Introduction Biodiesel is a liquid biofuel obtained by chemical processes from vegetable oils or animal fats and an alcohol that can be used in diesel engines, alone or blended with diesel oil. ASTM International (originally known as the American Society for Testing and Materials) defines biodiesel as a mixture of long-chain monoalkylic esters from fatty acids obtained from renewable resources, to be used in diesel engines. Blends with diesel fuel are indicated as ‘‘Bx’’, where ‘‘x’’ is the percentage of biodiesel in the blend. For instance, ‘‘B5’’ indicates a blend with 5% biodiesel and 95% diesel fuel; in consequence, B100 indicates pure biodiesel.
2.1.1 Advantages of the Use of Biodiesel
Some of the advantages of using biodiesel as a replacement for diesel fuel are [1–4]: • Renewable fuel, obtained from vegetable oils or animal fats. • Low toxicity, in comparison with diesel fuel. • Degrades more rapidly than diesel fuel, minimizing the environmental consequences of biofuel spills. • Lower emissions of contaminants: carbon monoxide, particulate matter, polycyclic aromatic hydrocarbons, aldehydes. • Lower health risk, due to reduced emissions of carcinogenic substances. • No sulfur dioxide (SO2) emissions. • Higher flash point (100C minimum). S. D. Romano and P. A. Sorichetti, Dielectric Spectroscopy in Biodiesel Production and Characterization, Green Energy and Technology, DOI: 10.1007/978-1-84996-519-4_2, Springer-Verlag London Limited 2011 7 • May be blended with diesel fuel at any proportion; both fuels may be mixed during the fuel supply to vehicles. • Excellent properties as a lubricant. • It is the only alternative fuel that can be used in a conventional diesel engine, without modifications. • Used cooking oils and fat residues from meat processing may be used as raw materials.
2.2 Raw Materials for Biodiesel Production The raw materials for biodiesel production are vegetable oils, animal fats and short chain alcohols. The oils most used for worldwide biodiesel production are rapeseed (mainly in the European Union countries), soybean (Argentina and the United States of America), palm (Asian and Central American countries) and sunflower, although other oils are also used, including peanut, linseed, safflower, used vegetable oils, and also animal fats. Methanol is the most frequently used alcohol although ethanol can also be used. Since cost is the main concern in biodiesel production and trading (mainly due to oil prices), the use of non-edible vegetable oils has been studied for several years with good results. 8 2 Introduction to Biodiesel Production Besides its lower cost, another undeniable advantage of non-edible oils for biodiesel production lies in the fact that no foodstuffs are spent to produce fuel . These and other reasons have led to medium- and large-scale biodiesel production trials in several countries, using non-edible oils such as castor oil, tung, cotton, jojoba and jatropha. Animal fats are also an interesting option, especially in countries with plenty of livestock resources, although it is necessary to carry out preliminary treatment since they are solid; furthermore, highly acidic grease from cattle, pork, poultry, and fish can be used. Microalgae appear to be a very important alternative for future biodiesel production due to their very high oil yield; however, it must be taken into account that only some species are useful for biofuel production. Although the properties of oils and fats used as raw materials may differ, the properties of biodiesel must be the same, complying with the requirements set by international standards.
2.2.1 Typical Oil Crops Useful for Biodiesel Production The main characteristics of typical oil crops that have been found useful for biodiesel production are summarized in the following paragraphs .
