Modification of the morphology, porosity and surface chemistry of lignin-based electrospun carbon materials

Lignin is a biopolymer that can be found as the main component of plants. It is obtained as a coproduct in the papermaking and biofuel industries. Owing to its high carbon and aromatic content, high availability and reduced cost, it is an excellent precursor for the preparation of highly valued carbon materials. Electrospinning is a suitable top-down technique for the preparation of polymeric fibers using high voltage electrical fields and polymer solutions of proper viscosity and conductivity. Organosolv lignins, which are extracted from lignocellulosic biomass using organic solvents, are soluble in ethanol, obtaining a solution that matches the requirement of the electrospinning process. In this way, it is possible to produce lignin-based porous carbon fibers using a coaxial electrospinning device [1]. This contribution summarizes our findings about the preparation of carbon materials with different morphologies and composition by processing lignin using electrohydrodynamic forces. Lignin spheres, beaded fibers, straight fibers, beaded tubes and straight tubes are obtained by using coaxial and triaxial spinnerets that allows the electrospinning of two or three different solutions at once [1], Fig. 1. Thermal stabilization in air is needed in order to avoid melting of lignin fibers during carbonization. Stabilization times of 48-96 hours are usually required in this step, decreasing the sustainability of the production process. Phosphoric acid can be added in small amounts in the lignin solution, shortening the time for achieve a successful thermostabilization of the fiber [2]. The carbonized materials show narrow microporosity and large surface area values (SBET from 600 to 1000 m2g-1) and additional pore size and volume can be developed by controlled gasification.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work was supported by the Spanish Ministry of Economy and Competitiveness and FEDER (CTQ-2015-68654-R)

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

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

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

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

Carbon-based biomass-derived catalysts for deoxygenation of fast pyrolysis bio-oil

Producing energy and chemicals from biomass is an interesting alternative for replacing conventional fossil sources with a renewable feedstock while enabling zero net greenhouse gases emissions. Particularly, fast pyrolysis of biomass waste enables the production of bio-oil, which can be upgraded to biofuels or value-added chemicals. The sustainability of this process can be enhanced by preparing carbon-based catalysts from the same biomass waste used as raw material for the biooil production, decreasing the inputs of the process and allowing recovery and recycle of the active phase by combustion of the carbon substrate. In this work, catalytic fast pyrolysis of olive stone residues was studied using mesoporous carbon-based acid catalysts prepared by activation with H3PO4 of olive stones.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

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

Estudio cinético de la desactivación de un catalizador de zirconio y fósforo sobre carbón activado en la reacción de metanol a dimetileter

El dimetil éter es un sustituto del diésel que puede producirse de forma sostenible mediante deshidratación de metanol obtenido por gasificación de biomasa. Los catalizadores usados en este proceso sufren una desactivación muy intensa por coque. Estudiar la cinética del proceso de desactivación en condiciones severas es necesario para escoger condiciones de operación adecuadas y desarrollar catalizadores más estables. En este trabajo se ha desarrollado un estudio cinético completo de la reacción de deshidratación metanol sobre un catalizador de zirconio soportado en un carbón activado con H3PO4 a temperaturas entre 450-550 ˚C y presencia de agua en la corriente. Los productos de reacción obtenidos fueron DME y en menor cantidad coque, metano y CO, observándose una desactivación gradual del catalizador. La formación de coque procede probablemente a través de un intermediario de formaldehido, y la presencia de agua no afecta al coque producido, pero reduce la formación de DME, al desplazar el equilibrio de reacción. En base a estos resultados, se desarrolló un modelo cinético tipo Langmuir-Hinshelwood, que incluye una función de desactivación dependiente del coque formado. El modelo cinético predice correctamente los rendimientos a los principales productos y el coque formado con el tiempo de reacción.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Caracterización de la fracción sólida de la pirólisis de residuos lignocelulósicos

Los carbonizados obtenidos a partir de pirólisis de residuos de origen lignocelulósico despiertan un creciente interés por sus aplicaciones potenciales como fuente de energía, adsorbentes de bajo coste y enmiendas de suelo. En este trabajo se han preparado carbonizados a partir de la pirólisis convencional de diferentes residuos biomásicos: cáscara de almendra, tallo de cáñamo, hueso de aceituna y lignina Kraft, a temperaturas de entre 400 y 800 °C, y velocidades de calentamiento entre 10 y 20 °C/min. Se ha analizado influencia de la composición en los diferentes biopolímeros sobre las propiedades físico químicas de los carbonizados. Los carbonizados presentan una microporosidad estrecha, mostrando áreas superficiales entre 240 y 500 m2/g y volumen de microporos estrechos de hasta 0.20 cm3/g, caso del carbonizado obtenido de hueso de aceituna a 800 °C, haciendo posible su uso como tamices moleculares o material de partida para preparación de carbones activos. En cuanto a su análisis inmediato y elemental, presentan contenidos de cenizas de entre 2 e 7%. Además, se han calculado los poderes caloríficos con valores superiores a 25 MJ/kg, y por tanto pueden ser empleados como combustibles sólidos.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech