Non-Asbestos Diaphragms

TABLE 4.7.5 Comparison of the Operating Cost of PMA and PMX Diaphragms [74] in MDC-55 Cells at 2.55kAm-2 

The tensile strength of the PMX diaphragm is about lOkgcm compared with 1-3 kg cm of the polymer bonded asbestos mat, and hence, the PMX diaphragm is not susceptible to erosion by the gas-solution mixture along the surface [74]. 

There have been various reports comparing costs of polymer-modified asbestos diaphragms and non-asbestos diaphragms. The non-asbestos diaphragm is not economical for low current density operations. At higher current densities, the life of the diaphragm should be substantially more than three years to be economically attractive, as evident from the cost comparison developed by PPG [85], and presented in Table 4.7.6. 

TABLE 4.7.6 Operating Cost ( /Ton of CI2) Diaphragm in MEXT-SS Cells Operating at 120 kA and 95% Current Efficiency 

eqnqMiiait cost, lost pfoductim and waste disposal 

---

P.C. Foller, D.W. DuBois, and J. Hutchins, PPG s Tephram Diaphragm The Ad table Non-Asbestos Diaphragm. In S. Sealy (ed.). Modem Chlor-Alkali Technology, vol. 7, Royal Society of Chemistry, Cambridge, UK (1998), p. 163. 

Chlorine Section Chlorine blowers asbestos diaphragms, ion-exchange membranes (perfluorinated) TiorFRP... 

Ddtzel O, Schneider L (2002) Non-asbestos diaphragm in chlorine-afkali electrolysis. Chtan Eng Technol 25 167-171... 

There is regulatory pressure to continue to reduce the use of asbestos. The chlor-alkali industry has been exempted from outright prohibition in many countries. In others, the use of asbestos in diaphragm cells has been banned. One should expect that the pressure will increase to eliminate asbestos. Most of the diaphragm-cell plants in Europe will in fact soon have been retired or converted to membranes or synthetic, non-asbestos membranes [40]. 

Environmental concern over the use of asbestos has increased in recent years. France, Saudi Arabia, and Norway have banned the use of asbestos as a separator in chlorine cells. These nations allowed local chlorine producers several years to install non-asbestos replacement separators in existing diaphragm cells or to replace the cells themselves with membrane cells. Under an amendment to the draft Asbestos Directive adopted by the EU Commission 4 May 1999, continued use of chrysotile asbestos will be allowed in existing diaphragm chlor-alkali plants. This exemption to the general EU ban on marketing and use of chrysotile asbestos will last until the end of a chlorine production unit s lifetime, or until suitable substitute materials for diaphragms are available. 

---