Isothermal Kinetics Modelling of the Fischer-Tropsch Synthesis over the Spray-Dried Fe-Cu-K Catalyst

The isothermal kinetics of the Fischer-Tropsch synthesis （FTS） over Fe-Cu-K spray-dried catalyst was studied in a spinning basket reactor. The experiments were carried out at a constant temperature of 523 K, n（H2）/n（CO） feed ratios of 0.8 2.0, reactor pressures of 1.1 2.5 MPa, and space velocity of 0.556× 10^-3 Nm^3/kgcat·s. Kinetic model for hydrocarbon formation was derived on the basis of simplified carbide mechanism to reduce the number of parameters. Two individual rate constants for methane and ethene were considered. Furthermore, the model was modified empirically by non-intrinsic effect, such as physisorption and fictitious olefin pressures that were taken into account, and the influences of secondary reaction of α-olefins on product distribution. The simulation results showed that the experimental phenomena of FTS and the deviations from ASF distribution, such as the relatively high yield of methane and low yield of ethene observed experimentally could be depicted basically.

Thermal Decomposition Mechanism and Non Isothermal Kinetics of Complex of [La_2(P-MBA)_6(PHEN)_2]2H_2O

The complex of [La 2(P MBA) 6(PHEN) 2]2H 2O (P MBA: p methylbenzoate and PHEN: 1,10 phenanthroline) was prepared and characterized by elemental analysis and IR spectroscopy. The thermal behavior of [La 2(P MBA) 6(PHEN) 2]2H 2O in dynamic nitrogen atmosphere was investigated by TG DTG techniques. The results show that the thermal decomposition process of the [La 2(P MBA) 6(PHEN) 2]2H 2O occurs in five steps. The empirical kinetic model for the first step thermal decomposition obtained by Malek method is SB(m,n). The activation energy E and the pre exponential factor lnA for this step reaction are 76.4 kJ·mol -1 and 24.92, respectively.

Study on Non-Isothermal Decomposition Kinetics of Ephedrini Hydrochloridum

The thermal decomposition processes of ephedrini hydrochloridum and its kinetics are studied by TG-DTG techniques. A combined method, which includes Achar method, Coats-Redfera method, and Ozawa method, is put forward for determining kinetic model under non-isothermal conditions. By applying the combined method, it is determined that the thermal decomposition of ephedrini hydrochloridum is subjected to cylindrical symmetric diffusion. And the reaction function isƒ(α)=2(1-α)?, apparent activation energy (115.26±3.55) kJ·mol−1, pre-exponential factor 4.62×108 s−1. Results show that the combined method is feasible and simple.

Synthesis, Characterization, Thermal Decomposition Mechanism and Non-Isothermal Kinetics of the Pyruvic Acid-Salicylhydrazone and Its Complex of Praseodymium(III)

The pyruvic acid salicylhydrazone and its new complex of Pr(III) were synthesized. The formulae C 10 H 10 N 2O 4 (mark as H 3L) and [Pr 2(L) 2(H 2O) 2]·3H 2O (L=the triad form of the pyruvic acid salicylhydrazone [C 10 H 7N 2O 4] 3- ) were determined by elemental and EDTA volumetric analysis. Molar conductance, IR, UV, X ray and 1H NMR were carried out for the characterizations of the complex and the ligand. The thermal decompositions of the ligand and the complex with the kinetic study were carried out by non isothermal thermogravimetry. The Kissinger's method and Ozawa's method are used to calculate the activation energy value of the main step decomposition. The stages of the decompositions were identified by TG DTG DSC curve. The non isothermal kinetic data were analyzed by means of integral and differential methods. The possible reaction mechanism and the kinetic equation were investigated by comparing the kinetic parameters.

