Branched-chain biofuels derived from hydroisomerization of palm olein using Ni/modified beta zeolite catalysts for biojet fuel production

Abstract

To overcome mass transfer limitation and adjust zeolite's acidity, the modification of beta zeolite via etching with hydrofluoric acid/ammonium fluoride (HF/NH4F) solution was revealed and the modified beta zeolite was then applied as a support of nickel (Ni) catalysts used for hydroisomerization of palm olein. HF/NH4F solution containing 0.25 M HF concentration was appropriate to enlarge original existing intercrystalline mesopores of beta zeolite (beta-0.25), which resulted to the higher pore volume. The Ni/beta-0.25 catalyst also exhibited the better Ni dispersion and lower acidity. These features suppressed overcracking and provided 43.4 wt% bio-jet fuel yield with 22.1 wt% iso-alkanes fraction when hydroisomerization was operated under 40 bar initial hydrogen (H2) pressure at 340 °C for 5 h. At 0.75 M HF concentration, the excessive leaching of aluminum species out of the zeolite framework provided beta-0.75 with very low acidity, which was ineffective to convert molecules of palm olein to bio-jet fuel range. Initial H2 pressure at 40 bar was sufficient to activate the hydroisomerization of palm olein over Ni/beta-0.25 catalyst to produce liquid biofuel containing iso−/n-alkane ratio of 2.61. The liquid biofuel/Jet A-1 blend at 50% (v/v) had freezing point and gross heating value of −58.9 °C and 43.7 MJ/kg, respectively.