Miguel A. Gilarranz

Pd-Al pillared clays as catalysts for the hydrodechlorination of 4-chlorophenol in aqueous phase.

Catalysts based on pillared clays with Pd-Al were synthesized from a commercial bentonite and tested for catalytic hydrodechlorination (HDC) using 4-chlorophenol (4-CPhOH) as target compound and formic acid as hydrogen source. Stable Pd-Al pillared clays, with a strong fixation of the active phase to the solid support were obtained since no Pd was detected in the reaction media. The incorporation of Pd to the pillared clay structure yielded catalysts with high activity in the reaction studied reaching a complete removal of the 4-CPhOH under mild conditions of temperature (50-70 degrees C). Phenol was not the only reaction product formed, since a more hydrogenated product such as cyclohexanone was detected in the effluent, which indicates additional hydrogenation of phenol. The influence of the method of introduction of Pd in the pillared clay (ion-exchange or impregnation) and Pd concentration in the catalytic activity were studied as well as other important operating variables such as reaction temperature, catalyst concentration, 4-CPhOH initial concentration and formic acid to 4-CPhOH molar ratio. The catalysts prepared suffered deactivation after three consecutive runs, probably due to carboneous deposits formation since no appreciable Pd leaching was observed.

Hydrodechlorination of 4-chlorophenol in water with formic acid using a Pd/activated carbon catalyst

This work reports on the feasibility of hydrodechlorination as a treatment technique for chlorophenols-bearing wastewaters using formic acid as a hydrogen source. 4-Chlorophenol (4-CPhOH) has been used as target compound and the experiments were carried out in batch and continuous mode with a commercial activated carbon-supported Pd (0.5 wt.%) catalyst. The variables studied in the batch runs were HCOOH/4-CPhOH molar ratio (10-1000), temperature (25-75 degrees C) and catalyst concentration (250-1000 mg/L). The continuous experiments were performed in a fixed bed reactor where aqueous solutions of formic acid and 4-CPhOH with molar ratios between 50 and 100 were continuously fed to the reactor, at different space-time values in the range of 10.7-42.8 kg(cat)h/mol. Reaction temperatures from 35 to 100 degrees C were tested and the pressure was fixed at 2.5bar. Conversion values above 99% for 4-CPhOH were obtained in batch experiments, but using a HCOOH/4-CPhOH molar ratio as high as 500. Moreover, most of the phenol produced was adsorbed on the catalyst. Continuous runs were performed to evaluate the efficiency of the catalyst under lower HCOOH/4-CPhOH ratios and to explore the possibility of converting phenol to more hydrogenated products. The results indicated that the HCOOH/4-CPhOH molar ratios needed were an order of magnitude lower than those required in batch runs to achieve conversions of 4-CPhOH close to 95%. Besides, phenol was not the only reaction product formed, since a more hydrogenated product such as cyclohexanone was detected in the effluent, which indicates additional hydrogenation of phenol in contrast to the behaviour observed in batch experiments. A loss of activity was observed in the continuous runs after 20-30 h on stream.

PHENOLIC OH GROUP ESTIMATION BY FTIR AND UV SPECTROSCOPY. APPLICATION TO ORGANOSOLV LIGNINS

The phenolic hydroxyl group content of 34 acetylated organosolv lignins, obtained by ethanol or methanol autocatalyzed pulping of Eucalyptus globulus was measured by FTIR spectroscopy. The absorbance of aromatic IR ester bands of acetylated lignins at 1765 cm−1 was employed to estimate the lignin phenolic hydroxyl group content. To compare different samples the spectra recorded were baseline corrected and normalized with the bands around 1500, 1600 and 1423 cm−1. Partial least-squares (PLS) and multiple linear regression (MLR) calibrations were carried out to establish a mathematical correlation between UV data sets and FTIR spectra. The best results were shown by the models obtained by PLS regression. In these models the band at 1766 cm−1 was normalized using the band at 1744 cm−1 and the baseline corrections were performed with the bands at 1423 cm−1 (ethanol lignin) and 1507 cm−1 (methanol lignin).

