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Traditional methods to develop biomass-based carbon adsorbents generally involve carbonization followed by chemical or physical activation. However, routes involving the hydrothermal treatment of biomass are receiving growing interest. In this work, two different strategies for the synthesis of sustainable CO2 adsorbents are compared, i.e., in situ ionic activation and hydrothermal treatment followed by activation with CO2. The latter is a green and simple procedure that does not require the addition of chemicals or acid-washing stages, and which leads to carbon adsorbents with relatively high CO2 adsorption capacity at low pressures, up to 0.64 mmol g−1 at 15 kPa and 50 °C, conditions relevant for postcombustion CO2 capture applications. On the other hand, in situ ionic activation can lead to carbon adsorbents with superior CO2 adsorption capacity in the aforementioned conditions, 0.78 mmol g−1, and with reduced cost and environmental impact compared to conventional chemical activation.

Pine cone leaves (PCL) and pine kernel shells (PKS), abundant by-products of the Spanish food industry, were selected as precursors for activated carbons (ACs) to adsorb CO2 selectively at industrial post-combustion capture conditions. The goal was to maximize the development of narrow microporosity in the final carbons to boost the CO2 adsorption capacity. We have designed kinetics and equilibrium of adsorption experiments with CO2/H2O/N2 on a selected AC derived from PCL in a thermogravimetric analyzer (TGA) at 50 °C and three partial pressures of CO2 to prove the suitability to capture CO2 from industrial off-gases. When humid flue gas streams were tested, competitive adsorption of CO2 and H2O occurred; however, the difference in the uptake rates favored CO2 adsorption in the early stages. The joint CO2 + H2O uptake was around 2 mmol g−1 at 50 °C in humid conditions, where CO2 reached the equilibrium uptake at the corresponding partial pressure for 15 and 32 vol% CO2 in the feed stream. Moreover, the dynamic performance was addressed by cyclic adsorption–desorption experiments representing different industrial post-combustion capture scenarios in a lab-scale fixed-bed rig. The selected AC showed a stable performance in adsorption-regeneration cycles and very remarkable CO2 capture capacity under dry conditions (up to 1.08 mmol g−1 at 50 ˚C for 30 vol% CO2). Kinetics analysis also supported the faster adsorption of CO2 under cement flue gas conditions.

Adsorption using bio-based adsorbents has been pointed out as an economical and environmentally benign technology for CO₂ gas separation and storage. A bio-based adsorbent can be fabricated from low-cost worldwide available biomass feedstock and bio-wastes from different industries (e.g., dairy manure, forestry, agriculture). As a result, it is a carbon rich material of hydrophobic nature, activated to gain high porosity development, and requires mild regeneration conditions. However, large-scale deployment of bio-based adsorption processes remains challenging. Our group has been intensively developing biomass-based adsorbents in conjunction with the design of tailored CO₂ adsorption-based cyclic processes for the envisioned application. Herein, key concepts on adsorption technology, biomass waste management, and different activation techniques for biomass-based adsorbent precursors are discussed. This review addresses the most relevant studies in the literature, from lab experimentation on a milligram scale (volumetric and gravimetric tests) to dynamic tests in bench or large-scale cyclic adsorption processes (i.e., pressure swing adsorption, temperature swing adsorption, vacuum swing adsorption). Therefore, the main target is to give a holistic view of the industrial applications where CO₂ separations with these materials are more suitable. Finally, concluding remarks and future perspectives of bio-based adsorbents in carbon capture are presented. © 2023 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Renewable clean H2 has a very promising potential for the decarbonization of energy systems. Sorption enhanced steam reforming (SESR) is a novel process that combines the steam reforming reaction and the simultaneous CO2 removal by a solid sorbent, such as CaO, which significantly enhances hydrogen generation, enabling high-purity H2 production. The CO2 sorption reaction (carbonation) is exothermic, but the sorbent regeneration by calcination is highly endothermic, which requires extra energy. Biogas is one of the available carbon-neutral renewable H2 production sources. It can be especially relevant for the energy integration of the SESR process since, due to the exothermic sorption reaction, the CO2 contained in the biogas provides extra heat to the system, which can help to balance the energy requirements of the process. This work studies different process configurations for the energy integration of the SESR process of biogas for high-purity renewable H2 production: (1) SESR with sorbent regeneration using a portion of the produced H2 (SESR+REG_H2), (2) SESR with sorbent regeneration using biogas (SESR+REG_BG), and (3) SESR with sorbent regeneration using biogas and adding a pressure swing adsorption (PSA) unit for hydrogen purification (SESR+REG_BG+PSA). When using biogas as fuel (Cases 2 and 3), these configurations were studied using air and oxy-fuel combustion atmospheres in the sorbent regeneration step, resulting in five case studies. A thermodynamic approach for process modeling can provide the optimal process operating conditions and configurations that maximize the energy efficiency of the process, which are the basis for subsequent optimization of the process at the practical level needed to scale up this technology. For this purpose, process simulations were performed using a steady-state plant model developed in Aspen Plus, incorporating a complex heat exchanger network (HEN) to optimize heat integration. A comprehensive parametric study assessed the

To achieve net zero carbon emissions from energy systems, biogas has become an attractive renewable resource for hydrogen production. The sorption enhanced steam reforming (SESR) process is proposed to produce high-purity hydrogen from biogas, enabled by combining the catalytic reforming reaction with the simultaneous CO2 removal by sorption in a single reactor. One of the most critical challenges in using biogas in conventional reforming processes is the presence of H2S since it may deactivate the reforming catalyst. Here we experimentally study the effect of the biogas H2S concentration on the H2 production by SESR, i.e., accounting for the presence of a CaO-based solid sorbent. This work was performed in a fixed-bed reactor using a Pd/Ni-Co hydrotalcite-like material (HT) catalyst and dolomite as CO2 sorbent. Biogas (60CH4/40CO2 vol.%) with different concentrations of H2S (150, 350, 500 and 1000 ppm) was evaluated. The catalyst did not deactivate for biogas H2S concentrations of 150 and 350 ppm during five cycles of the SESR process. However, a slight decrease in the catalyst activity was detected under higher sulfur concentrations after the third SESR cycle. Sulfur was detected in the spent catalyst and sorbent materials, with a higher proportion in the sorbent for the highest H2S concentration tested (1000 ppm). H2 yield decreased by 10.8% and 4.5% points for biogas H2S concentrations of 500 and 1000 ppm after five cycles, respectively, while H2 purity decreased by only 3 vol.% and 2 vol.% points, respectively.

H2 production by sorption enhanced steam reforming (SESR) of bio-oil/biogas blends was demonstrated in a fluidized bed reactor. It combines steam reforming (SR) with simultaneous CO2 capture by a solid sorbent. SESR was performed on a Pd/Ni-Co catalyst derived from a hydrotalcite-like material (HT) using dolomite as CO2 sorbent. Bio-oil from fast pyrolysis of biomass is a carbon–neutral and renewable energy source with great potential for clean H2 production by steam reforming processes. Biogas is also a promising renewable bio-based resource for hydrogen generation that can be used to increase the H2 production of a biomass-based plant. In turn, it could improve the energy efficiency of the process due to the exothermic reaction of the CO2 contained in biogas with the sorbent. Bio-oil composed of acetic acid and acetone (1/1 mol/mol) and biogas composed of CH4 and CO2 (60/40 vol%) were used as fuels. They were blended (50 wt% bio-oil + 50 wt% CH4) to study the SESR process. Effects of temperature, steam/C molar ratio, and pressure on the process performance were evaluated. SESR results showed an effective reforming of bio-oil/biogas blends and an enhancement in the H2 production and fuel conversion compared to conventional SR. Higher temperature and steam/C ratio, but lower pressure, favored H2 yield and purity. High H2 yield (87.1%) and H2 purity (98.6 vol%) were obtained at 625 °C and 2.5 bar (steam/C molar ratio three times higher than the stoichiometric value). The thermodynamic energy analysis of the SESR of bio-oil/biogas blends rendered 1.34% higher cold gas efficiency (CGE) than bio-oil SESR.

