Other Separation Processes

Among the other separation processes, one can cite the following  

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Process Concepts. Hybrid systems involving gas-phase adsorption coupled with catalytic processes and with other separations processes (especially distillation and membrane systems) will be developed to take advantage of the unique features of each. The roles of adsorption systems will be to efficiently achieve very high degrees of purification to lower fouUng contaminant concentrations to very low levels in front of membrane and other separations processes or to provide unique separations of azeotropes, close-boiling isomers, and temperature-sensitive or reactive compounds. 

Alternative approaches are to be found in the hterature. Derivations of the above equations are given in numerous texts (2,10—12), which also describe graphical or analytical solutions to the problem. Many of these have direct analogues in other separation processes such as distillation (qv) and hquid—hquid extraction, and use plots such as the McCabe-Thiele diagram or Ponchon-Savarit diagram. 

An improved solvent extraction process, PUREX, utilizes an organic mixture of tributyl phosphate solvent dissolved in a hydrocarbon diluent, typically dodecane. This was used at Savannah River, Georgia, ca 1955 and Hanford, Washington, ca 1956. Waste volumes were reduced by using recoverable nitric acid as the salting agent. A hybrid REDOX/PUREX process was developed in Idaho Falls, Idaho, ca 1956 to reprocess high bum-up, fuUy enriched (97% u) uranium fuel from naval reactors. Other separations processes have been developed. The desirable features are compared in Table 1. 

Products. In all of the instances in which crystallization is used to carry out a specific function, product requirements are a central component in determining the ultimate success of the process. These requirements grow out of how the product is to be used and the processing steps between crystallization and recovery of the final product. Key determinants of product quaHty are the size distribution (including mean and spread), the morphology (including habit or shape and form), and purity. Of these, only the last is important with other separation processes. 

The principal applications of mass transfer are in the fields of distillation, gas absorption and the other separation processes involving mass transfer which are discussed in Volume 2, In particular, mass transfer coefficients and heights of transfer units in distillation, and in gas absorption are discussed in Volume 2,. In this section an account is given of some of the experimental studies of mass transfer in equipment of simple geometry, in order to provide a historical perspective. 

Screening (continuous, commercial) and sieving (batch, laboratory test generally confined for size determination) are essentially mechanical separations of particles based on size, accomplished by using a perforated surface that serves as a go-no-go gauge. Both processes, like all other separation processes, have the drawback that a complete separation is seldom obtained, and some potential oversize/undersize particles are always left in the undersize/oversize fraction. 

Impacts of Adsorptive Separation Versus Other Separation Processes... 

Recognizing the need for a more economically and environmentally friendly citric acid recovery process, an adsorptive separation process to recover citric acid from fermentation broth was developed by UOP [9-14] using resin adsorbents. No waste gypsum is generated with the adsorption technique. The citric acid product recovered from the Sorbex pilot plant either met or exceeded all specifications, including that for readily carbonizable substances. An analysis of the citric acid product generated from a commercially prepared fermentation broth is shown in Table 6.2, along with typical production specifications. The example sited here is not related to zeolite separation. It is intent to demonstrate the impact of adsorption to other separation processes. 

When developing a liquid phase adsorptive separation process, a laboratory pulse test is typically used as a tool to search for a suitable adsorbent and desorbent combination for a particular separation. The properties of the suitable adsorbent, such as type of zeolite, exchange cation and adsorbent water content, are a critical part of the study. The desorbent, temperature and liquid flow circulation are also critical parameters that can be obtained from the pulse test. The pulse test is not only a critical tool for developing the equilibrium-selective adsorption process it is also an essential tool for other separation process developments such as rate-selective adsorption, shape-selective adsorption, ion exchange and reactive adsorption. 

Any economic advantage of a solvent extraction process over other separation processes for metals can be lost if the loss of solvent from the system becomes too high. 

The treatment costs for the GHEA Associates process depend on the soil matrix, properties, chemical composition of the contaminants, and other site-specific factors. The commercial-scale, integrated process, consists of the extraction and wash liquor purification steps. The estimated costs for the process range from 50 to 80 per ton of soil treated. Other separation processes have estimated treatment costs ranging from 90 to 200 per ton (D13377H, pp. 793, 799). 

Some of the topics we discuss in this chapter are essential for understanding processes such as MEUF. The same ideas can also be used for other separation processes (e.g., protein separation in reverse micelles) and in genetic engineering, as mentioned in Vignette 1.3 in Chapter 1. We also see in this chapter other applications such as using micelles as microreactors, i.e., using the unique environment inside micelles for catalysis and material synthesis. 

Thus the addition of n-pentane to mixtures of p-xylene and m-xyiene permits complete separation of the xylenes which form a binary eutectic with 11.8% para. Without the n-pentane, much para is lost in the eutectic, and none of the meta is recoverable in pure form. A detailed description of this process is given by Dale (1981), who calls it extractive crystallization. Other separation processes depend on the formation of high melting molecular compounds or clathrates with one of the constituents of the mixture. One example is carbon tetrachloride that forms a compound with p-xylene and alters the equilibrium so that its separation from m-xylene is... 

Fig. 3. Schematic of electrodialysis slack used in desalination and other separation processes...

Similar properties are needed for other types of membranes in use such as MF, UF, and NF membranes. Improved membranes may be used in other separation processes, not necessarily related to water [46-48],... 

From a kinetic standpoint (4), mass transfer per unit volume in distillation is limited only by the diffusional resistances on either side of the vapor-liquid interface in turbulent phases, with no inerts present, In almost every other separation process, there are inert solvents or... 

In spite of the availability of modem computer-aided techniques for curve fitting, these and other relatively simple, empirical equations are still found to be useful for the analysis of chemical engineering data (e.g. in the context of pressure swing adsorption or other separation processes). 

By analogy with other separation processes, the relative distribution in multicomponent systems can be analyzed in terms of a selectivity coefficient Omn = mCn nCm [Rubiu and Jorne, Ind. Eng. Chem. Fun-dam., 8, 474 (1969) J. Colloid Interface Sci., 33, 208 (1970)]. 

As a general rule, gas separation by membranes is most attractive in applications where a product purity of 95% or lower is acceptable or the feed flow-rate is not too high. As the required purity approaches 100%, the membranes become less cost effective than other separation processes. This is particularly true with single-stage units. For more stringent applications, some traditional separation processes are preferred or required to integrate with the membrane system. 

To design or control an evaporation or condensation process, you must know the conditions at which the transition from liquid to vapor or vapor to liquid takes place. Design or control of other separation processes such as distillation, absorption, and stripping also requires information on the conditions at which phase transitions occur and on the compositions of the resulting phases. This section outlines the required calculations for a relatively simple class of mixtures. 

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