Electron paramagnetic resonance of sonicated powder suspensions in organic solvents

Laajimi, Héla; Mattia, Michela; Stein, Robin S.; Bianchi, Claudia L.; Boffito, Daria C.

doi:10.1016/j.ultsonch.2021.105544

Cited by 14 publications

(9 citation statements)

References 62 publications

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“…Regardless of the conditions, TG produced more DE than PG. TG has a higher surface tension (41.1 mN/m for TG and 38.0 mN/m for PG, at 20 °C) and lower vapor pressure than PG (0.006 kPa for TG versus 0.011 kPa for PG, at 20 °C), which results in a higher cavitation intensity. , Indeed, bubbles form more readily when operating with solvents of high vapor pressure, low viscosity, and low surface tension, but at the expense of cavitation intensity. In fact, the higher the vapor pressure of the liquid, the greater the concentration of vapor in the bubbles, which mitigates collapse.…”

Section: Results and Discussionmentioning

confidence: 99%

Sonocatalytic Biodiesel Transesterification to Produce a Lubricant

Laajimi

Zorainy

Schieppati

et al. 2022

Ind. Eng. Chem. Res.

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The growth of the machinery and automotive industry drives interest toward the production of biolubricants due to their better lubricating properties and their low carbon footprint compared to petroleum-based lubricants. However, their traditional synthesis is long and energy-intensive. We intensified the production of biolubricants from canola oil methyl esters using ultrasound. NaOH catalyzed the transesterification of two polyalcohols (propylene and trimethylene glycols). We varied the ultrasound power, temperature, type of alcohol, and alcohol/ biodiesel molar ratio. Trimethylene glycol produced 90 ± 1.9% of biolubricant at 80 °C and 62 W with a molar ratio of 0.25. Calcium oxide supported on silica (CaO/SiO 2 ) also catalyzed the reaction under optimal conditions. The yield of the CaO/SiO 2 -catalyzed reaction was two times lower than that obtained with NaOH. We surveyed the loading of CaO over SiO 2 , the catalyst loading in the reactor, and its leaching and reusability. A mass percentage of 50% CaO to SiO 2 yielded 46 ± 3.2% lubricants at 3% by weight of the reactants' total mass. After three reaction cycles, the ultrasound did not alter the particle size (e.g., mean diameters of fresh and used catalysts were 31 and 32 μm, respectively), but it leached the active sites, which reduced the activity of the catalyst for successive uses.

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Section: Results and Discussionmentioning

confidence: 99%

Sonocatalytic Biodiesel Transesterification to Produce a Lubricant

Laajimi

Zorainy

Schieppati

et al. 2022

Ind. Eng. Chem. Res.

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“…This technique appears reliable; however, the main limitation is the need to perform ultrasound experiments in the vicinity of the EPR equipment, as radicals require to be spin-trapped and analyzed by EPR instantaneously. 131…”

Section: Physical Methodsmentioning

confidence: 99%

“…Recently, electron paramagnetic resonance (EPR) spectroscopy coupled with spin trapping agents has been adopted to identify and quantify acoustically generated radicals in organic solvents, including mixtures containing suspended solids. This technique appears reliable; however, the main limitation is the need to perform ultrasound experiments in the vicinity of the EPR equipment, as radicals require to be spin-trapped and analyzed by EPR instantaneously …”

Section: Characterization Methods Of Ultrasound Systemsmentioning

confidence: 99%

“…The addition of dispersed solids, such as powders, has mixed effects on the cavitation activity . A promoting role of the presence or generation of solid particles on cavitation has been suggested − due to powder surface and pores acting as a source for cavitation nuclei. On the other hand, other studies reported a decrease in cavitation activity upon the addition of solid particles, possibly due to attenuation of sound waves via scattering …”

Section: Guidelines For Experimental Parametersmentioning

confidence: 99%

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Sonoprocessing: From Concepts to Large-Scale Reactors

et al. 2021

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Intensification of ultrasonic processes for diversified applications, including environmental remediation, extractions, food processes, and synthesis of materials, has received attention from the scientific community and industry. The mechanistic pathways involved in intensification of ultrasonic processes that include the ultrasonic generation of cavitation bubbles, radical formation upon their collapse, and the possibility of fine-tuning operating parameters for specific applications are all well documented in the literature. However, the scale-up of ultrasonic processes with large-scale sonochemical reactors for industrial applications remains a challenge. In this context, this review provides a complete overview of the current understanding of the role of operating parameters and reactor configuration on the sonochemical processes. Experimental and theoretical techniques to characterize the intensity and distribution of cavitation activity within sonoreactors are compared. Classes of laboratory and large-scale sonoreactors are reviewed, highlighting recent advances in batch and flow-through reactors. Finally, examples of large-scale sonoprocessing applications have been reviewed, discussing the major scale-up and sustainability challenges.

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“…Laajimi et al measured, by electron paramagnetic resonance, the radical generation in organic solvents in the presence of silica particles – 10 nm, 0.25 µm, and 19 µm – and concentrations – 0.5 % and 3 % by mass. They discuss the mechanism and how to maximize radical formation in the solution, with important consequences for sonocatalysis [7] . Ehsani et al studied instead cavitation for fouling remediation.…”

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confidence: 99%