Title: Organometallic complexes comprising phosphonite ligands, and their use in catalyzing olefin oligomerization
Abstract: A catalytic composition for oligomerizing olefins, in particular ethylene, comprises mixing at least one nickel complex, prepared by reacting a nickel salt with a phosphonite ligapd, with at least one hydrocarbylaluminum compound in a molar proportion with respect to the nickel of not more than 8" and selected from the group formed by tris(hydrocarbyl)aluminum compounds, chlorinated or brominated hydrocarbylaluminum compounds and aluminoxanes.
Patent Number: 6,864,209 Issued on 03/08/2005 to Speiser, et al.
| Inventors:
|
Speiser; Fredy (Schiltigheim, FR);
Braunstein; Pierre (Strasbourg, FR);
Saussine; Lucien (Croissy sur Seine, FR)
|
| Assignee:
|
Institut Francais du Petrole (Rueil Malmaison Cedex, FR)
|
| Appl. No.:
|
402153 |
| Filed:
|
March 31, 2003 |
Foreign Application Priority Data
| Current U.S. Class: |
502/117; 526/161; 526/169 |
| Intern'l Class: |
B01J 031//00; B01J 037//00; C08F 004//02; C08F 004//60; C08F 004//44 |
| Field of Search: |
502/117
526/161,169
|
References Cited [Referenced By]
U.S. Patent Documents
Other References
Patent Abstract of Japan--vol. 1998, No. 02, Jan. 30, 1998, and JP 09 268
132 A (Mitsubishi Chem Corp), Oct. 14, 1997.
XP-002224757--Organometallics 2000, 19, 2676-2683, Ruthenium Complexes with
Novel Tridentate N,P,N Ligands Containing a Phosphonite Bridge between Two
Chiral Oxazollnes. Catalytic Activity in Cyclopropanation of Olefins and
Transfer Hydrogenation of Acetophenone, Pierre Braunstein et al.
|
Primary Examiner: Bell; Mark L.
Assistant Examiner: Pasterczyk; J.
Attorney, Agent or Firm: Millen, White, Zelano & Branigan, P.C.
Claims
What is claimed is:
1. A catalytic composition comprising a mixture of:
at least one nickel complex containing at least one phosphonite ligand
having the general formula LN.sub.1 X.sub.2 in which L is a bidentare or
trideniate phosphonite ligand with general formula:
##STR6##
in which R represents a monovalent hydrocarbon radical containing up to 12
carbon atoms, and radicals A.sub.1 --O-- and A.sub.2 --O--, which are
identical or different, are alkoxy radicals carrying a nitrogen-containing
heterocycle, and X is a halide anion, an acerylacetonate anion or a
carboxylate anion;
with at least one hydrocarbylaluminum compound selected from the group
consisting of tris(hydrocarbyl)aluminum compounds, chlorinated and
brominated hydrocarbylaluminum compounds with general formula AlR".sub.m
Y.sub.3-m in which R" is a hydcocarbyl radical containing 1 to 6 carbon
atoms, Y is a chlorine or bromine atom and m is a number from 1 in 3, and
aluminoxanes;
in an Al/Ni mole ratio of 8/l or less.
2. A composition according to claim 1, wherein R represents an alkyl, aryl,
aralkyl, alkaryl, cycloalkyl or substituted aryl radical.
3. A composition according to claim 1, wherein in the phosphonite ligand,
radicals A.sub.1 --O-- and A.sub.2 --O--, which are identical or
different, are optionally substituted alkoxy-pyridine or alkoxy-oxazoline
radicals.
4. A composition according to claim 3, wherein that each of radicals
A.sub.1 --O-- and A.sub.2 --O-- has one of the following general formulae:
##STR7##
in which radicals R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and
R.sub.7, which are identical or different, are each a hydrogen atom,
linear or branched alkyl radical, or aryl, aralkyl or alkaryl radical
containing 1 to 12 carbon atoms, and radical R.sub.5 is at any one of the
free positions in the aromatic ring.
5. A composition according to claim 1, wherein in the nickel complex, X
represents a Cl, Br or I anion, acetylacetonate, acetate or
trifluoroacetate.
