Cesar Augusto Moraes Abreu

Iron is one of the most common constituents in groundwater, and affordable decentralized options for removing residual iron remain limited. This study valorizes two abundant agro-industrial residues, sugarcane bagasse and green coconut mesocarp, as biosorbents for removing residual iron from water, using iron(III) as the model adsorbate. The materials were characterized by SEM, FTIR, EDS and pH_PZC analyses, and their performance was evaluated through batch equilibrium and fixed-bed adsorption experiments. Simple, low-intensity pretreatments improved performance without high-temperature activation or hazardous reagents. Batch equilibrium isotherms were best described by the Sips model (Adj. R² > 0.97), with model-predicted maximum capacities of 0.25 and 0.56 mg·g⁻¹ for treated bagasse and mesocarp, respectively. Translated to continuous operation, fixed-bed columns achieved capacities of 0.66 and 0.44 mg·g⁻¹, with breakthrough behavior well captured by the Thomas, Yoon–Nelson, and Yan models. Although capacities are modest, they are well matched to the low iron levels typical of point-of-use polishing, where very low material cost and wide availability outweigh raw capacity. By converting waste that is otherwise landfilled into functional treatment media, this work offers a practical, circular-economy route toward safer drinking water in decentralized, resource-limited settings.

Introduction: In this study, the mass transfer effects in a triphasic reaction conducted in a slurry reactor were evaluated to optimize operational parameters (gas flow, stirring speed, temperature, and solid mass), aiming to understand how these parameters influence the efficiency of the reactor. The reactor was operated at 25°C and 1.0 bar under mechanical stirring, in a semi-batch mode, where the liquid and solid phases were in batch mode, while the gas phase was in continuous mode. The evaluation was performed at stirring speeds ranging from 200 to 500 rpm and airflow rates between 50 and 200 L h⁻¹. The results highlighting the limiting effects of mass transfer indicated that the gas-liquid volumetric mass transfer coefficient (kLa) ranged from 0.0152 to 0.0768 s⁻¹. For glycerol oxidation in a slurry reactor, the mass transfer of oxygen in a 30 g L-1 glycerol solution was evaluated, yielding a kLa value of 0.046 s⁻¹. Objective: The objective of this study is to investigate the mass transfer effects in a three-phase reactor, characterizing mechanical agitation and gas dispersion to enhance oxygen transfer, as demonstrated by the model reaction. Theoretical Framework: The main concepts and theories that underpin the research are mass transfer in multiphase and reactive systems, including two-film theory, the effects of operational parameters on a slurry reactor, and its behavior. Also, the development of a dynamic measurement. Method: The methodology adopted for this research comprises a three-phase reactor, and a kinetic study was conducted. Data collection was carried out by measuring the concentration of oxygen and applying the subtle equations shown in the main text. Results and Discussion: The study found that increasing the stirring speed and gas flow significantly enhanced the volumetric mass transfer coefficient (kLa), reaching a maximum value of 0.076 s⁻¹. Temperature had a positive influence on kLa, especially at higher gas flows, while glycerol concentration reduced oxygen transfer due to increased viscosity. The solid mass had a lesser effect compared to the gas flow. These findings support efficient reactor operation with minimal resource usage. Research Implications: These insights contribute to a deeper understanding of the transport phenomena that govern catalytic oxidation processes, offering a valuable tool for rational reactor design and scale-up, especially in systems limited by gas-liquid transfer. Moreover, the methodology and results support the development of efficient and cost-effective oxidation systems for applications such as glycerol valorization. Originality/Value: This study presents an integrated analysis of operational parameters affecting gas-liquid mass transfer in a slurry reactor. Using a dynamic and precise method based on in situ oxygen measurements, it accurately quantifies kLa under varying conditions. The approach enables optimized slurry reactors, reducing excess and improving efficiency.

The hydrogenation processing of carbohydrates from wastewaters of processed starch sources was evaluated in the presence of a formulated Ni- Ru/activated carbon catalyst in a slurry reactor under H2 pressure and heat fed by a solar thermal system. Heat transfer to the reactor via thermal fluid flowing through a thermal solar system allowed operations at temperatures of 453 K, 473 K and 493 K, where saccharide hydrogenolysis predominated. The experimental data were interpreted by the reaction mechanism involving the solid phases of the catalyst, including activated carbon, Ni and Ru. Fast hydrolysis and hydrogenation were considered and the hydrogenolysis on C-C and C-O bonds of starch-derived oligosaccharides exerted control. The effects compatible with the kinetic-operational development allowed estimation of the specific reaction rates of the reaction steps involving the production of polyols and glycol.

