Methods for producing polyethylene. Technology for producing high and low pressure polyethylene
In the history of science, some discoveries occurred by accident, and the materials in demand today were often the byproduct of some experiment. Quite by accident, aniline dyes for fabric were discovered, which subsequently gave an economic and technical breakthrough in light industry. A similar story happened with polyethylene.
Discovery of material
The first case of polyethylene production occurred in 1898. While heating diamesotan, German-born chemist Hans von Pechmann discovered a strange precipitate at the bottom of the test tube. The material was quite dense and resembled wax; the scientist’s colleagues called it polymethylline. This group of scientists did not go beyond chance, the result was almost forgotten, and no one was interested. But still the idea hung in the air, requiring a pragmatic approach. And so it happened, more than thirty years later polyethylene was rediscovered as an accidental product of a failed experiment.
The English take over and win
The modern material polyethylene was born in the laboratory of the English company Imperial Chemical Industries. E. Fossett and R. Gibson conducted experiments involving gases of high and low pressure and noticed that one of the components of the equipment in which the experiments were carried out was covered with an unknown waxy substance. Interested side effect, they made several attempts to obtain the substance, but without success.
M. Perrin, an employee of the same company, managed to synthesize the polymer two years later. It was he who created the technology that served as the basis for industrial production polyethylene. Subsequently, the properties and qualities of the material were changed only through the use of various catalysts. Mass production of polyethylene began in 1938, and it was patented in 1936.
Raw materials
Polyethylene is a hard polymer white. Belongs to class organic compounds. What is polyethylene made from? The raw material for its production is ethylene gas. The gas is polymerized at high and low pressure, resulting in raw material granules for further use. For some technological processes, polyethylene is produced in powder form.
Main types
Today, the polymer is produced in two main grades: LDPE and PNP. The material manufactured at medium pressure is a relatively new invention, but in the future the quantity of the product produced will continue to grow due to improving characteristics and a wide field of application.
Produced for commercial use the following types material (classes):
- Low density or another name - high pressure(LDPE, LDPE).
- High density, or low pressure (LDPE, PNP).
- Linear polyethylene, or medium pressure polyethylene.
There are also other types of polyethylene, each of which has its own properties and scope of application. Various dyes are added to the granular polymer during the production process, making it possible to obtain black polyethylene, red or any other color.
PVD
The chemical industry is involved in the production of polyethylene. Ethylene gas is the main element (from which polyethylene is made), but not the only one required to obtain the material.
- The heating temperature is up to 120 °C.
- Pressure mode up to 4 MPa.
- The process stimulator is a catalyst (Ziegler-Natta, a mixture of titanium chloride with an organomelalic compound).
The process is accompanied by the precipitation of polyethylene in the form of flakes, which then undergo a process of separation from the solution followed by granulation.
This type of polyethylene is characterized by higher density, resistance to heat and tearing. The scope of application is various types of packaging films, including for packaging hot materials/products. From granular raw materials of this type of polymer, parts for large-sized machines are made by casting, insulating materials, high-strength pipes, consumer goods, etc.
Low-pressure polyethylene
There are three ways to produce ENP. Most enterprises use the “suspension polymerization” method. The process of obtaining ENP occurs with the participation of a suspension and constant stirring of the feedstock; a catalyst is required to start the process.
The second most common production method is solution polymerization under the influence of temperature and the participation of a catalyst. The method is not very effective, since during the polymerization process the catalyst reacts and the final polymer loses some of its qualities.
The latest method for producing polyethylene polymers is gas-phase polymerization; it is almost a thing of the past, but is sometimes found in individual enterprises. The process occurs by mixing the gas phases of the raw material under the influence of diffusion. The final polymer is obtained with heterogeneous structure and density, which affects the quality of the finished product.
Production occurs in the following mode:
- The temperature is maintained between 120°C and 150°C.
- The pressure should not exceed 2 MPa.
- Catalysts for the polymerization process (Ziegler-Natta, a mixture of titanium chloride with an organomelalic compound).
