Hydrotreating (HVO) – Advantages over FAME and properties
Section: ADVANCED BIOFUELS
Series: HVO
- Hydrotreating (HVO) – Advantages over FAME
and properties
- Posts: HVO
Hydrotreating is an alternative process to
esterification to produce diesel from biomass. Traditionally, diesel components
produced from vegetable oils are made by an esterification process. In fact,
HVO are commonly referred to as renewable diesel or green diesel in order to
distinguish from Fatty Acid Methyl Esters (FAME), best known as biodiesel.
Other acronyms are also used depending on the feedstock, such as Rape Seed
Methyl Ester” (RME), “Soybean Methyl Ester” (SME), “Palm Oil Methyl Ester”
(PME) or “Used Cooking Oils Methyl Ester (UCOME).
In the HVO production process, hydrogen is used
to remove the oxygen from the triglycerides and does not produce any glycerol
as a side product. Additional chemicals, like methanol for FAME production, are
not needed. Hydrogenation removes all oxygen from the vegetable oils while
esterification does not.
Both FAME and HVO production processes use
intermediates generated from natural gas. Figures published by the Renewable
Energy Directive 2009/28/EC (“RED”) show that life cycle greenhouse gas
emissions of HVO are slightly lower than those of FAME if both are made from
the same feedstock.
Figure 1. Simplified scheme showing inputs and
outputs of esterification and hydrotreating processes for biofuel production
considering rapeseed as feedstock [extracted from Reference 1]
The quality of FAME is known to depend on the
properties of the feedstock and this limits what feedstocks may be used in cold
climates. In general, the feedstock used in the HVO process can be of the same
or lower quality than that of the biodiesel process. A slight disadvantage of
the HVO process lies in the feedstock sourcing. Although the range of potential
raw materials is wide, there is a long list of parameters that need to be
tested to avoid damages to the plant.
Properties of HVO have much more similarities
with high quality sulphur free fossil diesel fuel than with FAME. As a matter
of fact, the properties of renewable diesel are very similar to the synthetic
gas-to-liquid (GTL) diesel fuels. Also, the same analytical methods as used
with fossil fuels are valid for renewable diesel.
Some strong points of HVO:
1. Highest heating value among conventional
biofuels.
Higher energy content compared to FAME, both in
MJ/kg and MJ/l.
The heating value of HVO (34.4MJ/l) is
substantially higher than that of ethanol (21.2MJ/l).
2. Severe winter and arctic grades available
due to the isomerization process.
Cold properties of HVO can be adjusted to meet
the local requirements by adjusting the severity of the process or by
additional catalytic processing.
“Cold Filter Plugging Point” (CFPP) can go down
to -20°C or even -50°C irrespective of the feedstock used. This makes HVO
suitable for use during cold winters even in Nordic countries as well as for
use as jet fuel.
3. Very high cetane number. Low density.
Sulphur-free and very low aromatics. Practically free of metals and ash-forming
elements.
4. It behaves in logistics, storage and use
like fossil diesel fuel (drop-in fuel).
No issues with: stability, water separation,
microbiological growth, impurities causing precipitation above cloud point.
They can be used in diesel engines without
blend walls or the modifications required for biodiesel.
REFERENCES
2 H. Aatola, M. Larmi, T. Sarjovaara: Hydrotreated Vegetable Oil (HVO) as a
Renewable Diesel Fuel: Trade-off between NOx, Particulate Emission, and Fuel
Consumption of a Heavy Duty Engine.
2008 SAE International.
3 Is HVO the Holy Grail of the world
biodiesel market? Greenea
Team, 2014.
