E. Fuente

Reactivity of pyrolyzed sewage sludge in air and CO2

Abstract Pyrolysis is currently being considered as an alternative method of treating sewage sludge. It yields residual oils and gases, which can be used as fuels, and a solid which can either be burned or physically activated with air or CO 2 . The aim of this work was to study the influence of different pyrolysis conditions (e.g. temperature and heating rate) on the reactivity in air and in CO 2 of carbonaceous materials obtained from these types of residues. An anaerobic sewage sludge produced in a Spanish urban waste water treatment plant, containing 5 wt.% moisture after air-drying, was pyrolyzed in an electrical laboratory furnace under different pyrolysis conditions. Non-isothermal reactivities (up to 1100°C) in air and in CO 2 of the carbonaceous materials obtained after pyrolysis were performed in a thermobalance. The TG and DTG curves obtained from these experiments are discussed.

Conventional and microwave pyrolysis of a macroalgae waste from the Agar–Agar industry. Prospects for bio-fuel production

A comparative study of the pyrolysis of a macroalgae industrial solid waste (algae meal) in an electrical conventional furnace and in a microwave furnace has been carried out. It was found that the chars obtained from both pyrolyses are similar and show good properties for performing as a solid bio-fuel and as a precursor of activated carbon. Bio-oils from conventional pyrolysis have a greater number of phenolic, pyrrole and alkane compounds whereas benzene and pyridine compounds are more predominant in microwave pyrolysis with a major presence of light compounds. The bio-gas fraction from microwave pyrolysis presents a much higher syngas content (H2+CO), and a lower CO2 and CH4 proportion than that obtained by conventional pyrolysis. Yields are similar for both treatments with a slightly higher gas yield in the case of microwave pyrolysis due to the fact that microwave heating favors heterogeneous reactions between the gases and the char.

Analysis of coal tar pitch : relations between thermal behaviour and composition

This paper discusses the influence of pitch composition on its thermal behaviour. The value of the approach consisting in the characterization of these materials by analysis of their volatile fraction is demonstrated. The pyrolysis of nine coal tar pitches was studied by thermogravimetric analysis (t.g.a.) and derivative thermogravimetry (d.t.g.). The coke yield was closely related to both the rate of weight loss and the temperatures at which the d.t.g. curve reached maxima. To obtain information about the influence of the structures present in pitches on their thermal behaviour, the composition of the volatile fraction (evaluated by gas chromatography) was considered. The degree of condensation and the relative proportions of the different kinds of polycyclic aromatic hydrocarbons in this fraction were related to important thermal parameters deduced through t.g.a. and d.t.g. High coke yields are associated with a highly condensed volatile fraction in which alternant peri-condensed polycyclic aromatic hydrocarbons predominate over non-alternant systems.

Reactivity of pyrolysis chars related to precursor coal chemistry

Abstract Changes in the air reactivity of sets of chars obtained from pyrolysis of five coals were determined. The effect of coal rank and pre-oxidation was assessed. The reactivities of the chars were determined by isothermal thermogravimetric methods performed at 500°C, temperature at which the reaction of chars with oxygen is kinetically controlled. The values of maximum reactivity, R max , the reactivity at various conversions, R X , the semi-reaction time, t 0.5 , and the reaction time, t 0.9 , were evaluated. Chars from high-rank coals showed lower reactivities and longer reaction times. Char reactivity increased with an increase in the pre-oxidation; the higher the O/C ratio of precursor coal, the higher the reactivity of the correspondent char. The presence of oxygen-containing groups in precursor coal is likely a key factor in char reactivity, related to the carbon active sites formed after decomposition of C(O) complexes during coal pyrolysis. Pre-oxidation caused an increase in the rate of heat flow during the reaction of chars. However, differential thermal analyses indicated that the calorific values of the chars are similar, regardless of rank and oxidation of precursor coals. Thus, the main factor responsible for the loss of calorific value of coals as a consequence of oxidation is the decrease in the energy produced from the burning of the volatile matter and not from the residual char.

