OILS IN THE ENVIRONMENT Aleksander Kołodziejczyk Department of Organic Chemistry, Faculty of Chemistry Gdansk University of Technology, Narutowicza 11, 80-952 Gdańsk, Poland

Introduction Although oils are very popular products used commonly both in our everyday life and in industry, our knowledge of their nature and structure is rather poor. In fact, everybody knows that an oil is any greasy liquid, insoluble in water. On the other hand, oils, as lipophilic substances, are soluble in most organic solvents, e.g. in ethers, esters, halohydrocarbons and hydrocarbons. However, this encyclopaedic definition based on physical properties does not relate to the very complex chemical nature of oils. Many diverse chemical compounds may occur as ingredients in any oily substance, since oil is not one definite product, nor a homogenous one; there are plenty kinds of oils. Apart from the commonly known crude oil, diesel oil, lubricating oils, and vegetable oils, there are other oils like essential, fish, synthetic, etc. There are also substances that only look like oil, however, they are not oils due to their solubility in water; e.g. greasy liquid soap, glycerol, oil of vitriol, or polyethylene glycol. The most popular oils serving as fuel or a heating medium contain hydrocarbons as their main component and may sometimes include even several additives to improve their properties. Hydrocarbons are also bulk ingredients of several other oily products, including lubricants, turbine oils, metal-working and hydraulic fluids. Crude oil, the main source of the abovementioned hydrocarbons, is often called mineral oil, even though it includes only traces of inorganic compounds as its ingredients. The adjective “mineral” was introduced to stress that mineral oil is extracted from minerals. Crude oil is also known under the name of petroleum, because it was found as a rock (Greek: petra) leakage. In fact, mineral oil is an organic substance due to its composition (hydrocarbons) and origin (a product of the decay of plants and animals). Edible oils, mainly vegetable and fish oils, belong to natural esters formed by acylation of glycerol with fatty acids. More precisely, they are triacylglycerols (TAGs), which means that three hydrogen atoms of the glycerol hydroxyl groups are substituted by acid residues. Essential oils, also known as fragrance oils, are other well-known group of natural oils. There is a great diversity of essential oils, which ingredients belong mainly to terpenes, although many other organic compounds occur in them. Trees, bushes, and herbs emit a hundred million tons of essential oils each year. They are raw materials in food, cosmetics and pharmaceutics industry. We can buy some of them in small phials as medicaments, fragrances, or spices. Another oil, badly smelling fusel oil, one of the side products of alcohol fermentation of sugars, is a mixture of primary alcohols (excluding ethanol), mostly isopentanol, with a smaller amount of n-propanol, isobutanol, and amyl alcohol (2methylbutan-1-ol). Apart from natural oils, there are synthetic oily substances (synthetic oils), including also hydrocarbons and other groups of organic compounds, like diesters, polyol esters, polyglycols, phosphate esters, polypropylene glycol, polyphenyl ethers, polychlorinated biphenyls (PCBs), fluorocompounds and silicones. Contemporary industry, motorization, shipping, aviation, and even household life cannot function without oils. The majority of oils is used as engine fuels (diesel, mazout), a smaller quantity, however, also a large volume (more than 40 million tons annually), is utilised as lubricants. Significant amounts of oils serve for consumption and heating, smaller quantities are used for illumination, cooling, therapy, fabric impregnation and for many other purposes. 1

Used oils pose serious ecological problems. Almost half of the volume of lubricating oils remains after exploitation and needs to be collected and processed in order to prevent contamination of soil, water and air. Also a large volume of fried oils needs to be neutralised. The susceptibility of oils to biodegradation depends on their chemical constitution. Petroleum products, most synthetic oils, including polychlorinated biphenyls, silicone oils, and hydrocarbons, are extremely durable in the environment. Triacylglycerols and other esters undergo biodegradation easily, if they are not highly concentrated. Hydrocarbons as the major component of oils The majority of commercial oils consist mainly of hydrocarbons. They predominate in the following oily products: - fuels (diesel, mazout); - heating (furnace) oil; - engine (motor) oils and other lubricants; - gear, turbine and hydraulic liquids, drawing oils, etc. All of them are complex mixtures of straight chain alkanes (n-alkanes), branched chain alkanes (isoalkanes), cycloalkanes (naphthenes) and arenes (aromatics) (Fig. 1). The hydrocarbon bulk component (95-100 %) of lubricating oils is called base oil or base stock. It determines the basic physical and chemical properties of the final products. Usually the lubricating oil base stock contains large amounts of long-chain isoalkanes (C20-C34), alkylcykloalkanes, and alkylarenes. Type of hydrocarbons in oils CH3(CH2)16CH3

C18H38

octadecane - an example of a group of straight-chain alkanes (n-alkanes), formerly called paraffins

branched alkane (isoalkane)

short-chain alkylcykloalkane

alkylated aromatics

long-chain alkylcykloalkanes Fig. 1. Type of hydrocarbons occuring in oils

The structure of hydrocarbon components has a significant influence on such properties of petroleum products as the octane number, the cetane number, viscosity, oxidation resistance, thermal stability and the value of the pour point. n-Alkanes are often undesirable ingredients of many petroleum products. They decrease the gasoline octane number. However, they are desirable as the main component in diesel fuel, because they have a high cetane number. On the other hand, long-chain n-alkanes decrease the cloud point of diesel fuel, as they are prone to crystallise in low temperatures, forming needle-shaped crystals (wax). Even a small amount of such crystals may immobilise a diesel engine by choking the fuel pipes and injectors.

