**4.2 Hypol process**

*Polypropylene - Polymerization and Characterization of Mechanical and Thermal Properties*

The improved impact strength attributes to the heterophasic ethylene-propylene copolymer scattered in the crystalline iPP matrix formed in the first reactor.

A typical Spheripol II process, which is one of the most employed process owned by Basell, consists of two liquid loop reactors and a gas phase reactor for

*Reactor configurations for olefin polymerization: (a) autoclave; (b) loop; (c) fluidized-bed; (d) vertical gas-*

In the past decades, the process configuration has evolved, driven not only by economics, but mainly by product performance. Multiple reactors allow for flexible operation during polymerization to make various polymers that can be considered a blend of multiple components (reactor blends). Along with the improvement of the catalyst technology, the major worldwide companies have developed their own PP process using multiple-stage technology or combining bulk and gas-phase polymerization: Spheripol (Basell), Hypol (Mitsui Chemicals), Unipol (Dow Chemical), Innovene (INEOS), Novelen (BASF), Spherizone (Basell), and Borstar (Borealis).

**24**

**Figure 13.**

**Figure 12.**

*phase; and (e) horizontal gas-phase [107].*

*Process of production of impact PP [107].*

**4.1 Spheripol process**

Mitsui Petrochemical has developed a similar process using bulk polymerization with their specific supported catalysts. In a Hypol I PP process (**Figure 14**), two conventional reactors in series are employed, with reaction heat removed by evaporation of cool liquid propylene in the reactors. The slurry containing PP particles is then fed into a heated flash vessel, in which the propylene is recovered for recycling use. One or two gas-phase reactors with stirring might be added in tandem with the two bulk polymerization reactors to produce impact polypropylene. The reactors in the 2nd Hypol process of Mitsui Chemicals are replaced with two loop reactors and gas-phase fluidized-bed. Similar with Spheripol process, Hypol processes are design with innovative HY/HS supported catalysts to be able to produce HPP, RPP and impact copolymers.

## **4.3 Unipol process**

Unipol polypropylene process technology, which has its roots in gas-phase polyethylene process of Union Carbide Corporation (UCC), is built around two vertical fluidized bed reactor systems. Dow's Unipol PP process is one of the most advanced processes used worldwide, which allows simplified process scheme and high cost-effective investment with less factory field and equipment. The process is stable and predictable. In the upper section of the vertical gas-phase reactor, there is an expandable pressure vessel, where it operates at 3.5 MPa and 65°C. The heat removal can be improved by charging liquid propylene and propane, and the operating conditions satisfy the dew point of the monomer; therefore, it achieved high energy efficiency. The fluidized-bed reactors have extensive back mixing and a short residence time of less than 1.5 h, which is beneficial to shorten transition product.

With Shell High Activity Catalyst (SHAC) of Dow (Now Grace) for the UNIPOL process, HPP, RPP, and impact PP could be produced using this Unipol technology. Especially, this process is suitable to develop and produce high-performance RPP and impact PP. The ethylene content of a RPP can be up to 7–8%, and be above 20% for an impact PP, and thus, the rubber phase could be above 40% in an industrial production. Impact copolymer is produced in the second reactor in **Figure 15**, where ethylene, hydrogen, and recycled propylene are fed to produce polymer particles containing isotactic PP and active catalysts generated from the first reactor. Then, the reactor polymer product (bottom) is sent to a gas/solid separator where the separated gas is recycled back to the top of the copolymer reactor. The final solid product is discharged from the separator to the purge tower.

#### **4.4 Spherizone process**

The concept of multizone circulating reactor (MZCR) was proposed by Basell two decades ago, and the Spherizone process employing the revolutionary reactor aims at improving product properties and broadening the range of products, despite the success of the Spheripol process. The Spherizone process, using Basell's HY and RGT catalysts, involves continuous circulating of the growing reactor granule between two interrelated zones operating under peculiar fluid-dynamic pattern,

**27**

reaction stage.

**Figure 15.**

*Unipol gas-phase fluidized-bed process.*

**4.5 Novelen process**

so the temperature is controlled stably.

