Fine Purification

Even with large air separation plants the amount of neon pre-enriched product is small, so that the final purification is often operated in a batch mode. 

Various processes exist, combining adsorption, catalysis, partial condensation and rectification for the isolation of neon. For example, the process applied by the Linde AG either in batch or continuous mode combines these unit operations in the following way [3.5]  

The cryogenic part of the apparatus, designed for the production of a few standard cubic meters per hour, is housed in two containers with a volume of about 1 m. Due to the vacuum- ( 1 Pa) and the super-insulation, the heat flow into the equipment is small and the low temperatures can be obtained via the Joule Thomson effect. 

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Optimal parameters for the extraction, washing and stripping of niobium were determined to be number of stages for all three processes - 4, volumetric ratios Vorg Vaqu are 1 1, 20 1 and 8 1, respectively. Additional fine purification of the extractant was recommended by stripping of tantalum and niobium remainders using a 0.5% wt. ammonia solution. This additional stripping leads to final concentrations of both tantalum and niobium in the extractant that are < 0.001 g/1. Table 62 shows the purity of niobium oxide prepared by the described method. 

When planning an industrial-scale bioprocess, the main requirement is to scale up each of the process steps. As the principles of the unit operations used in these downstream processes have been outlined in previous chapters, at this point we discuss only examples of practical applications and scaling-up methods of two unit operations that are frequently used in downstream processes (i) cell separation by filtration and microfiltration and (ii) chromatography for fine purification of the target products. 

After the initial purification steps of salt precipitation of an aqueous two-phase extraction, an enzyme is often already pure enough for preparative use. If a high degree of purity or even homogeneity is required, such as for biochemical investigations of a novel enzyme, fine purification steps have to be added. The most common such step is chromatography. 

Persistent interest in studying the clathrate systems is largely caused by the great diversity of areas of their practical application. They can be used in efficient fine purification of substances, in isomer separation [95,96], in the development of energy-saving water desalination technologies, etc. In recent... 

ROP (Figures 12.20 and 12.21) is the route which delivers by far the highest proportion of PLA chips available on the market. The other routes produce only minor amounts or did not get past the pilot scale. Figure 12.21 depicts the steps of an ROP process, starting from lactic add. In the first part lactide is formed, which - after fine purification is converted by ROP to PLA. 

If a fuel should be used which is available right now all over the world, LPG is still the best choice. For this reason, reforming systems for LPG have been developed for combination with a PEFC. The reaction temperature for the steam reforming of LPG is as high as 650-700 °C, thus a longer start-up period for heating the system to the required operation temperature is inevitable. Due to the temperature level, the CO concentration at the reformer exit is high and has to be further reduced by CO shift conversion and if needed also a CO fine purification like selective CO oxidation reaction. Thus, the required low CO concentration in the... 

Due to this low production rate, the pre-product is often stored in a tank, which is periodically transported to a central fine-purification plant. In order to keep... 

Kr/Xe-fine-purification plants are available in numerous designs, combining the separation techniques cryogenic rectification, catalysis, adsorption, chemisorption or membrane separation. They may be operated continuously or, due to the small capacities, in batch mode. 

Neon production is performed in two steps. In the first step, a neon enriched gas with about 50% of Ne, 3% of H2, 16% of He and 31% of N2 (see Fig. 3.1) is obtained in a small column (6) integrated into the air separator. The neon enriched gas is often stored in pressure cylinders and transported to a central fine-purification plant. There, in the second step, neon is recovered with the required purity. 

In the diaphragm process, the removal of sulfate is not always necessary because 504 can be removed from the cell liquor as pure Na2S04 during the concentration process. In the membrane process, the brine must be purified to a much higher degree to avoid the deterioration of the membrane. The Ca and Mg " concentration must be < 0.02 ppm (20 ppb), so a second, fine purification step is required (see Section 7.2.1). 

Brine System. The brine system for the diaphragm process is the simplest of the three — there is neither dechlorination nor sulfate precipitation, except in some very specific cases — and makes up only 3 - 4 % of the capital investment. The brine system is the most complex for the membrane process, for fine purification by ion exchange is necessary. However, the two- or three-fold greater depletion of the brine in the membrane process allows the brine system to be smaller than that for the mercury process. Therefore, the cost of the brine system for either process is approximately the same, 4 - 7 % of the total. 

For a long time the water solutions of monoethanol amine (NH2CH2CH2OH) have been largely used in the chemical industry for purification of technological gases f m H2S and also fixnn CO2. Now ftiis process can be successfully used for economically profitable fine purification of gases fiom these components. 

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