Molecular distillation processes

Evaluation of Tocopherol Recovery Through Simulation of Molecular Distillation Process... 

Taking all of these concerns into consideration, in the present work, we propose a molecular distillation process for tocopherol (vitamin E) recovery using as a raw material the crude deodorizer distillate of soya oil (DDSO). The determination of several physical-chemical properties must be made through correlations and/or predictions, in order to have a better characterization of the system that will be studied. Then, the DISMOL simulator can be used to evaluate tocopherol recovery from crude DDSO, in order to determine the feasibility of the process and the best experimental conditions for the falling film molecular distillation. The simulator used was a DISMOL, which was developed by Batistella (12). Tocopherols need to present a low acidity level (< 2%) and purity according to their application (from 30 to 90%). The price varies according to this concentration. Squalene is tolerable in tocopherol concentration, but fatty acids must be eliminated during the process. 

Distillation processes exploit the low volatility of cholesterol compared to the major triacylglycerols of milk fat for removal of cholesterol. Vacuum and short-path molecular distillation processes can efficiently remove cholesterol but it may be achieved at the expense of removing some low-molecular weight triacylglycerols and flavor components of the milk fat. Vacuum steam distillation is commonly used for refining fats and can also be used to refine milk fat. Cholesterol-reduced milk fat, which was produced by steam distillation, has been used successfully to formulate butter, cream and ice cream (Schroder and Baer, 1991, Elling et al., 1995, 1996). If the flavor of milk fat is to be preserved, the flavors can be trapped and re-incorporated into the milk fat that has been stripped of cholesterol (Boudreau and Arul, 1993). 

An expired U.S. patent describes molecular distillation of WGO (47). Initially, WGO was degummed by using phosphoric acid and water. Bleaching was carried out with activated clay followed by distillation using a centrifugal molecular distillation unit. Free fatty acids were removed at 140-200°C and below 50 mTorr. It was claimed in the same patent that a Vitamin E concentrate was prepared from purified WGO by a second-stage molecular distillation process carried out at 220-300°C and pressures less than 25 mTorr (47). 

Current methods for fractionating fi oil include selective removal of saturated as well as mono-xmsaturated fatty acids such as C20 l and C22 l by urea cortplexing, adsorption, chromatography, and fractional and/or molecular distillation processes. These are cumbersoaone and time consuming. Particularly undesirable are methods vhich require the use of difficult-to-remove organic solvents from the fini ed products. Use of hi tenperatures also introduces the possibility of cilteration of the fatty acids and formation of toxic derivatives. 

Molecular distillation process represents a type of vaporization at low pressure and low temperature. The transesterification can also be used as pre-step in molecular distillation process, like centrifuge distillatory. Batistella and Maciel studied the extraction in palm oil with 2,400 ppm of carotenoids applying a centrifugal distillator and a falling film distillator. The first process obtained a decomposition of 12 % at 155 °C and 25 % at 175 °C. The centrifugal distillator results in loss of 13 % at 190 °C and 14 % at 210 °C [83]. 

The areas of application for these vacuum pumps are all within the rough and medium vacuum range, the principal vacuum range for chemistry processes. Only the short path and molecular distillation processes rely also high-vacuum pumps like the diffusion pump or even the turbomolecular pump (kinetic gas pumps). High-vacuum pumps are not covered in this book. For these refer to [2, 3]. 

Godleski JJ, Stearns RC, Katler M, Hastings CL. Detection of elements by electron spectroscopic imaging and analysis of electron energy loss spectra in alveolar macrophages prepared by slam-freeze molecular distillation processing. EMSA Proc 1990 48 776-777. 

Although all four tocopherols have been synthesized as their all-rac forms, the commercially significant form of tocopherol is i7//-n7i a-tocopheryl acetate. The commercial processes ia use are based on the work reported by several groups ia 1938 (15—17). These processes utilize a Friedel-Crafts-type condensation of 2,3,5-trimethylhydroquinone with either phytol (16), a phytyl haUde (7,16,17), or phytadiene (7). The principal synthesis (Fig. 3) ia current commercial use iavolves condensation of 2,3,5-trimethylhydroquiQone (13) with synthetic isophytol (14) ia an iaert solvent, such as benzene or hexane, with an acid catalyst, such as ziac chloride, boron trifluoride, or orthoboric acid/oxaUc acid (7,8,18) to give the all-rac-acetate ester (15b) by reaction with acetic anhydride. Purification of tocopheryl acetate is readily accompHshed by high vacuum molecular distillation and rectification (<1 mm Hg) to achieve the required USP standard. 