The material of this manufacturing method is characterized by rigidity, high density, and low elasticity. Therefore, its scope of application is industry. Technical polyethylene is used for the manufacture of large-sized containers with increased strength characteristics. In demand in the construction industry, chemical industry, it is almost never used for the production of consumer goods.
Properties
Polyethylene is resistant to water, many types of solvents, and does not react with salts. When burning, the smell of paraffin is released, a blue glow is observed, and the fire is weak. Decomposition occurs upon exposure nitric acid, chlorine and fluorine in gaseous or liquid state. During aging, which occurs in air, cross-links are formed in the material between chains of molecules, which makes the material brittle and crumbling.
Consumer qualities
Polyethylene is a unique material, familiar in everyday life and production. It is unlikely that the average consumer will be able to determine how many items from it he encounters every day. In the global production of polymers, polyethylene occupies the lion's share of the market - 31% of the total gross product.
Depending on what polyethylene is made of and production technology, its qualities are determined. This material sometimes combines opposite indicators: flexibility and strength, ductility and hardness, strong elongation and resistance to tearing, resistance to aggressive environments and biological agents. In everyday life, we use bags of various densities, disposable tableware, plastic lids, parts of household appliances and much more.
Areas of use
The use of polyethylene products has no restrictions, any industry or human activity accompanied by this material:
- The polymer is most widely used in the manufacture of packaging materials. This part of the application accounts for about 35% of all raw materials produced. This use is justified by its dirt-repellent properties and the absence of an environment for the occurrence of fungal infection and vital activity of microorganisms. One of the successful finds is a polyethylene sleeve with wide application. By varying the length at his own discretion, the user is limited only by the width of the package.
- Remembering what polyethylene is made of, it becomes clear why it has become widespread as one of the best insulating materials. One of its qualities in demand in this area is the lack of electrical conductivity. Its water-repellent properties are also irreplaceable, which has found application in the production of waterproofing materials.
- Resistance to the destructive power of water as a solvent allows the production of polyethylene pipes for domestic and industrial consumers.
- The construction industry uses the noise-insulating qualities of polyethylene and its low thermal conductivity. These properties were useful in the manufacture of materials based on it for insulation of residential and industrial facilities. Technical polyethylene is used for insulation of thermal routes, in mechanical engineering, etc.
- The material is no less resistant to aggressive environments of the chemical industry; polyethylene pipes are used in laboratories and chemical production.
- In medicine, polyethylene is useful in the form of dressings, prosthetic limbs, it is used in dentistry, etc.
Processing methods
Depending on how the granulated raw material was processed, it will depend on what grade of polyethylene will be obtained. Common methods:
- Extrusion (extrusion). It is used for packaging and other types of films, sheet materials for construction and finishing, cable production, polyethylene sleeves and other products are produced.
- Casting method. Mainly used for making packaging materials, boxes, etc.
- Extrusion blow molding, rotary. Using this method, volumetric containers, large containers, and vessels are obtained.
- Reinforcement. Using a certain technology, reinforcing elements (metal) are placed into the formed mass of polyethylene, which makes it possible to obtain construction material increased strength, but at a lower cost.
What is polyethylene made from, besides the main constituent substances? A process catalyst and additives that change the properties and qualities of the finished material are required.
Recycling
The durability of polyethylene is its advantage as a consumer product and its disadvantage as one of the main environmental pollutants. Today, waste processing - recycling - is becoming important. All grades of polyethylene can be recycled and re-converted into granular raw materials, from which many popular consumer and industrial products can be made.
Plastic caps, bags, bottles will decompose in a landfill for hundreds of years, and the accumulated waste poisons vital natural resources. World practice demonstrates an increase in the number of polyethylene processing enterprises. While actually collecting garbage, such companies sanitize it and crush it. Thus, resources are saved, protection environment and production of in-demand products.
