Support gibbsite

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. 

Figure 10.12. (a) Predicted total soluble concentration of aluminum (Al-fs) supported by gibbsite as a function of pH and tlie imposed Al-citrate chemical speciation models. The associated distributions of Al-citrate species in the equilibrium solutions are shown for the following models (h) Motekaitis and Martell (1984) (c) Gregor and Powell (1986) (d) Lakatos et al. (2001) (e) Hanis et al. (2003) (/) Essington et al. (2005). The imposed conditions included 0.01 mol L NaNOj. 10 mol L citis. 25°C and 1 atm, and log... 

In titrations at pH 5.20 and 5.00 the size of Alb units, as indicated by the OHb/Alb ratio seems to reach a maximum at 2.4, which could be interpreted as a boundary in the transition of Alb to Ale, microcrystalline gibbsite. Some additional support for this hypothesis can be obtained from experiments of Parthasarathy and Ruffle (8), who used ultrafiltration to separate polymeric Alb from Ale. They observed that the polymeric material passed through a filter having a nominal porosity of 20 X. Preliminary experiments we have made with this technique indicated that our Alb fraction also can pass through this membrane, but Ale docs not. 

The thermal decomposition of gibbsite was chosen to illustrate the application of modem instrumental and computing techniques to preparative controlled reaction rate methods for making reproducible catalysts or catalyst supports of high surface area at atmospheric pressure. Gibbsite is one form of aluminium trihydroxide, Al(OH)3, the other being the mineral bayerite [6]. The thermal decomposition of gibbsite is complex, and is influenced both by crystallite size and water vapour pressure. Two processes, which may overly under certain conditions, have been identified [7] ... 

Inoue, M. Kitamura, K., and Inui, T., Synthesis of wide-pore alumina support from Gibbsite, J. Chem. Technol. Biotechnol., 46(3), 233-248 (1989). 

Different catalysts were used when the Claus process was reintroduced in refineries in 1940-1950. Bauxite, for example, which was already available in refineries to hydrodesulfurize straight-mn naphthas, is a variable mixture of gibbsite and boehmite with iron and silica impurities. When calcined to activate the alumina, it is converted to a catalyst with about 1-12% ferric oxide supported on y-alumina. Bauxite catalysts were successfully used in the Claus process, giving a sulfur conversion greater than 90%. ... 

---