Non-isothermal crystallization kinetics of wood-flour/polypropylene composites in the presence of b-nucleating agent

The influence of aryl amide compounds（TMB）as b-nucleating agents, on the non-isothermal crystallization of a wood-flour/polypropylene composite（WF/PP）prepared by compression molding was investigated by wide-angle X-ray diffraction and differential scanning calorimetry. TMB was proved to be an effective b-crystalline nucleating agent for WF/PP. The DSC data showed that the crystallization peak temperature（Tp） increased and the half-time（t1/2） decreased with the addition of TMB.Three theoretical models were used to analyze the nonisothermal crystallization process. The modified Avrami method and Mo method successfully explained the nonisothermal crystallization behavior of PP and its composites. Their activation energies for non-isothermal crystallization were determined basing on the Kissinger method.

Isothermal Aging Kinetics in CuZnAl Shape Memory Alloy

Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each temperature.The isothermal aging kinetics fits in Avrami equation and the time exponent n decreases with the increase in aging temperature.The apparent activation energy for the isothermal aging process was measured to be 109.0kJ/mol,which is about equal to that of a relaxation internal friction peak at about 200℃ (f≈1 Hz) in the alloy.

Studies on Non-isothermal Kinetics of Thermal Decomposition of Strontium Chloride Hexahydrate

The thermal decomposition of the strontium chloride hexahydrate and its kinetics were studied under non isothermal condition in nitrogen by thermogravimetric and derivative thermogravimetric techniques. The intermediate and residue for each decomposition were identified from TG curve. The non isothermal kinetic data were analyzed by the Achar method and the Coats Redfern method. The possible reaction mechanisms were suggested by comparing the kinetic parameters. The kinetic equation for the first stage can be expressed as d α /d t = A exp(- E/RT)(1-α ), the second stage, d α /d t = A exp(- E/RT)3(1-α ) 2/3 , and the third stage, d α /d t = A exp(- E/RT)3/2(1-α ) 2/3 [1-(1- α ) 1/3 ] -1 . Mathematic expressions of the kinetic compensation effects of each stage of the thermal decomposition reaction were also obtained.

THE STRUCTURE OF AGGREGATION STATE AND ISOTHERMAL CRYSTALLIZATION KINETICS OF NYLON-1010

The structure of aggregation state and isothermal crystallization behavior of Nylon-1010 have been studied by WAXD,DSE,Variance-Range Function and density measurement.The results show that crystallization of Nylon-1010 has the most suitable annealing temperature,the crystals of the Nxlon-1010 are two-dimension heterogeneous nucleation.Both low treatment temperature and high crystallization te,temperature are disadvantageous for Nylon-1010 crystal growth.

Oxidation pathway and kinetics of titania slag powders during cooling process in air

The oxidation pathway and kinetics of titania slag powders in air were analyzed using differential scanning calorimetry(DSC)and thermogravimetry(TG).The oxidation pathway of titania slag powder in air was divided into three stages according to their three exothermic peaks and three corresponding mass gain stages indicated by the respective non-isothermal DSC and TG curves.The isothermal oxidation kinetics of high titania slag powders of different sizes were analyzed using the ln-ln analysis method.The results revealed that the entire isothermal oxidation process comprises two stages.The kinetic mechanism of the first stage can be described as f(α) = 1.77(1-α) [-ln (1-α)]^((1.77-1)/1.77),f(α)= 1.97(1-α) [-ln (1-α)]^((1.97-1)/1.97),and f (α) = 1.18(1-α) [-ln (1-α)]^((1.18-1)/1.18).The kinetic mechanism of the second stage for all samples can be described as f (α)=1.5(1-α)^(2/3)[1-(1-α)^(1/3)]^(-1).The activation energies of titania slag powders with different sizes(d_(1)<0.075 mm,0.125 mm<d_(2)<0.150 mm,and 0.425 mm<d_(3)<0.600 mm)for different reaction degrees were calculated.For the given experimental conditions,the rate-controlling step in the first oxidation stage of all the samples is a chemical reaction.The rate-controlling steps of the second oxidation stage are a chemical reaction and internal diffusion(for powders d_(1)<0.075 mm)and internal diffusion(for powders 0.125 mm<d_(2)<0.150 mm and 0.425 mm<d_(3)<0.600 mm).

