Abstract
This work presents an in-depth kinetic thermal degradation comparison between traditional monocationic and the newly developed dicationic ionic liquid (IL), both coupled with a bromide (Br−) anion by using non-isothermal thermogravimetric analysis. Thermal analyses of 1-butyl-1-methylpyrrolidinium bromide [C4MPyr][Br] and 1,4-bis(1-methylpyrrolidinium-1-yl)butane dibromide [BisC4MPyr][Br2] were conducted at a temperature range of 50–650 °C and subjected to various heating rates, which are 5, 10, 15, 20 and 25 °C/min. Thermogravimetric analysis revealed that dicationic IL, [BisC4MPyr][Br2] is less thermally stable compared to monocationic [C4MPyr][Br]. A detailed analysis of kinetic parameters, which are the activation energy (Ea) and pre-exponential factor (log A), was calculated by using Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Starink. This study revealed that the average Ea and log A of [BisC4MPyr][Br2] are lower than [C4MPyr][Br], which may be contributed to by its low thermal stability. Conclusively, it proved that the Ea and log A of ILs are strongly related to the thermal stability of ILs.
Highlights
The first ever ionic liquids (ILs) were founded by Paul Walden in 1914, as he discovered ethyl ammonium-nitrate [EtNH3 ][NO3 ], which had a melting point less than 12 ◦ C [1]
The measurement was conducted at room temperature and the chemical shift was reported in parts per million with TMS as an internal standard
This indicates a better thermal stability of mono-[C4 MPyr][Br] compared to [BisC4 MPyr][Br2 ]. This result is opposed to studies performed by Bender et al and Fareghi et al, in which they reported a better thermal stability for dicationic imidazolium-based ILs [28,29]
Summary
The first ever ionic liquids (ILs) were founded by Paul Walden in 1914, as he discovered ethyl ammonium-nitrate [EtNH3 ][NO3 ], which had a melting point less than 12 ◦ C [1]. This discovery has become a foundation that inspires researchers to synthesize various ILs, such as 1-ethylpyridinium bromide-aluminium chloride [C2 Py][Br-AlCl3 ], 1-butylpyridinium chloride-aluminium chloride [C4 Py][Cl-AlCl3 ] and 1-buty-3-methylimidazolium chloride [2,3,4]. Thermal stability, viscosity, hydrophobicity and conductivity, can be changed according to the application of interest, due to the availability of various cation and anion combinations [7].
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