22.214.171.124 Rapeseed and Canola
Rapeseed adapts well to low fertility soils, but with high sulfur content. With a high oil yield (40–50%), it may be grown as a winter-cover crop, allows double cultivation and crop rotation. It is the most important raw material for biodiesel production in the European Community. However, there were technological limitations for sowing and harvesting in some Central and South American countries, mainly due to the lack of adequate information about fertilization, seed handling, and storage (the seeds are very small and require specialized agricultural machinery). Moreover, low prices in comparison to wheat (its main competitor for crop rotation) and low production per unit area have limited its use. Rapeseed flour has high nutritional value, in comparison to soybean; it is used as a protein supplement in cattle rations. Sometimes canola and rapeseed are considered to be synonymous; canola (Canadian oil low acid) is the result of the genetic modification of rapeseed in the past 40 years, in Canada, to reduce the content of erucic acid and glucosinolates in rapeseed oil, which causes inconvenience when used in animal and human consumption. Canola oil is highly appreciated due to its high quality, and with olive oil, it is considered as one of the best for cooking as it helps to reduce blood cholesterol levels. 2.2 Raw Materials for Biodiesel Production 9 126.96.36.199 Soybean It is a legume originating in East Asia. Depending on environmental conditions and genetic varieties, the plants show wide variations in height. Leading soybean producing countries are the United States, Brazil, Argentina, China, and India. Biodiesel production form soybean yields other valuable sub-products in addition to glycerin: soybean meal and pellets (used as food for livestock) and flour (which have a high content of lecithin, a protein). Grain yield varies between 2,000 and 4,000 kg/hectare. Since the seeds are very rich in protein, oil content is around 18%.
188.8.131.52 Oil Palm
Oil palm is a tropical plant that reaches a height of 20–25 m with a life cycle of about 25 years. Full production is reached 8 years after planting. Two kinds of oil are obtained from the fruit: palm oil proper, from the pulp, and palm kernel oil, from the nut of the fruit (after oil extraction, palm kernel cake is used as livestock food). Several high oil-yield varieties have been developed. Indonesia and Malaysia are the leading producers. International demand for palm oil has increased steadily during the past years, the oil being used for cooking, and as a raw material for margarine production and as an additive for butter and bakery products. It is important to remark that pure palm oil is semisolid at room temperature (20–22C), and in many applications is mixed with other vegetable oils, sometimes partially hydrogenated.
Sunflower ‘‘seeds’’ are really a fruit, the inedible wall (husk) surrounding the seed that is in the kernel. The great importance of sunflower lies in the excellent quality of the edible oil extracted from its seeds. It is highly regarded from the point of view of nutritional quality, taste and flavor. Moreover, after oil extraction, the remaining cake is used as a livestock feed. It must be noted that sunflower oil has a very low content of linoleic acid, and therefore it may be stored for long periods. Sunflower adapts well to adverse environmental conditions and does not require specialized agricultural equipment and can be used for crop rotation with soybean and corn. Oil yield of current hybrids is in the range 48–52%.
184.108.40.206 Peanut The quality of peanut is strongly affected by weather conditions during the harvest. Peanuts are mainly used for human consumption, in the manufacture of peanut 10 2 Introduction to Biodiesel Production butter, and as an ingredient for confectionery and other processed foods. Peanuts of lower quality (including the rejects from the confectionery industry) are used for oil production, which has a steady demand in the international market. Peanut oil is used in blends for cooking and as a flavoring agent in the confectionery industry. The flour left over, following oil extraction, is of high quality with high protein content; in pellet form, it is used as a livestock feed.
220.127.116.11 Flax Flax is a plant of temperate climates, with blue flowers. Linen is made with the threads from the stem of the plant and the oil from the seeds is called linseed oil, used in paint manufacture. Flax seeds have nutritional value for human consumption since they are a source of polyunsaturated fatty acids necessary for human health. Moreover, the cake left over, following oil extraction, is used as a livestock feed. The plant adapts well to a wide range of temperature and humidity; however, high temperatures and plentiful rain do not favor high yields of seed and fiber. Flax seeds contain between 30 and 48% of oil, and protein content is between 20 and 30%. It is important to remark that linseed oil is rich in polyunsaturated fatty acids, linolenic acid being from 40 to 68% of the total.
Safflower adapts well to dry environments. Although the grain yield per hectare is low, the oil content of the seed is high, from 30 to 40%. Therefore, it has economic potential for arid regions. Currently, safflower is used in oil and flour production and as bird feed. There are two varieties, one rich in mono-unsaturated fatty acids (oleic acid) and the other with a high percentage of polyunsaturated fatty acids (linoleic acid). Both varieties have a low content of saturated fatty acids. The oil from safflower is of high quality and low in cholesterol content. Other than being used for human consumption, it is used in the manufacture of paints and other coating compounds, lacquers and soaps. It is important to note that safflower oil is extracted by means of hydraulic presses, without the use of solvents, and refined by conventional methods, without anti-oxidant additives. The flour from safflower is rich in fiber and contains about 24% proteins. It is used as a protein supplement for livestock feed.
