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Abstract: Two series of carbon dioxide adsorbents were prepared from almond shells, by carbonisation followed either by activation with CO2 or by heat treatment in the presence of ammonia gas (amination). Both procedures gave carbons with high CO2 adsorption capacities in pure CO2 as well as in a binary mixture of 15% CO2 in N2. Activation with carbon dioxide significantly developed porosity in the samples, mostly in the micropore domain, while amination at 800°C moderately developed narrow microporosity in the char and incorporated stable nitrogen functionalities, which enhanced CO2 selectivity. Amination showed two additional advantages over conventional activation with CO2: a greater carbon yield and a shorter soaking time. [Copyright &y& Elsevier]

Abstract: In this work a series of carbon adsorbents were prepared from a low-cost biomass residue, olive stones. Two different approaches were studied: activation with CO2 and heat treatment with gaseous ammonia. The results showed that both methods are suitable for the production of adsorbents with a high CO2 adsorption capacity, and their potential application in VSA or TSA systems for postcombustion CO2 capture. It was found that the presence of nitrogen functionalities enhances CO2 adsorption capacity, especially at low partial pressures. [Copyright &y& Elsevier]

Different carbon materials were tested as precursors for the production of CO2 adsorbents. The chemical modification of the surface of the prepared adsorbents was studied by means of three different approaches: impregnation with amines, electrophilic aromatic substitution, and heat treatment in the presence of ammonia. The samples were chemically characterized and the porous texture was evaluated from the N2 adsorption isotherms at -196°C. The CO2 adsorption capacities of the adsorbents at 25 and 100°C were evaluated in a thermogravimetric analyzer. In general, the incorporation of basic nitrogen functionalities enhanced the CO2 capture capacities of the modified carbons, but this increase depended on the textural properties of the support and the surface modification methodology. CO2 adsorption capacities of up to 111 mgCO2/g at room temperature were attained. All the tested samples were completely regenerated when subjected to heat treatment at 100°C under inert atmosphere. [ABSTRACT FROM AUTHOR]

Abstract: The reduction of anthropogenic CO2 emissions to address the consequences of climate change is a matter of concern for all developed countries. In the short term, one of the most viable options for reducing carbon emissions is to capture and store CO2 at large stationary sources. Adsorption with solid sorbents is one of the most promising options. In this work, two series of materials were prepared from two commercial activated carbons, C and R, by heat treatment with gaseous ammonia at temperatures in the 200–800°C range. The aim was to improve the selectivity and capacity of the sorbents to capture CO2, by introducing basic nitrogen-functionalities into the carbons. The sorbents were characterised in terms of texture and chemical composition. Their surface chemistry was studied through temperature-programmed desorption tests and X-ray photoelectron spectroscopy. The capture performance of the carbons was evaluated by using a thermogravimetric analyser to record mass uptakes by the samples when exposed to a CO2 atmosphere. [Copyright &y& Elsevier]

Abstract: Oxy-fuel combustion is a GHG abatement technology in which coal is burned using a mixture of oxygen and recycled flue gas, to obtain a rich stream of CO2 ready for sequestration. An entrained flow reactor was used in this work to study the ignition and burnout of coals and blends with biomass under oxy-fuel conditions. Mixtures of CO2/O2 of different concentrations were used and compared with air as reference. A worsening of the ignition temperature was detected in CO2/O2 mixtures when the oxygen concentration was the same as that of the air. However, at an oxygen concentration of 30% or higher, an improvement in ignition was observed. The blending of biomass clearly improves the ignition properties of coal in air. The burnout of coals and blends with a mixture of 79%CO2–21%O2 is lower than in air, but an improvement is achieved when the oxygen concentration is 30 or 35%. The results of this work indicate that coal burnout can be improved by blending biomass in CO2/O2 mixtures. [Copyright &y& Elsevier]

Abstract: Adsorption on porous solids is an emerging alternative for CO2 capture that seeks to reduce the costs associated to the capture step. The enhancement of a specific adsorption capacity may be carried out by increasing the affinity of the adsorbent surface to CO2. Nitrogen enrichment is reported to be effective in introducing basic functionalties that enhances the specific adsorbent–adsorbate interaction for CO2. In this work a templating technique was used to produce highly porous nitrogen enriched carbons from melamine–formaldehyde resins. Nitrogen incorporated into the polymer matrix results in the greater stability of the adsorbents in terms of volatile and thermal loss of nitrogen. CO2 capture performances were evaluated between 25°C and 75°C in a thermobalance. CO2 adsorption capacities up to 2.25mmolg−1 of CO2 at 25°C were achieved. Both texture and surface chemistry influence the CO2 capture performance of the adsorbents. The carbonisation temperature used during the synthesis step controls the nitrogen functional groups present, as determined by XPS, with the loss of triazine nitrogen with increasing carbonisation temperature proposed to account for the decreased CO2 affinity. [Copyright &y& Elsevier]

Abstract: Debris samples from braking tests carried out with carbon/carbon discs, mounted in a reduced-scale bench, have been studied by X-ray diffraction, thermogravimetry coupled with mass spectrometry, and N2 physisorption at −196°C. The tests were carried out at low temperature with a high friction coefficient. Two materials with different structural orders (d 002 =338 and 344nm, respectively) were studied. Debris samples from both materials are similar: they are essentially amorphous and contain up to 10% of oxygen. The specific surface areas are about 180m2/g. However, a careful examination of the experimental results clearly shows some differences depending on the starting materials. Debris from the less ordered material contains fewer carboxylic groups, the specific surface areas of debris obtained from the more ordered material are systematically larger, and debris samples from both materials may be differentiated by the XRD pattern of the small fraction of starting material they contain. Thus, materials with different structural orders yielded similar debris resulting from the severe mechanico-chemical processes involved but retained a slight but clear memory of the material from which they came. [Copyright &y& Elsevier]

