CO2 Gasification Of Char Research Articles

Vanadium-catalysed gasification of carbon and its application in the carbothermic reduction of barite

Sodium vanadate, a waste from Bayer's alumina process was used as a catalyst in the CO 2 gasification of active charcoal. The catalytic effect was quite evident with the observed enhanced rate of gasification accompanied by the typical compensation effect. This effect has been able to predict the observed anamolous behaviour of the vanadium catalysed carbothermic reduction of barite.

Synthesis of a high-yield activated carbon by oxygen gasification of macadamia nut shell charcoal in hot, liquid water

Abstract Macadamia nut shells (‘macshells’) were pyrolyzed at elevated pressure to produce a high-yield charcoal. This macshell charcoal was carbonized at 950°C, reacted with oxygen dissolved in flowing hot liquid water at 100 bar and temperatures between 100 and 200°C, and carbonized again at 950°C to produce an activated carbon. Using this procedure, activated carbons with iodine numbers as large as 615 were manufactured with burnoffs as low as 13% (by weight of the carbonized charcoal). Doubling of the water flow rate and halving of the particle size did not affect the measured rates of oxygen chemisorption and gasification. These observations, together with calculated small values of the Thiele modulus, are consistent with the conclusion that the chemisorption and gasification rates were not mass transfer limited. Variations in the dissolved oxygen concentration had little effect on the oxygen chemisorption and gasification rates, suggesting that the order of reaction in oxygen was near zero. The overall yield of the activated carbon from the dry, raw macadamia shell feedstock was about 25 wt%.

Internal consistency of coal gasification reactivities determined in bench-scale reactors: effect of pyrolysis conditions on char reactivities under high-pressure CO2

Relationships between char preparation conditions and CO2-gasification conversions have been examined using a wire-mesh, a fluidised-bed and a ‘hot-rod’ (fixed-bed) reactor. Conversions from the direct gasification of untreated coal have been compared with those from the gasification of chars prepared: (i) in-situ under helium in each reactor, before switching over to CO2; and (ii) from gasification in all three reactors of a char sample, pre-prepared in the fixed bed reactor. Conversions from direct gasification were slightly higher than experiments where samples were first pyrolysed in situ and gasified under CO2 in the same reactor. In some cases, conversions were within experimental error. Under these conditions and within several percentage points, the pyrolysis and gasification steps may be considered as additive. Lower overall conversions observed in the hot-rod reactor have been attributed to the combined effect of: (i) formation of a low reactivity char—owing to tar-solids contact leading to secondary char deposition; and (ii) poor contact between char and the reactive gas. In the wire-mesh and the fluidised-bed reactors, direct CO2-gasification conversions were considerably larger than those determined using the common sample of char, pre-prepared in the hot-rod (fixed-bed) reactor. This sharp drop in overall conversion shows that care must be taken in interpreting reactivity data from ‘two-reactor, two-step’ procedures where char preparation conditions are not identical to those of the gasification step. A broadly linear relationship has been observed between conversions from a pilot plant reactor and direct CO2-gasification in the bench-scale high-pressure wire-mesh reactor. Despite differences between operating parameters in the two reactors, the results suggest that data from the wire-mesh reactor may be successfully used to compare relative coal reactivities under pilot-plant gasification conditions.

An Environmental Scanning Electron Microscopy Study of Activated Charcoal Gasification Catalyzed by MoO3 in Air and in Oxygen and by a Eutectic Alloy of MoO3 and V2O5 in Air

An environmental scanning electron microscope (ESEM) was used to study the gasification of an activated carbon catalyzed by MoO3 in air and oxygen atmospheres and by a eutectic mixture and alloy of MoO3 and V2O5. In an air atmosphere, the melting of MoO3 starts at 630 °C and the reaction occurs by preferential gasification on the edges of carbon particles. In an O2 atmosphere, however, homogeneous gasification is observed in all directions. This difference can be explained by more extensive oxidation of the carbon surface in an oxygen atmosphere and the more effective spreading of the catalysts on charcoal surfaces. The ESEM experiments showed that some particles of the eutectic alloy of MoO3 and V2O5 had higher melting points than those of the single oxides. The analysis of alloy particles by EDS and by electron microprobe indicated that large areas of single oxides are segregated and encapsulated by the other oxide in some alloy particles. It is proposed that the encapsulation of either oxide (MoO3 or V...

