ORIGINAL ARTICLE Effect of thermo-responsive switchable solvents on microalgae cells’ disruption and non-isothermal combustion kinetics Emmanuel Galiwango 1 & Mukhtar Ismail 1 & Muhammad Sajjad Ahmad 2 & Sulaiman Al-Zuhair 1 Received: 20 April 2020 /Revised: 14 June 2020 /Accepted: 13 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract The effect of the exposure to thermo-switchable solvent (TSS) on cell wall disruption of Chlorella sp. microalgae was investi- gated. The combustion and kinetic behaviors of microalgae cells treated with TSS, which was maintained at its hydrophilic state for 1.5 h to disrupt the cell wall, were analyzed and compared with those of undisrupted cells. The X-ray diffraction (XRD) results showed a clear drop in the crystallinity of the TSS-treated samples, which was mainly due to the degradation of the cellulosic material. The results were confirmed from the thermogravimetric analysis, which showed a drop in the cellulosic material from 71.9% in the untreated sample to 49% for TSS-treated sample. The activation energy of TSS-treated sample from different non- isothermal models was 44.90–157.97 (FWO), 103.09–492.19 (KAS), and 100.60–478.89 kJ mol −1 (Starink). The values were lower at low conversions (x ≤ 0.5) than untreated samples whose activation energy was 70.67–152.98 (FWO), 195.38–465.58 (KAS), and 190.39–453.11 kJ mol −1 (Starink). The low activation energies for all models of TSS-treated samples indicate that less energy would be required for the thermal conversion processes, as compared with the untreated samples. The tested model- free methods reduce mass transfer limitations, with Flynn-Wall-Ozawa (FWO) compensating for experimental errors, whereas Kissinger-Akahira-Sunose (KAS) and Starink for providing precision to kinetic data depending on a good constant degree of conversion. The reaction mechanism was represented well by the Malek and Popescu. The results presented in this work provide deeper understanding of the effect of TSS on microalgae cell wall disruption. Keywords Thermo-responsive switchable solvent . Microalgae . Non-isothermal kinetics modeling . Characterization 1 Introduction Among the possible oil sources for biodiesel production, microalgae appear to be the most promising, owing to their high lipid productivity [1]. In addition, microalgae cultivation does not require arable land and many strains can grow in saline water. Furthermore, microalgae are photoactive micro- organism capable of fixing atmospheric CO 2 by photosynthe- sis, which adds the advantage of CO 2 emissions mitigation and at the same time eliminating the need for organic sub- strates. Microalgae naturally accumulate between 20 and 50% oil of its dry weight, which can be further enhanced under stress conditions [2]. At an average oil content of 30%, microalgae oil productivity of 58,700 L/ha, which is over ten times higher than that of all oil crops [3]. Among the various microalgae strains cultivated for biodiesel produc- tion, Chlorella sp. has been the most extensively studied [4]. The interest in these strains is mainly due to their rapid growth and relatively high oil content [5]. Testing 30 different microalgae strains showed that under optimum growth condi- tions, the lipid productivity of Chlorella sp. was in the range of 32–45 mg/L/day, which is among the highest [6]. For effective extraction of oil, the harvested microalgae have to be completely dried and their rigid cell walls have to be disrupted before introducing the extraction solvent. Conventional drying processes, however, are either time-con- suming, as in the case of sun drying, or energy intensive and expensive, as in the case of spray drying, and can cause deg- radation of thermosensitive compounds [7]. It has been report- ed that by eliminating the drying step, a significant energy saving, reaching 25%, can be achieved [8]. In addition, microalgae cells have rigid cell walls, which comprise mainly * Sulaiman Al-Zuhair s.alzuhair@uaeu.ac.ae 1 Department of Chemical and Petroleum Engineering, UAE University, P.O. Box 15551, Al Ain, United Arab Emirates 2 Department of Chemical Engineering, University of Waterloo, Waterloo, ON, Canada Biomass Conversion and Biorefinery https://doi.org/10.1007/s13399-020-00893-w