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The environmental impact of traditional fuels and related greenhouse gas emissions (GHGE) has promoted policies driven towards renewable fuels. This review deals with green diesel, a biofuel obtained by catalytic deoxygenation of edible and non-edible biomasses. Green diesel, biodiesel, and petrodiesel are compared, with green diesel being the best option in terms of physical–chemical properties and reduction in GHGE. The deoxygenation process and the related types of catalysts, feedstocks, and operating conditions are presented. Reactor configurations are also discussed, summarizing the experimental studies. Several process simulations and environmental economic analyses—up to larger scales—are gathered from the literature that analyze the potential of green diesel as a substitute for petrodiesel. In addition, current industrial processes for green diesel production are introduced. Future research and development efforts should concern catalysts and the use of waste biomasses as feedstock, as well as the arrangement of national and international policies.

Filtering-catalytic candles, filled with an annular packed-bed of commercial Ni-catalyst pellets (∼600 g), were successfully tested for in situ syngas cleaning in a fluidized-bed biomass steam gasifier [Fuel Process. Technol.2019, 191, 44−53, DOI: 10.1016/j.fuproc.2019.03.018]. Those tests enabled the macroscopic evaluation of gasification and gas cleaning as a whole, requiring a more specific assessment of the catalyst performance inside the filter candle. To this end, steam reforming tests of tar key compounds (naphthalene and toluene; thiophene in traces to observe sulfur deactivation) were performed with a laboratory-scale packed-bed reactor containing the same catalyst pellets (

Selective hydrogenation of vegetable oils is a significant step in the synthesis of several precursors for the preparation of bioplastics and biodiesel. In this work, a commercial Lindlar catalyst (palladium on calcium carbonate; poisoned with lead) was used as an efficient catalyst in the selective partial hydrogenation of canola and sunflower oils. Different operating conditions (pressure, temperature, and catalyst amount) were tested, and results were achieved by gas chromatography analysis of methyl esters obtained by the transesterification of the triglycerides. The optimized reaction conditions (0.4 MPa, 180 °C, 4 mgcatalyst/mLoil) were determined for the hydrogenation of linoleic acid (C18:2) and linolenic acid (C18:3) with 84.6 and 90.1% of conversion, respectively, into 88.4% relative percentage of oleic acid (C18:1) with low formation of C18:0 (stearic), below 10%, with stability of the catalyst during several cycles with maximum C18:1 relative percentage ranging between 86.6 and 80.7%.

For about 10 years, this research group has developed and utilized a particle grain model (PGM), to simulate CO2-capture carried out by CaO-based porous particles. Chemical kinetics and diffusion parameters were either taken from literature studies or fixed by fitting experimental sorption data. As recently observed, this procedure was not fully satisfactory and revealed systematic, minor discrepancies between PGM numerical results and experimental data when predicting sorbents behavior during the initial chemically controlled regime of carbonation. This work deals with the experimental determination of kinetic and diffusion parameters, utilized in the PGM, by means of straightforward thermogravimetric analysis (TGA) tests on small samples of materials to be evaluated for CO2 sorption and sorption-enhanced processes. To validate this procedure, the carbonation of two Ni–CaO–mayenite combined sorbent-catalyst materials (CSCMs) was studied in TGA. The experimental data so obtained were used to infer carbona...

The European research project CLARA (G.A. 817841) has studied pretreated residual biomasses for chemical looping gasification. This work investigated devolatilizations of wheat straw pellets (raw, torrefied, and torrefied-washed) at 700 °C, 800 °C, and 900 °C, performed in fluidized beds made of sand or three oxygen carriers (OCs): integral-average values (gas yield, H

The production of blue hydrogen through sorption-enhanced processes has emerged as a suitable option to reduce greenhouse gas emissions. Sorption-enhanced steam–methane reforming (SESMR) is a process intensification of highly endothermic steam–methane reforming (SMR), ensured by in situ carbon capture through a solid sorbent, making hydrogen production efficient and more environmentally sustainable. In this study, a comprehensive energy model of SESMR was developed to carry out a detailed energy characterization of the process, with the aim of filling a current knowledge gap in the literature. The model was applied to a bench-scale multicycle SESMR/sorbent regeneration test to provide an energy insight into the process. Besides the experimental advantages of higher hydrogen concentration (90 mol% dry basis, 70 mol% wet basis) and performance of CO2 capture, the developed energy model demonstrated that SESMR allows for substantially complete energy self-sufficiency through the process. In comparison to SMR with the same process conditions (650 °C, 1 atm) performed in the same experimental rig, SESMR improved the energy efficiency by about 10%, further reducing energy needs.