Kinetics of Therm al Decom position of[ Eu_2( p- M O B A)_6(phen)_2]( H_2 O)_2 in Static Air Atmospher

The thermal decomposition of [Eu 2( p MOBA) 6(phen) 2](H 2O) 2 ( p MOBA=C 8H 7O 3, methoxybenzoate; phen=C 12 H 8N 2, 1,10 phenanthroline) and its kinetics were studied under the non isothermal condition in air by TG and DTG methods. The intermediate and residue for each decomposition were identified from TG curve. The non isothermal kinetic data were analyzed by the Achar method and Coats Redfern method. The possible reaction mechanisms were suggested by comparing the kinetic parameters. The kinetic equation for the first stage can be expressed as d α /d t = A exp(- E/RT )[-ln(1- α )] -1 , the second stage and the third stage d α /d t = A exp(- E/RT )3/2(1- α ) 4/3 [1/(1- α ) 1/3 -1] -1 . The mathematical expressions of the kinetic compensation effects of each stage of the thermal decomposition reaction were also obtained.

KINETICS OF STRAIN-INDUCED PRECIPITATION OF (Nb,V) CARBONITRIDE IN A MICROALLOYED STEEL

The kinetics of the isothermal precipitation of(Nb,V)CN in Nb-V alloys has been investi- gated by using the Formastor-press simulator and the extraction replica method.Under four deformation amounts(0,10,30,50%)and three temperatures(1100,1000,850℃), four types of kinetic curves were found.

The Effect of Self-nucleation on Isothermal Crystallization Kinetics of Poly(butylene succinate)(PBS) Investigated by Differential Fast Scanning Calorimetry

Differential fast scanning calorimetry（DFSC） was employed on the study of self-nucleation behavior of poly（butylene succinate）（PBS）.The ultra-fast cooling ability of DFSC allows investigating the effect of self-nucleation on the isothermal crystallization kinetics over a wide temperature range.Crystallization half-time,instead of crystallization peak temperature,was used to describe the self-nucleation behavior,and the self-nucleation domain for the samples crystallized at different temperatures was determined.Due to the competition between homogenous nucleation and self-nuclei,the effect of self-nucleation was less pronounced at high supercooling than that for the sample isothermally crystallized at higher temperature.An efficiency scale to judge the efficiency of nucleating agents from the crystallization half-time was also introduced in this work.

Thermodynamic and Kinetic Studies of Effective Adsorption of 2,4,6-trichlorophenol onto Calcine Mg/Al-CO_3 Layered Double Hydroxide

Adsorption of 2, 4, 6-trichlorophenol（TCP） onto the calcined Mg/Al-CO_3 layered double hydroxide（CLDH） was investigated. The prepared Mg/Al-CO_3 layered double hydroxide（LDH） and CLDH were characterized by powder X-ray diffraction（XRD） and thermo gravimetric analyzer-differential scanning calorimeters（TG-DSC）. Moreover, 2,4,6-trichlorophenol（TCP） was removed effectively（94.7% of removal percentage in 9h） under the optimized experimental conditions. The adsorption kinetics data fitted the pseudosecond-order model well. The Freundlich, Langmuir, and Tempkin adsorption models were applied to the experimental equilibrium adsorption data at different temperatures of solution. The adsorption data fitted the Freundlieh adsorption isotherm with good values of the correlation coefficient. A mechanism of the adsorption process is proposed according to the intraparticle diffusion model, which indicates that the overall rate of adsorption can be described as three steps.

Isothermal Crystallization Kinetics and Crystalline Morphologies of Poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate)Copolymers

In this study, the isothermal crystallization kinetics and crystalline morphology of poly（butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate）（PBAC）, which refers to a copolyester containing a non-planar ring structure, were investigated by differential scanning calorimetry and polarized optical microscopy, and compared with those of neat poly（butylene 1,4-cyclohexanedicarboxylate）（PBC）. The results indicate that the introduction of butylene adipate（BA） unit into PBAC did not change the intrinsical crystallization mechanism. But, the crystallization rate and ability, and equilibrium melting temperature of PBAC copolymers were reduced. All PBC and PBAC copolymers could only form high density of nucleation from melt at given supercooling, while no Maltese cross or ring-banded spherulites could be observed. PBAC copolymers with a high amount of BA unit became amorphous after quenching with liquid nitrogen from melt, while PBC and PBAC copolymers with a low amount of BA unit could still form a large amount of nuclei under the same treatment.

