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How is polyethylene and polypropylene produced? If it\u2019s very short, then first short fragments of monomers are made from long molecules of hydrocarbon raw materials, and then they are again joined into infinitely long chains.
\nBut during this process, substances undergo amazing chemical transformations. Some go through the heat, stronger than on Venus, and the pressure is higher than in the Mariana Trench, while others are \u201cboiled\u201d at the temperature of ordinary borsch. The secrets of creating polymers are revealed by the technologists of the Tomsk petrochemical enterprise.<\/p>\n
Raw materials from nowhere<\/p>\n
Where do the polymers come from? From the gas. And you can answer with the words of a children’s joke: “out of nowhere.” And all because the base raw material for polymers is associated petroleum gas, which until recently was simply flared during hydrocarbon production.
\nThese are the metamorphoses. Oil workers and gas workers extract raw materials, which are then used primarily as fuel in automobiles and power plants. However, oil and gas contain many side impurities, which make up the raw materials for polymers. But for this, impurities must be isolated and delivered over thousands of kilometers for processing. Oil and gas workers are engaged in a different matter, and therefore associated petroleum gases (APG) are often simply flared, polluting the atmosphere.
\nGas and petrochemical companies acquire APG for further processing and emit a mixture of gases called NGL (wide fraction of light hydrocarbons). This is where the polymers begin. SIBUR processes BFLH, dividing the mixture into its constituent components. The output is liquefied hydrocarbon gases, or LPG.
\nThey are engaged in gas processing at eight SIBUR plants in the Khanty-Mansiysk and Yamalo-Nenets Autonomous Districts. For further transportation, hydrocarbon gases are converted to liquid. At \u201cTomskneftekhim\u201d LPG come in tanks by rail.
\nThe next important stage in the conversion of hydrocarbons is pyrolysis, from the Greek “pyros” – fire and “lysos” – decay. In the process of pyrolysis, monomers are obtained, which serve as the basic raw material for polymers.<\/p>\n
Stage 1: from long to short<\/p>\n
The production cycle at Tomskneftekhim begins with the manufacture of monomers. The raw materials that came by rail and were poured into special storages are fed through a pipeline to a pyrolysis furnace, where they are heated to temperatures above 800 \u00b0 C. This is almost twice as hot as on the surface of Venus, there is \u201conly\u201d 460 C. When heated decomposition of long hydrocarbon molecules into shorter components \u2014 monomers \u2014 occurs.<\/p>\n
The reaction is in tube furnaces. At the first stage, the raw material is mixed with steam and heated to a temperature of about 600 \u00b0 C; further heating takes place in coil tubes, which the gas flies through in just a few tenths of a second.<\/p>\n
In the process of pyrolysis, there are dozens of types of chemical transformations that occur both in parallel and sequentially. Their goal is to obtain monomers: ethylene and propylene. So far, in the hands of petrochemists, pyrogas is a gaseous mixture consisting of many different components and formed in pyrolysis furnaces.<\/p>\n
To isolate the monomers, the pyrogas now needs to pass no longer fire, but \u201ccopper pipes\u201d for sure. After exiting the furnace, it passes through a number of technological units where water, resins, and other substances in this case are separated. By the way, they cannot be called production waste. So, butadiene is sent to the plant in Tolyatti, where rubber is made from it, and then tires. Aromatic fractions of hydrocarbons are used in the manufacture of varnishes, paints, solvents and other similar products. And water is fully used in production, for example, for cooling or generating steam.<\/p>\n
The final process for the production of monomers – the separation of the mixture into individual components, occurs in gas separation columns. Finally, ethylene and propylene appear here.<\/p>\n
By the way, ethylene is practically not found in nature. Only in small quantities is formed in the tissues of plants and animals as an intermediate metabolic product. He also has the properties of phytohormones – accelerates the ripening of fruits.<\/p>\n
In monomer production plants it is not crowded. Automated process control systems \u2014 ACS TP \u2014 take on the lion’s share of the work. The busiest place is the control room, where people monitor the parameters and adjust them using the engines on the monitors of their workstations.<\/p>\n