The aim of this work is to identify the effect of the CaO phase as a CO2 sorbent and mayenite (Ca12Al14O33) as a stabilizing phase in a bi-functional material for CO2 capture in biomass syngas conditioning and cleaning at high temperature. The effect of different CaO weight contents is studied (0, 56, 85, 100 wt%) in sorbents synthesized by the wet mixing method. These high temperature solid sorbents are upgraded to bi-functional compounds by the addition of 3 or 6 wt% of nickel chosen as the metal active phase. N2 adsorption, X-ray diffraction, scanning electronic microscopy, temperature-programmed reduction analyses and CO2 sorption study were performed to characterize structural, textural, reducibility and sorption properties of bi-functional materials. Finally, sorption-enhanced reforming of toluene (chosen as tar model), of methane then of methane and toluene with bi-functional compounds were performed to study the best material to improve H2 content in a syngas, provided by steam biomass gasification. If the catalytic activity on the sorption enhanced reforming of methane exhibits a fast fall-down after 10–15 min of experimental test, the reforming of toluene reaches a constant conversion of 99.9% by using bi-functional materials.

The European research project CLARA (chemical looping gasification for sustainable production of biofuels, G.A. 817841) investigated chemical looping gasification of wheat straw pellets. This work focuses on pretreatments for this residual biomass, i.e., torrefaction and torrefaction-washing. Devolatilizations of individual pellets were performed in a laboratory-scale fluidized bed made of sand, at 700, 800, and 900 °C, to quantify and analyze the syngas released from differently pretreated biomasses, experimental data were assessed by integral-average parameters: gas yield, H2/CO molar ratio, and carbon conversion. A new analysis of devolatilization data was performed, based on information from instantaneous peaks of released syngas, by simple regressions with straight lines. For all biomasses, the increase of devolatilization temperature between 700 and 900 °C enhanced the thermochemical conversion in terms of gas yield, carbon conversion, and H2/CO ratio in the syngas. Regarding pretreatments, the main evidence is the general improvement of syngas quality (i.e., composition) and quantity, compared to those of untreated pellets, only slighter differentiations were observed concerning different pretreatments, mainly thanks to peak quantities, which highlighted an improvement of the H2/CO molar ratio in correlation with increased torrefaction temperature from 250 to 270 °C. The proposed methods emerged as suitable straightforward tools to investigate the behavior of biomasses and the effects of process parameters and biomass nature.

In order to adapt hydrotalcite based sorbents (LDO) to high temperature CO2 sorption and suitable temperature for tar steam reforming, the addition of CaO was investigated, maintaining their structure to keep porosity and accessibility but mostly assure the CO2 sorption stability during sorption/desorption cycles. In co-precipitation synthesis, various interlayer anions with different sizes and valences (carbonate, oxalate, and stearate) and various pH values were studied for different Mg/Ca ratios. The characterization of these sorbents (LDO) by TGA, XRD, N2 adsorption, SEM, sorption capacity, and sorption/desorption stability (cyclic TGA) permitted to understand the effect of the various synthesis conditions and to highlight the interest of oxalate use as interlayer anion. Typical LDH sand roses were formed with carbonate and oxalate anions after calcination until Mg/Ca/Al ratio = 1/2/1. For carbonate, this optimal ratio reached the highest sorption capacity and CaO sites accessibility at 600°C, better than pure CaO. However, the best stability during cycles was obtained with the sorbent from oxalate and Mg/Ca/Al ratio = 1.5/1.5/1 at pH 10 for which sorption results were almost the best values observed. For these two samples, the observed macroporosity were associated to the highest specific surface area and pore volume.Statement of NoveltyIn hydrotalcite structure, a width interlayer space permits to integrate various anions (CO32-, SO4-2, or NO3-) in order to modify CO2 sorption kinetics and capacity. The spheroidal “sand rose” morphology observed with CO32- anions explained the large BET surface area and the better CO2 sorption capacity. Stearate (and longer molecules) exchange was extensively studied as long-carbon-chain organic anion and allowed a better CO2 capture performance.This work focuses on another interlayer anion (oxalate) with the same valence of carbonate (2), a shape and valence different to stearate (1), and not yet reported in the literature. The novelty is to demonstrate that oxalate can replace carbonate as interlayer anion and moreover stearate by a less toxic one.

