Fatty acids, crystallization

Several examples can be found in the literature where the authors attempted to trace the origin(s) of method-dependent monolayers. For instance, Mtngins et al. reported the influence of the solvent on n(A) curves for octadecyltrimethyl ammonium bromide spread from five different solvent mixtures or from crystals on a substrate of 0.1 M NaCl in which the surfactant is insoluble. At a given area k was found to differ between the various spreading solvents by a variation of 0.3 mNm" at low F to 3 mN m" at high F. Iwahashi et al. ) found that n A] curves obtained for the spreading of fatty acid crystals depended on the sizes and shapes of the crystals, apparently caused by irregular dissolution rates. For a comprehensive discussion see ref. ). 

Figure 7,6 Three frequent arrangements of the oligomethylene chains in fatty acid crystals and derived lipids. The hexagonal packing is less tight than the other two and gives rotational freedom to chains and head groups. ...

Figure 2.6.6 Odd-even effects in (a) crystalline bilayers in fatty acid crystals and (b) bolaamphipMlic monolayers on gold. The odd homolog form less stable assemblies in both cases, and both effects are caused by a tilting of the layers (see text).

In bilayers one also observes odd-even effects because of tilt. Here it is the fitting of terminal methyl groups in the even case that causes, for example, better solubility and higher melting points of even-numbered fatty acid crystals as compared to odd-numbered homologs. 

Ernst J, Sheldrick WS, and Euhrop JH (1979) The structures of the essential unsaturated fatty acids. Crystal structure of linoleic acid and evidence for the crystal structures of alpha-linoleic and arachidonic acid. Z Naturforsch 34b 706-711. 

Ucuhuba oil, 51, 95 Ultraviolet spectroscopy, 273,444,471 Umbelliferae, 52 Undecanoic acid, 1,345,350,351 Unesterified fatty adds in milk, 167 Unripe seeds, 184 Unsaponifiable content, 262 Unsaponifiables, 477 Unsaturated fatty acids crystal structure, 347 NMR, 273... 

Such growth spirals have been observed on the surface of a great variety of crystals. Figure 2.34 shows such a spiral on the (001) face of a fatty acid crystal. The step heights observed range from one building block to several tens of that height. It has been observed that the movement of steps is not constant, but rather sometimes behaves like traffic, there are jams and steps can pile up. 

When fatty acids crystallize, the saturated acids are oriented as depicted by the simplified pattern... 

Thermodynamically, the fatty acid crystals, after being wetted by the surfactant solution, transfer from the liquid oil into water solution. The oil droplets then coalesce to give the lighter olein phase. The separated stearin is remelted to remove residual water/surfactant, and then reprocessed to the desired level of purity. 

Additives acting on the pour point also modify the crystal size and, in addition, decrease the cohesive forces between crystals, allowing flow at lower temperatures. These additives are also copolymers containing vinyl esters, alkyl acrylates, or alkyl fumarates. In addition, formulations containing surfactants, such as the amides or fatty acid salts and long-chain dialkyl-amines, have an effect both on the cold filter plugging point and the pour point. 

Electron diffraction studies are usually limited to transferred films (see Chapter XV), One study on Langmuir films of fatty acids has used cryoelectron microscopy to fix the structures on vitrified water [179], Electron diffraction from these layers showed highly twinned structures in the form of faceted crystals. 

Transmission electron microscopy (TEM) can resolve features down to about 1 nm and allows the use of electron diffraction to characterize the structure. Since electrons must pass through the sample however, the technique is limited to thin films. One cryoelectron microscopic study of fatty-acid Langmuir films on vitrified water [13] showed faceted crystals. The application of TEM to Langmuir-Blodgett films is discussed in Chapter XV. 