The main challenge of adsorption consists in the production of materials that can be used in real situations. This study comprehensively describes the CO2 and H2O adsorption behavior of honeycomb-shaped sorbents commonly used in rapid pressure swing adsorption cycles (RPSA). With this purpose, the kinetics and equilibrium of adsorption of CO2/H2O/N2 mixtures on three honeycomb carbon monoliths (793, 932, and AM03) were assessed in a thermogravimetric analyzer (TGA) under different postcombustion capture scenarios (temperature of 50 °C and several concentrations of CO2). The kinetics study exhibited that the single adsorption of CO2 and H2O can be adequately described by the Avrami and exponential decay-2 models, respectively. As expected, the three carbon monoliths presented fast adsorption of CO2 from a CO2/H2O mixture. Furthermore, when humid flue gas was considered, overall adsorption kinetics were governed by CO2. Besides, the experimental data fitting to the intraparticle diffusion model showed that gradual CO2 and H2O diffusion toward the micropores was the rate-limiting stage. The obtained results give a better insight into the selective adsorption of CO2 and the potential of honeycomb carbon monoliths to separate CO2 from humid flue gas in the context of the cement industry. Carbon monolith 793 is the best carbon monolith candidate to capture CO2 under the evaluated conditions: a capacity of adsorption of 1 mmol of CO2 g-1 and favorable kinetics in 32 vol % CO2 and 4 vol % H2O(v), at 50 °C and 101.3 kPa.

Woody biomass pellets' demand for primary energy production is increasing. To guarantee sustainable and cost-efficient pellet production the diversification of biomass feedstock is mandatory. In this work it is proposed to re-use the solid biochar obtained from pyrolysis of eucalyptus (PEc) at 700 °C as an additive to produce enhanced pine sawdust (PIN) pellets. The process required the addition of glycerol as a lubricant in a percentage of 1 and 2 wt% per 5 and 10 wt% of pyrolyzed eucalyptus in the blend, respectively. Small additions of PEc enhanced PIN pellets’ grindability and water-resistance, providing products with remarkable values of durability (up to 99%), net calorific value (up to 20 MJ/kg), energy density (up to 13.3 GJ/m3), and particle density (up to 1.24 g/cm3). N, S, chlorine, and heavy metals contents were also analyzed. The proposed pellets fulfill the A1/A2 and the I1/I2 quality classes for domestic and industrial wood pellets, respectively. A preliminary economic evaluation indicated that pellets made up from a mixture of 90% PIN and 10% PEc are competitive compared to raw PIN pellets, with expected savings in the costs of production, energy, transport, and construction of a storage site of 4, 13, 10 and 7%, respectively.

Pressure Swing Adsorption (PSA) is one of the implemented technologies for removing carbon dioxide in biogas streams. Different adsorbents, mostly zeolite-based, and process configurations have been patented and commercially demonstrated. In this study, we have developed a numerical model to successfully describe the dynamic performance of biomass-derived activated carbon in biogas purification. It is the first step in designing a biomass-based carbon capture unit within the bioenergy and circular economy context. Microporous activated carbon pellets prepared from pine sawdust by physical activation with CO2 was the adsorbent material choice. The model was built with the fittings of single-component adsorption isotherms of CO2 and CH4 at different temperatures to the Langmuir-Freundlich model and the Ideal Adsorbed Solution Theory (IAST) to account for multicomponent adsorption. The kinetics of mass transfer in the solid phase was described by the Linear Driving Force model (LDF). The dynamic simulations were performed with the aid of the commercial software Aspen Adsorption and experimental data previously obtained in the laboratory used for the model validation [1]. The model was applied to address the separation performance of a biogas upgrading biomass-based PSA process by running a parametric study to determine the influence of key performance parameters. The sensitivity analysis concluded that a single stage 4-step PSA can produce methane with a purity above 95% and a recovery of around 60% in a configuration with P/F ratios (quotients of molar flows of CH4 in the purge and the feed streams) between 0.67 and 1 for an adsorption pressure of 3 bar.

Energy generation from non-hazardous waste streams, which are unfeasible to be reused or recycled, can help overcome some of the problems related to fossil fuel depletion, global increase in energy demand and waste generation management under restricted landfilling. One of the main drawbacks of waste-to-energy strategies is the poor combustion properties of waste, which densification could help to circumvent. This work studies the co-pelletization of refused derived fuel (RDF) and pine sawdust (PIN) in a continuous pilot pellet mill that resembles industrial pelletization. The effect of RDF contents up to 90 wt% on a set of parameters has been assessed: pelletization energy consumption, physical properties (durability, particle and bulk densities), net calorific value and energy density of the obtained pellets. In addition, slagging, fouling and corrosion, phenomena associated with combustion, were estimated from the ash composition. Results showed that obtaining pellets with a low RDF loading (2–9 wt%) was feasible. They accomplished ISO 17225-2 solid biofuels standard for industrial use, and presented low deposition and corrosion risks. On the other hand, pellets with 30–90 wt% RDF were also manufactured and complied with the UNE-EN 15359:2012 solid recovered-fuel standard for energy recovery in incineration and co-incineration plants. All the produced pellets presented durability and net calorific value above 96.9% and 10.7 MJ/kg, respectively. Energy density higher than 10.6 GJ/m3 was obtained for pellet formulations with RDF content up to 50 wt%. It was demonstrated that the blends of RDF and PIN can provide high-quality pellets with a high load of waste material, under the same operational conditions required for PIN pelletization. It is a versatile process that can be tailored to different product requirements depending on the end-use. It promotes energy recovery and generates value out of a waste fraction with no relevant use, adding economic and environment

The implementation of carbon capture, use, and storage in the cement industry is a necessity, not an option, if the climate targets are to be met. Although no capture technology has reached commercial scale demonstration in the cement sector yet, much progress has been made in the last decade. This work intends to provide a general overview of the CO2 capture technologies that have been evaluated so far in the cement industry at the pilot scale, and also about the current plans for future commercial demonstration.

H2 production from biogas (60%CH4 + 40%CO2) by sorption enhanced steam reforming (SESR) was thermodynamically and experimentally studied in a fluidized bed reactor. Biogas is an interesting renewable biomass resource for hydrogen production due to its sustainable nature. SESR combines the catalytic reforming reaction of biogas with simultaneous CO2 removal in a single step. A Pd/Ni–Co hydrotalcite-like material (HT) was used as catalyst and dolomite as CO2 sorbent. The effects of temperature (550–800 °C), steam/CH4 molar ratio (2–6) and gas hourly space velocity (GHSV) (492–3937 mL CH4 gcat−1 h−1) on the process performance were evaluated. CO2 in biogas was effectively removed by the sorbent from the gas phase at 550–700 °C, without influencing the reforming process. H2 yield increased with temperature from 550 to 650 °C, but H2 concentration decreased at temperatures higher than 600 °C, requiring a tradeoff between both parameters to select an optimum operating temperature. H2 purity of 98.4 vol% was obtained at 550–600 °C and H2 yield of 92.7% was reached at 650 °C. Higher steam/CH4 ratios enhance the process, whereas higher space velocities decrease H2 yield. Results demonstrate that high-purity high-yield biohydrogen can be produced by the SESR of a renewable biomass resource as biogas.