C-21 dicarboxyhc acids are produced by Westvaco Corporation in Charleston, South Carolina in multimillion kg quantities. The process involves reaction of tall oil fatty acids (TOFA) (containing about 50% oleic acid and 50% hnoleic acid) with acryhc acid [79-10-7] and iodine at 220—250°C for about 2 hours (90). A yield of C-21 as high as 42% was reported. The function of the iodine is apparendy to conjugate the double bond in linoleic acid, after which the acryhc acid adds via a Diels-Alder type reaction to form the cycHc reaction product. Other catalysts have been described and include clay (91), palladium, and sulfur dioxide (92). After the reaction is complete, the unreacted oleic acid is removed by distillation, and the cmde C-21 diacid can be further purified by thin film distillation or molecular distillation. 

The operating principle of steam-jet ejectors is explained in Volume 1, Chapter 8. Then-specification, sizing and operation are covered in a comprehensive series of papers by Power (1964). Diffusion pumps are used where very low pressures are required (hard vacuum) for processes such as molecular distillation. 

A few last details may be given about Keyes, which should further demonstrate the crucial importance of the evolution of organic industries immediately after the first world war. After studying under G. N. Lewis, Keys focused not only on lacquers, as we have seen, but also on synthetic dyes. Later on, he moved toward petroleum chemistry and specialized in problems of molecular cracking because he also had a good deal of experience in distillation processes while he worked for the U.S. Industrial Alcohol Company of New York in the early 1920s (43). 

Separation of dibenzothiophene derivatives from petroleum oil fractions has been achieved by integrated approaches in which fractionating processes such as isothermal distillation, vacuum fractionation, and molecular distillation have been combined with spectroscopic methods including mass spectrometry and NMR spectroscopy. " Dibenzothiophenes have also been concentrated in sharp chromatographic fractions obtained, for example, by, alumina gel percolation, and have been detected by gas chromatography. Gas chromatography has also been used to... 

Figure 3 shows the relationships between the temperatures and molecular weight distributions for 6 successive regions of the Til profile in Figure 1. Interestingly, regions a, b and c, primarily representing the low temperature components, show relatively narrow MW distributions around M values which markedly increase with temperature. This is consistent with the proposed interpretation of the low temperature hump as a vacuum desorption and distillation process rather than as a pyrolytic process. By contrast, regions d, e and f, representing the major Til maximum in Figure 1, exhibit much broader MW...

In the removal of water vapor from liquids or in their distillation, particularly in degassing columns, vacuum filling, and resin-casting plants, as well as in molecular distillation, the production of as large a liquid surface as possible is important. In all wet processes the provision of the necessary heat for evaporation of the moisture is of great importance. 

Today s petroleum distillation plants are compared with the units in existence in 1925, and a review is presented of the advances during the past 25 years in construction practices and materials, instrumentation, and engineering design, which have made possible the current technology. The theory and application of special processes, such as azeotropic and extractive distillation and Hypersorption, are discussed. The development of molecular distillation and rotary columns is described to indicate possible trends to be expected in the future. 

The traditional extraction processes do not provide a method for selective fractionation of the oleoresin components. This fractionation must be carried out in additional processing steps, involving further use of organic solvents or costly processes such as molecular distillation. 

Most of the properties change somewhat from one end to the other of industrial columns for effecting separations, so that the mass transfer coefficients likewise vary. Perhaps the property that has the most effect is the mass rate of flow which appears in the Reynolds number. Certainly it changes when there is a substantial transfer of material between the two phases in absorption or stripping and even under conditions of constant molal overflow in distillation processes, the mass rate of flow changes because of differences of the molecular weights of the substances being separated. As a practical expedient, however, mass transfer coefficients are evaluated at mean conditions in a column. 

This process is an evaporation that is conducted at such low pressures that the distance between the hot and condensing surfaces is less than the mean free path of the molecules. Each unit is a single stage, but several units in series are commonly employed. Molecular distillation is applied to thermally sensitive high molecular weight materials in the range of 250-1200 molecular... 

Three processes were compared for volatile extraction from fat matrix high vacuum degassing, cold-finger molecular distillation, and reduced pressure steam distillation. 

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