Phenol-formaldehyde Resin Char Research Articles

Heterogeneous reaction of N2O with phenol-formaldehyde resin char and NO formation, reduction and inhibition at high temperature

N2O as one of the most important nitrogen oxides harmful to the environment, has been found to be closely related to NO in air-staged combustion. The effect of PFR (phenol-formaldehyde resin) char without nitrogen source on N2O reduction and NO formation was first studied in a high-temperature fixed bed reactor. The inhibitor was creatively used to change the reaction path of N2O to NO, to understand better the phenomenon of NO second rise in the industrial boilers. The results show that the reduction efficiency of N2O by PFR char increases with the increase of temperature. Higher oxygen concentration at a lower temperature is beneficial to promote the reduction of N2O by forming carbon active sites, but opposite at higher temperature. In the transitional atmosphere, the reducibility of char to NO that converted from N2O decreases with the increase of temperature, even lower than 0.2 at high temperature, which cannot prevent the second rise of NO. The iodine inhibitor can increase the reaction progress of R6 and then causes the rapid decomposition of N2O through reaction (R13). The iodine changes the of O-radicals' path in the reaction through the reaction (R10)–(R13), which acts as a “Porter”, converting O-radical to O2 and inhibiting the formation of NO. This study hopes to provide new ideas and solutions for the follow-up of ultra-low NOx emissions.

The performance of electric double layer capacitors using particulate porous carbons derived from PAN fiber and phenol-formaldehyde resin

Activated carbon fibers are known to contain pores with a small resistance for electrolyte migration while possessing a large electrical resistance between the fibers. A carbon powder derived from pulverization of PAN-based carbon fibers was examined as an electrode for electric double layer capacitors using H 2SO 4 as the electrolyte solution. The performance of conventional-type activated carbon powders derived from phenol-formaldehyde resin char was also measured for comparison. The fiber-derived carbon exhibited an electrical resistance comparable to that of the conventional carbons while showed a larger specific capacitance as well as a lesser extent of capacitance decrease at high currents due to a smaller pore resistance. An ultimate capacitance as high as 290 F g −1 can be reached for this fiber-derived carbon powder (with a BET surface area of ≈1300 m 2 g −1). This large capacitance value was suggested to be associated with the high activity feature of the pore wall.

Preparation of molecular sieving carbon from waste resin by chemical vapor deposition

Molecular sieving carbons (MSCs) were prepared from carbonized phenol–formaldehyde resin wastes by the chemical vapor deposition (CVD) of the pyrolyzed carbon from hydrocarbon species. The pore size of the MSCs could be controlled in the range 0.37–0.42 nm by changing the hydrocarbon species pyrolyzed, the pyrolyzing temperature, and the processing time. It is shown that some of the MSCs have an excellent selectivity for separating CO 2 and CH 4, and others for separating C 3H 8 and C 3H 6. As the mechanism for controlling the pore size during CVD processing, we elucidated that the adsorption of hydrocarbon molecules first takes place on the pore surface and then the adsorbed hydrocarbons pyrolyze into carbon. Therefore, the pore size of the MSC can be adjusted by controlling the amount hydrocarbon adsorbed on the phenol–formaldehyde resin char.

Comparison of structural parameters of PF carbon from XRD and HRTEM techniques

A new technique to obtain structural parameters L c , L a and d, of phenol formaldehyde resin char (PFC) from TEM images has been developed. Similar structural parameters were also obtained from XRD technique and a comprehensive comparison of the results from the two techniques was made. The present study shows a good agreement between the results from the two techniques. The TEM technique also provided additional information about the distribution of layer size with stacking number, which can not be obtained from XRD technique.

C−NO reaction in the presence of O 2

The reactions of NO with pure carbons, phenol-formaldehyde resin char and amorphous 13C, were examined at 850°C in the presence of O2. Previous studies revealed that some of the nitrogen in NO was trapped on the carbon surface, and it plays an important role in the C−NO reaction. In order to quantitatively investigate the formation and removal of N-containing complexes on the carbon surface, C(N), in the presence of O2, a detailed material balance in the course of NO reduction over the carbons, was established by using both mass spectrometer and gas chromatography. The presence of O2 greatly enhanced the NO reduction rate. It was found that the N2 and N2O production rates increased, whereas the accumulation of C(N) considerably decreased with increasing O2 concentration. The C−NO reaction mechanism in the presence of O2 was examined by step response experiments at 850°C, where the reactant gas was switched from 14N16O/16O2 to 15N18O/18O2. Analysis of the product gases after the feed gas switch gives much information on the reaction pathways. It was suggested that the most dominant N2 formation route is the reaction between C(N) and NO gas under the present conditions. This mechanism is the same as observed previously in the absence of O2. The reaction of C(N) with O2 at 850°C was also carried out, and the principal product was found to be N2 in the early stage and NO in the later stage. As one of the possible roles of O2 on the NO reduction by carbon, the increase of C(N) turnover by the action of O2 was suggested: that is, O2 assists the liberation of C(N) from the carbon surface to produce gaseous products.

