Tomás Cordero

Predicting heating values of lignocellulosics and carbonaceous materials from proximate analysis

A simple equation based on proximate analysis (volatile matter and fixed carbon contents) is presented which allows calculation of the higher heating value of lignocellulosics as well as the charcoals resulting from their carbonization. The equation has been tested with different lignocellulosic wastes and chars obtained from carbonization at different temperatures. Deviations from the experimental heating values fall in most cases below 2%. A comparison is presented with some other equations from the literature based on proximate, ultimate and chemical analysis data. As a general conclusion the equation proposed in this paper leads to comparable and in many cases more accurate predictions of heating values and has the advantage of being applicable to a wide range of carbonaceous materials, requiring only a simple, rapid and cheap proximate analysis of the samples.

Preparation and characterization of activated carbons from eucalyptus kraft lignin

Abstract Preparation of activated carbons from eucalyptus kraft lignin has been investigated. A pretreatment method has been established to avoid partial fusion and swelling in the carbonization stage. Carbonization has been studied at different temperatures and the structure of the microporous chars has been characterized. Activated carbons have been prepared from CO2 partial gasification of chars obtained at 823 and 1073 K. Both chars show a comparable behavior regarding to the evolution of porous structure. Activation increases both total and narrow microporosity and develops a substantial mesoporosity. At high burnoff levels, macroporosity becomes also significant. BET surface areas in the vicinity of 1,300–1,400 m2/g have been achieved at burnoff levels around 70–75% which correspond to overall carbon to lignin yields of about 10%–11% (d.a.f. basis).

On the kinetics of thermal decomposition of wood and wood components

Abstract A kinetic analysis of the thermal decomposition of eucalyptus sawdust, cellulose and eucalyptus kraft lignin has been accomplished from temperature-programmed reaction experiments, using two different approaches: the first assumes an overall reaction model, whereas in the second, pyrolysis is viewed as a process consisting of multiple reactions in parallel and a distribution of activation energies is derived. The results obtained reveal that the simple first approach, which leads to overall values of the apparent kinetic parameters allows a fairly good reproduction of the experimental curves, although in the case of wood a two-stage analysis was necessary. No improvement was noticed with the use of activation energy distribution functions resulting from the multiple reaction treatment, except for cellulose and lignin at high conversion, whereas the steep region of the weight-loss curve for cellulose is better described with the overall reaction model.

CO2 gasification of eucalyptus wood chars

Chars obtained from Eucalyptus grandis sawdust at different carbonization temperatures were gasified with CO2 in isothermal and non-isothermal t.g. experiments. At low and intermediate conversion values the reactivity can be reasonably well explained in terms of the development of surface area as gasification proceeds. At high conversion values a steep increase in reactivity is observed which can be attributed to the increasing catalytic effect of the metallic constituents (mainly Na and K) of the inorganic matter present in the chars. Activation energies in the range 230–261 kJ mol−1 are obtained.

Activated carbons from Uruguayan eucalyptus wood

Activated carbons were prepared from eucalyptus wood chars and the results of CO2, CO2-O2 and steam activation were compared. The carbonization step gave rise to a narrow micropore structure and a highly developed macroporosity which increased slightly upon CO2 activation and significantly upon steam activation. This last process led also to a widening of micropore size distribution and developed the mesoporosity more than CO2 activation did. The presence of O2 accompanying CO2 in the activating gas increased the micro- and macroporosity of the carbons. No net destruction of microporosity was observed even at high burnoff levels and with as much as 5 vol. % O2 in the activating gas.

High-temperature carbons from kraft lignin

High-temperature carbons have been prepared from kraft lignin on thermal treatment up to 3073 K. The structure of these high-temperature carbons has been studied by X-ray diffraction and Raman spectroscopy. The interlayer spacing obtained from XRD approaches the d002 value of graphite as the heat treatment temperature is increased. The (002) diffraction peak of the higher temperature carbons shows a modulated profile, which has been attributed to the presence of both graphitic or highly ordered carbon, and turbostratic or less ordered carbon. The average thickness of graphite-like crystallites evaluated from XRD increases with increasing heat treatment temperature. Raman spectra confirm the progressive structural ordering as treatment temperature increases. The E2g line-width decreases and its frequency shifts to a value close to the 1582 cm−1 of graphite. At the same time a substantial decrease in the intensity of the band in the 1350 cm−1 region can be observed, indicating a decreasing proportion of imperfect carbon. The evolution of the 2700 cm−1 line-width indicates a progressive onset of three-dimensional order as the heat treatment temperature increases. The O2-gasification X-T curves of the high-temperature carbons show an increasing oxidation resistance with increasing heat treatment temperature, in agreement with a higher structural ordering and a lower surface area. The inorganic impurities of the precursor (mainly Na) seem to enhance the onset of structural ordering, and the oxidation resistance of the 3073 K carbon prepared from high-ash lignin proved to be similar to that of graphite SP-1.