In this work a series of solid sorbents were synthesized by immobilizing liquid amines on the surface of a mesoporous alumina. The samples were chemically characterized and BET surface areas calculated from the N2 adsorption isotherms at 77 K. The CO2 capture performance of the sorbents and their thermal stability was studied by thermogravimetric methods. The effect of amine loading on the CO2 capture performance of the prepared sorbents was also evaluated. Analysis of TG-DTG curves showed that thermal stabilization of the amines is significantly improved by immobilizing them on an inorganic support. Temperature-programmed CO2 adsorption tests from 298 K up to 373 K at atmospheric pressure, proved to be a useful technique for assessing the capacity of sorbents for CO2 capture. Alumina impregnated with diethylenetriamine presented the highest CO2 adsorption capacities throughout the tested temperature range. [ABSTRACT FROM AUTHOR]

Abstract: The use of biomass to produce energy is becoming more and more frequent as it helps to achieve a sustainable environmental scenario. However the exploitation of this fuel source does have drawbacks that need to be solved. In this work, the torrefaction of woody biomass (eucalyptus) was studied in order to improve its properties for pulverised systems. The process consisted in a heating treatment at moderate temperature (240, 260, 280 °C) under an inert atmosphere. The grindability of raw biomass and the treated samples was compared and an improvement in the grindability characteristics was observed after the torrefaction process. Thermogravimetric analysis of the samples was carried out in order to study their reactivity in air. The DTG curves of the torrefied biomass showed a double peak nature. The kinetic parameters were calculated for each reaction stage. The torrefaction process was found to influence the parameters of the first stage, whereas those corresponding to the second remained unaffected. [Copyright &y& Elsevier]

Char particle combustion is the slowest step in the combustion of coal, therefore char reactivity and texture have an important influence on this process. In this work, two coals were devolatilised in an entrained flow reactor and the chars obtained were burned under different experimental conditions in order to achieve various degrees of burnoff. Char reactivity was determined by means of non-isothermal thermogravimetric analysis, and the conversion-time data were evaluated by the random pore model proposed by Bhatia and Perlmutter. Char texture was characterised by means of N2 and CO2 adsorption isotherms. The surface areas obtained were used to calculate intrinsic reaction rate parameters. It was found that under chemical controlled conditions, the available surface area during combustion is best represented by the N2 surface area. [ABSTRACT FROM AUTHOR]

Abstract: The success of CO2 capture with solid sorbents is dependent on the development of a low cost sorbent with high CO2 selectivity and adsorption capacity. Immobilised amines are expected to offer the benefits of liquid amines in the typical absorption process, with the added advantages that solids are easy to handle and that they do not give rise to corrosion problems. In this work, different alkylamines were evaluated as a potential source of basic sites for CO2 capture, and a commercial activated carbon was used as a preliminary support in order to study the effect of the impregnation. The amine coating increased the basicity and nitrogen content of the carbon. However, it drastically reduced the microporous volume of the activated carbon, which is chiefly responsible for CO2 physisorption, thus decreasing the capacity of raw carbon at room temperature. [Copyright &y& Elsevier]

Abstract: In the present work, the mechanisms involved in NO–char heterogeneous reduction have been studied using a synthetic coal char (SC char) as carbon source. Another synthetic char (SN char) without nitrogen in its composition has also been employed in these studies. Isothermal reduction tests at different temperatures have been carried out. Two temperature regimes were considered: low temperature (T <250°C) where NO chemisorption takes place and high temperature (T >250°C) where NO–C reaction occurs. Step response experiments combining consecutive reaction stages with NO and 15NO were performed in order to determine the role of nitrogen surface complexes, C(N), in the reduction process. The results revealed N2 and CO2 to be the main reduction products under the experimental conditions employed in this work. NO chemisorption at lower temperatures results in N2 emission and surface complexes (mainly oxygenated) formation, while char gasification by NO involves a direct NO attack on the char surface to form surface complexes. As a consequence of desorption of these complexes new sites of reaction are created. [Copyright &y& Elsevier]

Abstract: Model compounds, with a controlled heteroatoms content and well-defined functionalities, were used to study the release of nitrogen compounds from char combustion. In the present work, the mechanisms involved in NO-char heterogeneous reduction were studied with a synthetic coal (SC) char as carbon source. Another synthetic char (SN) without any nitrogen in its composition was also employed in these studies. Temperature programmed reduction (TPR) tests with a gas mixture of 400ppm NO in argon and with isotopically labelled nitric oxide, 15NO (500ppm 15NO in argon), were carried out. The gases produced were quantitatively determined by means of MS and FTIR analysers. Under the conditions of this work the main products of the NO-C reaction were found to be N2 and CO2. The main path of reaction involves the formation of surface nitrogen compounds that afterwards react with nitrogen from the reactive gas to form N2. It was observed that fuel-N also participates in the overall heterogeneous reduction reaction, although to a lesser extent. [Copyright &y& Elsevier]

Knowledge of surface properties is essential for understanding the reaction mechanisms involved in several coal conversion processes. However, due to the complexity and heterogeneity of coal this is rather difficult and the use of known model compounds could be a valuable tool. Single model compounds have been widely used, but they give a quite simplified picture. In this work a mixture of model compounds in a phenol-formaldehyde matrix was cured in order to create cross-linked structures. The obtained synthetic coal was pyrolysed in a fixed bed reactor, under helium atmosphere. The surface composition of the chars was evaluated by XPS, adsorption gravimetry of water vapour, temperature-programmed desorption and potentiometric titration. Texture was characterised by N2 and CO2 adsorption isotherms at 77 and 273 K, respectively, and immersion calorimetry in benzene. The results obtained from the different techniques were contrasted in order to give an overview of the surface properties (chemical and physical) of the samples studied. Chars obtained under the same operating conditions from a high volatile bituminous coal were used as a reference. [Copyright &y& Elsevier]

