Francisco Sobrón

Modeling of biomass fractionation in a lab-scale biorefinery: Solubilization of hemicellulose and cellulose from holm oak wood using subcritical water.

Lignocellulose fractionation is a key biorefinery process that need to be understood. In this work, a comprehensive study on hydrothermal-fractionation of holm oak in a semi-continuous system was conducted. The aim was to develop a physicochemical model in order to reproduce the role of temperature and water flow over the products composition. The experiments involved two sets: at constant flow (6mL/min) and two different ranges of temperature (140-180 and 240-280°C) and at a constant temperature range (180-260°C) and different flows: 11.0, 15.0 and 27.9mL/min. From the results, temperature has main influence and flow effect was observed only if soluble compounds were produced. The kinetic model was validated against experimental data, reproducing the total organic carbon profile (e.g. deviation of 33%) and the physicochemical phenomena observed in the process. In the model, it was also considered the variations of molecular weight of each biopolymer, successfully reproducing the biomass cleaving.

Hydrothermal hydrolysis of grape seeds to produce bio-oil

In the present work, the hydrothermal hydrolysis of grape seeds focused on the production of bio-oil was studied. The grape seeds composition in terms of lignin, sugars, ash, extractives and bio-oil was determined. The composition of grape seeds was: 17.0 wt% of extractives; 36.8 wt% of sugars (hemicellulose and cellulose); 43.8 wt% of lignin and 2.4 wt% of ash. The grape seeds were hydrothermally treated using three different temperatures: 250 °C, 300 °C and 340 °C employing a semi-continuous reactor. The solid residue varied from 25.6–35.8 wt% depending on the hydrolysis temperature. The maximum yields of light (15.7 wt%) and heavy bio-oil (16.2 wt%) were achieved at 340 °C. The Arrhenius parameters for the kinetics of grape seeds hydrolysis in our system were k0 = 0.995 g min−1 and Ea = 13.8 kJ mol−1. The increment of the flow rate favoured the mass transfer in the system and so, the hydrolysis rate. However, the maximum hydrolysis rate was found at a water surface velocity of 2.3 cm min−1.

Model-based measurements of diffusion of sulfuric acid into water using Raman spectroscopy.

The diffusion of molecular species within a sulfuric acid–water system has been monitored by Raman spectroscopy, a thermodynamic-chemical model of the mass transport properties of the species has been established, and its parameters optimized. It has been shown that the non-ideality of this multicomponent system plays a crucial role in its mass transport properties, which have been explained in terms of a diffusion model for the molecular species. The individual effective diffusion coefficients are not constant (characteristic of ideal systems) but are a function of the concentration of the species in solution. The model has been conceived in such a way that it can be adapted to any multicomponent mixture when the equilibriums among the ions are known. Raman spectroscopy provides the means to derive the speciation and concentration of species in multicomponent systems, and we have shown that the model-based measurement of the diffusion properties using Raman is a robust and accurate technique that allows for measuring the individual diffusion coefficients of the species in the mentioned system.

In-situ Raman analysis of the precipitation sequence of sulphate minerals using small droplets: application to Rio Tinto (Spain)

Raman spectroscopy has been used for a comparative study of the sulphates mineral sequence precipitation in Rio Tinto (Huelva, Spain) under natural and laboratory conditions. In natural conditions spectra were performed in-situ with portable instruments. In laboratory, spectra were performed using a simulator of the riverbank conditions and also small droplets of liquid on different substrates. The capability of the micro-Raman spectroscopy to detect in a fast and reliable way the mineral phases at the mineral grain scale allow a precise identification of these phases as function of time. The use of small droplets increases this capability reducing the experimental time and allowing reproducing the process under greater supersaturation conditions. Finally, a series of computer modeling algorithms have been developed to compare the experimental process with the theory based on the equilibrium properties of the solutions and precipitation kinetics.