Polyethylene production energy requirements

Using the data in Table V, it is possible to determine the amount of energy required and the quantity of air pollutants released per 1000 lb of production of polyethylene sacks. The results are shown in Fig. 15. At 0% recycle, polyethylene sacks (on an equal use basis, 2 polyethylene sacks per paper sack) require approximately 20% less energy than paper sacks. However, as the recycle rate increases, this difference in energy requirement decreases linearly. At recycle rates above 80% there appears to be no significant difference in energy requirements for polyethylene and... 

Table 7.11 lists the cradle-to-gate aggregate US-averaged values of energy required, solid waste, and GHGs produced during the production of polyethylene and polypropylene. Polyethylene and polypropylene are made from natural gas and petroleum. The amount of energy and water that are needed to make polyethylene and polypropylene plastic pellets well as the amount of solid waste, pollution, and GHG generated during production is provided in Table 7.11. The polyethylene pellets are...

An analysis of the flows of energy involved in the production of any product is only one aspect of life cycle assessment. often one may wish to calculate the emissions and energy burdens associated with a specific product, e.g., the production of low density polyethylene resins, so that the potential and actual environmental and health effects associated with the use of the necessary resources and environmemental releases can be calculated. However, the focus of this article is the determination of the total, (both direct and indirect), energy required for the production of the product of interest, (energy flow analysis). 

Figure 1.11 Fossil energy requirement for petrochemical polymers and PLA. The cross-hatched area of the bars represent the fossil energy used as chemical feedstock (i.e., fossil resource to build the polymer chain). The solid part of the bars represented the gross fossil energy used for the fuels and operation supplies used to drive the production processes. PC = polycarbonate HIPS = high-impact polystyrene GPPS = general purpose polystyrene LDPE = low-density polyethylene PET SSP = polyethylene terephthalate, solid-state polymerization (bottle grade) PP = polypropylene PET AM = polyethylene terepthalate, amorphous (fiber and film grade) ...

The energy required to synthesize and manufacture biodegradable plastics is shown in Table 15.1, along with values for high density polyethylene (HOPE) and low density polyethylene (LDPE). PHA biopolymers presently consume similar energy inputs to PEs. New feed stocks for PHA should lower the energy required for their production. 

Apart from pure starch polymers (as discussed so far), starch polymers containing petrochemical copolymers are also commercially available. The more of these copolymers is added, the higher the overall energy requirements are (Table 3). Nevertheless, the values are still clearly lower than those for polyethylene (PE), which belongs to the petrochemical polymers with the lowest energy requirements for production. 

The cradle-to-factory gate energy requirements for PLA are 20-30% below those for polyethylene, while GHG emissions are about 15-25% lower. The results for PHA vary greatly (only energy data are available). Cradle-to-factory gate energy requirements in the best case (66.1 GJ/t) are 10-20% lower than those for polyethylene. PHA does not compare well with petrochemical polymers for more energy intensive production processes. 

The report concludes with the statement The replacement of polyethylene by paper carrier bags makes no sense ecologically. The production of polyethylene carrier bags requires less energy, and in the process results in less burden to the environment. There is no significant difference in the disposal of polyethylene and paper bags at landfill sites or in incineration plants ... 

Radiation cross-linking of polyethylene requires considerably less overall energy and less space, and is faster, more efficient, and environmentally more acceptable. Chemically cross-linked PE contains chemicals, which are by-products of the curing system. These often have adverse effects on the dielectric properties and, in some cases, are simply not acceptable. The disadvantage of electron beam cross-linking is a more or less nonuniform dose distribution. This can happen particularly in thicker objects due to intrinsic dose-depth profiles of electron beams. Another problem can be a nonuniformity of rotation of cylindrical objects as they traverse a scanned electron beam. However, the mechanical properties often depend on the mean cross-link density. ... 

In a typical 80,000 tons/year plant, capital costs were about 220 per metric ton in 1974. To produce 1000 kg of polymer, 1030 kg of monomer is needed, together with 1 kg of hydrogen and 25 kg of diluent. Catalyst and miscellaneous chemicals cost about 4 per 1000 kg of polyethylene pellets produced. For production, 300 kg of medium-pressure steam, 800 kg of low-pressure steam, 530 kWh of electrical energy, 200 m3 of water, 30 m3 of nitrogen, and 600 m3 of air are also required. To polymerize propylene in suspension, the same technology can be used. Catalysts now available [based on TiCl3 (see Table II)] make it unnecessary to separate isotactic from atactic materials. 

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