Jam polypropylene is licensee of Basell`s Spheripol process that produces a wide range of premium quality polypropylene products.
Today’s Spheripol process is the result of 40 years of continual improvement. However, to truly appreciate the unique capabilities of this technology, it is helpful to understand the evolution of the PP industry and the breakthroughs that led to discovery of the Spheripol process.
In the 1960s, PP processes employed first-generation low-yield catalysts (<1000 kg PP/kg catalyst) in mechanically stirred reactors filled with an inert hydrocarbon diluents. Polymer produced with these catalysts had unacceptably high residual metals and contained 10 percent atactic PP, which required separation. Removal of catalyst residues and atactic PP involved treatment of the polymer with alcohol, multiple organic and/or water washings, multistage drying, and elaborate solvent, amorphous, and catalyst separation systems. These processes were costly and difficult to operate; they also required extensive water treatment facilities and catalyst residue disposal systems.
An intermediate step was reached with the second-generation catalyst, increasing yield (6000 to 15,000 kg PP/kg catalyst) and isotacticity but not yet at a level that allowed simplification of the production process.
In the 1970s, the discovery of third-generation high-yield catalysts (15,000 to 30,000 kg PP/kg catalyst) eliminated the need for catalyst residue removal, but atacticity was still unacceptably high. This simplified the washing but did not eliminate the atactic recovery steps.
In the 1980s, fourth-generation high-yield, high-selectivity (HY/HS) catalysts (30,000 kg PP/kg catalyst) eliminated the need for catalyst and atactic removal. This further simplified the process and improved product quality. Other breakthroughs occurred in the process design through the refinement of gas-phase and bulk polymerization reactors that led to the development of Spheripol technology in 1982.
Today, the capabilities of the Spheripol process are further enhanced by the current catalyst generation, which has the ability to produce new families of reactor-based products with improved properties. They offer even greater control over morphology, isotacticity, and molecular weight and continually challenge new frontiers in the development of propylene polymers.
By mid-2003, 91 Spheripol PP lines had been licensed for a capacity of over 16 million t/yr. Spheripol technology accounts for 45 percent of all high-yield, high-selectivity PP technologies available.
The Spheripol process, using HY/HS catalysts supplied by Basell, has the unique ability to produce polymer spheres directly in the reactor. The Spheripol process is a modular technology. In its most widely adopted configuration, the polymerization section involves the following main units:
Simplified process scheme of Spheripol process
Bulk polymerization employs jacketed tubular loop reactors completely filled with liquid propylene to produce homopolymer, random copolymer, and terpolymer. The catalyst, liquid propylene, and hydrogen for molecular weight control are fed continuously into the loop reactor. Residence time in the reactor is lower than other technologies because of the high monomer density and increased catalyst activity. The polymerization reaction is exothermic; the heat of reaction is removed by means of cooling water circulating into the reactor jackets. The loop reactor is used because it offers low cost and high heat transfer and maintains uniform temperature, pressure, and catalyst distribution. The low residence time also results in short transitions during grade changes, whereas the complete filling of the reactors eliminates any risk of contamination between different grades owing to the presence of an interface between the actual reaction volume and disengagement.
A homogeneous mixture of porous PP spheres (where active catalyst resides) suspended in liquid propylene is circulated inside the reactor loop by means of a dedicated pump. If the production of random copolymer or terpolymer is desired, ethylene and/or butane-1 are fed – in defined ratio with the plant capacity – into the loop reactor. This process achieves very high solid concentration (at least 50 percent by weight) and excellent heat removal (by water circulation in the reactor jacket) and temperature control (no hot spots). The resulting polymer is discharged continuously from the reactor into a first-stage degassing vessel. Unreacted propylene is recovered, condensed, and pumped back into the loop reactor.
For the production of impact and specialty impact copolymers, the obtained polymer is fed to a gas-phase fluidized-bed reactor that operates in series with the loop reactors. (This gas-phase reactor can be bypassed when homopolymer or random copolymer is produced.) In this reactor, an elastomer (ethylene/propylene rubber) polymerizes within the homopolymer matrix that resulted from the first reaction stage. The carefully developed pores inside the homopolymer particle allow the rubber phase to grow inside without showing the sticky nature of the rubber to upset operations by forming agglomerates.
Polymer discharged from the reactors flows to a low-pressure separator and subsequently to a steam treatment vessel where catalyst residues are neutralized and the dissolved monomer is removed, recovered, and recycled back to the reactor system.
From the steamer, polymer is discharged into a small fluidized-bed dryer with a hot nitrogen closed-loop system to remove the moisture. The final product is conveyed to an extrusion unit, where it is mixed with additives and extruded to pellets.
Safety and Environment
Basell has a safety record unmatched in the industry. By 2003, Basell technologies had achieved nearly 7 million operating hours without any major incident.
Spheripol process plants are designed to meet the particular requirements of individual liscensees, yet they are flexible enough to be expanded easily to meet future needs as the business develops. Two critical design elements that are expanded easily include capacity and product range.
A range of single-line capacities from 40 to 450 kt/yr is available for homopolymer, random copolymer, or heterophasic impact copolymer either using polymer (99.5 percent typical assay) or chemical-grade (94 percent typical assay) propylene. This wide capacity range and the modular installation approach allow, within limits, easy debottlenecking. This minimizes initial capital costs and allows new capacity to be added later when required.
The product range also can be expanded easily. Often new entrants to the PP business will build a plant to produce only homopolymer and random copolymer products because these are the least expensive, are easy to operate, and their products account for 75 percent of all PP sold in the world. A basic homopolymer plant can be expanded easily at a later date to produce heterophasic impact and specialty impact copolymers. Impact copolymers are more specialized products, which require additional capital investment and technical support.
There is also a list of suitable suppliers and designs for critical equipment, enabling purchasers to benefit from the most economical pricing available.
In comparison with any wholly gas-phase technology, a Spheripol process plant offers on a single polymerization line the widest range of homopolymers, random copolymers, and terpolymers, as well as heterophasic impact and specialty copolymers covering all PP application fields. Intense efforts in product application development for all the major market areas in the world ensures that Basell’s PP products keep a leading position in most profitable market segments, with excellent results in PP specialties and “high quality” demanding application introduction and market position.
Key to this versatility is the application of Basell’s high-yield, high-selectivity Avant catalysts.
The Spheripol process has proven to be extremely reliable. In use since 1982, it has been continuously refined and optimized. Yearly worldwide surveys of operating Spheripol process lines reveal an average on-stream operability of around 98 percent. Of an average 2 percent downtime, less than 1 percent is due to process features.
Spheripol process plant capital and operating costs are among the lowest in the industry as a result of
Products and Applications
Random copolymers can be produced with excellent optical properties and seal initiation temperatures in compliance with the U.S. Food and Drug Administration (FDA) regulations for food contact.
Heterophasic copolymers with outstanding low-temperature behavior, high-impact strength and enhanced stiffness can be obtained in a wide range of melt viscosities.
Typical customer applications using polypropylene manufactured from the Spheripol process include: