JPS6224441B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention produces ethylene alone or comonomers and/or comonomers with ethylene under high temperature and pressure in an elongated tubular reactor.
Or it relates to a method of polymerizing a telogen (modifier). The process yields products at relatively high conversion rates and without loss of optical or physical properties. It is well known in the art to polymerize ethylene to solid polyethylene in an elongated tubular reactor at high temperatures and pressures in the presence of free radical or free oxygen producing initiators that decompose at or above the polymerization temperature to produce free radicals. It is Japanese. Various types of tubular reactor systems have been initiated and used on an industrial scale. One of the more basic systems uses a pressurized stream of ethylene, an initiator, and optionally a modifier.
This includes feeding one end of a tubular reactor consisting of one reaction zone and one cooling zone. Due to the exothermic nature of this reaction, the temperature increases to a maximum or peak temperature as the reaction progresses, and considerable heat is released. Thermal control methods must be used to prevent violent unrestrained reactions and explosions and to increase conversion. One way to achieve thermal control is to use long tubular reactors that provide some degree of temperature control due to the relatively large ratio of heat dissipation surface to reactor volume. Such thermal control is also achieved by using a reactor equipped with a cooling jacket. Additionally, instead of introducing ethylene at one point in the reactor, injecting it as a side stream at one or more points downstream of the reaction tube increases conversion and maintains effective control of the polymerization reaction. was discovered. This injected ethylene acts not only as a coolant but also as a monomer for further polymerization (U.S. Pat. No. 3,725,378
(see specification). Another method using multiple side streams is described in U.S. Patent No.
It is disclosed in the specification of No. 3628918. This patent discloses three reaction zones, three cooling zones, and two monomer side streams. One of said side streams is introduced before the second reaction zone and the other before the third reaction zone for the cooling zone, which has a larger diameter than the first and second reaction zones. All conventional polymerization systems generally attempt to obtain extremely high conversion rates without compromising the optical and physical properties of the resulting polymer. For example, the two reaction zone and three reaction zone processes described above can achieve conversions of about 20-25 percent. It has been assumed and observed to date by those skilled in the art that for conversions on the order of about 25 percent, optical and physical properties drop rapidly regardless of the pressure and temperature of polymerization. Polyethylene quality, especially haze, is influenced by many mechanisms. Haze increases with increasing high molecular weight components. Maintaining a high flow number, preferably greater than about 0.31 m ² /sec (3.3 ^{ft 2} /sec), maximizes the proportion of turbulence and eliminates long straight chains that form in predominantly laminar flow. Minimize change. On the other hand, increasing the average pressure in the reaction zone reduces the high molecular weight component in the molecular weight distribution by reducing the amount of long chain branching, thereby improving haze. An increase in the average or peak temperature in the reaction zone increases the long chain branching of the polymerization reaction. This increase in high molecular weight components in the molecular weight distribution increases haze. Furthermore, it is known that increasing polymer concentration due to relatively high conversion rates generally increases the likelihood of long chain branching forming on the polymer molecules. Such high conversion increases long chain branching and thus reduces optical properties. In other words, it is generally accepted that the degree of haze increases. It has been discovered that significant increases in conversion can be obtained with high or only slight increases in haze. More specifically, it has been discovered that the pressure and temperature of the reactants in a polymerization reaction in a tubular reactor are more important in determining the quality of the product than the absolute level of conversion obtained. It is therefore possible to obtain high quality products while obtaining conversions of monomeric reactants to polymer of 25 percent or more. It is contrary to the conventional wisdom of those skilled in the art that high quality can be obtained with a conversion of 25 percent or more. A tubular reactor containing a plurality of reaction zones and a subsequent cooling zone, the reactor comprising at least a first and a second
