JPH0477502A - Height control of bed of fluidized bed in vaporphase polymerization - Google Patents

Abstract

PURPOSE:To control height of fluidized bed so that a fluidized bed reactor can be stably operated by pressure difference in high accuracy between an upper space zone and a fluidized bed zone of the reactor for a long period of time by detecting pressure of the upper space zone and the fluidized bed zone of the reactor from pressure removal ports of an empty chamber having a specific cross-sectional area charged with granules or powder in the interior. CONSTITUTION:In subjecting an olefin to vapor phase polymerization using a reactor fluidized bed type, the reactor 1 of fluidized bed type equipped with a blower 13, a cooler 14 and a gas circulating piping 12 is charged with an olefin 7, hydrogen 6, a catalyst 8, a cocatalyst 5 and nitrogen 17. A gas is fed from the gas circulating piping 12 to the reactor by the blower 13, uniformly dispersed by a dispersion plate 4 to form a fluidized bed 3. Pressure at the fluidized bed zone 3 and pressure at an upper space zone 2 of the fluidized bed are detected from pressure removal ports 9 and 10 of an empty chamber having >=1cm<2> cross-sectional area packed with granules or powder in the interior, pressure difference between both the zones is measured by a differential pressure measuring device 11, and the height of fluidized bed is controlled to polymerize the olefin in vapor phase.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for controlling the height of a fluidized bed when polymerizing olefins using a gas phase fluidized bed. More specifically, the present invention relates to a method for accurately measuring the pressure difference between the inside of the fluidized bed and the space above the fluidized bed by improving the structure of the pressure outlet, thereby controlling the height of the fluidized bed with high precision.

[Prior Art] An olefin gas phase polymerization apparatus using a fluidized bed is already known. For example, according to Japanese Patent Publication No. 47-13962, the main components of a fluidized bed gas phase polymerization apparatus include (I) formation of a fluidized bed by polymer particles, and (IT) homogenization of olefin residue dispersion by a residue dispersion plate. , (nl) fluidization of the particles with olefin gas and removal of the heat of polymerization, (TV) circulation of olefin gas and cooling with an external heat exchanger, (V) feet of solid catalyst, (VI) feed of cocatalyst, and ( (2) Controlling the bed height of the fluidized bed and extracting polymer particles are mentioned.

In order to operate a fluidized bed gas phase polymerization apparatus stably, it is extremely important to control the bed height of the fluidized bed at a constant level.

That is, if the bed height is constant, the amount of polymer particles in the reactor is approximately constant as long as other conditions are constant.
As a result, the average residence time of the particles also remains constant. If the bed height is too high, not only will the residence time be extended, but polymer particles will be more likely to fly out of the fluidized bed. The ejected particles enter the circulation waste piping and accumulate in areas other than the reactor, causing a polymerization reaction and producing bulky polymers, which is undesirable. In addition, when the bed height is too low, the residence time becomes short and polymer particles containing the remaining active catalyst are taken out as a product, which is not preferable.

If a catalyst is fed to a fluidized bed reactor during operation, the bed height of the fluidized bed will necessarily increase due to the formation of polymer particles. For the reasons mentioned above, it is necessary to maintain the bed height constant by discharging an amount of polymer particles corresponding to this increased height. The method of measurement is important.

Since it is impossible to visually observe the bed height with normal industrial equipment, conventionally, pressure detection terminals are attached to the lower part of the waste dispersion plate of the fluidized bed and the space above the fluidized bed, and this total differential pressure is measured. The bed height of the fluidized bed is estimated by The total differential pressure measured in this case is generally expressed by the following formula (total differential pressure) = (pressure loss of gas distribution plate) + (weight of fluidized bed) = (α
°p°u2+pB°HB°g) x 76g where ρ: dregs density (kg/m3) U: gas flow rate in the holes of the gas distribution plate (m/5ee) ρB
= Particle bed average density in fluidized state (kg/m3) HB: Bed height in fluidized state (m) g: Acceleration of gravity (m/sec2) g: Gravity conversion factor (kg-tIl/g-sec2) )
α: Constant If other conditions do not change at all in the above equation,
If the total differential pressure is kept constant, the floor height HB remains constant. However, in actual operation of a polymerization reactor, various conditions vary, so it is not always possible to keep the bed height HB constant just by controlling the total differential pressure to be constant. . For example, even if other conditions are constant, fluctuations will occur in the following cases: (a) When the holes in the waste dispersion plate become clogged (due to melting of polymer particles, etc.) →U increases. .

