Products from sun and air

A PILOT plant containing an entire process chain to produce renewable fuels and chemicals from air-captured CO2 and solar power was launched today.

The Soletair demo plant was developed by Finland’s VTT Technical Research Centre and Lappeenranta University of Technology (LUT). Their aim was to explore a multi-sectoral approach to the future electrification of the chemical industry – when fossil fuels are no longer burnt, but hydrocarbons are still needed.

The project is based entirely at LUT’s solar power plant in Lappeenranta, and over the coming months will produce 200 L of fuels and other products for research purposes. It places the full process chain, from power generation to hydrocarbon production, in one location using four separate units. Units are mobile, and have been designed for distributed, small-scale production that can be increased by simply adding more.

The first of these units, the original solar photovoltaic power plant, powers the process. It includes 827 panels, both mono- and poly-crystalline silicone, over an area of 1500 m2, with a peak power of 206.5 kW.

The majority of power generated is used in the second step of the process, hydrogen production. High-purity hydrogen gas is produced at elevated pressures through proton exchange membrane (PEM) water electrolysis. This process can be connected to operate in tandem with real-time solar PV production data, or with user-defined patterns. Further along in the chain, hydrogen is used with recycled CO2 to produce renewable fuels, raw materials, and chemicals. It can also be used in chemical energy storage for a fuel cell, with losses during conversion.

The third unit is for direct air capture (DAC) of CO2 as a carbon source. The current DAC unit is a modified version of air-scrubbing units for civil shelters, using an adsorption/desorption process with solid amine-functionalised polystyrene spherical beads to trap CO2. Excess air is then purged, followed by heating to 80°C to produce CO2 gas and water. Heating and vacuuming are then applied for two hours to collect 3.8 kg/day CO2.

The fourth unit on site is the mobile synthesis unit (MOBSU), which uses Fischer-Tropsch synthesis to combine carbon and hydrogen and produce valuable products. Two production lines are currently being developed side-by-side, which are tailored for either natural gases or liquid and wax components. The process has two steps: first, CO2 is converted to CO by reverse water gas shift reaction, which balances a gas mixture of CO, CO2, H2 and H2O at 800 °C with a precious metal catalyst. Constant pressure is maintained, to avoid compression between process steps. Secondly, CO and H2 react to hydrocarbons.

The result is a wide range of products. The project’s coordinator, Pekka Simell of VTT, said: “The liquid hydrocarbon product contains about 30–35 wt% of gasoline fraction, C5–C12, and about 65–70 wt% middle-distillate fraction, C13–C22. In addition to liquid products, paraffin wax which can be hydrocracked to gasoline and middle-distillates is formed.”

Although the demo plant was launched just today, the individual units have been operated separately for a number of months. Simell acknowledged that during development a few issues had to be overcome.

“The major challenges have related to available pressure from the electrolysis and DAC units, and the need for compression to the synthesis operating pressure. In other words – what is the optimal operation pressure?

“Another issue is the optimal storage capacity for H2 and CO2, how often we need to run the synthesis unit to standby mode. We should get first answers to these questions during this project.”

VTT and LUT, who have invested €1m (US$1.1m) in the equipment, believe that information gathered during the project will be useful for the commercialisation of the technologies. After the piloting phase, synthesis units will be used in a number of EU projects over the coming years, and the partnership hopes that a platform will be established for conducting research with international companies.

For more information on the process, see http://soletair.fi/technical-specifications/