Preparación de nanofibras de carbono y cerámica para aplicaciones en Ingeniería Química

Esta tesis presenta el uso de las técnica de electrospinning para preparar fibras y tubos de carbono y/o cerámica con diámetros submicrométricos, pudiéndose soportar nanopartículas de metales en sus superficies en el mismo paso de preparación. Se obtuvieron mallas de submicrofibras de óxidos de zirconio, silicio, de carbono y composites carbono-cerámico, estudiándose su aplicación como catalizadores y adsorbentes en reacciones de interés en la biorrefinería y en la eliminación de contaminantes

Kinetic study of steam gasification of lignocelullosic biomass char obtained from pyrolysis

Hydrogen plays a key role in the energy transition towards a more sustainable model based on renewable energies, as it has the capacity to solve two major problems: i) reducing dependence on fossil fuels and ii) reducing greenhouse gas emissions. Currently, approximately 85 % of the world hydrogen production comes from fossil fuel technologies without CO2 capture. In this sense, a promising alternative for the substitution of these fuels may be biomass gasification with water vapor, due to its high availability and low cost, where the gas produced can be used directly as fuel or raw material to produce high value-added chemicals. The aim of this work is to perform the steam gasification of the solid residue obtained from biomass pyrolysis to optimize the hydrogen production. Three types of lignocellulosic biomass (almond shell, olive stone and hemp) were evaluated as raw material for steam gasification. Biomass samples were obtained by conventional pyrolysis in a fixed-bed reactor at a temperature of 800 °C, a heating rate of 10 °C/min for 1 h, obtaining a char that was later gasified in a downdraft fixed-bed reactor, using steam as the reacting agent (30 % vol.), in a temperature range between 800 °C and 900 °C. A kinetic model that takes into account the gas product distribution and the weight loss during the gasification reaction was developed using representative gas-solid models such as the volumetric model (VM), the grain model (GM) and the random pore model (RPM).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Catalytic fast pyrolysis of olive stone for bio-oil deoxygenation.

In this work, conventional, fast and catalytic fast pyrolysis of olive stone residues were studied with a commercial catalyst with mild acidity, γ-Al2O3, an activated carbon from olive stones (AC) prepared by chemical activation with phosphoric acid and the same activated carbon loaded with Zr as active phase (ACZr). The results showed that fast pyrolysis has a higher content of liquid fraction (64 %wt) than that obtained in conventional pyrolysis (52 %wt), due to cracking reactions occur at a lesser extent. In the catalytic fast pyrolysis, the acid character of the catalysts favors the cracking and deoxygenation reactions that reduce the production of the liquid fraction, mainly producing an increase in the phenols species and a decrease in the acid species. On the other hand,a clear increment in the content of CO can be observed (conventional and catalytic fast pyrolysis, respectively), due to decarbonylation reactions, which are favored in the presence of catalysts.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Effect of heating rate and H3PO4 as catalyst on the pyrolysis of agricultural residues

This study reports the effect of heating rate and the addition of H3PO4 on the pyrolysis of three representative agricultural wastes of different lignocellulosic composition, namely pistachio shell, bitter orange peel, and saffron petal. Pyrolysis was carried out at 500 °C in a fixed-bed, lab scale reactor. Slow pyrolysis provided lower water contents in the liquid fraction. Fast pyrolysis increased the liquid yield for all the feedstocks, promoting the formation of phenolic, ketone/aldehyde compounds. It also enhanced the formation of water for all the agricultural residues. In addition, the energy content in the gas fraction is promoted due to a higher concentration of light hydrocarbons, methane, and hydrogen. However, when high inorganic matter is found in the feedstocks, the formation of CO2 is favored, hindering the energy improvement. The treatment of the biomass with H3PO4 significantly increased the solid fraction, producing a huge porosity development in the char (surface area over 1600 m2/g in pistachio shell product), at the cost of liquid fraction, which is mostly composed of water, with small amounts of acetic acid, phenol and toluene. The results pointed out that pyrolysis of agricultural waste can be targeted to achieve different products by switching pyrolysis conditions such as the heating rate and the treatment of the biomass with H3PO4.RRR, JMR, JRM and TC thank MICINN (RTI2018-097555-B-100) and Junta de Andalucía (P18-RT-4592) for financial support. Funding for open access charge: Universidad de Málaga/CBUA

A Kinetic Model Considering Catalyst Deactivation for Methanol-to-Dimethyl Ether on a Biomass-Derived Zr/P-Carbon Catalyst