using a reactor adapted to introduce a monomer sidestream after the reaction zone and, according to the invention, using an additional reaction cooling zone due to the reduction in operating temperature in the preceding reaction zone. This achieves such high conversion rates. Approximately 0.31m ² / in the reaction zone
sec (approximately 3.3 ft ² /sec) and the pressure drop in the tubular reactor between the inlet of the first reaction zone and the outlet of the last reaction zone is 1750~3500Kg/ ^cm2 (25000~
Approximately 420Kg/cm ² when operating at a pressure of 50000psi)
(approximately 6000 psi). As used herein, flow number is the bulk fluid velocity (m/sec) multiplied by the diameter (m). According to the present invention, a polyethylene or ethylene copolymer is produced in an elongated tubular reactor having ^an inlet and ^an outlet at a pressure of about 20,000 psi to about 60,000 psi. A method is provided. The method provides at least about 0.31 m ² /sec
(approximately 3.3 ft ² /sec) flow rate of reactants through multiple reaction zones (each followed by a cooling/remanufacturing zone downstream) and free radical generating material injected at the tip of each reaction zone. adding at least one final reaction zone and a cooling zone to reduce the operating temperature in the preceding reaction zone to at least increase the conversion of ethylene to polyethylene while maintaining product haze. The improvement is to increase it to 28%. Preferably, the reactor has three or four reaction zones with or without injection of cooling gas to facilitate cooling. However, according to the invention it is also possible to use four or more reaction zones. An unexpected feature of the present invention is that by adding an additional reaction zone to the prior art process and reducing the operating temperature in the prior reaction zone,
It is possible to increase the conversion of monomer to polymer without reducing the quality of the product. More specifically, a conventional tubular reaction tube with two reaction zones adds a third reaction zone and is approximately 4.4°C
(approximately 40〓) to approximately 21.1℃ (approximately 70〓), i.e. approximately 15 to
The first 2 so that △T decreases by 20%
By lowering the operating temperature in one reaction zone, it can be converted to include three reaction zones, increasing conversion by 6 to 10 percent and maintaining haze. However, according to the present invention, some temperature reduction is used and the pressure difference between the reaction zones is minimized so as to operate at the highest average pressure;
i.e. maintain a minimum pressure drop. More preferably, a conventional three reaction zone tubular reactor containing one or two cold side streams is converted to a four reaction zone tubular reactor using two cold gas cooling streams to achieve a conversion of 28 percent or more. efficiency and maintain high product quality. Furthermore, the operation △T in the first three reaction zones is adjusted from approximately 15.6℃ (approximately 60〓) to approximately 32.2℃ (approximately 90℃).
By reducing the ΔT drop to about 15-20 percent, products with high optical properties can be obtained. If haze is not a critical criterion, a relatively small temperature drop in the first section of the reactor and the favorable effect of using an additional reaction zone to increase conversion can lead to even larger conversion increases. (conversion increase up to 10-12 percent). However, in all cases the pressure drop is minimized to maximize the uniformity of the product produced in each successive zone. Although the present invention is not limited to a particular configuration of tubular reactor, modifier, comonomer system, operating pressure or temperature change, or initiator system, the pressure drop within the reactor is
from the entrance of the reaction zone to the exit of the last reaction zone.
Maintained below 420Kg/cm ² (approximately 6000psi), October 1975
As described in ^U.S. patent application Ser.
3.3ft ² /sec) or higher. Tubular reactors are usually sectioned or integrally jacketed of suitable length with an inner diameter of about 0.50 to 3 inches, preferably about 1.0 to 2.5 inches. It is a long and thin tubular body. This tubular reactor is usually about 1000:1 to
It has a length/diameter ratio of 60000:1. The specific length employed will depend on the specific tube construction of the final design, as sufficient heat removal is required. This tubular reactor is approximately 1400 to 4200Kg/cm ² (approx.
Operated at pressures from 20,000 to 60,000psi). 420
Pressures range ^{from about 2100 to about 3500 Kg/cm 2 (} approximately
30,000 to about 50,000 psi). The temperature maintained in the reactor varies and is primarily controlled by the particular initiator system used.
