Abstract: The deactivation mechanism of a commercial Rh/CeO2 ZrO2 catalyst in raw bio-oil steam reforming has been studied by relating the evolution with time on stream of the bio-oil conversion and products yields and the physicochemical properties of the deactivated catalyst studied by XRD, TPR, SEM, XPS, TPO and TEM. Moreover, the reversibility of the different deactivation causes has been assessed by comparing the behavior and properties of the catalyst fresh and regenerated (by coke combustion with air). The reactions were carried out in an experimental device with two units in series: a thermal treatment unit (at 500 °C, for separation of pyrolytic lignin) and a fluidized bed reactor (at 700 °C, for the reforming reaction). The results evidence that structural changes (support aging involving partial occlusion of Rh species) are irreversible and occur rapidly, being responsible for a first deactivation period, whereas encapsulating coke deposition (with oxygenates as precursors) is reversible and evolves more slowly, thus being the main cause of the second deactivation period. The deactivation selectively affects the reforming of oxygenates, from least to greatest reactivity. Rh sintering is not a significant deactivation cause at the studied temperature.

DOI: 10.1016/j.ijhydene.2018.12.073

It is being a very busy end and start of new academic year... and our productivity is very high indeed. Here is a list of our recent publications

Abstract: In the present study, the hydrodynamics and heat transfer parameters of a conical spouted bed with a draft tube were investigated under the pyrolysis conditions using computational fluid dynamics (CFD) technique. The Eulerian-Eulerian approach in conjunction with the kinetic theory of granular flow (KTGF) was applied, and some important parameters, such as pressure drop, solid volume fraction, particle velocity, and heat transfer coefficients between the wall and the bed were evaluated. The impact some solid-wall boundary conditions, such as specularity coefficient (φ), and particle-wall restitution coefficient (ew), have on the heat transfer and hydrodynamics of the bed were studied. The CFD predictions were in close quantitative agreement with measurements in terms of heat transfer coefficients and pressure drop. It was found that both specularity and particle-wall restitution coefficient have a significant influence on the pressure drop and heat transfer coefficients, with the effect on pressure drop being higher than on heat transfer coefficients.

DOI: 10.1016/j.applthermaleng.2017.08.044

Abstract: The characterization of coke deposited on a Ni/La2O3‐αAl2O3 catalyst used in the steam reforming of bio‐oil has been studied by temperature programmed oxidation (TPO) coupled with different in situ techniques: thermogravimetry (TG), modulated thermogravimetry (MTG), FTIR spectroscopy with mass spectrometry (MS), Raman spectroscopy, and differential scanning calorimetry (DSC). The steam reforming of bio‐oil was carried out in a reactor equipment with two steps in series, comprising bio‐oil thermal treatment (500 °C) and subsequent reforming in a fluidized bed reactor (550–700 °C; and steam‐to‐carbon ratio, 1.5–6). TG/MS‐TPO experiments identify encapsulating and filamentous coke, and a more detailed analysis using other in situ techniques enable to characterize the nature and location of 4 types of coke: (i) an encapsulating coke with aliphatic nature placed in the most superficial layers; (ii) an encapsulating coke with higher aromatic nature in inner layers; (iii) the most superficial layers of a filamentous coke, further from active sites and with a more carbonized structure compared to encapsulating coke; and (iv) an innermost and mainly polyaromatic filamentous coke with a low oxygenates content.