Coal pyrolysis is the initial, accompanying reaction of a number of coal conversion processes such as hydrogenation, combustion and gasification. However, because of the inherent complexity of coal composition, it is difficult to describe coal pyrolysis clearly. Single model compounds have been used before in order to provide additional insight into the complex processes that occur in the pyrolysis of coal. Yet the picture obtained is a simplified one and certain important aspects such as coal structure, interactions between different surface groups and cross-links are omitted. The approach used in this work involves the preparation of a synthetic coal, SC, with a known structure by curing a mixture of single, well-defined model compounds. By means of chemical characterisation, the SC was shown to contain the macroscopic features of a high volatile coal (proximate and ultimate analyses). FTIR characterisation revealed the presence of functional groups similar to those of coal in the structure of the SC. Temperature-programmed pyrolysis tests were performed in a thermobalance linked to a mass spectrometer and a Fourier transform infrared analyser (TG/MS/FTIR). The thermal behaviour of the synthetic coal (i.e., rate of mass loss and the evolution profiles of gaseous compounds during pyrolysis tests) is very similar to that of the high volatile bituminous coal which was used as a reference material. The great advantage of using SC lies in the fact that its composition and structure can be accurately determined and employed in subsequent applications in basic and mechanistic studies. [Copyright &y& Elsevier]

A mixture of carbon compounds was pyrolysed under an inert atmosphere at different temperatures in a fixed bed reactor. The resultant chars were characterised in terms of texture and thermal behaviour. Textural characterisation of the chars was carried out by N2 and CO2 adsorption isotherms at −196 and 0 °C, respectively. Char isothermal reactivity in air at 500 °C, and in CO2 at 1000 °C, was performed in a thermogravimetric analyser (TGA). Temperature-programmed combustion tests under 20% oxygen in argon were also performed in the TGA linked to a mass spectrometer (TGA/MS). The results showed that char textural properties do not always relate well to their reactivity. Not only do physical properties (e.g. surface area, porosity) but also chemical properties (e.g. active sites concentration and distribution) play an important role in the reaction of carbonaceous material and oxidant. On the other hand, in terms of chemical composition the chars obtained from the mixture of carbon compounds were very similar to the chars produced under the same experimental conditions by a high volatile bituminous coal. The fact that carbon compounds are well known makes it easier to obtain knowledge about the functional groups present in synthetic char, and to study the mechanisms of heterogeneous reactions such as the reduction of NO with carbon. [Copyright &y& Elsevier]

Hydrogen production by sorption enhanced steam reforming (SESR) of bio-oil model compounds was thermodynamically and experimentally studied by mixing acetic acid (AcH) and acetone (AcCO), in a fluidized bed reactor. In the SESR process the catalytic reforming reaction and CO 2 removal by sorption were carried out simultaneously in a single reactor. The SESR of the model compounds and their blends was performed under atmospheric pressure over a Pd/Ni–Co hydrotalcite-like material (HT) catalyst using dolomite as CO 2 sorbent. The effects of the reaction temperature (475–725 °C), steam/C molar ratio and weight hourly space velocity (WHSV) were studied. For the SESR of acetic acid, acetone and their blends it was observed that the H 2 yield and H 2 concentration increase as the temperature increases, reaching a maximum value, and then they decrease with the temperature. It was also found that the CH 4 concentration decreases as the temperature increases, while the CO and CO 2 concentrations increase with the rise in temperature. High steam/C molar ratio values and low WHSV values favor the H 2 yield and H 2 concentration, while they lead to a decrease in the CH 4 concentration. Hydrogen purities as high as 99.2–99.4% with small amounts of methane, CO and CO 2 were obtained for the SESR of the model compounds of bio-oil and their blends at a temperature of 575 °C at atmospheric pressure. The effect of temperature on the SESR of the blends of model compounds of bio-oil is similar to that of the individual model compounds studied, except in the fact that lower H 2 yield values are obtained by the SESR of the blends (83.3–88.6%) compared to the individual model compounds (90.2–95.9%), a decrease which becomes more noticeable as the proportion of acetone in the blend is increased. [ABSTRACT FROM AUTHOR]

Biomass samples (pine, black poplar and chestnut woodchips) were torrefied to improve their grindability before being combusted in blends with coal. Torrefaction temperatures between 240 and 300 °C and residence times between 11 and 43 min were studied. The grindability of the torrefied biomass, evaluated from the particle size distribution of the ground sample, significantly improved compared to raw biomass. Higher temperatures increased the proportion of smaller-sized particles after grinding. Torrefied chestnut woodchips (280 °C, 22 min) showed the best grinding properties. This sample was blended with coal (5–55 wt.% biomass). The addition of torrefied biomass to coal up to 15 wt.% did not significantly increase the proportion of large-sized particles after grinding. No relevant differences in the burnout value were detected between the coal and coal/torrefied biomass blends due to the high reactivity of the coal. NO and SO 2 emissions decreased as the percentage of torrefied biomass in the blend with coal increased. [ABSTRACT FROM AUTHOR]

An environmentally friendly and low cost adsorbent, PPC (patent application filed González (2013)), produced from an abundant residue from the food industry, coffee grounds, is presented and evaluated as CO 2 adsorbent in postcombustion conditions. PPC is a high bulk density pelletized carbon with adequate properties for its use in fixed-bed adsorption applications. The equilibrium capacity for CO 2 at low partial pressures, relevant for the postcombustion case, in the 25–50 °C temperature range is superior to that of reference carbons, both in mass and volume basis. PPC presents equilibrium selectivity for CO 2 over N 2 , with CO 2 /N 2 equilibrium separation factor values of 15–25 at 50 °C and 130 kPa for CO 2 concentrations between 9% and 31%. Moreover, it presents fast adsorption kinetics, which makes it a good candidate for rapid swing adsorption cycles. Different VSA cycle configurations were carried out at 50 °C in the fixed-bed adsorption unit to evaluate the performance of the adsorbent in cyclic operation. The adsorbent did not show any sign of deactivation over extended operation. [ABSTRACT FROM AUTHOR]

