JPS582307A - Production of ethylene polymer through solution polymerization process - Google Patents

Abstract

PURPOSE:Polymerization is carried out using a coordinated polymerization initiator under such conditions as the polymer dissolves uniformly in a solvent containing an aliphatic hydrocarbon, then the polymer solution is heated to cause separation into the high polymer-concentration phase and the low one and the solvent is removed from the high concentration phase to give the titled polymer. CONSTITUTION:The polymerization of ethylene or a mixture thereof with a copolymerizable monomer is carried out using a coordinated polymerization catalyst so that the polymer formed dissolves uniformly in a hydrocarbon solvent containing at least 50wt% aliphatic hydrocarbons and the resultant polymer solution is taken out of the polymerizer 1. Then, the solution is combined with a high-temperature catalyst 9 by means a mixer 5 and sent to the phase separated 2 where the solution is heated to effect separation and the dilute phase is taken out of the upper layer through line 7 and the concentrated one is from the lower layer through line 6. The solvent in the dilute phase is vaporized in the flush tank 3 and the vapor 10 is condensed and sent to the polymerizer 1, while the solvent and unreacted monomers in the concentrated phase 6 are removed to give the objective polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for solution polymerizing ethylene and concentrating the resulting polymer solution by phase separation.

A method of solution polymerizing ethylene using a coordination polymerization catalyst is known. Usually, polymerization is carried out in the presence of a hydrocarbon solvent at a temperature higher than the temperature at which the resulting polymer dissolves, for example 120 to 250°C.
will be combined. It is also known to heat the resulting polymer and then apply vacuum to flash evaporate the solvent and unreacted monomer and concentrate the polymer solution. In addition, when polymerizing with aliphatic hydrocarbons at high temperatures, the polymer solution forms two phases,
It is known from JP-A-55-157606 that the polymer tends to separate into a concentrated phase and a dilute phase, resulting in a non-uniform polymer. Although the phase separation phenomenon is known, knowledge regarding the concentration of each phase has not been reported.

The present inventors have continued to study intensively on a method that utilizes the phase separation phenomenon for concentrating and separating polymers, and that can also obtain homogeneous polymers, and as a result, they have arrived at the present invention.

That is, the present invention uses a coordination polymerization catalyst to contain at least 50% by weight of ethylene alone or ethylene and a hydrocarbon monomer copolymerizable with ethylene, including at least 50% by weight of aliphatic group hydrocarbons.
Polymerizing in a hydrocarbon solvent containing polymerization conditions such that the produced polymer is uniformly dissolved in the solvent, heating the resulting polymer solution,
Two phases: a concentrated phase with a high polymer concentration and a dilute phase with a low polymer concentration.
This is a method for producing a crystalline ethylene polymer, which is characterized by phase separation into phases and further removing the solvent and unreacted monomers from the concentrated phase to obtain a polymer.

The monomers used in the invention are ethylene and hydrocarbons copolymerizable with ethylene, such as alpha-olefins and dienes, such as propylene, butene-1, pentene-1,
1, hexene-1,4-methylpentene-1, octene-1, decene-1,1,4-hexene? diene, 1,7-octadiene, ethylidenenorbornene, bicyclo-(2
, 2, 1) -2,5-hebutane, 1,4-butadiene, etc. Ethylene and two or more comonomers may be polymerized.

The resulting polymer has an ethylene content of 80% by weight, is crystalline, and has an average molecular weight of i, o o o to i o o
o, o o o.

As the coordination polymerization catalyst used in the present invention, all known catalysts can be used. In other words, the so-called Ziegler catalyst consisting of a combination of a transition metal compound of groups Ⅰ to ■ and an organometallic compound of groups Highly active catalysts that do not require catalyst removal are being developed, such as the catalyst described in JP-A No. 53-40696, and catalysts 120-350 described in JP-A No. 56-28206.
Catalysts synthesized from organic magnesium, inorganic halogen compounds, titanium compounds, and vanadium compounds that exhibit high activity even at high temperatures of °C can also be suitably used.