DOI: 10.1002/cctc.201701942

Abstract: The valorization of biomass (pine wood) for hydrogen production has been studied in a two-step process, comprising pyrolysis and subsequent steam reforming of the volatiles produced in the first step. This work focuses on the deactivation of the Ni commercial catalyst used in the second step. Pyrolysis of biomass has been performed in a conical spouted bed reactor at 500 °C, and the in-line catalytic steam reforming of the pyrolysis volatiles, in a fluidized bed reactor at 600 °C. Deactivated catalyst samples were recovered at different values of time on stream, and analyzed by means of XRD, N2 adsorption-desorption, SEM and TEM microscopies, TPO, Raman and FTIR spectroscopies. The results show that the deactivation is mainly due to the encapsulation of Ni particles by coke, together with Ni sintering, to a lesser extent (from a Ni particle size of 25 nm in the reduced fresh catalyst, to 39 nm at 100 min). The former is ascribed to the condensation of oxygenates (particularly phenols), and the latter is inevitable within the current conditions. As the fraction of uncovered Ni particles decreases with time on stream, the deposition of encapsulating coke is slowed down (from a formation rate of 0.30 mgcoke gcatalyst−1 min−1 to 0.20 mgcoke gcatalyst−1 min−1, at 0–50 min and 50–100 min on stream, respectively), promoting the deposition of coke on the catalyst support (with a formation rate of 1.04 mgcoke gcatalyst−1 min−1 at 50–100 min on stream), with a more carbonized structure and formed through the thermal decomposition of phenols in the reaction medium.

DOI: 10.1016/j.apcatb.2018.04.002

Abstract: A model has been proposed and validated for the prediction of biomass combustion rate in a conical spouted bed. The model couples the intrinsic kinetics for the process and the flow pattern of the gaseous stream in the unit. The kinetics is described based on a reaction scheme consisting in simultaneous devolatilization and combustion involving the three biomass constituents, i.e., hemicellulose, cellulose and lignin. The gas flow pattern in the combustion chamber and subsequent cleaning system has been modelled using a compartimental model based on two continuous perfectly mixed vessels and a plug flow vessel. Tracer tests have been conducted to determine the residence time distribution in the whole unit and the parameters of the compartimental model. Batch combustion tests have been carried out to determine the composition of the outlet gaseous stream and the evolution of conversion with time, whose fitting to the kinetic model allowed calculating the parameters of best fit (frequency factors and activation energies). The model suitably predicts the evolution of combustion rate in a conical spouted bed, and therefore is a useful tool for the design of industrial plants based on this technology.

DOI: 10.1016/j.fuel.2018.04.060

Abstract: The second step of chlorine-mediated methane valorization into hydrocarbons has been investigated using a HZSM-5 zeolite catalyst. A parametric study has enabled to set the reaction network, which is dominated by the dual cycle mechanism and secondary reactions of light olefins. This network explains the formation of methane, light olefins, C5+ aliphatics, paraffins, aromatics and coke. Under the optimal conditions, the light olefin selectivity is >70%, of which >40% corresponds to propylene. Coke is originated in the zeolite micropores and then grows within the matrix meso- and macropores.

DOI: 10.1016/j.jiec.2017.12.042

Abstract: Demand for propene as a petrochemical building block keeps growing, while its availability has been decreased by the adoption of shale gas resources, among others. Efforts to optimize its production by conventional means (including modified fluid catalytic cracking) and new on-purpose production technologies (including ethene to propene (ETP) and olefin cracking) are being pursued. This work reviews the progress made on olefin conversion processes, including the ETP reaction, which is still under development, and the cracking of butenes and higher olefins (C5–C8). The factors analyzed include the catalytic performance of different zeolite materials and their modifications to increase catalyst stability, yield, and selectivity to propene, as well as the effect of operating conditions, reaction thermodynamics, and mechanisms involved. The work is complemented by a survey of commercial technologies and developments on olefin conversion processes.

DOI: 10.1080/01614940.2018.1432017

Abstract: Catalytic pyrolysis of high density polyethylene (HDPE) on HZSM-5 catalyst and an iron-alumina pillared montmorillonite, prepared in laboratory (FAMO), was performed by means of a conical spouted bed reactor. This type of reactor is a suitable technology for plastic pyrolysis due to its high heat and mass transfer rates and excellent performance in the handling of sticky solid materials. The pyrolytic process carried out on HZSM-5 catalyst gave significant yield of gaseous products (above 74 wt%), while FAMO catalyst gave high yields of waxes, particularly rich in diesel hydrocarbon range (C11–C21). Waxes obtained by subjecting HDPE to thermal pyrolysis had a higher range of molecular weight. Waxes have been characterised using different techniques, such as gel permeation chromatography (GPC), polidispersity (PD), Fourier transform infrared (FTIR) spectroscopy, Simulated Distillation, and TDP.

