S. Román

Conversion of tomato-peel waste into solid fuel by hydrothermal carbonization: Influence of the processing variables.

In this work, the influence of the variables temperature, residence time, and biomass/water ratio on the hydrothermal carbonization (HTC) of tomato peel was investigated. The implementation of a Design of Experiments - Response Surface Methodology approach allowed to identify the importance of each variable, as well as their interactions, in both the reactivity (solid yield) and energy densification (increase in higher heating value). The HTC residence time and specially temperature had a major effect on the process, increasing the solid yield and promoting energy densification. Ratio had a minor effect although under certain temperature and time conditions, it was a decisive parameter. Solid yields in the range 27.6% and 87.7% with corresponding high heating values 23.6-34.6 MJ kg(-1) were obtained. From the statistical processing of the experimental data obtained pseudo-second order models were developed. It was proven that these approaches envisaged the hydrochar final characteristics successfully. From the elemental analysis and the FTIR spectra, it was possible to investigate the HTC pathway, which was defined as a combination of several processes; considering dehydration and decarboxylation reactions and especially lignin depolimerization reactions, which lead to the formation of monomeric radicals. Moreover, the surface morphology of selected hydrochars by Scanning Electron Microscopy (SEM) showed the original structure scaffold, with minor changes between hydrochars prepared under different conditions.

Oxidation of MCPA and 2,4-d by UV Radiation, Ozone, and the Combinations UV/H2O2 and O3/H2O2

Abstract The phenoxyalkyl acid derivative herbicides MCPA (4-chloro 2-methylphenoxyacetic acid) and 2,4-d (2,4-dichlorophenoxyacetic acid) were oxidized in ultrapure water by means of a monochromatic UV irradiation and by ozone, as well as by the combinations UV/H2O2 and O3/H2O2. In the direct photolysis of MCPA, the quantum yield at 20°C was directly evaluated and a value of 0.150 mol Eins−1 was obtained in the pH range 5–9, while a lower value of 0.41 × 10−2 mol Eins−1 was determined at pH = 3. Similarly, for 2,4-d a value of 0.81 × 10−2 mol Eins−1 was deduced, independent of the pH of work. The influence of the additional presence of hydrogen peroxide was established in the combined process UV/H2O2, and the specific contribution of the radical pathway to the global photo-degradation was evaluated. The oxidation by ozone and by the combination O3/H2O2 was also studied, with the determination of the rate constants for the reactions of both herbicides with ozone and hydroxyl radicals at 20°C. These rate constants for the direct reactions with ozone were 47.7 and 21.9 M−1 s−1 for MCPA and 2,4-d respectively, while the found values for the rate constants corresponding to the radical reactions were 6.6 × 109 and 5.1 × 109 M−1 s−1.

Study of the Mechanisms Involved in the Adsorption of Amitriptyline from Aqueous Solution onto Activated Carbons

Two commercial activated carbons (DA and CB) differing in their porosity (one being microporous and the other mesoporous) and in their surface chemistries (one being acidic and the other basic in character) were modified by thermal and oxidizing treatment in order to change their surface properties. The changes induced by these processes were studied by means of ultimate analyses, nitrogen adsorption isotherms measured at −196 °C, mercury porosimetry, FT-IR spectroscopy and determination of their point of zero charge (PZC) values. Subsequently, the adsorption of amitriptyline onto both the pristine and treated carbons was studied at pH values of 3 and 7 and a temperature of 25 °C. The results obtained allowed the possible mechanisms governing the adsorption process to be analyzed in order to optimize the type of adsorbent needed to remove this particular drug from aqueous solution.