Lignin behavior during the autocatalyzed methanol pulping of Eucalyptus globulus. Changes in molecular weight and functionality.

Summary The molecular weight distribution and functional group contents (phenolic and carbonyl) of lignin samples from the autocatalyzed pulping of Eucalyptus globulus wood were determined. A total of 17 pulping runs were carried out at different conditions according to a surface response design experimental matrix (central composite). The influence of pulping temperature (170–200°C), pulping time (40–120 min) and methanol concentration (30–70%, w/w) on the characteristics of the isolated lignins was studied. Empirical models were developed and used to predict the lignin properties as a function of the cooking conditions. Under high temperature, long cooking time and low alcohol concentration, a rise in functional groups content and a drop in molecular weight of lignin

The effect of autocatalyzed ethanol pulping on lignin characteristics

The development of phenolic hydroxyl and carbonyl groups and the changes in the molecular weight of lignin during the autocatalyzed ethanol-water pulping of Eucalyptus globulus wood was modeled. The models were developed using a response surface method and were employed to study the influence of cooking temperature, cooking time and ethanol concentration on lignin characteristics. The functional groups content was found to increase as the cooking time was risen and the concentration of ethanol in the pulping liquor was reduced. These cooking conditions lead to a more extensive cleavage of the bonds between lignin units due to the longer treatment, higher temperature and increased acidity of the pulping liquor. The cleavage of lignin bonds resulted in the occurrence of new functional groups and a reduction in lignin molecular weight. The steady decrease in molecular weight with the intensity of cooking conditions indicates that lignin condensation does not play an important role under the conditions studied.

Identification of by-products and toxicity assessment in aqueous-phase hydrodechlorination of diuron with palladium on activated carbon catalysts

The hydrodechlorination (HDC) of diuron in aqueous phase with hydrogen using two different activated carbon-supported Pd catalysts was studied. A commercial activated carbon and one prepared by chemical activation of grape seeds with phosphoric acid (GS) were evaluated as supports, being the catalysts tested in a wide range of temperature (30-100 °C) and space-time (78-311 kgcat h mol(-1)). Diuron conversion was above 70% under all the conditions tested. The Pd catalyst supported on GS showed the highest activity in terms of diuron conversion within the temperature range studied, allowing nearly complete conversion above 50 °C. However, a gradual loss of activity with time was observed for this catalyst. A complete route of hydrogenation of diuron was elucidated. Two reaction routes one leading to fenuron and another to aniline were identified. As the temperature and space-time were increased, the formation of fenuron (via monuron) was found to be favored. The toxicity of the reaction products was evaluated, being the route to fenuron and monuron, the one giving rise to a significant decrease of ecotoxicity.

Improved synthesis and hydrothermal stability of Pt/C catalysts based on size-controlled nanoparticles

A novel method for the preparation of stable Pt/C catalysts with size-controlled nanoparticles has been developed. The method is based on in situ synthesis of the nanoparticles (reduction with NaBH4 in the presence of a support and PVP). Compared to the conventional ex situ route (colloidal synthesis followed by impregnation), this in situ route yields smaller nanoparticles (2.5–3.9 nm) of narrower size distribution. The catalysts prepared by the in situ synthesis showed a higher stability in water at 80 °C, indicating a stronger interaction between the support and the metallic phase. Hydrothermal stability tests were also conducted under conditions equivalent to those of aqueous phase reforming (200 °C, 17 bar and water and diluted acetic acid). Hydrothermal treatment proved to be an excellent method to improve the resistance to leaching of the catalysts. Metal loss was negligible while PVP was almost completely removed from the catalyst; hence, most of the porosity was recovered and the dispersion measured by CO chemisorption increased from 5 to 34–75%. Water at 200 °C was more effective than diluted acetic acid for the removal of PVP. TEM images confirmed that the Pt nanoparticles did not undergo significant changes either in size or morphology upon the hydrothermal treatment, and XPS analysis showed a homogeneous distribution of Pt nanoparticles within the catalyst granules.

