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Ethylene-propylene rubber production process and its technical and economic analysis Ethylene-propylene rubber (EPR) is a kind of ethylene that came out after the invention of Ziegler-Natta catalyst and the emergence of polyethylene and polypropylene. Copolymer rubber with propylene as the basic monomer is divided into two categories: ethylene-propylene rubber (EPM) and ethylene-propylene diene rubber (EPDM). The former is a copolymer of ethylene and propylene ； The latter is a copolymer of ethylene, propylene and a small amount of non-conjugated diene. EPR has many excellent properties that other general-purpose synthetic rubbers do not have. In addition, the monomer is cheap and easy to obtain and has a wide range of uses. It is the fastest growing among the seven major foreign synthetic rubber varieties since the 1980s. Its output, production capacity and consumption are in developed countries. * * It ranks third in China, second only to styrene-butadiene rubber and butadiene rubber. In 1998, the world's total EPR production capacity was approximately 102 tons, and consumption was 814,000 tons. Preliminary statistics show that consumption in 1999 was approximately 836,100 tons and is expected to reach 980,000 tons in 2003. The demand growth rate of EPR from 1998 to 2003 was 3.8%, which was higher than the demand growth rate of styrene-butadiene rubber and butadiene rubber. At present, FPR industrial production process routes include solution polymerization, suspension polymerization and gas phase polymerization. The technical status and points to be discussed will be discussed in detail below, and a technical and economic comparison will be made. 1. Solution polymerization process 1.1 Technical status Industrialization was achieved in the early 1960s. After continuous improvement and improvement, the technology has matured and is used by many new devices. It is the leading technology in industrial production, accounting for approximately 77.6% of the total FPR production capacity. This process is a homogeneous reaction carried out in a solvent that can dissolve both the product, the monomer, and the catalyst system. It usually uses linear alkanes such as n-hexane as the solvent, and uses the V-A1 catalyst system. The polymerization temperature is 30 to 50C, the polymerization pressure is 0.4 to 0.8 MPa, and the mass fraction of the polymer in the reaction product is generally 8% to 10%. The process basically consists of raw material preparation, chemical preparation, polymerization, catalyst removal, monomer and solvent recovery and refining, as well as coagulation, drying and packaging. However, since each company has its own patented technology in certain parts or control aspects, each company has its own unique process implementation method. Representative companies include DSM, Exxon, uniroya1, DuPont, Japan's Mitsui Petrochemicals and JSR Corporation. The most typical representative among them is DSM. It is not only the world's largest EPR producer, but also has four sets of equipment in the Netherlands, the United States, Japan, and Brazil, all of which use solution polymerization processes, accounting for 1/4 of the world's total EPR production capacity through solution polymerization processes. This company will be used as an example below. DSM uses hexane as the solvent, ethylidenenorbornene (ENB) or dicyclopentadiene (DCPD) as the third monomer, hydrogen as the molecular weight regulator, and VOCL3-1/2AL2Et3CL3 as the catalyst. In addition, in order to improve the catalyst activity and reduce its dosage, accelerators are also added. The catalyst dosage, pretreatment method, and accelerator type are the proprietary technologies of DSM. The reaction material is pre-cooled to -500C in the second stage. According to the production grade, a single kettle or two kettles are operated in series. The volume of the polymerization tank is approximately 6m3. The polymerization reaction conditions are: The temperature is lower than 650C, the pressure is lower than 2.5 MPa, and the reaction heat is used for adiabatic heating of the reactor. Under the action of alkaline devanadium agent and hot water, the residual vanadium catalyst in the polymer glue enters the water phase and is completely removed through two phase inversion processes. Unreacted monomers are recovered through secondary vacuum flash evaporation and recycled. At this time, stabilizers and other additives are added to the glue (filling oil is added when producing oil-filled grades). After stripping and steaming out the remaining ethylene, propylene and most of the solvent, the skimming liquid is sent to two series-connected coagulation kettles for condensation, and is further steamed out to recover the residual hexane solvent for recycling. After dehydration, the JC colloidal slurry enters the drying system and is then briquetted or packaged as powder. The waste hot air containing ENB is sent to the incinerator for incineration, and the vanadium-containing sewage is sent to the sewage devanadium unit. Under the neutralization and flocculation effect of the vanadium removal agent, vanadium enters the vanadium slag and is regularly sent to the landfill for burial. The vanadium-depleted sewage is discharged to the sewage treatment plant for treatment. DSM Company's EPR solution polymerization technology is mature and advanced and has the following advantages:: (1) Low investment and optimized process. The superior design of the reactor can meet the mixing requirements of the reaction materials, and can accurately control the polymerization process parameters and product quality. The polymer glue concentration is high and the amount of circulating solvent is small. The polymerization tank is small but has high production intensity. The raw materials and circulating monomers do not need to be refined. The catalyst efficiency is high, the vanadium content in the three wastes is low, and the production flexibility is high. (2) The production operation cost is low, the annual operation time of the device is long, the consumption of raw materials and catalyst is low, and an advanced control system is used to control production. (3) Product quality is extremely competitive. The catalyst residue content in the product is low, there are few defective products in production, product grades can be switched flexibly, and the amount of switching waste is small. Product characteristics can be adjusted according to user requirements. There are many product grades, and the Mooney value can be adjusted within a wide range of 20 to 160. The quality is stable, the repeatability is good, the product specification index has a narrow range of changes, and the product processing performance is excellent. 