جستجوی مقالات مرتبط با کلیدواژه « activation energy » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

The increasing production of non-degradable polymer wastes such as polystyrene (PS) and expandable polystyrene (EPS) is known as one of the most important environmental issues. Pyrolysis is one of the strategic and suitable methods for recycling of non-degradable polymeric wastes to fuels and useful chemicals. Therefore, investigation of pyrolysis kinetic of polystyrene waste, especially for available materials in Iran, is an essential issue for their use in industries. Obtaining the polystyrene pyrolysis kinetic can be used in designing industrial reactors and where it has economic credibility, styrene monomers can be produced in an industrial scale from polystyrene wastes.

Polystyrene (PS) and expandable polystyrene (EPS) samples that are available in Iran were collected, and their TGA analysis was performed in a nitrogen atmosphere in the temperature range of 25 to 600oC, at heating rates of 5, 10, 15, and 20 C/min, and sample mass changes were measured. The activation energy of pyrolysis was estimated by the Coats Redfern (CR), Ozawa Flynn Wall (OFW), Kissinger Akahira Sunose (KAS), Augis Bennetis (AB) and Vyazovkin methods.

The Vyazovkin model can predict the experimental data better than the other models, and therefore this model was used to estimate the activation energy. The activation energies of PS and EPS were calculated in the range of 158-201 kJ/mole and 182-195 kJ/mole, respectively. Furthermore, the pre-exponential factors of PS and EPS were estimated by Vyazovkin approach as 3.08×1012 and 1.05×1015, respectively. The results of kinetic analysis of polystyrene (PS) and expandable polystyrene (EPS) pyrolysis of samples in Iran can help simulate waste recycling processes and consequently reduce the environmental problems.

The aim of this research was the investigation on kinetic of curing reaction of polyurethane binder based on hydroxyl terminated polybutadiene (HTPB). This reaction is of particular interest in advanced polyurethane composite materials.

HTPB diol was dynamically cured using differential scanning calorimetery (DSC) at different heating rates (5, 10, 20 and 40° C/min) with curing agents of Toluene Diisocyanate (TDI) and Isophorone Diisocyanate (IPDI) in presence and absence of Dibutyltin Dilaurate (DBTDL) catalyst. Kinetic parameters were calculated using Kissinger, Ozawa and isoconversion models. Urethane formation and viscosity build-up during cure reaction was studied by Fourier Transform Infrared Spectroscopy (FT-IR) and rotational visocmetery (RV) methods.

Results showed that activation energy, enthalpy, progress and the rate of reaction were influenced by type of curing agent and the presence of catalyst. Kinetic models showed activation energy was reduced about 1 kJ/mol at each 0.05 unit increase in the degree of cure. The activation energy of HTPB-TDI-DBTDL binder system versus degree of cure was reduced slower in comparison to HTPB-IPDI-DBTDL binder system. Decrease in activation energy at degrees of cure higher than 90% was intensified as probable diffusion of low molecular weight molecules into polymer chains. Enthalpy of reaction in HTPB-TDI-DBTDL binder system at heating rates of higher than 10° C/min was independent of heating rate, whereas in HTPB-IPDI-DBTDL binder system the enthalpy of reaction is highly dependent on heating rate. Chemorheological results showed that rate of curing reaction for binder systems are in the order of HTPB-TDI-DBTDL>HTPB-IPDI-DBTDL>HTPB-TDI.

It is important to study the kinetics of rubber cooking in order to know the speed and time of cooking the mixture, as well as phenomena such as fragmentation and reversal. The rupture of the rubber compound during storage and before the main cooking operation causes major problems. The phenomenon of reversal also occurs in some tires that are prone to the destruction of sulfur bonds, and ultimately reduces the quality of the part produced. In this paper, after the general introduction of the cooking curve, which is necessary to determine the cooking parameters, how to measure the constant speed of the cooking reaction that depends on the reaction temperature and also the activation energy to start this reaction using oscilloscope disk )ODR( rheometers, Animated disc or die-casting )MDR( and rubber process analyzer )RPA( as well as Differential Scale Thermometer )DSC( are examined by referring to various researches.

In this research infrared radiation was used for drying of quince slices. For this reason, the influence of drying temperature of 50, 60, 70 and 80 °C acquired by 51, 73, 98 and 12 W infrared lamp was investigated. Drying results showed that the drying rate increased with increasing temperature. The drying decreased up to 60% when temperature was increased from 50 to 80 °C. Affected by the lamp power from 51 to 125 W, the moisture content diminished from 453% (d.b.) to 16% (d.b.). Modeling of drying process using genetic algorithm-artificial neural networks (GA-ANNs) with 3 inputs (drying time, drying temperature and the slice enter temperature) and one output (the amount of moisture ratio (MR)) was done. The modeling results demonstrated a network with 7 neurons in hidden layer and tangent hyperbolic transport function could precisely predict the moisture content of slices during drying (R2 = 0.9997 and RMSE = 0.0044). This precision for optimized GA-ANNs was even higher than that of Midilli model -the best empirical model- (R2 = 0.9987-0.9994 and RMSE = 0.0068-0.0098) at all the temperatures tested. The results obtained from the sensitivity analysis by the optimized neural networks revealed that the center temperature of slices was the most pronounced factor (0.0044) to control the MR. Increase in temperature resulted in an increase in the effective diffusivity coefficient, so that this coefficient reached to 26.1×10-9 m2/s at 80 °C from the initial value of 10.8×10-9 m2/s at 50 °C. The activation energy (Ea) calculated for the quince slices were 28.68 kJ/mol.