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March
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HYDROCARBON
ENGINEERING
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Chemical additives.
Polynuclear aromatics.
Sulfur.
Used oil disposal
There are several ways to dispose of used oil. A significant
amount is improperly disposed of by dumping it into the
ground, sewer, or waste. However, many regions have made it
illegal to dispose of used oil improperly. This is because when
used oil is disposed of without any treatment, the toxic
substances within it will contaminate rivers, groundwater and
soil. More importantly, many of these toxic chemicals are
carcinogenic and can cause serious health issues.
Used oil is also commonly used as fuel in boilers and
furnaces, which, since used oil is mostly composed of
hydrocarbons, means it is high in energy density. Each gallon can
produce approximately 41.4 MJ/kg,
1
therefore, burning used oil
is considered more economical and energetically beneficial
than disposing of it. However, when used oil is burned it
produces carcinogenic material, metal organics, acid halides,
particulates, sulfur oxides and nitrogen oxides, which are
released into the atmosphere. Table 1 is a list of substances and
their designations when used oil is burned in furnaces. The data
from Table 1 assumes that a space heater is used. In general,
space heaters are not equipped with waste gas controls,
therefore heavy metals can escape into the atmosphere. It is
possible to use pre-treatment techniques to filter out some of
the heavy metals and neutralise some toxic substances before
burning the used oil, however, the effectiveness of
pre-treatment is far from ideal. All of the substances in Table 1
are toxic to humans and can cause serious health conditions, if
excessive amounts are released. For example, lead, cadmium
and chromium are carcinogenic materials.
Moreover, SO
X
in the atmosphere is a precursor to acid rain.
The ash leftover from burning is highly concentrated in heavy
metals and toxic substances. In most cases, the ashes are
disposed of in the trash or onto soil, meaning the
environmentally damaging components will be dispersed and
potentially contaminate the soil and underground water.
Some industrial furnaces are equipped with waste gas
controls to prevent excessive heavy metals from entering the air.
However, even with the waste gas treatment, other substances
such as PO
X
, SO
X
, NO
X
, and HCl are still released.
Recycling/re-refining used oil
Recycling and re-using a resource is always a more sustainable
alternative to dumping, disposing or burning. Clean and
re-usable base oil can be extracted from used oil and
categorised (Table 2).
The following are the recycle/re-refining technologies
available today:
Acid clay treatment.
Vacuum distillation.
Clay treatment.
Solvent extraction.
Hydrotreating.
Acid clay treatment is an older technology that removes
contaminants and produces Group I base oil that can be
re-used in lower grade lubricant applications. This process has
Table 1.
Various substances' designation when
used oil is burned without waste gas treatment
2
Substance Designation when burning used oil in space
heaters
Lead
>50% to air, balance to deposits
Cadmium >50% to air, balance to deposits
Chromium <50% to air, balance to deposits
Zinc
Approximately 50% to air, balance to deposits
Sulfur
SO
X
to air
Nitrogen
NO
X
to air
Polynuclear
hydrocarbon
CO
X
to air
Chlorinated
hydrocarbons
HCl to air
Phosphorous PO
X
to air
Phenols
CO
X
to air
Waste
streams
Ash deposits
Notes: SO
X
= sulfur oxides, NO
X
= nitrogen oxides,
HCl = hydrogen chloride, PO
X
= phosphorous oxides,
CO
X
= carbon oxides.
Table 2.
Mineral oil-based base oil specifications
Sulfur
Saturates Viscosity index
Group I
>300ppm ≤90% 80 – 120
Group II
≤300 ppm ≥90% 80 – 120
Group III ≤300 ppm ≥90% ≥120
Figure 1.
Relative burden to environment between
re-refining and crude refining.
3
Figure 2.
Closed loop collection and re-refining of
used oil.