Industrial tubular reactor-polymerizers are series-connected heat exchangers of the "pipe in pipe" type. The reactor tubes have a variable diameter (50 - 70 mm). Separate links of the "tubular" are connected by massive hollow slabs-rolls. Pipes and rolls are equipped with jackets connected in series with each other. As a heat carrier for heating ethylene and removing excess heat, superheated water with a temperature of 190 - 230 0 C, which enters the jacket of the tubular reactor 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 a constant temperature regime in the reactor and ensure efficient heat removal, additional ethylene and initiator are introduced into various zones along the length of the reactor. A multi-zone reactor is more productive than a single-zone one. A single-zone reactor at the maximum reaction temperature (300 0 C) provides 15-17% ethylene conversion in one pass. A two-zone reactor reaches 21–24% conversion at the same temperature. In a three-zone reactor, the degree of conversion 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 by zones at the same level.
The performance of the reactor depends on its size, therefore, currently used with various lengths pipes and diameter. For reactors high power pipe length reaches 1000 m or more.
Technological process of polyethylene production high pressure in a tubular reactor consists of the following stages:
mixing of fresh ethylene with return gas and oxygen,
two-stage gas compression,
polymerization of ethylene in the condensed phase (density of ethylene 400 - 500 kg / m 3),
separation of high-pressure polyethylene and unreacted ethylene entering the recycle,
polyethylene granulation.
For dyeing, stabilization and filling, appropriate additives are introduced into high-density polyethylene, after which it is melted and granulated.
In Fig.1. presented circuit diagram production of high pressure polyethylene in a tubular reactor in a continuous way.
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. Then oxygen is introduced into the flow and the mixture enters the three-stage compressor of the first stage 3 , where it is compressed 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 stage, where it is compressed to 245 MPa. After the first stage of compression, ethylene is cooled in a refrigerator, cleaned of grease in separators, and after the second stage at a temperature of about 70 0 C without cooling, it enters the tubular reactor through three inlets 6 for polymerization.
The production of polyethylene, the most demanded polymer, is based on the polymerization reaction of ethylene gas. It is a thermoplastic polymer, a class of organic polyphenols. Its popularity is explained by a whole range of technological properties that make it possible to produce many household products and products for various fields from it. industrial production. An important factor in the demand for this material is its low cost compared to analogues used in the same areas.
Brief business analysis:
Business setup costs:150 - 250 thousand dollars
Relevant for cities with a population: with no restrictions
Situation in the industry:low competition
The complexity of organizing a business: 4/5
Payback: 12 - 14 months
The main types of polyethylene
- HDPE - polyethylene low pressure, or PVP - high density;
- LDPE - high pressure, or PNP - low density;
- PSD - medium pressure, or PSP - medium density.
In addition to these types of polymers, there are others: cross-linked - PEX, foamed and chlorosulfonated (CSP) polyethylenes.
Polyethylene is one of the most widely used modern materials in production:
- packaging, shrink, agricultural and other types of films;
- water, gas and other types of pipes;
- various synthetic fibers;
- containers for various kinds of liquids;
- a wide range of building materials;
- sanitary products;
- crockery and household items;
- insulating materials for electric cables;
- parts for cars, machine tools, various equipment, tools and other equipment;
- prostheses for dentistry and other types of endoprosthesis;
- polyethylene foam.
A wide range of consumer properties of polyethylene is due to a whole range of chemical, physical, mechanical and dielectric characteristics of this material. Therefore, it is in demand in the radio-electrotechnical, cable, chemical, construction, medical and many other industries.
Special varieties of this material, such as polyethylene foam, cross-linked, supermolecular, chlorosulfonated, are effectively used in production. building materials. Although polyethylene itself is not structural in structure, fiberglass reinforcement makes it possible to use it in structural composite products.
Polyethylene is also used as a recyclable material. Its waste is perfectly recycled for further use.
Polyethylene production technology
A polyethylene polymer is obtained as a result of a chemical reaction for the polymerization of ethylene under various conditions and in the presence of certain catalysts. Depending on the reaction conditions - temperature, pressure and catalysts, polyethylene acquires radically different characteristics.
Most often, three types of polyethylene have practical value - low, medium and high pressure. Therefore, it is worth considering the technology for obtaining these particular materials. It should be noted that medium-density polyethylene is considered just a type of HDPE and the technology for their production is no different.
Production of low-density polyethylene
HDPE is produced from purified ethylene gas. The process takes place at a temperature of 100-150°C at a pressure of up to 4 MPa. A catalyst must be present in the polymerization reaction: either triethylaluminum or titanium tetrachloride. The process can be continuous or short-term, with interruptions.
There are a number of technologies for the production of polyethylene, differing in the type of structures used, the size of the reactor, and the method of purification of the polymer from the catalyst. Whole technological process broken down into three stages:
- polymerization of polyethylene;
- cleaning it from the catalyst;
- drying.
