a chemical reaction means, such as combustion,...
TRANSCRIPT
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Fuel
Any material that is burned or altered in order to obtain energy and to heat
or to move an object
• Fuel releases its energy either through
– a chemical reaction means, such as combustion,
– or nuclear means, such as
• nuclear fission or
• nuclear fusion.
Energy
• Renewable - Created about as fast as it is consumed - months, years, decades (trees, nuclear fusion, sunlight, wind, etc.)
• Nonrenewable – Consumed much faster than it forms; created slowly - millions of years (fossil fuels, nuclear fission, etc.)
Energy Units
• Joule: One joule is the amount of energy required to perform the following physical actions:
– The work done by a force of one newton travelling through a distance of one metre;
– The work required to move an electric charge of one coulomb through an electrical potential difference of one volt; or one coulomb volt, with the symbol C·V;
– The work done to produce the power of one watt continuously for one second; or one watt second. Thus a kilowatt hour is 3,600,000 joules.
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Energy Units
• Calorie: The energy needed to increase the temperature of a gram of water by 1 °C depends on the starting temperature and is difficult to measure precisely.
• British Thermal Unit (BTU) - the amount of energy required to raise the temperature of one pound of water 1 F at its maximum density.
• Kilowatt hours is the product of power in kilowatts multiplied by time in hours
• Kilowatt Hours and BTUs are related in the following conversion: 1 Kilowatt Hour = 3,413 BTUs
Conversion of Energy Units – 1 calorie = 4.1868 Joules – 1 BTU = 1055.06 Joules – 1 BTU = 251.996 calories
World Energy Resource Consumption
• Non-renewable – Petroleum = 36.6% – Natural Gas = 23.3% – Coal = 26.5% – Nuclear fission = 6.3% – In 2009 nuclear power met 13–14% of the world's electricity demand
• Renewable – Hydroelectric = 2.2% – Biomass (wood) = 10.4% – Biogas (methane), liquid biomass, geothermal, solar, wind, and wave
energy = 0.7% – Nuclear fusion (e.g., reaction similar to that of the Sun) - technology is still
in infancy; currently not available for use as an energy resource – As of 2010, about 16% of global final energy consumption comes from
renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from hydroelectricity.
Chemical Energy (as of 2005)
Chemical Energy sources
• Much of the chemical energy produced by life forms, such as fossil fuels, is derived from the utilization of solar energy through photosynthesis.
• There are two major categories:
– Fossil fuel
– Biofuel
Fossil Fuels
• hydrocarbons, primarily coal and petroleum (liquid petroleum or natural gas), formed from the fossilized remains of dead plants and animals by exposure to heat and pressure in the Earth's crust over a long period of time
• are non-renewable resources because reserves are being depleted much faster than new ones are being formed.
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Origin of Fossil fuels
• Formed from the preserved remains of organisms that have settled to the sea (or lake) bottom in large quantities under anoxic conditions.
– Anoxic waters are areas of sea water or fresh water that are depleted of dissolved oxygen.
– This condition is generally found in areas that have restricted water exchange.
Origin of Fossil fuels
• This organic matter, mixed with mud, is buried under heavy layers of sediment.
• The resulting high levels of heat and pressure cause the organic matter to chemically alter, first into a waxy material (known as kerogen), and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis
• Terrestrial plants, on the other hand, tend to form coal.
Comparative figures
• 1 litre of regular gasoline is the time-rendered result of about 23.5 metric tons of ancient organic material deposited on the ocean floor.
• The total fossil fuel used in the year 1997 is the result of 422 years of all plant matter that grew on the entire surface and in all the oceans of the ancient earth
Types of Fossil Fuels
• Petroleum Oil
• Natural gas
• Coal
• Oil shales
• Tar sands
• Gas hydrates
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Coal
• Most of our coal was formed about 300 million years ago, when much of the earth was covered by steamy swamps
• Through metamorphism, water and volatiles are squeezed out, leaving essentially carbon.
• Generally Carboniferous and Permian in age.
• It differs from oil, which comes from oceans, in that the ‘hard parts’ of plants remain. As a result, the final product is a solid rock.
Coal
• As plants and trees died, their remains sank to the bottom of the swampy areas, accumulating layer upon layer and eventually forming a soggy, dense mat of organic material called peat
Coal
• Continued burial by overlying sediment/rock layers changes peat into higher grades of coal:
– Lignite (avg ~30% Carbon)
– Subbituminous (avg ~40% C)
– Bituminous (avg ~66% C)
– Anthracite (avg ~92% C)
– Higher carbon content also indicates higher heat content (burning temperature, BTU) and lower impurity content.
Coal and Peat
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Types of Coal
• Anthracite
– highest carbon content, between 86-98%
– heat value of nearly 8,000 KJ-per-kg
– most frequently used for home heating
• Bituminous
– has a carbon content ranging from 45-86%
– heat value of 5,500 to 7,500 KJ-per-kg
– used primarily to generate electricity and make coke for the steel industry
Types of Coal
• Subbituminous – has a carbon content ranging from 35-45%
– heat value between 4,300 and 6,500 KJ-per-kg
– generally has a lower sulfur content than other types • makes it attractive for use because it is cleaner burning
– used primarily as fuel for steam-electric power generation
• Lignite
– has a carbon content ranging from 25-35%
– heat value ranging between 2,000 and 4,100 KJ-per-kg
– mainly used for electric power generation
Environmental Problems with Coal
• There are significant environmental costs associated with the extraction, transport, and combustion (burning) of coal
• coal is still the dirtiest energy source around the world
Environmental Problems with Coal
– When it is burned, coal releases a number of problem pollutants: • Mercury – a known nervous system toxin • Sulfur – which leads to the formation of acid
rain • Nitrogen – which also contributes to acid rain
as well as smog • Carbon dioxide – the chief global warming gas
• Acid mine drainage is also a product of coal extraction – Refers to the outflow of acidic water from
(usually) abandoned mines or coal mines
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Problems with Coal Mining
Underground shafts and tunnels are dug to follow a coal seam (layer)
– Problems include:
• subsidence (slow, or rapid - cave-in)
• black lung disease for miners
• exposure to high levels of radon gas
• methane gas explosions
• underground fires or floods
Problems with Coal Mining
Sinkholes formed by collapse of abandoned mine shafts
Coal Mining Coal Mining
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Uses of Coal
• Coal is primarily used to generate electricity.
• Manufacturing plants and industries use coal to make chemicals, cement, paper, ceramics, and metal products
• Distillation of Coal releases methanol and ethylene which are used to make products such as plastics, medicines, fertilizers, and tar
• Certain industries consume large amounts of coal
– concrete and paper companies burn coal
– the steel industry uses coke and coal by-products to make steel for bridges, buildings, and automobiles
Comparison of Major Types of Fossil Fuel
• Oil contains 17% less C/unit energy than coal
• Natural gas contains 43% less C/unit energy than coal
• Natural gas contains 31% less C/unit energy than oil
• Gas<Oil<Coal
Petroleum Oil
• The term petroleum, comes from Greek meaning "rock oil", or crude oil
• It is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds.
Petroleum Oil
• Proportion of hydrocarbons in petroleum is highly variable and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils.
