Separation efficiency parameters

The identification of separated componnds is primarily based on their mobility in a snitable solvent, which is described by the Rp valne of each compormd. Kowalska et al. have nicely discnssed in greater detail the theory of planar chromatography and separation efficiency parameters in Chapter 2 of the third edition of the Handbook of Thin-Layer Chromatography, published in 2003. 

Determination of separation efficiencies from pilot-plant data is also affected by axial dispersion. Neglecting it yields high or values. Literature data for this parameter have usually not been corrected for this effect. 

There are relationships between the independent size separation device parameters and the dependent size separation efficiencies. For example, the apparent bypass value does not affect the size distribution of the fine stream but does affect the circulation ratio, ie, the ratio of the coarse stream flow rate to the fine stream flow rate. The circulation ratio increases as the apparent bypass increases and the sharpness index decreases. Consequendy, the yield, the inverse of the circulating load (the ratio of the feed stream flow rate to the fine stream flow rate or the circulation ratio plus one), decreases hence the efficiencies decrease. For a device having a sharpness index of 1, the recovery efficiency is equal to (1 — a). 

This parameter was introduced in the ISO/EN and DIN standard quoted earlier. In order to have good polymer separation efficiency, the following criterion has to be met ... 

One of the most important properties of a chromatographic column is the separation efficiency. A measure of this parameter could be the difference of the retention volume for two different compounds. The result of a GPC analysis is usually, however, only one large peak, and a separation into consecutive molar mass species is not possible. Additionally there is no standard for higher molar masses consisting only of a species that is truly monodisperse. Therefore, the application of the equation to the chromatographic resolution of low... 

Increasing the speed of analysis has always been an important goal for GC separations. All other parameters being equal, the time of GC separations can be decreased in a number of ways (1) shorten the column (2) increase the carrier gas flow rate (3) reduce the column film thickness (4) reduce the carrier gas viscosity (5) increase the column diameter and/or (6) heat the column more quickly. The trade-off for increased speed, however, is reduced sample capacity, higher detection limits, and/or worse separation efficiency. 

An increase in any one operating parameter generally increases all others as well. For example, increasing the flow rate will increase both separation efficiency and pressure drop, and vice versa. 

For the simulation of SMB-separations efficient software packages,based on the Triangle-Theory, are commercially available. The number of columns, the column dimensions, the theoretical number of plates in the columns, the feed concentration, the bi-Langmuir adsorption isotherm parameters and the number of cycles need to be defined by the user. Then the separation is simulated and values for the flow rate ratios, the flow rates, the switching time and the quality of the separation, purity and yield, are calculated. Based on these values an actual separation can be performed. However, some optimization/further development is usually necessary, since the simulations are based on an ideal model and the derived parameters and results therefore can only be taken as indications for the test runs. 

The committee notes that the laboratory tests established operating parameters for hydrocyclone operation that involve careful control of pressures and flows to achieve desired separation efficiencies. No tests were performed to demonstrate the robustness of hydrocyclone operation during the pressure and flow swings that might be expected during normal operations of a full-scale facility. 

Development of short monolithic silica columns with high efficiencies (up to 200.000 plates per meter) and high-speed separations, performance parameters that can be obtained with column packed with sub-2 pm particles, but achieved with monolithic silica columns at very lower system back-pressure. 

This chapter will only deal with the possible gas transport mechanisms and their relevance for separation of gas mixtures. Beside the transport mechanisms, process parameters also have a marked influence on the separation efficiency. Effects like backdiffusion and concentration polarization are determined by the operating downstream and upstream pressure, the flow regime, etc. This can decrease the separation efficiency considerably. Since these effects are to some extent treated in literature (Hsieh, Bhave and Fleming 1988, Keizer et al. 1988), they will not be considered here, save for one example at the end of Section 6.2.1. It seemed more important to describe the possibilities of inorganic membranes for gas separation than to deal with optimization of the process. Therefore, this chapter will only describe the possibilities of the several transport mechanisms in inorganic membranes for selective gas separation with high permeability at variable temperature and pressure. 

Capillary electrophoresis offers a set of important advantages that make it a premier technique for the investigation of enantioselective effects in the affinity interactions between chiral drugs and cyclodextrins. The most important advantage of CE is the inherently high separation efficiency offered by this technique. As already known, the most important contributors to peak resolution (R) are a separation selectivity (a) and an efficiency (N). A relationship between these parameters in CE is described by the following equation (2) ... 

