Experimental and computational investigation of the electrocatalytic hydrogenation of phenol in an electrochemical cell

2004 ◽  
Vol 82 (5) ◽  
pp. 641-648 ◽  
Author(s):  
A Chagnes ◽  
F Laplante ◽  
F Kerdouss ◽  
P Proulx ◽  
H Ménard
Keyword(s):  
Fluidized Bed ◽  
Cathodic Polarization ◽  
Volume Fraction ◽  
Fluid Dynamic ◽  
Aqueous Media ◽  
Vitreous Carbon ◽  
High Porosity ◽  
Electrocatalytic Hydrogenation ◽  
Reticulated Vitreous Carbon ◽  
Fluidized Bed Electrode

The electrocatalytic hydrogenation (ECH) of phenol was carried out in aqueous media with a commercial Pd/Al2O3 (5% w/w) catalyst. A porous matrix of reticulated vitreous carbon (RVC) was used to study the porosity – stirring speed coupling (PSSC) effect on the phenol hydrogenation to form cyclohexanone and cyclohexanol. In accordance with the PSSC, the electrode can act as a fluidized bed electrode or as an agglomerated electrode. Fluidized bed electrodes develop for low porosity matrices (10–30 ppi, ppi = pores per inch) at high stirring speeds (>600 rpm), while agglomerated electrodes are obtained for high porosity matrices (60–100 ppi) with moderate stirring speeds under cathodic polarization. The distribution of the volume fraction of the particles and the agglomeration of the particles have been simulated by computational fluid dynamic (CFD) methods with FLUENT software. For the agglomerated electrode, the numerical simulations demonstrate the beneficial contribution of the cathodic polarization to the agglomeration process. However, at 650 rpm, for the fluidized bed electrode, the volume fraction of the particles in the RVC does not account for the distinction in the ECH efficiency between the 30 ppi matrix and the 100 ppi matrix. For a given amount of Pd/Al2O3 catalyst, it is observed that the ECH rates depend on the PSSC and increase in the following order: 100/650 < 30/650 < 100/200. Key words: electrocatalytic hydrogenation (ECH), CFD, fluid mechanics, porous media, powder, porosity – stirring speed coupling (PSSC), reticulated vitreous carbon (RVC).

Considerations about phenol electrohydrogenation on electrodes made with reticulated vitreous carbon cathode

2003 ◽  
Vol 81 (3) ◽  
pp. 258-264 ◽  
Author(s):  
François Laplante ◽  
Louis Brossard ◽  
Hugues Ménard
Keyword(s):  
Physical Vapor Deposition ◽  
Detrimental Effect ◽  
Aqueous Media ◽  
Vitreous Carbon ◽  
Electrocatalytic Hydrogenation ◽  
Reticulated Vitreous Carbon ◽  
Composite Powders ◽  
Agglomeration Process ◽  
Adsorption Of Organic Molecules

The electrocatalytic hydrogenation (ECH) of phenol was carried out in aqueous media with catalytic powders. The catalytic powders were composed of palladium nanoaggregates deposited on various substrates such as Al2O3, BaSO4, and BaCO3. Composite powders are trapped (upon stirring) into a reticulated vitreous carbon (RVC) matrix, allowing a rapid in situ build-up of the electrode and alleviating the use of a binder, since the latter may have a detrimental effect on the ECH. For a given amount of noble metal (5% palladium by weight), it is observed that the ECH of phenol to cyclohexanol increases in the following order: Pd/BaCO3 < Pd/BaSO4 < Pd/Al2O3. It is deduced that the ECH rate is largely dependent on the adsorption of organic molecules on the nonmetallic substrate, and a model is considered to explain such a behavior. The ECH of phenol is also feasible at a reasonable rate with composite Pd/Al2O3 (0.25% Pd by weight) powders fabricated by physical vapor deposition because the peripheral distribution of Pd nanoaggregates is favorable towards the ECH.Key words: electrocatalytic hydrogenation (ECH) of phenol, reticulated vitreous carbon (RVC), alumina-based catalyst, agglomeration process, adlineation point, adsorption.

