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Petroleum products

The products obtained from petroleum can be classed into four groups: I-fuels; II- lubricating oils, paraffins, etc.; III-miscellaneous petroleum products; and IV-chemical and petrochemical products.

Group I includes liquefied hydrocarbon gases, fuels for carburettor engines [gasolines], fuels for jet (kerosene) and turbojet engines , Diesel fuels, boiler fuels; Group II-various lubricating oils, paraffins, ceresins and petrolatum; Group III- plastic greases, bitumenns, coke, etc.; and group IV- hydrocarbons of various classes which serve as starting materials for organic or petrochemical synthesis.

I. Liquefied hydrocarbon gases and fuels

Liquefied hydrocarbon gases consist mainly of propane and butane and sometimes may contain small quantities of propylene and butylene. They have found the widest application as domestic fuel which may be commercial propane (at least 93 % of propane), commercial butane (at least 93 % of butane) or their mixture (in winter time, with a greater proportion of propane).

Liquefied gases or their constituents of higher purity are used as starting materials for the manufacture of various chemical products and olefines [by pyrolysis].

1. Fuels for carburettor Engines

This group of fuels includes aviation and motor gasolines and tractor kerosene. An important characteristic of these fuels is the pressure of saturated vapours, kPa, which should be 29.3 to 47.9 for aviation gasolines, 66.5 to 93.4 for motor gasolines (not more than 66.5 for summer grades).

The fractional composition of fuels is also of large importance. For instance, the 10% boiling point of gasoline (the point at which 10% of the fuel boils off) can characterize the starting properties and reliability of an engine starting under various conditions, in particular, at a low temperature of the ambient air. The 50% boiling point of gasoline characterizes the speed of engine heating during starting, the smoothness of switching from one operating mode to another, and the stability of engine operation. The 90% and 97.5% boiling points of aviation gasoline and the temperature of the end of boiling of motor gasoline determine the homogeneity of the fuel mixture, i.e. the completeness of fuel combustion in the engine. This is extremely important, since with incomplete combustion of the fuel, liquid substances can penetrate into the crankcase and dilute the lubricating oil and thus cause a quick wear of the engine. Besides, incomplete combustion causes a stronger pollution of the air.

Antiknock rating is another important characteristic of fuels which determines their proper combustion in carburettor engines. With detonation (knock-type) combustion, the rate of flame front propagation increases very quickly and causes explosion, or knock, in an engine; as a result, the engine may quickly be put out of operation. The antiknock rating of fuels is evaluated in terms of the octane number (ON).

Aviation Gasolines (state Standard GOST 1012-72). They are used as fuel for carburettor-engine planes and helicopters. In the USSR, aviation gasoline is available in the following grades: B-70, B-100/130, and B-91/115. The grading includes a letter B and a number indicating the octane number or two numbers: The numerator indicating the octane number and the denominator, the rating. Aviation gasolines are prepared by mixing (compounding) of a base gasoline (obtained by catalytic cracking or catalytic reforming), high-octane components (isooctane, alkyl gasoline, isopentane, benzene hydrocarbons, etc.), tetraethyl lead (TEL) and other additives raising the octane number, and of inhibitors i.e. substances preventing fuel oxidation (with aviation gasoline, oxy- diphenylamine is used for the purpose). These components are taken in proportions required to make gasoline of the desired grade and quality.

The boiling-off points of gasolines should not exceed the following temperatures: 90% boiling-off point 1450C; 50% 1050C; and 10% from 750 to 880C. The content of TEL (g/kg of gasoline) should be not more than 2.7 for grade B-100/130 and from 2.5 to 3.3 for other grades, except for B-70 which contains no TEL.

Motor Gasolines. These grades of gasoline are employed in automobile carburettor engines. One of the most important indices of their quality is the anti-knock rating which is expressed in terms of the octane number.

Octane number is numerically equal to the content of isooctane (% by volume) in a mixture with n- heptane, which is equivalent in its detonation intensity in a single cylinder engine to the fuel being tasted under standard conditions. The octane numbers of isooctane is taken conditionally to be 100 and that of n-heptane, zero. The octane numbers are determined by using mixture of these two hydrocarbons. The current control of fuels is done by using what is called secondary reference fuels having various values of the octane number.

Octane numbers can be determined by various methods. The motor method uses apparatuses of the type IT9-2M and UIT-65 to measure the octane number of motor and aviation gasolines. Motor gasolines can also be tested by what is called the research method in apparatuses of the type IT9-6 and UIT-65 (State Standard GOST 8226-66). The temperature method(State Standard GOST 3337-52) with the use of IT9-5 apparatus is employed to determine the antiknock of high- octane aviation gasolines (ON 100 or higher). The pressurization method (State Standard GOST 3368-68) with the use of IT9-1 apparatus is used to determine the rating of aviation gasolines in rich mixtures.

The octane number of gasoline increases on addition of benzene hydrocarbons and isomeric paraffin hydrocarbons and also on a decrease of the point of full boiling-off. If these measures fail to give gasoline with a desired octane number, an antiknock agent is added. Various metalorganic and organic substances can be used as antiknock agents. The most popular antiknock is tetraethyl lead Pb(C2H5)4 in the form of ethyl liquid.

