IONIC CONTAMINANTS REMOVAL FROM POLYMER CEMENTS USING A MOLTEN COMPONENT

Abstract: The present invention provides a process for removing ionic contaminants from a polymer cement containing ionic contaminants comprising: i) contacting the polymer cement with a molten component capable of reacting with the ion contaminants; and ii) separating the molten component from the polymer cement so obtained.

Description: IONIC CONTAMINANTS REMOVAL FROM POLYMER CEMENTS USING A MOLTEN COMPONENT The present invention relates to a process for removing ionic contaminants from polymer coments. Many polymerisation operations utilize a metal catalyst. In some instances where the productivity is extremely high or where the end use does not require pure polymer, the metal can simply be left m the composition. However, in many instances the metal must be removed before the polymer can be uti ized. Filtration has long been known as a method of removing insoluble metal contaminants. However, filtration of viscous polymer solutions is generally slow and expensive. It is well known to extract metal with aqueous solutions of acids or chelates. This approach is frequently unsatisfactory because of emulsion formation, requirements of extended setting times, or the saturation of the organic phase with water. Also polymers, particularly elastomers, have limits on how harshly they can be treateα without decomposing. It is an object of the present invention to provide a process for removing ionic contaminants from polymer cements . Accordingly, the present invention provides a process for removing ionic contaminants from a polymer cement containing ionic contaminants comprising l) contacting the polymer cement with a molten component capable of reacting with the ionic contaminants; and n) separating the molten component fror the polymer cement so obtained. In this way emulsion formation can advantageously be avoided. In Figure 1 a flow diagram is shown of a polymerisation process including initiator removal followed by hydrogenation and polymer cement recovery; and in Figure 2 a flow diagram is shown of an alternative embodiment of the present invention wherein polymer is produced, hydrogenated and thereafter metal contaminants are removed. In accordance with the present invention it has been found that the use of a molten component such as a bisulphate salt for removing ionic contaminants such as lithium catalyst residue from polymer solutions avoids emulsion formation. This has the further benefit of allowing easier separation after the treatment is complete since the molten phase is substantially more dense than the organic phase. Further, rather than having to accept a trade-off m effectiveness m order to avoid the introduction of large amounts of water, the molten system has more capacity to remove contaminants than an aqueous composition has. The molten component can be any material which is liquid under the conditions employed for the ionic contaminants removal and which is capable of reacting with the contaminants without significantly harming the polymer. Suitably, the molten component is a salt or a salt hydrate. Acid salts, organic acids, chelating agents, and eutectic mixtures of salts are suitable. Initiator removal from lithium catalysed elastomers can suitably oe carried out at a temperature in the range of from 30 to 150°C, preferably at a temperature m the range of from 50 to 80°C, and more preferably at a temperature in the range of from 60 to 70°C. Thus, sodium bisulphate monohydrate whicn melts at 58.5°C is ideally suited for such a reaction because of its melting point and its ability to provide a source of acidic protons. Salts such as mono basic sodium phosphate dihydrate (sodium dihydrogenphosphate dihydrate), sodium orthophosphite pentahydrate, sodium acid phosphite pentahydrate, and sodium sulphate decahydrate can also be used but are less desirable because of larger amounts of water of hydration. In accordance with the present invention undesirable ionic contaminants can be removed from any polymer cement whether a true solution or a dispersion of polymer m a liquid diluent. The ionic contaminants may be the same type of ionic contaminant or they may be different types of ionic contaminants. Generally, the present process is utilized to remove metal ions from solutions of polymer in organic solvents or in the monomer utilized m preparing the polymer. The impurities removed are normally metallic ions from a polymerisation catalyst or from catalyst used for subsequent treatment such as hydrogenation, although the invention is applicable to the removal of any other undesirable ions, especially cations, including components such as ammonium ions. Thus, the