Crystallizers fatty acid separation

Solvent Crystallization. Two processes, one utilizing acetone (Armour) and the other employing methanol (Emery), are well known. Using the latter, fatty acid is dissolved in 90 percent aqueous methanol in a 1 2 acid/ solvent ratio by the application of heat. The resulting solution is then cooled to H 5°C in a multi-tubular crystallization chamber equipped with scrapers for efficient heat transfer. The crystallized fatty acids are removed by filtration. The filter cake is melted and stripped of any residual solvent to yield the refined stearin fraction, and then the liquid stearin is converted to flakes or powder by a variety of processes, for example, chill roller, and the like. The mother liquor from the filtration is stripped to obtain the olein fraction. The separated stearin and olein fractions have a variety of commercial applications in both the chemical and food processing industries. 

There are two commercial solvent crystaUi2ation processes. The Emersol Process, patented in 1942 by Emery Industries, uses methanol as solvent and the Armour-Texaco Process, patented in 1948, uses acetone as solvent. The fatty acids to be separated are dissolved in the solvent and cooled, usually in a double-pipe chiller. Internal scrapers rotating at low rpm remove the crystals from the chilled surface. The slurry is then separated by means of a rotary vacuum filter. The filter cake is sprayed with cold solvent to remove free Hquid acids, and the solvents are removed by flash evaporation and steam stripping and recovered for reuse (10). 

Armour (2) A process for separating fatty acids by fractional crystallization from acetone. 

Chevreul named the other major principles he found in animal fat fatty acids , and showed that they occurred in the proportions of three fatty acids to each glycerol. When separated from the glycerol, fatty acids dissolve in alcohol and, by repeated extraction and precipitation with salts, could be purified sufficiently to form crystals. 

Many methods exist to separate triglycerides into fractions on the basis of their degree of unsaturation. These include fractional crystallization from solvents, and separation by column and thin layer chromatography (TLC). The classes of triglycerides may then be studied and after methylation the fatty acid content determined by GLC. Yet even this is not the whole story since the position of fatty acids on the triglyceride molecule may uniquely affect the physical and biological properties of the lipid. 

A nonaqueous reversed-phase high-performance liquid chromatography (NARP-HPLC) with refractive index (RI) detection was described and used for palm olein and its fractions obtained at 12.5°C for 12-24 h by Swe et al. (101). The objective of their research was to find the optimum separation for analysis of palm olein triglycerides by NARP-HPLC, and to find a correction factor to be used in calculating CN and fatty acid composition (FAC). The NARP-HPLC method used to determine the triglyceride composition was modified from the method of Dong DiCesare (88). Palm olein was melted completely at 70°C in an oven for 30 min prior to crystal-... 

The phase behavior of a synthetic lecithin, dipalmitoyllecithin, as analyzed by Chapman and co-workers (5), is diagrammed in Figure 3. The main features are the same as in the phase diagram of egg lecithin a mixture of numerous homologs. As a consequence of the variation in fatty acid chain length, the chain melting point is lowered which means that the critical temperature for formation of liquid crystalline phases is reduced. This temperature is about 42 °C for dipalmitoyllecithin, and, if the lamellar liquid crystal is cooled below this temperature, a so-called gel phase is formed. The hydrocarbon chains in the lipid bilayers of this phase are extended, and they can be regarded as crystalline. The gel phase and the transitions between ordered and disordered chains are considered separately. 

A surfactant molecule is an amphiphile, which means it has a hydrophilic (water-soluble) moiety and a hydrophobic (water-insoluble) moiety separable by a mathematical surface. The hydrophobic tails of the most common surfactants are hydrocarbons. Fluorocarbon and perfluorocarbon tails are, however, not unusual. Because of the hydrophobic tail, a surfactant resists forming a molecular solution in water. The molecules will tend to migrate to any water-vapor interface available or, at sufficiently high concentration, the surfactant molecules will spontaneously aggregate into association colloids, i.e., into micelles or liquid crystals. Because of the hydrophilic head, a surfactant (with a hydrocarbon tail) will behave similarly when placed in oil or when put in solution with oil and water mixtures. Some common surfactants are sodium or potassium salts of long-chained fatty acids (soaps), sodium ethyl sulfates and sulfonates (detergents), alkyl polyethoxy alcohols, alkyl ammonium halides, and lecithins or phospholipids. 

The hydrolysis is industrially conducted by acid or base catalysis (temperatures 210°C-260°C) or by enzymatic hydrolysis in the case of sensitive fatty acids. The resulting crude product mixture is separated and purified mainly by means of distillation or crystallization, and more rarely by adsorption or extraction. 

The following processes are used commercially for the separation of such fatty acids mechanical pressing, solvent crystallization, and hydrophilization. 

Milk fat, with its great variety of fatty acids, also has a very large number of glycerides. It is possible, by, for example, fractional crystallization from solvents, to separate milk fat in a number of fractions with different melting points (Chen and deMan 1966). Milk fat is peculiar in some respects. Its short-chain fatty acids are classified chemically as saturated compounds but... 

Stacking gap. In contrast, p polymorph has all-trawi-hydrocarbon chains and these rigid chains cannot adjust themselves to their circumstance. Therefore, p polymorph shows a eutectic phase. As for the LLL/PPP and LLL/SSS mixtures, eutectic phases occur for aU polymorphs. Because of large differences in carbon numbers for fatty acid chains between LLL and PPP (An = 4), and between LLL and SSS (An = 6), there are very large methyl-end stacking gaps in these crystals. Therefore, the increased entropy of methyl-end stacking becomes predominant and phase separation must be favored thermodynamically for all polymorphs. 

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