All hydrocarbons can be written in the following order of increasing effect of TEL on octane number: paraffin-naphenes-benzenes-olefins. With an increase in the content of TEL in gasoline, its effectiveness diminishes. The sensitivity of gasolines to TEL decreases sharply with an increasing concentration of sulphur which reacts with lead and petrifies the effect of TEL. For that reason, the starting materials of certain processes and some grades of gasoline are purified from sulphur compounds before adding TEL.

The grades of motor gasoline produced in the USSR are as follows: A-66, A-72, A-76, AI-93 and AI-98 (the digits are octane numbers). All these grade can be ethylated, except for A-72. The content of TEL in them should not exceed 0.6 g/kg in A-66, 0.41 g/kg in A-76 and 0.82 g/kg in AI-93 and AI-98. The octane number of grade AI-93 and AI_98 is measured by the research method and that of the other grades, by the motor method. For easier operation of engines, motor gasolines are manufactured as summer and winter kinds, the latter, as has been given earlier, having a higher pressure of saturated vapours. Besides, they have (except for grade AI-980 different temperature of boiling-off of intermediate fractions and of the end of boiling. The fractional composition of motor gasolines is given below (numbers in numerators and denominators are boiling-off points respectively for summer and winter kinds of gasoline, 0C).

A-66 A-72, A-76

AI-93 AI-98

Beginning of boiling, at least

Boiling-off points, lower limit:

10%

50%

90%

End of boiling 35/-

79/65

125/125

195/160

205/185 35/-

70/55

115/100

180/160

195/185 35/-

70/-

115/-

180/-

195/-

New, more efficient makes of automobile engines have a high compression ratio and can be run only on high-octane gasoline. Motor gasolines are prepared by mixing (compounding) various components: high-octane gasolines of catalytic cracking and catalytic reforming, alkylates and isomerizates of light fractions of preliminary distillation. For preparation of gasoline with lower octane numbers (especially of grade A-66), use is also made of gasolines of thermal cracking and coking, gasolines obtained by straight-run distillation of petroleum, which have a higher temperature of boiling off, and dearomatized products (refined petroleum) obtained in the manufacture of benzene hydrocarbons by catalytic reforming of gasoline fractions.

Since tars, if present in gasoline, can disturb the operation of engines, their content in gasolines is limited at 7 mg/100 ml in grade A-66 and 5 mg/100 ml in the other grades. The chemical stability of gasolines is checked by determining the induction period which should constitute at the manufacturer at least 450 min for grade A-66, 600 min for A-72, and 900 min for the other grades.

2. Fuels for diesel engines.

In Diesel engines, air is compressed and its temperature rises and Diesel fuel injected into the engine is ignited by the hot air. The capability of diesel fuels for self- ignition is measured in term of cetane number.

Cetane number is the index of ignitability of diesel fuel, which is equal numerically (in per cent) to the content of cetane (n-hexadecane C16H34) in a mixture with -methylnaphthalene C11H10, which possesses the same ignitability in a single-cylinder engine under standard testing conditions as the fuel being examined. The cetane number of cetane proper is taken equal to 100 and that of -methylnaphthalene, zero. The cetane number depends on fuel composition: the highest cetane number is shown by paraffin hydrocarbons, a lower, by naphthenes and the lowest, by benzene hydrocarbons which for that reason are undesirable in diesel fuels. The cetane number can be raised by mixing diesel fuel with certain components containing paraffin hydrocarbons of normal structure or by giving special additives.

Diesel engines are divided into three classes: high-speed engines (above 1000 rpm) for agricultural machines, Diesel locomotives, cross-country vehicles, etc.; medium-speed engines (500-1000 rpm) for large locomotives and as auxiliary motors on ships; and low-speed engines (less than 500 rpm) employed as main marine engines and Diesel-generators.

Depending on the content of sulphur in the original petroleum, diesel fuel fractions may be low-sulphurous (up to 0.2 % S) and sulphurous (0.7 to 1.8 % S). The content of sulphur can be reduced by hydrogen refining. Low-sulphur fuels are advantageous in being less corrosive and less liable to carbonization; besides, they form exhaust gases low in sulphurous and sulphuric anhydrides. The viscosity of diesel fuels also standardized to ensure proper atomization and reliable operation of the fuel-supply system. Heavy fractions in the fuel can cause in complete combustion and smokes in exhaust gases and carbonization in the engine.

Medium-speed diesel engines can be run heavy distillate fuels and low-speed ones, on fuels obtained by dilution of fuel oils by distillates, including diesel fractions, to obtain the desired viscosity from 36 to 67 mm2/s at 500C]. The setting point of the mixture may be from -5 to 50C.

3. Boiler Oils (fuel oils)

Fuel oils are used in many branches of national economy, in particular, at thermal power plants.

