R. Moliner

FTIR study of the evolution of coal structure during the coalification process

Abstract A series of coals varying in rank from peat to semi-anthracite was studied by Fourier Transform infrared spectroscopy (FTIR) and curve-fitting analysis in order to gain additional information on coal structure and the main structural changes that take place during the coalification process. Several structural parameters based on FTIR data and curve-resolved bands were calculated. These parameters provide quantitative evidence of the increase of aromaticity and the loss of aliphatic and oxygen-containing structures with increasing maturation. The analysis of the aromatic CH out-of-plane region (900-700 cm−1) reveals the loss of aromatic substituents up to the stage of bituminous coal and the subsequent increase in the degree of aromatic condensation with increasing coalification. The ratio of aromatic carbons to carboxyl groups (1605 cm−1/1605 cm−1 + 1705 cm−1) appears to be a suitable parameter for assessing the natural maturation of coal. Copyright

FT-i.r. investigation on char formation during the early stages of coal pyrolysis

Abstract The transformation of coal into char during low-temperature pyrolysis was studied by Fourier transform infrared (FT-i.r.) spectroscopy and solvent swelling measurements. Pyrolysis was carried out in a nitrogen-swept fixed-bed reactor at temperatures of 300–600 °C. Three Spanish coals varying in rank from lignite to bituminous were studied. The samples show very different cross-linking behaviour, related to CO 2 and H 2 O evolution at low temperatures and to methane release at higher temperatures. The FT-i.r. examination shows that the aliphatic structures and the oxygen-containing functional groups (carboxyl and hydroxyl) are easily removed from chars, while aromatic hydrogen tends to increase with increasing pyrolysis temperature. Curve-fitting analyses for the 3000-2700 and 900-700 cm −1 regions permit the variations in the distribution of methyl and methylene groups and in the degree of aromatic substitution and condensation, respectively, to be evaluated as a function of temperature. Several structural parameters based on FT-i.r. data have been calculated for the chars. These structural parameters provide evidence on the loss of aromatic substituents and the process of hydrogen transfer to aromatic structures during pyrolysis.

Performance of zinc oxide based sorbents for hot coal gas desulfurization in multicycle tests in a fixed-bed reactor

Zinc oxide based sorbents doped with CuO or TiO2 have been studied in 5-cycles tests in a fixed-bed reactor, as regenerable sorbents for desulfurization of coal gas at high temperature (600°C). TiO2 increases the stability of ZnO and zinc ferrite, under the reducing power of coal gas, and the sorbent porosity. However, it also increases the H2S concentration in the outlet gas before breakthrough, and the sorbent reactivity is not substantially modified. In addition, the presence of TiO2 makes more difficult the formation of mixed oxides and the behaviour of the fresh sorbents is usually different than that of the first regenerated samples. The presence of CuO increases sorbent reactivity and the efficiency for the first 1–3 cycles is excellent. Unfortunately, neither CuO nor TiO2 can prevent the excessive decay in performance of the studied sorbents as the number of cycles increases. This feature appears correlated, not with structural changes as shown by XRD, but with a decrease of the sorbent porosity due to progressive thermal sintering. The presence of iron oxides in the sorbent composition causes different behaviour with the appearance, after breakthrough, of COS in sulfidation and H2S and elemental sulphur in regeneration.

Characterization of Mn and Cu oxides as regenerable sorbents for hot coal gas desulfurization

To enhance the formation of different mixed oxides, which potentially might stabilize copper in oxidation states 2+ and/or 1+, regenerable sorbents for hot coal gas desulfurization have been prepared by calcination at 950°C of MnO2 and CuO powders in different mole ratios. The fresh sorbents were sulfided at 600°C using a simulated coal gas from cylinders, reduced in identical operating conditions compared to sulfidation in the absence of H2S, and regenerated at 710°C in oxidising atmosphere. Successive sulfidation–regeneration cycles were carried out in a quartz fixed-bed reactor. The fresh, reduced, sulfided or regenerated sorbents were characterized by SEM-EDX, XRD, TPR, XPS and FTIR spectroscopy. The study shows that, under the reducing power of coal gas at the operating conditions used, manganese oxides cannot prevent the reduction of copper oxides and, consequently, the expected beneficial effect derived from copper oxide addition, reducing the equilibrium H2S concentration in the outlet gas to very low levels cannot be achieved. In addition, copper oxides do not prevent the tendency of manganese-based sorbents to form sulfate species in an oxidative atmosphere and the regeneration of these sorbents has to be carried out at higher temperature.

Non-isothermal versus isothermal technique to evaluate kinetic parameters of coal pyrolysis

Abstract In this paper, the application of the non-isothermal versus the isothermal technique to evaluate kinetics parameters of coal pyrolysis is discussed. The same reaction model (multiple parallel independent, MPI with distribution activation energies, DAE) is assumed and the same data treatment is applied with the aim of attributing the differences to the experimental technique used. The evolution of the total volatiles and individual gaseous species in the pyrolysis of two low-rank coals has been evaluated. Kinetic parameters obtained by using non-isothermal treatment agree with the parameters found in the literature. The non-isothermal technique (with constant heating rate) has been confirmed as a powerful tool to study the kinetics of coal pyrolysis.