6. A composition according to claim 1, wherein the phosphonite ligand has
one of the following general formulae:
##STR8##
in which radicals R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6,
R.sub.7 and R.sub.8 are identical or different and are each a hydrogen
atom, linear or branched alkyl radical and aryl, aralkyl or alkaryl
radicals containing 1 to 12 carbon atoms, and R.sub.5 and R.sub.8 are each
at any one of the free positions in the aromatic ring.
7. A composition according to claim 1, wherein the phosphonite ligand has
one of the following general formulae:
##STR9##
in which radicals R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6,
R.sub.7 and R.sub.8 are R.sub.9 identical or different and are each a
hydrogen atom, linear or branched alkyl radical and aryl, aralkyl or
alkaryl radical containing 1 to 12 carbon atoms, and R.sub.5, R.sub.8 and
R.sub.9 are each at any one of the free positions in the aromatic ring.
8. A composition according to claim 1, wherein the hydrocarbylaluminum
compound is dichloroethylaluminum, ethylaluminum sesquichloride,
chlorodiethylaluminum, chlorodiisobutylaluminum, triethylaluminum,
tripropylaluminum, triisobutylaluminum or methylaluminoxane.
9. A composition according to claim 8, wherein said hydrocarbylaluminum
compound is chlorodiethylaluminum.
10. A composition according to claim 1, wherein the components of the
catalyst are brought into contact in a solvent comprising a saturated,
olefinic unsaturated or aromatic hydrocarbon to form a catalytic solution.
11. A composition according to claim 10, wherein the concentration of
nickel in the catalytic solution is in the range 1.times.10.sup.-5 to 0.1
moles/l.
12. A composition according to claim 1, wherein the mole ratio between the
hydrocarbylaluminum and the nickel complex is in the range of 1/1 and 8/1.
13. In a process comprising catalytically oligomerizing ethylene, the
improvement wherein the catalyst is according to claim 1.
14. A process according to claim 13, wherein the ethylene oligomerization
reaction is carried out at a pressure of 0.5 to 15 MPa and at a
temperature of 20.degree. C. to 180.degree. C.
15. A composition according to claim 11, wherein the mole ratio between the
hydrocarbylaluminum and the nickel complex is in the range of 1/1 and 8/1.
16. A composition according to claim 4, wherein the hydrocarbylaluminum
compound is dichloroethylaluminum, ethylaluminum sesquichloride,
chlorodiethylaluminum, chlorodiisobutylaluminum, triethylaluminum,
tripropylaluminum, triisobutylaluminum or methlyaluminoxane.
17. A composition according to claim 1, wherein the Al/Ni mol ratio is in
the range of 6/1 to 1/1.
18. A composition according to claim 4, wherein the Al/Ni mol ratio is in
the range of 6/1 to 1/1.
19. A composition according to claim 6, wherein the Al/Ni mol ratio is in
the range of 6/1 to 1/1.
20. A composition according to claim 7, wherein the Al/Ni mol ratio is in
the range of 6/1 to 1/1.
21. A composition according to claim 4, wherein R.sub.1, R.sub.2, R.sub.3,
R.sub.4, R.sub.5, R.sub.6 and R.sub.7, which are identical or different,
are each methyl, ethyl, isopropyl, isobutyl, tert-butyl, cyclohexyl,
phenyl or benzyl.
22. A composition according to claim 1, wherein X is a carboxylate anion of
the formula R'COO in which R' is alkyl, cycloalkyl, alkenyl, aryl, aralkyl
or alkaryl, in each case having up to 20 carbon atoms and in each case
optionally substituted with fluorine or chlorine.
23. A composition according to claim 10, wherein said solvent is hexane,
cyclohexane, heptane, butane, isobutene, a mono-olefin containing 4 to 20
carbon atoms, a di-olefin containing 4 to 20 carbon atoms, benzene,
toluene, ortho-xylene, mesitylene, ethylbenzene, or chlorobenzene.
24. A composition according to claim 16, wherein the phosphonite ligand has
one of the following general formulae:
##STR10##
in which radicals R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6,
R.sub.7 and R.sub.8 are identical or different and are each a hydrogen
atom, linear or branched alkyl radical, or aralkyl or alkaryl radical
containing 1 to 12 carbon atoms, and R.sub.5 and R.sub.8 are each at any
one of the free positions in the aromatic ring.