The degree of cell separation is an important parameter to be evaluated in perfusion systems. This can be done through the use of some concepts as cell separation efficiency, grade efficiency, and cut size. These concepts are applicable to any equipment whose performance remains constant if the operational conditions do not change. They are valid, therefore, for equipment such as sedimenting centrifuges, hydrocyclones, gravitational settlers, etc. 

The major problem in PAH analysis is separation and conclusive identification of individual isomeric compounds, since the biological properties of many PAHs are isomer-specific. Another problem is the unavailability of many reference standards, making optimization of GC-operating parameters and column preparation methods for isomer separation difficult. The best possible separation efficiency is crucial for identification and quantitation of PAHs in any environmental sample. In addition, PAHs must be separated from other classes of compounds mostly encountered in environmental samples. 

Chromatographic Resolution. To optimize column-coating conditions and operating parameters glass capillary columns coated with various silicone-based stationary phases were tested with difficult-to-separate groups of PAH standards and Complex samples. The SE5 -coated columns performed excellently with respect to separation efficiency, column bleed and long-term stability. Other observers have had similar results with this... 

The chromatographer is always a prisoner of a triangle whose apexes correspond to resolution, speed and capacity - three parameters that are in conflict (see Fig. 1.11). An optimised analytical separation uses the potential of the most efficient parameter selectivity. Thus, in this triangle, the optimised conditions are close to the apex corresponding to resolution. 

The separation efficiency for a given membrane with a particular binary gas mixture will be dependent mainly upon three factors gas composition, the pressure ratio between feed and permeate gas, and the sepration factor for the two components. A higher separation factor gives a more selective membrane, resulting in a greater separation efficiency. This parameter is a function of the membrane material and is determined by the individual gas permeation rates. 

Under the particular feed conditions and element arrangement for this test, the criteria of less than 3.5% C02 in the residual stream could not be reached without experiencing some loss in separation efficiency. This goal could be achieved, however, by operating at higher flow rates with more elements in series. The conclusion arrived at from these data, therefore, is that there is a critical minimum flow rate for given feed gas conditions and element array. In order to maximize system performance this parameter must be taken into consideration when designing a full size system. 

Devolatilization of Residual Toluene Residual toluene is continuously removed from a polymer melt stream of 454 kg/h at 230°C and 0.006 weight fraction of toluene, at a vacuum of 20 torr. The density of the polymer is 0.98 g/cm3, and the Florry-Huggins interaction parameter is yl2 = 0.43. (a) Calculate the equilibrium concentration, we- (b) If equilibrium is reached, that is, Wf = we, where uy is the final concentration, calculate the separation efficiency Fs = (wo — Wf)/wQ. (c) If the final concentration wy = 2we, calculate Fs- (d) Calculate for (c) the volumetric flow rate of the vacuum pump removing the volatiles. 

Fig. 9.52 Separation efficiency of a three-chamber co-rotating disk devolatilizer of 450°F PS melt containing 1500-3000 ppm styrene, fed at 42-lb/h into 0.54-in-wide chambers at 50-torr absolute pressure, as a function of disk speed and with flow rate as a parameter. Broken curves show calculated residence times. [Reprinted by permission from P. S. Mehta, L. N. Valsamis, and Z. Tadmor, Foam Devolatilization in a Multichannel Co-rotating Disk Processor, Polym. Process. Eng., 2, 103-128 (1984).]...

Most chromatographic systems employ process control of operating parameters. These may well be built into the instrument. Temperature control is particularly important, especially for contemporary techniques such as chiral recognition and protein interaction.23 In liquid chromatography, for instance, temperature directly effects retention, separation efficiency, and selectivity. Stability of temperature is thus extremely important, since variations of more than 1°C can lead to noticeable effects.24... 

In electrochromatography with porous particles, a (3 factor for the pore volume (Pta) as well as for the interstitial volume (Poul) can be defined. (Note For monolithic or continuous columns, only a single EOF screening factor can be defined for the pore volume.) An important parameter in the discussion of the effects of pore flow on the separation efficiency is the pore-to-interstitial flow ratio (0, which is defined as [18]... 

---