Green diesel, also known as renewable diesel, is a diesel
substitute of renewable origin (vegetable oils and fats). Green
diesel should not to be confused with biodiesel (FAME) as it is
produced via catalytic hydroprocessing of vegetable oils and fats
[28] and not transesterification.
Catalytic hydroprocessing is a common refinery process aiming
to increase hydrogen to carbon ratio, decrease the concentration
of heteroatoms and metals, and reduce the boiling point of
petroleum fractions. Catalytic hydroprocessing of vegetable oils is
focused on producing a high quality biodiesel product that is
compatible with existing diesel fuel infrastructure. The Green
diesel technology consists of two steps, one catalytic hydrotreatment
step which will produce normal paraffins, and one catalytic
isomerization step which will lead to a mixture of n- and isoparaffins
[29].
Green diesel consists mainly of paraffins and is free of
aromatics, oxygen and sulphur. As a result, this paraffinic fuel
has higher cetane number and higher heating value compared to
FAME. Another advantage is that catalytic hydroprocessing leaves
no by-products, unlike FAME which is accompanied by glycerine.
Furthermore, as hydroprocessing includes desulphurization reactions,
Green diesel is a low sulphur fuel (o10 ppmwt) with very
low green house gas emissions (GHG) [30]. Green diesel can be
produced from several types of vegetable oil without compromising
fuel quality, while rapeseed and palm oil are the most
commonly used.
The cetane number of green diesel ranges between 80 and 99,
which is much higher compared to diesel standards, rendering it a
competitive diesel substitute. The density range of green diesel is
0.77–0.83 g/ml which also meets the diesel–biodiesel standard
[31–33]. Its net heating value is between 42 and 44 MJ/kg, which
is almost similar to that of conventional diesel [34,35], while its
low aromatic content (o0.1%wt) leads to cleaner combustion
according to Aatola [35]. Regarding its cold flow properties, itspour point ranges from 1 to 29 1C while its cloud point is from
25 to 30 1C. Finally, green diesel has a flash point of 68–120 1C,
thus it is safe for handling and storage.
Green diesel is a new biofuel which however is currently
produced in industrial scale. The first commercial scale hydroprocessing
plant with a capacity of 170,000 t per year was started
up in summer 2007 at Neste Oil’s Porvoo oil refinery in Finland.
This technology is branded as ‘‘NExBTL’’ [36].