Process extraction

Distillate is brought in contact with the solvent, and aromatics and polars are preferentially dissolved in the solvent phase. Saturates do not dissolve and remain in the hydrocarbon or dispersed phase. The hydrocarbon phase is lower in density than the solvent phase and rises as bubbles through the continuous phase. After separation the raffinate and extract solution are sent to their respective solvent recovery sections. Integration of a hydrofiner on the raffinate product is in some lube plants for heat integration because this eliminates the need for an additional hydrofiner furnace. 

An example of a typical rotating disc contactor is shown below. 

There are several factors that affect extraction efficiency and in general the efficiency depends on the mixing/settling and coalescence characteristics of the system. Important factors include  

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Catacarb process An extraction process used to remove carbon dioxide from process gases by scrubbing the hot gases with potassium carbonate solution containing additives which increase the hydration rate of the gas in the solution. The Vetrocoke process is similar. See Benfield process. 

Edeleanu process An extraction process utilizing liquid sulphur dioxide for the removal of aromatic hydrocarbons and polar molecules from petroleum fractions. 

There are of course liquid-liquid equilibria between hydrocarbons and substances other than water. In practice these equilibria are used in solvent extraction processes. The solvents most commonly used are listed as follows ... 

The extraction processes are based on the property of these solvents to dissolve preferentially hydrocarbons of a certain chemical nature. 

Hydrorefining can substitute for extraction processes such as furfural where it integrates perfectly into the conventional process scheme. 

Fig. 1. Exit route of xenon in simulations of the extraction process. The xenon atom is solid black. The atoms of the residues surrounding the exit path are shown a.s spheres, and the protein backbone is shown as a thin curve. On the left, the xenon is viewed through the exit between residues on the right, the view is from (ho side and the direction of the tug is marked with a line.

A linear dependence approximately describes the results in a range of extraction times between 1 ps and 50 ps, and this extrapolates to a value of Ws not far from that observed for the 100 ps extractions. However, for the simulations with extraction times, tg > 50 ps, the work decreases more rapidly with l/tg, which indicates that the 100 ps extractions still have a significant frictional contribution. As additional evidence for this, we cite the statistical error in the set of extractions from different starting points (Fig. 2). As was shown by one of us in the context of free energy calculations[12], and more recently again by others specifically for the extraction process [1], the statistical error in the work and the frictional component of the work, Wp are related. For a simple system obeying the Fokker-Planck equation, both friction and mean square deviation are proportional to the rate, and... 

Attention is directed to the great advantage of continuous extraction over manual shaking in a separatory funnel for liquids or for solutions which tend to froth or which lead to emulsification comparatively little difficulty is experienced in the continuous extraction process. 

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

Extraction of metal ions Extraction processes Extraction resistance Extractive distillation... 

Caustic Soda. Diaphragm cell caustic is commercially purified by the DH process or the ammonia extraction method offered by PPG and OxyTech (see Fig. 38), essentially involving Hquid—Hquid extraction to reduce the salt and sodium chlorate content (86). Thus 50% caustic comes in contact with ammonia in a countercurrent fashion at 60°C and up to 2500 kPa (25 atm) pressure, the Hquid NH absorbing salt, chlorate, carbonate, water, and some caustic. The overflow from the reactor is stripped of NH, which is then concentrated and returned to the extraction process. The product, about 62% NaOH and devoid of impurities, is stripped free of NH, which is concentrated and recirculated. MetaUic impurities can be reduced to low concentrations by electrolysis employing porous cathodes. The caustic is then freed of Fe, Ni, Pb, and Cu ions, which are deposited on the cathode. 

The component C in the separated extract from the stage contact shown in Eigure 1 may be separated from the solvent B by distillation (qv), evaporation (qv), or other means, allowing solvent B to be reused for further extraction. Alternatively, the extract can be subjected to back-extraction (stripping) with solvent A under different conditions, eg, a different temperature again, the stripped solvent B can be reused for further extraction. Solvent recovery (qv) is an important factor in the economics of industrial extraction processes. 