25. A composition according to claim 16, wherein the phosphonite ligand has
one of the following general formulae:
##STR11##
in which radicals and R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6,
R.sub.7, R.sub.8 and R.sub.9 are identical or different and are each a
hydrogen atom, linear or branched alkyl radical, or aryl, aralkyl or
alkaryl radical containing 1 to 12 carbon atoms, and radicals R.sub.5,
R.sub.8, and R.sub.9 are each at any one of the free positions in the
aromatic ring.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to olefin oligomerization, in particular
ethylene oligomerization.
In a first aspect, the invention provides a novel catalytic composition. In
a further aspect, the invention provides a process for oligomerizing
olefins, in particular ethylene, using said catalytic composition.
2. Description of the Prior Art
It is well known that .alpha.-mono-olefins such as ethylene, propylene or
1-butene can be oligomerized with catalytic systems based on transition
metals such as nickel, chromium, titanium, zirconium or other metals, in
the presence of a co-catalyst such as a hydrocarbylaluminum compound, a
hydrocarbylaluminum compound or an aluminoxane. However, many
Ziegler-Natta type catalysts have low activity when the proportion of
co-catalyst is small, and result in a large consumption of co-catalyst
since a mole ratio of aluminum to transition metal of more than 10 is
often necessary to obtain a sufficiently active catalyst.
SUMMARY OF THE INVENTION
It has now been found that, unexpectedly, a catalytic composition obtained
by mixing at least one nickel complex containing at least one phosphonite
type ligand in combination with at least one hydrocarbylaluminum compound
in a relatively low proportion compared to 10:1 of prior art catalysts,
has an improved activity for olefin oligomerization, in particular
ethylene oligomerization.
DETAILED DESCRIPTION OF THE INVENTION
The catalytic composition of the invention is defined as comprising a
mixture:
of at least one nickel complex containing at least one phosphonite ligand
having the general formula LNiX.sub.2 in which L is a bidentate or
tridentate phosphonite ligand with general formula:
##STR1##
in which R represents a monovalent hydrocarbon radical containing up to 12
carbon atoms and radicals A.sub.1 --O-- and A.sub.2 --O--, which may be
identical or different, are selected from alkoxy radicals carrying a
nitrogen-containing heterocycle and X is a halide anion, an
acetylacetonate anion or a carboxylate anion;
with at least one hydrocarbylaluminum compound selected from the group
formed by tris(hydrocarbyl)aluminum compounds, chlorinated or brominated
hydrocarbylaluminum compounds with general formula AlR".sub.m Y.sub.3-m in
which R" is a hydrocarbyl radical containing 1 to 6 carbon atoms, Y is a
chlorine or bromine atom and m is a number from 1 to 3, and aluminoxanes;
in an Al/Ni mole ratio of 8/1 or less.
More precisely, in the general formula of the bidentate or tridentate
phosphonite ligand:
##STR2##
A.sub.1 --O-- and A.sub.2 --O--, identical or different, can be selected
from alkoxy-pyridine and alkoxy-oxazoline radicals. More precisely,
radicals A.sub.1 --O-- and A.sub.2 --O-- can have the following general
formulae:
##STR3##
in which radicals R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and
R.sub.7, which may be identical or different, are selected from a hydrogen
atom, linear or branched alkyl radicals, aryl, aralkyl or alkaryl radicals
containing 1 to 12 carbon atoms. Radical R.sub.5 can be at any one of the
free positions in the aromatic ring. By way of non-limiting example, said
substituents can be selected from methyl, ethyl, isopropyl, isobutyl,
tert-butyl, cyclohexyl, phenyl and benzyl radicals.
In formula 1, radicals A.sub.1 and A.sub.2 can be identical, for example in
the ligands shown below:
##STR4##
Further, in formula 1, radicals R and A.sub.1, R and A.sub.2 or A.sub.1 and
A.sub.2 can be bonded together and form part of the same cyclic radical,
such as those shown in the formulae below:
##STR5##
In formulae 4 to 7 above, radicals R.sub.1, R.sub.2, R.sub.3, R.sub.4,
R.sub.5, R.sub.6, R.sub.7, R.sub.8 and R.sub.9 have the definitions given
above for radicals R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6
and R.sub.7.
