Polyisobutylene production process with improved efficiencies and/or for forming products having improved characteristics and polyisobutylene products produced thereby

Abstract

A process for production of polyisobutylene includes subjecting a reaction admixture comprising isobutylene, a diluent for the isobutylene, which may be isobutane, and a catalyst composition, that may include a BF.sub.3/methanol catalyst complex, to reaction conditions suitable for causing at least a portion of the isobutylene to undergo polymerization to form a polyisobutylene product including polyisobutylene molecules. At least a fraction of the polyisobutylene molecules thus produced have alpha position double bonds and the polyisobutylene product has a number average molecular weight (M.sub.N) and a polydispersity index (PDI). The concentration of the diluent in the reaction admixture may be manipulated to control or change any one or more of (a) the relative size of the fraction, (b) the number average molecular weight of the product, (c) the polydispersity index of the product and (d) the relative size of the portion. The diluent concentration may be held constant to maintain any one or more of such characteristics constant.

Claims

1. A process for production of polyisobutylene comprising: subjecting a reaction admixture comprising isobutylene, a diluent for said isobutylene and a catalyst composition to reaction conditions in a reaction zone suitable for causing at least a portion of said isobutylene to undergo polymerization to form a polyisobutylene product including polyisobutylene molecules, at least a fraction of said polyisobutylene molecules having alpha position double bonds, said polyisobutylene product having a number average molecular weight and a polydispersity index; choosing a diluent concentration corresponding to a pre-selected value of at least one parameter selected from the size of the fraction or the molecular weight; maintaining the admixture at said chosen diluent concentration to thereby hold said parameter at said pre-selected value; treating said product to remove diluent and unreacted isobutylene therefrom; and recycling at least one of the diluent and the unreacted isobutylene back to said zone, wherein said diluent consists essentially of isobutane and a C.sub.3-C.sub.16 1-alkene.

2. The process as set forth in claim 1, wherein the diluent comprises a mixture of isobutane and 1-butene.

3. A process for production of polyisobutylene comprising: subjecting a reaction admixture comprising isobutylene, a diluent for said isobutylene and a catalyst composition to reaction conditions suitable for causing at least a portion of said isobutylene to undergo polymerization to form a polyisobutylene product including polyisobutylene molecules, at least a fraction of said polyisobutylene molecules having alpha position double bonds, said polyisobutylene product having a number average molecular weight and a polydispersity index, said polyisobutylene product having at least one parameter that is variable as a function of the concentration of said diluent in said admixture, said at least one parameter comprising (a) the relative size of said fraction, (b) the number average molecular weight of said product, (c) the polydispersity index of said product or (d) the relative size of said portion; choosing a diluent concentration corresponding to a pre-selected value of at least one parameter; and maintaining the admixture at said chosen diluent concentration to thereby hold said parameter at said pre-selected value, wherein diluent comprising a C.sub.3-C.sub.16 1-alkene and optionally a C.sub.3-C.sub.16 alkane is provided to a reactor independently of fresh isobutylene monomer.

4. The process according to claim 3, wherein the independently provided diluent consists essentially of isobutane and a C.sub.3-C.sub.16 1-alkene.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in detail below wherein like numerals and letters indicate like features and wherein:

(2) FIG. 1 is a schematic diagram illustrating a laboratory reactor arrangement set-up for conducting isobutylene polymerization processes in accordance with the invention;

(3) FIG. 2 is a graph showing the variation of polymer alpha (vinylidene) double bond content with changing diluent concentration (data at 40° F.);

(4) FIG. 3 is a graph showing molecular weight (M.sub.N) and polydispersity index (PDI) trends with changing diluent concentration (data at 40° F.) (filled symbols show M.sub.N values—left axis; unfilled symbols show PDI—right axis);

(5) FIG. 4 is a graph showing conversion trends with changing diluent content;

(6) FIG. 5 is a schematic diagram depicting a PIB production process equipped for continuous recycling of isobutylene and/or diluent;

(7) FIG. 6 is a graph showing variations in M.sub.N with changing diluent (isobutane) concentration;

(8) FIG. 7 is a graph showing variations of viscosity (v) with changing diluent (isobutane) concentration;