metal ions which can be removed from the polymer cement in accorαance with the present invention include lithium, nickel and aluminium ions. In instances where metal may be present in metallic form, i.e. zero valent metal, the composition can be subjected to an oxidation treatment to convert the metal to a metal ion. There must be sufficient contact between the molten component and the ionic contaminant being removed to ensure that a chemical reaction can take place. Presumably the removal proceeds by ion exchange as shown by the following exemplary equation wherein an excess of sodium bisulphate monohydrate ana a solution of elastomer prepared using a dilithium initiator followed by ethylene oxide to terminate the reaction and introduce an oxygen at each end between the lithium and the polymer chain. 2NaHSθ4-H2θ(l) xs + Lι-0~O-Lι → 2NaLιSθ4 + HO-OH + xsNaHSθ4-H2θ As noted above in the case of contaminants in the metallic state such as nickel remaining from a hydrogenation reaction, oxidation may be required prior to extraction as depicted below. Nι° + H2O + l/20 2 → Nι +2 + 20H ~ then 2NaHS04-H2θ + Nι +2 + 20H ~ →Na2Nι(Sθ4)2 + 2H20. After the ion exchange, or neutralization of the lithium alkoxide with the sodium bisulphate monohydrate or other suitable molten salt, the resulting sodium lithium sulphate can be dissolved in the molten excess sodium bisulphate monohydrate. The molten salt, being more dense than the organic phase allows rapid phase separation and avoids the emulsion problems which would be encountered if an aqueous extraction system were utilized. The process can suitably be carried out on either a continuous or batch basis with contact time as little as 1 minute or as much as 24 hours. Preferably, the contact time is in the range of from 5 minutes to 5 hours, more preferably in the range of from 10 minutes to 2.5 hours . The contacting can be carried out by stirring, shaking or tumbling using static mixers, mixer-settlers, centrifugal contactor or other conventional devices. A continuous process can be used whereby the two phases are passed cocurrently or countercurrently, for instance through a column equipped with rotating paddles. Whether a continous or batch process is used at the conclusion of the reaction, the material is simply allowed to settle which occurs very quickly because of the density of the molten phase. At this point, the two phases may be separated by any conventional means such as decantation or draining off of the lower phase in either a batch or continuous mode. Preferably the separation is effected by decantation using a εightglass or conductivity probe to detect the interface. The molten component will normally be used in an excess relative to that needed to react with the ionic contaminants so as to provide a more dense continuous liquid phase to contain the removed material. Thus, the ratio of molten component to impurities can be m the range of from 2:1 to 200:1 based on equivalents, which in the case of sodium hydrogen sulphate monohydrate to remove lithium ions is the same thing as being based on moles. Preferably, an equivalent ratio in the range of from 2:1 to 100:1 would be utilized. More preferably, an equivalent ratio in tne range of from 2:1 to 30:1. Actually, the upper limit is set only by economic conditions since anything more than 200:1 would offer little extraction advantage and would be more expensive. Polymers produced by alkali metal initiated polymerisations are sometimes used without any further treatment prior to recovery from the reaction mixture. Frequently, however, a polymer with reduced aliphatic unsaturation is desired which necessitates a hydrogenation step. This is preferably carried out prior to polymer recovery and utilizes a catalyst which can adα additional metals to the reactior composition. In some instances it is believed that the removal of alkali metal from a polymer solution generated by anionic polymerisation, prior to its hydrogenation, is beneficial. Accordingly, this invention can be utilized to remove metal contaminants such as lithium ions immediately after the polymerisation followed by separation of the phase containing the removed ionic contaminants and either direct recovery of the polymer or hydrogenation of the polymer prior to recovery. Particularly with dilithium-imtiated polymerisations where it is desired that the ultimate product be hydrogenated it is desirable to utilize the present invention to remove the lithium ions prior to hydrogenation. Hydrogenation techniques are for instance set out in U.S. 3,700,633 and U.S. 4,970,254 which are hereby incorporated by reference. Alternatively, it is possible to carry out the hydrogenation in the presence