Halogen recovery with mixed solvent for halogenating unsaturated isoolefin copolymer

Abstract

A process for producing a halogenated isoolefin copolymer, the process comprising contacting an unsaturated isoolefin copolymer cement, the cement comprising an unsaturated isoolefin copolymer dissolved in an organic solvent with a cosolvent, under halogenation conditions, a halogenating agent, an oxidant, the cosolvent being a compound of Formula (I): R1-COO-R2 (I) Where R1 is a H or a C1-3 alkyl moiety and R2 is a C1-5 alkyl moiety. The process provides improved halogen recovery.

Description

[0001] HALOGEN RECOVERY WITH MIXED SOLVENT FOR HALOGENATING UNSATURATED ISOOLEFIN COPOLYMER

[0002] Field

[0003] This application relates to a process for halogenating an unsaturated isoolefin copolymer.

[0004] In the standard process for brominating butyl rubber to form bromobutyl rubber, molecular bromine (Br2) is used as the brominating agent. The process results in the evolution of hydrogen bromide (HBr), as a by-product which, under normal conditions, does not further brominate the butyl rubber polymer. Therefore, the theoretical maximum fraction of bromine present in the reaction mixture which can be introduced into the butyl rubber polymer is 50%. However, in practice the fraction is usually less than 45%, and is less than 35% in both laboratory and production plant settings.

[0005] Known methods (WO 2020 / 124222, US 2014 / 0309362, US 3,018,275, US 5,681 ,901) to enhance bromine utilization during butyl rubber bromination involve the application of at least 0.5 mol per mol of brominating agent of a water-soluble oxidizing agent, such as organic peracid or hydrogen peroxide, which re-oxidizes the hydrogen bromide back to elemental bromine. The oxidizing agent can be an aqueous solution, or an aqueous emulsion in an organic solvent. Since the oxidizing agent is only soluble in water, the rate of reaction is governed by the rate in which the reactants can exchange between the organic and aqueous phases, thus requiring a longer reaction time.

[0006] Further, the methods utilizing hydrogen peroxide require very low concentrations of water to be present in the bromination medium. The benefits observed from the use of hydrogen peroxide in the bromination medium decrease dramatically with water concentrations greater than 1 wt%, presenting significant challenges and cost industrially, because additional equipment and energy may be needed to reduce the water content in the bromination medium from 10-20 wt% down to below 1 wt%.

[0007] In addition, when water is present in a rubber cement, oxidizing agents, such as organic peracid or hydrogen peroxide tend to stay in the aqueous phase. As a result, not all HBr can be oxidized into Br2 and thus, more oxidant and bromine are required to obtain a brominated butyl rubber with a specific or a higher functional bromine content. There remains a need for a cost-effective, efficient process for improving halogen utilization during halogenation of an isoolefin copolymer to reduce the usage of halogen, especially for bromine, which is an expensive raw material.

[0008] It has been found that cosolvents, preferably aliphatic esters, used in mixed solvents during the bromine recovery process improves bromine recovery and reduces the amount of bromine required.

[0009] In one aspect, there is provided a process for producing a halogenated isoolefin copolymer, the process comprising contacting an unsaturated isoolefin copolymer cement, the cement comprising an unsaturated isoolefin copolymer dissolved in an organic solvent with a cosolvent, under halogenation conditions, a halogenating agent, an oxidant, the cosolvent being a compound of Formula (I):

[0010] R1-COO-R2 (I) where: R1 is a H or a C1-3 alkyl moiety; and R2 is a Ci_5alkyl moiety.

[0011] The present halogenation process advantageously results in increased halogen utilization by providing an additional pathway for oxidizing hydrogen halide (HX) formed during halogenation of the unsaturated isoolefin copolymer back to molecular halogen (X2). The process provides as good or better bromine recovery compared to similar processes (e.g., processes utilizing peracid alone or hydrogen peroxide alone) in which no cosolvent is added because less amount of bromine is required. The process does not radically affect the microstructure and molecular weight of the resulting halogenated isoolefin copolymer, and the ability to use less oxidant to achieve the same or better halogenation efficiency is further beneficial to maintaining the microstructure and molecular weight of the halogenated isoolefin copolymer.

[0012] Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art. Brief of the Drawinqs

[0013] For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which:

[0014] Fig. 1 illustrates the process for producing a halogenated copolymer in mixed solvent with halogen recovery.

[0015] Fig. 2 depicts a graph of BAE (mol%) vs. water concentration (wt%) showing the effect of water concentration on bromine recovery when using mixed solvent (hexane / ethyl acetate) compared to pure hexane.

[0016] Fig. 3 depicts a contour plot from Design of Experiments showing the correlation between ethyl acetate volume and Br2 volume to produce BUR with different functional bromine.

[0017] Fig. 4 shows the statistically analysed results of a Design of Experiments, showing the increase of functional Br with the increase of bromine volume.

[0018] Fig. 5 shows the statistically analysed results of a Design of Experiments, showing that the functional Br increase with the increases with ethyl acetate until 213.0 mL of ethyl acetate (18.6 vol%) is added.

[0019] Fig. 6 shows the statistically analysed results of a Design of Experiments, showing that the functional Br is independent of the volume of hydrogen peroxide when the hydrogen peroxide ranges from 4.3-5.3 mL.

[0020] Fig. 7 shows the minimized volume of Br2, ethyl acetate and hydrogen peroxide calculated by DoE to prepare BUR with 0.9 mol% functional Br.