At the same time, Tomskneftekhim went further and introduced APC (Advanced Process Control) systems for the production of monomers. This is a global practice for managing complex processes. Everyone can imagine how an autopilot works in aviation: after making a flight mission, an aviator does not interfere in the process of controlling a ship unnecessarily, but only controls it. Similarly, the operation of the improved process control system at the pyrogas separation unit looks like. APC independently monitors the performance of the entire installation and every minute in the 24\/7 mode, reconfigures them, selecting and maintaining optimal operating modes of technological units. APC also real-time informs about the quality of products and manages quality indicators according to a predetermined algorithm.<\/p>\n
\u201cYes, APC is a kind of\u201c autopilot \u201dfor a process plant, but with more advanced optimization functions. The APC system controls the installation, and I, as an operator, control the APC system, \u201dsays Alexey Kotov, a senior apparatchik.<\/p>\n
Monomer production is an ongoing process. In those 20 minutes while we watched the operator \u201ccommunicate\u201d with the APC system, a total of more than 15 tons of monomers were released from the gas separation columns. Ethylene and propylene are ready for further transformations.<\/p>\n
The petrochemical industry is based on enterprises with pyrolysis plants. Monomers are the basic raw material for further transformations and the production of polymeric materials.
\nThe pyrolysis unit, built and put into operation in Tomsk in 1993, was at that time the largest domestic unit for the production of ethylene and propylene. Its productivity is 300 thousand tons per year (it is considered according to the design capacity of ethylene production). The number by world standards is not the largest, but such a volume fully meets the needs of Tomskneftekhim polymer production for raw materials, there is even a small margin of capacity for ethylene.<\/p>\n
Polyethylene production: extraterrestrial conditions<\/p>\n
Further short, but very valuable molecules of ethylene and propylene are sent for polymerization, during which the monomers are linked together, forming chains containing hundreds of thousands and millions of molecular units. Hence the name “poly”, in Greek – “numerous.”
\nTwo types of polymers are produced at Tomskneftekhim: polyethylene and polypropylene. The first – by polymerization of ethylene, the second, respectively, “crosslinking” of propylene.<\/p>\n
In the USSR, an industrial method for producing polyethylene was developed in 1939. Six years later, bottles for shampoos and liquid soaps began to be made from it, which replaced glass containers. In 1957, the Soviet Union first produced a bag of polyethylene intended for packaging products.<\/p>\n
In 1993, the production of polyethylene was established at Tomskneftekhim. Three years ago, a comprehensive reconstruction was completed at this production facility – capacity was increased and the range of products was expanded. However, the development of the plant did not stop there – the technological processes are being optimized and are still being automated more and more.<\/p>\n
We begin our acquaintance with the production of polyethylene. Tomskneftekhim produces high-pressure or low-density polyethylene. Here is such a correlation.<\/p>\n
For this, equipment with a beautiful name is used – a tubular reactor of ideal displacement. Visually, this is a large screw pipe with a double wall, laid in layers for greater compactness. At Tomskneftekhim, the polymerization reactor consists of three zones, its length is about two kilometers. Ethylene is fed into the reactor, where it is converted to a polymer at high temperature and under high pressure. By the way, due to the high pressure, the parts of the polymerization reactor are made of weapons grade steel, and the trunks of artillery and tank guns are made of the same.<\/p>\n
\u201cThe ethylene compression unit – it all starts from here,\u201d explains Alexander Chertenkov, head of the polymerization unit. – Ethylene from the production of monomers comes here under a pressure of 15 atmospheres. This is very small for us, and we compress it to 2300 atmospheres. Compression occurs in stages, because at each stage it is necessary to cool the gas.<\/p>\n
And already compressed ethylene is sent to the polymerization unit. So, for the process of \u201ccross-linking\u201d polyethylene, three things are needed – the pressure is three times higher than at the bottom of the Mariana Trench, namely 2400 atmospheres, the temperature, as in the mouth of a volcano, and the chemicals that start an active reaction chain. They are called initiators. Previously, it was ordinary oxygen, but now, along with oxygen, more modern and effective initiators based on organic peroxides are used.<\/p>\n