The solvent used in the present invention is a solvent containing at least 50% by weight of an aliphatic hydrocarbon, and preferably the remainder is an alicyclic hydrocarbon. It has been found that it has various advantages over hydrocarbons, such as the following, and is of high industrial value. First of all, the use of aliphatic hydrocarbons results in a much lower solution viscosity of the polymer than that of cycloaliphatic hydrocarbons;
~70%. In solution polymerization, 5- Low viscosity is a very big advantage. If the viscosity is high, the power required for the polymerization vessel will increase, and the monomer, catalyst,
This is accompanied by accumulating difficulties such as insufficient mixing of the solvent and difficulty in removing heat from the polymerization vessel jacket. In order to keep the solution viscosity below a certain value, when an alicyclic hydrocarbon solvent is used, the polymer concentration must be lower than that of an aliphatic hydrocarbon solvent. This requires the use of a large amount of solvent, which is disadvantageous in terms of solvent loss and solvent purification costs.

The second feature of aliphatic hydrocarbon solvents is that they have a higher specific heat, lower latent heat of vaporization, and lower boiling point than alicyclic hydrocarbons. A large specific heat means that the temperature rise due to polymerization heat is small. In general, coordination polymerization catalysts are more likely to be deactivated as the temperature increases, so the higher the polymerization temperature, the more difficult it is to achieve high activation. Therefore, the fact that polymerization can be carried out at a relatively low temperature with little increase in polymerization temperature means that a small amount of catalyst is required and it is easy to obtain a highly active catalyst without the need for a catalyst removal step. The low latent heat of vaporization and low boiling point mean that the amount of steam, etc. required for separating and recovering the solvent from the polymer solution and refining the recovered solvent is small, and This has the advantage that residual solvent can be easily removed.

The third feature of aliphatic hydrocarbon solvents is that aliphatic hydrocarbons and mixtures thereof can be obtained at lower cost as a fraction of petroleum.

If the content of aliphatic hydrocarbon in the solvent used is less than 50% in the lower phase, not only will the above-mentioned features not be exhibited, but the phase separation temperature will be high and close to the critical temperature, making separation difficult.

Examples of hydrocarbon solvents that can be used in the present invention include:
Butane, isobutane, pentane, hexane, heptane,
Aliphatic hydrocarbons such as octane, isooctane, dodecane, undecane, cyclopentane, methylcyclopentane,
Alicyclic hydrocarbons such as cyclohexane are used alone or as a mixture of two or more, and light naphtha or mixed hexane, which is a petroleum fraction, is used. Among these, mixed hexane, which is industrially used in large quantities as a fraction of petroleum, is preferably used. The composition of mixed hexane varies depending on the conditions of rectification, but usually contains 25-70% n-hexane, 5-30% methylcyclopentane, 15-60% 2-methylpentane and 3-methylpentane, and others. C1~
C7 hydrocarbons are 1-5%.

The polymerization temperature must be such that the polymer solution is uniformly dissolved in the solvent, and the temperature must be 100"C or higher and 250"C or higher.
Must be less than or equal to If the temperature is lower than 100°C, the polymer often tends to solidify and settle. Also, JP-A-55-15
7606, when an aliphatic hydrocarbon solvent is used, once a homogeneously dissolved polymer solution is further heated, the solution separates into a two-phase solution, the upper phase being a dilute phase and the lower phase being a dilute solution. It is known to be a dense phase. The temperature at which these two phases separate (hereinafter referred to as the precipitation temperature) is determined by the monomer composition of the polymer, the molecular cap, the molecular weight distribution, the m@ of the solvent and unreacted monomers, and the composition and weight of the polymer in the case of a mixed solvent. It varies depending on the combined concentration and the pressure of the system, and although the temperature cannot be determined generally, if it is higher than 250"C, phase separation will be severe and it cannot be used.

The above precipitation temperature of a specific polymer in a specific solvent under a specific pressure can be determined by a light transmittance test or visual test using a glass autoclave or an iron autoclave equipped with a glass sight glass, or by irradiating the iron autoclave with radiation to determine the density. It can be measured by detecting discontinuous lines. Knowing the precipitation temperature determines the polymerization temperature range for obtaining the homogeneous polymer of the present invention.