[0021] Detailed Description

[0022] The process provides for a procedure to produce a halogenated isoolefin copolymer from an unsaturated isoolefin copolymer. The unsaturated isoolefin copolymer preferably comprises repeating units derived from at least one isoolefin monomer and repeating units derived from at least one copolymerizable unsaturated monomers, and optionally repeating units derived from one or more further copolymerizable monomers.

[0023] Suitable isoolefin monomers include hydrocarbon monomers having 4 to 16 carbon atoms. In one embodiment, the isoolefin monomers have from 4 to 7 carbon atoms. Examples of suitable isoolefins include 2-methyl-1-butene, 3- methyl-1-butene, 2-methyl-2-butene, 4-methyl-1 -pentene, 4-methyl-1 -pentene and mixtures thereof. A preferred isoolefin monomer is isobutene (isobutylene).

[0024] Suitable copolymerizable unsaturated monomers include multiolefins, p-methyl styrene, p-pinene or mixtures thereof. Multiolefin monomers include hydrocarbon monomers having 4 to 14 carbon atoms. In some embodiments, the multiolefin monomers are conjugated dienes. Examples of suitable conjugated diene monomers include isoprene, butadiene, 2-methylbutadiene, 2,4-dimethylbutadiene, piperylene, 3-methyl-1 ,3- pentadiene, 2,4-hexadiene, 2-neopentylbutadiene, 2-methyl-1 ,5-hexadiene, 2,5-dimethyl-

[0025] 2.4-hexadiene, 2-methyl-1 ,4-pentadiene, 4-butyl-1 ,3-pentadiene, 2,3-dimethyl-1 ,3- pentadiene, 2,3-dibutyl-1 ,3-pentadiene, 2-ethyl-1 ,3-pentadiene, 2-ethyl-1 ,3-butadiene, 2- methyl-1 ,6-heptadiene, cyclopentadiene, methylcyclopentadiene, cyclohexadiene, 1-vinyl- cyclohexadiene and mixtures thereof.

[0026] The halogenatable isoolefin copolymer may optionally include one or more additional copolymerizable monomers. Suitable additional copolymerizable monomers include, for example, styrenic monomers, such as alkyl-substituted vinyl aromatic comonomers, including but not limited to a C1-C4 alkyl substituted styrene. Specific examples of additional copolymerizable monomers include, for example, a-methyl styrene, p-methyl styrene, chlorostyrene, cyclopentadiene and methylcyclopentadiene. Indene and other styrene derivatives may also be used. In one embodiment, the halogenatable isoolefin copolymer may comprise random copolymers of isobutylene, isoprene and p-methyl styrene.

[0027] In one embodiment, the halogenatoable isoolefin copolymer may be formed by copolymerization of a monomer mixture. Preferably, the monomer mixture comprises about 80-99.9 mol% of at least one isoolefin monomer and about 0.1-20 mol% of at least one copolymerizable unsaturated monomer, based on the monomers in the monomer mixture. More preferably, the monomer mixture comprises about 90-99.9 mol% of at least one isoolefin monomer and about 0.1-10 mol% of at least one copolymerizable unsaturated monomer. In one embodiment, the monomer mixture comprises about 92.5-97.5 mol% of at least one isoolefin monomer and about 2.5-7.5 mol% of at least one copolymerizable unsaturated monomer. In another embodiment, the monomer mixture comprises about

[0028] 97.4-95 mol% of at least one isoolefin monomer and about 2.6-5 mol% of at least one copolymerizable unsaturated monomer.

[0029] If the monomer mixture comprises the additional copolymerizable with the isoolefins and / or copolymerizable unsaturated monomers, the additional copolymerizable monomer preferably replaces a portion of the copolymerizable unsaturated monomer. When a multiolefin monomer is used, the monomer mixture may also comprise from 0.01% to 1% by weight of at least one multiolefin cross-linking agent, and when the multiolefin crosslinking agent is present, the amount of multiolefin monomer is reduced correspondingly.

[0030] The unsaturated isoolefin copolymer may be prepared by any suitable method, of which several are known in the art. For example, the polymerization of monomers may be performed in a diluent in the presence of an initiator system (e.g., a Lewis acid catalyst and a proton source) capable of initiating the polymerization process. A proton source suitable in the present invention includes any compound that will produce a proton when added to the Lewis acid or a composition containing the Lewis acid. Protons may be generated from the reaction of the Lewis acid with proton sources to produce the proton and the corresponding by-product. Such reaction may be preferred in the event that the reaction of the proton source is faster with the protonated additive as compared with its reaction with the monomers. Proton generating reactants include, for example such as water, alcohols, phenol thiols, carboxylic acids, and the like or any mixture thereof. Water, alcohol, phenol or any mixture thereof is preferred. The most preferred proton source is water. A preferred ratio of Lewis acid to proton source is from 5:1 to 100:1 by weight, or from 5:1 to 50:1 by weight. The initiator system including the catalyst and proton source is preferably present in the reaction mixture in an amount of 0.02-0.1 wt%, based on total weight of the reaction mixture.

