Activation of waste tire char upon cyclic oxygen chemisorption-desorption

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Industrial and Engineering Chemistry Research, © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/abs/10.1021/ie801764xActivation of waste tire char upon cyclic oxygen chemisorption-desorption permits a controlled development of porosity versus burnoff using air as feed gas for the activation process. A slow but monotonical increase of BET surface area is obtained from cycle to cycle. Initially the process led to the development of mesoporosity without generating micropores and then the micropore volume is increased whereas a decrease of narrow mesopore (20-80 nm) volume is observed, probably as a consequence of mesopore widening. Although the S BET reaches relatively low values (below 250 m2/g) even after 15 cycles, this surface development is associated with low burnoff values (around 22% for indicated BET surface area) and corresponds in an important percentage (up to about 50%) to external (nonmicropore) area. Temperatures around 210 and 550 °C for chemisorption and desorption, respectively, have been found as optimum for the purpose of preparing granular mesoporous carbons which can be interesting candidates as catalytic supports for liquid phase applicationsThe authors greatly appreciate financial support from the Spanish Ministerio de Educación y Ciencia (CTQ2006-13512

Effect of size and oxidation state of size-controlled rhodium nanoparticles on the aqueous-phase hydrodechlorination of 4-chlorophenol

Unsupported size-controlled Rh nanoparticles of different size and oxidation state were tested as catalysts models in aqueous phase hydrodechlorination (303-318K, 1atm) using 4-chlorophenol (4-CP) as target compound. A chemical reduction method was employed for the synthesis of the nanoparticles using methanol and poly(N-vinyl-2-pyrrolidone) (PVP) as reducing and capping agent, respectively. The size of Rh nanoparticles was in a narrow range (1.9-4.9nm) whereas Rhn+/Rh0 ratio values were found within a wide range (0.56-3.89).High 4-CP conversion values (c.a. 100%) were achieved at low Rh concentration (2.45·10-3gL-1). Phenol, cyclohexanone, cyclohexanol and traces of cyclohexane were identified as reaction products. A wide range of activity values (1.7-29.4mmolg-1min-1) were obtained, being equivalent to the measured in a previous work with unsupported Pd nanoparticles, in spite of the fact that Rh supported catalysts have generally been reported as less active than Pd ones in liquid phase hydrodechlorination. As the size of Rh nanoparticles decreased the activity increased reaching a maximum at 2.8nm, lower size values leading to a significant decrease of activity. A remarkable dependence of activity on the Rhn+/Rh0 ratio was found, thus a higher activity corresponded to a higher relative amount of zero-valent Rh in the nanoparticles samples. Regression models were developed in order to address the significance of nanoparticles size and oxidation state for the prediction of selectivity to cyclohexanone and cyclohexanol at varying reaction times. A crossed effect of particle size and Rhn+/Rh0 ratio was identified as a significant factor influencing the selectivityWe greatly appreciate financial support from the Spanish MCYT (CTQ2009-09983 and CTQ2012-32821) and CAM (REMTAVARES S-2009/AMB-1588). J.A. Baeza thanks to the Spanish MICINN a research grant (BES-2010-030059

Grape seed carbons for studying the influence of texture on supercapacitor behaviour in aqueous electrolytes

Microporous carbon materials having a negligible contribution of mesopores have been synthesised by cyclic oxidation/desorption of grape seeds char using air, ozone and HNO3 as oxidant agents. By adequate selection of the operating conditions (oxidation procedure and number of cycles), it is possible to tune the volume and pore size distribution (PSD) of carbon materials and therefore determine the influence of carbon textural properties on the electrochemical behaviour of carbon-carbon symmetric supercapacitors operating in different aqueous electrolytes. The results confirm that although energy density can be improved using neutral electrolytes because of their higher stability potential window compared to acidic or basic electrolytes, it is important to adapt the textural properties of the carbon materials to improve the ions' diffusion inside the porosity for assuring the charging of the double layer at high current densities to reach high power densitiesThe authors greatly appreciate the financial support from the Spanish Ministerio de Ciencia e Innovación (CTQ2009-09983