• The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various benzene ring-containing hydrocarbons
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Composition of Petroleum Oil
Composition by weight
Element Percent range
Carbon 83 to 87%
Hydrogen 10 to 14%
Nitrogen 0.1 to 2%
Oxygen 0.1 to 1.5%
Sulfur 0.5 to 6%
Mining of Petroleum Oil
• Petroleum is found in porous rock formations in the upper strata of some areas of the Earth's crust.
BASICS OF CRUDE OIL
• Crude oils are complex mixtures containing many different hydrocarbon compounds that vary in appearance and composition from one oil field to another.
• Crude oils range in consistency from water to tar-like solids, and in color from clear to black. An "average" crude oil contains about 84% carbon, 14% hydrogen, 1%-3% sulfur, and less than 1% each of nitrogen, oxygen, metals, and salts.
• Crude oils are generally classified as paraffinic, naphthenic, or aromatic, based on the predominant proportion of similar hydrocarbon molecules. Mixed-base crudes have varying amounts of each type of hydrocarbon. Refinery crude base stocks usually consist of mixtures of two or more different crude oils.
BASICS OF CRUDE OIL
• Crude oils are also defined in terms of API (American Petroleum Institute) gravity. The higher the API gravity, the lighter the crude. For example, light crude oils have high API gravities and low specific gravities. Crude oils with low carbon, high hydrogen, and high API gravity are usually rich in paraffins and tend to yield greater proportions of gasoline and light petroleum products; those with high carbon, low hydrogen, and low API gravities are usually rich in aromatics.
• Crude oils that contain appreciable quantities of hydrogen sulfide or other reactive sulfur compounds are called "sour." Those with less sulfur are called "sweet." Some exceptions to this rule are West Texas crudes, which are always considered "sour" regardless of their H2S content, and Arabian high-sulfur crudes, which are not considered "sour" because their sulfur compounds are not highly reactive.
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Crude oil (with a high API) being poured into a beaker.
Crude oil on fingers!
Three Principal Groups or Series of Hydrocarbon Compounds that Occur Naturally in Crude Oil
• a. Paraffins. The paraffinic series of hydrocarbon compounds found in crude oil have the general formula CnH2n+2 and can be either straight chains (normal) or branched chains (isomers) of carbon atoms. The lighter, straight-chain paraffin molecules are found in gases and paraffin waxes. Examples of straight-chain molecules are methane, ethane, propane, and butane (gases containing from one to four carbon atoms), and pentane and hexane (liquids with five to six carbon atoms). The branched-chain (isomer) paraffins are usually found in heavier fractions of crude oil and have higher octane numbers than normal paraffins. These compounds are saturated hydrocarbons, with all carbon bonds satisfied, that is, the hydrocarbon chain carries the full complement of hydrogen atoms.
Three Principal Groups or Series of Hydrocarbon Compounds that Occur Naturally in Crude Oil
• b. Aromatics are unsaturated ring-type (cyclic) compounds which react readily because they have carbon atoms that are deficient in hydrogen. All aromatics have at least one benzene ring (a single-ring compound characterized by three double bonds alternating with three single bonds between six carbon atoms) as part of their molecular structure. Naphthalenes are fused double-ring aromatic compounds. The most complex aromatics, polynuclears (three or more fused aromatic rings), are found in heavier fractions of crude oil.
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Three Principal Groups or Series of Hydrocarbon Compounds that Occur Naturally in Crude Oil
• c. Naphthenes are saturated hydrocarbon groupings with the general formula CnH2n, arranged in the form of closed rings (cyclic) and found in all fractions of crude oil except the very lightest. Single-ring naphthenes (monocycloparaffins) with five and six carbon atoms predominate, with two-ring naphthenes (dicycloparaffins) found in the heavier ends of naphtha.
Other compounds found in crude oil
• a. Sulfur Compounds. Sulfur may be present in crude oil as hydrogen sulfide (H2S), as compounds (e.g. mercaptans, sulfides, disulfides, thiophenes, etc.) or as elemental sulfur. Hydrogen sulfide is a primary contributor to corrosion in refinery processing units. Other corrosive substances are elemental sulfur and mercaptans. Moreover, the corrosive sulfur compounds have an obnoxious odor.
• b. Oxygen Compounds. Oxygen compounds such as phenols, ketones, and carboxylic acids occur in crude oils in varying amounts. c. Nitrogen Compounds. Nitrogen is found in lighter fractions of crude oil as basic compounds, and more often in heavier fractions of crude oil as nonbasic compounds that may also include trace metals such as copper, vanadium, and/or nickel. Nitrogen oxides can form in process furnaces. The decomposition of nitrogen compounds in catalytic cracking and hydrocracking processes forms ammonia and cyanides that can cause corrosion.
Other compounds found in crude oil • d. Trace Metals. Metals, including nickel, iron, and vanadium are often
found in crude oils in small quantities and are removed during the refining process. Burning heavy fuel oils in refinery furnaces and boilers can leave deposits of vanadium oxide and nickel oxide in furnace boxes, ducts, and tubes. It is also desirable to remove trace amounts of arsenic, vanadium, and nickel prior to processing as they can poison certain catalysts. e. Salts. Crude oils often contain inorganic salts such as sodium chloride, magnesium chloride, and calcium chloride in suspension or dissolved in entrained water (brine). These salts must be removed or neutralized before processing to prevent catalyst poisoning, equipment corrosion, and fouling. Salt corrosion is caused by the hydrolysis of some metal chlorides to hydrogen chloride (HCl) and the subsequent formation of hydrochloric acid when crude is heated. Hydrogen chloride may also combine with ammonia to form ammonium chloride (NH4Cl), which causes fouling and corrosion. f. Carbon Dioxide. Carbon dioxide may result from the decomposition of bicarbonates present in or added to crude, or from steam used in the distillation process. g. Naphthenic Acids. Some crude oils contain naphthenic (organic) acids, which may become corrosive at temperatures above 450° F when the acid value of the crude is above a certain level.
CRUDE OIL PRETREATMENT (DESALTING)
• Crude oil is recovered from the reservoir is mixed with a variety of substances: gases, water and dirt (minerals).
• Before certain varieties of crude oil can be processed at all, they must go through a process called “desalting.”
• This process removes water, salts, and other solid materials that otherwise could damage the equipment at a refinery.
• If these crude oil contaminants are not removed, they can cause operating problems during refinery processing, such as equipment plugging and corrosion as well as catalyst deactivation.
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CRUDE OIL PRETREATMENT (DESALTING)
• Desalting essentially means that the crude oil is dehydrated (water is removed) so that the impurities settle out.
• Desalting is a water – washing operation performed at the production field and at the refinery site for additional crude oil cleanup. If the petroleum from the seperators contains water and dirt, water washing can remove much of the water – soluble minerals and entrained solids.
• Synthetic crude is crude that was processed at the source. It does not require desalting at the refinery. Thus, the waste water and contaminants that are a byproduct of desalting are not an issue for refineries that use synthetic crude oil.
CRUDE OIL PRETREATMENT (DESALTING) • The two most typical methods of crude-oil desalting, chemical and
electrostatic separation, use hot water as the extraction agent. In chemical desalting, water and chemical surfactant (demulsifiers) are added to the crude, heated so that salts and other impurities dissolve into the water or attach to the water, and then held in a tank where they settle out. Electrical desalting is the application of high-voltage electrostatic charges to concentrate suspended water globules in the bottom of the settling tank. Both methods of desalting are continuous. A third and less-common process involves filtering heated crude using diatomaceous earth
• The desalted crude feedstock is preheated using recovered process heat. The feedstock then flows to a direct-fired crude charge heater where it is fed into the vertical distillation column just above the bottom, at pressures slightly above atmospheric and at temperatures ranging from 650° to 700° F (heating crude oil above
these temperatures may cause undesirable thermal cracking).
