|Title of Invention||
"A MULTI STAGE PROCESS FOR BROMINATING A COPOLYMER OF A C4 TO C7 ISOMONOOLEFIN AND A PARA-ALKYLSTYRENE"
|Abstract||A multi stage process for brominating a copolymer of a C4 to C7 isomonoloefin and a para-alkylstyrene comprising: a) forming a solution of said copolymer in organic solvent in a first reactor zone; b) contacting said solution with elemental bromine and an organic free radical initiator at a temperature 0° C to 150° C, for a period of time of 1 minute to 4 hours to form a reaction product mixture comprising a partially brominated copolymer and an in-situ generated hydrogen bromide; c) transferring said reaction product mixture to a second reactor zone and contacting said mixture with an oxidizing agent capable of converting said hydrogen bromide to free bromine; and d) continuing said bromination in said second reactor zone until a brominated copolymer containing at least 0.05 mole % of bromoalkyl groups is obtained.|
|Full Text||PROCESS FOR HALOGENATION OF
BACKGROUND OF THE INVENTION
Field of the Invention.
The invention relates to an improved process for halogenating copolymers of a €4 to C?
isomonoolefin and a para-alkylstyrene.
Description of the Related Art.
Halogenation process in which a polymer is reacted with a halogenating agent to
produce a halogenated polymer containing chemically bound halogen are well known in
the art. For example, halogenated copolymers comprising a €4 to C? isomonoolefin,
e.g., isobutylene, and fro.m about 0.5 to 10 wt% of a conjugated diene, e.g., isoprene
(commercially known as butyl rubber), may be readily prepared using relatively facile
ionic reactions by contacting the polymer, preferably dissolved in organic solvent, with
a halogen source, e.g., molecular bromine or chlorine, and heating the mixture at a
temperature ranging from about 20°C to 90°C for a period of time sufficient for the
addition of free halogen in the reaction mixture onto the polymer backbone. Such
processes are generally disclosed in US Patent 2,732,354.
A major inefficiency in such process is that the theoretical fraction of halogen present in
the reaction mixture which can be placed on the polymer is 50%, and the actual
utilization is usually less than 45%. iVTost of the remaining halogen fraction will
combine with hydrogen extracted from the polymer to form a hydrogen halide byproduct
which, under normal conditions, does not halogenate the polymer. This byproduct
is subsequently neutralized with an alkaline material and washed from the
polymer reaction product as described, for example, in US Patent 5,077,345.
One known method to enhance the efficiency of butyl rubber ionic halogenation
involves the inclusion in the reaction media of at least 0.5 mole per mole of
halogenating agent of an oxidizing agent such as hydrogen peroxide, which oxidizes the
hydrogen halide by-product as it forms back to ionic halogen. This regenerated
halogen is thus available to further halogenate the butyl rubber thereby increasing the
halogenation utilization by as much as 70%. Such process is disclosed in US Patent
3,018,275 and in UK Patent 867,737.
Another process for improving the bromination efficiency in rubber bromination
processes is to conduct the reaction in the presence of elemental bromine and an
aqueous solution of an organic azo compound such as azodiisobutronitrile and/or an
alkali or alkaline earth metal hypochlorite, as disclosed in EP 0709401 Al.
A new class of halogenated copolymers have been discovered which offer many of the
same properties as halogenated butyl rubber, but are even more ozone and solvent
resistant. These materials are the halogenation product of random copolymers of from
about 10 to 99.5 wt% of a C4 to C7 isomonoolefin, such as isobutylene, and from about
0.5 to 90 wt% of a para-alkylstyrene comonomer such that at least some of the alkyl
substituent groups present in the styrene monomer units contain halogen.