Extraction, a unit operation, is a complex and rapidly developing subject area (1,2). The chemistry of extraction and extractants has been comprehensively described (3,4). The main advantage of solvent extraction as an industrial process Hes in its versatiHty because of the enormous potential choice of solvents and extractants. The industrial appHcation of solvent extraction, including equipment design and operation, is a subject in itself (5). The fundamentals and technology of metal extraction processes have been described (6,7), as has the role of solvent extraction in relation to the overall development and feasibiHty of processes (8). The control of extraction columns has also been discussed (9). 

Supercritical Extraction. The use of a supercritical fluid such as carbon dioxide as extractant is growing in industrial importance, particularly in the food-related industries. The advantages of supercritical fluids (qv) as extractants include favorable solubiHty and transport properties, and the abiHty to complete an extraction rapidly at moderate temperature. Whereas most of the supercritical extraction processes are soHd—Hquid extractions, some Hquid—Hquid extractions are of commercial interest also. For example, the removal of ethanol from dilute aqueous solutions using Hquid carbon dioxide... 

Table 4. Extractive Processes for the Separation of Benzene—Toluene—Xylene Mixture from Light Feedstocks ...

Extraction of C-8 Aromatics. The Japan Gas Chemical Co. developed an extraction process for the separation of -xylene [106-42-3] from its isomers using HF—BF as an extraction solvent and isomerization catalyst (235). The highly reactive solvent imposes its own restrictions but this approach is claimed to be economically superior to mote conventional separation processes (see Xylenes and ethylbenzene). 

Anhydrous Acetic Acid. In the manufacture of acetic acid by direct oxidation of a petroleum-based feedstock, solvent extraction has been used to separate acetic acid [64-19-7] from the aqueous reaction Hquor containing significant quantities of formic and propionic acids. Isoamyl acetate [123-92-2] is used as solvent to extract nearly all the acetic acid, and some water, from the aqueous feed (236). The extract is then dehydrated by azeotropic distillation using isoamyl acetate as water entrainer (see DISTILLATION, AZEOTROPIC AND EXTRACTIVE). It is claimed that the extraction step in this process affords substantial savings in plant capital investment and operating cost (see Acetic acid and derivatives). A detailed description of various extraction processes is available (237). 

Fractional extraction has been used in many processes for the purification and isolation of antibiotics from antibiotic complexes or isomers. A 2-propanol—chloroform mixture and an aqueous disodium phosphate buffet solution are the solvents (243). A reciprocating-plate column is employed for the extraction process (154). 

Other Metals. Because of the large number of chemical extractants available, virtually any metal can be extracted from its aqueous solution. In many cases extraction has been developed to form part of a viable process (275). A review of more recent developments in metal extraction including those for precious metals and rare earths is also available (262). In China a complex extraction process employing a cascade of 600 mixer—settlers has been developed to treat leach Hquor containing a mixture of rare earths (131). 

The depressed prices of most metals in world markets in the 1980s and early 1990s have slowed the development of new metal extraction processes, although the search for improved extractants continues. There is a growing interest in the use of extraction for recovery of metals from effluent streams, for example the wastes from pickling plants and electroplating (qv) plants (276). Recovery of metals from Hquid effluent has been reviewed (277), and an AM-MAR concept for metal waste recovery has recentiy been reported (278). Possible appHcations exist in this area for Hquid membrane extraction (88) as weU as conventional extraction. Other schemes proposed for effluent treatment are a wetted fiber extraction process (279) and the use of two-phase aqueous extraction (280). 

In general, the foUowing steps can occur in an overall Hquid—soHd extraction process solvent transfer from the bulk of the solution to the surface of the soHd penetration or diffusion of the solvent into the pores of the soHd dissolution of the solvent into the solute solute diffusion to the surface of the particle and solute transfer to the bulk of the solution. The various fundamental mechanisms and processes involved in these steps make it impracticable or impossible to describe leaching by any rigorous theory. 