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Additionally, n-alkanes lower viscosity because the translocation of their molecules is hindered by a strong Van der Waals interaction between their long molecules. Whereas branched alkanes and cycloalkanes, even alkylated, improve the lubricity of oils due to the spherical shape of their molecules - they can slide like balls in the sliding bearing (Fig. 2.).

n-alkanes have a tendency to aggregate and crystallise; their lubricity is low because translocation of their molecules is hindered

branched alkanes and cycloalkanes display high lubricity due to the spherical shape of their molecules

Fig. 2. Physical properties of compounds are determined by the shape of their molecules

Aromatics are not good ingredients of lubricants as they are chemically reactive. Their easy oxidation usually starts a chain of complex reactions that involve also other components of the lubricating oils, causing a dramatic decrease of lubricity and shortening the oil lifetime. Additionally, the viscosity of aromatics responds relatively poorly to changes in temperature (low viscosity index). They are undesirable in furnace fuel, naphtha, and other heating media. However, they are excellent ingredients of gasoline as they increase the octane number. Special additives are used to improve the physical and chemical properties of lubricants. The following agents are among them: dispersants, detergents, antioxidants, demulsifiers, antifoam, pour point depressants, metal passivators, corrosion inhibitors, anti-wear additives, sulphur scavengers, and viscosity index improvers. According to their chemistry, they belong to a large variety of compounds, like alkyl sulphides (thioethers), amides, amines, acids, alcohols, benzotriazoles, ethers, esters, formaldehyde resins, imidazolines, phenols, phenolates, phosphates, phosphites, polymethylacrylates, different kinds of polymers, polymethoxysiloxanyl salicynates, soaps, succinimides, succinates, sulphonates, sulphur compounds and zink-dithiophosphates. The additives are usually hydrophobic organic compounds as they should be soluble in hydrocarbons. All distilled-fractions of petroleum are a complex mixture of hydrocarbons. The light fractions usually contain 100÷200 hydrocarbon individuals, though almost 1000 such compounds have been identified in gasoline of various origin. The higher fractions of crude oil contain a much higher number of ingredients, e.g. an oleic fraction can contain thousands of hydrocarbon individuals and minor amounts of nitrogen, sulphur, and oxygen derivatives. The exact composition of higher petroleum fractions is usually not specifically defined, rather compound classes are given in their specifications. Often value of total petroleum hydrocarbons (TPH) is determined; also the content of n-alkanes, isoalkanes, cycloalkanes and aromatics is listed. Moreover, typical lengths of hydrocarbon chains are specified for given fractions: C4÷C12 (gasoline), C7÷C12 (stoddard solvent, naphtha), C4÷C16 (aviation fuel), C8÷C20 (diesel fuel), C20÷C25-40+ (mineral-base oils). Hydrocarbon-base oils Diesel oil (diesel fuel) Diesel oil serves as a fuel for diesel engines (internal-combustion, or compression-ignition engines, in which the fuel is ignited in the cylinder by the high temperature of compressed air). The major part of diesel oil components is the middle distilled-fraction of petroleum (about 90% boils at 290÷360oC), often blended with products obtained from cracking of the 3

