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

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 CO₂ Sorption on Li₂ZrO₃ Based Sorbents

In this study, the Li₂ZrO₃ based sorbents with different compositions were synthesized by the solid-state reaction method from the mixtures of Li₂CO₃, K₂CO₃ and ZrO₂. CO₂ sorption properties of Li₂ZrO₃ 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. Li₂CO₃/K₂CO₃-doped Li₂ZrO₃ sorbent with the composition of 36.23 wt % Li₂CO₃, 55.12 wt % ZrO₂ and 8.65 wt % K₂CO₃ was considered to achieve excellent capability for high temperature CO₂ sorption and presented the maximum sorption rate at 525 °C and 0.15 atm of CO₂ 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 CO₂ sorption process while the main CO₂ sorption occurred during the second phase. An improved iterative Coats–Redfern method was used to evaluate nonisothermal kinetics of the CO₂ sorption process, and the kinetic parameters were derived by the MATLAB model. The Fn <i>n</i>^th-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