Industrial tubular polymerization reactors are series-connected pipe-in-pipe heat exchangers. The reactor tubes have a variable diameter (50 – 70 mm). The individual links of the “tubular” are connected by massive hollow slabs. Pipes and rolls are equipped with jackets connected in series to each other. Superheated water with a temperature of 190 - 230 0 C is used as a coolant for heating ethylene and removing excess heat, which enters the jacket of a tubular reactor in a countercurrent to ethylene and to the flow of the reaction mass. The use of high temperatures is necessary to prevent the formation of a polymer film on the pipe walls. To maintain constant temperature regime in the reactor and to ensure effective heat removal, additional ethylene and initiator are introduced into different zones along the length of the reactor. A multi-zone reactor is more productive than a single-zone reactor. A single-zone reactor at a maximum reaction temperature (300 0 C) provides 15 - 17% ethylene conversion in one pass. A two-zone reactor achieves 21–24% conversion at the same temperature. In a three-zone reactor, the conversion degree increases to 26 – 30%. The productivity of a four-zone device increases slightly compared to a three-zone one.
To obtain constant indicators of the properties of polyethylene, it is necessary to maintain the temperature in the reactor at the same level in zones.
The performance of the reactor depends on its size, so they are currently used with different pipe lengths and diameters. For high-power reactors, the pipe length reaches 1000 m or more.
The technological process for the production of high-density polyethylene in a tubular reactor consists of the following stages:
· mixing fresh ethylene with return gas and oxygen,
· two-stage gas compression,
· polymerization of ethylene in the condensed phase (ethylene density 400 - 500 kg/m 3),
· separation of high-density polyethylene and unreacted ethylene entering recycling,
· polyethylene granulation.
To color, stabilize and fill, high-density polyethylene is injected with appropriate additives, after which it is melted and granulated.
In Fig.1. A schematic diagram of the production of high-density polyethylene in a tubular reactor using a continuous method is presented.
From the gas separation shop, fresh ethylene at a pressure of 0.8 - 1.1 MPa enters the collector 1 and then into the mixer 2 , in which there is no pressure with return ethylene. Next, oxygen is introduced into the flow and the mixture enters a three-stage compressor of the first stage 3 , where it compresses to 25 MPa. After each compression stage, ethylene is cooled in refrigerators, separated from the lubricant in separators, and then enters the mixer 4 , in which it is mixed with return high-pressure ethylene from the separator 7 . The mixture is then sent to a two-stage compressor 5 the second cascade, where it is compressed to 245 MPa. After the first stage of compression, ethylene is cooled in a refrigerator, cleared of lubricant in separators, and after the second stage at a temperature of about 70 0 C without cooling, it enters a tubular reactor through three inlets 6 for polymerization.
Polyethylene is the cheapest non-polar synthetic polymer that belongs to the class of polyolefins. Polyethylene is solid white matter, having a grayish tint.
The first to study the polymerization of ethylene was the Russian chemist Butlerov in 1873. But an attempt to implement it was attempted in 1884 by the organic chemist Gustavson.
Polyethylene production technology + video on how to do it
Everyone is involved in the production of polyethylene large companies petrochemical industry. The main raw material from which polyethylene is produced is ethylene. Production is carried out at low, medium and high pressure. As a rule, it is produced in granules that have a diameter of 2 to 5 millimeters, sometimes in powder form. Today there are four main methods for producing polyethylene. As a result, we obtain: high-density polyethylene, low-density polyethylene, medium-density polyethylene, as well as linear high-density polyethylene. Let's look at how MDV is produced.
HDPE is formed at high pressure by the polymerization of ethylene in an autoclave or tubular reactor. Polymerization in the reactor is carried out by a radical mechanism under the influence of oxygen, organic peroxides, such as lauryl, benzoyl or mixtures thereof. Ethylene is mixed with an initiator, then heated to 700 degrees and compressed by a compressor to 25 megapascals. After this, it enters the first part of the reactor, in which it is heated to 1800 degrees, and then into the second part of the reactor to carry out polymerization, which occurs at a temperature ranging from 190 to 300 degrees and a pressure from 130 to 250 megapascals. In total, ethylene is in the reactor for no more than 100 seconds. Its conversion rate is 25 percent. It depends on the type and quantity of initiator. The ethylene that has not reacted is removed from the resulting polyethylene, after which the product is cooled and packaged.