The polymerization process at the molecular level resembles a family series. When heated, the initiator \u201cgives\u201d free radicals to a disparate family of monomers. These are those particles that are most needed: they interact with ethylene molecules, and those, thanks to the attached free radical, gain the necessary activation energy. Ethylene molecules become more friendly and able to attach new ethylene molecules, transferring their activation energy to them, and thus beginning the growth of the polymer chain. It turns out a molecule that can contain up to several hundred thousand monomers.<\/p>\n
The real polymers come out of the polymerization unit, although still in the form of a viscous melt. It remains for the polymers to take shape – to become solid white granules.<\/p>\n
Stage 3: from the “meat grinder” to the silos<\/p>\n
The molten polymer is extruded. At this stage, the material passes through a kind of meat grinder, which forms round granules from it. They look exactly like a finished product, but before being sent to the consumer, the granulate should spend about another day in a huge capacity – \u201crest\u201d, as the petrochemists say. Each silo holds 600 tons of finished product, and a total of 820 tons of polyethylene are produced at Tomskneftekhim per day.<\/p>\n
Remember the episode from the famous movie “Amelie”, where the main character loved to run her hand in a bag of lentils? I also managed to get tactile joy by dropping my hand in a bag with brand-new granules selected for laboratory research on quality parameters. At Tomskneftekhim, a laboratory equipped with high-precision equipment operates at each production site: in order to \u201cissue\u201d a product a quality certificate, which is obligatory when delivering polymers to processors, it is necessary to examine the product in more than 15 parameters.<\/p>\n
The packaging of finished polyethylene and the packaging of bags on pallets are also fully automated. Granules are packed in bags; more than 5000 bags of 25 kilograms per hour. Then these bags with a confident automatic \u201chand\u201d are stacked on pallets and in a few seconds they are covered with a film using the stretch hood technology (English \u201cstretch hood\u201d). The bags are inside the general package, which, by the way, is also made of polyethylene produced at Tomskneftekhim. It prevents the penetration of dust and moisture.<\/p>\n
And the filling equipment at Tomskneftekhm automatically weighs the bags with an error of up to 20 grams, eliminates metal objects from getting into them with the help of a metal detector.<\/p>\n
Now polymers will travel thousands of kilometers. Pallets are shipped by road, loaded onto wagons, as well as onto cargo ships for transportation by sea. Tomsk polymers are supplied to all regions of Russia, to Belgium, Poland, Ukraine, Vietnam, China, Kazakhstan, Uzbekistan and other countries.<\/p>\n
Processors turn polyethylene into a modern packaging film, insulating material, a variety of household goods, decorative packaging, adhesive tape and even housings of household appliances and medical goods. Polyethylene, or rather films from it, is an indispensable material for farmers. More than 70% of the Russian territory is a risky farming zone. And smart assistants to farmers: greenhouse, mulching films based on polyethylene – help to get an acceptable crop and optimize the cost of building greenhouses.<\/p>\n
Polyethylene packaging can extend the shelf life of products by 30%. Its advantages are its ability to respond flexibly to various external influences that affect the composition and quality of the transported products. Another area of \u200b\u200bapplication of polyethylene is cable sheathing. By the way, cable products manufactured in Tomsk have a sheath made of polyethylene produced at Tomskneftekhim.<\/p>\n
Even medical products are made of polyethylene, in particular, medical orthoses that retain their shape perfectly, while they are lightweight, optimally flexible, well springy: everything you need when restoring the body during fractures and sprains.<\/p>\n
Polypropylene “soup”<\/p>\n
