Page 304 - Synthetic Fuels Handbook
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290                        CHAPTER NINE

           other fuel oils including #2 low sulfur diesel fuel and #1 diesel/kerosene but the exact blend
           depends on the operating environment.
             Biodiesel may contain small but problematic quantities of water. Although it is hydro-
           phobic (nonmiscible with water molecules), there are indications that biodiesel, it is said to
           be, at the same time, is hygroscopic to the point of attracting water molecules from atmo-
           spheric moisture. In addition, there may be water that is residual to processing or resulting
           from storage tank condensation. The presence of water is a problem because: (a) water
           reduces the heat of combustion of the bulk fuel which means more smoke, harder starting,
           less power, (b) water causes corrosion of vital fuel system components: fuel pumps, injector
           pumps, and fuel lines, (c) water freezes to form ice crystals at 0°C (32°F) and the crystals
           provide sites for nucleation and accelerate the gelling of the residual fuel, and (d) water
           accelerates the growth of microbe colonies, which can plug up a fuel system so biodiesel
           users who have heated fuel tanks therefore face a year-round microbe problem.
             Chemically, transesterified biodiesel comprises a mix of mono-alkyl esters of long-chain
           fatty acids. The most common form uses methanol to produce methyl esters as it is the cheap-
           est alcohol available, though ethanol can be used to produce an ethyl ester biodiesel and
           higher alcohols such as isopropanol and butanol have also been used. Using alcohols of higher
           molecular weights improves the cold flow properties of the resulting ester, at the cost of a less
           efficient transesterification reaction. A lipid transesterification production process is used to
           convert the base oil to the desired esters. Any free fatty acids in the base oil are either converted
           to soap and removed from the process, or they are esterified (yielding more biodiesel) using
           an acidic catalyst. After this processing, unlike straight vegetable oil, biodiesel has combustion
           properties very similar to those of petroleum diesel, and can replace it in most current uses.
             A by-product of the transesterification process is the production of glycerol. For every
           unit of biodiesel that is manufactured, 0.1 unit of glycerol is produced. Originally, there
           was a valuable market for the glycerol, which assisted the economics of the process as a
           whole. However, with the increase in global biodiesel production, the market price for this
           crude glycerol (containing 20 percent water and catalyst residues) is lower and affords an
           operational challenge. Usually the crude glycerol has to be purified, typically by perform-
           ing vacuum distillation after which the refined glycerol (of more than 98 percent purity)
           can then be utilized directly, or converted into other products.
             The extra lubrication provided by biodiesel fuel helps improve the longevity of your
           engine, as well as boosting engine performance, also helping eliminate engine knocks and
           noise. In addition, biodiesel fuel can be stored in any type of tank and has a much higher
           flash point (approximately 300°C) compared to petrodiesel approximately (150°C).


           9.6 HYDROCARBONS

           Biodiesel fuel can be made from renewable resources, such as, vegetable oils and animal
           fats. For example, there are certain species of flowering plants belonging to different fami-
           lies which convert a substantial amount of photosynthetic products into latex. The latex of
           such plants contains liquid hydrocarbons of high molecular weight (10,000). These hydro-
           carbons can be converted into high grade transportation fuel (i.e., petroleum). Therefore,
           hydrocarbon producing plants are called petroleum plants or petroplants and their crop as
           petrocrop. Natural gas is also one of the products obtained from hydrocarbons. Thus, petro-
           leum plants can be an alternative source for obtaining petroleum to be used in diesel engines.
           Normally, some of the latex-producing plants of families Euphorbiaceae, Apocynaceae,
           Asclepiadaceae, Sapotaceae, Moraceae, Dipterocarpaceae, and others are petroplants.
           Similarly, sunflower (family Composiae), Hardwickia pinnata (family Leguminosae) are
           also petroplants. Some algae also produce hydrocarbons.
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