Bernard Freedman

Variables affecting the yields of fatty esters from transesterified vegetable oils

Transesterification reaction variables that affect yield and purity of the product esters from cottonseed, peanut, soybean and sunflower oils include molar ratio of alcohol to vegetable oil, type of catalyst (alkaline vs acidic), temperature and degree of refinement of the vegetable oil. With alkaline catalysts (either sodium hydroxide or methoxide), temperatures of 60 C or higher, molar ratios of at least 6 to 1 and with fully refined oils, conversion to methyl, ethyl and butyl esters was essentially complete in 1 hr. At moderate temperatures (32 C), vegetable oils were 99% transesterified in ca. 4 hr with an alkaline catalyst. Transesterification by acid catalysis was much slower than by alkali catalysis. Although the crude oils could be transesterified, ester yields were reduced because of gums and extraneous material present in the crude oils.

Transesterification kinetics of soybean oil 1

Transesterification of soybean oil (SBO) and other triglycerides with alcohols, in the presence of a catalyst, yields fatty esters and glycerol. Di- and monoglycerides are intermediates. Reactions are consecutive and reversible. Rate constants have been determined for each reaction with a computerized kinetic program. The effects of the type of alcohol, 1-butanol or methanol (MeOH); molar ratio of alcohol to SBO; type and amount of catalyst; and reaction temperature on rate constants and kinetic order were examined. Forward reactions appear to be pseudo-first order or second order depending upon conditions used. Reverse reactions appear to be second order. At a molar ratio of MeOH/SBO of 6:1, a shunt reaction was observed. Energy of activation was determined for all forward and reverse reactions under a variety of experimental conditions from plots of log k vs 1/T. Values ranged from 8–20 kcal/mol.

Quantitation in the analysis of transesterified soybean oil by capillary gas chromatography 1

A rapid quantitative capillary gas Chromatographic method has been developed for studying transesterification of soybean oil (SBO) to fatty esters. Standard solutions containing methyl linoleate, mono- , di- and trilinolein were analyzed with a 1.8 m X 0.32 mm SE- 30 fused silica column. The effect of carrier gas flow on reproducibility was determined. Prior to analysis, mono- (MG) and diglycerides (DG) were silylated with N,O- bis(trimethylsilyl) trifluoroacetamide.Tridecanoin was used as an internal standard. From plots of area and weight relationships, slopes and intercepts for all four compound classes were determined. Agreement between the measured and calculated compositions of the standard solutions was good; the overall standard deviation was 0.4. Slopes and intercepts also were determined for SBO and its methyl and butyl esters. Complete separation of ester, MG, DG and triglyceride was obtained in 12 min by temperature programming from 160 to 350 C. This method of analysis gave excellent results when used in a kinetic study of SBO transesterification.

Heats of combustion of fatty esters and triglycerides

Gross heats of combustion (HG) have been measured for three classes of fatty esters and two classes of triglycerides (TGs). The esters included saturated methyl esters, Me 6:0–22:0; saturated ethyl esters, Et 8:0–22:0; and unsaturated methyl esters, Me 12:1–22:1, Me 18:2 and Me 18:3. The TGs included the saturated TGs, C 8:0–22:0, and unsaturated TGs, C 11:1, C 16:1, C 18:1, C 18:2, C 18:3, C 20:1 and C 22:1. HG were measured in a Parr adiabatic calorimeter according to a modification of ASTM D240 and D2015. Linear regression analysis (LINREG) yielded equations that related HG to carbon number (CN) or chain length, electron number (EN) or number of valence electrons and molecular weight (MW). Calculated HG values from CN, EN, or MW were nearly identical. Thus, any one of these three variables can be used to predict HG satisfactorily. R squared values for all equations were 0.99. Equations for correlating HG of saturated or unsaturated TGs with molecular characteristics of these molecules have not been reported. With LINREG, we developed equations that permitted predictions of HG from structures of the saturated and unsaturated TGs. Equations for predicting HG of methyl and ethyl esters were compared to those in the literature and were found to be more accurate and precise.

Predicting Cetane Numbers of n-Alcohols and Methyl Esters from their Physical Properties

Cetane numbers (C#) for the homologous series of straight-chain, saturated n-alcohols, C5−C12 and C14, were determined according to ASTM D 613. Measured C# ranged from 18.2–80.8 and increased linearly with carbon number (CN). Regression analyses developed equations that related various physical properties or molecular characteristics of these alcohols to calculated C#. The degree of relationship between measured and calculated C# was expressed as R2. The decreasing order of the precision with which these properties correlated with C# was: boiling point (bp)>melting point (mp)>CN>heat of combustion (HG)>refractive index (n20D)>density (d). This ranking was based upon R2 (0.99–0.96) and the Average % error (2.8–7.2%). C# were also determined for straight-chain homologs of saturated methyl esters with CN of 6, 10, 12, 14, 16 and 18. C# ranged from 18.0–75.6 and increased curvilinearly with CN. Equations were also developed that related physical properties of these esters to C#. The precision with which these properties correlated with C# was: bp>viscosity (V)>heat of vaporization (HV)>HG>CN>surface tension (ST)>mp>n20D>d. R2 ranged from 0.99 for bp to 0.98 for d. Equations for the alcohols were linear or quadratic, while equations for the esters were linear, quadratic or cubic based upon statistical considerations that included a Student’s t-test. With related physical properties and these equations, accurate predictions of C# can be made for saturated n-alcohols and methyl esters.

