Purity and recovery

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. 

In the case of the Molex process, the pulse test separation between the desired normal paraffins and the non-normal feed components produces discrete and separate peaks. This high degree of separation means a Molex unit can achieve high degrees of purity and recovery but the ultimate purity and recovery are dictated by non-ideal conditions such as back mixing or flow mal-distributions. 

The fifth and final adsorbent characteristic is zeolite type. The adsorbent used in the Molex process is a proprietary and is a particularly effective adsorbent for normal paraffin separation [4, 5] and has achieved purity and recovery targets for the Molex processes. A sampUng of various molecules (and their corresponding dimensions) that Molex can easily separate is listed in Table 8.1. As discussed in Chapter 6, a zeoUtes s pore structure is dependent on its silica aluminum ratio and the proprietary Molex adsorbent possess a uniform repeating three-dimensional porous structure with pores running perpendicular to each other in the x. 

Since this is a countercurrent operahon, the selective volume of the adsorbent enters the top of this zone containing only desorbent. As the adsorbent passes countercurrent against the feed, it ultimately reaches bottom of the zone which is the feed point. By this time, the adsorbent s selective volume is filled with normal paraffins. This zone may contain as many as eight beds and as few as three. Product purity and recovery requirements dictate how many beds are required. 

In Sorbex terminology, a gasoline Molex unit is classified as a low purity and low recovery Sorbex unit since typical purity and recovery targets are greater than 85% n-paraffin purity while operating at greater than 90% feed n-paraffin recovery. 

Since the detergent Molex process is both a high normal paraffin purity and recovery process, it is designed with the full allotment of Sorbex beds in addition to the four basic Sorbex zones. The detergent Molex process utilizes a split desorbent. This means it consists of a mixture of n-pentane and iso-octane. The zone flush primarily consists of isooctane and its purpose is to keep the desorbent (n-... 

In PSA air separation the adsorbent, despite its low loading and shallow slope, is actually adsorbing and removing from the gas phase 79mol% of the dry feed stream. In H 2 purification there are generally a few more contaminants to remove, the H2 is essentially non-adsorbed, high purity and recovery of the product gas is quite important to the process economics. 

The definition of product oxygen recovery defines the minimum required feed rate for a specified product purity and recovery. That relationship is that the feed flow must be the product oxygen purity (%) divided by the recovery (% of feed O2) and divide also by the mole fraction of O2 in feed air. For 20.9 mol% O2 in air this is ... 

It has been mentioned that purity and recovery are very significant drivers for the business of hydrogen purification. Today PSA hydrogen purifiers can deliver purities of several nines 99.9% purity while simultaneously recovering nearly 90% of the hydrogen found in the feed gas. 

From a correlation similar to Figure 14.7, the velocity of the mobile phase for the scaled up column to obtain the equal value of can be determined. In the case where particles with a smaller radius are used, an operation with a higher interstitial velocity will be possible to attain the same resolution with the same column height, and thus this increases the productivity. The resolution between a target and a contaminant can be estimated by Equation 11.23 to calculate the purity and recovery of the target. 

For a preparahve applicahon, focus is on recovering the targeted products while ophmizing produchon costs. The object of the separation is to reach the purity and recovery yield required for one or more specific components of the feed mixture. To maximize produchon, injechons are made as often as possible. The amount of stahonary phase used is set in order to minimize the costs of the product, equipment, and eluent consumption. Figure 12.2 presents the preparahve chromatogram of the same compounds as in Figure 12.1, where the injected amount is maximized in order to ophmize the process [5]. 

If a tradeoff between purity and recovery is necessary, which is more important ... 

While optimizing purity and recovery for the large-scale system, some of the concerns were ... 

Purity and Recovery Analysis of the Separated Cell Product... 

Table 6.9. Recoveries and Product Specifications in Each Distillation Task in Figures 6.10 and 6.11. [Adopted from Mujtaba and Macchietto, 1994] Purities in bold face indicate the desired product specifications. Other purity and recovery specifications (decision variables of type (b are set at typical values.

The difference between the product value and the total costs can now be determined for each value of S. This difference is the profit from the separation as a function of S. The profit curve will normally show a maximum (unless restricted by constraints). The highest profit will set the optimum value of S. Going back to the Fig. 3.2 diagram for the optimum value of S, the optimum D/F value can be determined. This procedure sets the optimum product purity and recovery values. 

Zeolites are used in separation processes for extracting p-xylene and m-xylene at high purity and recovery. There are zeolitic processes for converting C3-C7 paraffins into aromatics. In addition, zeolitic processes can co-produce aromatics and chemical-grade light olefins, or co-produce superior feedstocks for catalytic reformers and naphtha crackers. 

High paraxylene purity and recovery (99.8+ wt% purity at up to 95% recovery)... 

UOP BTX, purification Reformate Carom process extraction of aromatics from non-aromatics at high purity and recovery using a proprietary solvent 5 1996... 

The purity of Ar in the high pressure cycles was limited to 50%. The purity and recovery were improved in subadnospheric cycles with a consequent loss of productivity. In blowdown steps, oxygen product was also concentrated to %-98% with recovery up to 90%. It is noted that 3 and 1 atm are the pressures of product in the two main industrial PSA air... 

Studies are underway to further improve the purity and recovery of the argon product. The results will be presented at the conference. 

Figure 3 Impact of P/F ratio on product purity and recovery for standalone PSA (H2 A, purity, , recovery, CH4 O, purity , recovery) and for integi ed system (H2 A, purity , recovery, CH4 , purity jj, recovery). CH4 concentration profiles in the PSA bed for a single and for the integrated stem. PSA alone a end of PRi(9s), O end of PR2(30s), A end of HPA. Integrated process end of PRi(9s), end of PR2, end ofHPA...

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