Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
D-1258
CAT~LYTIC OXYCRACKING
OF POLYNUCLEAR AROMATIC HYDROCARBONS
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a process for converting fused
polynuclear aromatic hydrocarbons or heavy oils containing
such aromatic materials either to monocyclic aromatic hydro-
carbons such as benzene, or to nonfused bicyclic aromatic
compounds such as fluorenone and biphenyl, which are con-
verted to benzene. More particularly, this invention is
directed to a process for cleaving the center ring of tri-
cyclic aromatics by catalytic oxidation and steam cracking to
produce monocyclic aromatic hydrocarbon products such as
benzene.
Descri tion of the Prior Art
P
High-boiling hydrocarbon fractions derived from fossil
fuel sources, such as coal and petroleum, normally contain
substantial quantities of fused polycyclic aromatic
hydrocarbons, such as phenanthrene, anthracene, and the l~ke
and their alkylated -derivatives. Although these compounds
are valuable when purified, the costs and difficulty of
purifying them by extraction are usually prohibitive. For
this reason, many investigat~rs have sought to convert such
polycyclic aromatic materials to monocyclic hydrocarbons,
such as benzene, by thermal hydrocracking. Some of these
prior art processes have been reviewed in ~.S. Patent
4,13~,452 to Beuther et al. Ben2ene yields from such
.' ' 1 .
$ ~
feedstocks are usually low because only saturated rings are
cracked. Hydrogenation usually begins with a terminal ring
and degrades the rings successively, as shown by Penninger et
al, American Chemical Society Symposium Series, Vol. 32, pp.
444-456 (published 1976). As a result, hydrogen consumption
is undesirably high. If a center ring becomes hydrogenated,
it usually undergoes dehydrogenation rather than cracking as
reported by Wiser et al, Ind Eng. Chem Prod. Res. Develop.,
9, 350 (1~70). Conventional catalytic hydrocracking, as
described by Langlois et al, Advances in Chemistry Series,
Vol. 97, pp. 62-64 (1970), also yields predominan~ly
bicyclic products.
The use of an oxidative process to make polycyclic aro-
matic hydrocarbons susceptible to thermal hydrocracking has
also been proposed. Sakai et al, U. S. Patent 4,097,541,
describes thermal hydrodecarbonylation of products, such as
9, 10-anthraquinone, and 9,10~phenanthrenequinone to biphenyl
and benzene by reaction with hydrogen at a temperature of
from about 932 to about 1652F at atmospheric pressure and in
the absence of a catalyst. Sakai also described the
production of monocyclic aromatics in 38~ yield by treatment
of a fraction containin~ naphthalene or more polycyclic aro-
matic hydrocarbons of a residual oil from a naphtha steam
cracker with atmospheric oxygen at 150C followed by reaction
with hydrogen. However, it was shown by Larsen et al,
Ind. Eng. Chem., 34, 183 (1942), that oxidation of phe-
nanthrene under similar conditions is extremely slow and
gives no carbonyl compounds, so that the monocyclic aromatics
observed by Sakai et al, were probably formed by some route
not involving oxidation of phenanthrene. Oxidation of
phenanthrene to 9,10 phenanthrenequinone requires much more
severe conditions as shown by Morotskii et al. Morotskii et
al, Chemical Abstracts, 67, 81982~ (1967) and 68, 68776 S
(1968), described the oxidation of phenanthrene over a
V2Os/K2SO4/SiO2 catalyst. Therefore, it is most likely that
Sakai in this experiment did not oxidize any aromatic rings,
but rather formed benzene from thermal hydrocracking of
naphthalene.
'Daly, in U. S. Patent 4,234,749, described a two-step
process by which anthracene, in either pure form or present
in mixtures of polynuclear aromatic hydrocarbons with normal
boiling points between about 338 and 716F, is oxidized with
molecular oxygen in the presence of a cerium salt catalyst,
and the product anthraquinone is then thermally cracked at
temperature of about 797 to 1400F to form benzene.
Similarly, Robinson et al, U. S. Patent 3,855,252, taught
that anthracene can be selectively oxidized to anthraquinone
in the presence of phenanthrene in synthetic blends or in
middle distillates from coal tar. This demonstrates that
anthracene is oxidized considerably faster than phenanthrene.