*Versatile Propylene-Based Polyolefins with Tunable Molecular Structure through Tailor-Made…*

and produces polymer particles with excellent morphology and tunable composition in the reactor. The versatility of the Spherizone process is demonstrated by the various high-quality products that include HPP, RPP, and some special products. Due to the unique design and operation, the MZCR process is capable of providing polymers with various components within the same catalyst granule in a short

In the so-called riser (**Figure 16**), the polymer particles and monomers flow upwards in a fast fluidization state. In the top, the rising gas is separated from the solid particles, which then enters and goes downward in the so-called downcomer. The circulation of the polymer particles is handled by the pressure balance between the two zones. In the multizone circulating reactor, HPP and RPP can be produced. Optionally, the multizone circulating reactor can then be connected with another gas-phase fluidized bed reactor, where ethylene-propylene copolymerization can take place to generate high impact PP. In this reactor, the EP rubber phase is generated within the HPP matrix discharged from the first

BASF's Novelen PP process is based on two gas-phase reactor vessels equipped with vertical helical agitators, which can provide excellent agitation for catalyst particle dispersion and heat transfer, for making HPP, RPP, and impact copolymers of ethylene-propylene using their specific high activity and stereospecific catalysts. The catalysts need to be well-dispersed in the polymer particle tank to avoid agglomeration of the granule particles, and this process is operated under conditions of 70–80°C and 3–4 MPa to keep the monomer gaseous in the reactors. Reaction heat can be effectively removed from the evaporation of liquid propylene,

The primary reactor can only be used to produce HPP and random copolymers of ethylene-propylene. For impact copolymers, the EP rubber phase is produced in

the 2nd vessels, by feeding propylene and ethylene into this reactor.

residence time, making them mix at a molecular scale.

*DOI: http://dx.doi.org/10.5772/intechopen.85963*

*Versatile Propylene-Based Polyolefins with Tunable Molecular Structure through Tailor-Made… DOI: http://dx.doi.org/10.5772/intechopen.85963*

*Polypropylene - Polymerization and Characterization of Mechanical and Thermal Properties*

Unipol polypropylene process technology, which has its roots in gas-phase polyethylene process of Union Carbide Corporation (UCC), is built around two vertical fluidized bed reactor systems. Dow's Unipol PP process is one of the most advanced processes used worldwide, which allows simplified process scheme and high cost-effective investment with less factory field and equipment. The process is stable and predictable. In the upper section of the vertical gas-phase reactor, there is an expandable pressure vessel, where it operates at 3.5 MPa and 65°C. The heat removal can be improved by charging liquid propylene and propane, and the operating conditions satisfy the dew point of the monomer; therefore, it achieved high energy efficiency. The fluidized-bed reactors have extensive back mixing and a short residence time of less than 1.5 h, which is beneficial to shorten transition product. With Shell High Activity Catalyst (SHAC) of Dow (Now Grace) for the UNIPOL process, HPP, RPP, and impact PP could be produced using this Unipol technology. Especially, this process is suitable to develop and produce high-performance RPP and impact PP. The ethylene content of a RPP can be up to 7–8%, and be above 20% for an impact PP, and thus, the rubber phase could be above 40% in an industrial production. Impact copolymer is produced in the second reactor in **Figure 15**, where ethylene, hydrogen, and recycled propylene are fed to produce polymer particles containing isotactic PP and active catalysts generated from the first reactor. Then, the reactor polymer product (bottom) is sent to a gas/solid separator where the separated gas is recycled back to the top of the copolymer reactor. The final solid

product is discharged from the separator to the purge tower.

The concept of multizone circulating reactor (MZCR) was proposed by Basell two decades ago, and the Spherizone process employing the revolutionary reactor aims at improving product properties and broadening the range of products, despite the success of the Spheripol process. The Spherizone process, using Basell's HY and RGT catalysts, involves continuous circulating of the growing reactor granule between two interrelated zones operating under peculiar fluid-dynamic pattern,

**26**

**4.4 Spherizone process**

**4.3 Unipol process**

*Hypol I PP process technology.*

**Figure 14.**

and produces polymer particles with excellent morphology and tunable composition in the reactor. The versatility of the Spherizone process is demonstrated by the various high-quality products that include HPP, RPP, and some special products. Due to the unique design and operation, the MZCR process is capable of providing polymers with various components within the same catalyst granule in a short residence time, making them mix at a molecular scale.