An Analytical-Experimental Study for the Determination of the Effective Thermal Conductivity of High Porosity Fibrous Foams

1999 ◽  
Author(s):  
Anandaroop Bhattacharya ◽  
Varaprasad V. Calmidi ◽  
Roop L. Mahajan
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Cross Sections ◽  
Comprehensive Analysis ◽  
Vitreous Carbon ◽  
High Porosity ◽  
Pore Density ◽  
Reticulated Vitreous Carbon ◽  
Fluid Media

Abstract In this paper, we present a comprehensive analysis for estimating the effective thermal conductivity of high porosity fibrous foams. Commercially available fibrous foams form a complex array of interconnected fibers with an irregular lump of metal at the intersection of two fibers. In our theoretical analysis, we represent this structure by a model consisting of two-dimensional hexagonal arrays where the fibers form the sides of the hexagons. The lump is taken into account by considering a square, hexagonal or circular blob of metal at the intersection. The analysis shows that the effective thermal conductivity of the foam depends strongly on the porosity and the ratio of the cross-sections of the fiber and the intersection. It has no systematic dependence on pore density. Further, the choice of the geometric configuration of the intersection affects the estimate of the effective thermal conductivity. Experimental data with aluminum and Reticulated Vitreous Carbon (RVC) foams, using air and water as fluid media are used to validate the analytical predictions. Finally, the experimental results are used to arrive at a simple, closed-form empirical correlation for estimating the effective thermal conductivity in terms of the porosity, and the solid and fluid conductivities.

Article

1999 ◽  
Vol 77 (7) ◽  
pp. 1225-1229 ◽  
Author(s):  
Pierre Dabo ◽  
André Cyr ◽  
Jean Lessard ◽  
Louis Brossard ◽  
Hugues Ménard
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Raney Nickel ◽  
Activated Charcoal ◽  
Vitreous Carbon ◽  
Electrocatalytic Hydrogenation ◽  
Reticulated Vitreous Carbon ◽  
Nickel Boride

Electrodes consisting of particles of a transition metal entrapped and dispersed in a reticulated vitreous carbon (RVC) matrix were prepared in situ by stirring the particles in the presence of an RVC cathode. Such electrodes were used for the electrocatalytic hydrogenolysis (ECHsis) of 4-phenoxyphenol, a compound representative of the 4-O-5 type linkage in lignins. The electrolyses were carried out under galvanostatic control in aqueous 1 M NaOH. Raney nickel, nickel boride, and transition metals supported on activated charcoal or alumina were used as catalytic powders. The extent and efficiency of the ECHsis of 4-phenoxyphenol was found to depend on the catalyst and on the temperature.Key words: electrocatalytic hydrogenation, electrocatalytic hydrogenolysis, 4-phenoxyphenol, Raney nickel, palladium on charcoal, palladium on alumina.

scholarly journals Non-spherical particle mixing behaviors by spherical inert particles assisted in a fluidized bed

2019 ◽  
Vol 17 (2) ◽  
pp. 509-524 ◽  
Author(s):  
An-Xing Ren ◽  
Tian-Yu Wang ◽  
Tian-Qi Tang ◽  
Yu-Rong He
Keyword(s):  
Fluidized Bed ◽  
Binary Mixtures ◽  
Volume Fraction ◽  
Fluid Dynamic ◽  
Rolling Friction ◽  
Spherical Particles ◽  
Industrial Processes ◽  
Vertical Orientation ◽  
Inert Particles ◽  
Particle Velocities

AbstractFluidized beds are widely used in many industrial fields such as petroleum, chemical and energy. In actual industrial processes, spherical inert particles are typically added to the fluidized bed to promote fluidization of non-spherical particles. Understanding mixing behaviors of binary mixtures in a fluidized bed has specific significance for the design and optimization of related industrial processes. In this study, the computational fluid dynamic–discrete element method with the consideration of rolling friction was applied to evaluate the mixing behaviors of binary mixtures comprising spherocylindrical particles and spherical particles in a fluidized bed. The simulation results indicate that the differences between rotational particle velocities were higher than those of translational particle velocities for spherical and non-spherical particles when well mixed. Moreover, as the volume fraction of the spherocylindrical particles increases, translational and rotational granular temperatures gradually increase. In addition, the addition of the spherical particles makes the spherocylindrical particles preferably distributed in a vertical orientation.

