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CHE 483 Petroleum Chem.pptxghdhgxdggxxghgddg
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- 2. COURSE OUTLINE CHE 482CPETROLEUM CHEMISTRY Week 1 Oil Extraction Week 2 Processes involved in oil extraction Week 3 Petrochemical Industry I Week 4 Petrochemical industry II Week 5 Quiz 1 Week 6 Polymer Industry I Week 7 Polymer Industry II Week 8 Polyethene Week 9 Butadienes Week 10 Quiz 2 Week 11 Revision NB: EACH WEEK IS EQUIVALENT TO THREE CONACT HOURS ON THE TIME TABLE
- 3. Introduction The termpetroleum comes from the Latin stems petra, “rock,” and oleum, “oil.” It is used to describe a broad range of hydrocarbons that are found as gases, liquids, or solids beneath the surface of the earth The two most common forms are natural gas and crude oil. Natural gas: Natural gas is a mixture of lightweight alkanes. It accumulates in porous rocks. Typically, it comprises of about 80% methane (CH4), 7% ethane (C2H6), 6% propane (C3H8), 4% butane and isobutane (C4H10), and 3% pentane (C5H12). The C3, C4, and C5 hydrocarbons are removed before the gas is sold.
- 4. The butanesremoved from natural gas are usually liquefied under pressure and sold as liquefied petroleum gases (LPG). Crude oil is a composite mixture of hydrocarbons (50-95% by weight) occurring naturally. The first step in refining crude oil involves separating the oil into different hydrocarbon fractions by distillation/fractionation Petroleum is found in many parts of the world which include the Middle East, Southern United States, Mexico, Nigeria, the former Soviet Union and in recent years Ghana
- 5. Sectional Objectives 1 Aftergoing through Weeks 1 & 2, you should be able to differentiate between the terms crude oil and natural gas explain the process involved in oil extraction characterise crude oil classify crude oil write the steps involved in petroleum refining state the importance of petroleum
- 6. Oil Extraction Thevast majority of petroleum is found in oilfields or reservoirs below the earth’s surface as the oil is sometimes under high pressure and can flow to the surface on its own without pumping. However, most wells require induced pressure using water, carbon dioxide, natural gas or steam in order to bring the oil to the surface. Petroleum refining has evolved continuously in response to changing consumer demand for better and different products. The original requirement was to produce kerosene as a cheaper and better source of light than whale oil. The evolution of the airplane created an initial need for high- octane aviation gasoline and then for jet fuel, a sophisticated form of the original product, kerosene
- 7. Oil Extraction Present-dayrefineries produce a variety of products including many required as feedstock for the petrochemical industry. Common petroleum products include gasoline, liquefied refinery gas, still gases, kerosene, aviation fuel, distillate fuel oil, residual fuel oil, lubricating oils, asphalt, coke and petrochemical feedstocks. Characteristics and classification of Crude Oil As has been mentioned, crude oils are complex mixtures containing many different hydrocarbon compounds that vary in appearance and composition from one oil field to another
- 8. Crude oilsrange in consistency from water to tar-like solids, and in colour 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. Composition of petroleum Crude petroleum(crude oil) contain hydrocarbon and non- hydrocarbon compounds. Hydrocarbon compounds 1. Paraffins - The paraffinic crude oil 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
- 9. The lighter,straight chain paraffin molecules are found in gases and paraffin waxes. The branched-chain (isomer) paraffins such as isobutene are usually found in heavier fractions of crude oil and have higher octane numbers than normal paraffins(straight chain). 2. Aromatics: The aromatic series include simple aromatic compounds such as benzene, naphthalenes and the most complex aromatics, the polynuclears which have three or more fused aromatic rings. They have high anti-knock value(higher octane numbers) and good storage stability. 3. Naphthenes (Naphtha): These are saturated hydrocarbon groupings with the general formula CnH2n, arranged in two 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 such as cyclohexane predominate. naphthenes (dicycloparaffins) are found in the heavier ends of naphtha.
- 10. 4. Alkenes (Olefins):Olefins such as ethylene, butene, isobutene are usually formed by thermal and catalytic cracking and rarely occur naturally in unprocessed crude oil. They are unstable and also improve the anti-knock tendencies of gasoline but not as much as the iso-alkanes. When stored, the olefins polymerise and oxidize. This tendency to react is employed in the production of petrochemicals. 5. Dienes and Alkynes: Examples of dienes or diolefins, are 1,2- butadiene(CH2CCHCH3) and 1,3- butadiene(CH2CHCHCH2). Acetylene(CHCH) is a typical alkyne. This category of hydrocarbons is obtained from lighter fractions through cracking.
