Solexol process

The Solexol process is similar to propane deasphalting. It was developed a few years later for the purification and separation of vegetable and fish oils 

In November, 1946, M. W. Kellogg Company, engineers and contractors of petroleum and chemical plants, announced to industry a solvent process for treating glyceride oils. Given the name Solexol, it was a development of a process used extensively throughout the world to fractionate lubricating oils from crude petroleum residues. The solvent used in the process is ordinary propane, familiar as liquefied petroleum gas or bottled gas.  

The separations performed in Solexol pilot plants, some of which were described in an article by H. J. Passino, are in many instances, little short of amazing, not only of themselves but in the infinite variety of things which have been done with a single solvent and in a single tower. However, in the almost five years since the announcement there has been a scarcity of information on the extent to which sound commercial operations have borne out the promise for plant explorations. 

At this writing there are five commercial Solexol plants in regular service, and a sixth is under construction. Furthermore two of the Solexol units are supplemented by a continuous fractional crystallization (or winterizing) process, not heretofore announced, which goes by the name of Propane Destearnizing. As the name suggests, it also employs versatile propane as solvent. (Dickinson and Meyers, 1952.) 

Dickinson and Meyers go on to describe triglyceride refining plants, some of which operate at throughputs as high as 200,000 Ib/day. In the same vein of excitement as exhibited by the authors who wrote about propane deasphalting, the authors of the Solexol paper describe the properties of near-critical and supercritical propane and the ability to extend these properties to the development and, more importantly, to the commercialization of a propane refining process. 

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The promise shown by supercritical fluid extraction led to the development of the Solexol process for the purification and separation of vegetable and fish oils. This process concentrated the polyunsaturated triglycerides in vegetable oils and the so-called vitamin A values from fish oils using propane as a selective solvent [5]. 

Dickinson and Meyers, 1952). It too uses propane as a selective solvent and its purpose is to concentrate the polyunsaturated triglycerides (the so-called drying oils) in vegetable oils and to extract the vitamin-A values from fish oils. The Solexol process is described in two publications (Dickinson and Meyers, 1952 Passino, 1949). Compare some descriptive phrases from an early paper with contemporary SCF developments for the case of propane-lube oil refining. 

A schematic diagram of the Solexol processing of fish oils is shown in figure 7.4. The fish oils are fed to a train of countercurrent extractors where column-to-column variations in temperature as well as temperature variations within each specific column can affect the solvent power of propane in a manner similar to that seen with propane deasphalting. 

Figure 7.4 A schematic diagram of the Solexol process for separating fish oils (Dickinson and Meyers, 1952).

Soave-Redlich-Kwong equation of state. 111 Soft lens monomer, 285 Solexol process, 150-152 Solid-gas equilibria, 55, 131 Solid-liquid behavior, 106 Solid-liquid-vapor (SLV), 28, 46, 49, 52, 55, 57, 104, 129, 130... 

Solexol process (3, 77, 134). The critical solution temperatures with propane of the various constituents of the oils and their solubilities at higher temperatures are sufficiently different to permit their separation in part. By increasing the temperature of a propanc-oil solution in stepwise fashion, the solubilities of the various oil constituents in groups are exceeded one by one, and they can be removed in the order of their molecular complexity or molecular weight. Thus, for example, a scheme for fractionating a sardine oil is outlined in Fig. 11.22 (134), whereby the oil is decolorized and separated into fractions of different degrees of unsaturation and a vitamin... 

Solexol process refining of sardine oil (134). Courtesy, American Chemical... 

As far as the authors are aware the only other extraction process with a near-critical solvent to come into use in the period 1924-1960 was the Solexol process for the purification of vegetable and fish oils using compressed propane [60-64]. (The underlying principles for this process are identical to those for the propane de-asphalting process.) In 1952 it appears that about five commercial Solexol plants were in service [45]. The present position is not quite so clear [65]. 

Passino, H.J. (1949) The solexol process. Industrial Engineering Chemistry Research, 41, 280. 

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