Thermokinetics of alkyl methylpyrrolidinium [NTf 2 ] ionic liquids Effect of alkyl chain on thermal stability Khurrum Shehzad Quraishi 1 • Mohamad Azmi Bustam 1 • Sooridarsan Krishnan 2 • M. Irfan Khan 1 • Cecilia Devi Wilfred 2 • Jean-Marc Le´veˆque 2 Received: 11 July 2016 / Accepted: 22 November 2016 / Published online: 9 February 2017 Ó Akade´miai Kiado´, Budapest, Hungary 2017 Abstract The thermal degradation of two ionic liquids (ILs) was investigated using thermogravimetric analysis (TG) to establish a relationship between the thermokinetics and thermal stability. N-butyl, N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMPyrro][NTf 2 ] and N- octyl, N-methylpyrrolidinium bis(trifluoromethylsul- fonyl)imide[OMPyrro][NTf 2 ] were subjected to thermo- gravimetric analysis at varying heating rates of 5, 10 and 20 °C min -1 in the temperature range of 50–600 °C. The data obtained were analysed for thermokinetics using Ozawa, Kissinger and Starink methods using differential thermogravimetric (DTG) techniques, and Flynn–Wall– Ozawa (FWO), Kissinger–Akahira–Sunose (KAS) and Starink methods using TG techniques. The results pro- duced very high regression coefficients (R 2 ) values around 0.996, which exhibited that they were best fitted by the kinetics equations. The average calculated activation energy (E a ) of [BMPyrro][NTf 2 ] using FWO, KAS and Starink methods was 128.6, 123.6 and 124 kJ mol -1 , respectively, and 113.7, 107.8 and 108.2 kJ mol -1 , respectively, for [OMPyrro][NTf 2 ] using same empirical methods. This emphasizes that the activation energy is strongly related to the length of the side alkyl chain of a given IL. In other words, the longer the side alkyl chain, the lower the activation energy. The E a trends with degree of conversion (a) suggest that a single mechanism without formation of intermediates or short-life intermediates was followed by the pyrolysis kinetics. This study introduced thermokinetics as a tool to study the thermal stability of ionic liquids. Graphical Abstract 200 300 400 500 200 300 400 500 600 0.0 0.5 1.0 1.5 2.0 2.5 100 Temperature/°C Temperature/°C Mass/% Deriv. mass/% °C –1 05 °C min –1 10 °C min –1 20 °C min –1 100 80 60 40 20 0 424.5 °C 426.8 °C 473.2 °C Keywords Ionic liquid  Thermogravimetric analysis  Thermokinetics  Model-free methods  Activation energy Introduction Ionic liquids (ILs) are a class of organic salts having a very long range of liquid state compared to conventional sol- vents, owing to their lower glass transition and melting temperatures. Nowadays, they are considered as green solvents of choice at high temperatures due to their non- & Jean-Marc Le´veˆque jean-marc.leveque@univ-smb.fr 1 Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia 2 Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia 123 J Therm Anal Calorim (2017) 129:261–270 DOI 10.1007/s10973-016-5994-5