Chlorine electrolytic cells

After listening intently, the operating foreman explained that mere traces of chrome salts in the brine system could create an explosive situation within the electrolytic chlorine cells. Traces of chrome salts in the feed brine to the chlorine cells liberate hydrogen gas in the chlorine cell gas. Hydrogen in the chlorine cell gas has a very wide explosive range. Installation of stainless steel equipment in sodium chloride brine systems has devastated chlorine processing equipment within other similar chlorine manufacturing plants. The maintenance foreman had the improper pump impeller removed immediately before any problems occurred. 

T. A. Liederbach, A.M. Greenbeig, and V.H. Thomas. Commercial Application of Cathode Coatings in Electrolytic Chlorine Cells, Commercial Application of Cathode Coatings in Electrolytic Chlorine Cells, In M.O. Coulter (ed.). Modem Chlor-Alkali Technology, Ellis Horwood, Chichester, (1980), p. 145. 

For example, direct isotope dilution analysis is used for mercury inventory in industry (Cowley et al. 1966 Enomoto et al. 1975). The mass X of mercury in electrolytic chlorine cells is determined using Hg, Hg, or a mixture of them. An aliquot of known mass Wo and activity Ao and hence known specific activity So is taken from a stock of mercury labeled with the tracer, added to each electrolytic cell, and left to mix. After homogenization, a sample of mercury is taken from each cell. The samples are shaken with 15-20% HCl to decompose amalgam. The mass W and activity A of the samples are measured to yield to S and, accordingly, X. The accuracy is better than 1%. 

Salt was first electrochemicaHy decomposed by Cmickshank ia 1800, and ia 1808 Davy confirmed chlorine to be an element. In the 1830s Michael Faraday, Davy s laboratory assistant, produced definitive work on both the electrolytic generation of chlorine and its ease of Hquefaction. And ia 1851 Watt obtained the first Fnglish patent for an electrolytic chlorine production cell (11). 

When magnesium oxide is chlorinated in the presence of powdered coke or coal (qv), anhydrous magnesium chloride is formed. In the production of magnesium metal, briquettes containing CaCl2, KCl, NaCl, MgO, and carbon are chlorinated at a temperature such that the electrolyte or cell melt collects at the bottom of the chlorinator, enabling the Hquid to be transferred directly to the electrolytic cells. 

At present about 77% of the industrial hydrogen produced is from petrochemicals, 18% from coal, 4% by electrolysis of aqueous solutions and at most 1% from other sources. Thus, hydrogen is produced as a byproduct of the brine electrolysis process for the manufacture of chlorine and sodium hydroxide (p. 798). The ratio of H2 Cl2 NaOH is, of course, fixed by stoichiometry and this is an economic determinant since bulk transport of the byproduct hydrogen is expensive. To illustrate the scde of the problem the total world chlorine production capacity is about 38 million tonnes per year which corresponds to 105000 toimes of hydrogen (1.3 x I0 m ). Plants designed specifically for the electrolytic manufacture of hydrogen as the main product, use steel cells and aqueous potassium hydroxide as electrolyte. The cells may be operated at atmospheric pressure (Knowles cells) or at 30 atm (Lonza cells). 

Recently, rhodium and ruthenium-based carbon-supported sulfide electrocatalysts were synthesized by different established methods and evaluated as ODP cathodic catalysts in a chlorine-saturated hydrochloric acid environment with respect to both economic and industrial considerations [46]. In particular, patented E-TEK methods as well as a non-aqueous method were used to produce binary RhjcSy and Ru Sy in addition, some of the more popular Mo, Co, Rh, and Redoped RuxSy catalysts for acid electrolyte fuel cell ORR applications were also prepared. The roles of both crystallinity and morphology of the electrocatalysts were investigated. Their activity for ORR was compared to state-of-the-art Pt/C and Rh/C systems. The Rh Sy/C, CojcRuyS /C, and Ru Sy/C materials synthesized by the E-TEK methods exhibited appreciable stability and activity for ORR under these conditions. The Ru-based materials showed good depolarizing behavior. Considering that ruthenium is about seven times less expensive than rhodium, these Ru-based electrocatalysts may prove to be a viable low-cost alternative to Rh Sy systems for the ODC HCl electrolysis industry. 

Using a polymer electrolyte membrane cell in which flowed through the anode chamber. The major intermediate chlorinated products from tetrachloroethene or tet-rachloromethane were trichloroethene or trichloromethane, and these were finally reduced to a mixture of ethane and ethene, or methane (Liu et al. 2001). 

Finally, there are some miscellaneous polymer-electrolyte fuel cell models that should be mentioned. The models of Okada and co-workers - have examined how impurities in the water affect fuel-cell performance. They have focused mainly on ionic species such as chlorine and sodium and show that even a small concentration, especially next to the membrane at the cathode, impacts the overall fuelcell performance significantly. There are also some models that examine having free convection for gas transfer into the fuel cell. These models are also for very miniaturized fuel cells, so that free convection can provide enough oxygen. The models are basically the same as the ones above, but because the cell area is much smaller, the results and effects can be different. For example, free convection is used for both heat transfer and mass transfer, and the small... 

The terms included in brackets and the succeeding terms are less reliable than the others. R. C. Tolman and A. L. Ferguson measured the e.m.f. of the same type of cell at 18° F. Dolezalek measured the e.m.f. of hydrogen-chlorine cells with cone, hydrochloric acid at 30° as electrolyte. G. N. Lewis and H. Storch have measured the free energy of hydrogen bromide inO l A-soln. and G. N. Lewis and M. Randall, that of hydrogen iodide. For HBr gas, at 25°, the latter give —12 592 Cals., and for HI gas, 310 cals. 

Each electrolytic application demands a unique approach to anode structure design and fabrication. Factors such as current distribution, gas release, ability to maintain structural tolerances, electrical resistance, and the practicality of recoaiing must be taken into account. The most commercially accepted design for diaphragm chlorine cells is that of the expandable anode (Fig. I). 

How many hours will it take to produce 1001b of electrolytic chlorine from NaCI in a cell that carries 1000 A The anode efficiency for the chlorine reaction is 85 percent. 

Many of the world s major chlor-alkali companies have developed their own mercury cells and the designs will differ in the way they seek to obtain the maximum electrode area and in the arrangement of the auxiliary equipment. The development of the cells during almost a century of electrolytic chlorine and caustic soda production and the variation in the cells recently available are described in the texts at the end of the chapter. 

In the zinc/chlorine cell, the chlorine is stored as chlorine hydrate, Cl2 xH20 (x = 6—10), which precipitates as a solid below 9.6°C. During charge the electrolyte, aqueous zinc chloride, is cooled in a reservoir, while during discharge the reservoir is heated under controlled conditions. The cell itself, however, can be simple the electrodes are graphite and can operate without catalyst and the cell can be constructed from PVC without a separator. There remain some problems with the morphology of zinc deposits. 

By definition, power expressed in watts is equal to amperes x volts, and energy expressed in watt-hours is equal to amperes x volts x time (in hours). Therefore, the calculation of energy consumption requires a knowledge of the overall reaction and the number of Faradays required to produce the desired product, the operating cell voltage, and the cell current efficiency, which is illustrated here for the case of electrolytic chlorine production. The main anodic electrochemical reaction during the electrolysis of brine is the discharge of the chloride ions to produce chlorine, as described by reaction (4). When the chlorine current efficiency, ci2> is 100%, one Faraday of electricity will produce... 

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