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Experiments have confirmed that the base-catalyzed methanolysis of vegetable oils occurs much slower than butanolysis because of the two liquid phases initially present in the former reaction. For the same reason, second-order kinetics are not followed. The use of a cosolvent such as tetrahydrofuran or methyl tertiary butyl ether speeds up methanolysis considerably. However, like one-phase butanolysis, one-phase methanolysis initially exhibits a rapid formation of ester, but then slows drastically. Experiments show that the half-life of the hydroxide catalyst is too long to explain the sudden slowing of the reaction. Similarly, lower rate constants for the methylation of the mono-and diglycerides are not a reasonable explanation. Instead the cause has been identified as the fall in polarity which results from the mixing of the nonpolar oil with the methanol. This lowers the effectiveness of both hydroxide and alkoxide catalysts. Increasing the methanol/oil molar ratio to 27 in the one-phase system raises the polarity such that the methyl ester content of the ester product exceeds 99.4 wt% in 7 min. This has obvious implications for the size of new methyl ester plants as well as the capacity of existing facilities.For several years, the transesterification of vegetable oils to form esters, and in particular, methyl esters, has received considerable attention. This is because of the current use of these methyl esters as petrodiesel substitutes. In Europe, environmental concerns and agricultural considerations have resulted in the construction of several fuel methyl ester plants, the largest, in Italy, having a capacity of 250,000 tons per year. The financial incentives for these plants are fuel tax relief and agricultural subsidies for farmers to grow vegetable oil crops, rather than not to grow other crops. Producers in Europe are looking not only to build new plants but also to increase the capacities of older plants. The formation of vegetable oil methyl esters by the base-catalyzed reaction of vegetable oils and methanol as shown in Scheme 1 is fairly slow, and in some instances stops before completion. In the last 10 yr very little work has been done on the kinetics of the transmethylation of vegetable oils to produce fatty acid methyl esters, presumably because it was believed that the reaction was well understood. Two bench mark papers by Freedman in 1984 (1) and 1986 (2) are probably responsible for this. The work described in the earlier paper established that for the base-catalyzed transmethylation, a 6:1 methanol/oil molar ratio was optimal. This results in greater than 95 wt% methyl esters in the product when 1.0 wt% sodium hydroxide, based on the oil, is used as catalyst. It also maintains the advantage of the natural separation of the glycerol by-product at the bottom of the reactor, whereas when too much methanol is added, the glycerol either does not separate or moves into a methanolrich upper phase. The use of sodium hydroxide, rather than sodium methoxide, is preferred because of the hazards and i...

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The effects of alcohol/oil molar ratio, base concentration, and temperature on the single-phase base-catalyzed ethanolyses of sunflower and canola oils were determined. The use of tetrahydrofuran as co-solvent, as well as higher than usual alcohol/substrate molar ratios, prevented glycerol separation. This allowed each reaction to reach equilibrium rather than just steady-state conditions. High conversions of oil lowered the concentrations of MG and DG surfactants in the products, and thereby mitigated the formation of emulsions usually associated with ethanolysis reactions. An alcohol/oil molar ratio of 25:1, together with the necessary amount of cosolvent, gave optimal results. At this molar ratio, despite equilibrium being achieved, ethanolysis, unlike methanolysis, did not quite produce biodiesel-standard material, the MG content being approximately 1.5 mass%. For methanolysis and 1-butanolysis, the corresponding values were 0.6 and 2.0 mass%, respectively. The use of 1.4 mass% KOH (equivalent to 1.0 mass% NaOH) led to ethanolysis equilibrium within 6-7 min at 23°C rather than 15 min when only 1.0 mass% was used. At 60°C, equilibrium was reached within only 2 min. Soybean and canola oils behaved the same.Paper no. J10264 in JAOCS 80, 367-371 (April 2003). KEY WORDS:Base-catalyzed ethanolysis, biodiesel standards, canola and sunflower oils, one-phase transesterification.The base-catalyzed formation of methyl and ethyl esters (EE) of FA from vegetable oils (TG) is important for several reasons. For many years, these esters have been commercially available in several European countries as renewable diesel fuel substitutes. In the year 2000, these esters were designated as allowable substitute fuels under the U.S. Energy Policy Act (EPACT). Although it is easier to make methyl esters, in some jurisdictions, it may be more desirable to make ethyl esters because the ethanol can be derived from renewable starch sources such as corn.The base-catalyzed formation of ethyl esters is difficult compared to the production of methyl esters. Specifically, the formation of stable emulsions during ethanolysis is a problem (1). Methanol and ethanol are not miscible with TG at ambient temperatures, and the reaction mixtures are usually mechanically stirred to enhance mass transfer. During the course of these reactions, emulsions usually form. In the case of methanolysis, these emulsions quickly and easily break down to form a lower glycerol-rich layer and an upper methyl ester-rich layer. In ethanolysis, these emulsions are much more stable and severely complicate separation and purification of the ester. The emulsions are caused in part by the formation of the intermediate MG and DG, which have both polar hydroxyl groups and nonpolar hydrocarbon chains. Therefore, these intermediates are strong surface-active agents and are used as such in the food industry as emulsifiers. In alcoholysis reactions, the catalyst, usually either sodium or potassium hydroxide, is dissolved in the polar alcohol phase, into which TG must transfer in...

