Catalytic effect of alkali metals on biomass pyrolysis kinetics

Biomass is a low-carbon, resource, which is finding increasing use for heating and the generation of electricity. Biomass pyrolysis plays a central role in its combustion and is therefore receiving extensive consideration. The decomposition of biomass is also a crucial step in both fast pyrolysis and various thermal processing techniques involved in chemical manufacturing. Potassium and sodium are well-known catalysts in the thermal reactions of biomass. An expression was developed linking the rate of thermal degradation of a biomass to its potassium or sodium content. Willow samples impregnated with different potassium or sodium concentrations were studied for their pyrolysis behaviour by thermogravimetric analysis, and apparent first order kinetics derived. The developed relation yields a maximum reaction rate constant and a metal saturation constant that can predict the rate of willow pyrolysis based on temperature and concentration of potassium or sodium. Effects of sequential washing using water, ammonium acetate, and hydrochloric acid were also explored.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Effects of surface rates for the series reaction A→ B→ C on successive separated spherical sites

A steady - state series reaction A →B → C, consisting of a first reaction A →B on sphere 1 of radius a1 with first order kinetic rate constant kA and reactant diffusivity DA, followed by a second reaction B → C on sphere 2 of radius a2 with a first order kinetic rate constant kB and a B chemical species diffusivity DB, occurs on two discrete chemically active spheres a center - to – center distance d apart. The twin spherical harmonic expansion method with a Neumann iterative solution of the coefficient equations is used to generate a rigorous solution for the rate of series reaction in terms of an expansion in the inverse dimensionless center - to - center sphere separation d ̅(=d⁄((a_1+a_2 ))) up to the inverse thirteenth power. The expansion coefficients depend on three dimensionless parameters (γ,λ_A,λ_B), where the dimensionless inverse surface kinetic constants are λ_A=D_A⁄a_1 kA on sphere 1, λ_B=D_B⁄(a_2 k_B ) on the sphere 2, while the geometry enters as the radius ratio γ=a_1⁄a_2 . Using these results an equivalent site kinetic change is imposed, first to λ_Aon site 1, then to λ_Bon site 2, to determine which site is more influential for the overall series reaction rate. Effects of γ geometry modification at several fixed kinetic surface site rates are examined. When either one of reactive spheres is diffusion controlled, various levels of λ kinetic controls at the other site or γ site geometries are generated to study the effects of site kinetics or geometry control on the series reaction rate. As the “other site” reaction rate also increases toward diffusion control, inflection points are observed to develop as precursors to a local maximum on the series reaction rate versus sphere separation curves. An application to the isomerization of n-pentane is presented

Gasification of Miscanthus x giganteus Pellets in a Fixed bed Pilot-scale Unit

Gasification of Miscanthus x giganteus (Mxgig), is highly promising due to the high efficiency of the process and the many advantageous properties of this crop. Pilot-scale, fixed bed gasification studies were performed utilizing this fuel at three temperatures (750, 850, and 950 degrees C) to determine the process effects of temperature on gas quality and tar yields. Simple thermodynamic equilibrium modeling was successfully applied to the pilot-scale gasification process. The Mxgig crop performed well, with best process stability reached at temperatures of 800 degrees C or higher. Average calorific values of the product gases were highest at around 850 degrees C at 5.2 MJ.m(-3). Tar yields gradually increased with increasing temperature and dropped after 900 degrees C. The presented thermodynamic equilibrium model conformed well with experimental results, deviating little in terms of O-2, CO2, H-2, and CH4 and no more than 8.1% in the case of CO. This indicates that simple modeling methods can be utilized to predict gas compositions for the pilot-scale.Web of Science6art. no. UNSP 9

A comprehensive comparative study on the energy application of chars produced from different biomass feedstocks via hydrothermal conversion, pyrolysis, and torrefaction

Understanding the suitability of different conversion technologies for different types of biomass feedstocks is crucial in delivering the full valorisation of different types of biomasses. This is novel research which presents an extensive comparative study on how three different thermal conversion technologies (torrefaction, pyrolysis, and semi-continuous hydrothermal conversion) and process interdependencies are influenced by different feedstocks (Rapeseed (RS), Whitewood (WW), Seaweed Laminaria digitata (LD))) for the optimisation of char (hydrochar/biochar) formation and their associated bioenergy applications. A wide range of processing conditions was analysed to optimise char formation and potential applications of these chars in energy production were extensively investigated. Based on the evaluation of char structures, hydrothermal conversion could be an applicable method for char production from WW and RS. The char yield of WW is in the range of 30–50 wt% at the early stage of hydrothermal carbonisation (HTC, 235 °C). Increasing temperature (>265 °C) decreased char yield but produced a higher HHV char (∼30 kJ/g). Approximately 90 wt% of LD dissolved into the water at low temperatures ( 34 kJ/g. Similarly, LD decomposed gradually with a char yield of 45 wt% at 400 °C, but with a low HHV (∼15 kJ/g) and high ash content (20 wt%). WW had relatively high char yield of ∼ 60 wt% during pyrolysis at 250 °C, with a HHV of 25 kJ/g. Although RS had a high char yield (∼75 wt%) with a high HHV (>30 kJ/g), the chars still contained a significant amount of volatiles. The WW char from these three thermal conversion technologies, and RS chars produced by pyrolysis and hydrothermal conversion, could have a potential application in bioenergy production. However, the ash content and low HHV make LD unsuitable for bioenergy applications

Exploring the Utilisation of Natural Biosorbents for Effective Methylene Blue Removal