Biogas is a valuable source of renewable energy produced from biodegradable organic materials via anaerobic digestion. The production of H2 by sorption enhanced steam reforming (SESR) of biogas has been studied thermodynamic and experimentally. A Pd/Ni–Co catalyst and dolomite as CO2 sorbent were used. The effect of biogas composition (CH4/CO2 vol.%) on the process was evaluated at 600 and 650 °C in a fluidized bed reactor using biogas CO2 concentrations of 5–50 vol.%. During conventional biogas steam reforming (SR), high CH4 partial pressures in the feed favor the process, producing high H2 concentrations. During biogas SESR, CO2 was effectively removed from the gas phase by the sorbent for all the biogas compositions, and it did not alter the process compared to pure methane. Steam methane reforming (SMR) and water-gas shift (WGS), together with carbonation, were the main reactions occurring during biogas SESR. Dry (or CO2) methane reforming did not occur under the conditions studied due to the relatively low temperature and the presence of steam. High H2 purity (98.4 vol.%) and H2 yield (91%) were experimentally obtained, pointing out the biogas SESR as a promising technology for the efficient production of high-purity, high-yield hydrogen from a renewable source.

Adsorption is an environmentally benign separation technology with no associated toxic emissions that presents potential to reduce the energy penalty of CO2 capture processes. Several adsorption based post-combustion CO2 capture processes have reached the pilot scale demonstration stage. These adsorption processes differ in the adsorbent used, mainly zeolites, carbon materials, solid amine sorbents, and supported alkali carbonates, but also in the process configuration: the method of regeneration (temperature, vacuum, concentration swing or a mixture of those) and the type of adsorbers used (fixed beds, rotary beds, moving beds, and fluidized beds). However, their lower stage of development compared to the benchmark technology, amine absorption, has prevented up to date their commercial development. In this work, adsorption-based post-combustion CO2 capture processes, based on sustainable carbon adsorbents in a multibed configuration, have been designed and assessed through process simulation in order to compare them to the benchmark technology using a common reference, i.e., an advanced supercritical coal power plant of 800 MWe, and similar specifications to enable a fair comparison. The cyclic adsorption processes have been modelled and simulated up to cyclic steady state (CSS) using a dynamic non-equilibrium non-isothermal mathematical model that takes into consideration competitive adsorption between the main flue gas components: N2, CO2 and H2O. Such model had been previously validated against experimental results. The CSS results entailed assessing the capture rate and the CO2 purity of the product for each particular adsorbent and process configuration combination, allowing identifying those that can meet the minimum capture rate (85%) and CO2 purity specifications (95%). Such processes were then compared to the benchmark technology in terms of overall energy consumption. Among the process configurations evaluated up to date, the configuration that employs a

According to the last report of the IPCC, global CO2 emissions must be net zero by 2040-2050 in order to have chances to limit global warming to 1.5 °C. Delayed action will rise the risks of climate change [1]. Despite the decarbonization efforts, coal remains the main energy source for electricity generation globally. Moreover, there are still coal power plants under construction and in planning stage, and it is unlikely that these facilities will shut down in a timeframe consistent with the climate goals. CO2 capture and storage technologies will be necessary to mitigate the emissions from existing facilities. In this work the feasibility of adsorption technology to capture the CO2 emitted by an advanced supercritical coal power plant of 800 MW is assessed through process simulation, and compared to the benchmark technology: amine scrubbing. Different adsorption technologies are being considered for postcombustion CO2 capture: fixed beds, moving beds, fluidized beds, and rotary beds, where the adsorbent can be regenerated by temperature (TSA), pressure (VSA), concentration (CSA) swing or a combination of them. Different types of adsorbents are also under consideration, with solid amines, carbons, and zeolites at the forefront positions. In this work cyclic multibed processes with indirect heat transfer that make use of carbon adsorbents are considered. Indirect heat transfer entails reducing cycle time and save thermal energy within the process [2]. Several process configurations have been evaluated: TCSA, VTSA, and VTCSA. In the CSA processes evaluated, steam is used in direct contact with the adsorbent to recover the adsorbed CO2. The potential of such processes is assessed through simulation. First, a cyclic process configuration is proposed and simulated with Aspen Adsorption up to cyclic steady state (CSS), using a detailed non-equilibrium non-isothermal model that considers competitive adsorption between the main flue gas components (i.e., N2, CO2 and H2O) t

