| MAKING BIODIESEL What is still widely unknown is that it is easy to make biodiesel for diesel engines using vegetable oil or animal fat. Biodiesel is sold commercially in Europe, America and Australia. On a small scale, vegetable oil is relatively expensive, but used products from the cooking industry is abundant and can easily and cheaply be converted into a biodiesel fuel that will mix in any quantity with conventional diesel. During heating, the amount of polymers in the oil may increase up to 15 wt% and thus may have negative influence on fuel characteristics. Therefore, the amount of polymers in waste oil is a good indicator for biodiesel production (Mittelbach M et al. JAOCS 1999, 76, 545). The transesterification process involves mixing at room temperature methanol (50% excess) with NaOH (100% excess), then mixing vigorously with vegetable oil and letting the glycerol settle (about 15% of the biodiesel mix). The supernatant is biodiesel and contains a mixture of methylated fatty acids and methanol, the catalyst remaining dissolved in the glycerol fraction. Industrially, the esters are sent to the clean-up or purification process which consists of water washing, vacuum drying, and filtration. An in situ alkaline transesterification was shown to be efficient in preparing fatty acid esters, the simple and direct process eliminating the expense associated with solvent extraction and oil cleanup (Haas MJ et al., JAOCS 2004, 81, 83). Transesterification may be processed using methanol, ethanol, isopropyl alcohol, or butanol, the catalyst being either sodium or potassium hydroxide. It was shown that the methanol/oil molar ratio influences largely the efficiency of the reaction and has important implications for the optimal size of methyl ester plants (Boocock DGB et al. JAOCS 1998, 75, 1167). Optimization of methanolysis of Brassica carinata oil has been examined considering the catalyst concentration as well as the reaction temperature (Vicente G et al., JAOCS 2005, 82, 899). Various reaction parameters for the synthesis of biodiesel from safflower oil were studied to improve the fuel production which was within the recommended standards with 96.8% yield (Meka PK et al., J Oleo Sci 2007, 56, 9). It must be pointed out that after separation of the glycerol phase produced during the reactions, a very low amount of glycerol remains in biodiesel. A maximum permissible concentration of 0.02 wt-% is set by the European norm as well as by the ASTM specification. Therefore, it is necessary to determine the amount of free glycerol in biodiesel. Among others, a simple and rapid method was described using HPLC with refractometric detection (Hajek M et al., Eur J Lipid Sci Technol 2006, 108, 666). It was experienced that 10 l of soybeans produced about 1.9 l of biodiesel. A liter of this fuel contains about 35,000 BTUs. If fats or solidified oil are used, it will need to heat up to 50°C the mixture prior to mixing with methanol and catalyst. If free fatty acids are present (used cooking oils), special pretreatment technologies are required (see website). Among lipid-rich materials of low value is soapstock, a co-product of the refining of edible vegetal oils. This mixture is generated at a rate of about 6% of the treated unrefined oil (45 MT per year in USA). An efficient procedure involving acid-catalyzed esterification of soapstock has been described (Haas MJ et al., J Am Oil Chem Soc 2003, 80, 97). The world biodiesel sources were in 2002 : rapeseed oil (84%), sunflower (13%), soybean oil (1%), palm oil (1%), and others (1%). Information on making biodiesel may be found in specific websites :
http://www.biodiesel.org
General biodesiel information : http://www3.me.iastate.edu/biodiesel/ http://www.biodieselfuelonline.com/ (the latest information on biodiesel) Other resources (discussion groups) :
http://www.egroups.com/group/BiodieselEuropean Biodiesel Board:
Update on negotiations on biofuel directives (21 February 2003)
A comprehensive review of problems of emissions and of small-, medium-, and industrial-scale production with numerous web resources and references may be found on the web : |