Environment, Reaction, Separation and Thermodynamics Group (GERST)

The research work developed under the general domain of chemical reaction engineering covers heterogeneous catalysis to the analysis of multiphase reactors, through the preparation and characterization of solid catalysts and functionalized polymeric materials. Fixed-bed, trickle-bed, bubble column, and slurry reactors have been analyzed under continuous, batch, or semi-batch operation within a large spectrum of reactive systems.

Steady-state and transient behavior of fixed-beds systems has been extensively addressed through simulation studies. Temperature runaway, multiplicity, and wrong-way behavior have been analyzed with pseudo-homogeneous and heterogeneous models including the intraparticle convection phenomenon. Multiscale design and integrated development of environmentally-based catalytic processes aiming at the design of multiphase reactive systems for the tailored application of high-performance environmental cleaning technologies have been using advanced Computational Fluid Dynamics (CFD) frameworks.

Environmental preservation regarding chemical treatment for gas and liquid effluents focuses our research on Advanced Oxidation Processes (AOPs), aiming the integration of different technologies mainly supported on heterogeneous catalysis as wet oxidation, ozonation, Fenton, photochemical processes (photo-Fenton, Photocatalysis) and electrochemical. Our spin-off company Adventech (http://www.adventech-group.com/) has been responsible for the in-situ application of our laboratorial research embracing a large spectrum of technologies.

The development of sustainable strategies to recover resources (nutrients, energy, water) from wastewater is a natural follow-up in our research group. Energy recovery from high organic-charged liquid effluents through biogas production in anaerobic systems has been considered. Bioaugmentation techniques will be investigated aiming at the development of specialized microorganisms to improve the digester robustness. In cooperation with our spin-off company, Adventech, it is our goal to integrate anaerobic digestion with steam reforming leading to renewable hydrogen production from biogas to be applied in fuel cells.

Experimental work has been performed to gather basic information useful for the design of industrial fixed-bed systems, through the determination of equilibrium isotherms and kinetic studies. Suitable mathematical models has been successfully applied for studying the dynamics of the processes in fixed bed. Some applications have included ion exchange with cyclic pH change for the recovery of biotechnological products (amino acids; proteins) and the recovery of valuable metals from effluents using low-cost adsorbents. Future research will be directed towards the recovery of precious metals (gold, silver, palladium, neodymium, etc.) from e-waste leachates.

The work carried out in this area has been focused on the application of commercial and synthesized ultra and nanofiltration membranes for the recovery of value-added compounds from aqueous streams. Mixed matrix membranes functionalized with inorganic nanoparticles, prepared by the inversion phase technique, have been used for the fractionation of kraft black liquor into hemicelluloses and lignin, as well as for the recovery of valuable phenolic compounds. The performance of these membranes is evaluated by subjecting them to different operating conditions in filtration units operated in dead-end and cross-flow modes. Different modeling approaches were adopted to describe the membrane fouling phenomena, for optimization and scaling purposes.

Seawater desalination by reverse osmosis and a hybrid ion exchange/nanofiltration system were addressed through experimental and computational work. In the past, the operating conditions of the Porto Santo desalination plant were assessed. Future research will include evaluating the energy consumption of seawater reverse osmosis desalination plants and the integration of processes (nanofiltration, ion exchange, and bipolar electrodialysis) for brine valorization in the context of the circular economy.

Carbon dioxide sequestration by mineral carbonation was developed in cooperation with Åbo Akademi University in Finland. Experimental work was carried out on the extraction of magnesium from silicate rocks (serpentinite) with ammonium sulfate. Furthermore, simulation studies using Aspen software to optimize the energy consumption of the overall process (solvent extraction/carbonation) were also performed. Studies focusing on CO2 separation using mixed matrix membranes functionalized with zeolites and ionic liquids, and mineral carbonation using alkaline industrial waste have been developed recently.

The waste management, recycling, and valorization of waste have been considered priority routes based on circular economy and biorefinery strategies. Recycle/valorization of inorganic waste (e.g. fly ashes, bottom ash, dregs from pulp mill, egg-shell, etc) has been addressed in ceramic materials and geotechnical applications. In specific situations, the treatment of solidification/stabilization has been applied to improve safety in disposal in landfills. Low-cost adsorbents have been applied to uptake phosphorus from urban wastewater. HP 14 (ecotoxicity) of diverse waste has been determined. In the case of organic biowaste, extraction of value-added compounds, followed by bioenergy recovery and biofertilizer production have been studied. The management of waste lubricant oil has been investigated, mainly based on regeneration processes for producing base oil.