To adapt hydrotalcite-based sorbents (also known as layered double hydroxides—LDHs) to high-temperature CO2 sorption compatible with tar steam reforming, the addition of CaO was investigated, maintaining the LHDs porosity and accessibility but mostly assuring the CO2 sorption stability during sorption/desorption cycles. In co-precipitation synthesis, the investigated parameters are (i) various interlayer anions with different sizes and valences (carbonate, oxalate, and stearate); (ii) various pH values; (iii) different Mg/Ca molar ratios. The characterization of these modified LDHs by TGA, XRD, N2 adsorption, SEM, sorption capacity, and sorption/desorption stability (cyclic TGA) allowed understanding the effect of the various synthesis parameters and highlighted the effect of oxalate use as the interlayer anion. After calcination of sorbent with Mg/Ca/Al ratio = 1/2/1, typical LDH sand roses were formed both with carbonate and oxalate anions: this former exhibited the highest sorption capacity and accessibility of CaO sites at 600 °C, higher than pure CaO. However, the best stability during cycles was obtained with the sorbent from oxalate and Mg/Ca/Al ratio = 1.5/1.5/1 at pH 10 for which comparable sorption results are reached. For these two samples, the observed macro-porosity was associated with the highest specific surface area and pore volume.

Continuous steady-state gasification tests were performed, in which mixtures of lignite and solid recovered fuel (SRF) were fed to a bench-scale facility at atmospheric pressure, loaded with the bottom product of a high-temperature Winkler gasifier as the fluidized bed material. The O2/fuel and steam/fuel ratios were varied from 0.3 to 0.4 and from 0.25 to 0.35, respectively, and the effects of the temperature were examined at different levels (700, 750, and 800 °C). The objective of the experimental campaign was to evaluate the effects of above mentioned operating conditions on the (i) quality of syngas expressed in terms of gas yield ( Y gas ) , cold gas efficiency ( η CG ) , and carbon conversion ( X C ); (ii) effectiveness in tar reduction; and (iii) improvement of the H2/CO molar ratio. Characterization analyses (grain-size distribution, scanning electron microscopy and energy-dispersive X-ray spectroscopy) were performed on the materials before and after the tests. Pressure-fluctuation signals were acquired during the tests to monitor the fluidization quality and diagnose the correlated incipient sintering or agglomeration of the bed particles. At 800 °C, the obtained results ( Y gas = 1.53 ; η CG = 79 % ; X C = 92 % ; tar content = 7.35 g/Nm3; H2/CO molar ratio = 0.96) demonstrated the convenient feasibility of gasification with the SRF–lignite mixture as a fuel (SRF/lignite = 0.5 wt/wt) and helped define the operating conditions for future pilot tests aiming for liquid fuel synthesis, although the best results were obtained at 800 °C with SFR/lignite = 0.2 wt/wt ( Y gas = 1.79 ; η CG = 93 % ; X C = 102 % ; tar content = 0.92 g/Nm3; H2/CO molar ratio = 0.84).

The chemical looping gasification of residual biomasses—operated in fluidized beds composed of oxygen-carriers—may allow the production of biofuels from syngas. This biomass-to-fuel chain can contribute to mitigate climate change, avoiding the accumulation of greenhouse gases in our atmosphere. The ongoing European research project Horizon2020 CLARA (G.A. 817841) investigates wheat-straw-pellets (WSP) and raw-pine-forest-residue (RPR) pellets as feedstocks for chemical looping gasification. This work presents experimental results from devolatilizations of WSP and RPR, in bubbling beds made of three different oxygen-carriers or sand (inert reference), at 700, 800, 900 °C. Devolatilization is a key step of gasification, influencing syngas quality and quantity. Tests were performed at laboratory-scale, by a quartz reactor (fluidizing agent: N2). For each pellet, collected data allowed the quantification of released gases (H2, CO, CO2, CH4, hydrocarbons) and mass balances, to obtain gas yield (ηav), carbon conversion (χavC), H2/CO ratio (λav) and syngas composition. A simplified single-first order-reaction model was adopted to kinetically analyze experimental data. WSP performed as RPR; this is a good indication, considering that RPR is similar to commercial pellets. Temperature is the dominating parameter: at 900 °C, the highest quality and quantity of syngas was obtained (WSP: ηav = 0.035–0.042 molgas gbiomass−1, χavC = 73–83%, λav = 0.8–1.0); RPR: ηav = 0.036–0.041 molgas gbiomass−1, χavC = 67–71%, λav = 0.9–1.0), and oxygen-carries generally performed better than sand. The kinetic analysis suggested that the oxygen-carrier ilmenite ensured the fastest conversion of C and H atoms into gases, at tested conditions.