PETROLEUM REFINING OPERATIONS • Fractionation (distillation) is the separation of crude oil in atmospheric and
vacuum distillation towers into groups of hydrocarbon compounds of differing boiling-point ranges called "fractions" or "cuts.“
• Conversion processes change the size and/or structure of hydrocarbon molecules. These processes include: – Decomposition (dividing) by thermal and catalytic cracking; – Unification (combining) through alkylation and polymerization; and – Alteration (rearranging) with isomerization and catalytic reforming.
• Treatment processes are intended to prepare hydrocarbon streams for additional processing and to prepare finished products. Treatment may include the removal or separation of aromatics and naphthenes as well as impurities and undesirable contaminants. Treatment may involve chemical or physical separation such as dissolving, absorption, or precipitation using a variety and combination of processes including desalting, drying, hydrodesulfurizing, solvent refining, sweetening, solvent extraction, and solvent dewaxing.
• Formulating and Blending is the process of mixing and combining hydrocarbon fractions, additives, and other components to produce finished products with specific performance properties.
• Other Refining Operations include: light-ends recovery; sour-water stripping; solid waste and wastewater treatment; process-water treatment and cooling; storage and handling; product movement; hydrogen production; acid and tail-gas treatment; and sulfur recovery.
Fractional Distillation of crude oil
• The mixture boils, forming vapor (gases); most substances go into the vapor phase.
• The vapor enters the bottom of a long column (fractional distillation column) that is filled with trays or plates. – The trays have many holes or bubble caps (like a loosened cap on a
soda bottle) in them to allow the vapor to pass through. – The trays increase the contact time between the vapor and the liquids
in the column. – The trays help to collect liquids that form at various heights in the
column. – There is a temperature difference across the column (hot at the
bottom, cool at the top).
• The vapor rises in the column. • As the vapor rises through the trays in the column, it cools.
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• When a substance in the vapor reaches a height where the temperature of the column is equal to that substance's boiling point, it will condense to form a liquid. (The substance with the lowest boiling point will condense at the highest point in the column; substances with higher boiling points will condense lower in the column.).
• The trays collect the various liquid fractions. • The collected liquid fractions may:
– pass to condensers, which cool them further, and then go to storage tanks
– go to other areas for further chemical processing
• Fractional distillation is useful for separating a mixture of substances with narrow differences in boiling points, and is the most important step in the refining process.
Atmospheric Distillation Tower
• The fractionating tower, a steel cylinder about 40 meters high, contains horizontal steel trays for separating and collecting the liquids. At each tray, vapors from below enter perforations and bubble caps. They permit the vapors to bubble through the liquid on the tray, causing some condensation at the temperature of that tray. An overflow pipe drains the condensed liquids from each tray back to the tray below, where the higher temperature causes re-evaporation. The evaporation, condensing, and scrubbing operation is repeated many times until the desired degree of product purity is reached.
Atmospheric Distillation Tower • Side streams from certain trays are taken off to
obtain the desired fractions. Products ranging from uncondensed fixed gases at the top to heavy fuel oils at the bottom can be taken continuously from a fractionating tower. Steam is often used in towers to lower the vapor pressure and create a partial vacuum.
• The distillation process separates the major constituents of crude oil into so-called straight-run products. Sometimes crude oil is "topped" by distilling off only the lighter fractions, leaving a heavy residue that is often distilled further under high vacuum.
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Vacuum Distillation Tower • In order to further distill the residuum or topped
crude from the atmospheric tower at higher temperatures, reduced pressure is required to prevent thermal cracking. The process takes place in one or more vacuum distillation towers.
• Vacuum tower may produce gas oils (fuel oils for agricultural, domestic and industrial engines and boilers), lubricating-oil base stocks, and heavy residual for propane deasphalting (using propane to remove and precipitate asphalt (A mixture of dark bituminous pitch with sand or gravel, used for surfacing roads, flooring, roofing) from petroleum stocks, such as for lubricating oils).
MAJOR REFINERY PRODUCTS • 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.
• 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, some of the critical qualities are freeze point, flash point, and smoke point. Commercial jet fuel has a boiling range of about 190°-274° C, and military jet fuel 54°-288° C. Kerosene, with less-critical specifications, is used for lighting, heating, solvents, and blending into diesel fuel.
• 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 204°-371° C. 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 cetane rating for good starting and combustion.
MAJOR REFINERY PRODUCTS • 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 viscosity and low sulfur content for environmental control. Coke and Asphalt. 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. 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. 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.
How does the petroleum industry define a "barrel"?
• The "barrel" is a volumetric unit commonly used in the petroleum industry and one barrel is equivalent to
– 42 U.S. gallons ... or
– 34.97 Imperial gallons ... or
– 158.99 liters ... or
– 5.615 Cubic feet
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• Almost none of the products that come out of the fractional distillation column is ready for market. Instead, they must be processed further, usually by:
– Solvent extraction or dewaxing
– Cracking: breaking large hydrocarbons iinto smaller ones
– Unification: combining smaller pieces
– Alteration: rearranging the various pieces.
Cracking
• The reduction in molecular weight of various fractions of oil through pyrolysis. Two major forms of cracking are thermal and steam cracking.
• Thermal cracking is mainly used to produce a mixture rich in ethylene and propylene. It has largely been replaced by steam cracking.
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Cracking
• The simple distillation of crude oil produces amounts and types of products that are not consistent with those required by the marketplace, subsequent refinery processes change the product mix by altering the molecular structure of the hydrocarbons.
• One of the ways of accomplishing this change is through "cracking," a process that breaks or cracks the heavier, higher boiling-point petroleum fractions into more valuable products such as gasoline, fuel oil, and gas oils. The two basic types of cracking are thermal cracking, using heat and pressure, and catalytic cracking.
Cracking
• It involves taking heavy oil such as kerosene or diesel and heating it to a high temperature in the presence of a catalyst. The large molecule breaks down into several smaller ones, some saturated, some unsaturated e.g.
Catalytic processes on petroleum hydrocarbons
• Catalytic hydrocracking – produces small alkanes from large alkanes by adding hydrogen.
• Catalytic cracking – produces small alkenes and alkanes by cracking in the absence of hydrogen.
• Catalytic Reforming – the alkanes and cycloalkanes are upgraded to higher octane number by conversion into aromatic compounds.
Fluid catalytic cracking (FCC) • Fluid catalytic cracking (FCC) is the most important
conversion process used in petroleum refineries. It is widely used to convert the high-boiling, high-molecular weight hydrocarbon fractions of petroleum crude oils to more valuable gasoline, olefinic gases, and other products.
• Cracking of petroleum hydrocarbons was originally done by thermal cracking, which has been almost completely replaced by catalytic cracking because it produces more gasoline with a higher octane rating. It also produces byproduct gases that are more olefinic, and hence more valuable, than those produced by thermal cracking.
• The feedstock to an FCC is usually that portion of the crude oil that has an initial boiling point of 340 °C or higher at atmospheric pressure and an average molecular weight ranging from about 200 to 600 or higher. This portion of crude oil is often referred to as heavy gas oil.
