Petrochemicals

Energy in the World

Human energy requirements begin from human existence itself. Since discovering fire, humans have burned whatever fuel they could find. Initially using easily accessible fuels such as wood and dung; later coal, oil and gas became important sources. Wood, the oldest known fuel, has lost commercial importance in developed countries but still holds commercial significance in less developed nations. More than 90% of the world's energy requirements are met by burning fossil fuels. These fuels, formed over millions of years through various geological processes, are unfortunately being consumed rapidly in a very short time. Since replacing them in a short timeframe is not even conceivable, humans have naturally turned to new sources beyond conventional energy sources. Nuclear energy is among the most important of these, considering both its acquisition and the precision required in its application stages. Although the share of energy sources such as solar, geothermal, wind and biomass in meeting energy requirements increases with each passing day, it remains quite low. Oil continues to hold its importance as the world's largest fuel and energy source today.

Formation of Crude Oil

It is known that petroleum is formed from organic matter in seas through various organic processes. However, two important theories have been proposed regarding the formation of crude oil. The Engler Theory, which is the most valid theory, is known as the organic theory and examines the formation process in four main stages. First Stage: Death and burial of organisms living in the seas such as fish, algae, plankton and similar creatures. This stage is defined as the biological formation stage. Second Stage: Transformation of solid organic matter into proto-petroleum and micro-petroleum, the initial liquids, through catalytic pathways. Bacteria provide the most important catalytic effect during the decomposition stage. This stage is defined as the catalytic formation stage. Third Stage: Movement of the formed liquid from its initial formation bed or reservoir to its final reservoir. This stage is defined as the migration stage. Fourth Stage: Change in the composition of proto-petroleum in this final reservoir to become petroleum. It is also known that natural structures such as porphyrin and glutamine are contained within crude oil. Because these structures contain nitrogen (N). Nitrogen exists in the peptide bonds of amino acids, which are the building blocks of proteins. Porphyrins are derived from chlorophyll. The structure of crude oil consists of hydrocarbons. However, nitrogen (N), sulfur (S) and oxygen (O) atoms are heteroatoms present in these organic compounds. The other theory was proposed by a Russian scientist. It appears as an inorganic theory. Oil, as is known, is a mixture of hydrocarbons composed of organic compounds containing Hydrogen (H) and Carbon (C) atoms in its structure. It proposes that simple organic molecules can be formed from certain inorganic origin substances. It proposes that as a result of reactions of water gas and similar molecules under the catalysis of melted iron in magma, carbon monoxide (CO) and hydrogen gas (H2) are formed, and these in turn form petroleum through certain syntheses under the catalysis of minerals containing Ni and Co found in the Earth's crust. However, the absence of free alkali metals in nature weakens this theory.

Classification of Crude Oil, Chemical and Physical Properties

The chemical composition and structure of crude oil vary depending on its location. Even petroleum extracted from the same location can sometimes contain different components. Crude oil also contains various oxygen, nitrogen and sulfur-containing compounds. The presence of some olefins (alkenes) with the general formula (CnH2n) as hydrocarbons has been detected in the high boiling sections of petroleum. Olefins boiling at low temperatures are not found in great abundance. Depending on the chemical structure of the hydrocarbons it contains, oil is divided into four main classes. 1. Paraffinic Base: This class contains saturated hydrocarbons (Alkanes CnH2n+2). They are thermodynamically very stable compounds. 2. Naphthenic Base (Cycloparaffins): This class contains saturated cyclic alkanes (Cycloalkanes CnH2n). Since they are saturated compounds, their activity is lower than olefins and aromatics. However, due to ring strain, they are more active compared to straight-chain paraffins. 3. Aromatic Base: This class contains cyclic, aromatic compounds with high unsaturation. Compounds with characteristics similar to Benzene, the first aromatic compound studied (CnH2n-6), are found. Small aromatics such as benzene and toluene with single rings are rarely found in crude oil. Polyaromatics with two or more rings are always present in the high boiling fractions of oil. 4. Mixed Structures: This class contains mixed components in certain proportions from the three other main groups mentioned above. Crude oil is generally dark brown in color. Rarely it may appear in light brown, yellow and reddish hues. Crude oil rich in asphalt is dark brown-black, brown; those without asphalt are red and yellow in color. All oils exhibit yellow-green to green-blue fluorescence properties. Depending on the light, medium and heavy oils they contain, and according to paraffinic and asphalt content, oils may be fluid or viscous. The odor of petroleum is composed of compounds with low boiling points present in its composition. Petroleum containing sulfur compounds such as hydrogen sulfide (H2S) and mercaptans (RSH) is odorous. Their specific gravities are generally determined as (0.72-1) g/cm3. Specific gravities depend on the quantity and type of low boiling point compounds they contain. The heat of combustion of petroleum also depends on its composition and has a heat value of (9600-11500) k.cal/kg. The flash point varies depending on the amounts of low boiling hydrocarbons and is (0-200)°C.

