Appendix I: CO2 as a feedstock for liquid fuel production
CO2 as afor liquid fuel production is a broad category for CO2 reuse, which includes conversion of CO2 to a number of alternative fuel products, including formic acid, methanol, dimethyl ether, ethanol, and other petroleum equivalent products. To produce these varied end products, a range of CO2 conversion technologies are proposed.
In general the primary energy input for these conversion technologies is renewable energy, with the current proponents focused on solar and geothermal energy. This is an important requirement for these technologies, as generally they have relatively low thermal efficiency (e.g. relatively small fraction of the energy input is converted to useful fuel). Consequently, The primary energy input needs to have a low CO2 emissions intensity. If fossil-fuel based energy were used as the primary input into CO2-based liquid fuel production, more CO2 would be released than if the fossil fuel were used directly as a fuel.
Proponents have developed their technology to widely differing extents. Some processes / solutions are only beginning to be investigated in laboratories and with laboratory scale demonstration reactors. On the other hand some companies claim to be commercialising their respective CO2 to fuels technology, whilst at least one company (Carbon Recycling International) is constructing a commercial project.
Technologies at the fundamental research stage are predominantly being developed in the United States. For example,is exploring the performance of titanium dioxide nanotube catalysts in the sunlight driven conversion of CO2 and H2O to methane and other light hydrocarbons, and Sandia National Laboratories has constructed a prototype device (the Counter Rotating Ring Receiver Reactor Recuperator, ‘CR5’) for high temperature solar conversion of CO2 and H2O to using a metal oxide catalyst.
Technologies beyond the fundamental research stage are listed in the table below.
|Organisation||Fuel product||Technology status|
|Carbon Sciences, USA||Light hydrocarbons||Moving from laboratory towards commercialisation|
|Joule Unlimited Inc (Joule), USA||Ethanol and diesel equivalent products||Moving from laboratory towards commercialisation|
|Mantra Venture Group (Mantra), USA||Formic acid||In negotiations for first commercial demonstration|
|Carbon Recycling International (CRI), Finland||Methanol||Constructing first commercial plant|
Carbon sciences, USA
Carbon Sciences claim to have developed enzyme-based biocatalyst technology for conversion of CO2 & H2O to light hydrocarbons (methane, propane, butane). The light hydrocarbons can then be further processed to liquid fuels. Publicly available information relating to Carbon Sciences technology is extremely limited, but it is stated that the process is executed at low pressure and temperature.
Carbon Sciences has made claim to multiple patent applications in recent years, but a comprehensive search of the US Patent and trademark office has failed to locate such patent applications. No response was received from Carbon Sciences following a request for information. A formal evaluation of Carbon Sciences is not possible given the information void that exists around the technology.
Joule Unlimited Inc. (Joule), USA
Joule claims to have developed product-specific photosynthetic organisms that produce hydrocarbons as a by-product of metabolism, and that survive in brackish water. Joule has not publicly released a detailed description of the specific micro-organisms they intend to utilise in commercial applications. A review of their patent application material suggests it could be a genetically modified strain of bacteria, though a range of other possibilities exist (yeasts,etc.).
Joule’s primary energy input to the conversion process is un-concentrated solar energy. Joule claim their technology has the potential to yield 25,000 gallons ofper hectare, which for a plant located in an area with a good solar resource (for example, California) equates to an overall solar energy conversion efficiency of 2.4 per cent. This is not dissimilar to the energy conversion efficiency of crops.
With reference to illustrations on Joule’s website, along with articles in the press, it is possible to determine that Joule’s organisms circulate within glass reactors supported with a steel frame. This kind of arrangement is capital intensive, with analogies to be drawn with the costs of solar thermal arrays.
Joule differentiates themselves from algal biomass production, highlighting the fact that they don’t produce biomass (or at least the biomass: oil production ratio is very low). No response was received from Joule following a request for information.
Mantra Venture Group (Mantra), USA
Mantra’s technology produces formic acid by direct reduction (electrolysis) of CO2 in water. It requires an electrical energy input of 8MWh/t CO2, which represents an electrolysis efficiency of 20 per cent when the energy content of the end product (formic acid) is considered.
Carbon Recycling International (CRI), Finland
CRI’s technology producesby catalytic reaction of CO2 and H2. CRI is presently constructing a commercial demonstration plant in Iceland.
