Chlorinating efficiency

Equation 16 is the correct material balance expression for calculating the chlorine efficiency of diaphragm cells. Whereas many approximate versions are used (8), the one closest to equation 16 is the "six equation" ... 

Additional energy to sustain the endothermic reaction is provided chemically by the addition of siUcon carbide grain or electrically by use of electrothermal fluidized beds (33—34), induction heating, or resistance heating. Chlorine efficiencies are typically 98% or better. 

The rate of chlorination of toluene relative to that of ben2ene is about 345 (61). Usually, chlorination is carried out at temperatures below 70°C with the reaction proceeding at a profitable rate even at 0°C. The reaction is exothermic with ca 139 kj (33 kcal) of heat produced per mole of monochlorotoluene formed. Chlorine efficiency is high, and toluene conversion to monochlorotoluene can be carried to about 90% with the formation of only a few percent of dichlorotoluenes. In most catalyst systems, decreasing temperatures favor formation of increasing amounts of -chlorotoluene. Concentrations of requited catalysts are low, generally on the order of several tenths of a percent or less. 

The effect of pH alone on chlorine efficiency is shown in Figure 3. Chlorine exists predominantly as HOCl at low PH levels. Between pH of 6.0 and 8.5, a dramatic change from undissociated to completely dissociated hypochlorous acid occurs. Above pH 7.5, hypochlorite ions prevail while above 9.5, chlorine exists almost entirely as OCl. Increased pH also diminishes the disinfecting efficiency of monochloramine. 

The VCM process can be balanced , so that only VCM is produced, or the plant can be designed to accommodate imported or exported EDC or HC1 streams. The process is automated for stable, safe operation with wide turndown capability. Also, the process is designed for easy startup and shutdown. Manpower, capital, operating and maintenance costs are low. Ethylene and chlorine efficiencies exceed 98+%. 

It may be noted that the oxygen evolution reaction (14) or (15) is thermodynamically favored over the chlorine evolution reaction. It results in the generation of electrons at the anode. Hence, the chlorine efficiency will be lower than the caustic efficiency. It is interesting to mention here that the caustic efficiency will never be 100% because of the oxygen evolution reaction, as the H+ generated via Eq. (14) must react with the OH ions generated at the cathode to preserve the electroneutrality of the system. 

Membrane cell chlorine current efficiency Chlorine efficiency losses from the formation of HOCl,... 

It follows from Eq. (5 8) that the chlorine current efficiency decreases with increasing formation of active chlorine species and chlorate in the anolyte, the increasing active chlorine species being formed not only by the reaction involving CI2, and OH species, but also by interaction between CI2 and alkalinity (i.e., Na2C03, NaHCOs, and NaOH) present in the feed brine. Hence, lowering the alkalinity of the feed brine, by acid addition, should improve the chlorine efficiency. 

The process chlorine efficiency, 6e determined from Eq. (71) assuming... 

It is important to note that the process chlorine efficiency is essentially the same as the cell caustic efficiency since, from Eq. (60), it can be seen that ... 

Errors Involved in the Energy Consumption and Efficiency Calculations. Error analysis using the propagation of errors technique, in Appendix 4.4.3, shows the error associated with the process chlorine efficiency to be 0.25% and the error in the energy consumption, AP, calculation to be 15kWhrton of CI2 as shown in Table 4.4.2. The analytical method, along with its precision is detailed in Table 4.4.3. 

High chlorine efficiency in all of the three ceU technologies can be realized by (1) lowering the alkalinity of the feed brine to negate the formation of OCl , HOCl, and CIO via reactions (16)-(18), and by (2) adding HQ to the feed brine, in order to reverse the equilibrium reaction (11) to liberate more gaseous Q2 from the anolyte. The other advantages associated with acid addition to the feed brine are ... 

The chlorine efficiency is SO-60 per cent and in a well-designed cell the current efficiency can reach 80 per cent. The general level of impurities (in ppm) is as follows ... 

High brine pH and reduced acidification costs versus lower chlorine efficiency, higher power consumption, and lower product purity... 

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