Industrial processes Bayer process

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

Recovery from Bayer Liquor. The significant amount of primary gallium is recovered from the alumina industry. The main source is the sodium aluminate Hquor from Bayer-process plants that produce large quantities of alumina. Several methods have been developed to recover gallium from Bayer Hquor. 

Cryolite. Cryofite [15096-52-3] Na AlF, is the primary constituent of the HaH-Hfiroult cell electrolyte. High purity, natural cryofite is found in Greenland, but its rarity and cost have caused the aluminum industry to substitute synthetic cryofite. The latter is produced by the reaction of hydrofluoric acid [7664-39-3] HE, with sodium aluminate [1302-42-7] NaA102, from the Bayer process... 

Eigure 1 illustrates the Bayer process as it is practiced in the 1990s. The primary purpose of a Bayer plant is to process bauxite to provide pure alumina for the production of aluminum. World production of Al(OH)2 totaled ca 55 x 10 t in 1988. Practically all of the hydroxide was obtained by Bayer processing and 90% of it was calcined to metallurgical grade alumina (AI2O2). However, about 10% of the bauxite processed serves as feedstock to the growing aluminum chemicals industry. 

Gibbsite is aii important technical product and world production, predominantly by the Bayer process, is more than 50 million metric tons aimuaHy. Alost (90%) is calcined to alumina [1344-28-1 j, Al202, to be used for aluminum production. Tlie remainder is used by the chemical industry as filler for paper, plastics, rubber, and as the starting material for the preparation of various aluminum compounds, alumina ceramics, refractories, polishing products, catalysts, and catalyst supports. 

Alumina. A pure although not necessarily a refractory grade of alumina is obtained from bauxite by the Bayer process. In this process, the gibbsite from the bauxite is dissolved in a caustic soda solution and thus separated from the impurities. Alumina, calcined, sintered, or fused, is a stable and extremely versatile material used for a variety of heavy industrial, electronic, and technical appHcations. 

FIGURE 3.1 Bayer process for alumina refining. (From U.S. EPA, Profile of the Nonferrous Metals Industry, publication EPA/310-R-95-010, U.S. EPA, Washington, DC, September 1995.)... 

Baekeland A process for making organic polymers by reacting phenols with formaldehyde. Based on an observation by A. von Bayer in 1872 and developed into an industrial process by L. H. Baekeland from 1905 to 1909. It was used to make Bakelite, one of the first commercial plastics. The first industrial manufacture began in Germany in 1910. 

Aluminium is one of the most abundant elements in the earth s crust, but, under feasible industrial conditions, can only be extracted by electrolysis. The process used is the electrolysis of aluminium hydroxide in molten cryolite (Na3AlF6) at 1030°C, pure aluminium hydroxide having been prepared from the mineral bauxite (hydrated aluminium oxide containing silica and some metal oxides such as iron) by the Bayer process. The cathode is carbon covered by molten aluminium metal and the anode is carbon, the total reaction being... 

CBPC matrix composites can incorporate a high volume of industrial waste streams such as fly ash, mineral waste such as iron taUings and Bayer process residue from the aluminum industry (red mud), machining swarfs from the automobile industry, and forest product waste such as saw dust and wood chips. Table 14.1 lists some of these waste streams and potential products or applications. 

Liittringhaus et al. 68) have isolated many interesting substances from the byproducts ( 8%) of the Bayer process. The mechanism has been fully clarified and shown to be an aryne route. When chlorobenzene or diphenylether are treated with sodium phenyl, the products are ortho metalated derivatives and benzyne. These give the same products which are formed in the industrial phenol synthesis. The most interesting compounds are 2- and 4-hydroxy biphenyl, 2,6-diphenyl- and 2,4-diphenyl-phenol l). For similar syntheses see 69). 

One of the industrial applications of hydrothermal precipitation is ordinary alumina production. The Bayer process is shown in Figine 1.7. T... 

In order to produce methyl isocyanate in good safety s conditions, Bayer A.-G. has developed an industrial process based on the reaction of diphenyl carbonate with N,N -dimethyl urea at high temperature according to scheme 158 (Ref. 212). 

Caustic soda, which has much wider application than soda ash in the chemical industry, was not produced in India until about 1940, presumably because it was little needed in industry until that time. It was used chiefly by the textile and soap industries, for which 25,000 tons were imported in 1938-1939. The emergence of three major products in later years increased the demand for caustic soda. These were viscous rayon, paper pulp, and alumina from Bayer process extraction of bauxite. 

AKOHIj and AI2O3 production is industrially almost exclusively by the Bayer process digestion of bauxite in sodium hydroxide... 

The industrial manufacture of aluminum hydroxide and aluminum oxide currently proceeds almost exclusively by the Bayer process i.e. by wet digestion of bauxite. The sinter- and melt-digestion processes with sodium carbonate and/or lime only have minor industrial importance. 

Sodium aluminate (theoretical formula NaA102) has a certain industrial importance not only as an intermediate in the digestion of bauxite in the Bayer process (see Section 3.2.4.2). USA production of sodium aluminate in 1993 was estimated to be 85 10- t/a. Sodium aluminate is produced by dissolving hydrated aluminum oxide in 50% sodium hydroxide. It is utilized in water purification, in the paper industry, for the post-treatment of Ti02-pigments, for the manufacture of aluminum-containing... 

Knowledge of the aluminium species present under alkaline conditions is of critical importance to industrial chemical operations such as the Bayer process in which the aluminium present in bauxite ores is dissolved in concentrated sodium hydroxide solution. Al NMR has been used to investigate the A1 coordination states in the resulting sodium aluminates after freeze drying (Bradley and Hanna 1994). At an OH Al ratio > 4.4, the predominant species is Na[Al(OH)4] (Q ) with a Al resonance at 86.6 ppm. A broader resonance at 71.3 ppm is probably composed of a variety of other poly-oxoanionic species such as [Al(OH2)(OAl)2] (Q ), [Al20(0H)6] (Q ) and... 

This reaction Moiseev reaction, cf. also Section 3.3.14.4 [2] was discovered in 1960 [1] and commercialized by Bayer, Hoechst, and some other companies [2] it can be performed both in the liquid and gas phase. The current industrial process for vinyl acetate monomer (VAM) is based on the gas-phase version with the formally heterogeneous Pd(Au-modified) catalyst. 

Alumina itself, the product of the Bayer process, is important for many industrial applications other than for the production of aluminum. The red mud wastes that comprise the impurities removed from bauxite during alumina preparation are employed in steel making, the manufacture of red pigments, and for the production of chemicals used for water and sewage treatment [44] (see Section 12.5.1). 

In the industrial process employed by Bayer AG, Germany, m-cresol and propylene, both in the liquid state, are pumped through a pressure tube reactor, filled with activated alumina. The process is performed at a molar ratio of m-cresol propylene of 1.07 at 350-360°C, 5kg/cm and LHSV of 0.25 hr. The reaction product consists of 25% m-cresol, 60% th3nnol and 15% other products. Thymol of 99% + purity is obtained by rectification of the crude product [1]. 

In practice, the Bayer process (Fig. 8.7), which has not yet been industrialized, starts with a steam-cracked C cut, for example, from which the butadiene and isobutene are extracted, and which therefore consists of about 20 per cent weight butanes and 80 per cent weight n-butenes. The butanes behave as a diluent The unit has three sections ... 

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