No abstract

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...

No abstract

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...

Polyol derived from soybean oil was made from crude soybean oil by epoxidization and hydroxylation. Soy‐based polyurethane (PU) foams were prepared by the in‐situ reaction of methylene diphenyl diisocyanate (MDI) polyurea prepolymer and soy‐based polyol. A free‐rise method was developed to prepare the sustainable PU foams for use in automotive and bedding cushions. In this study, three petroleum‐based PU foams were compared with two soy‐based PU foams in terms of their foam characterizations and properties. Soy‐based PU foams were made with soy‐based polyols with different hydroxyl values. Soy‐based PU foams had higher Tg (glass transition temperature) and worse cryogenic properties than petroleum‐based PU foams. Bio‐foams had lower thermal degradation temperatures in the urethane degradation due to natural molecular chains with lower thermal stability than petroleum skeletons. However, these foams had good thermal degradation at a high temperature stage because of MDI polyurea prepolymer, which had superior thermal stability than toluene diisocyanate adducts in petroleum‐based PU foams. In addition, soy‐based polyol, with high hydroxyl value, contributed PU foam with superior tensile and higher elongation, but lower compressive strength and modulus. Nonetheless, bio‐foam made with high hydroxyl valued soy‐based polyol had smaller and better distributed cell size than that using low hydroxyl soy‐based polyol. Soy‐based polyol with high hydroxyl value also contributed the bio‐foam with thinner cell walls compared to that with low hydroxyl value, whereas, petroleum‐based PU foams had no variations in cell thickness and cell distributions.