heavier fractions of crude oil. There are mainly (60 ÷ 90%) alkanes (normal, branched and cyclic) in diesel oil. The molecular structure of the compounds has a significant influence on the quality of fuel. n-Alkanes increase its ignition value (cetane number), while isoalkanes, cycloalkanes and aromatics have poor ignition quality (low cetane number). The content of aromatics in diesel oils ranges from 10 ÷ 40%, whereas share of aromatics in furnace oils, which are manufactured on the same petroleum fraction as diesel oil, should be much lower because burning such hydrocarbons pollutes the environment. Combustion of aromatics in typical furnaces is not completed due to the insufficiency of oxygen supply, resulting in high contents of soot in the fumes. There are two grades of diesel oil, No. 1 and No. 2. The number of carbons in the hydrocarbon chains in No. 1 diesel fuel (DF1) ranges from C8 ÷ C18, with the majority in the C10 ÷ C14 range (its composition is similar to kerosene or Jet A fuel). It is designed for highspeed engines, and is required for use in extremely low temperatures. DF1 does not look like oil; it rather resembles naphtha or some solvent. Carbon chains in No. 2 diesel fuel (DF2) range from C8 ÷ C26, with the majority in the C10 ÷ C20 range. DF2 is greasy and looks like oil. Furnace oil serves as a heating medium in all types of oil furnaces. Its hydrocarbon composition is similar to diesel oil. Usually furnace oil has a smaller amount of cracking process products, less aromatics, and much less additives, if any. Use of furnace oil to run diesel engines may cause serious damage. Lubricating oils The main component of lubricating oils is usually a very heavy boiling fraction of crude oil (b.p. > 380oC), synthetic hydrocarbons, or other synthetic compounds. This part of lubricating oils, called “base oil” or “base stock”, composes 95 ÷ 100% of commercial products; the rest are special additives needed to improve physical and chemical properties of the final products. The additives help to prolong the lifetime of the oil. Engine oil without additives had to be replaced every 1300 ÷ 1800 km, whereas the modern engine oils tolerate driving without oil replacement for more than 20 000 km. The base oils determine the main physical properties of the final product. There are several categories of base oils. The first three of them are called mineral-base oils as they originated from petroleum and differ only in the depth of the conversion of the neat oil fractions. Group I base oils, the cheapest ones, are obtained by the solvent refining of petroleum oil fraction that removes the major part of n-alkanes and other impurities. They may also be subjected to other treatment, e.g. solvent dewaxing to keep the oil from freezing at low temperature. They contain more than 10% of aromatics and more than 0,03% of sulphur. To manufacture Group II base oils, additional purification is needed in order to decrease the content of aromatics below 10% and sulphur contamination to no more than 0,03%. Aromatics are removed by solvent extraction and wax is not removed but converted into isoalkanes in a hydroisomerisation process. Additionally, Group II base oils often contain oil after catalytic isomerisation. Viscosity index of these two groups of base oils is almost the same, however, Group II secures the longer lifetime of the final products and, being better purified, is almost colourless. In many applications, modern Group II base oils are used to produce turbine and lubricating oils that assure a level of performance similar to the one achieved by more expensive synthetic oils made from polyalphaolefins (PAO) which belong to Group IV base oils. In the production of Group III base oils several technological processes are involved, including hydrocracking, hydroizomerisation and hydrotreating, which are usually combined

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to convert and reshape molecules of hydrocarbons of poor lubricity (n-alkanes) into higher quality base oil ingredients (isoalkanes and alkylated cycloalkanes). These technologies greatly improve the chemical stability and temperature performance of the hydrocarbon components. Group III base oils are often called unconventional, as opposed to conventional Group I and II base oils. The superiority of the unconventional base oils is visible in the value of their viscosity index – 120+ compared to 80+ for the conventional ones. The quality of modern Group III base oils was recently improved so much that they have supplanted traditional synthetic oils (PAO) in many applications. Group IV base oils (PAO) are currently called traditional synthetic base oils, as they are composed of hydrocarbons just as mineral oils, but they are manufactured in a synthetic way by oligomerisation of alkene monomers. Chemically they are branched alk-1-enes, formerly known as polyalphaolefins (PAO), also named olefin oligomers, olefin polymers (incorrectly), or simply synthetic hydrocarbons. The adjective “synthetic” was introduced to distinguish them from mineral oils of petroleum origin and to emphasise their superiority over others when they were commercialised in the second part of 20th century. Later, other hydrocarbon and non-hydrocarbon synthetic oils appeared in the market. The possibility of the synthesis of designed hydrocarbons by oligomerisation of alkenes allows to tailor the hydrocarbon molecules to specific requirements. It is worth noticing that PAO base oils are not such a complex mixture as mineral-base oils, as they are composed primarily of expected oligomers (trimers, tetramers, etc. of the chosen monomers), (Fig. 3). C4H9 I

C4H9 I

CH2=CH + CH2=CH

catalyst

C4H9 I

C4H9 I

→ CH3−CH−CH=CH

hex-1-ene, C6

dimer, C12

catalyst

C4H9

I

C4H9 I

C4H9 I

→ CH3−CH−CH2−CH−CH=CH

C4H9 I CH2=CH

trimer, C18

Fig. 3. Oligomerisation of hex-1-ene

Traditional synthetic base oils are made by the catalytic oligomerisation of straight α-alkenes having six or more carbon atoms. PAOs serve as engine, gear, transmission lubricants, and ingredients of greases and hydraulic fluids. They are better than others for applications in extreme temperatures. However, mineral-base oils are more popular than synthetic ones as they are cheaper. PAOs are used to fulfil the high requirements of the modern equipment and to prolong the time they may serve. Non-hydrocarbon synthetic oils Group V base oils are synthetic oils not included in Group IV. The following chemical compounds are among them: - polyglycol fluids; - diesters of dibasic acids; - polyesters – esters of polyhydroxyalkohols; - phosphate esters; - alkylated aromatics, e.g. dialkylbenzenes; - silicones. There are more types of synthetic lubricants. The large number of chemically different lubricants is a consequence of the fact that there is no one definite lubricant superior to others in all respects and there is no known versatile one that could be applied for any specific use.