Electrochemical Performance of Hierarchical Porous Carbon Materials Obtained from the Infiltration of Lignin into Zeolite Templates

Hierarchical porous carbon materials prepared by the direct carbonization of lignin/zeolite mixtures and the subsequent basic etching of the inorganic template have been electrochemically characterized in acidic media. These lignin-based templated carbons have interesting surface chemistry features, such as a variety of surface oxygen groups and also pyridone and pyridinic groups, which results in a high capacitance enhancement compared to petroleum-pitch-based carbons obtained by the same procedure. Furthermore, they are easily electro-oxidized in a sulfuric acid electrolyte under positive polarization to produce a large amount of surface oxygen groups that boosts the pseudocapacitance. The lignin-based templated carbons showed a specific capacitance as high as 250 F g(-1) at 50 mA g(-1) , with a capacitance retention of 50 % and volumetric capacitance of 75 F cm(-3) at current densities higher than 20 A g(-1) thanks to their suitable porous texture. These results indicate the potential use of inexpensive biomass byproducts, such as lignin, as carbon precursors in the production of hierarchical carbon materials for electrodes in electrochemical capacitors.

Recent Inventions in Glycerol Transformations and Processing

Many patents claiming new processes for the conversion of glycerol into valuable-added chemicals are appearing in recent years as a result of glycerol availability since it is the main by-product in the biodiesel production and in other processes concerning biomass as raw material. In a future biorefinery glycerol will remain as a platform molecule. Present review describes a selection of such patents and shows the potential of glycerol as raw material in such future chemical industries (biorefineries).

Influence of Water Vapor on the Adsorption of VOCs on Lignin‐Based Activated Carbons

Abstract Activated carbons with a wide range of burn‐off degrees obtained from Eucalyptus kraft lignin have been used to study the influence of the presence of water vapor on VOCs adsorption. The amount adsorbed and the rate of adsorption of both benzene and water vapor increase with activated carbon burn‐off as a consequence of an increase of micropore volume, broadening of micropore size distribution and increasing development of meso‐ and macroporosity. Similar results were found for MEK and methanol. Benzene is only partially desorbed at the adsorption temperature and an appreciable amount of it remains in the carbon, most likely in the narrow micropores. On the contrary, water vapor is completely desorbed at the adsorption temperature and its adsorption profile clearly exhibits two steps with different adsorption rates, associated to water molecules adsorbed on the active sites given rise to cluster formation and further migration and filling of the micropores. Adsorption with mixtures of VOC and water vapor has been carried out. The total amount adsorbed by the carbon, near the equilibrium point, is higher than in the case of the stream containing only the VOC. The adsorption rates for the mixtures streams are similar to that for the corresponding streams containing only the VOC in the case of carbons with a well developed porous structure. However, the presence of water vapor increases the rate of adsorption on the activated carbons with narrower microporosity. Saturation of the activated carbon with water vapor prior to the adsorption of a mixture containing benzene and water vapor has shown little effect on the amount of benzene adsorbed, suggesting that water and benzene molecules are adsorbed in different sites on the carbon surface.

Lignin-based activated carbons for adsorption of sodium dodecylbenzene sulfonate: Equilibrium and kinetic studies

The adsorption of sodium dodecylbenzene sulfonate (SDBS) from its aqueous solution at different temperatures has been studied using three activated carbons prepared in our laboratory. Lignin was used as raw material for the preparation of activated carbons (ACs). The results of the adsorption equilibrium were analyzed and fitted to the Langmuir model. Thermodynamic magnitudes were estimated as well, and their values indicated that the adsorption processes were spontaneous and exothermic. The kinetic study showed that the processes are of second apparent order related to the concentration of the vacant active centers on the surface of the activated carbons. The values of the effective internal diffusion coefficients have been calculated applying the equations developed by Crank and Vermeulen.