- 11. Non-hydrocarbons 1. Sulphur Compounds:Sulphur may be present in crude oil as hydrogen sulphide (H2S), as mercaptans, sulphides, disulphides, thiophenes, etc. or as elemental sulphur. Each crude oil has different amounts and types of sulphur compounds, but as a rule the proportion, stability, and complexity of the compounds are greater in heavier crude-oil fractions.(ie. the heavier the crude oil the more complex, stable and the higher the proportion of sulphur it contains) Sulphur is an undesirable component because of its strong offensive odour, corrosion, air pollution by some of its compounds and its effect of reducing tetraethyl lead (anti-knock agent).
- 12. The combustionof petroleum products containing sulphur compounds produces undesirables such as sulphuric acid(H2S04) and sulphur dioxide(SO2). Catalytic hydrotreating processes such as hydrodesulfurization remove sulfur compounds from refinery product streams. Sweetening processes either remove the obnoxious sulfur compounds or convert them to odourless disulfides, as in the case of mercaptans. 2. Oxygen Compounds: Oxygen compounds such as phenols, ketones, and carboxylic acids occur in crude oils in varying amounts. 3. 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. Nitrogen oxides can form in process furnaces.
- 13. The decompositionof nitrogen compounds in catalytic cracking and hydrocracking processes forms ammonia and cyanides that can cause corrosion. 4. 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. 5. Salts: Crude oils often contain inorganic salts such as sodium chloride, magnesium chloride, and calcium chloride in suspension or dissolved in entrained water (brine) in the form of an emulsion.
- 14. These saltsmust 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 oil is heated. Hydrogen chloride may also combine with ammonia to form ammonium chloride (NH4Cl), which causes fouling and corrosion. Salt is removed mainly by mechanical or electrical desalting. 6. 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. 7. Naphthenic Acids: Some crude oils contain naphthenic (organic) acids, which may become corrosive at temperatures above 230°C when the acid value of the crude is above certain level
- 15. Lecture 2 PROCESSES INVOLVEDIN OIL EXTRACTION
- 16. Petroleum Refining Thepetroleum industry began with the successful drilling of the first commercial oil well in 1859, and the opening of the first refinery two years later to process the crude into kerosene Today, petroleum refinery products obtained include gasoline, kerosene, propane, fuel oil, lubricating oil, wax, and asphalt Refining crude oil involves two kinds of processes: First, there are physical processes which simply refine the crude oil (without altering its molecular structure) into useful products such as lubricating oil or fuel oil Petroleum refining begins with distillation, or fractionation, which separates crude oil in atmospheric and vacuum distillation towers into groups of hydrocarbon compounds
- 17. The differingboiling-point ranges of compounds are called “fractions” or “cuts.” Secondly, there are chemical conversion processes which alter the size and/or molecular structure of hydrocarbon molecules to produce a wide range of products, some of them known by the general term petrochemicals. Conversion processes include: Decomposition (dividing) by thermal and catalytic cracking; Unification (combining) through alkylation and polymerization; and Alteration (rearranging) with isomerization and catalytic reforming As seen above, the major chemical conversions include cracking, alkylation, polymerisation, isomerisation and reforming
- 18. The convertedproducts are then subjected to various treatment and separation processes Treatment Processes are intended to prepare hydrocarbon streams for additional processing and to prepare finished products. Treatment may involve chemical or physical separation such as dissolving, absorption, or precipitation using a variety and combination of processes including hydrodesulfurizing and sweetening Formulating and Blending is the process of mixing and combining hydrocarbon fractions, additives, and other components to produce finished products with specific performance properties. Integrated refineries incorporate fractionation, conversion, treatment, and blending operations and may also include petrochemical processing.