[0031] Alkyl aluminum halide catalysts are a particularly preferred class of Lewis acids for catalyzing solution polymerization reactions in accordance with the present invention. Examples of alkyl aluminum halide catalysts include methyl aluminum dibromide, methyl aluminum dichloride, ethyl aluminum dibromide, ethyl aluminum dichloride, butyl aluminum dibromide, butyl aluminum dichloride, dimethyl aluminum bromide, dimethyl aluminum chloride, diethyl aluminum bromide, diethyl aluminum chloride, dibutyl aluminum bromide, dibutyl aluminum chloride, methyl aluminum sesquibromide, methyl aluminum sesquichloride, ethyl aluminum sesquibromide, ethyl aluminum sesquichloride and any mixture thereof. Preferred are diethyl aluminum chloride (Et2AICI or DEAC), ethyl aluminum sesquichloride (Eti 5AICI15 or EASC), ethyl aluminum dichloride (EtAICh or EADC), diethyl aluminum bromide (Et2AIBr or DEAB), ethyl aluminum sesquibromide (Eti.sAIBri.s or EASB) and ethyl aluminum dibromide (EtAIBr2or EADB) and any mixture thereof. In a particularly preferred initiator system, the catalyst comprises ethyl aluminum sesquichloride, preferably generated by mixing equimolar amounts of diethyl aluminum chloride and ethyl aluminum dichloride, preferably in a diluent. The diluent is preferably the same one used to perform the copolymerization reaction.

[0032] The diluent may comprise an organic diluent. Suitable organic diluents may include, for example, alkanes, chloroalkanes, cycloalkanes, aromatics, hydrofluorocarbons (HFC) or any mixture thereof. Chloroalkanes may include, for example methyl chloride, dichloromethane or any mixture thereof. Methyl chloride is particularly preferred. Alkanes and cycloalkanes may include, for example, isopentane, cyclopentane, 2,2- dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, 3-methylpentane, n-hexane, methylcyclopentane, 2,2-dimethylpentane or any mixture thereof. Alkanes and cycloalkanes are preferably C6 solvents, which include n-hexane or hexane isomers, such as 2-methyl pentane or 3-methyl pentane, or mixtures of n-hexane and such isomers as well as cyclohexane. The monomers are generally polymerized cationically in the diluent at temperatures in a range of from -120°C to +20°C, preferably -100°C to -50°C, more preferably -95°C to -65°C. The temperature is preferably about -80°C or colder.

[0033] Where the diluent comprises chloroalkanes (e.g., methyl chloride) in a slurry polymerization process, the diluent as well as any residual monomers may be removed from the unsaturated isoolefin copolymer by flash separation using steam. Removal of the diluent and residual monomers in such a ‘wet’ process leaves a polymer containing a significant amount of water. The polymer is dissolved in organic solvent to provide a polymer cement having a significant water content, for example 1 wt% or greater or 1.5 wt% or greater, based on total weight of the cement. In some embodiments, the water content of the cement may be 0-30 wt% or 0-25 wt%, 1-30 wt% or 1 .5-15 wt% or 2-30 wt% or 2-20 wt% or 2-15 wt% or 5-20 wt% or 5-15 wt% or 5-10 wt% or 10-15 wt%, based on total weight of the cement.

[0034] Where the diluent comprises chloroalkanes (e.g., methyl chloride) or alkanes (e.g., hexanes) in a slurry or a solution polymerization process, the diluent as well as any residual monomers may be removed from the unsaturated isoolefin copolymer by flash separation using a heated organic solvent in which the unsaturated isoolefin copolymer is soluble or by simple distillation. Where simple distillation is used, some of the organic diluent may remain as organic solvent in the cement. Removal of the diluent and residual monomers in such a ‘dry’ process provides a polymer cement containing less water, for example less than 1 wt%, or even 0 wt%, water based on total weight of the cement.

[0035] To form the halogenated isoolefin copolymer, the unsaturated isoolefin copolymer may be subjected to a halogenation process using a halogenating agent under halogenation conditions. Halogenation can be performed by adapting a process known by those skilled in the art (for example the procedures described in Rubber Technology, 3rd Ed., Edited by Maurice Morton, Kluwer Academic Publishers, pp. 297-300 or United States Patent US 5,886,106 issued March 23, 1999, the contents of both of which are herein incorporated by reference) and modifying the process as described herein.

[0036] Halogenating agents useful for halogenating the unsaturated isoolefin copolymer may comprise molecular chlorine (Cl2) or molecular bromine (Br2) and / or organo-halide or inorganic halide precursors thereto, for example dibromo-dimethyl hydantoin, trichloroisocyanuric acid (TCIA), n-bromosuccinimide, sodium bromide, hydrogen bromide or the like. Preferably, the halogenating agent comprises chlorine (Cl2) or bromine (Br2), more preferably bromine. Preferably, halogenation comprises bromination. The amount of halogenating agent added is controlled to provide a final functional halogen content of at least 0.05 mol%, preferably 0.05 - 2.5 mol%, in the halogenated isoolefin copolymer. The amount of halogenating agent used has a linear relationship with the final halogen content (i.e., the functional halogen amount) on the halogenated isoolefin copolymer. A larger amount of halogenating agent leads to a larger functional halogen amount in the halogenated isoolefin copolymer.

[0037] Halogenation is performed in a mixed solvent reaction medium comprising an organic solvent and a cosolvent. The organic solvent is preferably an aliphatic solvent. The organic solvent preferably comprises an alkane, more preferably hexanes or pentanes. In an embodiment, the pentane is iso-pentane.

[0038] The cosolvent useful in the present process is a compound which is miscible with the organic solvent, has limited solubility with water and does not react with the halogenation agent. To achieve improved bromine recovery, the solubility of the oxidant should be greater in the cosolvent than in the organic solvent. The cosolvent is preferably an aliphatic ester. More preferably the cosolvent is a compound of formula (I)

[0039] • R1-COO-R2 (I)

[0040] Preferably R1 = H or a C1.3 alkyl moiety and R2 = Ci_5alkyl moieties.