Experimental Design Technique on Removal of Hydrogen Sulfide using CaO-eggshells Dispersed onto Palm Kernel Shell Activated Carbon：Experiment,Optimization,Equilibrium and Kinetic Studies

This study presents the use of chicken eggshells waste utilizing palm kernel shell based activated carbon（PKSAC） through the modification of their surface to enhance the adsorption capacity of H2S. Response surface methodology technique was used to optimize the process conditions and they were found to be： 500 mg/L for H2S initial concentration, 540 min for contact time and 1 g for adsorbent mass. The impacts of three arrangement factors（calcination temperature of impregnated activated carbon（IAC）, the calcium solution concentration and contact time of calcination） on the H2S removal efficiency and impregnated AC yield were investigated. Both responses IAC yield（IACY, %） and removal efficiency（RE, %） were maximized to optimize the IAC preparation conditions. The optimum preparation conditions for IACY and RE were found as follows： calcination temperature of IAC of 880 ℃, calcium solution concentration of 49.3% and calcination contact time of 57.6 min, which resulted in 35.8% of IACY and 98.2% RE. In addition, the equilibrium and kinetics of the process were investigated. The adsorbent was characterized using TGA, XRD, FTIR, SEM/EDX, and BET. The maximum monolayer adsorption capacity was found to be 543.47 mg/g. The results recommended that the composite of PKSAC and Ca O could be a useful material for H2S containing wastewater treatment.

Adsorption of 5.5’-Disulfonicindigotin(5.5’-DI)onto Green Coconut Fiber(Cocos nucifera L.):Kinetic and Isotherms

Green coconut fiber (Cocos nucifera L.) has been largely used in solid-phase extraction. The effect of the initial dye concentration (1.91, 3.02 and 4.02) × 10-5 mol&#183L-1 and solid phase contact (SPE) time were evaluated at different temperatures (283, 298 and 313) K at pH 2. Kinetic experimental data were applied to three simplified kinetic models: pseudo-first order, pseudo-second order, and intraparticle diffusion. The adsorption of 5.5’-DI onto the solid phase showed excellent fit to the pseudo-second order model. At 283, 298 and 313 K the maximum sorption, qmax,exp, for the lowest initial concentration (Co = 1.91 × 10-5 mol&#183L-1) of 5.5’-DI were (5.01, 5.24 and 6.14) × 10-4 g&#183g-1;for Co = 3.02 × 10-5 mol&#183L-1 (0.93, 1.01 and 1.03) × 10-3

Removal of cobalt(II) ion from aqueous solution by chitosan–montmorillonite

Montmorillonite （MMT） modified with chitosan （CTS, molecular weight = S x 104） was applied to remove heavy metal cations by using Co2＋ as a model ion. An increase in MMT interlayer distance observed from X-ray diffraction indicates the intercalation of CTS into MMT. Together with the results of scanning electron microscopy and Fourier transform infrared spectroscopy, it was concluded that the composite material of CTS and MMT （CTS-- MMT） was prepared successfully. The mass ratio of CTS to MMT had a strong influence on the adsorption performance of CTS-MMT. The highest adsorption value of 150 mg/g was obtained over the composite material with CTS to MMT mass ratio of 0.25, which is much higher than those reported in other studies. The adsorption isotherms and kinetic results indicated that Co2＋ was adsorbed over CTS-MMT in a multilayer model, and the chemical sorption of Co2＋ was determined to be the rate-limiting step.

