scholarly journals Current Issues in Sol-Gel Reaction Kinetics

1990 ◽  
Vol 180 ◽  
Author(s):  
Roger A. Assink ◽  
Bruce D. Kay
Keyword(s):  
Reaction Kinetics ◽  
Sol Gel ◽  
Early Time ◽  
Acid Catalyst ◽  
Reaction Rates ◽  
Reaction Conditions ◽  
Reaction Rate Constants ◽  
Condensation Reactions ◽  
Experimental Findings ◽  
Kinetics Of

ABSTRACTThis paper surveys a few of the current issues in sol-gel reaction kinetics. Many times seemingly modest changes in reactants or reaction conditions can lead to substantial differences in the overall reaction rates and pathways. For example, qualitative features of the reaction kinetics can depend on catalyst concentration. At very high acid-catalyst concentrations, reverse reactions are significant for TMOS solgels, while for moderate acid-catalyst concentrations, reverse reactions are substantially reduced. The reaction kinetics of two similar tetraalkoxysilanes: tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS), can be markedly different under identical reaction conditions. Under acid-catalyzed reaction conditions, a TMOS sol-gel undergoes both water- and alcoholproducing condensation reactions while a TEOS sol-gel undergoes only water-producing condensation. The early time hydrolysis and condensation reactions of a TMOS sol-gel are statistical in nature and can be quantitatively described by a few simple reaction rate constants while the reaction behavior of a TEOS sol-gel is markedly nonstatistical. A comprehensive theory of sol-gel kinetics must address these diverse experimental findings.

scholarly journals Exploring early time points of vimentin assembly in flow by fluorescence fluctuation spectroscopy

Lab on a Chip ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 735-745
Author(s):  
Eleonora Perego ◽  
Sarah Köster
Keyword(s):  
Reaction Kinetics ◽  
Photon Counting ◽  
Early Time ◽  
Fluorescence Fluctuation Spectroscopy ◽  
Microfluidic Mixing ◽  
Time Points ◽  
Photon Counting Histogram ◽  
Kinetics Of

The combination of photon counting histogram and microfluidic mixing reveals early time points in reaction kinetics of biomolecule aggregation.

scholarly journals Reaction Kinetics of Levulinic Acid Synthesis from Glucose Using Bronsted Acid Catalyst

2021 ◽  
Author(s):  
Meutia Ermina Toif ◽  
Muslikhin Hidayat ◽  
Rochmadi Rochmadi ◽  
Arief Budiman
Keyword(s):  
Reaction Kinetics ◽  
Glucose Concentration ◽  
Levulinic Acid ◽  
Acid Catalyst ◽  
Operating Conditions ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Initial Glucose Concentration ◽  
Brönsted Acid ◽  
Kinetics Of

Abstract Glucose is the primary derivative of lignocellulosic biomass, which is abundantly available. Glucose has excellent potential to be converted into valuable compounds such as ethanol, sorbitol, gluconic acid, and levulinic acid (LA). Levulinic acid is a very promising green platform chemical. It is composed of two functional groups, ketone and carboxylate groups which can act as highly reactive electrophiles for nucleophilic attack so it has extensive applications, including fuel additives, raw materials for the pharmaceutical industry, and cosmetics. The reaction kinetics of LA synthesis from glucose using hydrochloric acid catalyst (bronsted acid) were studied in a wide range of operating conditions, i.e., temperature of 140-180 oC, catalyst concentration of 0.5-1.5 M, and initial glucose concentration of 0.1-0.5 M. The highest LA yield is 48.34 %wt at 0.1 M initial glucose concentration, 1 M HCl, and temperature of 180 oC. The experimental results show that the bronsted acid catalyst's reaction pathway consists of glucose decomposition to levoglucosan (LG), conversion of LG to 5-hydroxymethylfurfural (HMF), and rehydration of HMF to LA. The experimental data yields a good fitting by assuming a first-order reaction model.

scholarly journals Kinetics of Transesterification of Croton megalocarpus Oil Using Alkaline Earth Catalysts with Conventional and Microwave Heating

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Anil Kumar ◽  
Henry K. Kiriamiti
Keyword(s):  
Microwave Irradiation ◽  
Alkaline Earth ◽  
Heterogeneous Catalysts ◽  
Methyl Esters ◽  
Chemical Properties ◽  
Reaction Rates ◽  
Conventional Heating ◽  
Reaction Rate Constants ◽  
Scanning Electron Micrography ◽  
Kinetics Of

Transesterification kinetics of Croton megalocarpus oil to produce fatty acid methyl esters (FAME) was studied using homogeneous NaOH and heterogeneous alkaline earth Nano MgO, MgO, Nano CaO, CaO, Reoxidized CaO, SrO, and BaO catalysts. Characteristic surface, bulk, and chemical properties of the heterogeneous catalysts were obtained which included surface area, pore properties, scanning electron micrography, X-ray diffraction, basic strength, and basicity. The catalyst porosity varied as Nano MgO > Nano CaO > MgO > CaO > CaO-RO > SrO > BaO and basicity as BaO > SrO > Nano CaO > CaO RO > CaO > Nano MgO > MgO. Catalysts NaOH, BaO, SrO, and Nano CaO gave a good FAME yield (>50%), and reaction order and rate constant have been reported for these catalysts, for both conventional heating and microwave irradiation. The overall reaction for NaOH was of 1st order for microwave irradiation with respect to triglyceride and of 2nd order with respect to triglyceride under conventional heating. For the heterogeneous catalysts, the overall reaction was of 3rd order, 2nd order with respect to triglyceride and 1st order with respect to methanol for both heating methods. Reaction rate constants for microwave irradiation were higher than those for conventional heating due to faster reaction rates under such heating. BaO was the most active heterogeneous catalyst, followed by SrO and Nano CaO, which was in accordance with their basicity.