1.2 Technical characteristics: The technology is relatively mature and the operation is stable. It is the main method for industrial production of EPR. ； There are many product varieties and brands, uniform quality, low ash content, and wide range of applications. ； The product has good electrical insulation properties. However, since polymerization is carried out in a solvent, mass and heat transfer are limited. The mass fraction of the polymer is generally controlled at 6% to 9%, and the highest is only 11% to 14%, resulting in low polymerization efficiency. At the same time, since the solvent needs to be recovered and refined, the production process is long, there is a lot of equipment, and the construction investment and operating costs are high. 2 Suspension polymerization process 2. Technical status There are not many EPR suspension polymerization product brands, and its uses are limited. It is mainly used for polyolefin modification. Currently, only Enichem and Bayer use it, accounting for 13.4% of the total EPR production capacity. This process is based on the principle that propylene has low activity in the copolymerization reaction, and ethylene is dissolved in liquid propylene for copolymerization. Propylene is both a monomer and a reaction medium. It relies on its own evaporation and refrigeration to control the reaction temperature and maintain the reaction pressure. The resulting copolymer is insoluble in liquid propylene and appears as a fine-grained slurry suspended in it. It can be divided into general suspension polymerization process and simplified suspension polymerization process. 2.1.1 General suspension polymerization process Enichem Company adopts this process: Acetyl propyl vanadium and AlEt2Cl are used as catalysts, diethyl dichloromalonate is used as activator, HNB or DCPD is the third monomer, and diethyl zinc and hydrogen are used as molecular weight regulators. Depending on the grade of the product produced, ethylene, propylene, the third monomer and the catalyst are added to a jacketed polymerization kettle with a multi-paddle stirrer. The reaction conditions are:: Temperature - 20~20oC, pressure 0.35~1.05MPa. The heat of reaction is removed by evaporation of the monomers in the reaction phase. The mass fraction of the suspended polymer in the reaction phase is controlled at 30% to 35%. The entire polymerization reaction is carried out under a high degree of automatic control. The generated polymer propylene slurry is sent to the scrubber intermittently (10 to 15 times/h), and the catalyst is deactivated with polypropylene glycol and then washed with NaOH aqueous solution. The suspension is sent to the stripping tower for stripping, and the unreacted ethylene, propylene and ENB are respectively refined in the recovery system and recycled. The rubber particle-water slurry is dehydrated through a vibrating screen, extruded and dried, pressed into blocks and packaged to obtain the finished product. The characteristics of this process are that no solvent is used for polymerization and refining, and the polymer concentration is high, which strengthens the production capacity of the equipment. At the same time, solvent circulation and recovery are omitted, saving energy. 2.1.2 Simplified suspension polymerization process This process was successfully developed on the basis of the general suspension polymerization process. It mainly uses a high-efficiency titanium series catalytic system. There is no need to remove the catalyst, and unreacted monomers can be returned to use without treatment. It is usually used in the production of EPM because unreacted third monomer cannot be easily removed by flash evaporation. Its process flow is: The reaction was carried out in a jacketed stirred tank, using TiC1, MgC12-A1 (i-Bu), catalyst system, the catalyst efficiency was 50kg polymer/g titanium, the reaction temperature was 27C, the pressure was 1.3MPa, and the mass fraction of the polymer was 33%. The steam material coming out of the reaction kettle is compressed to 2.7 MPa and cooled before returning to the reaction kettle. The polymer slurry is flash evaporated to remove unreacted monomers without refining. After compression and cooling, it is directly recycled to the reactor for use. The polymer from which the monomers are removed can be used as a finished product without purification. Products can be in powder, flake or granular form. In recent years, Enichem has adopted an improved V-A1 catalytic system, which has increased the catalyst efficiency to 30-50kg polymer/g vanadium, eliminating the need for washing and removing the catalyst, and also simplifying the process flow. 2.2 Technical characteristics The characteristics of the EPR suspension polymerization process are: The polymerization product is insoluble in the reaction medium propylene, and the system viscosity is low, which improves the conversion rate. The mass fraction of the polymer is as high as 30% to 35%, so its production capacity is 4 to 5 times that of the solution method. ； No solvent recovery, refining and condensation processes, simplified process flow, low infrastructure investment ； Can produce very high molecular weight varieties ； Product cost is lower than solution method. Its shortcomings are: Since no solvent is used, it is difficult to remove residual catalyst from the polymer. ； There are few product varieties and brands, poor quality uniformity, and high ash content. ； Polymers are suspended particles that are insoluble in liquid propylene, and it is difficult to keep them in a suspended state. Especially when the polymer concentration