A necessary condition for the normal course of the polymerization reaction is a constant temperature, which is maintained with the help of the supplied ethylene and its volumes. The polymerization process with the participation of a catalyst has its drawbacks - the resulting product is inevitably contaminated with catalyst residues.
It not only stains polyethylene in an unacceptable Brown color, but worsens it Chemical properties. To eliminate this drawback, the catalyst is destroyed, and then dissolved and filtered. The resulting polymer is washed in a special centrifuge, to which methyl alcohol is added.
After washing, it is wrung out, substances are added to it that increase its strength and appearance. To improve the external qualities, wax is added, which gives the polyethylene a shine. Further, the polymerization product enters the dryers and granulation shops. The main grades of polyethylene are produced in powder form, composite grades - in the form of granules.
Production of high-density polyethylene
LDPE is produced at a temperature of at least 200 ° C, at a pressure of 150 to 300 MPa, oxygen acts as an activator of the reaction. Polymer production equipment - autoclave and tubular reactors.
A tubular reactor is a long tube-shaped vessel in which the polymerization reaction takes place under high pressure. The polymer, in the form of a melt, is removed from the reactor and enters the intermediate pressure separator, where it is isolated from unreacted ethylene. Then, according to technological scheme it enters and exits the extruder in the form of granules, and is sent for further processing. This technology is the most demanded among manufacturers.
Autoclave reactors are cylindrical, vertically arranged units in which the polymerization of ethylene takes place with a reaction initiator. Reactors differ in reaction conditions, including heat removal conditions. Concentrations of initiators and parameters of the reaction mass.
Flow differences chemical reactions. Different types equipment and other differences cause structural features the resulting polymerization product.
Despite the type of reactor, the scheme for the production of LDPE for them is the same:
- supply of raw material and initiator to the receiver of the reactor;
- heating ingredients and increasing pressure parameters;
- intermediate supply of raw materials and initiator;
- isolation of unreacted ethylene and its collection for reuse;
- cooling the obtained polymer, pressure relief;
- final product granulation, washing, drying, packing.
Foamed polyethylene, or PPE, is a polymer with a porous structure and high performance and specifications. It is widely used as thermal insulation material in construction and instrument-making engineering, as well as as a packaging material and in other areas.
The production technology of this polymer is characterized by a certain complexity. For its complete cycle, special equipment is needed: mixers, loaders, cooling devices, high pressure pumps. But the most important equipment in the production of polyethylene foam are extruders. LDPE is used as a raw material, freons and alkane mixtures, for example, butane, are used as blowing agents.
Depending on the features of the production technology, two types of PPE are distinguished - crosslinked and non-crosslinked. The foaming process takes place under a certain pressure and at a high temperature. Stages of the technological process:
In order to avoid the costs of large-scale production of polymers, one can take advantage of their recycling. A high-quality granulated polymer product is produced from recycled materials, which, in terms of its characteristics, is in no way inferior to the primary polymer product obtained.
The raw material is crushed. Then, it is washed and dried in a centrifuge. The cleaned raw material goes through the agglomeration operation and goes to granulation. It is the end product of polyethylene recycling.
Equipment for the production of polyethylene differs in accordance with the purpose and type of processed raw materials. The technological chain is represented by the following equipment:
- one or more extruders-granulators;
- cutting machine;
- loaders working on the basis of vacuum;
- pumps equipped with filters for melts;
- vibrating screens;
- cooling baths;
- conveyors;
- bunker for raw material supply;
- mills.
The purchase of new basic equipment for the production of polyethylene can be in the range of 120-200 thousand dollars. New domestic equipment will cost half as much.
How to organize a polyethylene production plant
Any manufacturing business begins with the development of a business plan.
Drawing up a business plan
The purpose of a business plan is to provide general information about the author of the project, a description of the products he is going to produce. The objectives of the project should also be disclosed, the production technology should be described in detail.
If this technology is new, then the business plan should present the conclusions of the relevant authorities on its safety for environment and people's health.
room
Industrial production, which is the production of polyethylene, should be located in the production area locality. For production premises there are certain sanitary and technical requirements. The floor space must not be less than 100 sq. meters, its height should not be lower than 10 meters. In production shops, there should be fire protection and good ventilation.
Paperwork
First of all, you need to register your business. It can be an individual entrepreneur or an LLC. It is also necessary to obtain permits in such instances:
- City Administration;
- fire, environmental and sanitary-epidemiological services;
- electrical supervision.
Cost calculation
First, the income from production is calculated:
- how much is spent on average for the production of a certain volume of output;
- what is its market value;
- what is the income.
- the cost of permits;
- preparation of the premises;
- purchase of equipment;
- purchase of raw materials.
Monthly expenses:
- wages for employees;
- payment for the rent of the premises;
- taxes and utilities.
Business Profitability
With the stable operation of the enterprise and with a good start-up capital for the purchase of equipment, this business pays off in 12-14 months. After a year of stable operation, the cost of equipment can fully pay off and the plant will bring a net profit.
