Continuous solvent extraction

Inks, another contaminant of secondary fibers, may be removed by heating a mixture of secondary fibers with surfactants. The removed inks are then dispersed in an aqueous medium to prevent redeposition on the fibers. Continuous solvent extraction has also been used to recover fibers from paper and board coated with plastics or waxes. 

Because of the diversity of contacting equipment available, it is unlikely that all these contactors will be available in any one laboratory or pilot plant. Consequently, unless test work is carried out on similar contactors, the system may not be optimized. Since mixer-settlers are the easiest to construct, are simple to operate, and require little room and low-flow rates, these contactors are, in many cases, the only ones used to investigate a continuous solvent extraction process. This is by no means ideal and may result in abandonment of a process that, using another type of contactor, could be found to be entirely satisfactory. 

Fig. 13.2 General scheme of a continuous solvent extraction contactor.

Staff, Continuous solvent extraction The early beginnings of a giant industry, J. Am. Oil Chem. Soc., 54, 202A-207A (1977). 

Davis, S.S., Elson, G., Tomlinson, E., Harrison, G., Dearden, J.C. (1976) The rapid determination of partition coefficient data using a continuous solvent extraction system. (AKUFVE). Chem. Ind. (London), 16, 677-683. de Kreuk, J.F., Hanstveit, A.O. (1981) Determination of the biodegradabUity of the organic fraction of chemical wastes. Chemosphere 10, 561-575. 

Hydraulic press oil mills remained in use as late as the 1950s before the last of them were replaced with continuous screw presses and continuous solvent extraction plants, both of which required far less labor and could process at much higher rates. 

In 1951, the V.D. Anderson Company was again the pioneer in mechanical screw pressing, being first to patent the process of using a mechanical screw press to continuously prepress oleaginous materials ahead of continuous solvent extraction plants. The company was awarded U.S. Patent 2,551,254 (5). 

The American company, French Oil Mill Machinery Company of Piqua, Ohio, developed continuous solvent extraction plants starting in 1939, using a multistage BoUman-type percolation extractor (3). Soon thereafter, the Belgian Company, Extraction De Smet, started manufacturing continuous multistage belt-type extractors in 1945. V.D. Anderson of Cleveland, Ohio, joined the solvent extraction equipment supply market in 1948 with continuous HUdebrandt-type immersion extractors (5). 

A small-scale chain conveyor type of extractor was developed in the 1940s at Iowa State University with the intent of using trichloroethylene solvent to extract soybeans. Crown Iron Works of Minneapolis, Minnesota, licensed the technology and extractor design, and supplied several continuous solvent extraction plants in 1951 using the new extractor and trichloroethylene solvent (6). The meal from these plants proved detrimental to animals, so the plants were either closed or converted to petroleum-based solvents (7). The chain-type extractor apparatus continued on and is the basis of the modern Crown Iron Works Model III extractor used today. 

In the first continuous solvent extraction plants in Germany, the meal was desolventized in Schnecken s desolventizers. The Schnecken s desolventizer design consisted of a series of steam-jacketed conveyors, stacked one above the other, which used indirect heat to desolventize the meal. This was the prevalent meal desolventizer design used by all equipment suppliers through the 1940s. 

When the distribution ratio is not highly favorable, it is still possible to obtain a quantitative and selective separation through the use of a countercurrent liquid extraction approach. Although such approaches are no longer practical, having largely been supplanted by instrumental techniques such as preparative HPLC and continuous solvent extraction, countercurrent separations are conceptually useful. These approaches can be applied to preliminary separation of complex mixtures or in the isolation of compounds that do not perform well in LC because of undesirable interaction with the stationary phase (irreversible adsorption, denaturation, etc.). For these reasons, most applications of countercurrent separations involve the isolation of natural or biochemical products from plant or animal extracts. As will be described below, countercurrent extractions form the theoretical basis for LLE cartridges. 

Process choice depends very much on raw material type and required plant capacity continuous solvent extraction is often the method of choice for high throughput. Direct solvent extraction is particularly used for seeds that are low in oil, such as soya. 

Further improve simulation of continuous solvent extraction by removing only the full miscella from the first extraction stage and recycling the other miscellas to the next extraction sequence by advancing by one stage. Use fresh solvent only at... 

Hydrometallurgical recovery Continued) solvent extraction, 192-194 polishing powders, 201—202... 

The choice of process depends, as stated, on the type of raw material but also on the desired plant capacity. Continuous solvent extraction plants are supplied for daily seed throughput of 100 to 3000 tonnes. The first three processes listed and batch solvent extraction can be used for less than 100 tonnes per day. 

Small-scale solvent extraction is often done batchwise in separation funnels or test tubes. However, for more elaborate extraction studies and industrial processes continuous extraction is usually preferred. All continuous solvent extraction equipment consists of a mixer for phase contact and mass transfer and a separation part for phase disengagement. The main types of continuously working apparatus are ... 

Luigi, Continuous Solvent Extraction of Oilseeds and Lecithin Production, Iwgi Express fofor-... 

R. Y. LYON, ITie Use of Neutron Detectors in Continuous Solvent Extraction Control, ISO-SA-28 (October 7, 1966). 

R.H. AtaUah, J. Ruzicka, G. Christian, Continuous solvent extraction in a closed-loop system. Anal. Chem. 

Column end heating can be an effective method for removing organic mobile phases such as w-hex-ane, but is not very effective for reverse phase separations that employ aqueous mobile phases. One method used to remove solutes from aqueous mobile phases is by extracting them into an organic solvent followed by solute deposition on an IR transparent substrate and solvent evaporation. However, on-line continuous solvent extraction greatly complicates LC-IR interfaces. 

The analysis of volatiles is generally accomplished by an extraction step, followed by concentration, chromatographic separation, and subsequent detection. Well-established methods of analysis include solvent extraction, static and dynamic headspace sampling, steam distillation with continuous solvent extraction, and supercritical fluid extraction. An overview of sample preparation methods is provided by Teranishi (2). The chromatographic profile will vary depending upon the method of sample preparation employed, and it is not uncommon to produce artifacts during this step (3,4). Thermally labile compounds may decompose in the heated zones of instruments to produce a chromatographic profile that is not truly representative of the sample. 

Kawa.se, J., M. Yamanaka, Continuous solvent-extraction method for the spectrophotometric determination of cationic surfactants. Analyst, 1979,104, 750-755. 

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