Sustainable marine fuel production through mild hydrotreating of catalytic fast pyrolysis bio-oil

Abstract

• Catalytic fast pyrolysis oil from pine was mildly hydrotreated to marine blendstock. • Lights < 140 °C were removed to increase flash point. • Products with < 5 wt% oxygen were miscible with very low sulfur fuel oil. • Products met ISO 8217 specifications for acid number, water, sediment potential. • Milder hydrotreating conditions reduced hydrogen consumption. Lignocellulosic biomass-derived biofuels have great potential to reduce sulfur and fossil carbon dioxide emissions from the maritime sector and help achieve the International Maritime Organization (IMO) targets and, at the same time, meet the increasing demand for low-carbon marine fuels. In this work, woody biomass-derived catalytic fast pyrolysis (CFP) oil was evaluated as an alternative to fossil marine fuels. CFP oil is not fully fungible with conventional marine fuels and needs to be further upgraded. The heavy organic fraction (bottom layer) of CFP oil, which constitutes 90 % of CFP oil, was hydrotreated at 300–350 °C, 103 bar (1500 psi) with weight hourly space velocities (WHSV) of 0.12–0.24 g/(gh). The aim was to produce a biofuel that meets key marine fuel properties required by ISO 8217 and is miscible with very-low-sulfur fuel oil (VLSFO). The bottom CFP oil with 23 wt% oxygen (dry basis) became significantly deoxygenated and contained < 0.01–5 % wt% oxygen at all hydrotreating conditions studied. Decreasing the hydrotreating temperature or increasing the WHSV reduced deoxygenation and hydrogenation. The hydrotreated oils were distilled at 140 °C to remove water and low-boiling compounds to increase the flash point for marine fuel cuts. The products after distillation were miscible with VLSFO and met all tested ISO 8217 specifications except for the product from the least severe condition having a slightly higher density (1020 vs. < 1010 kg/m 3 ). A comparative techno-economic analysis with conceptual scale-up of the four experimental cases showed that lower hydrotreating severity with higher space velocities, allowing the retention of more oxygen in the fuel, can reduce hydrotreating costs by up to 30 % within the 0.12–0.24 g/(gh) WHSV range. Cost benefits were achieved by using smaller reactor and catalyst volumes, resulting in up to 1/3 less hydrogen consumption. Higher oxygen retention and less hydrogenation of the fuel also contribute to heavier molecules with lower fuel volatility (and higher flash points) and can thus generally allow larger proportions of the hydrotreated products to be suitable for use as marine fuel.

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