Recovery of chlorine

Musty and Nickless [353] used Amberlite XAD-4 for the extraction and recovery of chlorinated insecticides and PCBs from water. In this method a glass column (20 x 1 cm) was packed with 2 g XAD-4 (60 - 85 mesh), and 1 litre of tap water (containing 1 part per 109 of insecticides) was passed through the column at 8 ml/min. The column was dried by drawing a stream of air through, then the insecticides were eluted with 100 ml ethyl ether-hexane (1 9). The eluate... 

The great advantage of the absorption process over the synthesis of a by-product was its direct recovery of chlorine. Such a process or one that uses chlorine in another on-site process with steady demand is the ideal. More vigorous liquefaction is one approach to reducing the amount of chlorine value to be disposed of, and it has usually been chosen as the substitute for absorption. In this chapter, we discuss the use of gas-separation membranes as an alternative. 

Lokhandwala et al. [6] have reported field and laboratory work on the recovery of chlorine from liquefaction tail gas. Results suggest the following ... 

Applying this information to a typical diaphragm-cell tail gas, Fig. 7.4 shows the logarithm of the amount of unrecovered chlorine versus the relative membrane area required. Recovery of chlorine is not far from a first-order process. As chlorine selectively passes through the membrane, the partial pressures of the impurities increase in the remaining gas. This causes their rates of permeation to increase. The membrane area required for permeation of, say, 30% of the nitrogen is less than twice that required for 15%. 

Table 7.3 Recovery of chlorine from cell gas with an oxygen content of no more than 0.7%. Data obtained from Fig. 7.10.

Table 7.4 Incremental recovery of chlorine by membranes (800 tonnes day 1 plant liquefaction conditions — 18°C and 450 kPa).

The simplest kind of cell construction, shown in Figure 19.19(d), suffices for the production of hydrogen by electrolysis of water and for the recovery of chlorine from waste HC1. The term filter-press cell is applied to this kind of equipment because of the layered construction. These two electrolyses are economically feasible under some conditions. Some details are given by Hine (1985). 

Microemulsions became well known from about 1975 to 1980 because of their use in "micellar-polymer" enhanced oil recovery (EOR) (35). This technology exploits the ultralow interfacial tensions that exist among top, microemulsion, and bottom phases to remove large amounts of petroleum from porous rocks, that would be unrecoverable by conventional technologies (36,37). Since about 1990, interest in the use of this property of microemulsions has shifted to the recovery of chlorinated compounds and other industrial solvents from shallow aquifers. The latter application (15) is sometimes called surfactant-enhanced aquifer remediation (SEAR). 

Pyle and Marcus [ 102] achieved low ppb detection limits for the determination of organochlorine insecticides in soil using accelerated solvent extraction followed by gas chromatography ion trap tandem mass spectrometry. Richter et al. [103] showed that accelerated solvent extraction gave essentially equivalent recoveries of chlorinated dibenzo-p-dioxins and dibenzofurans from soil compounds to Soxhlet extraction, but in less time and using much less solvent. 

Wendell Dunn A family of chlorine beneficiation processes based on selective chlorination of ores in a fluidized bed. Developed by W.E. Dunn of Chlorine Technology in Australia in the 1970s, primarily for beneficiating ilmenite. The first such commercial ilmenite beneficiation plant, completed in 1991, was that of Bene-Chlor Chemicals Private, Madras, India. The entire process, including recovery of chlorine by oxidizing the ferrous chloride, was piloted by Heubach in... 

Minet, Ronald G., and Tsotsis, Theodore T. Recirculating fluidized-bed process and apparatus for the recovery of chlorine from hydrogen chloride, ES 2010473 (1989). 

Y. Ding and J. Winnick, Electrolytic Recovery of Chlorine from Hydrogen Chloride Gas with Fused Molten Salt Electrolyte. /. Appl. Electrochem. 26, 143-146 (1996). 

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. 

High quality - ACF has low catalytic activity and a short adsorption and desorption cycle time (approx. 10 min). The solvent is less decomposed in the process. In the recovery of chlorine-containing solvents, it produces less acids as decomposition products. Thus it is less corrosive to the materials of construction. Also, the recovered solvent is of better quality. 

Full processing of chlorine gas (Fig. 6.6) takes a hot, wet vapor at approximately atmospheric pressure and converts it to a cold, dry liquid under significant positive pressure. The common processing steps therefore are cooling, drying, compression, and liquefaction. The severity of the two latter processes depends on the desired degree of recovery of chlorine as the liquid and on the composition of the gas produced in the cells. The major impurities in this gas will be ... 

FIGURE 9.40. Recovery of chlorine from tail gas by absorption. 

This reaction was used in the small-scale production of chlorine. It operated under modest conditions (100-110°C), but corrosion problems were severe and the stoichiometry limited the recovery of chlorine to 50%. Practical values were 35-40%. On the positive side, the reactor gas had a high ( 90%) concentration of chlorine [6]. In early operation, manganese chloride was a waste product. In 1866, Weldon achieved recycle of the manganese value by treating the chloride with lime while steaming with air or oxygen at 55-60°C ... 

The catalyst transfers back and forth between the two reactors, as in Fig. 15.5, and effectively carries the chlorine value from the chlorinator to the oxidizer, where it can be released as chlorine gas. For this reason, the process was dubbed the Catalytic Carrier Process. Separation of the two stages allows each to operate at its own optimum conditions, and higher conversion of HCI to CI2 is the result. This process has operated on a pilot scale in Spain, but no commercial operation has been reported. A study of projected economics [19] based on the optimistic assumptions of quantitative conversion of HCI vapor to chlorine and the recovery of chlorine by absorption in the prohibited solvent CCI4 indicated that this process had advantages over certain other oxidation processes... 

Ding and Winnick [52] studied the recovery of chlorine from a molten LiCl-KCl eutectic. The usual oxidation of the chloride ion takes place at the anode. The cathode generates hydrogen gas from anhydrous HCl, at the same time replacing the chloride ion ... 

The decomposition voltage for the process is low, as with the Kyoto cell (Section 15.2.2.3). A possible application for this approach is the recovery of chlorine from liquefaction tail gas and other dilute streams. 

A promising approach to selective recovery of chlorine from the inerts in the vent gas is to electrochemically reduce chlorine to chloride at the cathode and oxidize the ion to chlorine at the anode. The selectivity arises because of the fast kinetics of the chlorine reduction reaction compared to that of the oxygen and carbon dioxide reduction... 

Barmashenko V, Jorissen J (2005) Recovery of chlorine from dilute hydrochloric acid by electrolysis using a chlorine resistant anion exchange membrane. J Appl Electrochem 35 1311-1319. doi 10.1007/ S10800-005-9063-1... 

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