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Fluid catalytic cracking (FCC)
• The FCC process vaporizes and breaks the long-chain molecules of the high-boiling hydrocarbon liquids into much shorter molecules by contacting the feedstock, at high temperature and moderate pressure, with a fluidized powdered catalyst.
• The catalysts used in refinery cracking units are typically solid materials (zeolite, aluminum hydrosilicate, treated bentonite clay, fuller's earth, bauxite, and silica-alumina) that come in the form of powders, beads, pellets or shaped materials called extrudites.
• In effect, refineries use fluid catalytic cracking to correct the imbalance between the market demand for gasoline and the excess of heavy, high boiling range products resulting from the distillation of crude oil.
Fluid catalytic cracking (FCC) • The fluid catalytic cracking process breaks large hydrocarbon
molecules into smaller molecules by contacting them with powdered catalyst at a high temperature and moderate pressure which first vaporizes the hydrocarbons and then breaks them.
Catalytic cracking
• There are three basic functions in the catalytic cracking process:
– Reaction: Feedstock reacts with catalyst and cracks into different hydrocarbons;
– Regeneration: Catalyst is reactivated by burning off coke; and
– Fractionation: Cracked hydrocarbon stream is separated into various products.
Catalytic Cracking
• The unsaturated products are used as feedstock for the polymer industry.
• The saturated products are usually high-octane branched chain alkanes suitable for making petrol.
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Catalytic Cracking using Steam
• Steam Cracking is carried out in the presence of steam. Typically, a naphtha feedstock (with a boiling point or bp of 70–200°C) is passed, along with steam, through a coiled tube heated by a furnace.
• The steam acts as a diluents and, thus, favors unimolecular reactions, which minimize radical chain termination steps, allowing cracking to continue; and it lowers the vapour pressure of the hydrocarbons, thereby reducing resid concentration and maximizing desired product formation.
Catalytic cracking can be done in the laboratory by heating mineral wool soaked in oil with a catalyst, producing a gas.
What might this gas be?
mineral wool soaked in oil
gaseous product
aluminium oxide catalyst
Catalytic cracking in the lab
Reforming
• The process re-arranges or re-structures the hydrocarbon molecules in the naphtha feedstocks as well as breaking some of the molecules into smaller molecules.
• The overall effect is that the product reformate contains hydrocarbons with more complex molecular shapes having higher octane values than the hydrocarbons in the naphtha feedstock.
• Byproducts are small amounts of methane, ethane, propane and butanes.
CATALYTIC REFORMING.
• Catalytic reforming is an important process used to convert low-octane naphthas into high-octane gasoline blending components called reformates.
• A catalytic reformer comprises a reactor section and a product-recovery section.
• Most processes use platinum as the active catalyst. Sometimes platinum is combined with a second catalyst (bimetallic catalyst) such as rhenium or another noble metal.
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CATALYTIC REFORMING
• The naphtha feedstock is mixed with hydrogen, vaporized, and passed through a series of alternating furnace and fixed-bed reactors containing a platinum catalyst. The effluent from the last reactor is cooled and sent to a separator to permit removal of the hydrogen-rich gas stream from the top of the separator for recycling.
• The liquid product from the bottom of the separator, called the reformate is then sent to a fractionator called a stabilizer (butanizer).
• The pressure at Catalytic reformers ranges from a low of 50-200psi to a high of 1000 psi.
ISOMERIZATION • In an isomerization reactor the paraffins are catalytically
isomerized to isoparaffins. For example, 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.
• There are two distinct isomerization processes, butane (C4) and pentane/hexane (C5/C6). – Butane isomerization produces feedstock for
alkylation.
– 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 (Gasoline comprised of only natural ingredients from crude oil or natural-gas liquids; for example, no cracked, polymerized, alkylated, reformed products).
• Solvent Treating • Solvent treating involves methods to remove the
impurities that remain after the initial distillation step. These methods usually are used both at intermediate stages in the process and just before the product is sent to storage. Essentially, these processes remove the impurities by adding solvents (a liquid that can dissolve another substance). Depending on the specific processes, the impurities either clump up and fall to the bottom by chemical reaction (known as precipitating), are evaporated away along with the solvent, or the product is chilled so that the impurities precipitate.
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Merox process
• Merox is an acronym for mercaptan oxidation. It is a proprietary catalytic chemical process used in oil refineries and natural gas processing plants to remove mercaptans from LPG, propane, butanes, light naphthas, kerosene and jet fuel by converting them to liquid hydrocarbon disulfides.
Merox process
• The Merox process requires an alkaline environment which, in some of the process versions, is provided by an aqueous solution of sodium hydroxide (NaOH), a strong base, commonly referred to as caustic. In other versions of the process, the alkalinity is provided by ammonia, which is a weak base.
Merox process
• Processes within oil refineries or natural gas processing plants that remove mercaptans and/or hydrogen sulfide (H2S) are commonly referred to as sweetening processes because they results in products which no longer have the sour, foul odors of mercaptans and hydrogen sulfide.
• The liquid hydrocarbon disulfides may remain in the sweetened products, they may be used as part of the refinery or natural gas processing plant fuel, or they may be processed further.
Merox process
• In all of the above Merox versions, the overall oxidation reaction that takes place in converting mercaptans to disulfides is:
• 4 RSH + O2 → 2RSSR + 2H2O • The most common mercaptans removed are: • Methanethiol - CH3SH [m-mercaptan] • Ethanethiol - C2H5SH [e- mercaptan] • 1-Propanethiol - C3H7SH [n-P mercaptan] • 2-Propanethiol - CH3CH(SH)CH3 [2C3 mercaptan] • Butanethiol - C4H9SH [n-butyl mercaptan] • tert-Butyl mercaptan - C(CH3)3SH [t-butyl mercaptan] • Pentanethiol - C5H11SH [pentyl mercaptan]
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Visbreaking • A visbreaker is a processing unit in oil refinery whose
purpose is to reduce the quantity of residual oil produced in the distillation of crude oil and to increase the yield of more valuable middle distillates (heating oil and diesel) by the refinery. A visbreaker thermally cracks large hydrocarbon molecules in the oil by heating in a furnace to reduce its viscosity and to produce small quantities of light hydrocarbons (LPG and gasoline). The process name of "visbreaker" refers to the fact that the process reduces (i.e., breaks) the viscosity of the residual oil. The process is non-catalytic.
Coking
• In “coking,” the residual that is left behind in the distillation tower is heated until is breaks down into oil, gasoline, and naphtha (which is further processed to make gasoline); the process leaves behind an almost pure residue of carbon called “coke,” which is sold.
• It is not the same as the coke produced in steel making (or “coke” in coca cola) !
• Hydrocracking • In general, catalytic cracking has replaced most uses of
thermal cracking. All forms of catalytic cracking break down complex compounds into simpler structures to increase the quality and quantity of the desirable products and decrease the amount of residuals. A similar process that is not as common as “catalytic cracking,” is called “hydrocracking.” I
• t is a two-step process that uses a different catalyst — a substance that helps cause a reaction but that does not take part in it — than catalytic cracking, as well as lower temperatures; it also involves high pressure and introduction of hydrogen (“hydrogenation”). It breaks down heavy oil into gasoline and jet fuel or kerosene. Hydrocracking was developed in the 1960s to increase production of gasoline and forms the basis for the modern petrochemical industry. It is used for feedstock that is difficult to process by either catalytic cracking or reforming because they contain substances that are considered “poisons” for the catalyst.