In the formula for the nickel complex, X can be a Cl, Br or I halogen
anion, an acetylacetonate, acetate or trifluoroacetate anion or more
generally a carboxylate anion R'COO.sup.- in which R' is a hydrocarbyl
radical, for example alkyl, cycloalkyl, alkenyl, aryl, aralkyl or alkaryl
containing up to 20 carbon atoms, preferably a hydrocarbyl radical
containing 5 to 20 carbon atoms, optionally substituted with halogen atoms
(fluorine or chlorine). The carboxylate anion can be selected from the
following non-limiting anions: octoate, 2-ethylhexanoate, stearate,
oleate, naphthenate and adipate.
The hydrocarbylaluminum compounds are selected from the group formed by
tris(hydrocarbyl)aluminum compounds, chlorinated or brominated
hydrocarbylaluminum compounds and aluminoxanes. Preferably, the
tris(hydrocarbyl)aluminum compounds and the chlorinated or brominated
hydrocarbylaluminum compounds have general formula AlR".sub.m Y.sub.3-m in
which R" represents a monovalent hydrocarbon radical containing up to 12
carbon atoms, for example, such as alkyl, aryl, aralkyl, alkaryl or
cycloalkyl, Y represents a halogen atom selected from chlorine and
bromine, for example, Y preferably being a chlorine atom, m takes a value
of 1 to 3, with m preferably being equal to 1.
Examples of such compounds with formula AlR".sub.m Y.sub.3-m that can be
mentioned are ethylaluminum sesquichloride, dichloroethylaluminum,
dichloroisobutylaluminum, chlorodiethylaluminum and triethylaluminum.
The phosphonite type ligands are prepared using the methods described in
the literature (P Braunstein et al., Organometallics 2000, 19, 2676-2683).
The nickel complex LNiX.sub.2 is prepared using methods that are known in
the literature for synthesizing nickel complexes with a neutral ligand.
Any process for preparing this compound is suitable, such as reacting the
phosphonite ligand with a nickel salt in an organic solvent, for example
an ether, an alcohol or a chlorinated solvent such as dichloromethane. The
complex can be prepared in situ in the solvent used for the
oligomerization reaction. In this case, the order for mixing the nickel
salt and the phosphonite ligand is not critical. However, it is preferable
to prepare in the first instance a solution of a nickel salt that is
soluble in an organic medium such as a nickel carboxylate and then to add
the phosphonite ligand.
The nickel complex and the aluminum co-catalyst can be brought into contact
in a solvent constituted by a saturated hydrocarbon such as hexane,
cyclohexane, heptane, butane or isobutane, by an unsaturated hydrocarbon
such as a mono-olefin or a di-olefin containing 4 to 20 carbon atoms, for
example, or by an aromatic hydrocarbon such as benzene, toluene,
ortho-xylene, mesitylene, ethylbenzene or chlorobenzene, used pure or as a
mixture.
The nickel concentration in the catalytic solution is generally from
1.times.10.sup.-5 to 0.1 moles/l, preferably 5.times.10.sup.-5 to
1.times.10.sup.-2 moles/l.
The mole ratio between the hydrocarbylaluminum and the nickel complex is in
the range 1/1 and 8/1, preferably in the range 1/1 to 6/1.
The order in which the two constituents of the catalytic composition is
mixed is not critical. However, it is preferable to add the
hydrocarbylaluminum compound to the solution of the complex.
The ethylene oligomerization reaction can be carried out at a total
pressure of 0.5 to 15 MPa, preferably 1 to 8 MPa, and at a temperature of
20.degree. C. to 180.degree. C., preferably 40.degree. C. to 140.degree.
C.
In a particular batchwise implementation of the catalytic oligomerization
reaction, a selected volume of the catalytic solution constituted as
described above is introduced into a reactor provided with the usual
stirring, heating and cooling means, then it is pressurized to the desired
pressure with ethylene, and the temperature is adjusted to the desired
value. The oligomerization reaction is kept at constant pressure by
introducing ethylene until the total volume of liquid produced represents
2 to 50 times the volume of the catalytic solution originally introduced,
for example. The catalyst is then destroyed by any usual means known to
the skilled person then the reaction products and solvent are extracted
and separated out.