According to the State Standard GOST 10585-75, fuel oil is graded as follows: marine grades F-5 and F-12 (light fuel), furnace fuel oil grade 40 (medium) and furnace fuel oil grade 100 (heavy fuel). The characteristics of fuel oils may vary appreciably in different grades. For instance, the relative viscosity of fuel oils should be respectively: not more than 5 and 12 mm2/s at 500C for marine grades and 8 and 16 mm2/s at 800C for furnace grades 40 and 100. Fuel oils of a higher viscosity have a higher flash point, which is specified at 80 and 90 for marine grades F-5 and F-12 (in a closed crucible) and at 900 and 1100C (in an open crucible) for furnace grades 40 and 100. The setting point of fuels is limited at -50 to 250C (or up to 42 for fuel oils obtained from high-paraffin petroleum). According to the sulphur content, fuel oils of each grade are divided into low-sulphurous (up to 0.5% S), medium-sulphurous (0.51 to 1.0 per cent), and high- sulphurous (1.01 to 3.5 %).

The quality of fuel oils is decided by the following characteristics: viscosity, which determines the ease of transportation of the fuel and the probable degree of heating for effective atomization; setting point, which determines the conditions of storage and application of the fuel at various temperatures of the air; sulphur content, which determines the degree of corrosion of the engine and the exhaust of sulphurous compounds to the atmosphere. One of the decisive characteristics of fuel oils is the heat of combustion (calorific value) which depends on their composition. The low calorific value of low-sulphurous and medium-sulphurous fuel oils (recalculated to dry fuel) must be not less than 41454 kJ/kg for furnace grades, 40470 kJ/kg for furnace grade 40, 40530 kJ/kg for furnace grade 100.

Fuel oil grades are chosen according to the conditions of operation of engines. Thicker (and cheaper) grades are commonly used at stationary plants where the fuel can be heated up and filtered. Marine grades of fuel oil (employed in marine power plants) differ from furnace grades in having a lower content of ash, water, sulphur and tars.

Fuel oils are prepared by mixing residual products of preliminary distillation (residual fuel oil, semigoudron and goudron) with residual products of thermal and some catalytic processes (cracking residue, gasoil, reflux, polymers) and residual products of oil manufacture.

4. Fuels for Jet and Gas-turbine Engines

Fuels for aviation jet engines are divided into two main groups: for subsonic and supersonic speeds. The latter must have an elevated density and a sufficiently high calorific value to ensure the required power of the engine and the desired flight range. At higher speeds of flight, fuel is heated much more.

Jet-engine fuels (aviation kerosene] are kerosene fractions of preliminary distillation of petroleum having the temperature of the beginning of boiling from 1500 to 1950C and the boiling-off point from 2500 to 3150C. Fuels for jet engines must easily be vaporizable, have a high calorific value (the lowest calorific value being not less than 42950-44 160 kJ/kg], high thermal stability, a low temperature of the beginning of crystallization (not higher than -600C) and cause no corrosion of engine elements. Jet-engine fuels of the highest thermal stability are obtained by catalytic refining in hydrogen under pressure.

Gas-turbine fuels for terrestrial machines differ from aviation kerosene by a wider fractional composition and higher content or sulphur (up to 3 %). Their relative viscosity at 500C must be not more than 2.

Exercises

Answer the following question

1. How many group can petroleum products be classed into? What are they?

2. Which group do the liquefied hydrocarbon gases belong to?

3. What are the main compositions of liquefied hydrocarbon gases?

4. How many important characteristic have fuels for carburettor engines got? What are they?

5. What can happen if there is a incomplete combustion?

6. What is the antiknock rating evaluated?

7. What is the octane number of a petroleum product?

8. Which kind of hydrocarbons have the higher octane number?

9. What do they do to increase the octane number of gasoline?

10. What are the limit content of TEL in the grades of motor gasoline in USSR?

11. The winter kind of motor gasoline has a higher pressure of saturated vapour than the summer, hasn't it?

12. In what is the chemical stability of gasoline checked?

13. For which fuels is the term cetane number used for?

14. What is the cetane number of petroleum products?

15. What does cetane number depend on?

16. What is the order of increasing the cetane number of hydrocarbon?

17. Which methods are used to raise the cetane number?

18. How are fuel oils classified?

19. By what is the quality of fuel oils decided?

20. What is the decisive characteristic of fuel oils?

21. Fuel oil grades are chosen according to the conditions of operation of engines, aren't they?

22. What are the thicker grades commonly used for?

23. How do they prepare fuel oils?

24. How do they classify fuels for aviation jet engines?

25. What are the characteristics of fuel for jet engines?

II. Lubricants, Products of Oil-paraffin Processing and Other Petroleum Products

In addition to high-quality fuels, lubricating materials are also essential for normal operation of various engines and mechanisms. All lubricants can be divided into four types: gaseous, solid, liquid, and semisolid (thickened), or greases.

Some gases can react with metals to form a lubricating film which lowers friction and wear. Solid lubricants, such as graphite or molybdenum disulphide, are employed at very high temperatures and under heavy loads where ordinary lubricants, including oils and greases, are ineffective. In this section, we shall discuss only lubricating oils and greases.