Anaerobic digestion in reactors at the lab scale has been addressed, for evaluating the biochemical methane potential (BMP) of diverse agro-wastes (tomato, winery, potato peel, municipal biowaste, etc.). Advanced strategies based on Near-infrared (NIR) spectroscopy have been applied for predicting BMP. Composting studies have been performed in a pilot plant located in our laboratory (self-heating reactors), where compositions involving diverse materials have been tested. The characterization analysis comprises raw material, along the process (monitoring), and also the finished composts, demonstrating their stability and maturity. The mathematical modeling of the processes has also been considered to optimize the operating conditions.

LCA methodology has been used to identify and qualify the environmental performance of a process or a product from “cradle to grave”, involving goal and scope definition, life cycle inventory analysis, life cycle impact assessment, and life cycle interpretation. This analysis has been performed through specific software (e.g. Simapro) to quantify the effect on the environment. The case studies involved not only residues (e.g. fly ashes into lightweight aggregates) but also Higher Education Institutions (HEIs), namely the University of Coimbra.

Soil remediation has been addressed for soil contaminated with PCB or heavy metals. For heavy metals, the remediation entails mainly their stabilization with calcium-rich composts (obtained by composting processes). The development of biofertilizers is in progress to restore organic-poor soil and close the carbon loop as well as to enrich the soil with nutrients recovered from wastewater.

The effect of association between solute/solvent molecules in the solubility is studied, at least in a semiquantitative way. There are few systematic studies of the effect of chemical forces on gas solubility, primarily because of the inherent difficulty of characterize these forces in a quantitative way. An automated apparatus was used to measure the solubilities of some HFCs, (CH₃F, CH₂F₂, CHF₃) and methyl halides (CH₃Cl and CH₃Br) in lower alcohols, aromatic solvents and in ionic liquids; the solubility of H₂S in ionic liquids (ILs) and in Deep Eutectic Solvents (DES) within the temperature range ≈ (285, 318]) K, at atmospheric pressure. The experimental data is treated by the chemical solution theory which accounts for the additional chemical equilibrium in the liquid phase to the conventional vapour-liquid equilibrium. Correlations between Henry´s constants and some chemical characteristic of the solvent are developed. The solubility data of the mentioned gases in the studied solvents were correlated with the Cubic Plus Association Equation of State CPA EoS, which incorporates an association term, and it was used the regular-solution theory as the basis to build an empirical model whose parameters are obtained through least-squares fitting of experimental values.

Purification of biodiesel is a critical processing step that requires continuous improvement to meet international standards. Thus, new biodiesel purification methods is an ongoing matter to be continued. The use of membranes will be studied for the removing of impurities as free glycerol and soaps as well as the use of deep eutectic solvents (DES) for extracting soaps, glycerol and residual catalyst.

Proteins are the most complex biological macromolecules abundant in living systems, with crucial functions in all biological processes. The identification of the factors that regulate protein stability is still a puzzle to be solved, with important biotechnological and biomedical applications. One of the strategies used to stabilize proteins is to modulate their environment. In this context, ionic liquids (ILs) and some salts have enormous potential compared to solvents toxic and volatile organics currently used. ILs and salts can promote the stability of proteins in the native state, induce their unfolding or accelerate folding processes. Thus, a program was recently started to evaluate the effect of these substances on the stability and structure of proteins (lysozyme and albumin). The work plan includes the evaluation of the variation in the density of aqueous protein solutions (via a vibrating tube densimeter), when subjected to thermal denaturation (298 to 373 K), at atmospheric pressure, and in the presence and absence of various concentrations of IL or salts. The measures of density will allow to determine the apparent molar volume of proteins, as a function of temperature and concentration of protein and IL (or salt), and consequently, the molar volume the infinite dilution of the protein. The results will allow to interpret chemically and physically the conformational change of proteins along the denaturing/folding process, especially those effects that involve the interaction of specific atoms of the protein with the water of hydration, in the presence and absence of IL/salt.

Additionally, the application of fluorescence methods, circular dichroism (CD), nuclear magnetic resonance (NMR), in protein-IL systems, will bring knowledge about the kinetics, thermodynamics and conformational changes that govern the structure of proteins as well as their folding, unfolding and refolding processes.

Various bacteria and viruses were being object of epidemiological studies on human population as well as their impact on different environment. Identifying a strong population infection by these microorganisms, this research highlights the water courses contamination with such biological pollutants, joining, this way, the general aim of assessing water quality and public welfare.

Bacteria are ubiquitous and can be found in many environments as active participants in those habitats or as contaminants and infectious agents. In this assumption and considering the concept of One Health, it is important to understand the presence of these bacteria in different environments, namely human, water, soil and wastewater.

Viruses were being object of epidemiological studies on human population as well as their impact on different environments. Identifying a high prevalence of infection by these microorganisms, highlights the water courses contamination with such biological pollutants, joining, this way, the general aim of assessing water quality and public welfare.