In most practical feedstocks derived from either coal or
petroleum sources, phenanthrene and substituted phenanthrenes
are present in significantly higher concentrations than
anthracenes and other polycyclic c,ompounds~ In an oxidation
process for conversion of the three-ring fraction of such
feedstocks to benzene or precursors of benzene, it is
desirable to effect controlled center-ring oxidation of phe-
nanthrenes as well as of anthracenes.
We have discovered that in the presence of suitable
catalysts, polycyclic aromatic hydrocarbons such as phe-
nanthrene and mixtures of phenanthrene with anthracene react
I:~.6~
with oxygen and steam in ~he vapor phase to form fluorenone
and biphenyl. It is known from the work of Richter - U.S~
Patent 3,210,432 and others that these intermediate compounds
can be converted to benzene by thermal hydrocracking. By
combining oxidative steam cracking and thermal
hydrodealkyation, a process has been devised to convert
3-ring and 4-ring aromatics into benzene in à high yield.
These oxycracking and thermal hydrocracking steps used in
combination provide an advantageous and novel method for the
conversion of trinuclear aromatics to provide monocyclic
aromatic hydrocarbon products such as benzene in high yields.
S~MMARY OF INVENTION
A primary object of the present invention is to provide a
process for converting fused tricyclic aromatic hydrocarbon
feedstock, such as phenanthrene, anthracene, fluorene and
mixtures thereof to fluorenone and biphenyl products by
catalytic reaction in the vapor phase with a molecular
oxygen-containing gas and with steam. The fluorenone and
biphenyl intermediate materials produced in the oxycracking
step are then thermally hydrocracked to produce benzene
product. The term "oxycracking" is used herein to denote the
basic process of this invention, because the center ring of a
fused polycyclic molecule can be both oxidized and cracked in
a single operation. Such fused trinuclear aromatic feed
materials to the oxycracking step can be provided by the
hydrodealkylation of heavy hydrocarbon materials. The
thermal hydrocracking of fluorenone and biphenyl
intermediates from the oxycracking step to produce benzene
can be performed in a separate thermal hydrocracking step;
however, such thermal hydrocracking is advantageously and
4 7
preferably performed in the same hydrodealkylation reaction
step used to produce the intermediate materials.
While we do not wish to be bound by any particular
theoretical explanation, we believe that the following
sequence of reaction steps is involved when the feedstock is
phenanthrene:
~ + - ~2 ~~~~~~~ ~ + ~2~ +C
Phenanthrene Fluorlnone
J, + H20
siphenyl
i~
Another object of the invention is to provide novel
bifunctional catalysts having activity for both the oxidation
and cracking reaction steps referred to above. Such catalysts
utilize two or more selected metal oxides deposited on an acidic
support such as alumina or silica alumina. Other objects of the
invention will become apparent from the description which
follows.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic flow diagram of a process for
hydrodealkylation of polynuclear aromatic feedstocks, followed
by catalytic oxycracking the residue 7 then by a thermal
hydxocracking step to produce benzene.
~ ~ 68fi~
Figure 2 is a flow diagram of the process utiliæing two
catalytic oxycracking steps and additional fractional
distillation steps.
DETAILED DESCRIPTION OF THE INVENTION
Feedstocks
Hydrocarbon feedstocks containing fused polynuclear aro-
matic molecules and which are suitable for reaction in the
basic oxycracking step of this invention include
phenanthrene, anthracene, fluorene, their alkyl derivatives
as further defined below, and techn,ical mixtures comprising
these substances. Because aliphatic side chains are subject
to oxidation with the undesired formation of carboxylic
acids, such side chains should be present in technical
feedstocks to an average extent ,of not more than about one
side chain per two trinuclear aromatic molecules. The
feedstock composition can be estimated in various ways, for
example, by means of nuclear magnetic resonance. By way of
illustration, a mixture of 2 moles phenanthrene, 1 mole of
methylphenanthrene and 1 mole of ethylphenanthrene has an
aromatic proton/aliphatic proton ratio of about 83/17 and an
aromatic carbon/aliphatic carbon ratio of about 95/S. The
side chains, if present, should be substantially free of
unsaturation.
Hydrocarbon raw materials containing trinuclear aromatic
hydrocarbons and which can be treated to provide feedstocks
suitable for the oxycracking reaction step include the
anthracene oil fraction from coke oven tar, heavy distillate
oilc from coal liquefaction processes, and products of
petroleum origin such as pyrolysis tars obtai,ned as by-
G
products from steam crackers used to make light olefins,coker gas oils, fluid catalytic cracker decant oils, etc.
