The production process of the fourth generation polypropylene mainly includes two categories as shown in the above figure, and the gas phase process is introduced here.
Research and development of the fumed polypropylene process began in the 1960s, and in 1967 BASF built a pilot plant for the fumed polypropylene process using a vertical stirred bed reactor in Ludwigshafen. In 1969, ROW, a joint venture between BASF and Shell, built the world's first 25,000 tons/year gas-phase polypropylene industrial plant in Wesseling, Germany, using a vertical stirred bed reactor, named the Novolen process. In the 1970s, the United States Amoco company developed a gas phase PP production process using a horizontal stirred bed gas phase reactor close to the piston flow. In the early 1980s, UCC applied its mature gas-phase fluidized bed Unipol polyethylene process to polypropylene production, introducing the Unipol gas-phase polypropylene process. Japan's Sumitomo company also developed a gas phase process using a gas phase fluidized bed at the same time. At present, the world's gas phase PP production process mainly includes BP's Innovene process, Chisso process, Unipol process, BASF's Novolen process and Sumitomo Chemical Company's Sumitomo process.
Innovene Process
Innovene process is also known as BP-Amoco process. The main feature of the process is the use of a unique horizontal stirred bed reactor close to the piston flow. With this unique reactor, copolymer products with very good rigidity and impact resistance can be produced due to the narrow particle residence time distribution. When ethylene is present, large particle copolymers can be formed instead of fine powders within the homopolymer particles, which will reduce the low temperature impact strength of the copolymer and form unnecessary colloids. Therefore, the very narrow reaction residence time distribution of the process can meet the requirements of high impact copolymers produced by multiple homopolymerization reactors in fully mixed reactors. In addition, due to this unique reactor design, the product transition time of the process is very short, and the theoretical transition time of the product is 2/3 shorter than that of the continuous stirring reactor or the fluidized bed reactor, so the product switch is easy and the transition product is few.
The Innovene process uses propylene flash evaporation to remove heat. Liquid propylene is injected into the reactor from various feed points in a manner that keeps the reactor bed dry. After vaporization, the partial pressure of the liquid propylene monomer is less than its dew point pressure and is sufficient to remove the reaction heat. In operation, the feed rate of liquid propylene and its vaporization in the reactor must be strictly controlled to ensure the balance between the drying degree of the bed, the degree of fluidization and the reaction temperature range. The air lock system is another feature of the process. When the material is transported from the first reactor to the second reactor, the air lock system prevents the two reactors from flowing into each other. Especially when producing copolymers, the gas phase composition of the two reactors is different, the first reactor contains a lot of hydrogen, while the second reactor contains ethylene and a small amount of hydrogen, if the hydrogen in the first reactor into the second reactor or the ethylene in the second reactor into the first reactor, will seriously affect the quality of the product, so the isolation of the two reactors is the key. The CD catalyst used in this process has good shape control, high activity and selectivity, which can control the formation of random polypropylene, the product has a high isotactic index, the polymerization product has narrow particle size distribution, good powder flow, low ash content, good color and so on. The process can be simplified by using the catalyst. Only one catalyst can be used to produce all grades of products, without the need to switch catalysts. CD catalyst activity is in the range of 25,000-55000kgpp /kg cat, depending on the purity of the feedstock and the number of reactors. The isotactic index of the produced powder products can reach up to 99%. Another feature of the CD catalyst is that it does not require pretreatment or pre-polymerization, can be added directly to the reactor, and the catalyst can produce all polypropylene products. The MFR of the homopolymerization product can range from 0.5g/10min to 100g/10min, and the toughness of the product is higher than that of other gas phase polymerization products. The MFR of random copolymerization products is 2-35g/10min, and its ethylene content can reach 7%-8% (mass fraction). The MFR of the impact copolymerization product is 1-35g/10min, and the ethylene content is 5%-17% (mass fraction).
