformers, cracking units, alkylation units also incorporates its own reaction products.

Modern crude oil distillation units operate continuously over long periods of time and are much larger than the fractional distillation units employed in chemical or other industries. Process rates are commonly delineated in American barrel.

Crude oil is withdrawn from storage tanks at ambient temperature and pumped at a constant rate through a series of heat exchangers in order to reach a temperature of about 120⁰ (250⁰f). A controlled amount of fresh water is introduced and the mixture is pumped into a distillating drum where it passes through an electronic field and a salt water phase is separated. (If the salt were not removed at a stage, it would be deposited later or the tubes of the furnace and cause plugging) the desalted crude oil passes through additional heat exchangers and then through steel alloy tubes in a furnace. There it is heated to a temperature between 315 and 400⁰ (600 – 750⁰f), depending on the type of crude oil and the end products desired. A mixture of vapour and unvaporized oil passes from the furnace into the fractionating column, a vertical cylindrical containing 20 to 40 fractiionating trays are of the sieve or valve type. Sieve trays are simple, perforated plates with small holes about 5 to 6mm (0.2 to 0.25 inch) in diameter. Valves trays are similar, except the perforations are covered by small metal disks that restrict the flow through the perforations under certain process conditions.

The oil vapour rise up through the coumn and are condensed to a liquid in a water-or air-cooled condenser at the top of the tower. A small amount of gas remains uncondensed and is piped into the refinery fuel-gas system.

A pressure control valve on fuel-gas maintains fractionating column pressure at the desired figure, usually near one standard atmosphere pressure, measured as approximately 1 bar, 100 kilo pascals (kpa), or 15 pounds per square inch (psi) part od the condensed liquid called reflux, is pumped and packed into the top of the column and decends from tray to tray. Contracting rising vapours as they pass through the slots in the trays. The liquid progressively absorbs heavier constituents from the vapour and in turn, gives up lighter constituents to vapour phase. Condensation and re-evaporation takes place on each tray. Eventually an equilibrium is reached in which there is a continual gradation of temperature and oil properties throughout the column, with the lightest constituents from vapour and in turn, gives up lighter constituents to the vapour phase. Condensation and re-evaporation takes place on earth tray. Eventually an equilibrium is reached in which there is a continual gradation of temperature and oil properties throughout the column, with the lightest constituent on the top tray and the heaviest on the bottom. The use of reflux and vapour-liquid contacting trays distinguishes fraction distillation from simple distillation columns.

VACUUM DISTILLATION: The principles of vacuum distillation resemble those of fraction distillation (commonly called atmospheric distillation to distinguish it from the vacuum method) except that larger-larger-diameter columns are sued to maintain capable vapour relocates at reduced operating pressures. A vacuum of 50 to 100mm of mercury absolute is produced by a vacuum pump or steam ejector.

The primary advantage of vacuum distillation is that it allows for distillating heavier materials at lower temperature than those that would be required at atmospheric pressure, thus avoiding thermal cracking of the components fining condition in the furnace are adjusted so that oil temperature, usually do not exceed 425⁰c (860⁰) the residue remaining after vacuum distillation called bitumen, may be further blended to produce road asphalt or residual fuel oil, or it may be used as a feed stock for thermal cracking or cooking units vacuum distillation units are essential parts of many processing schemes designed to produce lubricants.

SOLVENT EXTRACTION: Are processed employed primarily for the removal of constituent that would have an adverse effect on the performance of the product in use. An important application is the removal of heavy aromatic compounds from lubrication oils. Removal improves the viscosity- temperature relationships of the product, extending the temperature relationship of the product. Extending the temperature range over which satisfactory lubricants oil are phenol and furfural.

ABSORPTION: Absorption processes are employed to recover valuable components such as propane/propylene and butane/butylenes from the vapours that leave the top of crude-oil or process- unit fractionating columns within the refinery. These volatile gases are bubbled through an absorption phiod, such as kerosene or heavy nalp, in equipment resembling a fractionating column the light products dissolve in the oil while the dry gases – such as hydrogen, methane, ethane and ethylene-pass through undesired. Absorption is more effective under pressure about 7 to 10 bars (0.7 to 1 mega pascal (mpa), or 100 to 15000ps, than it is at atmospheric pressure.

The enriched absorption fluid is heated and passed into a stripping column and is reused in the absorption tower.

HYDRO CRACKING: One of the most far-reaching developments of the refining industry in point by the availability of hydro as a by-product of catalytic reforming since the 1980s, hydrogen processing has become so prominent that many refineries now in cooperate hydrogen manufacturing plants in their processing schemes.

Through hydro cracking processes a similar feedstock to the catalytic cracking unit. It offers even greater flexibility in product yields. The process can be used for producing gasoline or jet fuels from heavy gas oils, for producing high-quality and how sulper contact and may be blended into final products without for the processing. Hydro cracked Naphtha on other hand is often low in octane and must be catalytically reformed to produce high-quality gasoline.

CATALYTIC CRACKING: The use of thermal cracking unit to convert gas oils into Naphtha dates from before 1920. These units produce small qualities or unstable Naphtha and large amounts of by product coke while they succeeded in providing small increase in gasoline yields. It was the commercialization of the fluid catalytic cracking processing in 1942 that really established the foundation of modern petroleum refining. The process not only provided a highly efficient means of converting high boiling gas oil into Naphtha to meet to rising demand high-octane gasoline, but it is also represented break through in catalyst technology.

The thermal cracking process functional largely in accordance with free-radical theory of molecular frame formation under conditions of extreme heat, the electron bond between carbon atoms in hydrogen carbon molecule can be broker, thus generating a hydrocarbon group with an unparred electron. The negatively charged molecule, called a free radical enters into reaction with other hydrocarbon.

Continually producing free radicals via the transfer of negatively charged hydride ions (H⁰). This is a carbon established that leads to a reduction in molecular size of cracking of components of the original feed stock.

As the cracking reactions proceed, carbon is deported on the catalyst particles. Since this deport impair the reaction efficiency, the catalyst is removed by centrifugal force and dropped back into the stripper section. In the stripping section, hydrocarbons are removed from the spent catalyst with steam, and the catalyst is transferred through the stripper stand pipe to the regeneration process (675 - 785⁰c or 1250 – 1450⁰f) heats the catalyst to the desired reaction temperature for re-contacting fresh feed into the unit in order to maintain activity a small amount of fresh catalyst is added to the system from time to time, and a similar amount is withdrawn.

The product obtained from primary distillation of crude oil are:

       i.            Fuel oil: This is a mix of heavy hydrocarbons which is obtained by diluting a heavy viscosity residue with high oil products such as gas oil.

     ii.            Kerosene: This is a product of crude oil that is largely obtained from the primary distillation of crude oil. The main use of kerosene is in aviation turbine engines (jet fuel) while its use for heating purpose is less relevant.

  iii.            Diesel (gas oil): This is also known as mobile distillate and is obtained both from specific during refining process.

  iv.            Gasoline: The is defined as a mix of light hydrogen, with molecules of 4 to 12 carbon atoms, liquid at ambient temperature and pressure conditions, suitable to be used for internal combustion engines with spark ignition.

     v.            Liquefied petroleum gas (LPG); is a mixture of a very light hydrocarbons with gaseous qualities at atmosphere pressure and which liquefied at environmental temperature and not very high pressure.

  vi.            Fuels: An initial distinction can be made with the fuels of petroleum origin. It is that between carburetants and combustibles. This distinction generally implies the mechanism by which the mixing with air in the phase that precedes combustion is done.