• Sustainable CO 2 bio-adsorbents were produced from PCL and PKS by single–step CO 2 activation. • BioACs presented significant uptake (∼2 mmol g−1 at 50 ⁰C) and fast CO 2 adsorption in binary CO 2 /H 2 O streams. • Under 4 vol% H 2 O, the adsorption of CO 2 is only impacted at CO 2 concentrations below 15–20 vol% • A joint Avrami's model suitably described PCL1H overall adsorption kinetics in the humid flue gas. • PCL1H showed steady cyclic adsorption–desorption performance in a fixed-bed lab-scale rig. 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 CO 2 selectively at industrial post-combustion capture conditions. The goal was to maximize the development of narrow microporosity in the final carbons to boost the CO 2 adsorption capacity. We have designed kinetics and equilibrium of adsorption experiments with CO 2 /H 2 O/N 2 on a selected AC derived from PCL in a thermogravimetric analyzer (TGA) at 50 °C and three partial pressures of CO 2 to prove the suitability to capture CO 2 from industrial off-gases. When humid flue gas streams were tested, competitive adsorption of CO 2 and H 2 O occurred; however, the difference in the uptake rates favored CO 2 adsorption in the early stages. The joint CO 2 + H 2 O uptake was around 2 mmol g−1 at 50 °C in humid conditions, where CO 2 reached the equilibrium uptake at the corresponding partial pressure for 15 and 32 vol% CO 2 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 CO 2 capture capacity under dry conditions (up to 1.08 mmol g−1 at 50 ˚C for 30 vol% CO 2). Kinetics analysis also supported the faster adsorption of CO 2 under cement flue gas conditions. [ABSTRACT FROM AUTHOR]

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. • Valorization of a solid waste, eucalyptus biochar (PEc), is proposed. • Pine sawdust (PIN) pellets with PEc and glycerol as additives are formulated. • PEc addition below 10 wt% enhances PIN pellets' heating value and energy density. • PEc addition below 10 wt% enhances PIN pellets' grindability and water-resistance. • PEc-PIN pellets are economically competitive when compared to PIN. [ABSTRACT FROM AUTHOR]

Abstract: The effect of oxidation upon the CO2 capture performance has been studied taking a phenolic resin carbon as the base material. Oxygen surface groups were introduced through liquid and gas phase oxidation treatments, using ammonium persulfate, nitric acid and air, respectively. The surface chemistry of the final carbon is strongly affected by the type of oxidation treatment: liquid phase oxidation introduces a greater amount of oxygen, mostly as carboxylic groups; these are absent in the gas phase oxidised sample that contains mainly ether and carbonyl functionalities. The porous texture of the samples is also affected by the oxidation treatment: through liquid phase oxidation the pore volume is somewhat reduced, while this is slightly developed by air treatment at 693K. Despite the reduction in the porous volume and the acidic surface, liquid-phase oxidised samples present greater CO2 adsorption capacity than the starting carbon due to Lewis acid–base interactions with the CO2 molecule. Moreover: oxidised samples are easily regenerated, and observed heats of adsorption are typical from physisorption processes, which will facilitate the adsorbent regeneration in cyclic adsorption processes. Oxidation is therefore proposed as a plausible modification technique for developing easy-to-regenerate carbon adsorbents with enhanced CO2 capture performance. [Copyright &y& Elsevier]

Abstract: In this work spent coffee grounds from single-use capsules were used as the starting material for producing low-cost activated carbons. The activation conditions were selected and optimised to produce microporous carbons with high CO2 adsorption capacity and selectivity, thus with potential to be used as adsorbents in postcombustion CO2 capture applications. Two activation methods are compared: physical activation with CO2 and chemical activation with KOH. The first method is considered less contaminant; however, leads to carbons with lower textural development and thus lower CO2 adsorption capacity than those obtained by activation with KOH. On the other hand, multicomponent adsorption cyclic experiments pointed out that the CO2/N2 selectivity of physically activated carbons is higher than that of chemically activated carbons. [Copyright &y& Elsevier]

Adsorption is one of the most promising technologies for reducing CO2 emissions and at present several different types of sorbents are being investigated. The use of sorbents obtained from low-cost and abundant precursors (i.e. solid wastes) appears an attractive strategy to adopt because it will contribute to a reduction not only in operational costs but also in the amount of waste that is dumped and burned in landfills every year. Following on from previous studies by the authors, in this work several carbon-based adsorbents were developed from different carpet wastes (pre-consumer and post-consumer wastes) by chemical activation with KOH at various activation temperatures (600–900 °C) and KOH:char impregnation ratios (0.5:1 to 4:1). The prepared materials were characterised by chemical analysis and gas adsorption (N2, −196 °C; CO2, 0 °C), and tested for CO2 adsorption at temperatures of 25 and 100 °C. It was found that both the type of precursor and the conditions of activation (i.e. impregnation ratios, and activation temperatures), had a huge influence on the microporosity of the resultant samples and their CO2 capture capacities. The carbon-based adsorbent that presented the maximum CO2 capture capacities at 25 and 100 °C (13.8 wt.% and 3.1 wt.%, respectively), was prepared from a pre-consumer carpet waste and was activated at 700 °C using a KOH:char impregnation ratio of 1:1. This sample showed the highest narrow microporosity volume (0.47 cm3 g−1), thus confirming that only pores of less than 1 nm are effective for CO2 adsorption at atmospheric pressure. [Copyright &y& Elsevier]

Abstract: Char reactivity has a strong influence on the gasification process, since char gasification is the slowest step in the process. A sample of waste PET was devolatilised in a vertical quartz reactor and the resulting char was partially gasified under a CO2 atmosphere at 925°C in order to obtain samples with different degrees of conversion. The reactivity of the char in CO2 was determined by isothermal thermogravimetric analysis at different temperatures in a kinetically controlled regime and its reactive behaviour was evaluated by means of the random pore model (RPM). The texture of the char was characterised by means of N2 and CO2 adsorption isotherms. The results did not reveal any variation in char reactivity during conversion, whereas the micropore surface area was affected during the gasification process. It was found that the intrinsic reaction rate of the char can be satisfactorily calculated by normalizing the reaction rate by the narrow micropore surface area calculated from the CO2 adsorption isotherms. It can be concluded therefore that the surface area available for the gasification process is the area corresponding to the narrow microporosity. [ABSTRACT FROM AUTHOR]