[0041] Some preferred examples of cosolvents of formula (I) include methyl formate, ethyl formate, propyl formate, isopropyl formate, n-butyl formate, sec-butyl formate, isobutyl formate, tertbutyl formate, n-pentyl formate, 1 ,1 -dimethylpropyl formate, 2,2-dimethylpropyl formate, 3- methylbutyl formate, 1-methylbutyl formate, 1-ethylpropyl formate, 1 ,2-dimethylpropyl formate, 2-methylbutyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, n-butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, n-pentyl acetate, 1 ,1 -dimethylpropyl acetate, 2,2-dimethylpropyl acetate, 3-methylbutyl acetate, 1- methylbutyl acetate, 1 -ethylpropyl acetate, 1 ,2-dimethylpropyl acetate, 2-methylbutyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, n- butyl propionate, sec-butyl propionate, isobutyl propionate, tert-butyl propionate, n-pentyl propionate, 1 ,1 -dimethylpropyl propionate, 2,2-dimethylpropyl propionate, 3-methylbutyl propionate, 1 -methylbutyl propionate, 1 -ethylpropyl propionate, 1 ,2-dimethylpropyl propionate, 2-methylbutyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, isopropyl butyrate, n-butyl butyrate, sec-butyl butyrate, isobutyl butyrate, tert-butyl butyrate, n-pentyl butyrate, 1 ,1 -dimethylpropyl butyrate, 2,2-dimethylpropyl butyrate, 3-methylbutyl butyrate, 1-methylbutyl butyrate, 1-ethylpropyl butyrate, 1 ,2-dimethylpropyl butyrate, 2- methylbutyl butyrate, or any mixture thereof. The cosolvent is more preferably ethyl acetate, isopropyl acetate, t-butyl acetate, or any mixture thereof. The cosolvent is even more preferably ethyl acetate.

[0042] The amount of cosolvent used in the halogenation reaction is preferably 1 - 43 vol%, more preferably 3.93 - 43 vol%, yet more preferably 14.2 - 18.6 vol% based on the total volume of organic solvent and cosolvent.

[0043] To improve efficiency of halogenation, the halogenation process is modified by contacting an unsaturated isoolefin copolymer cement, in which the unsaturated isoolefin copolymer is dissolved in an organic solvent and a cosolvent, with a halogenating agent and an oxidant. A two-phase reaction medium is formed comprising an aqueous phase and an organic phase comprising the organic solvent and the cosolvent. Due to the greater solubility of the oxidant in the cosolvent, the oxidant in-situ oxidizes halide produced in the halogenation process, in both the aqueous phase and the organic phase, back into molecular halogen to improve halogen atom efficiency of the halogenation process. In an embodiment, Figure 1 illustrates the process for producing a halogenated copolymer. As illustrated in Figure 1 , the cosolvent is miscible with hexanes but immiscible with water. With the assistance of the cosolvent, the oxidant is extracted from the aqueous phase to the organic phase providing an additional pathway for bromine recovery via route 2. Because the oxidation of the HBr back into Br2 occurs directly in the organic phase in route 2, it is believed that the regeneration of Br2in route 2 will be more efficient as compared to route 1 , as transferring of HBr from the organic phase to the aqueous phase and transferring of regenerated Br2from the aqueous phase to the organic phase are not required. Halogenation may be conducted for a length of time to achieve the desired level of halogenation. The length of time is preferably 60 minutes or less. Even at 20 minutes or less, or at 10 minutes or less, or at 5 minutes or less, significant halogenation of the unsaturated isoolefin copolymer may be achieved. Preferably, halogenation is conducted for a minimum of 1 minute. Preferably, the halogenation time is 1-60 minutes, or 1-20 minutes, or 1-10 minutes, or 1-5 minutes.

[0044] Halogenation may be conducted at any suitable temperature and is preferably conducted at a temperature up to about 90°C. In some embodiments, the temperature may be up to about 80°C. In other embodiments, the temperature may be up to about 65°C. The increased halogenation efficiency at lower temperatures is more pronounced at higher concentrations of the unsaturated isoolefin copolymer in the reaction medium. Temperatures in a range of 0-70°C or 0-50°C or 0-45°C or 15-45°C or 20-45°C or 40-45°C or 30-70°C or 20-60°C or 23-54°C or 23-45°C or 10-35°C or 20-30°C are preferred.

[0045] Halogenation may be conducted with or without mixing the reaction medium. Preferably, the reaction medium is mixed during halogenation. Mixing can be accomplished by any suitable method, for example by stirring, agitating and the like. More preferably, the reaction medium is stirred, preferably at a rate of 500 rpm or more. Stirring is more preferably accomplished with a mechanical stirrer.

[0046] The unsaturated isoolefin copolymer is preferably present in the reaction medium in an amount of 1-60 wt%, based on total weight of the reaction medium. More preferably, the unsaturated isoolefin copolymer is present in an amount of 5-50 wt%, even more preferably 5-40 wt%, yet more preferably 10-33 wt%, even yet more preferably 10-30 wt%, for example 25 wt%, based on total weight of the reaction medium.

[0047] The aqueous phase is formed from the aqueous solution or aqueous emulsion of the oxidant, from water generated by the halogenation reaction and / or from any additional water contained in the unsaturated isoolefin polymer cement. The aqueous solution of oxidant together with the water generated by the halogenation reaction typically form less than 4 wt% of the reaction medium, for example 0.16-3.6 wt%, based on total weight of the reaction medium.