Due to the piston flow reactor design, the residence time distribution of the catalyst is narrow, the rubber phase distribution of the impact copolymer is more uniform, and the performance is better, especially the balance performance of impact resistance and rigidity is better. The process can also use a reactor to produce homopolymer and random copolymer, but the process also has shortcomings, the ethylene content of the product (or the proportion of rubber components) is not high, can not obtain high impact and ultra-high impact grades of PP products. Another important feature of the process is that the polymerization reaction can be stopped quickly and smoothly (about 15-20 minutes) by stopping the catalyst injection, and can be restarted after a few hours, without affecting the internal conditions of the reactor and the quality of the polymer. In the event of an accident such as a power outage, the reactor can stop within 3 minutes by releasing the reactor pressure under the accident stop or slow stop state, and can start again after re-pressurizing and injecting the catalyst. Because Innovene process is short, the reactor design is unique, the polymerization pressure is relatively low, and there is no large rotating equipment, the power consumption is among the lowest in various PP processes. Because it is a gas phase polymerization system, it is not necessary to use steam to heat the liquid propylene discharged with the polymer as in the liquid phase method, so the steam consumption is very small, and the energy consumption of the production of homopolymerization products is the lowest in various processes. The Innovene gas-phase process, like other gas-phase processes, does not have a large amount of liquid hydrocarbons in the polymerization system and is inherently safer than the bulk process. The operating pressure of the Innovene gas phase process reactor is the lowest among the various process technologies. The polymerization system has no waste water discharge and is a clean production process. At present, there are more than 10 sets of polypropylene production plants using Innovene process technology in the world, with a total production capacity of about 3 million tons/year, accounting for about 7.6% of the world's total polypropylene production capacity.
The first set and the third set of PP units of Yanshan Petrochemical and Chemical Plant in China are produced by this process. The first set, Innovene gas phase polypropylene production unit of IneOS, has a designed production capacity of 120,000 tons/year. The third set, IneOS Innovene vapor phase polypropylene production plant, designed production capacity of 200,000 tons/year, after renovation, the actual production capacity of 280,000 tons/year.
The first set of polypropylene production plant produces PPH pipe special material B1101, transparent material K4912, B4808, K4818, medical material B4902, B4908, high rigidity and high flow K1840, K1860, K1885, geoglyph grid T1701, T2701, Ternary copolymer polypropylene F5606, F5006, C5608, C5908 and other brands; The second set of polypropylene production plant is dedicated to producing PPR pipe special material 4220; The third set of polypropylene production plant produces PPR pipe special material 4400, PPB pipe special material B8101, low VOC impact copolymerization K7726H, K7760H, K7100, high rubber high impact copolymerization K9820H, K9829H, bottle cap material K6606, impact copolymerization K8303, Automotive materials K9016, K9026 and other brands.
Yangzi Petrochemical and Secco Petrochemical also have Innovene fumed polypropylene production plants.
Chisso's polypropylene process was developed on the basis of Innovene vapor process technology, and there are many similarities between the two, especially the reactor design is basically the same. Compared with Innovene vapor process technology, Chisso vapor polypropylene process technology has the following two unique features, the process is more suitable for the production of high ethylene content of impact copolymerization products. The first reactor of the Chisso process is arranged on top of the second reactor, and the discharge from the first reactor is fed by gravity into a simple air lock device, which is then fed into the second reactor with propylene air pressure. The two reactors of the Innovene gas phase process are arranged in parallel and horizontally. The discharge of the first reactor is fed into the high precipitator by pressure difference, the separated unreacted gas is compressed and pressurized by the compressor, and then recycled back to the reactor after condensation. The polymer powder is fed into the air lock by gravity and into the second reactor by acrylic pressure. Compared to the two, the Chisso process is simpler in design and uses less energy. The Chisso vapor polypropylene process uses the THC-C catalyst developed by Toho Titanium, which is highly reactive and selective, controlling the formation of amorphous polymers while maintaining the production of isotactic polymers with high yields. The polypropylene produced by using the catalyst has good shape, less fine powder, narrow particle size distribution and good fluidity, and is easy to be transported to the second reactor. The typical activity of THC-C catalyst is 25,000-40000kGpp /kgcat, but the catalyst needs to be pre-treated, prepared into a slurry with hexane, and treated with a small amount of propylene for several hours, otherwise the fine powder in the product will increase, the fluidity will decrease, and the operation of the copolymerization reactor will be difficult. Chisso's vapor polypropylene process enables the production of a full range of products. The MFR of polymeric powder products in the reactor is usually less than 20g/10min, the MFR range of homopolymer products is 0.5-45g/10min, and the typical MFR range of random copolymers is 1.5-35g/10min, with a maximum ethylene content of 5% (mass fraction). Impact copolymer products have an MFR range of 0.5-65g/10min and ethylene content of up to 15% (mass fraction). Chisso vapor polypropylene process to produce random copolymer has a very low sealing temperature, suitable for BOPP film. For the BOPP grade of homopolymer, the stereoscopic degree can be controlled, suitable for a variety of applications, such as high processability and high rigidity - low thermal shrinkage film. At present, there are mainly 6 sets of production plants using Chisso vapor polypropylene process in the world, with a total production capacity of 1.422 million tons/year, accounting for about 3.6% of the world's total PP production capacity.
