JPH0460132B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a reciprocating compressor used to compress fluids used in ethylene polymerization processes, particularly in ethylene and α-olefin copolymerization processes, to extremely high pressures. It is related to.

BACKGROUND OF THE INVENTION Single-stage or multi-stage reciprocating compressors are commonly used to compress fluids to pressures above 150 bar. Inside the cylinder of this reciprocating compressor, a piston plunger or cylinder jacket is housed and a sealing element is used. In the case of a piston plunger, the sealing element is at least one stationary seal made of several parts; in the case of a cylinder jacket, the sealing element is at least one movable segment integral with the piston. In the case of a stationary packing, a dynamic seal is provided between the stationary packing and the piston plunger, and in the case of a moving segment, a dynamic seal is provided between the cylinder jacket and the moving segment.

The present invention is particularly suitable for fluids that meet at least one of the following three conditions: (1) fluids that contain trace amounts of abrasive particles; (2) fluids that are not self-lubricating and the addition of external lubricants is (3) A fluid that does not have self-lubricating properties and can be used as a solvent for the lubricant, although an external lubricant can be added.If the fluid to be compressed does not meet any of the above three conditions, especially if the fluid does not have self-lubricating properties. with and/or without traces of abrasive particles; and/or
Alternatively, if the surfaces in contact with the dynamic sealing element are lubricated, the compressor can operate stably for more than 7000 hours without requiring special attention to the materials of the compressor components.

For example French patent no. 1584529, no. 2025887
No. 2099267 and No. 2313399, a process in which ethylene or a mixture of ethylene and a polar comonomer is polymerized at high temperatures in the presence of free radical initiators under pressure up to 150-3000 bar. In the reciprocating compressors used, the piston langier or cylinder jacket is generally made of treated steel, cast iron or a metal carbide such as tungsten carbide, and the sealing element is 9% tin, 0.3% phosphorus.
Made of bronze with ~1%, balance copper, e.g. UE9P bronze. These materials can be used if the ethylene of the compressed fluid does not contain any traces of abrasive particles.

On the other hand, if the fluid to be compressed meets at least one of the above three conditions, a reciprocating compressor whose parts are made of commonly used materials cannot operate satisfactorily. In other words, the number of hours of operation before failure is in the hundreds, and without lubrication and/or
Or several tens of hours if the fluid contains abrasive particles. In order to analyze the cause of this shortcoming, we examined the surface of the sealing element with an optical and electron microscope and found that the cause of wear in the sealing element of compressors is that the surface of the sealing element wears out very quickly. I understand.

Problems to be Solved by the Invention The purpose of the present invention is to solve various technical problems when compressing a fluid that meets at least one of the above three conditions to a pressure of 150 bar or more using a reciprocating compressor. It is in.

SUMMARY OF THE INVENTION The present invention provides an extremely high temperature fluid for use in ethylene polymerization processes having at least one piston plunger or cylinder jacket made of cast iron, steel or tungsten carbide and at least one sealing element. In a reciprocating compressor for compressing to pressure, the sealing element is composed of at least one metal alloy consisting of bronze or a titanium-based alloy, and of polytetrafluoroethylene, polyimide and polyimide-amide. It is characterized in that it is made of a composite material of at least one polymer selected from the following or a graphite-silver sintered compound.

Function The present invention is based on the discovery that by using the above-mentioned composite material as a material for the sealing element of a reciprocating compressor used in the ethylene polymerization process, it is possible to operate the compressor continuously for a long time without trouble.

The composite material constituting the sealing element of the invention is itself known. In other words, the bronze that makes up this composite material is particularly
Examples of alloys containing titanium as a main component include alloys of titanium and silver, such as UE9P bronze.
Mention may be made of an alloy of 94% by weight titanium and 6% by weight silver.

The polymer constituting the composite material is selected from the group constituted by polytetrafluoroethylene, polyimide and polyimideamide. The polymer can optionally be filled with graphite and/or glass fibers and reinforced with woven bronze fabric.

The ratio of the two components constituting the composite material can be selected depending on the application.

The above two types of components forming the composite material constituting the sealing element of the reciprocating compressor of the present invention can be combined by the following two methods.

The first bonding method is a bonding method using an adhesive. Preferred adhesives are those having a peel strength of 3 KN/m or more at 100°C on a test piece with a width of 10 mm.

A second bonding method is for example vacuum soldering using gold-germanium alloy or silver.
vide) form. With this joining method,
Preference is given to using a composite material with a geometry of polymer or graphite-silver sintered compound inserted into an alloy ring.

The reciprocating compressor of the present invention can be used under the following conditions.
It can be operated without any problems for more than 1000 hours: (a) If the temperature of the fluid to be compressed, liquid or gas, is in the range of -30 to +200°C during the entire compressor process (b) If the temperature of the fluid If the pressure is 150 bar or more, (c) the average speed of the relative reciprocating motion of the compressor parts is 5
m/S (d) When the compressed fluid contains traces of abrasive particles in an amount such that the coefficient of friction is approximately 0.5 (e) When the compressed fluid does not have self-lubricating properties and If external lubricant cannot be supplied. The fluid targeted by the present invention is a liquid or gas that has a temperature in the range of -30 to 200°C at all stages of the compressor, and may be various chemical substances such as helium and ammonia. - Can be applied with particular advantage to mixtures with olefins, hydrogen or saturated hydrocarbons, such as propane, butane.

That is, the reciprocating compressor according to the present invention has various uses in the chemical industry, and can be used for polymerization of ethylene or copolymerization of ethylene and α-olefin under high pressure.

