Note: Descriptions are shown in the official language in which they were submitted.
-- 1 -- 203~8~ ~
This invention relates to a process ~or
deoiling wastes. In particular, a process is dis~
closed comprising the treatment of an oily sludge or
soil to produce clean solids and to recover waste oil
capable of being reprocessPd in a refinery.
BACKGROUND OF THE INVENTION
Petroleum refineries have need to dispose of
wastes comprised of oily sludges (oil-solid or oil-
solid-water mixtures) produced in wastewater treatment
facilities and hydrocarbon storage tanks. Land-
treatment (landfarming~ has been a low cost disposal
method for such wastes. However, in some jurisdic
tions, landfarming is coming under stricter control
and is now subject to more extensive permit require-
ments. Moreover, certain types of oily sludges cannot
be landtreated due to the biorefractory nature of the
oil contained therein. For example, some refinery
tank bottom sludges (e.g., coker hot slop tank sludge
and cat fractionator bottoms sludge~ contain viscous
oil and high levels of biorefractory polynuclear
aromatic components, which are not suitable for
disposal through landtreatment~
Removing the oil from an oily sludge and
then, instead of landtreating, simply landfilling the
remaining solids in a unsecured landfill could be an
attractive waste management option, provided that
deoiling of the sludge can be done cost effectively to
produce an essentially oil-free solids product.
Conventional deoiling processes and services are
costly and in some cases do not achieve complete oil
removal. Extraction-based technologies, using light
203~a7
hydrocarbons (C3-C5) or special solvents, rely on
recovery and recycle of their solvent, and may leave
asphaltene fractions of the oil on the solids.
It is therefore an object of the present
invention to provide a flexible low cost process for
deoiling waste sludges. It is a ~urther object to be
able to handle oily sludges containing biorefractory
wastes. It is a still further object of the invention
to remove the oil from oily sludges without requiring
deasphalting o~ the waste oil or solvent separation
and recycle. It is a still ~urther object of the
invention to be able to deoil a sludge at a low
pressure and temperature.
Various processes for treating oily sludges
are disclosed in the prior art. U.S. Patent No.
3,696,021 to Cole et al. discloses mixing an oily
sludge with light hydrocarbons passing through a
conduit. Solids, water and oil are separated in a
drum. The oil is heated in a vessel and distilled in
a tower to separate heavy oil and recirculate the
light oil. The solids are used for landfill.
U.S. Patent No. 4,01~,780 to ~cCoy mixes an
oily sludge with a diluent recycle oil and heats the
mixture with steam to recover the oil and ~orm dry
solids for a landfill. U.S. Patent No. ~,097,378 to
St. Clair di~closes mixing sludge with oil and then
treating the same with recycle oil. ~.S. Patent No.
4,264,453 to Mraovich discloses filtering coka from
oil wastes mixed with a diluent oil. U.S. Patent Nos.
4,686,048 and 4,741,840 to Atherton et al. prepares
sludge fines for a landfill by mixing the sludge with
a hydrocarbon diluent.
- 3 - 20318 ~7
u.s. Patent No. 4,264,453 addressPs the
treatment of coal tar wastes and use~ a non-aromatic
diluent with sur~actants to render the wastes (coke
fines, viscous oil, water) amenable to separation by
filtration. U.S. Patent No. 3,696,021 usas butane,
pentane or their mixture as a solvent and requires a
high temperature (300-400F) and a high pressure
(500-600 psig) separation of solvent from waste oil.
U.S. Patent No. 4,686,048 uses a hydrocarbon type
solvent having a boiling point when mixed with water
of less than 212F. In addition, it requires mixing
of filtered cake with 100% to 1500% water, and dis-
tilling the mixture to remove the residual solvent
from the solids.
Various patents disclose combining a waste
sludge with a refinery stream. U.S Patent No.
4,206,001 discloses a process for separating solid and
liquid materials in an FCC rundown tank to p~rmit
liquids to be returned to refinery process streams.
The process comprises the addition of a selected
refinery stock, preferably kerosene-like, into the
rundown tank, followed by~washing of solids with an
aqueous solution, and subsequent settling to separate
the aqueous and organic phases. U.S Patent No.