(9) FIG. 8 is a graph showing variations of PDI with changing diluent (isobutane) concentration; and

(10) FIG. 9 is a graph showing variations of alpha (vinylidene) double bond content with changing diluent (isobutane) concentration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) Reference will now be made in detail to preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

(12) The concepts and principles of the invention described herein are generally applicable in connection with each of the various PIB reactors and PIB production processes illustrated in the '913, '999, '152 and '401 patents discussed above, and should be applicable in connection with all reactors and reactor systems that are used for the production of highly reactive and/or mid-range vinylidene content PIB polymer products using liquid phase polymerization procedures. In this regard, it is to be noted that the feedstock for such reactors may comprise either isobutylene or an admixture of isobutylene and a suitable non-reactive diluent (solvent) therefor. Suitable feedstocks are described generally in the '913, '999, '152 and '401 patents discussed above. A particularly preferred feedstock comprises a high purity isobutylene monomer having a composition as set forth below in Table 2.

(13) TABLE-US-00002 TABLE 2 Concentrations of individual components of Isobutylene stream Component Weight % Methane 0.026 Ethane  0.0006 Propane  0.0024 Propylene 0.027 Isobutane 0.064 N-butane 0.010 Butene-1 0.016 Isobutylene 99.84  T-butene-2 0.010 C-butene-2 0.063 1,3 butadiene 0.007 C.sub.5 + 0.007

(14) In accordance with the concepts and principles of the invention, in the liquid phase production of polyisobutylene, an important and formerly unknown relationship between diluent concentration and the alpha vinylidene content of the product has been discovered. That is to say, in accordance with the concepts and principles of the invention, it has been discovered that an increase in diluent concentration in the reaction admixture generally results in higher alpha position (vinylidene) double bond concentration in the product. Moreover, in the same manner, an increase in diluent concentration leads generally to greatly improved (narrower) polydispersity indices. In these regards, and in further accordance with the invention, the diluent content in the reaction admixture may be 50 weight % or less, may desirably be 30 weight % or less, and may optimally be 10 weight % or less. Ideally, the desired diluent for isobutylene may be isobutane. However, in a more general sense, the desirable diluent should simply be capable of dissolving both isobutylene and polyisobutylene and should be inert to the polymer forming reactions taking place in the reactor. In this latter regard, a C.sub.3-C.sub.16 alkane or alkene, or a mixture of such substances, may be used as the diluent. Desirably, the diluent may be a C.sub.3-C.sub.16 1-alkene such as, for example, butene-1. In another sense, the diluent may advantageously comprise a mixture of hydrocarbons such as, for example, C.sub.4s and other light hydrocarbons.

(15) As mentioned above, the processes of the present invention may generally and suitably be used in connection with the equipment and processes described in the '913, '999, '152 and '401 patents. However, for further clarity, the invention will be described here in connection with a simplified experimental reaction system 10 shown schematically in FIG. 1.

(16) With reference to FIG. 1, the experimental reaction system 10 may desirably include a loop reactor 10, a recirculation pump 12, an isobutylene monomer inlet 14 which may include a pump 16, a diluent inlet 18 which also may include a diluent pump 20, an inlet 22 for the catalyst complex (initiator), and chilling system 24 to remove the heat of the exothermic polymerization reaction. As shown, the loop reactor 10 may include segments 10a, 10b and 10c as well as a pipe 26 which interconnects segments 10a and 10c as shown and provides a place for connection of pump 12. And as can be seen in FIG. 1, a chilling system 24 for the system may desirably include cooling jackets 24a, 24b and 24c respectively for the reactor segments 10a, 10b and 10c, a chilling fluid inlet 28 and a chilling fluid outlet 30. In addition, the system may also include a feedstock inlet 32, where the isobutylene monomer and a diluent are received and admixed for introduction into the reactor, and a product outlet 34 where the crude polymer product is withdrawn from the system.