of alkali metal initiator and thereafter remove both the alkali metal initiator and the hydrogenation catalyst cations. It is sometimes desirable to incorporate functional groups at the ends of polymer chains, particularly elastomeπc polymer chains. This can be done with dilithium initiators simply by adding a terminating agent such as ethylene oxide which gives terminal lithium-oxygen structures at each end of the polymer. However, such polymers tend to form gels. Polymers formed from monolithium initiators can be terminated with ethylene oxide to give a OLi structure at one end which can be utilized for incorporating a functional group, but this leaves the other enα without a functional group. Recently, a technique nas been developed to provide functional groups at each end, utilizing what is called a protected functional initiator (PFI) . Such techniques are described in U.S. 5,416,168, and WO 91/12277 which are hereby incorporated by reference. These processes utilize an initiator having the structure R'OR'Li where R" is a protecting group, i.e. R3SιOR'Lι where the R groups are alkyl or a pair of alkyl groups and hydrogen and R' is an alkylene group. After the polymerisation is complete, termination with ethylene oxide results in the conventional LiO-polymer structure at one end and results in no change at the other end, since it is protected by the protecting group. Thereafter the protecting silyl group can be removed by a technique called "αeprotection" . It has been found in accordance with the present invention that in such protected functional initiator systems the employment of the molten component results in "deprotection" and removal of the undesirable metal contaminants. This overall process can be exemplified as follows where the precursor to the protected functional initiator is produced from tπmethylsilyl chloride and 3-chloro-2, 2-dιmethylpropanol . This product is reacted with litnium to give the initiator. Polymer is then formeα from a monomer such as 1, 3-butadιene and the reaction terminated with ethylene oxide. A molten component is then utilized m accordance with this invention to "deprotect" thus removing tne organosilyl group from one end and removing the lithium from the other. This can be viewed broadly as follows: R-OR-T ^~^ M Oϋ Cpr0teα» HO — κ ι /<^ /NI OH This can be viewed more speci f ical ly as follows - The polymer present m the polymer cement is suitably made by polymerising a monomer selected from the group consisting of conjugated dienes, monovmyl- aromatic hydrocarbons or mixtures thereof with a protected functional initiator as described hereinbefore. By polymer cement is meant polymer dissolved in a solvent which can be the monomer or other suitable solvent. Suitably, the polymer is selected from the group consisting of polybutadiene, polyisoprene, butadiene-isoprene copolymers, butadiene- styrene copolymers and isoprene-styrene copolymers. Preferably, the polymer comprises a block copolymer composition comprising at least one poly (monovinyl- aromatic hydrocarbon) block and at least one poly(conjugated diene) block. In Figure 1 there is shown, for illustrative purposes, one embodiment of the present invention wherein monomer, solvent and catalyst are introduced via feed line 10 into a reaction zone formed by reactor 12. The reaction mixture is stirred by means of a blade 14 which is rotated by shaft 16. Polymer cement comprising lithium terminated polymer and solvent are withdrawn by a first transfer line 18 and introduced into a lithium removal zone formed by contact vessel 20, contents of which are mixed by agitator means 22 which is similar to shaft 16 and blade 14. Molten sodium bisulphate monohydrate is transferred from a storage zone formed by storage vessel 24 to contactor vessel 20 via a second transfer line 26. The sodium bisulphate monohydrate is heated to a molten condition in vessel 24 by conventional heating means not shown. A heavier lower phase of excess sodium bisulphate monohydrate containing sodium lithium sulphate as a result of removal of lithium from the polymer cement is withdrawn from a contactor vessel 20 via lithium containing salt removal line 28. A portion of partly spent used salt can be recovered via first recovery line 30 controlled by valve 31 while the salt necessary for Ni and AC removal is transferred via third transfer line 32 to a hydrogenation catalyst removal zone formed by catalyst removal vessel 34. If desired, excess molten salt can be used so as to give a higher salt to polymer cement ratio m contact vessel 20. If this is done, the excess can be removed via line 35 controlled by valve 37 and recycled to storage vessel 24. The contents thereof are mixed by means of