18.104.22.168 Castor Seed
The castor oil plant grows in tropical climates, with temperatures in the range 20–30C; it cannot endure frost. It is important to note that once the seeds start 2.2 Raw Materials for Biodiesel Production 11 germinating, the temperature must not fall below 12C. The plant needs a warm and humid period in its vegetative phase and a dry season for ripening and harvesting. It requires plenty of sunlight and adapts well to several varieties of soils. The total rainfall during the growth cycle must be in the range 700–1,400 mm; although it is resistant to drought, the castor oil plant needs at least 5 months of rain during the year. Castor oil is a triglyceride, ricinolenic acid being the main constituent (about 90%). The oil is non-edible and toxic owing to the presence of 1–5% of ricin, a toxic protein that can be removed by cold pressing and filtering. The presence of hydroxyl groups in its molecules makes it unusually polar as compared to other vegetable oils.
22.214.171.124 Tung Tung is a tree that adapts well to tropical and sub-tropical climates. The optimum temperature for tung is between 18 and 26C, with low yearly rainfall. During the harvest season, the dry nuts fall off from the tung tree and are collected from the ground. Nut production starts 3 years after the planting. The oil from tung nuts is non-edible and used in the manufacture of paints and varnishes, especially for marine use.
126.96.36.199 Cotton Among non-foodstuffs, cotton is the most widely traded commodity. It is produced in more than 80 countries and distributed worldwide. After the harvest, it may be traded as raw cotton, fiber or seeds. In cotton mills, fiber and seeds are separated from raw cotton. Cotton fiber is processed to produce fabric and thread, for use in the textile industry. In addition, cotton oil and flour are obtained from the seed; the latter is rich in protein and is used in livestock feed and after further processing, for human consumption.
Although jojoba can survive extreme drought, it requires irrigation to achieve an economically viable yield. Jojoba needs a warm climate, but a cold spell is necessary for the flowers to mature. Rainfall must be very low during the harvest season (summer). The plant reaches its full productivity 10 years after planting. The oil from jojoba is mainly used in the cosmetics industry; therefore, its market is quickly saturated.
12 2 Introduction to Biodiesel Production
Jatropha is a shrub that adapts well to arid environments. Jatropha curcas is the most known variety; it requires little water or additional care; therefore, it is adequate for warm regions with little fertility. Productivity may be reduced by irregular rainfall or strong winds during the flowering season. Yield depends on climate, soil, rainfall and treatment during sowing and harvesting. Jatropha plants become productive after 3 or 4 years, and their lifespan is about 50 years. Oil yield depends on the method of extraction; it is 28–32% using presses and up to 52% by solvent extraction. Since the seeds are toxic, jatropha oil is nonedible. The toxicity is due to the presence of curcasin (a globulin) and jatrophic acid (as toxic as ricin).
Avocado is a tree between 5 and 15 m in height. The weight of the fruit is between 120 and 2.5 kg and the harvesting period varies from 5 to 15 months. The avocado fruit matures after picking and not on the tree. Oil may be obtained from the fruit pulp and pit. It has a high nutritional value, since it contains essential fatty acids, minerals, protein and vitamins A, B6, C, D, and E. The content of saturated fatty acids in the pulp of the fruit and in the oil is low; on the contrary, it is very high in mono-unsaturated fatty acids (about 96% being oleic acid). The oil content of the fruit is in the range 12–30%.
Microalgae have great potential for biodiesel production, since the oil yield (in liters per hectare) could be one to two orders of magnitude higher than that of other raw materials. Oil content is usually from 20 to 50%, although in some species it can be higher than 70% . However, it is important to note that not all microalgae are adequate for biodiesel production. High levels of CO2, water, light, nutrients and mineral salts are necessary for the growth of microalgae. Production processes take place in raceway ponds and photobiological reactors . Leading oil crops used in biodiesel production are indicated in Box 2.1