Hydroprocessing characteristics of palm fatty acid distillate in palm oil into low-carbon biofuel

Abstract

As the hydroprocessed esters and fatty acids (HEFA) process is being commercialized to manufacture sustainable aviation fuel, the feedstock is shifted from edible oils to low-purity residues. As a hydroprocessing feedstock, this study focused on a byproduct in palm processing, palm fatty acid distillate (PFAD) mainly composed of free fatty acids (FFA) that is virtually the hydrodeoxygenation intermediate because the rates of involved reactions largely depend on the PFAD concentration in the feed, thereby altering product distribution including saturated C15-18 hydrocarbon products. As a result of hydroprocessing the mixtures of refined palm oil (RBDPO) with PFAD over Pt/Al2O3, side reactions derived from FFA intermediate (hydrogenation to fatty alcohols, esterification to wax esters, ketonization, and ester/ketone hydrodeoxygenation) were found to take place, which was accelerated as the PFAD was more present in the feed. Furthermore, the activity results obtained by tuning reaction variables such as time, H2 pressure, temperature, and catalyst amount identified that the higher concentration of PFAD with strong adsorption on the catalyst was responsible for the side reactions. Therefore, it could be suggested to add the PFAD of 40 wt% or less into refined glyceride feedstock when the reaction conditions used in this work are employed. If the addition of more PFAD is desired, it would be necessary to develop a hydroprocessing catalyst to prefer the adsorption of hydrogen to that of FFA intermediate. Consequently, this work can serve as a guideline for utilizing FFA-containing raw materials for the HEFA process.