More preferred materials are elastomeric copolymers of isobutylene and paramethylstyrene
containing from about 0.5 to about 20 wt% para-methylstyrene wherein
up to about 65% of the methyl substituent groups present on the benzene ring contain a
bromine or chlorine atom, preferably a bromine atom. These copolymers (hereafter
referred to as HI-PAS) have a substantially homogenous compositional distribution
such that at least 95% by weight of the polymer has a para-alkylstyrene content within
10% of the average para-alkystyrene content of the polymer. They are also
characterized by a very narrow molecular weight distribution (Mw/Mn) of less than
about 5, more preferably less than about 2.5, viscosity average molecular weights in the
range of from about 500,000 up to about 2,000,000, and a glass transition temperature
(Tg) of below about 50°C. Halogenated copolymers of this type are disclosed in US
Patent 5,162,445, the complete disclosure of which is incorporated herein by reference.
As described in the '445 patent, HI-PAS copolymers contain no ethylenic backbone
unsaturation as does butyl rubber, and therefore halogenation is carried out under free
radical halogenation conditions using light as an initiator or using an organic free radical
initiator. Halogenation occurs essentially exclusively on the alkyl substituent groups
and, in the case of para-methylstyrene, benzylic halide functionality is formed.
However, even under such free radical halogenation conditions, the halogen utilization
in the process is typically only about 45% or less.
SUMMARY OF THE INVENTION
The invention provides a process for halogenating a copolymer of a €4 to C?
isomonoolefin and a para-alkylstyrene comprising contacting said copolymer under free
radical halogenation conditions with a halogenating agent and hydrogen peroxide, and
recovering said halogenated copolymer containing at least about 0.05 mole% of
In another embodiment of the invention, a process is provided for halogenating a
copolymer of a €4 to C? isomonoolefin and a para-alkyl styrene comprising:
a) contacting said copolymer with a halogenating agent and an organic
free radical initiator under free radical halogenation conditions to form a reaction
product mixture containing a partially halogenated copolymer and in-situ generated
b) contacting said reaction product mixture from step (a) with an
oxidizing agent capable of converting said hydrogen halide to free halogen; and
c) continuing said halogenation until a halogenated copolymer containing
at least about 0.05 mole % of haloalkyl groups is obtained.
In yet another embodiment of the invention, a multi stage process for brominating a
copolymer of C4 to C? isomonoolefin and a para-alkystyrene is provided comprising:
a) forming a solution of said copolymer in organic solvent in a first reactor
b) contacting said solution with elemental bromine and an organic free
radical initiator under free radical bromination conditions to form a reaction product
mixture comprising a partially brominated copolymer and in-situ generated hydrogen
c) transferring said reaction product mixture to a second reactor zone and
contacting said mixture with an oxidizing agent capable of converting said hydrogen
bromide to free bromine; and
d) continuing said bromination in said second reactor zone until a
brominated copolymer containing at least about 0.05 mole% of bromoalkyl groups is
DFTATT.F.D DESCRIPTION OF THE INVENTION
As pointed out above? the copolymers which provide the halogenation substrate in
accordance with this invention are random copolymers containing from about 10 to
99.5 wt% of a C4 to C7 isomonoolefin and correspondingly about 0.5 to 90 wt% of a
copolymerized para-alkylstyrene having the structure:
in which R and R1 are independently selected from the group consisting of hydrogen,
alkyl, primary aikyl halides, secondary alkyl halides, and mixtures thereof. Preferably R
and R1 are hydrogen, Ci to Cs alkyl, or d to C$ primary or secondary alkyl and most
preferably R and R1 are hydrogen.
The more preferred copolymers are copolymers of isobutylene and para-methylsryrene
and the most preferred copolymers are elastomeric copolymers containing from about
0.5 to about 20 wt% para-methylstyrene. These copolymers and their method of
preparation are disclosed in the above mentioned US Patent 5,162,445. For
convenience, these copolymers are hereafter referred to as "I-PAS copolymers".
