Scrubbing, reaction hazard

Sulfa-scrub A process for removing low concentrations of hydrogen sulfide from gas streams by reaction with hexahydrotriazine. The product is water-soluble, non-corosive, and non-hazardous. Developed by the Quaker Petroleum Chemical Company in 1991. 

Prevent hazards to the environment by following accepted waste disposal procedures. Chemical reactions may require traps or scrubbing devices to prevent the escape of toxic substances. 

Sulfur tetrafluoride is a hazardous and highly toxic gas [4], in some aspects comparable with phosgene [12]. For reactions with SF4 with or without HF autoclaves made from Hastelloy C with Monel 400 piping and valves are recommended [13]. When handling SF4 sufficient ventilation must be provided and protective goggles and gloves should be worn. On autoclave depressurization, excess SF4 and HF should be scrubbed with potassium hydroxide solution. 

Any hazard evaluation must thus include an examination of all phases of the process. As with the example above, one area which is often ignored involves the quenching, scrubbing, and disposal of reactions. It must be remembered that these reactions suffer the same consequences of scale-up as the more productive components of the process. 

Electrolysis is the reaction of either oxidation or reduction taking place at the surface of conductive electrodes immersed in an electrolyte, under the influence of an applied potential. This process is used for reclaiming heavy metals from concentrated aqueous solutions. Application to waste water treatment may be limited because of cost factors. A frequent application is the recovery for recycle or reuse of metals, like copper, from waste streams. Pilot applications include oxidation of cyanide waste and separation of oil-water mixtures. Gaseous emissions may occur and, if they are hazardous and cannot be vented to the atmosphere, further treatment, such as scrubbing, is required. Waste water from the process may also require further treatment. 

Another problem is the detoxification of the hazardous wastes that are already present in the environment. Efforts are thwarted by the problan of how less toxic are the detoxification products in themselves Thus, in incineration, for instance, what are the toxicides of all the final combustion products Called products of incomplete combustion, or PlCs, these are the myriad by-products and coproducts of the competing reactions that occur during combustion, and for that matter, during any chemical conversion, more or less. Can they ever be fully detected and analyzed Or if selectively scrubbed, what is to be the disposition of the absorbed materials What is called detoxification may be merely a further dispersion throughout the ecosphere, and a process of trading one set of problems for another. 

The possibility of reaction of wash chemicals with deposits in the column should be considered. The route of venting or disposing of any hazardous reaction products must be adequately planned. In one incident (7), hydrogen sulfide was liberated to the atmosphere following reaction of an acid used for washing with deposits in a caustic scrubbing system. 

Separation of acetylene from the monomer by scrubbing with ammoniacal cuprous chloride (CAUTION This procedure may lead to the formation of metal acetylides among the reaction products. Acetylides of heavy metals are said to be explosive, especially when dry. Partially dried acetylides may present similar hazards) ... 

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