Solvent recovery process

There are numerous applications in solvent recovery processes where evaporation equipment are employed. Figure 14 provides an example of a process scheme for toluene-di-isocyanate recovery. This is an example of continuous vacuum evaporation of distillation residues. 

Skladany, G.J., J.M. Thomas, G. Fisher and R. Ramachandran. The Design, Economics and Operation of a Biological Treatment System for Ketone Contaminated Ground and Solvent Recovery Process Waters. Presented at the 42nd Annual Purdue Industrial Waste Conference, Purdue University, West Lafayette, Indiana, 1987. 

The styrene concentrate is fed to a solvent recovery process or an extractive distillation process. The solvent selectively pulls the styrene out of the hydrocarbon mixture. The styrene raffinate, sans styrene, is sent back to be mixed with the pygas (although it can also be fractionated to pull out a high quality mixed xylene.)... 

The effluent from the reactor is cooled in a heat exchanger. The EO, byproducts, and unreacted ethylene are separated in a water-wash column in a manner just like the solvent recovery process described in Chapter 2. The EO is absorbed by the water while the by-products (mainly CO2, plus the everpresent cats and dogs in small quantities), and unreacted ethylene are not. The EO/water solution is then steam-stripped and purified by fractionation. 

The fermentation step to produce penicillin GA is the major cost element in the overall process to produce 6-APA. This is substantially due to the high cost of sterile engineering (Table 4.6 and 4.7). Clarification, extraction and solvent recovery steps are also significant, a reflection of the dilute and impure composition of fermentation broths. The concentration of 6-APA in the final broth has a big effect on total process costs. Thus increasing final 6-APA concentrations from 1.2-6.0% have been calculated to reduce production costs by over 50% (Table 4.8). By contrast the 6-APA production step cost is quite small, and is less that half the cost of the solvent recovery process (Table 4.6). The costs of the immobilized enzyme is not insignificant in a recent calculation it was estimated at 2.5 /kg 6-APA (Rasor and Tischer, 1998). 

The overhead is reheated and enters an adiabatic acetylene hydrogenation reactor, which transforms the acetylene selectively to ethylene and ethane. As an alternate, a solvent-recovery process can be applied without reheating the gas. 

FIG. 5 Solvent recovery process using activated carbon beds. 

The overhead solvent vapor in solvent recovery processes or boiler water vapor in power plant applications typifies vapor products. Blowdown refers to the periodic or continuous purging of the bottoms used to control buildup of undesirable material in the liquid phase when producing a vapor product. ... 

In the spinning of Rhovyl, the spinning chamber and the solvent recovery process form a closed system, and each spinning position is independent. Because a large quantity of carbon disulfide is used, special attention must be paid to prevent accidents such as explosion. 

Solvent recovery processes, both for recapture from air and water and for working up to a reusable... 

Toluene is very stable at any temperature typical of a solvent recovery process so there is no risk of it cracking or decomposing if it is held at its boiling point. 

This section discusses a solvent recovery process developed by Kureha Engineering Co. Ltd., Japan. In this continuous process, spherical particles of activated carbon (AC) circulate in the adsorption and desorption columns by fluidization. In the adsorption column, the particles form fluidized beds on multi-trays to adsorb the solvent in counter-current contact with the feed gas. The cleaned gas is released from the top of the adsorption-column to the atmosphere. 

Figure 22.2.8. Flow diagram of solvent recovery process.

The performance of the ACF solvent recovery process can be summarized as follows Since ACF has lager surface area and smaller bulk density than particulate activated carbon, PAC, ACF s filling density becomes 1/10 of PAC s. 

As these commercial exanples illustrate, the conplete extraction process includes the extraction unit and the solvent recovery process. This is shown schematically in Figure 13-1. In many applications the downstream solvent recovery step (often distillation or a chemical stripping step) is more expensive than the actual extraction step. Woods (1995. Table 4-8) lists a variety of commercial processes and the solvent regeneration step enployed. A variety of extraction cascades including single-stages, countercurrent cascades, and cross-flow cascades can be used we discuss these later. 

Figure 12.1.27 shows the relationship between the separation factor and the solubility of solvents in water. The separation of solvent by a pervaporation membrane occurs less efficiently as solvent solubiUty increases.The more concentrated the solution of solvent, the faster is the separation (Figure 12.1.28). Separation of hexane from a mixture with heptane is similar (Figure 12.1.29). The acrylic membrane shows good selectivity. These examples demonstrate the usefidness of pervaporation membranes in solvent recovery processes.

FIGURE 5.7 Solvent recovery process using activated carbon beds. (From Derbyshire, F., Jag-toyen, M., Andrews, R., Rao, A., Martin-Gullon, I., and Gmlke, E.A., in Chemistry and Physics of Carbon, L.R. Radovic, Ed., Marcel Dekker, New York, 2001, Vol. 27. With permission.)... 

Various solvents can be used as extraction agents, for example hexane, ethanol (96%) or hexane/ethanol mixtures. Benzene, cyclohexane, acetone, chloroform, and ether are also used however. The solvent destroys the cell wall of the alga and extracts the oil from the aqueous phase (medium) owing to the higher lipid solubility in organic solvents as compared to water. The solvent recovery process takes place in a subsequent distillation stage. 

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