Anke Brems

RECYCLING AND RECOVERY OF POST-CONSUMER PLASTIC SOLID WASTE IN A EUROPEAN CONTEXT

The disposal of waste plastics has become a major worldwide environmental problem. The USA, Europe and Japan generate annually about 50 million tons of post-consumer plastic waste, previously landfilled, generally considered as a non-sustainable and environmentally questionable option. Landfill sites and their capacity are, moreover, decreasing rapidly, and legislation is stringent. Several European Directives and US legislation concern plastic wastes and the required management. They are briefly discussed in this paper. New processes have emerged, i.e., advanced mechanical recycling of plastic waste as virgin or second grade plastic feedstock, and thermal treatments to recycle the waste as virgin monomer, as synthetic fuel gas, or as heat source (incineration with energy recovery). These processes avoid land filling, where the non-biodegradable plastics remain a lasting environmental burden. The paper reviews these alternative options through mostly thermal processing (pyrolysis, gasification and waste-to-energy). Additional research is, however, still needed to confirm the potential on pilot and commercial scale. [Acknowledgments. The research was partly funded by the Fundamental Research Funds for the Central Universities RC1101 (PR China) and partly funded by Project KP/09/005 (SCORES4CHEM Knowledge Platform) of the Industrial Research Council of the KU Leuven (Belgium).]

Polymeric cracking of waste polyethylene terephthalate to chemicals and energy.

ABSTRACT Polyethylene terephthalate (PET) is a widely used thermo-plastic. PET residues represent on average 7.6 wt% of the different polymer wastes in Europe. Pyrolysis of these wastes is attracting increasing interest, and PET is a potential candidate for this thermal process. The paper measures and discusses the kinetics of the pyrolysis reaction in terms of the reaction rate constants as determined by dynamic thermogravimetric analysis, with special emphasis on the required heating rate to obtain relevant results. The product yields and compositions are also determined. Gaseous products represent 16–18 wt%. The amounts of condensables and carbonaceous residue are a function of the operating mode, with slow pyrolysis producing up to 24 wt% of carbonaceous residue. Major condensable components are benzoic acid, monovinyl terephthalate, divinyl terephthalate, vinyl benzoate, and benzene. The present paper complements previous literature findings by (1) the study of the influence of the heating rate on the reaction kinetics in dynamic pyrolysis tests, (2) the iso-thermal investigation in a fluidized bed reactor to pyrolyze PET, and (3) the assessment of upgrading and recovery of the products. The paper concludes with a proposed reactor recommendation for PET pyrolysis, in either the bubbling or circulating fluidized bed operating mode. IMPLICATIONS Plastic solid waste (PSW) represents up to 8% by wt and 20% by volume of household waste. Landfill disposal wastes valuable energy and chemical feedstock. Incineration for energetic valorization (waste-to-energy) is applied for ∼50% of PSW. To date, research focuses increasingly on pyrolysis, which has the advantage over incineration of producing value-added chemicals, even from commingled or mixed feedstock. The process gains in efficiency and yield if PSW fractions are collected separately or presegregated. The cost of separate collection is easily overcome by the value of the pyrolysis products. The pyrolysis of polyethylene terephthalate is developed as an example of the above.

Recovery and recycling of post-consumer waste materials. Part 2. Target wastes (glass beverage bottles, plastics, scrap metal and steel cans, end-of-life tyres, batteries and household hazardous waste)

The first part of the review paper dealt with general information and covered the specific sectors of paper/cardboard and aluminium cans. The present Part 2 should be read in conjunction with Part 1 and assesses the recovery and recycling of additional post-consumer waste sectors, i.e. glass beverage bottles, plastics, scrap metal and steel cans, end-of-life tyres, batteries and household hazardous waste. For each of the sub-sectors, the specific products are described, the recycling processes briefly evaluated and both environmental and research aspects summarised. The waste availability, the existing and further developing recovery and recycling technologies, and the economic rewards stress the importance of this waste management sector.

Recovery and recycling of post-consumer waste materials. Part 1. Generalities and target wastes (paper, cardboard and aluminium cans)

Recycling of post-consumer waste materials is gaining increased interest due to public awareness, legislative promotion and imposition, economic benefits and appropriate technologies being available. The present paper does not deal with municipal solid waste as such, but only with the recyclable constituents. The paper does not aim at presenting recycling process details and/or fundamental research results, but reviews the major recyclables with their reuse potential, recycling technologies used, problems, solutions and potential areas of future research and development. These target recyclables include paper and cardboard, aluminium cans, glass beverage bottles, scrap metal and steel cans, scrap tyres, batteries and household hazardous waste. The present paper sets the overall picture and deals with paper, cardboard and aluminium cans only. A second part of the paper assesses the other target recyclables. The assessment of the waste availability, the existing and currently developed recovery and recycling technologies, and the economically rewarding markets while recycling, stress the technical, economic and environmental importance of this waste management sector. The activities associated with the recovery and recycling of post-consumer wastes require a strong sustainable engineering input at all phases of the treatment, from input quality control, to the selection of the most appropriate technology and the delivery of the recyclables as readily reusable feedstock.