2,487,103 teaches adding a heavy naphtha fraction to
sludge, followed by addition o~ water for hydrolysis
and phase separation. U.S Patent No. 3,696,021 dis-
closes mixing refinery sludges with light hydrocarbons
to deoil the solids, followed by gravitational separa-
tion and steaming of ~e separated solids to remove
the light hydrocarbons Other patents in this area
include U.S. Patent Nc 2,413,310, U.S. Patent No.
3,079,326; U.S. Patent ~. 1,092,386; and U.S. Patent
No. 1,092,386.
'
_ 4 _ 2~3~
BRIEF DESCRIPTION OF THE INVENTION
The present invention is directed to a
process for the deoiling of oily sludges so that the
remaining solids can be disposed of econo-mically, for
example, in landfills. According to the invention,
the sludge is treated with one or more solvents
obtained from a refinery unit. In one preferred
embodiment, the sludge is first treated with a heavy
aromatic stream, for example from a cracking unit.
ThP residual solids are then treated with a light
solvent such as naphtha, followed by low energy
evaporation of thP solvent by evaporation or gas
stripping. In another preferred embodiment, a single
solvent is employed to extract and deoil the sludge,
which is then separated into liquid and solid phases.
The liquid phase is returned to the refinery for
reprocessing and the solid phas~ is dried to remove
remaining liquids. The resulting clean and essen-
tially oil free solids is then suitable for low cost
disposal.
BRIEF DESCRIPTION OF T~E DRAWINGS
The process of the invention will ke more
clearly understood upon reference to the detailed
discussion ~elow in conjunction with to the drawings
wherein:
FIG. 1 shows a simplifi~d process flow
diagram illustrating one ambodiment for practicing the
subject invention wherein two separate solvent extrac-
tions of an oily sludge produces a clean solids
product for low cost disposal: and
_ 5 _ 2~3 ~ ~ 7
FIG. 2 shows a simplified pracess ~low
diagram illustrating a second embodiment o~ the
present invention wherein a single solvent is employed
to extract a was~e oily sludge and wherein a solids
residue is dried to prod~ce a clean solids product for
landfill.
DETAILED DESCRIPTION OF THE INVENTION
Th present invention is direated to a
process ~or deoiling an oily sludge produced in a
re~inery, comprising (a) in an extraction zone, mixinq
the sludge with a solvent comprising a distillate
stream from a refinery unit, whereby oil components of
the sludge are extracted into the solvent; (b~ in a
separation zone, separating the mixture formed in the
extraction zone into at least two streams, a first
stream comprising said solvent with extracted oil, and
a second stream comprising substantially all of the
solids in said sludge, whereby said solids are
depleted of its oily content; and (c) in a stripping
zone, drying the solids with a stripping gas to
produce a relatively dry solids containing material
which can be readily disposed of, for exampl , by
means of a landfill.
In one pre~erred embodiment, an oily sludge
produced in a refinery is treated according to a
process involving the use of two di~ferent solvents.
This embodiment comprises (a) in a first e~traction
zone, mixing the sludge with a relatively heavy
solvent comprising an aromatic distillate tream from
a refinery unit, whereby oily components o~ the sludge
are extracted into the solvent: (b) in a separation
zone, separating the mixture formed in the first
extraction zone into at least two ~treams, a ~irst
. ~3~7
-- 6 --
stream comprising said relatively heavy solvent
(including extracted oil) and a second stream compris-
ing substantially all of the solids in said sludge,
whereby said sludge is depleted of its oily content;
(c) recycling a~ least a portion of said ~irst stream
to said refinery for reprocessing in a refinery unit;
(d) in a second ex~raction zone, mixing said sludge
residue with a relatively light solvent comprising a
hydrocarbon distillate from a refinery unit, whereby
remaining relatively heavy solvent is displaced; and
(e) in a stripping zone, drying the mixture formed in
the second extraction zone with a stripping gas to
produce a clean relatively dry solids containing
material suitable for landfilling.
This latter embodiment, comprising a
two-step oil displacement process involving two
different kinds of solvent streams, ensures maximum
removal of heavy molecular weight oil in the waste
(due to a first~stage treatment by a high aromatic,
heavy solvent) and produces essentially oil-free
solids (due to a second~stage treatment by a light
solvent)~ The process advantageously does not require
recovery of solvents from a oil-solvent mixture.
Rather the latter mixture is recycled to the refinery
~or reprocessing.