• Hydrotreating • “Hydrotreating,” is a process that removes certain
constituents — nitrogen, sulfur, oxygen, and metals — that are considered “contaminants” in the liquid petroleum.
• These materials can damage the refinery equipment and impair the quality of the finished product. It also is used in advance of catalytic cracking to improve yields and to upgrade the quality of the product. Essentially, the process works by mixing the feedstock with hydrogen, heating it, and then passing it through a catalytic reactor.
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Hydrotreating…. • The reactor converts the contaminants to other forms that
can be separated; the result is a gas stream that, after treatment, can be used to fire the furnaces at the refinery, and a liquid stream that can be blended or used as feedstock.
• Practically all the naphtha that is fed to catalytic reforming units is hydrotreated to remove arsenic, sulfur, and nitrogen that would damage the catalyst. The resulting product, called reformate, is fed to the gasoline blending pool. Byproducts of this process include hydrogen, which is recycled within the refinery and used in hydrotreating or hydrocracking.
Unification
• Unlike cracking, which separates the large hydrocarbons into smaller ones, “unification” does the reverse. The process creates compounds that are used in making chemicals and in blending gasoline, and generates hydrogen, which may be used in hydrocracking or may be sold.
• Reforming • The major process is “catalytic reforming,” which
converts low-octane products into components that can be blended into high-octane gasoline. It also produces hydrogen that can be recycled and used in other processes.
• Reforming is the result of a number of reactions that occur simultaneously. The reformer includes a reactor (which may consist of alternating furnaces and fixed-bed reactors) and a section for product recovery.
• Most processes use platinum as the catalyst, although it may be combined with a second substance.
• Alkylation
• Finally, the structure of the hydrocarbon may be rearranged, rather than broken or combined, to produce a product.
• In alkylation, certain gases (known as “low molecular weight”) are mixed with a catalyst.
• This catalytic process was developed in the 1940s to produce high-octane aviation gasoline, clean-burning fuels, and materials to produce explosives and synthetic rubber.
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• Treating and Sweetening • Some intermediate and finished products may be
treated and sweetened, in most cases to remove unwanted sulfur. Treating is a means to remove certain substances that are considered “contaminants” in the finished product. These contaminants can include sulfur, nitrogen, oxygen, certain metals, and salts.
• Sweetening is a major refinery treatment for gasoline and improves color, odor, and stability; it also reduces the concentration of carbon dioxide. These processes can be accomplished by addition of acid or other compounds, by heating the product, or through use of catalysts.
• Asphalt Production • The residual materials from the refining process
can be used to produce asphalt. • Asphalt for roads is processed in vacuum
distillation, where it is heated and sent to a column under vacuum to prevent it from cracking (further separating into other materials).
• When the asphalt will be used for shingles or other roofing materials, it is produced by air blowing.
• It is heated almost to the point where it will evaporate and then sent to a tower, where hot air is injected. A third process is solvent deasphalting.
Asphalt Production… • This process uses propane or hexane as a solvent;
it produces lubricating oil, materials that can be recycled in other parts of the refining operation, and asphalt. The process feeds the material and propane into a tower at closely controlled mixtures, temperatures, and pressures, and separates the material on a rotating disc. The products are evaporated and exposed to steam to recover the propane, which is recycled in the operation.
Blending • Blending is the physical mixing of a number of
different hydrocarbons to produce a product. • Products can be blended through manifolds or in
tanks and other vessels. • The products can be blended by injecting the
correct amounts of each component; additives to improve performance can be added both during and after blending to provide specific characteristics that would not otherwise be present.
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A Small quiz
Are these statements about crude oil refining true or false?
1 Crude oil must be refined before it is used.
2 Fractional distillation works because different molecules have different boiling points
3 Large molecules are broken into smaller molecules during fractional distillation
4 Small molecules collect at the bottom of the fractionating column
5 Each fraction of refined crude oil contains a mix of compounds with similar boiling point
6 Catalytical cracking breaks down large alkanes into smaller alkanes and alkenes
Products from the Refinery • Asphalt also known as bitumen, is the sticky, black and highly
viscous liquid or semi-solid present in most crude petroleums and in some natural deposits; it is a substance classed as a pitch.)
Main Uses of Asphalt • The primary use (more than 80%) of asphalt is in road
construction and maintenance, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete.
• Its other main uses are for bituminous waterproofing products, including production of roofing felt and for sealing flat roofs. Only about 1% is used for waterproofing, damp-proofing, insulation, and paints.
• Other uses are in hydraulics, to protect metals against corrosion, and in electrical laminate adhesives, synthetic turf bases and sound insulation materials.
• Fuel Oil - The Fuel Oil is made of long hydrocarbon chains, particularly Alkanes, Cycloalkanes and aromatics.
• The term “Fuel Oil” is also used in a strict sense to refer only to the heaviest commercial fuel that can be obtained from crude oil, heavier than Gasoline and Naphtha.
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• Diesel is collected in the range 250-350 degrees Celsius, and has hydrocarbons with average of 12 carbon atoms (typically contain between 8 and 21 carbon atoms per molecule). Diesel is used as a fuel in motor vehicles, and as a heating oil.
• Naphtha is a product of the refining of crude oil. Naphtha is collected in the range 60-100 degrees Celsius, and has hydrocarbons with 5-9 carbon atoms.
• Naphtha is an intermediate product that is processed to produce petrol for use as a fuel in motor vehicles.
• Lubricating oil contains hydrocarbon chains with 20-50 carbon atoms, with light lubricating oil at the lower end of this range with a low viscosity.
• Lubricating oil boils in the range 300-370 degrees Celsius, and is used to lubricate motor vehicles and industrial machines.
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Kerosene
• Kerosene (also called jet fuel) is a product of the refining of crude oil. Kerosene is collected in the range 175-325 degrees Celsius, and has hydrocarbons with 10-18 carbon atoms. Kerosene is used as a fuel in aero plane jet engines.
• Gasoline (also called petrol) is a product of the refining of crude oil. Gasoline is collected in the range 40-205 degrees Celsius, and has hydrocarbons with 5-12 carbon atoms. Gasoline is used as a fuel in motor vehicles.
• Heavy fuel oil is also known as heavy gas oil or residual fuel oil.
Heavy fuel oil….
• Fuel oil is any liquid petroleum product that is burned in a furnace or boiler for the generation of heat or used in an engine for the generation of power.
• Carbon Chain length varies from 12 – 70 carbons.
• Heavy fuel oil is a high-viscosity residual oil requiring preheating to 104 - 127 °C.
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Gasoline
• Gasoline or petrol is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines
• It consists mostly of aliphatic hydrocarbons
• The bulk of a typical gasoline consists of hydrocarbons with between 5 and 12 carbon atoms per molecule.
Gasoline
• A typical gasoline is predominantly a mixture of alkanes, cycloalkanes, and alkenes. The exact ratios can depend on:
– the oil refinery that makes the gasoline, as not all refineries have the same set of processing units.
– the crude oil feed used by the refinery.
– the grade of gasoline, in particular the octane rating
• The specific density of gasoline is 0.71–0.77 kg/l
Gasoline
• An important characteristic of gasoline is its octane rating
• Octane rating is measured relative to a mixture of 2,2,4-trimethylpentane (an isomer of octane) and n-heptane.
