Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02337594 2001-02-20
NON-DESTRUCTIV$ OIL RECOVERY METHOD
FIELD OF THE INVENTION
This invention relates to the removal and
recovery of waste oil or other petroleum hydrocarbons
from substrates, particularly the non-destructive
removal of such waste products.
BACKGROUND OF THE INVENTION
When petroleum hydrocarbons, such as motor
oil, brake fluids, heating oils and the like, are
deposited on a porous or non-porous substrate, it
adheres to the surface. This results in a contaminated
substrate with undesirable environmental and commercial
effects.
In the first instance, where the contaminated
substrate is no longer useful for its original purpose,
such as in the case of oil tanks for heating oil, the
resulting contaminated material is not recyclable and
the used tanks are stored in a dump. If conventional
methods and chemicals were to be used to clean the
tanks, the resulting hazardous and toxic effluent would
need to be incinerated or land filled, which only
relocates the pollution.
In the second instance, where the removal and
relocation of the substrate is not possible or feasible,
such as in the case of driving and parking surfaces for
motor vehicles, the petroleum deposits on the surfaces
are washed away by rain water or wash Water, resulting
in pollution. Removal of the accumulated hydrocarbons
using conventional methods and chemical degreasers
results in chemical mixtures of questionable or
undetermined properties that are not recyclable or
illegal to discharge. In this instance, the effluent
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must be relocated, which results in simply transferring
the pollution from one location to another. This
detracts from the commercial viability of the process.
If a surface has high porosity (such as
asphalt), typically a solvent, such as gasoline,
kerosene or mineral spirits, can be employed to remove a
petroleum hydrocarbon deposit, hereinafter simply
referred to as "oil". If adhesion of the oil to the
surface has occurred, the solvent must be of sufficient
strength to dissolve the oil and penetrate to the
substrate. Apart from creating a fire hazard, there are
three inherent problems associated with this method.
The first is that when attempting to remove refined
petroleum hydrocarbon from an asphalt surface, the
solvent used must be of sufficient strength to penetrate
the surface deposit. As a result, the strong solvent
emulsifies a large part of the asphalt along with the
deposit and leaves a residue that can become flammable.
Technically, this is considered destructive removal, and
will contribute to accelerating the breakdown of the
asphalt as well as acting as a bond breaker if a coating
or sealant is to be applied to the surface after
cleaning. The second problem is that the resulting
effluent may not be recyclable depending on the solvent.
The third problem is that the solvent will disperse the
hydrocarbon and leave a residue. It does not suspend
the hydrocarbon to allow for removal. In the case of
asphalt, a large stain will be apparent after washing,
requiring further treatment for removal.
The same problems that occur with the above
solvents occur with commercially available degreasers
and detergents. However, typically these products are
not of sufficient strength to penetrate the oil and thus
overcome the adhesion of the oil to the surface.
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Acids, bleaches, paint strippers contaminate
the waste effluent beyond repair and are not recyclable.
It is an object of the present invention to
alleviate the above-mentioned difficulties.
SU1~2AR,Y OF THE INVENTION
According to the invention there is provided a
method of non destructive recovery of a petroleum
hydrocarbon from a contaminated substrate, comprising
the steps of separating the hydrocarbon substantially
intact from the substrate by applying a hydrocarbon
removing agent comprising an aqueous solution of an
alkali and a surfactant to the substrate; and collecting
the hydrocarbon separated from the substrate.
Also according to the invention, there is
provided a method of non destructive recovery of a
petroleum hydrocarbon from a contaminated substrate,
comprising the steps of separating the hydrocarbon
substantially intact from the substrate by applying a
hydrocarbon removing agent to the substrate; and
collecting the hydrocarbon separated from the substrate,
wherein said separating the hydrocarbon from the
substrate comprises the steps of applying a separation
agent to the substrate to effect adhesion failure of the
hydrocarbon, thereby to release the hydrocarbon intact
from the substrate; and applying a surfactant to suspend
the hydrocarbon removed from the substrate; said
separation agent and said surfactant collectively
comprising said hydrocarbon removing agent.