In this description, the terms "waste" and
"wastes" refer to oil~contaminated material, including
oily sludge and oily soil. ~hen referring to an oily
sludge, it will be apparent to those skilled in the
art that the same applies to an oily soil, for
example.
In general, the invention herein described
is a refinery integrated process employing an
203~ 8a7
-- 7 --
intermediary hydrocarbon stream as a solvent to
extract oil from wastes, and utilizing the refinery
for reprocessin~ of the resulting oil-solvent mixture.
The processing steps can be carried out in a batch,
continuous, or semi-continuous mode using single or
multiple vessels built as a mobile or stationary unit.
The scope and extent of treatment of an oily
sludge according to the present process may depend on
the properties of the sludge and its oil (e.g~, the
amount of heavy hydrocarbons such as asphaltenes), the
desir d quality specification o~ the solid product,
and the ultimate disposal method ~or the solids.
The process of this invention can be used
with both dry and wet sludges. However, the water
content of the sludge should be low enough (preferably
less than 50%) to permit an effective contact between
the oily solids and solvent. A sludge containing
greater than 50% water can be dewatered separately by
pretreatment or dewatered during the separation (e.g.
centrifuge) step of the process.
Where the sludge to be treated contains
significant amounts of especially asphaltenic and
viscous oil, then the aforemantioned mul~i-extraction
process, employing two diff~rent solvents is pre-
ferred. As previously indicated, a fixst extraction
step involves treatment o~ the sludge with a heavy
solvent such as a low value, highly aromatic distil-
late stream ~rom a thermal or catalytic cracking unit
of a refinery to dissolve and displace the sludga-oil
without causing deasphalting. A second extraction
step involves treatment o~ the solids or sludge
residue from the first extraction step with a light
solvent such as a low value naphtha to displace the
203~7
- 8 -
heavy solvent (or sludge-oil), and to permit low
energy removal of the light solvent from the solids
product.
The solvent employad in a first extraction
zone suitably comprises at least 20 percent by weight
aromatics, preferably 40 to 75 percent aromatics, and
has a boiling point of 100 to 600C, preferably 160 to
400C. Suitable solvents include light heating oil or
heavy naphtha distillate from a cat cracker. The
relatively lighter solvent employed in a second
extraction zone suitably is a refinery stream boiling
in the range of 24 to 300C, preferably 35 to 175~C.
Although an aromatics content o~ 2 to 5 percent is
pre~erred, a much higher percent of aromatics is
suitable when using a toluene or xylene type solvent.
Suitable solvents in the second extraction zone
include light and/or heavy naphtha such as light
natural naphtha (LNN), heavy natural naphtha (HNN),
powerformer feed, light cat naphtha (LCN), reformate,
heavy cat naphtha (HCN) and splitter overhead (SPOH).
Hydrocarbon streams comprising primarily Cs to Cg
hydrocarbons with at least 2 percent aromatics content
are suitable sources of solvents for the second
extraction.
In the event that the present invention is
practiced with a single extraction zone u~ing single
solvent, then this solvent i suitably of the kind
mentioned above with respect to the second extraction
zone in the multi-extr~ction zone proce-~s.
Extraction ac~ording to the present process
may be suitably carrie~ ~ut at a sludge to oil weight
ratio varying from abo~t 2~1 to 1:5, at atmospheric
pressure, and at a temperature below th~ initial
203~8.3~
g
boiling point of the solvent utilized. Preferably,
the oily waste is mixed with a distillate stream in a
waste/distillate ratio of 2:~ to 1:~ at 10 to 100C.
Mixing is continued until the liquid phase properties
do not change, and/or approach levels expected from a
theoretical blend of waste oil and solvent in the same
ratio. However, if the sludge contains high concen-
trations of emulsified water and if the water hinders
effective mixing during extraction, then the condi-
tions and solvents can be selected to permit evapora-
tion of water during extraction.
Following extraction, a liquid-solid
separation is carried out, preferably by gravity
settling, which is continued until the supernatant
suspended solids concentration reaches an equilibrium
level or a level acceptable ~or reprocessing of the
supernatant. As an option, water can be added during
or after gravity settling to displace intra-particle
oil (minimize oil remaining in solid phase) and to
form a layer between the oil and solid phases to aid
in the removal of the supernatant. However, if solid
settling characteristics do not permit a reasonably
fast separation of solid and liquid, or the solid
concentration of the supernatant is higher than
reprocessing specifications, then a mechanical separa-
tion, for example, filtration or centrifugation, may
be employedO Mixing and settling may occur in the
same or separate tanks and can be carried ou~ in the
original product storage tanks containing the waste or
in temporary tanks. The liquid supernatant from the
solid-liquid separation is returned to the refinery
slop system and from there to an appropriat~ refinery
unit (e.g., tanks, distillation, FCC, etc.) or blended
into crude for reprocessing.