DOI: 10.1016/j.jaap.2017.12.015

Abstract: A study has been carried out on the hydrodynamic performance of a fountain confinement device used in conical spouted beds for the treatment of Geldart A and B type particles. Stability and particle elutriation have been analysed for beds provided only with this device and those provided with this device and two types of draft tubes, namely, open sided draft tube and nonporous draft tube. Stability is greatly improved when only the fountain confiner is used, but the draft tubes are required for significantly avoiding bed elutriation in spouted beds. The modified conical spouted bed has been located in a map of operating conditions together with the remaining gas-solid contact regimes. The fountain confiner provides a dramatic increase in the applicability range of spouted beds. Thus, unlike the traditional use of spouted beds for Geldart D type particles, this device allows operation with Geldart A, B and D particles, with a small fraction of C particles.

DOI: 10.1016/j.powtec.2017.12.090

Abstract: A full 3D model of a conical spouted bed equipped with an open-sided draft tube was simulated using CFD-DEM embedded in a commercial CFD code ANSYS-FLUENT. The dense discrete phase model (DDPM) with DEM closure for particle–particle interaction available in the FLUENT was used for the particulate phase. The dispersed k-ε turbulent model was used in the computational model for the gas phase. The geometry used in the simulation for both the contactor and the open-sided draft tube was identical to that of a pilot plant in which the hydrodynamic studies were carried out. The influence of the open-sided draft tube was studied by using two configurations, one flushed with the bed surface and the other one protruding above the bed surface. The CFD-DEM results indicated that the accuracy of model predictions significantly depends on the modification in the Gidaspow drag function. The predicted pressure drops and fountain heights were consistent with the experimental data. New aspects of particle flow pattern, axial solid velocity, solid volume fraction in the bed, and power spectral density have also been discussed.

DOI: 10.1016/j.jtice.2017.09.051

Abstract: A study has been carried out on the applicability of the correlations proposed in the literature for calculating peak and spouting pressure drops to biomass materials. These parameters are essential for estimating energy consumption in spouted beds and depend on the contactor geometry, operating conditions and the type of particles. Five biomass materials have been studied based on their suitability for energy production by combustion and their different size, density and shape factor. Both peak and spouting pressure drops increase as particle size and density are increased and shape factor is decreased. Correlations have been proposed based on those already reported in the literature for regular materials. The influence of particle size and density is more pronounced in these irregular biomass materials than in regular ones, especially in the peak pressure drop. Shape factor is also highly influential, which is reflected on the greater influence of the static bed height for irregular materials, especially for the spouting pressure drop.

DOI: 10.1016/j.jtice.2017.09.001

Abstract: This work investigates the correlation of the reaction conditions (temperature and steam-to-carbon ratio (S/C)) and the reaction medium composition with the deactivation behavior of a Ni/La2O3-αAl2O3 catalyst used in steam reforming of bio-oil, aiming at sustainable hydrogen production from lignocellulosic biomass. The reaction was performed in an in-line two-step system consisting of thermal treatment of bio-oil at 500 °C for retaining the thermal pyrolytic lignin and in-line steam reforming of the remaining oxygenates in a fluidized bed catalytic reactor. The reforming step was conducted at 550 and 700 °C and S/C ratios of 1.5 and 6. Fresh and deactivated catalyst samples were characterized using XRD, SEM, TEM, TPO, XPS, Raman and FTIR spectroscopy. The catalyst deactivation was mainly due to the amorphous and encapsulating coke deposition whose formation is attenuated when both the temperature and S/C ratio are increased. Although the highest catalyst stability is attained at 700 °C and/or an S/C ratio of 6, Ni sintering is noticeable under these conditions. The encapsulating coke is highly oxygenated, in contrast with the more aromatic and condensed nature of filamentous coke. Based on the correlation between the composition of the coke and the reaction medium, it was established that bio-oil oxygenates are the precursors of the encapsulating coke, particularly phenols and alcohols, whereas CO and CH4 are the possible precursors of the coke fraction made of filaments whose contribution to catalyst deactivation is hardly significant.