Biogenic residues are a promising feedstock to produce liquid biofuels via chemical looping gasification (CLG), but they form ashes with a high inorganic matter content, thus causing agglomeration and deposition in CLG-fluidized beds made of oxygen carriers (OC). The aim of this work is to develop pretreatments for residual biomasses to prevent this issue. Raw forest pine (as a reference material) and wheat straw residues were considered. The latter were pretreated by torrefaction at 250, 260, or 270 &deg, C and through the washing of torrefied biomasses. Torrefaction encouraged a de-chlorinating effect, while washing allowed the removal of 30&ndash, 40% of S, 60&ndash, 70% of K, and 40&ndash, 50% of P. The analysis of pressure fluctuation signals (standard deviations and dominant frequencies) was utilized to verify the improvement of the performance of treated biomass in fluidized beds: three OCs were, respectively, coupled with ashes from all biomasses, then fluidized from 700 to 1000 &deg, C at two and three times the minimum fluidization velocity. The diagnostic method used to analyze pressure fluctuations was shown to be effective for detecting the incipient fading of bubbling fluidization. This phenomenon was related to the agglomeration or the severe fragmentation of OC particles mixed with ashes, thanks to scanning electron microscopy and particle-size measurements. These characterizations and pressure fluctuations analyses confirmed the general improvement of wheat straw performances after pretreatments.

This study aims to investigate the CO2 sorption capacity of hydrochar, obtained via hydrothermal carbonization (HTC). Silver fir sawdust was used as a model material. The batch runs went at 200 &deg, C and up to 120 min. The hydrochar was activated with potassium hydroxide impregnation and subsequent thermal treatment (600 &deg, C, 1 h). CO2 capture was assayed using a pressure swing adsorption (PSA) process. The morphology and porosity of hydrochar, characterized through Brunauer-Emmett-Teller, Barrett-Joyner-Halenda (BET-BJH) and scanning electron microscopy (SEM) analyses, were reported and the sorbent capacity was compared with traditional sorbents. The hydrochar recovered immediately after the warm-up of the HTC reactor had better performances. The Langmuir equilibrium isotherm fits the experimental data satisfactorily. Selectivity tests performed with a model biogas mixture indicated a possible use of hydrochar for sustainable upgrading of biogas to bio-methane. It is conceivably a new, feasible, and promising option for CO2 capture with low cost, environmentally friendly materials.

An experimental study was performed on sorption enhanced steam methane reforming (SESMR) by Ni-mayenite reforming catalyst and CaO-mayenite CO2-sorbents with several CaO contents. Materials were synthesized, characterized (by XRD, BET and BJH methods, TPR) and tested in a micro-reactor, comparing two configurations: two separated, consequential packed-beds and the more usual raw mixing. Ni-mayenite always allowed a high, stable CH4 conversion (>93%). A generalized direct effect from CO2 capture emerged on water gas shift reaction extent, while enhancement of methane conversion took place only in raw mixing. In practical applications, investigated materials are bound to face alternatively reforming and sorbent regeneration conditions: an automated bench-scale system was used to perform 205 SESMR/regeneration cycles, with separate beds of Ni-mayenite and CaO-mayenite (30 wt% free-CaO), proving good activity and stability throughout cycles (stable CH4 conversion > 95%, pre-breakthrough CO2 concentration

This review is focused on Sorption Enhanced Steam Methane Reforming (SESMR), an emerging process intensification of traditional Steam Methane Reforming (SMR), to produce H2 by a more environmental friendly exploitation of natural gas, thanks to in-situ CO2 capture. Ni and CaO are respectively the most investigated materials for SMR catalysis and CO2 capture, used either on separated particles or in Combined Sorbent Catalyst Materials (CSCM); the latter is potentially more advantageous from the process point of view. Preferential conditions for SESMR based on Ni and CaO are about 650 °C and 1 atm, allowing to obtain H2 with high purity (more than 95 vol% vs. 76 vol% in industrial SMR, both on dry dilution-free basis). For a continuous process, multicycle CaO regeneration is needed, by means of high temperature calcination (800–950 °C). The exploitation of Solid Oxides Fuel Cells (SOFC) flue hot gases, as well as oxy-fuel combustion, are suggested as regeneration strategies in studies concerning SESMR industrial scale-up, in combinations of packed beds or fluidised bed reactors with solid recirculation. Future studies should investigate materials stability in relevant industrial conditions, e.g. more severe regenerations under highly concentrated CO2 at high temperatures, or in presence of steam.