The temperature is usually in the range of about 150-350°C or higher, preferably about 160-327°C or higher, more preferably about 165-315°C, and varies depending on the reaction zone. Initiators suitable for use in the present invention are free radical generating substances. Examples of such free radical generators are oxygen, e.g. hydrogen peroxide,
Decanoyl peroxide, t-butylperoxyneodecanoate, t-butylperoxypivalate, 3,5,5-trimethylhexanoylperoxide, diethylperoxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxyiso Butyrate, benzoyl peroxide, t-butyl peroxyacetate, t-
Peroxide compounds such as butyl peroxybenzoate, di-tert-butyl peroxide and 1,1,3,3-tetramethylbutyl hydroperoxide, alkali metal persulfates, perborates and percarbonates and e.g. azobisisobutyl These include, but are not limited to, azo compounds such as lonitrile. Among them, organic peroxides are preferred. Mixtures of the above initiators can be injected into various reaction zones. This initiator or mixture thereof can be introduced directly into the main ethylene stream or with an ethylene side stream when the reaction mixture is at a suitable temperature to reinitiate the polymerization reaction. The feedstock used in the present invention is primarily ethylene or ethylene containing telogen (modifier) or comonomer. Known telogens or modifiers for use herein include saturated aliphatic aldehydes such as formaldehyde, acetaldehyde and the like, saturated aliphatic ketones such as acetone, diethyl ketone, diamyl ketone and the like, saturated aliphatic alcohols such as methanol, ethanol, propanol and analogs thereof, paraffins or cycloparaffins such as pentane, hexane, cyclohexane and analogs thereof, aromatic compounds such as toluene, diethylbenzene, xylene and analogs thereof, and other compounds used as chain terminators, Examples include carbon tetrachloride and chloroform. The process of the present invention can be used to produce copolymers of ethylene containing one or more polymerizable ethylenically unsaturated monomers having CH ₂ =C groups, The group undergoes addition polymerization. These copolymers can be produced in the presence or absence of modifiers. A polymerizable ethylenically unsaturated monomer having a CH ₂ =C〓 group undergoes addition polymerization,
These include, for example, α-monoolefins such as propylene, butene, pentene, etc., acrylic, haloacrylic and methacrylic acids, esters, nitrile acids, such as acrylic acid, chloroacrylic acid, methacrylic acid, cyclohexyl methacrylate, methyl acrylate, acrylonitrile, acrylamide, vinyl and vinylidene halides, N-vinylamides, vinyl carboxylates such as vinyl acetate, N-vinylaryls such as styrene, vinyl ethers, ketones or other compounds such as vinylpyridine,
and its analogues. The copolymer and telogen or modifier are used to modify the properties of the resulting ethylene polymer. The term "polyethylene" as used herein should therefore be understood to encompass so-called modified ethylene polymers and single polyethylene. Haze is a property of the product that varies depending on reactor construction and operating conditions. A haze in the range of about 3.5 to 5.0 percent is generally required for high clarity polyethylene films. The haze properties described above typically decrease with increasing operating temperature, decreasing operating pressure, and/or increasing polymer conversion. Surprisingly, the present invention allows for higher conversions than were possible with conventional methods while maintaining haze characteristics comparable to or better than those of conventional low conversion methods. did. Even higher conversions can be achieved, for example, by selecting appropriate operating pressures and temperature ranges, i.e. minimizing the pressure drop and reducing the operational peak temperatures of the first three reaction zones. This is made possible by converting the reactor into a four-zone tubular reactor. As fluids generally move through the reactor, the resulting product is affected by pressure drop, residence time at elevated temperature, and free radical attack on the polymer present at each initiator injection point.
It has more or less satisfactory haze, but this causes side chain branching reactions, leading to an increase in haze. Therefore, reactors with high conversion rates and four reaction zones cannot be expected to yield ethylene polymers with acceptable optical and physical properties for transparent films. As used herein, the term "haze" refers to ASTM-D-1003-
It is the percentage of transmitted light that is dissipated from the incident light by forward scattering as it passes through a polymeric species, as measured by 61. Acceptable physical properties for polymers made according to the present invention are a density of about 0.91 to 0.935, preferably about 0.92 to 0.93, and a melt index of about 0.1 to 40, preferably about 0.3 to 30. As used herein, the melt index of a polymer is measured as the weight (in grams) of resin extruded through a standard orifice at 180°C in 10 minutes when a standard load is applied to the molten polymer (ASTM- (See D-1238-57T). In order to explain the invention in all respects, a tubular reactor for the production of polyethylene is shown in the drawing.
