Hydroisomerization and hydrocracking of normal pentane over various mordenite catalysts

Abstract

Mordenite catalysts with various cations were prepared by a reflux ion exchange technique using chloride or nitrate salts and were tested for activity in the hydroisomerization and hydrocracking of n-pentane. The extent of sodium ion exchange possible followed the order NH 4 + > Ba 2+ > Sr 2+ > Be 2+ > Ca 2+ > Mg 2+ > La 3+. Maximum catalytic activities for H-M, Ca-M and La-M occurred at calcination temperatures of 510, 525, and 400 °C, respectively. Weight loss during calcination followed the order Be > Mg > Ca > Sr > Ba indicating that the smaller cation mordenites can accommodate more adsorbed water. Increasing degrees of Na + ion exchange in HM, CaM, SrM, and BaM resulted in increased n-pentane hydroisomerization and hydrocracking activity. The activity increase was small for SrM and BaM and for HM with less than 80% exchange. Activity increased very rapidly beyond 80% exchange for HM and appeared to increase substantially for Ca-M from 68 to 72% exchange. Although conversion was low for Be, Mg, Ca, Sr, Ba, and LaM, the following activity order for both n-pentane hydroisomerization and hydrocracking was obtained: Be > La > Mg > Ca > Sr > Ba. The cracked products consisted of relatively more propane and butanes for the smallest cation form (BeM) and relatively more methane for the largest cation form (BaM), indicating a selectivity effect. A constant effect of cation size for the alkaline earth group catalysts was evident from the Arrhenius plots, and a simple factor for cation size was introduced into the equation for the apparent rate constant so that a single Arrhenius line was obtained. Addition of nickel to the above catalysts increased activity substantially, especially for hydrocracking. Very high hydrocracking conversions over Be, Mg, Ca, Sr, Ba, and LaM were obtained at temperatures between 370 and 480 °C at a WHSV of 23.0 g/h-g. The relative order of enhancement by adding nickel was Ba > Sr > Ca > La > Mg > Be. The catalysts containing nickel produced relatively more butanes and propane and less methane than the same catalysts without nickel. The average activation energies for hydroisomerization and hydrocracking were 20.1 and 22.9 kcal/g-mole, respectively, without nickel and were 41.2 and 46.4 kcal/g-mole, respectively, with nickel. BeM and LaM gave peculiar Arrhenius plots which could not be explained with existing data.