A NEW CLASS MESOPOROUS ALUMINOPHOSPHATES AS POTENTIAL CATALYSTS IN THE UPGRADING PETROLEUM FEEDSTOCKS

A comprehensive investigation was conducted towards the synthesis and catalytic evaluation of high surface areas, uniform pore size, mesoporous aluminophosphates (AlPO{sub 4}) as potential catalysts for the upgrading of heavy petroleum feedstock, such as heavy crudes and petroleum residuum. The influence of several synthesis variables (including, the nature of the reactants, chemical composition of reaction mixtures, time and temperature) on the synthesis and physicochemical characteristics of the resulting products was explored. Phosphoric acid and three different aluminum sources, namely, aluminum hydroxide, aluminum isopropoxide and psuedobohemite alumina, were used as the inorganic precursors. Cetyltrimethylammonium chloride (C{sub 16}TACl) surfactant was used as charge compensating cation and structure directing agent in the surfactant-micellar-mediated synthesis pathway employed. Synthesis were conducted from reaction mixtures within the following typical molar composition range: xAl{sub 2}O{sub 3}:P{sub 2}O{sub 5}:yC{sub 16}TMACl: zTHMAOH: wH{sub 2}O, where x = 0.29-2.34, y = 0.24-0.98, z = 0.34-1.95, w = 86-700. Selected materials were evaluated for the conversion of isopropylbenzene (cumene) in order to understand the nature of any acid sites created. The synthesis products obtained depended strongly on the molar composition of the synthesis mixture. A lamellar (layered) phase was favored by synthesis mixtures comprised of low Al/P ratios (&lt;0.33), low TMAOH content, high C{sub 16}TACl concentrations and high synthesis temperature (110 C). Formation of the desired hexagonal (tubular) phase was favored by higher Al/P ratios and TMAOH content, pH range between 8-10, low C{sub 16}TACl concentration and ambient temperature. The aluminum source had significant influence on the products obtained. With aluminum hydroxide (A1(OH){sub 3}) as the hydroxide source, the resulting hexagonal phase in the ''as-synthesized''form demonstrated well defined ordered mesoporous structure for synthesis mixtures of Al/P ratios in the range of 0.47-1.25, above which increasingly disordered products were observed. The products were however unstable to calcination in air above 400 C to remove the organic template, under which structural collapsed was observed. Products formed using pseudoboehmite alumina (catapal B), were more thermally stable than those formed with aluminum isopropoxide, though all products experienced some degree of structural collapsed on calcination and yielded micro- or micro-mesoporous materials ranging from low (&lt;500 m{sup 2}/g) to high surface areas (&gt;500 m{sup 2}/g) and pore sizes ranging from microporous (&lt; 1.5 nm) in some products to mesoporous (up to 3.6 nm) in other. Improvement in thermal stability was not observed when Mg and Co or bridging organic functional groups were incorporated with the mesoporous framework. The products showed negligible activity for the conversion of cumene at 300 C. Further research is necessary to investigate alternative synthesis strategies to strengthen and improve the thermal stabilities of these aluminophosphates.

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