scholarly journals Higher propene yield by tailoring operating conditions of propane oxidative dehydrogenation over V2O5/γ-Al2O3

2015 ◽  
Vol 80 (3) ◽  
pp. 355-366 ◽  
Author(s):  
Yousef Zaynali ◽  
Seyed Alavi
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Oxidative Dehydrogenation ◽  
Atmospheric Pressure ◽  
Operating Conditions ◽  
Propane Conversion ◽  
Propane Oxidative Dehydrogenation ◽  
Wet Impregnation ◽  
Vanadia Catalyst ◽  
Oxygen Ratio

Supported vanadia catalyst was successfully synthesized using wet impregnation of ?-Alumina to study Propane Oxidative Dehydrogenation (POD). The prepared catalysts were characterized with XRD, BET, and TPR tests. In a broad temperature range (340 to 630?C), effects of vanadia loading (2.7, 5.4, and 9 wt%) and propane to oxygen ratio (3/1 to 1/3) were thoroughly investigated on propane conversion as well as propene yield at atmospheric pressure. Results indicate that by increasing the vanadia content the activity of catalyst increases while selectivity to propene decreases monotonically. As the temperature increases from 340?C to 630?C, yield to propene shows ascending behavior in case of all catalyst samples. Yield to propene shows a climax with changing propane to oxygen ratio from 3/1 to 1/3. The yield increases with increase in oxygen partial pressure of feed until equimolar ratio of propane and oxygen, then it declines with further increase of oxygen partial pressure. A maximum propene yield of 17% was experienced on catalyst with 2.7wt% vanadia at temperatures at 550?C.

The Effects of Oxygen Vacancy Concentration on the Mechanical Properties of Zirconia and Ceria-Based Electrolytes for SOFCs

2009 ◽  
Author(s):  
Toshiyuki Hashida ◽  
Yohei Takeyama ◽  
Kazuhisa Sato
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Fracture Surface ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Fracture Strength ◽  
Atmospheric Pressure ◽  
Small Punch ◽  
Testing Method ◽  
Partial Pressures

In this paper, we discuss the effects of different oxygen partial pressures on the deformation property and fracture characteristics of representative constituent materials for solid oxide fuel cells (SOFCs). The elastic modulus and fracture strength of 8 mol% yittria stabilized zirconia (8YSZ) and 10 mol% gadolinia doped ceria (10GDC) treated under different oxygen partial pressures were evaluated using the small-punch testing method in this study. The specimens of 8YSZ and 10GDC prepared by a sintering process were treated at 800 °C under an oxygen partial pressure in the range of 0.21 to 10−22 atm for 1 hour. The treated specimens were then fast cooled down to a room temperature, and their mechanical properties were measured under an atmospheric pressure condition by using the small-punch testing method. The experimental results revealed that both the elastic modulus and fracture strength of the 10GDC decreased drastically when the oxygen partial pressure of the treatment was less than 10−15 atm, whereas no significant variation in both the mechanical properties was observed for the 8YSZ. The elastic modulus and fracture strength of 10GDC for the treatment under 10−22 atm was reduced down to 10–20% of those treated under the atmospheric pressure. SEM observations revealed that the fracture surface of the 10GDC specimens was changed from transgranular mode to intergranular mode when the oxygen partial pressure was reduced, whereas the fracture surface of the 8YSZ specimens was transgranular regardless of the different oxygen partial pressures.

Comparison of the Ablation Mechanism of C/C-SiC Composite under Atmospheric and Low Pressure

2014 ◽  
Vol 91 ◽  
pp. 134-139 ◽  
Author(s):  
Roberson J. Silva ◽  
Homero S. Maciel ◽  
Alexei M. Essiptchouk ◽  
Gilberto Petraconi
Keyword(s):  
Surface Temperature ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Atmospheric Pressure ◽  
Thermal Protection ◽  
Sample Surface ◽  
Low Pressure ◽  
Protective Oxide ◽  
Maximum Surface ◽  
Maximum Surface Temperature

Comparisons of heating tests at atmospheric pressure and low pressure by using a thermal plasma torch were performed. A constant heat flux on the sample surface was applied in the study of the oxidation mechanism of C/C-SiC composite, used in thermal protection systems. The SEM and EDS analysis show an intensive glassification at the surface, which are strongly depend on the oxygen partial pressure and the sample surface temperature. For vacuum conditions, at maximum surface temperature of 1450 °C and the oxygen partial pressure of about 66 Pa, a uniform passivation layer of SiO2 is formed. At atmospheric pressure, under an oxygen partial pressure of 2.1×104 Pa, the maximum surface temperature is 400 °C higher than obtained in vacuum, reaching levels of 1850°C. Under these conditions, the protective oxide layer is partially volatilized with time, increasing the specific mass loss rate by a sublimation of the composite, directly exposed to the plasma jet. This effect is alike to what occurs in the process of transition from passive to active oxidation of SiC.

