Transcript Chapter 1
Part 4.2 Refining and Processing Objectives • After reading the chapter and reviewing the materials presented the students will be able to: • Understand structure of hydrocarbons in oil and gas • Examine distillation and cracking process • Analyze hydro treating and blending fuels • Discuss petrochemical plants and processes • Explain product marketing, sales, and distribution Introduction • Crude oil and natural gas are converted into fuels, lubricating oils, waxes, asphalt, and petrochemicals. • Crude oil contains impurities such as oxygen, nitrogen, sulfur, salt, water, and trace metals. • Natural gas is a mixture of hydrocarbon gases and impurities such as water, nitrogen, and carbon dioxide. • Some refinery products go to petrochemical plants where they are changed into chemicals used to make products ranging from fertilizers to plastics. The Early Days • The United States government required Standard Oil Company to break up into three separate companies in 1911 that later became Exxon, Mobil, and Chevron. • These three companies along with Shell and BP were the dominant forces in the refining business. • The United States consumes about 25% of the world’s crude oil production and produces 35% of its own oil needs. • The largest crude oil producer, Saudi Aramco, refines only about 25% of its production. • Exxon, Shell, and BP refine almost twice as much crude oil as they produce. • The United States produces about 5 million barrels per day of crude and about 2.4 million barrels per day of gas condensate. • World production is around 84 million barrels per day. Structure of Hydrocarbons in Oil and Gas • Crude oil is a varying mixture of hydrocarbons giving its specific characteristics such as color, viscosity, density, boiling point, and ability to flow. • Refineries and gas processing plants separate hydrocarbons into paraffins, isomers, olefins, naphthenes, and aromatics. Paraffins • The simplest paraffin is methane, the main ingredient of natural gas. • Paraffins have names ending with ane, such as ethane or propane. • Hydrocarbons with few carbon atoms (1 to 4) are light in weight and are gases under normal atmospheric pressure. • Hydrocarbons with more carbon atoms are heavier and are either liquid or solid. Isomers • Paraffins with four or more carbon atoms can have more than one arrangement of atoms resulting in an isomer. • Isobuatane is an isomer of normal butane. • Isobutane boils at a temperature different from normal butane, causing different chemical reactions in the refinery. • Because paraffins and isomers have the greatest possible number of hydrogen atoms, they are called saturated hydrocarbons. Aromatics • Aromatic hydrocarbons contain a ring of six carbon atoms. • This type of structure is known as a benzene ring. • The most important aromatics in refinery production are benzene, toulene, and xylene. Napthenes • The carbon atoms of napthenes form rings rather than chains. • Hydrocarbons in this group have names that begin with the prefix cyclo to indicate a ring structure. • An example is cyclohexane, a hydrocarbon often ocuring in natural gasoline. Olefins • Olefins are chains of carbon atoms with attached hydrogen atoms. • Olefins with one double bond have names ending in ylene or ene, and olefins with two double bonds have names ending in adine. • Common olefins are ethylene, propylene, and butylene. Other Elements • Crude oil might contain oxygen, nitrogen, sulfur, and metals. • If crude oil contains appreciable quantities of sulfur or sulfur compounds, it is called sour crude. • If it contains little or no sulfur, it is called sweet crude. Refining Crude Oil • Every refinery begins the processing by separating crude oil into different components, called fractions or cuts – groups of hydrocarbons with the same boiling point range or similar properties. • An assay determines what hydrocarbons and impurities are present and in what amounts. • An assay classifies the crude oil in one of three groups based on the composition of its components as paraffin base, asphalt base, and mixed base. • Paraffin base crude oil is a good source of paraffin wax, quality motor lubrication oils, and high grade kerosene. • Asphalt base crude oil is suitable for making high quality gasoline and roofing and paving materials. • Mixed base crude oils contain considerable amounts of both paraffin and asphalt. Virtually all products can be obtained from mixed base crude oils. Refining Process • At first, a process called fractional distillation was the only method of producing gasoline. • However the amount of gasoline and diesel fuel that could be produced from crude oil was insufficient to satisfy consumer demand. • Two types of processes were developed: fluid catalytic cracking, and hydrocracking. Fractional Distillation • Every refinery begins the processing of crude oil by separating it into different cuts or fractions by distillation. • Because crude oil is a mixture of hydrocarbons that boils or vaporizes at different temperatures, heating it to a certain temperature allows one fraction to boil off while others remain liquid. • In atmospheric distillation, the process takes place at atmospheric pressure in a tall cylindrical steel tower called distilling column. • The liquids flows to the bottom of the column and is removed. • The lightest hydrocarbons remain gaseous and pass out through the top of the column. • Light distillates include naptha and kerosene. • Middle distillates are made into diesel fuels, furnace oils, naptha, and other products. Fractional Distillation • Vacuum distillation separates light and heavy gas oil from the botoms, the heaviest residue. • Light and heavy gas oils are further processed to produce gasoline, and lubricating oils. • The bottoms are processed to make fuels, asphalt, sealants, lubricating oils, wax, and coke. Cracking • Cracking is a chemical process that breaks down the heavier residues into lighter products such as gasoline and distillate fuels. • Heavier hydrocarbons have limited markets and are therefore not very useful in their natural state. • Catalytic cracking uses a catalyst in a chemical reaction. • Thermal cracking uses heat to break down the bottoms from vacuum distillation and sometimes the heavy oils from catalytic cracking. • Hydrocracking is catalytic cracking in the presence of