Pyrolytic behaviour of Spanish oil shales and their kerogens

Abstract A comparative study of the thermal behaviour of selected Spanish oil and their kerogen concentrates has been carried out. The oil shales differ in geological age, depositional environment, source location and degree of maturity. The influence of the amount and composition of mineral matter in the thermal behaviour of the oil shales and its influence on the amount of hydrocarbons released has been assessed. In mineral matter-rich samples, the mineral matter is responsible for a delay in the hydrocarbon generation during thermal heating and also retains part of the generated hydrocarbons, which might lead to erroneous kerogen typing when using thermal methods. The most immature samples are characterised by relatively higher proportion of oxygen-bearing functional groups which are more labile bonded to the kerogen and are released at lower temperatures during pyrolysis. Temperatures of initiation of kerogen cracking have shown to be more sensitive to reflect the maturity than temperatures of maximum rate of hydrocarbons release under the low heating rates used in this study. The most aliphatic and oxygen-rich kerogen have shown to yield the highest conversion to shale oil whereas the initially most aromatic kerogens are more prone to condense yielding higher coke amounts.

Pyrone‐Like Structures as Novel Oxygen‐Based Organic Superbases

these pyrone-like compounds are combina-tions of non-neighbouring carbonyl and ether oxygen atoms atthe edges of a graphene layer. Thus, this generic designationwould include not only g-pyrone derivatives but also struc-tures where the two oxygen atoms are located in differentrings. Although there are no reported data, within ourknowledge, for these latter pyrone-like systems, we haverecently demonstrated using ab initio calculations that theyshow a broad spectrum of base strength (around 12 pK

Chapter 6 – The Basicity of Carbons

This chapter covers most of the aspects related to the capacity of some carbon materials to act as proton sinks. The first section is devoted to some fundamental definitions, historical background, relevance, and, particularly, the assessment of the basicity of carbons. The concept of basic site on the surface of carbons is also introduced. Four types of basic sites, namely oxygen surface functional groups, heteroatom (other than oxygen) surface functional groups, basal planes and edges, and inorganic (or mineral) matter, are proposed as the main contributors to the basicity of carbon materials. The main core of the chapter describes these four families in terms of occurrence, relative basic strength, and accessibility. Special attention is paid to some of the controversies that still remain when ascribing the basicity of carbon materials to one particular site over the rest. Finally, some open questions are drawn to stress the need for further fundamental research in the field of carbon basicity.

Removal of odour-causing compounds using carbonaceous adsorbents/catalysts prepared from sewage sludge

This paper discusses H(2)S, NH(3) and VOCs removal by sewage-sludge-derived materials with outstanding chemical and textural properties. These materials were obtained from different precursors using different chemical and thermal treatments. Results show that the H(2)S removal process entailed a catalytic conversion of H(2)S to S or SO(4) (2-) species. On the other hand, adsorption is the main mechanism governing the performance of sludge-based materials for NH(3) and VOCs. Retention capacities (x/M values) obtained for some of the sludge-based adsorbents/catalysts are similar to those obtained with commercial activated carbons selected as reference materials.

Impact of oxy-fuel combustion gases on mercury retention in activated carbons from a macroalgae waste: Effect of water

The aim of this study is to understand the different sorption behaviors of mercury species on activated carbons in the oxy-fuel combustion of coal and the effect of high quantities of water vapor on the retention process. The work evaluates the interactions between the mercury species and a series of activated carbons prepared from a macroalgae waste (algae meal) from the agar-agar industry in oxy-combustion atmospheres, focussing on the role that the high concentration of water in the flue gases plays in mercury retention. Two novel aspects are considered in this work (i) the impact of oxy-combustion gases on the retention of mercury by activated carbons and (ii) the performance of activated carbons prepared from biomass algae wastes for this application. The results obtained at laboratory scale indicate that the effect of the chemical and textural characteristics of the activated carbons on mercury capture is not as important as that of reactive gases, such as the SOx and water vapor present in the flue gas. Mercury retention was found to be much lower in the oxy-combustion atmosphere than in the O2+N2 (12.6% O2) atmosphere. However, the oxidation of elemental mercury (Hg0) to form oxidized mercury (Hg2+) amounted to 60%, resulting in an enhancement of mercury retention in the flue gas desulfurization units and a reduction in the amalgamation of Hg0 in the CO2 compression unit. This result is of considerable importance for the development of technologies based on activated carbon sorbents for mercury control in oxy-combustion processes.