The_Catalyst_Review_April_2023 - 3

Industry Perspective
The views expressed are those of the individual author and may not reflect those of The Catalyst Review or TCGR.
Sustainable Fuels and Green Hydrogen
By Shaun Dyke
The transition from the fossil fuel economy to the renewable economy has started with
the electrification of a wide range of products, across many sectors of the economy,
along with a nascent hydrogen sector trying to establish itself (again) as a long-term
option for heavy road transport and long-haul aviation routes.
Stark evidence of the accelerating impact of climate change has led to a groundswell
of mainly younger people who want to see government, institutional and industry
action that locks in the move away from fossil fuels, sooner rather than later. Don't
underestimate the influence of young people on their parents and grandparents and the
choices they may make.
Catalytic hydrotreating
units are central to the
production of jet fuel
and diesel.
As refineries transition from commodity producers of bulk transport fuels to chemical
feedstock machines, the short-to-medium term impact will be a reduction of gasoline
demand as electric and plug-in hybrid electric vehicles gain market share - a trend that
will accelerate, especially as battery electric vehicle production costs fall, solid-state
battery technology matures and charging infrastructure becomes more widespread. Diesel and, in particular, jet fuel demand will remain
stronger for some time to come but even in these markets, the pressure to produce sustainable or more sustainable fuels will become
difficult to ignore.
Short- and Medium-term Areas of Focus
Catalytic hydrotreating units are central to the production of jet fuel and diesel, and hence, any steps that can be made to improve the
sustainability of these fuels will be a move in the right direction, through the introduction of renewable feedstocks and green hydrogen.
Renewable or sustainable diesel (green diesel) and aviation fuel (sustainable aviation fuel, or SAF), compatible with existing infrastructure
and engine technology, are mainly produced from vegetable oils or fatty acids or contain these materials mixed with other components.
Vegetable oils and fatty acids are generally made up of a mixture of (tri-)glycerides, which have a significant oxygen content.
The most common vegetable oil feedstocks for these units are soybean, palm and rapeseed oil. Animal fats or tallow (fatty acids) from
meat processing waste and fish fat from fish processing waste can also be used as feedstocks. Following the extraction processes for these
renewable feedstocks, they can be fed to a hydrotreater unit with little further pretreatment.
Tall oil or crude tall oil (CTO) is a by-product of the wood pulp industry and comprises fatty acids, rosins and sterols. The fatty acids can be
separated from the CTO in a distillation process and sent to the hydrotreater. Wood waste and even algae are also being developed as
potential feedstocks for hydrotreaters.
These feedstocks are not fully compatible with hydrotreating units running conventional fossil-based feedstocks due to the high
hydrogen demand and the highly exothermic reactions involved with treating these oxygen rich feeds, which also commonly include
other contaminants in significant quantities, such as phosphorous, sodium, and calcium. The treating reactions, almost exclusively
hydrodeoxygenation (HDO), can produce significant quantities of methane and propane, as well as CO2
and CO. CO2
/CO cannot be
allowed to build up in the recycle gas or the treating catalyst will become inhibited. For these reasons, co-processing in standard refinery
hydrotreaters is normally limited to 5-7% of renewable feedstocks. Different catalyst formulations and unit configurations are required for
treating renewable feedstocks in higher proportions.
Used cooking oils (UCO), have been collected and processed through standard diesel hydrotreaters for years, as a low volume
supplemental feedstock. After filtration, UCO can also be fed direct to an hydrotreater processing 100% renewable feedstocks, an
eco-hydrotreater.
An eco-hydrotreater uses a two-stage process to convert renewable vegetable oil/fatty acid feedstocks to renewable diesel and SAF.
The first stage performs demetallation (HDM) and HDO reactions using a NiMo catalyst, which strongly favors HDO over decarboxylation
reactions, limiting the formation of CO2
and CO. The removal of oxygen in the feed is complete. The second stage reactor performs
dewaxing (hydro-isomerisation) reactions, to adjust the cold properties and cetane of the product, and some selective hydrocracking
reactions, if the aim is to maximize the yield of SAF. The separation (removal of water and any CO/CO2
distillation sections are very similar to a conventional hydrotreater.
Continue on page 19
The Catalyst Review
April 2023
3
and recovery of hydrogen) and the

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