KR101072676B1 - Transition process in gas phase polymerization - Google Patents

Transition process in gas phase polymerization Download PDF

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KR101072676B1
KR101072676B1 KR1020100012277A KR20100012277A KR101072676B1 KR 101072676 B1 KR101072676 B1 KR 101072676B1 KR 1020100012277 A KR1020100012277 A KR 1020100012277A KR 20100012277 A KR20100012277 A KR 20100012277A KR 101072676 B1 KR101072676 B1 KR 101072676B1
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value
reaction
transition
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KR20110092702A (en
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한재혁
장호식
오상준
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삼성토탈 주식회사
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/18Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
    • B01J8/24Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08FMACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F10/00Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08FMACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00Processes of polymerisation
    • C08F2/34Polymerisation in gaseous state

Abstract

The present invention relates to the final value and instantaneous value of the polymer characteristic value due to the variation of the set value of the operating variable for controlling the density and the melt flow index, which are the polymer characteristics, in the transition process for converting the polymer characteristics during the polyolefin polymerization in the gas phase fluidized bed. By predicting the production value early in the conversion process and changing operating parameters during the conversion process, it provides a transition process that minimizes the production of transition grade products and makes it possible to achieve the desired physical properties within 3BTO without the production of poor grade products.

Description

TRANSFER PROCESS IN GAS PHASE POLYMERIZATION

The present invention relates to a final value of the physical property of a product in a polymerization reactor in a transition (conversion) process in which a setting value of a property control operating parameter is changed to control the properties of a polymer produced by a polymerization reaction in a gas phase polymerization reaction in a catalytic fluidized bed. The present invention relates to a transition process that can predict offset and instantaneous generation values to prevent off grade products that can occur in the transition process and to minimize transition grade products.

Controllable variables that affect the main physical properties of the polymers produced in the gas phase polymerization reaction are melt flow, expressed in density and melt index (MI).

Density is controlled by comonomers inserted into the main monomer, generally ethylene or propylene is used as the main monomer and ethylene or other than ethylene such as ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, etc. as the comonomer Alpha-olefins are used. The density is controlled by the comonomer / main monomer molar ratio, which mole ratio has a different operating range depending on the catalyst system properties used. In the gas phase polymerization reaction, when the density is 0.915 g / cm 3 or less, the sintering phenomenon of the polymers rapidly progresses to form sheets and molten masses, which causes the reaction operation to be impossible. Therefore, the comonomer / main monomer molar ratio needs to be adjusted so that the newly produced polymer in the reactor can be produced in a safe zone away from the dangerous zone close to the density.

The melt index is determined by the molecular weight of the polymer, and in the olefin polymerization reaction the molecular weight of the polymer is controlled by hydrogen, a chain transfer agent, substantially by the hydrogen / monomer molar ratio. The correlation of the melt index by hydrogen / monomer is very different depending on the catalyst system used. The melt index is also changed by the concentration of alkylaluminum used as catalyst activator.

In a commercial process for producing polymers, the process of transitioning from one grade to another is often done for the production of polymers with different property values. In this case, transition process grades, which are products between grades, are essentially generated, and defective grades outside of each grade range are generated upon incomplete manipulation of operational control variables (see FIG. 10). The efficient operation of commercial processes requires a technology that minimizes the production of transition process grades between grades and prevents the generation of defective grades.

The polymerization reaction using the gas phase fluidized bed has a longer residence time than other polymerization processes. Therefore, when switching from a certain grade in production to a specific grade with different properties, the BED change takes a long time, and the product generated during this time is treated as an out-of-grade product (transition stage product), causing loss. do. Therefore, to minimize this, traditionally overshooting method is used a lot. However, this method often causes reaction instability by entering the above-mentioned dangerous zones in which the properties of the instant product are detrimental to the production of polymers, and the method of accurately predicting the final properties from the initial properties is also unsatisfactory. . In addition, when the physical property conversion process is performed together with the conversion of a catalyst having a large difference in reactivity but not in a catalyst system having the same reactivity, it is difficult to obtain valid information from past data.

In polyolefin polymerization, Ziegler-Natta catalysts and metallocene supported catalysts are commercially used. The two catalysts have significant differences in the reactivity with hydrogen controlling the melt index and with the comonomer controlling the density. That is, the metallocene catalyst has a hydrogen reactivity of 500 to 1000 times higher than that of the Ziegler catalyst, and is 5 to 10 times higher in the copolymerization with the comonomer.