Kinetics, in situ X-ray diffraction and environmental scanning electron microscopy of activated charcoal gasification catalyzed by vanadium oxide, molybdenum oxide and their eutectic alloy

Mechanisms of carbon oxidation catalyzed by vanadium pentaoxide (V 2O 5) and molybdenum trioxide (MoO 3) have been a subject of controversy. Two complementary in situ techniques, X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), were used in this work to study the gasification of an activated charcoal catalyzed by the two metal oxides, their eutectic alloy and the binary mixture with the eutectic composition. Gasification experiments were carried out at relatively low temperatures (300–650 °C) in an XRD cell (1 atm) and ESEM (2.2 Torr) to monitor phase transformations and morphological changes of oxide catalysts, respectively. The experimental results showed that MoO 3 and V 2O 5 particles in contact with active carbon surfaces are reduced to oxides with lower oxidation states, e.g. MoO 2 and V 6O 13, respectively. The reduction of MoO 3 to MoO 2 on the carbon surface prevents the sublimation of MoO 3 which takes place readily on a quartz surface under the same conditions. The formation of V 6O 13, on the other hand, causes more extensive spreading of the catalyst on carbon surfaces, since V 6O 13 has a lower melting point than V 2O 5. Based on the XRD and ESEM observations, it is clear that phase transformations of metal oxides during gasification depend on their interactions with carbon surfaces. The phase transformations of the metal oxides, play, in turn, a significant role in carbon gasification, as evident from the kinetic data obtained for the catalytic gasification of the activated charcoal sample. The synergy observed between the components of the eutectic mixture is discussed, comparing the XRD and ESEM observations.

96/04844 Calculation and exergy analysis of process schemes for coal gasification to produce coke, methanol, energy and heat accompanied by a catalytic liquid phase purification of gases and toxic components

CO2 gasification of a gas-coal char catalysed by Na2CO3 and K2CO3 was studied using a fixed-bed reactor at 790–1020°C and 0.2 MPa. The gasification rate increased with increasing temperature. With increasing addition of Na2CO3 in the range 9–25 wt% and K2CO3 in the range 5–20 wt% the rate increased sharply. The catalytic effect of K2CO3 was greater than that of Na2CO3. The effect of catalyst loading on rate showed saturation above 25 wt% for Na2CO3 and 20 wt% for K2CO3. The reaction rate constants and activation energies were measured in the ranges 850–960°C and catalyst loading 1–16 wt%. In this catalytic gasification reaction a compensation effect appeared; the isokinetic temperatures were 1289°C for Na2CO3 and 1466°C for K2CO3.

Oxygen and CO2 Gasification of Chars from Wood Treated with Iron(II) and Iron(III) Sulfates

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOxygen and CO2 Gasification of Chars from Wood Treated with Iron(II) and Iron(III) SulfatesGlenn R. Ponder and Geoffrey N. RichardsCite this: Energy Fuels 1994, 8, 3, 705–713Publication Date (Print):May 1, 1994Publication History Published online1 May 2002Published inissue 1 May 1994https://doi.org/10.1021/ef00045a027RIGHTS & PERMISSIONSArticle Views95Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Catalytic gasification of active charcoal by carbon dioxide: influence of type of catalyst and carbon particle size

Catalytic gasification of coal has many technical advantages. Investigations have been undertaken to select an efficient and cheap catalyst for gasification of carbon and to determine the optimum particle size if any. The results of the gasification study have been correlated with the carbothermic reduction of iron ore.

