Solvent Treating or Extraction Processes

Just as vacuum distillation permits e processing of black crude oils for lubricants, so the solvent processes tend to erase the old crude oil marketing system by which only a few crude oils were considered satisfactory for lubricant manufacture. By solvent methods, the original properties of the oil can be changed so that a uniform grade of oil can be manufactured from a wide variety of crude oils. Of the many processes that have been proposed it liow appears that the Furfural, Duo-Sol, Phenol, Edeleanu, and Propane processes have established their usefulness. Table 11-1 indicates the extent of solvent operations. However, if improvement of 

Processes Percentage (approx.) Bpd Number of plants (approx.) 

Although solvent processes have been applied primarily to lubricating oils, the increasing usefulness of these processes in separating hydrocarbons from one another (Fig. 20-16), particularly in connection with fractionation, should not be overlooked, nor the application of solvent extraction to the purification of gasoline, kerosene, diesel fuel, solvents, butadiene (Fig. 20-16), etc. ° Originally refiners sought to learn how 

Foster, A. L., Vacuum Distillation, Chemical Treatment Make Quality Lubricating Oils, Oil Gas J., Sept. 28, 1946, p. 78. 

Saegebarth et al.. High Octane Number Blending Stocks. . . Solvent Extraction, Ref. Nat. Gaso. Mfr., June, 1937, p. 256. 

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Almost all solvent solutions used in solvent extraction processes require treatment, either before their initial use or after being stripped of the extracted species. After preparation of the solvent by mixing appropriate amounts of extractant, modifier, and diluent, the solution is treated by contacting with an appropriate aqueous solution before entering the extraction stage. Such pretreatment is generally referred to as equilibration of the solvent. 

Acid soluble rare earth salt solution after the removal of cerium may be subjected to ion exchange, fractional crystalhzation or solvent extraction processes to separate individual rare earths. Europium is obtained commercially from rare earths mixture by the McCoy process. Solution containing Eu3+ is treated with Zn in the presence of barium and sulfate ions. The triva-lent europium is reduced to divalent state whereby it coprecipitates as europium sulfate, EuS04 with isomorphous barium sulfate, BaS04. Mixed europium(ll) barium sulfate is treated with nitric acid or hydrogen peroxide to oxidize Eu(ll) to Eu(lll) salt which is soluble. This separates Eu3+ from barium. The process is repeated several times to concentrate and upgrade europium content to about 50% of the total rare earth oxides in the mixture. Treatment with concentrated hydrochloric acid precipitates europium(ll) chloride dihydrate, EuCb 2H2O with a yield over 99%. 

In this context, extraction means any process by which a fluid (air or water) comes into contact with a material to which the pollutant has an affinity. The affinity can be a physical trapping modified by some form of surface energy or a solvent extraction process based on enthalpic principles. The result is that the fluid is pumped through the sorption medium and the pollutant is reduced or eliminated from the fluid. Despite limitations, the most common sorption medium is activated charcoal — a form of charcoal treated with oxygen to open millions of tiny pores between the carbon atoms. It is amorphous and is characterized by high adsorptivity for many gases and vapors. 

Now, depending on the extraction process, and what is begin extracted, the filtered solvent mixture is either treated with chemical reagents, filtered, and then evaporated, or simply evaporated to remove the solvent and leave behind the extracted substance. In some cases, this step can be quite complex, as some extraction process require treatment with multiple reagents, titrations, filtrations, ect., in order to facilitate proper extraction. It should be noted that exact instructions will be given for each extraction process where applicable. 

Mechanical expression of rice bran yields less oil, 10-12%, than solvent extraction, 16-18%. Rice bran is treated with steam and dried prior to pressure expression. Prepressing is usually carried out at 70 kg/cm followed by oil expulsion at 105-316 kg/cm (9). As a result of the low yield of oil from mechanical extraction, residual oil in the bran is recovered with hexane. Hexane extraction can be performed by batch or a continuous operation. Continuous operation uses countercurrent flow to improve mass transfer. Solvent extraction at high temperatures results in higher crude oil yield, but the crude oil is of lower quality. A new oil-extraction process, which involves premolding of rice bran at 14% moismre content and <40°C followed by hexane extraction at <15°C, was reported to yield a light-colored crude oil with no wax (9). 

The process may be operated continuously. The end result of the solvent extraction process is to separate the original solution into two streams a treated stream or raffinate, and a recovered solute stream, which may contain small amounts of water and solvent. Therefore, solvent extraction is a recovery process, because the solute chemicals are generally recovered for reuse, resale, further treatment, or disposal. 

A liquid-liquid extraction process produces a solvent-rich stream called the extract that contains a portion of the feed and an extracted-feed stream called the raffinate. A commercial process almost always includes two or more auxiliary operations in adcfition to the extraction operation itself. These extra operations are needed to treat the extract and raffinate streams for the purposes of isolating a desired product, recovering the solvent for recycle to the extractor, and purging unwanted components from the process. A typical process includes two or more distillation operations in addition to extraction. 

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