30 research outputs found
Investigation of Ni/SiO2 catalysts prepared at different conditions for hydrogen production from ethanol steam reforming
Ni/SiO2 catalysts prepared by a sol–gel method have been investigated for hydrogen production via steam reforming of ethanol using a continuous flow, fixed bed reactor system. Chemical equilibrium calculations were also performed to determine the effects of temperature and molar steam to carbon ratio on hydrogen production. The acidity of the preparation solution (modified by nitric acid and ammonia) and calcination atmosphere (air and N2) were investigated in the preparation of the catalysts. BET surface area and porosity, temperature-programmed oxidation (TPO), X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterise the prepared catalysts. The BET surface area was reduced when the solution acidity was lowered during the sol–gel preparation process. A pH value less than 2.0 was necessary to achieve high metal dispersion in the catalyst. Smaller NiO particles were obtained when the catalyst was calcined in N2. Material balances on ethanol steam reforming at 600 °C using the prepared Ni/SiO2 catalysts were determined, and higher hydrogen production with lower coke deposition on the reacted catalysts were also obtained from the catalysts calcined in N2 atmosphere
Study on non-isothermal kinetics and the influence of calcium oxide on hydrogen production during bituminous coal pyrolysis
Thermogravimetric kinetics of crude glycerol.
The pyrolysis of the crude glycerol from a biodiesel production plant was investigated by thermogravimetry coupled with Fourier transform infrared spectroscopy. The main gaseous products are discussed, and the thermogravimetric kinetics derived. There were four distinct phases in the pyrolysis process of the crude glycerol. The presence of water and methanol in the crude glycerol and responsible for the first decomposition phase, were shown to catalyse glycerol decomposition (second phase). Unlike the pure compound, crude glycerol decomposition below 500 K leaves behind a large mass fraction of pyrolysis residues (ca. 15%), which eventually partially eliminate in two phases upon reaching significantly higher temperatures (700 and 970 K, respectively). An improved iterative Coats-Redfern method was used to evaluate non-isothermal kinetic parameters in each phase. The latter were then utilised to model the decomposition behaviour in non-isothermal conditions. The power law model (first order) predicted accurately the main (second) and third phases in the pyrolysis of the crude glycerol. Differences of 10-30 kJ/mol in activation energies between crude and pure glycerol in their main decomposition phase corroborated the catalytic effect of water and methanol in the crude pyrolysis. The 3-D diffusion model more accurately reproduced the fourth (last) phase, whereas the short initial decomposition phase was poorly simulated despite correlation coefficients ca. 0.95-0.96. The kinetics of the 3rd and 4th decomposition phases, attributed to fatty acid methyl esters cracking and pyrolysis tarry residues, were sensitive to the heating rate
High Temperature CO<sub>2</sub> Sorption on Li<sub>2</sub>ZrO<sub>3</sub> Based Sorbents
In this study, the Li<sub>2</sub>ZrO<sub>3</sub> based sorbents
with different compositions were synthesized by the solid-state reaction
method from the mixtures of Li<sub>2</sub>CO<sub>3</sub>, K<sub>2</sub>CO<sub>3</sub> and ZrO<sub>2</sub>. CO<sub>2</sub> sorption properties
of Li<sub>2</sub>ZrO<sub>3</sub> based sorbents were investigated
by analyzing the phases and microstructure changes with the help of
thermogravimetric analysis, X-ray diffraction and scanning electron
microscopy. The thermodynamic calculations were carried out based
on the second law of thermodynamics. Li<sub>2</sub>CO<sub>3</sub>/K<sub>2</sub>CO<sub>3</sub>-doped Li<sub>2</sub>ZrO<sub>3</sub> sorbent
with the composition of 36.23 wt % Li<sub>2</sub>CO<sub>3</sub>, 55.12
wt % ZrO<sub>2</sub> and 8.65 wt % K<sub>2</sub>CO<sub>3</sub> was
considered to achieve excellent capability for high temperature CO<sub>2</sub> sorption and presented the maximum sorption rate at 525 °C
and 0.15 atm of CO<sub>2</sub> partial pressure. The sorbent kept
rather stable for multicycles sorption and regeneration, and maintained
its original capacity during 12 cycle processes. There were three
distinct phases in the nonisothermal CO<sub>2</sub> sorption process
while the main CO<sub>2</sub> sorption occurred during the second
phase. An improved iterative Coats–Redfern method was used
to evaluate nonisothermal kinetics of the CO<sub>2</sub> sorption
process, and the kinetic parameters were derived by the MATLAB model.
The Fn <i>n</i><sup>th</sup>-order reaction model predicted
accurately the main phases and differences in the activation energies
and the frequency factors for different sorbents in the sorption phases
corroborated different mechanism integral functions and reaction orders