In the so-called riser (**Figure 16**), the polymer particles and monomers flow upwards in a fast fluidization state. In the top, the rising gas is separated from the solid particles, which then enters and goes downward in the so-called downcomer. The circulation of the polymer particles is handled by the pressure balance between the two zones. In the multizone circulating reactor, HPP and RPP can be produced. Optionally, the multizone circulating reactor can then be connected with another gas-phase fluidized bed reactor, where ethylene-propylene copolymerization can take place to generate high impact PP. In this reactor, the EP rubber phase is generated within the HPP matrix discharged from the first reaction stage.

### **4.5 Novelen process**

BASF's Novelen PP process is based on two gas-phase reactor vessels equipped with vertical helical agitators, which can provide excellent agitation for catalyst particle dispersion and heat transfer, for making HPP, RPP, and impact copolymers of ethylene-propylene using their specific high activity and stereospecific catalysts. The catalysts need to be well-dispersed in the polymer particle tank to avoid agglomeration of the granule particles, and this process is operated under conditions of 70–80°C and 3–4 MPa to keep the monomer gaseous in the reactors. Reaction heat can be effectively removed from the evaporation of liquid propylene, so the temperature is controlled stably.

The primary reactor can only be used to produce HPP and random copolymers of ethylene-propylene. For impact copolymers, the EP rubber phase is produced in the 2nd vessels, by feeding propylene and ethylene into this reactor.

**Figure 16.** *Multizone circulating reactor [118].*

#### **4.6 Innovene process (BP Amoco)**

Instead of the vertical agitator of the BASF process, the INEOS's PP process uses one or two horizontally stirred reactors. Uncondensed monomers and hydrogen are injected into the reactors from the base to maintain the gas composition, while condensed recycled monomers are discharged into the top of the reactor to provide cooling. Fluidized-bed deactivation system is used in both horizontal reactors to avoid particle agglomeration. Homopolymers, random copolymers, and impact copolymers can be produced in this process using highly effective CD series catalysts. This process is suitable for the production of highimpact copolymers with high rubber content, and the rubber phase content could be up to 50%.

#### **4.7 Borstar process**

The Borstar PP process developed by Borealis is based on a double loop reactor and a fluidized-bed reactor in tandem connection for the production of HPP and RPP. The loop reactor is operated under supercritical conditions with increased comonomer and hydrogen concentration, and higher temperature avoiding gas bubbles. For producing the impact PP, additional one or two fluidized-bed reactors are connected in series, as illustrated in **Figure 17**.

**29**

**Figure 17.**

*Versatile Propylene-Based Polyolefins with Tunable Molecular Structure through Tailor-Made…*

Using the HY/HS catalysts of Borealis, which are prepared from emulsion strategy from two-phase liquid/liquid contact, Borstar PP technology produces highperformance HPP and RPP with very low ash content and narrow molecular weight distribution in the supercritical loop reactor due to excellent heat removal and high productivity. The rubber phase (EPR) of the impact copolymers is typically generated through the 3rd and 4th gas-phase reactors. Using the multi-reactor processes described, it is feasible and practical to further broaden PP material properties

*Borstar polypropylene process scheme (four-reactor setup) :(a) prepolymerizer; (b) loop reactor; (c) first gas-phase reactor; (d) second gas-phase reactor; (e) third gas-phase reactor; (f) coolers; (g) separators; (h)* 

Autoclaves, tubular or loop reactors all could be used in a solution process. Different from the slurry and gas-phase process, the solution polymerization process is generally operated at a much higher temperature above 100°C, and in order to form a homogeneous uniform solution, a reaction solvent is added to dissolve the catalyst and polymer generated during the polymerization. Typically, the average residence time is much lower (5–20 min) in contrast with the bulk or gas-phase process (1–4 h). Since polymerization takes place in a more uniform solution, heat and mass transfer resistances are avoided, and this homogeneous process is practical for the production of ethylene-polypropylene copolymer elastomers, EPDM rubbers and stereoblock PP with soluble Ziegler-Natta catalysts, metallocenes, and post-metallocenes. Although conventional HPP could be produced in a solution process, the overall cost is too high to produce them due to requirements for use of

Solution polymerization process is also very appropriate for production of the atactic PP and PP-based elastomers. Commercial equipment developed to make atactic PP has been announced by Himont (Canada), El Paso (Texas), and Huls (Germany). Special PP-based polyolefins are also produced using the solution process by Exxon, Dow Chemical, and other companies. Propylene-ethylene

meeting up the ever-demanding customer needs.

solvent and additional process for removal of the solvent.