Sorption enhanced steam methane reforming (SE-SMR) was performed to maximize hydrogen production and contemporary remove CO 2 from the product stream using bi-functional sorbent-catalyst compounds. Samples were tested at two different scales: micro and laboratory. The CaO amount varied in the CaO–Ca 12 Al 14 O 33 sorbent system synthesized by wet mixing (CaO content of 100 wt%, 56 wt%, 30 wt%, or 0 wt% and balance of Ca 12 Al 14 O 33 ) which were upgraded to bi-functional compounds by impregnation of 3 wt% of Ni. Nitrogen adsorption (BET/BJH), X-Ray Diffraction (XRD), Temperature-Programmed Reduction (TPR) and Scanning and Transmission Electronic Microscopy (SEM and TEM, respectively) analyses were performed to characterize structural and textural properties and reducibility of the bi-functional materials and evaluate their catalytic behavior. A fixed sorbent composition CaO–Ca 12 Al 14 O 33 (56 wt% of CaO and Ca 12 Al 14 O 33 balance), was chosen to study the effect of different weight hourly space times (WHST) and CH 4 stream compositions in SE-SMR activity. Impregnated mayenite at both micro and laboratory scales showed stable H 2 content of almost 74%, with CH 4 conversion of 72% similarly to the values reported by the sample containing 30 wt% of CaO in the post-breakthrough. Sample with 30 wt% of CaO showed promisingly behavior, enhancing H 2 content up to almost 94.5%. When the sorption enhanced reaction is performed roughly 89% of CH 4 conversion is achieved, and after the pre-breakthrough, the catalyst worked at the thermodynamic level. During cycling sorption/regeneration experiments, even if CO 2 removal efficiency slightly decreases, CH 4 conversion and H 2 yield remain stable.

Work Package 4 (WP4) of the European research project ASCENT developed combined sorbent-catalyst materials (CSCM) for sorption enhanced steam methane reforming (SESMR), based on nickel (Ni) and calcium oxide (CaO). ASCENT WP4 experiment on Ni/CaO/mayenite systems obtained from wet mixing and wet impregnation synthesis methods was conducted. Effects from Ni precursor (Ni (CH3COO)2 · 4H2O or Ni(NO3)2 · 6H2O), Ni load (from 3 wt.%-10 wt.%), and free CaO load (from 0 wt.%-54 wt.%) were investigated for 26 materials through characterizations and reforming reactivity tests in a packed-bed microreactor (650°C, 1 atm). Evidence emerged about the detrimental influence of low Ni/CaO ratio on the reforming catalytic activity of solid inventories, made of CSCM or even of the raw mixing of CaO-mayenite and Ni-mayenite particles. Catalytic materials were active towards reforming only when derived from Ni(NO3)2 · 6H2O. Based on this, the best CSCM (with the lowest free CaO content and the highest Ni load from nickel nitrate) was chosen to further study its industrial applicability by multicycle SESMR/sorbent-regeneration tests in a bench-scale packed-bed rig and attrition tests according to ASTM D5757-11. The CSCM was stable and active for 200 cycles with regenerations in N2 at 850°C, while a progressive loss of its activity occurred with regenerations in CO2 at 925°C as the cycle number increased due to Ni sintering. Its performance in the attrition tests was comparable to that of calcined dolomite.

The reduction of CO2 emissions and solid waste disposal are critical issues with high importance for the environmental protection. Gasification is a promising process for sustainable energy production, because it can produce a versatile gaseous fuel starting from a wide range of organic feedstocks, and with reduced greenhouse gas emissions compared to combustion. Lignite is an abundant carbonaceous resource in Europe and in this work, gasification tests were carried out with lignite and a lignite and Solid Recovered Fuel (SRF) mixture, to evaluate the quality of gas produced from co-gasification of waste materials, in view of the final uses of the gas. Experimental gasification tests were carried out in a bench scale fluidized bed gasifier at different operating temperatures; the results were evaluated in terms of gas composition, tar content and conversion rates. In addition, characterization analyses were carried out on materials before and after the tests, and pressure fluctuation signals were analysed in order to evaluate the fluidization quality of the bed inventory. 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-NDlicense

A one-dimensional kinetic model for steam‑oxygen gasification of refuse derived fuel in a bubbling fluidized bed reactor has been developed. The model incorporates the reaction network of steam‑oxygen gasification within the fluid dynamics of a fluidized bed to predict waste and tars conversion, gas composition and overall gasification performance. The model was validated by comparing outlet products composition and temperature profile with experimental data from a pilot-scale fluidized bed gasifier, operated at different conditions. The model showed accurate predictive capability and ease of computation. The effects of the operating conditions on gas yield and process efficiency were evaluated and the most appropriate fuel feeding height, equivalent ratio and the relative amount of steam to inject were identified.

