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Review of typical production process technologies for polypropylene resin; Introduction to Basell Corporation. Basell Corporation is a global producer of polyolefins; it was formed through the merger of Targor, Elenac, and Montell. It is a joint venture in which German company BASF and Dutch company SHELL each hold a 50% stake. Its main activities include the production, sale, and transfer of patent technologies related to PP and PE. Basell currently has 7,800 employees. Its production capacity for polypropylene is 5.79 million tons per year (28 units), for polyethylene it is 2.65 million tons per year (16 units), for synthetic raw materials it is 700,000 tons per year (18 units), and for catalysts it is 360,000 tons per year (3 units). These facilities are spread across 18 locations; the company also has 9 joint ventures in South America and East Asia. Its products are consumed in more than 120 countries around the world. First-generation loop process: Montell’s SPHERIPOL process ； Second-generation loop process: Basell’s SPHERIPOL process. (1) Spheripol process: Basell, which owns the Spheripol process, is a company established in 1999 as a joint venture in the polyolefins sector by Montell, a wholly-owned subsidiary of Shell, Targor, a wholly-owned subsidiary of BASF, and Elenac (a joint venture held 50% by BASF and 50% by Shell). Basell is currently the world’s largest producer of polypropylene; it operates 28 polypropylene plants in 17 locations, with a total production capacity of 5.7 million tons per year. At the same time, it is also the world’s largest patent holder for polypropylene; by 1999, Basell had granted licenses for 85 Speripol polypropylene plants, resulting in a total annual production capacity of 13 million tons for polypropylene plants using this technology. The company possesses strong research and design capabilities, and has always been at the forefront in the research, development, and production of polypropylene. The Spheripol process is a polymerization technique that combines liquid-phase prepolymerization with simultaneous liquid-phase homopolymerization and gas-phase copolymerization. This process uses an efficient catalyst, allowing the particle size distribution of the resulting polypropylene powder to be adjusted, making it possible to achieve both a wide and a narrow distribution. The homopolymerization reactor consists of two series-connected loop reactors, and it features a high heat transfer coefficient, high yield per unit volume, fast flow rates, uniform distribution of the catalyst system, easy control of reaction conditions, rapid product conversion, a simple structure, and low requirements regarding materials. Since the polymer particles produced by homopolymerization are large and spherical in shape, they not only have good flowability but are also less likely to be carried away by air currents compared to fine powders. Therefore, the gas-phase reactor in this process uses a dense-phase fluidized bed design; there is no need for a large space at the top for gas-solid separation as in dilute-phase fluidized bed reactors. This allows for a reduction in the reactor’s volume, thereby lowering costs and energy consumption. Due to the excellent properties of the catalyst used in this process, along with an optimal polymerization process and a design that balances the residence time during the polymerization reaction with the full utilization of the catalyst’s effects, the product can achieve the desired properties without further processing. A wide range of multi-purpose products can be manufactured, including terpolymerizations and polyolefin alloys. Their homopolymer and random copolymer products are characterized by high purity, excellent optical properties, low volatile content, and no odor. Polyphase copolymer products feature high rigidity, high impact resistance, and high crystallinity. The Spheripol process has now evolved to its second generation. Compared with the first-generation technology that uses single-loop reactor systems, the second-generation technology employs double-loop reactor systems, resulting in significantly higher operating pressures and temperatures, and enables the production of bimodal polypropylene. The catalyst system uses fourth-generation or fifth-generation Z-N high-efficiency catalysts; a hydrogen separation and recovery unit has been added, the high-pressure and low-pressure degassing equipment for polymers has been improved, and the steaming, drying, and propylene emergency emission units have also been upgraded, thereby enhancing operational flexibility and efficiency. Consumption of raw material monomers and various utility services also decreased significantly. Products based on the second-generation Spheripol technology exhibit significant improvements in both the number of available grades and product quality compared to the first-generation technology. The number of reactor grades has increased from 48 to 94, the particle size of the products is more uniform, and the melt flow index range is wider, ranging from 0.3 to 1600. It is also possible to produce new grades with high rigidity, high crystallinity, and low heat-sealing temperatures. II. Unipol Process The Unipol process is a gas-phase fluidized-bed polypropylene process that was jointly developed by Lyondell Chemical and Shell in the mid-1980s. It involves adapting the fluidized-bed technology used in polyethylene production to polypropylene production, with success. This process employs an efficient catalyst system, with the main catalyst being a highly effective supported catalyst, and the co-catalysts being triethylaluminum, diethyloxyaluminum, and electron donors. The Unipol process features simplicity, flexibility, cost-effectiveness, and safety ； This process can produce a