The overall extraction process is sometimes subdivided into two general categories according to the main mechanisms responsible for the dissolution stage (/) those operations that occur because of the solubiHty of the solute in or its miscibility with the solvent, eg, oilseed extraction, and (2) extractions where the solvent must react with a constituent of the soHd material in order to produce a compound soluble in the solvent, eg, the extraction of metals from metalliferous ores. In the former case the rate of extraction is most likely to be controUed by diffusion phenomena, but in the latter the kinetics of the reaction producing the solute may play a dominant role. 

Separation of a fat or oil from its source material can be accompHshed by several different methods. Selection of an extraction process is based on (/) obtaining oil substantially undamaged and relatively free of undesirable impurities, (2) achieving the highest practical yield, and (J) obtaining the maximum economic return on the oil and coproducts. 

A. P. Lama2e and D. Charquet, in K. C. Liddell and co-workers, eds.. Refractory Metals Extraction, Processing and Applications, The Minerals, Metals Materials Society, Warrendale, Pa., 1990, pp. 231—253. 

The solution leaving the flotation cell, containing about 0.4 g/L iodine, is sent to a kerosene solvent extraction process to recover the dissolved product. After neutralization with soda ash to the initial incoming alkalinity, the solution is returned to the nitrate lixiviation process. The iodine-chaiged kerosene is contacted with an acidic concentrated iodide solution containing SO2, which reduces the iodine to iodide. 

Pentanedione is widely used in extraction processes for the separation and purification of metals because of its abiUty to form covalent metal chelates. It is also used as an intermediate in the production of heterocycHc substances and dyes, as a fuel additive (324), and in metal plating and resin modification. 

Liquid—Liquid Extraction. The tiquid—tiquid extraction process for the rare-earth separation was discovered by Fischer (14). Extraction of REE using an alcohol, ether, or ketone gives separation factors of up to 1.5. The selectivity of the distribution of two rare-earth elements, REI and RE2, between two nonmiscible tiquid phases is given by the ratio of the distribution coefficients DI and D2 ... 

Battery breaking technologies use wet classification to separate the components of cmshed batteries. Before cmshing, the sulfuric acid is drained from the batteries. The sulfuric acid is collected and stored for use at a later stage in the process, or it may be upgraded by a solvent extraction process for reuse in battery acid. 

The electrowinning process developed by Ginatta (34) has been purchased by M.A. Industries (Atlanta, Georgia), and the process is available for licensing (qv). MA Industries have also developed a process to upgrade the polypropylene chips from the battery breaking operation to pellets for use by the plastics industry. Additionally, East Penn (Lyons Station, Pennsylvania), has developed a solvent-extraction process to purify the spent acid from lead—acid batteries and use the purified acid in battery production (35). 

Pyrometallurgy. Metallurgy involved in winning and refining metals where heat is used, as in roasting and smelting. PyrometaHurgy is the oldest extractive process and is probably the most important. 

Production of a metal is usually achieved by a sequence of chemical processes represented as a flow sheet. A limited number of unit processes are commonly used in extractive metallurgy. The combination of these steps and the precise conditions of operations vary significantly from metal to metal, and even for the same metal these steps vary with the type of ore or raw material. The technology of extraction processes was developed in an empirical way, and technical innovations often preceded scientific understanding of the processes. 

The concentration of most metals in the earth s cmst is very low, and even for abundant elements such as aluminum and iron, extraction from common rock is not economically feasible. An ore is a metallic deposit from which the metal can be economically extracted. The amount of valuable metal in the ore is the tenor, or ore grade, usually given as the wt % of metal or oxide. Eor precious metals, the tenor is given in grams per metric ton or troy ounces per avoirdupois short ton (2000 pounds). The tenor and the type of metallic compounds are the main characteristics of an ore. The economic feasibihty of ore processing, however, depends also on the nature, location, and size of the deposit the availabihty and cost of a suitable extraction process and the market price of the metal. 

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