As described above, the conventional method of reducing the defective product by overshooting is easy to enter the dangerous area when the historical data is sufficient and maintains the linear relationship of the copolymerization reaction and the hydrogen reaction relationship that is gentle like the Ziegler Natta catalyst system. If not, it can be used. However, in the case of metallocene catalysts, the difference in reactivity with the existing catalysts is rapid, and the slope of the change in the physical properties of the gas phase composition ratio of hydrogen / ethylene, comonomer / main monomer, which is a control variable, is very rapid, and thus the metallocene in the Ziegler catalyst In the case of replacement with a catalyst or from a metallocene catalyst to a Ziegler catalyst, and in the operation of a metallocene catalyst, when the overshooting method is used, a large amount of defective grade products out of the normal physical area are rather produced. The likelihood of production increases, and reaction instability also increases. In particular, the Ziegler catalyst is not affected by factors other than the gaseous composition of hydrogen / ethylene in the control of the melt index, but in the case of metallocene catalysts, it is also influenced by the concentration in the reactor of alkyl aluminum and other reaction stabilizers, which are activators. Receive. Therefore, when the conventional overshooting method used for preventing the bad grade and reducing the transition product in the transition process when using the Ziegler catalyst is applied to the conversion of the physical properties of the metallocene catalyst, Due to the high copolymerization reactivity, the situation easily enters the danger zone, and especially when the melt index of the instant product is very low in the melt index control, a problem arises in that a large amount of gel is formed in the final product. Therefore, in the case of the operation of the metallocene catalyst, it is impossible to predict the final value of the variable for controlling the physical properties from other historical data. Therefore, there is a need for a new transition process method for the gas phase polymerization process.

Regarding the transition method of the gas phase fluidized bed polymerization reaction, US Pat. No. 5,627,242 discloses a method for controlling the gas phase fluidized bed polymerization reaction to perform the transition from the initial reaction to the target reaction. Some embodiments of the patent change the control variable to a predetermined median, and then change the variable to its target value to perform the transition while reducing the amount of poor grade product produced during the transition. However, the U. S. Patent No. 5,627, 242 does not suggest reducing the amount of bad grade product produced during the transition, and there is no suggestion on how to identify the generation of bad grade product or entry into the reaction risk zone.

U. S. Patent No. 6,846, 884 discloses a method of controlling resin properties during the preparation of a polyolefin, and in some embodiments cooperatively manipulates the reaction temperature in conjunction with a second process variable manipulation to control resin flow properties to transfer (e.g., one Is shifted from the polymer grade to another grade of polymer production), in this way minimizing the amount of bad grade material produced during the transition. The patent also describes a method of reducing the amount of poor grade polyolefins produced during the transition from the production of the first polyolefin to the production of the second polyolefin (during the continuous polymerization), wherein the second polyolefin is combined with the first polyolefin. Are prepared at different reaction temperatures. The target reaction temperature for preparing the second polyolefin is compared with the initial reaction temperature, after which the reaction temperature is changed by overshooting to a value approximately above or below the target temperature and the inlet of the reaction gas is controlled. If desired, the changed reaction temperature and gas composition can be maintained at an initial changed level until the average resin flow index of the total polyolefins in the reactor is within an acceptable range of the target resin flow index of the second polyolefin, at which point As the average resin flow rate approaches the target resin flow rate, the reaction temperature may be moved to the target reaction temperature. However, U. S. Patent No. 6,846, 884 does not propose a specific method for resetting reaction conditions to reduce the amount of poor grade material produced during the transition prior to performing the transition to another reaction in the middle of the transition step. .

U.S. Pat.No. 7,343,225 (Korean Patent Publication No. 10-2008-0019045) discloses a method for reducing poor grade products during reaction transition when using metallocene catalysts in gas phase fluidized bed reactors. The embodiment of the patent proposes to minimize instantaneous grades by identifying instantaneous and average generated values of resin properties during the transition process and reflecting them in the control parameter reset. However, the method does not reach the target within the commercially required 3BTO because the target time of arrival constant is typically more than four bed turn over (BTO). In addition, although the second transition step starts from the bed properties at the time of resetting when the control variable is reset, the final properties are expected, but the expected properties are assumed to be the final properties. In addition to errors in actual values and predictions, it is possible to reduce bad grade products, but the problem of excessive overshooting increases the possibility of entering the danger zone.

In the case of applying a sensitive catalyst system with a large variation in physical properties to physical property control variables such as a metallocene catalyst system in the gas phase polymerization process, the relationship between the operating variables and the property values applied at the previous operation time is difficult to be applied to the subsequent different operating modes. This is most often the case. Therefore, there is a need for a method capable of estimating the final value of the property value according to the change of the control variable at every operation. On the other hand, when the overshooting is excessively performed in the case of the metallocene catalyst as mentioned above, since the physical properties of the instantaneous polymer enter the inoperable region, it often causes reaction instability. There is a need for a systematic transition process in which the properties of instantaneous products are generated in the stable region while minimizing the generation of defective grades.

