Showing papers on "Carbochemistry published in 1991"
TL;DR: In this article, the chemical and thermal responses of six dried coals on exposure to a flow of oxygen or air were studied using isothermal differential thermal analysis (DTA) and temperature-programmed in situ diffuse reflectance infrared Fourier Transform spectroscopy (DRIFTS).
180 citations
TL;DR: In coal pyrolysis O-containing structures such as ether bridges and phenolic groups play an important role as mentioned in this paper, and their reactions were studied by non-isothermal pyroplysis of a high volatile bituminous coal and some model polymers with gas Chromatographic detection of the gaseous pyrolys products.
87 citations
TL;DR: In this paper, the pyrolysis of brown coal samples and bituminous coal maceral concentrates was investigated by non-isothermal thermogravimetry, and the TG data for these coals reveal a two-stage pyroolysis process.
Abstract: The pyrolysis of a suite of brown coal samples and bituminous coal maceral concentrates is investigated by non-isothermal thermogravimetry. The TG data for these coals reveal a two-stage pyrolysis process. The activation energy for the primary pyrolysis stage is considerably higher than that for the secondary pyrolysis stage. It is evident that a particular coal may be characterised by the weighted mean apparent pyrolysis activation energy which correlates with the corresponding specific energy of the coal.
81 citations
TL;DR: Transient (unsteadystate) kinetics, a relatively new technique for studying noncatalytic gas/solid reactions, has been used successfully to further our understanding of char (carbon) gasification as mentioned in this paper.
Abstract: Transient (unsteady-state) kinetics, a relatively new technique for studying noncatalytic gas/solid reactions, has been used successfully to further our understanding of char (carbon) gasification. It provides the unique capability of separately determining the reaction rate constant (site reactivity or turnover frequency) and the number of active sites participating in the reaction (reactive surface area). Its application to the uncatalyzed gasification of coal-derived chars and polymer-derived carbons is illustrated. In particular, the heretofore elusive quantitative understantding of their reactivity variations with conversion has been achieved for gasification in both carbon dioxide and oxygen
72 citations
TL;DR: In this paper, a novel method for converting FeCl{sub 3} to an active, Cl-free Fe catalyst for coal gasification is studied, which shows a high activity for gasification with steam at around 950 K.
Abstract: In this paper, a novel method for converting FeCl{sub 3} to an active, Cl-free Fe catalyst for coal gasification is studied. Fe cations alone can be incorporated into low-rank coals from an aqueous solution of FeCl{sub 3} by using NH{sub 3}/NH{sub 4}Cl solution. Some Fe cations are exchanged with the protons in carboxyl groups. The Cl-free Fe results in a finely dispersed catalyst, which shows a high activity for gasification with steam at around 950 K. The degree of rate enhancement by the Cl-free catalyst depends on char conversion, Fe loading, and temperature. The chemical form of the Fe catalyst on devolatilization and during gasification is Fe{sub 3}O{sub 4}. The catalytic activity is discussed in terms of the dispersion of Fe{sub 3}O{sub 4} particles.
65 citations
TL;DR: This article showed that pre-swelling of bituminous and lower-rank coals with a suitable solvent, followed by removal of the swelling agent, significantly enhances conversion and product quality during subsequent liquefaction.
64 citations
TL;DR: In this paper, a comparison of the TPD pattern of H2S evolution for high-rank coal with those of chars made from lower-rank coals at 400 and 750 °C shows that they are remarkably similar and suggests that the thermal reactions induced in sulphur species in laboratory pyrolysis experiments could be related to those that occur as a result of thermal reactions during coal metamorphism.
63 citations
TL;DR: In this article, the influence of functional groups in coal on cross-linking reactions during pyrolysis was investigated, and the early stages of CO2 and H2O evolution are directly related to the cross-link observed at low temperatures (<400 °C, which inhibits tar production.
52 citations
TL;DR: In this article, the features of three catalyst groups, alkali, alkaline earth and iron-group metals, are compared and the rate change during coal gasification is discussed.
51 citations
TL;DR: Fourier transform infrared spectra were reported for an activated carbon, two pitches and two coals as a function of carbonization temperature (773-1073 K) and temperature (573-773 K) of subsequent oxidation treatment as mentioned in this paper.
50 citations
TL;DR: The physicochemical properties and catalytic activities of an intriguing clans of compounds based on iron and tin oxides treated with varying amounts of sulfate anion and employed for the direct liquefaction of three Argonne coals of varying ranks are reported in this article.
