Evaluation of acetanilide and antipyrine adsorption on lignin-derived activated carbons.

In this study, the removal of two emerging pollutants (EPs), antipyrine and acetanilide, through adsorption on activated carbons (ACs) prepared by chemical activation of Organosolv lignin with H3PO4 were evaluated. ACs with different pore size distribution were obtained at different impregnation ratios (H3PO4/lignin, 0.5-3.0 w/w) and activating temperatures (500-900 °C). The porosity and surface chemistry of the ACs were determined, and a bimodal size distribution of micropores and narrow mesopores was observed for the different ACs. These ACs were tested for antipyrine and acetanilide adsorption in aqueous solutions in a batch system at 20 °C and low concentration levels (0.5-10 ppm). In general, the ACs exhibited higher adsorption affinity to acetanilide than to antipyrine due to its smaller molecular size. Langmuir adsorption isotherm was able to describe the adsorption equilibrium data. A new Linear Driving Force (2-LDF) kinetic model, based on the bimodal size distribution of micropores and narrow mesopores observed for the ACs has been developed. The new model provided a more accurate description of the batch adsorption rates than that obtained from conventional kinetic models, and also enabled to relate the pore size distribution of the adsorbent with the adsorption kinetics. The validity of this model was checked in small-scale column fixed bed adsorption for the AC showing the highest affinity for both EP. The kinetic model and equilibrium adsorption isotherm obtained from the batch experiments were successfully used to provide an accurate description of the bed service time and the full breakthrough profile of acetanilide and antipyrine.

Electrospinning of Magnetite-Polyacrylonitrile Composites for the Production of Oxygen Reduction Reaction Catalysts.

In this study, electrospun carbon fiber electrodes were prepared by the carbonization of PAN-Fe3O4 electrospun fibers at 800 °C for their use as catalysts in the oxygen reduction reaction in an alkaline electrolyte. Magnetic nanofiber mats were fabricated using a needle-free electrospinning method by incorporating magnetic nanoparticles into a polymer solution. Electrochemical tests revealed that the oxygen reduction reaction (ORR) activity is optimized at an intermediate magnetite loading of 30% wt. These catalysts not only show better performance compared to their counterparts but also achieve high selectivity to water at low potentials. The onset and half-wave potentials of 0.92 and 0.76 V shown by these samples are only slightly behind those of the commercial Pt 20%-carbon black ORR catalyst. The obtained results point out that the electrospinning of PAN-Fe3O4 solutions allows the preparation of advanced N-Fe ORR catalysts in fibrillar morphology.

A Kinetic Model Considering Catalyst Deactivation for Methanol-to-Dimethyl Ether on a Biomass-Derived Zr/P-Carbon Catalyst.

A Zr-loaded P-containing biomass-derived activated carbon (ACPZr) has been tested for methanol dehydration between 450 and 550 °C. At earlier stages, methanol conversion was complete, and the reaction product was mainly dimethyl ether (DME), although coke, methane, hydrogen and CO were also observed to a lesser extent. The catalyst was slowly deactivated with time-on-stream (TOS), but maintained a high selectivity to DME (>80%), with a higher yield to this product than 20% for more than 24 h at 500 °C. A kinetic model was developed for methanol dehydration reaction, which included the effect of the inhibition of water and the deactivation of the catalyst by coke. The study of stoichiometric rates pointed out that coke could be produced through a formaldehyde intermediate, which might, alternatively, decompose into CO and H2. On the other hand, the presence of 10% water in the feed did not affect the rate of coke formation, but produced a reduction of 50% in the DME yield, suggesting a reversible competitive adsorption of water. A Langmuir-Hinshelwood reaction mechanism was used to develop a kinetic model that considered the deactivation of the catalyst. Activation energy values of 65 and 51 kJ/mol were obtained for DME and methane production in the temperature range from 450 °C to 550 °C. On the other hand, coke formation as a function of time on stream (TOS) was also modelled and used as the input for the deactivation function of the model, which allowed for the successful prediction of the DME, CH4 and CO yields in the whole evaluated TOS interval.

Acid Mesoporous Carbon Monoliths from Lignocellulosic Biomass Waste for Methanol Dehydration.

Activated carbon monoliths (ACMs), with 25 cells/cm2, were prepared from the direct extrusion of Alcell, Kraft lignin and olives stones particles that were impregnated with phosphoric acid, followed by activation at 700 °C. These ACMs were used as catalysts for methanol dehydration reaction under air atmosphere. ACM that was prepared from olive stone and at impregnation ratio of 2, OS2, showed the highest catalytic activity, with a methanol conversion of 75%, a selectivity to dimethyl ether (DME) higher than 90%, and a great stability under the operating conditions studied. The results suggest that the monolithic conformation, with a density channel of 25 cells/cm2 avoid the blockage of active sites by coke deposition to a large extent. Methanol conversion for OS2 was reduced to 29% in the presence of 8%v water, at 350 °C, although the selectivity to DME remained higher than 86%. A kinetic model of methanol dehydration in the presence of air was developed, while taking into account the competitive adsorption of water. A Langmuir-Hinshelwood mechanism, whose rate-limiting step was the surface reaction between two adsorbed methanol molecules, represented the experimental data under the conditions studied very well. An activation energy value of 92 kJ/mol for methanol dehydration reaction and adsorption enthalpies for methanol and water of -12 and -35 kJ/mol, respectively, were obtained.