Also as a metallocene catalyst In the case of initiating a reaction in a gas phase fluidized bed reactor, the reaction is initiated by initiating catalyst injection with a gas phase composition for producing a resin product at a value close to the target physical property. In this case, the new reaction product has a low melt index. To prevent gel formation and sheet formation by low density, a melt index of 1g / 10min or more and a density of 0.920g / cm 3 or more are intended as a start-up target. In order to prevent gel formation and stability of reaction, it is advantageous to perform initial operation in the region of high melt index and high density, but this causes a problem of a large amount of defective grade products. Therefore, there is a need for a switching method that allows the initial operation in the area that does not cause the problem to reach the final target value at the minimum BTO.

Theoretically, after 3 BTO of the reactants in the reactor after the conversion of the catalyst or the change of the setpoint of the property control parameters, at least 95% of the resin in the bed must be replaced by the new product. Therefore, the operator's concern is that within 3BTO, the entire bed will be stably reached and replaced with the desired physical properties.

In order to solve the above problems, the present invention provides a final target property value by minimizing a transition step product while ensuring reaction stability without a bad grade product in a transition process for changing polymer properties in a gas phase fluidized bed polymerization process. To provide a transition process that reaches within 3BTO.

The present invention is stably within 3BTO without a bad grade product in the final target property value in the conversion step of converting the property control parameters, especially when applied to a metallocene catalyst system having a very high reactivity and sensitivity to the property control parameters compared to the conventional Ziegler catalyst. It is to provide a transition process that can be reached.

In addition, the present invention, when producing a polyolefin with a Ziegler catalyst in the gas phase fluidized bed, the reaction is terminated, the conversion to a metallocene catalyst in the reaction proceeds, it is possible to stably reach the target properties within 3BTO without poor grade product It is to provide a transition process.

According to the present invention, the transition process for changing the physical properties of the polymerization product in the gas phase fluidized bed polymerization process comprises the following steps (1) to (11):

(1) changing a set value of an operating variable for changing a property value;

(2) proceeding with the reaction under the change condition after changing the set value;

(3) calculating a bed change number from the reactant discharge as the reaction proceeds;

(4) calculating, from the bed change calculation step (3), the bed content of the new product in the bed created after the operating variable set point change step (1);

(5) estimating the final achieved physical properties using mixing rules from the calculated in-bed content of the new product;

(6) measuring the physical properties of the reactor effluent in which the reactants prior to the operating parameter setpoint change and the new product reactants are mixed;

(7) matching the measured property value trend line with the trend line obtained from the expected final reached property setting in step (5) to determine the property at 3BTO (bed turn over);

(8) determining a relationship between the operating conditions and the physical properties from the physical properties in the operating conditions before the setpoint change and the final achieved physical properties expected in the operating conditions after the setpoint change obtained in step (5);

(9) modifying the final attainable property target so as not to produce a poor grade product within 3BTO from the relation obtained in step (8), and determining operating conditions consistent with the changed target value;

(10) repeating step (1) to step (7) with the changed operating condition in step (9);

(11) maintaining altered operating conditions such that the reactants reach target properties within 3 BTO without producing poor grade products by repeating step (10).

In the transition process for changing the physical properties of the polymer in the gas phase fluidized bed polymerization process according to the present invention, the operating parameters are also referred to as control variables, and include one or more of gas phase composition, temperature, reaction pressure, catalyst composition, and catalyst activator. do.

In the transition process for changing the physical properties of the polymer in the gas phase fluidized bed polymerization process according to the present invention, the polymerization product is preferably polyolefin.

In the transition process for changing the physical properties of the polymer in the gas phase fluidized bed polymerization process according to the present invention, the physical properties of the polymerization product are density and melt flow characteristics.

In the transition process for changing the physical properties of the polymer in the gas phase fluidized bed polymerization process according to the present invention, a preferred catalyst system for use in the polymerization reaction is a metallocene catalyst having a structure represented by the following formula (I) supported on silica It is composed of a metallocene catalyst and a catalyst activator for polyolefin polymerization prepared by.

(THI) 2 R "MQ p (I)

Wherein THI is a substituted or unsubstituted tetrahydroindenyl derivative, and R ″ is a structural crosslink that imparts steric stiffness between two THI groups; M is from group IIIB, IVB, VB or VIB Is a transition metal of choice; Q is a hydrocarbyl group or halogen having 1 to 20 carbon atoms; p is a number having a valence of M-2.

Examples of preferred catalyst activators that can be used in the catalyst system are alkylaluminum compounds or aluminoxanes.