Abstract: The thermal characteristics and kinetics of coal, biomass (pine sawdust) and their blends were evaluated under combustion conditions using a non-isothermal thermogravimetric method (TGA). Biomass was blended with coal in the range of 5–80wt.% to evaluate their co-combustion behaviour. No significant interactions were detected between the coal and biomass, since no deviations from their expected behaviour were observed in these experiments. Biomass combustion takes place in two steps: between 200 and 360°C the volatiles are released and burned, and at 360–490°C char combustion takes place. In contrast, coal is characterized by only one combustion stage at 315–615°C. The coal/biomass blends presented three combustion steps, corresponding to the sum of the biomass and coal individual stages. Several solid-state mechanisms were tested by the Coats–Redfern method in order to find out the mechanisms responsible for the oxidation of the samples. The kinetic parameters were determined assuming single separate reactions for each stage of thermal conversion. The combustion process of coal consists of one reaction, whereas, in the case of the biomass and coal/biomass blends, this process consists of two or three independent reactions, respectively. The results showed that the chemical first order reaction is the most effective mechanism for the first step of biomass oxidation and for coal combustion. However, diffusion mechanisms were found to be responsible for the second step of biomass combustion. [Copyright &y& Elsevier]

Abstract: The current situation in the energy sector suggests the possibility of using biomass in co-combustion systems as an alternative to other fuels. In the case of the North of Spain the amount of forest residues that is generated guarantees it as a valuable source of energy for the future. However, an effective exploitation of these residues must first overcome a number of serious problems such as transport, storage, handling and pre-treatment, to meet the requirements of the power plants. The aim of this work is to study the influence of storage time on the moisture content and chemical and combustibility properties of pine woodchips. Their combustibility behaviour was evaluated by means of the following tests: heating value, ash composition, slagging/fouling indices, and the combustion profiles obtained from TG analysis. As a result of the weather conditions in the North of Spain open-air storage in the area under study is not suitable for dry pine woodchips, although their combustion behaviour remains practically unaltered. [Copyright &y& Elsevier]

Abstract: The non-isothermal thermogravimetric method (TGA) was applied to a bituminous coal (PT), two types of biomass, chestnut residues (CH) and olive stones (OS), and coal–biomass blends in order to investigate their thermal reactivity under steam. Fuel chars were obtained by pyrolysis in a fixed-bed reactor at a final temperature of 1373K for 30min. The gasification tests were carried out by thermogravimetric analysis from room temperature to 1373K at heating rates of 5, 10 and 15Kmin−1. After blending, no significant interactions were detected between PT and CH during co-gasification, whereas deviations from the additive behaviour were observed in the PT–OS blend. However, for the two coal–biomass blends, the gasification behaviour resembled that of the individual coal, as this component constituted the larger proportion of the blend. The temperature-programmed reaction (TPR) technique was employed at three different heating rates to analyze noncatalytic gas–solid reactions. Three nth-order representative gas–solid models, the volumetric model (VM), the grain model (GM) and the random pore model (RPM) were applied in order to describe the reactive behaviour of the chars during steam gasification. From these models, the kinetic parameters were determined. The best model for describing the reactivity of the PT, PT–CH and PT–OS samples was the RPM model. VM was the model that best fitted the CH sample, whereas none of the models were suitable for the OS sample. [Copyright &y& Elsevier]

The reactivity in steam of five different types of solid fuels (two coals, two types of biomass and a petcoke) has been studied. The fuel chars were obtained by pyrolysis in a fixed-bed reactor at a temperature of 1373 K for 30 min. The gasification tests were carried out by thermogravimetric analysis (TG) at different temperatures and steam concentrations. The reactivity study was conducted in the kinetically controlled regime and three representative gas-solid models, volumetric model (VM), grain model (GM) and random pore model (RPM), were applied in order to describe the reactive behaviour of the chars during steam gasification. The kinetic parameters of these models were derived and the ability of the models to predict conversion and char reactivity during gasification was assessed. The best model for describing the behaviour of the samples was the RPM. The effect of the partial pressure of steam in gasification was studied, and the reaction order with respect to steam was determined. The reactivity of the chars was compared by means of a reactivity index. Biomass exhibited a higher reactivity than coals and petcoke. However, significant differences in reactivity were observed between the two types of biomass used, which could be due to catalytic effects. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this work was to investigate the role of porous and chemical heterogeneities of activated carbons in the adsorption of naphthalene from aqueous media. A commercially available activated carbon was used as the adsorbent, and its surface heterogeneity was systematically altered by heat treatment at 450 and 850°C, obtaining a series of carbons with various oxygen contents and similar surface functionalities. The results confirmed that the adsorption of naphthalene depends strongly on the pore size distribution of the adsorbent, particularly narrow microporosity. Moreover, oxygen functionalities reduced the accessibility and affinity of naphthalene to the inner pore structure via formation of hydration clusters. Consequently, the hydrophobic/hydrophilic character of the adsorbent is important, since it dominates the competitive adsorption of water. Adsorbents with a high non-polar character (i.e., low oxygen content) have proven to be more efficient for naphthalene adsorption. [Copyright &y& Elsevier]

The aim of this work was to correlate the textural and chemical features of carbonaceous adsorbents with the adsorption capacity of naphthalene from aqueous phase, at the concentration in which this compound is usually found in wastewater from coke ovens. The study reveals that the adsorption capacity in different carbon materials depends not only on the textural characteristics of the material but also on the functionalities of the activated carbons. The micropores of the adsorbents, particularly those of narrower diameter, were found to be active sites for the retention of naphthalene. In contrast, the modification of the surface chemistry of the carbon materials led to a decrease in the adsorption capacities. Dispersive forces play an important role, and adsorbents with a higher non-polar character have proven to be more efficient for the naphthalene adsorption. This behaviour has been linked to the presence of specific interactions between the basal planes and the polyaromatic structure of the naphthalene molecule. [Copyright &y& Elsevier]

