Hydrocarbon Processing - January 2022 - 64

Bio-Based Processing
TABLE 1. Comparison of crude oil to biofeedstocks
Vegetable oil
Triglycerides and free fatty acids
Diesel range lipids
Metals/inorganics and
other contaminants
Pyrolysis bio-oil
Characteristics
As many as 400 components
High oxygen
Variable aromatics levels
Water content
Oxygen removal
Cracking/isomerization
for some products
Fractionation
Processing requirements
Oxygen removal
Cracking of large molecules
De-aromatization
Fractionation
Compositions
Carbon, wt%
Oxygen, wt%
Hydrogen, wt%
Sulfur, wt%
Nitrogen, wt%
77.6
10.4
11.7
0.0006
0.0011
some bio-based oils can be used directly
as a fuel, the process of upgrading for better-quality
products is attractive. Upgrading
bio-based oil requires the removal or
reduction of oxygen atoms. Processing or
coprocessing bio-based oils in refineries
is a low-cost route because the processing
infrastructure, supply chain and distribution
network not only support but
accelerate bio-based oil production.1
In
refineries, the most likely tie-in points for
using bio-based products are the diesel
hydrotreater (DHT) and the FCCU.
Alternatively, there are potentially
cheaper future feedstocks, such as cellulosic
biomass, which can be decomposed
using pyrolysis to make bio-based pyrolysis
oil. This can be used directly as a fuel
for various heaters or further upgraded in
the hydrotreater or the FCCU. Pyrolysis
oil is dissimilar to its petroleum counterpart,
containing approximately 300 different
carbon molecules and up to 40%
oxygen, which means that it requires significantly
more (costly) hydrogen during
hydrotreating than lipid-based biofeedstocks
like vegetable oil.2
Pyrolysis oil is
acidic, less stable, contains high amounts
of water and has low energy density (H/C
ratio = 0.2). A project funded by the European
Union (EU)-4Refinery-is
investigating the processing of blended
vegetable and pyrolysis oil feeds, as these
are technically easier to handle in existing
64 JANUARY 2022 | HydrocarbonProcessing.com
54-65
28-40
5-7
< 0.05
0-0.2
infrastructure than 100% pyrolysis oil. A
summary of the different potential feedstock
characteristics is provided in TABLE 1.
Coprocessing routes. Industrially,
three routes to producing saleable diesel
from a mix of biofeedstock and crude
(FIG. 2) include:
1. Injecting a drop-in, lipid-based
biofeed into the existing DHT
2. Using a purpose-built, standalone
vegetable oil hydrotreater, the
diesel from which is blended
with conventional diesel to obtain
the correct product properties
(e.g., cloud point)
3. Incorporating a drop-in lipid
(and potentially lignocellulosic)
biofeed into the existing FCCU.
The first two routes rely on lipid-based
biomass, such as vegetable oil, oil crops,
algae or tallow-although pyrolysis and
hydrothermal liquification oils are both
under investigation for future use. Pinho
et al. carried out test runs on a pilot-scale
FCCU for coprocessing vacuum gasoil
(VGO)-which is its normal feed-with
pinewood chips.3
While lipid feedstocks
can be converted relatively easily into
biodiesel or green diesel, they are more
expensive than lignocellulosic ones. Conversely,
they generally contain much less
oxygen, meaning less hydrogen demand
during hydroprocessing. Furthermore,
81.4
6-18
8.7
0.01
0.095
83-86
< 1
11-14
< 4
-
the upgrading technology for these
compounds is already well-developed in
industry and requires a relatively small
investment when incorporated into existing
refineries. The amount of upgrading
required for lipid biomass is related to the
desired degree of biodiesel blending.
Direct injection into the DHT. The first
process route is the most common. In this
route, the lipid biomass is pretreated (e.g.,
degummed) to remove contaminants
before it is added to the DHT. The catalyzed,
hydrogen-rich, high-temperature
(300°C-400°C) and high-pressure (40
barg-100 barg) environment of the DHT
simultaneously deoxygenates the biofeedstock
molecules to produce H2
O and
desulfurizes the petroleum diesel compounds
to form H2
S. CO2 is also formed
through decarboxylation of the biofeed
molecules. Methane, propane and carbon
monoxide (CO) are also produced
as byproducts. The hydrogenated chemical
structure produced in this manner has
long, unbranched hydrocarbon chains,
which results in a biodiesel with a cloud
point much greater than petroleum diesel.
Therefore, this method of coprocessing
will generally only permit a maximum of
10% biofeed before the blended product
begins to exhibit cold flow issues.
The Preemraff Göteborg oil refinery in
Sweden has successfully coprocessed up
Oxygen removal
Cracking of larger molecules
De-aromatization
Hydrothermal liquefaction
Lower oxygen content
Lower water content
Crude oil
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