Basic Refining Processes

As a result of basic refining operations applied to crude oil in petroleum refineries, primary products are obtained. Crude oil as extracted from the ground is a mixture that cannot be used directly. These operations consist of various physical and chemical processes. The following refining processes are applied to crude oil from which salt water has been removed. 1. Atmospheric Distillation: Crude oil contains hydrocarbons boiling up to 500°C as a mixture. It is the process of separating hydrocarbons boiling up to ~350°C by utilizing the differences in their boiling points. Continuous distillation is performed in a distillation tower (distillation column) consisting of trays, each with a different temperature. This distillation is performed under atmospheric pressure. As a result of the process, those with similar boiling points are collected in fractions and form primary products. From the top of the column, the lightest products are obtained as liquefied petroleum gas (LPG); from the section below it, in the (38-120)°C range, light gasoline (naphtha) is obtained. As one moves downward, the fraction between (120-180)°C is taken as heavy gasoline, the fraction between (170-270)°C as kerosene, and the fraction between (200-360)°C as heavy kerosene products. From the bottom of the column, the heaviest products are separated and sent to the vacuum distillation unit. In the vacuum distillation unit, the hydrocarbons in the bottom product (heaviest ones) obtained from the atmospheric distillation unit are distilled. The distillation column used here is shorter in length. Because the number of products is small. High distillation temperature (350-500°C) requires high preheating temperature. This accelerates the formation of problems such as coking in the furnace. Vacuum distillation is applied to separate very high boiling substances without destroying their structures. As the column pressure decreases, the boiling point also decreases. Vacuum distillation is used in producing mineral oil, asphalt and heavy kerosene to be fed to the catalytic cracking section. 2. Cracking: The process of breaking down hydrocarbons with high boiling points (large molecular weight) by thermal or catalytic methods into products with lower boiling points but higher commercial value. 3. Reforming: Modifying the structures of hydrocarbons in the heavy gasoline fractions through catalytic reactions without changing their carbon numbers to produce high-value gasoline. Production of aromatic compounds such as benzene and toluene is achieved. 4. Polymerization: Combining two, three or four C3 and C4 olefins (alkenes CnH2n) resulting from cracking to produce higher value products. 5. Alkylation: Production of a new hydrocarbon with branched structure and high octane number by combining a small olefin with an isoparaffin. Paraffins with branched structures burn more efficiently. For this reason, the goal is particularly to increase the number of branched molecules to increase the octane number of gasoline. Thus, both stable compounds in storage and compounds with efficient combustion reactions are increased in number. 6. Isomerization: Obtaining the commercially higher value hydrocarbon or the one necessary for a particular process from hydrocarbons with the same carbon numbers. 7. Sulfur Removal: Since most sold products are used as fuels, to prevent the formation of gases such as sulfur dioxide (SO2) from combustion, sulfur is chemically separated from the products. The most important sulfur removal method is "Hydrodesulfurization." Thus, sulfur in the product is converted to hydrogen sulfide (H2S) compound and removed. Hydrogen sulfide is also separated into its components by another reaction; hydrogen gas and elemental sulfur are made available for use.