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Polyglycols Polyglycols are represented by several polymers, including polyethylene glycol – H(OCH2CH2)nOH and polyethylene glycol dimethyl ether. They have good lubricity, a high viscosity index, and are stable in high temperatures. They have been applied as automotive hydraulic fluids, industrial gear oils, metal working fluids, and gas compressor oils. Most polyglycols are soluble in water and their solutions in water serve as fire resistant fluids. Diesters of dibasic acids Diesters of long-chain alcohols and dibasic acids provide excellent lubricity in low temperature, low volatility, high flash point, and good thermal stability; however, they are prone to hydrolysis so they have to work in anhydrous conditions. The products of their hydrolysis promote corrosion. Diesters of dibasic acids are fluids recommended for aircraft engines and compressors, as well as for preparation of greases for use in low temperatures. They undergo chemical and biological degradation easily. C2H5

C2H5

I

C2H5

I

I

2 CH3(CH2)3CHCH2OH + HOOC(CH2) 7COOH → CH3(CH2)3CHCH2OOC(CH2) 7COOCH2CH(CH2)3CH3 2-ethylhexan-1-ol

azelaic acid

bis-2-ethylhexyl azelate

Fig. 4. Synthesis of diester of dibasic acid

Bis-2-ethylhexyl azelate (Fig. 4.) is one of the most popular diesters used as base-oil for lubricant preparation. The lack of a hydrogen atom in the β-position to hydroxyl group makes its molecule very resistant to decomposition. Polyol esters Polyol esters are prepared by acylation of polyols (diols, triols or tetraols), (Fig. 5.). They have similar properties to diesters of dibasic acids, including the same disadvantages, e.g. susceptibility to hydrolysis, however, they show higher thermal stability and a much lower coefficient of friction than lubricants based on mineral oils or PAOs. An addition of 5 ÷ 10% of polyol esters to mineral oil or to PAOs significantly lowers the coefficient of friction of the resulting lubricant. Currently, modern jet aircrafts almost obligatorily use lubricating oils based on polyol esters. They are also used for gas turbines working in high temperature and for preparing hydraulic and heat exchange fluids. There is a large variety of polyol esters, including esters of neopentylpolyol (NPG), pentaerythritol (PE), 1,1,1-tris(hydroxymethyl)propane (trimethylolpropane – TMP), di(trimethylolpropane) (diTMP), dipentaerythritol (diPE), and others. Among acids used for acylation of polyols there are saturated-, monounsaturated-, short-, long-, straight-, or branched acids, e.g. adipic, heptanoic, oleic, and stearic acid. CH2−OH I

H+

CH2−OOCR I

4 RCOOH + HO−CH2−C−CH2−OH → RCOO−CH2−C−CH2−OOCR I

HO−CH2 pentaerythritol

I

RCOO−CH2 tetraacylpentaerythritol

Fig. 5. Synthesis of polyol esters

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Alkylated aromatics Synthetic aromatic hydrocarbons, as some other base oils, have found applications in the production of engine, gear, hydraulic, air compressor, and gas turbine oils. They have very good low temperature fluidity, and lubricants based on them are appropriate for work in subzero temperatures. They are also extremely oxidation and hydrolysis resistant, and stable at high temperatures, but they are very resistant to biodegradation. Alkylated aromatics were introduced into practice as lubricants in the 1930s but they did not gain importance until the 1970s, when Americans started to develop the petroleum industry in Alaska and the use of heavy equipment in low temperatures was necessary. Alkylated aromatics are produced by alkylation of benzene. Isomers of dialkylbenzenes (Fig. 6.) are the major components of the aromatic base stock.

orto-dialkylbenzene

meta-dialkylbenzene

para-dialkylbenzene

Fig. 6. Isomers of dialkylbenzene

Phosphate esters Alkyl esters of phosphoric acid are very expensive due to their complex synthesis. However, they are lubricants of choice because they are fire resistant. They have been employed in aircraft and in underground mining hydraulic systems, and wherever fire resistance is critical. Silicones Silicones, though well known due to their wide application as a sealing material in the building construction, are not very popular as lubricants because they are unserviceable for steel surfaces. They are water sensitive and easily undergo transformation to an abrasive polymerised product. Silicones have a high viscosity index, high thermal stability, and good low temperature performance. They are used as a component of certain greases, torsion dampers and automotive brake fluids. Originally they were used in the space program. Renewable oils There are three main classes of oils that are derived from renewable biological materials: vegetable, fish, and essential oils. Both vegetable and fish oils are triacylglycerols (TAGs) which belong to the same chemical group of compounds as esters of polyols (a synthetic lubricant). Glycerol – trihydroxyalcohol (triol) of systematic name propan-1,2,3-triol – forms triacylglycerol derivatives, (Fig. 7.) as a result of its acylation with fatty acids. H2CO-COR I