[EN] The solid waste management and treatment industry is facing new challenges as part of the transition to a green economy in today’s society. Waste recycling and reuse are the measures of prior concern for the management hierarchy established by the European Union. In cases where this is not feasible, it is preferable, both from an environmental and economic point of view, to recover energy from waste instead of disposing of it in a landfill. Anaerobic digestion to obtain biogas and energy recovery through incineration have become two of the most promising and fastest-growing strategies in recent years. On the one hand, waste incineration produces heat and/or electricity; however, it also generates large amounts of CO₂. On the other hand, anaerobic digestion is an alternative route for treating the organic fraction of municipal waste. Biogas from this process is an important renewable source of methane. The presence of CO₂ in biogas reduces its energy content. Therefore, its separation is of paramount importance. In order to minimize the impact of an integrated waste management process, it is essential to separate CO₂ from the different gas streams. This doctoral dissertation focuses on CO2 capture, by means of adsorption on solid sorbents, in a waste management facility. The study carried out encompasses both the preparation of the adsorbent material and its evaluation, as well as the design of the adsorption process. The sustainability of the whole process played a key role in the design of the research., The first stage focuses on the preparation of the adsorbent material. The production of activated carbons from low-cost biomass precursors by physical activation was proposed. The possibility of using pine sawdust and different species of microalgae was studied and the influence of pre-treatments such as hydrothermal carbonization or oxidation, depending on the precursor, was assessed.In order to perform a first screening regarding their potential as CO2 adsorbents, the adsorption capacity of the activated carbons was evaluated under static conditions by means of a thermogravimetric analyzer. Based on the experimental data gathered, the mass transfer mechanism involved in the adsorption of CO2 was studied using the intraparticle diffusional model. In a second phase, the performance of the adsorbents under dynamic conditions was tested in a fixed-bed unit over consecutive adsorption−desorption cycles. For this purpose, the adsorbents prepared from pine sawdust were selected. The maximum CO2 capture capacities (breakthrough curves) were determined in both CO2/N2 and CO2/CH4 binary mixtures at different pressure and temperature conditions. Since both gaseous streams, incineration flue gas and biogas, contain significant amounts of water vapor, the effect of its co-adsorption with other gaseous components was evaluated., The dynamic evaluation was completed with a series of cyclic experiments in conditions close to the real ones encountered in an industrial process, i.e., avoiding saturation of the bed, for its application in a waste incineration plant. The third stage consists in the design and optimization of a cyclic process of adsorption and desorption. This required the analysis and evaluation of multiple parameters: the number of columns, the configuration of steps, the operating pressure and temperature, regeneration strategies, etc. These parameters, together with the properties of the adsorbent, determine both the degree of purity and the recovery of the product (CO2 in this case). The experimental data of adsorption equilibrium, kinetics and the physical properties of the adsorbent bed were employed to develop numerical models based on mass, momentum and energy balances, relevant to CO2 separation. For this purpose, the commercial software Aspen Adsorption™ was used. The model was validated against the experimental results obtained in the fixed-bed unit, which allows it to be used in the simulation of the CO2 adsorption-desorption process with other configurations., [ES] Las industrias de gestión y tratamiento de residuos sólidos deben afrontar nuevos retos en el contexto de la transición hacia una economía verde a la que se enfrenta la sociedad actual. El reciclado y la reutilización de los residuos son las opciones prioritarias en la jerarquía de gestión de la Unión Europea. Cuando esto no es posible, es preferible, tanto desde el punto de vista medioambiental como económico, recuperar el contenido energético de los residuos en vez de depositarlos en vertedero. La digestión anaerobia para la obtención de biogás y la valorización energética, mediante incineración, son las dos estrategias más interesantes y con mayor crecimiento en los últimos años. La incineración de residuos permite obtener calor y/o electricidad, pero genera grandes cantidades de CO₂. Por otro lado, una manera alternativa para poder procesar la fracción orgánica de residuos municipales es la digestión anaerobia. El biogás procedente de este proceso es una importante fuente renovable de metano. La presencia de CO₂ en el biogás reduce su valor energético, por lo que su separación presenta un gran interés. Con el fin de reducir al máximo el impacto de sus actividades, resulta esencial la separación de CO₂ de las distintas corrientes gaseosas generadas en el proceso de gestión integral de residuos. La presente Tesis Doctoral se enmarca dentro de la temática de captura de CO₂ mediante adsorción con sólidos, en una instalación de gestión de residuos. El trabajo desarrollado abarca, tanto la preparación del material adsorbente y su evaluación, como el diseño del proceso de adsorción y, todo ello, manteniendo las premisas de sostenibilidad., La primera etapa se ha centrado en la preparación del material adsorbente. Se ha propuesto la producción de carbones activados usando precursores biomásicos de bajo coste mediante activación física. Se ha estudiado la posibilidad de emplear serrín de pino y distintas variedades de microalgas y se ha evaluado la influencia de la carbonización hidrotermal o la oxidación, según el precursor, como tratamientos previos. Con objeto de realizar un primer cribado respecto a su potencial como adsorbentes de CO2, se ha evaluado la capacidad de adsorción de los materiales preparados en condiciones estáticas en termobalanza. A partir de los datos experimentales se ha estudiado también el mecanismo de transferencia de materia, durante el proceso de adsorción, mediante el modelo difusional intraparticular. En una segunda etapa se ha evaluado el comportamiento de los adsorbentes en condiciones dinámicas, en un dispositivo de lecho fijo, mediante ciclos múltiples de adsorción y desorción. Para ello se han utilizado adsorbentes preparados a partir de serrín de pino. Se han determinado las capacidades máximas de captura de CO2 (curvas de ruptura), tanto en mezclas binarias CO2/N2 como CO2/CH4, en distintas condiciones de presión y temperatura. Puesto que ambas corrientes, incineración y biogás, presentan contenidos en vapor de agua significativos, se ha evaluado el efecto de su co-adsorción con los otros componentes gaseosos., La evaluación dinámica se ha completado con la realización de experimentos cíclicos en condiciones próximas a las reales en un proceso industrial, es decir, sin saturación del lecho, para su aplicación en una instalación de incineración de residuos. La tercera etapa se ha centrado en el diseño y la optimización de un proceso cíclico de adsorción y desorción; ha sido necesario analizar y evaluar múltiples parámetros: número de columnas, configuración de las etapas, presión y temperatura en las condiciones de operación, estrategias de regeneración del adsorbente, etc. Estos parámetros, junto con las propiedades del adsorbente, determinan tanto la pureza como la recuperación del producto (CO2 en este caso).Los datos experimentales de equilibrio y cinética y las propiedades físicas del lecho de adsorción obtenidos previamente han sido empleados para el desarrollo de modelos numéricos, basados en balances de materia y energía, aplicables a la separación de CO₂. Para ello se ha utilizado el software Aspen Adsorption™. Se ha validado el modelo con los resultados experimentales obtenidos en el lecho fijo, lo que ha permitido su uso posterior en la simulación del proceso de adsorción-desorción de CO2 empleando otras configuraciones.

The performance of vacuum swing adsorption-based processes applied to CO2 capture in Waste-to-Energy plants is explored for the first time. CO2 capture and storage (CCS) are gaining increasing attention in this sector. The analysis of simple cycle configurations for this particular application provides a reference scenario to explore the potentiality of the adsorption technology. Under these premises, the objective of this study is to maximize the CO2 separation from the flue gas of a solid waste incineration facility. Three vacuum swing adsorption (VSA) and one vacuum and temperature swing adsorption (VTSA) configurations were assessed in a fixed-bed laboratory unit and the influence of the cycle design, the number of columns and the operational conditions were analyzed. The adsorbent employed is an activated carbon produced from pine sawdust, a forestry by-product with great availability in our region. Mathematical modeling developed in Aspen Adsorption complemented the experimental study which in turn validated the created model. Additional simulations were performed to further evaluate the effect that the different vacuum swing adsorption configurations have on product purity and recovery. With relatively simple configurations consisting of a maximum of 4-beds, CO2 recoveries above 95% were achieved and CO2 purity was increased from 8% to approximately 35–40%.

Vacuum, temperature and concentration swing adsorption processes, have been designed to capture 85% of the CO2 emitted by an advanced supercritical coal fired power plant of 800 MW taken as reference, and to produce a concentrated product with 95% of CO2 (dry basis) using a sustainable carbon adsorbent inside the tubes of a tube-bundle adsorber. Indirect heat transfer is used to increase productivity and to conserve energy within the process. Two different configurations of the cyclic process have been evaluated at cyclic steady state through dynamic process simulation, using a detailed non-isothermal non-equilibrium fixed bed adsorption model that takes into consideration competitive adsorption between the main flue gas components: N2, CO2 and H2O. Simulation results indicate that the purity and recovery constraints can be met with a specific heat duty of 2.32 MJth kg−1 CO2 and a specific electric consumption of 0.66 MJe kg−1 CO2. The main advantage of this process is that the specific heat duty, which is lower than the benchmark amine absorption technology, could be satisfied using waste heat.

A novel multibed heat-integrated vacuum and temperature swing adsorption process has been designed to capture 85% of the CO2 emitted by an advanced supercritical coal fired power plant of 820 MWe taken as reference, and to produce a concentrated product with 95% of CO2 using a microporous carbon obtained from olive stones. The overall performance of the post-combustion CO2 capture process has been evaluated from the results of the dynamic simulation of the process at cyclic steady state, using a detailed non-isothermal non-equilibrium dynamic fixed-bed adsorption model that takes into consideration competitive adsorption between the main flue gas components: N2, CO2 and H2O. The proposed process operates between 30 °C and 1.05 bar and 80 °C and 0.05 bar. The specific heat duty of the process, 2.41 MJth kg−1 CO2, which is lower than the benchmark amine absorption technology, can be satisfied using waste heat. On the other hand, its electricity consumption, 1.15 MJe kg−1 CO2, is higher. Increasing the pressure of the production step reduces significantly the energy demand of the process, but also its capture rate. Substantial improvements in performance can be expected from adsorbent development. Adsorption is an environmentally benign technology with great potential to mitigate CO2 emissions from industrial processes with unused waste heat sources.