1. Lubricating and other Oils

Petroleum processing industry manufactures mineral oils of many kinds: motor oils (aviation, diesel and automobile grades), industrial oils, turbine oils, electroinsulating oils, compressor oils, etc.

Viscosity is the most important characteristic of all kinds of oil. On the one hand, it should be sufficiently low to ensure lubrication and easy start of engines at low temperatures and, on the other, sufficiently high to lubricate properly even the hottest parts of an engine. This requirement is met by oils having a high viscosity index. Other important characteristics of oils are their oxidation stability at the elevated temperature, a low setting point (especially for winter grades), good anticorrosive properties, and others.

All grades of lubricating oils for modern mechanisms and engines, especially for diesel engines and the like, contain additives which improve their performance.

Diesel and automobile oils are made by mixing purified residual and distillate oils.

Aviation Oils. These are employed for lubricating of aviation piston engines. They are prepared from goudron residue after distillation of specially selected petroleum grades by deep refining with selective solvents and sometimes by mixing with distillate oils.

Aviation engines operate under heavy loads and at high temperatures, so that the oils for them will have a high chemical stability and great lubricating power.

Industrial Oils. These are intended for lubrication of machines and mechanism of industrial equipment which operate at relatively low temperatures and of pairs of machines and engines not subjected to the effect of steam, hot air or gases. There is no strict scientific classification of industrial oils. They are commonly classified by their viscosity and by the conditions and fields of application. Depending on viscosity, industrial oils are divided into light (3.5-10 mm2/s at 500C), medium (10-58 mm2/s at 500C), and heavy (11-96 mm2/s at 500C). Depending on the conditions of application, they are classed into oils for light and moderate speeds and loads and heavy-duty oils, and by the fields of application, into oils for gear transmissions, slip guides, spindles, instrument oils, break-in oils, and special oils. These grades of oil are prepared by using base oils of selective purification produced from eastern grades of petroleum.

Industrial oils should be pressure-and corrosion-resisting, retain their fluidity at the working temperatures, and be stable against foaming and oxidation.

Turbine oils. These are used for lubrication of bearings and auxiliary mechanisms of turbomachines (steam and gas turbines, turbocompressors, hydraulic turbines, marine turbines, etc.); they are also used as pressure fluids. Turbine oils without additives are produced by contact acid refining, those with additives are manufactured by selective refining from low-sulphurous and sulphurous grades of petroleum. Additives improve their antioxidizing, deemulsifying, anticorrosive and antifoaming properties. Some grades oils contain antiwear additives. Turbine oils must have a high chemical stability and separate easily from water which enters occasionally the lubrication system.

Insulating oils. Oils are liquid dielectrics and therefore can be used for insulation of current-conducting elements of electric equipment (transformers, capacitors, cables, etc.). Insulating oils also serve for removing heat and favour quick are extinction between electric contacts. This group of oils includes transformer, capacitor and cable oils.

Transformer oils have found the widest application in the group. They are intended for long operation at 70-80 0C in the atmosphere of air and for that reason should possess a very high chemical stability and should not form low- molecular acids on oxidation. Besides, transformer oils should naturally have dielectric characteristics. Most grades of transformer oils have a viscosity of not more than 9 mm2/s at 50 0C, exceptions being grade ATM-65, arctic transformer oil, with a viscosity of not more than 3.5 mm2/s at 50 0C and grade T-1500 (for equipment of transmission lines for 1500kV) whose viscosity is limited at 8 mm2/s at 50 0C. Transformer oils cannot be replaced by other kinds of oil.

Compressor oils. These oils serve for lubrication of cylinders, valves and piston rods of compressor operating at temperatures of 200-2500C and pressures of 20-25 Mpa. The main requirement to compressor oils is that they should have an appropriate oxidation stability. Compressor oil grade 12 M, of a kinematic viscosity of 11-14 mm2/s at 100C, is intended for single-stage horizontal and vertical compressors for a pressures 0.7-0.8 MPa and for two-stage compressor for an average pressure up to 5 Mpa. Compressor oil grade 19T, of a kinematic viscosity of 17-21 mm2/s at 1000C, is employed in multi-stage high-pressure compressors (for 20-30 MPa). The oxidation stability of these oils is ensured by deep refining.

Oils for steam engines. They are divided into two main groups: for saturated-steam and for superheated-steam machines. These oils are distinguished by a low evaporability and a high viscosity (the kinematic viscosity at 1000C is 9-13 mm2/s for cylinder oil grade 2 and 44-64 mm2/s for grade 52 vapour oil). Cylinder oils of the first group are prepared from distillates and those of the second group, from residues by deasphalting with propane or by distillation of goudron in high vacuum.

Synthetic oils. These oils are essentially organic or elementoorganic compounds [containing silicon, iron, etc.] and are intended for heavy-duty applications.

2. Paraffine, ceresins and petroleum

Paraffins. These are soft [liquid] or solid petroleum products of crystalline structure obtained from distillates of paraffinic and high- paraffinic grades of petroleum.

Solid petroleum paraffins are crystalline products of white to bright- brown colour, depending on the amount of oil. The oil content in paraffins may vary within 0.8-0.5 per cent for high- purified grades and up to 2.2-2.3 and even 5 per cent for other grades.