A study of the CNO reaction by using isotopically labelled C and NO

The role of O- and N-containing surface species in the course of NO reduction over phenol-formaldehyde resin char and amorphous 13C was investigated. The presence of O-containing complexes on the char surface was shown to increase the reactivity towards NO by providing free reactive sites. The presence of O 2 also enhanced the NO reduction reaction greatly. A mass balance during temperature-programmed reaction indicated nitrogen accumulation on the char surface. The reaction mechanism was examined by a transient kinetic approach, in which the reactant gas was switched from 14N 16O to 15N 18O. The surface N-containing species produced and accumulated in the first stage, C( 14N), was found to react with 15N 18O, yielding 14N 15N. This indicated that one N 2 formation path is the reaction between nitrogen-containing surface compound and NO.

Structural study of a phenolformaldehyde char

An extensive description of the chemical and structural properties of a phenolformaldehyde resin char has been made. The phenolformaldehyde char used is a high purity carbon with a developed porosity. An extensive characterization of its structure has been performed with techniques such as Scanning Electron Microscopy (SEM), Scanning Tunneling Microscopy (STM) and Neutron Diffraction. The study carried out shows some important differences in respect to the proposed structure for activated carbons. The results obtained reveal the existence of globular structures of different shapes and dimensions. These aggregations are composed of graphite layers with an order that extends to about 7 Å.

アルカリ土類炭酸塩を用いた石炭チャーのＣＯ２ガス化 鉱物質による活性低下

Yallourn (YL), Taiheiyo-Kushiro (TK), Grose Valley (GV), and Tatung Yunkang (TY) coal chars loaded with various alkaline earth carbonates were gasified with carbon dioxide by a thermobalance. The measured catalytic activity of additions was mainly discussed in terms of the reaction with mineral matters in the coal char checked by X-ray diffraction (XRD).All the carbonates except for magnesium raised the gasification reactivity of coal chars, but the catalytic effect was not so large as that on phenol-formaldehyde resin char (PFC) free from ash. The catalytic activity was particulary small with GV-and TK chars of higher ash content and their gasification residues at 900°C produced XRD peaks assingned to aluminosilicates (Ca2Al2SiO7, CaAl2Si2O8, SrAl2Si2O8, and BaAl2Si2O8) and silicates (Ca3Si2O7, SrSiO3, BaSi2O5, and Ba2SiO4) which could not be observed with the PFC residue. Deminerallization of the two chars by acid treatment enhanced the catalytic effect and the XRD peaks disappeared. According to temperature-programmed XRD, the above alkaline earth aluminosilicates and silicates were formed at about 700-750°C. Above this temperature, the pronounced catalytic activity loss was found to occur. These results indicate that, during the gasification, alkaline earth carbonates react with alumina and silica components of coal ash to lose their catalytic activities.

炭素質のＣＯ２ガス化反応に対するアルカリ土類金属塩化物の触媒活性 炭素質と触媒との接触性

In the gasification of phenol-formaldehyde resin char (PFC) added alka-line earth chlorides of Mg, Ca, Sr, and Ba as catalysts by carbon dioxide, the catalytic activ-ity measured by thermogravimetry (TG) was discussed in connection with the contact be-tween catalyst species and carbon and the chemical transformation of the catalyst in the gasification temperature range by means of contact angle measurement (CAM) and X-ray diffraction (XRD).According to temperature-programmed TG curves obtained, the catalytic activity se-quence was found to be Ca> Sr > Ba > Mg. This was different from the order Ba > Sr-Ca > Mg for carbonate and nitrate already reported. The catalytic mechanism of the chloride would be based on the cyclic raction of oxide-carbonate similarly to acetate from the result by XRD. But, the information of CAM indicated that the catalytic activity of chlorides was more greatly governed by the melting and wetting on PFC than the chemical change into the corresponding oxide and carbonate.

Catalytic activity of physically-mixed nickel compounds on the CO 2 gasification of phenol-formaldehyde resin char

In order to account for the various activities of different nickel compounds in low temperature catalytic gasification of carbon the reducibility of individual nickel compounds in carbon dioxide to metallic was studied by thermogravimetry and the behaviour of mixture of nickel salts with a phenol-nickel formaldehyde resin char was investigated by temperature-programmed X-ray diffraction analysis. A correlation was found between the order of reducibility of the nickel salts and their order of activity in catalytic gasification. Low temperature gasification up to 98 wt% was demonstrated for char mixed with nickel acetate (up to 9/10 wt% Ni), which suggests that there may be good prospects for finding a method of complete gasification with nickel.