Since the precipitation point of alicyclic hydrocarbons is higher than that of aliphatic hydrocarbons, in order to raise the precipitation point of the solvent, it is preferable to increase the ratio of alicyclic hydrocarbons. Furthermore, since generally the higher the number of carbon atoms, the higher the precipitation temperature, one method is to use a hydrocarbon with a large number of carbon atoms. Furthermore, since generally the precipitation temperature is higher when the polymerization pressure is higher, it is also effective to apply a pressure higher than the equilibrium pressure of the system in order to increase the precipitation temperature.

The concentration of the polymer in the solution depends on the molecular weight of the polymer, but is usually 5 to 30% by weight.

9- The polymer solution thus obtained is heated and separated into two phases, a lower concentrated phase and a lower diluted phase. The lower phase is further subjected to a step of removing the solvent and unreacted monomers, and the polymer is separated. The solvent and unreacted monomer are recovered from the upper phase.

Various heat exchangers such as shell and tube heat exchangers and double tube heat exchangers can be used to heat the polymer solution, but it is preferable to heat the solvent used for polymerization in advance. A preferred method is to heat the combined solution to a temperature or higher, mix it with a predetermined amount of the polymerization solution, and bring the temperature of the solution to a precipitation temperature or higher. This is because if phase separation occurs within the heat exchanger, concentrated liquid will deposit on the heat transfer surface, reducing heat transfer efficiency and causing problems such as the heat exchanger becoming clogged with concentrated liquid. .

Diluting the polymer solution with a pure solvent immediately before concentrating the polymer by phase separation may seem disadvantageous at first glance, but the phase separation phenomenon shows that the concentration of the concentrated phase does not change much even if the concentration of the supplied polymer solution is reduced. Considering these characteristics, it is thought that this is not such a disadvantage, and that the advantage of being able to omit the inefficient step of heating a highly viscous polymer solution is considered to be greater.

The concentration of the polymer solution after dilution with a solvent is 2 to 20% by weight, preferably 5 to 15% by weight, and its phase separation temperature is 150 to 300''C.

The temperature and supply amount of the diluting solvent are appropriately set based on the phase separation temperature, the temperature of the polymerization solution, and the discharge amount.

A polymer solution heated above the precipitation temperature separates into upper and lower parts over time due to the difference in specific gravity. The time required for phase separation is usually 5 minutes to 2 hours, and it is possible to shorten the time required for phase separation by minimizing heat convection within the system and heating to a temperature as high as possible above the precipitation temperature. .

A preferred method for phase separation is the length/diameter ('L
In a vertical phase separation tank with 4A)) of 3 to 10, preferably 4 to 8, the boundary line between the two phases is detected with a level meter using radiation, and the outlet valves of the upper and lower phases are opened. This is a method of supplying a polymer solution to the boundary line position using a phase separation tank that can maintain the boundary line at a constant position.

The residence time of the polymer solution in the phase separation tank is preferably 5 minutes to
It is 1 hour, more preferably 10 to 40 minutes. Preferably, the boundary line is located approximately at the center of the tank height.

Although it varies depending on the phase separation conditions, the polymer concentration in the concentrated phase is 30% by weight or more, and the concentration in the dilute phase is 10% or less. If the concentration of the concentrated phase is less than 30% by weight or the amount of the dilute phase exceeds 10%, the separation efficiency will be poor. Preferably concentrated phase concentration 40~
It is preferable to select phase separation conditions such that the dilute phase concentration is 80% or less and the dilute phase concentration is 5% or less.

After the concentrated phase containing the polymer is continuously extracted, the polymer is separated through a process to remove the solvent and unreacted monomers, such as a flushing process and a process using a vented extruder. Ru.

A portion of the dilute phase is recovered as a gas and the remainder as a liquid, for example through a flashing process.

The liquid may be heated, mixed with the polymerization solution again, and recycled. Furthermore, before and after the separation step, the p-filtration catalyst may be removed or unreacted monomers may be removed by flushing.