Capturing CO2 with solid adsorbents can be often limited by heat transfer during the regeneration process rather than mass transfer during the adsorption process. The use of a low-heat capacity adsorbent would result in a lower energy penalty for the regeneration step. Specific heat capacity (Cp) data knowledge of solid adsorbents is still scarce in the literature. To gather information in this regard, activated carbons (ACs) prepared from different precursor materials, synthesis conditions, activating agents and surface modifications have been experimentally tested. The specific heat capacity has been evaluated at temperatures ranging from 50 to 190 °C, relevant for temperature swing adsorption (TSA) based CO2 capture processes. A thermogravimetric analyser/differential scanning calorimeter (TGA/DSC) has been used for the experimental testing. Cp values of the evaluated adsorbents evidenced significant dependency on temperature: adsorbents either showed a linear upward trend with temperature –phenolic resin-derived ACs- or they peaked at a determined temperature range –biomass based ACs-. This peak has been ascribed to oxidation reactions of biomass based carbons during the experiment. It is noteworthy that adsorbent surface modification plays a key role in the specific heat capacity of the resultant carbon. Likewise, the acid and basic character of the carbon surface has been identified as key parameter for effective regeneration in TSA processes. AC adsorbents with an acidic character are undesirable owing to their higher specific heat capacities.

Pellets for industrial use were produced from blends of pine sawdust (PIN) and alternative residual biomasses in a pilot-scale pelletizer. The effect of the pelletization temperature (T = 50–80 °C) and biomass moisture content (MC = 14–20%) on pine sawdust pellet quality was studied by using response surface methodology (RSM). Pelletization performance was evaluated on the basis of the durability, bulk density, moisture content, lower heating value (LHV), energy density, diameter, length and density of the pellets. From the RSM analysis, a maximum durability value of 99.4% was obtained at T = 80 °C and MC = 16.6%. Under these conditions, all the parameters showed values within the required range of industrial pellet qualities, i.e., a bulk density of 616 kg/m3, a pellet moisture content of 7.6%, a lower heating value (as received) of 18 MJ/kg, a diameter of 6.2 mm and a length of 23.4 mm. Blends of pine sawdust with eleven unconventional biomass samples were then pelletized under the optimum conditions to obtain pellets for industrial use according to the categories of quality defined by ISO 17225-2. Blends of pine sawdust with almond shells (AS) and olive stones (OS) contents of up to 30 wt%, as well as with pine cone leafs (PCL) contents of up to 15 wt%, produced I1 pellets. Blends of pine sawdust with coffee dregs (CD), coffee husks (CH) and grape pomace (GP) proportions of up to 10 wt%, as well as with hazelnut shells (HS), miscanthus (MIS), pine kernel shells (PKS) and switchgrass (SG) contents of up to 15 wt%, and also with a PCL content of between 15 and 30 wt%, generated I3 class pellets. Classification was not possible for cocoa shells (CS) mixed with pine sawdust due to the low bulk density of the pellets. Energy consumption resulting from the pelletization of the blends was evaluated with values ranging from 0.09 to 0.33 kWh/kg, while the pelletization of pine sawdust required 0.18 kWh/kg. The addition of alternative biomass feedstocks to pine sawdust may

[EN] The consequences of climate change are already noticeable. Even if greenhouse gas emissions were significantly reduced, global warming would continue over the coming decades and the effects would ever be perceptible in the centuries to come. For this reason, the international community is committed to achieving carbon neutrality between 2050-2100. This critical situation will require the deployment of all available technologies during this transition period. One of the main paths towards mitigating CO₂ emissions from large point stationary sources is through the application of carbon capture and storage technologies. In recent years, considerable research effort has been devoted to this aim. Among the wide variety of processes able to capture CO₂, is adsorption, the subject of this PhD dissertation. Over the last decade, research on new low cost adsorbent materials with a high CO₂ capture performance, particularly in postcombustion capture applications, has been very intensive. Within this context, it is of the utmost importance to evaluate the performance of the adsorbents under humid conditions and in the presence of other pollutants in the gas stream so as to assess conditions representative of real industrial applications. It was the circumstances just described that motivated the research into the effect of water vapour on postcombustion CO₂ capture as part of the present PhD thesis.The main objective of the PhD thesis has been to address the performance of biomass-based CO₂ adsorbents in postcombustion capture conditions where the level of humidity is very high. A set of carbons has been produced and optimised by means of different methodologies so as to enhance the selectivity towards CO₂ in the presence of water as well as to maximise CO₂ uptake under these conditions., The ability of an activated carbon to adsorb CO₂ under postcombustion capture conditions is ascribed to its microporosity. However, CO₂ uptake is reduced in humid environments due to the coadsorption of water vapour. The present PhD dissertation, addresses this issue directly, focusing on the adsorption of water vapour on biomass-based activated carbons and on the strategies available for reducing water uptake by means of surface chemistry modification. It was found that all of the evaluated post-treatments reduced water uptake at low pressures to some extent but only amine impregnation succeeded under conditions close to saturation. Likewise, the production of biomass-based activated carbons has been optimised and their potential for CO₂ adsorption under humid conditions maximised by combining different experimental procedures including the design of experiments by means of Response Surface Methodology and modelling methods. Analysis of the equilibrium of adsorption by means of isotherms together with the dynamic performance of beds of adsorbent by means of breakthrough curves and sorption-desorption cycles provided data needed in support of the great potential of biomass adsorbents such as those produced in this study to capture CO₂ under postcombustion conditions. The CO₂ capture performance of coffee-based activated carbons was optimised and enhanced by means of hydrothermal carbonisation followed by activation in CO₂ atmosphere. The results achieved are more far-reaching than those reported in the patent ES2526259. On the other hand, under a constant relative humidity of 20%, a bed of a biomass carbon doped with potassium carbonate achieved a CO₂ uptake of up to 2 mmol g-1 at 50 ºC and 14 kPa CO₂. This result was accompanied by an outstanding volumetric CO₂ uptake., [ES] Las consecuencias del cambio climático ya son perceptibles. Aunque las emisiones de gases de efecto invernadero se redujesen notablemente, el calentamiento de la Tierra continuaría durante décadas y sus efectos se sufrirían durante los siglos venideros. Por este motivo, la comunidad internacional ha adquirido el compromiso de alcanzar la neutralidad de emisiones de carbono entre 2050-2100. Esta situación requerirá contar con todas las tecnologías de mitigación disponibles en el periodo de transición. Una de las principales formas de mitigar las emisiones de CO₂ de grandes fuentes estacionarias son las tecnologías de captura y almacenamiento de carbono. De ahí que en los últimos años se haya dedicado un esfuerzo investigador considerable a su desarrollo. Entre el amplio abanico de procesos capaces de captar CO₂, la presente Tesis Doctoral se centra en la adsorción. Durante la última década se ha intensificado la búsqueda de materiales adsorbentes con un alto rendimiento en la separación de CO₂, así como un coste bajo, especialmente si su aplicación es en procesos de captura de CO₂ postcombustión. En este contexto, es fundamental el estudio de su comportamiento bajo condiciones de humedad y en presencia de otras impurezas en la corriente gaseosa, condiciones representativas de las reales en el ámbito industrial. Estas circunstancias han motivado la presente Tesis Doctoral, en la cual se ha evaluado el efecto del vapor de agua en la captura de CO₂ postcombustión. El objetivo principal de esta Tesis Doctoral ha sido estudiar el rendimiento de carbones activados biomásicos para la adsorción de CO₂, en condiciones de postcombustión donde la humedad es muy significativa. Para ello, se han preparado y optimizado estos carbones aplicando diferentes metodologías, para incrementar su selectividad hacia el CO₂ en presencia de humedad, así como maximizar su capacidad de captación de CO₂ en estas condiciones., La capacidad de adsorción de CO₂ de los carbones activados en condiciones de postcombustión reside en su microporosidad; sin embargo, la captación de CO₂ se ve disminuida en atmósferas húmedas debido a la co-adsorción de agua. Este aspecto ha sido evaluado en la presente memoria de Tesis Doctoral, donde se ha investigado sobre la adsorción de vapor de agua en carbones activados biomásicos y las posibles estrategias para reducirla actuando, fundamentalmente, sobre la química superficial. Todos los post-tratamientos evaluados redujeron la adsorción de vapor de agua a bajas presiones, pero solamente la impregnación con aminas es efectiva en condiciones próximas a la saturación. Asímismo, se han desarrollado diferentes procedimientos experimentales, que incluyen una combinación única de diseño de experimentos mediante la Metodología de Superficies de Respuesta y diversos métodos de modelización, para optimizar la producción de los carbones biomásicos y maximizar su capacidad de captación de CO₂ en presencia de humedad. Mediante el análisis del comportamiento termodinámico en el equilibrio (isotermas de adsorción) y del comportamiento dinámico de lechos de adsorbente (curvas de ruptura y ciclos de sorción-desorción) se presenta una visión completa de la potencialidad de los carbones activados biomásicos para la captura de CO₂ en condiciones de postcombustión. Se ha optimizado y mejorado el comportamiento en captura de CO₂ postcombustión de un carbón activado, preparado a partir de residuos de café postconsumo, mediante tratamiento hidrotermal y posterior activación. Los resultados obtenidos suponen un avance respecto a la patente ES2526259. Por otro lado, en condiciones de humedad relativa constante del 20%, el lecho de carbón activado biomásico producido mediante impregnación con carbonato potásico, alcanzó una capacidad de captura de CO₂ de 2 mmol g-1 a 50 ºC y 14 kPa de CO₂. Este resultado se complementa con una excepcional capacidad en términos volumétricos.

