Jan Bimer

The characterization of nitrogen-enriched activated carbons by IR, XPS and LSER methods

The aim of this work is to study the efficiency of the nitrogen enrichment by urea of lignites and the induced changes of the adsorptive properties towards volatile organic compounds (VOCs) of the activated carbons derived from these modified precursors. The study is made using infrared and X-ray photoelectrons spectroscopies and the LSER (linear solvation energy relationship) modeling. Four activated lignites derived from the same raw material, original or enriched with nitrogen, are characterized in this way. The effect of the chemical treatment by urea and of the burn-off amount are investigated in term of evolution of the chemistry of the studied materials. The influence of these parameters on the selective behavior of the activated lignites towards two pairs of VOCs is also discussed in terms of molecular interactions using the LSER approach. The results show that the chemical treatment of the raw material is successful, leading to significant enrichment with nitrogen under pyridinic form at the surface of the activated carbons. Moreover, they reveal some selective properties well explained by the LSER analysis and spectroscopic measurements. The selective character of the studied materials is modulated by the duration of the activation step.

Adsorption of H2S or SO2 on an activated carbon cloth modified by ammonia treatment

The aim of this research is to investigate how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H2S and SO2 in humid air at 25 8C. Surface basic nitrogen groups were introduced either by treatment with ammonia/air at 300 8C or with ammonia/steam at 800 8C. The pore structure of the samples so prepared was examined by adsorption measurements. Changes in the surface chemistry were assessed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and temperature programmed desorption (TPD). The change of ACC activity could not be merely attributed to surface nitrogen groups but to other changes in the support. Ammonia/steam treatment improved ACC performance the most, not only by introducing nitrogen surface groups, but also by extending the microporosity and by modifying the distribution of surface oxygen groups. Successive adsorption–regeneration cycles showed important differences between oxidative retention of H2S and SO2 and the subsequent catalyst/support regeneration process.

Transport and sorption of water vapour in activated carbons

The adsorption of water vapour on microporous carbons derived from the carbonization of coconut shell has been studied. The adsorption and desorption characteristics of water vapour on the activated carbons were investigated over the pressure range p/p0 0–0.95 in a static water vapour system. In these experiments the process of water adsorption/desorption was investigated by both kinetic and equilibrium experimental data. Activated carbons differing by the degree of burn-off have shown the importance of the microstructure. A carbon enriched with nitrogen functions underlined the influence of the surface chemistry.

Comparison of three active carbons using LSER modeling: prediction of their selectivity towards pairs of volatile organic compounds (VOCs)

Abstract In order to classify chemically modified active carbons in terms of selectivity towards pairs of Volatile Organic Compounds (VOCs), and in order to follow their chemical treatment, two active lignites were characterized by the Linear Solvation Energy Relationship (LSER) equation of Abraham et al. Results are compared to those obtained with a commercial active carbon used as a reference material. Three LSER equations were determined by using gas–solid partition coefficients at infinite dilution of 13 probe molecules in gas chromatographic method of elution by characteristic point. In this way, the three active carbons were characterized in term of molecular interaction parameters. Their significance is discussed and is in good agreement with known chemical composition data. The study shows that the commercial material is the most selective adsorbent for the test-pair (methylethylketone/dichloroethane) and that both activated lignites are selective for the other test-pair of VOCs. Then, the limits of the predictions of selectivity towards the test-pair of VOCs (methanol/dichloromethane) are also discussed.

Solvolysis of three Polish coal samples by treatment with N-methyl-2-pyrrolidinone and an NaOHCH3OH mixture☆

Abstract This study concerns the extractable materials obtained by solvolysis of three Polish coals. N-methyl-2-pyrrolidinone extraction and NaOH CH 3 OH treatment of these coals were compared using several analytical procedures (extrography, sonication, gas capillary column chromatography, and i.r. and 1H n.m.r. spectroscopy). Thermodesorption, on line with gas chromatography and mass spectrometry, was also applied to these coal samples.

Effect of chemical pretreatment on coal solubilization by methanol-NaOH

Chemical pretreatment including reduction with metallic potassium (K-THF-isopropanol), reductive methylation (K-THF-CH3I), decarboxylation, reduction with LiAlH4 and O-methylation was used to modify the structure of coals. The effect of this pretreatment on solubilization by methanol-NaOH was evaluated. The results indicate that preliminary reduction with potassium enhances the reactivity of coal, whereas preliminary reductive methylation decreases its susceptibility to solubilization. The other three pretreatments, involving elimination, transformation or derivatization of the carboxyl and hydroxyl groups in coal, also have negative effects on solubilization, showing that these groups, apart from participating in the physical effects of disintegration and dissolution of the coal in the reaction medium, greatly affect coal reactivity.

The nature of the synergistic effect of binary tetralin-alcohol solvents in Kansk-Achinsk brown coal liquefaction

Abstract Kansk-Achinsk brown coal hydrogenation and swelling in tetralin, in low molecular alcohols, in other solvents and in binary mixtures were studied. Tetralin was found to be the most effective liquefaction solvent, but methanol and ethanol were the active ones in coal swelling. Synergistic effects were observed when the mixtures of tetralin and methanol or ethanol were used for liquefaction and swelling. The effect of binary solvents was shown to be due to the ability of alcohol components to cause brown coal to swell improving the availability of the fragments of coal matter for the reactive hydrogen donor tetralin molecules.

Coal characterization for liquefaction in tetralin and alcohols

Abstract Kansk-Achinsk lignite hydrogenation in tetralin, isopropanol, ethanol and methanol was studied. Tetralin was the most active solvent. Synergetical effects were observed when the mixture of tetralin and alcohols was used for liquefaction. The variations in liquid product composition were analysed by a mechanistic numerical model incorporating two competing reactions: alkylation and hydrogen donation. The effect of preliminary O -methylation with (CH 3 ) 2 SO 4 , reduction with LiAlH 4 and with K/isopropanol and reductive methylation with K CH 3 J on the oxygen functional group composition and liquefaction behaviour were examined for three coals with different rank. Coal pretreatments were shown to cause dramatic effects on the oxygen-containing group distribution. The liquefaction reactivity with methanol in the presence of ZnCl 2 and NaOH catalysts decreased slightly. The liquefaction behaviour is strongly influenced by coal rank.

Preliminary oxidation effect on the conversion of coal in the reaction with methanol and sodium hydroxide

Abstract Coals of different rank were oxidized with performic acid to the stage of regenerated humic acids. Both crude and oxidized coals were treated with methanol and sodium hydroxide at 350°C. The final products obtained from the oxidized coals showed higher degree of hydrogenation and solubilization as compared with the corresponding products from crude coals.

Quantitative relation between the macromolecular characteristics of brown coal and its reactivity in conversion with tetralin

Abstract The reactivity of Kansk-Achinsk brown coal in thermochemical conversion with tetralin is a linear function of the network flexibility, which is primarily controlled by ionic cross-linking with carboxylate bridges via polyvalent cations such as Ca2+.