- 19. Octane number About 10% of the product of the distillation of crude oil is a fraction known as straight-run gasoline, which served as a satisfactory fuel during the early days of the internal combustion engine As the automobile engine developed, it was made more powerful by increasing the compression ratio. Modern cars run at compression ratios of about 9:1, which means the gasoline-air mixture in the cylinder is compressed by a factor of nine before it is ignited Straight-run gasoline burns unevenly in high compression engines, producing a shock wave that causes the engine to “knock,” The challenge for the petroleum industry was to increase the yield of gasoline from each barrel of crude oil and to decrease the tendency of gasoline to knock when it burned. It was found that:
- 20. Branched alkanesand cycloalkanes(naphthene or cycloparraffins) burn more evenly than straight-chain alkanes. Short alkanes (C4H10) burn more evenly than long alkanes (C7H16). Alkenes burn more evenly than alkanes. Aromatic hydrocarbons burn more evenly than cycloalkanes. The most commonly used measure of a gasoline's ability to burn without knocking is its octane number Octane numbers compare a gasoline’s tendency to knock against the tendency to knock of a blend of two hydrocarbons heptane and 2,2,4-trimethylpentane, (isooctane). Heptane produces a great deal of knocking while isooctane is more resistant to knocking
- 21. Gasoline's thatmatch a blend of 87% isooctane and 13% heptane are given an octane number of 87. There are three ways of reporting octane numbers. Measurements made at high speed and high temperature are reported as motor octane numbers while measurements taken under relatively mild engine conditions are known as research octane numbers. The road-index octane numbers reported on gasoline pumps are an average of these two. Road-index octane numbers for a few pure hydrocarbons are given in the Table 1. on the next slide.
- 22. HYDROCARBON OCTANE NUMBER Heptane0 2-Methyheptane 23 Hexane 25 2-Methylhexane 44 1-Heptane 60 Pentane 62 1-Pentene 84 Butane 91 Cyclohexane 97 2,2,4-Trimethlpentane (isooctane) 100 Benzene 101 Toluene 112 Table 1: Octane Numbers of crude oil hydrocarbon
- 23. By 1922a number of compounds had been discovered that could increase the octane number of gasoline. Adding as little as 6 ml of tetraethyl lead to a gallon of gasoline, for example, can increase the octane number by 15 to 20 units. Another way to increase the octane number is thermal reforming. At high temperatures (500-600oC) and high pressures (25-50 atm.), straight-chain alkanes isomerize to form branched alkanes and cycloalkanes, thereby increasing the octane number of the gasoline. Running this reaction in the presence of hydrogen and a catalyst such as a mixture of silica (SiO2) and alumina (Al2O3) results in catalytic reforming, which can produce a gasoline with even higher octane numbers The presence of alkenes in thermally cracked gasolines increases the octane number (70) relative to that of straight-run gasoline (60), but it also makes thermally-cracked gasoline less stable for long-term storage
- 24. Thermal cracking(usedto obtain olefins from crude) has therefore been replaced by catalytic cracking, which uses catalysts instead of high temperatures and pressures to crack long-chain hydrocarbons into smaller fragments for use in gasoline. Catalytic Cracking Ethylene and propylene are the most important organic chemical feedstocks accounting for over 50-60% of all organic chemicals. But because of their relatively high reactivities, very few olefins are found in natural gas or crude oil. Therefore, they must be manufactured by cracking processes The purpose of cracking is to break complex hydrocarbons into simpler molecules in order to increase the quality and quantity of lighter, more desirable products and decrease the amount of residuals
- 25. The decompositiontakes place by catalytic action or heating in the absence of oxygen (pyrolysis). The catalysts used in refinery cracking units are typically zeolite, aluminium hydrosilicate, treated bentonite clay, fuller’s earth, bauxite, and silica-alumina (SiO2-Al2O3) all of which come in the form of powders, beads, or pellets There are three basic functions in the catalytic cracking process: ( RRF) Reaction - Feedstock reacts with catalyst and cracks into different hydrocarbons Regeneration - Catalyst is reactivated by burning off coke Fractionation - Cracked hydrocarbon stream is separated into various products.