Activated carbon from grape seeds upon chemical activation with phosphoric acid: Application to the adsorption of diuron from water

The preparation of activated carbon from grape seeds was studied by chemical activation with phosphoric acid. Grape seeds were pretreated with sulfuric acid to improve wettability and impregnated at different grape seed to phosphoric acid ratios (1:1-1:4). The impregnated grape seeds were carbonized in a static horizontal furnace at temperatures between 350 and 550°C. Microporous activated carbons with some contribution of mesoporosity were obtained. The best results in terms of surface area (1139m2/g) and mesopore volume (0.24cm3/g) development were observed for a grape seeds to phosphoric acid ratio of 1:3 and a carbonization temperature of 500°C. The activated carbon prepared shows granular morphology and an egg shell structure that favors application in liquid phase. The activated carbon was tested in the adsorption of diuron from aqueous phase. The adsorption rate was measured within the temperature range of 15-45°C. First and second order rate equations and intraparticle diffusion model were checked to fit the kinetic dataWe greatly appreciate financial support from the Spanish MCYT (CTQ2009-09983 and CSD2006-44) and CAM (REMTAVARES S-2009/AMB-1588). M. Al Bahri thanks to the Spanish MICINN a research grant (CTQ2006-13512

Aqueous phase reforming of starch wastewater over Pt and Pt-based bimetallic catalysts for green hydrogen production

This work analyses the application of aqueous phase reforming (APR) for green hydrogen production from starch industry wastewater. This work reports for the first time on the direct conversion of a high molecular weight biomass polymer contained in wastewater in contrast to low molecular weight substrates mainly reported in the literature. The potential of this type of feedstock was evaluated by varying the starch source (rice, potato, sweet potato and cassava) and the type of catalyst (carbon supported Pt, PtRu, PtPd, PtRe and PtRh catalysts). In APR experiments at 220 °C with synthetic wastewater, PtRu/C and Pt/C catalysts achieved the highest H2 yield values, around 51 mmol H2 per g of organic carbon in the initial wastewater, close to 2.6 times higher than that reported in the literature of brewery wastewater, a promising substrate. The lack of free aldehyde or keto groups due to glycosidic bonds between glucose units in starch results in higher conversion to gas and H2 production compared to APR of glucose. This fact shows that APR has more feedstock flexibility than that previously reported for light compounds. In the experiments with real wastewaters, the organic matter removal was influenced largely by the starch source: the best APR performance (28.5 mmol H2 gTOCi−1) was obtained for rice processing wastewater, which is characterized by the highest starch concentration and the lowest protein content. Poor performance was observed in the APR of potato processing wastewater, probably due to catalyst deactivation caused by protein fractio

Development of porosity upon physical activation of grape seeds char by gas phase oxygen chemisorption–desorption cycles

Activation of grape seeds char upon cyclic oxygen chemisorption-desorption permits a controlled development of porosity versus burn-off using air as a cheap activation agent. In this work the influence of chemisorption and desorption temperature and the number of cycles is investigated. A fast increase of BET surface area (SBET) is obtained in the two first cycles; that increase becomes then lower although the SBET continues increasing upon the successive cycles. Regarding the Dubinin-Astakhov surface area (SDA) a slow increase was observed from cycle to cycle. The activation process led to the development of both micro and mesoporosity. Under the optimum conditions for surface area development, i.e. an oxidation temperature of 275°C and desorption temperatures between 850 and 950°C, values of 1129-1256 and 1339-1219m2/g were obtained for SBET and SDA, respectively. Porosity was found to increase mainly during the desorption stage, although chemisorption also led to some surface area development. SEM characterization showed that the activated carbon maintained the granular morphology of the seeds even after 10 cycles showing the egg-shell structure of the precursor with longer and deeper cracks at the outer surface. The activated carbons showed a good mechanical strength during attrition testsThe authors greatly appreciate financial support from the Spanish Ministerio de Ciencia e Innovación (CTQ2009-09983

Porous structure and morphology of granular chars from flash and conventional pyrolysis of grape seeds

