J.F. González

Fixed-bed pyrolysis of Cynara cardunculus L. Product yields and compositions

The pyrolysis of Cynara cardunculus L. was studied with the aim of determining the main characteristics of the charcoal formed and the nature and quantity of gases produced. Variables investigated were temperatures between 300°C and 800°C, particle sizes between 0.4 and 2 mm diameter, initial sample weights between 2.5 and 10 g, and nitrogen flow rates between 100 and 300 cm3/min. Experiments were carried out isothermally. Under the conditions of this study, particle size, nitrogen flow rate, and initial sample weight generally did not exert any influence, whereas temperature was very significant. An increase in this variable led to an increase in the fixed carbon content, gases produced and, to a lesser extent, ash percentage. On the other hand, volatile matter and solid yields decreased with increasing temperature. The principal gases generated were H2, CH4, CO and CO2. Heating values of both gas and solid phases were determined from gas composition and elemental analysis. The quality of charcoals and heating value allow the conclusion that the optimal temperature for pyrolysis should be between 600°C and 700°C. Finally, a kinetic study of the pyrolysis, based on gas generation from thermal decomposition of the residue, was carried out. From this model, rate constants for the formation of each gas and their corresponding activation energies were determined.

Pyrolysis of two agricultural residues: Olive and grape bagasse. Influence of particle size and temperature

The pyrolysis of olive and grape bagasse has been studied with the aim of determining the main characteristics of the charcoals formed and the nature and quantity of gases and liquids produced. Variables investigated were temperature between 300 and 900°C and particle size between 0.4 and 2 mm diameter. Experiments were carried out in an isothermal manner. As a general rule, particle size does not exert any influence, whereas temperature is a very significant variable. Thus an increase in this variable yields an increase in the fixed carbon content, gases produced and, to a lesser extent, ash percentage. On the other hand, volatile material and solid yields decrease with increasing temperature. The principal gases generated are H2, CH4, CO and CO2, while among the liquid components the presence of methanol, acetone, furfuryl alcohol, phenol, furfural, naphthalene and o-cresol has to be highlighted. Heating values of both gas and solid phases were determined from gas composition and elemental carbon analysis. The quality of charcoals and heating value allow the conclusion that the most convenient temperature for the pyrolysis should be between 600 and 700°C, at which the production of liquids is at its maximum. Finally, a kinetic study of the pyrolysis, based on gas generation from thermal decomposition of residues, has been carried out. From this model, rate constants for the formation of each gas and their corresponding activation energies were determined.

Pyrolysis/gasification of agricultural residues by carbon dioxide in the presence of different additives: influence of variables

Pyrolysis/gasification of grape and olive bagasse by CO2 under different experimental conditions has been studied. Variables investigated were particle size, temperature, type and concentration of additive and chemical washing with sulfuric and phosphoric acid solutions. Compounds like H2, CH4, CO and methanol, acetone, furfuryl alcohol, furfural, naphthalene, phenol and o-cresol were identified as components of gas and liquid fractions obtained from pyrolysis/gasification processes. Particle size had no influence, while temperature was a significant variable yielding increases of fixed carbon and gas content. In most of cases, a temperature between 600 to 700°C lead to a maximum liquid production. The principal additive used was ZnCl2, concentration of this salt exerted a positive effect on hydrogen production, about 5 to 8 times higher than that obtained in the absence of additive. As far as structural characteristics of activated carbon are concerned, the increase of temperature, ZnCl2 and acid solution concentrations (during chemical washing) lead to an increase of the specific surface area.

Steam gasification of Cynara cardunculus L. : influence of variables

A study of the steam gasification of Cynara cardunculus L. was carried out in order to characterise the gas phase with a view to its energy use, analysing the influence of water partial pressure, particle size, and temperature. The main gases generated were H2, CH4, CO, and CO2, with a higher heating value between 10 and 11 MJ/N m3. The gas in greatest proportion was H2; that in the smallest proportion was methane, which was pyrolytic in origin. Within the range of variables studied, the particle size had no significant effect on the process. Temperature and water partial pressure exerted positive effects on the main parameters of the process, increasing the reaction rate, the gas yield and production, the conversion and the energy generated per kilogram of initial residue (Cynara). The experimental results show that the water–gas shift reaction is the main determinant of the composition of the gases. For this reaction, an increase in temperature leads to a greater formation of CO, and an increase in water partial pressure to a greater formation of CO2. The energy yield of the gasification process presented values between 0.5 and 0.85. Temperature and water partial pressure had a positive effect on this parameter.

Thermodynamic characterization of a regenerated activated carbon surface

Calorimetric measurements of the immersion enthalpy in different liquids of a set of regenerated activated carbons have been employed to analyze the effect of a regeneration process on the extension of the accessible surface area and the hydrophobic character of the carbons by comparison with the original carbon. The modifications in the hydrophobicity of the activated carbons are quantified by the analysis of the surface free energy of the solids and its dispersion and non-dispersion components. It has been found that regeneration treatment of the original carbon increases its accessible surface area and hydrophobicity. However, the opposite effects take place when regeneration is done on the same carbon previously saturated with p-nitrophenol (PNP) or p-chlorophenol (PClP).

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.

Solar Radiation Map of Extremadura from Other Weather Data

Abstract In a previous work, we have found correlation expressions that permit to estimate the mean monthly values of daily diffuse and direct solar irradiation on a horizontal surface in function of some weather parameters. In this work, the incident radiation on a horizontal surface has been estimated in thirty zones of Extremadura by means of weather data from existing stations located in these zones and its orography. The weather data used have been the monthly average values of the highest temperatures and the sunshine fraction. These monthly average values have been obtained from measurements carried out in the weather stations during the period 1985-2002. The results are presented as interactive maps in Arcview language, associated to a conventional data base.