Causticization reaction

The clarified green Hquor is used for slaking the lime. For one to two hours, the mixture is passed through a series of tanks equipped with agitators. The causticizing reaction is as follows ... 

Amines remove the bulk of the H2S primary amines also remove the COj. Amine treating is not effective for removal of mercaptan. In addition, it cannot remove enough H2S to meet the copper strip corrosion test. For this reason, caustic treating is the final polishing step downstream of the amine units. Table 1-3 illustrates the chemistry of some of the important caustic reactions. 

Caustic Alkali from Alkali Carbonate, NaOH Causticizing Reaction... 

If chemicals with caustic and cytotoxic effects reach the alveoh, hfe-threatening corrosion of the pulmonary tissue can result. If hquid penetrates into the alveoli as a consequence of a local caustic reaction, a pulmonary edema can form. Usually, the formation of such an edema occurs hours to days after exposure - a typical example of a latent effect The following chemicals are well known for formation of pulmonary edemas ... 

Triclocarban (TCC, trichlorocarbanilide, Cutisan, Nobacter, Solubacter, CAS no. 101-20-2). This is an antiseptic and bacteriostatic used in antimicrobial soap bars, deodorants, antiperspirants. Photoallergic and phototoxic reactions were reported (Hasan and Jansen 1996). Cross reaction occurs with other halogenated salicylanilides. Caustic reaction on skin and mucosa was reported (Barriere 1973). Allergic reactions are not uncommon, and can result in pigmentation afterwards. The patch-test concentration is 2% pet. 

In early designs, the reaction heat typically was removed by cooling water. Crude dichloroethane was withdrawn from the reactor as a liquid, acid-washed to remove ferric chloride, then neutralized with dilute caustic, and purified by distillation. The material used for separation of the ferric chloride can be recycled up to a point, but a purge must be done. This creates waste streams contaminated with chlorinated hydrocarbons which must be treated prior to disposal. 

C7H6O2 Oily liquid of aromatic odour b.p. 196°C. (t is prepared by the action of chloroform and caustic potash on phenol (the Reimer-Tiemann reaction) or by the oxidation of the glucoside salicin. It is easily reduced to salicyl alcohol or oxidized to salicylic acid. 

The most important reaction of the sulphonic acids is their conversion into phenols by fusion with caustic alkalis. When they are fused with potassium cyanide, nitriles are obtained, e.g. benzonitriie from ben-zenesulphonic acid. 

The gas is passed through caustic soda solution to remove any sulphur dioxide or carbon dioxide produced in side reactions. Carbon monoxide is also obtained when an ethanedioate (oxalate) is heated with concentrated sulphuric acid ... 

The saponiflcatlon equivalent or the equivalent weight of an ester is that weight in grams of the ester from which one equivalent weight of acid is obtainable by hydrolysis, or that quantity which reacts with one equivalent of alkali. The saponification equivalent is determined in practice by treating a known weight of the ester with a known quantity of caustic alkali used in excess. The residual alkali is then readily determined by titration of the reaction mixture with a standard acid. The amount of alkafi that has reacted with the ester is thus obtained the equivalent can then be readily calculated. 

Most aromatic acid chlorides impart a strongly acid reaction when shaken with water (compare Section 111,88). All are completely hydrolysed by boiling with solutions of caustic alkalis and yield no product volatile from the alkaline solution (compare Eaters, Sections 111,106 and IV, 183). They may be distinguished from acids by their facile reactions with alcohols (compare Section 111,27), phenols (compare Section IV,114), and amines (compare Sections 111,123 and IV.lOO). 

Phenol condenses with phthahc anhydride in the presence of concentrated sulphuric acid or anhydrous zinc chloride to yield the colourless phenolphthalein as the main product. When dilute caustic alkah is added to an alcoholic solution of phenolphthalein, an intense red colouration is produced. The alkali opens the lactone ring in phenolphthalein and forms a salt at one phenolic group. The reaction may be represented in steps, with the formation of a h3q)othetical unstable Intermediate that changes to a coloured ion. The colour is probably due to resonance which places the negative charge on either of the two equivalent oxygen atoms. With excess of concentrated caustic alkali, the first red colour disappears this is due to the production of the carbinol and attendant salt formation, rendering resonance impossible. The various reactions may be represented as follows ... 