The present invention makes it possible to produce a homogeneous polyethylene polymer using a solvent containing 50% or more of aliphatic hydrocarbons, which has various industrial advantages, and to concentrate it efficiently. I have to say that this is extremely significant.

Examples of the present invention are shown below, but the present invention is not limited in any way by these examples.

Example 1 Using a 601 autoclave with a stirrer, 170'C,
Ethylene was continuously polymerized under liquid ring conditions of 50 atm. The detailed conditions are as follows.

(1) Solvent i mixed hexane (composition: 58% by weight of n-hexane, 20% by weight of methylcyclopentane, 14% by weight of 3-methylpentane, 6% by weight of 2-methylpentane,
Other C7-C6 hydrocarbons 2%) (2) Supply amount ethylene 7.0 Kg/hr Solvent 30.0 KVhr Catalyst Note 1)
■Component 0.2'mmot/hr@l "13 mm
oLlhr 13- Hydrogen 0.002 mmoL/hr Average residence time approximately 1 hour (3) Polymerization vessel outlet composition Ethylene 1. OKV'hr Solvent 3' 0. OKmhr polymer 6.0 Kg/hr (total) '3'7.0 Kg/hr (
4) Polymer properties Melt index Note 2) 4.0 Density Note 3)" 0.965 Fisheye None Note 1) The catalyst was synthesized as follows in accordance with JP-A-56-28206.

(1) Synthesis of hydrocarbon solvent soluble organomagnesium compound (1) Magnesium powder 5 and 9 were added to a 200 t autoclave which had been purged with nitrogen. Of the mixed solution of 20.81 tons of n-butyl chloride and 60 tons of heptane, 2°t was introduced into the autoclave. After heating the autoclave and stirring under reflux to start the reaction, the remaining n-butyl chloride was added dropwise over 2 hours under reflux, and after completion of the reaction, stirring was continued for 1 hour. In addition, klCl
t (On-CtHo) 12 Hepta 7 containing mot
201 was added and the reaction was carried out at 70°C for 2 hours to obtain an organomagnesium compound solution. As a result of the analysis,
The composition of the complex with AtMg7. s (n-C, HQ)
la9' (On-C4Hg)g,.

The organic metal concentration was 0.86 molL.

Note that AlCl2 (On -C4H9) was synthesized by reacting aluminum powder, AtC4, n-C, %OH in heptane at a molar ratio of 1:2:3.

■Capacity 25 equipped with catalyst component synthesis dropping cylinder and water-cooled reflux condenser
．． Oxygen and moisture inside the OL autoclave were removed by nitrogen substitution, and trichlorosilane 0 was removed under a nitrogen atmosphere.
．． 1 molL of hebutane solution2. Ot and heptane3. O4 was charged and the temperature was raised to 70°C.

Next, 0.233 t of the above component (i) and 2.0 t of hebutane were added. Ot
was charged into the dropping cylinder. The mixture was added dropwise over 1 hour while stirring at 70'C, and the reaction was further allowed to proceed at this temperature for 1 hour.

The reaction solution became a white suspension. To this white suspension, 2.77 t of heptane containing 3.49 titanium tetrachloride and 3.1 g of vanadyl trichloride was introduced, and the reaction was carried out at 70°C for 1 hour. The resulting solution is used as a catalyst component.

Triisobutylaluminum was used as the round catalyst component.

The amount of the catalyst component supplied in the above (2) is expressed as the total number of moles of the titanium compound and vanadium compound in the catalyst component list, and the amount of the catalyst component fed is expressed as the number of moles of the aluminum compound.

Note 2) Melt index is determined according to ASTM D-1238 under conditions of temperature 190°C, load 2.16 kg.
t' was measured.

Note 3) Density was measured by the method of ASTM D-1,505.

As shown in FIG. 1, the polymerization liquid 8 discharged from the polymerization vessel 1 is mixed with a high temperature catalyst 9 of 220"C in a static mixer 5, and then the length/diameter (L/D) -6
The mixture was continuously supplied to the phase separation tank 2 of No. 201 for phase separation. A dilute phase from the upper phase was taken out through line 7, and a concentrated phase from the lower phase was taken out through line 6. The phase separation tank 2 used an adiabatic system to keep the temperature in the system constant. The phase separation boundary line was detected using a gamma ray level meter, and was controlled using control pulps 12 and 13 to maintain the boundary line at a constant position.