hydrogen. Rearranging Hydrocarbon Molecules • A refinery can use several chemical processes to rearrange hydrocarbon molecules to produce high quality gasoline, jet fuel, and petrochemicals. • Alkylation refers to the chemical combining of light molecules with isobutane to form isoparaffins that make high octane gasoline. • Isomerization is a chemical process that rearranges straight chain hydrocarbons (paraffins) into hydrocarbons that have branches (isoparaffins). • Catalytic reforming is a process for upgrading napthas into high octane gasoline and petrochemical feedstock. Reforming uses heat, pressure, and a catalyst to bring about desired chemical reaction. Solvent Extraction • Solvent extraction is the use of a solvent to selectively dissolve a particular compound and remove it from a mixture of hydrocarbons. • Deasphalting is the removal of asphaltic substances that tend to form carbon deposits when lubricating oils are heated. • BTX recovery: Benzene, toulene, and xylene are separated from reformed naptha and sold as petrochemical feedstock. Treating • • • • Treating either removes contaminants from crude oil or converts them into harmless compounds. Dehydration and Desalting: Salts foul and corrode the equipment. When salts are suspended in the water, they can be removed by heating the oil and allowing the water and salt solution to settle out. If they are in a stable emulsion, chemicals or an electric current must be used to break the emulsion and allow the water salt solution to separate from the oil. Hydrotreating: Hydrotreating is used to remove sulfur, nitrogen, and metals from crude oil fractions. The feed is mixed with a stream of hydrogen, heated, and sent to a reactor where a series of reactions takes place in the presence of a fixed bed catalyst. The hydrogen combined with nitrogen and sulfur to form ammonia and hydrogen sulfide, and metals are deposited on the catalyst. Sulfur Recovery: Hydrogen sulfide, a highly poisonous gas can be converted into sulfur which can be converted into ammonium thiosulfate, a fertilizer. A furnace heats the hydrogen sulfide in the presence of oxygen to form sulfur and water. Blending and Using Additives • Gasoline: Refineries blend gasoline with ethanol to meet US federal regulations. • Diesel Fuel: Diesel fuels are blended from gas oils and kerosene. They are hydrotreated to meet the low sulfur specifications for road diesel which is 15 ppm. • Furnace and Residual Fuel Oils: Residual fuels are blended with heavy gas oils to make them pour more easily and to reduce sulfur content to acceptable levels. Petrochemicals • Petrochemicals are used to make products from detergents to plastic bottles. • Aliphatic Petrochemicals: are straight chain hydrocarbons, either saturated (paraffins) or unsaturated (olefins). These petrochemicals ultimately go to factories that make plastics, solvents, synthetic rubbers, and synthetic fibers. • Aromatic Petrochemicals: are unsaturated petrochemicals with six carbon atoms in a ring such as benzene, toulene, and xylene. They are used to make plastics, resins, fibers, and elastomers. • Inorganic Petrochemicals: include sulfur and ammonia. Carbon black is used to make synthetic rubbers, printing ink, and paint. Sulfur is used to make sulfuric acid which is used in the manufacture of steel, fertilizer, paper, and other chemicals. A Petrochemical Plant • Each petrochemical plant uses different processes, procedures, facilities and auxiliary operations, since they are designed to produce different petrochemicals. • Olefin Units: The primary job of the olefin unit is to provide ethylene and propylene for the polymer unit as well as for sale to other chemical or plastic producers. • Polymer Units: Polypropylene and ethylene are combined to make polypropylene and polyethylene. Refining Capacity • • • • • A company must expect enough profit over the life of the refinery to justify the amount of capital required to build it. Product Sales and Distribution: Consumer products such as gasoline and home heating oil are usually sent directly from the refinery via pipeline, tanker, barge, or railroad to an installation terminal. From the terminal, products are transported to bulk plants serving smaller communities or directly to service stations, airports, homes, or businesses. Environmental Considerations: The refining process uses a lot of water for cooling and other processes. Water and air emissions must be treated before release from the refinery. Water Quality: Refineries use chemical treatment tanks, holding ponds, and oil degrading bacteria to remove contaminants such as hydrogen sulfide, ammonia, phenols, and salts from the water. Air Quality: Toxic air emissions that are of particular concern to refineries are volatile organic compounds (VOCs). They cause smog and ozone formations near the ground. Dust is another problem in refineries. Summary • • • • • • • • • • • • • The United States consumes about 25% of the world’s crude oil production and produces 35% of its own oil needs. World production is around 84 million barrels per day. Refineries and gas processing plants separate hydrocarbons into paraffins, isomers, olefins, naphthenes, and aromatics. If crude oil contains appreciable quantities of sulfur or sulfur compounds, it is called sour crude. If it contains little or no sulfur, it is called sweet crude. Paraffin base crude oil is a good source of paraffin wax, quality motor lubrication oils, and high grade kerosene. Asphalt base crude oil is suitable for making high quality gasoline and roofing and paving materials. Mixed base crude oils contain considerable amounts of both paraffin and asphalt. Virtually all products can be obtained from mixed base crude oils. Cracking is a chemical process that breaks down the heavier residues into lighter products such as gasoline and distillate fuels. Treating either removes contaminants from crude oil or converts them into harmless compounds. Petrochemicals are used to make products from detergents to plastic bottles. Each petrochemical plant uses different processes, procedures, facilities and auxiliary operations, since they are designed to produce different petrochemicals. Environmental Considerations: Water and air emissions must be treated before release from the refinery. Home Work • 1. What is sour crude and what is sweet crude? • 2. What is cracking?