scholarly journals Direct Benzyl Alcohol and Benzaldehyde Synthesis from Toluene over Keggin-Type Polyoxometalates Catalysts: Kinetic and Mechanistic Studies

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Allam Djaouida ◽  
Mansouri Sadia ◽  
Hocine Smaïn
Keyword(s):  
Benzyl Alcohol ◽  
Partial Oxidation ◽  
Product Distribution ◽  
Operating Conditions ◽  
Catalyst Composition ◽  
Rate Limiting Step ◽  
Ft Ir ◽  
Keggin Polyoxometalate ◽  
Catalyst Systems ◽  
Rate Limiting

The catalytic activity of various Keggin polyoxometalate catalysts has been investigated in the gas-phase partial oxidation of toluene to produce benzyl alcohol and benzaldehyde. The catalyst systems HPMo12O40, HPMo11VO40, FePMo12O40, and PMo11FeO39 were prepared and characterized by FT-IR, UV-visible, SEM, XRD, TGA, and cyclic voltammetry. The acid/base properties were evaluated using the decomposition of isopropanol. Catalytic studies were carried under atmospheric pressure and over the temperature range 200°C–350°C, using carbon dioxide as a mild oxidant. Toluene conversion and product distribution depend mainly on the catalyst composition and operating conditions. In addition to benzaldehyde, benzyl alcohol is obtained with a high selectivity on the PMo11FeO39 catalyst. The kinetic data show that the reoxidation of the reduced catalyst is the rate-limiting step for the partial oxidation reaction of toluene.

scholarly journals Effect of Prior Oxidation on the Reduction Behavior of Magnetite-Based Iron Ore During Hydrogen-Induced Fluidized Bed Reduction

2021 ◽  
Author(s):  
Heng Zheng ◽  
Daniel Spreitzer ◽  
Thomas Wolfinger ◽  
Johannes Schenk ◽  
Runsheng Xu
Keyword(s):  
Fluidized Bed ◽  
Partial Oxidation ◽  
Iron Ore ◽  
Reduction Rate ◽  
Deep Oxidation ◽  
Initial Reaction ◽  
Oxidation Treatment ◽  
Rate Limiting Step ◽  
Rate Limiting ◽  
Prior Oxidation

AbstractMagnetite-based iron ore usually shows a high sticking tendency and a poor reducibility in the fluidized bed because of its dense structure. To enhance the fluidization and reduction behaviors of magnetite-based iron ore during hydrogen-induced fluidized bed reduction, the effect of a prior oxidation treatment is investigated. The results show that the untreated magnetite-based iron ore cannot be fluidized successfully in the tested temperature range between 600 °C and 800 °C. At 600 °C reduction temperature, the de-fluidization can be avoided by a prior oxidation treatment. At higher reduction temperatures, the fluidization behavior can be further improved by an addition of 0.5 wt pct MgO. Magnesiowüstite (FexMg1−xO) is formed, which decreases the contact chance of the sticky surface between particles. Regarding to the reduction rate, a prior partial oxidation is more beneficial compared to deep oxidation. The kinetic analysis shows that MgO could promote the initial reaction. The reaction rate limiting step is no longer diffusion but chemical reaction for prior partly oxidized samples. A prior partial oxidation combined with an addition of MgO is considered to be a promising pretreatment method for a successful processing of magnetite-based iron ore.

scholarly journals Statistically Guided Synthesis of MoV-Based Mixed-Oxide Catalysts for Ethane Partial Oxidation

Catalysts ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 370
Author(s):  
Juan Jimenez ◽  
Kathleen Mingle ◽  
Teeraya Bureerug ◽  
Cun Wen ◽  
Jochen Lauterbach
Keyword(s):  
Acetic Acid ◽  
Partial Oxidation ◽  
Mixed Oxide ◽  
Structural Integrity ◽  
Product Distribution ◽  
Catalytic Performance ◽  
Oxide Catalysts ◽  
Acid Yield ◽  
Mixed Oxide Catalysts ◽  
Catalyst Composition

The catalytic performance of Mo8V2Nb1-based mixed-oxide catalysts for ethane partial oxidation is highly sensitive to the doping of elements with redox and acid functionality. Specifically, control over product distributions to ethylene and acetic acid can be afforded via the specific pairing of redox elements (Pd, Ni, Ti) and acid elements (K, Cs, Te) and the levels at which these elements are doped. The redox element, acid element, redox/acid ratio, and dopant/host ratio were investigated using a three-level, four-factor factorial screening design to establish relationships between catalyst composition, structure, and product distribution for ethane partial oxidation. Results show that the balance between redox and acid functionality and overall dopant level is important for maximizing the formation of each product while maintaining the structural integrity of the host metal oxide. Overall, ethylene yield was maximized for a Mo8V2Nb1Ni0.0025Te0.5 composition, while acetic acid yield was maximized for a Mo8V2Nb1Ti0.005Te1 catalyst.

