Polyolefins manufacturing processes

One characteristic of the polyolefin industry is that it is capital-intensive. This is a dimension of economic impact—the amount of money to be invested to create this industry. Unlike the downstream polymer processing and converting industry (where the classical start-up might be imagined as one small moulding machine in a garage), even the smallest polyolefin manufacturing process (the Hills PB-1 plant at start-up was just 3000 tons per annum) involves capital investment in the order of millions of dollars. 

R. L. Magovern, Current polyolefin manufacturing processes, Polym. Plastics Technol. Eng. 

Figure 2.35 Flow diagram of a typical polyolefin manufacturing process.

The overall conversion in the loop polymerization reactor is very high for a polyolefin manufacturing process, and the conversion per pass is limited by the amount of monomer that is needed to carry the polymer out of the reactor. It is desirable to operate the reactor at as high a slurry density as possible to get the highest throughput and the highest conversion. Typically, loop reactors operate at slurry concentrations of about 45-50 wt% polymer. 

Most polyolefin manufacturing processes today utilize conventional heterogeneous Ziegler-Natta catalysts. Several types of these Ziegler-Natta catalysts are stereospecific, i.e. the insertion of asymmetric monomers into the growing polymer chain in a given orientation is favored over all other possible orientations, leading to the production of isotactic... 

Finally, the adaptation of existing polyolefin manufacturing process to metallocene catalysts requires only minor changes, which makes use of these catalysts economically viable. 

Shaw selected a combination of polyolefin resins as the base polymer of choice for its substitute, EcoWorx . Due to the low toxicity of its feedstocks, superior adhesion properties, dimensional stability, and its ability to be recycled, EcoWorx meets all of the design criteria necessary to satisfy the needs of the marketplace from a performance, health, and environmental standpoint. Research also indicated that the post-consumer carpet tile had a positive economic value at the end of its useful life. The cost of collection, transportation, elutriation, and return to manufacturing processes is less than the cost of using virgin raw materials. This is a truly recyclable (or Cradle to Cradle) product and is a good example of how substitution through innovation can make economic as well as environmental sense. ... 

Patent Number US 5883145 A 19990316 CROSSLINKED FOAM STRUCTURES OF POLYOLEFINS AND PROCESS FOR MANUFACTURING... 

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. 

Patent Number EP 702032 A2 19960320 CROSSLINKED FOAM STRUCTURES OF ESSENTIALLY LINEAR POLYOLEFINS AND PROCESS FOR MANUFACTURE... 

A cross-linked polyolefin foam sheet is produced by two methods using chemical cross-linking and by two methods of radiation cross-linking. The two well-established manufacturing processes for polyolefin foams using radiation cross-linking are the Sekisui process and Toray process. The differences between these two manufacturing methods are mainly in the expansion step, which is almost always done separately. However, the... 

Flow diagram of the manufacturing process for polyolefin foams using radiation cross-linking. 

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. 

Developments by the polyolefin manufacturers in recent years have significantly changed the demands placed on plants processing these products. The new demands are due partly to greatly increased reactor throughputs. 

Decane is a constituent in the paraffin fraction of petroleum and is also present in low concentrations as a component of gasoline. It is used as a solvent, in organic synthesis reactions, as a hydrocarbon standard, in the manufacture of petroleum products, in the rubber industry, in the paper processing industry, and as a constituent in polyolefin manufacturing wastes. Decane is a flammable liquid (at room temperature) that is lighter than water. 

Ziegler-Natta catalysts play a dominant role in polyolefins manufacture. More than 50 million tonnes per annum of polyethylene and polypropylene are now produced by means of Ziegler-Natta catalysis. Since the first discoveries, more than 50 years ago, many breakthroughs and innovations have been made in catalyst and process chemistry and technology, leading to ever more efficient manufacturing processes, and also to increasing control over polymer structure and properties. 

Untreated, many polymers, in particular polyolefins, are hydrophobic and therefore tend to repel water and water-based substances. The oxidation of the film through flame surface treatment increases the surface energy of the film, making the material less repellent of water, improving film wettability. Increasing wettability is a necessary component of many manufacturing processes that require water-based inks and adhesive materials to be applied to the polymer film surface. 

---