[0048] The reaction medium may contain 0-20 wt%, based on total weight of the reaction medium, of additional water arising from water contained in the unsaturated isoolefin polymer cement depending on the process used to prepare the polymer cement. The additional water is water from the unsaturated isoolefin polymer cement and does not include the water used to prepare the aqueous solution of the oxidant or the water generated by the halogenation reaction. It is an advantage of the present process that the reaction medium may contain significant amounts of additional water, for example 1-20 wt% additional water, based on total weight of the reaction medium. In some embodiments, the additional water may comprise or 1 .5-15 wt% or 2-20 wt% or 2-15 wt% or 5-20 wt% or 5-15 wt% or 5-10 wt% of the reaction medium, based on total weight of the reaction medium. Even so, in some embodiments the reaction medium may contain an insignificant amount of additional water, for example less than 1 wt% additional water, or even 0 wt% additional water, based on total weight of the reaction medium.

[0049] The oxidant may be any suitable oxidant for converting hydrogen halide to free halogen. Some examples include hydrogen peroxide, metal salts of hydrogen peroxide, organic peracids, metal salts of organic peracids, inorganic oxyacids, metal salts of inorganic oxyacids, and the like, and mixtures thereof. Metal salts preferably comprise alkali metal cations (e.g., Li+, Na+, K+or mixtures thereof) as the metal of the salt. In some embodiments, the oxidant comprises H2O2, NaHSOs, Na2S20s, NaCIO, NaBrO, NaBrCh, NalOs, NaCIO, NaCIOs, NaCIO4, NalO4, NaOO(CO)R5 where R5 is a C1-8 alkyl moiety, KHSO5, K2S2O8, KCIO, KBrO, KBrO3, KIO3, KCIO3, KCIO4, KIO4, KOO(CO)R5where R5is a C1-8 alkyl moiety, compounds that generate the aforementioned oxidants, or mixtures thereof.

[0050] The process may further comprise recovering halogenated isoolefin copolymer containing at least 0.05 mol% of chemically combined halogen.

[0051] In the present process, all or some of the halogenating agent may comprise hydrogen halide (HX) added to the aqueous phase. Because HX is converted into molecular halogen (X2) by the oxidant in both the organic and aqueous phase, the added HX can act as a source of halogenating agent.

[0052] EXAMPLES

[0053] Materials and Methods’.

[0054] Isobutylene-isoprene polymer (HR, BB2030) and Epoxidized Soybean Oil (ESBO) were obtained from ARLANXEO (Sarnia, Ontario, Canada site). The remaining materials were used as received: Hexanes (VWR), Ethyl acetate (Sigma-Aldrich), Isopropyl acetate (Fluka), t-Butyl acetate (Sigma-Aldrich), Sodium Hydroxide (VWR), 99.99% Bromine (Sigma Aldrich), 35 wt% Peracetic Acid (PAA) Solution (Evonik), 30 wt% Hydrogen Peroxide (Sigma-Aldrich), Calcium Stearate (Alfa Aesar) and lrganox™-1010 (BASF).

[0055] Nuclear Magnetic Resonance (1 H NMR) spectroscopy was conducted on a Bruker DRX 500 MHz spectrometer (500.13 MHz). The chemical shifts (0, ppm) in all 1H NMR spectra were referenced relative to TMS (1 H 0 = 0.00 ppm).

[0056] Bromination reactions

[0057] 250.0 g of isobutylene-isoprene copolymer (butyl rubber, HR) was cut into small pieces and added to a 5 L jacketed baffled reactor equipped with an overhead stirrer filled with pre-determined volume of hexanes and a cosolvent. Stir speed was set to 150 rpm while the base material pieces were added to the reactor. The solution was stirred for 24 hours to fully dissolve the butyl rubber. After the isobutylene-isoprene copolymer had fully dissolved, pre-determined volume of water was added to the reactor via a pipette to provide a butyl rubber cement.

[0058] A circulating bath connected to the jacketed reactor was set to 45°C to heat the reactor and the butyl rubber cement was stirred at 350 rpm for 30 minutes. Oxidant was then added by a pipette, followed by the addition of bromine (Br2) with a syringe, and the reaction was stirred with stirring rate of 500 rpm for 5 mins, 30 mins or 60 mins in some examples.

[0059] After the reaction, a pre-determined amount of a 2.5 M NaOH solution was added to the reaction medium to quench the reaction. An additional 250 mL of water was added to aid in mixing. The mixture was continued to stir at 350 rpm for 5 minutes. An additional 1 L of water was added and allowed to stir at 350 rpm for another 5 minutes. Stirring was reduced to 150 rpm and continued for an additional 5 minutes. The reactor stirring was stopped and the water phase was drained through the bottom drain valve. The cement of brominated isobutylene-isoprene copolymer was washed with additional water until the pH was 7, to remove any residual inorganic salts. A solution of polymer stabilizers (4.52 g of calcium stearate, 0.125g of lrganox™-1010, and 3.25 g of ESBO) in hexanes was added to the reactor and the cement stirred for 5 more minutes. The cement was drained and steam coagulated using low pressure steam for approximately 1 hour. A small piece of the brominated polymer sample was cut from the final product and dried in the vacuum oven at 60°C overnight for analysis. Bromine utilization calculations

[0060] Bromine utilization in the bromination process may be measured using bromine atom efficiency (BAE), which is given by the following equation: atoms of Br on polymer

[0061] BAE(° / o) = x 100% atoms of Br from bromine added to reaction

[0062] Atoms of Br on polymer is calculated from1H-NMR. Atoms of Br from bromine added to the reaction is calculated by volume of bromine used in reaction. From the equation, it is evident that ideal conditions would yield a BAE of 50%, where 50% of the Br is in waste HBr. Therefore, the theoretical maximum fraction of bromine present in the reaction mixture which can be introduced into the butyl rubber polymer is 50%. However, in practice the BAE is usually less than 45%, for example 30-45% or 35-45%.

