Feedstock-based Biodiesel Fuels
Edible Oil-based Biodiesel Fuels
Ramos et al. (2009) study the properties of vegetable-oil-based biodiesel fuels in a paper with 981 citations. They transesterify ten refined vegetable oils using potassium methoxide as a catalyst and standard reaction conditions (reaction time, 1 h; weight of catalyst, 1 wt.% of initial oil weight; molar ratio methanokoil, 6:1; reaction temperature. 60°C). They find that some critical parameters, such as oxidation stability, cetane number, iodine value, and the cold filter plugging point, were correlated with the methyl ester composition of each biodiesel, according to two parameters: the degree of unsaturation and the long chain saturated factor.
Freedman et al. (1986) study the transesterification kinetics of soybean oils in an early paper with 813 citations. They find that transesterification of soybean oil and other triglycerides with alcohols, in the presence of a catalyst, yields fatty esters and glycerol, whereas di- and monoglycerides are intermediates and reactions are consecutive and reversible. They examine the effects of: the type of alcohol, 1-butanol or methanol (MeOH); the molar ratio of alcohol to soybean oil; the type and amount of catalyst; and the reaction temperature on rate constants and kinetic order. They find that forward reactions are pseudo-first order or second order, depending upon conditions used, whereas reverse reactions are second order. At a molar ratio of MeOH/soybean oil of 6:1, they observe a shunt reaction.
Vicente et al. (2004) study biodiesel production from sunflower oils in a paper with 789 citations. They compare different basic catalysts, sodium methoxide, potassium methoxide, sodium hydroxide, and potassium hydroxide for the methanolysis of sunflower oil. They carry out all the reactions under the same experimental conditions in a batch-stirred reactor and with the subsequent separation and purification stages in a decanter. They find that the biodiesel purity was near 100 wt% for all catalysts. However, near 100 wt% biodiesel yields were only obtained with the methoxide catalysts. Yield losses were due to triglyceride saponification and methyl ester dissolution in glycerol. The obtained biodiesel met the measured specifications, except for the iodine value, according to the German and EU draft standards. Although all the transesterification reactions were quite rapid and the biodiesel layers achieved nearly 100% methyl ester concentrations, the reactions using sodium hydroxide turned out to be the fastest.
Saka and Kusdiana (2001) study biodiesel production from rapeseed oil in a paper with 687 citations. They use supercritical methanol without using any catalyst. They carry out the experiment in a batch-type reaction vessel preheated to 350 and 400°C and at a pressure of 35-65 MPa, and with a molar ratio of 1:42 of the rapeseed oil to methanol. They find that, in a preheating temperature of 350°C, 240 s of supercritical treatment of methanol was sufficient to convert the rapeseed oil to methyl esters. Although the prepared methyl esters were basically the same as those of the common method with a basic catalyst, the yield of methyl esters by the former was higher than that by the latter. This new supercritical methanol process required the shorter reaction time and simpler purification procedure because of the unused catalyst.
Haas et al. (2006) estimate costs of biodiesel production from soybean oils in a paper with 604 citations. They develop a computer model to estimate the capital and operating costs of a moderately sized industrial biodiesel production facility. The major process operations in the plant were continuous-process vegetable oil transesterification, and ester and glycerol recovery. Crude, degummed soybean oil was specified as the feedstock. Annual production capacity of the plant was set around 37.8 x 106 1 (10 x 106 gal). Facility construction costs were US$11.3 million. The largest contributors to the equipment cost, accounting for nearly one-third of expenditures, were storage tanks to contain a 25-day capacity of feedstock and product. At a value of US$0.52/kg ($0.236/lb) for feedstock soybean oil, they predict a biodiesel production cost of US$0.53/1 ($2.00/gal). The single greatest contributor to this value was the cost of the oil feedstock, which accounted for 88% of total estimated production costs. There was a direct linear relationship between the production costs and the cost of the feedstock, with a change of US$0.020/l ($0.075/gal) in product cost per US$0.022/kg ($0.01/lb) change in biooil cost. Process economics included the recovery of glycerol, and its sale into the commercial glycerol market as an 80% w/w aqueous solution, which reduced production costs by approximately 6%. The production cost of biodiesel varied inversely and linearly with variations in the market value of glycerol, increasing by US$0.0022/l ($O.OO85/gal) for every US$0.022/kg (SO.Ol/lb) reduction in glycerol value.