• Gasoline is also one of the sources of pollutant gases.
• It produces carbon dioxide, nitrogen oxides, and carbon monoxide in the exhaust of the engine which is running on it.
PETROL AND OCTANE NUMBERS
• A number of things happen to the petrol in the internal combustion engine, including:
• Petrol is vaporised • The vapour is mixed with air • The petrol-air mixture is compressed • The mixture is ignited by a spark from the spark plug
and burned • The gases produced by the combustion reaction
expand • Expansion causes the piston to move i.e. kinetic energy
is produced.
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PREMATURE IGNITION in Petrol Engines
• The more the gases in engine are compressed, the more they heat up. Sometimes this causes ignition before the spark is produced.
• This is intended in a diesel engine, where there is no spark plug, but in a petrol engine the occurrence is called auto-ignition or knocking or pinking. This is quite a problem as it can cause loss of power, with obvious danger, or damage to the engine. It can be prevented in two ways during petrol manufacture: – Use of additives
– Use of a suitable mixture of high-octane compounds.
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OCTANE RATING
• The octane rating is a measure of the tendency of a fuel to auto-ignite. The lower the octane rating the more likely it is that auto-ignition will occur. Clearly, high-octane fuels are more desirable. The scale is an arbitrary one. Two compounds were chosen, heptane (C7H16) and 2,2,4-trimethylpentane (CH3C(CH3)2CH2CH(CH3)CH3).
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OCTANE RATING
• Heptane has a high tendency to auto-ignite, so it was given an octane number of 0.
• On the other hand, 2,2,4-trimethylpentane has a low tendency to auto-ignite, so it was given a rating of 100.
• A mixture of these two compounds containing 95% of 2,2,4-trimethylpentane is said to have an octane number of 95 (2,2,4-trimethylpentane was formerly known as iso-octane, hence the terms “octane number” or “octane rating”).
• A mixture of compounds with an identical tendency to auto-ignite, under the same conditions of compression, would thus also be given an octane rating of 95.
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Additives in Petrol
Two types of additive have been in use in recent decades, lead compounds and oxygenates.
(1) Lead compounds e.g. tetra ethyl lead.
• These work by preventing the type of reactions that cause knocking. They have been in use since the 1920s, but have long been criticised for their harmful environmental effects—the lead compounds present in exhaust fumes are toxic. Their use has been phased out in many countries including Kenya.
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Additives in Petrol
(2) Oxygenates e.g. alcohols or ethers
• These compounds work by raising the octane number of the fuel. They cause less pollution, because apart from not containing lead, they produce lower levels of carbon monoxide when they burn. The most commonly used oxygenate is MTBE (methyl tertiary butyl ether). The schematic name is 2-methoxy-2-methylpropane. Its octane rating is 118.
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Petrodiesel
• Petroleum diesel, also called petrodiesel, or fossil diesel is produced from the fractional distillation of crude oil between 200 °C and 350 °C at atmospheric pressure, resulting in a mixture of carbon chains that typically contain between 8 and 21 carbon atoms per molecule.
• The density of petroleum diesel is about 0.85 kg/l , about 18% more than petrol (gasoline)
Diesel Fuels • Alkanes from nonane to, for instance, hexadecane
(an alkane with sixteen carbon atoms) are liquids of higher viscosity, less and less suitable for use in gasoline. They form instead the major part of diesel and aviation fuel.
• Diesel fuels are characterised by their cetane number, cetane being an old name for hexadecane. Cetane number or CN is a measure of a fuel's ignition delay; the time period between the start of injection and the first identifiable pressure increase during combustion of the fuel.
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Hexadecane (cetane)
Definition of Cetane:
• 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.
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Chemical relevance • Cetane (also called Hexadecane) is an alkane hydrocarbon
with the chemical formula C16H34. • It ignites very easily under compression, so it was assigned
a cetane number of 100, while alpha-methyl napthalene was assigned a cetane number of 15 . All other hydrocarbons in diesel fuel are indexed to cetane as to how well they ignite under compression. The cetane number therefore measures how quickly the fuel starts to burn (auto-ignites) under diesel engine conditions. Since there are hundreds of components in diesel fuel, with each having a different cetane quality, the overall cetane number of the diesel is the average cetane quality of all the components. There is very little actual cetane in diesel fuel.
• Typical Values • Generally, diesel engines run well with a CN from
40 to 55. Fuels with higher cetane number which have shorter ignition delays provide more time for the fuel combustion process to be completed. Hence, higher speed diesels operate more effectively with higher cetane number fuels. There is no performance or emission advantage when the CN is raised past approximately 55; after this point, the fuel's performance hits a plateau.
How Does Cetane Number Affect Diesel Engine Operation?
• There is no benefit to using a higher cetane number fuel than is specified by the engine's manufacturer.
• Diesel fuels with cetane number lower than minimum engine requirements can cause rough engine operation. They are more difficult to start, especially in cold weather or at high altitudes. They accelerate lube oil sludge formation. Many low cetane fuels increase engine deposits resulting in more smoke, increased exhaust emissions and greater engine wear.
• Overall fuel quality and performance depend on the ratio of parafinic and aromatic hydrocarbons, the presence of sulfur, water, bacteria and other contaminants, and the fuel's resistance to oxidation.
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Cetane Rating Scale
• The reference fuel for the lower end of the cetane number scale is 2,2,4,4,6,8,8-heptamethylnonane with an assigned cetane number of 15.
• The cetane number scale is then defined as follows: CN = % by volume hexadecane + 0.15 * (% by volume heptamethylnonane)
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2,2,4,4,6,8,8-Heptamethyl-nonane
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Petrodiesel
• Diesel-powered cars generally have a better fuel economy than equivalent gasoline engines and produce less greenhouse gas emission.
• Petrodiesel is composed of about 75% saturated hydrocarbons (primarily paraffins including n, iso, and cycloparaffins), and 25% aromatic hydrocarbons (including naphthalenes and alkylbenzenes).
• The average chemical formula for common diesel fuel is C12H23, ranging from approx. C10H20 to C15H28
What is the difference between low sulphur diesel fuel, off-road diesel fuel and regular sulphur diesel fuel?
• Low sulphur diesel fuel - This fuel contains less than 500 parts per million (0.05 wt per cent) sulphur, required for on-road applications, and may be used off-road.
• Off-road diesel fuel - This refers to diesel fuel that is used for off-road purposes (i.e., (i.e., mining, farming, marine, etc.). This fuel is frequently dyed red or "marked" to show that it is exempt from provincial road taxes.
• Regular sulphur diesel fuel - This fuel contains less than 5,000 parts per million (0.5 wt per cent) sulphur, may not be used on-road, and is usually used in off-road applications such as farming, forestry and marine.
Biodiesel
• Biodiesel, is a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats.
• Biodiesel blend, is a blend of biodiesel fuel with petroleum-based diesel fuel designated BXX, where XX is the volume percent of biodiesel.
