One reason the EU sent as much as 12.1 million tonnes of plastic to landfill (2013 figure) is that the waste material is a complex mixture of plastics which cannot easily be used to make new products.
Mixed plastic is difficult to separate, so once the higher value, easily identifiable plastics such as bottles are removed the remaining material has a relatively low value and landfill is often the only cost-effective solution.
While many technologies exist for separating mixed plastics, in the main they come with large capital and operational costs. This means that vast quantities of plastics are needed to run a commercially viable plastics recycling facility, with material being transported large distances to maintain the volumes of feedstock required.
As a result, only the ‘easiest’ and highest value plastics are sorted, with the remainder shipped off either to the Far East or the EU for landfill and incineration.
Studies have shown that up to 70% of plastic waste streams can be polypropylene (PP) and polyethylene (PE) which, when separated, are high-value plastics used in a wide range of products. But when mixed together, and with other plastics, their value is negligible. Existing technologies struggle to separate PP and PE because both float in water, so sink/float tanks are not useful, while a large amount is coloured black, which prevents optical or infrared sorters from being used.
Grangemouth-based Impact Solutions recognised this problem, and set itself a challenge to come up with a technology which could separate these two plastics on a scale which would allow local recycling facilities to invest in a cost-effective way.
As a small company with a large involvement in plastics R&D, Impact came across a technology that was being used to mix liquids and thought it could be used as a separation technology for waste plastics. Three years later, the company is now finalising its first commercial demonstration unit.
Impact first investigated the technology under a grant-funded project, supported by the Scottish Environmental Technology Network (SETN), to look at a fairly simple separation of polymers with very different densities: PE and polystyrene (PS) using water as a separation medium. The technology uses baffled oscillation where Impact ‘shuggles’ a mixed polymer/water slurry (with polymer granulated to approximately 10mm flake) to achieve separation. The lower density polymer moves to the top.
The initial work with SETN proved that there was potential in using this technology on a commercial scale, and a large programme of work was undertaken with the help of a Scottish Enterprise Smart award, lasting 18 months.
During this work, a breakthrough was made when, by clever design of the shuggler and optimising water flows, Impact was able to separate very close density polymers (PP and PE to 97% purity). Here the densities are 0.90g/cc and 0.95g/cc, respectively. Water was used as the separation medium rather than expensive lower, or higher, density fluids, which sets the technology apart from existing density separation systems.
Impact has been able to separate plastics with densities as close as 0.035g/cc by the technology. As part of the Scottish Enterprise grant project, Impact was able to demonstrate the separation of PP and PE and of acrylonitrile butadiene styrene (ABS) and high-impact polystyrene (HIPS) on a 10-litre (10kg an hour) lab-scale rig.
Due to the success and potential of the technology, a further project, supported by Zero Waste Scotland, enabled Impact to build a full-scale commercial demonstration unit which is now being operated at WRC, a commercial plastic recycler near Glasgow.
The technology was scaled up from a 10kg/ hr unit to a 1,000kg/hr unit over a period of three months, with the help of Wrights Recycling Machinery, a family-run business with 45 years of experience of designing and supplying recycling machinery, based in Guiseley, West Yorkshire. Wrights’ expertise in design and build allowed the technology to be scaled from lab size to a full commercial unit. A patent for the technology was applied for in 2014.
The commercial demonstration unit has shown that the technology – called the baffled oscillation separation system – is capable of separating these difficult plastics to 90+% purity at one tonne/hr (target 95% purity). Typically, the value of mixed waste PP/PE or ABS/HIPS can be increased by up to £200 a tonne if pure polymers (>90%) can be separated.
So for a unit capable of one tonne/hr, during one year it should process up to 2,000 tonnes with an added value of around £400,000. With the cost of the unit planned to be around a third of that, and with low operational costs, payback time will be less than six months for the waste operator. And with demand for pure PE and such from compounders, there are clear opportunities.
Impact sees the process being relevant for a wide range of feeds. The simplest separation is perhaps bottle-top regrind (BTR), which is a mix of PE and PP used for the bottle top and the seal, and small amounts of polyethylene terephthalate (PET), used in the bottle itself.
There is a large quantity of this material produced as a by-product of the recycling of PET bottles. But the compounders who use the resulting PE have to blend it away in small quantities so as to not introduce too much PP into their final product. Impact’s technology can separate out the PET and then produce 95% purity PE and PP. This then is very attractive to the compounders who will pay a premium for the pure polymer.
Most other PE and PP mixes can be separated using the technology, making it an ideal solution to process the mixed polyolefin bales that are found on waste sites around the UK. It is a straightforward process to grind the polymers to a 10mm flake size and then feed the separation unit.
Contamination in the form of heavy polymers (PET, PVC and so on) and dirt is taken out from the bottom of the unit. In the lab, Impact demonstrated that ABS and HIPS could be separated in a similar way. This is the area where the company will develop the system next because there are large quantities of mixed ABS and HIPS arising from postindustrial waste in the UK.
The technology separates three density fractions: light, medium and heavy. It should therefore be possible to separate a complex mixture of polymers by linking together multiple units, where the output from the light or medium fraction is then passed to a second unit for further separation.
To date there has been considerable interest in the technology across the UK industry, with a strong ‘pull’ from potential users. Impact believes the low capital cost of the equipment and low cost to operate will mean that the process can be utilised by almost all waste processors and not just restricted to large sites as per current sorting technology.
The commercial demonstration unit is now commissioned and Impact, along with its partner WRC, is starting a programme to optimise and define the separation characteristics across a wide range of feedstocks.
Impact will initially supply a small number of units to the marketplace and aims to start full commercial sales this month. Initially, its focus is the UK market, but the technology is applicable to the rest of the world, with a large potential market in the US. Plastic recycling is more established across the EU, with less destined for landfill, but large quantities are still sent for incineration with energy recovery.
Better separation will allow more pure waste polymers to be used by compounders, so reducing virgin polymer use. Impact believes its technology has great potential, and will help to divert a significant percentage of material away from landfill.
Steven Burns is development manager at Impact Solutions
- See the technology at the RWM show on the Wrights Recycling Machinery stand 5S10-T011