- 26. Catalytic Reforming Catalyticreforming is an important process used to convert low- octane naphthas into high-octane gasoline blending components called reformates. Depending on the properties of the naphtha feedstock (as measured by the paraffin, olefin, naphthene, and aromatic content) and catalysts used, reformates can be produced with very high concentrations of toluene, benzene, xylene, and other aromatics useful in gasoline 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. The reactions that occur in catalytic reforming may be summarized as follows
- 27. Dehydrogenation ofcyclohexanes(naphthenes) to aromatics Dehydrogenation of paraffin’s to olefins Isomerisation of alkylcyclopentane to cyclohexane Dehydroisomerisations of alkylcyclopentenes to aromatics Dehydrocyclisation of paraffins to aromatics Hydrocracking of paraffins Dealkylation of gem-dialkyls formed in dehydrocyclisation. Prob 1. Write structural reactions for each of these reformations. + 3H2 Pt/Pd Pt + H2
- 28. Prob. 2 Read and write short notes on the following (a) Polymerization (b) Alkylation (c) Sulfur recovery (d) Hydrogen sulphide scrubbing (e) Uses of petroleum
- 29. Lecture 3 PETROCHEMICAL INDUSTRY I
- 30. Adipic Acid Adipic acid, COOH-(CH2)4-COOH, is one of the most important commercially available aliphatic dicarboxylic acids Typically, it is a white crystalline solid, slightly soluble in water and soluble in alcohol and acetone
- 31. Typically, itis a white crystalline solid, slightly soluble in water and soluble in alcohol and acetone Its consumption and production is dominated by the United States. Of the 2.3 million metric tons of adipic acid produced worldwide, about 42% is produced in the United States which also consumes 62% of total production. Western Europe produces about 40%, Asia-Pacific 13%, while the other regions account for the remaining 5%.
- 32. Production Process Almost all of the commercial adipic acid is produced from cyclohexane in a continuous process as shown in the reaction below. C6H12 + 2O2 C6H11OH + C6H11O Cyclohexane is air-oxidize at a temperature of 150 - 160 oC and about 8 to 10 atm. in the presence of a cobalt catalyst.
- 33. The productis a cyclohexanol-cyclohexanone (ketone-alcohol, or KA) mixture. The mixture is distilled to recover unconverted cyclohexane which is recycled to the reactor feed The resultant KA mixture may then be distilled for improved quality before being sent to the nitric acid oxidation stage. This process yields 75 to 80 mole percent KA, with a ketone to alcohol ratio of 1:2
- 34. The reactionproceeds as follows: C6H11OH + C6H11O + zHNO3 HOOC(CH2)4COOH + xN2O +yNO 50 to 60% nitric acid in the presence of a copper-vanadium catalyst is reacted with the KA mixture in a reactor at 60 to 80 oC and 0.1 to 0.4 MPa. Conversion yields of 92 to 96 percent are attainable when using high-purity KA feedstock
- 35. As thereaction is highly exothermic, the heat of reaction is usually dissipated by maintaining a high ratio (40:1) nitric acid to KA mixture, Upon reacting, nitric acid is reduced to nitrogen oxides: NO2, NO, N2O, and N2. The dissolved oxides are stripped from the reaction product using air in a bleaching column and subsequently recovered as nitric acid in an absorption tower.
- 36. The N2and N2O are released to the atmosphere. Nitrogen oxides, entering the lower portion of the absorber, flow countercurrent to a water stream, which enters near the top of the absorber. Unabsorbed NO is vented from the top while diluted nitric acid is withdrawn from the bottom of the absorber and recycled to the adipic acid process. The stripped adipic acid/nitric acid solution is chilled and sent to a crystallizer, where crystals of adipic acid are formed.
- 37. The crystalsare separated from the mother liquor(the liquid remaining after a substance has crystallized out) using a centrifuge and transported to the adipic acid drying and/or melting facilities. The mother liquor is separated from the remaining uncrystallized adipic acid in the product still and recycled to the reactors.
- 38. Uses Adipic acidconsumption is linked almost 90% to nylon. Nylon is used for everyday applications such as electrical connectors, cable tires, fishing lines, fabrics, carpeting, and many other useful products. Technical grade adipic acid is used to make plasticizers, unsaturated polyesters for production of rigid and flexible resins and foams, wire coatings, elastomers, adhesives and lubricants. Food grade adipic acid is used as a gelling aid, acidulant, leavening and buffering agent.