Biodiesel Raw Materials
Oil or Fat Alcohol
Soybean Methanol (common)
Corn Ethanol
Canola
Cottonseed Catalyst
Sunflower Sodium hydroxide
Beef tallow Potassium hydroxide
Pork lard
Used cooking oils
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Biodiesel Attributes
• High Cetane (avg. over 50)
• Ultra Low Sulfur (avg. ~ 2 ppm)
• High Lubricity, even in blends as low at 1-2%
• High Energy Balance (3.2 to 1)
• Low Agriculture Inputs: Soybeans
• 78% Life Cycle CO2 Reduction
• Renewable, Sustainable
• Domestically Produced
• Reduces HC, PM, CO in existing diesel engines
• Reduces NOx in boilers and home heating
Biodiesel Materials Compatibility
• Biodiesel and biodiesel blends will form high sediment levels when in contact with the following metals: – Brass, – Bronze, – Copper, – Lead, – Tin and – Zinc
• Biodiesel is compatible with: – Stainless Steel, – Aluminum
Tips for Biodiesel Handling
• Fuel tanks should be kept as full as possible to reduce the amount of air and water entering the tank.
• Storage in on-site tanks should be limited to less than 6 months. The storage container should be clean, dry, and dark.
• Copper, brass, lead, tin and zinc should not be used to store biodiesel.
• Equipment with biodiesel blends in the fuel system should not be stored for more than 6 months.
When switching from diesel fuel to biodiesel blend, it may be necessary to change the fuel filter an extra time or two.
• One outcome of improper handling of biodiesel may be microbial contamination.
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Natural Gas
• It is a gas consisting primarily of methane.
• It contains methane and can be classified into two major groups: – Fossil Natural Gas
– Biogas
• Fossil natural gas- Natural gas is commercially produced from oil fields and natural gas fields.
• It sometimes contains significant quantities of ethane, propane, butane, and pentane—heavier hydrocarbons removed prior to use as a consumer fuel—as well as carbon dioxide, nitrogen, helium and hydrogen sulfide
Composition of Fossil Natural Gas
• Mostly methane CH4
• Some ethane C2H6
• Propane C3H8
• Butane C4H10
• Hydrogen H2
• Some Nitrogen, carbon dioxide, hydrogen sulphide
Biogas
• When methane-rich gases are produced by the anaerobic decay of non-fossil organic matter (biomass)
• Sources of biogas include swamps, marshes, and landfills (see landfill gas), as well as sewage sludge and manure by way of anaerobic digesters, in addition to enteric fermentation (fermentation that takes place in the digestive systems of ruminant animals) particularly in cattle
Oil Shale
• Fine-grained sedimentary rocks containing waxy insoluble hydrocarbons called kerogen
• Can be converted to oil at temperatures in excess of 500 C
• 5 to 25% is recoverable organic material
• Rich oil shales burn like coal
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OIL SPILLS
• Oil is the most common pollutant in the oceans.
• The majority of oil pollution in the oceans comes from land.
• When oil leaks or spills into water it floats on the surface of both freshwater and saltwater.
• Oil floats because it is less dense than water. It’s easier to clean-up an oil spill because of oil’s lower density.
Mild Oil Spill
Serious oil spill
HOW TO CLEAN UP AN OIL SPILL
• Mechanical • Booms- It’s easier to clean-up oil if it’s all in one spot,
so equipment called containment booms act like a fence to keep the oil from spreading or floating away. Booms float on the surface and have three parts: a ‘freeboard’ or part that rises above the water surface and contains the oil and prevents it from splashing over the top, a ‘skirt’ that rides below the surface and prevents the oil from being pushed under the booms and escaping, and some kind of cable or chain that connects, strengthens, and stabilizes the boom. Connected sections of boom are placed around the oil spill until it is totally surrounded and contained.
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Boom
An oil containment boom is laid out in the waters of Treasure Pass near La., on July 31, 2010 in response to the Gulf of Mexico oil spill.
• Skimmers- Once you’ve contained the oil, you need to remove it from the water surface.
• Skimmers are machines that suck the oil up like a vacuum cleaner, blot the oil from the surface with oil-attracting materials, or physically separate the oil from the water so that it spills over a dam into a tank. Much of the spilled oil can be recovered with skimmers.
• The recovered oil has to be stored somewhere though, so storage tanks or barges have to be brought to the spill to hold the collected oil.
• Skimmers get clogged easily and don’t work well on large oil spills or when the water is rough.
Skimmers
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• Sorbents- These are materials that soak up liquids by either absorption or adsorption. Oil will coat some materials by forming a liquid layer on their surface (adsorption). This property makes removing the oil from the water much easier. This is why hay is put on beaches near an oil spill or why materials like vermiculite are spread over spilled oil.
• One problem with using this method is that once the material is coated with oil, it may then be heavier than water. Then you have the problem of the oil-coated material sinking to the bottom where it could harm animals living there.
• Absorbent materials, very much like paper towels, are used to soak up oil from the water’s surface or even from rocks and animal life on shore that becomes coated with oil.
Sorbent •FiberDuck Socks are perfect to clean up small oil spills on land or in water. •Quickly absorbs hydrocarbons such as crude oil, diesel oil and gasoline. •Socks are also designed to contain spills around machine bases. •These water-repellent socks are made from highly absorbent hydrophobic fiber and will float indefinitely. •Their durable polypropylene skin is UV-, chemical- and tear-resistant
Chemical
• Chemicals, such as detergents, break apart floating oil into small particles or drops so that the oil is no longer in a layer on the water’s surface.
• These chemicals break up a layer of oil into small droplets.
• These small droplets of oil then disperse or mix with the water. The problem with this method is that dispersants often harm marine life and the dispersed oil remains in the body of water where it is toxic to marine life.
A plane releases chemical dispersant over the Gulf of Mexico oil spill.
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• Biological • Bioremediation- There are bacteria and fungi that naturally
break down oil. This process is usually very slow- it would take years for oil to be removed by microorganisms. Adding either fertilizer or microorganisms to the water where the spill is located can speed up the breakdown process. The fertilizer gives the bacteria and fungi the nutrients they need to grow and reproduce quicker. Adding microorganisms increases the population that is available to degrade the oil. A drawback to adding fertilizers is that it also increases the growth of algae.
• When the large numbers of algae die they use up much of the oxygen so that there isn’t enough oxygen in the water for animals like fish.
Crude oil spill bioremediation
Physical • Burning- Burning of oil can actually remove up to
98% of an oil spill. The spill must be a minimum of three millimeters thick and it must be relatively fresh for this method to work.
• There has been some success with this technique in countries such as Canada.
• The burning of oil during the Gulf War was found not as large a problem as first thought because the amount of pollution in the atmosphere did not reach the expected high levels.
Burning a crude oil spill
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Burning a crude oil spill
• The decision whether or not to burn a slick at sea is often contentious.
• Issues such as the distance of the oil from the damaged vessel or from a populated area; the potential toxicity of the resultant smoke; the nature of the oil; the likelihood of the burn being successful; and the fate of any unburned residues all require careful attention before attempts are made to ignite the oil.
Burning a crude oil spill
• Fire proof containment boom and an ignitor will most probably be required for a burn to be undertaken.
Environmental degradation related to crude oil extraction by Oil Companies • In the recent past, a number of oil companies in
the world have been cutting corners by disregarding set-down rules related to crude oil extraction with serious implications on the environment.
• In the past 2 years, the Gulf of Mexico in US experienced the worst oil spill caused by the company BP.
• The next 5 slides will show what havoc SHELL company has caused on NIGERIA in the past 10 years…
Burning crude oil spill at Ogoniland (Niger Delta) in Southern Nigeria
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More photos of environmental effects of crude oil spill at ogoniland
More photos of environmental effects of crude oil spill at ogoniland
Shell oil-heads leaking at K-Dere, Ogoni A member of the Bodo community, in the Ogoniland region of Nigeria's Rivers State, tries to separate crude oil from water
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Is Kenya immune from environmental disaster related to crude oil extraction?
