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Because of the extraction of the oil component, an alternative boutique use of leaf and twig could be
as feedstock for compost however additional agricultural waste would probably be required to achieve
correct component ratios. Some synergies may exist with abattoirs with respect to the production of
high value compost however the concentrations of heavy metals in the leaf material and or extracted
liquid could be an issue.
Table 4.3 presents data on the production of mallee oil. The extraction costs are nominal based on the
energy requirement for the extraction process on gas costs only. In an industrial process, energy would
be supplied from combustion of used product, with the nominal saving being absorbed by fixed and
variable costs associated with the process.
Table 4.3 Value of feedstock components for Mallee Oil for boutique and industrial use
Oil Value ($/kg) $10 $2
Tree component leaf & twig whole tree leaf & twig whole tree
Extraction cost ($/kg) $ 0.84 $ 1.08 $ 0.84 $ 1.08
Product Value ($/kg) $9.16 $8.92 $1.16 $0.92
Product yield (kg/gt) 18.0 10.5 18.0 10.5
Value/gt freshweight at $ 164.81 $ 93.69 $ 20.81 $ 9.69
factory
Residual product
Wet leaf & twig
+ separated
woodchip
Wet leaf & twig
& woodchip
Wet leaf & twig
+ separated
woodchip
Wet leaf & twig
& woodchip
Residual Product Value
* 100% of
woodchip
* 65% of leaf &
twig
* 90% of
woodchip
* 65% of leaf &
twig
* 100% of
woodchip
* 65% of leaf &
twig
* 90% of
woodchip
* 65% of leaf &
twig
Table 4.3 indicates that:
• For the boutique market with an oil price of $10/kg ex-factory, feedstock value at the factory is
in the order of $165/green tonne for leaf and twig components of the tree if pre-separated, or
$94/green tonne for the whole tree if the entire harvested product is processes.
• The value of leaf and twig based on industrial oil prices are $21/green tonne for leaf and twig if
separated prior to the process or $10/green tonne if the whole tree is run through the extraction
process. The increased thermal requirement to process the whole tree instead of leaf (and twigs)
only equates to approximately $0.24/kg of oil. Whilst this is barely significant in the case of
boutique oil, it is highly significant in the economics of industrial oil.
These costs indicate that oil extraction for industrial use is not a viable “stand-alone” use of harvested
malle in a large scale industry; however oil extraction from the separated leaf and twig material can
potentially give an additional income stream. After oil extraction has been undertaken:
• If pre-separated, the full value of the woodchip would still be available, however if the
woodchip was subjected to steam extraction, some degradation would have occurred, along
with an increase in moisture content;
• The reduced alkali levels in leaf and twig material can be anticipated to reduce potential
problems associated with combustion of these products, thus potentially increasing their value;
• Work at Curtin University ( http://asdi.curtin.edu.au/csrp/projects/4c2.html) indicates that after
oil extraction, leaf and twig material actually convert into a higher value metallurgical charcoal
than wood.
• To capitalise on this value, it would be necessary to efficiently re-dry and process the material.
The energy required to achieve this would be equivalent to combusting approximately 35% of
the material.
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