Growth of the Chlor-Alkali Industry

ENVIRONMENTAL CONSIDERATIONS AFFECTING THE GROWTH OF THE CHLOR-ALKALI INDUSTRY... 

The purpose of this handbook is to elucidate the basic chemistry and chemical engineering principles involved in the chlor-alkali technologies, and to thoroughly discuss the various operations involved in manufacturing chlorine and caustic. The status of the chlor-alkali industry is also discussed along with issues relevant to the future growth of the industry and the environmental concerns. 

The world production capacity of chlorine reached 53 million tons in 2002 from approximately 22 million tons in 1970 [1-7] and is expected to increase to 65 million tons by the year 2015 [8]. In this chapter, the major manufacturing processes and the factors affecting the growth pattern of the chlor-alkali industry are presented. 

In spite of their importance, relatively little information exists in the literature concerning the fundamental physicochemical properties of these membranes. This is due both to their proprietary nature and to the rapid growth of the technology. Also, what information is available is dispersed in a wide range of sources, ranging from the literature specializing in macromolecules to that devoted to the chlor-alkali industry. This work attempts to provide, in one volume, an overview of both the fundamental properties and the technological aspects of the field. 

The last two chapters cover the topics of the production of chlorine and caustic and the phenomena of electrolytic gas evolution. In Chapter 5, Hine et al. describe the engineering aspects of the three processes used in the chlor-alkali industry, and in Chapter 6, Sides reviews the macroscopic phenomena of nucleation, growth, and detachment of bubbles, and the effect of bubbles on the conductivity of and mass transfer in electrolytes. 

The continued growth of vinyl chloride monomer, both domestically and globally, will ensure a sink for the bulk of the chlorine and adequate though tight caustic supplies for the pulp and paper industry. The tight caustic soda market will permit caustic producers to recover a larger portion of their chlor-alkali production costs from merchant caustic sales. The portion chargeable to chlorine will be lowered, and more ethylene dichloride capacity for VCM/PVC production will be installed. 

The use of polyperfluorosulfonic acid membranes as the cell separator was first demonstrated about three decades ago. Yet it was not until the mid-1980s when the economic advantages of membrane cells over the traditional mercury- and diaphragm-cell technology were fully demonstrated—consequent to better membrane performance, higher caustic product concentrations, and lower power consumption. Retrofitting chlor-alkali facilities with membrane cells accounted for much of the growth and sustenance of this industry over the past two decades. 

The rapidly growing use of C102 in the pulp and paper industry has led to the rapid growth of sodium chlorate, NaC103, production in recent years. Sodium chlorate is produced by the electrolysis of NaCl brine in a cell that is very similar to a diaphragm chlor-alkali cell, except that it has no diaphragm. The overall reaction is as follows ... 

The majority of the chlorine produced is used internally within the chemical industry for the manufacture of polyvinyl chloride, chlorinated hydrocarbons, propylene oxide, etc, (Table 3.1), Hence, it is common to find chlor-alkali plants as part of very large, integrated chemical complexes and the capacity of such plants may be 0,5 x 10 tons Ci2/yean On the other hand, concern about the transport and storage of liquid chlorine has led to a different trend towards smaller plants sited close to the user This is particularly attractive when there is an almost balanced requirement for both chlorine and sodium hydroxide, e.g. in pulp and paper mills (Table 3,1). A typical plant in this application may have a capacity of 10 ions Cl2/year, On an even smaller scale, the same concerns lead to a need for plants, for example, to provide Cl to prevent biological growth on... 

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