Special grades of paraffine are manufactured in the USSR for application in food industry. They are obtained by deep refining of raw paraffins and employed mainly for impregnation of packing materials either contacting loose fry foodstuffs [grade P-2 with the oil content up to 0.9 per cent by mass] or non-contacting [grade P-3, oil content up to 2.3 per cent by mass]. Paraffin grade P-1 [oil content up to 0.5 per cent by mass] is used for the same purposes as grade P-2, and also in candy industry.

The fusion point of paraffin grades P-1, P-2, P-3 is respectively 54, 52 and 500C.

Ceresins. Ceresin is mixture of solid hydrocarbons obtained in processing and refining of ozokerite, unpurified petroleum ceresin or their mixtures. Ceresins are used for making greases, wax alloys, insulating material, etc.

The most important characteristic of cerecins is the dropping point, 0C. According to the state standard GOST 2488-73, the dropping point is the basis of grading of ceresins [the grade of ceresin manufactured in the USSR are disignated respectively 80, 75, 67 and 57]. The volume resistivity at 1000C is specified only for grade 80 ceresin: it should be not less than 1*1012 ohm cm.

Synthetic high-fusion ceresin has the highest dropping point. It is a mixture of solid hydrocarbons of the methane series, mostly of normal structure, which are obtained by synthesis of carbon monoxide and hydrogen [Fisher-tropsch process ]. According to the state GOST 7658-74, the dropping point of this of ceresin must be not less than 1000C and the volume resistivity at 1000C, not less than 1014 ohm cm.

Medical [liquefied] Petrolatum. This product is obtained by fusion of ceresin, paraffin, purified petrolatum or their mixtures with petroleum oil. Its dropping point is 37-500C.

Capacitor Petrolatum. It is employed for filling in and imprenating of capacitors. Its kinematic viscosity at 600C must be at least 28 mm2/s. An important specified characteristic of this product is the volume resistivity, which must be at least 1*1012 ohm cm at 1000C.

Exercises

Answer the following question

1. How many type can lubricants be divided? What are they?

2. What are the effects of lubricants?

3. Viscosity is the most important characteristic of all kinds of lubricant, isn't it?

4. Which properties must the viscosity of lubricating oils must be have?

5. What are the characteristics of lubricating oils?

6. What are the purposes of aviation oils?

7. What are the characteristics of aviation oils?

8. How can industrial oils be classified?

9. How can additive type for industrial oils be prepared?

10. What are the properties of industrial oils?

11. What are turbine oils used for?

12. What are insulating oils include?

13. Which grade of insulation oil have the widest application?

14. What are the applications of compressor oils?

15. How can they prepare the cylinder oils for steam engines?

16. What are the applications of the solid petroleum paraffins?

17. What is ceresin?

18. What is ceresin used for?

19. The most important characteristic of ceresin is the dropping point, isn't it?

20. How can they prepare medical petrolatum?

21. What is capacitor petrolatum?

II Miscellaneous Petroleum Products

Greases. Grease is a thick salvelike product consisting of oil and a thickener. Various soaps [calcium- sodium, aluminium, lithium, barium, etc.] are commonly used as thickeners. Greases thickened by hydrocarbon components [ceresin, paraffin or petrolatum] are mainly employed for protective coatings. They are physically and chemically stable, but their operating range is limited to temperatures of 50-600C. Special greases are also produced, in which various compounds are used instead of oil as a liquid base.

Greases are employed in cases where mineral oils cannot ensure proper lubrication of machines and mechanism, and also for tightening gaps. Greases are often used as slushing compounds; they protect mechanisms against corrosion during storage and then can serve as lubricants in operation.

Petroleum Bitumens. Bitumens are usually obtained by oxidation of goudrons from heavy tarry grades of petroleum, and also by mixing with asphalt, extracts of oil manufacture and asphaltile. The main characteristics of bitumens are; [needle] penetration, ductility, and softening temperature which characterizes the thermal stability of bitumen. The penetration and ductility at low temperature determine, in combination, the capacity of bitumen to retain its elasticity.

Petroleum bitumens are mainly used in road construction. Dirt and gravel roads are sometimes impregnated by liquid bitumen obtained by dilution of bitumen with a less viscous petroleum product, such as fuel oil. Some special grades of bitumen are made for application in civil engineering and for manufacture of paints and varnishes, electroinsulating materials, etc.

Petroleum acids and their sails. Petroleum acids, mainly naphtenic, are present in some grades of petroleum. They are separated during alkali refining of fuel and oil distillates as sodium salts [soaps] and employed for manufacture of naphtenate soap, acidol and acidol- naphtenate soap. Naphtenate soap [contain 43 per cent of petroleum acids] is a mixture of sodium soaps of petroleum acids, mineral oil and water. Acidol [contains 42- 50 per cent of petroleum acids] consists of petroleum acids with an admixture of mineral oil. Acidol - naphtalenate soap [67-70 per cent of petroleum acids] is a mixture of free naphtenic acids and their sodium soaps. All these products are employed as substitutes of fats in manufacture of industrial soaps, since they possess high emulsifying and foaming properties. They are also used in the textile industry for dyeing, for wood impregnation, as drying agents in paints and for some other purposes. A general requirement to these products is that the content of mineral oil be not above a specified limit.

