Polyolefin Production Processes

Sittig, M., Polyolefin Production Processes, Chemical Technology Review No. 79, New Jersey, Noyes Data Corp., 1976, p. 9. 

Knowledge of the coordination polymerisation of olefins would not be complete without consideration of the types of process used in industry for polyolefin manufacture. Problems encountered in production influence developments in the area of catalysis in olefin polymerisation, an improvement in a catalyst being defined as leading to a reduction in the cost of making the polymer or giving better product properties. Therefore, the principal types of polyolefin production involving coordination catalysts of various types are dealt with briefly. Since modern polyolefin production processes offer a versatile range of polymers, the main commercially available olefin polymerisation products and their typical uses are also considered. 

Sittig, M. Polyolefin production Processes, Park Ridge, Noyes 1976... 

A recent review of polyolefin production processes (18) provides information on types of equipment used and operating conditions. Summarized in the following sections are the major processes in current use. 

Many modifications to the basic stirred autoclave design have been made to improve its heat transfer characteristics those commonly used in polyolefin production processes include the use of external coolers, overhead condensers or internal cooling coils. 

M. Sittig, Polyolefin Production Processes, Noyes Data Co., Park Ridge, N.J., 1976. 

Since their discovery over a decade ago, late transition metal a-diimine polymerization catalysts have offered new opportunities in the development of novel materials. The Ni(II) catalysts are highly active and attractive for industrial polyolefin production, while the Pd(II) catalysts exhibit unparalleled functional group tolerance and a propensity to form unusually branched polymers from simple monomers. Much of the success of these catalysts derives from the properties of the a-diimine ligands, whose steric bulk is necessary to accelerate the insertion process and inhibit chain transfer. 

A review is presented of the nitrogen autoclave process for the manufacture of crosslinked polyolefin foams. Process and product developments over the last few years are summarised and future possibilities are described. Process developments include use of higher temperatures and pressures to produce foams having densities as low as 10 kg/cub.m. Product developments include foams based on HDPE/LDPE blends, propylene copolymers and metallocene-catalysed ethylene copolymers. The structure and properties of these foams are compared with those of foams produced by alternative processes. 5 refs. 

It is traditional to begin books about polyurethanes by defining the class of polymers that has come to be known as polyurethanes. Unlike olefin-based polymers (polyethylene, polypropylene, etc.), the uniqueness of polyurethane is that it results not from a specific monomer (ethylene, propylene, etc.), but rather from a type of reaction, specifically the fonnation of a specific chemical bond. Inevitably, the discussion in traditional books then progresses to the component parts, the production processes, and ultimately the uses. This is, of course, a logical progression inasmuch as most tests about polyurethanes are written for and by current or aspiring PUR (the accepted abbreviation for conventional polyurethanes) chemists. Unlike discussions about polyolefins where the monomer, for the most part, defines the properties of the final product, a discussion of PURs must begin with the wide variety of constituent parts and their effects on the resultant polymers. 

A major application of these types of molded products would be for interior uses in automobiles, such as head liners, door panels, and dashboards. Although this is a low-cost, low-performance application, it represents a very laige-volume market. Indeed, wood is already utilized in applications of this type, but as a finely ground flour that serves as a filler (up to 40%) in extrusion-molded polyolefin products. The use of recycled fiber in this process and the one described above offers the potential of even greater cost reductions, combined with alleviation of solid waste disposable problems. 

Titanium-based solid-state catalysts for the industrial production of polyolefin materials were discovered in the early 1950 s and have been continually improved since then (see Section 7.3). Due to the high degree to which they have been perfected for the production of large-volume polyolefin commodities, they continue to dominate the processes presently used for polyolefin production. Despite (or because of) this product-oriented perfection, only limited degrees of variability with regard to some relevant polymer properties appear to be inherent in these solid-state catalysts. 

Discussion Point DPI At present the production of polyolefin materials is based almost exclusively on petroleum. However further increases in crude-oil prices might make other potential sources competitive. Identify three alternative olefin sources, formulate the essential chemical reactions necessary for each production process and try to assess advantages, disadvantages and relative likelihoods of industrial implementation for such processes. 

Figure 3. Typical process flow sheet for linear polyolefin production...

Input material for the production process is dirty, mixed plastic material from private households. One of the main tasks of the production process is to prepare hard plastics (e. g. HD-PE, PS, PVC-U and PET) as well as foils (LD-PE) which are difficult to handle in milling processes. The composition of the waste material differs in a wide range, main parts are the polyolefines. 

The major processes for polyolefins production using Ziegler-Natta catalysts involve polymerization in the gas phase or in slurry, including bulk liquid monomer in the case of propylene. LLDPE is also produced via a solution process operating at temperatures in the range 130-250 °C. 

The predecessor company of BASELL (Montecatini Edison, Himont, Montell, Basell) has always been strongly committed to the research and development of new catalysts for polyolefin, and specifically polypropylene, production and in the continuous improvement of the production processes. 

Processes of ethene/a-olefin copolymerization are of great practical importance. Copolymerization of ethene with small amounts of highest a-olefins (1-butene, 1 -hexene, 1 -octene) allows one to produce linear low density polyethylene (LLDPE), which is one of the most widely used large-scale polyolefin products. Polypropylene, modified with small amounts of ethene, exhibits higher impact strength compared to isotactic homopolypropylene. Copolymerization of propene with large amounts of ethene and terpolymerization of ethene/propene/diene result in amorphous elastomer materials (rubbers) [103]. 

Polyolefin can be considered as an interdisciplinary material that needs the collaboration from different disciplines such as chemistry, physics, computer science, and engineering. The integration of different fields leads to new advanced technology and economic competitiveness to modify polyolefins for different applications. Polyolefins are replacing many other materials in diverse uses, and the scientists are trying to find new production, processing, and applications for the polyolefins with more friendly environment routs through new polymerization processes, modified catalysts and improved additives to have a wider application of these materials. 

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