Alternative processes caustic soda

Because of its volatility, the cobalt catalyst codistills with the product aldehyde necessitating a separate catalyst separation step known as decobalting. This is typically done by contacting the product stream with an aqueous carboxyhc acid, eg, acetic acid, subsequently separating the aqueous cobalt carboxylate, and returning the cobalt to the process as active catalyst precursor (2). Alternatively, the aldehyde product stream may be decobalted by contacting it with aqueous caustic soda which converts the catalyst into the water-soluble Co(CO). This stream is decanted from the product, acidified, and recycled as active HCo(CO)4. 

Landfors J (1993) Alternative on-site caustic soda production in the paper and pulp industry, Electrochem Processing, Innovations and Progress, April 21-23, Glasgow Sunblad B (1992, Eka Nobel) Can CA 2,071,810 Chem Abstr 118 194663f... 

Cadmium also may be recovered from zinc ores and separated from other metals present as impurities by fractional distillation. Alternatively, the cadmium dust obtained from the roasting of zinc ore is mixed with sulfuric acid. Zinc dust is added in small quantities to precipitate out copper and other impurities. The metal impurities are removed by filtration. An excess amount of zinc dust is added to the solution. A spongy cadmium-rich precipitate is formed which may he oxidized and dissolved in dilute sulfuric acid. Cadmium sulfate solution is then electrolyzed using aluminum cathodes and lead anodes. The metal is deposited at the cathode, stripped out regularly, washed and melted in an iron retort in the presence of caustic soda, and drawn into desired shapes. More than half of the world s production of cadmium is obtained by elecrolytic processes. 

With the advent of dimensionally stable anodes and perfluorinated ion exchange membranes, over the past decade and a half, came an alternative method for the manufacture of chlorine and caustic soda. This new process produces a food grade product without pollution. 

Antimony, arsenic, tin, and sulfur. Two methods of reducing/removing these elements from lead are available. The choice depends on the final level required in lead product. If the elements are to be removed from the bullion, the softening process is used. Alternatively, to reduce these elements to a specified level, caustic soda and/or sodium nitrate is stirred into the kettle held at about 500°C. This latter method is commonly referred to as the Harris process. 

To free the aromatic nitro products from the phenolic impurities, two alternative procedures may be compared with the extraction process commonly used industrially at present. In this, the organic product layer after nitration is first washed with water to remove free acids and then washed with dilute sodium hydroxide (usually 1 to 4N, 15% excess). The separated aqueous phase is neutralised by excess mineral acid to liberate the phenols, 60% to 80% of which separate cind may be removed. The aqueous phase is still saturated with phenols cind is an obnoxious effluent. The process also involves the continuous consumption of caustic soda and strong acid, with consequent high operating costs. 

Increasingly, industry is being required to limit its emissions of acidic gases. Limestone reacts with the most common acidic gases (i.e. SO2, SO3, HCl and HF), and is considerably less expensive than alternative alkaline materials, such as lime (see chapter 29), sodium carbonate/bicarbonate and caustic soda. It is, therefore, not surprising that considerable effort has been put into developing processes using limestone as an absorbent. 

A wide range of chemicals are used in water treatment. Lime is used both as an alkali and as a source of calcium ions. As an alkali, it competes in certain processes with caustic soda and soda ash. The choice between alternative chemicals is generally based on economic factors and on the ease of use in a particular installation. 

With two-compartment cells the cathodic efficiency also represents the total current efficiency of the process. In the three-compartment cells, the current efficiency for sulfuric acid production (anodic efficiency) must also be taken into consideration. The overall current efficiency of electrolysis is represented by the lower of the two efficiencies. If, for example, the anodic efficiency is lower than the cathodic, acidity builds up in the sodium sulfate compartment during operation so that the cathodic current efficiency progressively decreases when it reaches the same value as the anodic, stationary process conditions are maintained. Therefore, the process is provided with a self-regulating mechanism. Alternatively, if the accumulation of acidity in the sodium sulfate compartment cannot be allowed, then a portion of the caustic soda produced can be fed into the sodium sulfate loop. The quantity of caustic soda available for use outside the electrolysis plant again represents the overall current efficiency, which still remains a function of the anodic efficiency. The anodic and cathodic current efficiencies can be made independent when the control of acidity in the sodium sulfate compartment is performed by means of sodium carbonate addition. 

In an alternative process, the fine-ground xenotime is treated by fusing it with molten caustic soda at 400 °C, or by mixing it with sodium carbonate and roasting at 900 °C for several hours. The hydroxide residue is dissolved in hydrochloric acid and filtered to remove impurities such as siUca, cassiterite etc. The rare earths are precipitated as oxalates by adding oxalic acid. The oxalates are oxidized to rare earth oxides (Gupta and Krishnamurthy 2005). 

Two current synthesis processes are commercialized, with the economically most successful one said to be the interface process, which involves the dissolution of bisphenol A in aqueous caustic soda and the introduction of phosgene in the presence of an inert solvent such as pyridine. An alternative method involves transesterification of bisphenol A with diphenyl carbonate at elevated temperatures. 

Sodium hypochlorite is most commonly produced by a continuous process in which dilute caustic soda solution and chlorine are fed into a specially designed, cooled reactor. Control of rate of chlorine addition is by monitoring of Redox potential. Temperature is controlled to below 38°C to avoid chlorate formation. Alternately, a batch process may be used in which chlorine is passed slowly into a cold 20°C NaOH solution through a sparge tube near the bottom of a tank. Air agitation is used and chlorine feed rate is kept low to minimise temperature rise. 

Oxalic Acid.—The jurciiaration of ovalic acid by the action ol nitric aiid on sugar was introduced bySchccle, and was used for some time as a technical process. I hc vanadium pent-o. ide aits as carrier of o ygen, being alternately leduccd to tctro. ide and re-o. idised. The picscnt commercial method is to heat sawdust with a mi. cturc of caustic potash and soda on Cohen s adv. p. o. c. ... 

It is common practice to equip a drainage system or sump with a pump to return the collected inventory to storage or process facilities. Alternatively, for certain toxic materials, the spill is sometimes altered chemically to a nonhazardous substance by draining the spillage to a basin filled with a neutralizing slurry where the reaction forms an insoluble sludge. For acids, in particular, soda ash, limestone, or weak caustic solutions may be used. The reacted product becomes a solid that is neutral and can be disposed of accordingly. 

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