High-pressure separator

In the previous sections, we indicated how, under certain conditions, pressure may be used to induce immiscibility in liquid and gaseous binary mixtures which at normal pressures are completely miscible. We now want to consider how the introduction of a third component can bring about immiscibility in a binary liquid that is completely miscible in the absence of the third component. Specifically, we are concerned with the case where the added component is a gas in this case, elevated pressures are required in order to dissolve an appreciable amount of the added component in the binary liquid solvent. For the situation to be discussed, it should be clear that phase instability is not a consequence of the effect of pressure on the chemical potentials, as was the case in the previous sections, but results instead from the presence of an additional component which affects the chemical potentials of the components to be separated. High pressure enters into our discussion only indirectly, because we want to use a highly volatile substance for the additional component. 

Superhcial gas velocity in separator high pressure zone... 

The Indian PHWR is a pressure tube type reactor using heavy water moderator, heavy water coolant (in a separate high pressure high temperature system) and natural uranium oxide fuel. 

Despite the excellent resolving powers of modem capillary chromatography, there are situations where the analyst may chose to prefractionate the aroma isolate. Some of the more common methods to prefractionate flavor isolates prior to GC analysis include acid/base separations, high pressure liquid chromatography (HPLC), silicic acid column chromatography and preparative GC. 

Bypass involves failures in the reactor coolant pressure boundary separating high pressure and low pressure systems. Normally, this involves the failure of at least two valves. For example, the valves separating the primary system from the Residual Heat Removal (RHR) system may fail, thus putting high pressure into the RHR system. Because the RHR system is normally constmcted with low pressure piping and components, it may fail outside containment, providing a direct path from the... 

Separation of low-molecular-weight materials. Low-molecular-weight materials are distilled at high pressure to increase their condensing temperature and to allow, if possible, the use of cooling water or air cooling in the column condenser. Very low... 

Figure 3.8a shows the temperature-composition diagram for a minimum-boiling azeotrope that is sensitive to changes in pressure. This azeotrope can be separated using two columns operating at different pressures, as shown in Fig. 3.86. Feed with mole fraction of A Ufa)) of, say, 0.3 is fed to the high-pressure column. The bottom product from this high-pressure column is relatively pure B, whereas the overhead is an azeotrope with jcda = 0-8, jcdb = 0.2. This azeotrope is fed to the low-pressure column, which produces relatively pure A in the bottom and in the overhead an azeotrope with jcda = 0.6, jcdb = 0.4. This azeotrope is added to the feed of the high-pressure column.

Refrigerated condensation. Separation by condensation relies on differences in volatility between the condensing components. Refrigeration or a combination of high pressure and refrigeration is needed. 

Sometimes it is extremely difficult to avoid vapor recycles without using very high pressures or very low levels of refrigeration, in which case we must accept the expense of a recycle compressor. However, when synthesizing the separation and recycle configuration, vapor recycles should be avoided, if possible, and liquid recycles used instead. 

Reverse osmosis is a high-pressure membrane separation process (20 to 100 bar) which can be used to reject dissolved inorganic salt or heavy metals. The concentrated waste material produced by membrane process should be recycled if possible but might require further treatment or disposal. 

Gas is sometimes produced at very high pressures which have to be reduced for efficient processing and to reduce the weight and cost of the process facilities. The first pressure reduction is normally made across a choke before the well fluid enters the primary oil / gas separator. 

Facilities for the treatment and compression of gas have already been described in earlier sections. However, there are a number of differences in the specifications for injected gas that differ from those of export gas. Generally there are no technical reasons for specifications on hydrocarbon dew point control (injected gas will get hotter not cooler) although it may be attractive to remove heavy hydrocarbons for economic reasons. Basic liquid separation will normally be performed, and due to the high pressures involved it will nearly always be necessary to dehydrate the gas to avoid water drop out. 

Capillary Electrochromatography Another approach to separating neutral species is capillary electrochromatography (CEC). In this technique the capillary tubing is packed with 1.5-3-pm silica particles coated with a bonded, nonpolar stationary phase. Neutral species separate based on their ability to partition between the stationary phase and the buffer solution (which, due to electroosmotic flow, is the mobile phase). Separations are similar to the analogous HPLC separation, but without the need for high-pressure pumps, furthermore, efficiency in CEC is better than in HPLC, with shorter analysis times. 

High-pressure liquid chromatography (HPLC) is simply a variant on LC in which the moving liquid stream is forced along under high pressure to obtain greater efficiency of separation. 

LC, or sometimes HPLC (high-pressure liquid chromatography), is a means of separating components of mixtures by passing them in a solvent through a chromatographic column so that they emerge sequentially. 

Another example is the purification of a P-lactam antibiotic, where process-scale reversed-phase separations began to be used around 1983 when suitable, high pressure process-scale equipment became available. A reversed-phase microparticulate (55—105 p.m particle size) C g siUca column, with a mobile phase of aqueous methanol having 0.1 Af ammonium phosphate at pH 5.3, was able to fractionate out impurities not readily removed by hquid—hquid extraction (37). Optimization of the separation resulted in recovery of product at 93% purity and 95% yield. This type of separation differs markedly from protein purification in feed concentration ( i 50 200 g/L for cefonicid vs 1 to 10 g/L for protein), molecular weight of impurities (<5000 compared to 10,000—100,000 for proteins), and throughputs ( i l-2 mg/(g stationary phasemin) compared to 0.01—0.1 mg/(gmin) for proteins). 

The urea solution leaving the stripper bottom contains about 12 wt% of NH and is further purified in the 1.8 MPa (18 bar) and 0.2 MPa (2 bar) recovery sections of the plant. The resultant NH and CO2 separated in the decomposers is absorbed and returned to the synthesis section by the high pressure centrifugal carbamate pump. 

Fig. 6. Adsorption capacity of various dessicants vs years of service in dehydrating high pressure natural gas (39). a, Alumin a H-151, gas 27° C and 123 kPa, from oil and water separators b, siUca gel, gas 38° C and 145 kPa, from oil absorption plant c, sorbead, 136-kPa gas from absorption plant ...

Until separation techniques such as chromatography (28,29) and counter-current extraction had advanced sufficientiy to be of widespread use, the principal alkaloids were isolated from plant extracts and the minor constituents were either discarded or remained uninvestigated. With the advent of, first, column, then preparative thin layer, and now high pressure Hquid chromatography, even very low concentrations of materials of physiological significance can be obtained in commercial quantities. The alkaloid leurocristine (vincristine, 22, R = CHO), one of the more than 90 alkaloids found in Catharanthus roseus G. Don, from which it is isolated and then used in chemotherapy, occurs in concentrations of about 2 mg/100 kg of plant material. 

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