Oxide supports for 12-tungstosilicic acid catalysts in …
12-Tungstosilicic acid, H 4 SiW 12 O 40 ..
Tungstic acid closely resembles molybdic acid in combining with phosphoric, arsenious, arsenic, boric, vanadic and silicic acids to form highly complex acids of which a great many salts exist. Of the phosphotungstic acids the most important is phosphoduodecitungstic acid, H 3 PW, 2040nH 2 O, obtained in quadratic pyramids by crystallizing mixed solutions of orthophosphoric and metatungstic acids. Two sodium salts, viz. Na2HPW12040nH 2 O and Na3PW12040 nH20, are obtained by heating sodium hydrogen phosphate with a tungstate. The most important silicotungstic acids are silicodecitungstic acid H8W10S1036.3H20, tungstosilicic acid, H 8 W 12 SiO 42.20H 2 O, and silicoduodecitungstic or silicotungstic acid, H8W12S1042.29H20. On boiling gelatinous silica with ammonium polytungstate and evaporating with the occasional addition of ammonia, ammonium silicodecitungstate is obtained as short rhombic prisms. On adding silver nitrate and decomposing the precipitated silver salt with hydrochloric acid, a solution is obtained which on evaporation in a vacuum gives the free acid as a glassy mass. If this be dissolved in water and the solution concentrated, some silicic acid separates and the filtrate deposits triclinic prisms of tungstosilicic acid. Silicotungstic acid is obtained as quadratic pyramids from its mercurous salt which is prepared from mercurous nitrate and the salt formed on boiling gelatinous silicic acid with a polytungstate of an alkali metal.
12-Tungstosilicic Acid - Thomas Sci
This chapter describes the use of heterogeneous catalysts comprising 12-tungstosilicic acid and mesoporous silicas, MCM-41 and SBA-15, for esterification of free fatty acid and oleic acid with methanol. The influence of various reaction parameters such as catalyst concentration, acid/alcohol molar ratio, and temperature was studied to optimize the conditions for maximum conversion of oleic acid. The catalysts show potential of being used as recyclable catalyst materials after simple regeneration. As an application, studies were carried out for biodiesel production from Jatropha oil, as feedstocks without any pretreatment, with methanol over the present catalysts. The catalytic activity of both the catalysts was correlated with the nature of the support.