Main and Intermediate Products Obtained from Crude Oil

A large portion (more than 90%) of petroleum products produced as a result of various physical and chemical operations in petroleum refineries are used as fuels. The remaining portion forms important inputs for various chemical industries, particularly petrochemicals. LPG (Liquefied Petroleum Gas): After propane (CH3CH2CH3) and butane (CH3CH2CH2CH3) are separated from other gases (H2, CH4, C2H6, C2H4) from light hydrocarbons released during refining operations, a mixture prepared in 50:50 or 40:60 ratios is liquefied under pressure and sold in steel cylinders. Butane and propane are gases with high combustion heat (Butane: 291,000; Propane: 22,450 k.cal/m3). In addition to use in homes for cooking and heating, they are used in automobile engines as fuel or in many fields as raw material in the chemical industry. Gasoline: The most fundamental product of the petroleum industry worldwide. All operations performed to increase, modify and improve gasoline yield in petroleum refining have paralleled developments in the automotive industry. Gasoline is a liquid containing hydrocarbons boiling between 38-204°C in its composition. This mixture contains C5-C12 hydrocarbons. Operations performed to improve the quality and efficiency of gasoline are synonymous with increasing the "octane number." The octane number "0" is assigned to n-Heptane, a straight-chain saturated compound, and "100" is assigned to 2,2,4-Trimethylpentane (isooctane), which has a branched structure. Kerosene: The product obtained in the refinery after gasoline. These fuels are hydrocarbon mixtures boiling between 180-360°C; they contain C10-C25 hydrocarbons. While formerly used only for lighting and heating, diesel and jet fuels are now produced from the broad range within this section. Every fuel used for military aircraft has a wider boiling range than that used for civil jet aircraft. Fuel Oils: Fuel oils are heavier than kerosene, high combustion heat (10,000 k.cal/kg) sections. They are generally divided into two types: light and heavy. Fuel oils have replaced coal in industry. The most important properties sought in these are as follows: a) Low pour point to enable easy flow in cold weather, b) Low sulfur content to prevent corrosion and odor, c) Sufficient quantity of light hydrocarbons to enable quick ignition of fuels in the burner, d) The mixing operation applied when making medium-weight fuels should be performed homogeneously so the product is stable. Lubricating Oils (Mineral Oils): Lubricating oils used to reduce friction of moving engine and machine parts, etc. are collected in two main sections: liquid and solid. Liquids are called mineral oils, solids are called greases. Mineral oils are petroleum fractions boiling at high temperatures and having high viscosity. The most important property of mineral oils is the viscosity (fluidity) index. Generally, as temperature increases, oils become thinner and viscosity decreases. The viscosity index is a relative measure showing resistance to this thinning. Desired properties of these oils are that they are homogeneous, have a relatively unchanged viscosity range at the temperatures where they are used, and are chemically stable substances. Mineral oils can be examined in three main sections: 1-Motor oils; 2-Industrial oils; classified as light, medium and heavy duty oils. 3-Oils used in metal processing; used in significant quantities as coolants. Grease (Solid Oil): Semi-solid substances made by adding 3-30% solid thickener to petroleum oils. Alkali and Al-salts (various soaps) of fatty acids are used as thickeners. They are used in place of liquid oils in systems that are not enclosed, where leakage cannot be prevented, and where foreign matter such as dust enters from outside. There are greases ranging from very soft to very hard. Melting points range between 70-180°C. In addition to soap, additives are added to greases that delay oxidation, increase resistance to rust and water. They are classified according to the type of thickener added. These additives are metal salt soaps, organic substances, special clays and advanced silicas. Petroleum Waxes (Waxy Substances): There are two types: paraffin and microcrystalline. Paraffin waxes are white and partly hard. They soften and melt between 40-80°C. Their structures contain mostly n-paraffins with 23-29 carbons. Microcrystalline ones are hard, substances with colors ranging from white to brown. Their structures contain mostly paraffins containing naphthenes with 34-70 carbons. Uses include; largely in the paper and cardboard industry, and in