Plastic’s durability and resistance to degradation have made it an invaluable packaging resource for processing, storing, transporting, protecting and preserving products. While certain plastic products like rigid #1 PET and #2 HDPE bottles and containers are easily identified, sorted, reprocessed and recycled at the end of their useful life, many plastic packages (and other mixed plastics) are not mechanically recycled due to contamination issues from the product, a lack of end markets for certain polymers, or the inability to separate multi-layer or composite plastic packaging structures.
In countries such as Germany, Austria and Sweden, the integration of efficient collection, advanced sorting and separation technologies, and selective end-of-life methods have worked together to create a well-managed waste management chain to maximize the reuse, recycling and energy potential of municipal solid waste (MSW) materials. But despite these advances, certain materials commonly found within the waste stream remain very difficult to manage at their end-of-life, particularly non-recyclable, contaminated and multi-layer plastics.
To enable the treatment of these materials, a new generation of conversion technologies have emerged that use pyrolysis and gasification methods to convert non-recyclable and contaminated waste plastics into fuel sources such as synthetic gas (called syngas), oils or liquid fuels which can be combusted. Not only do these processes enable the recovery of the materials, they can create a valuable source of alternative energy and heat for homes and buildings, and electricity for local grids.
Feedstocks and OutputsPyrolysis is defined as, “the thermal decomposition of organic and synthetic waste materials at elevated temperatures in the absence of oxygen.” The primary differences between pyrolysis and gasification are the energy required for the processes and the amount of oxygen included in the system. Gasification typically requires more heat within the thermal decomposition of the feedstock and uses controlled releases of oxygen; pyrolysis operates at lower temperatures in the absence of oxygen.
While gasification plants are able to utilize biomass (biological material), food waste, non-recycled plastics and mixed MSW as feedstocks, pyrolysis requires a more pure feedstock, often comprised of only plastics. The syngas that is produced from these processes can be rerouted into the conversion system to meet some of the system’s energy needs, or it can be extracted and combusted. Plastic-to-fuel conversion technologies that use pyrolysis can produce products ranging from a gasoline-diesel fuel blend to a product not much different from sweet crude oil, both of which need to be refined for use. Some systems can even produce diesel fuel ready for use in vehicles and combustion engines.
After the thermal treatment of the appropriate feedstock, both pyrolysis and gasification processes will produce byproducts such as ash or slag that often need to be disposed of within a landfill, posing potential disposal and/or treatment concerns. The potential for leaching from ash requires specific linings within the landfill it is disposed. Slag, the byproduct produced by the inorganic materials and minerals from the feedstock treated by gasification, is essentially non-leaching and sometimes can be converted to other byproducts such as landscaping or cinder blocks and floor/roof tiles.
Limited ApplicationPyrolysis and gasification technologies have been around for decades, but the inability to develop these technologies on a commercial scale in an economically viable manner has hindered their application to treat waste. High up-front capital costs, the need for a highly skilled, educated labor force to run and monitor the equipment and processes, and the often-required third parties to further refine or blend the fuel outputs have all limited their widespread development.
Other factors have also impacted their application. Many past pilots and trials of these conversion technologies did not yield very desirable end products due to a combination of the technology itself and the difficulty in securing the correct feedstock for the different systems to work efficiently. Since plastic-to-fuel conversion technologies only treat the mixed plastic and scrap plastic portion of the waste stream, they are not a comprehensive solution for municipalities who want landfill alternatives for their entire MSW stream.
Thermal conversion processes like pyrolysis and gasification have raised concerns similar to those surrounding waste-to-energy incineration, including environmental impacts from emissions generated, the landfilling and potential leachate from the residual ash or slag left after treatment of feedstock, and the possible use of recyclable materials as feedstocks having negative impact on material recovery rates (however, many countries with high energy recovery rates also have high recycling rates).
The public’s complaints about the noise, smell and aesthetic appearance of WTE facilities may translate to all facilities employing conversion technologies.
Poised for GrowthRising energy and fuel costs continue to drive the need for further production of both renewable and alternative fuels, and MSW is poised to become an increasingly reliable source. Currently, 14 states have classified MSW as a preferred resource under their Renewable Portfolio Standards (RPS) policies and some – including New Mexico, Montana and Virginia – have incentive policies in place that promote MSW as a renewable resource. In addition, Missouri not only recognizes the benefits of fuel production from waste, but classifies pyrolysis and thermal depolymerization of waste materials as renewable energy production and provides tax incentives for MSW facilities.