Multivariate analysis was used to study the influence of the biomass characteristics on the gasification process. Ten lignocellulosic biomass samples (almond shells –AS–, chestnut sawdust –CHE–, torrefied chestnut sawdust –CHET–, cocoa shells –CS–, grape pomace –GP–, olive stones –OS–, pine cone leafs –PCL–, pine sawdust –PIN–, torrefied pine sawdust –PINT–, and pine kernel shells –PKS–) were gasified in a bubbling fluidized bed gasifier under an air-steam atmosphere. Statistical analysis was applied to the variables that described the results of the gasification process, i.e., gas concentration, gas production (moles), calorific value of the product gas, energy density, and cold gas efficiency, together with the main biomass properties, such as those derived from the elemental and proximate analyses, the higher heating value (HHV), the particle density, and the elemental composition of the ashes. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were applied to the data of biomass properties and gasification parameters in order to elucidate which feedstock features had a more determinant influence on the gasification process. Both HCA and PCA revealed a clear separation of the biomass samples into two main groups on the basis of the gasification results. The results indicated that PKS, PCL, PINT, OS and PIN biomasses were characterized by high production of combustible gases, such as CO and CH4, high conversion and cold gas efficiency during gasification. This indicated that the most important biomass properties for promoting the gas production, calorific value of the product gas, gasification conversion and energy efficiency were the C and H contents and the HHV of the biomass. However, biomasses CS and GP were mainly characterized by high H2 concentration and H2/CO molar ratio in the gas product, which was mainly related to the higher H/O ratio and K2O ash content of the biomass. The H2 concentration in the product gas was negatively rela

Solid sorbents with enhanced capacity and selectivity towards CO2 are crucial in the design of an efficient capture process. Among the possible alternatives, K2CO3-doped activated carbons have shown high CO2 capture capacity and rapid carbonation reaction rate. In this work, a sustainable and low-cost approach is developed with a biomass-based activated carbon or biocarbon as support. The CO2 capture performance in cyclic sorption–desorption operation and the sorption kinetics have been investigated under different scenarios in a purpose-built fixed-bed set-up. Independent of the H2O concentration in the flue gas, a constant relative humidity (∼20%) in the K2CO3-doped biocarbon bed promoted the carbonation reaction and boosted the CO2 sorption capacity (1.92 mmol/g at 50 °C and 14 kPa partial pressure of CO2). Carbonation is slower than physical adsorption of CO2 but wise process design could tune the operation conditions and balance capture capacity and sorption kinetics.

La creciente necesidad de reducir las emisiones de CO2 a la atmósfera hace necesario el desarrollo de nuevas tecnologías que puedan aplicarse en todos los grandes focos emisores. La Captura y Almacenamiento de CO2 (CAC) se postula como una de las tecnologías necesarias y que puede contribuir de forma importante en la reducción de dichas emisiones, tanto para su aplicación en grandes centrales térmicas como en el sector industrial. Este trabajo muestra el estado actual de la tecnología CAC tanto a nivel mundial como a nivel nacional, para posteriormente centrarse en aquellas tecnologías más adecuadas para la industria del cemento. En este sentido, la oxicombustión y especialmente la realizada para la calcinación de la caliza (oxicalcinación) parece ser la más adecuada en instalaciones de nueva construcción, mientras que en instalaciones existentes es preferible la utilización de procesos post-combustión. Finalmente se muestran las diferentes iniciativas que se están desarrollando a nivel mundial para la captura de CO2 en la industria del cemento.

The design of a pressure swing adsorption (PSA) system requires the development of a complex model that can describe the dynamics of adsorption in a fixed-bed, which means a labor intensive and time consuming work, especially when several adsorbents are going to be compared. Therefore, it would be very useful to establish a simple procedure to quickly assess the performance during the early stages of PSA systems design. The aim of this work is to develop a simplistic approach that drives the decision-making process on the adsorbent in a shorter time. A combined experimental and numerical study of CO2/CH4 adsorption is presented. Thus, three commercial activated carbons are compared in their performance to separate CO2 from biogas under PSA conditions by means of equilibrium adsorption data. A straightaway model, developed to approach PSA systems in a very simple way, where the only input is equilibrium of adsorption data, has been adopted. The Adsorption Figure of Merit (AFM), CO2 purity and CO2 recovery were selected as performance indicators and they have pointed out one of the activated carbons, MC27, as the most promising adsorbent candidate to separate CO2/CH4 by means of PSA. A sensitivity analysis of the process performance as a function of the bed dimensions has been addressed using the developed short-cut model.

