Production of Biofuels from Hydrodeoxygenation and Hydroisomerization of Triglycerides with Metal-Supported SAPO-11 Molecular Sieves

Abstract

Hydroprocessing of fats and oils is being implemented as the main alternative to fossil fuels. Industrial-scale routes are based on a complex sequence of reactors and unit operations of separation: hydrodeoxygenation, fractionation, downstream hydrocracking/hydroisomerization, and final purification. In the present work, one-step conversion of triglycerides using nonsulfided metalloaded silicoaluminophosphates-11 (SAPO-11) molecular sieves is proposed to convert triglyceride feedstocks to isomerized renewable hydrocarbons. Different noble (Pd, Pt) and transition (Ni, Cu) metals were impregnated onto a SAPO-11 molecular sieve. The resulting bifunctional catalysts were characterized by ICP-OES, adsorption−desorption N 2 at −196 °C, n-propylamine temperature-programmed desorption, X-ray fluorescence spectroscopy, SEM, and TEM. The catalytic behavior was tested in a stirred tank reactor device, using refined vegetable oil as reference triglyceride. The operation conditions were set at 50 bar, 350 °C under 800 rpm stirring. The effect of the different metals on the catalytic performance was evaluated in terms of conversion of triglycerides, yield to hydrocarbons (naphtha, kerosene, diesel, and heavy fractions), and isomerization activity. The highest yield to liquid hydrocarbons of 73.1% was obtained for a nickel-based SAPO-11 with an 8% metal loading. Among the different metals evaluated (Pt, Pd, Ni, Cu), nickel showed the highest isomerization activity with the highest iso/n-paraffins ratio of 0.92. In all cases, a fraction of heavy hydrocarbon was obtained, suggesting that long residence time led to undesired side reactions.