JPH0460131B2 - - 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.

PRIOR ART Conventionally, single-stage or multi-stage reciprocating compressors are used to compress 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 in which at least one of the following three conditions apply: (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 plunger or cylinder jacket is generally made of treated steel, cast iron or a metal carbide such as tungsten carbide, and the sealing element is made of 9% tin,
Bronze with 0.3-1% phosphorus, balance copper, e.g. UE9P
made of 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. That is, the number of hours of operation without 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 using an optical and electron microscope and found that the cause of wear in the sealing element of a compressor 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 at least one piston plunger or cylinder jacket and at least one piston plunger or cylinder jacket.
In a reciprocating compressor for compressing fluids to extremely high pressures used in the ethylene polymerization process, the reciprocating compressor has two sealing elements, in which at least the portion where the piston plunger or cylinder jacket and the sealing element are in contact with each other has a weight of 80 to 99 mm. % of at least one compound selected from carbides, nitrides, oxides and borides of metals selected from the group consisting of tungsten, chromium and titanium, and 1 to 20% by weight of cobalt, nickel. , aluminum, and at least one metal binder selected from the group consisting of aluminum and alloys thereof.

Function The present invention is based on the discovery that by using the above-mentioned material as a material for members that move relative to each other in a reciprocating compressor used in the ethylene polymerization method, continuous operation can be performed for a long time without trouble.

The materials used in the present invention are known per se and are not subject to the present invention.

According to the invention, the material constituting the sealing element and the material constituting the piston plunger or cylinder jacket are made of the same material.
It should be noted that the composition ratio of the material constituting the sealing element and the material constituting the piston plunger or cylinder jacket can be different, and in some cases, the secondary properties of the materials constituting these two parts, For example, the crystal form, lattice constant, and/or melting point of the metal binder may be different.

The metal binder preferably has a face-centered cubic crystal system or a close-packed hexagonal crystal system, a lattice constant within the range of 2.51 to 4.10 Å, and a melting point of at least
Preferably it is 1453°C.

The reciprocating compressor of the present invention can be used under the following conditions.
It can be operated without any problem for a period of more than 2000 hours: (a) if the temperature of the fluid to be compressed, liquid or gas, is in the range -30 to +200°C during the entire compressor process; (b) If the pressure of the fluid is greater than or equal to 150 bar, (c) the average velocity of the relative reciprocating motion of the compressor members 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 in all stages of the compressor, and may be various chemical substances such as helium and ammonium. - olefins, hydrogen or saturated hydrocarbons, such as propane,
It can be applied particularly advantageously in mixtures with 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, it is stated in 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. Usable transition metal halides include chromium,
There are π-allyl or benzyl complexes of zirconium and titanium, trichlorides of vanadium and titanium (which may also be eutectic with aluminum chloride in the form TiCl ₃ 1/3 AlCl ₃ ), which can be used as needed. It is used by being supported on a carrier made of a magnesium halide, monohalide, or hydrohalide. These compounds can be used in the presence of complexing agents such as lower alcohols, metal alcoholates, 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. Monomer from this separator 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, the particle size is
Low molecular weight polymer particles of 250 μm are included, and these low molecular weight polymer particles cause wear. That is, the catalyst residues in the recirculated fluid are compressed and their content reaches 0.5 ppm or more, causing wear of the sealing elements of the compressor.

Therefore, the reciprocating compressor of the 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 reacted. It can be used in ethylene polymerization processes where the ethylene from the separator contains at least 0.5 ppm of catalyst system residue in the ethylene polymerization process where the ethylene is recycled to the vessel. 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. A reciprocating compressor for compressing fluids used in the ethylene polymerization process to very high pressures, which has at least one piston plunger or cylinder jacket and at least one sealing element, comprising at least one piston plunger or cylinder jacket and at least one sealing element. The part where the plunger or cylinder jacket and the sealing element are in contact with each other is made of 80-99% by weight of carbides, nitrides, oxides and borides of metals selected from the group consisting of tungsten, chromium and titanium. At least one compound selected from the above, and at least one metal binder selected from the group consisting of cobalt, nickel, aluminum, and alloys thereof in an amount of 1 to 20% by weight. A reciprocating compressor characterized in that it is made of seed material. 2. Claim 1 in which the metal binder has a face-centered cubic or close-packed hexagonal crystal structure
The reciprocating compressor described in Section. 3. The reciprocating compressor according to claim 1 or 2, wherein the metal binder has a lattice constant within the range of 2.51 to 4.10 Å. 4. The reciprocating compressor according to any one of claims 1 to 3, wherein the metal binder has a melting point of 1453°C or higher. 5 The average speed of relative motion of the reciprocating compressor is 5 m/s
A reciprocating compressor according to any one of claims 1 to 4 below. 6. A reciprocating compressor according to any one of claims 1 to 5, used for compressing a fluid to a 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. A reciprocating compressor according to claim 11, which is used legally.