Activation energies and frequency factors in the thermal decomposition of paraffin hydrocarbons

1952 ◽  
Vol 214 (1119) ◽  
pp. 471-481 ◽  
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Apparent Activation Energy ◽  
Molecular Mechanisms ◽  
Activation Energies ◽  
Small Surface ◽  
Molecular Reaction ◽  
Methyl Pentane

Further evidence supports the view that the thermal decomposition of paraffin hydro­carbons occurs by simultaneous chain and non-chain (molecular) mechanisms, the latter being isolated by addition of suitable inhibitors such as nitric oxide. It is concluded that certain small surface effects are secondary disturbances of an essentially homogeneous reaction. With one group of hydrocarbons, type 1, including ethane (propane), iso -butane, iso -pentane, neo -pentane and neo -hexane, this molecular reaction is of the normal unimolecular kind, showing a single transition from the first order towards the second as the pressure drops, and an activation energy which is independent of the initial pressure. In the second group, type 2, including n -butane and higher normal paraffins, 2∙3-dimethyl butane, 2-methyl pentane and 3-methyl pentane, the molecular reaction seems to be a super­position of two unimolecular reactions with different pressure dependences and different activation energies. There is a double order transition, and a marked variation with pressure of the apparent activation energy. This apparent activation energy is influenced by the addition of certain gases (propylene, ethane, propane) in such a way as to be in any given case a unique function of the total pressure of paraffin plus added gas. The frequency factors in the equation k = A e -E/RT have been determined. With the paraffins of type 2, the ‘high- pressure’ components of the reaction give values within the range expected by the theories which relate A to a vibration frequency, and assume the localization of the critical energy in a single bond. With some of the paraffins of type 1 the frequency factors are outside the probable range (10 12 to 10 14 s -1 ), and the values suggest that the transition states may be less sharply defined than the localization condition demands. The apparent values of the frequency factors associated with the ‘low-pressure’ components of the reactions are still higher and appear to demand a special interpretation which must be the subject of further investigation.

scholarly journals The Landscape of microRNAs in βCell: Between Phenotype Maintenance and Protection

2021 ◽  
Vol 22 (2) ◽  
pp. 803
Author(s):  
Giuseppina Emanuela Grieco ◽  
Noemi Brusco ◽  
Giada Licata ◽  
Daniela Fignani ◽  
Caterina Formichi ◽  
...  
Keyword(s):  
Diabetes Mellitus ◽  
Metabolic Disorders ◽  
Molecular Mechanisms ◽  
Β Cell ◽  
Physiological Mechanisms ◽  
Effective Strategies ◽  
Chronic Hyperglycaemia ◽  
Shed Light

Diabetes mellitus is a group of heterogeneous metabolic disorders characterized by chronic hyperglycaemia mainly due to pancreatic β cell death and/or dysfunction, caused by several types of stress such as glucotoxicity, lipotoxicity and inflammation. Different patho-physiological mechanisms driving β cell response to these stresses are tightly regulated by microRNAs (miRNAs), a class of negative regulators of gene expression, involved in pathogenic mechanisms occurring in diabetes and in its complications. In this review, we aim to shed light on the most important miRNAs regulating the maintenance and the robustness of β cell identity, as well as on those miRNAs involved in the pathogenesis of the two main forms of diabetes mellitus, i.e., type 1 and type 2 diabetes. Additionally, we acknowledge that the understanding of miRNAs-regulated molecular mechanisms is fundamental in order to develop specific and effective strategies based on miRNAs as therapeutic targets, employing innovative molecules.

scholarly journals Effect of CaO on catalytic combustion of semi-coke

2021 ◽  
Vol 10 (1) ◽  
pp. 011-020
Author(s):  
Luyao Kou ◽  
Junjing Tang ◽  
Tu Hu ◽  
Baocheng Zhou ◽  
Li Yang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Combustion Rate ◽  
Activation Energies ◽  
Combustion Reaction ◽  
Tg Analysis ◽  
Conversion Rates ◽  
Apparent Activation Energies ◽  
Ozawa Integral Method ◽  
Addition Amount