LDPE is produced in the form of both unpainted and colored granules. The production of low-density polyethylene is carried out using three main technologies. The first is polymerization, which occurs in suspension. The second is polymerization, which occurs in solution. Hexane serves as such a solution. The third is gas-phase polymerization. The most common method is solution polymerization. Polymerization in solution is carried out in a temperature range from 160 to 2500 degrees and pressure from 3.4 to 5.3 megapascals. Contact with the catalyst lasts approximately 10-15 minutes. Polyethylene is released from the solution as a result of solvent removal. First of all, in the evaporator, and then in the separator and in the vacuum chamber of the granulator. Granular polyethylene is steamed with water steam.
HDPE is produced in the form of both undyed and colored granules, and sometimes in powder form. The production of medium pressure polyethylene is carried out as a result of the polymerization of ethylene in solution. Medium pressure polyethylene is produced at a temperature of approximately 150 degrees, a pressure of no more than 4 megapascals, and also in the presence of a catalyst. PSD falls out of solution in the form of flakes. The product obtained in the manner described above has a weight-average molecular weight of no more than 400 thousand, and a degree of crystallinity of no more than 90 percent. The production of linear high-density polyethylene is carried out using chemical modification of LDPE. The process occurs at a temperature of 150 degrees and approximately 30-40 atmospheres. Linear low-density polyethylene is similar in structure to polyethylene high density, however, it is distinguished by longer and more numerous lateral branches. The production of linear polyethylene is carried out in two ways: the first is gas-phase polymerization, the second is liquid-phase polymerization. She is currently the most popular. As for the production of linear polyethylene by the second method, it is carried out in a liquefied bed reactor. Ethylene is fed into the reactor, and the polymer, in turn, is removed continuously. However, the level of the liquefied layer in the reactor is constantly maintained. The process occurs at a temperature of about one hundred degrees, pressure from 689 to 2068 kN/m2. The efficiency of this polymerization method in the liquid phase is lower than that of the gas phase.
Video how to do it:
It is worth noting that this method It also has its own advantages, namely: the installation size is much smaller than that of equipment for gas-phase polymerization, and the capital investment is much lower. Almost similar is the method in a reactor with a mixing device using Ziegler catalysts. This creates the maximum output. Not so long ago, technology began to be used for the production of linear polyethylene, which results in the use of metallocene catalysts. This technology makes it possible to obtain a higher molecular weight of the polymer, thereby increasing the strength of the product. LDPE, HDPE, PSD and LDPE differ from each other, both in their structure and properties, respectively, and they are used to solve various problems. In addition to the above methods of ethylene polymerization, there are others, but they are not widely used in industry.
Products made of polyethylene (PE), along with other polymeric materials, are widely used in the world as an excellent substitute for traditional materials such as metals, wood, glass, natural fibers, textiles and other industries. Polypropylene pipes are rapidly replacing metal pipes in utilities and industry. Due to this, world production polypropylene is growing at a very fast pace.
Polyethylene of various grades (LLDPE, LDPE, HDPE) continues to hold a leading position among large-scale plastics. In 2012, global polymer production amounted to 211 million tons, with 38% or 80 million tons. accounted for PE of various brands. It is expected that in 2015, global PE production will reach 105 million tons.
Figure 1. The ratio of different types of polymers in global production, 2012.
PE can be considered the most popular polymer material, primarily due to its comparative simplicity, reliability and relatively low cost of its manufacture. So for the production of 1 t of PE in all modern technologies no more than 1,005 - 1,015 tons of ethylene and 400-800 kWh of electricity are required. In most areas where plastics are used there is no need to use other materials. For the same reason, the second most popular material is polypropylene (25%).
