FEEDSTOCK RECYCLING

The only current type of feedstock recycling that is applicable to addition polymers is processes based on heat-induced degradation, generally pyrolysis. Pyrolysis involves heating in the absence of oxygen to temperatures where the molecular 

Structure of the material breaks down. It can be applied to pure or to mixed feedstocks, including mixtures of plastics and other organic compounds. In all cases with a mixed feedstock, and in many cases even with a pure polymer, the resultant product contains a wide variety of compounds, some liquid and some gas. Separating out pure streams for use as chemical raw materials is often not economically viable. The most common use for these materials is as fuel, after separation only into gas and liquid streams. 

Besides mechanical recycling, the conversion of waste plastics into a petrochemical feedstock is another way for the recovery of the organic materials from a polymer waste. A basic problem is the removal of organobromine compounds. 

A study concerning the pyrolysis of HIPS and other polymers in the presence of PET has been reported (51). The presence of PET in a mixture of plastics influences significantly the formation of pyrolysis products. The formation of the liquid fraction decreases and the formation of gaseous products increased during the thermal decomposition. A waxy residue is observed in addition to a solid carbon residue. 

The presence of a calcium hydroxide carbon composite captures the major portion of chlorine and bromine content out from the liquid fraction. In contrast, in the presence of PET, even a combination of calcium a hydroxide carbon composite and an iron oxide carbon composite is not effective to remove halogen the liquid products completely (51). 

In contrast, an iron oxide carbon composite has been reported that is highly effective in removing both bromine and chlorine from a blend of brominated HIPS and PVC in the course of catalytic thermal degradation, with respect to the liquid fraction of the products of pyrolysis (52). The amounts of chlorine and bromine in the solid have been given. However, a through chlorine balance has not 

In the carbon and wax residues, antimony compounds have been observed, obviously emerging form the synergistic mixtures of the flame retardants used (51). 

Depolymerisation by chemical means is called solvolysis and produces monomers and oligomers. The chemical reactions used to create condensation polymers such as PET, PA and PC can be reversed to convert them into their 

The three major thermal depolymerisation processes are pyrolytic liquefaction, gasification and hydrogenation. If heat is applied to waste plastics in the absence of air the process is called pyrolysis if done with a controlled oxygen flow it is called gasification. Hydrogenation is a modification of the refining process for petroleum. 

Pyrolytic liquefaction produces liquid precursor products or synthetic crade oil that are suitable as refinery feedstock for new monomers. Further products from this process are non-condensable gas, which is used to provide process heat, and solid residues in the form of char. 

Mixed polymer streams can be handled in addition to a certain level of nonplastic contaminants, which improves the economy of the process. Even paper and food can be pyrolysed simultaneously to give other chemical products. Consequently the method is ideal for commingled plastics and composites [25], An additional advantage is that when contamination can be reduced to a minimum, both the matrix and the reinforcing material can be recovered from polymer-based composites. 

Liquid fuels can be produced by carbon hydrogenation. Plastics waste is ground into small pieces and introduced into a reactor where it is depolymerised by heat at high pressure in an excess of hydrogen [52]. The result is a high-quality petrochemical feedstock that can be cracked into saturated hydrocarbons and syncrude. This is in turn is used in the synthesis of new polymer. The advantage with this process is the ease of separation of side products such as heavy metals, sulphur and chloride. Furthermore existing oil refinery units, such as thermal 

Hydrolysis Hydrolysis of plastics (Lopez-Eonseca et al., 2009) with water or dilute alkali yields monomers or other compounds. Thermoset polyurethane foam for instance is hydrolyzed into polyols and amines by superheated steam at 230-315°C in about 15min (Lonescu, 2005). 

FIGURE 9.7 Basic recovery options available for plastics waste. 

Similarly, PET can be hydrolyzed under acidic or basic conditions to yield terephthalic acid (Carvalho etal., 2006 Paszun and Spychaj, 1997 Sato et al., 2006). 

Glycolysis Reacting PET with excess ethylene glycol in the presence of sodium sulfate yielded BHET (see below) as the primary product (Shukla et al., 2009 Viana et al., 2011 Wang et al, 2009). 

Aminolysis of PET with ethanolamine yields bis(2-hydroxy ethylene) terephthalamide (BHETA) (Shukla and Harad, 2006). 

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J. Aguado and D. Serrano, Feedstock Recycling of Plastic Wastes, Royal Society of Chemistiy, Cambridge, 1999 p. 34. 

Plastics Waste - Feedstock Recycling, Chemical Recycling and Incineration... 

Section 3 discusses options for feedstock recycling of mixed plastic waste ... 

Section 7 gives a brief discussion of the pros and cons of feedstock recycling compared to other ophons. 

Feedstock recycling implies a change of the chemical structure of the material, where the resulting chemicals are used for another purpose than producing the original material ... 

The difference between chemical and feedstock recycling is pecuhar. As we will see in the next sections, there is, in essence, hardly any technology that recycles polymers into its own monomers. In this report we will concentrate on feedstock recycling, but in this broad definition we will include chemical recycling as well, see Section 5. 

Concerning feedstock recycling of mixed plastic waste (MPW) with a low chlorine content, the following initiatives seem to be most promising. They are either operating in practice, have operated in the past, or have a fair chance of becoming operational in the short-term. Methods include ... 

A LCA on treatment options of MPW was performed by the Dutch Centrum voor Energiebesparing en Schone Technologie (CE, Delft) in 1994. This LCA used the VEBA process as an example for feedstock recycling (a.ll). Another LCA was performed by Heyde and Kremer (a.6). Particularly the CE studies suggested that the VEBA process was a bit less advantageous than the Texaco process, mainly due to the fact that the Texaco process does not need agglomeration of MPW as pre-treatment, whereas the VEBA process apparently does. 

As indicated in the former chapter most processes for feedstock recycling have limitations with regard to the maximum allowable chlorine input. This makes those processes problematic for the treatment of PVC-rich MPW. Hence, a number of initiatives has been developed for the treatment of PVC waste. All these processes seek to recover the chlorine present in PVC in a usable form (HCl or a saleable chloride salt). The processes include ... 

The next step would be to build a large scale plant of 50 ktonnes per year. However, such an investment needs financing and a commitment of the European PVC industry to this initiative (i.e., a choice for this technology as the feedstock recycling process for PVC waste). Building the plant would take about 5 years. At this stage, it seems that within the PVC industry there is more support for the Linde and Vinyloop processes. 

Linde KC A in Germany offers another technology for feedstock recycling that has been developed on the... 

Apart from MPW and PVC, several feedstock recycling processes have been developed for some specific plastics. In this respect, the most important plastics are ... 

Obviously, there are more traditional treatment options for plastic waste than feedstock recycling. In the next chapter I will compare the feedstock option with more traditional options, here some data are given on the latter. In this section, I will discuss the following technologies ... 

Finally, other relevant treatment options for plastics waste include landfill and mechanical recycling. Since these options (unlike Vinyloop and cement kiln incineration) are not even similar to feedstock recycling we discuss them here only very briefly. Mechanical recycling of plastics (be it PVC or other plastics), needs dedicated collection of the plastic waste in question. This is only possible for selected plastic flows (high volumes, recognisable products, products consisting mainly of one plastic). Landfill can accept plastic waste in any waste context (pure plastic type, MPW, mixed materials). I will only address the costs of these alternative technologies. 

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