Abstract Generally, adding a certain amount of an additive to pulverized coal can promote its combustion performance. In this paper, the effect of CaO on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric (TG) analysis. The results show that adding proper amount of CaO can reduce the ignition temperature of semi-coke and increase the combustion rate of semi-coke; with the increase in CaO content, the combustion rate of semi-coke increases first and then decreases, and the results of TG analysis showed that optimal addition amount of CaO is 2 wt%. The apparent activation energy of CaO with different addition amounts of CaO was calculated by Coats–Redfern integration method. The apparent activation energy of semi-coke in the combustion reaction increases first and then decreases with the increase in CaO addition. The apparent activation energies of different samples at different conversion rates were calculated by Flynn–Wall–Ozawa integral method. It was found that the apparent activation energies of semi-coke during combustion reaction decreased with the increase in conversion.

scholarly journals Improvement in Carbonization Efficiency of Cellulosic Fibres Using Silylated Acetylene and Alkoxysilanes

Fibers ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 84
Author(s):  
Maria Mironova ◽  
Igor Makarov ◽  
Lyudmila Golova ◽  
Markel Vinogradov ◽  
Georgy Shandryuk ◽  
...  
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Thermal Behavior ◽  
Comparative Studies ◽  
Decomposition Reaction ◽  
Activation Energies ◽  
Composite Fibers ◽  
Carbon Yield ◽  
Pyrolysis Reaction ◽  
Cellulosic Fibres

Comparative studies of the structure and thermal behavior of cellulose and composite precursors with additives of silyl-substituted acetylene and alkoxysilanes were carried out. It is shown that the introduction of silicon-containing additives into the cellulose matrix influenced the thermal behavior of the composite fibers and the carbon yield after carbonization. Comparison of the activation energies of the thermal decomposition reaction renders it possible to determine the type of additive and its concentration, which reduces the energy necessary for pyrolysis. It is shown that the C/O ratio in the additive and the presence of the Si–C bond affected the activation energy and the temperature of the beginning and the end of the pyrolysis reaction.

Characteristics and thermal decomposition kinetics of wood-SiO2 composites derived by the sol-gel process

Holzforschung ◽  
2017 ◽  
Vol 71 (3) ◽  
pp. 233-240 ◽  
Author(s):  
Ke-Chang Hung ◽  
Jyh-Horng Wu
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Apparent Activation Energy ◽  
Sol Gel ◽  
Weight Percent Gain ◽  
Weight Percent ◽  
Decomposition Kinetics ◽  
Thermal Decomposition Kinetics ◽  
Sol Gel Process ◽  
Kinetics Of

Abstract Wood-SiO2 composites (WSiO2Cs) were prepared by means of the sol-gel process with methyltrimethoxysilane (MTMOS) as a reagent, and the physical properties, structure and thermal decomposition kinetics of the composites has been evaluated. The dimensional stability of the WSiO2Cs was better than that of unmodified wood, especially in terms of the weight percent gain (WPG), which achieved values up to 30%. The 29Si-NMR spectra show two different siloxane peaks (T2 and T3), which supports the theory about the formation of MTMOS network structures. Thermal decomposition experiments were also carried out in a TG analyzer under a nitrogen atmosphere. The apparent activation energy was determined according to the iso-conversional methods of Friedman, Flynn-Wall-Ozawa, modified Coats-Redfern, and Starink. The apparent activation energy between 10 and 70% conversion is 147–172, 170–291, 189–251, and 192–248 kJ mol−1 for wood and WSiO2Cs with WPGs of 10, 20, and 30%, respectively. However, the reaction order between 10 and 70% conversion calculated by the Avrami theory was 0.50–0.56, 0.35–0.45, 0.33–0.44, and 0.28–0.48. These results indicate that the dimensional and thermal stability of the wood could be effectively enhanced by MTMOS treatment.