2~3~
-- 10 --
Following extraction and solid-liquid
separation, the solids are subjected to a drying step,
comprising the removal of final (light) solvent. This
is suitably accomplished either by stripping (nitro-
gen, steam, etc~) or by evaporation at a temperature
consistent with the boiling point o~ the solvent.
The above-described procedure can be carried
out in multiple stages, the number depending on
specific application and performanc2 re~uirements.
When utilizing a single solvent, then at least 3 and
preferably 4 to 6 separate extraction stages are
carried out to achieve the desired solids product
specifications. Each stage comprises a solvent-sludge
mixing/extraction step, and a solids-liquid separa-
tion, followed by a recycle of the solids phase to the
mixing/extràction zone i~ separate tanks for the
mixing/extract and solids/li~uid separation are used
and a further extraction stage is reguired.
FIG. 1 shows a first embodiment of the
present process which employs two different solvents
to produce clean solids for low cost disposal.
Referring to FIG. 1, an oily sludge ~eedstream l is
admixed with a relatively heavy solvent stream 3
comprising an aromatic refinery distillate. Optional-
ly, if the water content of the sludge is relatively
high, it is possible to sub~ect the sludge to a
preliminary gross dewatering in zone 5, for example by
mechanical filter press or centrifuging, as is wall
know to those skilled in the art. (The broken lines
in the ~igure indicate optional steps.) The sludge
and solvent mixture is introduced into a first extrac-
tion zone 7 wherein the oily components o~ the sludge
are solubilized in the solvent. It is to dewater the
mixture optional at this staqe~ instead of preliminary
2 ~
- 1~
to extraction, by removing a water phase. The extrac-
tion zone effluent is thereafter introduced into a
first separation zone 11, wherein solids are separated
from liquids. As mentioned above, this separation can
be accomplished in various ways as will be understood
by those skilled in the art, although the presently
preferred low cost method is by means of gravity
settling. Water to aid in liquid-solid separation is
optionally introduced into the mixture at this stage.
The heavy solvent, containing the oil extracted from
the sludge, is then removed via stream 13 and sent
back to the refinery for reprocessing. Optionally, a
water phase may be formed at this stage and removed
via stream 15. The separated wet solids from the
first separation zone 11 is then sent via line 14 to a
second stage extraction comprising light solvent
treatment, wherein the wet solids are mixed with a
light solvent stream 17, for example comprising
naphtha or any Cs to C7 refinery unit overhead stream.
The solvent-solids mixture is thereafter introduced
into a second extraction zone 19, wherein the solids
are further deoiled by e~traction of remaining oily
components into the light solvent and any residual
heavy solvent is displaced. The solvent-extract-
solids mixture in stream 21 is then introduced into a
second separation zone 23 wherein the following
streams are produced: a solvent stream 25, an option-
al water stream 27, and a wet~solids stream 29. Water
is optionally introduced into the second separation
zone. The separated solvent stream 25 comprises the
light solvent and any heavy solvent remaining in the
wet solids. The wet solids in stream 29 at this point
are subjected to strip drying in zone 33 to produce an
essentially dry solids stream 35 for reuse or dis~
posal, for example, in a clean landfill or backfill.
8 ~ ~
- 12 -
The light solvent in stream 37 is sent for reprocess-
ing in the refinery.