Fundamental studies of methyl iodide adsorption in DABCO impregnated activated carbons

Methyl iodide capture from a water vapor stream using 1,4-diazabicyclo[2.2.2]octane (DABCO)-impregnated activated carbons is, for the first time, fundamentally described here on the atomic level by means of both molecular dynamics and grand canonical Monte Carlo simulations. A molecular dynamics annealing strategy was adopted to mimic the DABCO experimental impregnation procedure in a selected slitlike carbon pore. Predictions, restricted to the micropore region, are made about the adsorption isotherms of methyl iodide, water, and nitrogen on both impregnated and bare activated carbon models. Experimental and simulated nitrogen adsorption isotherms are compared for the validation of the impregnation strategy. Selectivity analyses of the preferential adsorption toward methyl iodide over water are also reported. These simulated adsorption isotherms sum up to previous experimental studies to provide an enhanced picture for this adsorption system of widespread use at nuclear plant HVAC facilities for the capture of radioactive iodine compounds.

Control of Several Emissions during Olive Pomace Thermal Degradation

Biomass plays an important role as an energy source, being an interesting alternative to fossil fuels due to its environment-friendly and sustainable characteristics. However, due to the exposure of customers to emissions during biomass heating, evolved pollutants should be taken into account and controlled. Changing raw materials or mixing them with another less pollutant biomass could be a suitable step to reduce pollution. This work studied the thermal behaviour of olive pomace, pyrenean oak and their blends under combustion using thermogravimetric analysis. It was possible to monitor the emissions released during the process by coupling mass spectrometry analysis. The experiments were carried out under non-isothermal conditions at the temperature range 25–750 °C and a heating rate of 20 °C·min−1. The following species were analysed: aromatic compounds (benzene and toluene), sulphur emissions (sulphur dioxide), 1,4-dioxin, hydrochloric acid, carbon dioxide and nitrogen oxides. The results indicated that pollutants were mainly evolved in two different stages, which are related to the thermal degradation steps. Thus, depending on the pollutant and raw material composition, different emission profiles were observed. Furthermore, intensity of the emission profiles was related, in some cases, to the composition of the precursor.

Modelling the Adsorption of p-Nitrophenol by the Boyd Method in Conjunction with the Finite Element Method

Adsorption kinetics are often studied by non-dimensional models that allow a good fitting of the experimental data. Nevertheless, their physical interpretation is very limited because the particle geometry is not considered. In this work, the adsorption kinetics of p-nitrophenol onto two commercial activated carbons with different textural and geometrical characteristics was studied. For this purpose, two types of models were used: zero-dimensional models which do not take the system geometry into account; and the Boyd model, which takes the shape of the adsorbent molecule into account. In contrast to previous published works, the Boyd model was solved by means of the finite element method using the commercial software COMSOL. This paper provides a new insight into the modelling of adsorption kinetics when non-spherical adsorbents are employed.

Towards sustainable micro-pollutants’ removal from wastewaters: caffeine solubility, self-diffusion and adsorption studies from aqueous solutions into hydrochars

ABSTRACT Hydrochars obtained via hydrothermal carbonisation of pistachio shells are both a sustainable and an efficient alternative to commercial activated carbons for the removal of micro-pollutants from wastewaters that are difficult to handle by conventional treatments. Here a combined experimental and molecular simulation approach is adopted for the study of the caffeine/hydrochars aqueous systems. This case study serves to tune a general framework for the rational customisation of surface functional groups on hydrochars for the selective adsorption of micro-pollutants from wastewaters. Caffeine’s solubility, self-diffusion and adsorption results from aqueous solutions at relevant conditions are presented. Insights about the role of surface functional groups over the caffeine adsorption mechanism into hydrochars are gained and discussed. GRAPHICAL ABSTRACT

Homogeneous Diffusion Solid Model as a Realistic Approach to Describe Adsorption onto Materials with Different Geometries

In this work, the adsorption kinetics of p-nitrophenol (PNP) onto several commercial activated carbons (ACs) with different textural and geometrical characteristics was studied. For this aim, a homogeneous diffusion solid model (HDSM) was used, which does take the adsorbent shape into account. The HDSM was solved by means of the finite element method (FEM) using the commercial software COMSOL. The different kinetic patterns observed in the experiments carried out can be described by the developed model, which shows that the sharp drop of adsorption rate observed in some samples is caused by the formation of a concentration wave. The model allows one to visualize the changes in concentration taking place in both liquid and solid phases, which enables us to link the kinetic behaviour with the main features of the carbon samples.