mixing means 36 which is similar to the shaft 16 and blaαe 14. This catalyst removal can be done by conventional means such as organic or unorgamc acids but is preferably done by means of contact with additional molten material such as that used for the lithium removal, i.e., molten sodium bisulphate monohydrate. The sodium bisulphate monohydrate introduced as previously shown via line 32 can be reheated if necessary by means of conventional heating means not shown. The heavier molten excess sodium bisulphate monohydrate phase containing dissolved sulphates of lithium, nickel and aluminum is withdrawn via hydrogenation catalyst containing salt removal line 38 and finished polymer cement removed via product recovery line 40. If desired, catalyst removal vessel 34 can be operated using an excess of the molten salt so as to give a higher salt to polymer cement ratio. This excess is then withdrawn via line 42 controlled by valve 44 and recycled to storage vessel 24. The remaining partly spent salt is then recovered via line 46 controlled by valve 48. Make-up salt is introduced via make-up line 50. This can either be new salt or salt recovered via lines 30 and/or 46 which has been purified. Since it is desirable in lithium initiated elastomer polymerisations to maintain essentially anhydrous conditions to avoid premature termination of the chains, and since water in the polymer cement is undesirable because of the potential for emulsion formation, it is preferred to maintain essentially anhydrous conditions throughout the system. Accordingly, the polymer cement effluent from the lithium removal zone can optionally be transferred via fourth transfer line 49 to a drying zone defined by drying vessel 51 having an agitator means 53. Sodium bisulphate from a holding zone defined by holding vessel 4 1 is transferred via fifth transfer line 55 to drying vessel 51 where it absorbs any water thus producing sodium bisulphate monohydrate which is transferred via sixth transfer line 57 to storage vessel 24. Polymer cement either directly from contactor vessel 20 via line 59 controlled by valve 63 or from optional drying vessel 51 is introduced into a hydrogenation zone formed by hydrogenation vessel 52 via seventh transfer line 54 where it is contacted with a catalyst such as a conventional nickel aluminum hydrogenation catalyst and with hydrogen, all of which can be introduced via introduction means 56 which can be a single line or a multiple lines. After conventional contact with the hydrogenation catalyst to effect conventional hydrogenation, the thus hydrogenated polymer cement is withdrawn via hydrogenated polymer withdrawal line 58 and introduced into the hydrogenation catalyst removal vessel 34. Alternatively, other water removal methods can be employed although this would give up the advantage of recycle to the Li removal step. In Figure 2, it is shown that a polymer cement from reactor 12 is introduced into hydrogenation vessel 52 via line 60 which is equivalent to line 54 of Figure 1, it being understood that there is no initial lithium removal step as m Figure 1 and generally no drying step either since the effluent should be dry at this stage. Effluent from hydrogenation vessel 52 is removal via line 58 and introduced into a zone for combined catalyst removal and deprotection formed by deprotection vessel 61. Sodium bisulphate monohydrate is introduced from an alternative storage zone defined by alternative storage vessel 62 via eighth transfer line 64 into the deprotection vessel 61 where it is contacted witn the polymer cement by means of agitator 66. A heavier molten phase of excess soαium bisulphate monohydrate containing both lithium from the deprotection and nickel and aluminum hydrogenation catalyst is withdrawn via metal containing salt removal line 68 and polymer cement is withdrawn via alternative product removal line 70. Deprotection vessel 61 can be operated with an excess of molten salt if desired so as to give a higher salt to polymer cement ratio in deprotection vessel 61. This excess is then withdrawn via line 72 and recycled to alternative storage vessel 62 via line 72 controlled by valve 74. Partially spent salt is removed via line 76 controlled by line 78 for recycle, discard or purification. Thus, m accordance with this embodiment of the present invention, α-ω-diol polymers are produced by the use of dilithium initiators or protected functional initiators. One family of PFIs produces hydroxy functionality in polymer molecules by hydrolysis of a protecting silanol group to produce the terminal alcohol. As shown in Figure 2, this embodiment of the invention makes possible the concurrent (1) hydrolysis of the protecting group to produce