[0063] In some previous methods (e.g., in US 3,018,275 and US 5,681 ,901) bromine utilization is measured using molecules of molecular bromine added to the reaction, which provides numerical results that are double the BAE because there are two atoms of bromine in every molecule of molecular bromine. Further, these previous methods use X-ray diffraction in order to estimate the amount of Br bound to the polymer. However, this method will also measure NaBr arising from the neutralization process, and which is trapped within the polymer matrix. Trapped NaBr does not necessarily measure the amount of Br chemically bound to the polymer, and generally provides numbers for bromine utilization efficiency that are higher than the actual efficiency.

[0064] Example 1: Cosolvent for bromination and bromine recovery

[0065] Ethyl acetate, isopropyl acetate and t-butyl acetate were compared as the cosolvent to hexanes for bromine recovery. The abilities of the cosolvents to dissolve butyl rubber, miscibility with hexanes and water as well as boiling temperature are listed in Table 1 .

[0066] Table 1

[0067] Properties of the cosolvent for bromine recovery As illustrated in Table 1 , the cosolvents are all miscible with hexanes but immiscible with water. Ethyl acetate, isopropyl acetate and t-butyl acetate are poor solvent for butyl rubber.

[0068] Example 2: Solubility of oxidant in cosolvent

[0069] To achieve bromine recovery with better performance, the cosolvent should have better solubility of the oxidants than hexanes alone. Therefore, the partition of hydrogen peroxide (H2O2) and peracetic acid (PAA) between the organic phase composed by hexanes / cosolvent vs. the aqueous phase were tested. As shown in Table 2, seven solutions composed of hexanes I ethyl acetate and water were prepared. The volume ratio of cosolvent in hexanes I ethyl acetate ranges from 0 to 40 wt% and the water remains consistent at 6 mL.

[0070] Table 2

[0071] Partition of H2O2between water and organic solvent composed by hexane and ethyl acetate

[0072] The H2O2concentration in the organic phase was tested by H2O2test strip (Quantofix peroxide 100). For sample 1 , no H2O2was detected in the organic phase indicating H2O2stays in the aqueous phase. In contrast, when ethyl acetate is added, H2O2was observed in the organic phase. In addition, with the increase volume of cosolvent, more H2O2was detected in the organic phase. Similar to H2O2, PAA also shows better solubility in the organic phase when ethyl acetate is added. Example 3: Solubility of rubber in organic solvent / cosolvent

[0073] The solubility of butyl rubber in hexanes / organic acetate was tested before bromination. 25 g of butyl rubber was mixed with different hexanes and ethyl acetate compositions in accordance with Table 3. It is apparent from Table 3 that butyl rubber was dissolved without the formation of precipitate in hexanes / ethyl acetate with ethyl acetate up to 43 vol%. Above 43 vol% of ethyl acetate, the butyl rubber in the mixed solvent swelled instead of being dissolved in the solvents. To avoid precipitation of butyl rubber during bromination, the volume percentage of ethyl acetate in the mixed solvent was kept below 43 vol%. It is believed that butyl rubber will have the same or slightly improved solubility in hexanes / isopropyl acetate and hexanes / t-butyl acetate than in hexanes / ethyl acetate given that isopropyl acetate and t-butyl acetate will be less polar due to increased number of carbons.

[0074] Table 3 Solubility of butyl rubber in 100 mL mixed solvent composed by hexanes and ethyl acetate

[0075] Example 4: Bromination and bromine recovery in hexanes / ethyl acetate mixed solvent.

[0076] The effect of ethyl acetate on the control bromination without bromine recovery was investigated. As shown in Table 4, C1 and C2 are control brominations without the addition of oxidant. The bromination in C1 was performed in hexanes and the bromination in C2 was performed in hexanes / ethyl acetate (9.53:1) mixed solvent. As is shown in Table 4, the addition of ethyl acetate did not change the bromination as the BAE of C1 and C2 are similar. For C3 and C4, when oxidants were added to the bromination process an increase in functional Br was observed, indicating the occurrence of bromine recovery. P1 and P2 are two brominations performed in hexanes / ethyl acetate mixed solvent with the addition of 30 wt% H2O2 and PAA solution, respectively. As shown in Table 4, P1 shows a 0.14 mol% functional Br improvement as compared to C3. P2 shows a 0.11 mol% functional Br increasement when compared to C4. As is apparent in Table 4, ethyl acetate does not affect the functional Br in the control samples, thus the improvement for P1 and P2 is attributed to the better solubility of H2O2 and PAA in hexanes / ethyl acetate than in hexanes alone.

[0077] Table 4

[0078] 250.0 g HR, 25 wt% HR, 6 wt% H2O, Br2(0.034 moles), 45 °C, 500 rpm, 5 mins

[0079] Example 5: Bromination and bromine recovery in other mixed solvents

[0080] In addition to ethyl acetate, isopropyl acetate was also studied as a cosolvent for bromine recovery. In contrast to Example 4, this example does not contain any water. As illustrated in Table 5, when 45 mL of ethyl acetate (P4) and isopropyl acetate was added (P5), improvement in functional Br and BAE are observed as compared to P3 in which no cosolvent is added.

[0081] Table 5 250.0 g HR, 25 wt% HR, 0 wt% H2O, Br2(0.034 moles),

[0082] 4.3 mL 30 wt% H2O2 solution, 45 °C, 500 rpm Example 6. Effect of amount of ethyl acetate on bromine recovery

[0083] The effect of the amount of ethyl acetate on bromine recovery was investigated by varying the volume ratio between hexanes and ethyl acetate. As suggested in Table 6, when the volume ratio of ethyl acetate increases from 0 to 3.9 to 43%, the BAE increases from 54.4% to 61.5% to 74.4 % accordingly. Mixed solvent with higher volumes of ethyl acetate were not performed to avoid precipitation of rubber cement as discussed in Example 3.