(17) In operation, a reaction mixture comprising isobutylene, a diluent for the isobutylene and a catalyst composition are recirculated by pump 12 through reactor segments 10a, 10b and 10c and pipe 26 while reaction conditions suitable for causing at least a portion of the isobutylene to undergo polymerization to form a polyisobutylene product including polyisobutylene molecules are maintained in the reactor 10. In the meanwhile, isobutylene and a diluent therefor are introduced into the reactor 10 via inlet 32, catalyst composition (initiator) is introduced into the reactor via inlet 22 and crude product is withdrawn from the system via outlet 34.

(18) Using the system 10, experiments were conducted maintaining the total flow rate of monomer to the reactor loop at 100 mL/min. Reactions were carried out at temperatures of 40° F. and 60° F. The pressure in the reactor loop was maintained at 200 psi. The internal diameter of the reactor tubes was 0.305″ and the total reactor volume was 228 cm.sup.3. Catalyst (initiator) flow was controlled at 0.02 mL/min such that the reaction set point was maintained. The recirculation rate in the reactor loop was 2 gpm. The catalyst composition comprised a complex of BF.sub.3 and methanol wherein the molar ratio of BF.sub.3 to methanol was 1:1. No modifier (methanol) was added to the reactor separately from the catalyst complex, although such a step might be desirable under some conditions. In this latter regard, the separate addition of modifier is described in detail in the '152 patent discussed above. A high purity isobutylene (purity >99.5 weight %) was used as the feedstock and a relatively high purity isobutane (purity 95 to 98 weight %) was used as the diluent.

(19) Experiments were conducted at various diluent concentration levels to study the effect of diluent concentration on alpha position double bond content, molecular weight (M.sub.N) and polydispersity index (PDI) of the product. In these experiments, the diluent level was varied between 0 and 27 weight %.

(20) The chain end concentrations of the isomers were measured using .sup.13C NMR spectroscopy. The molecular weight measurements were made using size exclusion chromatography (SEC).

(21) The results of the experimentation are illustrated in FIGS. 2, 3 and 4. FIG. 2 shows variations in alpha position double bond isobutylene isomer content with changes in isobutane diluent concentration at 40° F. And as can be seen in FIG. 2, alpha isomer content increases with increased diluent concentration. Thus it is clear that the alpha isomer content of the product may be increased simply by increasing the concentration of the diluent in the reaction admixture. Also it is clear that if other conditions dictate, the alpha isomer content of the product may be decreased simply by decreasing the concentration of the diluent in the reaction admixture.

(22) With reference to FIG. 3, the influence of diluent concentration on number average molecular weight (M.sub.N) and polydispersity index (PDI) can be seen. In FIG. 3, M.sub.N values are shown on the left axis and are represented by the filled symbols, while PDI values are shown on the right axis and are represented by the unfilled symbols. Of particular interest is the large drop in PDI at almost constant molecular weight between 0 and 10 wt % of diluent (isobutane) concentration. This may be of particular benefit in meeting the commercially valuable polydispersity specifications for PIB polymers. Thus it is clear that the PDI of the product may be decreased simply by increasing the concentration of the diluent in the reaction admixture. Also it is clear that if other conditions dictate, the PDI of the product may be increased simply by decreasing the concentration of the diluent in the reaction admixture. Furthermore, it is clear that the molecular weight of the product may be decreased simply by increasing the concentration of the diluent in the reaction admixture. Also it is clear that if other conditions dictate, the molecular weight of the product may be increased simply by decreasing the concentration of the diluent in the reaction admixture.

(23) With reference to FIG. 4, it can also be seen that the rate of conversion of isobutylene into polyisobutylene increases with increasing diluent content. This perhaps can be attributed to the fact that higher diluent concentrations in the reactor may provide improved heat transfer characteristics.

(24) As can be seen from the foregoing, alpha isomer content increases, polydispersity decreases, conversion increases and molecular weight decreases with increasing isobutane diluent concentration. Trends similar to those observed at 40° F. were also observed when the polymerization reactions were conducted at 60° F. Tabulated experimental data is reported below in Tables 3 and 4. As can be seen, these Tables also show the concentration of alpha and beta isomers in the polyisobutylene product obtained.

