JPS5830885B2 - Polyolefin purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing purified polyolefins.

More specifically, the present invention relates to a method for purifying polyolefins to sufficiently remove catalyst residues.

If polyolefins produced using so-called Ziegler-type catalysts remain as they are, catalyst components remain, which adversely affects product quality.

Therefore, various methods have been proposed as such purification methods.

As one of these methods, a polyolefin hydrocarbon suspension produced using a so-called Ziegler type catalyst is treated with an alcohol to deactivate or decompose the catalyst (hereinafter referred to as alcohol treatment).

), followed by extracting the catalyst residue in a water extraction step and washing the polyolefin.

However, in this method, if the pH of the aqueous phase is not at least strongly acidic (pH 2 or less) or at least strongly alkaline (pH 12 or higher), hydroxides of metal components in the catalyst are generated during water extraction. It is difficult to sufficiently extract and remove the catalyst residue.

In this extraction process, the catalyst residue is actively precipitated in the aqueous phase by adjusting the pH value to a weakly alkaline condition of 5 or more.
, 48-7511), but the concentration of catalyst residue in the product obtained in this case was at an unacceptably high concentration level at the time of the patent application, and does not meet current demands from the product quality perspective. It's something you can't get.

On the other hand, methods in which the aqueous phase is treated under strong acidity with a pH value of 2 or less not only requires expensive corrosion-resistant materials due to the problem of corrosion in the process, but also requires complicated operations in terms of wastewater treatment, etc. I need.

In addition, in the method of treating the aqueous phase under strongly alkaline conditions with a pH value of 12 or higher, glass-lined equipment cannot be used, and expensive corrosion-resistant materials are required because alkali stress corrosion cracking of heat exchange equipment, etc. becomes a problem. Not only that, but also complicated operations are required in terms of wastewater treatment, etc.

Therefore, it is of great industrial significance to develop a method that can sufficiently and easily extract catalyst residues from polyolefins by water extraction in a mild pH range in response to product quality issues.

The present invention aims to solve these problems,
Investigation of the causes of the above-mentioned drawbacks of the water extraction process,
As a result of intensive studies on improvement methods, we found that in non-aqueous systems, a specially selected organic compound is added to a hydrocarbon suspension of polyolefin for treatment (hereinafter, this process is referred to as a special treatment process), followed by water extraction. This goal was successfully achieved through processing.

Now, the polyolefin to be purified in the method of the present invention is a polyolefin produced using a Ziegler type catalyst.

As is well known, this catalyst is composed of a combination of a compound of a metal selected from Groups 1 to VIA of the periodic table and a hydride or organometallic compound of a metal from Groups 1 to 2 of the periodic table. be.

As the first component of the catalyst, various materials can be used as is well known, but a particularly preferred one is a titanium-based Ziegler type catalyst, specifically a combination of titanium trichloride or a halide of another metal. Examples include eutectics and mixed crystals.

Further, these halides may be a pulverized product, a mixture of two or more types, a mixture with other organic compounds, or a complex compound, and furthermore, a trivalent or tetravalent titanium compound supported on a suitable carrier. It's okay.

Various types of second components can be used for the second component of the catalyst, but particularly preferred are organoaluminum compounds, particularly alkylaluminum halides.

In addition to these two components, the catalyst also contains N, 0. Various compounds containing P or Si, etc., and tertiary compounds such as unsaturated hydrocarbons may be included.

Examples of the polyolefin in the present invention include a-olefins such as ethylene, propylene, butene-1,4-methylpentene-1,3-methylbutene, and polymers or copolymers of mixtures of these α-olefins. The most typical examples are polypropylene, poly(propylene/ethylene) copolymer, poly(propylene/1-butene) copolymer, and poly(propylene/ethylene/1-butene) terpolymer.

Although any method may be used for the polymerization reaction of the α-olefin of the present invention, it is usually carried out in the presence of hydrocarbons as a suspending medium.

Such hydrocarbons include hydrocarbons kept in a liquid state such as propane, butane, pentane, hexane, heptane, etc.
Alternatively, an excess of monomer is used which remains liquid at the polymerization reaction pressure.

Note that it is also within the scope of the present invention to use a hydrocarbon suspension in which a polyolefin obtained by a so-called gas phase polymerization method, which is polymerized in a gaseous monomer, is dispersed in the suspension medium.