Now, with increasing separation and collection of organic waste and more efficient sorting and separation of MSW, an increasing feedstock supply to serve as inputs for these processes can be found in the rejected, non-recycled material and plastic scrap from local material recovery facilities. In addition to serving as a much-needed fuel and energy source, these conversion processes could help divert non-recyclable waste from US landfills. And internationally, the technologies are being targeted to potentially combat diminishing landfill capacity, while avoiding the increasing cost of landfill tipping fees. These technologies may also help countries comply with increasingly stringent legislative requirements related to landfilling of waste, such as the EU Landfill Directive, which specifies required reduction in the percentage of certain wastes landfilled, waste acceptance criteria, and treatment requirements before landfilling.
Commercial ExpansionThe benefits of plastic-to-fuel conversion technologies have prompted significant developments in recent years to employ the processes on a commercial scale in Asia and the EU.
In Thailand, landfills are being mined at two locations to recover metals for recycling, organics for anaerobic digestion (another conversion technology) to create biogas, and plastics for a plastics-to-fuel system created by Polymer Energy to make oil.
In the UK, investments for plastics to fuel pyrolysis technologies, including the efforts by Cynar Plc. to build 10 facilities in the next three years modeled from their active commercial scale plastics to fuel facility in Ireland, is indicative of the country’s attempt to increase its plastics diversion and recovery rates using these technologies.
Japan, often at the forefront of advancing plastics-to-fuel technologies, has multiple active plastic-to-fuel facilities, mainly employing pyrolysis technologies to treat MSW and industrial scrap feedstocks.
In China, the company Plastic Advanced Recycling Corp. employs two systems to treat waste plastics that have been rejected by recyclers and paper mills.
Germany uses gasifiers mainly in small-scale applications for combustion and heating purposes, primarily through the treatment of biomass, but is exploring larger scale pyrolysis and gasification applications to treat certain fractions of MSW as Germany attempts to maximize the energy value of all their waste with virtually no landfilling.
Pilots Hold PromiseIn January 2012, a report titled “Environmental and Economic Analysis of Emerging Plastics Conversion Technologies” prepared for the American Chemistry Council by RTI International, took a gate-to-gate life cycle inventory approach (limited in scope) by reviewing data from a number of sources including, but not limited to, technology vendors, publicly available literature, federal reports, industry reports and trade associations, to quantify the inputs and outputs of comparable technology systems. The study, while not comprehensive, estimated energy and carbon equivalent emissions savings using gasification to treat one ton of MSW, and using pyrolysis to treat one ton of waste plastics, compared to the disposal of the wastes within a landfill.
In the US, there is a growing interest in the application of conversion technologies to help meet waste management, energy and fuel needs, particularly through gasification technologies. The US Department of Energy’s World Gasification Database 2010, which tracks the operating and pilot-level gasifiers around the world, forecasts “with 63 percent of total planned capacity growth, North America has the potential to lead the world’s regional growth through 2016.” But to date, only about seven gasification demonstration and commercially operating facilities were located in North America that process post recovered MSW and/or waste plastics. It’s estimated that it will take nearly 5 - 10 years for these facilities to transition to commercial scale operations, so the opportunity for these facilities to be an economically realistic and environmentally beneficial option for MSW diversion from the landfill will depend greatly on the success of the first generation of facilities.
A number of pilot scale plastic-to-fuel facilities employing pyrolysis technologies are currently being tested and funded domestically. These technologies are further along than pyrolysis or gasification technologies focused on treating mixed MSW. Agilyx, Climax Global Energy, Polyflow, Envion, GEEP, JBI, and Vadxx are just a few of the companies with pilot-scale pyrolysis facilities in the U.S., with Agilyx’s backed by companies such as Waste Management, the world’s largest waste management firm, and Total S.A., a large international oil company. These types of partnerships, if proven to produce a successful end-of-life management of waste plastics, could increase the management of the non-recyclable, post-MRF-processed plastic portion of the municipal and industrial waste stream for use as fuel while avoiding disposal in increasingly burdened landfills.
More Research NeededWith only a small number of active conversion facilities in North America – primarily demonstration plants operating in batch test modes, not with the continuous supply and treatment of proper feedstocks – more research is needed to responsibly and accurately determine the environmental aspects of the application of these conversion technologies and assess the environmental life cycle aspects of larger-scale thermal conversion technologies against comparable end-of-life alternatives such as WTE mass burn incineration and landfilling with and without methane capture. While conversion technologies may provide a useful treatment method to post-sorted and processed non-recyclable plastics and mixed MSW, their larger scale application is still young. The waste management hierarchy set forth for member states within the EU Waste Framework Directive prioritizes reuse and recycling of waste materials over recovery (for energy) or disposal (landfilling). Unique end-of-life options for problematic plastic waste can be beneficial moving forward, but efforts to reduce our overall production of waste, while improving diversion and recovery rates to maximize mechanical plastic and materials recycling, should be the focus of improving waste management chains globally. As the environmental and economic impacts of conversion technologies are further investigated, their position within regional waste management hierarchies will become clearer.
American Chemistry Council
US Department of Energy