Valorization of palm-based fatty acid distillate byproducts through coupling ketonization with hydrotreating: Changing the long-chain distribution of paraffinic hydrocarbons

Abstract

Free fatty acids (FFAs) are prone to undesirable side reactions in hydrotreating of bio-feedstocks and hence should be reduced to improve catalytic performance. The simple reaction option for this purpose is to handle acid ketonization before hydrotreating. Although the ketonization reaction itself is well explored, its effects on the characteristics of hydrotreating products are worth being addressed to valorize them into various fuels. This study focuses on the reaction steps of TiO2-catalyzed ketonization and subsequent Pt/Al2O3-catalyzed hydrotreating, using three model FFAs and palm-based FFAs such as palm kernel fatty acid distillate (PKFAD) and palm fatty acid distillate (PFAD). From the results obtained using the model FFAs, most of product species were assigned and an overall reaction network could be established, thereby distinguishing product groups of monomers, dimers, and trimers in terms of the mole of FFA added. Furthermore, PKFAD ketonization was identified to broaden the carbon number distribution of hydrotreating paraffinic hydrocarbons while PFAD ketonization into dimeric/trimeric products contributed to the production of hydrotreating long-chain paraffins with the carbon number of more than twenty and enriched iso-paraffins. Consequently, coupling ketonization with hydrotreating for FFA-rich feedstocks is effective in enhancing the hydrotreating conversion and controlling the carbon number distribution and isomer fraction of paraffinic hydrocarbons.