wide range of products, including homopolymers, random copolymers, and impact copolymers, using only minimal equipment. The operating conditions can be adjusted over a broad range to maintain uniform product properties. The reduced number of devices in use results in less maintenance work, thereby improving the reliability of the system. Due to the inherent limitations of fluidized bed reaction kinetics, coupled with the low operating pressure which reduces the amount of material stored in the system, this process is safer to operate than other processes, as there is no risk of equipment overpressure in the event of an accident or loss of control. This process generates no liquid waste, and there is very little hydrocarbon emission into the atmosphere; as a result, its impact on the environment is minimal. Compared to other processes, it is easier to meet various strict requirements regarding environmental protection, health, and safety. Another notable feature of this process is its ability to be combined with supercooled conditions, namely the so-called supercooled gas-phase fluidized bed process (SCM). By increasing the proportion of the liquid phase in the reactor to 45%, this technology can boost existing production capacity by 200%. Since the amount of liquid is not a fundamental factor behind the instability of the fluidized bed or the formation of polymer lumps, the key operational variables in this technology are the density of the expanded bed, as well as the ratio of its expanded bulk density to its settled bulk density. Since supercooled state operation can most effectively remove the heat of reaction, it enables the reactor to increase its production capacity by more than twice without an increase in volume, resulting in significant savings in investment. III. Borealis Process: The Nordic chemical company that possesses the Borealis process technology was established in 1994. It is the fourth largest polyolefin producer in the world, focusing on the production of polyethylene in the bimodal form. The company entered the polypropylene sector in 1999 and built its first polypropylene plant in 2000. Borealis’ polypropylene process utilizes a modular structure and multi-stage polymerization technology, enabling precise control over the molecular weight distribution and the production of products that combine stiffness with toughness. The Borealis process uses a loop reactor and a gas-phase reactor as the basic modules to produce homopolymers. This design can effectively control the molecular weight distribution and the product’s isotacticity. Its loop reactor operates in a supercritical state, with a reaction temperature of 80–95°C and a reaction pressure of 5–6 MPa. In this state, the liquid inside the reactor becomes a supercritical fluid, with a lower density and strong heat transfer capacity. Since catalyst activity increases at high temperatures, the reaction conversion rate rises, resulting in a lower amount of soluble oligomers. More hydrogen can be added in the supercritical state, thus enabling the production of products with a very high melt flow index MFR. By using a gas-phase reactor as part of the basic module, the outlet of the loop reactor does not require steam heating to vaporize the unreacted monomers, as these monomers are automatically vaporized due to pressure changes once they enter the gas-phase reactor. Moreover, the heat absorbed during vaporization helps to remove the heat generated in the gas-phase reaction. This design focuses more on the comprehensive utilization of energy compared to a dual-loop reactor, and the yield of the loop/gas-phase reaction is easier to control. Another feature of the Borealis process is its advanced process control system, BorAPC; compared to traditional DCS systems, its multivariable controllers enable the input and output of large amounts of data ； It has predictive capabilities, enabling the estimation of future values and providing feedback ； Handle boundary conditions efficiently and safely to prevent exceeding process limits. By using BorAPC, production fluctuations can be reduced, **improving the reproducibility of reactions and the stability of product quality. Since the polymerization reaction takes place at critical conditions, the catalyst is required to possess excellent overall performance under extreme reaction conditions. The catalyst unique to the Borealis process is based on Ti/Zr and features high activity, heat resistance, and sensitivity to hydrogen. At high temperatures, its molecular weight distribution narrows, approaching the properties of single-site catalysts, enabling the production of polymers with a high degree of randomness, flexible polypropylene, and polypropylene with efficient nucleation (without the need for added nucleators). However, since this process began to develop in the 1990s, it has a shorter history of development compared to other processes, and it accounts for a small proportion in the global polypropylene technology market. IV. The Amoco Process: In 1979, Amoco (now merged with BP to form BP-Amoco) built the first gas-phase homopolymerization plant for polypropylene in the United States. In 1980, Chisso obtained a license to use Amoco’s gas-phase process technology, and subsequently developed a process for producing gas-phase impact copolymer products. In 1985, the two companies agreed to collaborate on further development of this process, which came to be known as the Amoco/Chisso process. In 1995, Amoco and Chisso separated and pursued technology development and transfer independently. A notable feature of the Amoco gas-phase process is its unique reactor design, which ensures good radial mixing of the materials inside the reactor along with low axial dispersion. The reactor is horizontal and equipped with mechanical stirring; the stirrer blades are at a 