Noureddini and Zhu (1997) study the kinetics of transesterification of soybean oil with methanol in a paper with 661 citations. They examine the effect of variations in mixing intensity (Reynolds number = 3,100-12,400) and temperature (3O-7O°C) on the rate of reaction, while the molar ratio of alcohol to triglycerol (6:1) and the concentration of catalyst (0.20 wt% based on soybean oil) were held constant. They find that the variations in mixing intensity impact the reaction, parallel to the variations in temperature. They propose a reaction mechanism consisting of an initial mass transfer-controlled region followed by a kinetically controlled region. The experimental data for the latter region are a good fit into a second-order kinetic mechanism. They finally determine the reaction rate constants and the activation energies for all the forward and reverse reactions.
Kusdiana and Saka (2001) study the kinetics of transesterification in rapeseed oil to biodiesel fuel as treated in supercritical methanol in a paper with 540 citations. They make runs in a bath-type reaction vessel ranging from 200°C at a subcritical temperature to 500°C at a supercritical state with different molar ratios of methanol to rapeseed oil. They find that the conversion rate of rapeseed oil to its methyl esters increased dramatically in the supercritical state, and that a reaction temperature of 350°C was the best condition, with the molar ratio of methanol in rapeseed oil being 42.
Granados et al. (2007) study biodiesel production from sunflower oil by using activated calcium oxide (CaO) in a paper with 507 citations. They use activated CaO as a catalyst in the production of biodiesel by transesterification of triglycerides with methanol. They find that CaO was rapidly hydrated and carbonated by contact with room air. A few minutes were enough to chemisorb a significant amount of H2O and CO2. The CO, was the main deactivating agent, whereas the negative effect of water was less important. The surface of the activated catalyst was an inner core of CaO particles covered by very few layers of Ca(OH)2. The activation by outgassing at temperatures of at least 973 K were required to revert the CO2 poisoning. The catalyst could be reused for several runs without significant deactivation. The catalytic reaction was the result of the heterogeneous and homogeneous contributions. Part of the reaction took place on basic sites at the surface of the catalyst, the rest was due to the dissolution of the activated CaO in methanol that created homogeneous leached active species.
Kim et al. (2004) study transesterification of vegetable oil to biodiesel using heterogeneous base catalysts in a paper with 507 citations. They develop an environmentally benign process for the production of biodiesel from vegetable oils using this catalyst. They adopt first an Na/NaOH/y-Al2O, heterogeneous base catalyst for the production of biodiesel. They optimize the reaction conditions, such as the reaction time, the stirring speed, the use of a co-solvent, the oil to methanol ratio, and the amount of catalyst. This heterogeneous base catalyst showed almost the same activity under the optimized reaction conditions compared to a conventional homogeneous NaOH catalyst. They estimate the basic strength of this catalyst and propose a correlation with the activity towards transesterification.
Nonedible Oil-based Biodiesel Fuels
Ramadhas et al. (2005) study biodiesel production from rubber seed oil with high ‘free fatty acids’ (FFAs) in a paper with 666 citations. They develop a two-step transesterification process to convert the high FFA oils to its monoesters. They find that the first step, acid catalyzed esterification, reduced the FFA content of the oil to less than 2%. The second step, an alkaline catalyzed transesterification process, converted the products of the first step to its monoesters and glycerol. The two-step esterification procedure converted rubber seed oil to its methyl esters. They find that the viscosity of biodiesel oil was nearer to that of diesel and that the calorific value was about 14% less than that of diesel.
Berchmans and Hirata (2008) develop a method to produce biodiesel from crude Jatropha curcas seed oil (JCO) having high FFAs (15%) in a paper with 564 citations.
They reduce the high FFA level of CJO to less than 1% by a two-step pretreatment process. The first step was carried out with a 0.60 w/w methanol-to-oil ratio in the presence of 1% w/w H,SO4 as an acid catalyst in a 1-h reaction at 50°C. After the reaction, the mixture was allowed to settle for 2 h and the methanol-water mixture separated at the top layer was removed. The second step was transesterified using 0.24 w/w methanol to oil and 1.4% w/w NaOH to oil as alkaline catalyst to produce biodiesel at 65°C. The final yield for methyl esters of fatty acids was ca. 90% in 2 h.
Azam et al. (2005) examine ‘fatty acid methyl ester' (FAME) profiles of seed oils of 75 plant species having 30% or more fixed oil in their seed/kernel in a paper with 500 citations. They find that the ‘saponification number’ (SN). iodine value (IV). and ‘cetane number’ (CN) of FAMEs of oils varied from 169.2 to 312.5, 4.8 to 212. and 20.56 to 67.47, respectively. They use fatty acid compositions, the IV, and the CN to predict the quality of the FAMEs of oil for use as biodiesel. The FAME of oils of 26 species, including Azadirachta indica, Calophyllum inophyllum, Jatropha curcas, and Pongamia pinnata, were most suitable for use as biodiesel, and they met the major specification of biodiesel standards of the USA, Germany, and the European Standard Organization. The FAMEs of another 11 species met the specification of the biodiesel standard of the USA only.