Catalytic Behavior of Alkaline Earth Metal Compounds on Carbon and Carbon Dioxide Reaction

Catalytic effect of the alkaline earth metal compounds of Mg, Ca, Sr and Ba on the reaction of phenol-formaldehyde resin char (PFC) with carbon dioxide was evaluated by using a thermo-balance. The catalyst of 0.5 atom% were mixed with PFC in a mortar grinder for 1 hour.It was found the thermogravimetric (TG) measurement that Ca, Sr and Ba compounds had appreciable catalytic action, and Ba compounds was the most effective additive among them, but Mg compounds was ineffective. In experiments of a series of anion species, these carbonate, oxide, hydroxide, nitrate and acetate, except Mg compounds, were shown to have larger catalytic effect than those chlorides and sulfates.The catalytic reaction mechanism of these compounds was inquired from measurement of TG curve in an atmosphere of CO2 or He and X-ray diffraction. The catalytic mechanism would be based on the cyclic reaction of oxidecarbonate for carbonate, oxide, hydroxide, nitrate acetate and even chloride, while for sulfate, another cycle of sulfidesulfate might be involved.

Preferential alignment of carbon layers around pores in hard carbon and multi-phase graphitization

The structure of a phenol formaldehyde resin char and its changes with heat treatment to temperatures from 1600 to 2700°C were investigated by polarized light microscopy and by X-ray diffraction. Concentrical carbon layers were observed to be aligned along the periphery of pores with diameters of the order of 100 μm. After removing the peripheral parts by wet oxidation, the specimens were subsequently heat-treated again up to 2700°C: this however produced no indication of graphitization in the residual. These results imply that the graphitization takes place in packets of carbon layers around pores which were formed in the processes of hardening and carbonization of the resin, while the isotropic carbon matrix is left ungraphitized. This may be the mechanism of the so-called multi-phase graphitization in hard carbons.

Microscopic observations of hard carbon heat-treated under pressure

The two hard carbons PH-7, a phenolformaldehyde resin char carbonized to 700°C and PH-15, which was the same PH-7 heat-treated for 60 min at 1500°C under reduced pressure, were heat-treated at various temperatures under pressure of 5 kbar and examined using a polarized light microscope. Bright golden-yellow areas with birefringence are observed at contacts between angular grains and these areas increase with the increase in HTT. The percentage increase in these optically anisotropic areas corresponds to the increase in the content of the graphitic component as determined by X-rays. The results show that large strains due to the concentration of the compressive stress at the contacts of the grains causes graphitization of hard carbons.

Effect of Pressure on Graphitization of Carbon. V. Electron Spin Resonance in Hard Carbon Heat-Treated under High Pressure

Abstract By means of the electron spin resonance (ESR), the graphitization process of a hard carbon (phenolformaldehyde resin char) under a pressure of 5 kbar was investigated in relation to the results of the X-ray diffraction analysis. In the ESR measurement, there is observed only a sharp Lorentzian line having g-value of about 2.003 for the products heat-treated at relatively low temperatures. On the other hand, gradual increase in the heat treatment temperature (HTT) leads to the appearance of new 15–20 G wide line having g-value of about 2.01, overlapping on the sharp one, and its absorption intensity tends to increase further with HTT. The appearance of the broad ESR line has been found always being accompanied by an abrupt increase of the content of graphitic component deduced from the analysis of (002) diffraction profile. From further investigation of features of these ESR lines as a function of ambient temperature, the sharp one is concluded that it originates from the so-called localized spin centers, while the broad one from the delocalized. The coexistence of these two signals suggests that the turbostratic and graphitic parts have enough extent to prevent the motional mixing of these spin centers, which has also been verified by the X-ray diffraction analysis.

Effect of Pressure on Graphitization of Carbon. IV. Abrupt Graphitization of Hard Carbon under 5 kbar

Abstract A hard carbon, phenolformaldehyde resin char carbonized to 700°C, was heat-treated under a quasi-hydrostatic pressure of 5 kbar at various temperatures between 1100–1800°C for the residence times of 3, 20 and 60 min. The graphitization process of the hard carbon under pressure consisted of three stages. In the first stage of the graphitization, the profile of (002) diffraction line was symmetrical. It means that there is only one component AH in the sample. In the second and third stages of graphitization, the (002) profile became composite. In the second stage, three components AH, G′H and G″H coexisted in the sample. The sum of the contents of the components G′H and G″H was less than 20% and increased gradually with heat treatment temperature. In the third stage, two components AH and G″H coexisted. The content of the component G″H increased abruptly up to more than 70% at about 1400, 1500 and 1700°C for the residence time of 60, 20 and 3 min, respectively. The components AH and G″H have the turbostratic and graphitic structures, respectively. The component G′H seemed to have the intermediate structure between turbostratic and graphitic structures.