DE2013497A1 - Process control in the manufacture of a polymer - Google Patents

Description

"Registration number 2158

Dr. F. Zumstein Sr. - Dr. E. Assmann Dr.R.Ko «nig« b «rg # r - Dipl.Phy * .R. Timber builder

Dr. F. Zam »tein Jim. P ο t · w I ο ι »wa I t · / t MI» ch »r> 2, Bräwliausstroß · 4 / III

STAMICARBON NV., HEERLEN (the Netherlands) , pressure regulation in the production of a polymer

The invention relates to a process control in the continuous Production of a polymer, according to the one or more in a reactor Monomers, hydrogen and a catalyst or one or more catalyst components and the supply of hydrogen on hand the measurement data is regulated. ·

Such a process control is from the American patent 3,356,667 known. To produce a polymer with constant properties, e.g. a constant melt index, in the case of the known regulation J Process the addition of hydrogen, the concentration of the polymer in the reactor, the temperature in the reactor and the size of the monomer stream fed in were measured and the melt index is calculated from the resulting measurement data and compared to the target value, whereupon based on the difference between the two Values the size of the hydrogen supply is set * You therefore determine the melt index not in a direct way because such a determination is so much That would not take time as a basis for. a useful one Regulation in »can be considered. With the known regulation, however, there are several Disadvantages associated. It is true that it is not the melt index itself, but the Factors determining the melt index assumed so in this way rapid intervention is possible. The regulation, however, is all the more imprecise the greater the percentage of the monomer (s) converted to the polymer (hereinafter referred to as conversion) increases, the known scheme becomes

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consequently, with a high conversion, no product of constant and desired good result; in addition, the equipment required is complicated and expensive.

The invention aims to provide a more precise control for setting the Polymer properties, which are also characterized by simplicity and practicality. This regulation is characterized in that the feed rate of the monomer (s), the temperature of the reactor ufld the conversion is kept approximately constant and determines the value of the monomer / hydrogen ratio in the stream emerging from the reactor is the hydrogen supply for the merge.

It has surprisingly been found that in this way, even with optimal conversion, a polymer with very constant properties is obtained. A slight change in the conversion results in a significant change in the monomer / hydrogen ratio after leaving the reactor, while the temperature remains almost constant. This regulation owes its great sensitivity to this fact. Here, high conversion is understood to mean a degree of conversion of over 90 %, for example 96-97 %.

Working at high conversions has certain advantages; so are they Low cost of recirculation of the monomers. It is also advantageous that Activity fluctuations only slightly influence the conduct of the process; that, As already said, the temperature remains practically constant is of the greatest importance in autothermal reactors.

The temperature of the reactor is preferably kept constant through Regulation of the amount of catalyst or catalyst components entering the reactor. These components are mostly single and in constant added to mutual proportions.

It is possible to check the melt index of a sample periodically, a determination that takes about half an hour to complete.

The invention is explained with reference to the drawing, in which an example of polyethylene production is shown. Show it:

1 shows part of a process diagram and i

Fig. 2 is a graph showing the relationship between the melt index of the product and the Athyle.n / Hydrogen ratio after leaving the reactor.

In a solution vessel 1 are in a stream 2, which is essentially consists of a solvent, in the present case gasoline, monomers mixed in, namely ethylene through line 3 and, for example, a little butylene through the line 4. The inflow quantities per unit of time are controlled by the quantity regulator 5 and 6 with associated control valves 7 and 8 kept constant. Line 9 is

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a drainage line connected to the vessel which prevents the Pressure increases too much.

The solution of the monomers in gasoline flows via pump. 10 to an absorption device 11, which is provided for the absorption of hydrogen, which flows through the line 12 with built-in control valve 13 is fed.

The content of the absorption vessel 11 flows via the line 14 and the cooler 15 to a reactor 16 continuously. This scheme is used one, if in the case of an adiabatic implementation of the reaction at a given Maximum temperature and a given minimum residence time result in increased production is desired. A quantity regulator 17 is connected to the line 14. The reactor 16 is equipped with a stirrer 18 bit. "

In the present case, the reactor enters through lines 19, ™

20 and 21 with built-in control valves 22, 23 and 24 include three catalyst components. These control valves are connected to the reactor by a Temperature regulator 25 actuated. -

The contents of the reactor go continuously via a line 26 built-in control valve 27. This valve is controlled by the flow regulator 17 in the addition line 14 is actuated. A test line branches off from line 26 so that the melt index can be determined regularly. From that through The current flowing through the line 26 is used to continuously determine the ethylene / hydrogen ratio, e.g. with the aid of a chromatograph 29, its measurement result is passed on to a controller 30 for actuating the control valve 13 in the hydrogen feed line 12.

By means of the above apparatus I) of the inflow are the mono- ä merenmengen kept constant, II), the current flowing through the reactor circulation rate maintained constant, ΊΙΙ) the amount of catalyst is set such that the reactor temperature remains constant, and IV) the hydrogen supply, depending on the ratio of ethylene: hydrogen regulated after leaving the reactor.

In diagram 2, ait CVH _{2 is} the ethylene / hydrogen ratio and with SI denotes the melt index. The two lines indicated by T and T _{0, respectively}

Λ. Α

represent the course of the two aforementioned quantities at temp. T and T,

where T ₁ > T_. The diagram shows that with the same C_ / H -X * 2 2

Ratio (a) a higher temperature T results in a higher SI value (b). In order to get a constant SI (c), the value of C_ / H_ must therefore be larger (d), which means that the amount of H must decrease at higher temperatures.

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With a higher conversion and a practically constant temperature, the value of C / H becomes smaller (e) because the amount of C decreases. In order to keep SI (c) constant, the C _o / H value must therefore be the same in this case

Ci At

Stay high so that the H “supply has to be reduced.

The invention can be used in a very wide variety of polymerization processes will; it can also be used in the production of homopolymers and copolymers, among other things of ethylene, butylene, butadiene and isoprene.

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Claims (2)

. PATENT CLAIMS \ yi · Process control for the continuous production of a polymer, according to which one or more monomers, hydrogen and one or more catalyst components are brought together in a reactor and the hydrogen supply is controlled on the basis of measurement data, characterized in that the supply of the monomer (s) , the reactor temperature and the conversion are kept approximately constant and the value of the ratio between the monomer (s) and hydrogen in the stream leaving the reactor is decisive for the amount of hydrogen supplied. "g 2. Process control according to claim 1, characterized in that the reactor temperature by adjusting the amount flowing into the reactor. Amounts of catalyst or catalyst components is kept constant. 009841 / 181S Blank page