System tripalmitin

In general similar phase behaviour trends were observed between the systems. Tripalmitin is the least soluble in ethane followed by palmitic acid. Methyl palmitate and ethyl palmitate show high solubility in ethane and show total miscibility at pressures below 15 MPa in the temperature range studied. As observed by Schwarz et al. [30] very little difference exists between the phase behaviour of ethane/methyl palmitate and ethane/ethyl palmitate systems, most probably due to the similarity in the nature of their structure. 

Figure 5 shows the Fisher-Tumbull plot for the crystallization of blends of PS in sesame oil (26, 42, 60, and 80%) (9). This model system is a complex crystallization system. PS is a mixture of TAG obtained through fractional crystallization from refined, bleached, and deodorized palm oil (14). Tripalmitin is the TAG with the highest melting temperature in PS (15), and here its concentration was 16.46% w/w ( 0.17%) (9). Our previous research showed that tripalmitin mostly determines the crystallization kinetics of PS and its blends with vegetable oils (i.e.. 

SCF processing is no different. In fact, a phase behaviour analysis is vital as it provides an estimation of the operating pressitfes required and also indicates whether separation fi om other components will be possible. This section will focus on the phase behavioiu of palmitic acid, methyl palmitate, ethyl pahnitate and tripalmitin in SC CO2, ethane and propane and concentrate on the data available and trends observed therein. In addition, the three solvents will be eompared and the effect of co-solvents, often used to decrease the operating pressiu e, will be eonsidered. In particular this section will focus on the phase transition pressures of the systems studied. The phase transition pressure indieates the pressitfe required for total solubility at the said temperature and composition. For the type of systems studied here, a higher phase transition pressure leads to a lower solubility, therefore lower phase transition pressures indieate improved solubility. 

A significant amount of data has been published on the VSE and VLE for the system C02/tripalmitin, as outlined in Table 6. To date, no detailed study has been conducted on the melting point depression of tripalmitin in SC CO2. Due to the similar melting point of tripalmitin and palmitic acid [9], a cut-off temperature of 320 K similar to that of palmitic acid in CO2 is assumed. The VSE and VLE of the system C02/tripahnitin is shown in Figure 7 and Figure 8, respectively. 

Figure 8. Pressure - composition (w2) plot for the C02 (1 )/tripalmitin (2) system at 343.15 to 363.15 K [25,33,52,53] (a) entire composition range and (b) detail of low molecular mass composition range.

Comparing the SVE and the VLE the same trends as for the C02/palmitic acid system are noted. Once again significantly higher solubilities are observed for liquid tripalmitin in CO2 compared to solid tripalmitin in CO2. 

All four systems behave in a generally similar manner. For VLE an increase in temperature leads to an increase in phase transition pressure, resulting in a decrease in solubility. For the VSE the C02/pahnitic acid system showed the opposite temperature effect while insufficient data are available to comment on the temperature dependence of solid tripalmitin in SC CO2. However, both the C02/palmitic acid and C02/tripalmitin systems showed that the solid solubility is approximately an order of magnitude less than that of the liquid. 

The data shows that at both temperatures the esters have the highest solubility followed by palmitic acid and that tripalmitin has the lowest solubility. It is also noted that the systems C02/methyl pahnitate and C02/ethyl palmitate have very similar phase behaviour and similar phase transition pressures. This is expected due to the similarity of the moleeules. However, despite the fact that Bharath et al. [55] foimd that for Ci8 and higher esters the methyl ester has a higher phase transition pressure than the ethyl ester, Figure 9 indicates that the phase transition pressmes are indeed very similar and from the data available in the present analysis no outcome can be given in this regard. 

