Raffinate stream

Xylene Isomerization. After separation of the preferred xylenes, ie, PX or OX, using the adsorption or crystallization processes discussed herein, the remaining raffinate stream, which tends to be rich in MX, is typically fed to a xylenes isomerization unit in order to further produce the preferred xylenes. Isomerization units are fixed-bed catalytic processes that are used to produce a close-to-equiUbrium mixture of the xylenes. To prevent the buildup of EB in the recycle loop, the catalysts are also designed to convert EB to either xylenes, benzene and lights, or benzene and diethylbenzene. 

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. 

W scrubs the extract free from the unwanted second solute. The second solute leaves the contac tor in the raffinate stream. 

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 case A the solvents are immiscible, so the rate of feed solvent alone in the feed stream F is the same as the rate of feed solvent alone in the raffinate stream R. In like manner, the rate of extraction solvent alone is the same in the stream entering S as in the extract stream leaving E (Fig. 15-12). The ratio of extraction-solvent to feed-solvent flow rates is therefore S /F = E /R. A material balance can be written around the feed end of the extrac tor down to any stage n (see Fig. 15-12) and then rearranged to a McCabe-Thiele type of operating line with a slope of F /S [Eq. (15-11)]. 

The ratio of wash solvent to extraction solvent is the same in the enriching section as in the stripping section if no solvent is added in the feed. The degree of separation to be achieved can be chosen for the process design, such as 99 percent of component b into the extrac-t stream and 99 percent of component c into the raffinate stream. Then the feed rate can be chosen so that the solute loadings in the extrac-t stream and... 

The equivalent TMB operating conditions and model parameters for the reference case were given in Table 9-1 and Fig. 9-9 presents the corresponding steady state internal concentration profdes obtained with the simulation package. The extract and raffinate purities were 97.6 % and 99.3 %, respectively the recoveries were 99.3 % and 97.6 % for the extract and raffinate streams. The solvent consumption was 1.19 L g and the productivity was 68.2 g/day - L of bed. 

Increasing the switch time interval is equivalent to decrease the solid flow rate and the net fluxes of components in all sections of the TMB unit will be pushed in the same direction of the liquid phase. This implies that, first, the more retained species will move upwards in section III and will contaminate the raffinate stream and the less retained species will move upwards in section IV, will be recycled to section I, and will contaminate also the extract stream. The decrease of the switch time interval will have similar consequences. The equivalent solid flow rate will increase and the net fluxes of component in all four sections of the TMB unit will be pushed in the opposite direction of the liquid phase. This implies that, first, the less-retained species will move downwards in section II and will contaminate the extract stream and the more retained component will also move downwards in section I, will be recycled with the solid to the section IV, and will contaminate the raffinate stream. It is possible to obtain simultaneously high purities and recoveries in a SMB, but the tuning must be carefully carried out. 

Due to the nature of the SMB process, in-process samples of the unwanted enantiomer and the enantiopure drug substance can be sampled at controlled times during the continuous process to assess the enantiomeric and chemical purity. One can monitor the process without system shutdown by diverting either the extract or the raffinate streams. Further monitoring of the receiving tanks can also be accomplished. 

Example The equation yx+1 — (a + I )yr + wyx l = 0, yQ = cQ and ym+i = x 1+ i/k represents the steady-state composition of transferable material in the raffinate stream of a staged countercurrent liquid-liquid extraction system. 

If the two solvents are immiscible, the solvent in the raffinate streams remains as A, and the added solvent in the extract streams as S. The material balances for the solute may then be written as... 

In this case the arrangement of the equipment is the same as for immiscible solvents although, as the amounts of solvent in the extract and raffinate streams are varying, the material balance is taken for the total streams entering and leaving each stage. 

The UOP rotary valve has been used in hundreds of Sorbex units across a variety of applications. The purpose of the rotary valve is to simply move the inlet and outlet ports of the net streams (feed, desorbent, raffinate, extract) around the 24 beds in stepwise fashion, creating a semi-continuous countercurrent flow of adsorbent relative to the entry and exit points of the net streams to and from the adsorbent chambers [25]. The rotary valve consists of a rotor plate pressed against a stator plate inside a pressure vessel that indexes the net desorbent, feed, extract and raffinate streams around the adsorbent chambers [26]. An alternative method of moving the inlet and outlet streams around the adsorbent chambers is used in other technologies where multiple automatic on-off valves at each distributor grid inlet are employed [5]. 