Ammonia capture from the gas phase by encapsulated ionic liquids (ENILs)

Encapsulated ionic liquids (ENILs) based on carbonaceous submicrocapsules were designed, synthesized and applied to the sorption of NH3 from gas streams. The ENILs were prepared using three different task-specific ILs with adequate properties for NH3 capture: 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate (EtOHmimBF4), choline bis(trifluoromethylsulfonyl)imide (CholineNTf2) and tris(2-hydroxyethyl)methylammonium methylsulfate [(EtOH)3MeNMeSO4]. The ENILs synthesized were analyzed by different techniques to assess their morphology, chemical composition, porous structure and thermal stability. The capture of NH3 was tested in fixed-bed experiments under atmospheric pressure. The influence of the type and load of IL, temperature (30, 45 and 60 °C) and NH3 inlet concentration was analyzed. Desorption of NH3 from the exhausted ENILs was also studied at atmospheric pressure and temperatures in the range of 150 to 200 °C. The ENILs prepared with task-specific ILs were found to be suitable for NH3 capture in the fixed-bed operation. These systems can be a promising alternative to conventional absorption or adsorption due to: (i) high sorption capacity controlled by IL selection, (ii) remarkable mass transfer rate, (iii) low sensitiveness to high temperatures of the gas stream, (iv) fast and complete regeneration of the exhausted ENIL at mild conditions; and (v) recovery of NH3.

Encapsulated Ionic Liquids for CO2 Capture: Using 1-Butyl-methylimidazolium Acetate for Quick and Reversible CO2 Chemical Absorption.

The potential advantages of applying encapsulated ionic liquid (ENIL) to CO2 capture by chemical absorption with 1-butyl-3-methylimidazolium acetate [bmim][acetate] are evaluated. The [bmim][acetate]-ENIL is a particle material with solid appearance and 70 % w/w in ionic liquid (IL). The performance of this material as CO2 sorbent was evaluated by gravimetric and fixed-bed sorption experiments at different temperatures and CO2 partial pressures. ENIL maintains the favourable thermodynamic properties of the neat IL regarding CO2 absorption. Remarkably, a drastic increase of CO2 sorption rates was achieved using ENIL, related to much higher contact area after discretization. In addition, experiments demonstrate reversibility of the chemical reaction and the efficient ENIL regeneration, mainly hindered by the unfavourable transport properties. The common drawback of ILs as CO2 chemical absorbents (low absorption rate and difficulties in solvent regeneration) are overcome by using ENIL systems.

Diuron Multilayer Adsorption on Activated Carbon from CO2 Activation of Grape Seeds

Granular activated carbons were obtained from grape seeds by pyrolysis at 600°C and subsequent physical activation with CO2 (750–900°C, 1–3 h, 25–74% burn-off). The carbon and ash content increased during the activation, reaching values of 79.0% and 11.4%, respectively. Essentially microporous materials with BET surface areas between 380 and 714 m2/g were obtained. The performance of the activated carbon in the adsorption of diuron in aqueous phase was studied within the 15–45°C temperature range. Equilibrium data showed that the maximum uptake increased with temperature from 120 to 470 µmol/g, also evidencing some dependence of the adsorption mechanism on temperature. Data were fitted to five isotherm models [Langmuir, Freundlich, Dubinin–Radushkevich, BET, and GAB (Guggenheim, Anderson, and de Boer)]. Kinetic data were analyzed using first- and second-order rate equations and intraparticle diffusion model. The second-order rate constant values obtained (2.8–13.5 × 10−3 g/µmol min) showed that the hollow core morphology of the material favors the adsorption kinetics.