HCO-COR’ I

H2CO-COR’’

R, R’, R’’: aliphatic chains; they may be saturated, monounsaturated or polyunsaturated. They are usually straight and contain odd numbers of carbon atoms (even numbers of C together with CO)

Fig. 7. Formula of triacylglycerols

As shown in the above formula, triacylglycerols are made up usually of different fatty acid residues, with a varying number of carbon atoms (chain length) and number of double bonds (mono- or polyunsaturated acids), with various proportion in a given fat (oil). The most popular fatty acid occurring in lipids is oleic acid (Fig. 8.), as it is a constituent of almost 50 % of all acid residues in fats and fatty oils, followed by linoleic, palmitic, linolenic,

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and stearic acid. Triacylglycerols are obtained mainly by extraction of plant and animal oily parts and are called fats when they are solids or oils when they are liquids. Unsaturated acids lower the melting point of TAGs. COOH

H3C oleic acid, [(9Z)-octadeca-9-enoic acid]

COOH

H3C palmitic acid, (hexadecanoic acid)

H 3C

COOH

COOH

H3C stearic acid, (octadecanoic acid)

linoleic acid, [(9Z,12Z)-octadeca-9,12-dienoic acid]

COOH

H3C linolenic acid, [(all-Z)-octadeca-9,12,15-trienoic acid]

unsaturated acids

saturated acids

Fig. 8. The most popular fatty acids

TAGs belong to very important biomolecules named lipids, which are defined as substances insoluble in water, that can be isolated from organic material by extraction with solvents of low polarity like ether or chloroform. Lipids include many other biocompounds, such as phospholipids, prostacyclins, prostaglandins, wax, and steroids. Part of them are liquid so they are oils as well. The annual world production of edible and soap oils and fats exceeded 140 mln tons in the year 2000; more than ¾ of them were oils. Oils are extracted mainly from oilseeds (soybeans, sunflower, cotton, rape and palm kernels) or fruit flesh (palm and olive). The soybean and palm oils have the largest annual output (25 and 21 mln tons respectively in the year 2000), followed by rapeseed oil (15 mln tons) and sunflower oil (10 mln tons). It is predicted that the production of soybean, sunflower seed, and groundnut oils will be decreased, while output of rape, cotton, palm and copra oils is expected to rise. Currently the highest increase of rapeseed oil production is observed due to its use as biodiesel. Fats, vegetable and fish oils are the main constituents of storage fat cells in animals and plants. They are synthesised in animal and plant cells, and make one of the three main classes of food, besides proteins and saccharides. They are not only a source of energy for organisms, but also important substrates for biosynthesis of many significant biomolecules, such as phospholipids, prostaglandins, prostacyclins, etc. Fats and oils are used as medicines, substrates for the production of soap, emulsion stabilisers, and impregnators. Triacylglycerols are sources of fatty acids and alcohols. A large group of polyunsaturated oils, so called drying oils, e.g. linseed and tung oils, are used for manufacture of paints and varnishes. Recently, the importance of vegetable oils has greatly increased, as they have become significant substitutes for petroleum products, mainly as renewable fuels and lubricants. Biofuels People have undertaken serious attempts to replace some petroleum products by renewable and safer materials. There were many reasons for such measures, among them the anxiety that the reserve of crude oil is limited and sooner or later the world shall be deprived of the most suitable source of energy. Moreover, the components of petroleum are toxic, poorly biodegradable, easily flammable, have a low flash-point and cause an increase in the greenhouse effect. Since the second part of the 20th century most governments, international organisations, and the public opinion have paid great attention to the protection of the environment. It has been acknowledged that petroleum products are extremely dangerous for the environment and people have realised the necessity of their total or at least partial elimination from everyday use. It turned out that they could be partially replaced by vegetable oils (triacyl-

