Chemical manufacturing, chemicals used sodium chloride

The primary useful property of phosphates that perhaps nothing else approaches, is the safety record of phosphates in manufacturing plants and households around the world. It was with this fact in mind that two candidates for new mineral fibers were chosen. There were at least eight other candidates that could have been selected. As noted, there are two general molecular forms of serpentine minerals that are referred to as asbestos. These are the chrysotile and the amphibole types. These two forms of asbestos are about as similar, chemically and physically, as sodium chloride and sucrose both are white crystalline solids. 

In converting ESBR latex to the dry mbber form, coagulating chemicals, such as sodium chloride and sulfuric acid, are used to break the latex emulsion. This solution eventually ends up as plant effluent. The polymer cmmb must also be washed with water to remove excess acid and salts, which can affect the cure properties and ash content of the polymer. The requirements for large amounts of good-quaUty fresh water and the handling of the resultant effluent are of utmost importance in the manufacture of ESBR and directly impact on the plant operating costs. 

Later, Du Pont in America developed its own ionically conducting membrane, mainly for large-scale electrolysis of sodium chloride to manufacture chlorine, Nafion , (the US Navy also used it on board submarines to generate oxygen by electrolysis of water), while Dow Chemical, also in America, developed its own even more efficient version in the 1980s, while another version will be described below in connection with fuel cells. Meanwhile, Fenton et al. (1973) discovered the first of a... 

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. 

Although sodium carbonate is needed in the manufacture of glass, very little is found in nature. It is made using two very abundant chemicals, calcium carbonate (marble) and sodium chloride (salt). The process involves many steps, but the overall reaction is... 

Chemists are not the only ones who make use of acid-base chemistry. In fact, most of the chemical manufacturing that goes on in the world is related to the production of four simple, but very useful, products—sulfuric acid, phosphoric acid, sodium hydroxide, and sodium chloride. 

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). 

Sodium carbonate (Na CO ) is the eleventh most used industrial chemical in the United States. It is commonly used as a bleaching agent and is manufactured in a two-step process. First, ammonia is combined with carbon dioxide to form sodium chloride and water, which reacts to form sodium bicarbonate and ammonium chloride (NH + CO + NaCl + H O —> NaHCOj + NH Cl). Sodium bicarbonate, commonly known as baking soda, is used as a leavening agent in baking, as an antacid to relieve stomach acid, and as a component for fire extinguishers. The second step is known as the Solvay process, wherein the sodium bicarbonate is heated and converted into sodium carbonate (NaHCO A— Na CO + H O + CO ). 

Chlorine gas is produced by the electrolysis of brine (sodium chloride) in Castner-Kellner cells (first operated in 1886), the main purpose of which is the production of sodium hydroxide solution. Williams (1972, p98) reports that the extent to which the Castner-Kellner process was worked in Britain depended on the ability to dispose of the chlorine. In this light the production of chlorinated organic compounds can be seen as a response to the need to use chlorine. The argument that we need to produce chlorinated organic compounds to use up chlorine was indeed put to me by manufacturers of polyvinyl chloride (PVC) at a DETR-organized seminar on the lifecycle assessment of PVC in July 2001 PVC is the only product made in sufficient quantities to use up all the chlorine produced by other processes. This suggests that if a particular use of a chemical is stopped, because there is a better (less hazardous) way of achieving that purpose, it will have knock-on effects on the availability of chemicals that are co-produced... 

Production of chlorine and sodium hydroxide by electrolysis of aqueous sodium chloride is the basis of the chlor-alkali industry, a business that generates annual sales of approximately 4 billion in the United States alone. Both chlorine and sodium hydroxide rank among the top 10 chemicals in terms of production Annual output of each in the United States is 11-12 million tons. Chlorine is used in water and sewage treatment and in the manufacture of plastics such as poly(vinyl chloride) (PVC). Sodium hydroxide is employed in making paper, textiles, soaps, and detergents. 

Its principal use is in steelmaking, but it also goes into the manufacture of chemicals, water treatment, and pollution control. In the Solvay process, calcium carbonate and sodium chloride are used to produce calcium chloride and sodium carbonate with ammonia (which is recycled) as a medium for dissolving and carbonating the sodium chloride and calcium hydroxide for precipitating calcium chloride from the solution. 

Sodium hydroxide has many different uses in the chemical industry. Considerable amounts are used in the manufacture of paper and to make sodium hypochlorite for use in disinfectants and bleaches. Chlorine is also used to produce vinyl chloride, the starting material for the manufacture of polyvinyl chloride (PVC), and in water purification. Hydrochloric acid may be prepared by the direct reaction of chlorine and hydrogen gas or by the reaction of sodium chloride and sulfuric acid. It is used as a chlorinating agent for metals and organic compounds. 

The Committee on Food Chemicals Codex notes that this method may be used only until the First Supplement to this edition is released in 2004. At that time, the committee will set a lead limit as low as practicable for sodium chloride. Manufacturers are encouraged to develop and validate methods for use in industrial settings and that are sensitive enough to detect lead in the amounts typically present in sodium chloride, and to propose such methods to the committee in a timely manner. 

Chlorine (0.19% of lithosphere) is produced mainly from NaCl which is either crystallised from brines or mined. The gas is a product of the electrolysis of aqueous sodium chloride for caustic soda production, with carbon anodes and a mercury cathode. It is also a by-product of the manufacture mainly of metallic sodium, but also of magnesium and calcium, by electrolysing the appropriate fused chloride. Its chief uses are as a bleach, a bactericide, and an industrial chemical. 

In Western Europe about two thirds of the sodium chloride is utilized in the chemical industry (industrial salt), of which more than 90% is for electrolysis to chlorine and sodium hydroxide and for sodium carbonate manufacture. For the remainder (common salt) the most important use is for the salting of roads, which is very strongly weather dependent and is declining for ecological reasons. For taxation reasons sodium chloride utilized for the salting of roads is denatured . 

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