he present study investigates the air-steam gasification of ten commercial and alternative lignocellulosic biomass fuels (pine sawdust, chestnut sawdust, torrefied pine sawdust, torrefied chestnut sawdust, almond shells, cocoa shells, grape pomace, olive stones, pine kernel shells and pine cone leafs) in order to evaluate the product gas composition and the process performance in a bubbling fluidized bed gasifier with focus on the different biomass properties. Accordingly, an effort to correlate the biomass characteristics with the gasification results has been done. Pine kernel shell (PKS) was used to test the effect of the gasification temperature (700, 800 and 900 °C), steam to air ratio in the gasifying agent (S/A = 10/90, 25/75, 50/50 and 70/30) and stoichiometric ratio (SR = 0.13 and 0.25) on the product gas composition, combustible gas (H2 + CO + CH4) production, H2/CO ratio, heating value, energy yield and cold gas efficiency of the obtained gas. Results showed that higher temperature and S/A ratio favored H2 production and gasification performance. A higher value of SR slightly affected the gas composition, but led to a higher process efficiency as a consequence of a higher biomass conversion into gaseous combustible products. All the biomass samples of different origin and characteristics were then gasified at the best experimental conditions found (900 °C, S/A = 70/30, SR = 0.25). Gasification of all the biomasses was feasible and H2 and combustible gas concentrations of 30–39 vol% and 59–78 vol% (inert gas-free basis), respectively, were obtained for the biomasses studied, with energy yields of 8–18 MJ/kgbiomass. Torrefied biomass showed similar combustible gas production than the corresponding raw biomass under the conditions studied, but it gave slightly higher H2 production and efficiency results. Possible correlations of the gasification performance parameters with biomass properties were also analyzed. The results showed positive effects of biomass

Biogas main components besides methane are carbon dioxide and water that often have to be removed to increase the calorific value of the gas. In this study the effect that the presence of water vapor has on CO2 separation from a biogas stream by means of adsorption on a lignocellulosic-based activated carbon is addressed. Binary CO2/CH4 breakthrough experiments at 30 °C to account for competitive adsorption under dry conditions were conducted at several feed compositions and adsorption pressures in a fixed-bed lab set-up. An adsorption selectivity factor was selected for analysis of the different cases. The results indicated that CO2/CH4 separation by adsorption on this material could be most promising at lower pressures., Humid gas mixtures were then evaluated in the fixed-bed set-up purposely adapted. The effect of water vapor co-adsorption on the separation of CO2 and CH4 was studied for different CO2/CH4 ratios, at 30 °C and atmospheric pressure. Under humid conditions the CO2 uptake was reduced but the CH4 uptake showed negligible influence of water vapor co-adsorption. Results also indicated that the presence of pre-adsorbed water vapor (saturated bed) reduced the capacity of the bed to adsorb CO2 and CH4 but it prompted CO2 adsorption over CH4 and hence facilitated the selectivity towards CO2 with respect to the dry case.

Twelve commercial and unconventional biomass fuels were evaluated in steam gasification; these include samples of hard (wood, almond, olive and pine kernel wastes) and soft (miscanthus, switchgrass, coffee, cocoa and grape wastes) biomass. Gasification tests at 700–1000 °C of biomass chars obtained from a bubbling fluidized bed reactor were performed in a TG analyzer. Steam gasification kinetics were extensively analyzed: an index of key parameters for the twelve biomasses and the correlation to biomass ash composition were developed. The random pore model (RPM) described the experimental reactivity best, with activation energies of 59–196 kJ mol−1. The study of their reactivities provided a ranking of fast-, medium- and slow-kinetics fuels. The influence of alkaline and alkaline-earth metals (AAEM) on reactivity revealed that K, Na and Mg had a positive effect while Si, P and Ca had a negative influence.

With faster growth rates and higher photosynthetic efficiencies than other terrestrial plants, microalgae biomass could be considered as a green, low-cost, alternative carbon source. This paper explores the potential use of various species of microalgae as activated carbon precursors. Chlorella and Spirulina were evaluated both as freeze-dried microalgae and in fresh paste form, while Acutodesmus Obliquus and Coelastrella sp. were studied only as paste. Activated carbons were produced using the selected species of microalgae as well as mixtures of pine sawdust and microalgae. Two different preparation routes were compared: with and without hydrothermal carbonization pretreatment before physical activation with CO2 in a single step. All samples were conformed into pellets prior to CO2 activation. The CO2 adsorption capacity of the microalgae derived carbons was assessed in conditions representative of a flue gas (10.5 vol.% CO2 at atmospheric pressure and 50 °C). Significant differences in terms of CO2 adsorption capacity, carbon yield and pellet density were obtained among the species studied. These preliminary results showed that activated carbons produced from microalgae mixed with pine sawdust and directly activated with CO2 are among the most promising adsorbents to capture CO2 from flue gas.

The EU FP7-funded HiPerCap project aims to develop novel post-combustion CO2 capture technologies and processes which are environmentally benign and have high potential to lead to breakthroughs in energy consumption and overall cost. Three different separation technologies are being evaluated on a fair basis: absorption, membranes and adsorption. In this work, some of the results related to the development of adsorption-based fixed bed systems are presented. The design and optimization of a multibed adsorption-based separation process requires the use of powerful simulators that can describe the non-steady state process. However, prior to use a mathematical model for process design this should be validated against experimental data. A VTSA experiment has been carried out in order to provide information on the cyclic performance of a microporous biochar. The working capacity of the adsorbent is reduced due to incomplete regeneration during cyclic operation, although it stabilizes at 0.5 mol CO2 kg-1 and 0.4 mol H2O kg-1 once cyclic steady state is reached. A non-isothermal non-adiabatic dynamic model of the VTSA cycle was built in Aspen Adsorption, which makes use of the Ideal Adsorbed Solution theory to account for competitive adsorption between N2, CO2 and H2O. The model satisfactorily describes the history of the temperature of the adsorbent, the pressure, the total mass flow rate of the effluent, and the working capacity at cyclic steady state of the VTSA experiment. The validated model will be used as a starting point for process development.

This work is the result of the collaboration between INCAR-CSIC (Spain) and CSIRO Energy (Australia) in the framework of the European Commission FP7 project HiPerCap (High Performance Capture) that started in January 2014. The HiPerCap project aims to develop novel post-combustion CO2 capture technologies and processes which are environmentally benign and have high potential to lead to breakthroughs in energy consumption and overall cost, involving all main separation technologies for post-combustion CO2 capture. The present contribution focuses on adsorption with low temperature solid sorbents as a promising technology to capture CO2 from the flue gas. More precisely, CSIRO and CSIC have developed CO2 adsorbents from different carbon precursors including petroleum pitch, phenolic resin and agricultural by-products. The performance of new materials can be evaluated either experimentally or by means of numerical simulations, but each methodology has drawbacks. Thus, it is of utmost importance to seek a simple method for evaluating and comparing materials on the basis of readily available adsorption data. It is well known that the ideal adsorbent has a high selectivity, a high working capacity, and a low adsorption enthalpy; however, in practice, it is very rare to find a material which combines all of these attributes. Therefore, the selection of the adsorbent will often involve a trade-off among these factors, making comparisons of varied adsorbents even more difficult. In this work, the potential of the activated carbons developed by INCAR-CSIC and CSIRO for a post-combustion CO2 capture process has been evaluated and compared by means of an adsorption performance indicator.