Other raw hydrocarbon sources include tar sand bitumens and
shale oils. While the normal boiling points of the most
useful raw material feedstock fractions can vary depending on
the size and number of aliphatic side chains present, in
general the boiling points will be within a broad range of
about 500-900F, and preferably 600-800F. Raw materials
which contain aliphatic groups in concentrations higher than
those defined above should be dealkylated before they are
used as feedstocks for the oxycracking reaction step of this
invention. The most preferred hydrocarbon feedstocks to the
oxycracking step are substantially free of aliphatic side
chains.
If the feedstock contains substantial amounts of sulfur
in compounds such as dibenzothiophene, these feeds could be
hydrodesulfurized prior to hydrodealkylation. It is also
possible to let the benzothiophene pass through the hydro-
dealkylation step for cracking in the oxycracking reactor.
~odes of Operation
According to the present invention, trinuclear aromatic
compounds such as phena~threne are reacted catalytically with
molecular oxygen and steam in the vapor phase to produce
fluorenone and biphenyl as principal products. The
oxycracking process step can be operated in either of two
basic modes. In one mode or embodiment, a single catalytic
reaction zone is used containing a single bifunctional
oxycracking catalyst. The catalysts may be used in fixed
beds, although fluidized catalyst beds can be used to advan-
. 6~ cl V~
tage in order to dis-sipate the exothermie heat of reaction.
In the other mode of operation, the reactants pass suc-
eessively through two catalytic reaction zones; the first
zone for oxidation reaction, and the second zone for steam
eracking reaction. Each reaction zone may be operated with a
different catalyst and at different temperatures and space
veloeities.
The steam eracking step can be effected at temperatures
of about 700~1100F, at spaee velocities of about 0.2-40
millimoles of hydrocarbon per hour per gram of catalyst, and
at water to hydroearbon molar ratios of at least about 5/1.
The proeess is operated at 5-50 psia pressure and is
preferably operated at about atmospheric pressure.
Catalysts useful for the vapor phase oxidation of tri-
eyelic aromatic hydroearbons include cobal~ or nickel
molybdate, and oxides of vanadium, molybdenum, titanium, tin,
antimony, bismuth, ehromium, manganese, iron, cobalt and
niekel.
Bifunetional catalysts having activity for both the oxi-
dation reaction and the steam eracking reaction typically
eontain two or more metal oxides. In general, these metal
oxides are seleeted for their activity in the separate reac-
tion steps as disclosed above, and may advantageously be
deposited on aeidic support materials such as alumina or
siliea-alumina. Particularly useful are catalysts comprising
eadmium or zinc oxide or mixtures thereof, and V2O5 or
MoO3 or mixtures thereof, both on a ~-alumina support.
Teehniques for the preparation of such catalysts are
generally known to khose skilled in the art. Thus, the
support material may be impregnated with an aqueous solution
of Cd(NO3)2 or 2n(N3)2 ~fter drying and calcining to
decompose the metal nitrates, these operations may be
repeated with a solution of NH4Vo3 or ammonium
heptamolybdate. Alternatively, the metal oxides may be
deposited on the support in the reverse order or
simultaneously. Aluminas with relatively large pores, such
as greater than about 50 Angstrom units, are preferred in
order to permit the polycyclic hydrocarbon molecules ~o dif-
fuse to and away from the reaction sites.
The molar ratio of oxygen to hydrocarbon feed may range
from about 1/1 to about 30/1. Air is the preferred oxygen-
containing gas, but mixtures o oxygen and nitrogen
containing more or less oxygen than is normally present in
air may also be used.
The molar ratio of steam to hydrocarbon in the
oxycracking step is not critical, but in general will be at
least about S/l. Reaction temperatures of about 800 to
1250F are suitable, and space velocities range from about
0.2 to 40 millimoles of hydrocarbon per hour per gram of
catalyst. Pressures substantially atmospheric are preferred.
