By Dr Stanislav Fulev and Lyudmila Skokova, H&S Anlagentechnik
H&S Anlagentechnik has developed an innovative technology and reactor installations for the chemical conversion of flexible polyurethane foam residues to polyol. The technology is based on an optimised acidolysis process and produces high-quality recycled polyols at a suitable production scale.
In comparison to previous recycling methods, polyols generated by this H&S techno logy have good reactivity and do not contain primary aromatic amines (methylene and toluene diamine), which are hazardous and not acceptable in bedding and upholstery foams.
Polyurethane foam manufacturers of both rigid or flexible types are showing a lot of interest in recycling technology.
For flexible foam, this is because the methods previously used, such as rebound foam for carpet underlay and sports mats, are no longer economically attractive. Prices for scrap flexible foam have slumped, for example, from €1.1/kg several years ago to €0.30/kg nowadays.
Chemical recycling is a more efficient way to convert residues. Another factor is that polyol prices are rising permanently. Moreover, the 'green' aspect of recycling is increasingly important, as everyone is pushed to decrease CO2 emissions.
Recycling is also one of the ways to cut greenhouse gas emissions and a closed production loop is also a highly sustainable route.
For rigid foam scrap, prices for disposal are also rising tremendously. In Europe, such scrap can no longer be disposed of in landfill, so it must be incinerated, and that is quite expensive.
Applications for mechanical recycled rigid foam, as powder, are limited. Also, since an enormous volume of rigid scrap is generated by processors such as the big sandwich panel manufacturers, recycling small amounts ground up as a powder filler cannot use it all. Of course the growing price of polyols also plays a role here
H&S Anlagentechnik already offers reactors and technology for recycling rigid PU foam into polyol, based on glycolysis (for example, scrap from sandwich panel production etc). This scrap should also be separated by type, and any mechanical contaminations filtered out. The quality of the resulting polyol enables substitution of the virgin one by up to 20 percent without quality loss, even improving the lambda coefficient of the resulting PU foam.
The recipe is: rigid PU foam scrap 45%; DEG -50%; additives (catalysts) – 5%
New acidolysis process
Waste foams suitable for recycling in this way include various conventional flexible foams, without and with fillers such as calcium carbonate. The process is suitable for production scrap, as it needs pure, separated material, so it is not designed for post consumer foam. This is a solution for foam manufacturers to recycle their own production scrap and return material back into the production cycle in a closed-loop scheme.
This technology for recycling high-resilience flexible foam is now being further developed at H&S Anlagentechnik's Sulingen, Germany site.
Input materials are PU residues shredded into chips of different size, which are dissolved in polyether polyols with molar mass of 1.500 - 6.000 g/Mol and hydroxyl functionality of 3, in the presence of carboxylic acids and corresponding catalysts. The process temperature is 230°C and the batch cycle on an industrial scale takes 10- 11h.
The proportion of materials used is: PU foam scrap - 42%; basic polyether polyol - 44%; acids - 12%; and catalyst - 2%.
A reactor with a volume of St/batch was used. Its capacity allows users to generate 2500 t/a of recycled polyol a year (5 t/batch, 2 shifts = lOt/day, 250 days/year = 2.500 t(year).
The quality of the recycled polyol has been checked for reproducibility in several trials in an industrial-size reactor.
The high quality and proper reactivity of the recycled polyol means it can be used to substitute for up to 20-25 percent of a conventional polyol, without any influence on the physical and mechanical properties of the PU foam. This was proven by a reasonable number of production-scale runs on a continuous slabstock line.
Produced PU foams were conventional foams with density of from 22 up to 40 kg/m².
All parameters - compression set, hardness resilience, support factor, tensile strength and elongation at break - are in the range of the control samples (Table 2).
The application range of reclaimed polyols is very wide, from comfort to technical foams, where the percentage of the recycled component can be higher than 25 percent.
During recycling of slabstock foam it is important not only to carry out the first recycling cycle, but also to convert the resulting foam several times again.
This was done in laboratory and production re-recycling tests. These showed that the chemical and physical parameters of recycled polyol, such as OH number and viscosity, are in a tolerable range.
Physical and mechanical properties of the resulted PU foams show no major deviation from the initial properties. Recycled polyol can be produced over at least 20 recycle without changing the process recipe.
For industrial-scale purposes we designed a special reactor unit consisting of the reactor itself, necessary accessories such as heating and cooling units, as well as activating and cooling tanks. The batch volume of the middle sized reactor is 2 - 5 tonnes. Reactors of bigger volume can be also produced.
In conclusion, this work shows that flexible foams produced with recycled polyol made using H&S's acidolysis technology are comparable with original foams and could be introduced into the market with no quality loss. Moreover the technology enables foamers to utilise their production residues in a very efficient way by reclaiming material for re-use i production. This has additional economical benefits, due to reasonable savings in raw material costs.
The manufacturing costs of l tonne of recycled polyol is about €900 ($1244).
Savings in raw material costs arise because costs to manufacture the recycled polyol are 28-30 percent lower than the market price of the original basic polyether polyol.