Thermal behavior and dehydroxylation kinetics of naturally occurring sepiolite and bentonite

Yılmaz, Müge Sarı; Kalpaklı, Yasemen; Pişkin, Sabriye

doi:10.1007/s10973-013-3152-x

Cited by 49 publications

(16 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It can be suggested that the layered structure of the catalyst has collapsed during the high temperature calcination. Our results are in accord with the data reported in the literature [24][25][26][27][28][29][30][31][32][33] indicating that sepiolite structure shows significant changes upon heating above 250 °C, which is accompanied by the loss of water from the material. These results and most literature data, however, disagreed with those presented in reference [18], which suggested that heating sepiolite to 500 °C does not cause any change in the catalyst structure.…”

Section: Resultssupporting

confidence: 93%

“…with previous reports [28][29][30][31], the micropores present in the original sepiolite (~ 0.8 nm in diameter) in the spaces between the silicate layers are no longer detected for the samples activated at temperatures above 200 °C for sepiolite and 100 °C for K-sepiolite. Although the thermal treatment process is essential to decompose the metal precursor with the formation of an oxide on the support, there is a significant change in the catalyst properties caused by heating it up to 400 °C, which is associated with the loss of water and the collapse of the layered structure.…”

Section: Resultssupporting

confidence: 62%

See 1 more Smart Citation

Catalytic performance of microporous materials for the production of renewable fuels

et al. 2018

View full text Add to dashboard Cite

ETS-10, zeolite A and sepiolite based nano-structured materials were prepared and modified with potassium containing compounds using ion-exchange or impregnation and evaluated as basic catalysts for transesterification of vegetable oils using microwave heating. The structural features of these catalysts were characterised in detail by the variable temperature in situ X-ray diffraction, N 2 adsorption-desorption, scanning electron microscopy with energy dispersive X-ray analysis and in situ FTIR spectroscopy using adsorption-desorption of acetylene as a basic probe in order to evaluate their structure-catalytic performance relationship in the methanolysis of triglycerides. A wide range of parameters were utilised in order to optimise the reaction conditions. Although a high yield of fatty acid methyl esters with almost 100% selectivity can be achieved in transesterification reactions in the presence of K-containing sepiolite, this system shows significant deactivation due to its structural degradation and loss of the active component during the reaction and regeneration cycles. In contrast, zeolite KA and ETS-10, which are thermally stable crystalline materials, demonstrated no decrease in their activity for up to four reaction runs, and therefore can be used as effective solid basic catalysts in this reaction. Here we explore for the first time how the thermal and structural stability of the supported clay can affect its activity, an essential issue which has not been sufficiently studied in the recent research related to the biofuel production over solid catalysts.

show abstract

Section: Resultssupporting

confidence: 93%

Section: Resultssupporting

confidence: 62%

Catalytic performance of microporous materials for the production of renewable fuels

et al. 2018

View full text Add to dashboard Cite

show abstract

“…Thus, the conclusions from most previous researchers are not applicable to the in-furnace process of kaolinite as a high-temperature sorbent. Some researchers investigated flash calcination of kaolinite as a new technology of kaolin processing and focused on the material properties of products such as pozzolanic properties, thermal properties, density and so on [13,18,19]. Unfortunately, these conclusions did not reflect the dehydroxylation and structural distortion of kaolinite in the furnace completely.…”

Section: Introductionmentioning

confidence: 99%

Dehydroxylation and Structural Distortion of Kaolinite as a High-Temperature Sorbent in the Furnace

Cheng

Xing

et al. 2019

Minerals

View full text Add to dashboard Cite

As a high-temperature sorbent, kaolinite undergoes the flash calcination process in the furnace resulting in the dehydroxylation and structural distortion, which are closely related to its heavy metal/alkali metal adsorption characteristics. We investigated the flash calcination of kaolinite by the experiments using a drop tube furnace and by the characterization of flash-calcined products using thermogravimetric-differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR)and nuclear magnetic resonance (NMR). There were three kinds of hydroxyl groups in kaolinite during flash calcination at 800–1300 °C, E-type (~50%, easy), D-type (~40%, difficult) and U-type (~10%, unable) according to the removal difficulty. The hydroxyl groups activation was believed to be the first step of the removal of E-type and D-type hydroxyl groups. The kinetics model of dehydroxylation groups at 900–1200 °C was established following Arrhenius equation with the activation energy of 140 kJ/mol and the pre-exponential factor of 1.32 × 106 s−1. At 800 °C, the removal of E-type hydroxyl groups resulted in the conversion of a part of VI-coordinated Al in kaolinite to V-coordinated Al and the production of meta-kaolinite. When the temperature rose up to 1200 °C, mullite was produced and a part of V-coordinated Al converted to IV-coordinated Al and VI-coordinated Al. Finally, the adsorption characteristics of kaolinite was discussed according to the results of dehydroxylation and structural distortion.

show abstract

“…In , the various aspects of formal kinetics in the solid phase have been discussed. Kinetics of nonisothermal thermolysis of natural minerals , layered double hydroxides , and other materials has been successfully investigated. Kissinger , Ozawa–Flynn–Wall (OFW) , Doyle , and Friedman methods have been used for mathematical processing of nonisothermal kinetic data.…”

Section: Introductionmentioning

confidence: 99%

The Study of Nonisothermal Kinetics of Dehydration of Gibbsite in a Mixture with Zinc Oxide

Prokof’ev

Petuhova

Gordina

2015

Int J of Chemical Kinetics

View full text Add to dashboard Cite

Nonisothermal kinetics of dehydration of gibbsite in a mixture with zinc oxide has been studied by Friedman analysis (differential method) and Flynn-Wall-Ozawa analysis (integral method). The values of the activation energy and preexponential factor depending on the decomposition extent of gibbsite to boehmite have been determined. It has been shown that both methods give similar results. It has been established that the activation energy has a maximum value of 150-170 kJ/mol in the start stages of thermolysis (for conversion extent of less than 0.3). During further dehydration, the activation energy is reduced to 100-110 kJ/mol. It has been found that comilling of the mixture results in decreasing activation energy to 40-50 kJ/mol for a conversion extent more than 0.8. This testifies to the transition of the dehydration process out of the kinetic mode to the diffusion mode. It was explained by the accumulation of mechanical energy in the form defects of crystal lattice of gibbsite at the comilling stage. C 2015 Wiley Periodicals, Inc. Int J Chem Kinet 47: 576-585, 2015

show abstract

Thermal behavior and dehydroxylation kinetics of naturally occurring sepiolite and bentonite

Cited by 49 publications

References 39 publications

Catalytic performance of microporous materials for the production of renewable fuels

Catalytic performance of microporous materials for the production of renewable fuels

Dehydroxylation and Structural Distortion of Kaolinite as a High-Temperature Sorbent in the Furnace

The Study of Nonisothermal Kinetics of Dehydration of Gibbsite in a Mixture with Zinc Oxide

Contact Info

Product

Resources

About