Feedstock recycling advantages

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. 

Post-consumer plastic waste recycling is discussed with special reference to feedstock recycling, the advantages it has over mechanical recycling, and the techniques involved. Chemolysis and thermolysis are explained, and... 

The decisive criterion in the case of wood substitution is the life expectancy ratio (LER) of the compared products made of mixed plastics or wood, respectively. Only above a certain limit value (in the examined case LER = >3.3) — that is, a clearly longer life cycle of the plastic product as compared with the wooden product—is the level of resource reduction in feedstock recycling/energy recovery reached. The situation is similar as far as acidification and eutrophication are concerned. Advantages are found only with regard to waste minimization. 

Secondary or mechanical recycling processes differ from tertiary or feedstock recycling and quaternary or energy recovery processes principally in the potential to retain some of the energy used from plastics production, and in general terms provide for financially advantageous options. 

Nowadays, many bio-based pol5miers are being developed one after another. In particular, recyclable bio-based polymers are of great interest and important materials from both a scientific and an environmental point of view, because bio-based polymers have the specific properties of being excellent "feedstock recyclability" and "carbon neutral," which are advantages that commodity plastics do not possess. 

A typical reactor operates at 600—900°C with no catalyst and a residence time of 10—12 s. It produces a 92—93% yield of carbon tetrachloride and tetrachloroethylene, based on the chlorine input. The principal steps in the process include (/) chlorination of the hydrocarbon (2) quenching of reactor effluents 3) separation of hydrogen chloride and chlorine (4) recycling of chlorine to the reactor and (i) distillation to separate reaction products from the hydrogen chloride by-product. Advantages of this process include the use of cheap raw materials, flexibiUty of the ratios of carbon tetrachloride and tetrachloroethylene produced, and utilization of waste chlorinated residues that are used as a feedstock to the reactor. The hydrogen chloride by-product can be recycled to an oxychlorination unit (30) or sold as anhydrous or aqueous hydrogen chloride. 

Chlorination of Ethylene Dichloride. Tetrachloroethylene and trichloroethylene can be produced by the noncatalytic chlorination of ethylene dichloride [107-06-2] (EDC) or other two-carbon (C2) chlorinated hydrocarbons. This process is advantageous when there is a feedstock source of mixed C2 chlorinated hydrocarbons from other processes and an outlet for the by-product HCl stream. Product ratios of tri- and tetrachloroethylene are controlled by adjusting the CI2 type="subscript">2 EDC ratio to the reactor. Partially chlorinated by-products are recycled to the chlorinator. The primary reactions are... 

The use of pyrolysis for the recycling of mixed plastics is discussed and it is shown that fluidised bed pyrolysis is particularly advantageous. It is demonstrated that 25 to 45% of product gas with a high heating value and 30 to 50% of an oil rich in aromatics can be recovered. The oil is found to be comparable with that of a mixture of light benzene and bituminous coal tar. Up to 60% of ethylene and propylene can be produced by using mixed polyolefins as feedstock. It is suggested that, under appropriate conditions, the pyrolysis process could be successful commercially. 23 refs. 

The resin supply system should be designed to take advantage of the raw materials in the lowest cost and most effective form. Additives tend to be more expensive than the base resin. Gravimetric rather than volumetric supply of the material is more conducive to minimizing the use of the more expensive feedstock components. The ability of the equipment to utilize reliably 100% of in-plant regrind, additive concentrates, and recycled materials is one of the most important factors to be considered. 

A project of this type achieves major economic advantages. Base petrochemical feedstocks are hydrotreated VGO and ethane. Both are low cost at this site. The combined DCC and ethylene unit reduces ISBL recovery cost significantly due to integration and recycle feedstock access. 

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