Polypropylene and polyethylene together can be called the most “universal” plastics. Based on their characteristics, both are not leaders. In terms of optical properties, all other materials leave polycarbonates behind, but mechanical characteristics- polyamides, in terms of electrical insulating properties - PVC, and PET is ideal for blow molding products. While not being an ideal material in all respects, PE shows a moderate second or third result in all areas, which makes it possible to use it for all purposes, and the combination of these properties with a much lower price and makes PE the most popular polymer material around the world.
PE was first obtained in 1873; its father can be considered the great Russian chemist Alexander Mikhailovich Butlerov, who was the first to study the polymerization reactions of alkenes. Another father can be considered his successor, the Russian chemist Gavrila Gavrilovich Gustevson, who continued the study of polymerization reactions. In the West, the discoverer of polyethylene is considered to be the German chemist Hans von Pechmann, who obtained PE using a more advanced method in 1899, then it was commonly called “polymethylene”.
Like many similar discoveries, PE was far ahead of its time, so it was undeservedly forgotten for more than 30 years. This is understandable; no one at the beginning of the century could have imagined that an incomprehensible jelly-like substance would make a real technological revolution, seriously weakening the position of traditional materials.
First industrial technology PE production began in 1935 using gas-phase technology from an English company ICI (Imperial Chemical Industries ). After this, the first PE production plants began to appear in Europe and the USA. Initially, the main purpose of this polyethylene was the production of wires, due to the good electrical insulating properties of polyethylene. New wires with polyethylene insulation replaced rubber ones and were widespread until they were replaced by PVC wires. However, time itself contributed to the real triumph of PE. The post-war years were characterized by an unprecedented increase in the purchasing power of citizens and increased demand for food and light industrial goods. The first supermarkets appeared. It was then that the plastic bag began to gain immense popularity all over the world.
It is noteworthy that one of the two PE production installations operating at OJSC Kazanorgsintez is precisely the installation of an English company ICI , model 1935,it is still in operation, being the oldest installation operating in Russia.
To understand the differences in production technologies, it is important to understand the species composition of polyethylene products produced. A clear distinction is made between high-pressure and low-density polyethylene and low-pressure and high-density polyethylene.
High pressure polyethylene LDPE/
LDPE
High-density polyethylene (LDPE), also known as low-density polyethylene (LDPE), in English name LDPE (Low-Density PE) is obtained at a high temperature of 200-260 0 C and a pressure of 150-300 MPa in the presence of a polymerization initiator (oxygen or more often organic peroxide). This density lies in the range of 0.9 - 0.93 g/cm 3 .
Low pressure polyethylene HDPE/
HDPE
Low-density polyethylene (HDPE), also known as high-density polyethylene (HDPE), in English name HDPE (High-Density PE) is obtained at a temperature of 120-1500C, a pressure below 0.1-2MPa in the presence of a Ziegler-Natta catalyst (mixture TiCl 4 and AlCl 3 ).
Table 1 . Comparative indicators of various types of polyethylene.
| Index | LDPE | PESD | HDPE |
| Total number of CH 3 groups per 1000 carbon atoms: | 21,6 | 5 | 1,5 |
| Number of CH3 end groups per 1000 carbon atoms: | 4,5 | 2 | 1,5 |
| Ethyl branches | 14,4 | 1 | 1 |
| Total number of double bonds per 1000 carbon atoms | 0,4—0,6 | 0,4—0,7 | 1,1-1,5 |
| including: | |||
| vinyl double bonds (R-CH=CH 2),% | 17 | 43 | 87 |
| vinylidene double bonds , % | 71 | 32 | 7 |
| trans-vinylene double bonds (R-CH=CH-R"), % | 12 | 25 | 6 |
| Degree of crystallinity, % | 50-65 | 75-85 | 80-90 |
| Density, g/cm³ | 0,9-0,93 | 0,93-0,94 | 0,94-0,96 |
Sometimes a distinction is made between medium-density polyethylene (MDPE), but it is usually classified as HDPE because these products have the same density and weight, and the pressure during the polymerization process at the so-called low and medium pressures is most often the same. Often, especially often in foreign literature, various linear high-pressure PE products are usually identified separately, as is done in Figure 1, but in general it would not be a mistake to consider them together with other LDPE products.