Investigations into the compensation effect at catalytic gasification of active charcoal by carbon dioxide

Some special features have been noticed in the catalytic gasification of active charcoal by CO 2. In the temperature range 770–920 °C, 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 catalysis due to ferric nitrate shows the reverse trend for the same carbon substrate. These differences in behaviour are also reflected in very different values of isokinetic temperature (1176 °C for sodium lignosulphate and 702 °C for ferric nitrate). This novel observation in compensation behaviour for two different catalysts on the same carbon can be explained on the basis of differing physical and chemical characteristics of the catalytic species.

A quantitative evaluation of active site number for CO2 gasification of various coal chars by temperature-programmed desorption method.

A temperature-programmed desorption (TPD) method was applied to the characterization of CO2 gasification of coal chars obtained by pyrolysis of coals of various ranks ranging from brown to sub-bituminous coals. Gasification was carried out at temperatures of 1073 and 1273 K and pressures from 0.4 to 1.6 MPa, using a high-pressure TGA apparatus. For all chars employed, the rate constant based on the initial char weight, kv, decreased with the progress of gasification. This variation of kv was unexplained in terms of the change in the BET surface area of the chars obtained at different conversions; in general, the rate constant based upon the surface area, ks, decreased with char conversion lower than about 0.2 and then remained constant before decreasing again at the conversion of 0.8 towards the completion of the reaction. The active site number, NCO, was evaluated on the basis of the amount of CO desorbed in TPD runs after CO2 was adsorbed. Thus, the rate constant per unit number of active sites, ka, was estimated on the basis of the NCO and the Kv values for chars having different conversion levels. The values of ka obtained at 1073 and 1173 K were found to be invariable for conversions up to about 0.8 to 0.9 and to be of the same order of the magnitude for all chars at a given temperature. However, in all cases they decreased with conversion in the range higher than 0.9. This decrease in char reactivity was attributed to variation in the carbon structure of the char. X-ray diffraction spectra indicated an appreciable growth of the graphite peak at the final stage of gasification.

石炭チャーの炭酸ガスによるガス化速度に及ぼす炭種の影響

Apparent rates of CO2 gasification of chars obtained from thirteen different kinds of coals were measured at temperatures of 1073-1273 K and under pressures of 0.3-1.6 MPa by means of a high pressure TGA apparatus. Changes of the surface area and the carbon structure of the reaction residue during gasification were also measured at various char conversions from 0 to 0.90.The initial surface area of char obtained by carbonization prior to gasification was shown to depend not only on the coal nature and carbonization temperature but also on the heating rate.For all chars employed the apparent initial reaction rate increased in proportion to P0.25. During gasification the surface area of the reaction residue increased rapidly at the early stage of the reaction and then decreased after showing a maximum which was greater for lower temperatures.The instantaneous rate based on the unit surface area also changed with the conversion. For all coal chars it decreased and leveled off at a conversion less than about 0.3. In a coversion range between 0.3 and 0.8 it was almost steady and decreased again towards completion of the reaction . Though the steady rate decreased with the rank of raw coal, the activation energies were approximately the same for all chars, being 190-210 KJ/mol.The growth of (002) peak in the X-ray diffraction spectrum for some kinds of chars, which was specified as caused by graphite structure formed during reaction, corresponded well to the decrease of instantaneous rate at the final stage of the reaction. The formation of graphite structure in such a low temperature was inhibited by deashing the char before gasification.

Catalytic CO 2-gasification of graphite versus coal char

The effects of alkali carbonate catalysts on the C0 2-gasification of Illinois No. 6 hvB bituminous coal char, demineralized Illinois No. 6 coal char, Pittsburgh No. 8 hvA coal char, Navajo subbituminous coal char, Reading anthracite coal char, North Dakota A lignite char and spectroscopic grade highest purity graphite are reported. Alkali carbonate salts are effective Boudouard catalysts for all these substrates, but salient differences between coal char and graphite reactivity are observed. To account for these differences, a redox mechanism based on alkali hydride intermediates is proposed.

Gasification of Charcoal by Hydrogen in the Presence of Platinum Catalyst

Gasification of Charcoal by Hydrogen in the Presence of Platinum Catalyst