No data is available for the system ethane/tripalmitin. In order to estimate the phase behaviour of the system ethane/tripalmitin one ean approximate the data to that of an alkane with the same molecular mass. Peters previously suggested this analogy for the propane/tripalmitin system [56]. The oxygen atoms are located centrally in the molecule and thus well shielded. Tripalmitin has 57 carbon and oxygen atoms in the molecular backbone and as such the ethane/tripalmitin system may be approximated by the ethane/n-heptapentacosane system as a first order approximation. While the VLE for the ethane/n-heptapentacosane system has not been measured, Schwarz et al. [57] published correlations that link the phase transition pressure with the number of carbon atoms. These correlations are used and the approximated phase behaviour of the system ethane/tripalmitin is presented in Figure 14. It should be noted that these correlations are based on data generated with the... 

Figure 15.Comparison of the pressure - composition (W2) for the systems ethane (l)/palmitic acid (2) [27], ethane (l)/methyl palmitate (2) [29], ethane (l)/ethyl palmitate (2) [30] and ethane (l)/tripalmitin (2) (generated as described above using the ethane/n-alkane correlation of Schwarz et al. [57]) systems...

Coorens et al. [31] conducted a detailed study on the phase behaviour of the propane/tripalmitin system. Their data is summarised in Table 13 and illustrated in Figure 19 for SVE and in Figure 20 for VLE phase behaviour. 

The VSE of the propane/tripalmitin system shows that the solubility is very much temperature and pressure dependent and that at constant pressure, significantly higher solubility can be attained at higher temperatures. Similar observations were made for the C02/tripalmitin system. 

The VLE phase behaviour of the propane/tripalmitin system is similar to that of the other compounds in propane. Total solubility can be attained at moderate pressure (< 12 MPa). 

Table 13. Literature data for the propane (l)/tripalmitin (2) system...

As for the propane/methyl palmitate data, the propane/tripalmitin data presented was generated using a linear relationship fitted to the experimentally published data of Coorens et al. [31]. Once again an exeellent fit was obtained (R > 0.997 in all cases), therefore illustrating the linear relationship between temperature and the phase transition pressure. Coorens et al. [31] also published vapoiu -liquid-liquid equilibrium data showing that the system has a three phase region between 349 and 370 K. However, eompositions were not ineluded. 

Comparing Figure 19 and Figure 20, it can be seen that the phase behaviour for the VSE and VLE is significantly different. As for the C02/palmitic acid and C02/tripalmitin systems, the VSE data shows an increase in solubility with temperature while the converse is true for the VLE data. Additionally, the solubility of the solid in propane is again much lower than that of the liquid in propane. Thus, while the absolute values of the pressure differ (a detailed analysis is presented below) the same trends as for the C02/tripalmitin system are present. 

Many of the comments made for the phase behaviour of palmitic acid and its derivatives in CO2 and in ethane are also valid for propane as SC solvent. Figure 21 shows a comparison of the propane/tripalmitin, propane/palmitie acid, propane/methyl palmitate and propane/ethyl palmitate systems. 

Figure 9.35 Sensitivities of LC-MS and LC-FID systems, (a) Response of a neutral lipid standard mixture (CE, cholesteryl palmitate TG, tripalmitin) injected on a 3.2 x 250mm column packed with lOjum silicic acid. Detector LC-MS interface system, methane chemical ionization, single ion monitors at m/e 211. (b) Response of neutral lipid standard mixture (CE = cholesteryl oleate, TG = triolein) injected on a 2.1 X 250mm column packed with 6-8//m Zorbax-Sil, Detector LC-FID system (Privett and Erdahl, 1978).

Two different systems of triacylglycerols, i.e. tricaprin and tristearin on the one hand and trilaurin and tripalmitin on the other, were studied in the solid state at three different concentrations 25 75, 50 50, 75 25 (w/w). For the tricaprin/tristearin system, the mixtures were melted at 80°C and then cooled to -50°C for 10 min. The temperature was finally increased to 10°C for 30 min. For the trilaurin/tripalmitin system, the mixtures were melted at 80 C and then cooled to -20°C for 10 min. The sample was first reheated to 0°C for 20 min and then to 20°C for 30 min before NMR measurements. 

The efficiency of fat synthesis may be calculated from the pathways described. The calculation for the synthesis of tripalmitin by the cytoplasmic system would be ... 

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