Hypochlorite temperature control

Solid Sta.te. The stabiHty of neutral calcium hypochlorite is primarily a function of moisture, lime, impurities, and temperature. Product containing - 7% water may lose 2—3% av CI2 during the first year when stored in warehouses without temperature control in moderate climates. Decomposition produces CaCl2, Ca(C102)2, and O2. 

It has been reported1 that, during the preparation of f-butyl hypochlorite according to the directions published in this series,2 an explosion occurred and caused moderate physical damage and minor injury to the operator. The cause of the accident has been attributed to lack of proper temperature control during addition of chlorine. It is strongly recommended that the reaction vessel be fitted with a thermometer that dips into the reaction mixture and that the rate of flow of chlorine be regulated so that the temperature of the reaction mixture never exceeds 20°. 

Noteworthy in the above reactions is the chemoselectivity and the absence of side reactions involving potentially reactive sites (i.e., electron-rich alkenes and aromatic rings and esters). However, on occasion such side reactions do occur (21—>22 and 23),57 although in this case temperature and hypochlorite concentration control minimize the formation of 23. 

Prevention of hot spots and efficient removal of the heat of reaction are very important because of the thermal instability of hypochlorites. The continuing reaction of hypochlorite to form unwanted byproducts is part of the discussion of emergency vent scrubbers (Section 9.1.10.3A), where it is more of an issue. Here, we note that the production of high-quality bleach depends on a consistent supply of chlorine in the tail gas and on adequate temperature control. The absorbing solution is therefore circulated by titanium centrifugal pumps around the reactor(s) through titanium coolers, usually of the plate-and-frame type. The recirculation of liquor in itself provides turbulence in the reaction zone, and the volume of circulation determines the maximum temperature possible in the reactor. A gas feed or the vaporization of a liquid chlorine supply may also be used to promote turbulence. 

Environment Internal Treated cooling water adjusted with sulfuric acid for pH control and sodium hypochlorite added as a biocide pressure 50 psi (345 kPa), temperature 100-120°F (38-49°C), water velocity 7 ft/s (2.1 m/s), pH 8.0-8.4, sulfate 500-1000 ppm, chloride 100-450 ppm, total hardness 500 ppm External Steam and condensate... 

In the first step the chlorine from the tail gas and chlorine feed reacts with the caustic in the jet-loop reactor. The advantage of the jet-loop reactor is that it also acts as a suction device for the gas stream. The residence time of the liquid in step one is dependent on the capacity of the hypochlorite production and liquid level in the tank and varies between 1 and 4 h. A heat exchanger in the loop controls the temperatures in steps one and two. The amount of caustic in the feed-tank of step two is the back-up for failure of chlorine liquefaction. 

The process is dependent upon temperature, pH and hypochlorite concentration, and must be carefully controlled to avoid thermal runaway reactions. The reaction itself, combined with settling times for the catalyst slurry, can take three to four days, and the end-product - heavy metal salts - must be handled as hazardous waste. 

This compound is a useful chlorinating reagent, and although relatively stable, its purification by distillation is not normally attempted. Primary and secondary hypochlorites readily explode when exposed to light, and even in the absence of light rapid decomposition occurs at room temperature. t-Butyl hypochlorite may be prepared by the interaction of t-butyl alcohol, sodium hydroxide and chlorine at low temperature, which must be carefully controlled during the reaction... 

When chlorine dioxide is used as a disinfectant, chlorite and chlorate are formed as by-products. These are sometimes monitored, but control can be achieved by control of the dose of chlorine dioxide applied, Chlorate may also form in significant quantities in hypochlorite that is stored for an extended period, particularly at higher ambient temperatures again, it is best controlled by management procedures. 

Sulfoxides (l)1,2 are generally prepared by controlled oxidation of sulfides (2) (see Chapter 4, p. 48) (Scheme 1). The choice of oxidant and the reaction conditions are critical to avoid further oxidation to the sulfone (see Chapter 10, p. 195). On a small scale, the preferred reagents are(i) sodium metaperiodate in aqueous methanol (0°C), (ii) m-chloroperbenzoic acid (MCPBA) in dichloromethane or ethyl acetate, the latter being more useful since it can be used at lower temperatures (-40°C), and (iii) t-butyl hypochlorite in methanol (Scheme 1). 

Disposable equipment should not be re-sterilized or re-used. 2. Ethylene oxide is a difficult process to control and the Department of Health discourages its use in hospitals. 3. Low temperature steam with formaldehyde is of value in the sterilization/disinfection of some heat-sensitive materials. 4. Chemical agents, e.g. gluteraldehyde, hypochlorite. 

The product factors which may need consideration include viscocity, cleanliness of fill, whether product froths or is corrosive, coefficient of expansion, volume to vacuity or ullage ratio, etc. Note that alcoholic based products have a higher coefficient of expansion than water, hence need a higher level of vacuity. Vacuity levels normally lie between 2% and 10%. Certain more volatile materials and chemical based products will create internal pressure according to the vapour pressure exerted for a given temperature. In certain instances, e.g. with peroxides, hypochlorites and similar products, pressure may be controlled by the use of venting closure systems. 

Section 9.1.9.3, on the deliberate production of bleach according to reaction (85), discusses the physical chemistry of the process and the need for careful control of the reaction conditions. In an emergency situation, good control of the temperature in the reaction zone may be absent, and side reactions are likely. One of these is the reaction of hypochlorite to chloride and chlorate ... 

Flow controllers set the rates of both streams, one being under flow-ratio control. In principle, either caustic soda or dilution water can be the master stream, with the other following it to maintain the ratio. Blending is controlled by a feedforward system, ultimately reset by the product concentration or density. Feedback from caustic concentration measurement (usually by density) could be used for final adjustment, but the concentration of the hypochlorite solution is the more important variable. The simple flow-ratio controller mentioned here can be replaced by a multi-stream version that allows use of other streams in addition to the principal 50% NaOH and dilution water. A cooler downstream of the mixing point removes the heat of dilution. The standard design is a titanium plate exchanger, which can also provide turbulence to complete the mixing process. Chlorine joins the diluted caustic in the reactor. Its rate of addition is controlled by an oxidation-reduction potential (ORP) instrument. The reaction mass recirculates from a collection tank around the system to reduce the increase of temperature across the reactor and to promote turbulence. The net production is removed from the tank, normally under level control. 

---