[0084] Table 6

[0085] 250.0 g HR, 25 wt% HR, 0 wt% H2O, Br2(0.034 moles), 4.3 mL 30 wt% H2O2solution, 45 °C, 500 rpm

[0086] Example 7. Effect of emulsifying agent on bromine recovery in mixed solvent

[0087] The effect of an oxidant emulsion on bromine recovery in a mixed solvent was investigated. Lutensol TO5 was used as an emulsifying agent to generate H2O2emulsion which was added to the bromination process. As shown in Table 7, the functional Br increased from 0.95 to 1.04 mol% when H2O2emulsion was used, indicating emulsifier can further improve the performance beyond cosolvent addition.

[0088] Table 7

[0089] 250.0 g HR, 25 wt% HR, 0 wt% H2O, Br2(0.034 moles),

[0090] 4.3 mL 30 wt% H2O2emulsion, 45 °C, 500 rpm, 5 mins Example 8. Effect of water content on bromine recovery in mixed solvent

[0091] It is known that the bromine recovery performance is dramatically compromised with the increase of water concentration in the cement when H2O2 is used as the oxidant. The water sensitivity of the bromine recovery performance of brominations in mixed solvent was investigated. Bromine recovery in hexanes / ethyl acetate mixed solvent was carried out with water concentration ranging from 0 to 12 wt%. As shown in Table 8, in pure hexanes, both the functional Br and BAE drops with the increase of water content. However, when ethyl acetate is added as a cosolvent, As illustrated in Figure 2, at the same water concentration, higher BAE is achieved when the bromine recovery is carried out in hexanes / ethyl acetate mixed solvent than in pure hexanes.

[0092] Table 8

[0093] 250.0 g HR, 25 wt% HR, Br2(0.034 moles), 4.3 mL 30 wt% H2O2 45 °C, 500 rpm, 5 mins

[0094] Example 9. Design of Experiments to determine efficiency of Br2usage

[0095] Due to the improved solubility of the oxidant in the organic phase, increase in functional Br and BAE are achieved when the bromine recovery is carried out in mixed solvent. With the addition of oxidant, Br2 usage is reduced due to the formation of Br2 regenerated from HBr. For bromine recovery performed in mixed solvent, it is feasible to further reduce the amount of Br2required to prepare Bl IR with 0.9 mol% functional Br, which is the typical functional bromine content of commercial bromobutyl. A design of experiments (DoE) was generated using Design-Expert 11 (Stat-Ease Minneapolis, MN, USA) to determine the amount of ethyl acetate and H2O2required to prepare BUR with 0.9 mol% functional bromine when the bromine usage is reduced. Three factors were investigated in the DoE: volume of bromine, volume of ethyl acetate and volume of 30 wt% H2O2. The volume range of the three factors is listed in Table 9. A response surface design (central composite) from the software Design Expert® is used for this experiment.

[0096] Table 9 Factors studied in DoE

[0097] As shown in Table 10, bromination reactions to produce bromobutyl rubber were conducted within the ranges described in Table 9. The functional Br is the response generated from the DoE. For the brominations from the DoE, no emulsifier Lutensol TO5 or water are added, and the bromine recovery were performed at 45 °C for 5 mins. The volume percentage of ethyl acetate ranges from 6.5 vol% to 27 vol% based on the total volume of hexane and ethyl acetate.

[0098] Table 10 List of experiment from DoE 25 wt% HR, 0 wt% H2O, 5 mins, 45 °C, 500 rpm

[0099] Figure 3 shows that increasing the volume of ethyl acetate in the mixed solvent is required when the bromine volume decreases. As apparent from Figure 3, to prepare a bromobutyl polymer with 0.9 mol% functional Br, an increase in the volume of ethyl acetate in the mixed solvent is required when the bromine volume decreases. Figure 4 shows that functional bromine increases when only the volume of bromine is increased in the reaction. Figure 5 shows that the functional Br increases when only the volume of ethyl acetate was increased in the reaction. The increase in functional bromine reached a plateau when 213 mL (18.6 vol%) or more ethyl acetate is added. The correlation between functional bromine and volume of hydrogen peroxide added to the bromination reaction is displayed in Figure 6. The functional Br remains unchanged when the volume of hydrogen peroxide increases from 4.3 mL to 5.3 mL.

[0100] The equation defining the relation between the mol% functional bromine content of the bromobutyl rubber based on the volume of bromine, denoted as “x”, and the volume of ethyl acetate, denoted in “y”, in the reaction. The equation is presented below as Equation 1.

[0101] Equation 1 : Functional Bromine Content

[0102] Functional Br = -0.021087+ (0.500726) (x)+ (0.002573)(y) - (6.05325E-06)(y2)

[0103] Thus, functional bromine is linear with respect to the volume of bromine and quadratic with respect to the amount of ethyl acetate. Using the optimization function of the DoE software, the minimum amount of ethyl acetate and hydrogen peroxide required to prepare bromobutyl rubber with 0.9 mol% functional Br are calculated if the bromine usage is reduced from 1.76 mL to 1.29 mL, which is a 26.7 % reduction. As illustrated in Figure 7, 212.5 mL of ethyl acetate (18.6 vol%) and 4.8 mL of 30% hydrogen peroxide are required to compensate for the reduction in Br2 usage based on Equation 1 . Example 10. Verification of DoE results

[0104] Experiments were performed using the optimized conditions generated by the DoE. As apparent in Table 11 , the conditions in P19 produced a bromobutyl polymer with a functional bromine content of 0.93% and a 26.7% reduction in bromine usage, which corresponds to the optimized conditions of the DoE.