H2 is produced via electrolysis of water. Modern systems for electrolysis of water may have efficiency in the vicinity of 65 per cent. A concentrated stream of CO2 is developed using conventional capture technology applied to an industrial source. According to CRI patent material, The two gas streams are combined and compressed to approximately 5MPa before entering a reaction loop where the mixture is heated to ∼225°C, reacted over a metal/metal oxide catalyst to produce methanol and water (equilibrium composition ∼20 per cent to 25 per cent), passed through a counter-flow heat exchanger, Then though a condenser where the methanol and water are separated out. Following the condenser the gas stream is combined with new feed gas, passes back through heat exchanger and returns to the reaction vessel. PB estimates the thermal efficiency of the catalytic process is 75 per cent or better.
CRI’s preferred embodiment is probably a conventional geothermal power station, as it is a low-emission source of electricity that still produces enough CO2 (typically) to use as a feedstock for the methanol production process.
Carbon Sciences – There are no projects identified.
Joule recently closed an US$30 million funding round, with the proceeds to be directed towards pilot plant operations at Leander, Texas. Joule is claiming a system that will be commercial-ready by 2012.
Mantra advises that a demonstration project inis planned to commence shortly. No further information is available regarding the size, cost, or exact location of the project. Korea has a grid emissions intensity of 444kg CO2/MWh.
CRI is currently constructing a 4.2 million litre per annum commercial demonstration plant in Iceland. Publicly available information suggests the renewable methanol plant will be located adjacent to the 76.5MW Svartsengi Geothermal Power Station, which will in effect be the source of power and CO2 (and potentially water) for the project. Note thathas an estimated grid emissions intensity of ∼ 310kg CO2/MWh. If the power supply to the renewable methanol project is considered to be solely from the Geothermal Plant (rather than from the grid), Then the emissions intensity will be lower still (∼171kg CO2/MWh), and will further benefit from the capture of a portion of the plants CO2 emissions for methanol production (down to 173kg/MWh). The CO2 will be captured using an solvent process.
Methanol will be blended with conventional unleaded petrol and sold at Olis gasoline stations throughout the greater Reykjavik area. CRI has stated that Iceland is an attractive location for project development because the petrol: electricity price ratio is one of the highest in the world – obviously a key measure of the likelihood of success for fuel synthesis projects based on electrolysis.
As a replacement for fossil fuels, The potential market for CO2 derived fuels is large, and global. Consumption of fossil fuels for transport in 2007 was 2297 Mtoe (Million tonnes of oil equivalent).
The main driver to support the commercialisation of the technology is the potential to penetrate the transportation energy market which is expected to see significant growth in the forthcoming years.
The price will be sensitive to the economics in supply, demand and price of petroleum and other alternative fuels.
The main commercial benefit of this technology is to provide an efficient fuel for wide scale use in the transportation sector. It is highly likely that the current transportation fuel sources (namely derived from fossil fuels) will be unable to meet the forecast demands in the forthcoming years hence, commercialisation of this technology would enable it to capitalise on the energy shortfall.
In an ideal embodiment of the CO2 to liquid fuels concept, The CO2 feedstock is converted into an energy carrier, but the energy input is renewable or has very low CO2 emissions intensity. The ideal embodiment gives potential for a reduction in CO2 emissions as compared to the combination of an uncaptured CO2 and fossil-fuel based economy.
Proponents argue that the ability to use existing petroleum-based infrastructure (transport, distribution, storage, engines, and vehicles) is a benefit of the CO2-to-liquid fuels approach, assuming the liquid fuels produced are comparable to petroleum diesel or gasoline (which is not always the case).
The widespread use of this technology will help governments meet their targets for low and zero-emission vehicles.
Some critical barriers include the low efficiency and high capital cost that is a characteristic of some of the CO2-to-liquid fuel technologies. It is likely that some technologies will never overcome these cost barriers and will consequently not be commercial.
Furthermore, here we are focused on the conversion of CO2 to a liquid fuel, with the transport sector as the main market. A potential barrier is that alternative transport systems (such as electric vehicles with regenerative braking coupled to a renewable energy powered electricity grid) may be a more competitive solution, with significantly higher overall energy conversion efficiency. At present, electric vehicles already have lower running costs than petroleum fuelled equivalent vehicles thanks to the relatively low cost of off-peak grid electricity and the benefits of regenerative braking. It is possible that in the longer-term electric vehicles will prove to be significantly cheaper.