Extraction process design

The Carver-Greenfield process (C-G process) is a patented drying and solvent extraction process designed to separate oil-soluble contaminants from liquid, solid, or slurry wastes. The process has been used extensively over the last 30 years to dry and extract compounds from a variety of wet, oily solids in various industries. C-G process units may consist of modular designs or custom made for large-capacity operations. 

A straightforward, though not optimal, solvent extraction process design would involve repetitive contacting of the sludge with fresh solvent until satisfactory cleanup has been achived. The feasibility of such a design can be easily verified through consecutive batch extraction experiments, and these experiments were also performed. 

Extraction, a unit operation, is a complex and rapidly developing subject area (1,2). The chemistry of extraction and extractants has been comprehensively described (3,4). The main advantage of solvent extraction as an industrial process Hes in its versatiHty because of the enormous potential choice of solvents and extractants. The industrial appHcation of solvent extraction, including equipment design and operation, is a subject in itself (5). The fundamentals and technology of metal extraction processes have been described (6,7), as has the role of solvent extraction in relation to the overall development and feasibiHty of processes (8). The control of extraction columns has also been discussed (9). 

Multicomponent systems containing four or more components become difficult to display graphically. However, process-design calculations can often be made for the extraction of the component with the lowest partition ratio K and treated as a ternaiy system. The components with higher K values may be extracted more thoroughly from the raffinate than the solute chosen for design. Or computer calculations can be used to reduce the tedium of multicomponent, multistage calculations. 

The main objective for calculating the number of theoretical stages (or mass-transfer units) in the design of a hquid-liquid extraction process is to evaluate the compromise between the size of the equipment, or number of contactors required, and the ratio of extraction solvent to feed flow rates required to achieve the desired transfer of mass from one phase to the other. In any mass-transfer process there can be an infinite number of combinations of flow rates, number of stages, and degrees of solute transfer. The optimum is governed by economic considerations. 

The ratio of wash solvent to extraction solvent is the same in the enriching section as in the stripping section if no solvent is added in the feed. The degree of separation to be achieved can be chosen for the process design, such as 99 percent of component b into the extrac-t stream and 99 percent of component c into the raffinate stream. Then the feed rate can be chosen so that the solute loadings in the extrac-t stream and... 

At the heart of a leaching plant design at any level—conceptual, pre-liminaiy, firm engineering, or whatever—is unit-operations and process design of the extraction unit or hne. The major aspects that are particular for the leaching operation are the selection of process and operating conditions and the sizing of the extrac tion equipment. 

In order to illustrate an example of process design for the manufacture of enantiopure drug substances on an industrial SMB system, consider manufacturing 10 ton/ year of an enantiopure drug. The racemic drug by definition is a 50 50 mixture of each enantiomer (products A and B). The goal is to process enantiopure drug substances in order to obtain 99 % purity for both the extract and the raffinate. 

In order to illustrate the critical process parameters of SMB process validation, we will consider the separation of the racemic drug as described in Process design. The study represents the effect of the influence of feed concentration, number of plates and retention factor on the second eluting enantiomer. The simulation of the process for different values of feed concentration is performed and the variations of the extract and raffinate purities are shown in Fig. 10.10. 

Experimental data, or predictions, that give the distribution of components between the two solvent phases, are needed for the design of liquid-liquid extraction processes and mutual solubility limits will be needed for the design of decanters, and other liquid-liquid separators. 

Perry et al. (1997) give a useful summary of solubility data. Liquid-liquid equilibrium compositions can be predicted from vapour-liquid equilibrium data, but the predictions are seldom accurate enough for use in the design of liquid-liquid extraction processes. 

The primary task in the design of an extractor for a liquid-liquid extraction process is the determination of the number of stages needed to achieve the separation required. 

Computer programs are available for the design of extraction processes and would normally be included in the various commercial process simulation packages available see Chapter 4. 

Container size and physical design the concentration of materials leachable from glass decreases with increasing container size. The concentration of leached materials will increase with increasing surface-to-volume ratio for a given container size. In containers treated by the glass manufacturer, this extraction process can be significantly retarded [5]. 

The last example differs from the previous examples in this section in that they involved discrete variables, while pressure and temperature are continuous functions. The same problem could also arise in the discrete case. For instance, although the initial design might favor crystallization over extraction, if the sequence of processing steps were changed the extractive process might be preferable. 

E. Gorin, C. J. Kulik, and H. E. Lebowitz, "Deashing of Coal Liquefaction Products Via Partial Deasphalting. 2. Hydrogenation and Hydro extract ion EffluentsINEC Process Design and Developments, Vol. 16, Jan. 1977. 

Citrex [Citric acid extraction] An improved version of the Citrate process, designed by Peabody Engineereed Systems. 

There are numerous refining methods employed to extract the fractions of petroleum liquids and gases. A particular refinery process design is normally dependent on the raw feedstock characteristics (e.g., crude oil and produced gas natural specifications) and the market demands (e.g., aviation or automotive gasolines), which it intends to meet. 

The precise liquid-liquid equilibria (LLE) data is necessary to rational design of many chemical processes and optimize extraction processes. Many researchers have investigated various kinds of multi-component systems in order to understand and provide further... 

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