Macroalgae are a natural oceanic resource of inexhaustible abundance for the biomass energy industry with growth rates that are three to four times greater than those of terrestrial plants. The objective of this study was to evaluate the sustainability of macroalgae as biomass for biorefining through two investigations. Firstly, the deposition of macroalgae was sampled through 28 collections on seven beaches in the city of Maceió, Brazil, over a two-year period using a zigzag sampling method, covering a deposition area of 135,000 m². From this, it was estimated that daily collection would yield 5.03 t/ha of dry biomass. Secondly, the calorific values of macroalgal biomass energy and pellet compounds were calculated. The lower calorific value (8.82 MJ/kg) found from a compound of 13 species analyzed was similar to that of the main biomass used in Brazil to obtain energy, i.e., sugarcane bagasse, which has been evaluated as 8.91 MJ/kg. Macroalgal biomass in the form of condensed energy pellets was found to have a higher calorific value of 20.18 MJ/kg, i.e., 1.2% greater than the average for terrestrial biomass pellets. Based on the results obtained, it was observed that macroalgal biomass has the possibility of becoming a new renewable feedstock with potential for bioenergy. The estimates for the deposition of biomass show possibilities for producing biofuels from marine algal raw material, which provides scope for creating another sustainable alternative for global energy issues with a reduction in environmental problems.

The reforming of methane with CO₂ was carried out efficiently in a fluidized bed reactor at 973 K under atmospheric pressure, taking advantage of the nickel catalyst efficiency achieved with a bed of particulate fines. The fluidization operation was characterized by determining a minimum velocity of 3.11 × 10⁻³ ms⁻¹ and higher velocities. The reactor worked with surface speeds of up to 1.84 × 10⁻² ms⁻¹, providing conversions from 45% to 51% and a syngas yield of 97%. The control base of the operation focused on the use of CO₂ was established through the reaction steps assumed for the process, including methane cracking, reverse Boudouard reaction, and RWGS (reverse reaction of water gas-shift). The reactor designed to operate in two zones was able to simultaneously process surface reactions and catalyst regeneration using feed with 50% excess CO₂ in relation to methane. Predictions indicating the production of syngas of different compositions quantified with the H₂/CO ratio from 2.30 to 0.91 decreasing with space-time were validated with the results available for process design.

The effects of mass transfer were quantified for the effective performance of mixtures between partially miscible phases, or for the promotion of their separations. To consolidate the analysis of heterogeneous liquid–liquid processes, variations in the composition of the liquid phases over the evolution of contact operations were considered, detailing the physical mechanisms involved in the mixtures of oil (soy, sunflower) and alcohol (methanol, ethanol), and in the separation between biodiesel and glycerin. Based on experimental evaluations, the average distribution coefficients for triglycerides (oil-alcohol) and glycerol (biodiesel-glycerin) were estimated at 1.31 and 1.46, and 3.42 × 10−2 and 4.06 × 10–2, for soybean and sunflower, respectively, while their mass transfer coefficients, depending on their concentration ranges in the phase, varied in orders of magnitude from 10−2 s−1 to 10–4 s−1. Including the values of the physical parameters, a heterogeneous model for the alkaline transesterification of soybean oil (methanol, ethanol, NaOH, 25°C, 40°C, 60°C, 600 rpm) was validated.

A comparative evaluation of alternative methane reforming processes as an option to steam reforming was performed by carrying out simulations of operations in a fixed bed reactor with a Ni (4.8 wt.%/γ-Al₂O₃) catalyst at 1023 K under 1.0 bar. Methane reforms, including processing with carbon dioxide (DRM, CH₄/CO₂), autothermal reform (ATRM, CH_4/H₂O/O₂), and combined reform (CRM, CH₄/CO₂/H₂O/O₂) had their operations predicted based on experimental data developed to represent their kinetic behavior, formalized with mechanisms and parametric quantifications. The performance of fixed bed reactor operations for methane conversions occurred with different reaction rates in the three alternative processes, and comparatively the orders of magnitude were 10², 10⁻¹, and 10⁻⁴ in CRM, ATRM, and DRM, respectively. According to each process, the methane conversions were oriented towards the predominant productions of hydrogen or carbon monoxide, indicating the kinetic selectivities of H₂, 86.1% and CO, 59.2% in CRM and DRM, respectively. Considering the possibility of catalyst deactivation by carbon deposition, its predicted yields are low due to the slow stages of its production and due to its simultaneous consumption through interactions with O₂, CO_2, and H₂O, reflecting favorably in additional productions of H₂ and CO.

OPERATIONAL ASSESSMENTS TO IMPROVE THE MONITORING OF PETROLEUM CATALYTIC HYDRODESULFURIZATION PROCESSING

Dry reforming of ethane and propane were carried out with a nickel catalyst (3.92% by weight/γ-Al2O3) to characterize the effects of fed light alkanes on the reforming process of natural gas. Conversions of individual alkanes, representing 74.7% for ethane and 96.0% for propane at 1073 K, promoted hydrogen yields of 43.6% and 66.0%, respectively. The conversion (81%) of a natural gas promoted a 95% hydrogen yield, where about 20% had been obtained from the light alkanes. The reaction steps from alkane dry reforming where hydrogen was produced (alkane cracking) provided carbon formation with a yield of 23%. A kinetics evaluation, based on experimental evidence that indicated two different sets of reaction steps for both ethane and propane processes, enabled the identification of the specific reaction rates of the cracking steps for each alkane. Reaction steps in the reforming process were considered as competitive reactions and the specific cracking reaction rates of both light alkanes were used to quantify the kinetic selectivities of hydrogen, calculated as 95.42% for ethane and 76.99% for propane.