Fuels & Lubricants Magazine

GREEN CORNER
fatty acids. The fatty acid from vegetable oil have
cracked stem appearance so the oil molecules tend to
coincide with the crystalline structure and crystallize
at a lower temperature. Double bonds of unsaturated
triglycerides are less compact and there are less intermolecular
interactions among them. Because of this, the
vegetable oils are at the ambient temperature in liquid
state and fats are in solid state. Saturated oils have a
better oxidation stability and a higher point of a melting
point than unsaturated. A higher degree of unsaturation
is also the reason for higher reactivity [6].
Typical properties of used cooking oil and animal fat
are shown in Table 1 and 2 respectively.
Table 1. Properties of used cooking oil
Property
UCO
Acid number
1.0 – 16.0 mg KOH/g
Density at 15 °C < 920.0 kg/m 3
Water content < 1.0 wt. %
Kinematic viscosity at 40 °C 35.0 – 45.0 mm2/s
Metal content
Ca
10 – 120 mg/kg
K
20 – 90 mg/kg
P
5 – 65 mg/kg
Fe
0 – 50 mg/kg
Na
10 – 60 mg/kg
Mg
0 – 25 mg/kg
Free fatty acids content < 6.0 wt. %
Table 2. Properties of animal fat
Property
AF
Acid number
10 – 20 mg KOH/g
Density at 15 °C > 915.0 kg/m 3
Water content < 1.0 wt. %
Kinematic viscosity at 100 °C 8 – 9 mm 2 /s
Metal content
Ca
260 – 500 mg/kg
K
40 – 160 mg/kg
P
260 – 450 mg/kg
Fe
5 – 25 mg/kg
Na
70 – 180 mg/kg
Mg
5 – 40 mg/kg
Free fatty acids content < 15.0 wt. %
In Croatia, during the 2016 year, 825 tons of used cooking
oil was collected which is only 0.2 kg per capita [7].
During the 2016 year, 1.3 tons of UCO was recovered,
which is 72 wt.% more than in the 2015 year. In addition
to the accumulated amounts of UCO, the reason lies in
the fact that part of the recovered amount in 2016 is collected
in the previous years and comes from a collector’s
storage tanks. All collected quantities, according to The
Environmental Protection and Energy Efficiency Fund
data, were recovered within the Republic of Croatia by
energy recovery.
The data from Croatian Environment and Nature
Agency are generated from data reported in Environmental
Pollution Register database, which includes
stakeholders outside the The Environmental Protection
and Energy Efficiency Fund system, shows that in 2016
year 5.3 tons of UCO was collected. More than 4 tons
were recovered while only 1.8 tons in Croatia and 2.3
tons were exported to other EU countries. The remaining
collected quantities (more than 1 ton) were temporarily
stored at the authorized collector’s warehouses.
The animal fats category 1 and 2 that is not used in the
production of animal feed in the Republic of Croatia is
about 2500 tons per year.
Due to the high content of triglycerides vegetable oils
and animal fats are suitable feedstock for production
of biofuels such as biodiesel. Transesterification is the
most often used process to transform vegetable oil into
biodiesel. The process is usually carried out at 60 °C and
atmospheric pressure. By reaction of higher fatty acids
and short chain alcohols triglyceride, most commonly
methanol, in the presence of an alkali catalyst such as
sodium or potassium hydroxide, fatty acid methyl ester
and glycerol are obtained as a secondary product. Biodiesel
can be blended up to 7% v / v in fossil diesel fuels
without modification on vehicles. Larger share requires
fuel injection system adaptation and may cause problems
with the fuel’s application properties. The last few years
of researching are moving in the direction of obtaining
fuels of the same characteristics as fossil fuels that can
be fitted without restriction, so called drop-in fuel. One
of these fuels is hydrotreated vegetable oil, which is a
good alternative to traditional biodiesel. It consists predominantly
of n- and iso-paraffins, and is obtained from
catalytic hydrotreating of used cooking oil under high
temperature and pressure conditions (350 – 400 °C and
50 – 80 bar). The main byproducts are n-paraffins with
a number of carbons between 15 and 18, and light gases:
CO2, CO and propane.
26 Fuels&Lubricants No. 3 OCTOBER 2018