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glycerols), which are renewable, not very ecotoxic, and easy to complete biodegradation. Only cheap TAGs can substitute petroleum products. Crude oil despite the great increase of its price is still one of the cheapest industrial raw materials. Additionally TAGs use as fuel should be liquid. The state of aggregation of TAGs (their fluidity) depends on their fatty acid composition: the higher the content of short chain and unsaturated acids, the higher the probability of fluidity of such triacylglycerols at room temperature. Moreover, not all oils are suitable for conversion into fuels. Oils with a lot of short chain acids are not good for transformation into fuels as their methyl or ethyl esters are too volatile. They are not useful for lubricants either, as their viscosity is too low. Solid fats are also unsuitable for conversion into liquid fuels, because they contain mainly long chain saturated acids, whose methyl esters are solid and have a high cloud point; e.g. m.p. + 39oC (methyl stearate), m.p. - 20oC (methyl oleate). Also oils containing a large amount of polyunsaturated acids are poor materials for petroleum substitutes, as they polymerise easily and form deposits. Three kinds of vegetable oils are cheap as they are produced in the largest scale: rape, palm, and soybean oils (15 ÷ 20+ mln tons annually each). Palm oil, although the cheapest one, is useless for biofuel and biolubricant production, as it contains too many short chain acids. Numerous different vegetable oils, animal fats and sewage fatty fractions, both neat and modified, have been tested as fuels for diesel engines. Nowadays, basically only rapeseed and soybean oils are practically utilised in the production of liquid fuels and lubricating oils. Such fluids are called biofuels and biolubricants as they are manufactured from renewable biomass, e.g. vegetable oils, and they are environmentally (biologically) friendly. Rapeseed oil, due to its acid composition (high content of oleic acid), is more suitable for fuel production than soybean oil. Direct application of neat oils as engine fuels is limited due to their chemical and physical properties, such as low viscosity, too low or too high volatility, high cloud point, and high temperature of ignition. Thus there is a need for chemical modification of vegetable oils before their use as fuels or lubricants. Usually, their transformation into methyl or ethyl esters in transesterification reactions with methanol or ethanol in the presence of a catalyst (Fig. 9) is enough to obtain good quality biodiesel. In the USA instead of the term “biodiesel” the name “alternative fuel” is used. It refers to any fuel, other than ethyl alcohol, that is derived from biological materials. The current annual world output of biodiesel is estimated at several mln tons. Its production is so simple that can be carried out at each farm growing rape or soybean. H2CO-COR

I catalyst HCO-COR’ + MeOH → RCOOMe + R’COOMe + R’’COOMe + CH2OHCHOHCH2OH I ← H2CO-COR’’

triacylglycerol (neat vegetable oil)

fatty acid methyl esters

glycerol

Fig. 9. Transesterification of neat vegetable oil into fatty acid methyl esters

Alkyl esters generated from vegetable oils have a higher cetane number than conventional diesel fuels. Composition of gaseous emission is similar for both kinds of fuels, there is even a lower concentration of hazardous pollutants (except NOx) in the case when fatty acid esters are used. Methyl esters obtained from rapeseed or soybean oils are used directly or are blended with conventional fuels. Addition of 2÷5% of such esters to mineral-based fuel can be used to run

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diesel engines without their modification. The definition of “alternative fuel” or “biodiesel” is not extended to mineral-based diesel fuels containing only a few percent of fatty acid methyl esters. Neat vegetable oils have been also tested as diesel fuel. They are cheaper than esters derived from them and have given satisfactory engine performance and power output in short-term trials. However, they cause serious engine problems in long-term use due to the coking of injector nozzles, sticking piston rings, dilution of crankcase oil, contamination of lubricating oil, and deposit precipitation. There are reports of successful use of a 70:30 rapeseed/DF1 mixture, or blends of ≤15 % rapeseed oil with DF2, or 80:20 DF2/sunflower oil. Also microemulsion fuel containing soybean oil, methanol, 2-octanol, and cetane enhancer was reported as the cheapest vegetable oil-based fuel which met the standards of diesel fuel. Biolubricants Already ancient machines (thousands of years ago) were lubricated by animal fats or vegetable oils (renewable lubricants). It was the industrial revolution which led to much higher requirements for quality of lubricants. The discovery of mineral oil (the first commercial oil wells were drilled in 1859) gave cheap and chemically stable lubricants. Modern devices equipped with fast moving or rotating parts (cars, aircraft, turbines, and others) need much better lubricants than neat vegetable oils or animal fats. These would be excellent lubricants, as they have a high viscosity index, good wear characteristics, high flash point and are easily biodegradable, if they did not exhibit poor thermal, oxidative and hydrolytic stability. To overcome these disadvantages some measures have been taken, including genetic modification of the oily plants (to reduce the content of polyunsaturated and short chain acids in produced oils), chemical modification (in order to replace glycerol by alcohols devoid of β-hydrogen atoms), and addition of special agents to improve their chemical and physical properties. On the market there are already several kinds of biodegradable vegetable oil-based lubricants obtained from soybean or rapeseed oils. Still, the use of vegetable oils as lubricants is limited not only due to the shortcomings mentioned above, but also because of their higher prices in comparison with mineral oil-based fluids. However, according to predictions, the price of mineral oil can exceed the price of vegetable oils within 10 years. In such a case there would be no obstacles to produce even 90% of all lubricants from biodegradable vegetable oils. The market share of biodegradable lubricants is currently rather insignificant. In the year 2000 only about 2% of biolubricants were used in EU and almost the same rate was all over the world, varied strongly depending on individual countries: 9 % in Scandinavia, 4 % in Germany, 0.2 % in UK and 0.1 % in France. In the year 2000, there was an expectation that they would double their market share by 2006; however, now it does not look possible. Coolants Vegetable oils turn out to be excellent components for the manufacture of coolants in machining applications. The lubricating film layer provided by vegetable oils is intrinsically strong and guarantees good lubricating ability. However, the higher price of vegetable oils compared to mineral oil-based coolants limits their wide practical application at the present time. Fish oils Fish oils and oils from other animals living in water are characterised by a considerable contribution of polyunsaturated acids, so they are very unstable and smell badly. The poly-

