Aluminium hydroxide production

Today the sulphonation route is somewhat uneconomic and largely replaced by newer routes. Processes involving chlorination, such as the Raschig process, are used on a large scale commercially. A vapour phase reaction between benzene and hydrocholoric acid is carried out in the presence of catalysts such as an aluminium hydroxide-copper salt complex. Monochlorobenzene is formed and this is hydrolysed to phenol with water in the presence of catalysts at about 450°C, at the same time regenerating the hydrochloric acid. The phenol formed is extracted with benzene, separated from the latter by fractional distillation and purified by vacuum distillation. In recent years developments in this process have reduced the amount of by-product dichlorobenzene formed and also considerably increased the output rates. 

The carbon black generated by a fire from a rubber source increases the smoke density other products are highly toxic and often corrosive. The halogens, phosphates, borates, and their acids evolved during a fire corrode metals and electrical and electronic equipment. Hence many of the fire retardants described below cannot be used in situations where the toxic gases evolved will create their own hazards. In these cases inorganic hydroxides are used, at filler-type addition levels. Aluminium hydroxide and magnesium hydroxide are used as non-toxic fire retardant systems. 

The rHBsAg is produced in an engineered S. cerevisiae strain and is likely purified subsequent to fermentation by a procedure somewhat similar to that presented in Figure 13.10. The final product is presented as a sterile suspension of the antigen absorbed onto aluminium hydroxide (adjuvant), in either single-use vials or pre-filled syringes. It also contains NaCl and phosphate buffer components as excipients. It is intended for i.m. injection, usually as 10 pg in a volume of 0.5 ml for infants/children or 20 pg (in 1.0 ml) for adults. The normal dosage schedule entails initial administration followed by boosters after 1 and 6 months. 

A number of mineral-based substances display an adjuvant effect. Although calcium phosphate, calcium chloride and salts of various metals (e.g. zinc sulfate and cerium nitrate) display some effect, aluminium-based substances are by far the most potent. Most commonly employed are aluminium hydroxide and aluminium phosphate (Table 13.13). Their adjuvanticity, coupled to their proven safety, render them particularly valuable in the preparation of vaccines for young children. They have been incorporated into millions of doses of such vaccine products so far. 

The production of flame retardant quahty aluminium hydroxide has recently been reviewed [98]. Various crystal forms of aluminium hydroxide exist, but that used for polymer appHcations is Gibbsite. This occurs widely in nature, usually in the rock bauxite, but the natural form is usually not suitable for direct use and synthetic products are nearly always employed. Most aluminium hydroxide is manufactured through the Bayer process used to make alumina for refractory applications. 

Many surface modifications are used with aluminium hydroxide, which responds to both silane and fatty acid treatments. Special proprietary silane coatings seem to be preferred for polypropylene applications [99]. Despite the production being water based, the preference seems to be for dry coating procedures. 

Fig. 7. Cross-sectional view of a pit. A, metal dissolution reaction, e.g. A1 -> Al3t + 3e, acid chlorides form, which produce hydrochloric acid and aluminium hydroxide on hydrolysis B, 2 Hh +2e- H2 C, porous corrosion product restricting oxygen access D, passive layer on the metal surface and E, inclusion acting as a local cathode.

Lake colours are made by precipitating a water soluble colour with an aluminium, calcium or magnesium salt on to aluminium hydroxide. The dye content can be varied from 10 to 40%. The particle size of the finished product must be small enough to give a speck-free but economical coverage. 

For this reason vaccine formulation tends to follow the traditional routes innovative formulations are rare. Aluminium hydroxide, aluminium phosphate and calcium phosphate are still the only registered vaccine adjuvants for humans. Veterinary vaccines have to rely on the same components, however, a few vaccines containing a mineral oil adjuvant (Marcol) or saponin (Quil A or derivatives) have passed the registration hurdles. It remains to be seen whether and under which restrictions these adjuvants can be used in the EEC after 1996 (see also below in "Additional requirements for veterinary products"). 

The effect of mechanical activation on the synthesis of mullite 3Al203 2Si02 from the mixtures of activated aluminium hydroxide and silica gel was studied by Klevtsov, Mastikhin, Krivoruchko et al. [36], According to NMR, the interaction between the initial components is observed at the stage of mechanical activation, hi activated mixtures, a transition of AP from octahedron into tetrahedron and pentahedron-tetrahedron ones is observed. The formation of mullite occurs under heating of activated mixtures at 1100°C, while for unactivated mixtures at 1400°C only. Lower temperature allows to obtain the product in fine disperse state (S=50 m /g). 

The author [4] observed the formation of a new phase (probably, double hydroxide of aluminium and magnesium) under mechanical activation of a mixture of magnesium and aluminium hydroxides in a planetary mill. The mentioned product decomposes at 800°C to form spinel MgAl204. 

It was shown in [18] that practically monophase fine barium hexaaluminate can be obtained by mechanical activation of a mixture of barium oxide with Y-AI2O3, which exhibits acid properties to a larger extent than a-Al203, and by consequent thermal treatments at increased temperature. The product then is grinded in the presence of water. The synthesis was shown to proceed almost completely after activation for 5 min in the AGO-2 planetary mill and thermal treatment at 1300°C for 1 h. Mechanical activation of the mixture of aluminium hydroxide with barium oxide, followed by thermal treatment at 900°C, results in the formation of the final product and a-Al203 as an admixture which remains even at 1300°C. Mechanochemical synthesis helped also to synthesize barinm hexaaluminate in which a part of aluminium cations is replaced with manganese, iron, cobalt cations. Such compounds are nsed as active ceramics in catalysis [17]. 

Lanthanum aluminate. Mechanochemical synthesis of lanthanum aluminate was carried out by the joint grinding of lanthanum oxide La203 with aluminium hydroxide or oxide in a planetary mill [20]. After activation for 120 min, a monophase product LaA103 with a large specific surface area was obtained. However, the formation of LaA103 was not observed when a-AI2O3 was used as an initial reagent. 

According to data [10,11], practically monophase anorthite can be synthesized after mechanical treatment of a mixture of calcium oxide with aluminium hydroxide and hydrated silica followed by thermal treatment at 1000°C for 4 h. Fig. 7.3 shows X-ray pattern of this mixture. After activation for 5 min (Fig. 7.3, curve 1), the reaction mixture exhibits a small amount of individual crystal calcium oxide (0.240 nm) and aluminium hydroxide (0.482, 0.436, 0.245 nm), while the major part of CaO is bound into an X-ray amorphous product. The annealing of the activated mixture at 1000°C gives anorthite (Fig. 7.3, curve 3) while the thermal treatment of non-activated mixture brings to the formation of intermediate product, wollastonite (Fig. 7.3, curve 2). The lines of this product are absent in X-ray patterns of the activated mixture. 

However, while oxidization may not change, interaction with the media may yield more soluble forms. A sparingly soluble metal compound can be considered as one for which a solubility product can be calculated, and which will yield a small amount of the available form by dissolution. However, it should be recognized that the final solution concentration may be influenced by a number of factors, including the solubility product of some metal compounds precipitated during the transformation/dissolution test, e.g. aluminium hydroxide. 

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