José P.S. Aniceto

Biomass‐Based Polyols through Oxypropylation Reaction

Biomass residues are a potential renewable source for the sustainable production of chemicals, materials, fuels, and energy embodying the so-called biorefinery concept. In this context, agro-forestry and agro-food industry by-products have attracted considerable interest of researchers in academia and industry as a renewable source of polymeric materials. The research developed to date on the valorization of biomass residues by converting them into polyols through oxypropylation is the subject of this review. These bio-based polyols exhibit properties similar to their petrochemical counterparts and, as such, can be used with economical advantage in the production of polyurethanes. The operating conditions of the oxypropylation reaction depend on the biomass and on the desired polyol properties. The discussion of their influence and the economic viability of the process are also presented.

Removal of Anionic Pollutants from Waters and Wastewaters and Materials Perspective for Their Selective Sorption

The presence of some anionic species, such as nitrate, nitrite, chloride, sulfide, fluoride, and cyanide, in water supplies may represent a serious environmental problem. In this work, the main sources and harmful effects of their bioaccumulation on living organisms are reviewed, as well as the most adopted technologies for their uptake. The major advantages and disadvantages of each methodology are also listed. In general, ion-exchange has been elucidated as the most suitable removal process. In view of that the most promising materials used to remove anionic pollutants from aqueous solutions are highlighted in this review. In particular, the major efforts towards the development of low-cost and easily available effective sorbents for water decontamination are covered. For instance, natural waste solid materials and derivatives have emerged as promising low-cost exchangers for selective anions uptake. Besides, a number of structural modifications including the introduction of more suitable surface functional groups or compensation species into the sorbent matrix have been investigated in order to enhance sorbents selectivity and capacity for anionic pollutants. The influence of speciation and removal conditions is also focused.

Simulated Moving Bed Strategies and Designs: From Established Systems to the Latest Developments

The simulated moving bed (SMB) technology has evolved significantly since its inception. The appearance of several variants to conventional SMB has led to better performance in productivity and product purity, and lower operating costs, thus creating new opportunities for different applications. This trend is clearly visible in the increasing number of papers and patents published in this field in recent years. This review aims to gather and discuss several modifications and operation modes that have been proposed, from the most well-known Varicol and PowerFeed to the latest Intermittent-SMB and variable external stream systems, giving particular emphasis to innovations and applications of each SMB strategy. SMB valve designs are also covered in this article for their importance in the application of the operation modes discussed, which require ever more flexible units capable of variable switch times, column expandability, zone bypasses, and reduced solvent consumption while still avoiding contamination through line sharing.

Modelling ion exchange kinetics in zeolyte-type materials using Maxwell-Stefan approach

AbstractIn this essay, the Maxwell-Stefan (MS) formalism was adopted to model the removal of cadmium(II) and mercury(II) ions from aqueous solutions using microporous titanosilicate ETS-4. The embodied transport mechanism is surface diffusion, since the small pore diameters of such zeolite-type materials imply that counter ions never escape from the force field of the matrix co-ions, mainly owing to the strong and long range electrostatic interactions. The parameters of the global model are the MS diffusivities of ion–ion and ion–solid pairs, and a convective mass transfer coefficient. The average absolute relative deviations (AARD) achieved for Cd2+/Na+/ETS-4 and Hg2+/Na+/ETS-4 systems were only 3.47 and 7.34%, respectively. The model calculates concentration profiles and their evolution along time under transient regime, being able to represent the initial steep branches of removal curves and subsequent transition to equilibrium, where kinetic curves are frequently very difficult to fit. The well-known ...

Maxwell–Stefan based modelling of ion exchange systems containing common species (Cd2+, Na+) and distinct sorbents (ETS-4, ETS-10)

Cadmium(II) is a toxic hazardous cation, whose presence in the environment causes great concern because of its bioaccumulation in organisms and bioamplification along food chain. Hence, the removal of cadmium compounds from industrial waters and wastewaters is particularly essential, which requires intensive experimental and modelling studies to deal with the problem. In this work, the ion exchange of Cd2+ ions from aqueous solution using microporous titanosilicates (ETS-4 and ETS-10) has been modelled using adapted Maxwell–Stefan equations for the ions transport inside the sorbent particles. The fundamentals of the Maxwell–Stefan equations along with correlations for the convective mass transfer coefficients have been used with advantage to reduce the number of model parameters. In the whole, the model was able to represent successfully the kinetic behaviour of 11 independent and very distinct curves of both studied systems (Cd2+/Na+/ETS-4 and Cd2+/Na+/ETS-10). The predictive capability of the model has been also shown, since several uptake curves were accurately predicted with parameters fitted previously to different sets of experimental data.