Polyethylene production costs

Metallocene-based polyethylene does not offer the lower production costs associated with LLDPE. Hence there will be a price premium for the new materials but this is felt to be justified in view of their improved property profile. 

An example of the way in which process competition works in the manufacture of plastics is the story of acrylonitrile. The first process for the production of this plastic was based upon the reaction between hydrogen cyanide and acetylene, both hard to handle, poisonous, and explosive chemicals. The raw material costs were relatively low as compared to materials for other monomers, but the plant investment and manufacturing costs were too high. As a result, originally acrylonitrile monomer (1950s) sold for about 30 cents per pound and the future of the material looked dim as other plastics such as polyethylene became available at much lower prices due to their lower production costs. 

As in any other process, so also in the high-pressure polymerization of ethylene, do capital costs, utilities, maintenance, manpower, and costs of raw materials contribute to the production costs of low-density polyethylene (LDPE). The cost structure is typical for the production of bulk chemicals but is strongly influenced by the requirements of a high-pressure process. 

In many cases, the linear low-density polyethylene (LLDPE) produced in low-pressure processes competes for the same market as LDPE. For this reason, in Figure 8.2-7 capital- and operation costs of the high-pressure polymerization are compared with those of a low-pressure solution process having the same capacity. Also, the production costs of the low-pressure process are dominated by the costs of the monomer, but some differences can be noted which are typical for the economics of low- and high-pressure processes. 

In contrast to polyethylene production, solution polymerisation at high temperature is rarely applied for isotactic polypropylene, but some special-purpose polypropylene grades are manufactured (Figure 3.57) [51]. However, the solution process, which yields isotactic polypropylene with a very low level of impurities, is characterised by high overall costs. The solution process is being used to make atactic polypropylene, to which it seems more suited [43],... 

Once the desired ethylene conversion is obtained, the reaction stream passes to a high-pressure separator where the bulk of the unreacted ethylene is removed from the product and recycled (Fig. 23.1 [4]). High-pressure separation of most of the unreacted ethylene conserves compression costs in much the same way as high-pressure hydrogen recovery does during ammonia production. After high-pressure ethylene separation the hot product moves to a low-pressure separator where the rest of the unreacted ethylene is removed. The polyethylene product is then extruded into cold water and pelletized, dried, and then either bagged or shipped in bulk containers for delivery to fabricators. 

Engineer Z of Super Plastics, Inc. is to estimate production costs of a new type of polyethylene produced by a competitor. She reviews the literature and her analysis indicates that the design and size of reactor are of key importance. She needs more information on the size of the reactor. Driving by the plant gives her a good idea on auxiliary equipment but not of the reactor. She is convinced that aerial photography would provide important information. 

Unlike consumer goods such as cars and clothes, most commercial chemical products are faceless (e.g., hydrochloric acid, polyethylene), and as a rule the customer is therefore only interested in sales incentives such as price, quality, and availability. All the research activities of an industrial enterprise must therefore ultimately boil down to three basic competitive advantages, namely, being cheaper and/or better and/or faster than the competitor. The AND combination offers the greatest competive advantage and is thus known as the world-champion strategy. Flowever, more often one must settle for the OR combination. The qualitive term cheaper can be quantified by means of a production cost analysis. Initially, it is sufficient to examine the coarse structure of the production costs. Thus, each item in Table 1-2 can be analysed individually and the... 

The polyethylene process just described was originally operated as a pilot plant with a reactor 0.1m in diameter, producing 50 tonnes per year. The largest operating reactor has a 4.5 m diameter reactor and is capable of producing 100 000 tonnes per year. With increased scale, the production cost per tonne of polymer decrease considerably. The production costs contain main elements. 

The Unipol process, initially developed for polyethylene production, was later extended to polypropylene manufacture. The process consists of a large fluidized-bed gas-phase reactor for homopolymer and random copolymer production, and a second smaller reactor for impact copolymer production. The second reactor is smaller than the first one because only 20% of the production comes from the second reactor. This reactor typically has a lower pressure rating as copolymerization is usually carried out at lower temperatures and pressures. Condensed mode operation is used in the homopolymer reactor but an inert diluent is not required because propylene is partially fed as a liquid. The copolymerization reactor is operated purely in the gas phase. The Unipol process has a unique and complex product discharge system that allows for very efficient recovery of unreacted monomer, but this does add complexity and capital cost to the process. 

Poly(lactic acid) (PLA) is a thermoplastic polyester characterized by mechanical and optical properties similar to polystyrene (PS) and polyethylene terephthalate (PET). It is obtained from natural sources, completely biodegradable and compostable in controlled conditions as already stated in previous chapters. PLA offers some key points with respect to classic synthetic polymers, since it is a bioresource and renewable, while raw materials are cheap and abundant compared to oil. From a commercial point of view, a non-secondaiy approach, it can embellish with the word green so fashioned for the major stream consumers. Legislation can also help the commercial diffusion of biopolymers. As an example, a decisive leap has been made with the control of non-biodegradable shopping bags distribution in the European Commission and many of its member states. In addition, PLA has received some interest from the industrial sectors because of its relatively low price and commercial availability compared with other bioplastics. This is the veiy key point for any successful polymer application. In fact, the current price of commercial PLA falls between 1.5 and 2 kg , which is sufficiently close to other polymers like polyolefins, polyesters or poly(vinyl chloride) (PVC). Clearly, the PLA market is still in its infancy, but it is expected that the decrease in the production costs and the improvement in product performance will result in a clear acceleration in the industrial interest for PLA uses. It is estimated that PLA consumption should reach... 

Chlorinated polyethylene elastomer (CPE) has been produced by the introduction of chlorine atoms onto the polyethylene backbone in order to reduce the crystallization ability of polyethylene. In addition, the enhancement in resistance to hydrocarbon oil, heat and weathering is also achieved. To gain desired properties of the final products, CPE has been blended with many polymers, including polyvinyl chloride, styrene-acrylonitrile and polyurethane. Compared to NR, CPE is relatively expensive and therefore the blending of CPE/NR is one of methods to reduce the production cost of the final products requiring CPE properties. Some researchers from Thailand are working with this kind of blend. ... 

Table 3.14 shows an overview of the production costs for the processes described for the production of polyethylene. All data have been standardised for the different processes by using USD 600/t as the feedstock price for both ethylene and butene-1. As can be seen for all processes, the impact of the feedstock price is about 80 %. All data used are based on ChemSystem (1996/97 for LDPE and LLDPE, 1999/2000 for HDPE) data for new large scale plants. 

The discovery of chromium (molybdenum) and titanium catalysts for the low pressure synthesis of polyethylene in the mid-1950s was a milestone in the preparation of plastics [1, 2]. Research efforts in the area have been greatly directed toward several commercial goals that comprise low production cost, which is related to an efficient process chain, and an appropriate property profile, which is related to a market requirement and/or an application [3]. The use of a supported catalyst that allows steering of the morphology of the product is an essential part of the production process [3,4]. The property profile of polyolefins can be substantially extended by dispersion of fillers into the material (http //www.matweb.com/). 

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