With a continuous operation, the following implementation is employed, for
example: the catalytic solution is injected at the same time as ethylene
into a reactor stirred by conventional mechanical means or by external
re-circulation, and kept at the desired temperature. It is also possible
to separately inject the components of the catalyst into the reaction
medium, for example the nickel complex comprising the phosphonite ligand
and the hydrocarbylaluminum compound. The ethylene is introduced via a
pressure controlled inlet valve which keeps the pressure constant. The
reaction mixture is withdrawn by means of a liquid level controlled valve
which keeps the liquid level constant. The catalyst is continuously
destroyed by any conventional means known to the skilled person, then the
reaction products and the solvent are separated, for example by
distillation. Untransformed ethylene can be recycled to the reactor.
The following examples illustrate the invention without limiting its scope.
EXAMPLE 1
a) Preparation of (NOPON)NiCl.sub.2 Complex
The phosphonite ligand 4 for which
R.sub.1.dbd.R.sub.2.dbd.R.sub.3.dbd.R.sub.4 =methyl and R.sub.8.dbd.H,
abbreviated to NOPON, was prepared using the methods described in the
literature (P Braunstein et al., Organometallics 2000, 19, 2676-2683).
The phosphonite ligand 4 (0.420 g, 0.998 mole) was dissolved in 30 ml of
tetrahydrofuran (THF) then, after adding one equivalent of nickel
chloride-dimethylether, NiCl.sub.2 (DME) (0.217 g, 0.998 mmole), the
solution was stirred for 24 hours. After evaporating off the solvent, the
green complex was taken up in dichloromethane, the solution was filtered
over celite, then concentrated. The green solid was vacuum dried. Yield:
0.660 g, i.e., 75%. This product was characterized by an infrared
absorption band at 1620 cm.sup.-1, characteristic of the C.dbd.N double
bond coordinated to nickel.
b) Ethylene Oligomerization
0.1.times.10.sup.-3 moles of nickel complex diluted with 25 ml of distilled
toluene and stored in an inert atmosphere was introduced, protected from
air and moisture, into a 50 ml glass flask placed in an inert atmosphere.
10 ml of the nickel solution prepared above, i.e., 0.04.times.10.sup.-3
moles of nickel, and 0.08.times.10.sup.-3 moles of dichloroethylaluminum
in solution in 5 ml of toluene were introduced in that order into a
stainless steel autoclave with a useful volume of 100 ml provided with a
jacket for regulating the temperature by oil circulation. The temperature
was raised to 30.degree. C. and the ethylene pressure was kept at 1 MPa.
After 70 minutes of reaction, ethylene introduction was stopped and the
reactor was cooled and degassed, then the gas and the liquid which had
been withdrawn with a syringe were analyzed by gas chromatography. 35 g of
ethylene had been consumed in 70 minutes. The composition of the products
is shown in Table 1. The growth factor for the geometrical Schulz-Flory
(SF) distribution is represented by k.sub..alpha..
EXAMPLE 2
Using the same apparatus as that described for Example 1 and the same
conditions with the exception that the ratio of the dichloroethylaluminum
to the nickel was 6/1 instead of 2/1, 41 g of ethylene was consumed in 70
minutes of reaction. The composition of the products is shown in Table 1.
EXAMPLE 3
a) Preparation of Nickel Complex
The procedure of Example 1 was used to prepare the complex, with the
exception that the ligand used to complex the nickel had formula 7 with
R.sub.5.dbd.H, R.sub.6.dbd.R.sub.7 =methyl, R.sub.8.dbd.R.sub.9.dbd.H.
Synthesis of ligand 7: the starting products were prepared using published
methods: S D Pastor et al., "Phosphorus and Sulphur", 1987, vol 31, p 71,
for 6-chloro-6H-dibenz[c,c] [1,2] oxaphosphorine, and D S Noyce et al., J
Org Chem 1973, 38, 2260, for 2-(2-pyridyl)-2-propanol.
