José J. Pis

Hypercrosslinked organic polymer networks as potential adsorbents for pre-combustion CO2 capture

Hypercrosslinked polymers (HCPs) synthesized by copolymerisation of p-dichloroxylene (p-DCX) and 4,4′-bis(chloromethyl)-1,1′-biphenyl (BCMBP) constitute a family of low density porous materials with excellent textural development. Such polymers show microporosity and mesoporosity and exhibit Brunauer–Emmett–Teller (BET) surface areas of up to 1970 m2 g−1. The CO2 adsorption capacity of these polymers was evaluated using a thermogravimetric analyser (atmospheric pressure tests) and a high-pressure magnetic suspension balance (high pressure tests). CO2 capture capacities were related to the textural properties of the HCPs. The performance of these materials to adsorb CO2 at atmospheric pressure was characterized by maximum CO2 uptakes of 1.7 mmol g−1 (7.4 wt%) at 298 K. At higher pressures (30 bar), the polymers show CO2 uptakes of up to 13.4 mmol g−1 (59 wt%), superior to zeolite-based materials (zeolite 13X, zeolite NaX) and commercial activated carbons (BPL, Norit R). In addition, these polymers showed low isosteric heats of CO2 adsorption and good selectivity towards CO2. Hypercrosslinked polymers have potential to be applied as CO2 adsorbents in pre-combustion capture processes where high CO2 partial pressures are involved.

Textural characterization of coals using fractal analysis

Abstract The aim of this study is to show how fractal analysis can be effectively used to characterize the texture of porous solids. The materials under study were series of coals oxidized in air at various temperatures for different time intervals. Data from mercury porosimetry determinations of samples was analyzed using fractal models. The methods employed were those proposed by Neimark, Friesen and Mikula and that developed by Zhang and Li. Some methods are able to supply a fractal profile or “fractal fingerprint” of materials, i.e. ranges of pore sizes with different fractal dimensions are detected. These fractal profiles are very sensitive to the oxidation treatment. The average fractal dimension can also be used as a valid parameter to monitor the textural evolution of the coals as the treatment progresses, as this behaves in a similar way to other textural parameters. The use of fractal analysis in conjunction with the results of classical characterization methods leads to a better understanding of textural modifications in the processing of materials.

Influence of coal oxidation upon char gasification reactivity

The objective of this work was to study the effect of coal air oxidation on char gasification reactivity. Three bituminous coals with different rank, from a low volatile bituminous coal to a high volatile C bituminous coal, were used. Isothermal runs were carried out in air, using particle sizes ranging between 48 and 855 μm. The experimental results showed that char reactivity increases with degree of the coal oxidation. The dependence of the rate constant on temperature exhibits an activation energy in the range 105–130 kJ mol−1. A slight increase in activation energy with coal oxidation extent was also detected. The changes in char textural development as a consequence of coal preoxidation explain the modifications of char reactivity. Good correlations were found between char reactivity, total surface area (TSA) and active surface area (ASA).

The effect of the textural properties of bituminous coal chars on NO emissions

NO is the primary product of the oxidation of char nitrogen, and in some combustion processes the NO can be reduced on the char surface to give N2O and/or N2. In this study a range of bituminous coals (low, medium and high volatile matter content) were pyrolysed in a fixed bed reactor at various heating rates. Textural characterisation was carried out by measuring true (He) and apparent (Hg) densities and N2 (−196°C) and CO2 (0°C) adsorption isotherms. Pore volume distributions and surface areas were obtained for the chars studied. A thermogravimetric analyser coupled to a quadrupole mass spectrometer (TG-MS) was used to study the combustion behaviour of the samples and the nitrogen compounds evolved during temperature-programmed combustion. Results are discussed in terms of the influence of both textural properties and reactivity on NO emissions and on the heterogeneous reduction of NO.

Modification of combustion behaviour and NO emissions by coal blending

Combustion profiles determined by TGA and experiments in a laminar entrained flow reactor (EFR) were used in this work to assess the relative combustion reactivities of different rank coals and their binary coal blends. The combustion behaviour of coal blends in TGA was greatly influenced by coal rank and the proportion of each component in the blend. Higher volatile coals exerted more influence in the low-temperature region and less reactive coals in the char combustion zone. The results in the EFR indicated that coal blends burnout and NO emissions show additivity in the case of similar nature coals. When one of the components was a high-rank coal, the burnout of the blend exhibited, in some cases, positive synergistic effects, while a clear deviation from linearity was found in NO emissions.