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unsaturated acids occurring in fish oils belong to essential fatty acids (EFA) and are an excellent supplementary source of these acids in case of their deficiency in a mammalian organism; they are used as medicaments and to enrich animal food. Triacylglycerols from fatty fishes contain unique ω-3-poly-unsaturated fatty acids (eicosapentaenoic acid – EPA and docosahexaenoic acid – DHA), which are able to lower the number of heart and arthritis diseases very effectively. Moreover, they are helpful in the treatment of such disorders as diabetes, ulcerative colitis, Raynaud’s disease, and peripheral vascular diseases. They prevent cancer, reduce pain and improve the frame of mind. According to recent research results fish oil supplementation helps to maintain the elasticity of artery walls, prevent blood clotting, reduce blood pressure and stabilise the heart rhythm. It has been estimated that over 85% people living in western countries are deficient in ω-3-polyunsaturated acids. It is worth knowing that there is a difference between cod liver oil and fish oils. Cod liver oil is extracted from cod liver and is rich in vitamin A and D, and contains only a small amount of ω-3-essential acids. Fish oils are extracted from flesh of fatty fishes, mainly from salmon and herring, and are rich in EPA and DHA. Essential oils Essential oils (EOs) are natural compounds produced by plants and accumulated in their special structures such as oil cells, glandular hair, cavities of heartwood, and oil or resin duct glands. They can be also emit to the air. EOs consist of volatile components with boiling points between 150÷300oC. They may occur in different parts of plants, e.g. in flowers, fruits, leaves, stems, wood, bark, or roots and are obtained by pressing of plant parts, water-steam distillation, solvent or fat extraction, and the newest way – by supercritical fluid extraction which is considered the most effective. There is a great variety of EOs, because the majority of plants produce aromatic volatile substances, and even different parts of the same plant can produce different oils, e.g. in the leaves of the cinnamon tree eugenol is the main component, while the oil of the bark of the cinnamon tree is dominated by cinnamaldehyde. In many EOs the number of identified components often exceeds one hundred individuals (in a particular oil). Usually one compound is dominating, however, the organoleptic properties may be determined by a minor or a trace component. The composition of a particular oil and the concentration of its ingredients, after isolation from biological material, often undergo changes in time, but usually our taste and sense of smell can recognise its originality easily. Chemically (Fig. 10.), the components of EOs are hydrocarbons, alcohols, esters, ethers, ketones, or even peroxides, whose parent compounds are mainly mono- or sesquiterpenes (dimers or trimers of isoprene). A lot of compounds occurring in EOs are chiral and frequently one isomer dominates in a specific oil, e.g. (+)-α-pinene occurs as the main components in turpentine oil from Germany, Poland, Russia, and the USA, while (-)-α-pinene dominates in turpentine from French pines. The best known EOs include: almond, anise, arachis, basil, camphor, caraway-seed, carnation, cedar, cinnamon, citrus, cotton-seed, cypress, dill, eucalyptus, fir, garlic, geranium, ginger, grapefruit, jasmine, juniper, lavender, lemongrass, lime, melissa, mint, mustard, neroli, orange, oregano, peanut, peppermint, pine, rose, sandalwood, spruce, tea tree, thyme, turpentine, vanilla, and others. Most of the substances smell pleasantly, but there are also stinking ones like garlic and mustard oils. The plants grown for commercial extraction of EOs contain usually 0,5÷5% of an essential oil. About half of essential oil production (regarding their financial value) is used in the food industry as aromatic additives to improve the flavour and taste of the food, to preserve it and to facilitate digestion. The oils can be also added to food in the form of spices. A large part of

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EOs is used in the perfume industry, either as direct cosmetic components or as starting material for synthesis of other ingredients. Some EOs are known as medicaments, e.g. camphor, eucalyptus, garlic, geranium, melissa, peppermint, or thyme oils. In the last several years, EOs have become popular due to their use in aromatherapy. Herbs, nice smelling flowers, roots and concentrated extracts from them were used for healing and improving the mental state of people in ancient times. Currently aromatherapy is a very popular branch of unconventional medicine. The smell of plants gives people a substitute of a natural environment they lived a long time ago. EOs are effective in small quantities. They penetrate an organism through the air passages, alimentary canal, mucous membranes and skin. There are several ways of treatment: inhalation, vaporisation, eating, skin care, bath, and massage. CH3

