Hydrogen manufacturing industry, chlorination

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). 

The products of the chlor-alkali process are all useful. Sodium hydroxide is used to make soaps and detergents. It is widely used as a base in many other industrial chemical reactions, as well. The hydrogen produced by the chlor-alkali process is used as a fuel. Chlorine has many uses besides water treatment. For example, chlorine is used as a bleach in the pulp and paper industry. Chlorine is also used in the manufacture of chlorinated organic compounds, such as the common plastic polyvinyl chloride (PVC). 

The most important and now almost the sole industrial method of manufacturing chlorine is the electrolysis of alkali chloride solutions during which hydrogen and alkali hydroxide are also produced. Often hydroxide production is more important so that chlorine is then a by-product. It is sometimes difficult to find a suitable market for chlorine. In those countries where the manufacture of chlorinated organic derivatives (primarily plastics) is a developed industry the situation is just the reverse and here the demand for chlorine is much greater than for hydroxides. 

Three processes are industrially operated in which aqueous solutions of sodium chloride are electrolyzed for the manufacture of chlorine, sodium hydroxide and hydrogen ... 

The non-electrolytic processes for the manufacture of chlorine from hydrogen chloride (Deacon, air oxidation of hydrogen chloride Weldon, manganese dioxide oxidation of hydrogen chloride) which marked the beginning of industrial chlorine chemistry, are currently of only minor importance. 

Anhydrous aluminum chloride is currently mainly manufactured by chlorination of liquid aluminum in ceramic-lined reaction vessels at 600 to 750°C, gaseous aluminum chloride being fed into condensation chambers. The reductive chlorination of aluminum oxide in the presence of coal (e.g. in the Alcoa process, see Section 3.2.3.2) is also operated industrially. Hydrated aluminum chloride is manufactured by reacting aluminum hydroxide with hydrochloric acid or hydrogen chloride. 

The well-known Ytong building materials are manufactured using this process. Aluminum can be used instead of zinc or magnesium. Other gas-forming additives e.g. hydrochloric acid/limestone or hydrogen peroxi-de/chlorinated lime have been described, but have hardly been used industrially. 

Appendix D2, Chemical oxidation with chlorine for inorganic (hydrogen cyanide) manufacturing industry. 

Chemical Oxidation (Chlorination) Used in Inorganic Chemical Industry (Hydrogen Cyanide Manufacturing Industry)... 

Industrially, chlorine is manufactured by the electrolysis of chloride salts (Curlin and Bommaraju, 1991). Three basic types of processes are used to produce chlorine, each process representing a different method of isolating the chlorine produced at the anode from the caustic soda and hydrogen produced at the cathode (Curlin and Bommaraju, 1991). Electrolytic processes currently in use are ... 

Industrial scale electrolyzers were developed early in the 20th century for the manufacture of chlorine and caustic soda from brine, and for the commercial production of hydrogen used in ammonia synthesis. Large water-electrolysis plants were constructed in Norway and Canada in the 1930 s, based on cheap hydroelectric power, and the hydrogen so produced was used in fertilizer manufacture. With the advent of natural gas and low cost petroleum, hydrogen production moved toward catalytic steam-reforming of hydrocarbons, and water electrolysis became less significant. 

The by-products are sodium hydroxide and hydrogen gas. Although the mercury is cycled back into the cell for reuse, some of it is always discharged with waste solutions into the environment, resulting in mercury pollution. This is a major drawback of the mercury cell. Figure 24.18 shows the industrial manufacture of chlorine gas. 

Each isomer has its individual set of physical and chemical properties however, these properties are similar (Table 6). The fundamental chemical reactions for pentanes are sulfonation to form sulfonic acids, chlorination to form chlorides, nitration to form nitropentanes, oxidation to form various compounds, and cracking to form free radicals. Many of these reactions are used to produce intermediates for the manufacture of industrial chemicals. Generally the reactivity increases from a primary to a secondary to a tertiary hydrogen (37). Other properties available but not Hsted are given in equations for heat capacity and viscosity (34), and saturated Hquid density (36). 

Hydrogen chloride and the aqueous solution, muriatic acid, find appHcation in many industries. In general, anhydrous HCl is consumed for its chlorine value, whereas aqueous hydrochloric acid is often utilized as a nonoxidizing acid. The latter is used in metal cleaning operations, chemical manufacturing, petroleum well activation, and in the production of food and synthetic mbber. 

Other industrial applications of electrolysis include extraction/purification of metals from ores, electroplating, and the manufacture of certain chemicals such as sodium hydroxide. In the latter, sodium chloride solution when electrolysed is converted to sodium hydroxide to produce chlorine at the anode and hydrogen at the cathode. Both of these gaseous by-products are collected for industrial use chlorine is used in the production of bleach and PVC hydrogen is used as a fuel, to saturate fats, and to make ammonia. 

The products of this electrolysis have a variety of uses. Chlorine is used to purify drinking water large quantities of it are consumed in making plastics such as polyvinyl chloride (PVC). Hydrogen, prepared in this and many other industrial processes, is used chiefly in the synthesis of ammonia (Chapter 12). Sodium hydroxide (lye), obtained on evaporation of the electrolyte, is used in processing pulp and paper, in the purification of aluminum ore, in the manufacture of glass and textiles, and for many other purposes. 

There is a need for accurate in-line hydrogen monitor in individual electrolyzers in chloralkali industry that will provide huge cost savings in chlorine manufacturing processes. Again, an in-line process monitor that can be installed in individual electrolyzers is highly desired. 

Hydrochloric acid (HCL) is also known as hydrogen chloride, and in a less than pure form it is commonly called muriatic acid. It is used by many industries and is mainly obtained as a by-product of the organic chloride chemicals used in the manufacturing of plastics. It can be produced in pure form by exploding a mixture of hydrogen and chlorine gases. The stomachs digestive juice is a form of hydrochloric acid. 

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