A Zr-loaded P-containing biomass-derived activated carbon (ACPZr) has been tested for methanol dehydration between 450 and 550 °C. At earlier stages, methanol conversion was complete, and the reaction product was mainly dimethyl ether (DME), although coke, methane, hydrogen and CO were also observed to a lesser extent. The catalyst was slowly deactivated with time-on-stream (TOS), but maintained a high selectivity to DME (>80%), with a higher yield to this product than 20% for more than 24 h at 500 °C. A kinetic model was developed for methanol dehydration reaction, which included the effect of the inhibition of water and the deactivation of the catalyst by coke. The study of stoichiometric rates pointed out that coke could be produced through a formaldehyde intermediate, which might, alternatively, decompose into CO and H2. On the other hand, the presence of 10% water in the feed did not affect the rate of coke formation, but produced a reduction of 50% in the DME yield, suggesting a reversible competitive adsorption of water. A Langmuir–Hinshelwood reaction mechanism was used to develop a kinetic model that considered the deactivation of the catalyst. Activation energy values of 65 and 51 kJ/mol were obtained for DME and methane production in the temperature range from 450 °C to 550 °C. On the other hand, coke formation as a function of time on stream (TOS) was also modelled and used as the input for the deactivation function of the model, which allowed for the successful prediction of the DME, CH4 and CO yields in the whole evaluated TOS interval.This research was supported by the Spanish Ministry of Science, Innovation and Universities and Junta de Andalucia through RTI2018-097555-B-I00 and UMA18-FEDERJA-110 projects, respectively. J.T.-L. also acknowledges the assistance of the Spanish Ministry of Economy, Industry and Competitiveness for the award of a predoctoral contract to become a Ph.D. (BES-2016-079237). Partial funding for open access charge: Universidad de Málag

MgO-containing porous carbon spheres derived from magnesium lignosulfonate as sustainable basic catalysts

The presence of alkalis in lignosulfonate allows an easy preparation of sustainable MgO-containing carbon catalysts with surface basicity by carbonization of magnesium lignosulfonate and/or further partial gasification of the produced char with CO2. Carbon spheres with different chemical and physical properties were obtained from lignosulfonate treated at temperatures ranging from 500 to 900 ºC. Carbonization at 900 °C generates hollow porous carbon spheres (pore volume of 0.20 cm3/g and apparent surface area of 465 m2/g) with magnesium content of 12%. A kinetic study of CO2 gasification of the carbon spheres obtained at 900 °C at temperatures in the range of 700 – 800 °C revealed that the gasification rate can be accurately described by the random pore model up to conversion values of 0.5. Based on this study, in order to develop additional porosity on the carbon spheres obtained at 900 °C, a partial gasification with CO2 at 750 °C for 30 min was carried out, reaching surface areas higher than 700 m2/g and 15.3% of Mg loading, with an overall preparation yield of 30%. All the obtained carbon materials were tested as catalyst for 2-propanol decomposition, showing a high selectivity to acetone, evidencing the basic character of these carbon catalysts. The highest activity and selectivity were shown by the CO2-activated carbon spheres (conversion and acetone selectivity higher than 90% at 420 °C), indicating that magnesium lignosulfonate is an attractive raw material for the preparation of sustainable carbon catalysts for biorefinery applicationsThe authors wish to thank MICINN (RTI2018-097555-B-100) and Junta de Andalucía (UMA18-FEDERJA-110 and P18-RT-4592) for financial support. M.G.R. acknowledges the assistance of MICINN through an FPU Grant (FPU 18/01402). // Funding for open access charge: Universidad de Málaga / CBU

Evaluation of acetanilide and antipyrine adsorption on lignin-derived activated carbons.

