Production of high pressure polyethylene

Contents

INTRODUCTION

CHAPTER 1. POLYELENE PRODUCTION

1.1. Acquisition Technology

1.2. Characteristics of initial components

1.2.1. Ethylene

1.2.2. Propylene

1.2.3. Initiators

1.3. Production Flow Chart

1.3.1. Polymerization mechanism

1.3.2. Process Diagram

1.4. Properties of the resulting material

1.5. Application of HPH

CONCLUSION

LIST OF SOURCES AND LITERATURE USED

Introduction

High pressure polyethylene is a material without which a person's life would be much less simple and comfortable. The HDPE has a number of advantages in applications in areas where high transparency and purity of the material are required, since it does not contain catalyst residues. It is more effective for PEDS for making thick-walled elastic articles. Its role both in the construction industry and in various industries is very high. It is hard to even imagine how many products are made of high pressure polyethylene: LDPE plastics by casting under the influence of pressure (polymer pipes, technical parts, etc.), thermal insulation materials from foam foam, electrical insulation materials (cable shells, etc.), HPH hot melt in the form of powder prepared by crushing HPH granules, etc.

High pressure polyethylene is obtained by polymerizing the hydrocarbon compound "ethylene" (ethene) under the influence of high temperatures (up to 1800), pressure up to 3000 atmospheres and with the participation of oxygen. HPH is a light, strong, elastic material. The starting material has good resistance to breaks and shocks. It is strong and easily withstands low temperatures, multiple compression and stretching. Furthermore, HP polyethylene is not toxic. Its use is safe for humans, animals and the environment.

Various conditions of the polymer synthesis process and a large number of different catalysts and initiators have been tested, which could help to increase the polymerization process speed and increase the molecular weight of the polymer. In particular, synthesis was carried out at increased (as far as the technical means of that time allowed) pressure. However, at a pressure of up to 10 MPa, it was possible to obtain only liquid polymers with a molecular weight in the range of 100,500, which were used in the art as synthetic lubricating oils. These oils were produced during the Second World War in Germany on an industrial scale. Only with the development of high pressure technology, that is, when designing and creating pressure lifting devices and apparatus for conducting a high pressure polymerization process, it was possible to obtain high molecular weight polyethylene. Several abbreviations are used to denote this polymer: LDPE (low density polyethylene); LDPE (lowdensity polyethylene); HDPE (high pressure polyethylene).

Chapter 1. polyethylene production

1.1. Acquisition Technology

Quality indicators, standards for GOST, the area of ​ ​ application of initial reagents, manufactured products are given in the appendix.

High pressure polyethylene includes the following components:

- Ethylene 99.9%;

- Propylene 0.05%;

- Oxygen 0,003%;

- Peroxid0,047%.

1.4. Properties of the resulting material

The material obtained as a result of the reaction by a radical mechanism has a molecular weight of 80-500 thousand and a crystallinity of 50-60%. A high pressure (HPH) or low density (LDP) polymer is an elastic soft material that is obtained by polymerizing ethylene in an autoclave or tubular reactor. A feature of the structure of HPH polyethylene is a large number of long and short branches that do not allow molecules with high molecular weight to create a crystalline structure. Therefore, the bonds between them are not strong, and this suggests that polyethylene has low tensile stability and increased ductility, as well as high fluidity in the melt [1].

PEVD properties in accordance with GOST 16337-77:

1. Density - 0.9000.939 g/cm3.

2. Melting point - 103110 ° С.

3. Bulk density - 0.50.6 g/cm3.

4. Hardness of ball pressing under specified load - (1,662,25) • 105 Pa; 1.72.3 kgf/cm2.

5. Shrinkage during casting - 1.03.5%.

6. Water absorption in 30 days - 0.020%.

7. Destructive bending stress - (117.6196.07) • 105 Pa; 120200 kgf/cm2.

8. Ultimate strength - (137.2166.6) • 105 Pa; 140170 kgf/cm2.

9. Specific volumetric electrical resistance - 10161017 Ohm • cm.

10. Specific surface electrical resistance - 1015 ohms.

11. Brittleness temperature for polyethylene with melt flow index in g/10 min

0.20.3 - not higher than minus 120 ° С,

0.61.0 - not higher than minus 110 ° С,

1.52.2 - not higher than minus 100 ° С,

3.5 - not higher than minus 80 ° С,

5.5 - not higher than minus 70 ° С,

7-8 - not higher than minus 60 ° С,

12 - not higher than minus 55 ° С,

20 - not higher than minus 45 ° С.

