Separation performance

The sohd can be contacted with the solvent in a number of different ways but traditionally that part of the solvent retained by the sohd is referred to as the underflow or holdup, whereas the sohd-free solute-laden solvent separated from the sohd after extraction is called the overflow. The holdup of bound hquor plays a vital role in the estimation of separation performance. In practice both static and dynamic holdup are measured in a process study, other parameters of importance being the relationship of holdup to drainage time and percolation rate. The results of such studies permit conclusions to be drawn about the feasibihty of extraction by percolation, the holdup of different bed heights of material prepared for extraction, and the relationship between solute content of the hquor and holdup. If the percolation rate is very low (in the case of oilseeds a minimum percolation rate of 3 x 10 m/s is normally required), extraction by immersion may be more effective. Percolation rate measurements and the methods of utilizing the data have been reported (8,9) these indicate that the effect of solute concentration on holdup plays an important part in determining the solute concentration in the hquor leaving the extractor. 

Again, corresponds to the area of a gravity settling tank capable of the same separation performance as the disk stack defined by the parameters included in equation 15. 

The sedimentation phenomenon that the Z-concept attempts to describe quantitatively is only part of the total task that the centrifuge has to accomplish. Thus, attempts to predict separation performance solely on the basis of Z-concepts have sometimes given disappointing results. 

For most large-scale processes, adsorbent particle size varies from 0.06 to 6 mm (0.0025 to 0.25 in), but the adsorbent packed in a fixed bed will have a fairly narrow particle size range. Pressure drop in adsorbers can be changed by changing the diameter to bed depth ratio and by changing the particle size (see Sec. 5). Adsorbent size also determines separation performance of adsorbent columns—increasing efficiency with decreasing particle size. In hquid-phase process-... 

A good solids-hquid separator performs well in service, both initially and over time. It operates rehably day after day, with enough flexibility to accommodate to normal fluctuations in process conditions, and does not require frequent maintenance and repair. Selection of such a separator begins with a preliminary hsting of a number of possible devices, which may solve the problem at hand, and usually ends with the purchase and instaUation of one or more commercially available machines of a specific type, size, and material of construc tion. Rarely is it worthwhile to develop a new land of separator to fill a particular need. 

Detection methods, whieh provide real information eonceming the separated substances, are necessary in order to be able to analyze the separation result and separation performance achieved by such a system. 

Toyopearl HW-75 resin, with pores larger than 1000 A, have been used in place of ultracentrifugation steps for the purification of plasmid DNA. Ultracentrifugation is a time-consuming process and requires expensive chemicals, such as cesium chloride. Toyopearl HW-75 resin provides superior separation performance for plasmid DNA and also provides high yields (54). 

Comparison of separation performance for quanrificarion of a high dp scb glucan fraction in a nb/lcb glucan sample... 

Briefly summarized, S-1000 shows better resolution in the high dp range, whereas the CL 2B system resolves low dp components better. Due to these differences in separation performance, the degree of polymerization distribution and degree of polymerization average values for the same sample obtained from broad scb— nb/lcb-transformed dextran calibration yielded dp = 29,900 glucose units for the S-1000 system and dp = 21,100 glucose units for the CL 2B system (Fig. 16.18). 

Consequently, inappropriate (P-6) and appropriate (P-6/S-200) separations yield significantly different results for the degree of polymerization distribution and average values of degree of polymerization (Fig. 16.27). In a first and qualitative evaluation, dp distribution achieved from P-6/S-200 differs significantly in symmetry from the dp distribution of P-6. In particular, differences in separation performance become obvious for high dp components. In a... 

Another TSK combination (precolumn -I- PWM -I 6000 -I 5000 -I- 4000 -I-3000) was tested on differences in separation performance between individual narrow distributed samples and mixtures of several narrow distributed samples. The result is summarized in Eig. 16.31 within experimental error the summed chromatograms (theory) of four narrow distributed glucans (dextran) match perfectly with the experimentally determined chromatogram of the mixture. The (theory/experimental) ratio, plotted for quantification of the match, in-... 

X 0.75 cm) Ve i = 28 ml = 50 ml eluent 0.05 M NaCI flow rate 0.80 ml/min detection Optilab 903 interferometric differential refractometer applied sample mass/volume 200 /tl of 2-mg/ml aqueous solutions sum of individual chromatograms (theory —) and (theory/experimental) ratio (—) plotted for quantification of deviations in separation performance between narrow distributed samples and broad distributed samples. 