Abstract: The regeneration of activated carbons used for the decontamination of water and wastewater polluted with organic compounds related to the pharmaceutical industry, has been studied in this work. To this end, the pyrolysis of exhausted activated carbons was performed in a quartz reactor. The influence of the pyrolysis of saturated activated carbons on their adsorptive capacities and porous structure was evaluated. Textural characterisation of the samples was carried out by helium density, and N2 and CO2 adsorption isotherms, at −196 and 0°C, respectively. Consecutive cycles of pyrolysis of activated carbons exhausted with phenol and salicylic acid, generated a widening of the microporosity, and a decrease in the apparent BET surface areas. The adsorptive capacities for phenol retention after a series of adsorption/pyrolysis cycles were found to decrease drastically. In contrast, consecutive cycles gave higher salicylic acid adsorptive capacities, as compared to phenol. The DTG pyrolysis profiles of the samples saturated with salicylic acid appeared at lower temperatures than those of phenol, which showed two peaks, while those exhausted with salicylic acid only showed one. These results provide evidence of the different adsorption mechanisms of these two pollutants. [Copyright &y& Elsevier]

Knowledge of the amount and distribution of active sites in carbons is of paramount importance for a better understanding of the kinetics involved in heterogeneous gas solid reactions. In this work a commercial active carbon, CM, was treated at several temperatures in order to obtain a series of samples with different textural and structural properties. The results showed that the loss of reactivity of the samples, determined by thermogravimetric analysis, is related not only to the lower surface area but also to the decrease in the amount of active sites due to a higher structural ordering. [ABSTRACT FROM AUTHOR]

The aim of this work was to determine the influence that an advanced demineralisation procedure has on the combustion characteristics of coal. A high-volatile bituminous coal with 6.2% ash content was treated in a mixture of hydrofluoric and fluorosilicic acids (HF/H2SiF6). Nitric acid was used either as a pretreatment, or as a washing stage after HF/H2SiF6 demineralisation, with an ash content as low as 0.3% being attained in the latter case. The structural changes produced by the chemical treatment were evaluated by comparison of the FTIR spectra of the raw and treated coal samples. The devolatilisation and combustibility behaviour of the samples was studied by using a thermobalance coupled to a mass spectrometer (TGA-MS) for evolved gas analysis. The combustibility characteristics of the cleaned samples were clearly improved, there being a decrease in SO2 emissions. [Copyright &y& Elsevier]

Emissions of nitrogen oxides during coal combustion are a major environmental problem. The chemically bound nitrogen in fuel accounts for up to 80% of total NOx emissions. In this respect, fundamental studies are needed to clarify the mechanisms and to identify the different species that are precursors in the formation of the NOx. Mass spectrometry (MS) has been used for decades as a successful technique in evolved gas analysis. However, MS is normally used to identify typical volatile compounds formed during coal pyrolysis (i.e. H2, CH4, CO, CO2 and H2O) but very few works on the detection by MS of nitrogen compounds during coal devolatilisation can be found. In this work, the possibility of detecting different nitrogen compounds by means of thermogravimetric–MS during the temperature-programmed pyrolysis of coal was evaluated. Interferences in the N-compounds MS signals were determined. The use of model compounds provided additional information on the MS response factors of the volatile compounds produced. [Copyright &y& Elsevier]

[Display omitted] • H 2 S poisoning of a Pd/Ni-Co HT catalyst is studied in cyclic biogas SESR experiments. • H 2 S removal by a dolomite sorbent depends on the H 2 S concentration in the biogas. • No catalyst deactivation after five SESR cycles for H 2 S concentrations below 350 ppm. • After three SESR cycles, the catalyst activity decayed slightly for 500–1000 ppm H 2 S. • H 2 purity decreased 2–3% after five SESR cycles for high H 2 S contents in the biogas. 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 CO 2 removal by sorption in a single reactor. One of the most critical challenges in using biogas in conventional reforming processes is the presence of H 2 S since it may deactivate the reforming catalyst. Here we experimentally study the effect of the biogas H 2 S concentration on the H 2 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 CO 2 sorbent. Biogas (60CH 4 /40CO 2 vol.%) with different concentrations of H 2 S (150, 350, 500 and 1000 ppm) was evaluated. The catalyst did not deactivate for biogas H 2 S 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 H 2 S concentration tested (1000 ppm). H 2 yield decreased by 10.8% and 4.5% points for biogas H 2 S concentrations of 500 and 1000 ppm after five cycles, respectively, while H 2 purity decreased by only 3 vol.% and 2 vol.% points, respectively. [ABSTRACT FROM AUTHOR]

Biogas is a valuable source of renewable energy produced from biodegradable organic materials via anaerobic digestion. The production of H 2 by sorption enhanced steam reforming (SESR) of biogas has been studied thermodynamic and experimentally. A Pd/Ni–Co catalyst and dolomite as CO 2 sorbent were used. The effect of biogas composition (CH 4 /CO 2 vol.%) on the process was evaluated at 600 and 650 °C in a fluidized bed reactor using biogas CO 2 concentrations of 5–50 vol.%. During conventional biogas steam reforming (SR), high CH 4 partial pressures in the feed favor the process, producing high H 2 concentrations. During biogas SESR, CO 2 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 CO 2) methane reforming did not occur under the conditions studied due to the relatively low temperature and the presence of steam. High H 2 purity (98.4 vol.%) and H 2 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. • CO 2 in biogas is effectively removed from the gas phase by the sorbent in SESR. • CO 2 content in biogas did not affect the SESR process performance. • No dry methane reforming occurred in the presence of steam at low temperatures. • H 2 purity of 98.4 vol% is obtained from the SESR of biogas with 50–95 vol% of CH 4. [ABSTRACT FROM AUTHOR]

