M. Teresa Izquierdo

Tail-end Hg capture on Au/carbon-monolith regenerable sorbents

In this work, a regenerable sorbent for Hg retention based on carbon supported Au nanoparticles has been developed and tested. Honeycomb structures were chosen in order to avoid pressure drop and particle entrainment in a fixed bed. Carbon-based supports were selected in order to easily modify the surface chemistry to favour the Au dispersion. Results of Hg retention and regeneration were obtained in a bench scale experimental installation working at high space velocities (for sorbent, 53,000 h(-1); for active phase, 2.6 × 10(8) h(-1)), 120 °C for retention temperature and Hg inlet concentration of 23 ppbv. Gold nanoparticles were shown to be the active phase for mercury capture through an amalgamating mechanism. The mercury captured by the spent sorbent can be easily released to be disposed or reused. Mercury evolution from spent sorbents was followed by TPD experiments showing that the sorbent can be regenerated at temperatures as low as 220 °C.

Sugarcane molasses as a pseudocapacitive material for supercapacitors

Oxygen-rich carbons were obtained from sugarcane molasses by two methods: direct carbonisation on one hand, and hydrothermal carbonisation and subsequent pyrolysis on the other hand. As no activation treatments were applied, the porous texture was poorly developed and mainly composed of ultramicropores with restricted access to electrolyte ions. Despite this, the directly carbonised molasses exhibited specific capacitances up to 153 F g−1 at 0.5 mV s−1 in 1 M H2SO4 electrolyte when tested as electrodes in a three-electrode system. Given the low specific surface areas of the carbons, the capacitance values were mainly assigned to their pseudocapacitance contributions. The latter were more adequately estimated by considering the NLDFT surface area (SNLDFT) than the BET area (ABET) due to the narrow porosity of the materials. Maximum values of pseudocapacitance contribution of 35.2% were attained for the carbon with a SNLDFT of 178 m2 g−1, which were explained by the high concentrations of surface oxygen groups, such as quinones and carbonyls.

Hydrogenation of coals catalysed by Mo effect and transformation of porous texture

Abstract The hydrogenation of 24 coals (LV bituminous to lignite) in the presence of Mo was studied. The hydrogenation temperatures were 300, 350 and 400°C, the hydrogen pressures 5 and 10 MPa, and the reaction time 30 min. At 300°C the Mo salts deposited on the coals do not decompose to the active MoS2 state, so the hydrogenation process is not significantly different from that in the absence of a catalyst and is influenced by the ease of diffusion, with a consequent increase in conversion with increasing macropore volume. At 350 and 400°C, MoS2 acts as a good catalyst and conversion is much greater than in the absence of a catalyst. Under these conditions, opening of pores in the coals has been detected as conversion increases; micropores develop to macropores in such a manner that the MoS2 particles can penetrate progressively into pores originally inaccessible, so an increase in the micropore volume or surface area favours conversion. This pore-opening is accompanied by an increase in cross-link density. At 5 MPa of H2, and increasing with temperature, some of the radicals formed are incorporated into the macromolecular structure by repolymerization reactions which result in blockage of the microporosity.

No removal in the selective catalitic reduction process over Cu and Fe exchanged type Y zeolites synthesized from coal fly ash

ABSTRACT The nitric oxide (NO) removal capacity of ion-exchanged zeolite Y obtained from coal combustion fly ash was evaluated in this work. Zeolite Y was exchanged either with Cu2+ or Fe2+ to obtain two different catalysts for the selective catalytic reduction of NOx from flue gas. The selective catalytic reduction experiments were carried out at temperatures ranging from 50°C to 350°C, water content 0% and 5% and 5% O2. In the absence of water, a total conversion of NO is obtained at 200°C for both zeolites, but important differences were found between zeolites LY-Cu and LY-Fe in the reduction of NO at temperatures lower than 200°C, and especially in the presence of water, that could be attributed to the different temperatures at which active species Cu2+ and Fe3+ are available for both ion-exchanged zeolites at the studied conditions. The greater surface area of zeolite LY-Cu can also contribute to its higher activity.The Spanish Ministry of Science and Innovation and the European Community (European Regional Development Fund) provided financial support for this work (Project No. CTM04252C02).

A critical short review of equilibrium and kinetic adsorption models for VOCs breakthrough curves modelling

Volatile organic compounds emission has important effects over the environment and human beings health. When these substances cannot be substituted, adsorption systems are still a very common solution to VOCs emission, but for their design, previous laboratory work is necessary: adsorption isotherms and breakthrough curves must be obtained. The first ones establish the maximal amount of adsórbate retained over the solid adsorbent for a certain pressure of the adsórbate, and the second ones define the adsorption process kinetics. Once this information is studied, a theoretical breakthrough time model can be built up, and then the scale up of the adsorption system can be developed. This process is rather complex for multicomponent gas mixtures, where a competition between adsorbates happens. Thus, the aim of this paper is to establish a guide for authors willing to develop breakthrough time prediction models for multicomponent systems through a critical review of different adsorption and kinetic models.

Influence of the porous nature of coals on Mo-catalysed hydrogenation kinetics

Abstract Mo-catalysed hydrogenation processes of four coals, ranked between lignite B and high volatile bituminous coals, are studied. Ammonium heptamolybdate was used as a catalyst precursor. Hydrogenations were carried out at 300, 350 and 400°C at a hydrogen pressure of 10 MPa, with reaction times ranging from 5 to 30 min. The maximum rate of the process, related to the textural characteristics of the coal, was calculated from the relationship between the conversion time and the reaction time. The results indicate that at 300°C the catalyst is not active and the reaction mainly depends on the efficiency of the mass transfer process and thus on the coal macropore volume. At higher temperatures, however, the process takes place catalytically and in this case the catalytic activity is influenced by the coal surface.