In order to achieve the stringent requirements on syngas quality for synthetic natural gas (SNG) production, conventional and advanced gas-cleaning technologies are presented, grouping them in two main categories: cold and hot gas cleaning. Particular attention was directed at tars, representing one of the major drawbacks of gasification processes: these heavy hydrocarbons should be avoided by primary treatments or eliminated by secondary treatments. The former include the optimization of gasification conditions such as the choice of reactor type, operating conditions, use of bed additives, and modifications in the gasifier design. The secondary treatments consist of physical methods, thermal and catalytic conversion of tar. Each contaminant (sulfur, chlorine, alkali, etc.) has to be deeply removed to protect the catalyst used for downstream reaction. After gas cleaning, a gas-conditioning step is needed before methanation reaction to adjust the H2/CO ratio close to 3 (stoichiometry of methanation reaction) and to avoid carbon formation.

The present paper describes the experimental tests for the recycling of fluid catalytic cracking catalysts (FCCCs). The process aims at the recovery of cerium (Ce) and lanthanum (La) as well as the reuse of the leaching solid residue that represents the actual problem in terms of global amount landfilled every year. Landfilling is still the main choice for the handling of such catalysts. This novel process proposes an alternative recycling approach that leads to the production of synthetic zeolites, that have several industrial applications. FCCC was leached by 1.5 mol/L of HNO3, HCl and H2SO4 solutions at 80 °C, for 2 h with a solid to liquid ratio of 20 %wt, and the two rare earth elements were recovered by precipitation with an overall yield in the range 70–80%. The solid residues from the leaching stage were used as the base material for the synthesis of the zeolites by means of a combined thermal-hydrothermal treatment. The characterization of the zeolites demonstrated that the Na-A phase was predominant over the Na-X phase. The zeolites were tested as sorbent material for CO2 separation from CH4, in order to simulate the upgrading of biogas to biomethane. The maximum adsorption rate of CO2 was 0.778 mol CO2/kg of zeolite at 3 bar, with a resulting CH4 recovery of 62% and 97 %vol as purity. Since the results in adsorption of CO2 were not satisfying, the same zeolites were used to remove heavy metals from a synthetic wastewater solution containing three metals. Equilibrium and kinetic models were also developed in order to describe the adsorption process. The maximum adsorption load was calculated by the Langmuir isotherm and resulted to be 24–32 mg/g for Ni, 52–60 mg/g for Zn and 122–181 mg/g for Cu. The results also showed that the kinetics of the adsorption process is almost fast, as after 1 h at least 95% of zinc and copper were removed, whereas the kinetics of nickel was slower for all the three zeolites. As a conclusion, the zeolites are more efficient in metal adsorption than CO2 capture, but other applications will be tested in the future.

Replacing coal and oil with natural gas reduces greenhouse gas emissions without weakening economic development. Sorption enhanced steam methane reforming (SESMR) is an emerging process for an affordable transition towards cleaner energy systems, as it exploits natural gas coupled with in-situ CO2 capture to produce hydrogen. SESMR is performed on a steam reforming catalyst and a sorbent (cyclically regenerated by calcination) or, alternatively and more efficiently, on bi-functional Combined Sorbent-Catalyst Materials (CSCM). A double fluidized bed (reformer and oxyfuel combustor for calcination) with circulation of particulate material is anticipated for continuous SESMR at commercial scale. In this work, a Ni-CaO-mayenite CSCM was investigated in multicycle experimental tests under mild (pure N2, 850 °C) and severe (pure CO2, 925 °C) regeneration conditions, in thermogravimetric analysis for CO2-capture/regeneration and in an automated packed bed test rig for SESMR/calcination: the evolution of Ni and CaO functionalities as functions of cycle number was highlighted, also with the aid of scanning electron microscopy. Moreover, experimental results obtained with the hybrid material, collected under mild regeneration conditions, were used to simulate both CO2 sorption in TGA and packed bed SESMR multicycle tests: a Particle Grain Model (PGM) and an Axial Dispersion Plug Flow Reactor (ADPFR) model were integrated numerically, respectively. The same parameter values needed to characterize the material behaviour allowed a good fitting of both types of multicycle tests, thus demonstrating the possibility to use CO2-capture TGA data as a predictive tool for the CSCM performance in SESMR, provided that the catalytic activity is preserved.

