Solvent adsorption trichloroethylene

Steam is hot ( 120°C or 250°C or somewhat higher). Adsorption of any solvent molecule (trichloroethylene, water, methylene chloride, etc.) is not favored at higher temperatures. 

A number of other systems are based on the use of polymers for adsorption of solvents, but perhaps of particular note is another process from the Dow Chemical Company [21]. Sorbathane is the trade name for the resin which has been specifically developed for the recovery of chlorinated solvents such as perchloroethylene and trichloroethylene. Units which use this resin are usually two-tank systems which sequentially adsorb and desorb. Adsorption is achieved by passage of the solvent-laden air through the resin which is characterised by a high surface area, small pore size, a swellable polymer matrix and fast adsorption kinetics. Desorption of the solvent occurs when the resin is heated to 80-90°C and the application of a vacuum of less than lOOmbar. The novelty and advantage of using this system is that adsorption and desorption of the stabilisers, required for these solvents, also occurs and therefore the need for restabilisation, as necessary following activated carbon recovery, is eliminated. 

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%. 

Figure 4.24 Adsorption of Solvent onto Adsorberrt as Trichloroethylene Vapor is Evacuated from Enclosed Vapor Degreaser...

Often substituted for one another to delay or resist negative environmental consequences, trichloroethylene and n-propyl bromide have similar performance as cleaning solvents (Ref 2, Chapter 2), good adsorption on activated carbon (Table 4.10) similar, compatibility in or with water (Table 4.10), and aggressive reactivity with water to produce... 

The complicated application involves use of lip vents attached to an open-top vapor degreaser in which each of the six solvents noted above is being independently used. The assumed feed and exit concentrations are 20 x and 1 x the exposure limit respectively. Complications arise from the intersection of three factors (1) the fictitious feed and exit concentrations to and from the adsorber are different for each of the six solvents (because they have different posted exposure limits. Footnote 55), (2) each solvent has a different adsorption vs. concentration response (Figure 4.17), and (3) each solvent has a different solubility (Table 4.10) in and with water (condensed steam). For example, the range of solvent concentrations for n-propyl bromide or trichloroethylene is 200 ppm to 10 ppm, and that for CFC-113 is 1000 ppm to 20,000 ppm. Solubility data of many cleaning solvents in water, and of water in cleaning solvents, are available in Appendix 1, Table A1-5. 

Within each of the two types of operation, a cost evaluation was completed of the adsorption unit fed separately with six different solvents (toluene, n-propyl bromide, perchloroethylene, methylene chloride, trichloroethylene, andCFC-113). 

Measured adsorption data for four cleaning solvents (methylene chloride, trichloroethylene, perchloroethylene, and CFC-113) are plotted in Figure A2-l . ... 

At a pore diameter of 3 nm, calculated adsorptive capacity of trichloroethylene, whose kinetic diameter is 0.62 nm (Chapter 4, Footnote 6), changes greatly over a significant range of concentrations of solvent in air. 

This can be seen from the calculated adsorption isotherms plotted in Figure A2-20 for several oxygenated solvents with different sfruaures, and data of trichloroethylene. 

The nature of the attraction between solvents and adsorption sites depends upon the nature of the solvents being adsorbed. Solvents with polar centers (chlorine atoms in trichloroethylene, for example) are attracted by mutual alignment of electron structures. Solvents with oxygen atoms (alcohols or ethers, for example) are attracted through hydrogen bonding... 

At the Ford Motor Company s spark plug plant in Fostoria, Ohio, trichloroethylene vapor in the air from degreaser units is recovered by adsorption on activated carbon. Two 72-in.-diameter adsorbers are used, each containing 1,300 lb of carbon pellets. The system is reported to be capable of recovering 400 to 450 gal. of liquid trichloroethylene per day with a collection efficiency of over 90%. Operating costs were only about 3% of the value of the recovered solvent (Anon.. 1969). 

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