Hiroyuki Kawashima

Removal of H2S from hot gas in the presence of Cu-containing sorbents

Three solids containing Cu oxides were tested as sorbents for H2S removal from hot gas at 600 °C. The formation of a surface layer of sulphides on pellet exterior affected Cu utilization for the sorbent prepared from Cu oxides alone. This improved for the sorbent prepared by impregnation of zeolite with Cu oxides, although complete utilization of Cu was not achieved. The combination of Cu oxides with SiO2 gave the most efficient sorbent. Oxidation of H2S to SO2 on admission of hot gas to the fixed bed was a common observation for all sorbents. The addition of steam to hot gas suppressed the SO2 formation.

Catalytic nitrogen release during a fixed-bed pyrolysis of model coals containing pyrrolic or pyridinic nitrogen

Abstract In order to study nitrogen release from different nitrogen structures during coal pyrolysis, two model coals containing pyrrolic or pyridinic nitrogen have been prepared using cellulose and phenolic nitrogen compounds. Nitrogen release during pyrolysis of the model coals without and with catalyst has been studied in a fixed-bed reactor at 50°C/min up to 1000°C. The pyrolysis results show that HCN rather than NH3 is formed from the decomposition of pyrrolic and pyridinic nitrogen, and iron catalyst is effective on nitrogen removal for pyrrolic and pyridinic nitrogen. It is especially noteworthy that calcium catalyst also promotes nitrogen removal significantly from both pyrrolic and pyridinic nitrogen.

Studies on structural changes of coal density-separated components during pyrolysis by means of solid-state 13C NMR spectra

Abstract Solid-state 13 C NMR spectra of density-separated components of four coals were measured to obtain insight into the structural changes in maceral groups during pyrolysis. Each sample was pyrolyzed at 573–973 K in N 2 flow at a heating rate of 3 K min −1 . In all the coals, the lighter components underwent greater structural changes than the heavier components. For lower rank coals, the structure changed significantly between 623 and 723 K, indicating that aromatization of the aliphatic moiety or the elimination of aliphatic side chains began at 623 K, and the condensation of the aromatic moiety began at 723 K. Pyrolytic reactivity was lower in higher rank coals. Aromatization of the aliphatic moiety or elimination of aliphatic side chains took place to a greater extent in lower than in higher rank coals. After pyrolysis at 773 K, the fractions of each carbon, as measured by solid-state 13 C NMR, were similar in all samples, which indicates that all samples had the same first-order structure after pyrolysis. Most of the reactivity of each sample was related to the proportion of aliphatic moieties present in each sample. Thus, it is concluded that the content of aliphatic moieties in each maceral group determines its reactivity.

Smectite and illite/smectite mixed-layer clay minerals in the Ashibetsu coals

Abstract Smectite, K-smectite and illite/smectite (I/S) mixed-layer minerals are found as expandable clay minerals in the Paleogene coal seams of the Ashibetsu coal mine in the Ishikari coal field, Hokkaido, Japan. As K-smectite often exists in tuff, tuffaceous shale and coal near tuff, and only occasionally in shale, the K-smectite is simply thought to represent detrital input from tuff. Smectite often exists in the coals near intercalated tuff, roof tuff and tuffaceous shale beds, but is not found in these sediments. Although many tuffs contain both K-smectite and I/S mixed-layer clay minerals, the smectite coexists with only K-smectite in many coals and the coal in which smectite occurs never has both of the other minerals. From these relationships it may be inferred that smectite was formed in the coal mainly from the I/S mixed layer and only partly from K-smectite. The I/S mixed-layer clay found in the tuff and tuffaceous shale is never accompanied by illite but the I/S mixed-layer clay in the shale is almost always accompanied by illite. I/S mixed-layer clay without illite exists in some coals near tuff and I/S mixed-layer clay with illite is often found in the other coals. These relationships mean that the I/S mixed-layer clay in the coal is also of detrital origin, derived from the same sources as both the tuff and the shale beds. The I/S mixed-layer clays plotted using Watanabes (1981, 1988) identification graph show a pattern consistent with illitization by diagenesis. The illitization appears to be related to the burial depth and/or coal rank. It is also shown that the mixed-layer clays in the shales have higher illite layer ratios than those in the tuffs, the tuffaceous shales and the coals without illite. From this evidence it appears that the composition of I/S mixed-layer clay depends mainly on processes associated with the source of the original sediment input.