Effect of Na^+ impregnated activated carbon on the adsorption of NH_4^+-N from aqueous solution

Two kinds of activated carbons modified by Na＋ impregnation after pre-treatments involving oxidation by nitric acid or acidification by hydrochloric acid （denoted as AC/N-Na and AC/HCl-Na, respectively）, were used as adsorbents to remove NH4＋-N. The surface features of samples were investigated by BET, SEM, XRD and FT-IR. The adsorption experiments were conducted in equilibrium and kinetic conditions. Influencing factors such as initial solution pH and initial concentration were investigated. A possible mechanism was proposed. Results showed that optimal NH4＋-N removal efficiency was achieved at a neutral pH condition for the modified ACs. The Langmuir isotherm adsorption equation provided a better fit than other models for the equilibrium study. The adsorption kinetics followed both the pseudo second-order kinetics model and intra-particle kinetic model. Chemical surface analysis indicated that Na＋ ions form ionic bonds with available surface functional groups created by pre-treatment, especially oxidation by nitric acid, thus increasing the removal efficiency of the modified ACs for NH4＋-N. Na＋-impregnated ACs had a higher removal capability in removing NH4＋-N than unmodified AC, possibly resulting from higher numbers of surface functional groups and better intra-particle diffusion. The good fit of Langmuir isotherm adsorption to the data indicated the presence of monolayer NH4＋-N adsorption on the active homogenous sites within the adsorbents. The applicability of pseudo second-order and intra-particle kinetic models revealed the complex nature of the adsorption mechanism. The intra-particle diffusion model revealed that the adsorption process consisted not only of surface adsorption but also intra-particle diffusion.

Investigation of acetylated kapok fibers on the sorption of oil in water

Kapok fibers have been acetylated for oil spill cleanup in the aqueous environment. The structures of raw and acetylated kapok fiber were characterized using Fourier transform infrared （FT-IR） spectroscopy and scanning electron microscopy （SEM）. Without severe damage to the lumen structures, the kapok fibers were successfully acetylated and the resulting fibers exhibited a better oil sorption capacity than raw fibers for diesel and soybean oil. Compared with high viscosity soybean oil, low viscosity diesel shows a better affinity to the surface of acetylated fibers. Sorption kinetics is fitted well by the pseudo second-order model, and the equilibrium data can be described by the Freundlich isotherm model. The results implied that acetylated kapok fiber can be used as the substitute for non-biodegradable oil sorption materials.

Adsorption of chlorophenols from aqueous solutions by pristine and surface functionalized single-walled carbon nanotubes

The adsorption of six kinds of chlorophenols on pristine, hydroxylated and carboxylated single-walled carbon nanotubes（SWCNTs） has been investigated. Pseudo-first order and pseudo-second order models were used to describe the kinetic data. All adsorption isotherms were well fitted with Langmuir, Freundlich and Polanyi–Manes models, due to surface adsorption dominating the adsorption process. The close linear relationship between log Kowand log Kdsuggested that hydrophobicity played an important role in the adsorption. The SWCNTs＇ adsorption capacity for chlorophenols was weakened by addition of oxygen-containing functional groups on the surface, due to the loss of specific surface area, the increase of hydrophilicity and the reduction of π–π interaction. The best adsorption capacity of pristine SWCNTs, SWCNT-OH and SWCNT-COOH for six chlorophenols varied from 19 to 84 mg/g, from 19 to 65 mg/g and from 17 to 65 mg/g,respectively. The effect of pH on the adsorption of 2,6-dichlorophenol（2,6-DCP）, was also studied. When p H is over the pK aof 2,6-dichlorophenol（2,6-DCP）, its removal dropped sharply. When ionic strength increased（Na Cl or KCl concentration from 0 to 0.02 mmol/L）,the adsorption capacity of 2,6-DCP on pristine SWCNTs decreased slightly. The comparison of chlorophenols adsorption by SWCNTs, MWCNTs and PAC was made, indicating that the adsorption rate of CNTs was much faster than that of PAC. The results provide useful information about the feasibility of SWCNTs as an adsorbent to remove chlorophenols from aqueous solutions.