At JSC NIITEKHIM, the historical practice has been to consider the production of PE as the sum of the production of LDPE and HDPE, classifying LLDPE as LDPE. This approach is logical, convenient and fully justified. In the same way, Rosstat divides production, separating ethylene polymerization products with a density of at least 0.94 (meaning HDPE) and ethylene polymerization products with a density of less than 0.94 g/cm 3 (LDPE).
The main difference between LDPE and HDPE is density. In this case, it is necessary to clearly understand that a copolymer is almost always used. Butene-1, Hexene-1, octene-1 or others. Pure homopolymer is very different from the modern polyethylenes we are used to and has very limited applications due to its very high density and low fluidity.
There are other more special types polyethylene. So they highlight linear low density PE- LLDPE or LLDPE , which is mainly used for the production of containers and packaging.
Bimodal PEThis is polyethylene, which is synthesized using a two-reactor cascade technology, i.e. there are two large fractions with different molecular weights - low molecular weight is responsible for fluidity, high molecular weight is responsible for physical and mechanical characteristics.
Crosslinked PE(PE-X or XLPE, PE-S) is an ethylene polymer with cross-linked molecules (PE - PolyEthylene, X - Cross-linked). The crosslinking is a three-dimensional network due to the formation of cross-links. Metallocene PE is an ethylene polymer obtained using catalysts with a single polymerization center. Usually denoted mLLDPE, mMDPE or mHDPE.
The most important copolymer of ethylene is Sevilen,
in foreign periodicals the name EVA is accepted - ethylene vinyl acetate.
Figure 2. Structure of consumption of LDPE, HDPE, Sevilen, as well as total consumption of PE by sector in Russia in 2014.Figure 2 shows the ratio of HDPE, LDPE and the most important of the ethylene copolymers, sevilene, in the consumption structure in Russia. The figure shows that the main sectors of PE consumption in 2014 were manufacturers of containers and packaging, films, pipes, household and household products, their share accounted for more than 86% of the total volume of consumed PE.
Wherein, different types PEs are in different demand across consumer sectors. For example, the PE pipe production sector is entirely represented by HDPE. HDPE is used for pipe production grades PE-100, PE-100+.
The opposite picture is visible in the case of film production. If only 6% of HDPE is used for film production, then the share of LDPE is already 43%, which makes HDPE the most suitable for this consumption sector. The same applies to the production of PE sheets, as well as cable production. In the production of containers and packaging, HDPE and HDPE are represented almost equally (30 and 28%). 13% of HDPE goes to the production of household and household products, while LDPE goes to about 18% for this purpose.
Ethylene and vinyl acetate copolymer - Sevilen is not represented as massively as HDPE and LDPE, its share in general production PE is only 0.65%. At the same time, twice as much Sevilen comes to Russian market via import. Sevilen is used for the production of household and household products - 42%, containers and packaging - 32%, films 15% and cables 6%.
Among the main licensors of polyolefin production technologies, there has long been a trend of consolidation and globalization of manufacturers. The number of participants in the technology market is shrinking; ultimately, only the largest players have the opportunity to develop their own technology. The main licensors of production technologies are presented in Table 2.
Table 2. Technology licensors and basic PE production technologies.
