Technology and economics of manufacture

In contrast with ethylene monomer production, many stages are needed to produce the monomers adipic acid and hexamethylene diamine for nylon 6,6 (Fig. 2.11). None of these stages is 100% efficient, although new catalysts have increased the efficiency of some stages. Since energy is consumed in each reaction stage, and the capital cost of the many reactors is high, the cost per tonne of nylon 6,6 is four or five times that of polyethylene. Moreover the scale of production is smaller by a factor of 50 the implications of this are explored later. 

The large-scale manufacture of addition polymers is usually via a continuous process, with monomer addition and polymer removal occurring at a 

The reactor can produce polyethylene homopolymer, or copolymers with butane, octane, etc. so the overall crystallinity of the product can be controlled. The molecular weight is controlled by additions of hydrogen, and the width of the molecular weight distribution can be changed by modifying the catalyst. 

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. 

Cost = monomer + energy + share of capital cost 

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