Release of volatile sulfur compounds during low temperature pyrolysis of coal

Abstract The behaviour of sulfur structures in coal during low temperature pyrolysis has been studied. Nine low rank coals with high organic and pyritic sulfur contents were heated in a swept fixed bed reactor (N2) up to 850 °C, and the evolved sulfur compounds were determined by sulfide electrode (H2S) and Fourier transform infrared (FT-i.r.) spectroscopy (SO2, COS). Evolution of H2S as a function of temperature passes through two peaks between 500–560 °C and 630–700 °C, related to the decomposition of organic and pyritic sulfur, respectively. Assignment of organic sulfur structures and pyritic sulfur to the two observed peaks of H2S evolution were tested using float-sink fractions with different mineral matter and pyrite contents (0.3–33 wt%). An important role of coal organic matter in pyrite decomposition to H2S was found. The evolution of COS with pyrolysis temperature, followed a trend similar to that for H2S. The evolved SO2 was related to the decomposition of iron sulfate from weathering of pyrite, but also with the presence of oxidation reactions during pyrolysis. The amount of sulfur removed from coal by pyrolysis varied from 35 to 64% of the total sulfur content for the assayed samples. Pyrolysis temperatures below 700 °C were sufficient to obtain desulfurization levels close to 90% of the total amount of sulfur which can be removed by pyrolysis.

Behaviour of different industrial waste oils in a pyrolysis process: metals distribution and valuable products

Abstract In the present paper, the results obtained in the pyrolysis of four industrial waste oils (automotive, hydraulic, machine and cutting oil) are shown. The pyrolysis has been carried out at atmospheric pressure and 600°C. The continuous injection of the samples was into the bottom part of the reactor using a pump. Liquid and gases fractions have been analysed, organic products by gas chromatography and metals concentration by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). The gases obtained are mainly formed by methane and light olefins, C 2 – C 4 , and the liquids contain an aromatic fraction of high industrial value. The behaviour of metals was also very different from one oil to another. Lead was the most affected metal in all of them, with a decrease ratio (concentration before and after the pyrolysis) from 165 for machine oil to 32 for the hydraulic oil. Pb, Cr, Cu, Ni, Pb and V were identified and quantified in each fraction. The results show that the automotive and machine waste oils are the better ones concerning the liquid yields. However, the hydraulic and cutting oils show a high conversion to gas products. The relationship between the type of waste oil and the products obtained is discussed.

Synergetic effects in the co-pyrolysis of coal and petroleum residues: influences of coal mineral matter and petroleum residue mass ratio

Abstract The influence of coal and mineral matter nature, and the coal/petroleum residue weight ratio, on the synergetic effects observed when coal and petroleum residues are copyrolysed has been studied. Two coals (Samca, a subbituminous one, Figaredo, a bituminous one, and a demineralised Samca coal) and three-coal/petroleum residue ratio (70/30, 50/50 and 40/60) have been used. Pyrolysis runs were carried out at analytical scale, by pyrolysis-gas chromatography in a pyroprobe 1000 CDS at 900°C and at atmospheric pressure. Synergetic effect on the yield of the main pyrolysis products has been evaluated and discussed with attention focused on valuable feedstock petrochemical products such as light olefines and light aromatic compounds. It is concluded that the intensity of the synergetic effects depends on the coal nature. In the Samca coal with petroleum residue mixtures, the increase in petroleum residue ratio promotes the production of light olefins, disfavouring the production of aromatic compounds. In contrast, for the Figaredo coal, petroleum residue ratio has not a significant influence on the synergetic effects. Coal mineral matter seems to play a negative effect on synergetic effects since an increasing of synergetic effect in light olefins and BTX has been observed after demineralisation of the Samca coal. However, this effect could be attributed to both, the removing of the mineral matter and the changes produced in the porous structure of coal by the acid treatment.

Functional group dependence of cross-linking reactions during pyrolysis of coal☆

This paper reports an investigation of the influence of functional groups in coal on cross-linking reactions during pyrolysis. A humic coal, two low rank coals and a bituminous coal were selected for this study. The evolution of species such as CO2, CH4 and H2O related to cross-linking reactions was monitored by gas chromatography and Fourier Transform infrared spectroscopy. Solvent swelling of coal chars in pyridine was used as a measurement of the extent of cross-linking. The results reported here prove that the early stages of CO2 and H2O evolution are directly related to the cross-linking observed at low temperatures (<400 °C), which inhibits tar production. Cross-linking produced at temperatures between 400 and 500 °C seems to be related to methane evolution. As tar is also evolved in this temperature range, the tar yield is less affected by the cross-linking related to CH4 evolution.

Effect of the pyrolysis process on the physicochemical and mechanical properties of smokeless fuel briquettes

A greater understanding of the physics and chemistry of lignite–biomass briquetting could lead to better briquette performances and cost-effectiveness making these fuels more attractive to both producers and consumers. With this aim, chars obtained from different low rank coals and biomasses (sawdust, straw, olive stone and almond shell) were used to prepare smokeless fuel briquettes and their physicochemical and mechanical properties were studied depending on the pyrolysis conditions. Coal was pyrolysed at temperatures between 500 °C and 700 °C and the temperature chosen to carry out pyrolysis was 600 °C due to the lowest content of sulphur per thermie in the pyrolized material. In order to study the influence of the pyrolysis process on the properties of the briquettes, biomasses were pyrolysed separately at 400 °C and 600 °C and together with the coal at 600 °C of temperature. The materials pyrolysed at 600 °C showed a lower content of volatile matter and a higher calorific value than the standard levels reported in the literature for materials to prepare smokeless briquettes. The briquettes were prepared by mixing the pyrolysed materials with humates as binder and Ca(OH)2 as sulphur sorbent. The briquetting process was followed by FT-IR, scanning electron microscopy (SEM), CO2 adsorption and the mechanical properties were tested evaluating their impact resistance, water resistance and compression strength. The best briquettes with respect to the mechanical properties were those prepared with coal and biomasses co-pyrolysed at 600 °C although some of them fixed a higher percentage of sulphur during pyrolysis due to the metal content of the biomasses.