CH3

H3C H3C (+)-α-pinene

H3C

CH3

CH2CH=CH2 CH3 CH3

H3C H3C (-)-α-pinene

H3 C

OMe O

(+)-camphor

OH eugenol

CH3

HO

(+)-(Z)-α-santalol

Fig 10. Some of examples of compounds occurring in essential oils

The world emission of biogenic volatile organic compounds (VOCs) is estimated for hundreds Mtons, and is about ten times greater then anthropogenic VOC emission. The biogenic VOCs contain about 50÷60% of isoprene, 10÷20% of monoterpenes (EOs), and some other compounds including higher terpenes. VOCs are emitted by deciduous and coniferous trees, herbs, and other plants. Coniferous forests produce at least 5 tons of volatile organic matter per km2 per year. The concentration of terpenes in a coniferous forest may range from 5÷1470 µg/m3 depending on the temperature. The average composition of coniferous forest vapour is the following: α-pinene (25÷50%), β-pinene (2÷20%), carenes (15÷30%), and limonene (2÷10%). The name of the Smoky Mountains in the USA was given because on warm, sunny days smoke covers the mountains like a cloud. It is a photochemical smog - an aerosol composed of VOCs and products of their decomposition. Oils and environment Oils belong to the most common pollutants. Some of them, which are produced in large quantities, are a serious threat for soil, water, air, animals, plants, and microorganisms. The threat is caused by leakage occurring during oil field exploitation, crude oil and fuel transportation (ships, cisterns, tank cars, or pipes), usage of fuel and lubricating oils, and food processing (dairy industry, slaughter houses, meat and fish industry, and fat factories, including vegetable oil refineries). Spills of millions tons of crude oil and oily products pollute oceans and other water reservoirs each year. Accidental oil spills during transportation are responsible for about 30 % of marine oil pollution. They do not happen very often but usually have a huge range and have a catastrophic effect on the marine and coastal wildlife. Oily waste waters, one of the major pollutants, are generated mainly by the following branches of industry: oil refinery, petrochemical, food, metal-finishing, metallurgical, and transportation. Accidental sources of oily waters are spills from offshore drilling, tanker collisions, and ruptures of pipelines. Several different techniques are used to remove oil from water, including adsorption, biological purification, centrifugation, coagulation, extraction, filtration, flotation, gravity separation, incineration, land treatment, ozonization, the photochemical method, and reverse osmosis. Beside these numerous method of waste water purification, the cheapest way is still discharging them anywhere though it is forbidden. Thousands of tons of oily waste are dumped into rivers, lakes, seas and soil each year. 12

Wars, road accidents, natural disasters and the dumping of used oils into the ground cause a contamination of huge volume of water and soil. About ten million tons of crude oil were spilled into the desert soil in Kuwait during the Gulf War. Hundreds of oil lakes were formed and 23 million cubic meters of soil were contaminated at that time. Oily soil can contain 10 ÷ 20 % of oil. Oil destroys the structure of soil by reducing its water and oxygen content and decreasing its penetrability. Such soil is useless for any cultivation. Remediation of soil contaminated with mineral oil is very difficult and takes a lot of time. There are two main ways of oily soil remediation: a/ treatment of excavated ground (ex situ) at special treatment sites and b/ bioremediation (in situ). The method a/ is expensive but secure high performance while way b/ also gives good results but takes years and its effectiveness is limited to 0,3 ÷ 0,7 m. Natural biodegradation of hydrocarbons may be speeded up by the inoculation of soil or waste water by highly active strains of microorganisms. Used (spent) lubricants are extremely hazardous for the environment. The annual world lubricant production exceeded 40 mln tons. Only about 50 % of that amount is collected as used oil. The rest is lost by leakage in the lubricating system, undergoes decomposition, and flows out from the lubricating parts (e.g. from band saws). Used oils are mixtures of oily base (hydrocarbons or synthetic compounds), fuel, broken additives, polychlorinated biphenyls (PCBs), soot, ash, dust, metal particles, and water. As millions of tons of used oils are collected, they should be regenerated. In fact, only a small volume (about 5 %) of used lubricants is re-refined. More than 2/3 of used oils is combusted and the rest (30 % in USA and 5 % in Germany) is disposed or dumped into the ground, rivers, trash or anywhere. Everyone should know that one litre of oil can contaminate one million litres of ground water. Moreover, combustion is not a good way of neutralisation of used oils, as it causes the pollution of air with heavy metals and dioxins. Additionally, hazardous compounds present in used oils, like PCBs and polynuclear aromatic hydrocarbons (PAHs), pose the threat for people’s health. PCBs are not natural compounds and the environment has been contaminated with them by human irresponsibility. They were the main component of high quality transformer, capacitor, and hydraulic liquids. Improper utilisation of used liquids of this kind (blending them with used engine oils and dumping into the ground) causes pollution of the environment. Now, the production and utilisation of PCBs is forbidden in most countries, however, they are extremely resistant to degradation and are still found in waste oils, animal fat, milk, water reservoirs, sediments, and soil. PCBs are cancerogenic, teratogenic, and cause serious liver, spleen, and kidney harms.

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