When packing of the porous materials is not sufficiently tight, repeated injection of a viscous solution leads to an increasing packing density, leaving a void space at the column inlet. When the void space was filled with extra porous materials, it was observed (1) that the resolution of HOPC decreased slightly compared with first-time use. When the column ceased to produce the void space, the separation performance became reproducible. 

Unfortunately, the fact that, in addition to the 2-D separation, a further increase in separation performance might be obtained by the use of multiple development... 

S. K. Poole and C. F. Poole, Evaluation of the separation performance of Empore thin layer chromatography sheets , 7. Planar Chromatogr. 2 478-481 (1989). 

The 2D chromatograms reveal additional components of the natural mixtures. They also give a map of the essential oil, which is helpful in the identification of the components by the position and the characteristic colours of the derivatives on the plate. A further, considerable improvement in the separation performance can be obtained by using overpressured layer chromatography (OPLC). Harmala et al. (70) used 2D OPLC for the separation of coumarins from the genus Angelica. Figure 10.15 shows the one-dimensional (a) and two-dimensional (b) OPLC separations of 16 coumarins. 

The high diffusivity and low viscosity of sub- and supercritical fluids make them particularly attractive eluents for enantiomeric separations. Mourier et al. first exploited sub- and supercritical eluents for the separation of phosphine oxides on a brush-type chiral stationary phase [28]. They compared analysis time and resolution per unit time for separations performed by LC and SFC. Although selectivity (a) was comparable in LC and SFC for the compounds studied, resolution was consistently... 

The macrocyclic antibiotic-based CSPs have not been used extensively in SFC. Two macrocyclic antibiotic CSPs, Chirobiotic T and Chirobiotic V, were included in a study of various CSPs in SFC. At least partial resolution of approximately half of the 44 test compounds could be obtained on these two CSPs in SFC [63]. A high concentration of modifier was necessary to elute some of the analytes. Enantioreso-lution of derivatized amino acids was also demonstrated in the same study. Flowever, a complex modifier comprised of methanol, water, and glycerol was required for separations performed on the Chirobiotic T CSP. The separation of coumachlor enantiomers on a vancomycin-based CSP (Chirobiotic V) in SFC is illustrated in Fig. 12-5 [32]. 

The separation performance of these systems (usually low-pressure, not close to critical conditions, and with similar components) can be predicted by Raoult s Law, applying to vapor and liquid in equilibrium. 

Continuous monitoring of the third-stage separator performance. If catalyst is showing up downstream, consider using more than the standard 3% flue gas underflow. The blowcase needs more attention than it usually gets. 

Centrifugation can be operated on a semi-continuous or continuous basis and there are several different types of centrifuges. Large scale tests have to be performed to choose the proper centrifuge (unloading speed, capacity, separation performance etc). 

The ionic or polar substances can be seperated without any reaction on specially treated chromatographic columns and detected refractometrically. This is necessary because alkyl sulfosuccinates show only small absorption in the UV-visible region no sensitive photometric detection can be obtained. Separation problems can arise when common steel columns filled with reverse phase material (or sometimes silica gel) are used. This problem can be solved by adding a suitable counterion (e.g., tetrabutylammonium) to the mobile phase ( ion pair chromatography ). This way it is possible to get good separation performance. For an explanation of separation mechanism see Ref. 65-67. A broad review of the whole method and its possibilities in use is given in an excellent monograph [68]. 

In the case of supported membranes also, the support can play an important role in the separation performance of the membrane in the gas as well as in the Hquid phase [101-103]. Transport in these support pores can be accurately described by the Dusty Gas Model [100, 104] although it is put forward by Kerkhof and Geboers that their Binary Friction Model is physically more correct [105]. 

Capillary electrophoresis is increasingly used in food analysis due to its separation performance combined with the short time of analysis. - CapiUary electrophoresis recently applied to colorant measurements includes technical variants such as capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography. ... 

Samples with higher protein levels (yogurts), are initially treated with hydrochloric acid and after protein precipitation the supernatant is filtered and injected into the HPLC column. The separations performed with a LiChroCART RP18 column used a mixture of acetonitrile and formic acid as the mobile phase. A baseline quantification of the carminic acid was possible in the presence of other coloring agents, with excellent recuperation, selectivity, accuracy, and precision. ... 

Gas separation performances (H2/n-butane, n-hexane/2-2 dimethylbutane) have been measured using a sweep gas (countercurrent mode) in order to increase the permeation driving force (no differential pressure was used) permeate and retentate compositions (see Figure 2) were analysed using on line gas chromatography. 

---