This paper presents a comprehensive analysis of the adsorbent capacity of five distinctly different biosorbents derived from untreated biomasses. The optimal adsorption capacity of seaweed (Laminaria digitata), horse chestnut husk, hazelnut husk, rapeseed residue, and whitewood to remove methylene blue (MB) dye was assessed by analysing the effects of particle size, pH, temperature, and initial dye concentrations. Furthermore, the adsorption kinetics, isotherms, and adsorption thermodynamics were investigated. The results showed that relatively high MB adsorption capacity was achieved by Laminaria digitata (~180 mg/g), in addition to a reasonable MB adsorption capacity of horse chestnut husk (~130 mg/g), hazelnut husk (~110 mg/g), and rapeseed residue (~80 mg/g). However, whitewood provides a relatively low adsorption capacity of below 20 mg/g. The best fit with experimental results regardless of biosorbent type was a pseudo-second-order kinetic model with the lowest mean absolute percentage error (ε, MAPE < 2.5%) and the highest correlation coefficients (R2 > 0.99). Although the pseudo-second-order kinetic model is often associated with chemisorption, the low enthalpy values (<29.30 kJ/mol) typically suggest that the adsorption process is more characteristic of physisorption, which involves weaker van der Waals forces rather than the stronger covalent bonds of chemisorption. This proposed a multi-step adsorption process involving both physisorption and chemisorption. The adsorption isotherm of Langmuir showed superior fitting results for Laminaria digitata and hazelnut husk. In contrast, rapeseed residue and horse chestnut husk fit better with the Freundlich adsorption isotherm. The Langmuir adsorption isotherms showed a maximum adsorption capacity of ~500 mg/g for Laminaria digitata, followed by horse chestnut husk (~137 mg/g), hazelnut husk (~120 mg/g), and rapeseed residue (~85 mg/g). The Gibbs free energy was negative for Laminaria digitata < horse chestnut husk < hazelnut husk < 0, which suggests that the removal of MB is thermodynamically favourable, as the adsorption process occurs spontaneously. The results of the study indicate that MB dye removal using untreated biomasses has the potential to be a low-cost valorisation option in the holistic whole life cycle valorisation pathway for Laminaria digitata, horse chestnut husk, and hazelnut husk

A comprehensive comparative study on methylene blue removal from aqueous solution using biochars produced from rapeseed, whitewood, and seaweed via different thermal conversion technologies

This paper presents, for the first time, a comprehensive comparative analysis of the potential of using biochars from three distinctly different UK-sourced biomass feedstocks, produced via three different thermal processing techniques, to adsorb methylene blue dye. Biochars were made from rapeseed, whitewood, and seaweed (Laminaria Digitata), produced via hydrothermal conversion, pyrolysis, and torrefaction. Adsorption kinetic models were developed for each biochar at different temperatures, pH and initial dye concentrations. Relatively high levels of methylene blue adsorption capacity were achieved by seaweed-based biochars (∼150 mg/g), with reasonable levels for rapeseed-based biochars (∼60 mg/g), whilst adsorption levels were found to be relatively low for whitewood-based biochars (<30 mg/g). A Pseudo-second-order kinetic model provided the best fit with experimental results. The Langmuir adsorption isotherm showed a better fit for seaweed biochars, while the Freundlich adsorption isotherm was a better fit for the rapeseed-based biochars. The Langmuir adsorption isotherms showed relatively high maximum adsorption capacity (Qo) for seaweed-based biochars; ∼175 mg/g for seaweed-Torrefaction and ∼ 117 mg/g for seaweed-Pyrolysis. Negative Gibbs free energy (ΔG°) values were observed for the seaweed-Torrefaction < seaweed-Pyrolysis < 0, which indicates that the methylene blue removal could be a thermodynamically favourable process due to the spontaneous nature of the adsorption. Our investigation has shown that the removal of methylene blue from wastewater could be a potential application for seaweed-based biochars as part of a holistic whole life cycle valorisation pathway. However, it is not suitable for all types of biomasses which emphasises the need for tailoring unique valorisation pathways for different types of biomasses

Catalytic conversion of methylated aromatics over wood-derived chars – the role of reforming agents and the effect of methyl groups

Toluene steam reforming was performed over three wood-derived chars and compared with a previously-reported pyrolytic conversion study. The heterogeneous mechanism of toluene decomposition was not directly affected by the introduction of steam, but it caused gasification of char and toluene-derived coke, which prolonged the initial high conversion efficiency. Conversely, when oxygen was used as a substitute for steam, a direct ring-opening reaction of toluene was observed, rather than solid carbon combustion. A comparison of benzene, toluene, and p-xylene conversion revealed that the presence of a methyl group on the aromatic ring enhanced its decomposition, regardless of the catalyst’s activity. However, a second methyl group did not further improve the conversion and only served to increase the intensity of secondary recombination reactions

A performance modelling study of integrating a MEA direct air capture unit with a CCGT absorber

Even in optimistic decarbonisation scenarios, there are most likely to be residual emissions that cannot be captured at source or avoided. Hence, research on CDR technologies, such as DACCS, to identify ways for effective deployment is essential for achieving net-zero targets. The scope of CCS deployment will rely on the amount of the residual emissions and, at the current standard for point sources of 90% to 95% CO2 capture, DACCS can be strategically significant to global economies. Possible integration opportunities for a DAC absorber with a conventional amine CCGT+PCC plant are examined, termed Co-DACCS. Modelling results suggest that the combination of an air absorber with a typical flue gas absorber can achieve specific reboiler duties down to 3.5 GJ/tCO2 for separating CO2 from the air, a value in the range of standalone CCGT+PCC applications. Depending on the configuration, there appears to be some trade-offs between DAC absorber capital cost and energy consumption. Ways to optimise combined operation and to make PCC plants ‘DACCS-ready’ are also discussed