The gas phase fluidized bed polymerization process applied to the transition process of the present invention may be performed by a conventional reaction system configured as shown in FIG. 1, for example. The reaction system consists of a gas phase fluidized bed reactor 10 consisting of a reactor upper extension 1 and a fluidized bed 2, a heat exchanger 3 and a compressor 4. The gas phase fluidized bed reactor 10 typically consists of a fluidized bed reaction zone and a so-called speed reduction zone. The fluidized bed reaction zone consists of a bed of mixed polymer particles, polymer particles already formed, and catalyst, which particles are fluidized by a continuous flow rate of gas monomers and diluents. The gas monomer is compressed through the compressor 4 and cooled through the heat exchanger 3 and then flowed into the bottom of the fluidized bed to remove the heat of polymerization while flowing the particles while passing through the reaction zone. The circulating gas stream passing through the fluidized bed reaches the top of the reactor to slow down the flow rate, whereby the particles stop rising and descend and return back to the fluidized bed, leaving only the gas stream to return to the heat exchanger to complete the circulating flow. The circulating gas stream comprises olefin monomers participating in the polymerization reaction, hydrogen as a molecular weight regulator and comonomers and catalyst activators as density regulators, which are continuously consumed as they enter the reaction as they pass through the fluidized bed. These mixtures are continuously introduced into the circulating gas in order to keep the monomers in the gas stream and their concentration constant. The resulting polymer also increases the volume of the fluidized bed, substantially increasing the fluidized bed height, and the operator periodically withdraws the product from the reactor to maintain a constant fluidized bed height.

In the fluidized bed polymerization process, the reactor temperature may be in the range of 30 ℃ to 110 ℃. In general, the reactor temperature is operated at the highest possible temperature to obtain maximum activity, taking into account the sintering temperature of the polymer product inside the reactor. The polymerization temperature, or reaction temperature, should typically be below the melting or sintering temperature of the polymer to be formed. Thus, the upper limit of the temperature can be determined by the melting temperature of the polyolefin produced in the reactor.

Certain steps of the present invention in the transition process for changing the physical properties of polymers in the gas phase fluidized bed polymerization process of the present invention, particularly in metallocene catalyst systems where the reactivity and sensitivity to physical property control parameters are very high compared to conventional Ziegler catalysts. By this, it is possible to reach the final target properties within 3BTO while minimizing the transition stage product and ensuring reaction stability without poor grade product.

1 is a process diagram illustrating a circulating gas phase fluidized bed reaction system that may be used in a gas phase fluidized bed polymerization process, which is comprised of a reactor upper extension 1, a fluidized bed 2, a heat exchanger 3, and a compressor 4.
Figure 2 is a working flow diagram showing the steps of the transition process according to an embodiment of the present invention for changing the physical properties of the polymer in the gas phase polymerization process.
3 is a graph showing a change ratio of the mixing ratio of the initial resin and the production resin according to the number of bed changes.
4 is a graph showing prediction curves and measured values of a melt index (g / 10 min) to which a mixing rule is applied.
5 is a graph showing a prediction curve and a measured value of the density (g / cm 3 ) to which the mixing rule is applied.
6 is a graph showing the relationship between the melt index (g / 10 min) and the control variable value.
7 is a graph showing predicted and measured values of the melt index (g / 10 min) final value when the hydrogen / ethylene gas phase composition ratio is changed.
8 is a graph showing the relationship between density (g / cm 3 ) and control variable values.
9 is a graph showing predicted and measured values of the final density (g / cm 3 ) value at the change of the comonomer / ethylene gas phase composition ratio.
FIG. 10 is a graph illustrating transition grade and defective grade regions that may occur in a process of transition from one normal grade to another.

Through the following examples, the melt index (ASTM D1238, 230 ° C., measured according to 2.16 kg, g / 10 min) and the density (g / cm 3 ) simultaneously with the conversion to the metallocene catalyst after completion of the reaction by the Ziegler-Natta catalyst. The transition process of changing the physical properties including) will be described in more detail.

Example 1

In the present embodiment, in the gas phase polymerization reactor, steps 1 to 7 of the transition stages described in the description of the present invention are performed to determine the final values after the instantaneous generation and the bed are completely replaced from the actual measured values of the emission and mixed emission characteristics. The method of calculating | requiring the expected value of the physical property was implemented.

The Ziegler catalyst used in this example was prepared by the following method as described in Korean Patent No. 0619153.

To a 1 L four-necked flask equipped with a mechanical stirrer, 12.7 g (0.525 mol) of magnesium metal and 1.4 g (0.005 mol) of iodine were added, and 600 ml of purified heptane was added and suspended. The temperature of this suspension mixture was raised to about 70 ° C., 15.2 ml (0.056 mol) of titanium propoxide and 7.2 ml (0.065 mol) of titanium tetrachloride were added thereto, and 84.1 ml (0.8 mol) of 1-chlorobutane were added at a constant rate. Added dropwise. After completion of the dropwise addition, the reaction was carried out for 2 hours to prepare a catalyst. The prepared catalyst was washed four times with sufficient hexane and then stored as a slurry in purified hexane. The results of component analysis in the catalyst slurry are as follows: total titanium: 8.24% by weight, trivalent oxide titanium: 85% by weight of total titanium.