The dilute phase solvent is flushed in flash tank 3,
The vapor 10 is either led to a purification system or returned to the polymerization vessel after cooling and condensation. It was also possible to generate steam from the cooler 14. In both cases, the high enthalpy of the solvent vapor could be utilized. The temperature of the flash tank was controlled at a constant 165"C.

A certain amount of the liquid solvent 11 in the flash tank is sent to the heat exchanger 4 by a pump 15, heated to 220''C, and then mixed with the polymer solution 8.

After removing the solvent from the concentrated phase 6 in a flash tank, it was taken out and dried under vacuum to obtain a polymer.

The temperature, polymer concentration, and flow rate in each line are as follows.

17- Drawing number Temperature Concentration Flow rate (C) @Amount
Mixer (5) 195 8.3 74
Dilute phase (7) 195 0.264 Dense phase (
6) As in 19560.010 and above, by utilizing phase separation without heating the polymer solution, 60
A polymer solution with a high concentration of % by weight could be obtained. Also, since most of the energy consumed to heat the solvent in the heat exchanger 4 is converted into enthalpy of the solvent vapor in the flash tank 3, in such a way that steam is generated by the heat exchanger 14, Most of that energy is recovered. From this, the method of the present invention can be said to be a method for separating polymers with low energy consumption.

Furthermore, the finally obtained polymer did not contain fish eyes and had excellent transparency. The transition metal content in the polymer was as low as 5 ppm or less, and catalyst removal was not required.

Example 2 Ethylene 7,0 Kf/'11r and solvent 30.0 Kg
Instead of supplying /lIr to the polymerization reactor, ethylene 7,0
Kg/'hr, butene-15Kvhr, solvent 25
Polymerization and separation of the concentrated phase were carried out under the same conditions as in Example 1 except that K9Ar was supplied. The polymer concentration in the dense phase is 5
5% by weight, MI of the obtained polymer is 4.5, density 0.9
20. No fish eyes were observed.

Incidentally, in both Examples 1 and 2, no phase separation occurred during polymerization.

[Brief explanation of the drawing]

The drawing is an explanatory diagram showing an example of the polymerization and phase separation steps in the method for producing an ethylene polymer of the present invention.

Claims (1)

[Claims] 1. Using a coordination polymerization catalyst, ethylene alone or ethylene and a hydrocarbon monomer copolymerizable with ethylene are added to a hydrocarbon solvent containing at least 50% by weight of aliphatic hydrocarbons. Polymerization is carried out under polymerization conditions such that the polymer is uniformly dissolved in the solvent, and the resulting polymer solution is heated to separate into two phases: a concentrated phase with a high polymer concentration and a dilute phase with a low polymer concentration. A method for producing a crystalline ethylene polymer, which comprises obtaining a polymer by removing a solvent and unreacted monomers. 2. The method for producing a crystalline ethylene polymer according to claim 1, wherein the solvent contains at least 50% by weight of an aliphatic hydrocarbon, and the remainder is an alicyclic hydrocarbon. 3. The polymerization temperature is 100-250%. The method for producing a crystalline ethylene polymer according to claim 1 or claim 2, wherein the temperature is .degree. 4. The method for producing a crystalline ethylene polymer according to claims 1 to 3, wherein the polymer solution is heated by mixing the solvent at a higher temperature than the polymer solution. 5. Supply the heated polymer solution to the boundary line position of the phase separation tank where the boundary line between the concentrated phase and the dilute phase is kept constant using a level meter and discharge pulp, and then 5. A method for producing a crystalline ethylene polymer according to claims 1 to 4, in which a more concentrated phase is simultaneously taken out continuously and a diluted phase is taken out from above. 6. The method for producing a crystalline ethylene polymer according to claims 1 to 5, wherein the concentration of the polymer in the dense phase is 30% by weight or more and the concentration in the dilute phase is 10% or less.