**4.8 Solution polymerization process**

*low-pressure degasser; (i) dryer; (j) purge bin [117].*

*DOI: http://dx.doi.org/10.5772/intechopen.85963*

*Versatile Propylene-Based Polyolefins with Tunable Molecular Structure through Tailor-Made… DOI: http://dx.doi.org/10.5772/intechopen.85963*

#### **Figure 17.**

*Polypropylene - Polymerization and Characterization of Mechanical and Thermal Properties*

Instead of the vertical agitator of the BASF process, the INEOS's PP process uses one or two horizontally stirred reactors. Uncondensed monomers and hydrogen are injected into the reactors from the base to maintain the gas composition, while condensed recycled monomers are discharged into the top of the reactor to provide cooling. Fluidized-bed deactivation system is used in both horizontal reactors to avoid particle agglomeration. Homopolymers, random copolymers, and impact copolymers can be produced in this process using highly effective CD series catalysts. This process is suitable for the production of highimpact copolymers with high rubber content, and the rubber phase content could

The Borstar PP process developed by Borealis is based on a double loop reactor and a fluidized-bed reactor in tandem connection for the production of HPP and RPP. The loop reactor is operated under supercritical conditions with increased comonomer and hydrogen concentration, and higher temperature avoiding gas bubbles. For producing the impact PP, additional one or two fluidized-bed reactors

**28**

be up to 50%.

**Figure 16.**

**4.7 Borstar process**

**4.6 Innovene process (BP Amoco)**

*Multizone circulating reactor [118].*

are connected in series, as illustrated in **Figure 17**.

*Borstar polypropylene process scheme (four-reactor setup) :(a) prepolymerizer; (b) loop reactor; (c) first gas-phase reactor; (d) second gas-phase reactor; (e) third gas-phase reactor; (f) coolers; (g) separators; (h) low-pressure degasser; (i) dryer; (j) purge bin [117].*

Using the HY/HS catalysts of Borealis, which are prepared from emulsion strategy from two-phase liquid/liquid contact, Borstar PP technology produces highperformance HPP and RPP with very low ash content and narrow molecular weight distribution in the supercritical loop reactor due to excellent heat removal and high productivity. The rubber phase (EPR) of the impact copolymers is typically generated through the 3rd and 4th gas-phase reactors. Using the multi-reactor processes described, it is feasible and practical to further broaden PP material properties meeting up the ever-demanding customer needs.

#### **4.8 Solution polymerization process**

Autoclaves, tubular or loop reactors all could be used in a solution process. Different from the slurry and gas-phase process, the solution polymerization process is generally operated at a much higher temperature above 100°C, and in order to form a homogeneous uniform solution, a reaction solvent is added to dissolve the catalyst and polymer generated during the polymerization. Typically, the average residence time is much lower (5–20 min) in contrast with the bulk or gas-phase process (1–4 h). Since polymerization takes place in a more uniform solution, heat and mass transfer resistances are avoided, and this homogeneous process is practical for the production of ethylene-polypropylene copolymer elastomers, EPDM rubbers and stereoblock PP with soluble Ziegler-Natta catalysts, metallocenes, and post-metallocenes. Although conventional HPP could be produced in a solution process, the overall cost is too high to produce them due to requirements for use of solvent and additional process for removal of the solvent.

Solution polymerization process is also very appropriate for production of the atactic PP and PP-based elastomers. Commercial equipment developed to make atactic PP has been announced by Himont (Canada), El Paso (Texas), and Huls (Germany). Special PP-based polyolefins are also produced using the solution process by Exxon, Dow Chemical, and other companies. Propylene-ethylene

copolymers referred to as commercialized Vistamaxx™ are launched successfully by ExxonMobil with a special metallocene catalyst. The VERSIFY™ Plastomers and Elastomers of propylene/ethylene-based copolymers are produced profitably with a new post-metallocene pyridyl amine catalyst system in solution process. Stereoblock PPs [17] are also produced by using oscillating metallocene, or a mixed catalyst systems of two metallocenes and/or post-metallocenes in the presence of chain transfer agent or chain shuttling agent, as mentioned above.
