DD301246A7 - Process control process for ethylene polymers of high homogeneity - Google Patents

Abstract

The invention relates to a method for controlling the polymerization process in the production of polyethylene of defined homogeneity by gas phase polymerization in the presence of known heavy metal catalysts and hydrogen as a chain regulator in continuous process control in polymerization, characterized in that the polymerization process by the process parameters: reactor inlet temperature, reactor control temperature, temperature at the distributor plate of the reactor, catalyst feed rate, bedstead in the reactor, hydrogen concentration in the reaction mixture and the concentration of the comonomers used with gradual change of one or more process parameters is controlled only if the stochastic fluctuation of these process parameters exceeds a safety value a ind i, where (formal) and the Uncertainty N of all process parameters exceeds a standard value of 0.45 n, where (Formula) where the Steue Reingriff done in differentially small steps so that the quotient (formula) is 0.01 / h and the resulting from the polymer process control changes in the process parameters (formula) go to 0, which in principle is assumed that also outside the listed in Table 1 Parameter further intervals of a rule-free driving style may exist, but this does not question the statements about rule-free driving periods according to the above relationships.

Description

-2- 301 24C

Characterization of the known prior art

It is known) to control the polymerization process for the production of polyethylene according to different physical characteristics (DDR standard 1975 TGL 29979/67 to 69, DDR standard 1980 TGL 26244). The corresponding quantities are obtained both as "online" process parameters and from manual analyzes (SCHRÖDER, E., MÜLLER, G., ARNDT, K.-F .: Guidelines for Polymer Characterization.Akademle-Verlag Berlin 1982, p. 193 and SCHRÖDER, E., FRANZ ₁ J., HAGEN, E .: Selected methods of Plastanalytik / Akademie-Verlag Berlin 1976 _, p 78). If the current parameters deviate from their predefined standard values, after dominant manual determination of the precipitation, an intervention in the polymerization process takes place, in which some process parameters are purposefully changed

 Disadvantages of this procedure are:

the sampling error in manual analysis by segregation processes in statistically distributed products,

- The lack of precision of laboratory analyzes, such. The density determination, the sieve analysis and the flow index,

- Above all, the generally not time-relevant control when using laboratory data and

the "hard" manual assessment of the individual parameters, for example in the form of a so-called stroke mode, which ignores the normal stochastic variation of the process.

The negative effects of this process evaluation mentioned above can be described as follows:

- Overrides the process by disregarding outlier errors of the laboratory analysis or by sampling errors and not time-relevant control,

- Control on the basis of imprecise laboratory values in actually not to be controlled driving periods (measuring error control).

- Control in stochastic deviations of individual values (so-called stroke modes), which are not necessarily controllable.

As a result of the overdrive, there are broad distribution polymers that are more difficult to process on automated processing lines than polymers with narrow property distributions. It can also give polymers with properties that are no longer in Lioferintervall, so production losses. The result is polymers with inhomogeneities, the so-called specks whose further processing can be brought only by uneconomical additional operations such as screening or increased energy input in the extrusion process in a desired shape for the customer. Continuous interventions in the process lead to additional technical inhomogeneities and, associated therewith, to increased demands on the operating team.

Object of the invention

It is the object of the invention to control the polymerization process with the same reliability with less effort in laboratory analysis and at the same time to produce more products of higher homogeneity.

Explanation of the essence of the invention

The invention is based on the object to develop a method for process control for the polyethylene production, which allows a time-relevant control of the stationary polymerization in the gas phase and produces polymers of high homogeneity.

According to the invention the object is achieved in that a method for controlling the polymerization process is used, which is characterized in that the polymerization process by the process parameters: reactor inlet temperature, reactor control temperature, temperature at the distributor plate of the reactor, catalyst flow rate, bed level in the reactor, hydrogen concentration in the reaction mixture and the concentration of the comonomers used is controlled with gradual change of one or more process parameters only if the stochastic fluctuation range of these process parameters exceeds a safety value ai, applies

II _n - i, I = Δ, <a "· ' M)

in the standard range of the parameter!

ii value of the parameter! at the time t

Δι Deviation of the measured value i from the optimum to the time t

ai safety interval for the size i,

and the uncertainty N of all process parameters exceeds a standard value of 0.45n, where

'n

N = Σ f (j _t ), (2)

ι = 1

η total number of measuring parameters (characteristics),

f (ii) value of the blur function of feature i for the current measured value i _t (at time t, with Ii ₁ ) = 1 for i ")

wherein the control intervention takes place in different small steps such that the quotient

-L_ (3)

i-Δ, 0.01 / h,

thereby applies

i absolute parameter

Δ, control time,

and the changes in the process parameters resulting from the polymer process

ΣΔ | - »min

go against 0, which in principle can be assumed that even outside of the parameters set out in Table 1, more intervals of a rule-free driving can exist, but this does not question the statement about rule-free driving periods according to the above relationships.