is high and a small amount of gel appears, the reactor is prone to gelatinization, and even equipment pipelines are blocked. ； The electrical insulation properties of the product are poor. 3 Gas phase polymerization process 3.1 Technical status The gas phase polymerization process of EPR was first industrialized by Himont Company in the late 1980s. UCC Company announced in the early 1990s that the gas phase EPR pilot plant was put into trial production, and its 91,000 tons/year gas phase EPR industrial device was officially put into production in 1999. Currently, the process accounts for 9% of total EPR production capacity. UCC's EPR gas phase polymerization process is the most representative. It is divided into three processes: polymerization, separation and purification, and packaging. The mass fraction of 60% ethylene, 35.5% propylene, and 4.5% ENB is added to the fluid bed reactor together with the catalyst, hydrogen, nitrogen and carbon black, and the gas phase polymerization reaction is performed at 50-65C and an absolute pressure of 2.07 kPa. The single-pass conversion rates of ethylene, propylene and ENB are 5.2% respectively. 0.58% and 0.4%. The unreacted monomer from the reactor is compressed by the circulating gas compressor and then enters the circulating gas cooler to remove the reaction heat, and is recycled back to the reactor together with the fresh feed gas. The EPR powder discharged from the reactor enters the purification tower without degassing and pressure reduction, and nitrogen gas is used to remove residual hydrocarbons. The gas from the top of the purification tower is condensed to recover ENB and then pumped back to the reflux bed reactor. The resulting particulate product enters the packaging process. 3.2 Technical characteristics Compared with the first two processes, the gas phase polymerization process has its outstanding advantages.: The process is short, with only three processes, while traditional processes have seven. ； No solvents or diluents are required, and no solvent recovery or refining processes are required. ； There is almost no three-heat emissions, which is conducive to ecological and environmental protection. However, the versatility of its products is poor, and all products are black. This is because in order to prevent the polymer from being too sticky, carbon black is used as a fluidization aid. Although white and colored products produced using silane clay and mica instead of carbon black have been successfully developed, the first set of industrial production units can still only produce black FPR. 4. Technical and economic comparison of various production processes. The technical and economic comparison of various FPR production processes is as shown in the table.: shown. As can be seen from Table 1, among the various production process routes of FPR, the solution polymerization process has the highest investment and cost. The high investment is due to the long process, difficulty in heat dissipation due to high viscosity, low equipment production intensity, too thin concentration of polymer flow after reaction (only 6% to 14%, 33% for suspension polymerization process), and higher costs for monomer and solvent recovery. ； The high cost is mainly due to high utility fees, depreciation fees, and fixed costs. This is due to the higher consumption of electricity and steam during the production process. The investment and cost of the suspension polymerization process are respectively equivalent to 77% and 88% of the solution polymerization process of the same scale. It has the characteristics of low investment, low raw material consumption and energy consumption, low production costs, and low three waste treatment costs. The investment and product costs of the gas phase polymerization process are the lowest, equivalent to 42% and 68% respectively of the solution polymerization process of the same scale. surface: Technical and economic comparison of various EPR production processes Project solution polymerization suspension polymerization gas phase polymerization production capacity/(10,000 t/a) 4.5 4.5 9.1 Investment,/million US dollars Within the boundary area 6900 5250 6000 Outside the boundary area 2510 2020 1900 Total investment 9410 7270 7900 Relative unit investment/% 100 77 42 Production cost/(USD/t) Raw materials 691 688 686 Utilities 178 103 34 Others 35 35 13 Variable cost/(USD/t) 904 826 733 Fixed cost/(USD/t) 200 168 83 Total cash cost/(USD/t) 1104 994 816 Discounted daily fee/(USD/t) 261 201 109 Total cost (USD/t) 1365 1195 925 Relative total cost/% 100 88 68 5 Conclusion In summary, although the EPR solution polymerization process has the highest investment and cost, its product has good overall performance, fast vulcanization speed, and wide range of product applications. It is currently the most widely used method abroad. The suspension polymerization process has a short production process and low investment and cost. However, the product performance has no outstanding advantages and the application range is narrow, so it is currently not as widely used as the solution polymerization process. The gas phase polymerization process product contains a large amount of carbon black and has poor versatility, which limits its scope of use, but its process flow is short. Efficient and clean production is conducive to reducing production costs and protecting the ecological environment. It has fundamental revolutionary significance for the long-used solution polymerization process. It is an inevitable trend in the future development of synthetic rubber industry technology and has become a competitive development and priority project for large foreign petrochemical companies. Although this process is still unsatisfactory, some companies are even cautious about it, and it is unlikely to soon replace the long-term industrial application of solution polymerization technology, but in the long run, its development prospects are optimistic. Moreover, this technology is expanding into the direction of polybutadiene rubber gas-phase synthesis technology, which will surely play a major guiding role in the future development of synthetic rubber production technology.