The present invention is based on the discovery that the utilization of halogen, even in a
free radical halogenation process as required in the halogenation of I-PAS copolymers,
can be substantially increased by carrying out the reaction in the presence of an
oxidizing agent which is added to the reaction medium either at the onset of the
halogenation reaction or, more preferably, in a second stage after the polymer has been
partially halogenated. The invention is particularly applicable to free radical
halogenation conducted using an organic free-radical initiator such as a bis-azo
compound and wherein the oxidising agent is added to the reaction media in a second
stage only after a substantial portion of the halogen source e.g., molecular bromine, has
been consumed in a first reaction stage. This sequential addition of the organic free
radical initiator and halogen source in a first stage and oxidizing agent in a second stage
has been found to minimize unwanted reactions between the organic free radical
initiator and the oxidizing agent and to maximize halogen utilization in such processes.
Halogenating agents which may be used as a source of halogen in accordance with the
invention include molecular bromine (Br2) or chlorine, bromine chloride, iodine
bromide and mixtures thereof Where the free radical halogenation is conducted with
the oxidizing agent present at the onset of the halogenation reaction, hydrogen bromide
or hydrogen chloride may be used as the halogen source. The preferred halogen source
is molecular bromine.
Since a considerable portion of the hydrogen halide, e.g., hydrogen bromide, generated
in-situ as a halogenation process by-product is oxidized to regenerate useful halogen,
smaller amounts of halogenating agent are initially required to achieve a given degree of
polymer halogenation than would be the case where the reaction is conducted without
the use of oxidizing agent. As a general rule, the amount of halogenating agent present
in the reaction media may vary between about 0.1 to 25 php (parts by weight per 100
parts by weight polymer), more preferably from about 0.2 to 10 php and most
preferably from about 0.2 to 6 php.
Any of the known free radical initiators can be used in the process. Free radical
initiators which are preferred in accordance with the invention include any source of
light, e.g., actinic white light or, where the reaction is conducted in the absence of light,
one or more organic free radical initiators. Preferred initiators are those which have a
half life of between about 0.5 and 2500 minutes under the desired reaction conditions,
and more preferably a half life of about 10 to 300 minutes. The amount of chemical
initiator employed may vary between about 0.02 to about 1 part by weight php,
preferably between about 0.02 and 0.4 parts by weight php. The most preferred
chemical initiators are az-obis compounds including azobisisobuty- ronitrile, 2,2'-azobis
(2,4,4 trimethyl pentane. nitrile), azobis (2-methyl butyro) nitrile and azobis (2,4
dimethyl valero) nitrile. Other radical initiators such as organic peroxides can also be
used provided they are relatively poor at hydrogen abstraction so that they react
preferentially with the molecular halogen molecules to form halogen atoms rather than
with the I-PAS copolymer or any solvent present in the reaction mixture to form alkyl
radicals or crosslinked structures.
The oxidizing agents which have been found suitable for the purposes of the present
invention are water soluble materials which contain oxygen. Preferred agents are
peroxides and peroxide forming substances as exemplified by the following substances:
hydrogen peroxide, sodium chlorate, sodium bromate, sodium hypochlorite or bromite,
oxygen, oxides of nitrogen, ozone, urea peroxidate, acids such as pertitanic,
perzirconic, perchromic, permolybdic, pertungstic, perunanic, perboric, perphosphoric,
perpyrophosphoric, persulfates, perchloric, perchlorate and periodic acids. Of the
foregoing, hydrogen peroxide and hydrogen peroxide-forming compounds, e.g., peracids
and sodium peroxide, have been found to be most suitable for carrying out the
The amount of oxidizing agent used in accordance with the invention depends on the
amount and kind of halogenating agent used. Generally from about 0.1 to about 3 mols
of oxidizing agent per mole of halogenating agent may be used. The preferred amount
of oxidizing agent present in the reaction mixture ranges from about 1 to 2 mols per
mol of halogenating agent.
The oxidizing agent may be introduced into the reaction zone as a solution in any
suitable diluent such as carbon tetrachloride, lower alcohol, ether or water. More
preferably, the oxidizing agent is introduced as an aqueous solution or water-in-oil
emulsion. When introduced as an aqueous solution, the solution may contain about 10-
85 wt% of the oxidizing agent; when introduced as an emulsion, the emulsion may
contain about 1-50 wt% of the oxidizing agent.