FIG. 2 shows a preferred embodiment of the
present process utilizing a single solvent. Referring
to FIG. 2, an oily sludge in stream 39 containing
preferably less than 50~ water is provided, for
example, by a feed hopper (not shown~ for complete
admixture with a solvent stream 44 in a m~xer/
extractor 45. The sludge in stream 39 and the solvent
in stream 44 are admixed in a 2:1 to 1:1 ratio by
weight of sludge to solvent. A feed hopper can be
operated in a semi-continuous mode, wherein the oily
sludge is fed for a set period of time to fill the
mixer/extractor 45 and the lines connected thereto~
The hopper is then is shut off. On the other hand,
the solvent is preferably delivered continuously to
the mixer/extractor 45, suitably a ribbon-type device
having a holdup of 3 to 5 minutes. The mixing energy
needed in the mixer/extractor 45 depends on the type
of sludge being processed, e.g. a heavy tank bottoms
(oil-solids) may require high shear mixing, whereas a
wet oil sludge may require only gentle agitation. The
mixer/extractor 45 performs the function o~ extrac-
tion, wherein the solvent extracts oily matter from
the sludge. The well mixed slurry from mixer;
extractor 45 i5 continuously discharged via line 47 to
a saparator 49 such as a centri~uge. Optionally,
water is introduced into the separator 49 to displace
intra-particIe oil, minimize oil remaining in the
solids-containing phase, and to form a layer between
the oil-containing phase and the solids-containing
phase to aid in the removal of the supernatant liquid.
The separator 49 produceæ a æolids cake which is
recycled back to the mixer/extractor 45 through line
51 by means of an apprspriate transporting device such
2~3~ 8~7
- 13 -
as a conve~or belt or auger (not shown). The
separated liquid stream 69 from the separator 49
enters a vessel or drum 71 wherein further settling
produces two phases, an upper so-called slop stream 73
and a lower water phase 75. The latter can be sent to
waste water treatment, and the slop stream 73 can be
sent ~o the refinery for reprocessing.
The solids recycle in line 51 is continued
until the solids have achieved the desired residual
oil quality, usually the equivalent of about 3-6
stages of extraction. When extraction is completed,
recycle o~ solids to the mixer/extractor 45 is stopped
and the solids emptied out before the feed hopper is
restarted. The solids are then diverted, ~or example
via a second auger (not shown) through a valve 53 to a
drier 55. The solids are batch dried at 90 to 150~F
with steam purge in line 57 to remove residual
solvent. The sweep gas in line 59 is passed through a
condenser 61 to recover the solvent~ The solvent is
either sent to the refinery for reprocessing or
recycled via stream 63 to vessel or drum 65, wherein
make-up solvent stream 67 may be introduced. ~as is
vented, if necessary, through an emission control
system (e.g., charcoal traps) via line 66.
The solids from the drier 55 are discharged
and may be sent in line 58 to a landfill or other
means o~ disposal. The clean solids product suitably
has an oil content below 1 percent, pre~erably below
O.5 percent and a PA~ (polynuclear aromatic hydro-
carbon) content below c~rtain ppm limits.
It will be aFsreciated by those ~killed in
the art that the proces~ scheme shown in FIG. 2 can
also apply with minor ~odification to a two solvent
2~3~37
- 14 -
extraction procPss o~ the kind shown generically in
FIG. 1. In such a case, a second solvent drum can be
added, with a line leading to the mixer/extractor 45.
After the oily sludge is extracted with the first
sol~ent from drum 65 via line 44, then a second
solvent can be introduced, by appropriate valve
change~ into the mixer for a second extraction, before
sending the solids to drier 55 through valve 53.
The following examples are given to
illustrate the present invention and to indicate its
unexpected degree of effectiveness. It is not
intended to limit the present invention to the par
ticular method employed, the particular sludge
composition, or the specific conditions of operation
employed in these examples.
Example 1
A sample of a filter backwash sludge from a
refinery water effluent treatment system was treated
in the lab according to the present invention. The
sludge contained 15.8 wt.% oil, 75.3 wt.~ water, and
8.9 wt.% solids. The sludge was first treated with a
heavy solvent comprising heating oil from a catalytic
cracking unit (LCH0). A gas chromatograph distilla-
tion curve of the LCHO is provided in Table 1 below:
Table 1
GC Distillation, C: IBP = 161
10% = 216
50% = 275
90% = 38~
FBP = 400
2~3~
The treatment conditions for a first and
second stage extraction are provided in Table 2 below:
Table 2
Treatment Conditions Staqe 1 Staqe 2
Sludge Solvent Ratio 1/1 wt/wt 1/2 wt/wt
Extraction Temperature lOO~C 22C (lab temp3
Extraction Pressure1 atm. 1 atm.
Extraction Time 2 hrs. 20 min.