Correlation of heats of combustion with empirical formulas for fatty alcohols

Gross heats of combustion (Hg) for the homologous series of saturated fatty alcohols C10–C22 were measured in a Parr adiabatic calorimeter according to ASTM D240 and D2015. The measured values for these alcohols ranged from 1582 to 3453 kg-cal/mole. We developed equations that related carbon number (CN) or chain length, electron number (EN) or number of valence electrons and molecular weight (MW) to calculated Hg by linear regression analysis (LINREG). These equations are: Hg=26.00+155.60 CN; Hg=26.00+25.94 EN; and Hg=−172.2+11.00 MW. R squared values for all three equations were 0.99. The results obtained with LINREG were compared to a literature method. Comparisons were made for both the fatty alcohols above and C1–C5, C7, C8 and C16 alcohols of the literature method. For the former alcohols there was no difference in accuracy or precision between the two methods. For the latter alcohols LINREG was both more accurate and precise. Measured Hg vs. chain length for C1–C22 alcohols showed a perfect linear relationship. Thus, knowing chain length, Hg can be predicted accurately for alcohols in this range.

Gas-liquid chromatography of hydroxy fatty esters: Comparison of trifluoroacetyl and trimethylsilyl derivatives

Transformations of hydroxy to keto fatty esters have been monitored successfully by converting the hydroxy compounds to their trifluoroacetyl (TFA) or trimethylsilyl (TMS) derivatives followed by gas-liquid chromatography (GLC). The TFA derivatives have shorter retention times, are better separated from the keto esters, and permit more complete resolution of saturated and unsaturated hydroxy fatty esters than the TMS derivatives. Improved methods for derivative preparation which are rapid and convenient are described. Methyl dimorphecolate (methyl 9-hydroxy-trans,trans,10,12-octadecadienoate), which is thermally unstable and cannot be chromatographed as the trifluoroacetate or free hydroxy compound, was chromatographed satisfactorily as the trimethylsilyl ether.

Conversion of methyl ricinoleate to methyl 12-ketostearate with Raney nickel

A convenient laboratory preparation of methyl 12-ketostearate is described. Methyl ricinoleate is converted to methyl 12-ketostearate in 70–75% yield by Raney nickel. The type and quantity of Raney nickel have a marked influence on the yield as well as on the time and temp required for the conversion. The reaction is not a direct isomerization as previously assumed but appears to be a two-step process. Methyl ricinoleate is hydrogenated rapidly to methyl 12-hydroxystearate which is then dehydrogenated slowly to the product. Hydrogenolysis of the alcohol function is a competing reaction which is minimized by the proper choice of reaction conditions.

Saturated keto esters from lesquerolic, dimorphecolic, and densipolic acids

SummaryThe naturally occurring, unsaturated, hydroxy fatty esters, methyl lesquerolate (methyl 14-hydroxy-cis-11-eicosenoate), methyl dimorphecolate (methyl 9-hydroxy-trans, trans-10,12-octadecadienoate), and methyl densipolate (methyl 12-hydroxy-cis,cis-9,15-octadecadienoate) have been converted to the corresponding saturated keto esters by tow routes. The unsaturated esters were subjected to a hydrogenation-dehydrogenation reaction in the presence of Raney nickel or their saturated derivatives were dehydrogenated by copper chromite catalysis. Yields of the keto esters are 65–82% in the nickel-catalyzed reactions, and 71–94% by copper chromite-catalyzed dehydrogenation. In the hydrogenation-dehydrogenation system the order of reactivity is: methyl lesquerolate>methyl dimorphecolate>methyl densipolate. Relationships between structure and reactivity of these compounds, methyl 12-hydroxystearate, and methyl ricinoleate are discussed.

Reductive amination of 12-ketostearic acid.

In the preparation of 12-aminostearic acid by reductive amination of 12-ketostearic acid, the keto acid is first contacted with ammonia under pressure to produce an intermediate, not isolated, which is then hydrogenated to give the product. Variables such as time and temperature of reaction, hydrogen pressure, and amount and type of catalyst were examined to find optimum conditions for high yield and purity of 12-amino-stearic acid. With a hydrogenation pressure of 500 psi and 10% Raney nickel catalyst an essentially quantitative yield of product was obtained having a purity of 94%. With 34% catalyst and 260 psi hydrogen, a 98% yield of 98% pure product was obtained.