Study on Kinetics of Octadecyltrimethylammonium Adsorption on Montmorillonite

2010 ◽  
Vol 158 ◽  
pp. 233-240
Author(s):  
Ping Chen ◽  
Xian Jun Lu ◽  
Jun Qiu ◽  
Gui Fang Wang
Keyword(s):  
Reaction Kinetics ◽  
Adsorption Process ◽  
Dynamic Change ◽  
Interlayer Spacing ◽  
Carbon Chain ◽  
Isothermal Adsorption ◽  
Adsorption State ◽  
Reaction Rate Constants ◽  
Chain Conformations ◽  
Kinetics Of

Using Octadecyltrimethylammonium (OTA) cations with long carbon chain to intercalate into Na-montmorillonite samples, the change of adsorption amount and adsorption state of OTA with the retention time was investigated. The sdudy on the reaction kinetics for the alkylammonium adsorption in the montmorillonite interlayers showed that the isothermal adsorption behavior fit in with a second order reaction kinetics equation. Reaction rate constants had great differences with application force of adsorption process. OTA in the montmorillonite interlayers through re-arrangement constantly at different time, adsorption state of OTA are analysised by XRD and FTIR. The interlayer spacing and diffraction peak relative intensity of montmorillonite/OTMA complexes shows a dynamic change, the alkyl chain conformations can change from “liquid-like” to “solid-like” with the reaction time. The arrangement of alkylammonium cations are more orderly.

Modification of Mesoporous CaZr4(PO4)6 and its Acid Catalytic Performance

2011 ◽  
Vol 396-398 ◽  
pp. 1851-1855
Author(s):  
Tian Si ◽  
Lin Hua Zhu
Keyword(s):  
Surface Acidity ◽  
Sol Gel ◽  
Acid Catalyst ◽  
Catalytic Performance ◽  
X Ray Diffraction ◽  
Reaction Conditions ◽  
Catalyst Sample ◽  
New Type ◽  
Temperature Programmed ◽  
N2 Sorption

A series of new type acid catalyst samples based on mesoporous CaZr4(PO4)6(CZP) belonging to NZP family synthesized by sol-gel method was obtained by Al, La, B incorporation in CZP or by heteropoly acid H3PW12O7•xH2O(HPW) loading on CZP, and their acid catalytic activity and selectivity were investigated by using α-pinene isomerization as a probe reaction. The phase, pore structure and surface acidity of the catalyst samples were characterized by X-ray diffraction (XRD), N2 sorption and NH3 temperature programmed desorption (NH3-TPD) respectively. The results showed that the surface acidity of CZP modified by elements incorporation and HPW loading was improved in a different extent. The conversion of α-pinene at 150 °C reached to 41 % over the catalyst sample noted as Al-CZP-0.15 in which the mole ratio of Al to Zr was 0.15. Under the same reaction conditions, the conversion of α-pinene was above 95 % over the CZP supported with 20-30wt. %HPW.

Kinetic mechanisms for mullite formation from sol-gel precursors

1990 ◽  
Vol 5 (9) ◽  
pp. 1963-1969 ◽  
Author(s):  
Dong X. Li ◽  
William J. Thomson
Keyword(s):  
Activation Energy ◽  
Reaction Kinetics ◽  
Single Phase ◽  
Sol Gel ◽  
Mullite Formation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffusion Controlled ◽  
Kinetic Mechanisms ◽  
Kinetics Of

The reaction kinetics for the formation of mullite (3Al2O3 · 2SiO2) from sol-gel derived precursors were studied using dynamic x-ray diffraction (DXRD) and differential thermal analysis (DTA). The reaction kinetics of diphasic and single phase gels are compared and different reaction mechanisms are found for each gel. Mullite formation in the diphasic gel exhibits an Avrami type, diffusion-controlled growth mechanism with initial mullite formation temperatures of about 1250 °C and an activation energy on the order 103 kJ/mole. On the other hand, mullite formation from the single phase gel is a nucleation-controlled process with an initial formation temperature of 940 °C and a much lower activation energy of about 300 kJ/mole.

Reaction kinetics of SiO2 and ZnOSiO2 sol-gel solutions

1993 ◽  
Vol 160 (1-2) ◽  
pp. 152-161 ◽  
Author(s):  
Brita Unger ◽  
Peter Popp ◽  
Ulrich Schade ◽  
Manfred Hähnert
Keyword(s):  
Reaction Kinetics ◽  
Sol Gel ◽  
Kinetics Of
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