- 39. Lecture 5: ThePolymer Industry
- 40. Introduction Industrialuse of polymers started when Goodyear discovered the vulcanization of rubber in 1839. Polymer research rapidly spread throughout the world after 1930 and this led to the development of many synthetic polymers including nylon, polyethylene and polyvinyl chloride. Polymers are high molecular weight compounds built up by the repetition of small chemical units known as monomers
- 41. They areeither natural or synthetic. The natural polymers include rubber, cellulose, wool, starch and proteins. The term polymer comes from two Greek words: “polys” which means “many” and “meros” which means “parts.” A polymer is therefore a high molecular weight compound made up of hundreds or thousands of many identical small basic units (monomers) of carbon, hydrogen, oxygen or silicon atoms. The monomers are linked together covalently in a chemical process known as polymerization. This is illustrated in Fig, 3.2
- 42. H H H C H3 C H3CH3 C H3 C H3 (3Z,7Z,11Z)-3,7,11-trimethyltetradeca-3,7,11-triene
- 43. Classification ofpolymers Polymers can be classified into three types: 1. Linear polymers in which the repeating units are similar to the links in a very long chain They are known as polymer chains. An example is polyethylene 2. Branched polymers in which some of the molecules are attached as side chains to the linear chains. The individual molecules are still discrete. 3. Three-dimensional cross-linked polymers in which branched chains are joined together by cross-linking in a process known as “curing”. Vulcanization of rubber is a curing process.
- 44. Properties ofpolymers Polymers have three main properties: Molecular weight: The molecular weight of polymers is not fixed because of varying chain length. Crystallinity: Because of high molecular weight and varying chain length, most polymers are amorphous and only semi-crystalline Those with high crystallinity are tougher, more opaque, more resistant to solvents, higher density and sharply defined melting point. Glass transition temperature
- 45. Glass transitiontemperature: At low temperature, even amorphous polymers are hard and brittle (glass-like). As temperature is increased, kinetic energy increases. . However, motion is restricted to short-range vibrations and rotations as long as glass-like structure is retained. At a certain temperature called the glass transition temperature, a polymer loses glass-like properties. It becomes softer and more elastomeric but it does not melt. If heating is continued further, the polymer will lose elastomeric properties and melt to a flowable liquid.
- 46. Types of polymerproducts Plastics A plastic is a material that contains as an essential ingredient, an organic substance of a large molecular weight, is solid in its finished state, and, at some stage in its manufacture or in its processing into finished articles, can be shaped by flow. In practice, a plastic is usually considered to be an amorphous or crystalline polymer which is hard and brittle at ordinary temperatures. If crystalline regions are present, they are randomly oriented.
- 47. Thermoplastics A thermoplasticmaterial is one which can be softened and molded on heating. They are elastic and flexible above a certain glass transition temperature. Nylon is a thermoplastic and it was the first commercial polymer to be made as a substitute for silk for making parachutes, vehicle tires, garments and many other products. Current uses include: fabrics, footwear, fishnets and carpets to mention but a few. The two special grades of Nylon are Nylon 6-6 and Nylon 6.
- 48. Prob. Write downuses of various thermoplastic materials Plastic type Uses Low density polyethylene (LDPE Packaging films, wire and cable insulation, toys, flexible bottles, house, High density polyethylene (HDPE) Bottles, drums, pipes, films, sheets, wire and cable insulation Polypropylene PP Automobile and appliances parts, furniture, carpets, film packaging Polyvinyl chloride PVC Construction, rigid pipes, flooring, wire and cable insulation, film and sheet Polystyrene Packaging (foam and film), foam, insulation, appliances, house ware
- 49. Lecture 6: Thermosettingplastics and Elastomers
- 50. Thermosetting plastics A material is one which involves considerable cross linking, so that the finished plastic cannot be made to flow or melt. Thermosetting plastics (thermoses) are polymer materials that cure or are made strong by addition of elements (e.g. sulphur) or addition of energy in form of heat (normally above 200o C) through some chemical reaction. Before curing process, they are usually in liquid form, powder or malleable forms that can be moulded to a final form or used as adhesives. The curing process transforms these materials into plastic or rubber through a cross linking process.
- 51. The crosslinks produce a three dimensional rigid structure of the material with large molecular weight and a high melting point. The three dimensional network of bonds in thermoses generally makes them much stronger than thermoplastics. This makes them suitable for high temperature applications up to the decomposition temperature of the material.
- 52. Prob. Drawthe structure of a cross linked polymer.
- 53. A thermosesmaterial cannot be melted and reshaped after forming and curing and therefore cannot be recycled unlike thermoplastics. Examples of thermoses include: polyester resin, vulcanized rubber, Bakelite and epoxy resins Uses of Thermosetting plastics Phenol-formaldehyde (PF) Electrical and electronic equipment, automobile parts, utensils handles, plywood adhesives, particle board binder, Urea-formaldehyde (UF) Similar to PF, textile treatment, coating, Unsaturated polyester (UP), Construction, automobile parts.