Biodiesel is made by the transesterification of vegetable oils to form alkyl FA esters. High levels of conversion (>99%) are required to lower the total concentration of free and chemically bound glycerol to that allowed by the ASTM standard (0.240 wt%) for biodiesel. A polar dye was used to visualize the phase behaviors in methanolysis, ethanolysis, and butanolysis. The dye was more strongly colored in more polar phases. Methanolysis and ethanolysis reactions commenced as two phases (alcohol and oil), then formed emulsions, and ended as two phases as glycerol-rich phases separated. Ethanolysis was more easily initiated by mixing than was methanolysis. Ethanolysis also exhibited a much longer emulsion period and slower glycerol separation. The glycerol-rich phase was smaller in volume in ethanolysis than in methanolysis. Butanolysis remained one phase throughout, and no polar phase existed at any time. The results are consistent with the known phase compositions in these reactions. The concentrations of MG, DG, and TG in the products with time in stirred reactions were consistent with the observed phase behavior in the dye experiments.Paper no. J11376 in JAOCS 83, 1041 -1045 (December 2006. KEY WORDS:Base-catalyzed transesterification, biodiesel, ethanol, methanol, phase behavior.Biodiesel, a clean-burning, safe, and environmentally friendly transportation fuel, is being used to reduce emissions in many countries. Biodiesel is currently made by the transesterification of vegetable oils (TG) with methanol in the presence of basic catalysts to form FAME, which have significantly lower viscosities than the oils. Transesterification consists of three consecutive, reversible reactions: the TG is converted stepwise to DG, then MG, and finally glycerol, with methyl ester being formed in each step. Because the combustion of the glycerol moiety in MG, DG, TG, and glycerol can lead to the formation of acrolein, a photochemical smog ingredient, the ASTM standard for biodiesel limits the total glycerol moiety (G T ) in the fuel to 0.240 wt%, as determined by Equation 1, where G, MG, DG, and TG are the weight percentages of glycerol, MG, DG, and TG, respectively. G T = G + 0.26 (MG) + 0.15 (DG) + 0.1 (TG) [1]As a result, high conversion (>99% of the ester bonds) is required to achieve the glycerol limit set by the standard. However, the necessary conversion is not achievable in one single pass by current processes. In the biodiesel industry, biphasic base-catalyzed transesterification is the most common method for making biodiesel. Methanol and oils are immiscible, and vigorous stirring is required to promote the mass transfer between the oil and methanol phases. The catalyst, usually sodium methoxide, is exclusively in the polar methanol phase. During the transmethylation, the reaction mixture passes from a biphasic (methanol and oil) system to a biphasic (methyl ester-rich and glycerol-rich) system, probably via an emulsion. These phase transitions affect the kinetics and steady-state position of the reactions, which are c...

Retention time measurements on reversed phase HPLC-columns over a 50 K temperature range are used to estimate the enthalpy of octanol-water phase transfer ∆ OW H for 38 organic compounds of environmental relevance, including selected chlorinated benzenes (CBzs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated naphthalenes (PCNs) and biphenyls (PCBs). Literature K OW values as a function of temperature for CBzs served as a reference. ∆ OW H for these compounds range from 13 to 32 kJ/mol, confirming a relatively minor temperature dependence of their partitioning between water and octanol. For the chlorinated aromatics a strong linear relationship between ∆ OW H and molar volume was observed. The temperature-dependent retention volumes are also used to estimate K OW of selected PCNs and PAHs at 25 °C.

Two-phase base-catalyzed transesterification of vegetable oils is the most common method for making biodiesel. The reaction starts as separate oil and alcohol phases. At the end of the reaction, the mixture, if allowed to settle, consists of an upper ester-rich layer and a lower glycerol-rich layer. The compositions of these layers from the methanolysis and ethanolysis of soybean oil were measured. Synthetic mixtures and actual reaction mixtures were used either to represent or generate steadystate reaction mixtures resulting from the initial condition of 6:1 alcohol/oil molar ratio and catalyst concentration (1.0 wt% sodium methoxide or 1.26 wt% sodium ethoxide). At 23°C, for methanolysis, 42.0% of the alcohol, 2.3% of the glycerol, and 5.9% of the catalyst were in the ester-rich phase at steady state. In ethanolysis, 75.4% of the ethanol, 19.3% of the glycerol, and 7.5% of the catalyst were in the ester-rich phase. The volume of the glycerol-rich phase decreased from methanolysis to ethanolysis to propanolysis; butanolysis remained monophasic throughout. The results explain some of the general kinetic behavior observed in transesterifications and provide useful information for alcohol recovery and product purification.Two-phase base-catalyzed transesterification of vegetable oils is the most common method for making biodiesel. The reaction, as normally practiced, commences as two phases. These are an upper methanol phase, in which the catalyst is dissolved, and a lower vegetable oil phase. Stirring initiates the reaction, which transforms to another two-phase system comprising an ester-rich phase and a glycerol-rich phase. When stirring is stopped, the glycerol-rich phase settles to the bottom. Since the production of biodiesel standard fuel requires extremely high conversion and efficient isolation of the ester from the glycerol by-product, it is particularly important to characterize the steady-state compositions of the final phases.Many studies (1-3) have shown that the transmethylation reaction decelerates prematurely. It was previously concluded that this was due to the destruction of catalyst through soap formation. Feuge and Gros (4) reported that for the ethanolysis of peanut oil, more than 50% of the catalyst was destroyed in the first 15-20 min at 50°C. Boocock et al. (5) measured the catalyst (NaOH) concentration for base-catalyzed methanolysis of soybean oil (SBO) at 23°C and found that 67-83% of the catalyst was "depleted" in about the same time. This was at first attributed to soap formation by the irreversible attack of hydroxide ion on ester groups. When the reaction mixture is acidified, this soap is converted into FA. However, if all of the catalyst is consumed (1.0 wt% sodium hydroxide based on the weight of oil) by this reaction, then after acidification the FFA content in the transesterified product will be 7.0%, which is equivalent to an acid number of 14 based on oleic acid. Such high values are not usually observed.In a later study, Zhou and Boocock studied the phase behavior of two-phas...