Electrical Conductivity Prediction in Langasite for Optimized Microbalance Performance at Elevated Temperatures

2002 ◽  
Vol 756 ◽  
Author(s):  
Huankiat Seh ◽  
Harry Tuller ◽  
Holger Fritze
Keyword(s):  
Electrical Conductivity ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
High Temperatures ◽  
Gas Sensors ◽  
Elevated Temperatures ◽  
Operating Conditions ◽  
Total Conductivity ◽  
Defect Model ◽  
Partial Pressures

ABSTRACTThe performance of the langasite-based crystal microbalance is limited due to reductions in its resistivity at high temperatures and reduced oxygen partial pressures. In this work, we utilize a recently developed defect model to predict the dependence of the ionic and electronic contributions to the total conductivity of langasite on temperature, oxygen partial pressure and acceptor and donor dopants. These results are used to select the type and concentrations of dopants expected to provide extended operating conditions for langasite-based gas sensors and crystal microbalances.

High Crystalline Cu2O Thin Films Prepared by Electric Current Heating Using Copper Wire

2014 ◽  
Vol 90 ◽  
pp. 66-71
Author(s):  
Tomoichiro Okamoto ◽  
Ko Yamazaki ◽  
Yuichiro Kuroki ◽  
Masasuke Takata
Keyword(s):  
Thin Films ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Electric Current ◽  
Atmospheric Pressure ◽  
Copper Wire ◽  
Time Response ◽  
Controlled Atmosphere ◽  
Electric Currents ◽  
Glass Substrates

Cu wires were heated by electric currents to fabricate Cu2O thin films. The films were successfully deposited on glass substrates placed above the wires at air pressures in the range of 100 - 40 Pa. Then the films were annealed in a controlled atmosphere and investigated the crystallinity, morphology and the time response to illumination of the films. After annealing at 800 °C at atmospheric pressure with oxygen partial pressure of 12 Pa, the crystallinity was increased and the time response of photoconduction was successfully improved.

pO2 stability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ

2011 ◽  
Vol 1309 ◽  
Author(s):  
Stefan F. Wagner ◽  
Simon Taufall ◽  
Christian Niedrig ◽  
Holger Götz ◽  
Wolfgang Menesklou ◽  
...  
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Chemical Stability ◽  
Coulometric Titration ◽  
Stability Limit ◽  
Operating Conditions ◽  
Perovskite Oxide ◽  
Low Oxygen ◽  
Electrical Measurements ◽  
Oxygen Pump

ABSTRACTThe mixed-conducting perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), given its outstanding oxygen ionic and electronic transport properties, is considered a promising material composition for oxygen transport membranes (OTM) operated at high temperatures.Its long-term stability under operating conditions is, however, still an important issue. Although the incompatibility of BSCF with CO2-containing atmospheres can be avoided by appropriate means (oxyfuel processes in the absence of carbon dioxide), the thermal as well as the chemical stability of BSCF itself are still under thorough investigation.This work is focused on the stability of BSCF in the targeted temperature range for OTM applications (700…900 °C) and in atmospheres with low oxygen contents. Previous studies in literature suggest limited chemical stability below oxygen partial pressures pO2 of around 10-6 bar.By using a coulometric titration method based on a zirconia “oxygen pump” setup, precise control of the oxygen partial pressure pO2 between 1 bar and 10-18 bar was facilitated. Combining electrical measurements on dense ceramic bulk samples performed as a function of pO2 with an XRD phase composition study of single phase BSCF powders subjected to various pO2 treatments, an assessment of the chemical stability of BSCF is facilitated as a function of oxygen partial pressure. It could thus be shown that the pO2 stability limit is considerably lower than previously assumed in literature.

Sign in / Sign up

Export Citation Format

Share Document