The halogenation reaction may be carried out in bulk or in solution, but is preferably
conducted by first dissolving the I-PAS copolymer in a suitable organic solvent such as
a C4 to Cio aliphatic, cycloaliphatic or aromatic liquid. Preferred solvents include
normal hexane, cyclohexane, normal pentane, normal heptane and benzene. Halogencontaining
solvents such as chlorobenzene, carbon tetrachloride and chloroform may
also be used. The polymer solution, which may contain from as little as 1 wt% polymer
or as much as 40 wt% polymer, is introduced into a reaction zone that is provided with
suitable means to permit intimate contact with the reactants. The temperature of the
polymer solution is adjusted to that which is most convenient for carrying out the
reaction in view of the various properties of the reactants and the volatility of the
solvent. To insure a fairly rapid reaction it is advisable to employ a reaction
temperature above 0°C, e.g., at least 5°C, and it is preferred to maintain the temperature
between about 20°C and 80°C. However, under certain conditions, especially where
less reactive materials are employed, it may be desirable to run the reaction at
temperatures ranging up to 150°C or higher.
Where the oxidizing agent is introduced into the reaction zone at the onset of the
halogenation reaction, it may be added prior to, concurrently with or subsequent to the
addition of the halogenating agent and chemical free radical initiator, where present.
More preferably, however, the oxidizing agent is not added to the reaction mixture until
after at least about 50 wt%, more preferably about 75 to 100 wt% of the halogenating
agent has been consumed in the halogenation reaction. Halogen consumption is
indicated, where molecular bromine is used as the halogenating agent, by a change in
color of the reaction mixture from reddish brown to a light tan or amber color.
Halogen consumption can also be calculated stoichiometrically as a function of reaction
speed under reaction conditions.
In another embodiment of the invention, the halogenation may be carried out in two or
more separate reaction zones. In this process, the halogenation reaction is carried out
as described above in a first reactor zone to form a reaction product mixture comprising
a partially halogenated copolymer and in-situ generated hydrogen halide by-product.
This reaction is also carried out until at least 50 wt%, more preferably at least 75 to 100
wt% of the added halogen source is consumed. Thereafter, the reaction mixture is
transferred to a second reactor zone where it is contacted under mixing conditions with
the oxidizing agent. The hydrogen halide generated in-situ in the first reactor zone is
regenerated into free halogen by the oxidizing agent in the second reactor zone, which
free halogen is then available for further halogenation of the copolymer in the second
reactor zone. The oxidizing agent may be added incrementally or all at once in said
second reactor zone or may be added or metered in a mixing zone positioned between
the first and second reactor zone.
After completion of the halogenation reaction, the polymer may be recovered by
conventional techniques, e.g., neutralization with dilute caustic, water washing and
removal of solvent such as by steam stripping techniques or by precipitation using a
lower alcohol such as isopropanol, followed by drying.
The halogenation of the I-PAS copolymer is generally conducted for a period of time of
from about 1 minute up to about 3 of 4 hours, depending on reaction conditions until a
halogenated copolymer containing at least about 0.05 mol% of haloalkyl groups is
achieved. In the more preferred embodiment and where the I-PAS copolymer contains
para-methylstyrene and the halogenating agent is bromine, the reaction is conducted
until the polymer contains from about 0.1 to about 10 mol% of benzylic bromine
(bromomethyl groups), more preferably from about 0.1 to about 2 mol% of benzylic
bromine. . Halogenated copolymers produced in accordance with this invention will
generally contain less than about 0.003 mol% of dibromo methyl groups, even at a high
degree of bromination.
The following examples are illustrative of the invention. The I-PAS copolymer used in
the examples is a random elastomeric copolymer of isobutylene and 7.5 wt% of paramethylstyrene
(PMS) having a Mooney Viscosity of 45 (1 + 8 at 125°C).