As the metallocene catalyst used in this example, a catalyst prepared by the following method as described in Korean Patent Application No. 10-2008-0081958 was used.

Dehydrated silica of XPO-2402 (average particle size 50 microns, surface area 300 m 2 / g, micropore volume 1.6 ml / g, OH concentration 1 mmol / g) was weighed 5 g under anhydrous conditions, and stirred in a slurry state using 30 ml of toluene. I was. It was injected into a 1 L reactor equipped with a stirrer and a cooling condenser. 75 ml of methylaluminoxane solution (10% by weight) was quantified in a measuring cylinder, and then mixed with 0.3 g of methylene catalyst component Et (THI) 2 ZrCl 2 , pre-quantified in 250 ml Schlenk, at room temperature and stirred for 5 minutes. To dissolve the solid metallocene catalyst and react at the same time. The methylaluminoxane-metallocene solution was added while maintaining the temperature of the reactor at 70 ° C. After stirring, the reaction temperature was raised to 110 ° C. At this temperature, the supporting reaction proceeded for 90 minutes. After the reaction was completed, the reaction was transferred to a Schlenk vessel, followed by decantation. After the reaction was stirred, the mixture was allowed to stand for 10 minutes, followed by decantation of the upper solution, and the reaction was first washed with 100 ml of toluene at -5 ° C. After the reaction was stirred, the reaction solution was allowed to stand, and after standing up, the upper solution was decanted and washed twice with 100 ml of toluene at room temperature. The resulting catalyst system was then washed with purified hexane and then dried under mild vacuum. The amount of supported catalyst prepared was 8.2 g. Al and Si content analysis of the catalyst were carried out to calculate the amount of methylaluminoxane supported from the Al content. The measured Al content was 21.2% by weight, and the calculated amount of supported methylaluminoxane was 45.5% by weight.

Transition stages 1-7

The initial bed was 65 kg produced from the Ziegler catalyst. The initial bed had a MI of 1.08 g / 10 min and a density of 0.9198 g / cm 3 .

The transition from the Ziegler catalyst to the metallocene catalyst was carried out in the following steps.

The injection of the Ziegler catalyst into the gas phase polymerization reactor was stopped and the injection of all reactants except nitrogen was stopped. A small amount of CO 2 was injected to kill the Ziegler catalyst remaining in the reactor. The catalyst deactivation process was carried out for 1 hour, and the bed flow was kept the same as during the catalyst deactivation process. After 1 hour, nitrogen purge was performed 10 times to remove residual CO 2 . Spreading nitrogen pressure 6kgf / cm 2 was then conducted in a manner that pressure was released to 1kgf / cm 2. Thereafter, ethylene, hydrogen, and 1-hexene were injected to form a gas phase composition for metallocene catalysis. The gas phase composition at the time of metallocene catalyst injection was adjusted to a hydrogen / ethylene molar ratio of 0.011, 1-hexene / ethylene molar ratio was maintained at 0.003. The partial pressure of ethylene was 50 mol%, and the rest was pressurized with nitrogen to make the reaction pressure 19 kgf / cm 2 . The reaction temperature was maintained at 80 ° C. As a promoter, trinormal-octyl aluminum was diluted to 10 mmol (mmol) in hexane, and 40 ppm of injected ethylene was injected to induce reaction start. The reaction was started after the injection of the metallocene catalyst, and the reactant was continuously discharged to maintain a constant bed amount when the bed amount was increased by the produced polymer. The exhaust reactant is a mixture of the initial polymer produced by the Ziegler catalyst and the polymer newly produced by the metallocene catalyst. Emissions were measured for melt index and density in 5 kg increments. Table 1 shows the cumulative emissions and measured physical properties.

Estimation of the mixing ratio and the physical properties of the emissions was carried out through the following procedure from the discharge and the bed volume.

The bed change is the total amount of polymer produced and discharged after initiation of the transition stage, divided by the weight in the bed, as a function of residence time (τ) and time (also referred to herein as bed turn over (BTO)).

According to the bed change, the initial polymer powder, which was 100% at the beginning of the transition stage, is replaced with the newly produced polymer powder, and the proportion of the newly produced polymer increases as shown in FIG. 3 according to the number of bed changes.

In the graph of FIG. 3, the curves (in-bed proportions of the product) were obtained from the integral obtained from the following mass balance equation.

