Triglycerides molar ratio

The most significant factor of alkali-catalyzed transesterification was the molar ratio of the alcohol and oil. The stoichiometry of alkali-catalyzed transesterification requires 3 mol of alcohol/1 mol of triglyceride to generate 3 mol of FAME and 1 mol of glycerol. Since the transesterification is composed of reversible and consecutive reactions, the increase in molar ratio of methanol will result in high conversion yields. 

A catalyst-free supercritical methanol method for biodiesel fuel production was proposed with the optimum conditions of 350°C, 20 MPa, a molar ratio of 42 in methanol, and a 4-min treatment period (12-13). This method has been proved to produce a high yield, because of simultaneous reactions of transesterification of triglycerides and methyl esterification of free fatty acids (10). The only shortcoming of this one-step method is that it requires a severe reaction condition compared with the conventional commercial method with acid or alkaline catalyst. Consequently, our method would require a special alloy to cover the high temperature and high pressure of the reaction system. 

Figure 2 presents the effect of the various volumetric ratios of water to rapeseed oil on the yield of fatty acids as prepared with both flow- and batch-type reaction systems at 270°C for 20 min. The volumetric ratios of 1/4 and 4 correspond to the molar ratios of 13 and 217, respectively. For the batch-type system, the hydrolysis rate of triglycerides seemed to be affected more by the amount of water, and a slightly better conversion was seen with the flow-type reaction system. Even though the volumetric ratio of 1/4 is equivalent to the molar ratio of 13 in water, which is theoretically higher than its stoichiometry of 3, the formation of fatty acids in both reaction systems was obviously low. In addition, it was found that at a volumetric ratio less than 2/3, it was difficult to separate hydrolysis products from the water portion that contained glycerol. On the other hand, the presence of water in fatty acids would have a negative effect on the methyl esterification reaction (15). 

Older biodiesel processes are essentially batchwise. The oil is submitted to transesterification in a stirred-tank reactor in the presence of a large amount of methanol, and base catalyst, mostly NaOH or KOH. An excess of methanol is necessary chiefly to ensure full solubility of triglyceride and keep the viscosity of the reaction mixture low, but also for shifting the chemical equilibrium. A minimum molar ratio methanoktriglyceride of 6 1 is generally accepted [16, 17, 29], The reaction... 

The optimal molar ratio of methanol/triglyceride is between 6 and 9. Adding small amounts of cosolvents, such as propane and tetrahydrofuran, can reduce the excess of methanol. 

Figure 14.10 Composition versus time during batch methanolysis of oleic triglyceride using NaOH 0.5% catalyst and molar ratio methanol/oil 6 1 at 60 and 50°C.

The extreme hypoalbuminemia of the nephrotic syndrome can be attributed to the sustained urinary loss of albumin (S39), but it is doubtful whether albumin deficiency plays a causal role in the hyperlipemia and hypercholesterolemia found in this condition. Low-density lipoprotein (LDL) (90% lipids) is converted by lipoprotein lipase in vivo to high-density lipoprotein (HDL) (70% lipids), and the liberated fatty acid anions are bound and transported by plasma albumin. In normal nonlipemic serum the mean nonesterifled fatty acid/albumin molar ratio is 0.95 0.04, while in nephrotic sera—lipemic because of accumulation of LDL-triglycerides —the corresponding ratio is about 3 (C4). The plasma hyperlipemia which is observed in the nephrotic syndrome, and can be induced in rats by injections of antikidney serum, has been considered to result from albumin deficiency (R26). However this suggestion is not borne out by more recent studies (R25) and is contradicted by the failure of LDL to accumulate in the blood of analbuminic subjects (03). Plasma lipemia in the nephrotic syndrome apparently is due to loss or inhibition of lipoprotein lipase activity. 

Three different fatty acids can occur from 27 different mixed triglycerides. To simplify the description, one- or two-letter abbreviations of fatty acids are used, such as B = butanoic (butyric), D = decanoic (capric or caprinic), H = hexanoic (caproic), L = linoleic, La = lauric, Ln = linolenic, M = myristic, O = oleic, Oc = octanoic (caprylic), P = palmitic, Po = palmitoleic, S = saturated, St = stearic, U = unsaturated and V = vaccenic. For example, the mixed triacylglycerol esterified with palmitic acid in position s -l, with stearic acid in the position sn-2 and oleic acid in the position sn-3 of glycerol is then called l-palmitoyl-2-stearoyl-3-oleoyl-s -glycerol (abbreviated to s -PStO). Racemate is a mixture of s -PStO and and s -OStP in a molar ratio of 1 1... 

The vapor phase leaving the deodorizer will comprise only the volatile component and the stripping agent, normally steam, because the triglyceride is effectively nonvolatile. Assuming that the vapor phase leaving the deodorizer obeys Dalton s law, i.e., the molar ratio of the components in the vapor phase will equal the ratio of their partial pressures. 

Hydrotalcite catalysts or layered double hydroxides as catalysts are reported to give high conversion and yields in transesterification of triglycerides. Development of hydrotalcite materials for immobilization of biocatalysts for transesterification can overcome the need for higher temperature for hydro-talcite-catalyzed transesterification, which usually requires higher molar ratio of methanol. Table 12.5 summarizes the applications of hydrotalcite and hydrotalcite like compoimds as heterogeneous base catalysts for the production of biodiesel. 

Deep eutectic solvents based on choline acetate (ChOAc), which have lower viscosities as compare to the ChCl/Urea eutectic mixture, have been also used as reaction media in several biocatalyzed transesterification reactions. In this sense, Zhao et al. reported the transesterification of ethyl sorbitate with 1-propanol by the lipase Novozym 435 Candida Antarctica lipase B immobilized on acrylic resins), achieving high initial rates (1 pmolmin g ) and selectivity (99%). Furthermore, in a model biodiesel synthesis system, the authors examined the transeterification of the lipid Miglyol oil 812 (a mixture of triglycerides of caprylic acid (C8) and capric acid (CIO)) with methanol, catalyzed by Novozym 435 in ChOAc/Gly (1 1.5 molar ratio). The biocatalytic reaction was very rapid in this eutectic mixture, with 97% conversion achieved after only 3 hours. 

---