Solvents. The paint- and- varnish industry uses most widely gasoline [fraction 45-1700C], while spirit [fraction 165-2000C], and solvent naphtha [mixture of xylenes] as solvents. In the food industry, the commonest solvents are extraction gasoline [fraction 70-950C] and petroleum ether [fractions 40-700C and 70-1000C]. In other industries, these and some other solvents [including benzene] can be employed. All solvents are specified for the content of benzene and unsaturated hydrocarbons and sulphur compounds.

Solvents are usually obtained from accompanying petroleum gases and low- sulphurous petroleum and in gas fractionation, preliminary distillation of petroleum and in catalytic reforming [from refining products]. The desired fraction in sometimes separated in deep- distillation plants. In many cases, the fractions obtained are specially purified [mostly to minimize the content of benzene hydrocarbons and sulphur compounds].

Domestic [illumination] kerosene. Domestic kerosene is obtained by straight- run distillation of petroleum. It should have a specified composition to ensure normal burning [mostly paraffin hydrocarbons], burn without forming fly ash [the height of non- smoky flame should be not less than 20 mm], and have an appropriate brightness of flame.

Coke. This is a product of petroleum coking, used for making electrodes, abrasives and some other materials and as a solid fuel. Electrode coke has the highest industrial significance for electrolytic manufacture of aluminium and making of artificial graphites which are used as antifriction materials in mechanical engineering.

Commercial carbon [carbon black]. This is an amorphous substance usually in the form of a powder with black spherical particles 30-40 m in diameter. Commercial carbon may be named channel black or furnace black depending on the method of manufacture. It is employed as a filler in the rubber and paint and varnish industry and as a dyer in the manufacture of printing ink, ebonite, electrodes, etc. The principal standardized characteristics of carbon black are as follows; adsorption, dispersion, colouring power, absence of foreign inclusions, uniform distribution [in rubber mixtures], and fractional composition.

At petroleum-processing plants, carbon black can be made from gases, green oil [obtained in pyrolysis of kerosene -solar oil fractions], coke residue [from coking plants], gas oil of catalytic cracking, and extracts of oil processing [more often after thermal treatment in cracking plants], coal tar pitch, and aromatized extracts from gas oil of secondary processes.

Softeners. Residual products of straight run distillation of petroleum ['softener' fuel oil], shale oil, and some products of oil processing can be used as softeners. They are employed in the rubber industry and as softeners of rubber mixtures in rubber regeneration.

Exercises

Answer the following question

1. What is the composition of grease?

2. What are the characteristics of grease?

3. What are grease employed?

4. How is bitumen prepared?

5. What are the main characteristic of bituments?

6. What is the main application of petroleum bituments?

7. What are other applications of petroleum bituments?

8. What is the main application of product of petroleum acids?

9. What are other applications of product of petroleum acids?

10. Which products of petroleum are used as solvents ?

11. In which industries are solvents used?

12. How are solvents obtained?

13. How is domestic kerosene obtained?

14. Which properties that flame of domestic kerosene should have?

15. What is coke used for?

16. How many is the dimension of particles of commercial carbon?

17. What is commercial carbon used for?

18. What are the principal standardized characteristic of commercial carbon?

19. What are softeners used for?

IV. Products of petrochemical and basic organic synthesis.

The industry of basic organic and petrochemical synthesis is a link between petroleum processing and chemical- recovery coke industries and all other branches of organic synthesis. It provides the latter with the required starting materials - organic products and, besides, supplies national economy with many valuable final products. Very many products of basic organic and petrochemical synthesis are intermediate, rather than end products. These include, in particular, many organic compounds of chlorine in which chlorine atoms can be substituted by other or groups of atoms.

Starting substances for polymer materials. Their manufacture plays an important part in basic organic synthesis and petrochemical synthesis. It provides starting materials for the manufacture of plastics, synthetic rubber, synthetic lacquers, glues, film materials, fibres, etc. Polymer materials are now made in hundreds of kinds having various properties and diverse applications. The most important among them are polyethylene, polystyrene, polyvinyl chloride, polypropylene, and synthetic rubbers. Many of them are used as starting materials for manufacture of commercial goods. For instance, various rubber articles, including tyres, are made from synthetic rubbers; many articles made from polyethylene and polypropylene can successfully replace non - ferrous metals, etc.

Plastifiers and other auxiliary substances for polymer materials. Along with the basic materials for manufacture of synthetic polymers, plastifiers and various auxiliary materials are also of large importance: they either facilitate the process of synthesis or improve the properties of final products. For instance, plastifiers [softeners] are added [in an amount of up to 30-40 per cent] to certain polymers [especially to synthetic rubbers and polyvinyl chloride] to improve the plastic and elastic characteristics of these materials.