At Tomskneftekhim, another type of polymer is produced – polypropylene, the second most popular after polyethylene. Polypropylene production was the first one built at Tomsk Petrochemical Plant in 1980. It is also the first large-capacity polypropylene plant in the country, at that time its capacity was 100 thousand tons per year. Her appearance was an industrial breakthrough of those years. Now the production capacity is 140 thousand tons per year. In 2016, a comprehensive reconstruction was completed at the production site – the key equipment was updated, the enterprise’s capabilities to produce special high-margin brands were expanded.<\/p>\n
Polypropylene, unlike polyethylene, is born without the use of high pressure and extremely high temperatures. The catalyst is responsible for the polymerization process. Thanks to him, the monomer molecules begin to \u201cmake friends with families\u201d and are connected to each other in long polymer chains. The reaction proceeds at a temperature of up to + 70 C and a pressure of 7.2 atmospheres, slightly higher than that in the water tap.<\/p>\n
Along with the base feed, a catalyst complex is introduced into the reactor – a special mixture containing the solvent, the catalyst itself and a number of auxiliary substances.<\/p>\n
Polymerization of propylene Tomsk technologists compare with the preparation of mega-borsch. They resort to such figurative comparisons when they need to very quickly explain the essence of the process to the townspeople who came on an excursion.<\/p>\n
Large capacity vessels are used as polymerization reactors. Each tank is equipped with a mixer and this reminds a household mixer. Pipelines are brought to it, through which raw materials and other necessary components are suitable. From the moment propylene is fed into the vessel until the polymer suspension exits, it takes up to five hours. Five o’clock, and the “soup” is ready. Then the whole mixture goes through the stages of separation of excess substances and turns into a white loose powder. It is dried in several stages and accumulated in the so-called analysis bins. Of these, laboratory assistants take samples for research.<\/p>\n
In order for polypropylene to be ready to go to the consumer, it is necessary to introduce additives into it, and also turn it into familiar round granules. So, the powder is sent to the extruders, where when heated it turns into a melt. Various additives are introduced into it that will help processors turn the polymer into products with the right qualities. These are light stabilizers that protect products from light, heat stabilizers that protect polymers from high temperatures, brighteners and other additives. The combination and dosage of these substances help create a wide range of brands.<\/p>\n
After the introduction of additives, the melt is pressed through a narrow hole of the die, from which it comes out in the form of a thin filament. The thread is immersed in water, cooled and cut into pellets with knives.<\/p>\n
Filling and packaging lines are identical to those in the production of polyethylene<\/p>\n
From polypropylene, processors throughout the country and abroad produce parts for household appliances and cars, sewer pipes, packaging for food, non-woven materials, including for baby disposable diapers, containers and medical devices.<\/p>\n
So, a disposable artificial lung – oxygenator, is made including polypropylene fibers and is indispensable in microvascular surgery. It is disposable oxygenators, the appearance of which was made possible thanks to the development of new polymers, that exclude infection during complex operations. This was noted by the chief cardiac surgeon of the Ministry of Health of Russia Leo Bokeria: \u201cPreviously, the oxygenator was permanent, it was made of metal, it was disinfected and put back on. And the most powerful microorganisms remained, infection was going on. Plastic artificial lungs turned the whole situation upside down. \u201d<\/p>\n
Products made from polyethylene and polypropylene, being fully recyclable, have a serious advantage over traditional materials. So, products from polymers are processed 100%; glass for 80%; 70% from paper; from aluminum for 80-100%; from steel by 94%.
\nPolyethylene and polypropylene complement each other in the market of modern polymeric materials. They are durable and lightweight, besides resistant to extreme temperatures, moisture, aggressive environments, microorganisms. Polymers seem to be created in order to meet the challenges of modern dynamic life.<\/p>\n
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How is polyethylene and polypropylene produced? If it\u2019s very short, then first short fragments of monomers are made from long molecules of hydrocarbon raw materials, and then they are again joined into infinitely long chains. But during this process, substances undergo amazing chemical transformations. Some go through the heat, stronger than on Venus, and […]<\/p>\n