Namely, the polymerization of ethylene is carried out between 140 and 300 °C at a pressure of over 500 bar in the presence of a Ziegler catalyst system.
French patent no.
It is known from No. 2021952. Various catalyst systems are known for use in ethylene polymerization and copolymerization of ethylene and α-olefins under high temperature and high pressure conditions. These catalyst systems generally contain at least one transition metal halide and at least one activator selected from hydrides and organometallic compounds of metals of groups 1 to 1 of the Periodic Table of the Elements. Possible transition metal halides include π-allyl or benzyl complexes of chromium, zirconium and titanium, trichlorides of vanadium and titanium (when in eutectic form with aluminum chloride in the form TiCl ₃ .1/3 AlCl ₃ ), and these are used by supporting them on a carrier made of a magnesium halide, monohalide, or hydrohalide, if necessary. These compounds include lower alcohols, metal alcoholates,
It can be used in the presence of complexing agents such as alkyl silicates, aryl or alkyl siloxanes, ethers or amines. Activators that can be used include trialkylaluminums, halogenodialkylaluminums and alkylsiloxanes.

In the above polymerization or copolymerization methods, the reaction mixture from the reactor is sent to a separator at a pressure of 50 to 500 bar to separate the polymer and unreacted monomers. From this separator the monomer is compressed to reaction pressure and recycled to the reactor.

In this case, it has been found that non-negligible amounts of catalyst residues, in particular low molecular weight polymers containing aluminum compounds or other reducing compounds, are entrained in the compressed unreacted monomer stream. Therefore, at the inlet of the compressor, particles with a particle size of 1 to 250 μm are used.
m of low molecular weight polymer particles enter, and these low molecular weight polymer particles cause wear. That is, the catalyst residues in the recirculated fluid are compressed to a content of 0.5 ppm or more, causing wear of the sealing elements of the compressor.

Therefore, the reciprocating compressor of the present invention is particularly suitable for polymerizing ethylene in a reactor in the presence of a Ziegler catalyst system at a pressure of more than 200 bar and a temperature of more than 170°C;
The mixture from the reactor is sent to a separator under a pressure of 50 to 500 bar, in which the polymer and unreacted ethylene are separated, and the ethylene from the separator is pressurized to the pressure of the reactor and transferred to the reactor. It can be used in ethylene polymerization processes where the ethylene from the separator contains at least 0.5 ppm catalyst system residue. Using the reciprocating compressor of the present invention, the polymerization process described above can be operated with high reliability.

The polymerization of ethylene can be carried out, for example, in the presence of 1 to 50% by weight of an inert hydrocarbon such as propane or butane and/or in the presence of up to 2 mol% hydrogen. This polymerization is carried out continuously, but any reactor such as an autoclave or a tubular reactor can be used. The reactor may have multiple reaction zones. The reciprocating compressor of the present invention is a copolymer of ethylene and α-olefin, such as propylene or butene-1, or ethylene and α-olefin.
It can also be used in the polymerization of terpolymers of olefins, such as propylene, and non-conjugated diolefins.

Claims (1)

Claims: 1. Compression of fluids used in the ethylene polymerization process to extremely high pressures, having at least one piston plunger or cylinder jacket made of cast iron, steel or tungsten carbide, and at least one sealing element. In a reciprocating compressor for A reciprocating compressor, characterized in that it is made of a composite material with at least one polymer selected from: or a graphite-silver sintered compound. 2. The reciprocating compressor according to claim 1, wherein the polymer is filled with graphite and/or glass fiber. 3. A reciprocating compressor according to claim 1 or 2, wherein the polymer is reinforced with a bronze woven fabric. 4. Reciprocating compression according to any one of claims 1 to 3, wherein the metal alloy of the composite material and the polymer or graphite-silver sintered compound are bonded by adhesive bonding or vacuum welding. Machine. 5. A reciprocating compressor according to claim 4, wherein the composite material is reinforced by inserting a polymer or graphite-silver sintered compound into the metal alloy ring. 6. A reciprocating compressor according to any one of claims 1 to 5, which is used to pressurize a fluid under a compression pressure of 150 bar or more. 7 The temperature of the fluid at all stages of the compressor ranges from -30 to +
A reciprocating compressor according to claim 6, wherein the temperature is between 200°C. 8. A reciprocating compressor according to claim 6 or 7, wherein the fluid contains traces of abrasive particles. 9. The reciprocating compressor according to any one of claims 6 to 8, wherein the fluid does not have self-lubricating properties and no external lubricant is added to the fluid. 10. The reciprocating compressor according to any one of claims 6 to 9, wherein the fluid does not have self-lubricating properties and an external lubricant can be added to the fluid, but it is a solvent for the external lubricant. 11. According to any one of claims 6 to 10, wherein the fluid is ethylene or a mixture of ethylene and at least one compound selected from the group consisting of α-olefins, hydrogen, and saturated hydrocarbons. Reciprocating compressor as described. 12 In the presence of a Ziegler catalyst system in a reactor
Ethylene is polymerized at a pressure of more than 200 bar and a temperature of more than 170°C, and the mixture from the reactor is sent to a separator under a pressure of 50 to 500 bar, in which the polymer and unreacted ethylene are separated. is used in ethylene polymerization processes in which the ethylene from the separator is pressurized to the reactor pressure and recycled to the reactor, and where the ethylene from the separator contains at least 0.5 ppm of catalyst system residue. The reciprocating compressor according to claim 11, which is used legally.