DOI: 10.1039/c7gc01432e

Abstract: The flash pyrolysis of waste truck-tyres was studied in a conical spouted bed reactor (CSBR) operating in continuous regime. The influence of temperature on product distribution was analysed in the 425–575 °C range. A detailed characterization of the pyrolysis products was carried out in order to assess their most feasible application. Moreover, special attention was paid to the sulphur distribution among the products. The analysis of gaseous products was carried out using a micro-GC and the tyre pyrolysis oil (TPO) by means of GC-FID using peak areas for quantification, with GC/MS for identification and elemental analysis. Finally, the char was subjected to elemental analysis and surface characterization. According to the results, 475 °C is an appropriate temperature for the pyrolysis of waste tyres, given that it ensures total devolatilisation of tyre rubber and a high TPO yield, 58.2 wt.%. Moreover, the quality of the oil is optimum at this temperature, especially in terms of high concentrations of valuable chemicals, such as limonene. An increase in temperature to 575 °C reduced the TPO yield to 53.9 wt.% and substantially changed its chemical composition by increasing the aromatic content. However, the quality of the recovered char was improved at high temperatures.

DOI: 10.1016/j.enconman.2017.03.051

Abstract: The continuous increase in the generation of waste plastics together with the need for developing more sustainable waste management policies have promoted a great research effort dealing with their valorization routes. In this review, the main thermochemical routes are analyzed for the valorization of waste polyolefins to produce chemicals and fuels. Amongst the different strategies, pyrolysis has received greater attention, but most studies are of preliminary character. Likewise, the studies pursuing the incorporation of waste plastics into refinery units (mainly fluid catalytic cracking and hydrocracking) have been carried out in batch laboratory-scale units. Other promising alternative to which great attention is being paid is the process based on two steps: pyrolysis and in-line intensification for olefin production by means of catalytic cracking or thermal cracking at high temperatures.

DOI: 10.1016/j.rser.2017.01.142

Abstract: The continuous pyrolysis-reforming of pine sawdust and high density polyethylene mixtures (25, 50 and 75 wt% HDPE) has been performed in a two-stage reaction system provided with a conical spouted bed reactor (CSBR) and a fluidized bed reactor. The influence HDPE co-feeding has on the conversion, yields and composition of the reforming outlet stream and catalyst deactivation has been studied at a reforming temperature of 700 °C, with a space time of 16.7 gcat min gfeeding−1 and a steam/(biomass + HDPE) mass ratio of 4, and a comparison has been made between these results and those recorded by feeding pine sawdust and HDPE separately. Co-feeding plastics enhances the hydrogen production, which increases from 10.9 g of H2 per 100 g of feed (only pine sawdust in the feed) to 37.3 g of H2 per 100 g of feed (only HDPE in the feed). Catalyst deactivation by coke is attenuated when HDPE is co-fed due to the lower content of oxygenated compounds in the reaction environment. The higher yield of hydrogen achieved with this two-step (pyrolysis-reforming) strategy, its ability to jointly valorise biomass and plastic mixtures and the lower temperatures required compared to gasification make this promising process for producing H2 from renewable raw materials and wastes.