It will be apparent to those skilled in the art that
these operational variables may be combined in a variety of
ways. For example, space velocities should typically be
increased when reaction temperatures are increased. Also,
while it is desirable to effect a high conversion of tri-
nuclear hydrocarbons to biphenyl in a single pass, the pro-
cess may be operated continuously with separation of the
biphenyl product by distillation or partial condensation and
recycle of the fluorenone and tricyclic hydrocarbons to the
oxycracking reactor.
DESCRIPTION OF PRE~ERRED EMBODIMENT
.
As shown by Figure 1, a polynuclear aromatic hydrocarbon
feedstock at 10 having a normal boiling range of 500-900F is
introduced with hydrogen 12 into hydrodealkylation reactor 14
where the feed material is hydrodealkylated with the hydrogen
to substantially remove alkyl side chains. Useful
hydrodealkylation reaction conditions are within the range of
1000-1500F temperature and 500-1200 psi hydrogen partial
pressu.re. It is important that excess hydrogen be maintained
in the reaction to prevent coking by having a relatively high
hydrogen circulation rate relative to feed rate of at least
about 5/1, and preferably exceeding~about 6/1. A hydrocarbon
gas stream is withdrawn at 18 and stream 2:0 containing a
hydrocarbon mixture is passed to successive fractional
distillation steps 2Z and 28 f or removal of benzene at 21 and
naphthalene at 21. A stream 29 containing biphenyl and
fluorene can be recycled to hydrodealkylation reactor 14 for
further reaction.
After fractionation steps at 22 and 28 to remove lighter
fractions, the resulting heavy liquid residue stream 30 con-
taining mainly phenanthrene is heated, vaporized and passed
to catalyst-containlng oxycracking reactor 32, along with
oxygen at 34 and steam at 35. ~ A desirable catalyst is
CdO/MoO3 on ~ -alumina. Oxycracking reaction conditions used
are 800-1200F temperature and 5-50 psia pressure. An
effluent gas containing CO2 and some SO2 is withdrawn at 33
and the liquid biphenyl-containing product is withdrawn at
36.
If the product stream 36 contains substantial amounts of
fluorenone and phenanthrene, these mate.rials can be separated
, .
from the liquid product by a distillation step at 40. The
resulting . :. biphenyl product withdrawn as
stream 41 can be passed to a separate thermal hydrocracking
reactor (not shown) for reaction to produce benzene product.
Useful hydrocracking reaction conditions are within the range
of about 1000-1500F temperature and
500-1200 psi hydrogen pressure. Hydrogen circulation rate
relative to feed rate to the hydrocracking reactor should be
at least about 4/1 and preferably exceeding 5/1 flow ratio to
prevent coking. However, stream 41 containing mainly
biphenyl is advantageously and preferably returned to
hydrodealkylation step at 14 for reactionO Bottoms stream 42
containing increased phenanthrene and fluorenone is recycled
to the oxycracking reactor 32 for further reaction to
increase the yield of fluorenone and biphenyl products.
It is pointed out that the hydrodealkylation reactor 14
used to prepare feedstock for the oxycracking reaction step
32 can also be used for splitting biphenyl, and even :for
splitting fluorenone, if these materials are substantially
free of phenanthrene. However, if the fluorenone contains
relatively large percentages of phenanthrene, it is pre-
ferable to recycle it back to the oxycracking reactor for
further cracking.
As an alternative embodiment, the oxycracking reaction
may be carried out in two steps as generally shown in Figure
2. This embodiment is similar to Figure 1 except an addi-
.
tional fractional distillation step is provided at 24 to
remove toluene and xylene at 25 for recycle with stream 29 to
hydrodealkylation reactor 14. Also, the heated phenanthrene
feed at 50 is passed with air at 52 and optional steam at 53
to first. catalytic reactor 54, which is maintained at
reaction cond-itions within the range of 800-1250F
temperature and 5-50 psia pressure. An effluent gas con-
taining CO2 and some SO2 is withdrawn at 51. The remaining
material is passed with additional steam 56 to a second
catalytic reactor 58, which is maintained at reaction con-
ditions within the range o~ 700-1100F and 5-45 psia. If
desired, the resulting fluorenone and biphenyl products can
be passed to a separate thermal hydrocracking reactor for
producing benzene. Similarly as in the Figure l.embodiment,
residue stream 60 containing fluorenone and phenanthrene is
cooled at 62 by stream 63 to remove water at 61 and then
passed to fractional distillation step 64. Overhead stream
containing fluorenone and biphenyl is returned to the
hydrodealkylation reactor 14, and ~ bottoms stream 66 is
recycled to the first oxycracking reaction step 54 for
~urther reaction to increase the yield of fluorenone and
biphenyl product.