In this study, the removal of two emerging pollutants (EPs), antipyrine and acetanilide, through adsorption on activated carbons (ACs) prepared by chemical activation of Organosolv lignin with H3PO4 were evaluated. ACs with different pore size distribution were obtained at different impregnation ratios (H3PO4/lignin, 0.5–3.0 w/w) and activating temperatures (500–900 ◦C). The porosity and surface chemistry of the ACs were determined, and a bimodal size distribution of micropores and narrow mesopores was observed for the different ACs. These ACs were tested for antipyrine and acetanilide adsorption in aqueous solutions in a batch system at 20 ◦C and low concentration levels (0.5–10 ppm). In general, the ACs exhibited higher adsorption affinity to acetanilide than to antipyrine due to its smaller molecular size. Langmuir adsorption isotherm was able to describe the adsorption equilibrium data. A new Linear Driving Force (2-LDF) kinetic model, based on the bimodal size distribution of micropores and narrow mesopores observed for the ACs has been developed. The new model provided a more accurate description of the batch adsorption rates than that obtained from conventional kinetic models, and also enabled to relate the pore size distribution of the adsorbent with the adsorption kinetics. The validity of this model was checked in small-scale column fixed bed adsorption for the AC showing the highest affinity for both EP. The kinetic model and equilibrium adsorption isotherm obtained from the batch experiments were suc- cessfully used to provide an accurate description of the bed service time and the full breakthrough profile of acetanilide and antipyrine.This work was supported by MCIN [TED2021-131324B–C21; PID2022-140844OB-I00] and European Union “NextGenerationEU”/ PRTR (MCIN/AEI/10.13039/501100011033); MINECO [FJCI-2015- 25788]. Funding for open access charge: Universidad de Malaga/CBUA

Kinetic study of propane ODH on electrospun vanadium oxide-based submicron diameter fiber catalyst

A rigorous kinetic study of the oxidative dehydrogenation (ODH) reaction of propane on a vanadium oxide-based submicron diameter fiber catalyst has been developed. The proposed kinetic model simulates the conversion- selectivity profiles, the surface coverage of the different adsorbed species and the oxidation state of the cata- lyst for the studied operating conditions of temperature, space–time and inlet partial pressures of propane and oxygen. The activation energy of the rate determining step (RDS), the first hydrogen abstraction from propane, is 104 kJ⋅mol 1. The model predicts that although the reaction seems to be pseudo-zero order with respect to oxygen in a broad range of conditions, the catalyst may not be fully oxidized during reaction. The accuracy of the model when predicting the oxidation state of the catalyst has been experimentally confirmed by analyzing the catalytic fixed bed after reaction. The reduction degree of the catalyst will depend on its intrinsic chemical nature and reaction conditions, increasing with the space–time and in detriment of the overall reaction rate. Conse- quently, the propane turnover frequency (TOF) will also depend on the reaction conditions and space–time, even changing along the fixed-bed reactor.Funding for open access charge: Universidad de Málaga / CBU

CO2 hydrogenation to methanol on In2O3/ZrO2 fibrillar catalysts.

Hydrogenation of CO2 to produce methanol is regarded as one of the most promising processes for achieving full deployment of carbon capture, utilization and storage technologies, which are needed to decrease the emission of greenhouse gases. In this communication, In2O3-ZrO2 nanostructured fibrillar catalysts, prepared by electrospinning technique, has been proposed for CO2 hydrogenation. The effect of the calcination temperature as well as the indium loading on the CO2 conversion have been evaluated.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Sustainable carbon-based nickel catalysts for the steam reforming of model compounds of pyrolysis liquids

Steam reforming of biomass-derived pyrolysis liquids (bio-oil) to produce hydrogen with carbon-based Ni catalysts is gaining attention due to their advantages in terms of cost, sustainability and activity. However, the catalytic activity at long times on stream is compromised by either coke deposition or gasification of the support. To face these drawbacks, two activated carbons have been studied as Ni catalyst support: a microporous carbon of high purity and a mesoporous carbon with phosphorus surface groups. The activity and long-term stability of these catalysts have been studied for the steam reforming of model compounds of bio-oil. The microporous support provided a slightly higher H2 production and lower contribution of methanation reaction. However, gasification of this support after 20 h led to a decline in the activity, and massive formation of carbon nanotubes and coke. Nevertheless, the resulting material maintained an outstanding stability with high and stable H2/CO ratio for 50 h. The P-containing catalyst showed a remarkable long-term stability, but lower H2/CO ratio. Carbon gasification was less significant in this catalyst due to the presence of surface phosphorus groups, and the generation of nickel phosphides, which hampers the growth of pyrolytic carbon and carbon nanotubes, leading to a superior stabilityThis work was supported by MCIN (PID2022-140844OB-I00) and MCIN and European Union “NextGenerationEU”/PRTR (MCIN/AEI/10.13039/501100011033) and (TED2021-131324B-C21). Funding for open access charge: Universidad de Malaga ´ / CBUA. P.C-R gratefully acknowledges University of Malaga for the support through a predoctoral grant