Among various types of plastifiers, one of the most important groups includes high - boiling esters [dibutyl phthalate, dioctyl phthalate, tricresyl phthalate] and some esters of higher alcohols and dicarboxylic acids and of higher carboxylic acids and diatomic alcohols. Softeners obtained at petroleum processing plants are used in the manufacture of synthetic rubbers. Other auxiliary substances used in polymer technology [and in other processes] include initiators, catalysts, inhibitors, regulators, etc.

Synthetic surfactants and detergents. Surfactants and detergents are used very widely in domestic life as powders and liquids for washing and cleaning. These substances are distinguished by a combination of hydrophobic and hydrophilic groups in the molecule. During washing, this facilitates wetting of the fabric and passage of dirt to the washing water. All surfactants and detergents are divided into ionogetic and non- ionogenic, depending on the presence or absence of groups capable of dissociating in aqueous solutions. Ionogenic substances, in turn, may be either anion- or cation- active, with their surface- active properties being determined respectively by anions or cations.

Most of anion- active surfactants are sodium salts of sulfonic acids and acid esters of sulphuric acid, in particular, [1] alkylarylsulfonates with a C10- C15 alkyl group; [2] alkylsulfonates with 12-18 carbon atoms; and alkylsulphates with an alkyl group roughly of the same length:

p-RC6H4SO2ONa R SO2ONa ROSO2ONa

In recent time, non- ionogenic substances have found a wide use. They are synthesized from ethylene oxide and various organic compounds- carboxylic acids, alcohols, amines, etc. having active hydrogen atoms. Their hydrophilic properties are due to a [CH2CH 2O]n chain obtained by successive attachment of molecules of ethylene oxide: RO-[CH2CH 2O]n-H. In order to improve their washing ability and lower the consumption, detergent substances might be mixed with various additives and these compositions are called washing means [in contrast to washing substances, or detergents, proper]. Such compositions [for instance, washing powders] contain sodium phosphate, pyrophosphate and hexamethaphosphate, sodium silicate, sulphate, carbonate, etc.

Synthetic fuels, lubricants and additives. This group includes synthetic motor and let fuels, lubricating oils, additives, antifreezing agents, braking and pressure fluids.

Solvent and extractive agents. Synthetic solvents and extractive agents may belong to various groups of organic compound: chlorine derivatives, ancohols, cellosolves, ethers, ketones, esters, etc.

Miscellaneous products. These include insecticides, medicaments and explosives.

Exercises

Answer the following question

1. What are the products of petrochemical and basic organic synthesis?

2. Most of products of petrochemical and basic organic synthesis are intermediate, aren't they?

3. Why does the manufacture of polymer materials play an important part in basic organic and petroleum synthesis?

4. What are the most important polymer materials?

5. What are polymer materials used for?

6. What are the effects of plastifiers and other auxiliary substances in manufacture of synthetic polymers?

7. For what are auxiliary substances used?

8. What is the structure of the molecules of surfactants and detergents?

9. What is the difference between ionogenic and non- ionogenic substances?

10. How are the hydrophilic properties of non- ionogenisc substances obtained?

11. What should we do to improve the washing ability and to lower the consumption?

Text 22

Distillation

The property that differentiates most petroleum products from each other is "volatility", or tendency to vaporize. More volatile products are called "lighter", less volatile products, "heavier". The volatility of a product is determined, of course, by the boiling points of its components. Inasmuch as distillation separates liquid by boiling points, distillation is the principal separation process.

Theory of Distillation

The basic principle of distillation is simple. When a solution is boiled, the lighter components vaporize preferentially and the solution is separated into a lighter overhead product and a heavier residue. For most petroleum applications, this simple operation does not suffice, and multistage units must be employed. Such units consist of cylindrical columns, or "towers", through which vapour and liquid streams pass countercurrently. Depending upon circumstances, feed may be charged at any point in the column. Products are withdrawn from the top and bottom and sometimes from intermediate points as well. Liquid withdrawn from the bottom is usually reboiled to supply vapours to the column; vapours from the top are condensed and a portion is returned as '"reflux". It seem paradoxical to build complex and expensive equipment to separate out an overhead product and then to return part of it to the separation zone. Indeed, many of technologists of the time considered refluxing foolish when it was first introduced. We may conclude from this that the function of reflux is somewhat obscure. Why it is used in multistage unit can best be illustrated by analogy with singlestage operations.

Staging. Consider a singlestage distillation system in which a solution is heated until half of it vaporizes, the vapour being separated from the liquid and condensed. Suppose that a two-component solution is processed in this system to concentrate the lighter component in the overhead fraction. Suppose further that the desired concentration is not attained. A more concentrated product could be obtained by charging the overhead to a second unit, and this procedure could be repeated until the desired concentration was obtained. Similarly, the heavier component could be concentrated in the bottoms cut by reprocessing successive residues. In either case, the yield of the desired product would be low. and large amounts of intermediate materials would be made. Yields could be improved by returning each intermediate material with the next charge to the preceding stage. By this means, all the original charge would be recovered ultimately in one or the other of the desired products. Such an operation is diagrammed in Fig. 1a; each stage in this diagram includes equipment to vaporize a portion of the charge and to condense the vapours. Although the indicated operation is possible, equipment would be complex and expensive, and labour and energy requirements would be high. The equipment could be simplified somewhat by converting each batch stage to continuous operation as shown in Fig. 1b, but the equipment would still be complex and the operation expensive. The next step is to eliminate vaporization and condensation equipment from the intermediate steps by permitting the vapour from each stage to pass directly into the stage above, where it mixes with the liquid from the next higher stage; the contained heat in the vapour substitutes for indirect heating of the liquid. Now all that remains is to house all the intermediate steps in a single column, and we have the modern distillation unit shown in Fig. 1c.

