Ignacio Martin-Gullon

Organic and inorganic pollutants from cement kiln stack feeding alternative fuels

In this work, an analysis of the emission of different pollutants when replacing partially the fuel type used in a cement kiln is done. The wastes used to feed the kiln were tyres and two types of sewage sludge. The increasing mass flow of sludge is between 700 kg h(-1) and 5,500 kg h(-1)1, for a total production of clinker of 150th(-1), whereas the fed tyres were in the flow range of 500-1,500 kg h(-1). Dioxins and furans, polycyclic aromatic hydrocarbons (PAHs) and other hydrocarbons, heavy metals, HCl and HF, CO, CO(2), NO(x) and other parameters of the stack were analyzed, according to the standard methods of sampling and determination, through more than 1 year in six series: one blank (no sewage sludge) and five more with increasing amount of sludge and/or tyres. The emission of PAHs and dioxins seems to increase with the amount of tyres fed to the kiln, probably due to the fed point used for this waste.

Dynamic pesticide removal with activated carbon fibers

Rapid small-scale minicolumn tests were carried out to simulate the atrazine adsorption in water phase with three pelletized pitch-based activated carbon fibers (ACF) and one commercial granular activated carbon (GAC). Initial atrazine solutions were prepared with pretreated ground water. Minicolumn tests showed that the performance of highly activated carbon fibers (surface area of 1700 m2/g) is around 7 times better than the commercial GAC (with surface area at around 1100 m2/g), whereas carbon fibers with medium activation degree (surface area of 1500 m2/g) had a removal efficiency worse than the commercial carbon. The high removal efficiency of the highly activated ACF is due to the wide-opened microstructure of the material, with an appreciable contribution of the low size mesopores, maintaining at these conditions a fast kinetic adsorption rate rather than a selective adsorbent for micropollutants vs. natural organic matter.

Kinetic model for the pyrolysis and combustion of poly-(ethylene terephthalate) (PET)

Abstract The kinetics of the global primary thermal decomposition of poly-(ethylene terephthalate) (PET) waste was studied in strict pyrolysis conditions and with different proportions of oxygen by TGA, between temperatures of 25 and 800°C. Prior to the decomposition, the polymer first melts at around 250°C. The pyrolysis of PET, which starts at 400°C, is modeled assuming that it is formed by two different parts which decompose by two independent reactions. The introduction of oxygen produces the appearance of a new process, which does not start until the pyrolysis finishes. This fact is interpreted as the combustion reaction of the char formed in the pyrolysis, and was modeled kinetically with a common combustion reaction to the solid char residues obtained from each initial fraction. One pyrolysis run and one combustion run at 850°C, at fuel-rich conditions were carried out to analyze the different gas compositions evolved, where an appreciable amount of poly aromatic hydrocarbons (PAH) was detected.

Pyrolysis and combustion kinetics and emissions of waste lube oils

Abstract The present work studies first the kinetics of the global primary thermal decomposition of raw waste lubricant oils in helium atmosphere conditions and with different proportions of helium:oxygen by TGA. In addition, pyrolysis and partial oxidation runs were carried out in a tubular reactor at 723 and 1123 K, where the volatiles and semivolatiles evolved were quantified by gas chromatography. TGA analysis shows nearly no difference between helium and helium–oxygen atmosphere, yielding no appreciable residue. Primary decomposition, which takes place between 450 and 700 K, can be modeled with two different processes: the main one (92.6% of the initial material) is an evaporation of the motor oil (with apparent zero order and a kinetic constant dependent on the mass and heating rate) and a small contribution of a typical solid carbonoceous pyrolysis. In the tubular reactor, gases evolved in pyrolysis at 773 K corroborate TG findings that the process is mainly an evaporation, with little changes with respect to the original chemical structure of the oil. Nevertheless, the gas composition changes completely in the presence of air, where the partial oxidation in the gas phase after evaporation yields lower chain paraffins and olefines. Gas evolution at 1123 K is completely different, yielding showing typical cracked flue gas composition: light gases with abundant olefins and poly-condensed aromatics.

