Co-hydrotreatment of yellow greases and the water insoluble fraction of pyrolysis oil part I: Experimental design to increase kerosene yield and reduce coke formation

Authors: PIRES, ANAMARIA - Washington State University; OLARTE, MARIEFEL - Pacific Northwest National Laboratory; Terrell, Evan; GARCIA-PEREZ, MANUEL - Washington State University; HAN, YINGLEI - Washington State University

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2022
Publication Date: 1/11/2023
Citation: Pires, A.P., Olarte, M., Terrell, E.C., Garcia-Perez, M., Han, Y. 2023. Co-hydrotreatment of yellow greases and the water insoluble fraction of pyrolysis oil part I: Experimental design to increase kerosene yield and reduce coke formation. Energy and Fuels. 37(3):2100-2114. https://doi.org/10.1021/acs.energyfuels.2c03250.
DOI: https://doi.org/10.1021/acs.energyfuels.2c03250

Interpretive Summary: In this study, the co-hydrotreatment of pyrolysis oil with yellow greases was explored for the production of bio-fuel. Co-hydrotreatment is a process by which unwanted oxygen content is removed from a liquid fuel, thereby increasing its overall quality and value. Pyrolysis is a technology that can convert renewable biomass materials like wood and grass into a crude oil surrogate, and yellow grease is the leftovers from waste cooking oil. These two types of liquids (pyrolysis oil and yellow grease) have some chemical compatibility that makes their co-processing for bio-fuel production more efficient. The final products of this studied oil processing technology include gasoline, diesel, and kerosene fuels, although additional research is needed to figure out how to make these bio-fuels more compatible for existing applications.

Technical Abstract: This paper reports the co-hydrotreatment of the water-insoluble (WIS) phase of commercial pyrolysis oil (also known as pyrolytic lignin) from BTG and yellow greases (waste cooking oil), aiming for the production of sustainable aviation fuels. In this paper, we use a sulfided NiMo/Al2O3, blended catalyst with 20 wt. % WSI and a central composite experimental design to identify processing conditions increasing kerosene yield and reducing coke formation. The input variables were: (1) reaction temperature (320°C, 350°C, and 380°C), (2) initial hydrogen pressure (5 MPa, 6 MPa, and 7 MPa), and (3) amount of catalyst (0.7, 1.0, and 1.3 g). The hydrotreated liquids were distilled to obtain gasoline (<150°C), kerosene (150 - 250°C), diesel (250 - 350°C), and residual oil (>350°C). The reaction temperature mainly affected the yield of gaseous, solid, and liquid products. Meanwhile, higher initial hydrogen pressure and catalyst loading increased the yield of kerosene and other distillates and decreased the coke formation. High temperature correlated with lower content of oxygenates in kerosene cuts. Based on our experimental results, we propose to conduct hydrotreatment studies at 380°C, initial H2 pressure of 7 MPa, and 1.3 g of catalyst. Compared to previous work, under the identified conditions, it was possible to improve the kerosene yield to more than 20 wt. % and reduce the yield of coke to close to 2.0 wt. %. The chemical composition and fuel properties of the gasoline, kerosene, and diesel cuts were thoroughly analyzed. The content of aromatics and phenols in the kerosene fraction produced at the conditions identified in this project exceeded the recommended values for sustainable aviation fuels. New strategies (such as blending, and more intense hydrotreatment for removal of oxygenated compounds) need to be implemented to reduce the content of these molecules in our final product.