Recovery of organic solvents

The recovery of useful components and the removal of harmful components from VOC present in industrial waste gases involves two different objectives. When the effluent stream contains a high concentration (1 to 2%) of the organic compound, then recovery and recycling is normally the principal objective. However, when the concentration of the pollutant is very low, of the order of 10 to 1000 ppm or even lower, then their capture and disposal is the preferred objective. 

The principle of solvent recovery of activated carbon adsorption has been known for almost a century a process was patented in 1905, but in practice the method was used in 1916 when vapors of volatile substances were recovered by using on activated carbon prepared by using chemical activation with zinc chloride. The solvent recovery became very important during World War 1, due to the shortage of solvents because the war industries needed them in large quantities. 

Some of the more important industries that produce solvent-contained air streams are printing dry cleaning and the manufacture of paints, polymers, adhesives, celluloid, rubber (e.g., rubber-coated fabrics), rayon, and gunpowder and extraction processes. The main solvents recovered by activated carbon adsorption are benzene, toluene, xylene, alcohols, acetone, petrol, ether, carbon disulfide, halocarbons (e.g., chloroform, carbon tetrachloride, trichloroethylene, methylene chloride, chlorobenzene, etc.). The major production facilities and the solvents recovered are listed in Table 5.3. In many cases the concentration of the organic solvent in waste gases is of the order of 1 to 2%. 

When allowed to mix with the atmosphere, the highly volatile nature of some of the solvents can create several unacceptable problems, such as fire and explosion hazards, and pollution of the enviromnent resulting in several health ailments. It is important, therefore, that the solvents be removed from the industrial exhaust streams 

Rubber industry, rubber-coated fabrics, rubber-asbestos goods Paint shops Celluloid production Plastics and artificial leather production Extraction processes Film and foil manufacture Adhesive plaster production 

The processing of reaction mixtures (e.g. through distillation and extraction) often involves the recovery of organic solvents. These recovered with high purity and recycled into production process. Process economy is thus improved. 

There are two types of solvent recovery (Fig. 36) and they can be differentiated as follows [35]  

BWTP Biological wosiewotar treolmflfit plant WIP-Wasle incineration plant PTC-Phase transformation catalyst 

BWTP = Biological wastewater treatment plant WIP = Waste incineration plant PTC = Phase transfonnation catalyst 

Methylation with j CH3CI and - phase trans formation catalyst (PTC) 

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Adsorption, which utilizes the ability of a solid adsorbent to adsorb specific components from a gaseous or a liquid solution onto its surface. Examples of adsorption include the use of granular activated carbon for the removal of ben-zene/toluene/xylene mixtures from underground water, the separation of ketones from aqueous wastes of an oil refinery, aad the recovery of organic solvents from the exhaust gases of polymer manufacturing facilities. Other examples include the use of activated alumina to adsorb fluorides and arsenic from metal-finishing emissions. 

Fleming. H.L.. 1990. Dehydration and recovery of organic solvents by pervaporation. in Proc. 8th Annual BBC Mcmbr. Planning Conf.. Cambridge. MA. USA, p. 293. 

Roach, J. W., Recovery of organic solvents from liquid mixtures, U.S. 4,508,597... 

A market has been developed for the recovery of organic solvents used in diverse industrial operations as processing mediums in the manufacture of plastics, explosives and as agents to apply a product to its intended use as in painting and printing. Many such solvents are volatile and the escape of such vapors into work rooms can create hazards to health, and from fire and explosion. As the amount of... 

Recovery of organic solvents from solvent residues, solvent - product mixtures, aqueous solutions, and production residues... 

K.-D. Henning, W. Bongartz, J. Degel, Adsorptive Removal and Recovery of organic Solvents,... 

As highlighted above a wide variety of technologies are available for the recovery of organic solvents. The choice of process can be confusing. Table 7.7 is provided as guidance on the appropriate techniques suitable for solvent recovery from gases, liquids and solids. Disposal methods are also listed for completeness. Detailed descriptions of each technology are provided in the text below. 

Figure 2 Scheme of a fractional distillalion system for organic solvent recovery 1, cooler 2, distillation column 3, fraction flasks 4, reboiler 5, fraction split valve 6, reflux valve TIS, TIC, TIA - temperature sensors FA - cooler sensor LA - solvent level sensor. (Reproduced with permission from Stepnowski P (2003) Recovery of organic solvents after chromatographic analysis. Analitique 4 39-41.)... 

Recovery of Organic Solvents. In connection with the recovery of volatile organic substances from aqueous solution, as in the separation of acetone or ethanol from aqueous solutions containing less than 5 per cent solute, Othmer, et al (131, 132) have shown that considerable savings can be expected in heat requirements if extraction by an appropriate high-boiling solvent followed by distillation of the extracted solute is used, as compared with direct rectification. 

ACFs have been successfully applied in many fields, such as the treatment of organic and inorganic waste gases, the recovery of organic solvent, air cleaning and deodorization, treatment of wastewater and drinking water, separation and recovery of precious metals, as medical adsorbents and protective articles, and in electrodes [57], Some of the most common applications of ACF are listed below Table 8.2. 

Although continuous processing of liquids is possible, it is restricted to liquids with low viscosity. Known industrial applications are the caffeine recovery from corresponding loaded CO2 streams (see Figure 8.10), processing of lipids, and the recovery of organic solvents from wastewater. 

Leemann, M., Eigenberger, G., and Strathmann, H. (1996). Vapor permeation for the recovery of organic solvents from waste air streams Separation capacities and process optimization. J. Membr. Sci. 113, 313. 

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