- 54. Marine accessories,epoxy protective coating, adhesives, electrical and electronics, industrial flooring, material composites. Melamine-formaldehyde (MF) Similar to UF, decorative panels, counter and table tops, dinnerware. In the fabrication of plastic objects, additives such as colourants, fillers, plasticizers, lubricants and stabilizers are commonly added to modify the physical and mechanical properties of the material.
- 55. Elastomers An elastomeric(or rubber) is a word having its origin from two words: “elastic” which means the ability to return to original shape when a force or stress is removed and “mere” which means “parts“ implying many parts or monomers. Therefore, an essential requirement of an elastomeric is that it must be elastic i.e. it must stretch rapidly under tension to several times its original length with little loss of energy as heat.
- 56. Industrial elastomershave high tensile strength and high modulus of elasticity. They are amorphous polymers with considerable cross-linkages. The covalent cross-linkages make the elastomer to return to its original structure or shape when the stress is removed. Without cross-linkages or with short chains, the applied force would result in a permanent deformation. They are usually thermoses that require vulcanization, but there are some which are thermoplastic.
- 57. Elastomers include: •Nitride rubber • Butyl rubber • Silicone rubber • Polyurethane rubber • Polysulphide rubber • Poly butadiene • Styrene-butadiene • Polyisoprene • Tetrafluoroethylene • Tetrafluoropropylene
- 58. Adhesives(Polymer name:Nitrile rubber) Monomers:Acrylonitrile &1,3-Butadiene The heated glue-pot which traditionally contained glues based on animal products such as hoof, horn and fish residues has been replaced by adhesives based on synthetic polymers. There is now a wide range of adhesives and sealants suited for a variety of tasks from polyvinyl acetate (PVA) wood, board and paper glues, to two-part epoxide resins for rivet-less bonding of metal panels.
- 59. Fibres Animal fibres,such as wool or silk, and vegetable fibres, such as cotton, continue to be used although there is a wealth of synthetic fibres such as cellulose acetate and nylon, acrylic and polyester. Carbon fibres for making advanced composites are produced by heat treatment of polyacrylonitrile and other synthetic fibres.
- 60. Films Animal membraneswere the only non-metallic film forming materials used before the availability of rubber and these found little application. The successful development of a drum for casting films from viscose led in the 1920s to the production of ‘Cellophane’- still a widely used material. In the 1930s, unsupported PVC films were manufactured but it was not until polyethylene was available in the 1940s that the production of films for bagging materials became commonplace.
- 61. Surface finishes Thepaint industry was traditionally based on naturally occurring ‘drying’ oils such as linseed but since the 1930s these have gradually been replaced by synthetic polymers. Because of toxicity problems from using paints based on solvents, many more finishes are now water- based polymer emulsions. Project Work Consider developing a polymer product for the Ghanaian market.
- 62. Lecture 7:Polyethylenes
- 63. Introduction Thereare three major classes of polyethylene. These are low density polyethylene (LDPE), high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). Pellets of these plastics are extruded and blown to produce film. This film is used for packaging and making plastic bags Ethylene is derived from either modifying natural gas (methane, ethane, propane mixture) or from the catalytic cracking of crude oil. In a highly purified form, it is piped directly from the refinery to a separate polymerization plant.
- 64. The PolyethyleneManufacturing Process Today, polyethylene manufacturing processes are usually categorized into “high pressure” and “low pressure” operations. The former is generally recognized as producing conventional low density polyethylene (LDPE) while the latter makes density (HDPE) and linear low density (LLDPE ) polyethylenes. The difference between these polyethylene processes and types is outlined below.
- 65. High pressure Polyethylene was first produced by the high pressure process by ICI, Britain, in the 1930’s. They discovered that ethylene gas could be converted into a white solid by heating it at very high pressures in the presence of minute quantities of oxygen: Ethylene + 10 ppm oxygen 1000 - 3000 bar gives polyethylene 80 - 300 0 C
- 66. The polymerizationreaction which occurs is a random one, producing a wide distribution of molecule sizes. By controlling the reaction conditions, it is possible to select the average molecule size (or molecule weight) and the distribution of sizes around this average molecular weight. The chains are highly branched (at intervals of 20 – 50 carbons). ICI named their new plastic “polythene” and found that they were able to produce it in a density range of about 0.915 to 0.930g cm3. It is known today as LDPE and has its single biggest usage in blown film.