(b,) When the composition of circulating dregs changes → ρ changes.

(-C) When the flow rate of circulating gas changes → U changes.

(d) When the bulk density of polymer particles changes (due to changes in catalyst, temperature, and pressure) →ρ changes.

In this way, the ug
, ρ8, ρ8, etc. change, so even if the total differential pressure is controlled to be constant, the value of HB is subject to fluctuations, making it nearly impossible to maintain an accurate floor height.

One way to avoid the above-mentioned troubles is to use a device for gas-phase polymerization of olefins in a stirred fluidized bed. It is disclosed that the differential pressure between an upper pressure detection end provided in an upper space area above the floor layer area and both branch ends is detected and controlled to be constant (
(Japanese Unexamined Patent Publication No. 113208/1983). However, in this case, it is recommended to let the purge scum flow to prevent clogging of the lower pressure detection end, and there are various problems caused by the use of purge scum and a decrease in pressure detection accuracy due to fluctuations in the flow rate. From this point of view, it is not always satisfactory.

There is also a device devised for detecting paratera levels in gas phase polymerization of polypropylene (U.S. Pat. No. 4,387,
(No. 593), however, this only has the function of indicating whether or not the floor height has reached a certain value, and cannot continuously measure the floor height.

Furthermore, since the structure of the detection end includes movable parts and spaces, there is a high possibility that the catalyst will enter there and cause a polymerization reaction, resulting in blockage by the produced polymer.

[Problem to be solved by the invention] In view of the above points, the present invention provides an olefin gas phase polymerization apparatus using a fluidized bed reactor without using purge gas in the pressure measurement piping. It is an object of the present invention to provide a method for measuring and controlling floor height in a stable and reliable manner.

[Means for Solving the Problems] As a result of intensive studies in accordance with the above objectives, the present inventors have devised the shape of the pressure detection end of the fluidized bed reactor to constantly measure the bed height. The inventors have discovered that this makes it extremely easy to control the floor height, and have arrived at the present invention.

That is, the present invention detects the pressure in the upper space area of the fluidized bed and the fluidized bed area when performing gas phase polymerization of olefin using a fluidized bed reactor, and controls the bed height based on the differential pressure between the two. In the method, the pressure outlet has a cross-sectional area of 1
The present invention provides a method for controlling the bed height, which is characterized in that the pressure outlet is made up of a void space of cm2 or more, and that the inside of the pressure outlet is filled with powder or granular material in advance.

The content of the present invention will be explained in detail below.

The fluidized bed reactor referred to in the present invention may be either equipped with a stirrer or without a stirrer.

The pressure outlet used in the present invention has a cross-sectional area of 1
It is in the range of 4 to 40 cm2 or more, preferably 4 to 40 cm2 or more. If the cross-sectional area is less than 1 cm2, polymer particles will clog inside the pressure tank during long-term operation, making measurement difficult. In order to avoid this drawback, purge gas is sometimes used, but in this case as well, its effectiveness decreases after a relatively short period of time, eventually leading to particle clogging. Furthermore, if the length of the pressure outlet is too short, particles may enter the detection piping after the outlet and cause the same trouble as described above, so it is preferable that the length be equal to or longer than the equivalent diameter of the cavity.

Furthermore, in the present invention, it is necessary to fill the inside of the pressure outlet with granular material in advance. If the polymerization reaction is started without filling the powder or granular material, it is not desirable because the polymer particles may enter the detection pipe after the pressure outlet in the early stage of operation as described above. The powder to be filled here is preferably an inert material with an average particle diameter of 500 to 2,000 μm, and inert polyolefin particles are particularly preferred. In a typical fluidized bed reactor, a seed polymer of the same type as the polymer particles is filled into the reactor before the start of operation, and at this time, it is particularly desirable to use the filled seed polymer as is.

An example of a structure in which the pressure outlet of the present invention is a circular pipe is shown in FIG. 1.

That is, fluidized bed reaction l! ! A lower pressure detection end 9 is provided at a position in contact with the fluidized bed 3 in the fluidized bed 3. The tip of the pressure detection end 9 is connected to a differential pressure measuring device 11 via a thin tube, and the pressure difference between the pressure detection end 9 and the pressure introduced from the upper pressure detection end (not shown) is measured.

