Extraction processes raffinate

Fig. 9. Schematic diagram of a UOP Sorbex process. D, E, F, R, and. f represent flow rates for desorbent, extract, feed, raffinate, and net sobds.

A schematic diagram of a six-vessel UOP Cyclesorb process is shown in Figure 15. The UOP Cyclesorb process has four external streams feed and desorbent enter the process, and extract and raffinate leave the process. In addition, the process has four internal recycles dilute raffinate, impure raffinate, impure extract, and dilute extract. Feed and desorbent are fed to the top of each column, and the extract and raffinate are withdrawn from the bottom of each column in a predeterrnined sequence estabUshed by a switching device, the UOP rotary valve. The flow of the internal recycle streams is from the bottom of a column to the top of the same column in the case of dilute extract and impure raffinate and to the top of the next column in the case of dilute raffinate and impure extract. 

The purified acid is recovered from the loaded organic stream by contacting with water in another countercurrent extraction step. In place of water, an aqueous alkafl can be used to recover a purified phosphate salt solution. A small portion of the purified acid is typically used in a backwashing operation to contact the loaded organic phase and to improve the purity of the extract phase prior to recovery of the purified acid. Depending on the miscibility of the solvent with the acid, the purified acid and the raffinate may be stripped of residual solvent which is recycled to the extraction loop. The purified acid can be treated for removal of residual organic impurities, stripped of fluoride to low (10 ppm) levels, and concentrated to the desired P2 s Many variations of this basic scheme have been developed to improve the extraction of phosphate and rejection of impurities to the raffinate stream, and numerous patents have been granted on solvent extraction processes. 

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. 

A beryUium concentrate is produced from the leach solution by the counter-current solvent extraction process (10). Kerosene [8008-20-6] containing di(2-ethylhexyl)phosphate [298-07-7] is the water-immiscible beryUium extractant. The slow extraction of beryUium at room temperature is accelerated by warming. The raffinate from the solvent extraction contains most of the aluminum and aU of the magnesium contained in the leach solution. 

The feed to a liquid-liquid extraction process is the solution that contains the components to be separated. The major liquid component in the feed can be referred to as the feed solvent. Minor components in solution are often referred to as solutes. The extraction solvent, or just plain solvent, is the immiscible liquid added to a process for the purpose of extracting a solute or solutes from the feed. The extraction-solvent phase leaving a liquid-liquid contactor is called the extract. The raffinate is the liquid phase left from the feed after being contacted by the second phase. A wash solvent is a hquid added to a liquid-liquid fractionation process to wash or enrich the purity of a solute in the extract phase. 

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. 

In order to illustrate the critical process parameters of SMB process validation, we will consider the separation of the racemic drug as described in Process design. The study represents the effect of the influence of feed concentration, number of plates and retention factor on the second eluting enantiomer. The simulation of the process for different values of feed concentration is performed and the variations of the extract and raffinate purities are shown in Fig. 10.10. 

A target purity of 99 % was established for both extract and raffinate. According to the simulation results, one can predict that a variation of the feed concentration range between 7.5 and 11 g will meet the required purity. The system was designed for a feed concentration equal to 10 g The influence of change in feed concentration on the purity of both extract and raffinate illustrates the robustness of SMB, and that the process tolerates fluctuations when critical parameters are stressed during process validation. 

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). 

The products of the solvent extraction process are tantalum strip solution, niobium strip solution and raffinate - liquid wastes containing impurities and residual acids. 

The raffinate from the selective extraction process contains mostly niobium. The tantalum extract is treated by steam stripping to obtain a tantalum strip solution. The method results in the effective separation and relatively high concentration of tantalum and niobium in the respective strip solutions. 

Some coffee companies use methylene chloride to take the caffeine out of regular coffee (and you drink that stuff ). In this solvent extraction process, what do you think are the solvent, the raffinate, the extract, and the feed ... 

Raffinate. In extraction processes, the stream that has had the extracted material removed from it is called raffinate, in contrast to the other produced stream, the extract. Usually associated with aromatics extraction from naphtha streams. 