OH terminated polymer; (2) removal of metal incorporated during synthesis of the polymer (Li) and (3) removal of metals introduced during optional hydrogenation (Ni and Al) . The present invention will now be illustrated by means of the following Examples. EXAMPLES Example 1 Removal of lithium from polymer cement before hydrogenation. A jacKeted reaction kettle was first charged with 613 g of a 20% wt solution of a sec-butyllithium initiated, butadiene-based, mono-polymer in cyclohexane, and 68.7 g of sodium bisulfate monohydrate. The mixture was then stirred at 500 rpm with a paddle stirrer and heated to 65°C where the hydrated salt was molten. The mixture was stirred in this manner for 2 hours and then allowed to cool. The lithium content of the organic phase was reduced from 359 ppm to 7 ppm, and was easily hydrogenated to remove 97o of the unsaturation. Example 2 Removal of lithium, nickel, and aluminum from polymer cement; with simultaneous production of hydroxide functionality by hydrolysis of a silanol protecting group In a similar manner, 410 g of 20° cyclohexane solution of a polymer produced by polymerising butadiene with a silicon-base protected functional initiator was placed in a jacketed kettle with 46.5 g sodium bisulfate monohydrate. The mixture was heated to 64C where the salt was molten and stirred while slowly bubbling a gas mixture of 5% oxygen in nitrogen through the solution. The levels of residual metals in the solution were reduced as shown: Pre-treatment Post-treatment Li 169 ppm 5 ppm Ni 59 ppm < 2 ppm Al 62 ppm < 2 ppm Simultaneously the silicon-based protecting group had been completely hydrolysed as determined by proton NMR and HPLC. Example 3 Removal of Li , Ni , and Al from a polymer cement by sodium dihydrogen phosphate dihydrate. 600 g of a 20" solution of a polymer produced by polymerising butadiene with a silicon-based protected functional initiator was contacted with 60 g of sodium dihydrogen phosphate dihydrate and heated to 73°C where the salt was molten and stirred in like manner for 6 hours. Treatment with the phosphate salt produced substantial reductions in the level of residual metals as shown. Pre-treatment Post-treatment Li 390 ppm 61 ppm Ni 181 ppm 96 ppm Al 165 ppm 86 ppm It will be clear from the above that in accordance with the present invention ionic contaminants can very attractively be removed from polymer cements.

Claims: C L A I M S 1. A process for removing ionic contaminants from a polymer cement containing ionic contaminants comprising l) contacting the polymer cement with a molten component capable of reacting with the ion contaminants; and ii) separating the molten component from the polymer cement so obtained. 2. A process according to claim 1, wherein the ionic contaminants comprise lithium, nickel and aluminium ions. 3. A process according to claims 1 or 2, wherein the polymer is selected from the group consisting of polybutadiene, polyisoprene, butadiene-isoprene copolymers, butadiene-styrene copolymers and isoprene-styrene copolymers. 4. A process according to any one of claims 1 to 3, wherein the molten component is present in an amount to give a mole equivalent ratio of molten component to ionic contaminant m the range of from 5:1 to 100:1. 5. A process according to any one of claims 1-4, wherein the polymer cement is contacted with the molten component at a temperature in the range of from 50 to 80°C. 6. A process according to any one of claims 1 to 5, wherein the molten component is a salt or a salt hyαrate. 7. A process according to any one of claims 1 to 6, wherein the molten component is sodium bisulphate monohydrate, the ionic contaminant is lithium and wherein the mole equivalent ratio of the sodium bisulphate monohydrate to lithium is in the range of from 10:1 to 30:1. 8. A process according to any one of claims 1 to 7, wherein the contacting is carried out for a period of time in the range of from 5 minutes to 5 hours. 9. A process according to any one of claims 1 to 8, wherein the polymer cement comprises a lithium initiated polymer in cyclohexane solution which is contacted with molten sodium bisulphate monohydrate for a period of time in the range of from 10 minutes to 2.5 hours at a temperature within the range of from 50 to 80°C, whereafter by liquid-liquid phase separation an upper polymer phase having a reduced content of lithium as a result of ion exchange with the molten sodium bisulphate monohydrate is obtained.

Inventors: MALVEN WILLIAM CHARLES, POTTER MICHAEL WAYNE, VEITH CARY ALAN, MALVEN, WILLIAM, CHARLES, POTTER, MICHAEL, WAYNE, VEITH, CARY, ALAN
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1997
Main classification: C08C2
IPC codes: C08C2, C08F6