The present invention is further illustrated by the
following examples, which are illustrative only and should
not be construed as limiting the scope of the invention~
EXAMPLE 1
In preparation of a CdO/MoO3/A12O3 catalyst, the catalyst
support used was a ~-alumina extrudate, 4.7 mm long x 1.6 mm
diameter, having surface area 96 m2/g, pore volume 0.537
cc/g, and minimum pore diameter about 64 Angstroms. The
support (81.0g) was impregnated with a solution containing
14.49 g of Cd(NO3)2~4 E12O and ~5 cc of water. After drying
at 220F and calcining at 920F, the catalyst weight was 83.4
g. Of this catalyst material, about 67.2 g was impregnated
with a solution of 6.9 9 of (NH4)6Mo7024~4H20 in 65 cc of
water. The final weight after drying and calcining as above
was 74.6 9. This final prepared catalyst sample contained
about 6.4 W ~ CdO and 7.7 W ~ MoO3.
EXAMPLE 2
A catalyst sample of CdO/V205/A1203/ catalyst was pre-
pared similarly to Example 1 from ~1203 (71.2 g), Cd(NO3)2.4
H20 (25.46 g) and NH4VO3 Go.965 g). The resulting catalyst
contained about 12.8 W % CdO and 0.9 W ~ V205.
EXAMPLE 3
Oxycracking reactions of phenanthrene over
CdO/MoO3/A1203 catalyst were carried out using experimental
apparatus fabricated from stainless steel pipe and tubing.
Liquid water and compressed air were mixed together and
passed through a heated tube in which the water was
vaporized. The resulting air-steam mixture was passed
through a reservoir containing molten feed material
comprising about 90~ phenanthrene, 8% anthracene, and 2
other materials. The resulting vapor mixture was passed
through a preheater then into the reactor. The reactor
volume was about 30 cc and contained about 25 cc of catalyst
comprising CdO/MoO3 on alumina support prepared as described
in Example 1. The reactor was heated uniformly by an
electrically heated fluidized sand bath. The vapors exiting
the reactor were condensed, and the organic product was
separated from water, weighed, and analyzed. Samples of the
uncondensed gases were collected periodically for analysis.
~ '7
The water feed rate was measured directly; air flow rate was
estimated from flo~rmeter readings. The dry product weight
was used to estimate phenanthrene feed rate. Reactor tem-
peratures were measured by thermocouples. Typical results
from this run are tabulated in Table 1 below:
.
TABLE 1
,~
Air flow rate (assumed atmospheric pressure),
mole/hr ~ 0.308
Water flow rate, cc/hr 171
Reactor temperature, F 1040
Reactor pressure, psig 0
Solid organic products collected, gm/hr 1.31
Solid Product Analysis, W ~
Phenanthrene 67.2
Fluorenone 25.9
Biphenyl 8.4
Off Gases Composition, V %
Carbon Dioxide 11.04
Carbon Monoxide 2.03
Oxygen 5~86
Phenanthrene evaporation rate, mole/hr 0.0128
O2/PN mole ratio 4.97
H2O/PN mole ratio 740
Space Velocity, total gases at reactor
temperature, sec~l
Space Velocity, millimoles phenanthrene per gram
of catalyst per hour 0.5
Phenanthrene going to respective products, M ~
Phenanthrene (unreacted) 52.6
Fluorenone 20.0
Biphenyl 7.6
CO by combustion 1.5
C2 by combustion 18.3
Additional oxycracking runs were made with the same 90%
phenanthrene feed using CdO/MoO3/A12O3 catalyst. Results are
shown in Table 2 below:
1 A
~ tB8~7
TABLE 2
OXYCRACKING PHENANTHRENE WITH CdO/MoO3/A1203 CATALYST
_
Run No. 9C lOB lOC 12C
Feedstream Flow Rates
Air, moles, hr. 0.31 0.30 0.30 0.30
Water, cc/hr. 157 159 156 150
Reaction Temp., F 1040 1110 1180 11~5
Solid Product Yield, g/hr. 8~6 -1.6 1.9 4.2
Solid Product Composition, W ~
Phenanthrene 78 68 69 80
Fluorenone 4.2 18 10 5.9
Biphenyl 1.8 11.5 9.3 3.2
It is noted that using feed stream of 90 W %
phenanthrene, significant amounts of the desired fluorenone
and biphenyl products were produced at reaction temperature
within the range of 1040-1185F, with the remainder of the
solid products being 68-80 W ~ phenanthrene.
