Martin is a senior PR consultant and CEO of Cleantech Media. Additionally, he writes as chief editor for the online-magazine cleanthinking.de. As a qualified and experienced journalist he supports start-up companies from the cleantech sector with strategic public relations solutions. Martin has been living and working in Leipzig, Germany, since 2006.
© sunfire© sunfire
Intelligent processes now enable the capture and conversion of atmospheric CO2 into environmentally friendly fuels. Cleantech firms Climeworks and sunfire have developed complementary technologies which facilitate both the effective filtering of CO2 out of the air and highly efficient hydrogen production. When carbon monoxide and hydrogen are mixed at 900 degrees Celsius they react to form synthesis gas – the basis for all long-chain hydrocarbons.
The Direct Air Capture (DAC) technology developed by the Zurich-based firm Climeworks AG over the last five years filters CO2 directly out of ambient air. It is based on a cycle of filtering and regeneration using a special solid filter material designed by Climeworks in cooperation with the EMAP research institute. The first step sees amines form a chemical bond with the CO2 and deposit themselves on the surface of the filter.
Once the filter is saturated it is heated to a temperature of approx. 100 degrees Celsius and releases CO2 with a high level of purity (99.9 per cent). The use of low-temperature heat is one of the key advantages of DAC technology and contributes to the profitability thereof. Whereas comparable techniques require the input of heat at a temperature of 800 degrees Celsius, the DAC technology developed by Climeworks sources around 90 of the energy required in the form of low-temperature heat.
Climeworks CO2 collectors filter 135 kilograms of CO2 per day and 50 tonnes of CO2 per year out of ambient air and can be installed in series in order to increase overall capacity where required. By way of comparison a car emits 150 grams of CO2 per kilometre and clocks up an average of approx. 15,000 kilometres per year. A single CO2 collector therefore offsets the CO2 emissions of 22 cars. The firm’s first industrial-scale CO2 filtering plant is set to be built in Switzerland in 2016 and will filter out an annual total of 900 tonnes of carbon dioxide which will be supplied to a nearby commercial greenhouse. The plant will consist of 18 CO2 collectors housed in three 40-foot containers. Climeworks will apply the insights gained during the project to the refinement of its products with the aim of using CO2 captured from ambient air for the production of synthetic fuels.
Complementary technology: High-temperature electrolysis from sunfire
This is where a partner such as sunfire comes in. The Dresden-based cleantech firm’s fuel synthesis technology is based on high-temperature steam electrolysis and can be reversed for the purposes of electricity generation. This reversible solid oxide cell (RSOC) technology is the first step in a Power to X process which continues with the production of synthesis gas which is then converted into long-chain hydrocarbons. End products include synthetic fuels such as gasoline, diesel and kerosene as well as waxes for the chemicals industry.
High-temperature electrolysis is a highly beneficial part of this process for a number of reasons. On the one hand it works at high pressure (> 10 bar) and at high temperature (> 800 degrees Celsius). On the other it splits gaseous water (i.e. steam) rather than liquid water into its constituent parts (oxygen and hydrogen). This is achieved at 90 per cent efficiency (in terms of calorific value). In contrast with other established electrolysis techniques (e.g. PEM or alkaline electrolysis) steam can be produced using waste heat from subsequent steps (enthalpy of reaction).
Another special feature of high-temperature electrolysis is the fact that the process extracts oxygen molecules rather than hydrogen molecules. This is of key significance as it also allows the Power to X process to be used to reduce the CO2 produced during steam electrolysis to carbon monoxide (CO) ready for synthesis (reverse water-gas shift reaction). The subsequent introduction of hydrogen yields a synthesis gas (CO and H2) which provides a basis for all long-chain hydrocarbons.
The synthesis gas can be converted into gasoline, diesel, kerosene and other raw products for the chemicals industry (-CH2-). Synthesis releases heat which is in turn used to vaporize water for the purposes of steam electrolysis. This makes it possible to achieve a high level of efficiency of around 70 per cent. sunfire has already successfully produced long-chain hydrocarbons using an industrial demonstration rig at its headquarters in Dresden, and in April 2015 Federal Minister of Education and Research Dr Johanna Wanka filled up her car with the first litres of synthetic diesel produced. The CO2 required can be captured directly from ambient air using the DAC technology developed by Climeworks, precipitated from biogas plants or extracted from other processes which give off waste gas.
The sunfire process is based on refined versions of both high-temperature steam electrolysis using solid oxide electrolysis cells (SOEC) and the water-gas shift reaction (the second step in the Power to Liquids process chain). What is more, sunfire is a true pioneer in the combination of these technologies with Fisher-Tropsch synthesis. This third step in the process is by far the most well-known element of synthetic fuel production, yet in many cases – for example in South Africa – Fischer-Tropsch synthesis is carried out using fossil fuels rather than CO2, water and green energy.
Environmental balance sheet and CO2 utilisation
The use of CO2 for the production of green hydrogen, waxes for the chemicals industry or synthetic fuels is accompanied by substantial environmental benefits. Even when used in combustion engines, synthetic fuel is at the very least carbon neutral. What is more, the use of wind power reduces direct emissions (i.e. the emissions caused as a result of rig operation) to zero – the “raw material” is nothing more than wind. The sunfire process therefore represents a fully closed carbon cycle as found in nature. CO2 is first extracted from ambient air using a Climeworks DAC unit. The sunfire rig then uses that CO2 to produce synthetic diesel which can be used to fuel combustion engines. The accompanying CO2 emissions equal the amount of CO2 extracted from the atmosphere and used to produce the fuel itself.
The main benefit is that the production of sunfire diesel requires exactly the same amount of CO2 as is emitted from the vehicle exhaust after combustion. This means that fuel production and combustion form a closed CO2 cycle. Total emissions (i.e. direct emissions from the combustion engine and indirect emissions attributable to rig production) have been determined with the aid of well-to-wheel analysis. The CO2 released by the combustion of synthetic diesel in an engine was found to equal the exact amount of CO2 extracted from ambient air for the purposes of fuel production. This essentially represents the closure of the carbon cycle and the achievement of CO2-neutral mobility. If all related emissions are factored in – including the construction and operation of the sunfire rig – total emissions from a vehicle run on synthetic diesel stand at less than 30 g/km (well-to-wheel). If fuel production is taken into account this represents a 70 % reduction when compared with vehicles run on fossil fuels.
The next step in the commercialization of sunfire’s technology is the realization of various projects. To give an example the next few months are set to see Boeing become the first partner to use sunfire’s RSOCs in the USA, with the two firms cooperating on the further development of the technology. Even once all technical aspects have been finalized the commercialization of the overall process will nevertheless still be dependent on political factors.
Since mid-2015, electricity-based fuels from non-biogenic sources have been included in legislation for the first time. More specifically they are now taken into account in the EU’s Renewable Energy Directive and Fuel Quality Directive as well as the German Federal Immission [sic] Control Act. The aforementioned EU directives have nevertheless yet to be adopted into national law. In Germany, a move by the Upper House to ensure the rapid, comprehensive implementation of those directives would be welcome. Switzerland is already a step ahead in this regard, yet even there the majority of investors are waiting to see what form national laws will take. With this in mind the legislative context is set to continue to play a decisive role in the further progress of Power to Liquids technology as it moves towards commercialization.