Microwave Ready Packaging

As product and packaging manufacturers seek to shrink and lighten materials, one item that's increasingly taking the market by storm is laminated packing. As the importance of recycling this waste stream grows, research has been published into a Microwave Induced Pyrolysis technology that promises to recover both energy and materials from such packaging. WMW investigates. Enval's Microwave Induced Pyrolysis process could allow laminated packaging materials to be targeted by recycling collections Image Credit: WRAP Laminated Packaging materials comprise of multiple layers of different materials - often aluminium and plastics - joined together to form a single sheet that combines the best properties of each layer. For many applications such materials offer numerous benefits over traditional materials, including reduced size and weight, better mechanical properties, extra cushioning and better barrier protection. Laminated packaging offers many environmental benefits. Its low weight improves the ratio of product to pack weight, reducing transport costs and ultimately reduces the weight of material to be disposed of. However the collection and recovery of recyclates is currently driven by weight-based targets. Thanks to their very design these pouches, bags and tubes are of low weight, relatively low value, and have to date been considered unrecyclable. In view of the growing use of these materials, the UK's Waste and Resource Action Programme (WRAP) recently commissioned environmental research specialists, Oakdene Hollins Research Consulting, to investigate the viability of using Microwave Induced Pyrolysis technology to recycle them. The technology Developed by Cambridge, UK based Enval - a spin-out from the Department of Chemical Engineering at the University of Cambridge - the process has been developed to focus on the recycling of aluminium-containing laminate structures. In general pyrolysis is a process in which an organic material, such as paper or plastic, is heated in the absence of oxygen causing the degradation of the material by effectively shortening its molecular length. This is without any oxidation, combustion or incineration taking place. In the Enval's process carbon is heated by microwaves and used as the heat source for the pyrolysis of the plastics - which themselves are not readily heated by microwave energy. To simplify feedstock sourcing for the trials only toothpaste tubes, pet food pouches, drinks pouches and coffee bags were used This provides an efficient, mechanically gentle heat exchange and causes the degradation of the plastics and the formation of pyrolysis oils, which can be used to generate electricity or as feedstock for speciality chemicals. Fragile aluminium foil remains undamaged after processing and is extracted as clean material suitable for reintroduction into the aluminium recycling supply chain. Potential feedstock In conducting its assessment of the process, Oakdene Hollins determined the mix of packaging formats and contamination to be of the utmost importance, with the waste materials used needing to closely mimic mixed post-consumer laminated packaging. To achieve this, the researchers conducted field tests at MRF and MBT facilities sorting waste materials obtained from actual household recycling collections, and from 'black bag' household waste respectively. The data produced allowed a simulated mix of post-industrial materials to be developed into a 'recipe' for testing. This feedstock was shredded into a two dimensional flake of approximately 30mm x 30mm using a standard four-shaft shredder and a quantity of products such as toothpaste and pet food was added to simulate real world waste feedstocks. Testing The pyrolysis tests were carried out by Enval using its continuous process pilot plant in Luton. Aluminium and hydrocarbon process outputs were analysed by the University of Cambridge. Each test commenced with heating the kiln - which contained carbon to absorb microwaves - and purging it with nitrogen. The kiln was the heated to the required reaction temperature while a small flow of purging gas (N2) flowed through it. The waste laminated plastic feedstock was continuously fed into the kiln through two hoppers that provided an air lock, with each trial treating between 87kg to 107kg. During pyrolysis of the laminates plastics broke down into lower molecular weight species and the aluminium was released from the laminated structure. Condensed products from the kiln were then collected in collection drums and the aluminium in the solids recovery pot. Gas sampling was possible at the exit of the condensation system by collection into a gas sampling bag which could be later analysed off site. After each test, samples of condensable and non-condensable products were analysed. Six trials were conducted during which greater understanding of the process and the effects of feedstock on the process was sought. According to the report, the trials show that Microwave Induced Pyrolysis is capable of processing waste laminated packaging. The average weight of aluminium recovered by the process is about 9.3% of the total feedstock weight. About 18% of the waste feedstock can be recovered as condensable yields (oils), a further 48% can be recovered as non-condensable combustible gases. Outstanding mass balance is water and the data collected was used to calculate costings for a commercial unit. Economics The adoption of laminated packaging has increased significantly in recent years. Researchers estimate that in the UK some 139,000 tonnes of such packaging is consumed each year, containing on average 9.7% aluminium foil by weight. The market has a growth rate of approximately 10% annually. In devising an economic model the researchers held discussions with waste collection authorities and determined that it would be possible to access one third of the total laminated packaging disposed by households, in commingled kerbside collections. The value for the hydrocarbon products both condensable and non-condensable was obtained by using the results of the chemical analysis, which determined the average calorific value for the two fractions to be 38.9 MJ/kg. Using a price for crude oil of $80 per barrel the researchers determined a 'value of energy' of 1.28 cents/MJ. This figure combined with the calorific value of the products gives a value of $496 per tonne of hydrocarbons. However, in practice this figure cannot be realised since 70% of the hydrocarbons are in gaseous form. In the financial analysis, the average value of the hydrocarbons from the process is taken as 50% of this estimate - $248 per tonne. In practice this fuel would best be used as heat energy, or to generate power within the recycling centre, thereby substituting for imported which costs approximately 2.88 cents/MJ, suggesting a value for the gases of around $1120 per tonne. Additionally, following discussions with Alupro, the researchers concluded that the value of the aluminium would be in the order of $1280 per tonne. Using these estimates, and taking into account a number of other factors, such as operating costs, license fees, transport costs and savings on landfill tax, the report concludes that a commercial facility processing 2000 tonnes per year could potentially provide a payback period of around four years. With their undoubted technical, financial and environmental benefits, the use of laminated films in packaging looks set to continue to grow. As countries around the world seek to not only reduce landfill, but to treat waste as far up the waste hierarchy as possible, the ability to recover both materials and energy from this growing waste stream offers great potential. If, as the report finds, the Enval Process is financially and environmentally beneficial, then microwave induced pyrolysis could be a technology whose time has come. However, as Claire Shrewsbury, packaging programme manager at WRAP points out, the next challenge will be to determine a viable route for collecting these materials from the waste stream. More Waste Management World Articles Waste Management World Issue Archives