Electrocatalytic hydrogenation of catechol on Rh–Al2O3 in different media — pH-Dependent reduction mechanism for intermediate formation

2006 ◽  
Vol 84 (12) ◽  
pp. 1640-1647 ◽  
Author(s):  
Anne Brisach-Wittmeyer ◽  
Nicolas-Alexandre Bouchard ◽  
Raymond Breault ◽  
Hugues Ménard
Keyword(s):  
Cyclic Voltammetry ◽  
Uv Spectroscopy ◽  
Aqueous Media ◽  
Intermediate Formation ◽  
Vitreous Carbon ◽  
Reduction Mechanism ◽  
Electrocatalytic Hydrogenation ◽  
Vis Spectroscopy ◽  
Ph Dependent ◽  
Henry Constants

The electrocatalytic hydrogenation of catechol was carried out in aqueous media in different pH ranges with Rh–Al2O3 powder catalyst. The reactions were conducted in an H-cell used as a dynamic cell, with a reticulated vitreous carbon electrode in contact with the catalyst powder as the working electrode. It was shown that the final product is 1,2-cyclohexanediol (cis and trans isomers) and that several intermediates are detected depending on the pH of the solution. Different media, from pH 5 to 13, were studied. One of the intermediates is 1,2-cyclohexanedione, detected at all pH values. The other is 2-hydroxycyclohexan-1-one, only observed at pH ≤ 7. To determine the mechanism of the reactions involved, the electrocatalytic hydrogenation of these intermediates to form the final 1,2-cyclohexanediol product was also conducted, and their UV spectroscopy and cyclic voltammetry data recorded. The influence of the nature of the solution was screened by measuring the Henry constant of each molecule.Key words: electrocatalytic hydrogenation of catechol, pH-dependent reduction mechanism, UV–vis spectroscopy, cyclic voltammetry, Henry constants.

scholarly journals Recent advances on modified reticulated vitreous carbon for water and wastewater treatment – A mini-review

Chemosphere ◽  
2021 ◽  
pp. 131573
Author(s):  
Vanessa M. Vasconcelos ◽  
Géssica O.S. Santos ◽  
Katlin I.B. Eguiluz ◽  
Giancarlo R. Salazar-Banda ◽  
Iara de Fatima Gimenez
Keyword(s):  
Wastewater Treatment ◽  
Vitreous Carbon ◽  
Reticulated Vitreous Carbon ◽  
Water And Wastewater Treatment ◽  
Recent Advances ◽  
Water And Wastewater

scholarly journals Post-Processing of Cold Sprayed Ti-6Al-4V Coatings by Mechanical Peening

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1038
Author(s):  
Niroj Maharjan ◽  
Ayan Bhowmik ◽  
Chunwai Kum ◽  
Jiakun Hu ◽  
Yongjing Yang ◽  
...  
Keyword(s):  
Surface Integrity ◽  
Volume Fraction ◽  
Aerospace Industry ◽  
Metal Alloys ◽  
High Porosity ◽  
Post Processing ◽  
Premature Failure ◽  
Additive Manufacturing Technology ◽  
Hammer Peening ◽  
Compressive Residual Stresses

Cold spray is an emerging additive manufacturing technology used in the aerospace industry to repair damaged components made of expensive metal alloys. The cold sprayed layer is prone to surface integrity issues such as high porosity and inadequate bonding at the substrate-coating interface, which may cause premature failure of the repaired component. This study explored the use of mechanical peening as a post-processing method to improve the surface integrity of the cold sprayed component by modifying mechanical properties near the surface. Two mechanical peening processes, deep cold rolling (DCR) and controlled hammer peening (CHP), were utilized to improve cold sprayed Ti-6Al-4V coating on the Ti-6Al-4V substrate. Experimental results indicate that DCR and CHP increase the strength of the bond between the coating and substrate due to introduction of compressive residual stresses. In addition, porosity is also reduced by as much as 71%. The improvement is attributed to both the compacting effect of peening processes and the increment in the volume fraction of deformed regions.

Sign in / Sign up

Export Citation Format

Share Document