Biomass gasification is a very promising process to produce energy from agricultural wastes; however, tar and particulate have to be removed in order to make the product gas exploitable. Catalytic filter candles inserted in the freeboard of a fluidized bed gasifier, perform hot syngas cleaning from particulate and promote the steam reforming reactions of tar and methane thanks to the addition of Ni-catalyst in their inner space. In this work, a 3D-CFD model is implemented in the FLUENT software, to simulate 6 catalytic candles housing in the freeboard of a pilot scale dual bubbling fluidized bed steam gasifier (100 kWth as biomass input). Main model parameters were derived from experimental results obtained with a bench scale gasification reactor, equipped with a ceramic filtering candle containing a commercial catalyst, to allow conditioning the raw syngas produced on site. Simulations were carried out to study the conversion of tar and methane in a real case application. The temperature drop along the gasifier freeboard causes very low conversion (≈15%) of tar produced inside the gasifier fluidized bed. It was found that small injections of O2 in the freeboard can rise the temperature and increase tar conversion up to 77%. Finally, simulations with raw syngas input subjected to primary tar removal by means of Fe-olivine as fluidized bed material resulted in high conversion rates and residual tar content lower than 1 g/Nm3.

In view of climate change containment, sorption enhanced steam methane reforming (SESMR) appears as an interesting production route for H2 with the additional advantage of CO2 capture application performed by high-temperature solid sorbents. CaO is largely employed as CO2 sorbent because of its low-cost mineralized forms (limestone and dolomite), of its high sorption capacity in the high temperature range compatible with steam methane reforming (SMR). Many recent studies have proposed purposely synthesized Ni-based reforming catalysts, used with high-temperature CO2 solid sorbents, or combined sorbent-catalyst materials (CSCM). For this last purpose, we studied the effect of Ni salt precursor (Ni nitrate hexahydrate or Ni acetate tetrahydrate) on properties and reactivity of Ni-mayenite catalysts or Ni-CaO-mayenite CSCM, synthesized by an already validated sequence of wet mixing (for sorbents synthesis) and wet impregnation (for catalysts and CSCM synthesis) methods. Although Ni acetate tetrahydrate was often reported as the best choice to improve textural properties, our study identified Ni nitrate hexahydrate as a definitely more suitable precursor than Ni acetate tetrahydrate in the purpose of developing efficient materials for SESMR. The dissimilar behaviors observed in reforming reactivity are related and explained by the differences in textural properties, Ni species dispersion, and reducibility.

Gasification is a very advantageous conversion process to obtain a fuel gas from organic wastes, however it also generates by-products, such as particulate and tar. These should be removed from the syngas for its smooth utilization in power generation devices and/or biofuels production. In this work, biomass gasification tests were carried out in a bench-scale fluidized bed gasifier with a ceramic filter candle filled with commercial Ni-catalyst pellets integrated in its freeboard, for the abatement of particulate and tar. The activity of catalyst was studied at different operating conditions (temperature and catalyst bed layout) and the results were analysed in terms of residual tar content and composition of the product gas. The catalyst resulted very effective, particularly in tests at higher temperature and with the partially filled candle configuration. Tars were reduced to 250 mg/Nm3 in the best case. The Ni-catalyst did not show deactivation during tests lasting 4 h.

In the near future, H2 is bound to become an important energy carrier used for surplus power storage and for sustainable transportation. An innovative technology for the production of a H2 rich gas is the Sorption Enhanced Reforming (SER) of hydrocarbons: a solid CaO-based sorbent is used to capture CO2 produced by reforming and water gas shift, enhancing the equilibrium. CaCO3 is decomposed in a fluidized bed oxy-combustion calciner and the sorbent recycled. In this work, the interest is focused on the Calcium Looping (CaL) cycle, more specifically on the combustor/calciner fluidized bed reactor of the pilot scale platform ZECOMIX (ENEA – 5 kmol/h of H2). The feasibility to feed O2 to a bubbling fluidized bed calciner by means of Oxygen Transport Membranes (OTM) is studied using a simulation model. The fluidizing flow rate is made of CO2 and CH4, preliminarily heated up to 700–850 °C by heat exchange with the output gas stream (above 900 °C); overall gas flow rate and methane content are enough to reach vigorous bubbling fluidization (u ≈ 10 umf) and temperature required by calcination, respectively. Cold model experimental tests with a cylindrical bubbling fluidized bed reactor with internals (vertical rods mimicking the OTM system) are carried out to support the design of the calciner unit in the ZECOMIX experimental platform. The hydrodynamic study is performed under ambient conditions to simulate fluidized bed expansion and to evaluate bubbles behavior in the calciner, in presence of vertical, tubular membranes for oxygen transfer.