(25) TABLE-US-00003 TABLE 3 Data showing the effect of diluent concentration on PIB properties at 40° F. Number Isobutane Average Concentration Concentration Diluent Molecular of Alpha of Beta Concentration Weight Polydispersity Isomer Isomer Other Conversion (wt %) (M.sub.N) Index (PDI) (Structure I) (Structure IV) Isomers Rate 0 3318 3.81 54.2 NA NA 17.9 5 3288 3.31 56.5 33.6 9.9 22.1 10 3155 2.47 59.9 32.3 7.8 24.6 15 2909 2.25 65.4 32.5 2.1 27.2 20 2724 2.22 73.41 18.1 8.4 29.1 27 1785 2.19 75.3 20.3 4.4 33.4

(26) TABLE-US-00004 TABLE 4 Data showing the effect of diluent concentration on PIB properties at 60° F. Number Isobutane Average Concentration Diluent Molecular of Alpha Concentration Concentration Weight Polydispersity Isomer of Beta Isomer Other Conversion (wt %) (M.sub.N) Index (PDI) (Structure I) (Structure IV) Isomers Rate 0 2249 2.71 53.0 NA NA 48.3 5 2373 2.23 54.4 34.8 10.8 52.3 10 2217 2.17 63.1 30.7 6.2 51.5 15 1637 1.91 69.5 25.3 5.2 57.5 20 1389 1.89 70.0 22.9 7.1 57.7 27 1109 1.85 73.3 17.6 9.1 62.3

(27) In further accordance with the concepts and principles of the invention, the process also may provide for the continuous recycle of diluent and/or unreacted isobutylene. Such a process is depicted schematically in FIG. 5. With reference to FIG. 5, a reaction admixture comprising isobutylene, a diluent for isobutylene (advantageously isobutane) and a catalyst composition (preferably a complex of BF.sub.3 and a complexing agent such as methanol) is subjected in reactor 200 to reaction conditions suitable for causing at least a portion of the isobutylene to undergo polymerization to form a polyisobutylene product including polyisobutylene molecules. The conditions in reactor 200 are such that at least a fraction of the thus produced polyisobutylene molecules in the product have alpha position double bonds and the polyisobutylene product has a number average molecular weight and a polydispersity index. Upon leaving the reactor 200, the crude polyisobutylene product is washed in a scrubber 202 to remove catalyst residue and is subjected to flashing in a crude flash zone 204 to remove diluent and unreacted isobutylene. The product is then appropriately beneficiated further in a flash unit 212 and delivered downstream via outlet 214. At least a portion of the diluent and unreacted isobutylene flashed in zone 204 may then desirably be continuously recycled overhead back to the reactor 200 via lines 206 and 208. The diluent concentration in the reaction admixture in reactor 200 may desirably be manipulated and/or kept constant at any given time at such a level that it provides maximum benefit to the process in maintaining a desired alpha isomer content as well as in maintaining a low PDI. This, of course, may be done by adding diluent via line 216. The feed rate of fresh isobutylene delivered via line 210 may then be determined by the isobutylene conversion rate in the reactor, i.e., the higher the conversion rate, the higher the rate of fresh isobutylene feed. In addition, whenever desired, the diluent concentration may be varied to alter the alpha isomer content of the product, the PDI of the product, the molecular weight of the product and/or the conversion rate. In this latter connection, it is noteworthy that the alpha isomer content of the product and the conversion rate vary directly with diluent concentration while product molecular weight and PDI vary indirectly with diluent concentration.

(28) Additional experimental data was gathered in connection with studies involving the synthesis of a highly reactive grade (alpha double bond content more than 80%) PIB using a scaled up version of a reactor which is set up essentially the same as the reactor 10. In connection with these studies, additional modifier is introduced essentially as described in the '152 patent. These studies reveal that it is greatly beneficial to operate the reactor using an isobutane diluent concentration of about 8-15 weight % and the following discussion is based on data derived therefrom.

(29) In these studies, a reaction temperature of about 27° F. was maintained employing a chiller temperature of about 5° F. The input flow rate (isobutylene+diluent) was approximately 26 gpm and the volumetric flow rate of the recirculation pump was about 1260 gpm.