The dried solids after treatment were essentially free
of oil (contained 1.4~ methylene chloride extractable
oil) and had a look of a natural soil with no hydro-
carbon odor.
Between the two extractions, the material
was allowed to settle by gravity overnight and the
supernatant decanted off. The supernatant contained
0.09 wt.% solids. The bottom settled material was
dried at 60C and 1 atm. pressure for 30 minutesO An
oil analysis of the dried solids (as measured by
soxhlet extraction with methylene chloride solvent)
showed 1.4 wt.% oil remaining on the solids and the
material looked very dry and looseO
Example 2
This example shows application o~ this
invention to a variety of sludges of different water
content using a variety of different solvents. The
properties of three different types of sludges (API
dewatexed separator bottoms, tank bottoms, and oily
woodchips) are provided in Table 3 below. In Table 4
.
2 ~ 7
- 16 -
are given the properties of the various solvents,
abbreviated SPOH (splitter overhead), LNN (light
natural naphtha), HNN (heavy natural naphtha), LCN
(light cat naphtha), and HCN (heavy cat naphtha).
Table 3
Untreated 51udge Properties
Weight ~
Oil Water Solids
API (dewatered)25 30 45
Separator Bottoms
Tank Bottoms 36 O~ 64
Oily Woodchips 7 47 46
Table 4
Solvent Properties
SPOH LNNHNN LCNHCN
GC Distillation, C
IBP 24 26 125 2187
10% 32 ~7 138 35162
50% 43 98 150 95198
90% 63 136164 17021~
FBP 72 146176 204261
The API sludge was pretr~ated (dewatered) to
reduce water content by a centrifuge while the tank
bottoms and oily woodchips were deoiled as is. All
operations were carried out at ambient temperature and
pressure. A 100 g portion o~ sludge was mixed with 75
2~ 7
- 17 -
g of solvent by hand (gentle agitation) for 3 minutes.
The slurry was separated using a lab centrifuge. The
solids ~rom the centrifuge were taken and remixed by
hand with 75 g of fr~sh solvent. The mixing and
separation was repeated until the solids had been
extracted 4 times, at which time they were dried at
137C for 2 hours. The dried solids were then
analyzed for residual oil and grease and the results
shown are in Table 5.
Table 5
Final Oil on De-piled Solids, wt~
Tank Bottoms API Separator Oily Wood
Chips
SPOH 0.6 0.3 0.5
LNN 0.2 0.4 0.6
HNN 0.2
LCN 0.2
HCN 0.6 0.5 0.5
In conclusion, the process simulated in the
lab resulted in solids with not more than 0.6% oil and
grease and therefore essentially clean.
Example 3
This example demonstrates that the present
process produces clean solids meeting quality specifi-
cations in terms of trace organics and metals. The
sludge treated was API saparator bottoms with an
oil/water/sludge weight ratio of 25/30/45. The
treatment conditions were the same as in Example 2~
using heavy cat naphtha (HCN) as the solvent, except
2~3~ 7
- 18 -
that the wet solids were dried at 100C under nitrogen
purge. The solids product was measured for gross
parameter oil, polynuclear aromatic hydrocarbons
(PAH), and metals content by standard tests. The
results are shown in Table 6 below.
Table 6
Solids After
Deoilin~
Parameter Oil, wt% 005
Volatiles, wppm
Benzene <0.05
Toluene <0.05
Xylenes 0.19
Ethylbenzene <0.05
PAH. ppm
Anthracene <2
Ben~o (a) Anthracene <2
Benzo (b) Fluoranthene <2
Benzo (a3 Pyrene ~2
Chrysene <2
Naphthalene 7.3
Phenanthiene 5.7
Pyrene 6.8
Leachate~ ma/L
Silver <0.05
Arsenic ~0.2
Barium 0.6
Boron <2
Cadmium <0.01
Chromium <0.05
Lead <0.2
The residual trace organic and leachate criteria for
the deoiled solids p~duct is suitable for clean
landfill under British ~olumbia, Alberta and Ontario
regulations in accorda~0 with regulatory limits.
The process ~f the invention has been
described generally ænd by way of example with
2~318f~3~
-- 19 -
reference to particular embodiments for purposes of
clarîty and illustration only. It will be apparent to
those skilled in the art from the foregoing that
various modifications of the process and materials
disclosed herein can be made without departure from
the spirit and scope of the invention.
