(78c) Maximizing Sustainable Aviation Fuel Production through Optimized Hydroprocessing of Bio-Oils

Introduction

Achieving climate neutrality in the transportation sectors requires large volumes of truly sustainable bio fuels to provide long-term solutions for sectors where direct electrification is not viable. Biomass can be used as a raw material for the production of fuels with low (potentially zero) carbon footprint [1]. Biofuel processes such as hydrotreating of vegetable oils can convert biomass into fuel through well-established technologies [2]. Topsoe A/S has been developing and refining the HydroFlexâ„¢ technology since 2004 to tailor the product and optimize the yields of both renewable diesel (RD) and sustainable aviation fuel (SAF) from bio-oil feedstocks.

Experimental/methodology

In this study, the target was to produce maximum SAF yield while minimizing the loss of overall liquid fuels, SAF+RD, yield. Experiments were carried out in Topsoe’s hydrotreating pilot plant facilities, using hydrotreated vegetable oil (HVO) and commercially available hydroprocessing catalyst. The tests were conducted in a once-through, fixed-bed, high-pressure pilot plant setup, loaded with 22 g of TK-920 D-wax™ which is specifically designed for dewaxing HVO and gas oil. The temperature was varied between 280 and 340°C, and the pressure applied was in the range of 40-80 barg. At each condition, gas and liquid samples were drawn and analyzed after reaching line-out. Gas and liquid analyses were carried out in order to close mass balance calculations and giving the basis for calculating yields and hydrogen consumption.

Furthermore, the feed and liquid products were subjected to a range of analytical methods to determine properties such as freezing point, simulated distillation, and density. The liquid products were fractionated to investigate the properties of the SAF and RD fractions separately. More comprehensive methods such as GC×GC-MS/FID/AED and GC-VUV were employed to give in-depth understanding of the chemical reactions taking place over the catalyst.

Results and discussion

The HVO was successfully converted to SAF and RD meeting the ASTM D7566 and ASTM D975 specifications, respectively. HVO is a liquid consisting mainly of normal paraffins with carbon numbers in the range C15-C18 resulting in poor cold flow properties. HVO produced by hydrotreating of vegetables oils or animal fats typically has a freezing point in the range of 22-28°C depending on the specific feedstock used. In order to meet SAF specifications both isomerization, to meet freezing point, and hydrocracking, to meet density and boiling point requirements, must be carried out. This is best done in hydroprocessing using a bi-functional catalyst or catalyst system tailor-made to minimize yield loss [3]. In Figure 1, transportation fuel yield, SAF and RD, is plotted as a function of SAF yield. Very high transportation fuel yields are obtained even for SAF yields larger than 20 vol% of fresh feed. The HydroFlex^TM process can be applied to advanced bio fuel production where the feedstock is based on e.g. lignocelloulosic- or sewage waste. Recent pilot plant test results show that it is possible to produce SAF based on advanced bio fuel feedstock.

References

[1] McKendry, P. Bioresour Technol 2002, 83, 37.

[2] Donnis, B. et al. Top Catal 2009, 52, 229.

[3] Kumar, H.; Froment, F. Ind. Eng. Chem. Res 2007, 46, 4075.