Distillation-extraction process

In the laboratory, a multi-stage liquid-liquid extraction can be performed by a simultaneous distillation-extraction process according to Likens-Nickerson [29] (Fig. 2.10). Here, the liquid matrix with the solute in one flask is evaporated together with an immiscible solvent in a second flask. Extraction takes place in the vapour phase where an intensive distribution of both phases is ensured. The condensed vapours from the two phases are separated via a siphon using their different densities and their reintroduction into the original flasks. As the distillation process is continued, extraction is repeated until the solute is exhausted in the original matrix. This method is very useful when traces of non-volatile solutes are present, which are only partly miscible... 

Vacuum can be applied in order to reduce thermal exposure. The cooling funnel requires a deep-freezing mixture. This extraction method can easily be transferred onto an industrial scale. An important application is essential oils in water where steam distillation is carried out. For the distillative extraction process, different water-immiscible solvents are used. Thermal deterioration and retrieval ratio in the solvent have been studied intensively for fragrance materials [30],... 

Oleoresln Capsicum - In a typical atmospheric pressure run, a quantity (1.A8 kg) of oleoresln was combined in a 12 1 round-bottomed flask with distilled water (6 1). Ether (200 ml) was used as extraction solvent. The steam distillation-extraction process was run for A hr. The resulting ether solution was dried (anhyd. sodium sulfate) and the ether distilled, leaving 2.A9 g of pepper components (containing 10% ether) 0,15% yield after correcting for residual solvent. 

Fresh Jalapeno Peppers - In a typical run, the peppers were quartered (5 kg) and added to boiling distilled water (5 1). The distillation-extraction process was run for four 2-hr periods, using freshly-distilled ether. A total yield of 0.1A3 g (0.0029%) was obtained after removal of solvent. 

Mixtures with low relative volatility or which exhibit azeotropic behavior. The most common means of dealing with the separation of low-relative-volatility and azeotropic mixtures is to use extractive or azeotropic distillation. These processes are considered in detail later. Crystallization and liquid-liquid extraction also can be used. 

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

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. 

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). 

The early developments of solvent processing were concerned with the lubricating oil end of the cmde. Solvent extraction processes are appHed to many usefiil separations in the purification of gasoline, kerosene, diesel fuel, and other oils. In addition, solvent extraction can replace fractionation in many separation processes in the refinery. For example, propane deasphalting (Fig. 7) has replaced, to some extent, vacuum distillation as a means of removing asphalt from reduced cmde oils. 

Solvent Extraction. Extraction processes, used for separating one substance from another, are commonly employed in the pharmaceutical and food processing industries. Oilseed extraction is the most widely used extraction process on the basis of tons processed. Extraction-grade hexane is the solvent used to extract soybeans, cottonseed, com, peanuts, and other oilseeds to produce edible oils and meal used for animal feed supplements. Tight specifications require a narrow distillation range to minimize solvent losses as well as an extremely low benzene content. The specification also has a composition requirement, which is very unusual for a hydrocarbon, where the different components of the solvent must be present within certain ranges (see Exthaction). 

After mixing, the solvent and waste are separated. The solvent with dissolved organics is called the extract. The waste remaining after extraction is called the raffinate. The extract may be sent to a distillation or steam stripping unit to separate the dissolved organics from the solvent and the solvent can be recycled back to the extraction process. The raffinate may require additional treatment or may be disposed or incinerated. 

Extraction and Extractive Distillation. The choice of an extraction or extractive distillation solvent depends upon its boiling point, polarity, thermal stabiUty, selectivity, aromatics capacity, and upon the feed aromatic content (see Extraction). Capacity, defined as the quantity of material that is extracted from the feed by a given quantity of solvent, must be balanced against selectivity, defined as the degree to which the solvent extracts the aromatics in the feed in preference to paraffins and other materials. Most high capacity solvents have low selectivity. The ultimate choice of solvent is deterrnined by economics. The most important extraction processes use either sulfolane or glycols as the polar extraction solvent. 

Fig. 7. Shell sulfolane extraction process. E, extraction ED, extractive distillation RC, recovery column.

The oxime is converted to caprolactam by Beckmann rearrangement neutralization with ammonia gives ca 1.8 kg ammonium sulfate per kilogram of caprolactam. Purification is by vacuum distillation. A no-sulfate, extraction process has been described, but incineration of the ammonium bisulfate recovers only sulfur values and it is not practiced commercially (14). 

Recoverability. The extrac tion solvent must usually be recovered from the extract stream and also from the raffinate stream in an extraction process. Since distillation is often used, the relative volatility of the extraction-solvent to nonsolvent components should be significantly greater or less than unity. A low latent heat of vaporization is desirable tor a volatile solvent. 

Distillation, extractive distillation, liquid-liquid extraction and absorption are all techniques used to separate binary and multicomponent mixtures of liquids and vapors. Reference 121 examines approaches to determine optimum process sequences for separating components from a mixture, primarily by distillation. 

Liquid solvents are used to extract either desirable or undesirable compounds from a liquid mixture. Solvent extraction processes use a liquid solvent that has a high solvolytic power for certain compounds in the feed mixture. For example, ethylene glycol has a greater affinity for aromatic hydrocarbons and extracts them preferentially from a reformate mixture (a liquid paraffinic and aromatic product from catalytic reforming). The raffinate, which is mainly paraffins, is freed from traces of ethylene glycol by distillation. Other solvents that could be used for this purpose are liquid sulfur dioxide and sulfolane (tetramethylene sulfone). 

