Carbon Gasification from a Molten Carbonate Eutectic

Abstract

This investigation explores the impact of using a ternary alkali metal carbonate eutectic, i.e., Li2CO3, Na2CO3, and K2CO3 (43.5: 31.5: 25 mol%, respectively), as a catalyst for carbon gasification under CO2 and non‐CO2 atmospheres. Gasification under CO2, i.e., the reverse Boudouard reaction, is a well‐understood process with considerable commercial interest. However, in the context of direct carbon fuel cell (DCFC) operations, it is a parasitic reaction because it consumes fuel without producing power. In this study, the effect on carbon gasification of a common DCFC electrolyte is examined. Thermogravimetric analysis shows gasification occurring in the absence of a CO2 atmosphere, which has significant implications for DCFCs using alkali metal carbonates as the secondary electrolyte. A combined reaction mechanism is proposed which entails gasification from carbonate and carbonate decomposition.

The interplay between ternary molten carbonate and biomaterials during pressurized slow pyrolysis

“…In addition to molten carbonate decomposition (eqn (1)), salt vaporisation and carbon–carbonate gasification (eqn (2)) are also expected to occur. 42,44 The reverse Boudouard reaction would also occur at these increased temperatures and has previously been proposed to be enhanced in the presence of molten carbonates as catalysts 5,42 as shown in eqn (3).C + CO 2 → 2COThis means mass changes observed at 800 °C could originate from several chemical reactions (eqn (1), eqn (2), and eqn (3)) and physical phenomena (eutectic vaporisation).…”

“…42 A number of other phenomena are also observable for carbonate salts when temperature reaches above 750 °C. Evidence suggests the salt mixture evaporates to an extent, 43 decomposes under N 2 via eqn (1) 44 and in the presence of carbon particles will be consumed in a carbon/carbonate gasification pathway (eqn (2)): 45 M 2 CO 3(1) → M 2 O (s) + CO 2(g) M 2 CO 3(1) + C (s) → M 2 O (s) + 2CO (g) These observations suggest that during slow pyrolysis treatment of biomaterials with ternary eutectic carbonate, the impact of salt will vary within the temperature range of 350 °C to 900 °C depending on final temperature. 19,42,43 Although additive pyrolysis is heavily studied, the consequence of both additives and pressure on the slow pyrolysis process, and resultant biochar's morphology, is still vague.…”

Modification of Biochar Formation during Slow Pyrolysis in the Presence of Alkali Metal Carbonate Additives

“…26−28 Increasing the number of components has the advantage of lowering the melting point. Commonly used in a direct carbon fuel cell (DCFC) 29,30 or molten carbonate fuel cell (MCFC) system, the reason why it is selected is because it has the lowest melting point of any carbonate combination, and therefore, the liquid phase is more likely to impact the Further, most of the available publications investigate fast pyrolysis or gasification of carbon materials in a bath of molten carbonate, 31−33 which preferences liquid and gaseous products of the pyrolysis process.…”

“…Molten salts also have shown catalytic behavior for a variety of reactions, particularly in carbonaceous fuel gasification and pyrolysis. , Molten salts consist of high thermal stability and high heat capacity, which can also be used as a moderate catalyst, particularly in gasification reactions. − As a result of the high melting point of molten salts, many researchers prefer to apply a binary or ternary mixture of salts rather than a single substance. − Increasing the number of components has the advantage of lowering the melting point. Commonly used in a direct carbon fuel cell (DCFC) , or molten carbonate fuel cell (MCFC) system, the reason why it is selected is because it has the lowest melting point of any carbonate combination, and therefore, the liquid phase is more likely to impact the devolatization of the biomass, which happens in this temperature region.…”

Review of molten carbonate-based direct carbon fuel cells

“…3, which shows that: the decomposition of carbonate can also produce CO 2 ; it has an influence on the DCFC performance (Eq. 5) [104]. One investigation showed a noticeable increase in over-potential at a higher current density, owing to the mass transfer process being prevented, but it was easy for the released CO 2 gas to make contact with the carbon and ions at the anode again, with a long-term discharge recorded [105].…”