This polyolefin is post-treated (refined) in the presence of the hydrocarbons.

Since the above-mentioned typical polyolefins are generally insoluble or sparingly soluble in hydrocarbon media, it is convenient to perform a purification treatment on a hydrocarbon suspension of the polyolefin.

As this suspension, one obtained from the polymerization step (polymerization slurry) can be used as it is.

The amount of hydrocarbon sac is arbitrary, but is generally between 100 and 900 parts by weight of the polyolefin.

As the hydrocarbon suspension of polyolefin to be targeted in the special treatment step of the present invention, either a hydrocarbon suspension during alcohol treatment or a hydrocarbon suspension after alcohol treatment can be used. .

Particularly selected organic compounds used in the particular process steps of the invention are carboxylic acid derivatives, such as formamide, N-methylformamide, N,N-dimethylmamide, acetamide or acetonitrile;
The amount used is the metal component (total number of moles of metal atoms) that makes up the catalyst contained in the polyolefin hydrocarbon suspension.
It is at least 0.1 times the amount by mole.

If the number of moles added is less than 0.1 mole times, the purpose cannot be sufficiently achieved.

There is no need to specifically stipulate the upper limit of usage, but
This is determined to avoid diseconomies in terms of variable costs due to increased usage after the desired effect is achieved.

That is, it is usually used in a range of 0.1 times to 100 times by mole, particularly preferably in a range of 1 times to 10 times by mole.

These organic compounds can be added as they are, but they can also be added in the form of being dissolved in a non-aqueous solvent or in the form of being dispersed in a non-aqueous medium.

The solvent or dispersion medium must be dry.

The treatment temperature in this step is from room temperature to the boiling point of the hydrocarbon medium of the polyolefin and the mixture of the above-mentioned organic compounds used in the automobile invention, but the polyolefin does not dissolve into the hydrocarbon suspension. It is preferable to carry out the process at a temperature below which there is no risk of swelling.

That is, it is carried out at a temperature ranging from normal to 80°C.

The processing time of this step is generally several minutes to several hours.

During the treatment, it is important to thoroughly mix and stir the polyolefin hydrocarbon suspension.

The special treatment step is thus followed by a conventional water extraction step.

The water extraction step is not a particularly new process and can be operated in a commonly known manner.

The water extraction temperature is from room temperature to the boiling point of the reaction mixture.

There is no need to specify the pH of the aqueous phase, but
As mentioned above, the features of the present invention can be particularly advantageously exhibited when operating in a mild pH range that is neither strongly acidic nor strongly alkaline.

In that case, it is not necessary to particularly add a pH adjuster, but the addition of an alkali, acid, or other buffering agent is also within the scope of the present invention.

Usable alkalis include sodium hydroxide, potassium hydroxide, sodium pyrophosphate, sodium carbonate, ammonia, etc. alone or in mixtures.

Usable acids include hydrochloric acid, acetic acid, phosphoric acid, nitric acid, etc. All well-known general compounds can be used as usable buffers.

Specific examples include combinations of potassium hydrogen phosphate and sodium hydroxide, combinations of sodium citrate, combinations of sodium citrate and sodium hydroxide, combinations of potassium dihydrogen phosphate and disodium hydrogen phosphate, Examples include a combination of borax and hydrochloric acid.

The water extraction step is a step in which the alcohol-treated product of the catalyst is extracted from the hydrocarbon medium into the aqueous phase.

Therefore, it is also possible to use agents that promote and stabilize water extraction, such as surfactants and chelating agents.

In addition, bleaching agents such as sulfites, bisulfites, and other fluorescent bleaches may be added to the aqueous phase to make polyolefins appear whiter, and various stabilizers such as antioxidants and processing stabilizers for polyolefin products may be added to the aqueous solution. It is also effective to add it to

Further, depending on their properties, these various stabilizers can be added to the polyolefin hydrocarbon suspension after the aqueous phase separation in order to prevent losses during the aqueous phase separation.

If the treated product is allowed to stand after the water extraction process is completed, it will be separated into an aqueous phase in which the catalyst residue is dissolved and retained, and a hydrocarbon suspension phase in which the polyolefin is retained in suspension.

By removing this aqueous phase, catalyst residues are removed from the hydrocarbon suspension phase and thus from the polyolefin.