• It is a pity that some of these companies (BP and SHELL) may venture to Turkana area here in Kenya (in the near future) and leave a trail of destruction (on the lake and adjacent areas) experienced elsewhere…
• They know that penalty for polluting the environment is fine of a few million dollars (which they have in plenty)!
Human toll on oil spill
Oil Cleanup workers are not being given protective masks
Human toll on oil spill
• And no respirators
Some glossary used in oil spills
• Pollutant: Any substance that contaminates or makes the environment impure. Pollutants are commonly man-made wastes.
• Absorption: The process of taking in another substance, in the same manner that a sponge would.
• Adsorption: When a liquid or solid takes up a substance and holds it on its surface, so that the substance coats the molecules of the solid or liquid.
• Dispersant: A chemical or material that when added to some other substance causes it to break apart and scatter about.
• Bioremediation: Using natural biological processes to correct or counteract an environmental hazard or ecological disaster. An example of bioremediation is adding fertilizer or bacteria to the water to help clean-up an oil spill.
• Ecosystem: An ecological unit of all the living organisms plus the nonliving, physical environment and how they function together.
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CALORIMETRY
• Calorimetry is the science of measuring quantities of heat, as distinct from “temperature”.
• The instruments used for such measurements are known as calorimeters.
• We shall be concerned only with oxygen bomb calorimeters, which are the standard instruments for measuring calorific values of solid and liquid combustible samples
CALORIMETRY
• The calorific value (heat of combustion) of a sample may be broadly defined as the number of heat units liberated by a unit mass of a sample when burned with oxygen in an enclosure of constant volume.
• In this reaction the sample and the oxygen are initially at the same temperature and the products of combustion are cooled to within a few degrees of the initial temperature
• Also the water vapor formed by the combustion is condensed to the liquid state.
CALORIMETRY
• the term calorific value (or heat of combustion) as measured in a bomb calorimeter denotes the heat liberated by the combustion of all carbon and hydrogen with oxygen to form carbon dioxide and water, including the heat liberated by the oxidation of other elements such as sulfur which may be present in the sample.
• The heat energy measured in a bomb calorimeter may be expressed either as calories (cal), or Joules (J).
Bomb Calorimeter
• A bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of combustion of a particular reaction.
• Bomb calorimeters have to withstand the large pressure within the calorimeter as the reaction is being measured.
• Electrical energy is used to ignite the fuel; as the fuel is burning, it will heat up the surrounding air, which expands and escapes through a tube that leads the air out of the calorimeter.
• When the air is escaping through the copper tube it will also heat up the water outside the tube.
• The temperature of the water allows for calculating calorie content of the fuel.
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Bomb Calorimeter
• Four essential parts are required in any bomb calorimeter: 1. a bomb or vessel in which the combustible charges
can be burned, 2. a bucket or container for holding the bomb in a
measured quantity of water, together with a stirring mechanism,
3. an insulating jacket to protect the bucket from transient thermal stresses during the combustion process, and
4. a thermometer or other sensor for measuring temperature changes within the bucket.
Bomb Calorimeter
Determination of heat content of fuels
• Oxygen Bomb Calorimeter
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Bomb Calorimeter: Standardization
• Before a material with an unknown heat of combustion can be tested in a bomb calorimeter, the energy equivalent or heat capacity of the calorimeter must first be determined.
• Consider a standardization test in which 1.651 grams of standard benzoic acid (heat of combustion 6318 cal/g) produced a temperature rise of 3.047°C.
Bomb Calorimeter: Standardization
• The energy equivalent (W) of the calorimeter (the “calorimeter constant”) is then calculated as follows:
• Note: 1 calorie = 4.18400 joules
The Fuel Test
• After the energy equivalent has been determined, the calorimeter is ready for testing fuel samples.
• Samples of known weight are burned and the resultant temperature rise is measured and recorded.
• The amount of heat obtained from each sample is then determined by multiplying the observed temperature rise by the energy equivalent of the calorimeter.
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Note: 1 calorie = 4.18400 joules
• Assume a fuel sample weighing 0.9936 gram produced a temperature rise of 3.234°C in a calorimeter with an energy equivalent (the “calorimeter constant”) of 2416 cal/°C.
• The gross heat of combustion (Hg) is then determined by multiplying the temperature rise by the energy equivalent, and dividing this product by the weight of the sample, e.g:
Problem
• A 1.000 g sample of octane (C8H18) is burned in a bomb calorimeter containing 1200 grams of water at an initial temperature of 25.00oC. After the reaction, the final temperature of the water is 33.20oC. The heat capacity of the calorimeter (also known as the “calorimeter constant”) is 837 J/oC. The specific heat of water is 4.184 J/g oC. Calculate the heat of combustion of octane in kJ/mol.
Solution
• Since this is a combustion reaction, heat flows from the system to the surroundings… thus, it is exothermic. The heat released by the reaction will be absorbed by two things:
(a) the water in the calorimeter and
(b) the calorimeter itself.
Solution: a. Calculate the heat absorbed by the water
(qwater)
m = 1200 grams
cwater = 4.184 J/goC
T = 33.20 – 25.00 = 8.20oC
qwater = (m)(c)( T), so
qwater = (1200 g)(4.184 J/g.oC )(8.20 oC )
= 41170.56 J
= 41.2 kJ
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Solution: b. Calculate the heat absorbed by the calorimeter (qcal)
• The temperature change of the calorimeter is the same as the temperature change for water. In this step, however, we must use the heat capacity of the calorimeter, which is already known. When using heat capacity, the mass of the calorimeter is not required for the calculation. (It’s already incorporated into the heat capacity). Ccal = 837 J/oC
T = 33.20 – 25.00 = 8.20oC qcal = (Ccal)( T), so so, qcal = (837 J/oC)(8.20 oC) = 6863.4 J = 6.86 kJ
Solution:
• The TOTAL heat absorbed by the water and the calorimeter is the sum of (a) and (b):
• 41.2 + 6.86 = + 48.1 kJ. (Remember, q is positive because the heat is being absorbed).
• The amount of heat released by the reaction is equal to the amount of heat absorbed by the water and the calorimeter. We just need to change the sign. So, qreaction = – 48.1 kJ
Solution:
• Since 1.000 gram of octane was burned, the heat of combustion for octane is equal to – 48.1 kJ/gram. In other words, when one mole of octane is burned, 48.1 kJ of heat is released from the reaction. What is the heat of combustion in kJ/mol?
1 mol of octane weighs 114 grams, so
(-48.1 kJ/g)(114 g/mol) = – 5483 kJ/mol.
Important properties related to liquid fuels
Property – Heat of combustion (kJ mol
–1)
– Boiling point (°C)
– Density (g mL–1
)
– Average molar mass (g mol–1
)
Important conversions • Heat of combustion per gram = Heat of combustion (kJ mol
–1) /
Average molar mass (g mol–1
)
• Volume (litres) = 1000 × Average molar mass (g)/ Density (g mL–1
)
• Heat of combustion per liter of fuel = Heat of combustion (kJ mol–1
) ×1000 × density (g mL
–1) /Average molar mass (g mol
–1)