- 67. Low pressure The initial discovery of LDPE was an accident. So was the discovery of HDPE in 1952. Researchers in Germany and Italy had succeeded in making a new aluminium based catalyst which permitted the polymerization of ethylene at much lower pressures than the ICI process: Ethylene 10 - 80 bar polyethylene 70 - 300 o C, Al catalyst
- 68. The productfrom this process was found to be much stiffer than previous products and had a density range of about 0.940 - 0.970g cm3. The increased stiffness and density were found to be due to a much lower level of chain branching. The new HDPE was found to be composed of very straight chains of ethylene with a much narrower distribution of molecular weights (or chain lengths) and a potentially very high average chain length.
- 69. In thelate 1950’s, DuPont Canada first applied the low pressure process to the production of LLDPE. LLDPE is made by copolymerizing of ethylene with a small amount of another monomer, typically butene, hexene or octene. The most common method used in industry is to polymerize ethylene by means of a fluidized reactor bed. A fluidized reactor bed consists of metallic catalyst particles that are ‘fluidized’ by the flow of ethylene gas.
- 70. This meansthat the catalyst particles are suspended in the ethylene fluid as ethylene gas is pumped from the bottom of the reactor bed to the top. Before the late 1970’s an organic peroxide catalyst was employed to initiate polymerization. However, because the organic peroxide catalyst is not as active as the metallic catalyst, pressures in excess of 100 times the pressure required with metallic catalysts were necessary.
- 71. Before ethyleneis sent to the fluidized bed, it must first be compressed and heated. Pressures in the range of 100-300 pounds per square inch (psi) and a temperature of 100 o C are necessary for the reaction to proceed at a reasonable rate. The catalyst is also pumped with the ethylene stream into the reactor. This is because polyethylene molecules remain stuck to the catalyst particle from which they were produced thus incorporating the catalyst within the polyethylene product. Hence the need to replenish the “consumed “ catalyst. The conversion of ethylene is low for a single pass through the reactor and it is necessary to recycle the unreacted ethylene. Unreacted ethylene gas is removed off the top of the reactor
- 72. After purification, ethylenegas is then recompressed and recycled back into the reactor. Granular polyethylene is gradually removed from the bottom of the reactor as soon as reasonable conversions have been achieved. Typically, a residence time of 3 to 5 hours results in a 97% conversion of ethylene
- 73. Whatever thetype of polyethylene produced, the end product is usually available in the form of small pellets, varying in shape (spherical, rectangular, cylindrical) depending upon the manufacturer’s equipment. During the manufacture of polythene products, it is melted to flow through a film extruder.
- 74. LDPE is thepreferred packaging material due to its limp feel, transparency, toughness, and the ability to rapidly take up the shape of the contents of the bag. The garbage bag is just one of many widely practical uses of plastic bags. Polyethylene film, produced by blown film extrusion, is commonly used for packaging of foodstuffs and other products. The thickness of the film produced tends to be from 20 - 200 am.
- 75. Lecture 8 :Styrene butadiene rubber
- 76. Styrene Butadiene Rubber(SBR) Introduction Emulsion polymerized styrene-butadiene rubber (E- SBR) is one of the most widely used polymers in the world today. Emulsion SBR is employed in many demanding applications, which enhance the quality of life and contribute significantly to our economy and standards of living. In the 1930’s, the first emulsion polymerized SBR known as Buna S was prepared by I. G. Farbenindustrie in Germany.
- 77. The U.S. Government in 1940 established the Rubber Reserve Company to start a stockpile of natural rubber and a synthetic rubber program. These programs were expanded when the United States entered World War II. The synthetic rubber efforts were initially focused on a hot polymerized (41° C) E- SBR. Production of a 23.5% styrene and 76.5% butadiene copolymer began in 1942. Cold polymerized E-SBR (5°C), that has significantly better physical properties than hot polymerized SBR, was developed in 1947.
- 78. Uses SBRis widely used for rubber belting, hose, flooring, molded goods, rubber soles, coated fabrics etc. It is compatible with natural rubber and has equal performance for automobile tyres. But it is inferior to natural rubber for heavy duty truck tyres.