Then, if necessary, add pure water to this hydrocarbon suspension phase.
The catalyst residue can be completely removed by washing more than once.

As one embodiment, a countercurrent water extraction process can be employed.

The hydrocarbon suspension phase of polyolefins treated in this way usually still contains small amounts of acidic substances, such as hydrogen chloride, derived from catalyst residues.

Therefore, in order to completely prevent corrosion caused by this, various neutralizing agents are essentially added.

Examples of neutralizing agents that can be used include ammonia, sodium hydroxide, ethylene oxide, and propylene oxide, with propylene oxide being particularly preferred.

These additions can be carried out singly or in combination, as is or in a solution state.

After the aqueous phase separation, the polyolefin hydrocarbon suspension is then used in separation equipment such as a centrifugal separator to remove most of the hydrocarbon medium, resulting in a polyolefin cake that is transferred to the next drying process, and after drying, the product is powdered. Alternatively, it can be further subjected to a granulation process to obtain product pellets.

Next, the main effects of the present invention will be explained in detail.

The present invention is based on the first aspect of the present invention, during the alcohol treatment of a polyolefin hydrocarbon suspension after the completion of the polymerization reaction, or prior to the water extraction step to the polyolefin hydrocarbon suspension after the alcohol treatment. By simply adding and treating the organic compound, the water extraction efficiency of the catalyst residue in the next water extraction step can be increased, and as a result, the concentration of the catalyst residue in the polyolefin powder or pellets can be significantly reduced.

Second, the present invention significantly reduces the concentration of acidic substances derived from catalyst residues, specifically hydrogen chloride is the most representative one, by significantly reducing the concentration of catalyst residues in polyolefins as described above. By lowering it, it is possible to suppress the occurrence of cooling roll deposits (usually referred to as roll staining) when polyolefin is subjected to extrusion film forming processing.

As a result, not only the workability of the film forming operation can be significantly improved, but also a stable and high quality polyolefin film can be obtained.

Thirdly, the present invention is capable of significantly reducing the concentration of catalyst residues in polyolefins as described above, resulting in highly stabilized polyolefins that have excellent color, heat resistance, and weather resistance. molded products can be obtained.

In other words, the polyolefin obtained by the present invention not only has a better hue of molded products thermoplasticized with the addition of a phenolic antioxidant, but also has better pressability than polyolefins obtained by ordinary alcohol treatment and water extraction. piece 1
As for the long-term thermal stability test result by 50° C. open test, the product of the present invention has better heat resistance and a slightly longer result.

Fourth, Kinobu found that compared to polyolefins obtained by conventional alcohol treatment and water extraction, when produced stretched films, the film has significantly superior transparency in both uniaxial and biaxial stretching. can be obtained.

The transparency of a stretched film depends on the amount of microbubbles, usually called voids, in the film, and the number of voids is determined by the amount of microscopic inorganic particles present in the polyolefin.

This relationship is shown in Table 1 and the Examples below.

The measurement of the number of voids in Table 1 was carried out in the same manner as in Example 1.

A commercially available film was used. As can be seen from Table 1, there is a good correlation between the transparency of the stretched film and the number of voids.

Although the present invention will be described in more detail with reference to Examples below, the effectiveness of the present invention is not limited by the Examples unless it exceeds the scope of the claims.

Example 1 (1) Heptane as solvent 0.61. Titanium trichloride as catalyst 0.2. ? , diethylaluminum chloride 1
g and hydrogen as a molecular weight regulator at 6 kg/ff.
22 ml was placed in a 21 autoclave under 1-G, and propylene was introduced at 70° C. for 6 hours under 9 kg/crit-G and polymerized to obtain a butane slurry in which 0.2 kg of polypropylene was polymerized.

(2) Next, add 30ml of n-butanol and hold at 70°C.
The mixture was stirred for 1.5 hours to perform catalytic decomposition.

(3) Next, add the organic compound listed in Table 2 in an amount equivalent to 6 times the mole of the total amount of Ti and A7, which are the metal components constituting the catalyst (hereinafter referred to as the amount equivalent to times the mole of catalyst metal). Then, stabilization treatment was performed at 60° C. and 1 atm for 1 hour.

(4) After that, pure water o, s, and g were added and stirred at 60°C for 2 hours.