Investigations on the changes in anaerobic biodegradability and biotoxicity of an industrial microbial biomass induced by a thermochemical pretreatment

2000 ◽  
Vol 41 (3) ◽  
pp. 137-144 ◽  
Author(s):  
J.P. Delgèns ◽  
V. Penaud ◽  
M. Torrijos ◽  
R. Moletta
Keyword(s):  
Anaerobic Digestion ◽  
Microbial Biomass ◽  
Operating Conditions ◽  
Thermochemical Pretreatment ◽  
Anaerobic Microorganisms ◽  
Rate Limiting Step ◽  
The Poor ◽  
Anaerobic Biodegradability ◽  
Physico Chemical ◽  
Rate Limiting

In the anaerobic digestion of solid wastes, hydrolysis is the rate limiting step and physico-chemical pretreatment is often required to promote solubilization of organic matter. As an illustration, anaerobic digestion was limited by the substrate solubilization step during continuous cultures performed with an industrial microbial biomass. In optimal operating conditions determined for the hydrolysis-acidogenesis step (T=35°C; pH=8.5; OLR=5.4 g COD/l.d) 50.6% COD solubilization was achieved. A thermochemical pretreatment based on sodium hydroxide addition, was used in order to enhance COD solubilization. Optimal conditions for COD solubilization were pH=12, T=140°C for 30 minutes. In these conditions, 70% COD solubilization was achieved. However, anaerobic biodegradability of the pretreated substrate was not improved and remained near 40%. The poor anaerobic biodegradability performances were attributed to the soluble molecules generated during the thermochemical pretreatment that were refractory and/or inhibitory to anaerobic microorganisms. Fractionation of the soluble pretreated microbial biomass by two methods (treatment with adsorbent resins and precipitation by pH adjustment) demonstrated that high molecular weight compounds (>100 kDa) are involved in the poor biodegradability and in the biotoxicity observed. Partial decolorization through resin use and acid precipitation remove these compounds. The consequence of their removal was an increase of the production of biogas.

scholarly journals Probing Differences in Mass-Transfer Coefficients in Beaker and Stirrer Digestion Systems and the USP Dissolution Apparatus 2 Using Benzoic Acid Tablets

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2168
Author(s):  
Timothy A. G. Langrish ◽  
Chao Zhong ◽  
Lizhe Sun
Keyword(s):  
Mass Transfer ◽  
Benzoic Acid ◽  
Reynolds Numbers ◽  
Operating Conditions ◽  
External Mass Transfer ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Rate Limiting Step ◽  
Dissolution Apparatus ◽  
Rate Limiting

Measurements of external mass-transfer coefficients for dissolution have been made with benzoic acid tablets with a diameter of 13 mm and approximately 3 mm thick, using two different dissolution systems. One system has been a beaker with a platform for the tablet and either 80 mL or 120 mL of water, with three different types of stirrers, and the other has been a USP dissolution apparatus 2 (paddle) with either 200 mL or 900 mL water. Various stirring speeds have also been used in the different pieces of equipment. The same mass-transfer coefficient may potentially be obtained from the same tablet by adjusting the operating conditions in the two different devices. The ranges of the external mass-transfer coefficients measured in both devices overlapped significantly, with the range being 0.193–4.48 × 10−5 m s−1 in the beaker and stirrer system and 0.222–3.45 × 10−5 m s−1 in the USP dissolution apparatus 2. Dimensional analysis of the results, using Sherwood and Reynolds numbers, shows that the Ranz–Marshall correlation provides a lower bound for estimates of the Sherwood numbers measured experimentally. Calculations of time constants for mass transfer suggest that mass transfer may be a rate-limiting step for dissolution and food digestion under some circumstances. The range of mass-transfer coefficients measured here is representative of other measurements from the literature, and the use of the Ranz–Marshall correlation supports the suggestion that this range of values should be generally expected in most situations.

scholarly journals Validation of Flory-Huggins model for phenol adsorption by Parthenium hysterophorus in a batch system

2019 ◽  
Vol 2 (2) ◽  
Author(s):  
Zakia Latif1 ◽  
Aliya Fazal2 ◽  
Muhammad Aziz Choudhary1 ◽  
Zahoor Ahmad1 ◽  
Muhammad Aslam Mirza1
Keyword(s):  
Active Sites ◽  
Cost Effective ◽  
Toxic Waste ◽  
Parthenium Hysterophorus ◽  
Phenol Adsorption ◽  
Rate Limiting Step ◽  
Adsorbent Surface ◽  
Ft Ir ◽  
Biomass Dosage ◽  
Rate Limiting

Parthenium hysterophorus weed powder was studied as adsorbent for phenol adsorption from its aqueous standardized solution. The adsorption of pollutant was found improving with an increase of biomass dosage and contact time. The intraparticle diffusion of phenol onto adsorbent surface was identified to be the rate limiting step. Linear form of Flory-Huggins model revealed preeminence to Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich due to highest value of R2. The remediation process was figured out as a physisorption rather than a chemical one based on value of E (0.21KJ/mol). Active sites of sorbent surface identified by FT-IR were oxygen containing functional groups. Recent study proposes cost effective utilization of toxic allergent for treatment of toxic waste.

scholarly journals A Review on Production of Light Olefins via Fluid Catalytic Cracking

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1089
Author(s):  
Zahra Gholami ◽  
Fatemeh Gholami ◽  
Zdeněk Tišler ◽  
Martin Tomas ◽  
Mohammadtaghi Vakili
Keyword(s):  
Catalytic Cracking ◽  
Product Distribution ◽  
Operating Conditions ◽  
Fluid Catalytic Cracking ◽  
Light Olefins ◽  
Feed Composition ◽  
Physical Strength ◽  
Catalyst Composition ◽  
Olefin Production ◽  
Fcc Catalysts

The fluid catalytic cracking (FCC) process is an alternative olefin production technology, with lower CO2 emission and higher energy-saving. This process is used for olefin production by almost 60% of the global feedstocks. Different parameters including the operating conditions, feedstock properties, and type of catalyst can strongly affect the catalytic activity and product distribution. FCC catalysts contain zeolite as an active component, and a matrix, a binder, and a filler to provide the physical strength of the catalyst. Along with the catalyst properties, the FCC unit’s performance also depends on the operating conditions, including the feed composition, hydrocarbon partial pressure, temperature, residence time, and the catalyst-to-oil ratio (CTO). This paper provides a summary of the light olefins production via the FCC process and reviews the influences of the catalyst composition and operating conditions on the yield of light olefins.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

Sign in / Sign up

Export Citation Format

Share Document