The issue of plastic waste is back in the headlines: the oceans are awash with tiny plastic particles, while landfill sites are bursting at the seams with burger boxes, discarded toys and other plastic debris.
Despite some well-established plastics recycling programmes – notably for PET soft drink bottles and PVC window frames – many forms of plastic are difficult to recover. Everything from crisp bags to clingfilm are simply thrown into general household waste, giving them a fast track to landfill.
There is, however, an emerging technology – called ‘plastics-to-oil’ (PTO) – that will convert potentially any waste plastics back into the molecules from which they were derived. The resultant oil can be purified and used like other oils: as fuel, or even as a building block for new plastics and other chemicals. The chemistry is fairly straightforward. Essentially, the plastics are subjected to pyrolysis – ie heated at high temperature in the absence of oxygen so that it does not combust – which degrades the long polymer chains into shorter hydrocarbon molecules.
According to the American Chemistry Council (ACC), this technology has the potential to process one-fifth of all the plastics going into US landfill. A number of companies – mainly in the US – are now trying to commercialise the process.
‘The basic chemistry in each case is the same,’ says Priyanka Bakaya, ceo of PK Clean, which runs a PTO facility in Salt Lake City, US. ‘It’s how you do the processing that makes the difference.’
PK Clean was spun out of the Massachusetts Institute of Technology (MIT) by Bakaya and chief technology officer Benjamin Coates, who designed and built the plant from scratch rather than using adapted off-the-shelf technology. ‘We looked at competing systems and thought we could make one that was more efficient and cost-effective,’ says Bakaya. PK’s plant, she says, has low capital and operating costs and a quick payback period. ‘We’ve made it highly automated, and try to recycle as much energy as we can,’ she says.
The process is continuous – rather than batch – and can be optimised to run at smaller throughputs. The ability to remove contaminants and use catalysts to drive the reaction help to make the process commercially viable.
Currently, PK Clean processes 10t of plastics every day, which it sources almost exclusively from two local materials recycling facilities (MRFs), to produce 66 barrels of oil – nearly 3000 gallons. The company is also looking to source plastics from local companies, as well as initiating a scheme to encourage restaurants to collect plastic packaging that would otherwise go into general waste. ‘Our current output is about as much as we can manage and the local supply of raw material is at the limit’, explains Bakaya. But there are many other areas across the US, with larger populations, she says, and her plan is to duplicate the Salt Lake City plant at different locations across the country – setting up a network of joint ventures, or selling plant equipment to new operators.
Revenue from the business is the oil, and while Salt Lake City is already home to five refineries – and can produce oil at a far cheaper price– it does at least mean there is a local market for PK Clean’s product. ‘There are buyers around and it’s a good fuel,’ says Bakaya. ‘Rather than sell directly, we usually work with middlemen who blend our product with other oils.’
PK Clean is not alone in its interest in plastics-to-oil processing. Around 1500 miles east of Salt Lake City – in the heart of the Midwest – RES Polyflow is investing in the technology to process everything from carpets and tyres, through partially filled ink and toner cartridges, to packaging film, automotive shredder residue and even buckets containing dried paint residue.
Construction of its new $90m facility, in Ashley, Indiana, will begin in mid-2016 and is expected to handle up to 60t waste/day and employ 136 people when it opens. RES already operates a smaller PTO plant at its headquarters in Perry, Ohio. At peak production, the company expects the new plant to be producing an annual 17m barrels of oil – specifically low-sulfur diesel fuel, octane enhancers and gasoline blendstocks – from around 100,000t of plastic scrap. Additional refining will provide other aromatics.
RES is actively encouraging companies with ‘difficult to recycle polymer or rubber material’ to get in contact – to ‘convert these items into marketable energy products and turn a cost centre into a profit centre’.
RES Polyflow is a member of the ACC’s Plastics-to-Fuel & Petrochemistry Alliance, with Agilyx, Cynar and Vadxx. Agilyx claims its Generation 6 technology can produce five times more energy than it consumes. Cynar, a largely European-based company, has plants in Spain and Ireland, and produces three different liquid fuels with its TAC technology. US-based Vadxx says it uses off-the-shelf equipment – and a patented process – to generate energy by ‘cooling, cleaning and cooling’ plastics waste. The company aims to process 60t/day of waste plastics, using its modular processing system, and plans to open up to 100 similar facilities across the US.
ACC has high hopes that the technology can grow into a thriving industry sector. In a report published in October 2014, the council estimated that the US could support up to 600 PTO facilities – which would employ some 9000 people.
ACC envisages two different scenarios, each of which could hit the target of processing 20% of all landfilled plastics. The first assumes a $10.5m investment per plant – which would handle 10,600t/year of plastics. The second, costing around $18.8m, would process 18,300t/year of material. In total, 600 small plants or 350 large plants would have an output of around 6.4m t.
According to the report, as well as direct employment, the plants would support an extra 17,000 jobs in industries related to plastics recovery.