Ethylene. Ethylene -- chemical compound, described by the formula C2H4, a colorless gas with a slight odor. It is the simplest alkene (olefin). Contains a double bond and therefore belongs to unsaturated compounds, has a high reactivity. Ethylene is practically not found in nature. In small quantities, it is formed in the tissues of plants and animals as an intermediate product of metabolism. Plays an extremely important role in the industry, the most produced organic compound in the world.
At present, the main source of ethylene production is the pyrolysis of gaseous and liquid saturated hydrocarbons: ethane, propane, and straight-run gasolines.
Ethylene properties:
Chemical formula H2C=CH2
Molecular weight 28.05
State - gaseous
Melting point 103.8 K (-169.2°C)
Boiling point 169.3 K (-103.7°C)
Density under normal conditions 1.26 kg / m 3
The density of liquid ethylene at 163.2 K (-109.8 ° C) - 610 kg / m 3
Flammability temperature 728 K (455°C)
Ethylene purity. For polymerization, ethylene must be thoroughly purified from impurities. Impurities to ethylene are divided into two main groups - inert and active. An inert impurity, present in a noticeable amount, for example 5-10%, reduces the concentration of ethylene by a significant amount, given the low compressibility of ethylene.
Active additives to ethylene, such as vinyl-type compounds, usually copolymerize with ethylene, change the properties of the resulting polymer and affect the rate of polymerization.
Depending on the content of impurities specifications It is planned to produce three grades of liquefied ethylene: A, B and C. Ethylene of grades A and B is used for the production of polyethylene and ethylene oxide. Ethylene grade B - for the production of other organic products. Ethylene liquefied must comply with the requirements and standards.
Catalysts (initiators). As catalysts for the polymerization of ethylene, mainly molecular oxygen and organic peroxides are used. Of the peroxides in industry, peroxide of di-tert-butyl, tert-butylperbenzoate, etc., has found the greatest use. The effect of the initiator depends on the degree and rate of its decomposition at a given temperature and on the ability of the formed radicals to react with the monomer.
Another factor characterizing the initiator is the content of active oxygen, i.e. theoretical percentage of active oxygen in pure peroxide.
In dry form, peroxides are explosive, their solutions in organic solvents are more stable and less explosive. Storage of initiators must be carried out under certain temperature conditions.
The main properties of the most common peroxide initiators are described below.
Di-tert-butyl peroxide (С8Н18О2)
Application temperature 513-553 K (240-280°C)
Molecular weight 146.2
Liquid, density 793 kg/m 3
Boiling point at 0.1 MPa - 463 K (190°C)
Peroxide is insoluble in water, soluble in most organic solvents
Storage temperature 298 K (20°C).
Tert-butylperbenzoate (С11Н14О3)
Application temperature 453-513 K (180-240°C)
Molecular weight 194
Liquid, density at 293 K (20 ° C) - 1040 kg / m 3
Boiling point at 0.1 MPa - 397 K (124°C)
Storage temperature 293 K (20°C).
The raw material for the manufacture of polyethylene films are polyethylene granules obtained by polymerization of ethylene. For the production of high and low pressure polyethylene, two technologies are used, involving the passage of the process at different conditions polymerization. HDPE and LDPE are produced at different temperatures and pressures. As a result, materials acquire different physical and chemical properties.
A little about production technology
The granules obtained under high pressure (1000-3000 kg/cm 2 ) have a lower intrinsic density of 0.925 g/cm 3 . The film obtained in this way is more "oily" to the touch. It is relatively transparent and stretches well without tearing. The material is characterized by shorter polymer chains. It is less crystalline and melts at temperatures above 100 C. These characteristics apply to high-density polyethylene, which is quite often referred to as LDPE.
Low pressure polyethylene or HDPE polymerizes at a pressure of 1-5 kg/cm 2 and reaches a density of 0.945 g/cm 3 . This type of polyethylene film is more crystalline, the polymer chains in it are longer, and the transparency is less. It takes more than heat- from 120C, so the energy costs for its production are higher. But even during operation this type polyethylene film can withstand higher temperatures.
Popular facts
It is very easy to distinguish LDPE from HDPE by eye: a polyethylene film made of low-pressure material always “rustles” when crushed. Domestic abbreviations are different from foreign LDPE corresponds to LDPE (Low Density PolyEthylene,) and HDPE - HDPE (High Density PolyEthylene). This is due to the fact that in Russia the classification is based on the pressure during the polymerization of polyethylene, and outside it - the density of the granules used. A material made at high pressure has a low density, while at a low pressure, on the contrary, it has a high density.
Where do we most often see plastic film products? Of course in stores. Think of the rustling matte packaging bags and T-shirt bags and know that they are made of HDPE. While the smooth packaging bags and bags with welded and die-cut handles are made of high pressure low density polyethylene. PVD products have a more aesthetic appearance and allow bright, colorful patterns to be applied to their surface.
In conclusion, it should be said that at present polyethylene has become the most widespread type of polymer material used in the packaging industry. It was invented first, but still its popularity in packaging remains one of the highest.