wax, match, insulating material industries, as rust preventive and in dentistry as filling material. Asphalt: Asphalt is a colloid of asphaltenes and polymer substances in petroleum oils. Brown-black asphaltenes are hydrocarbons poor in hydrogen. They contain considerable amounts of sulfur, oxygen and nitrogen. Polymer substances called resins are brown-colored, sticky semi-solid substances. Asphalts made from the heaviest fraction of oil have also been found in nature in various forms. Primary uses are road construction and waterproofing. A typical road asphalt contains about 30% asphaltenes and about 40% resins. Other Products: Heavy liquids and solids remaining from various refining operations are consumed alone or by adding to other fuels. Depending on the type of crude oil processed, various organic solvents and chemicals are obtained. Light and heavy naphthas are used as solvents in various industrial sectors. These chemicals produced from the gasoline section are: 1. Petroleum Ether: The lightest gasoline fraction. It is the fraction distilled between 25-89°C. Used in extraction operations and in pharmaceuticals. 2. Test Gasoline: The gasoline fraction distilled between 60-140°C. Used in the extraction of vegetable oils and in cleaning textile materials. Refineries processing high sulfur petroleum have special sulfur production facilities. Petroleum is also, for various applications to meet the requirements of daily civilization worldwide; a natural production source of monomers, which are raw materials for numerous polymers of industrial importance in terms of production and use globally. The most important of these can be listed as follows: 1. Ethylene: The smallest two-carbon alkene with the molecular formula C2H4. Obtained from cracking reactions. Primarily for the production of polyethylene (HDPE and LDPE) polymers; vinyl chloride obtained by its chlorination is also used as the monomer in polyvinyl chloride (PVC) polymer production. PVC is among the polymers with the highest industrial use, particularly in door and window manufacturing. 2. Propylene: A three-carbon alkene with the molecular formula C3H6. Obtained from cracking reactions. The polymer obtained from the polymerization of this monomer has uses as synthetic wool. 3. Butylene and Isobutylene: Isomers of four-carbon alkene with the molecular formula C4H8. Obtained from catalytic cracking reactions of heavy gasoline fractions or from the steam cracking unit of naphtha. Isobutylene is particularly an important monomer used in butyl rubber production. 4. 1,3-Butadiene: A monomer obtained from catalytic dehydrogenation reactions of n-butane with the molecular formula C4H6. Used in synthetic rubber production. 5. Styrene: The compound with the molecular formula C6H5-CH=CH2, this monomer known as phenyl ethylene; is obtained from the dehydrogenation of ethyl benzene, obtained by alkylating benzene through Friedel-Crafts alkylation reaction, over aluminum chloride, solid phosphoric acid or silica-alumina catalysts. This monomer is used in the production of light packaging material called "foam" in common parlance (polystyrene foam), styrene rubber and polystyrene plastics. 6. Chloroprene: A monomer known by the molecular formula C4H5Cl (2-chloro 1,3-butadiene). Obtained from acetylene and hydrogen chloride. Acetylene is first dimerized to monovinyl acetylene. The resulting molecule then reacts with hydrogen chloride and chloroprene is formed. The polymer obtained from this monomer is used in synthetic rubber production. 7. Benzene and Its Derivatives: Benzene with the molecular formula C6H6 is obtained from cyclohexane in the catalytic reforming unit in refining operations. As a result of alkylation reactions of benzene, toluene (methylbenzene) and xylene (dimethyl benzene) ortho, meta and para isomers are obtained. Phenol (hydroxy benzene) is also obtained as a result of the reaction of chlorobenzene, a benzene derivative, with sodium hydroxide. All of these produced compounds are organic solvents of very high industrial importance. Instructor Ayşın Küçükparmaksız - Kocaeli University - Kocaeli Vocational School of Higher Education Chemistry and Chemical Processing Technologies - Refinery and Petrochemistry Technology Program Coordinator

Bibliography 1. Introduction to Petrochemistry Technology-I 2. Introduction to Petrochemistry Technology-II lecture notes. 3. Modern Petroleum Technology, PART 2, Fifth Edition, Edited by G. D. HOBSON, JOHN WILEY & SONS, Copyright 1984 by The Institute of Petroleum, London. 4. Petroleum Refining Technology, Assoc. Prof. Ömer KULELİ, CAĞ-LAYAN KİTABEVİ, 1st Edition (1981).