Biomass commonly presents poor physical properties and low energy density that need to be enhanced. Torrefaction and densification are two of the most suitable techniques to this aim. In this work the pelletization of torrefied pine, blended with solid (raw pine and grape pomace) and liquid (glycerol) additives at low temperature (i.e., 40–80 °C) was carried out in a continuous bench-scale flat die pellet mill that simulates the features of a production-scale system. Among all the tested blends, four formulations fulfilled the requirements of the EN-Plus and ISO 17225-2 Industrial Pellets quality standards, which make them suitable fuels for both residential heating systems and power plant boilers. The produced pellets hold higher heating values between 18.8 and 21.7 MJ/kg, energy densities in the range 12.18–15.33 GJ/m3 and optimum physical properties (L = 20–25 mm, Ø = 6.1–6.2 mm, ρ p = 1.1–1.2 g/cm3), in line with the reference pine pellets. A preliminary economic analysis was pursued proving that the improvements observed in formulations of torrefied pine, with 20 wt.% glycerol and with 10 wt.% grape pomace and 10 wt.% glycerol, may provide savings up to 20% in construction and transport costs. • Torrefied pine pelletization conducted in a continuous bench-scale flat die pellet mill. • Blends of torrefied pine, pine, grape pomace and glycerol were tested. • Best pellets selection based on durability, physical properties and ENPlus standards. • Torrefied pellets highest energy density value was 23% higher than raw pine pellets. • Torrefied pellets cost competitive for big installations and long-distance transport. [ABSTRACT FROM AUTHOR]

• The optimum pelletization conditions for pine sawdust were determined by RSM. • The best pellet quality was obtained with biomass moisture content of 16.6% at 80 °C. • Industrial quality pellets can be obtained from wood and residual biomass blends. • Contents of 30 wt% of almond shells and olive stones yield high quality pellets. 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 therefore serve to reduce energy consumption in industrial pelletization. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Biomass samples were gasified in air-steam in a bubbling fluidized bed at 900 °C. • PCA and HCA classified the biomass samples on the basis of gasification results. • The separation of the biomass samples was mainly based on conversion to CO and CH 4. • C and H contents and HHV of biomass had a positive effect on gasification conversion. • The H/O and K content of the biomass favored the H 2 concentration and H 2 /CO ratio. Abstract 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 CH 4 , 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 H 2 concentration and H 2 /CO molar ratio in the gas product, which was mainly related to the higher H/O ratio and K 2 O ash content of the biomass. The H 2 concentration in the product gas was negatively related to the O and VM contents of the biomass. Therefore, it can be concluded that the use of multivariate statistical techniques for analyzing gasification data facilitated to draw valuable conclusions about the influence of the biomass properties on the gasification results. [ABSTRACT FROM AUTHOR]

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 CO 2 separation from a biogas stream by means of adsorption on a lignocellulosic-based activated carbon is addressed. Binary CO 2 /CH 4 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 CO 2 /CH 4 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 CO 2 and CH 4 was studied for different CO 2 /CH 4 ratios, at 30 °C and atmospheric pressure. Under humid conditions the CO 2 uptake was reduced but the CH 4 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 CO 2 and CH 4 but it prompted CO 2 adsorption over CH 4 and hence facilitated the selectivity towards CO 2 with respect to the dry case. [ABSTRACT FROM AUTHOR]

Highlights • A range of biomass types has been successfully gasified in a bubbling fluidized bed. • Best gasification conditions were 900 °C, S/A = 70/30 and SR = 0.25 for PKS biomass. • Torrefied biomass showed slightly higher efficiency results than raw biomass. • Positive effects of HHV, VM and C contents of the biomass on gas and energy yields. Abstract The 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 (H 2 + CO + CH 4) production, H 2 /CO ratio, heating value, energy yield and cold gas efficiency of the obtained gas. Results showed that higher temperature and S/A ratio favored H 2 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 H 2 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/kg biomass. Torrefied biomass showed similar combustible gas production than the corresponding raw biomass under the conditions studied, but it gave slightly higher H 2 production and efficiency results. Possible correlations of the gasification performance parameters with biomass properties were also analyzed. The results showed positive effects of biomass volatile matter content, C content and high heating value (HHV) on the CO and combustible gas contents, calorific value of the product gas, as well as gas and energy yields. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Most practical applications of solids in industry involve porous materials and adsorption processes. A correct assessment of the equilibrium and kinetics of adsorption is extremely important for the design and operation of adsorption based processes. In our previous studies we focused on the evaluation of the equilibrium of CO 2 /CH 4 adsorption on cherry stone-based carbons. In the present paper the kinetics of adsorption of CO 2 on two cherry stone-based activated carbons (CS-H 2 O and CS-CO 2 ), previously prepared in our laboratory, has been evaluated by means of transient breakthrough experiments at different CO 2 /CH 4 feed concentrations, at atmospheric pressure and 30 °C. A commercial activated carbon, Calgon BPL, has also been evaluated for reference purposes. Three models have been applied to estimate the rate parameters during the adsorption of CO 2 on these carbons, pseudo-first, pseudo-second and Avrami’s fractional order kinetic models. Avrami’s model accurately predicted the dynamic CO 2 adsorption performance of the carbons for the different feed gas compositions. To further investigate the mechanism of CO 2 adsorption on CS-H 2 O, CS-CO 2 and Calgon BPL, intra-particle diffusion and Boyd’s film-diffusion models were also evaluated. It was established that mass transfer during the adsorption of CO 2 from CO 2 /CH 4 is a diffusion-based process and that the main diffusion mechanisms involved are intra-particle and film diffusion. At the initial stages of adsorption, film diffusion resistance governed the adsorption rate, whereas intra-particle diffusion resistance was the predominant factor in the following stages of adsorption. [ABSTRACT FROM AUTHOR]