45-degree angle to the stirrer shaft, enabling slow and uniform mixing of the entire reaction bed. The catalyst is added at one end of the reactor, while the polymer powder exits from the other end. The residence time distribution of the material is close to that of plug flow, and it is relatively narrow; as a result, a balance can be maintained between the impact strength and stiffness of the product. The heat removal method in the Amoco process is propylene flashing. Liquid propylene is injected into the reactor from various feed points in a manner that keeps the reactor bed dry. Once the liquid propylene vaporizes, the partial pressure of its monomer is lower than its dew point, which is sufficient to remove the heat of reaction. During operation, it is necessary to strictly control the feed rate of liquid propylene and its vaporization in the reactor, in order to maintain a balance among the degree of dryness of the bed, its fluidization level, and the reaction temperature range. The air lock system is another feature of this process. When the material is transferred from the first reactor to the second reactor, the air lock system prevents cross-flow between the two reactors. Especially when producing copolymers, the gas compositions in the two reactors differ: the first reactor contains a large amount of hydrogen, while the second reactor contains ethylene along with a small amount of hydrogen. If hydrogen from the first reactor enters the second reactor, or if ethylene from the second reactor enters the first reactor, it will severely affect the quality of the product. Therefore, it is crucial to isolate the two reactors from each other. The main catalyst in this process is Amoco’s patented CD catalyst, which features high activity and high selectivity. The melt flow index of the products manufactured by this process ranges from 0.1 to 60, enabling the production of products in which low-temperature impact strength and flexural modulus are in balance. The drawback of this process is that the ethylene content in the product (or the proportion of the rubber component) is low, making it impossible to obtain products with high or ultra-high impact resistance. Although products with high ethylene content have been produced in experimental facilities, they have not yet been commercialized. V. Novolen process: In 1969, BASF built the first industrial vapor-phase plant with an annual capacity of 25,000 tons at its Rhine Olefins plant in Germany; this process was named “Novolen”. In 1987, BASF reached an agreement with its two license holders, ICI and Quantum, to jointly research and develop the Novolen technology. Previously, BASF used low-cost second-generation catalysts, which required the products to undergo dechlorination and deodorization processes. In 1990, BASF developed a high-yield catalyst that enabled an increase in reactor output while eliminating the dechlorination step. In 1999, BASF and Shell merged their polyolefin businesses to form Basell. Under antitrust laws, a company cannot own both the Speripol and Novolen polypropylene patent technologies simultaneously; therefore, Basell sold the Novolen technology and related business to Lummus and Equistar. There are 19 polypropylene production plants around the world that use Novolen technology (9 in Asia-Pacific, 4 in Western Europe, and 2 each in the United States and South America), with a combined production capacity of 3.13 million tons per year. The Novolen process uses two 75m3 vertical gas-stirred tank reactors, with each reactor having a capacity of 180,000 tons per year. To achieve a production capacity of over 300,000 tons per year, the Novolen process allows for flexible arrangement of the reactors, enabling the two reactors to be connected in series or in parallel as needed, thus offering high production flexibility. Homopolymers, random copolymers, and terpolymers can be produced using a single reactor ； Impact-resistant or block copolymers can be produced using tandem twin reactors ； Using parallel twin reactors can increase the production capacity of homopolymers by 70-100%. The catalyst system used in the Novolen process is not ideal, as its activity is insufficient, requiring a relatively large amount of catalyst. The volatile components remaining in the polymer severely affect the product quality; therefore, the resulting polypropylene products need to undergo degassing treatment. The gas-phase reactor used in the Novolen process is equipped with a twin-screw agitator, which enables uniform distribution of the catalyst among the monomers undergoing gas-phase polymerization. This helps to maintain a consistent titanium/aluminum/donor ratio in each polymer particle, thereby addressing the issue of poor uniform distribution between the gas and solid phases in gas-phase polymerization. However, its drawback is that it consumes much more power than liquid-phase stirring, and the auxiliary systems required for the extrusion granulation unit are relatively complex. The heat removal method in the polymerization reactor relies on the circulation of propylene gas. Liquid propylene is pumped into the reactor, where its vaporization helps to absorb some of the heat generated during the polymerization reaction. The unreacted gaseous propylene is condensed using water to be turned back into a liquid state, after which it is pumped back into the reactor for use. Since the reaction heat of propylene polymerization is 2093.4 KJ/Kg, and the latent heat of vaporization of liquid propylene is 334.9 KJ/Kg, 6–7 tons of circulating gas are required to remove the polymerization reaction heat from 1 ton of propylene. The Novolen process can produce a wide range of polypropylene resins, with melt flow indices MFR ranging from 0.1 to 100, an isotacticity level of 90–99%, and a tensile modulus that can reach up to 2400 Mpa.