[0105] Table 11.

[0106] 250.0 g HR, 25 wt% HR, 0 wt% H2O, 5 mins, 45 °C, 500 rpm

[0107] The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.

Claims

Claims:1 . A process for producing a halogenated isoolefin copolymer, the process comprising contacting an unsaturated isoolefin copolymer cement, the cement comprising an unsaturated isoolefin copolymer dissolved in an organic solvent with a cosolvent, under halogenation conditions, a halogenating agent, an oxidant, the cosolvent being a compound of Formula (I):R1-COO-R2 (I) where:R1 is a H or a C1-3 alkyl moiety; andR2 is a C1-5 alkyl moiety;2. The process of claim 1 , wherein the compound of Formula (I) is methyl formate, ethyl formate, propyl formate, isopropyl formate, n-butyl formate, sec-butyl formate, isobutyl formate, tert-butyl formate, n-pentyl formate, 1 ,1 -dimethylpropyl formate, 2,2- dimethylpropyl formate, 3-methylbutyl formate, 1 -methylbutyl formate, 1 -ethylpropyl formate, 1 ,2-dimethylpropyl formate, 2-methylbutyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, n-butyl acetate, sec-butyl acetate, isobutyl acetate, tertbutyl acetate, n-pentyl acetate, 1 ,1 -dimethylpropyl acetate, 2,2-dimethylpropyl acetate, 3- methylbutyl acetate, 1-methylbutyl acetate, 1-ethylpropyl acetate, 1 ,2-dimethylpropyl acetate, 2-methylbutyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, n-butyl propionate, sec-butyl propionate, isobutyl propionate, tertbutyl propionate, n-pentyl propionate, 1 ,1 -dimethylpropyl propionate, 2,2-dimethylpropyl propionate, 3-methylbutyl propionate, 1-methylbutyl propionate, 1-ethylpropyl propionate, 1 ,2-dimethylpropyl propionate, 2-methylbutyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, isopropyl butyrate, n-butyl butyrate, sec-butyl butyrate, isobutyl butyrate, tert-butyl butyrate, n-pentyl butyrate, 1 ,1 -dimethylpropyl butyrate, 2,2-dimethylpropyl butyrate, 3-methylbutyl butyrate, 1-methylbutyl butyrate, 1-ethylpropyl butyrate, 1 ,2- dimethylpropyl butyrate, 2-methylbutyl butyrate, or any mixture thereof, more preferably ethyl acetate, isopropyl acetate, t-butyl acetate, even more preferably, ethyl acetate.

3. The process of claims 1 or 2, wherein the amount of cosolvent is 1 - 43 vol%, more preferably 3.90 - 43 vol%, yet more preferably 14 - 19 vol% based on the total volume of organic solvent and cosolvent.

4. The process of any one of claims 1 to 3, wherein the oxidant comprises hydrogen peroxide, metal salts of hydrogen peroxide, organic peracids, metal salts of organic peracids, inorganic oxyacids, metal salts of inorganic oxyacids or mixtures thereof.

5. The process of any one of claims 1 to 4, wherein the oxidant comprises H2O2, NaHSOs, Na2S2O8, NaCIO, NaBrO, NaBrO3, NalO3, NaCIO, NaCIO3, NaCIO4, NalO4, NaOO(CO)R5where R5is a Ci_8alkyl moiety, KHSO5, K2S2O8, KCIO, KBrO, KBrO3, KIO3, KCIO3, KCIO4, KIO4, KOO(CO)R5, compounds that generate the aforementioned oxidants, or mixtures thereof.

6. The process of any one of claims 1 to 5, wherein the oxidant is an aqueous solution or an aqueous emulsion.

7. The process of any one of claims 1 to 6, wherein the cement has a water content of 0.1 wt% or greater based on total weight of the cement.

8. The process of claim 7, wherein the water content of the cement is 1.5 wt% or greater.9 The process of claim 7, wherein the water content of the cement is 1-30 wt%.

10. The process of claim 7, wherein the water content of the cement is 2-20 wt%.1 1. The process of any one of claims 1 to 10, wherein the unsaturated isoolefin copolymer cement is produced by polymerizing at least one isoolefin monomer and at least one copolymerizable unsaturated monomer in an organic diluent and removing the organic diluent and residual monomers by flash separation with steam.

12. The process of claim 1 1 , wherein the at least one isoolefin monomer is isobutene and the at least one copolymerizable unsaturated monomer is isoprene, p-methyl styrene or p-pinene.

13. The process of claim 12, wherein the at least one isoolefin monomer is isobutene and the at least one copolymerizable unsaturated monomer is isoprene, and the unsaturated isoolefin copolymer further comprises one or more additional copolymerizable monomers selected from the group consisting of a-methyl styrene, p-methyl styrene, chlorostyrene, cyclopentadiene, methylcyclopentadiene and indene.

14. The process of any one of claims 1 1 to 13, wherein the organic diluent comprises methyl chloride.

15. The process of any one of claims 1 to 14, wherein the halogenating agent is Br2.

16. The process of any one of claims 1 to 15, wherein the unsaturated isoolefin copolymer is present in the reaction medium in an amount of 10-33 wt%, based on total weight of the reaction medium.

17. The process of any one of claims 1 to 16, wherein the contacting the unsaturated isoolefin copolymer cement with the halogenating agent is conducted for 1-60 minutes at a temperature in a range of 20-70 °C, preferably 20-45 °C.

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