V * dC / dt = v * C in -v * C = v * [C in -C]

If you separate the variables for integration

dC / [C in -C] = (v / V) dt = (1 / τ) dt

Where C is integrated from C o to C, t is from 0 to t,

ln [(C in -C o ) / (C in -C)] = t / τ

Since C o is 0 and C in is 1

C = 1-Exp (-t / τ) = 1-Exp (-BTO)

In the above equations,

V: Bed weight (kg)

v: Creation rate (kg / hour)

V / v = τ (average residence time) (hours)

BTO: Bed Turnover

C: In-bed concentration (ratio) of new product (influent)

C in : ratio of new product in product (influent) = 1

C o : In-bed concentration (ratio) of new product at the beginning of the transition phase = 0

By applying the bed mixing ratio, initial property value and final property expected value obtained in the above relations to the mixing law applied to each property value, the properties of the mixture in the bed (emissions for each hour) and the properties of the instant product are estimated by the following method. This was compared with the measured value. The law of mixing properties is as follows.

Since the melt index (g / cm 3 ) among the physical properties is converted into an exponential function, it was obtained by the following equation 1 by applying the mixing ratio shown in FIG. 3 as an index mean value:

Equation 1: ln [MI_m] = C a * ln [MI_a] + C b * ln [MI_b]

In Formula 1, MI_a is the melt index of the initial product; MI_b is the melt index of the new product; MI_m is the melt index of the polymer mixed and discharged in the bed; C a and C b represent the mixing ratios of the initial product and the new product, respectively. MI_b is the melt index of the new product, but it is also the final target reached within 3BTO if the property control parameters are maintained after modification.

Density (g / cm 3 ) is a general average value was obtained by the following equation 2 by applying the mixing ratio as follows:

Equation 2: Density_m = C a * Density_a + C b * Density_b

In Equations 1 and 2, density_a is the density of the initial product; Density_b is the density of the new product; And C a and C b represent the mixing ratio of the initial product and the new product, respectively.

In practice, the final target value of the property is the value that is the target value when the control variable is changed at the beginning of the initial transition stage, and is unknown until the completion of the transition stage. Therefore, the measured values actually measured in the transition stage are displayed on a graph, and the expected physical property values (MI_m, density_m) of the mixture in the reactor generated by inputting the final target values into MI_b or density_b in Equations 1 and 2 above. Was calculated according to the number of bed changes, and this curve curve was used to predict the final value of the physical properties after the bed was completely replaced.

Table 1 below shows the bed change and the ratio of the newly produced resin polymer in the bed, and the expected properties of each bed change were compared with the actual values by using the mixing rule from the initial and final properties. Indicated. 4 and 5 were created using this.

4 and 5 show the prediction curve and the measured value of the melt index and density according to the mixing rule, respectively.

The prediction curves of FIGS. 4 and 5 were prepared by changing the final target values in Table 1 below from 1.5BTO to obtain the predicted values, and selecting the final target values corresponding to the measured values before 1.5BTO. As can be seen in Figures 4 and 5, when MI is the final target value of 4g / 10 minutes, and density is the final target value of 0.925g / cm 3 , the measured value and the expected curve according to the bed changes A match was found. It was confirmed that the predicted value curve by the final value MI 4g / 10min determined by 1.5BTO and the density 0.925g / cm 3 was consistent with the measured value even after 1.5BTO.

TABLE 1

Figure 112010008942536-pat00001

Example 2

In this embodiment, two target value changes are made using a method of predicting the final achieved property value from the measurement of the emission proposed and verified in Example 1 and a combination of the control variable and the property value without generating a bad grade. The final target was achieved within 3BTO.

Transition stages 1-7

The final target value of the polymer resin physical properties obtained in this example is a resin having a MI of 0.7 to 0.9 g / 10 min and a density of 0.9175 to 0.9185 g / cm 3 .

The bed used in this example was a polymer produced by the Ziegler catalyst, the initial physical property value MI was 1.10 g / 10 min, and the density was 0.9196 g / cm 3 . In order to terminate the reaction by the Ziegler catalyst, the injection of the Ziegler catalyst was stopped and a small amount of CO 2 was injected as the reaction terminator to terminate the reaction. After purging 10 times with nitrogen to remove CO 2 , ethylene, hydrogen, and 1-hexene were injected to form a gas phase composition corresponding to the reaction region of the metallocene catalyst. The molar ratio of hydrogen / ethylene was 0.006 and the molar ratio of 1-hexene / ethylene was adjusted to 0.003. The partial pressure of ethylene was 50 mol%, and the rest was pressurized with nitrogen to make the reaction pressure 19 kgf / cm 2 . The reaction temperature was maintained at 80 ° C.

The reaction was initiated by injecting a metallocene catalyst into the gas phase polymerization reactor, and the reaction product was discharged as the reaction proceeded. The change in bed was calculated by measuring the discharge every 2 hours, and the physical properties of the discharge were measured.

The MI was analyzed by the same method as in Example 1 with actual values up to 1.0 BTO, and when the hydrogen / ethylene molar ratio of 0.006 was maintained continuously, the MI finally converged to 0.53. This is shown in Table 2 and FIG.