When left to stand still, the mixture separated into two layers: the upper layer was a polypropylene hepkun slurry, and the lower layer was an aqueous phase in which the catalyst decomposition products were dissolved and retained.

After separating the lower layer, 0.8A of pure water was added again and the temperature was increased to 0.8A at 60°C.
Stirred for 5 hours.

The aqueous phase was separated, and the heptane phase containing butanol and soluble polypropylene was then centrifuged to obtain a polypropylene cake.

This polypropylene cake was dried under reduced pressure to obtain polypropylene powder 0.2 to 9.

The intrinsic viscosity of this polypropylene powder measured in tetralin at 135°C is 2.1, and the isotactic part is 9.
It was Section 8.

(5) To this polypropylene powder, add 0.4 parts by weight of butylated hydroxyl toluene and 0.4 parts by weight of calcium stearate, mix thoroughly with a mixer, and mix thoroughly with a mixer.
m1) at a temperature of 190° C. and a rotation speed of 5 Orpm for 5 minutes, the bath melt was cut to obtain polypropylene pellets.

(6) Hot press the obtained pellets (press temperature 2
20'C) with a thickness of 300μ (referred to as press piece A)
A press sheet with a thickness of 2 times (referred to as press piece B) was prepared.

(Quick cooling temperature is 40°C) (7) Punch out a circular sample of 50 mm ψ from the press piece B and apply it to a fluorescent X-ray analyzer for analysis (hereinafter referred to as rFX analysis).

) Then, Ti, A7 and CI in polypropylene
The residual concentration of was as shown in Table 2.

(8) Press piece A 10C1'ILX 10cm was used as a stretched original fabric, and a stretched film with a thickness of about 15μ was obtained by simultaneous two-wheel stretching at a stretching temperature of 120°C and a stretching ratio of 4x4 using a research biaxial stretching machine manufactured by Wakagi Seisakusho. It was created.

(9) Next, the number of voids with a diameter of 10μ or more per 1 d of the stretched film obtained by the above method was counted by the phase contrast method (bright contrast, magnification: 100x) using an optical microscope, and the results were calculated per 15μ in thickness. It is shown in Table 2.

(10) A 50 mm ψ punched piece of press piece B was used as a sample, and the hue was measured using a color difference meter manufactured by Nippon Heavy Industries KK.

The hue of polypropylene can be represented by the degree of yellow coloring, and the b value is a measure of this.
It has a small color and can therefore be said to be colorless.

The results in this case are shown in Table 2.

(25+u+ψ punched from 1υ press piece B was used as a sample, and held at 150°C in an open state to study the number of hours required for thermal deterioration (referred to as LTH8 value).

The results are shown in Table 2. Comparative Example 1 The same operations as in Example 1 were performed except that the addition treatment of the compound (3) of Example 1 was not performed, and the evaluation results are shown in Table 2.

Example 2 In Example 1, formamine change the amount of code used * *Other than the above considerations, all operations were the same as in Example 1.

The evaluation results are summarized in Table 3. Example 3, Comparative Example 2 Heptane 0.61 as solvent, titanium trichloride 0 as catalyst
．． Using 2g of diethyl aluminum chloride and 1g of diethylaluminum chloride, hydrogen was added as a molecular weight regulator at 6kg/cwt・G.
2rull, ethylene at 60℃, 9kg/i・G 6
Propylene was introduced while controlling the average flow rate so that the total amount was 600 m1 over time, and propylene was heated at 60°C.
Induction for 6 hours under 9 kg/cyit-G,
A butane slurry was obtained by polymerizing a 0.2 ky fluoropylene-ethylene copolymer.

The following operations were performed in exactly the same manner as in Example 1 and Comparative Example 1.

When the propylene-ethylene copolymer finally obtained was measured in tetralin at 135°C, the intrinsic viscosity was 2.6, the isotactic part was 920; Content is 4wt%
Met.

Other evaluation results are summarized in Table 4.

Claims (1)

[Claims] 1 Adding formamide, N-methylformamide, N,N-dimethylformamide, acetamide or acetonitrile to a hydrocarbon suspension of a polyolefin produced using a Ziegler type catalyst during or after alcohol treatment, and adding a catalyst to it. A method for purifying polyolefin, which comprises adding at least 0.1 times the mole of the constituent metal components, followed by water extraction.