Abstract: The physicochemical properties and catalytic activities of an intriguing clans of compounds based on iron and tin oxides treated with varying amounts of sulfate anion and employed for the direct liquefaction of three Argonne coals of varying ranks are reported in this paper. The sulfated transition-metal oxides have become a topic of interest partly because of their unusual properties, one of these being their so called «superacidity»
TL;DR: In this paper, a new coal flash pyrolysis method was developed for drastically increasing the total volatile matter and the liquid products under mild conditions, which was achieved by swelling the coal with solvent at 100-250 o C under a pressurized atmosphere.
Abstract: A new coal flash pyrolysis method was developed for drastically increasing the total volatile matter and the liquid products under mild conditions. The original idea of this method lies in the realization of effective hydrogen transfer from the hydrogen donor solvent to the coal fragments during the flash pyrolysis. To realize it, we found the contact at the molecular level between the solvent and the coal functional groups was essential in addition to the matching of the dehydrogenation rate of the solvent and the primary decomposition rate of coal. Contact at the molecular levels was achieved by swelling the coal with solvent at 100-250 o C under a pressurized atmosphere (1 MPa). When two coals were swollen by tetralin, tetralin penetrated into the micropores of its molecular size by enlarging the pores
TL;DR: In this paper, the intermolecular interaction responsible for the solvent-induced association was investigated using solvent treatment and elemental and spectroscopic analyses, and the results implied that interactions other than van der Waals' forces and hydrogen bonds cause this association.
TL;DR: In this article, the amount of catalyst that can be stabilised on the carbon increases in the order Na < K < Cs and depends on the amount oxygen in the carbon.
TL;DR: In this paper, the role of microporous surface area in uncatalyzed carbon gasification was investigated in two high-surface-area synthetic carbons, and the results showed that the appropriate total surface area is critical to the calculation of meaningful intrinsic reactivities and is the logical starting point in the quest for an improved fundamental understanding of the factors that determine carbon dioxide reactivity.
Abstract: The gasification in oxygen and carbon dioxide of two high-surface-area synthetic carbons was studied in order to investigate the role of microporous surface area in uncatalyzed carbon gasification. The identification of the appropriate total surface area for carbon gasification is critical to the calculation of meaningful intrinsic reactivities and is the logical starting point in the quest for an improved fundamental understanding of the factors that determine carbon gasification reactivity. Two microporous chars having markedly different macropore volumes were selected for study. Low-temperature gasification reactivities, vapor adsorption isotherms, and adsorption equilibration times were measured for the chars at various stages of conversion, and individual surface feature of char particles were examined as a function of conversion by a captive-particle SEM technique
TL;DR: In this paper, the authors discuss three recent papers, in which beneficial effets of adding nondonor species to the donor solvent were reported, in light of the solvent-mediated hydrogenolysis model for coal liquefaction.
Abstract: The traditional mechanism for coal liquefaction ties liquefaction ability of a solvent with its scavenging ability and cannot explain synergistic effects between solvent components. Such effects are naturally anticipated by mechanisms that involve interaction between components to generate reactive components. This paper discusses three recent papers, in which beneficial effets of adding nondonor species to the donor solvent were reported, in light of the solvent-mediated hydrogenolysis model for coal liquefaction-a model we have previously proposed. The nondonor species, which in these cases are polycyclic aromatic hydrocarbons, are good acceptors of hydrogen and react with hydroaromatic donors to give cyclohexadienyl radicals, which are capable of engendering hydrogenolysis, thereby increasing the overall rates. The PCAH species also help minimize wasteful transfer of hydrogen that would otherwise lead to reduced but uncleaved products. In this case the beneficial effect is reflected in the efficiency of hydrogen utilization. Finally, we extend this line of reasoning to the context of coprocessing coals and heavy oils. We use semiquantitative estimates for the fate of aliphatic radicals in the presence and absence of PCAH components to suggest that the PCAH components provided by coals convert aliphatic radicals, which are ineffective in causing bond scission, into cyclohexadienyl radicals that can do so
TL;DR: In this paper, the activity and characterization of finely dispersed iron-and molybdenum-containing catalysts based on the soluble precursors Fe(CO) 5 and Mo(CO 6, and on the finely divided (average crystallite size of 30-80 A) sulfated metal oxide superacids such as Fe 2 O 3 /SO 4 2− and SnO 2 /SO4 2− for coprocessing reactions were investigated.
