Sustainable Conversion of Carbon Dioxide into Diverse Hydrocarbon Fuels via Molten Salt Electrolysis

Ossama Al-Juboori,Farooq Sher,Tahir Rasheed,Saba Rahman,George Z Chen

doi:10.1021/acssuschemeng.0c08209

Abstract

In recent decades, the unlimited use of fossil fuels mostly for power generation has emitted a huge amount of carbon dioxide in the atmosphere which in return has led to global warming. Here we use green technology, the molten salt electrochemical system comprising of titanium and mild steel as a cathode with graphite anode whereas molten carbonate (Li2CO3-Na2CO3-K2CO3; 43.5:31.5:25 mol%), hydroxide (LiOH-NaOH; 27; 73 and KOH-NaOH; 50:50 mol %) and chlorides (KCl-LiCl; 41-59 mol%) salts as electrolytes This study investigates the effect of temperature, feed gas ratio CO2/H2Oand use of different cathode materials on hydrocarbon product along with current efficiencies. Gas chromatography and mass spectroscopy have been applied to analyze the gas products. According to GC results, more specific results in terms of high molecular weight and long chain hydrocarbons were obtained by using titanium cathodic material rather than mild steel. The results revealed that among all the electrolytes, molten carbonates at 1.5V and 425˚C produced higher hydrocarbons as C7H16 while all other produced CH4. The optimum conditions for hydrocarbon formation and higher current efficiencies in case of molten carbonates were found to be 500oC under a molar ratio of CO2/H2O of 15.6. However, the current efficiencies do not change on increasing the temperature from 425 to 500oCand is maintained at 99% under a molar ratio of CO2/H2O of 15.6. The total current efficiency of the entire cathodic product reduced clearly from 95 to 79% by increasing the temperature under a CO2/H2O ratio of 9.2 due to the reduction of hydrocarbon generation in this case, despite the formation of C7H16. Therefore, due to its fast electrolytic conversion rate and low cost (no use of catalyst) the practice of molten salts could be an encouraging and promising technology for future investigation for hydrocarbon fuel formation.

Highlights

With the increasing population, the demand for the energy resources have been increased drastically which in turn has resulted in the higher concentration of CO2 in the atmosphere
The molten salt used for electrolysis should possess the ability to be used at low operating temperatures without solidification in order to perform the process in the liquid state
Salt should have high CO2 capturing capacity and sufficiently negative cathodic limit in terms of the individual reduction of CO2 and H2O to CO and H2 respectively28. 3.1.1 Molten Carbonates The ternary mixture of Li2CO3-Na2CO3-K2CO3 (43.5, 31.5, and 25.0) mol% has been chosen as it provides the lowest melting point of 397oC amongst all forms of inorganic molten carbonates

Summary

Introduction

The demand for the energy resources (fossil fuels) have been increased drastically which in turn has resulted in the higher concentration of CO2 in the atmosphere. Air pollution due to the burning of fossil fuels has surplus the fatality rate of cardiovascular, pulmonary and other various diseases 2.the approach to minimize CO2 emission by using renewable sources of energy including solar, wind, geothermal as well as nuclear have gained much attention in the last few years[3, 4]. These renewable resources do not include sequestration of CO2 through their electricity generation. Solid oxide electrolysis, photo catalytic reduction, proton exchange membrane, thermochemical cycles and electrolysis using molten salts are the various types of CO2conversion techniques explored in recent years[6,7,8]

Methods

Results

Conclusion