Feed gas is introduced through line A to preheater B, which preheats the feedstock to its starting temperature. This tubular reactor C has an inner diameter of 1.27~7.62cm (0.5~
3.0 inches). The four zones 1, 3, 5 and 7 are reaction zones, and the four cooling zones 2, 4, 6 and 8 respectively and 0.635 cm
(0.25 inch) smaller in diameter. The initiator 10 is introduced at the rear of the preheater B and, after reaching the minimum starting temperature, also at the ends of the cooling zones 2, 4 and 6. The supply of monomer side streams 9 for cooling and pressure drop reduction also takes place at the ends of the cooling zones 2 and 4. The table shows the inner diameter of the tube in each zone, the calculated bulk fluid velocity in each zone, and the calculated flow number in each zone based on the specific design. In any particular design, the diameters of the various zones are within the tube size ranges described above.

Table: The ratio of the injected sidestream monomer feed to the inlet monomer feed is adjusted to maximize the cooling provided by the feed stream and to maintain the polymerization reaction at the desired operating temperature. The temperature must be maintained to obtain the desired heat distribution for polymerizing the portion of monomer introduced. For example, if the ratio of injected side stream to monomer from the inlet is too large, the temperature after mixing will be below the starting temperature of some initiators. In such cases, it is necessary to further heat the mixture until it returns to the starting temperature range. The temperature of the monomers injected depends on the ratio of the latter to the monomers at the inlet and should be kept low so as to ensure optimal cooling in practice. Monomers cooled below ambient temperature can be used as large heat sinks. However, the lowest temperature at which the injected monomer feed will be cooled at any injection point is also governed by the resulting temperature of the reaction mixture after injection, which also depends to some extent on the initiator used. Thus, the specific formula for optimum operating conditions will vary depending on the construction of every reactor and will also depend on the desired product properties. flow rate, split flow between the injected monomer and the monomer from the inlet, the temperature of the injected monomer, the gas and injection point location, and the initiator used for the desired combination of polymerization temperature and pressure conditions. It must be related to the specific structure of the system and reactor. These can be easily calculated by those skilled in the art.

[Brief explanation of the drawing]

The drawing shows a four reaction zone tubular reactor according to features of the invention with side streams and different diameters for high conversion, reaction zone boundary layer control and pressure drop control. 1, 3, 5, 7...reaction zone, 2, 4, 6, 8...
...Cooling zone, 9...Side stream, 10...Initiator, B...
Preheater.

Claims (1)

[Claims] 1. In an elongated tubular reactor having an inlet and an outlet, about 1400 Kg/cm ² (about
20,000 psi) to about 4,200 ^Kg /cm ² (about 60,000 ^psi ), the method comprising:
sec) through a plurality of reaction zones (with a cooling/remanufacturing zone downstream of each reaction zone) and injecting a free radical generating material at the beginning of each reaction zone, at least Add one final reaction zone and cooling zone to increase the operating temperature in the preceding reaction zone from 15.6°C (60〓) to 22.2°C
(90〓) or 15 to 20%, resulting in a conversion of ethylene to polyethylene of at least 28% while maintaining a product haze of about 3.5 to 7.5. 2. The method of item 1, wherein the ethylene side stream is injected into the first and second cooling zones. 3 Operating pressure is 1750Kg/cm ² (25000psi) ~ 3500
The method according to claim ¹ , wherein the pressure is 50,000 psi. 4 Pressure drop over the entire length of the reactor is 420Kg/
The method according to paragraph ¹ above, which does not exceed 6000 psi. 5 The number of flows is at least 0.37m2 ^/ sec (4.0ft/
sec). 6. The method of claim 2, wherein the tubular reactor includes four reaction zones and a cooling/remanufacturing zone. 7. The method of claim 1, wherein the reduction in operating temperature range is about 5-30%. 8. The process of claim 1, wherein the tubular reactor comprises 3 or 4 reaction zones and 3 or 4 cooling/remanufacturing zones and no ethylene sidestream.