Change of nitrogen functionality of 15N-enriched condensation products during pyrolysis

Changes in the nitrogen functionality of 15 N-enriched condensation products prepared from glucose and 15 N-glycine were investigated during pyrolysis at 600-1000 °C. The structural changes in the condensation products were studied by means of solid-state 13 C and 15 N NMR spectroscopies. During pyrolysis, the aliphatic moieties of the condensation products decomposed and evolved as gas and tar. At pyrolysis temperatures above 600 °C, almost all the carbon in the chars were converted to aromatic carbon. After pyrolysis, large amounts of nitrogen remained in the chars as char nitrogen (char-N), and about 30% of the nitrogen was eliminated from the chars as HCN and NH 3 . With increasing temperature, the production of HCN and NH 3 increased and the amount of char-N decreased. By combining X-ray photoelectron spectroscopy and NMR results, detailed results for nitrogen fractions in chars were obtained. During pyrolysis, the fraction of unsubstituted pyrrole-N decreased and the fraction of quaternary-N increased. The fraction of pyridine-N remained almost constant at temperatures below 800 °C, but at 900 °C and above, the fraction of pyridine-N decreased. The fraction of substituted pyrrole-N showed minimum at 800 °C. On the basis of these results, structural changes of nitrogen functional groups during pyrolysis are discussed.

Molecular simulation of relaxation behaviors of coal-aggregated structures

Abstract Upper Freeport coal (Argonne Premium Coal Sample, APCS 1) was extracted and fractionated with a carbon disulfide/ N -methyl-2-pyrrolidinone mixed solvent, acetone and pyridine at room temperature, and three extract fractions were obtained: acetone-soluble (AS), acetone-insoluble–pyridine-soluble (PS) and pyridine-insoluble (PI) fractions. A molecular dynamics (MD) computer simulation method was used to study the structural relaxation behaviors of the fractions during heating. The calculation was carried out at 373–773 K in order to see changes in various properties by heat. For the PS and PI fractions, the temperature at which the average volume of unit cell discontinuously changed was observed. The DSC thermograms of PS and PI showed a reversible endothermic peak at 610–710 and 650–710 K, respectively, corresponding to the temperature ranges in which the structural relaxation was estimated by the simulation. The simulation suggests that the endothermic peak is the result of physical relaxation of the aggregated structures through dissociation of nonbonded interactions.

A modified solid-state 13C CP/MAS NMR for the study of coal

Abstract A ramped-amplitude cross-polarization (RAMP-CP) was applied to coal measurement by solid-state 13 C NMR. Usual CP pulse sequence consists of a 1 H 90° pulse, the CP pulses and data acquisition under high-power 1 H decoupling. In the RAMP-CP pulse sequence in this study, 13 C spin-lock amplitude was changed linearly during CP while 1 H spin-lock amplitude was constant. The parameters for RAMP-CP/MAS measurement, Δ ω 1C (the change in the field strength of the spin-lock for 13 C ) and total contact time, were estimated for Upper Freeport coal using solid-state 13 C NMR. The results show that the signal intensity of the coal can be increased compared with the usual CP/MAS method by using the RAMP-CP/MAS method. Under the condition that the 1 H field strength was at 62.5 kHz, by using RAMP-CP/MAS method, the signal intensity of Upper Freeport coal increased compared with the CP/MAS method at Δ ω 1C =0.625–3.125 kHz and the total contact time was 2 ms.

Synergetic photocatalysts derived from porous organo Ti–O clusters pillared graphene oxide frameworks (GOFs)

Unique nanocomposites comprising thin TiO2 nanoplates and lamellar carbon sheets were derived from organo Ti–O clusters pillared graphene oxide (GO), a porous layered framework synthesized by intercalating GO layers with organo-Ti reagents via a simultaneous intercalation and hydrolysis process. The nanocomposites display both high adsorption capacity and enhanced photocatalytic activity towards methyl orange (MO), promising as synergetic photocatalysts for the removal of organic contaminates in a water environment.

4 A/cm 2 , 7kV normally-off diamond-emitter vacuum switch

We have been proposed ultra-high voltage vacuum switches using diamond pin diode-type electron emitters with a negative electron affinity. Based on the previous 10 kV demonstration, our recent progress on high current operations above 1 A/cm2 in the vacuum switch is presented. High voltage of 7kV normally-off operation was confirmed, and then we evaluated the capability of this device based on our model.

Progress on diamond PIN diode emitters with negative electron affinity for high-voltage d.c. vacuum switches

We have reported on ultra-high-voltage vacuum switches using diamond pin diode-type electron emitters with negative electron affinity. Based on the previous 10-kV demonstration, we present our recent progress on high-current operations at 4 A/cm2 in these vacuum switches. We confirmed a normally-off mode at a high voltage of 7 kV; in addition, we evaluated the capability of this device based on our model.