Another advantage of the above-mentioned control is that in driving periods that are characterized solely by stochastic fluctuations, no manual analyzes are needed because the laboratory words for product characterization from technical parameters of similar driving periods are predictable.

embodiment

From driving periods of previous polymerizations, morphological blur functions are determined for 8 selected non-mutually correlated parameters for 386 complexes of the S 9 and 948 complexes for the S 2 driving style (Table 1, Lines 2 and 3 and Lines 4 and 5) (Fig 1). They depict the process of good driving with homogeneous products. The maximum of the blur function \ represents the optimum travel range of each parameter i; on V ₂ i "the uncertainty function gives the range of uncontrolled driving according to Eq. (1). Outside of these areas, marked with -><in Figure 1, a forced regulation takes place when Eq. (2) is not satisfied. In principle, it can be assumed that other similarly useful intervals could exist outside of the parameters listed in Table 1 for a quiet driving style. For example, for a higher production rate, features 2,4 and 8 would have higher values, but the other values remain the same. The morphological blur function of these features then shifts by a constant amount to higher values, but remains identical in their statement.

As the embodiment in Table 2 shows, batches of stochastically varying polymers have high blurring powers (lines 1 and 2). Conversely, very small thickness values indicate an unstable mode of polymerization.

Exemplary embodiment Table 3 shows that, in undisturbed driving, samples of high similarity in the technical parameters must inevitably coincide in the laboratory values (line 2). The prediction error ^r line 3 is approximately in the order of magnitude of the precision of the laboratory values line 4 and corresponds to the delivery interval line 5.

Table 1. Parameters for controlling polymerization for S 9 and S 2 types

grade parameter technical parameters i distributor pacing H ₂ C3 / C4 real catalyst according to Temperature ° C plate C ₂ H ₄ Nm ³ / h % " bed stand delivery rate Q-II) Reactor reactor 97.9 NMVH 3.23 14.34 m kg / h regulation input 2736 9.9 0.27 2) n 102 65.9 S9 ± 0.5 ± 0.4 ± 0.7 (386 meas 271 ± 0.2 -To, 18 dates) 8 | ± 0.1 ± 4.4

(948 measurement data)

94.4 97.4

± 0.6

51.9 93.9 2825 1.53 0.26

± 3.7 ± 2.1 ± 203 ± 0.77 ± 0.05 ± 0.12

0.53 0.98

± 0.13

"referring to% circulating gas ²¹ Symbol explanation in the text.

Table 2. Exemplary embodiments of the characterization of polymers according to technical parameters

charge

date

08/07/88

Average Quantity Comment

7.22

Homogeneity test (s) "

09/07/88

5.88

outside the maximum, but unregulated

"β - ♦ 0 homogeneous product, S -» 100 highly inhomogeneous product.

61 10/7/88 0.53 End of the type journey (crossing product) »100 38 > 30.4.88 2.86 inhomogeneous product »100

Table 3. Prognosis of laboratory data from technical parameters in undisturbed driving

charge deviation ij Laboratory Values Xi P comment 46 50 0.47 0.5 23.4 24.3 0.948 0.950 Labormeßwerte Xi 0.03 0.9 0,002 forecast error 3 O ₁ 0.054 0.45 0,003 Precision of the laboratory procedure IT ₀ - T ₁₁ I 0.2 β 0,002 agreed delivery interval

Figure 1. Distribution of 948 objects of the S 2 driving style with the characteristic "real bedstand" - »« - area without regulation

1.O *

H X

0.5 4 << Mt.

X ΧΧΛ K

χ < κ κ ^ x

X XxXX XK XKXKK

KK X * HX H K

VX ^- Kn χ \ x XX ¹ VXXkX k **> I

1,

Claims (1)

Process for controlling the polymerization process in the production of polyethylene of defined homogeneity by means of gas phase polymerization in the presence of known heavy metal catalysts and using propene or butene or mixtures thereof and hydrogen as chain regulator in continuous process control in polymerization, characterized in that the polymerization process by the process parameters: Reaktoreingangstemperatur , Reactor control temperature, temperatures of the distribution plate of the reactor, catalyst flow rate, bed level in the reactor, hydrogen concentration in the reaction mixture and the concentration of comonomers used in gradual change of one or more process parameters is controlled only if the stochastic fluctuation of these process parameters exceeds a safety value a, applies I i _n - i, I = Δι <a _{i #} i _n standard range of the parameter! i _t value of the parameter! at the time t Δι Deviation of the measured value i from the optimum to the time 8j safety interval for the size i, and the uncertainty N of all process parameters exceeds a standard value of 0.45η, where η total number of measuring parameters (characteristics),
f (it) value of the blurring function of the feature i fürden current Meßwerti _t (zurZeitt, with (i _t) = 1füri _n), wherein the control intervention takes place in different small steps such that the quotient i
i-Δ, 0.01 / h,
daoei applies i absolute parameter
A _t control time, and the changes in the process parameters resulting from the polymer process go to 0 field of use The invention relates to a method for controlling the polymerization process in the production of polyethylene of defined homogeneity by gas phase polymerization in the presence of known heavy metal catalysts and using propene or butene, their mixtures and hydrogen as chain regulators in continuous process control in polymerization by means of blur functions.