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Further objects and advantages of the
invention will become apparent from the description of
preferred embodiments of the invention below.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
According to one embodiment of the invention,
the recovery of deposited oil or other petroleum
hydrocarbons (hereafter generally referred to as
"deposit" or "deposits") from paved surfaces for the
purpose of recycling, comprises several steps, i.e.:
(i) Penetration of the deposit;
(ii) separation of the deposit from the
surface, i.e. effecting "adhesion
failure" of the deposit;
(iii) suspension and movement of the
deposit; and
(iv) collection and neutralization of the
product.
The first two steps are applied to achieve
penetration and separation of the deposit from the paved
surface without contaminating or damaging the petroleum
hydrocarbon. To accomplish this objective, an alkali,
such as potassium hydroxide (KOH), in aqueous solution
with a surfactant, is used. The concentrations of the
alkali and surfactant can be varied depending on the
porosity of the substrate and the adhesion level of the
petroleum hydrocarbon, as well as the amount of
hydrocarbon present. The very properties of refined
petroleum that make it useful for lubrication of moving
parts, such as high temperature resistance and
viscosity, are the same properties which cause the
difficulty in penetrating an oil stain to effect
adhesion failure. Thus, the use of acids and/or
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bleaching agents for removing oil stains in conventional
methods.
The best way to understand why a cleaning
chemical must accomplish all three objectives of
penetration, separation, or adhesion failure, and
suspension without damaging the petroleum hydrocarbon so
that the deposit can be collected and recycled, is to
explain first what constitutes a "petroleum hydrocarbon
stained substrate" and what does not. A stained paved
or driving surface occurs when spilled petroleum
hydrocarbon has penetrated and has been allowed
sufficient time to adhere to the substrate. If motor
oil is spilt on a clean cement surface and immediately
scrubbed with household dish washing liquid and water,
all or most of the oil can be removed. Recycling of the
material would then be a matter of collection, be it
recyclable absorbent material, pressure washing,
vacuuming or a combination of these methods. In the
above situation, adhesion has not occurred and thus the
surface is technically not stained. Vrhen the substrate
is stained, a bond or adhesion occurs between the oil
and the surface. If the same motor oil is spilt and
left for several days, the oil has time to penetrate the
surface and adhere or bond. If it is attempted to clean
this same surface with household dish washing liquid and
water, only the surface oil is removed. The same is
true for the majority of commercially available
degreasers. This is why acid washing has become the
preferred method of oil stain removal in conventional
methods.
The present method of causing adhesion failure
to occur, comprises adjusting the amount of alkali in
the cleaning agent according to the substrate and
allowing an appropriate dwell time so that the agent can
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penetrate the hydrocarbon stain. This process can be
accelerated by increasing the concentration of the
alkali component in the cleaner, as well as using
mechanical means, such as increasing the application
pressure of the cleaning equipment as well as the water
temperature, since neither mechanical attack or hot
water is not sufficient on its own. The alkali
component of the cleaner is adjusted from about l~ to
about 50~ of by volume of the total volume of aqueous
solution containing the alkali and the surfactant.
The third step comprises suspension of the
hydrocarbon and movement of the resulting suspended
hydrocarbon and cleaner emulsion. When the bond between
the petroleum hydrocarbon and the substrate is
successfully broken, collection of the oil becomes
possible. Typically, pressure washing is employed to
move the oil to collection material or equipment and/or
it is flushed down the drain. However, during this
procedure, oil may disperse over a large area and leave
a large stain or residue. This stain increases in
direct proportion to the porosity of the substrate. To
avoid this problem, the cleaning agent also comprises a
surfactant or suspension agent that suspends the oil so
that it can be moved without settling back onto the
surface. The surfactant may comprise an enzyme based
ionic surfactant. The concentration of the surfactant
is adjusted according to the substrate so that the oil
droplets do not coalesce in portions large enough to be
re-deposited on the surface. The amount of surfactant
must be increased in proportion to the porosity of the
surface and the amount of hydrocarbon. The objective is
the suspension of the hydrocarbon. In most field
applications the percentage of surfactant is between 1
and 5~ by volume of the aqueous solution i.e. about l~
for a low porosity surface, about 3~ for a medium
CA 02337594 2001-02-20
porosity surface and about 5~ for a high porosity
surface. The amount of surfactant can be adjusted on
location as required by the person doing the work. The
higher the percentage of surfactant the greater the
suspension capacity. If desired, the cleaning agent may
comprise more than one surfactant.