As a result of analyzing the density with the actual measurement value up to 1.31 BTO, when the 1-hexene / ethylene molar ratio of 0.003 was maintained continuously, the density was finally converged to 0.9245 g / cm 3 .

This is shown in Table 4 and FIG.

Transition stage 8

In transition stage 8, the relationship or graph between the property variables and the control variables was prepared by using the gas phase composition initially set in the transition stage and the expected expected physical properties obtained in step 7 when the composition was maintained.

The relationship graph was prepared by adding a relationship value between the property variable and the control variable identified in Example 1 (see FIGS. 6 and 8).

Transitional stage 9

In the transition step 9, the control variable value corresponding to the target physical property range was confirmed from the relationship graph confirmed in the transition step 8 (FIGS. 6 and 8), and the operation set value was corrected to this value and operated. This value was obtained by interpolation or extrapolation in the created relationship graph.

In relation to the MI, the hydrogen / ethylene molar ratio setpoint for the first correction of the operating setpoint is 1.2 higher than the target MI of 0.7-0.9 g / 10 min in order to more accurately predict the expected value through interpolation during the second change. A value of 0.00072 aimed at g / 10min was set.

Regarding the density, the 1-hexene / ethylene molar ratio setpoint for the first change of the operating setpoint was operated at a value of 0.0075, which is a molar ratio corresponding to a range forming 0.920 g / cm 3 , which is higher than the final target property. As described above, setting the range to form a density higher than the final target property value is to prevent the density of the instantaneous polymer from entering the low density region beyond the safe driving region. Step 9 was performed between 1 BTO and 1.3 BTO.

Although the melt index of the newly produced polymer by the metallocene catalyst has a target value in the same range as the melt index value in the reactor, the range of control variables operated by the reactivity difference is different from that of the Ziegler catalyst. Therefore, it is the purpose of the transition process to minimize the grade of the defect by accurately obtaining the set point for the control variable value (gas composition molar ratio) for forming the same melt index in the stable region of operation, and to reach the target value within 3BTO. If the wrong setting of the hydrogen / ethylene molar ratio leads to a sharp drop in the melt index, the formation of gels due to the formation of ultra-high molecular weights will cause the entire bed to be poorly graded.

In the case of the density of the newly produced polymers as well, the incorrect setting of the 1-hexene / ethylene molar ratio will lead to a sharp drop in density, resulting in unstable process operation.

Transition stage 10

By the method of Steps 2 to 7, the physical property measurement and the prediction value by the first correction performed in the transition step 9 were obtained.

The initial value is the physical property value of the resin in the bed at the time of the first transition modification, and the mixing ratio according to the bed change is applied again as the initial value (see Table 3 and Table 5).

In the case of MI, the MI was estimated to be 1.2 g / 10 min when the hydrogen / ethylene molar ratio obtained from the physical property measurement up to the 1.9 bed change point by the first correction was kept at 0.00072.

In the case of the density, the density of 0.919 g / cm 3 was expected when the 1-hexene / ethylene molar ratio obtained from the physical property measurement up to 2.08 BTO by primary correction was continuously maintained at 0.0075.

The property values and control variable values obtained through this transition step 10 were additionally reflected in the relationship graphs (FIGS. 6 and 8).

Transitional stage 11

In this transition step 11, the same method as the target value correction performed in steps 9 to 10 was repeated.

In the second correction, the control variable values corresponding to the final target value were determined within 3BTO by using the control variable property relationship graph which is more accurate due to the first correction operation, and the operation was performed with these values.

The initial value is the physical property value of the resin in the bed at the time of the second correction, and the initial value is used to apply the mixing ratio according to the bed change again (see Table 3 and Table 5).

Table 2 and Table 3 below show the change in the melt index according to the modification of the control variables (hydrogen / ethylene ratio) over the second stage from the relationship between the properties of the transition stage and the setpoint.

TABLE 2

Figure 112010008942536-pat00002

[Table 3]

Figure 112010008942536-pat00003

As shown in Table 3, the control variable set value was modified at 1.10 BTO (step 9), and the control parameter set value was modified once again at 1.90 BTO to allow the melt index to enter the target value of 0.8 to 1.0 within 3 BTO. When the second setpoint is corrected at 1.90 BTO, the initial control parameter value and the melt index vs. hydrogen / ethylene gas phase composition ratio relationship graph obtained at the first change (Fig. 6) are interpolated at the final target melt index of 0.8 g / 10 minutes. The corresponding gas phase composition ratio was read and used. FIG. 7 shows the changed melt index expected trend line and the measured value when the second set value of the hydrogen / ethylene gas phase composition ratio is corrected.

Tables 4 and 5 below show the change in density according to the control variables (comonomer / ethylene ratio) modification over the second order from the density and setpoint relations of the transition stages.