| Name | Owner | Type of polymerization | Products |
| UNIPOL PE | UnionCarbide | Gas phase | LLDPE, HDPE |
| INNOVENE | BP Chemicals | Gas phase | LLDPE, HDPE |
| Innovene G | BP Chem. | Gas phase | LLDPE, HDPE |
| EXXPOL | Exxon-Mobil | Gas phase | LLDPE, HDPE |
| COMPACT (Stamylex) | DSM | Solution | LLDPE, HDPE |
| SPHERILENE | Basell | Gas phase, cascade | LLDPE, HDPE |
| HOSTALEN | Basell | Gas phase, cascade | HDPE |
| LUPOTECH T | Basell | In bulk | LDPE, Sevilen |
| ENERGX | Eastman Chemical | Gas phase | LLDPE, HDPE |
| SCLAIRTECH | NOVA Chemicals | Gas phase | LLDPE, HDPE |
| BORSTAR PE | Borealis | Suspension, cascade | LLDPE, HDPE |
| PHILLIPS | Phillips | Suspension | LLDPE, HDPE |
| CX | Mitsui Chemicals | Gas phase, cascade | HDPE |
The leading players in the global market in terms of existing capacities in the world are Dow and Carbide, whose Unipol technology is the most popular technology in the world. Another equally popular technology is Innovene, owned by BP . The merger between Dow and UnionCarbide in 2000 gave Dow control of UnionCarbide's 50 percent stake in Univation.
All production technologies can be divided according to the operating principle of the polyethylene synthesis reactor. Technologies Unipol, Innovene, Exxpol, Spherilene, Hostalen, Sclairtech and CX (Mitsui ) are based on the gas-phase polymerization reaction of ethylene and a copolymer. The reaction occurs at 70-110 0 C, pressure 15-30 bar in the presence of Ziegler-Natta catalysts.
Hostalen Technologies - Basell and CX - MitsuiChemicals They also provide a second polymerization reactor according to a cascade scheme. This makes it possible to obtain bimodal high-density PE by mixing two large fractions with different molecular weights - low molecular weight, which is responsible for fluidity, and high molecular weight, which is responsible for physical and mechanical characteristics. Gas-phase synthesis of polyethylene is characterized by low capital and operating costs and allows the production of both LDPE and HDPE in a wide range. This is why gas-phase technologies are most popular in Russia and in the world.
DSM proposes a technology for producing PE using solution synthesis. It produces LLDPE using its proprietary COMPACT Solution technology (Stamylex) in combination with Ziegler catalysts. COMPACT technology - a highly flexible polymer production process High Quality. Synthesis in solution is carried out at a temperature of 150-300 0 and a pressure of 30-130 bar in the presence of Ziegler-Natta catalysts or a metallocene catalyst. Octene is used as a solvent. In the case of using a second liquid-phase reactor, it is also possible to obtain bimodal PE. The technology is characterized by higher capital costs and operating costs compared to gas-phase synthesis. Among large producers of linear polyethylene, COMPACT technology is used by LG Chemicals and Hyundai Petrochemical Co.
BorstarPE - Borealis and Philips propose a technology for producing low-density PE in a suspension of isobutane, in which the reaction occurs at 85-100 0 C, a pressure of 4.2, after which the resulting mixture is separated and degassed at 80-85 0 C. A special loop ( slurryloop )reactor. It is possible to use a cascade scheme for producing bimodal PE using a second reactor.
Figure 3. Types of PE production plants. Reactor principles in diagrams.
From Figures 3 and 4 it is clear that there is no universal method for obtaining all types of PE. Each method for producing PE covers only part of the production of polyethylene. The widest range of products can be obtained from gas phase reactor, Unipol, Innovene, Exxpol, Spherilene, Hostalen, Sclairtech and CX (Mitsui), however each of these technologies, in turn, also has its own limitations. Most full list Unipol/UnipolII technology can offer products, but even this technology has significant limitations, mainly relating to high-density PE products with a low flow index. Such products are used for the manufacture of blow molded HDPE products, films and pipes; in these cases, bimodal PE is required, for the production of which, in turn, a cascade reactor is used, consisting of two sequential reactors with different polymerization conditions.
Figure 4. Principles of production and types of products produced.
The cascade reactor can be implemented for both gas-phase (Spherilene and Hostalen, both Basell) and suspension (Philips) polymerization processes. However, dual reactor plants have much higher capital costs and are more difficult to maintain.
For types of high-density polyethylene intended for extrusion molding, a high flow index is required. Such products are used for polyethylene pipes. So the numbers in the most famous pipe brands PE 60, PE 80, PE 100, PE 100+ correspond to their fluidity index.