Abstract: We have recently reported on the catalytic activity of sulfated iron and tin oxides for the direct liquefaction of coal (Energy Fuels 1991, 5, 497-507) and on the activity of the soluble precursor, Fe(CO) 5 , for coprocessing of Illinois No. 6 coal with Maya ATB residuum (650°F+) (Energy Fuels 1990, 4, 231-237). This paper addresses the activity and characterization of finely dispersed iron- and molybdenum-containing catalysts based on the soluble precursors Fe(CO) 5 and Mo(CO) 6 , and on the finely divided (average crystallite size of 30-80 A) sulfated metal oxide superacids such as Fe 2 O 3 /SO 4 2− and SnO 2 /SO 4 2− for coprocessing reactions
TL;DR: In this paper, the authors observed that catalysis due to sodium lignosulphate leads to a decrease in the values of the kinetic parameters E and A with increase in catalyst concentration, while catalytic due to ferric nitrate shows the reverse trend for the same carbon substrate.
TL;DR: In this paper, the catalytic effects of zinc chloride (ZnCl2) in slow pyrolysis of two Spanish high sulphur coals were studied and it was shown that the behavior of ZnCl 2 was modified by the presence of organic sulphur and minerals such as calcite and pyrite in the coals.
TL;DR: In this paper, the authors show that the lignin-assisted depolymerization of coal at 325 o C improves the quality and yield of coal under moderate pressure and temperature conditions.
Abstract: Addition of lignin to coal is synergistic in that it significantly improves the quality and yield (by up to 33%) of the liquid products produced from coal under moderate pressure and temperature conditions. For example, the liquids obtained by lignin-assisted depolymerization of coal at 325 o C contain appreciably lower amounts of the undesirable high molecular weight benzene-insoluble compounds, and higher quantities of the desirable lower molecular weight asphaltenes and pentane-soluble fractions over the corresponding fractions in liquids that are obtained by processing either coal or lignin under identical conditions. The experimental data conclusively show that, in addition to the favorable influences of the lignin-assister depolymerization listed above, lignin also enhances the stability of the coal depolymerization reaction
TL;DR: In this article, the three major maceral groups (vitrinites, fusinites and liptinites) were separated from a single coal, Pingshuo bituminous coal, and nine model coals were prepared by mixing the individual macerals in different amounts.
TL;DR: In this paper, x-ray photoelectron spectroscopy (XPS) was used to investigate surface oxygen content before and after pretreatment and reaction in carbon pre-oxidation.
TL;DR: In this article, a flowing-solvent (F-S) liquefaction reactor with a continuous solvent sweep through a fixed bed of coal has been developed, where solubilized products are continuously swept out of the reaction zone.
TL;DR: In this paper, the authors have shown that the overall reactivity in gasification reactions decreases in the order O2 >NO >N2O. They also showed that the O 2 > NO > N2O ratio increases with the temperature of the celluose char.
TL;DR: In this article, the results of tests carried out with coals of varying ash content have been briefly summarised in order to indicate the operability of the gasification system with Indian coals.
TL;DR: In this paper, the co-solvent effect of tetralin and ethanol on supercritical toluene extraction of coal has been investigated, and it was shown that tetralins increased the conversion and liquid yield of coal.
TL;DR: In this paper, the effect of mild alkylation and solvent swelling on the reactivity of coal was evaluated under both direct hydroliquefaction and coal/oil co-processing conditions, at both low and high severity reaction conditions.
TL;DR: In this paper, the effects of liquid water treatment on Wyodak coal were studied in the presence of n-undecane replacing water in batch reactors with quartz liners for periods of 30 min or 5 h with added N2 (500 psi cold).
TL;DR: In this paper, Fourier transform infrared spectroscopy has been used to study the evolution of the structure of bituminous coal and its pyridine extraction products during oxidation.
TL;DR: In this article, the effects of catalyst loading and char conversion on the local structure of iron catalysts during the steam gasification of brown coal have been studied by transmission Mossbauer spectroscopy and extended X-ray absorption fine structure analysis.
Abstract: The effects of catalyst loading (0.5-10 wt % as Fe) and char conversion on the local structure of iron catalysts during the steam gasification of brown coal have been studied by transmission Mossbauer spectroscopy and extended X-ray absorption fine structure spectroscopy. During the steam gasification, iron species exist as highly dispersed ultrafine particles of FeOOH and as crystalline Fe 3 O 4 . The proportion of the former was higher at low char conversion in the low-loading sample and decreased with increase in the amount of iron loading and in char conversion. The ultrafine FeOOH is likely active species for steam gasification of brown coal, since the specific catalytic activity is closely related to the amount of this species