The ACC does warn, however, that state and local governments need to update several relevant laws in order to stimulate the market, arguing that outdated regulatory definitions – such as those for solid waste – have been overtaken by PTO technologies. ‘Definitions of the solid waste code are not written for the technologies of today and may be outdated. This creates a significant barrier for new innovations, such as plastics-to-oil technologies,’ says the ACC.
Crucially, the report finds that PTO plants should be regulated as manufacturing facilities, rather than solid waste disposal facilities. This is because most plastics brought to these facilities have already been sorted – and so are effectively feedstock, not waste. ‘Solid waste should only describe those materials that cannot be sorted and upgraded for re-use,’ the report states.
Hydrocarbons are not the only fuel obtainable from plastics. Hydrogen from the phenolic plastics used in printed circuit boards (PCBs) is another possibility. A team of international researchers, led by Andoni Salbidegoitia at the University of the Basque Country in Spain, has developed a technique to break down the plastics in PCBs and generate a clean hydrogen stream (Fuel Processing Technology, doi: 10.1016/j.fuproc.2015.01.006).
There is certainly no lack of raw material for the process. Waste electrical and electronic equipment (WEEE) is a mounting problem. The researchers say that around 40m t are generated every year, of which only a fraction is treated or recycled. As well as having a large plastics content, the PCBs also contain metals – some valuable, like gold and palladium, and some hazardous like lead and cadmium.
In the process, the PCBs are pulverised in a grinder, mixed with lithium, potassium and sodium carbonates, and nickel powder. Steam gasification takes place at 550–675°C, which Salbidegoitia explains is lower than the traditional process because of the eutectic carbonate mixture and the nickel. The technique can recover metals from the waste, and convert the plastics into usable hydrogen. ‘We obtain hydrogen at 80% purity,’ says Salbidegoitia. The hydrogen gas could be sold as a raw material to petrochemical refineries, or it could be purified and used in fuel cells.
Two reactions are taking place at the same time, he says: pyrolysis of the phenolic material to form carbon char; and gasification of the carbon char to form hydrogen, carbon monoxide and carbon dioxide. The team has applied for a Japanese patent on the technique, and hopes to extend the technology to the US and Europe in future. Meanwhile, the researchers are trying to understand the mechanism of the reactions to optimise the process so that it is commercially viable.
Whether a process is converting WEEE plastics into hydrogen or waste plastics into oil, the technical problem is less about the chemistry and more about the engineering. But the main challenge is far more fundamental: diverting waste plastics away from landfill and into either a recycling plant or a PTO facility.
Despite being non-natural resources, these feedstocks are almost limitless: for plastic bottles alone, the amount collected in the US in 2014 was 1.4m t, less than one-third of the total. With the right collection schemes in place – for these and other plastics – that’s an awful lot of oil to be made.
Meeting the challenges
A study published in June 2015 by the American Chemistry Council (ACC) and carried out by the Ocean Recovery Alliance, identified the main challenges to PTO as:
- variable feedstock quality: certain resins produce higher liquid petroleum yields, while high contamination rates can lead to greater char management costs and higher chlorine production;
- feedstock volume: while PTO targets resins that are not easily recycled, it may end up competing for ‘traditional’ plastic feedstocks;
- wastewater: processes that de-salt and condition oils, for example, will need to add this back-end process – which may raise costs;
- customers: relatively small output volumes mean there may be limited demand for the products;
- funding: high levels of perceived investment risk and a limited understanding of the technology have restricted the number of potential investors.
- However, the study also found that a number of strategies are being put in place to try and address these concerns, including:
- improved process efficiency: many operators are configuring their plants for continuous rather than batch production, while reducing energy and water needs and boosting onsite electricity generation;
- correct system sizing: many suppliers are aiming for small, modular system designs;
- improved feedstock access: some operators are co-locating with a materials recycling facility (MRF) to ensure consistent supply and low transportation costs.
The report also sounded a warning regarding oil prices: ‘System economics may be negatively impacted with sustained low prices for crude oil and refined fuels. Operators must invest in additional R&D to ensure greater resilience to future drops in petroleum product prices.’
Slow going in the UK
While PTO may be gaining a pace in the US, this is not the case in the UK. An application to build the UK’s first PTO plant – by Australian-owned P-Fuel – has been withdrawn in the face of stiff local opposition.
The company applied to run a PTO facility in Appley Bridge in Lancashire, but around 1500 local residents signed an online petition against the plans. In addition, local planning officers recommended that the application be turned down on the grounds that the facility is contrary to a policy that safeguards the site for small scale rail-based uses and because the company did not demonstrate that the plant would not have adverse impacts on air quality and noise. The plant was to be situated within the local green belt – which angered local residents.
There seems to be some misunderstanding as to how the process works: media reports implied the plant would burn plastic waste to turn it into fuel, but P-Fuel says that its patented process – like other forms of pyrolysis – does not constitute burning because it is done in the absence of oxygen.
The company also claims that its process is more efficient that other PTO techniques. ‘The novelty of the P-Fuel design lies in the far infrared internal heating rods, which are not prone to “coking” problems,’ it says.
Lou Reade is a freelance science writer based in Kent, UK