.
EXAMPLE 4
Further oxycracking runs were made using 90~ phenanthrene
feedstock with other catalysts comprising CdO/V2Os on alumina
and nickel molybdate. The results of these experiments are
shown in Table 3.
TAB LE 3
OXYCRACKING PHENANTHRENE WITH OTHER CATALYSTS
Run No. 6C 8~ 14A
Catalyst(a) V V N
Feedstream Flow Rates
Air, moles, hr. 0~85 0.850.475
Water, cc/hr. 138 145 107
Reaction Temp., F(b) 1240 825 930
Solid Product Yield, g/hr. 1.3 2.2 3.2
Solid Product Composition, W ~
Phenanthrene 81 66 74
Fluorenone 8.3 20 9.4
Biphenyl 3.1 3.1 1.8
(a)V indicates CdO/V2OS/Al2O3 catalyst
N indicates nickel molybdate (H-Coal catalyst)
(b)Exothermic reactions
Similarly as for Example 4, 90 W % phenanthrene feed w~s
successfuly oxycracked using different catalysts to produce
significant amounts of fluorenone and biphenyl products. It
was observed that the oxycrac~ing reaction with the catalyst
containing vanadium was more exothermic than with the other
catalysts. Anthracene, naphthalene and one or more uniden-
tified compounds were observed in some of the solid products.
Losses of hydrocarbon values due to combustion occurred to
some extent.
- EXAMPLE 5
' ' '
This example describes the oxycracking reaction as used
in a commercial-scale, fixed-bed~type reactor. The mole
ratio used for phenanthrene/oxygen/water is l/6/17.
A mixture of air (140 standard cubic feed per second) and
steam (13,750 pounds per hour) is preheated to about 600F.
16
t~ '~
Phenanthrene feedstock (8000 pounds per hour) is heated to
about 400F and pumped into an evaporator, in which it is
vaporized by contact with .the warmer steam-air mixture. The
resulting vapor stream is fed to the reactor, which comprises
an array of about 10,000 tubes, each 1 inch diameter and
containing about 1.2 liters of catalyst. The catalyst con-
sists of cadmium and molybdenum oxides supported on alumina
having about 0.060-inch-diameter particle size as extrudates.
The catalyst-filled tubes are cooled by a fused salt mixture
and maximum temperature is maintained in the range of
1000-1100F. The molten salt mixture is circulated through
heat exchangers in which process steam is generated.
The gases leaving the oxycracking reactor are partially
cooled by a heat exchange step to about 180F. The conden-
sable aromatic products are separatèd from the water and
gases, and the resuIting condensed organic products are fed
into a fractional distillation unit for separation into a
biphenyl stream taken overhead and a bottoms stream
consisting essentially of fluorenone and phenanthrene. The
biphenyl overhead stream is passed to a thermal hydrocracking
unit, while the distillation bottoms product of mainly
phenanthrene and fluorenone is recycled to the oxycracking
reactor for further reaction to increase the product yi.eld.
The mixture of water vapor and gases is further cooled to
about 85F to effect condensation of biphenyl and most of the
water; the composition of the resulting vent gase.s is shown
in Table 4. An approximate material balance for the feed and
product streams to the oxycracking step is also provided
below in Table 4.
TABLE 4
MATERIAL BALANCE FOR OXYCRAC~ING REACTION
Feed Reaction
Streams, Products, Stack Gases
~ Lb/Hr Lb/HrComposition, V
Phenanthrene 8000 320
Water 13753 14748 4.1
Oxygen 8629 1622 3;6
Nitrogen 30202 30202 77.0
Fluorenone - 243
~iphenyl - 4776 0.001
2 - 7345 11.9
CO - 1329 3~4
Total 60584 60584 100.0
Although this invention has been described in terms of
the accompanying drawings and preferred embodiments, it will
be appreciated by those skilled in the art that many modifi-
cations and adaptations of the basic process are possible
within the spirit and scope of the invention, which is
defined solely by the following claims.
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