Hybrid Films with Graphene Oxide and Metal Nanoparticles Could Now Replace Indium Tin Oxide

Graphene oxide (G-O), a highly oxidized sheet of sp(2)-hybridized carbon with insulating electrical properties, can be transformed into graphene if it is adequately reduced. In the past, researchers believed that reduced G-O (rG-O) could be highly conducting, but it has been shown that the presence of extended vacancies and defects within rG-O negatively affect its electrical transport. Although these observations indicated that rG-O could not be used in the fabrication of any electronic device, in this issue of ACS Nano, Ruoffs group demonstrates that rG-O can indeed be used for producing efficient transparent conducting films (TCFs) if the rG-O material is coupled with Au nanoparticles (Au-NPs) and Ag nanowires (Ag-NWs). The work further demonstrates that these hybrid films containing zero-dimensional (Au-NPs), one-dimensional (Ag-NWs), and two-dimensional (rG-O) elements exhibit high optical transmittance (e.g., 90%) and low sheet resistance (20-30 Ω/□), with values comparable to those of indium tin oxide (ITO) films. In addition, Ruoffs group notes that the presence of Ag-NWs and rG-O in the films showed antibacterial properties, thus demonstrating that it is now possible to produce flexible TCFs with bactericidal functions. The data show that smart hybrid films containing rG-O and different types of NPs and NWs could be synthesized easily and could result in smart films with unprecedented functions and applications.

Kinetic law for solids decomposition. Application to thermal degradation of heterogeneous materials

Abstract The kinetic expressions considered for the decomposition of heterogeneous solids, with several reactions and inert compounds, are discussed. Proposals of the best way for expressing the kinetic equations are presented, as a consequence of the mathematical analysis used. A discussion on the number of parameters that can be obtained in the correlation of experimental data is also presented. In addition, a method for comparing the kinetic constants is proposed. This analysis is applied to thermal decomposition data of several wastes where potential laws have been considered.

Interrelation between the kinetic constant and the reaction order in pyrolysis

Abstract A numerical method for calculating the kinetic constants of the thermal decomposition of heterogeneous solids is proposed, considering the interdependence between the pre-exponential factor and the reaction order. This method is applied to the pyrolysis of poly-(ethylene terephtalate) with satisfactory results. The kinetic constants calculated with this method during the optimization goes preferably to parameters with correct physical meaning, and therefore, a lower number of iterations in the optimization calculation system is needed. The interdependence of the pre-exponential factor and the reaction order restricts the possible solutions of the calculations, and produces more valid solutions in the calculation procedure.

Influence of the carbonization heating rate on the physical properties of activated carbons from a sub-bituminous coal

Abstract The effect of the coal carbonization step heating rate on the reactivity of the chars obtained, as well as on their porous structure development in the subsequent activation step, was analyzed. Different types of carbonization process were investigated, combining a low heating rate (5 K/min) and high heating rate (hundreds of K per second) in this step. Chars obtained in these processes were activated at 1123 K with CO2 at three burn-off degrees. Chars from carbonization experiments at high heating rates showed a higher reactivity than those subjected to slow heating rates and yielded a slightly increased surface area of activated carbons. A mathematical model has been developed that is capable of simultaneously correlating the 77 K N2 adsorption isotherms of all samples obtained as a function of the burn-off and the heating history in the carbonization step.

Steam-activated carbons from a bituminous coal in a continuous multistage fluidized bed pilot plant

Abstract A vertical three-stage fluidized bed pilot plant, with downcomers, was designed and built in order to study the continuous process of the production of activated carbons from a high-volatile bituminous coal from the Puertollano basin (Spain), by steam activation. The pilot plant can operate with a production of up to 40 kg per day. Very good activated carbons were produced at the selected operating conditions. The effect of the following operating conditions on the reactivity and adsorption characteristics of the activated carbons was analyzed: (1) carbonization conditions (one- and two-step activation), (2) activation temperature (800–850 °C), and (3) steam gas velocity (1.5–3 times the minimum fluidization velocity). Carbonization conditions considerably affect the reactivity of the chars obtained; the faster the carbonization process, the higher the reactivity. Nevertheless, the effect of this variable on the development of porosity is not very relevant, and consequently the direct activation process is an attractive alternative to the two-step (carbonization and activation) process. On the other hand, both temperature and steam flow rate (affecting the reaction rate) have a marked effect on the development of porosity.

Stable operating velocity range for multistage fluidized bed reactors with downcomers

Abstract A model for predicting the gas velocity stability range is presented for multistage fluidized bed systems with downcomers, when the solid mass flux is very low. The model was successfully applied to a laboratory scale two-stage perspex system, operating in continuous regime, and was capable of correlating the stability limit. This model was used to design a three-stage pilot plant fluidized bed reactor for preparing activated carbons. The stable operation limit for this system was also successfully predicted by the model proposed in this paper.