12. Tangent of dielectric loss angle at frequency 10100 - 0.00020.0005.

13. Dielectric constant at frequency 1010 Hz - 2.252.31

Chemical properties: PEVD is determined by the nature of its molecular and supramolecular structure. PEVD macromolecules are long chains of CH2 groups. The polymer is partially crystallized. The share of the amorphous part is 60-80%. The number of CH3 groups and respectively tertiary carbon atoms is in the range of 1.5-2.5 per 100 ° C, the number of bonds C = C mainly vinylidene, is about 0.3-0.5 per 1000 ° C. The PEHD exhibits high resistance to alkalis at any concentration. There is no discernible effect on the PEVD and aqueous solutions of basic, neutral and acidic salts. The effect of strong oxidants such as potassium nitrite, potassium permanganate and potassium dichromate is very poorly expressed. The effect on HEPD of organic liquids depends to a large extent on temperature. At room temperature, HPLC does not dissolve in a large number of organic solvents for a long time. Diffusion and gradual swelling occur.

Electrical properties: PEVD has high dielectric properties due to the structure of its macromolecules. Their combination with physico-mechanics; chemical and chemical properties make PEVD a high-quality dielectric that is widely used.

The PEVD is characterized by a small value of dielectric prony;. Tsenicity, low values ​ ​ of dielectric losses, large specific; electrical resistance and high electrical strength

Optical properties: PEVD - light transmission, light scattering, reflection from the surface and refractive index - like other properties of PEVD, are determined by the features of the molecular and supramolecular structure. Due to the absence of polar groups and the fact that more than 97% of the PEVD molecules consist of - CH2- groups, PEVD is the most transparent polymer in a wide range of wavelengths - from the UV and visible region to the far infrared region of the spectrum up to the millimeter range.

In the visible region of the spectrum, the HDPE has a high light transmission. Thus, the integral transmission in the range of 400-800 nm of the 50 μm-thick PEVD film is about 80%. The value of light transmission is limited by reflection and scattering on surfaces, as well as internal scattering. The reflection coefficient of light from the surface of the film depends to a large extent on its quality. Strong scattering is observed, for example, in extrusion films [2].

1.4. Application of HPH

The modern world is difficult to imagine without plastic. Today, everything that surrounds us for a third consists of various kinds of plastics. We are so used to them that we do not always notice them in everyday life. At the same time, plastics is a profitable business that brings its owners millions of dollars a year. Among them, the most common and most profitable is the production of polyethylene.

The field of application of high pressure polyethylene is quite wide. For the most part, high pressure polyethylene is used to discharge:

LDPE films, open and in the form of a HPH sleeve for bags and bags,

LDPE plastics by pressure casting (polymer pipes, technical parts, etc.),

blow products (bottles, canisters, etc.),

heat insulation materials from foam foam,

electrical insulation materials (cable shells, etc.),

HPH thermoclay in the form of powder prepared by crushing HPH granules.

Polyethylene is easily machined in a variety of ways - it can be drilled, sawed, plated, etc. Polyethylene parts may be welded [3].

Due to its high anticorrosion properties, polyethylene is a valuable material for chemical equipment operating at high temperatures. Such coatings are typically applied by vortex or flame spraying. During vortex spraying under the action of blown air in the apparatus, vortex motion of polyethylene powder is created. A part is placed in this stream and a uniform dense coating is obtained.

High pressure polyethylene products are used in electrical engineering, automotive industry, construction, etc. High pressure polyethylene pipes are of unparalleled strength and are recommended for installation in residential communication systems.

Conclusion

High pressure polyethylene is a solid elastic substance of matte or pearlescent white color, resembling paraffin to the touch; it has no smell, is not poisonous, combustible (it continues to burn when taken out of the flame). Polyethylene belongs to the group of thermoplastic polymers. Possessing a good combination of physicomechanical, chemical and electrical insulation properties, it is easily processed by all methods used in the processing of thermoplastics - rolling, pressing, injection molding, blowing, etc. Polyethylene can be machined well: turning, cutting, drilling, milling, stamping and straining on conventional machines used in metal processing. The ability to soften through the hole is used when applying polyethylene insulation and cladding to electrical cables. It is possible to compress the polyethylene in admixture with powders to produce porous polyethylene [5].

Improvement of polyethylene production efficiency should be carried out by introduction of high unit capacity units and intensification of production based on scientific and technological progress. Increasing the efficiency of reactors due to intensification and increasing the efficiency of their operation does not require a large capital cost and is carried out by improving the design of reaction devices and optimizing the polymerization process.

An effective increase in the productivity of a unit of reaction volume is possible by increasing the conversion of ethylene per pass, which is mainly influenced by the following factors:

1. reducing the temperature of the gas supplied to the polymerization;

2. Increasing the temperature in the reaction zone;

3. increasing the pressure (to create a homogeneous reaction medium and increase the concentration of ethylene, etc.

The quality of polyethylene of industrial grades is regulated by GOST, the production of each grade is regulated by the process sheet, i.e. indicating the technological regime for all parameters of polyethylene production. Still, in industrial production, the possibility of deviating any parameters affecting the polymerization process from the given [2] is not excluded.

Чертеж1.dwg