The third desorbent characteristic is that the desorbent material must be easily separated from the two Sorbex process products extract and raffinate. The adsorbent chamber s composition profile produces extract and raffinate streams comin-gled with desorbent. In order for the process to be economical, the separation of the feed components from the desorbent (achieved through fractionation) is set by the boiling point differences between the species. Depending on the selectivity possessed by the desorbent over that of the feed normals, the subsequent desorbent rates needed to flush feed normal paraffins from the adsorbent s selective volume and the resulting extract or raffinate streams from the Sorbex chambers could contain in some cases more than 50% desorbent. High concentration of desorbent demonstrates the importance of the desorbent characteristics when selecting a desorbent. 

The fifth and final desorbent characteristic is that the desorbent must not react with any feed components that would impart any negative characteristics on either the final extract and raffinate streams. This is important not only for the desired paraffin product purity but also for retaining the desorbent inventory. Therefore, a desorbent s reactivity must be quantified early in the desorbent selection process. 

Unlike the gasoline Molex process that employs a iso-butane and n-butane desorbent mixture, the MaxEne process employs a heavy desorbent system. A heavy desorbent system means that the bottom product from both the Sorbex extract and raffinate frachonation columns is desorbent while the feed components are recovered as overhead products. In the MaxEne process case, heavy normal paraffin such as n-dodecane is employed as the desorbent though desorbents as light as n-decane and as heavy as n-tetradecane are possible candidates too. 

The nomenclature used in solvent extraction has been defined in Chapter 1 and is illustrated in Fig. 8.1. Not all of the steps shown in this figure will be found in every extraction process, but equally there may be occasions where it is necessary to add additional steps for example, to recover the extractant from the scrub raffinate. So while Fig. 8.1 is not a completely general flow diagram it covers most of the processes likely to be found in practice. Variations of this flow sheet will become apparent during the remaining chapters. 

Raffinate A term used to describe the material recovered from an extraction process. Examples of refinery raffinates include lubestock recovered from furfural or methylpyrrolidone extraction and kerosene recovered from S02 extraction. Furfural, methylpyrrolidone, and S02 extraction processes are employed to remove aromatic compounds. 

Figure 3 also illustrates the rapid growth of lubricating oil solvent extraction processes. From the point of view of popularity, furfural, phenol, and the Duosol processes are outstanding. Most of the recent developments have been improvements in the solvent recovery systems to minimize solvent consumption, to reduce costs, and in the treater sections, to increase raffinate yield. 

Solvent losses constitute an expensive item which must be predicted when designing and evaluating commercial solvent extraction processes. A solvent make-up cost of 250,000 annually would not be unusual for a large lubricating oil solvent extraction plant of this loss, it is likely that only 40 to 60% would be found in the residual streams from raffinate and extract strippers. The balance would disappear as leakage, decomposition, and unexpected upset losses. 

Controls other than those of flow and level also may be needed in some cases, of which examples are on Figure 3.17. The scheme of part (a) maintains the flow rate of solvent in constant ratio with the main feed stream, whatever the reasons for variation in flow rate of the latter stream. When there are fluctuations in the composition of the feed, it may be essential to adjust the flow rate of the solvent to maintain constancy of some property of one or the other of the effluent streams. Figure 3.17(b) shows reset of the solvent flow rate by the composition of the raffinate. The temperature of an extraction process ordinarily is controlled by regulating the temperatures of the feed streams. Figure 3.17(c) shows the... 

Use of reflux is most effective with Type II systems since then essentially pure products on a solvent-free basis can be made. In contrast to distillation, however, extraction with reflux rarely is beneficial, and few if any practical examples are known. A related kind of process employs a second solvent to wash the extract countercurrently. The requirements for this solvent are that it be only slighly soluble in the extract and easily removable from the extract and raffinate. The sulfolane process is of this type it is described, for example, by Treybal (1980) and in more detail by Lo et al. (1983, pp. 541-545). 

Modolo, G., Asp, H., Vijgen, H. et al. 2008. Demonstration of a TODGA-based continuous counter-current extraction process for the partitioning of actinides from a simulated PUREX raffinate, PartB Centrifugal contactor runs. Solvent Extr. Ion Exch. 26 (1) 62-76. 

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