DOI: 10.1016/j.enconman.2017.01.008

Abstract: Waste truck tyre valorization by fast pyrolysis has been performed in a conical spouted bed reactor in the 425–575 °C range. The tyre pyrolysis oil (TPO) yield was found to decrease with increasing temperature whilst the yield of gas increased. The effect of temperature on TPO properties has been studied in order to establish the best possible valorization route. FTIR and chromatographic analysis revealed the presence of some undesired compounds with sulphur, nitrogen or oxygen functionalities (benzotiatholes, nitriles and carboxylic acids amongst others) and an increase of TPO aromaticity with increasing temperature. The carbon and sulphur content and the heating value of the TPO increased with temperature. The simulated distillation showed that approximately 70% of the TPOs produced at 425 and 475 °C correspond to diesel range, whereas that TPO obtained at 575 °C is between diesel and gasoline range. The properties of the TPOs evidenced their potential to substitute conventional fuels. However, some of them need to be improved, i.e., by reduction of the sulphur, nitrogen and aromatic content. Additionally, the TPO obtained at 425 and 475 °C could be an important source of limonene and that at 575 °C of xylenes, although current removal methods present some limitations.

DOI: 10.1016/j.energy.2017.03.163

Abstract: This study pursues the development and characterization of a fountain enhanced spouting regime. This novel gas solid-contact method combines the advantages of fountain confined conical spouted beds with those of draft tube conical spouted beds. The aim of confining the fountain, and therefore attaining a clearly differentiated regime, is to progress towards a highly efficient conical spouted bed reactor for biomass gasification. Accordingly, and in order to delve into the knowledge of the regimes attained in this contact method, a study has been conducted by analyzing the influence operating parameters (temperature, gas flow rate, particle size and bed mass) and draft tube geometry (tube diameter and entrainment zone height) have on hydrodynamics. Fountain confinement allows greatly enlarging the fountain region, especially the height, which improves the contact between reacting gases and the catalyst. Moreover, the residence time distribution, and therefore the average residence time, may be optimized by confining and enlarging the fountain zone. These features promote tar cracking and so increase biomass conversion efficiency, which are highly relevant facts for use of conical spouted bed reactors in gasification.

DOI: 10.1016/j.fuel.2017.05.014

Abstract: This work focuses on the removal of the tar derived from biomass gasification by catalytic steam reforming on Ni/Al2O3 catalysts. Different tar model compounds (phenol, toluene, methyl naphthalene, indene, anisole and furfural) were individually steam reformed (after dissolving each one in methanol), as well as a mixture of all of them, at 700 °C under a steam/carbon (S/C) ratio of 3 and 60 min on stream. The highest conversions and H2 potential were attained for anisole and furfural, while methyl naphthalene presented the lowest reactivity. Nevertheless, the higher reactivity of oxygenates compared to aromatic hydrocarbons promoted carbon deposition on the catalyst (in the 1.5–2.8 wt.% range). When the concentration of methanol is decreased in the feedstock and that of toluene or anisole is increased, the selectivity to CO is favoured in the gaseous products, thus increasing coke deposition on the catalyst and decreasing catalyst activity for the steam reforming reaction. Moreover, an increase in Ni loading in the catalyst from 5 to 20% enhances carbon conversion and H2 formation in the steam reforming of a mixture of all the model compounds studied, but these values decrease for a Ni content of 40%. Coke formation also increased by increasing Ni loading, attaining its maximum value for 40% Ni (6.5 wt.%).

DOI: 10.1016/j.enconman.2016.12.092

Abstract: The performance of SAPO-18 and SAPO-34 catalysts has been compared during the conversion of ethylene or 1- butene to propylene. This comparison has been made in terms of activity (conversion), selectivity and stability against coke deposition. The SAPOs were synthesized, agglomerated, calcined, characterized and tested in a fixed-bed reactor at 500 °C. The spent catalysts (after 5 h on stream) were characterized to assign the location and nature of coke. The results point to the higher activity and stability of SAPO-18 catalyst in the conversions of each reactant (ethylene or 1-butene), which has been explained on the basis of its acidity, pore topology and above all, the faster diffusion of aromatics causing deactivation. Thus, the SAPO-18 catalyst suffers slower coke deposition, while this coke is of lighter nature (more aliphatic and less aromatic). The advantages of SAPO-18 over SAPO-34 catalyst are more relevant for the transformation of 1-butene, where the propylene selectivity and yield increase over time, as secondary reactions are selectively neglected and coke condensation is slowed down.

DOI: 10.1016/j.apcata.2017.08.036