The development of adsorption-based technologies for post-combustion CO2 capture requires finding an adsorbent with adequate equilibrium and transport properties. Structured adsorbents are appealing for fixed-bed TSA processes, because they present lower pressure drop and higher thermal conductivity than conventional adsorbent beds, which facilitates the use of higher flowrates and shorter cycle times, maximizing throughput. In this work, the equilibrium of adsorption of the main flue gas components, CO2, N2, O2 and H2O over two carbon honeycomb monoliths with different textural development has been measured in a pressure and temperature range of interest for post-combustion CO2 capture: between 0 °C and 70 °C and up to 120 kPa for CO2, N2, and O2, and between 30 °C and 70 °C up to the corresponding saturation pressure for H2O. The maximum adsorption capacity and isosteric heat of adsorption follows the order: H2O > CO2 > N2 ≈ O2. The carbon monoliths present equilibrium selectivity towards CO2 and H2O over N2 and O2 at typical flue gas conditions. Moderate activation is preferred to maximize the CO2 adsorption capacity and selectivity in these conditions. The Toth model was employed to fit the equilibrium data for the adsorption of CO2, N2, and O2 with highly satisfactory results. The adsorption isotherms of H2O presents the characteristic “s” shape of hydrophobic adsorbents, with low uptakes at low relative pressures, which will facilitate H2O desorption during cyclic operation. These were fitted using the extended CMMS model, which describes satisfactorily the experimental data in the full relative humidity range. The adsorption kinetics were preliminary evaluated by measuring the rate of mass uptake from a mixture with 10% CO2 (balance N2) at 30 °C, 50 °C and 70 °C, and the data were fitted to the linear driving force model to obtain the kinetic rate constants.

Biomass shows characteristics that makes it a promising feedstock for complementing traditional fossil fuels as main energy source. It is somewhat limited by its generally poor physical properties, but these can be enhanced by densification processes like torrefaction and pelletization. The aim of the present work is to evaluate the influence of different solid biomass additives (almond shell, cocoa shell, grape pomace, Miscanthus, olive pomace and olive stone), and parameters such as temperature, moisture content and glycerol addition upon pine sawdust, PIN, and its torrefied counterpart, PINT, pelletization performance, paying special attention to their abrasion index, higher heating value and energy density. It was observed that the addition of small quantities of lignin-rich solid additives, like grape pomace, enhances the natural binding properties of both PIN and PINT during pelletization using a bench-scale device. It was also found that a 13% overall moisture content and a glycerol addition of between 10 and 20% improve the pelletization properties of PIN and PINT, respectively, and increase their energy density when compared to the raw samples.

Activated carbons for adsorption of CO2 under flue gas conditions were prepared by means of hydrothermal carbonization (HTC) and subsequent CO2 activation of spent coffee grounds. The HTC of the samples consisted of their heating at moderate temperature with a high water content in autoclave. A preliminary screening concluded that 1:2 biomass/water ratio (spent coffee grounds as received) and no chemicals added during HTC with further activation in CO2 at 800°C for 1 h are suitable conditions to produce the CO2 adsorbents. In addition, the response surface methodology (RSM) successfully evaluated the combined effect of HTC temperature and dwell time, to maximize the CO2 capture capacity within the experimental region. Both the lowest temperature and dwell time (120°C, 3 h) resulted in the maximum CO2 capture capacity (2.95 wt.%). Two activated carbons (ACs) were then produced: one via hydrothermal carbonization optimized by means of response surface methodology (RSM) followed by CO2 activation (HC‐Co) and the other one by single‐step CO2 activation as described in the Group's patent ES2526259 (AC‐Co). Analysis of the features and performances of the two ACs revealed superior chemical and textural characteristics on HC‐Co for CO2 adsorption under post‐combustion capture conditions; HTC process is the sole responsible of this enhancement. Moreover, the proposed methodology to produce CO2 adsorbents from spent coffee grounds represents a more energy‐efficient approach

Con la publicación de este cuarto volumen nuestra plataforma completa la serie de monografías elaboradas por sus expertos sobre las tecnologías de captura, transporte, almacenamiento y usos del CO2 (tecnologías CAC). La captura, primera de las fases y sobre la que profundiza este libro, es la etapa que da sentido a las demás y, por tanto, la que condiciona toda su gestión posterior. Se trata, además, del área que más desarrollo ha experimentado durante estos últimos años, en los que sus tres líneas de trabajo fundamentales (pre-combustión, post-combustión y oxicombustión) han sido ampliamente estudiadas y desarrolladas. Ello hace posible que al día de hoy se encuentren preparadas para dar el salto a la escala comercial. Pero, como cabría esperar en un área con elevado potencial de innovación, se han iniciado ya los trabajos en tecnologías de segunda y tercera generación, tales como la de carbonatación-calcinación o el empleo de membranas, que están llamadas a rebajar aún más el coste asociado a la gestión de la tonelada de CO2 evitada. Existe un consenso internacional en que la demanda mundial energética, a pesar de las fluctuaciones económicas de los últimos años, seguirá aumentando y también en que una parte sustancial de la misma, ya sea en generación de electricidad o en su empleo por un abanico amplio de industrias, continuará siendo cubierta por energía fósil. Consecuentemente, el desarrollo y uso de las tecnologías CAC es irrenunciable. En resumen, este documento se presenta como lectura de referencia para quien desee conocer en profundidad unas tecnologías que hoy ya se muestran fundamentales. Por nuestra parte, continuamos trabajando para que su implantación en nuestro país ayude al cumplimiento de los compromisos de reducción de emisiones que España adopte en cada momento y para que asimismo se logre el beneficio del desarrollo económico e industrial de un sector del CO2 competitivo.

The effect of devolatilization conditions (pressure and temperature) on the steam gasification kinetics and reactivity of coal chars was investigated. For this purpose, five different rank coals were selected: a lignite (LT), two high-volatile bituminous coals (DT and SA), a low-volatile bituminous coal (DI), and a semianthracite (HV). The coal chars were obtained by devolatilization in a novel pressurized fixed-bed reactor at temperatures of 800, 900, and 1000 °C and pressures of 1, 5, 10, and 20 atm. The reactivity of the chars was studied by isothermal thermogravimetric analysis in a kinetically controlled regime at different temperatures under a steam atmosphere. The reactive behavior of the chars was evaluated by means of the random pore model (RPM), which satisfactorily described the steam gasification of the coal chars. The gasification apparent reaction rate increased as the devolatilization pressure increased, whereas this parameter decreased as the devolatilization temperature increased.

The effect of operating conditions (pressure and temperature) on char morphology and structure during coal devolatilization was studied. For this purpose, five different rank coals were selected: a lignite, three bituminous coals, and a semi-anthracite. The coal chars were prepared by devolatilization in a novel pressurized fixed-bed reactor. The pyrolysis experiments were carried out isothermally at temperatures of 800, 900, and 1000 °C and pressures of 1, 5, 10, and 20 atm. The chars obtained from the bituminous coals at elevated pressure experienced a high degree of swelling, whereas those from the lignite and semi-anthracite were hardly affected at all by pressure. The devolatilization temperature did not appear to have any significant effect on char morphology below 1000 °C. The reactivity of the char samples prepared under different pyrolysis conditions was studied by isothermal thermogravimetric analysis at 1000 °C under a steam atmosphere. The chars obtained at elevated pressure were found to be more reactive than those produced at atmospheric pressure. An increase in the pyrolysis temperature led to a decrease in char reactivity.