The fourth step comprises collection and
neutralization of the emulsion. Neutralization is
necessary when the alkali portion of the cleaner is too
high for discharge. Neutral pH is considered to be
between 7 and 7.5. When the emulsion is neutralized,
the resulting material is petroleum, hydrocarbon, salt
and water. The objective of this part of the process is
to collect the hydrocarbon in such a manner that it can
be recycled. Assuming the hydrocarbon was not damaged
or contaminated in the previous steps, the hydrocarbon
can be collected by using absorbent material that can be
blended into the emulsion and/or by using absorbent
material that can be cleaned and reused. In the case
where an oil and water separator is available or the
effluent is vacuumed and collected, it can be placed
directly into this equipment for separation and
recycling.
Generally, paved surfaces fall into three main
categories:
(a) Asphalt, being typically a driving
surface composed of a combination of low
grade petroleum obtained as residue in
the refining process and aggregate of
varying mass.
(b) Cement type surfaces, either poured in
place or prefabricated and installed.
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This category primarily includes bricks,
payers, cement and concrete slabs.
(c) Traffic membrane which is not to be
confused with sealers. Traffic
membranes are typically combinations of
epoxies and/or urethanes that are
overlain on top of other driving
surfaces for the purpose of
waterproofing and abrasion resistance.
A more detailed description of the process for
each of the above surface types is given below. In the
following description the hydrocarbon is referred to as
"oil".
(a) Asphalt: On older asphalt, a stronger
mixture of oil remover can be used (35
to 50~ by weight KOH) to penetrate the
oil. On newer asphalt, 20~ KOH is
sufficient. The cleaner is applied to
the stained area and allowed to dwell
for 20 to 40 minutes. When the alkali
portion of the cleaner has penetrated to
the surface and caused adhesion failure,
the enzyme based surfactant will suspend
the oil. Sufficient dwell time can be
identified when a stain can be wiped
clean and the cleaning solution under
the oil is not saturated with oil. At
this point, depending on the collection
method the resulting effluent or
emulsion can be neutralized. The
surfactant component of the cleaner will
still suspend the oil. To increase
production speed, a mixture of l~ KOH
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can be sprayed on the parking lot
surface. This simply assists in moving
the waste oil over the surface.
However, prior to discharge of the
effluent, pH levels need to be tested.
Ideal pH is between 7 and 7.5. The
majority of the oil can be collected at
the stain by using absorbent material
that can be blended with the effluent or
cleaned and/or vacuuming and then
separating the oil for recycling. For
production purposes, using a pressure
washer to move the effluent to a
centralized collection area is generally
preferable. The neutralized effluent
can also be flushed into an oil water
separator as the cleaning agent has not
contaminated the waste oil.
(b) Cement: Depending on the porosity of the
surface, the alkali component of the
cleaner is adjusted to between 10 and
20~ by weight. The dwell time of the
cleaner is between 15 to 40 minutes.
The cleaning method is the same as for
asphalt, except that the surfactant does
not need to be pre-sprayed on the rest
of the surface due to the lower porosity
of the surface.
(c) Traffic membranes: If adhesion has
occurred, typically a dilution of 2 to
10~ by weight of KOH is sufficient to
cause adhesive failure and suspension.
At this point, the same cleaning method
as above applies.
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The method of wiping the surface to test for
sufficient dwell time ascertains whether all the
required steps have been effected, excluding moving,
collecting and recycling. On asphalt, the cleaner will
suspend the oil and the cleaner will be the same colour
and texture as unused cleaner and the asphalt will be
slippery and will not emulsify in the chemical. A
stronger cleaner or chemical will emulsify the asphalt
and the mixture will be black. A weaker mixture will
not penetrate and again the mixture will be black. On
cement and traffic membranes, the same effect applies.
The substrate can be inspected visually. If a cleaner
is to strong, etching or damage to a membrane can occur,
this will contaminate the waste effluent and negate the
process.
While only preferred embodiments of the
invention have been described herein in detail, the
invention is not limited thereby and modifications can
be made within the scope of the attached claims.