A solution of 2-(2-pyridyl)-2-propanol (0.580 g, 4.26 mmole) in 30 ml of
tetrahydrofuran was cooled to -78.degree. C. then stirred for one hour
after adding one equivalent of butyllithium. A solution of
6-chloro-6H-dibenz[c,e] [1,2] oxaphosphorine (1 g, 4.26 mmole) in solution
in 20 ml of tetrahydrofuran was then added dropwise and the mixture was
allowed to warm up slowly to 20.degree. C. with stirring over about 15
hours. After hydrolysis with degassed water, extraction with ether, drying
the organic phase over MgSO.sub.4 and evaporating off the solvent, 1.16 g
of a yellow oil was obtained in a yield of 80%.
.sup.1 H-NMR (CDCl.sub.3):
.delta. (ppm): 1.74 (3H, C(CH.sub.3).sub.2), 1.76 (3H, C(CH.sub.3).sub.2),
7.17-7.35 (m, 4H, OPh), 7.65 (m, 1H, py-H.sub.4), 7.44 (m, 1H,
py-H.sub.5), 7.60 (m, 1H, py-H.sub.3), 7.43-8.04 (m, 4H, PPh), 8.04 (t,
1H, py-H.sub.4, .sup.3 J(H,H)=6.0 Hz), 9.2 (d, 1H, py-H.sub.6, .sup.3
J(H,H)=8.1 Hz)
.sup.31 P-NMR (CDCl.sub.3):
.delta. (ppm): 119.8
b) Ethylene Oligomerization
The apparatus described and used in Example 1 was employed under the same
conditions. The ratio of dichloroethylaluminum to nickel was 2/1. The
composition of the products is shown in Table 1.
EXAMPLE 4
The procedure of Example 3 was followed with the exception that the ratio
of dichloroethylaluminum to nickel was 6/1 instead of 2/1.
EXAMPLE 5
a) Preparation of Nickel Complex
The procedure of Example 1 was employed, with the exception that the ligand
used to complex the nickel had formula 6 with
R.sub.1.dbd.R.sub.2.dbd.R.sub.3.dbd.R.sub.4 =methyl,
R.sub.8.dbd.R.sub.9.dbd.H.
Ligand 6 was prepared in a yield of 75% using methods described in the
literature by reacting
4,4'-dimethyl-2-(1-hydroxy-1-methylethyl)-4,5-dihydrooxazole with
6-chloro-6H-dibenz[c,e] [1,2] oxaphosphorine, in the presence of
triethylamine (see references above).
.sup.1 H-NMR (CD.sub.2 Cl.sub.2):
.delta. (ppm): 1.30 (6H), 1.38 (3H); 1.62 (3H); 4.01 (2H), 7.1-7.7 (m, 6H),
7.98 (m, 2H).
.sup.31 P-NMR (CD.sub.2 Cl.sub.2):
.delta. (ppm): 120.9
b) Ethylene Oligomerization
The apparatus described and used in Example 1 was employed under the same
conditions. The ratio of dichloroethylaluminum to nickel was 2/1. The
composition of the products is shown in Table 1.
TABLE 1
Distribution of oligomers
(wt %) k.sub..alpha. Productivity
Example C4 C6 C8 C10+ SF (g ethylene/g of Ni/h)
1 75.8 22.2 1.8 0.2 0.14 12,700
2 70.4 26.8 2.6 0.2 0.16 15,000
3 81.4 17.0 1.4 0.2 0.11 21,100
4 74.8 22.5 2.5 0.2 0.15 27,400
5 72.9 25.5 1.5 0.1 0.17 21,200
The preceding examples can be repeated with similar success by substituting
the generically or specifically described reactants and/or operating
conditions of this invention for those used in the preceding examples.
Also, the preceding specific embodiments are to be construed as merely
illustrative, and not limitative of the remainder of the disclosure in any
way whatsoever.
The entire disclosure of all applications, patents and publications cited
above and below, and of corresponding French application 02/04,107, filed
Mar. 29, 2002, are hereby incorporated by reference.
From the foregoing-description, one skilled in the art can easily ascertain
the essential characteristics of this invention and, without departing
from the spirit and scope thereof, can make various changes and
modifications of the invention to adapt it to various usages and
conditions.
*
