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Appendix D: CO2 as a feedstock for polymer processing
Polymers are made up of large chains of repeating structural units, generally formed with a carbon backbone, and displaying a wide range of physical properties. Polymers can be created form natural sources (such as rubber) or synthetic sources.
Currently, The most widely used feedstock in polymer production is petroleum derived, such as ethylene or propylene which, once reacted, make-up chains in polyethylene (PE) or polypropylene (PP), respectively. PE and PP represent the largest volume of polymers currently produced. PE is used to produce a range of items including plastic bags, milk bottles and film wrap. PP creates and forms parts of item such as automotive components, textiles and polymer banknotes.
A new approach to polymer processing is to combine traditional feedstocks with CO2 to synthesise polymers and high value chemicals. The technology transforms waste carbon dioxide into polycarbonates using a proprietary zinc based catalyst system, which reacts CO2 and epoxide molecules. An epoxide is a three-membered ring molecule, such as ethylene oxide. Based on the type of epoxide used, The polymer will have different properties – hard, soft, transparent, or opaque. The zinc-based catalyst allows the CO2 to react at low temperature and pressure in a very efficient manner, providing a low energy pathway for utilising CO2 to manufacture plastics and chemicals.
The polymers created by this process are polypropylene carbonate (PPC) and polyethylene carbonate (PEC). Such polymers can contain up to 50 per cent carbon dioxide or carbon monoxide and therefore have a significantly reduced carbon and energy footprint compared to the materials they will replace. Therefore this technology creates a useful demand for CO2 as a product, which waste CO2 sources could supply, while reducing demand for finite oil based feedstocks.
The potential of CO2 as a feedstock was discovered back in 19698, when CO2 and epoxide were first copolymerised over a zinc catalyst by researchers. Having a widely available feedstock was a significant discovery, however the process was limited at the time by needing large amounts of energy to break the CO2 bonds and form polymer chains.
Through the use of a new proprietary catalyst which is claimed to reduce the energy of polymerisation, production of CO2 based plastic material is currently performed on a pilot scale by Novomer Ltd at Kodak Speciality Chemicals facility in Rochester, NY, and has been since December 2009. To date, Novomer have demonstrated the process in a 1,500 litre batch reactor and are investigating processing polymers using a continuous flow reactor to improve production cost.
Simultaneously, The polymers are being tested in a range of conversion processes that include thin film extrusion to blow moulded bottles. Materials produced are being offered to potential customers for testing. Testing has indicated Novomers plastics are comparable or superior to traditional petroleum based plastics.
In March 2010, Novomer partnered with Praxair to supply the required repurposed CO2 and Kodak Specialty Chemicals, a unit of Eastman Kodak to support polymer process development and scale-up. At the end of the project, in addition to enabling commercial-scale manufacturing capabilities for sustainable materials with several contract manufacturers, it is expected that several products will be customer qualified requiring commercial scale production of PPC polymers on a global basis.
Using CO2 as a polymer feedstock is possible through the use of a zinc based catalyst system, which reacts CO2 and epoxide molecules via a low energy pathway. Research into the catalyst system was investigated and developed by the Coates group, a part of Cornell University. The catalyst is now the system used by Novomer in their pilot plant. Novomer is involved in a range of development activities, from polymer synthesis to application testing.
Novomer are currently operating a pilot scale plant and are developing the process towards commercialisation, by investigating production of the polymer through a continuous flow reactor to improve costs. The most economical location for a commercial facility with access to CO2 feedstock is also being determined.
The polymer itself is being developed with specific focus on optimisation and testing which impurities can be tolerated in the CO2 supply source, The type of potential conversion processes (e.g. blow moulding and thin film extrusion) and testing of properties by potential customers to determine future applications.
Assisting Novomer to develop its polymer for commercial production, The following grants have gone into funding the above activities:
- Department of Energy US$2.6 million grant to demonstrate the innovative reuse of CO2.
- New York State Energy Research & Development (NYSERDA) US$475,000 for two phases of work, included a feasibility study and commercialization activities for the coatings and packaging markets.
- National Science Foundation US$400,000 to develop a continuous flow manufacturing process to make CO2-based polymers.
Based on Novomer figures from their proprietary catalyst, it is estimated their polymers contain up to 50 per cent CO2 by mass. CO2 will be generated from a point sources (e.g. syngas production, natural gas sweetening, coal power production), which will likely require an additional processing step to increase the degree of purification. Considering the global PP market alone in 2007 was 45.1 Mt (Novomer 2010), if PPC can compete with this market, CO2 utilisation could be significant. Total market share would see 22.5 MtCO2 used as feed stock annually.
As a finished product, PPC could have a very long life cycle depending on the application which it’s designed, giving CO2 potential permanence of storage.
Initial studies have also indicated that aliphatic (compounds in which carbon atoms are linked in open chains) polycarbonates can be recycled via hydrolysis reactions and in some cases biodegraded. Aliphatic polycarbonates in ideal compost conditions can degrade in six months9. CO2 will be released back into the atmosphere in this case, making CO2 storage non-permanent.
