Bauxite as a Sugar Refining Adsorbent W. A. LA LANDE, JR. The Porocel Corporation, Philadelphia, Penna.
Bauxite, a naturally occurring hydrated oxide of aluminum, has been thcrmally activated to produce a highly efficient adsorbent for the refining of sugar sirups and liquors. Laboratory data indicate t h a t the percolation of defecated solutions through activated bauxites raises the apparent purity 3-10 per cent in the case of sirups and u p to 2 per cent for high-purity liquors. The invert cont e n t of the solution is decreased 4-34 per cent. Decreases of 20-80 per cent in the ash content are observed following filtration through artivated bauxite. The optimum refining efficiency is produced b y activating and regenerating the adsorbent in the range 600-900" F. The pH of the filtrates depends partly on the activation and,'or regeneration temperature to which the adsorbent is sub-
mitted, the filtrate pH decreasing as the calcination temperature of the bauxite is raised. The colors of activated bauxite-filtered sugar solutions are brilliant and vary from water-white to a rich amber. The high refining efficiency of the adsorbent is maintained after repeated use. Bauxite is superior to bone char in ash and invert adsorption, and produces filtrates of higher purity than char. The color removal efficiencies of the two adsorbents are approximately equal. The physical properties and handling characteristics of bauxite are not radically different from the other adsorbent materials used in the sugar refining industry. Since, however, activated bauxite is inorganic, regeneration by heating in the presence of oxygen, after w-ashing, is simple and rapid.
AUXITE, the chief ore of aluminum, is a hydrated oxide of the metal, usually found associated with silica, iron oxide, and titanium dioxide as impurities. The United States industry mines about 8 per cent of the total annual world bauxite output of approximately 4 million tons. Arkansas supplies 95 per cent of the domestic production. Bauxite is processed mainly for the manufacture of aluminum, aluminum chemicals, abrasives, cement, and refractories. A comparatively new and increasingly imporhant commercial use of bauxite depends on the high adsorptive power of the thermally activated mineral. It is now a standard decolorizing adsorbent in the petroleum industry (4, 6) and is also used for the catalytic desulfurization of the lighter petroleum fractions ( I O ) . The use of bauxite as a carrier and catalyst in admixture with other substances is the subject of many patents. Other reported applications related to its adsorptive characteristics include the production of olefins by the catalytic decomposition of ethers (8),the catalytic preparation of alkyl chlorides by the interaction of hydrochloric acid and olefins in the presence of the mineral (11), the adsorption from solution of various dyes ( 6 ) , the chromatographic separation of the pancreatic enzymes lipase and trypsin from mixtures ( I d ) , and the defecation and refining of crude sugar solutions (1, 2, 3, 7). The object of this paper is to report laboratory experiments on the last-named use of bauxite, especially as applied to the refining of sugar sirups and liquors by the percolation technique.
some workers consider the mineral a mixture of the various hydrated oxides of alumina (gibbsite, Alp03.3H20, to diaspore, AlO.OH). Bauxites vary in color from light tan to dark red. High-grade ores contain 75-90 per cent of alumina (volatilefree basis) and u p to 30 per cent of volatile matter (mostly water). I n the preliminary work leading to the experiments on which the data presented in this paper are based, various bauxites were tested for sugar refining efficiency. The highly ferruginous ores (8-20 per cent ferric oxide) were found to be of relatively low efficiency and tended to yield traces of iron to the filtrates. I n general, the orange and red bauxites, regardless of their total iron content, are inferior to the light tan or gray-tan ores. The alumina content is a rough index of the efficiency of the bauxite, although there is only a slight variation among the ores of higher purity. The hardness of the bauxites varies with the composition and physical form of the mineral. The claylike bauxites are soft, but the massive, oolitic, and pisolitic structures are relatively hard. Granulated bauxite is softer than bone char but, like the latter adsorbent in the char house, is subjected to repeated (and more violent) handlings in the petroleum filter plant.
Experimental Procedure The primary object of these experiments v a s to determine the sugar refining characteristics of bauxite by a series of regulated and reproducible tests. No attempt was made to simulate plant operating conditions precisely. MATERIALS.All the data are based on experiments made with a thermally activated Arkansas bauxite known commercially as Porocel filter bauxite. The lump ore shows the pisolitic structure characteristic of many types of bauxite. This product was used in the form of 10-30 mesh granules with a settled volume weight of 57.5-58 pounds per cubic foot. The adsorbent is light tan in the natural state and becomes slightly darker as a result of activation. First-quality service bone char, sugar liquors, and sirups were obtained from a large refinery. The solutions were processed as soon as