Removal of reaction products can shift the equilibrium, forcing the reaction to go to completion. This can be effected by evaporation of products from the reaction mixture (reactive distillations), extraction (including supercritical extraction) of products from the reaction mixture (reactive extractions), or membrane processes. Counter- and cocurrent operation also falls within this category. If the reaction is equilibrium-limited or inhibited by reaction products countercurrent operation outperforms cocurrent operation. 

In liquid-solid extraction (LSE) the analyte is extracted from the solid by a liquid, which is separated by filtration. Numerous extraction processes, representing various types and levels of energy, have been described steam distillation, simultaneous steam distillation-solvent extraction (SDE), passive hot solvent extraction, forced-flow leaching, (automated) Soxh-let extraction, shake-flask method, mechanically agitated reflux extraction, ultrasound-assisted extraction, y -ray-assisted extraction, microwave-assisted extraction (MAE), microwave-enhanced extraction (Soxwave ), microwave-assisted process (MAP ), gas-phase MAE, enhanced fluidity extraction, hot (subcritical) water extraction, supercritical fluid extraction (SFE), supercritical assisted liquid extraction, pressurised hot water extraction, enhanced solvent extraction (ESE ), solu-tion/precipitation, etc. The most successful systems are described in Sections 3.3.3-3.4.6. Other, less frequently... 

Figure 3.2 The three-step Soxhlet extraction process of the Soxtec extraction system (a) solubilisation of extractable matter from sample immersed in boiling solvent (b) rinsing of extracted solid and (c) concentration of extracted sample and collection of distilled solvent for reuse or disposal. Reproduced by permission of FOSS Analytical A/S, Hillerdd...

Not all of the classical extraction processes are suitable for ultrasonic enhancement. For example, among the existing techniques used to obtain bio-active extracts from plant material (direct distillation, water steam distillation, organic solvent extraction, maceration, cold/hot fat extraction, etc.) [195] the water steam distillation is not amenable to ultrasonic enhancement. 

In some processes, a component may be recycled around two or more units in a closed loop. For example, the solvent in an absorption or liquid extraction process will normally be recovered by distillation and recycled. In this situation it will be necessary to introduce the solvent as a pseudo fresh-feed and the to remove it from the recycle loop by introducing a dummy stream divider, purging one stream. 

CAA [Cuprous ammonium acetate] A general process for separating alkenes, di-alkenes, and alkynes from each other by extraction of their cuprous complexes from aqueous cuprous ammonium acetate into an organic solvent. Exxon used it for separating C4 fractions containing low concentrations of butadiene. The liquid-liquid extraction processes for butadiene have all been replaced by extractive distillation processes. 

Dualayer Distillate A process for extracting organic acids from petroleum fractions, using an aqueous solution of sodium cresylate. Developed by the Mobil Oil Company in the 1950s. 

An autocatalytic reaction may be able to proceed in. the absence of the catalyst. In some cases the catalytic product may be removed as it forms, by distillation, extraction, precipitation, or some other means. The process, A => B + P, may have the rate equation... 

In all extraction processes, the important feature is the selective nature of the solvent, in that the separation of compounds is based on differences in solubilities, rather than differences in volatilities as in distillation. In recent years, it has become possible to use computerised techniques to aid in the choice of a solvent with the required selectivity and to design appropriate molecular structures. 

Often it is called, reasonably enough, benzene concentrate or aromatics concentrate. Benzene concentrate is about 50% benzene, plus some other C5 s, Ce s, and Cys. All of them boil at about 176°F, the boiling point of benzene. Since the boiling temperature of the benzene is so close to that of the other hydrocarbons in the concentrate stream, simple fractionation is not a very effective way of isolating the benzene from benzene concentrate. Instead, one of two processes is used to remove the benzene, solvent extraction process or extractive distillation. The two differ in the primary mechanism they use. One operates on a liquid-liquid basis, the other on a vapor-liquid basis. 

Like the solvent extraction process, extractive distillation relies on the intimate contact of the liquid solvent and the aromatics concentrate vapors to allow the aromatics to be preferentially dissolved in the solvent. The usual list of solvents includes DEG (Diethylene glycol), TEG (Triethylene glycol), NMP (N-methyl pyrrolidone), or methyl formamide. 

When butadiene is produced in olefins plants or in refinery crackers, they come mixed with relatively large volumes of the other C4 family. Sometimes the other C4S need not be separated from each other, for example if they are going to be used for allcylation plant feed. In that case, the butadiene can be separated from the other C4S by extractive distillation. This process uses a solvent that will preferentially dissolve butadiene, ignoring the other components in the stream. 

As documented in Chapter 5, zeolites are very powerful adsorbents used to separate many products from industrial process steams. In many cases, adsorption is the only separation tool when other conventional separation techniques such as distillation, extraction, membranes, crystallization and absorption are not applicable. For example, adsorption is the only process that can separate a mixture of C10-C14 olefins from a mixture of C10-C14 hydrocarbons. It has also been found that in certain processes, adsorption has many technological and economical advantages over conventional processes. This was seen, for example, when the separation of m-xylene from other Cg-aromatics by the HF-BF3 extraction process was replaced by adsorption using the UOP MX Sorbex process. Although zeolite separations have many advantages, there are some disadvantages such as complexity in the separation chemistry and the need to recover and recycle desorbents. 

Solvent extraction processes usually run at ambient pressures and temperatures. If higher pressures are applied, it is mostly because a higher extraction temperature is required when equilibrium or mass transfer conditions are more favorable at an elevated temperature. Distillation, on the other hand, is usually carried out at higher temperatures and ambient pressures. To avoid thermal degradation, the pressure sometimes has to be lowered below ambient pressure. Distillation is based on the differences in vapor pressures of the components to be separated, whereas solvent extraction utilizes the differences in intermolecular interactions in the liquid phase. 

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