The above structure is essential for the pressure outlet (lower pressure detection end) in the fluidized bed area, but the pressure outlet (upper pressure detection end) in the upper space area of the fluidized bed is usually blocked by particles. It is not necessarily necessary as it rarely occurs. However, it is desirable to use the structure of the present invention also at the upper pressure sensing end in consideration of the behavior of the polymer particles due to unexpected sudden changes in operating conditions.

The mounting position of the pressure outlet in the present invention is as follows. That is, the lower pressure sensing end is located above the gas distribution plate and within the fluidized bed area, and the upper pressure sensing end is located above the fluidized bed area and within the upper space area. The outlet is installed by penetrating the side wall of the reactor and protruding outward at right angles to the vessel wall, in the same way as in normal cases. However, it needs to have a structure that can hold the powder inside, and is usually installed horizontally.

Next, an example of the fluidized bed reactor according to the present invention will be explained with reference to FIG.

Reactant gas is circulated through the reactor 1 by a loop including a blower 13, a cooler 14, and a flow rate controller (not shown). The gas that has entered the reactor 1 is uniformly dispersed by the gas distribution plate 4, and then rises inside the reactor 1 while forming a fluidized bed 3. The differential pressure between the lower pressure detecting end 9 and the upper pressure detecting end 10 is guided to a differential pressure measuring device 11 and measured to confirm the height of the fluidized bed. Same pressure detection end 9.10 and differential pressure measuring device 1
In order to prevent condensation of propylene, 1-butene, etc., the detection piping between the two is preferably heated by a method that does not involve winding a steel pipe passed through steam.

Hydrogen is supplied into the system through piping 6, the olefin mixture through piping 7, and nitrogen through piping 17, respectively.

Further, the catalyst is supplied to the reactor 1 from the pipe 8, and the co-catalyst is supplied to the system through the pipe 5 together with the gas flow.

The produced polymer particles are appropriately taken out of the system through the discharge ball bubbles 15 and 16 so that the differential pressure measured by the differential pressure measuring device 11 becomes constant.

[Effects of the invention] In the polymerization reaction of polyolefin using a gas phase fluidized bed,
By improving the shape of the pressure outlet of the reactor,
It has become extremely easy to accurately measure and control the height of the fluidized bed, and the stable operation of the polymerization reaction over a long period of time has become possible.

[Examples and Comparative Examples] The present invention will be specifically explained below based on Examples and Comparative Examples, but the present invention is not limited by these.

Example 1 A fluidized bed reactor with a diameter of 25 CI [l] similar to that shown in FIG. 2 was used. As the lower and lower pressure detection ends, short pipes (pressure outlet ports) having the same shape and having an inner diameter of 25 IDI11 and a length of 130 mm were installed at positions 85 cm and 240 cm above the dispersion plate, respectively.

12 kg of previously dried linear low density polyethylene with an average particle diameter of t, soo μm was filled into the reactor as a seed polymer, and this filling amount reached a height sufficient to cover the lower pressure sensing end. Next, the gas in the system was circulated by a blower at a flow rate of 88 fI13/h, and the temperature was maintained at 60°C by adjusting the temperature of the circulating gas.

Hydrogen/ethylene ratio in gas phase (molar ratio, same below) 0.1
4. The amounts of each gas were adjusted so that the propylene/ethylene ratio was 0.45 and the nitrogen concentration was 25 mol%, and the total pressure was maintained at 20 kg/cm2·G.

0.2g/h of triethylaluminum as co-catalyst
The catalyst component molecule j is fed as a hexane solution at a rate of r.
, Mg, and AI supported on silica.
The polymerization reaction was started by feeding at a rate of 5 g/hr.

The production rate of the obtained ethylene-propylene copolymer was 2.4 kg/hr, and its properties were MFRO,!
58 g/10 min, density 0.9015 g/ct
The particles were clean particles with a white appearance and an average particle size of 1,450 μm.

The differential pressure was measured very well and the operation progressed smoothly.

When the reactor was stopped for inspection on the 13th day after the start of operation, the inside of the reactor was found to be extremely clean.