A deep understanding of the interaction and competition between different gases on adsorption processes is essential for the design and optimization of industrial units. Two biomass-derived activated carbons (CS-CO 2 and CS-H 2 O), synthesized in our laboratory, were evaluated as selective adsorbents for the separation of CO 2 from CO 2 /CH 4 mixtures. Adsorption isotherms of the pure gases (i.e., CO 2 and CH 4 ) were performed in a high-pressure magnetic suspension balance at three different temperatures (303, 323 and 343 K) up to 1000 kPa and the data were correlated using the Sips and Toth models. The Ideal Adsorbed Solution Theory (IAST) was applied to predict the binary adsorption equilibrium. The results were validated by means of experimental breakthrough tests in a fixed-bed set-up. The isosteric heats of adsorption were estimated from the pure component adsorption data by means of the Clausius–Clapeyron equation and the Sips and Toth equations. All of the equilibrium data were integrated in a performance indicator defined so as to be able to evaluate the adsorbent in terms of selectivity, working capacity and adsorption enthalpy under conditions relevant to the specific application. Although both CS activated carbons had similar textural features, CS-CO 2 showed a better overall performance than CS-H 2 O for the separation of CO 2 from CO 2 /CH 4 mixtures. Our results highlight the importance of carrying out a deep analysis of the adsorption equilibrium under conditions relevant to the foreseen application in order to identify the most suitable adsorbent. [ABSTRACT FROM AUTHOR]

The biological production of H 2 by dark fermentation is being extensively investigated due to the great potential of the two-phase hydrogen/methane fermentation process for recovering energy from carbohydrate-rich wastes. However, the purification of the bio-hydrogen and biogas obtained is needed to produce high-purity H 2 and CH 4 streams appropriate for industrial application. In this study, the performance of three activated carbons (No1KCla-600, No1KClb-1000 and No2OS-1000), synthesized from phenol–formaldehyde resins, as potential adsorbents for CO 2 capture from bio-hydrogen and biogas streams has been evaluated under dynamic conditions. Adsorption–desorption cycles by means of temperature swings were conducted at ambient temperature and atmospheric pressure with CO 2 /H 2 (40/60 and 70/30 vol.%) and CO 2 /CH 4 (50/50 vol.%) binary gas mixtures in a purpose-built fixed-bed set-up. The performance of the resin-derived carbons to separate CO 2 was superior to that of reference commercial carbons in terms of CO 2 uptake, breakthrough time and column efficiency. These adsorbents presented high CO 2 /H 2 and CO 2 /CH 4 selectivity values, were easily completely regenerated and did not show capacity decay after multiple cycling. Breakthrough capacities reached 2.11 and 2.03 mmol g −1 at 25 °C for 70/30 CO 2 /H 2 and 50/50 CO 2 /CH 4 , respectively. The No2OS-1000 adsorbent, produced from phenol–formaldehyde resin and olive stones (20:80 wt.), gave the greatest values of CO 2 capture capacity on a volumetric basis and CO 2 /CH 4 selectivity, which may be advantageous to biogas purification applications because it reduces the size of the necessary equipment. [ABSTRACT FROM AUTHOR]

The main drawbacks of developing carbon adsorbents from pine sawdust, an abundant biomass feedstock, are the low carbon yield of the process and the poor mechanical properties of the resulting carbons. In an attempt to overcome these limitations, the effect of the addition of coal tar pitch was assessed. Adsorbent pellets were produced from pine sawdust and coal tar pitch by activation with CO 2 . The preparation process was optimized by using as decision variables the carbon yield and the adsorption performance of the adsorbents in conditions representative of post-combustion capture applications (10% CO 2 at atmospheric pressure and at 50 °C). Subjecting the composite pellets to a pre-oxidation treatment with air increased the carbon yield of the production process, and also improved the adsorption kinetics and capacity of the final adsorbents. The prepared adsorbents present a high carbon yield, a superior mechanical resistance and a competitive adsorption performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • SESR of bio-oil/biogas blends leads to renewable high-purity H 2 production. • H 2 yield of 87.1% is experimentally obtained at 625 °C and 2.5 bar. • H 2 purity of 98.6 vol% is achieved at 625 °C and 2.5 bar. • Higher temperature and steam/C molar ratio, but lower pressure, favor H 2 production. • Biogas addition increases the energy efficiency of the bio-oil SESR process by 1.34%. H 2 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 CO 2 capture by a solid sorbent. SESR was performed on a Pd/Ni-Co catalyst derived from a hydrotalcite-like material (HT) using dolomite as CO 2 sorbent. Bio-oil from fast pyrolysis of biomass is a carbon–neutral and renewable energy source with great potential for clean H 2 production by steam reforming processes. Biogas is also a promising renewable bio-based resource for hydrogen generation that can be used to increase the H 2 production of a biomass-based plant. In turn, it could improve the energy efficiency of the process due to the exothermic reaction of the CO 2 contained in biogas with the sorbent. Bio-oil composed of acetic acid and acetone (1/1 mol/mol) and biogas composed of CH 4 and CO 2 (60/40 vol%) were used as fuels. They were blended (50 wt% bio-oil + 50 wt% CH 4) 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 H 2 production and fuel conversion compared to conventional SR. Higher temperature and steam/C ratio, but lower pressure, favored H 2 yield and purity. High H 2 yield (87.1%) and H 2 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. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an experimental and numerical study on co-firing olive waste (0, 10%, 20% on mass basis) with two coals in an entrained flow reactor under three oxy-fuel conditions (21%O2/79%CO2, 30%O2/70%CO2 and 35%O2/65%CO2) and air–fuel condition. Co-firing biomass with coal was found to have favourable synergy effects in all the cases: it significantly improves the burnout and remarkably lowers NOx emissions. The reduced peak temperatures during co-firing can also help to mitigate deposition formation in real furnaces. Co-firing CO2-neutral biomass with coals under oxy-fuel conditions can achieve a below-zero CO2 emission if the released CO2 is captured and sequestered. The model-predicted burnout and gaseous emissions were compared against the experimental results. A very good agreement was observed, the differences in a range of ±5–10% of the experimental values, which indicates the model can be used to aid in design and optimization of large-scale biomass co-firing under oxy-fuel conditions. [Copyright &y& Elsevier]

Highlights: [•] Low-cost microporous biochars are obtained by single-step activation with oxygen. [•] This process entails energy savings compared to conventional two-step activation. [•] Activation at high temperatures with low oxygen content favours narrow porosity. [•] Biochars obtained in these conditions present high CO2/N2 selectivity. [•] These biochars present CO2 working capacities competitive to that of zeolite 13X. [ABSTRACT FROM AUTHOR]