[Table 4]

Figure 112010008942536-pat00004

TABLE 5

Figure 112010008942536-pat00005

As can be seen in Tables 4 and 5, the control variable set value was firstly modified at 1.45 BTO, and the control variable set value was secondarily modified at 2.08 BTO, so that the density was set at 0.9185 to 0.9175 g as the final target value at 3.06 BTO. / cm 3 could be entered (density measurement at 3.06 BTO: 0.9185 g / cm 3 ). As can be seen from Table 5, the expected density value at this point is 0.9184g / cm 3 It can be seen that the very accurate value is predicted. In the second correction of the set value at 2.08BTO, the final target density, 0.9175 g / cm, was extrapolated by extrapolating from the initial control variable value and the density- 1-hexene / ethylene gas phase composition ratio relation graph obtained in the first change (Fig. 8). The gas phase composition 0.0095 corresponding to 3 was read and used. 9 shows the expected trend line and the measured value of the changed density when the set value is changed over two times. As a result, all of the transition steps of the present invention are performed, and as shown above, the transition step grade can be minimized while ensuring the reaction stability without defective grade product in the transition process to the metallocene catalyst after the completion of the reaction by the Ziegler-Natta catalyst. In order to achieve the final target properties within 3BTO, we have completed the method.

The above embodiment is an embodiment in the transfer process between heterogeneous catalysts, but the present invention can also be applied to the physical property transfer process between homogeneous catalysts.

Claims (6)

  1. A transition process for changing the physical properties of a polymerization product in a gas phase fluidized bed polymerization process comprising the following steps (1) to (11):
    (1) changing a set value of an operating variable for changing a property value;
    (2) proceeding with the reaction under the change condition after changing the set value;
    (3) calculating bed changes from reactant emissions as the reaction proceeds;
    (4) calculating, from the bed change calculation step (3), the bed content of the new product in the bed created after the operating variable set point change step (1);
    (5) estimating the final achieved physical properties using a mixing rule from the calculated in-bed content of the new product;
    (6) measuring the physical properties of the reactor effluent in which the reactants prior to the operating parameter setpoint change and the new product reactants are mixed;
    (7) matching the measured property value trend line with the trend line resulting from the expected final reached property setting in step (5) to determine the property at 3BTO (bed turn over);
    (8) determining a relationship between the operating conditions and the physical properties from the physical properties in the operating conditions before the setpoint change and the final achieved physical properties expected in the operating conditions after the setpoint change obtained in step (5);
    (9) modifying the final attainable property target so as not to produce a poor grade product within 3BTO from the relation obtained in step (8), and determining operating conditions consistent with the changed target value;
    (10) repeating step (1) to step (7) with the changed operating condition in step (9); And
    (11) maintaining altered operating conditions such that the reactants reach target properties within 3 BTO without producing poor grade products by repeating step (10).
  2. 2. The process of claim 1, wherein said operating parameter comprises at least one of a gas phase composition, a temperature, a reaction pressure, a catalyst composition, and a catalyst activator.
  3. 2. The process of claim 1, wherein said polymerization product is a polyolefin.
  4. The process of claim 1, wherein the polymer properties are density and melt flow characteristics.
  5. The method of claim 1, wherein the catalyst system used in the polymerization reaction is composed of a metallocene catalyst for polyolefin polymerization and a catalyst activator prepared by supporting a metallocene catalyst having a structure represented by the following formula (I) on silica. The transition process for changing the physical properties of the polymerization product in the gas phase fluidized bed polymerization process:
    (THI) 2 R "MQ p (I)
    (Wherein THI is a substituted or unsubstituted tetrahydroindenyl derivative, and R ″ is a structural crosslink that imparts steric stiffness between two THI groups; M is Group IIIB, IVB, Group VB or Group VIB) Is a transition metal selected from Q is a hydrocarbyl group or halogen having 1 to 20 carbon atoms; p is a number having a valence-2 of M).
  6. 6. The process of claim 5, wherein said catalyst activator is an alkylaluminum compound or an aluminoxane.
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1669373A1 (en) 2004-12-07 2006-06-14 Nova Chemicals (International) S.A. Adjusting polymer characteristics through process control
EP1669372A1 (en) 2004-12-07 2006-06-14 Nova Chemicals (International) S.A. Adjusting polymer characteristics through process control
WO2008076386A1 (en) 2006-12-18 2008-06-26 Univation Technologies, Llc Method for reducing and/or preventing production of excessively low density polymer product during polymerization transitions

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1669373A1 (en) 2004-12-07 2006-06-14 Nova Chemicals (International) S.A. Adjusting polymer characteristics through process control
EP1669372A1 (en) 2004-12-07 2006-06-14 Nova Chemicals (International) S.A. Adjusting polymer characteristics through process control
WO2008076386A1 (en) 2006-12-18 2008-06-26 Univation Technologies, Llc Method for reducing and/or preventing production of excessively low density polymer product during polymerization transitions

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