Chisso Polypropylene process diagram
Formosa Plastics USA Chisso Plant with annual output of 360,000 tons (Texas)
Unipol technology
Unipol process is a gas-phase fluidized bed PP process jointly developed by United Carbon and Shell in the mid-1980s, which is a process of transferring the fluidized bed process applied in polyethylene production to PP production. The high efficiency catalyst system is used in the process, the main catalyst is the high efficiency carrier catalyst, the cocatalyst is triethylaluminum and the electron donor. It has the characteristics of simplicity, flexibility, economy and safety. It can produce homopolymer and random copolymer products by using only one main reactor of boiling bed. The operating conditions can be adjusted in a wide range to keep the product performance uniform. Another significant feature of the process is that it can be used in conjunction with the ultra-condensing process, the so-called ultra-condensing gas phase fluidized bed process (SCM). Since the supercondensation operation can most effectively remove the reaction heat, it can improve the production capacity of the reactor without increasing the volume. For example, by increasing the proportion of liquid phase in the reactor to 45%, the existing production capacity can be increased by 200%, which is of great significance for saving investment. In addition, the process route is short, there is no special requirement for the material, the main reactor and its downstream equipment are ordinary carbon steel (except extrusion granulation unit), more than 65% of the pipe is ordinary carbon steel, coupled with its footprint is small, the device has great production potential, low product cost, good performance, and thus has a strong competitiveness.
The process can produce a full range of products including homopolymer, random copolymer and impact copolymer with less equipment, and only one main boiling bed reactor can produce homopolymer and random copolymer. The operating conditions can be adjusted in a large operating range to keep the product performance uniform; Due to the small number of equipment in this process, the maintenance workload is smaller and the reliability of the device is improved. Due to the limitation of the reaction dynamics of the fluidized bed and the reduction of the reserves of materials in the system due to the low operating pressure, the process is safer than other processes, and there is no danger of equipment overpressure when the accident is out of control. This process has no liquid waste discharge and very few hydrocarbons are released to the atmosphere, so the environmental impact is very small, and it is easier to meet stringent environmental, health and safety specifications than other processes. The Unipol process uses the SHAC series of catalysts, which do not require pre-treatment or pre-polymerization, and can produce any type of PP product using the same catalyst.
The Unipol polypropylene process uses two tandem reactor systems to produce impact copolymerization products with a wide MFR molecular weight distribution. The MFR of commercial homopolymer products is 0.5-45g/10min, and products with MFR up to 100g/10min can be produced. For random copolymerization products, the ethylene content of the industrialized product brand is 0.5% to 5.5% (mass fraction), the highest ethylene content is 7% (mass fraction), and the ethylene content of the product produced by the pilot plant can reach 12% (mass fraction); Commercially produced impact copolymers have up to 21% ethylene content (35% rubber phase content), and pilot plants can produce products with up to 60% rubber phase content (mass fraction). Unipol process impact copolymer products also have a good balance of impact resistance and rigidity.
At present, 40 production units in 15 countries around the world are produced using the Unipol process, with a total production capacity of 7 million tons/year, accounting for about 13.5% of the world's total polypropylene production capacity.