- 79. Manufacturing Process SBR is produced by the copolymerization of butadiene with styrene in the approximate proportion of 3:1 by weight. In the emulsion process, which produces general purpose grades, the feedstocks are suspended in a large proportion of water in the presence of an initiator or a catalyst and a stabiliser. A continuous process is employed. In the solution process, the copolymerisation proceeds in a hydrocarbon solution in the presence of an organometallic complex
- 80. This canbe either a continuous or batch process. The emulsion polymerization process has several advantages. It is normally used under mild reaction conditions that are tolerant to water and requires only the absence of oxygen. The process is relatively robust to impurities and amendable to using a range of monomers. Additional benefits include the fact that emulsion polymerization gives high solids contents with low reaction viscosity and is a cost-effective process. The physical state of the emulsion (colloidal) system makes it easy to control the process. Thermal and viscosity problems are much less significant than in bulk polymerization.
- 81. TUTORIAL QUESTIONS 1.From what you have read about crude oil and natural, what is the composition of (i) Crude oil Ans: An “average” crude oil contains about 84% carbon, 14% hydrogen,1%-3% sulfur, and less than 1% each of nitrogen, oxygen, metals, and salts. (ii) Commercial natural gas Ans: Commercial natural gas is made up of about 80% methane (CH4), 7% ethane (C2H6), 6% propane (C3H8), 4% butane and isobutane (C4H10), and 3% pentane (C5H12). The C3, C4, and C5 hydrocarbons are removed before the gas is sold. (iii) LPG? Ans: The butanes removed from natural gas are usually liquefied under pressure and sold as liquefied petroleum gases (LPG). 2. Explain how petroleum refining has evolved over the years as product specifications changed. Ans: Petroleum refining has evolved continuously in response to changing consumer demand for better and different products. The original requirement was to produce kerosene as a cheaper and better source of light than whale oil. The evolution of the airplane created an initial need for high-octane aviation gasoline and then for jet fuel, a sophisticated form of the original product, kerosene. Present-day refineries produce a variety of products including many required as feedstock for the petrochemical industry. Common petroleum products include gasoline, liquefied refinery gas, still gases, kerosene, aviation fuel, distillate fuel oil, residual fuel oil, lubricating oils, asphalt, coke and petrochemical feedstocks. 3. Why is sulphur undesirable in fuel and how is it removed by hydrodesulphurisation? Sulphur is an undesirable component because of its strong offensive odour, corrosion, air pollution by some of its compounds and its effect of reducing tetraethyl lead (anti-knock agent). The combustion of petroleum products containing sulphur compounds produces undesirables such as sulphuric acid(H2S04) and sulphur dioxide(SO2).
- 82. TUTORIAL QUESTIONS 4.Write short notes on (i) cracking Ans: Cracking is the thermal decomposition of a substance, especially crude petroleum in order to obtain petrol/gasoline. The purpose of cracking is to break complex hydrocarbons in simpler molecules in order to increase the quality and quantity of lighter, more desired products and decrease the amount of residuals. The decomposition takes place by catalytic action or by heating in the absence of oxygen (pyrolysis). (ii) reforming Reforming is a catalytic process in which short-chain organic molecules combine to form larger ones which are used in the petroleum industry. It is an important process used to convert low-octane naphthas to high octane gasoline blending components called reformates. Depending on the properties of the naphtha feedstock (as measured by paraffins, olefins, naphthenes and aromatics) and catalyst used, reformates can be produced with very high concentrations of toluene, benzene, xylene and other aromatics useful in increasing the octane number of gasoline. 5. From internet search and / or other resources: (i) Write equations that show how phthalic anhydride is used in the manufacture of alkyd resins. (ii) find a paint formulation that contain an alkyd resin.
- 83. 6. Writeall the equations using the structural formula of the main raw materials and products for the main reactions that take place during the manufacture of phthalic anhydride and adipic acid. 7. Name 10 materials that you use daily which are made of synthetic organic polymers 8. Vinyl chloride undergoes copolymerization with 1,1-dichloroethylene to form a polymer, commercially known as Saran. Write equations for this polymerisation. 9. Using the format used for the learning of polyethylene and styrene–butadiene rubber, write 3-5 page paper on polyvinyl chloride. 10. Discuss briefly the environmental effects of plastic products
Editor's Notes
- #23 Thus isomerization of straight-chain alkanes to form branched chain alkanes is a thermal reforming process.
- #43 Curing is a chemical process employed in polymer chemistry and process engineering that produces the toughening or hardening of a polymer material by cross-linking of polymer chains. It is strongly associated with the production of thermosetting polymers.