Synthesis and Thermal Analysis of C16H13N5O3 and its Complexes with Rare Earth

2013 ◽  
Vol 749 ◽  
pp. 521-526
Author(s):  
Si Jiao Wang ◽  
Xiang Rong Liu ◽  
Chao Chao Song ◽  
Shun Shen Zhao ◽  
Lan Ying Yan ◽  
...  
Keyword(s):  
Activation Energy ◽  
Thermal Analysis ◽  
Thermal Decomposition ◽  
Rare Earth ◽  
Apparent Activation Energy ◽  
Elemental Analysis ◽  
Rare Earth Complexes ◽  
Thermal Gravimetric ◽  
Decomposition Processes ◽  
Ft Ir

The 2-carboxybenzaldehyde-1H-benzotriazol-1-aceylhydrazone (C16H13N5O3) has been synthesized and used in preparing thirteen novel rare earth complexes. The complexes were characterized by elemental analysis, FT-IR, and UV-Vis, and the formula is RE (C16H11N5O3)·NO3·xH2O·yC2H5OH (RE=La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Yb) and RE(C16H12N5O3)2·NO3·5H2O (RE=Gd, Dy, Y) .The thermal decomposition processes of the thirteen complexes were studied by thermal gravimetric technology and their apparent activation energy values were calculated by Kissingers and Ozawass method.

Altered expression of major renal Na transporters in rats with unilateral ureteral obstruction

2003 ◽  
Vol 284 (1) ◽  
pp. F155-F166 ◽  
Author(s):  
Chunling Li ◽  
Weidong Wang ◽  
Tae-Hwan Kwon ◽  
Mark A. Knepper ◽  
Søren Nielsen ◽  
...  
Keyword(s):  
Ureteral Obstruction ◽  
Molecular Mechanisms ◽  
Free Water ◽  
Fractional Excretion ◽  
Unilateral Ureteral Obstruction ◽  
Altered Expression ◽  
Compensatory Increase ◽  
Type 3

It has been demonstrated previously that ureteral obstruction was associated with downregulation of renal AQP2 expression and an impaired urinary concentrating capacity (Li C, Wang W, Kwon TH, Isikay L, Wen JG, Marples D, Djurhuus JC, Stockwell A, Knepper MA, Nielsen S, and Frøkiær J. Am J Physiol Renal Physiol 281: F163–F171, 2001). In the present study, changes in the expression of major renal Na transporters were examined in a rat model with 24 h of unilateral ureteral obstruction (UUO) to clarify the molecular mechanisms of the marked natriuresis seen after release of UUO. Urine collection for 2 h after release of UUO revealed a significant reduction in urinary osmolality, solute-free water reabsorption, and a marked natriuresis (0.29 ± 0.03 vs. 0.17 ± 0.03 μmol/min, P < 0.05). Consistent with this, immunoblotting revealed significant reductions in the abundance of major renal Na transporters: type 3 Na+/H+exchanger (NHE3; 24 ± 4% of sham-operated control levels), type 2 Na-Pi cotransporter (NaPi-2; 21 ± 4%), Na-K-ATPase (37 ± 4%), type 1 bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1; 15 ± 3%), and thiazide-sensitive Na-Cl cotransporter (TSC; 15 ± 4%). Immunocytochemistry confirmed the downregulation of NHE3, BSC-1, and TSC in response to obstruction. In nonobstructed contralateral kidneys, a significant reduction in the abundance of inner medullary Na-K-ATPase and cortical NaPi-2 was found. This may contribute to the compensatory increase in urinary production (23 ± 2 vs. 13 ± 1 μl · min−1 · kg−1) and increased fractional excretion of urinary Na (0.62 ± 0.03 vs. 0.44 ± 0.03%, P < 0.05). In conclusion, downregulation of major renal Na transporters in rats with UUO may contribute to the impairment in urinary concentrating capacity and natriuresis after release of obstruction, and reduced levels of Na-K-ATPase and NaPi-2 in the contralateral nonobstructed kidney may contribute to the compensatory increase in water and Na excretion from that kidney during UUO and after release of obstruction.

scholarly journals Organ-Based Response to Exercise in Type 1 Diabetes

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Lisa Stehno-Bittel
Keyword(s):  
Type 2 Diabetes ◽  
Skeletal Muscle ◽  
Type 1 Diabetes ◽  
Molecular Mechanisms ◽  
Tissue Level ◽  
Significant Research ◽  
Response To Exercise ◽  
Increased Activity

While significant research has clearly identified sedentary behavior as a risk factor for type 2 diabetes and its subsequent complications, the concept that inactivity could be linked to the complications associated with type 1 diabetes (T1D) remains underappreciated. This paper summarizes the known effects of exercise on T1D at the tissue level and focuses on the pancreas, bone, the cardiovascular system, the kidneys, skeletal muscle, and nerves. When possible, the molecular mechanisms underlying the benefits of exercise for T1D are elucidated. The general benefits of increased activity on health and the barriers to increased exercise specific to people with T1D are discussed.