Sorption Enhanced Steam Methane Reforming (SESMR) involves carbon-capture and natural gas exploitation to produce H2. A 2-particle system (Ni-catalyst and CaO-based sorbent particles), and a CSCM (obtained by granulating powders of that 2-particle system) were studied in multicycle SESMR/regeneration at atmospheric pressure, with reforming at mild temperature (650 °C) and oxidative regeneration under pure CO2 (925 °C), conditions relevant for hypothetical industrial-scale SESMR. 200 cycles (>500 h non-stop per test) were performed for both systems in a packed bed reactor, highlighting a satisfactory catalytic stability and a decrease in sorption capacity explained by after-test characterizations (PXRD, BET-BJH methods, SEM-EDS, TEM). In view of industrial applications in fluidized-beds, resistance to attrition of investigated materials was determined according to ASTM D5757-11, at SESMR/regeneration process temperatures: results compared well with a reference Fluid Catalytic Cracking (FCC) catalyst, purposely designed for applications in industrial fluidized-beds.

Palladium nanoparticles supported on Mg/Ca hydrotalcites catalyze the hydroarylation reaction of different alkynes and alkenes with aryl iodides under air in MeCN. The reaction of tertiary propargylic alcohols (1) with aryl iodides (2) yields, stereoselectively, γ,γ-diarylallylic alcohols (3) in moderate to high yields and high selectivity. Also, the HT/Pd hydroarylation reaction with aryl iodides was attempted on norbornene and α,β-unsaturated ketones affording, respectively, exo-aryl bicyclo[2.2.1]heptanes and β-aryl ketones in moderate to high yields. All the reactions described benefit from using a heterogeneous catalyst with evident advantages in terms of reaction purification and recyclability of the catalyst.

This paper deals with a Ni-CaO-mayenite combined sorbent-catalyst material (CSCM) for sorption enhanced steam methane reforming (SESMR), with Ni and CaO fractions optimized for a multicycle SESMR/sorbent regeneration process (10 wt% and 13.5 wt% respectively). The CSCM was purposely synthesized by wet mixing followed by wet impregnation. Used characterization methods were XRD, BET and BJH methods, SEM/EDS, STEM/EDS, TPR, TGA. The CSCM reactivity was checked by a 3 h reforming test in a microreactor. The material was then subjected to two hundred and five SESMR/regeneration cycles utilizing a fully automated bench scale rig with a packed bed reformer/calciner reactor: a very stable and satisfactory performance was observed, without decline of Ni catalytic activity and CO2 sorption capacity over a 15 days no-stop test. This stability towards multicycle operation was confirmed by after-test characterizations.

Heavy organic compounds produced during almond shells gasification in a steam and/or air atmosphere, usually called tar, are drastically reduced in the product gas by using simultaneously in one vessel a ceramic filter placed in the freeboard and a mixture of olivine and dolomite particles in the fluidized bed of the gasifier. The content of tar in the product gas during a reference gasification test with air, in presence of fresh olivine particles only, was 8600mg/Nm3 of dry gas. By gasifying biomass with steam at the same temperature level of 820°C in a bed of olivine and dolomite (20% by weight), and in the presence of a catalytic ceramic filter inserted in the freeboard of the fluidized bed gasifier, the level of tar was brought down to 57mg/Nm3 of dry producct gas, with a decrease of more than two orders of magnitude.

Fuel Cells fed with locally produced biogenous primary fuels can convert renewable energy into electricity with high efficiencies, in an environment friendly and CO 2 -neutral manner. The paper analyses different biomass conversion processes, gas conditioning technologies, fuel cells typologies and power plant configurations, focusing on the most suitable gasification and anaerobic digestion processes coupled to high temperature fuel cells. The paper shows that the conversion systems have to be analysed from global perspective including feedstock, processes and plant configurations in order to obtain high reliability and efficiency and low emissions. Indeed, the presence, in the raw produced gas, of particulate, organic and inorganic impurities renders the coupling of biomass-derived gases and Fuel Cells problematic, especially in the case of gasification. However, recently developed hot gas cleaning technologies could improve energy efficiency and lower operational costs for high-temperature utilizations of the biomass-derived gas. Finally, further research and demonstration activities are required in order to improve power plant reliability and reduce global capital cost, especially at the more suitable small scale size.