Global distribution map of Unipol devices
In recent years, China has also introduced DOW Chemical's UNIPOL polypropylene plant, a total of 9 sets, with a total capacity of 2.81 million tons. These companies are Fushun Petrochemical, Guangxi Qinzhou Petrochemical, Sichuan Petrochemical, Sinochem Quanzhou Refinery, Datang Duolun, Shenhua Baotou, Lianhong Group, Donghua Yangzijiang Petrochemical, China Coal Yulin and so on.
The Novolen process.
The Novolen process was developed by BASF. Novolen gas phase process uses a vertical stirred reactor with double spiral tape, which can distribute the catalyst evenly in the gas phase polymerization monomer, and maintain a certain ratio of titanium/aluminum/electron donor for each polymer particle as far as possible, so as to solve the problem of difficult uniform distribution between the gas and solid phases in gas phase polymerization. The heat removal mode of polymerization reactor is based on the circulation of propylene gas. Liquid propylene is pumped into the reactor, part of the polymerization reaction heat is absorbed through the vaporization of propylene, and the unreacted gaseous propylene is liquefied after condensation with water, and then pumped back to the reactor for use. Novolen process can produce a wide range of polypropylene products, product melt index range of 0.1-100g/10min, product isotactic index of 90%-99%, tensile modulus up to 2400MPa. However, because the process is in the form of stirring mixing, the residence time of the material in the polymerization tank is difficult to control evenly, so that the molecular weight of the product is wider, the Ti, Cl ions and ash in the product are increased, the catalyst activity is low, the amount is relatively large, and the residual volatile components in the polymer seriously affect the product quality, so the obtained PP product may need to be deodorized.
Vertical stirring reactor for Novolen unit
At present, there are more than 20 sets of production plants using Novolen process in the world, with a total production capacity of about 4.32 million tons/year, accounting for about 10.9% of the world's total PP production capacity. There are 4 sets of domestic production plants using BASF's Novolen gas phase process, with a total capacity of 2.15 million tons/year. The main equipment is Fujian United, Shenhuining Coal, Formosa Plastics Ningbo, Jinxi Petrochemical and so on.
Sumitomo Craft
The Sumitomo production process was developed by Sumitomo Chemical Company in Japan in 1981 and industrialized in 1985. The process uses a series of gas-phase fluidized bed reactors (two or three series reactors), the use of self-developed highly selective catalyst DX-V, product crystallinity is high, can produce a wide range of polypropylene products. At present, there are 4 sets of PP production plants using Sumitomo process in the world, with a total production capacity of about 375,000 tons/year, accounting for about 0.9% of the world's total polypropylene production capacity.
Since the 1990s, Basell's Spheripol loop/gas phase process has dominated the global polypropylene production process. Followed by Dow's Unipol gas phase process, NTH company's Novolen gas phase process, BP company's Innovene gas phase process, Mitsui Company's Hypol autoclave body process, and slurry production process is gradually phased out.
In recent years, the proportion of polypropylene production plants with gas phase and bulk process in the world has increased year by year, and the polypropylene plants under construction and newly built around the world will basically adopt gas phase process and bulk process. In particular, the rapid increase in gas-phase processes is challenging the Spheripol process, which ranks first. According to NTJ, since 1997, 55% of the new polypropylene capacity licensed worldwide has been in the Novolen gas phase process, and the gas phase process will gradually increase in the future.
Compared with the slurry method and liquid phase bulk method, the gas phase production process has the following characteristics: it can adjust the product variety in a wide range. It is easy to control the molecular weight and copolymer content of propylene products. Suitable for the production of impact resistant polypropylene. Good safety, easy to drive and park. The amount of material per unit reactor volume is only 1/5 of the slurry process and 1/35 of the bulk process.
The reactor types of various gas phase processes can be divided into four types: fluidized bed, vertical fluidized bed with wall scraper, vertical stirring bed, horizontal stirring bed, as shown in the figure below.
It can be seen that the investment and production costs of several processes are not different, indicating that the economy of mainstream polypropylene process technology is very close.
The situation of economic comparison is not exactly consistent with the current situation of process technology occupying market share. Since the economic difference of various process technologies is not significant, other influencing factors are more important in the selection of process technology, especially the level of patent fees, product varieties and performance ranges, flexibility of product switching, performance of large-scale devices and other reference factors.