This work studies the influence of the operating conditions used in the pyrolysis of grape seeds on the morphology and textural properties of the chars resulting. Flash and conventional (283Kmin-1 heating rate) pyrolysis have been used within a wide range of temperature (300-1000°C). The effect of a pretreatment for oil extraction has also been studied. The porous structure of the chars was characterized by adsorption of N2 at 77K, Ar at 77K and 87K, and CO2 at 273K and mercury intrusion porosimetry. The morphology was analyzed by scanning electron microscopy. All the materials prepared revealed an essentially microporous structure, with a poor or even negligible contribution of mesopores. Increasing pyrolysis temperature led to higher specific surface areas and lower pore size. The highest specific surface area values occurred within 700-800°C, reaching up to 500m2g-1 with pore sizes in the 0.4-1.1nm range. No significant morphological changes were observed upon carbonization so that the resulting chars were granular materials of similar size than the starting grape seeds. The hollow core structure of the chars, with most of the material allocated at the periphery of the granules can help to overcome the mass transfer limitations of most common (solid or massive) granular activated carbons. The chars showed a good mechanical strength during attrition tests. These chars can be potential candidates for the preparation of granular carbons molecular sieve or activated carbons raw materialsThe authors greatly appreciate financial support from the Spanish Ministerio de Ciencia e Innovación (CTQ2009-09983

Ozone as oxidation agent in cyclic activation of biochar

Granular activated carbons were produced from grape seed biochar by cyclic activation with ozone. In each cycle, char was first oxidized by exposure to ozone and then subjected to high temperature in inert atmosphere to desorb oxygen groups formed. The study assessed the influence of operating conditions in the development of porosity, from a starting biochar with narrow microporosity (SBET: 47 m2 g− 1, SDA: 505 m2g− 1) prepared by flash pyrolysis of grape seed at 800 °C. The variables studied were the number of cycles applied and the oxidation and desorption temperatures (250–275 and 850–950 °C, respectively). High oxidation temperatures led to higher burn-off, which was also found to increase with the number of activation cycles. The burn-off needed to achieve a high surface area was lower than in conventional physical activation. After 7–9 activation cycles, activated carbons with SBET higher than 1200 m2 g− 1 and SDA above 1500 m2 g− 1 were obtained. The use of ozone resulted in mainly microporous activated carbons (0.37–0.52 cm3 g− 1) with very low contribution of mesopores (< 0.04–0.07 cm3 g− 1). The mean micropore size increased with the number of activation cycles due to pore widening, while mesopore mean size decreased along the cycles. The activated carbons showed a unique granular morphology with a hollow core and a porous shell, which is maintained even after 10 activation cyclesThe authors greatly appreciatefinancial support from the Spanish Ministerio de Ciencia e Innovación (CTQ2012-32821

Preparation of granular activated carbons from grape seeds by cycles of liquid phase oxidation and thermal desorption

Activation of grape seed char upon successive cycles of liquid phase oxidation followed by high temperature desorption permits a tailored development of porosity. In this work three different oxidants (HNO3, H 2O2, and (NH4)2S2O 8), have been tested and the desorption temperature has been varied within 850-950 C upon 10 activation cycles. A high increase of BET surface area was observed in the first five cycles with HNO3 as oxidizing agent giving rise to values higher than 1200 m2 g- 1 at around 50% burn-off. Activation with H2O2 and (NH 4)2S2O8 led to a significantly lower development of surface area, with 600 and 800 m2 g- 1 respectively at that burn-off. The analysis of the pore size distribution showed that porosity was generated through the creation of new micropores and widening of existing ones upon activation with HNO3 and (NH4) 2S2O8, whereas H2O2 mostly led to the widening of the narrow micropores already existing in the starting char. The activated carbons obtained are essentially microporous, with some small contribution of mesoporosity in the HNO3 series (V micro = 0.69 cm3 g- 1; Vmeso = 0.07 cm3 g- 1). SEM images showed that the activated carbons maintained the granular morphology of the seeds after 10 cycles showing a hollow core structure with a wall thickness of about 200 μmThe authors greatly appreciate the financial support from the Spanish Ministerio de Ciencia e Innovación (CTQ2009-09983