Juan 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 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.

Industrial wastewater advanced oxidation. Part 2. Ozone combined with hydrogen peroxide or UV radiation

The oxidation of two wastewaters with ozone combined with hydrogen peroxide or UV radiation (254 nm) has been studied. The oxidation yields of these systems were compared with those from ozonation alone at similar experimental conditions. It was found that O3H2O2 oxidation leads to important increases in COD degradation rate (i.e. 86% at pH 6 in tomato wastewaters). The differences between the oxidation types (O3 and O3H2O2) diminish with increase in pH. With distillery wastewaters the presence of hydrogen peroxide hardly increases the oxidation rate. However, the combination of O3UV radiation was the best oxidation method applied because of the improvements achieved in both COD and TOC disappearance rates compared to those of ozonation alone, regardless of wastewater type treated. As happened with other oxidation systems, the COD and TOC reductions were higher in tomato wastewater oxidation. Different kinetic parameters were also determined in order to quantify the reactivity of wastewaters towards the oxidation systems applied.

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.

Industrial wastewater advanced oxidation. Part 1. UV radiation in the presence and absence of hydrogen peroxide

The oxidation of two wastewaters collected from distillery and tomato processing plants with UV radiation (254 nm) alone and combined with hydrogen peroxide has been investigated. Distillery wastewaters are refractory to UV radiation but the presence of hydrogen peroxide leads to different COD reductions which indicates that the process is mainly due to the action of radicals. Tomato wastewaters, on the other hand, show a higher reactivity even with UV radiation alone. The quantum yield for tomato wastewaters with an initial COD of 930 mg O2l−1 was found to be 0.7 mol O2 photon−1 and decreased with reaction time. The combined effect of UV radiation and hydrogen peroxide at a 0.01 M concentration on tomato wastewaters leads to about 25% COD reduction while TOC was unchanged. The contribution of radical reactions in this process was higher than 60%.

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

Improvement of domestic wastewater primary sedimentation through ozonation

Abstract The use of ozone as an aid for flocculation‐coagulation of domestic wastewaters has been studied. Jar tests of ozonated and non‐ozonated wastewater at different coagulant (hydrated aluminum and ferrous sulfate salts) and flocculant (calcium hydroxide and A‐201 polyelectrolyte) doses have been conducted to obtain optimum floc size. Settling experiments have then been carried out to follow changes of total COD conversion and surface area of a primary settling tank needed to reach a given percentage particle separation. The results show that the use of preozonation provides beneficial results to both improve COD conversion and reduce the sedimentation surface area.

Catalyzed gasification of active carbon by oxygen: influence of catalyst type, temperature, oxygen partial pressure and particle size

A thermogravimetric study of the oxygen gasification of a commercial active carbon using Co, Ni and Cu as catalysts has been carried out. This follows a previous study of the influence of the particle size, gas volumetric flow rate, initial sample weight temperature and oxygen partial pressure an non-catalytic gasification. The results show that for T   50 cm3 min−1 and Mo   Cu > Ni. A kinetic study applied to both types of gasification has allowed the activation energy and the reaction order with respect to oxygen and the catalyst to be determined. In all cases both the activation energy and the Arrhenius pre-exponential factor are lower in the catalytic gasification. This brings about the existence of an isokinetic point for the catalytic and the non-catalytic processes, which were also determined. © 2000 Society of Chemical Industry