Polymers created in part from CO2 could replace traditional petroleum based plastics such as polypropylene, polyethylene, polystyrene and polyvinyl chloride if the properties of PPC remain the same for application in a wide range of areas traditional plastics are employed.
Potential markets where PPC could be used:
- Enhanced oil recovery: PPC surfactants can be pumped into oil reservoirs with supercritical CO2.
- The surfactants improve the solubility of CO2 increasing oil recovery and creating permanent storage for the CO2 within the surfactants.
- Coatings: PPC polyols can be used for a wide variety of coating purposes including: protective finishes for wood and metal in industrial and automotive applications, furniture, flooring and appliance coatings in domestic products and metal can linings for food products.
- Packaging: PPC display many of the properties thermoplastics do, including stiffness, impact resistance, and oxygen barrier protection, allowing for use in the food and general packaging applications. They can be also formed into a variety of forms using common manufacturing processes, such as:
- Injection Moulding
- Extrusion – Film and Sheet
- Blow Moulding
Barrier protection can be further increased using polyethylene carbonate (PEC), with barrier properties over 100 times (Novomer 2010) greater than petroleum-based plastics. Oxygen oxidises and promotes biological growth leading to food spoilage, so barrier layers are commonly added to packaging plastics, creating a potentially large market for this application.
Size of market
The global markets for polyethylene and polypropylene were approximately 80mt and 45mt respectively, representing the two largest polymer markets. The polymer market is expected to see a stable growth of c.6 per cent until 2015.
The main driver for the wide scale commercialisation of the technology is the potential to enter the polymer market. Even a relatively small market share of around 10 per cent would result in approximately 12.5 Mt of polycarbonate polymers produced annually. Additionally the ability to store CO2 on a semi-permanent basis will help drive the technology forward, particularly in regions where a carbon scheme exists.
Level of investment required (to advance the technology)
There is currently no publicly available information regarding the costs and investment requirements for implementation of the technology.
Potential for revenue generation
The potential revenue generation is high if, as Novomer claim, The polycarbonate plastics can be (a) accepted as a suitable alternative to existing petroleum based plastics and (b) sold at a competitive price. A small share of the existing polymer market could potentially provide stable returns.
At present, There are no stand-out commercial benefits for this technology, as it is unlikely that the polycarbonate products will be superior to those already existing in the plastics market, nor is it likely that they can be produced and sold at a lower price. Therefore, it is unlikely that consumers will choose the polycarbonate polymers over the existing petroleum based products.
Although Novomer claim that the technology can be used by existing polymer manufacturers it is doubtful that they will invest in the technology infrastructure without a significant identified economic benefit.
There are a number of benefits associated with the use of CO2 as polymer feedstock:
- The chemicals and materials contain up to 50 per cent carbon dioxide or carbon monoxide and are claimed to have a significantly reduced carbon and energy footprint compared to the materials they will replace.
- Traditional chemical industry infrastructure can be used to manufacture the plastic.
- Polymers are reported to have a broad range of material characteristics, from stiff solid plastics to viscous liquids, based on the molecular weight (or “size”) of polymer chains.
- PPCs are reported to have suitable stiffness, impact resistance, and oxygen barrier properties that allow them to be used in food and other flexible and rigid consumer packaging applications where these properties are critical.
- The use of carbon dioxide and carbon monoxide as feedstock instead of the corn-based feedstock used by other biodegradable plastics, means that the production of plastic will not compete with food production.
- Traditional barrier protection polymers (e.g. ethylene vinyl alcohol (EVOH) and polyvinylidene chloride (PVDC)) contribute greenhouse gases through large energy demands in the manufacturing process. PEC has similar properties yet sequesters CO2 and will in turn displace the CO2 of manufacture if the original product is replaced.
There are a number of significant issues that need to be resolved for successful development of the technology. These include:
- Technology is still at a relatively early stage – it has only been demonstrated at a small scale (using a batch reactor).
- Being aliphatic polycarbonates, degradation could occur in as short as 6 months under the right compost conditions. CO2 will be released back into the atmosphere in this case making CO2 storage non-permanent.
- CO2 is a very stable molecule and takes significant energy to split and allow reaction. Therefore this process was traditionally expensive and would contribute significant green house gas emissions on a commercial scale of production through the energy demands (assuming fossil fuel generated power). Research into new catalysts like Novomer have performed could improve this by lowering the activation energy of reaction. This is important as the cost of production must be equivalent to traditional polymers if CO2 constructed polymers are to compete commercially.
- The source of CO2 and the purity required could mean additional polishing at the point of source is required, increasing cost.
- The main market target is the packaging industry which is a low end application so acceptance will be entirely driven by cost. PPC will have to compete with traditional polymers on a cost basis to win market share, otherwise it will be left to high end niche applications such as medical devices.