Abstract
For co-processing of bio-oil and conventional fossil feed in existing refinery fluid catalytic cracking (FCC) units, little attention has been paid to the increased aromatics and basic nitrogen content in the feed associated with the introduction of bio-oil and how it affects FCC performance. In this contribution, the effect of blending two bio-oils obtained from different catalytic treatment of wheat-straw pyrolysis vapors with atmospheric residue was tested using a microactivity testing unit (MAT). The catalysts used for the pyrolysis vapor phase upgrading included i) a Na/γ-Al2O3 deoxygenation catalyst, and ii) a Pt/TiO2 catalyst in combination with H2 atmosphere. The oxygen content of both bio-oils was similar at ~ 7–8 wt%, but the Na/γ-Al2O3 bio-oil had a lower total acid number (TAN) of 5 mg KOH/g and a higher basic nitrogen (BN) content of 0.7 wt% compared to the Pt/TiO2 bio-oil (15 mg KOH/g, 0.4 wt% BN).The processing of the upgraded bio-oils in blends with atmospheric residue in MAT increased the yields of dry gas, CO, CO2, and coke at the expense of naphtha (decrease by 2.8 percentage points) and decreased the conversion by ~ 2.5 percentage points. This is attributed to the high aromaticity and basic nitrogen content of the two bio-oils. The lower basic nitrogen content and higher degree of saturation for the Pt/TiO2 bio-oil may explain its slightly higher conversion (by ≤ 1 percentage points) compared to the Na/γ-Al2O3 bio-oil.This contribution provides important information for refinery operators interested in FCC co-processing of fossil oils and biomass-derived pyrolysis oils with elevated content of nitrogen and aromatics.
Highlights
The integration of bio-oils produced from renewable sources in to day’s fossil-based refineries can make an important contribution to mitigate climate change
In contrast to reported decreases in H2 yield upon co-processing of bio-oil, [17,28,36,95,96], the present study found similar or higher H2 yields compared to the 100% fossil case
While the determination of biogenic carbon in the products using e.g. the 14C methodology [89,96,100] was not possible in this study due to the limited amount of liquid product produced, it seems highly likely that the observed increase in coke and CO/CO2 yields can be attributed to the introduced bio-oils
Summary
The integration of bio-oils produced from renewable sources in to day’s fossil-based refineries can make an important contribution to mitigate climate change. To rapid poisoning of the active sites via coking [49,50] and elevated concentrations of aromatics and phenols which are considered coke precursors It was of interest in the present study to investigate if different types of pyrolysis VPU strategies may allow to obtain bio-oils with reduced nitrogen content, which may reduce the need for removing N via hydrotreating (HDN) of the bio-oil prior to FCC cracking. By evaluating the effect of co-processing on the FCC performance and providing a detailed chemical analysis of the bio-oils, in particular with respect to nitrogen speciation and aromatics, this study can support petroleum refineries in their evaluation of utilizing the agricultural residue wheat straw as a renewable source for the production of fuels and chemicals via fast pyrolysis [9,10,60,61,62,63]
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