The raffinate and extract streams leave the UOP Parex unit adsorption section via the UOP rotary valve and are respectively routed to the raffinate and extract columns for separation of the mixed xylene components from the PDEB as shown in Figure 7.4. Because the desorbent has a higher boiling point than the mixed xylenes, the desorbent exits the bottom of the distillation column and is pumped back to the adsorbent chamber section. The mixed xylene raffinate stream is taken as a side cut from the raffinate column to remove water. The extract p-xylene stream is taken from the top of the extract column and routed to a finishing column where any toluene that was in the Parex feed is removed. The p-xylene product exits the bottom of the finishing column. The adsorbent has some selectivity for toluene as well as p-xylene. 

The fourth and final zone in SMB technology is known as the buffer zone which separates the outgoing raffinate stream containing the undesired C8s... 

MX Sorbex unit is on the order of one-tenth the size of the Parex unit raffinate stream within the same aromatics complex. This flow configuration where m-xylene capacity is added to an existing aromatics complex has been commonly adopted. A few m-xylene producers do not also produce p-xylene at the same site. In such cases, flow configurations have included once through m-xylene extraction of a mixed xylene stream or an MX Sorbex unit and Isomar unit integrated within a loop, with the same flow configuration as is conventionally used for a Parex unit and Isomar unit loop. 

The UOP Ebex process has been available for license since the 1970s. This process is a rejective simulated moving bed process where the ethylbenzene is the least adsorbed member of the mixed xylenes and is recovered in high purity in the raffinate stream [47]. Other liquid phase simulated moving bed concepts selective for ethylbenzene have been considered. These would ostensibly require less adsorbent circulation per unit feed because ethylbenzene is typically at <20% concentrahon in mixed xylenes [48, 49]. A process is disclosed by Broughton [50] that produces a pure m-xylene stream along with a pure ethylbenzene stream. 

The second desorbent characteristic is that the desorbent material must be compatible with both the particular adsorbent and the feed mixture. Specifically, the desorbent must not reduce the capacity of the adsorbent or normal paraffin selectivity with respect to the raffinate components. Additionally, desorbent materials must not react with any feed component Both the extract stream and the raffinate streams consist of a mixture of feed components with desorbent and any chemical reaction prevent product recovery. 

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. 

In 1998, UOP announced the development of a new Sorbex process called the MMP Sorbex process [15-19] that was capable of simultaneously separating both Cio i6 mono-branched paraffins and Cio i6 normal paraffins from a corresponding kerosene stream or n-paraffin-depleted Molex raffinate stream. Previously, no commercial process existed to isolate significant quantities of mono-methyl paraffin derived from either kerosene or n-paraffin depleted kerosene. Mono-methyl paraffins are desirable because they are needed for a new type of anionic surfactant. 

In bioseparations, the solute concentration in the feed is usually low, therefore, the changes of the extract and the raffinate streams are negligible. We can assume that F = R and S = E. In that case, we have only two unknown variables, x and y, so we can solve it to obtain,... 

Assess quality and quantity of products and wastes arising through the treatment of product and raffinate streams, which contain not only nitric acid, but also organic compounds (i.e., complexants, reductants, etc.). The treatment methods significantly affect the cost and safety issues of the reprocessing. 

The behavior of Tc in the PUREX process was first reported by Siddall in 1959 (67), and since then, not only its distribution (68), but also its detrimental effects (69) have been clarified. Thus, control of Tc in the PUREX process was envisaged in that most of the dissolved Tc is finally directed to the raffinate stream at the first cycle... 

In the reverse TALSPEAK process, the An(III) + Ln(III) fraction is first coextracted from a feed, the acidity of which has to be reduced to 0.1 M by denitration or nitric acid extraction. An(III) are then selectively stripped using DTPA in citric acid (1 M) at pH 3 (hence the name reverse TALSPEAK process), and the Ln(III) are finally stripped by 6 M HN03. Attempts to apply this TALSPEAK variant to the treatment of actual UREX + raffinates are reported in the literature, but they involve several steps. The problematic Zr and Mo elements are first removed by direct extraction with HDEHP (0.8 M in di-iso-propylbenzene) from the high-acidity raffinate stream arising from the UREX + co-decontamination process (238). The remaining fission products and actinides can then be concentrated by acid evaporation and denitration processes. This concentrate is further diluted to a lower acidity (e.g., [HN03] = 0.03 M) to allow the coextraction of An(III) and Ln(III) by the TALSPEAK solvent. 

The flowsheet has three aqueous effluents. The first is the decontaminated aqueous raffinate stream. For economic reasons, entrained solvent in the raffinate must be recovered test results show that coalescers are practical and effective [89], In the baseline SWPF, the raffinate stream will be transferred to the Saltstone Facility, where it will be disposed of in a cementitious low-activity waste form called saltstone. The... 

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