Influence of char structure on reactivity and nitric oxide emissions

The aim of this study was to investigate the influence of coal rank and operating conditions during coal pyrolysis on the resultant char texture properties, morphology and reactivity. A range of bituminous coals were pyrolysed in a fixed bed reactor at different heating rates. It was found that the higher the heating rate and the lower the coal rank, the more microporous chars were obtained. Isothermal (500 °C) gasification in 20% oxygen in argon of the chars was carried out using a differential thermogravimetric system (DTG). The results of this work indicated that the increase in the availability of char-active surface sites led to an increase in char reactivity, not only for oxygen but also for other reactive gases, in particular NO, diminishing emissions during the combustion process.

Simulation of secondary fragmentation during fluidized bed combustion of char particles

A computer program has been developed in order to simulate the secondary fragmentation process during fluidized bed combustion of a population of char particles. The simulation intends to predict the evolution of char particle size distribution during combustion. It is based on two statistical functions, one which accounts for the probability density that a particle of a given size breaks into fragments and the other for the size distribution on the basis of the number of fragments generated by the breaking up of the particle. The parameters involved in the simulation have been obtained by minimizing the difference between theoretical predictions and experimental results. The latter were obtained by image analysis of partially burnt samples of anthracite char (d0 = 1,98 and 3.50 mm, 750 < Tb < 950 °C) and graphite particles (d0 = 1.98 mm, 850 < Tb < 950 °C) in a laboratory-scale fluidized bed reactor (inner diameter 5 mm).

Structural Changes in Polyethylene Terephthalate (PET) Waste Materials Caused by Pyrolysis and CO2 Activation

For ecological reasons, there is an increasing demand for recycling polyethylene terephthalate (PET) wastes in developed countries. Although one potential application might be its utilisation for the production of activated carbons, the behaviour of these wastes when subjected to different heat treatments and activation processes is still not very well known. In the present work, samples with different degrees of burn-off were prepared by pyrolysis in an inert atmosphere and subsequent CO2 activation at high temperatures. The derived changes in the textural and structural properties of the residual solids were studied by helium picnometry, N2 and CO2 adsorption isotherms, powder XRD, Raman spectroscopy and XPS. The study reveals that CO2 activation of PET wastes develops a carbonaceous matrix with micropores. Helium measurements showed that the mass density of the activated samples increased as the degree of burn-off increased. Characterisation studies revealed that the structural changes derived from pyrolysis and further CO2 activation mostly involved a progressive decrease in the number of structural units.

Raw Materials, Selection, Preparation and Characterization

Among the different energy sources, biomass wastes hold most promise for the near future. Biomass is considered a neutral carbon fuel because the carbon dioxide released during its use is an integral part of the carbon cycle. Increasing the share of biomass in the energy supply contributes to diminishing the environmental impact of CO2 and to meeting the targets established in the Kyoto Protocol. The use of biomass waste material as a fuel, however, has certain drawbacks related with its high-moisture content, low-energy density and the problem of reducing the size of the biomass, especially in the pulverized range of entrained flow gasifiers. Currently, there is increasing interest in developing new processes for the pre-treatment of biomass wastes, through the modification of their properties prior to gasification, so as to make them more attractive for their subsequent use. Pelletization is a proven technology for improving biomass properties, whereas torrefaction is considered a plausible alternative for decreasing the moisture content, increasing the energy density and greatly facilitating the handleability and grindability properties of the torrefied material.

Distribution of PAH generated in fluidized bed combustion and pyrolysis experiments

Publisher Summary This chapter discusses the distribution of Polycyclic aromatic hydrocarbons (PAH) generated in fluidized-bed combustion and pyrolysis experiments. PAH is quantified following the extraction of samples recovered from fluidized-bed combustion (FBC) tests on Spanish lignite (Aragon) at various combustion temperatures and air/fuel ratios in a pilot plant scale FBC unit. A selection of the results are detailed and discussed with respect to the sampling, extraction, and analysis procedures. FBC conditions markedly affect the amount of PAHs produced and emitted into the atmosphere. Maximum PAH concentrations occur at low temperatures, when combustion is less efficient, and at high air excesses. In the PAH recovery from the materials of the different sampling points, supercritical fluid extraction (SFE) provides a more reliable method for high molecular weight compounds than Soxhlet extraction. Observations are made under fluidized-bed pyrolysis conditions, where condensation reactions predominate at higher temperatures.