Bemoyl chloride may replace acetyl chloride as a class reagent it possesses the advantage that it is only very slowly decomposed by cold water and consequently may be employed for detecting alcohols even in aqueous solution. The reaction is usually carried out in aqueous solution containing sufficient caustic alkali to decompose any excess of benzoyl chloride into the water-soluble alkali benzoate (Schotten - Baumann reaction compare Section IV,52). The benzoyl esters formed are insoluble in water ... 

The product of this reaction can be removed as an azeotrope (84.1% amide, 15.9% acetic acid) which boils at 170.8—170.9°C. Acid present in the azeotrope can be removed by the addition of soHd caustic soda [1310-73-2] followed by distillation (2). The reaction can also take place in a solution having a DMAC-acetic acid ratio higher than the azeotropic composition, so that an azeotrope does not form. For this purpose, dimethylamine is added in excess of the stoichiometric proportion (3). If a substantial excess of dimethylamine reacts with acetic acid under conditions of elevated temperature and pressure, a reduced amount of azeotrope is formed. Optimum temperatures are between 250—325°C, and pressures in excess of 6200 kPa (900 psi) are requited (4). DMAC can also be made by the reaction of acetic anhydride [108-24-7] and dimethylamine ... 

Chlorine and caustic soda are coproducts of electrolysis of aqueous solutions of sodium chloride [7647-14-5] NaCl, (commonly called brine) following the overall chemical reaction... 

The catholyte from diaphragm cells typically analyzes as 9—12% NaOH and 14—16% NaCl. This ceUHquor is concentrated to 50% NaOH in a series of steps primarily involving three or four evaporators. Membrane cells, on the other hand, produce 30—35% NaOH which is evaporated in a single stage to produce 50% NaOH. Seventy percent caustic containing very Httie salt is made directiy in mercury cell production by reaction of the sodium amalgam from the electrolytic cells with water in denuders. 

Faraday s law states that 96,487 coulombs (1 C = 1 A-s) are required to produce one gram equivalent weight of the electrochemical reaction product. This relationship determines the minimum energy requirement for chlorine and caustic production in terms of kiloampere hours per ton of CI2 or NaOH... 

Aqueous solutions of caustic soda aie highly alkaline. Hence caustic soda is ptimatily used in neutralization reactions to form sodium salts (79). Sodium hydroxide reacts with amphotoric metals (Al, Zn, Sn) and their oxides to form complex anions such as AlO, ZnO. SnO ", and (or H2O with oxides). Reaction of AI2O2 with NaOH is the primary step during the extraction of alumina from bauxite (see Aluminum compounds) ... 

MetaUic ions are precipitated as their hydroxides from aqueous caustic solutions. The reactions of importance in chlor—alkali operations are removal of magnesium as Mg(OH)2 during primary purification and of other impurities for pollution control. Organic acids react with NaOH to form soluble salts. Saponification of esters to form the organic acid salt and an alcohol and internal coupling reactions involve NaOH, as exemplified by reaction with triglycerides to form soap and glycerol,... 

The only caustic soda production process besides electrolysis is the soda—lime process involving the reaction of lime with soda ash ... 

Sodium Hydroxide. Before World War 1, nearly all sodium hydroxide [1310-93-2], NaOH, was produced by the reaction of soda ash and lime. The subsequent rapid development of electrolytic production processes, resulting from growing demand for chlorine, effectively shut down the old lime—soda plants except in Eastern Europe, the USSR, India, and China. Recent changes in chlorine consumption have reduced demand, putting pressure on the price and availabiHty of caustic soda (NaOH). Because this trend is expected to continue, there is renewed interest in the lime—soda production process. EMC operates a 50,000 t/yr caustic soda plant that uses this technology at Green River it came onstream in mid-1990. Other U.S. soda ash producers have aimounced plans to constmct similar plants (1,5). 

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