In this example, light initiated bromination of the copolymer was conducted under three
separate conditions, i.e., (a) without the addition of oxidizing agent; (b) oxidizing agent
added concurrently with Br2 and (c) oxidizing agent added only after the substantial
depletion of the Br2.
a) 109.5 grams of I-PAS elastomer were dissolved in 620.5 grams of
cyclohexane in a baffled glass flask equipped with a dropping funnel to form a 15 wt%
solution. The flask was equipped with a 150 watt tungsten light bulb mounted next to
the flask and a turbine mixer. Next, a 3 wt% Br2 charge (based on polymer weight)
was added dropewise to the flask maintained at about 20°C while exposed to light
radiation. The bromination reaction was terminated (neutralized by NaOH) after the
reddish brown Br2 color in the reaction mixture had faded to a light tan color. The
resulting neutralized cement was washed in water until neutral and the brominated
polymer was precipitated in isopropanol and dried in a vacuum.
b) Part (a) was repeated except that 4.9 grams of emulsified 35%
hydrogen peroxide in hexane (about a 2:1 peroxide to halogen mole ratio) was added
to the reaction mixture concurrently with the addition of Br2.
c) Part (a) was repeated except that 4.39 grams of the emulsified
hydrogen peroxide were added to the reaction mixture after the reddish brown Br2
color in the reaction mixture had faded to a light tan color. The reaction was continued
for 7 minutes prior to neutralization.
The samples of brominated polymers were submitted for NMR analysis and results are
shown in Table 1.
Bromine Charge: 3 wt% or 2.12 mole% based on polymer.
Table 1 shows the results of light initiated bromination of I-PAS cement with and
without H2O2 addition. The data clearly indicate that the addition of H2O2 significantly
improved the bromine utilization as reflected by the 80% increase of BrPMS content on
polymer. The sequence of H202 addition (either added simultaneously with Br2 or after
most Br2 was consumed) has little impact on bromine utilization. This suggests that the
Br radical does not react/interfere with the bromine regeneration function of H2O2 in a
light initiated process.
The data also indicate that the amount of undesirable Br2PMS was extremely small
(0.02 mole%) even at 45% PMS conversion (or 1.56 mole% BrPMS on polymer).
This suggests that the reduced cement acidity during the Regenerative Bromination
may retard the formation of Br2PMS. Therefore a higher BrPMS content can be
achieved via this process without a significant amount of B^PMS formation relative to
convention bromination processes.
In this example, the bromination reaction is initiated using a bis azo chemical initiator
2,2'-azobis(2,4,4 trimethyl pentane nitrile), referred to as VAZOJ-52 and using the
sequence of addition of oxidizing agent as in Example 1.
a) 76.2 grams of I-PAS elastomer were dissolved in 431.8 grams of
cyclohexane in a baffled glass flask equipped with a dropping funnel to form a 15 wt%
solution. Next, a 0.2 wt% VAZO-52 charge (based on polymer weight) was added to
the reactor flask and the contents were gently heated to 50°C at atmospheric pressure.
Thereafter, a 3wt% Br2 charge (based on polymer weight) was added dropwise to the
flask maintained at 50°^. After bromine addition was complete, the reaction was
continued at 50°C for 10 minutes, after which the halogenated polymer was neutralized
and recovered as in Example 1.
(b) Part (a) was repeated except that 3.2 grams of emulsified 35%
hydrogen peroxide aqueous emulsion in hexane (about a 2:1 peroxide to halogen mole
ratio) was added to the reaction media concurrently with the addition of Bra.
(c) Part (a) was repeated except that 3.2 grams of the emulsified hydrogen
peroxide were added to the reaction mixture after the reddish brown Bra color in the
reaction mixture had faded to a light tan color. After the peroxide addition, the
reaction was continued for an additional 50 minutes prior to neutralization.
