J.M. Encinar

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 automobile tyre waste. Influence of operating variables and kinetics study

Abstract Shredded automobile tyres were pyrolysed in an N2 atmosphere. The compositions and properties of the different fractions were determined over a range of temperatures (350–700°C) and heating rates (5–20 K min−1). Char yields fell and gas yields rose with increasing temperature. The oil fraction yield passed through a maximum at 550–575°C. The decline at higher temperatures was likely due to strong cracking increasing the gas yield. Increasing the heating rate led to similar results to those obtained with temperature. Production from the tyre feedstock was approximately 37–40% char, ∼55% oil and 4–11% gas, with medium higher heating values of 28 MJ kg−1, 39.7 MJ kg−1 and 34 MJ N−1 m−3, respectively. The char had a high fixed-carbon content and could be used to manufacture category-A briquettes. Aliphatic and aromatic hydrocarbons and hydroxyl compounds were the major components of the oil. The gases were identified as H2, CO, CH4, CO2, C2H4 and C2H6. We studied the kinetics of the thermal decomposition of the feedstock using isothermal and non-isothermal thermogravimetric methods at different temperatures (400–600°C) and heating rates (5–50 K min−1). The results indicated that the isothermal pyrolysis process consisted of one stage and the non-isothermal three stages.

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.

Study of biodiesel production from animal fats with high free fatty acid content.

The aim of this work was to obtain biodiesel from animal fats, an inedible feedstock. Three different types of fats were used to produce biodiesel; their main characteristic was high free fatty acid content. Animal fats were transesterified with acid catalyst and basic catalyst with and without pre-esterification. Biodiesel of 89.0 wt.% ester content was obtained by acid-transesterification (9 wt.%H2SO4, 6:1 methanol:fats molar ratio, 60 °C, 48 h). Pre-esterification conditions were studied for different fats and acid catalysts: 0.5 wt.%H2SO4 or 1.0 wt.%p-TsOH, 6:1 methanol:fats molar ratio, 65 °C and 4 h made it possible to obtain fats with acid value less than 0.5% FFA. Pre-treatment was effective for fats with different FFA content. Alkali transesterification of esterified fats resulted in a product with 97.3 wt.% ester content. Biodiesel quality was evaluated and most of properties were well within EN 14214.

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.

Pyrolysis of maize, sunflower, grape and tobacco residues

Pyrolysis of four agricultural residues (maize, sunflower, grape and tobacco) has been carried out in order to quantify their energy content. The main characteristics of the charcoals formed and the nature and quantity of gases produced have been determined. The process was studied batchwise by varying the reaction time (15–60 min) and temperature (400–700°C). Reaction times higher than 30 min do not exert any influence while increasing temperature yields high fixed carbon solids, low volatile content and slight increases in ash. The increase in temperature is specially important to increase the production of gas, mainly hydrogen. From gas composition and proximate analysis, the heating power of gas and solid phases have been determined. A kinetic model of pyrolysis based on gas generation has been accomplished. From this model, rate constants of gas formation at different temperatures and activation energies have also been determined. ©1997 SCI

Henry And Mass Transfer Coefficients In The Ozonation Of Wastewaters

Abstract A procedure for the determination of Henry and mass transfer coefficients in an ozone-industrial wastewater system is presented. The method is applied to the ozonation of a tomato plant industrial wastewater, developed in the slow kinetic regime. In so doing, molar balances of ozone (in gas and water phases) are used together with gas-liquid reaction kinetic theory. While Henrys coefficients obtained are similar to those corresponding to ozonation in organic-free water, significant deviations are observed regarding the mass transfer coefficient.

Azo Dye Ozonation Film Theory Utilization for Kinetic Studies

Abstract The ozonation kinetics of three azo dyes (Direct Yellow 27, Direct Blue 1 and Acid Black 52) in aqueous solution has been studied. Two types of reactors have been used, an agitated tank for studying the influence of variables and the stoichiometry, and an agitated cell for kinetic measurements. Both the film theory and the modes of ozone action on organic matter have been considered for obtaining the kinetic rate constants. A model of ozone absorption in the fast pseudo–m–th ozone order kinetic regime with two parallel reactions fits satisfactorily the experimental results. From it, the kinetic constants of both reactions have been evaluated.

Kinetic Study of the Ozonation of Some Industrial Wastewaters

Abstract Kinetic studies of the ozonation of two wastewaters released by distillery and tomato processing plants have been carried out. Once it has been assumed that an irreversible gas-liquid reaction is developed between ozone and the matter present in the water, the film theory concept was applied to this system for kinetic determinations. The evolution of the organic and inorganic matter with ozonation time has been followed by the chemical oxygen demand. The procedure allows the determination of the rate coefficients of ozone with the wastewaters treated. According to the results obtained, ozone is consumed through fast reactions which take place near the water-gas interface during an initial period. This period is used to determine the rate coefficients. Then, at more advanced ozonation times, the reactions become slower and hence they take place in the bulk of the water, articularly for the case of tomato wastewaters. Values of the rate coefficient allow us to establish both the kinetic regime of a...