The Thermal Decomposition of Silver(I) Oxide

1960 ◽  
Vol 13 (4) ◽  
pp. 431 ◽  
Author(s):  
JA Allen
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Lattice Parameter ◽  
Activation Energies ◽  
Metallic Silver ◽  
Cent Oxygen ◽  
Total Oxygen ◽  
The Third ◽  
Limiting Value ◽  
Silver Atoms

The thermal decomposition of precipitated silver(I) oxide in a vacuum has been studied over the range 100-350 �C. Three regions are identified : in the fist, 100-200 �C, the activation energy is 30 kcal, 5 per cent. of the total oxygen is evolved, and the lattice parameter increases to a limiting value ; in the second, 200-300 �C, the activation energy is 50 kcal, and a further 1-2 per cent. oxygen is evolved; in the third, above 300 �C, metallic silver crystallizes, the oxide lattice contracts to a constant value, and the activation energy becomes 36 kcal. The activation energies in the three regions are interpreted as being associated, respectively, with (i) the diffusion of silver into the oxide lattice, (ii) the formation of aggregates of silver " atoms " not conforming to the normal silver lattice in an oxide lattice saturated with silver, and (iii) the reaction at the interface between metallic silver and the oxide.

Decomposition Kinetics of Switchgrass: Estimating Activation Energy

2014 ◽  
Vol 881-883 ◽  
pp. 726-733
Author(s):  
Gui Ying Xu ◽  
Jiang Bo Wang ◽  
Ling Ping Guo ◽  
Guo Gang Sun
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Apparent Activation Energy ◽  
High Purity ◽  
Isoconversional Methods ◽  
Decomposition Kinetics ◽  
Heating Rates ◽  
Model Free ◽  
Chemical Utilization ◽  
Kinetics Of

TG analysis was used to investigate the thermal decomposition of switchgrass, which is a potential gasification feedstock. 10 mg switchgrass sample with the particles between 0.45 and 0.70 mm was linearly heated to 873 K at heating rates of 10, 20, 30 K/min, respectively, under high-purity nitrogen. The Kissinger method and three isoconversional methods including Friedman, Flynn-wall-Ozawa, Vyazovkin and Lenikeocink methods were used to estimate the apparent activation energy of switchgrass. With the three isoconversional methods, it can be concluded that the activation energy increases with increasing conversion. The four model free methods reveal activation energies in the range of 70-460 kJ/mol. These activation energy values provide the basic data for the thermo-chemical utilization of the switchgrass.

scholarly journals Two-level inhibition of galK expression by Spot 42: Degradation of mRNA mK2 and enhanced transcription termination before the galK gene

2015 ◽  
Vol 112 (24) ◽  
pp. 7581-7586 ◽  
Author(s):  
Xun Wang ◽  
Sang Chun Ji ◽  
Heung Jin Jeon ◽  
Yonho Lee ◽  
Heon M. Lim
Keyword(s):  
Binding Site ◽  
Molecular Mechanisms ◽  
Transition Period ◽  
Transcription Termination ◽  
Growth Type ◽  
Down Regulation ◽  
Type Switch ◽  
Specific Mrna

The Escherichia coli gal operon has the structure Pgal-galE-galT-galK-galM. During early log growth, a gradient in gene expression, named type 2 polarity, is established, as follows: galE > galT > galK > galM. However, during late-log growth, type 1 polarity is established in which galK is greater than galT, as follows: galE > galK > galT > galM. We found that type 2 polarity occurs as a result of the down-regulation of galK, which is caused by two different molecular mechanisms: Spot 42-mediated degradation of the galK-specific mRNA, mK2, and Spot 42-mediated Rho-dependent transcription termination at the end of galT. Because the concentration of Spot 42 drops during the transition period of the polarity type switch, these results demonstrate that type 1 polarity is the result of alleviation of Spot 42-mediated galK down-regulation. Because the Spot 42-binding site overlaps with a putative Rho-binding site, a molecular mechanism is proposed to explain how Spot 42, possibly with Hfq, enhances Rho-mediated transcription termination at the end of galT.

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