NMR analysis of these brominated polymers showed results as indicated in Table 2.
Bromine Charge: 3 wt% or 2.12 mole% based on polymer.
The data in Table 2 indicate that when H2O2 was added into the cement simultaneously
with Br2, the reddish color of Br2 stayed significantly longer than the control and the
bromine utilization was only about 20% higher than the control. It suggests that the
VAZO radicals can react/interfere with H2O2 and a significant amount of the H202
might have been destroyed by VAZO radicals before it could react with HBr and
regenerate the Br2.
However, when H2O2 was added after most of the Br2 was consumed (based on
cement color), the BrPMS on polymer and the bromine utilization were increased by
about 80% from the control run under similar conditions. It is most likely that, after the
initial Br2 charge was consumed, the VAZO radical concentration was reduced
(according to the half-life of VAZO at 50°C) and the HBr concentration in cement was
the highest so that the fast reaction between H2O2 and HBr became predominant.
The data show that the Regenerative Bromination process can be used in processes by
including the addition of H2O2 between two reactors. In such a scenario, a reduced Br2
charge can be added and consumed in the first reactor and then the HiC^ can be added
between the first and second reactors (into a high shear in-line mixer) to convert all
HBr back to Br2 before it reaches the second reactor. Assuming proper temperature in
the second bromination reactor, most of the regenerated Br2 would be consumed and
thus significantly less caustic is needed to neutralize the residual Br2 and/or HBr in the
1. A multi stage process for brominating a copolymer of a C4 to C7 isomonoloefin and a
a) forming a solution of said copolymer in organic solvent in a first reactor zone;
b) contacting said solution with elemental bromine and an organic free radical initiator at a temperature 0° C to 150° C, for a period of time of 1 minute to 4 hours to form a reaction product mixture comprising a partially brominated copolymer and an in-situ generated hydrogen bromide;
c) transferring said reaction product mixture to a second reactor zone and contacting said mixture with an oxidizing agent capable of converting said hydrogen bromide to free bromine; and
d) continuing said bromination in said second reactor zone until a brominated copolymer containing at least 0.05 mole % of bromoalkyl groups is obtained.
2. The process as claimed in claim 1 wherein said free radical initiator is bisazo compound selected from the group consisting of azobisisobutyronitrile, azobis (2-methyl butyro) nitrile. 2.2'-azobis (trimethyl pentane nitrile). and azobis (2,4 dimethyl valero) nitrile.
3. The process as claimed in claim 1 wherein said copolymer from step (d) contains at least 10.0 mole % of bromalkyl groups.
4. The process as claimed in claim 1 wherein said copolymer contains from 0.1 to 1.0 mole % of bromomethyl groups.
5. The process as claimed in claim 1 wherein at least 50 wt % of said bromine is consumed in step (b).
6. The process as claimed in claim 1 wherein contact of said mixture from step (b) and said oxidizing agent occurs in a mixing zone positioned between said first and second reactor zones.
7. The process as claimed in claim 1 wherein said oxidizing agent is hydrogen peroxide.
8. The process as claimed in claim 1 wherein the molar ration of said oxidizing agent to
said halogenating agent is in the range of from 0.1 to 3.
9. The process as claimed in claim 1 wherein said copolymer contains at least 80 wt %
of isobutylene and from 0.5 up to 20 wt % of paramethylstyrene.
10. A multi stage process for brominating a copolymer of a C4 to C7 isomonoloefin and a
para-alkylstyrene substantially as herein described with reference to the foregoing
|Indian Patent Application Number||1855/DEL/2005|
|PG Journal Number||40/2010|
|Date of Filing||18-Jul-2005|
|Name of Patentee||EXXONMOBIL CHEMICAL PATENTS, INC.|
|Applicant Address||5200 BAYWAY DRIVE, BAYTOWN, TEXAS 77520, USA.|
|PCT International Classification Number||C08F 255/08|
|PCT International Application Number||N/A|
|PCT International Filing date|