<Comparative Example 1> The same apparatus as in Example 1 was used, and the position of the pressure/force outlet was also the same. The shape of the upper pressure detection end is the same as in Example 1, but the lower pressure detection end is a stainless steel tube with an inner diameter of 2 mm inserted 30 mm into the inside of the cage wall, and nitrogen is flowed into the stainless steel tube! 50ON1/
h? It was played constantly.

Preparation The same amount of seed polymer as in Example 1 was charged to the reactor.

Using the same catalyst as in Example 1, ethylene
A polymerization reaction of 1-butene copolymer was carried out at a hydrogen/ethylene ratio of 0.28, a 1-butene/ethylene ratio of 0.38, a nitrogen concentration in the gas phase of 46 mol%, and a catalyst supply rate of 1.0 g/h.
The experiment was carried out under the same conditions as in Example 1 except that r was changed.

The production rate of the polymer is 3 kg/hr, and its properties are M F Ro, 90 g/10 lll1n, and density 0.9.
07537cm3, white in appearance, and average particle size of 1.
It was a loose particle of 590 μm.

After 23 hours had elapsed after the start of catalyst supply, the differential pressure gauge became incorrect, so the operation was stopped. When the inside of the reactor was inspected, it was found that the tip of the stainless steel tube used for the lower pressure detection end was clogged with molten polymer.

<Comparative Example 2> A polymerization reaction of an ethylene/1-butene copolymer was carried out using the same apparatus, catalyst, and conditions as in Comparative Example 1, except that nitrogen was not flowed to the lower pressure detection end.

After starting the catalyst supply, when BhrH was flowing, the tip of the stainless steel tube with an inner diameter of 2 mm used for the lower pressure detection end became clogged, so the operation was stopped.

<Example 2> Using the same apparatus and pressure outlet as in Example 1, a polymerization reaction of an ethylene/1-butene copolymer was carried out.

1214 g of par-dried linear low-density polyethylene with an average particle size of 800 μm was filled into the reactor as a seed polymer, and the lower pressure detection end was also filled.

As a catalyst, a silica-supported Ti-Mg-A I-based highly active solid catalyst, which was an improved version of the one used in Example 1, was used. Also, the temperature was 80°C and the hydrogen/ethylene ratio was 0.10.
The same conditions as in Example 1 were used except that the 1-butene/ethylene ratio was 0.40 and the triethylaluminum feed rate was 0.8 g/hr.

The production rate of the polymer was 3.1 kg/hr, and its properties were M F Ro, 86 g/10 min, and density 0.9.
203 g/cm”, with a white appearance and an average particle size of 85
It has a smooth ladle of 0μm.

The differential pressure was maintained at fil+ and operation continued normally, and after 26 days of operation, it was stopped and the inside of the Fi tea appliance was inspected, and it was found to be extremely clean.

Comparative Example 3> The same equipment and pressure outlet as in Example 1 were used.

Preparation: 6 kg of the same type of seed polymer as in Example 1 was filled into the reactor, or in this case, the filling height of the seed polymer did not reach the height of the lower pressure detection end, so the detection end was filled with the seed polymer. There was nothing I could do about it.

Using the same catalyst as in Example 2, ethylene and
A polymerization reaction of a 1-butene copolymer was carried out.

3 hours after the start of catalyst supply, an indication of the bed height rising due to the production of polymer particles began to appear on the differential pressure measuring device, and after that the bed height continued to rise steadily and was kept constant. While controlling the temperature, the produced polymer particles were extracted as appropriate.

However, after 12 hours had elapsed, the differential pressure indication became defective, so the operation was stopped. When the inside of the reactor was inspected, the inside of the lower pressure detection end was not found to be full of polymer particles, but it was found that some of them had melted and essentially blocked the pressure outlet.

[Brief explanation of the drawing]

FIG. 1 is an enlarged vertical sectional view of an embodiment of a pressure outlet of the present invention, and FIG. 2 is an explanatory diagram of an embodiment of a fluidized bed reactor. Patent applicant: Japan Petrochemical Co., Ltd.

Claims (1)

[Claims] (1) In a method of performing gas phase polymerization of olefin using a fluidized bed reactor, detecting the pressure in the upper space area of the fluidized bed and the fluidized bed area, and controlling the height of the fluidized bed by the differential pressure between the two, A method for controlling bed height, characterized in that the pressure outlet is composed of a cavity with a cross-sectional area of 1 cm^2 or more, and the inside of the pressure outlet is filled with powder or granular material in advance.