Solar STEP coal conversion: Fully solar-driven thermo- and electrochemical process for efficient transformation of coal to light fuel plus hydrogen

- Solar STEP coal conversion process is without the input of any other forms of energy and chemicals.
- The process gains the combination and coupling of thermo- and electrochemistry for the reduction of the working potential.
- The process could be operated at 320 °C or lower temperature under the atmosphere pressure.
- High Efficiency of Solar STEP Coal Conversion is explored in the process.
- The products exhibited the methane and O-containing organic compounds plus hydrogen with low CO2 emissions.

In this paper, the Solar Thermal Electrochemical Process (STEP) for coal conversion has been successfully introduced and developed for theoretical and experimental demonstration of efficient coal conversion to light fuel with perfectly coupling the solar thermo- and electrochemistry to lift the efficiency of solar utilization and lower endothermic reaction electrolysis potential. By adjusting two chemical processes powered by the solar thermal and electrical fields, the coal was efficiently and selectively converted to light fuel synergistically plus the hydrogen with the sole input of the solar energy and low emission of CO2. Just because the electricity is integrated into the thermolysis, it has found one way to combine the electrochemistry to the existing coal thermolysis technology so they work more efficiently with the easy selectivity of hydrocarbon fuel and O-containing compounds. The process, characterized with interaction of balancing and controlling the thermal and electrochemical components, provides lower potential and higher efficiency compared with the conventional coal thermolysis. The results show that the yields of the coal gasification and liquefaction were greatly improved with the coupling of thermolysis and electrolysis by reaching 38.5% and 48.8% at 360 °C. The analytical data reveal that the products consist of abundant hydrogen, dominant hydrocarbons and rare O-containing compounds. The yield and selectivity were easily controlled by tuning the temperature and electrolysis current. Based on the results of the experimental analysis, the pathway and mechanism are proposed and explained for the STEP coal conversion process. Due to the combination of the solar thermo- and electrochemical process, this mechanism is shifted from the one reaction of the conventional thermolysis to the dual reaction involving electro-assisted thermolysis and thermo-assisted electrolysis. This study has important implications for the demonstrations of a novel approach of the efficient and energy-saving conversion of coal to light fuel driven by solar energy. The process has realized a transformation of low grade energy to high grade one by the proper utilization of solar energy and rational distribution of the heat and electricity to specific chemical reactions.

134