Hypochlorite process technology

Almost 40 years later the Lummus Co. patented an integrated process involving the addition of chlorine along with the sodium chloride and sodium hydroxide from the cathode side of an electrolytic cell to a tertiary alcohol such as tertiary butanol to produce the tertiary alkyl hypochlorite. The hypochlorite phase separates, and the aqueous brine solution is returned to the electrolytic cells. The alkyl hypochlorite reacts with an olefin in the presence of water to produce a chlorohydrin and the tertiary alcohol, which is returned to the chlorinator. With propylene, a selectivity to the chlorohydrin of better than 96% is reported (52). A series of other patents covering this technology appeared during the 1980s (53—56). 

Preference should be given to the membrane process due to its less polluting characteristics over other technologies. In addition, the scrubbing of chlorine from tail gases to produce hypochlorite is highly recommended. 

Traditionally, processes have used a single destruction technique, and this has historically been the case also for HYDECAT . Thus, nearly all installed processes treat the waste hypochlorite at the concentration it exits the scrubbing system down to concentrations suitable for discharge (Fig. 26.2). The key aspect in the re-evaluation described herein is to question the practices of firstly single technology and secondly end-of-pipe treatment the destruction of the hypochlorite exclusively in the blowdown stream from the scrubber. That is, it is questioned whether installation of a single treatment technique solely to process the effluent at its natural concentration from the scrubber loop is necessarily the best process option. This chapter will consider the two parts of the question paraphrased above sequentially. 

Abbott, P.E.J., Carlin, M., Fakley, M.E., Hancock, F.E. King, F. (1991) ICIHYDECAT process for the catalytic destruction of hypochlorite effluent streams. In Modern Chlor-Alkali Technology (ed. T.C. Wellington), Vol. 5, pp. 23-34. Published for SCI by Elsevier Science, Amsterdam. 

A complementary approach to the synthesis (1R,2S)-1 has been developed by Merck using (.S, .S )-Mnl.CI catalyst in a hypochlorite medium to provide (IS, 2/0-indene oxide 26. This intermediate was converted without isolation to r/.v-aminoindanol in a stereoselective and regioselective manner using Ritter technology (Scheme 24.2). Several key issues, detailed later in this chapter, have been addressed and resolved in both Jacobsen s AE52 and Ritter technology50 to develop a reproducible and practical large-scale process for the synthesis of enantiopure d.s-aminoindanol. 

Chorine based oxidants (particularly the element itself and sodium hypochlorite) are used in a number of areas of the chemical industry. Chlorinated intermediates such as epichlorhydrin and chlorinated solvents have traditionally been extensively used in a variety of chemical processes. Environmental pressure, both consumer based and legislative, is currently being exerted, and will increase in the future, for the reduction, and probably eventual removal, of the use of these reagents and intermediates. H202 based technology is well placed to offer environmentally acceptable alternatives and is already used in many areas for this reason. 

In recent years, a number of electrolytic processes have utilized membranes in producing both anodic and cathodic products. By far, however, the most important application of this technology has been in the chlor-alkali industry. Intense commercial and academic interest has been focused into this field during the past decade so that ion exchange theory as applied to membranes is in a more advanced state than any of the other ion exchange systems. The primary examples of industrial chlor-alkali electrochemistry are found in the production of chlorine, caustic soda and potash, hydrogen and hypochlorite (1) (4). 

P.E.J. Abbott, M. Carlin, M.E. Fakley, M.E. Hancock, and F. King, ICI Hydecat Process for the Catalytic Destruction of Hypochlorite Effluent Streams. In T.C. Wellington (ed.), Modem Chlor-Alkali Technology, vol. 3, Elsevier Applied Science, London (1992), p. 23. 

Other chapters deal with utility systems, cell room design and arrangement (with an emphasis on direct current supply), alternative processes for the production of either chlorine or caustic without the other, the production of hypochlorite, industrial hygiene, and speculations on future developments in technology. There is an Appendix with selected physical property data. 

The membrane process enables addition of hydrochloric acid into anolyte for neutralization of the OH ions, which enter through the membrane from catholyte (see Fig. 1). Moreover, anolyte can be acidified for reduced by-product formation. Oxygen evolution then is decreased to less than 0.5 vol.% in the anode gas and generation of hypochlorite and chlorate is completely suppressed (see reactions (3) and (5)-(7) in section 2 of entry Chlorine and Caustic Technology, Overview and Traditional Processes ). However, the addition of acid has to be performed very carefully with sufficient mixing of the anolyte, usually by the mammoth pump effect of the produced chlorine gas. The pH value must nowhere fall below 2. Otherwise, the carboxylic acid fixed ions (see upper part of Fig. 2), which are the anions of a relatively weak acid, will combine with H" ions and lose their activity so that the membrane is damaged. 

The last decade has seen the introduction of a number of small electrolysis cells for the generation of either hypochlorite or chlorine gas in many applications, either type of cell could, in principle, be employed and the choice will then depend on technological factors. In the water and effiuent-treatment industry, the common applications of on-site chlorine and hypochlorite cells will include the treatment of sewage (particularly at remote sites), the sierilkatton of water for food processes and hospital laundries, the treatment of water on board ships and for swimming pools, the treatment of cooling water at coastal power stations to prevent the growth of shellfish and seaweed in the pipes and the enhanced... 

RDE Refining of Cyanide Industriai Wastewaters Cyanides are used in many industrial processes such as surface treatment and noble metal plating. After several cycles the baths must be renewed in order to maintain the same operating conditions. The conventional physicochemical process applied to eliminate cyanide from liquid effluents is mainly oxidation by hypochlorite or ozone. Depleted wastewaters contain O.lmg/L of free cyanide and may be rejected into the environment. The new environmental regulations are more restrictive and concern both free and total cyanide. RDE technology was applied in order to reduce both free and complexed cyanide levels. 

---