Column Sections. The part of the column above the feed inlet is called the "rectifying section", and the part below it is called the "stripping section". The two sections have different purposes. One serves to increase the purity of a product; the other increases its recovery. In Fig. 1a, for example, stages 2, 4, and 6, which correspond to the rectifying section, increase the purity of the light product taken overhead. The liquid leaving stage 1 contains a considerable amount of the light component, and steps 3, 5, and 7, which correspond to the stripping section, strip the light component out and thereby improve its recovery in the overhead. For the heavy product, the functions of the two sections are reversed; the rectifying section improves recovery, the stripping section, purity. In some applications only one or the other of these two sections is required, depending upon the particular purity and recovery requirements of the operation.

Extractive and Azeotropic Distillation

Because distillation separates by virtue of differences in volatility, distillation can not normally be used to separate close- boiling materials. However, when the materials to be separated are chemically dissimilar, modified distillation procedures can be used. Examples are the separation of butenes from butanes and of toluene from isooctane. In such cases; an extraneous liquid can be added which has an affinity for one of the components in the charge; as a result the relative volatilities of the original components change, and separation becomes possible. If the added material is less volatile than the original components, it is added at the top of the column and withdrawn from the bottom, and the operation is called extractive distillation. If the added material is more volatile than the original components, it is added at the top of the column or with the feed and is withdrawn in the overhead product; the operation is then called azeotropic distillation.

Solvents and Entrainers. In extractive distillation, the extraneous liquid is called a solvent; in azeotropic distillation, it is called entrainer. In either case, its effectiveness is determined by its concentration in the liquid phase. Consequently, the boiling point of an entrainer is limited; it must be about as volatile as the lighter feed components so that it will pass overhead, but it must not be so volatile that it will disappear from the downflowing liquid stream much above the bottom of the tower. An entrainer must be separable, of course, from the overhead product- by distillation or by some other technique. Similarly, a solvent in extractive distillation must be separable from the bottoms product. How the entrainer or the solvent is separated from the overhead or bottoms product is an important consideration, because large volumes must be used. To be effective in changing the relative volatilities of the original components, an entrainer or a solvent must constitute at least 40% of the liquid phase [60], and its concentration is usually much higher.

Effects of Reflux. In extractive distillation, reflux has two opposing effects. By increasing the counterflow of liquid and vapor, increasing the reflux promotes the separation. However, increasing the reflux lowers the concentration of the solvent in the liquid streams; this lessens its effect in spreading the volatilities of the original feed components and thus retards their separation. Because of these conflicting effects, there is apt to be sharp optimum in the reflux rate for an extractive distillation operation.

Feed Preparation. Only narrow-boiling materials are charged to extractive or azeotropic distillation. The reason may be seen most readily from an example. Consider extractive distillation for the separation of toluene from a mixture with isooctane, which normally boil very closely to toluene. Lower- boiling materials [like hexane and benzene] and higher - boiling materials [like isononanes] are first separated by ordinary distillation. The sharpness of removing the light ends affects only the amount of material charged to extractive distillation. On the other hand, the purity of the toluene product will depend upon the sharpness of prefactionating the heavy ends out of the feed.

How poor removal of heavy ends affects product purity may be seen by considering the normal volatilities of the feed components and how they are affected by the presence of a solvent. Toluene and isooctane boil together, and isononanes are about half as volatile. In the concentration usually employed, a solvent approximately doubles the volatilities of the paraffins relative to toluene. In the presence of the solvent, then, the isononanes have about the same volatility as toluene, and their separation is very difficult, and sometimes impossible.

Even when heavy materials can be taken overhead in extractive distillation, they may be very undesirable in the feed. When phenol is used as the solvent, for example, volatility relationships are such that heavy paraffins in the overhead tend to carry some phenol with them. Phenol is expensive, and only small losses can be tolerated.

Exercises

Answer the following question

1. What is the principle of distillation?

2. What are the distilling towers?

3. Where can they withdraw product of distillation?

4. What is reflux?

5. What do they do to increase the pure of products?

6. What are the rectifying section and stripping section?

7. What are the purposes of them?

8. When must they add the extraneous liquid in distillation?

9. What is the extractive distillation?

10. What is the azeotropic distillation?

11. What are a solvent and an entrainer?

12. What is the boiling point of entrainer like?

13. What are the important characteristics of solvent and entrainer?

14. Which materials are used in extractive or azeotropic distillation?