In the presence of excess fatty acid, different soap crystalline phase compounds can form, commonly referred to as acid—soaps. Acid—soap crystals are composed of stoichiometric amounts of soap and fatty acid and associate in similar bilayer stmctures as pure soap crystals. There are a number of different documented acid—soap crystals. The existence of crystals of the composition 2 acid—1 soap, 1 acid—1 soap, and 1 acid—2 soap has been reported (13). The presence of the acid—soaps can also have a dramatic impact on the physical and performance properties of the finished soap. The presence of acid—soaps increases the plasticity of the soap during processing and decreases product firmness, potentially to the point of stickiness during processing. Furthermore, the presence of the acid—soap changes the character of the lather, decreasing the bubble size and subsequently increasing lather stabiUty and... 

Black Liquor Soap Acidulation. Only two-thirds of a typical black Hquor soap consists of the sodium salts of fatty acids and resin acids (rosin). These acids are layered in a Hquid crystal fashion. In between these layers is black Hquor at the concentration of the soap skimmer, with various impurities, such as sodium carbonate, sodium sulfide, sodium sulfate, sodium hydroxide, sodium Hgnate, and calcium salts. This makes up the remaining one-third of the soap. Cmde tall oil is generated by acidifying the black Hquor soap with 30% sulfuric acid to a pH of 3. This is usually done in a vessel at 95°C with 20—30 minutes of vigorous agitation. Caution should be taken to scmb the hydrogen sulfide from the exhaust gas. 

The rosin column spHt is controUed by the fatty acid content specified for rosin. This is usuaUy set at 2% fatty acids. At the high temperature near the bottom of the column and the reboUer, rosin dimerizes to some extent. By taking rosin from the column as a sidestream above the bottom, its rosin dimer content is minimized. Because of its high purity, sidestream rosin product is prone to crystallization. 

Distillation By-Products. Of the CTO distiHation by-products, ie, pitch, heads, and DistiHed TaH Oil (DTO), only the last, a unique mixture of rosin and fatty acids, has significant commercial value. Pitch and heads are used as fuel the former has a fuel value of 41,800 kj/kg. TaH oil heads have outstanding solvent properties, but also have a bad odor, which is hard to remove. They contain a relatively high fraction of palmitic acid which can be recovered by crystallization. 

In crystallizing fatty acids, solvent polarity does not influence crystal form as much as temperature and concentration (9). Infrared (9,10) and wide-line nmr spectra (11) as well as x-ray methods (12,13) can be used to detect the various crystalline forms. 

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). 

Cocoa butter substitutes and equivalents differ greatly with respect to their method of manufacture, source of fats, and functionaHty they are produced by several physical and chemical processes (17,18). Cocoa butter substitutes are produced from lauric acid fats such as coconut, palm, and palm kernel oils by fractionation and hydrogenation from domestic fats such as soy, com, and cotton seed oils by selective hydrogenation or from palm kernel stearines by fractionation. Cocoa butter equivalents can be produced from palm kernel oil and other specialty fats such as shea and ilHpe by fractional crystallization from glycerol and selected fatty acids by direct chemical synthesis or from edible beef tallow by acetone crystallization. 

Crystallization and Polymorphism of Fats and Fatty Acids, edited by Nissim Garti and Kiyotaka Sato... 

The hydrolysis is performed as a continuous countercurrent reaction in tall reaction towers (height 15-20 m, diameter 0.7 m). The reaction time amounts to 60-90 min. Reaction products are as well obtained an aqueous glycerin solution (about 15%) as on a mixture of raw fatty acids [50]. The free fatty acids are carefully distilled with the aid of a thin film evaporator (2-10 mbar, 260°C maximum) [51]. Crystallization and transwetting are additional methods for fractionation of fatty acid mixtures. 

Fujiwara et al. studied the precipitation phase boundary diagrams of the sodium salts of a-sulfonated myristic and palmitic acid methyl esters in the presence of calcium ions [61]. The time dependency of the precipitation showed that the calcium salts have an extremely slow crystallization rate at room temperatures. This is the reason for the good hardness tolerance of the a-sulfonated fatty acid methyl esters. 

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