(30) The catalyst flow rate was adjusted (ideally to between 0.03 and 0.05 weight % of the feed rate) such that a constant operating temperature was maintained. As per the '152 patent, the modifier was introduced separately into the reactor maintaining a methanol to catalyst ratio of 0.63:1 to synthesize a highly reactive (high vinylidene content) PIB product. In a highly reactive product, it is desirable for the molecular weight (M.sub.N), the PDI and the viscosity to be within certain limits, usually dictated by product specifications. One such product may have the following specifications: M.sub.N-2100 to 2500; PDI-1.6 to 2.2; Kinematic Viscosity (v)—1500 to 1750; and Alpha double bond content—Greater than 80 mole %. The usual aim of the manufacturing process is that all these specifications be met simultaneously.

(31) In connection with the foregoing, the Kinematic viscosity (v) was measured using Cannon Fenske tubes immersed in a viscosity bath (Koehler KV3000). The M.sub.N and PDI measurements were obtained using SEC measurements as described earlier. The values obtained for the different parameters are as shown in FIGS. 6 thru 9. The dark heavy lines on the graphs show the desired specification parameters.

(32) An essentially pure isobutane stream having a composition as set forth in Table 5 below was obtained from ISGAS for use in an effort to isolate the effects on PIB production of minor impurities in the isobutane diluent, although in a real practical sense it is generally not feasible to use such a material in a commercial operation. The total oxygenate content of the pure diluent stream was less than about 5 ppm (≈3.4 ppm methanol; ≈1.4 ppm MTBE).

(33) TABLE-US-00005 TABLE 5 Purity of individual components of Isobutane diluent (99.8% purity) Components Weight % Propane  0.02 Isobutane 99.79 N-butane  0.18

(34) The experimental set-up and conditions for these efforts were essentially the same as those described above in connection with reaction system 10. The experimental data obtained as a result of these efforts are set forth below in Table 6.

(35) TABLE-US-00006 TABLE 6 Product properties obtained using high purity Isobutane Alpha position Isobutane double diluent bond concentration Kinematic content weight % M.sub.N PDI Viscosity mole %  0 3292   4   3489 61.4  8 3197.7 2.55 2693 58.5 13 2946.9 2.48 2637 59.9 18 2883   2.43 2628 60.1 25 2751   2.29 2213 60.3

(36) It can be observed from Table 6 that the major advantage of being able to operate so as to produce a PIB having decreased polydispersity was achieved. That is to say, a substantial decrease in PDI and simultaneously in viscosity is achieved with increasing diluent concentration, while almost constant molecular weight is maintained. This is beneficial in a commercial sense for meeting both M.sub.N and PDI/viscosity specifications simultaneously. However, there is almost no change in the alpha double bond content with increasing isobutane diluent concentration as was observed in the case of lower purity isobutane.

(37) In view of the foregoing it is clear that the present invention provides a mechanism for greatly reducing both PDI and viscosity by increasing diluent concentration with no substantial corresponding decrease in molecular weight. In addition, both viscosity and PDI can be maintained within specifications while achieving a target molecular weight. This is especially important in the production of HR (high vinylidene) grades of PIB where controlling the polydispersity and viscosity within specifications is of paramount importance. Moreover, the use of a lower purity isobutane diluent resulted in higher alpha double bond content as compared to high purity isobutane diluent. This could be the result of the presence of other hydrocarbon components in the feed or could be due to the presence of oxygenates other than methanol. With regard to the foregoing, it seems to be more likely that the other oxygenates play a role in the increased vinylidene content. In accordance with our studies, the primary suspect is dimethyl ether. These oxygenates play a role similar to additional methanol that is added as a modifier. As is known, methanol is also an oxygenate which may be added in a controlled manner to regulate vinylidene content.

(38) It appears that the invention provides the greatest benefit when the PIB production process is operated using a diluent concentration in the range of from about 8 to about 15 weight %, beyond which the gains are diminished as M.sub.N starts to decrease, especially when a lower purity (industrial grade) isobutane diluent is employed.

(39) Although alpha position double bond content increases with increasing isobutane dilution (in the impure isobutane example), the more desired manner to control alpha content is by setting a suitable methanol to catalyst ratio. This is due to the fact that there usually is minimal control in an industrial setting over feedstock composition.