Yuji Matsumura

High catalytic activity of pitch-based activated carbon fibres of moderate surface area for oxidation of NO to NO2 at room temperature

Catalytic oxidation of NO (380 ppmv) to NO2 over activated carbon fibres of moderate surface area (∼800 m2 g−1) at room temperature was carried out, to develop oxidative removal of NO from flue gas. The heat treatment of pitch-based activated carbon fibres of moderate surface area markedly increased the conversion of NO to 87% in dry air, 62% in air of 80% relative humidity and 24% in wet air (100% r.h.) at 25°C and a ratio of fibre mass to gas flow rate of 1.0 × 10−2g min mL−1. The strong inhibiting effect of humidity on the activity of the as-received fibres was moderated by heat treatment of the fibres at 850°C. A lower concentration of 10 ppmv NO markedly reduced the oxidation, the conversions being 24 and 5% in dry and wet (100% r.h.) air respectively. The catalytic activities of other pitch-based fibres of different surface area were also much inferior in moist air above 60% r.h.

Kinetic study of the continuous removal of SOx on polyacrylonitrile-based activated carbon fibres: 1. Catalytic activity of PAN-ACF heat-treated at 800°C

Continuous removal of SO2 as aqueous H2SO4 over polyacrylonitrile-based activated carbon fibres (PAN-ACF) was studied kinetically at room temperature to determine the effects of SO2 (20–1000 ppmv), O2 (0–10 vol.%) and H2O (0–10 vol.%) concentrations and WQ ratio (mass of ACF/volumetric flow rate of gas). An oxygen level > 3 vol.% was sufficient to provide steady-state removal of SO2. Higher inlet SO2 concentrations gave higher SO2 outlet concentrations, while more H2O and a higher WQ ratio increased the SO2 removal. On the basis of this kinetic study, the rate-determining step is postulated to be aqueous H2SO4 desorption from the ACF bed, which makes sites available for further SO2 adsorption. Hence a lower SO2 concentration, more H2O, and a higher WQ ratio are compensating factors in achieving the complete removal of SO2 by continuous recovery of aqueous H2SO4 at the outlet.

Effects of carbon black addition on preparation of meso-carbon microbeads

Abstract The preparation of meso-carbon microbeads (MCMB) has been studied by heat-treating two synthetic isotropic naphthalene pitches at 380–430 °C for 1-12 hours in the presence of several types of carbon blacks. A larger number of beads with small diameter, ranging from 1 to 10 μm, were obtained. The yields of the beads assessed volumetrically by microscope and gravimetrically by pyridine extraction reached to as high as 45 vol% and 30 wt%, respectively. A particular heat-treatment temperature (400 °C) appears optimum to give a narrower size distribution of the spheres than other temperatures (380 and 420 °C) with 1 wt% carbon black. The lower temperature and longer time with 3 wt% Ketjen Black favored the formation of uniform size of beads. The carbon black appears to enhance the nucleation and to inhibit the growth and coalescence of the mesophase sphere. In the presence of carbon blacks the synthetic isotropic pitches tended to produce extracted spheres consisting of basic domain units in coagulated forms.

Efficient preparation of meso-carbon microbeads from synthetic isotropic pitch derived from naphthalene

Abstract An efficient preparation of mesophase spheres was attempted from synthetic isotropic pitches of naphthalene oligomers. A large number of spheres of rather uniform diameter were obtained by the carbonization at 380 °C for 20 h. Volumetric and yields of spheres in the pitch were volumetrically measured under the optical microscope and extracted; a pyridine soluble fraction as high as 42 vol% and 15 wt%, respectively was reached. Such a difference in the yields suggests that the spheres prepared in the present study included a significant amount of the pyridine soluble fraction. The extracted sphere carried a number of pores, leaving rod-like units. Self-assembling units of pyridine insoluble fraction produced in the mesophase are suggested to be precipitated to form a spherical shape.

Kinetic study of the continuous removal of SOx using polyacrylonitrile-based activated carbon fibres: 2. Kinetic model

Abstract Sulfur dioxide was continuously converted to aqueous sulfuric acid using a polyacrylonitrile-based activated carbon fibre catalyst (PAN-ACF) in a packed-bed reactor system. The qualitative effects of residence time and oxygen, nitrous oxide, sulfur dioxide, and water concentrations were reported in Part 1. The conversion conditions were chosen to be typical of those expected in flue gas streams: sulfur dioxide 20–1000 ppmv, oxygen 0–10 vol.% and water 0–20 vol.%. A power-law model was developed to describe the steady-state concentration of sulfur dioxide in the exit gas. Sulfur dioxide reaction rate was proportional to catalyst weight, oxygen concentration to the 0.25 power, sulfur dioxide concentration to the 0.123 power and water concentration to the 1.01 power. The model was used to compare the effects of reactor operating conditions on the outlet concentration of sulfur dioxide.

Preparation of mesocarbon microbeads by dispersing mesophase pitch in isotropic pitches

Abstract Mesocarbon microbeads of 1–10 μm were prepared through dispersing the synthetic mesophase pitches in synthetic isotropic pitches and successive solvent extraction. The suitable ratio of mesophase pitch/isotropic pitch, temperature and rapid agitation at dispersion were found to be key factors to obtain the high yields of tetrahydrofuran and pyridine insoluble microbeads which were 34 and 20 wt%, of the highest yield, respectively. In contrast, the combinations of coal tar derived mesophase pitch/synthetic pitch or synthetic mesophase pitch/petroleum A240 pitch failed to disperse spheres of mesophase pitch in the isotropic matrix, leaving bulk grains of mesophase pitch at the bottom of the matrix. The melt mesophase pitch of adequate viscosity is dispersed by the agitation into viscous droplets in the isotropic matrix, while the droplets stay afloat because of their similar specific gravities. The lighter component in the droplet of the mesophase pitch was extracted into the isotropic matrix while the mesophase pitch is melted, leaving spheres of smooth surface. Extraction by the solvent at a lower temperature than the softening point leaves mesocarbon microbeads isolated, removing the solvent soluble fraction.

New fluorine-carbon compound prepared by the direct fluorination of mesophase pitch

Abstract Mesophase pitch derived from coal tar was directly fluorinated by fluorine gas in order to prepare a new fluorine-carbon compound at temperatures between 50°C and 130°C. The obtained compound (pitch fluoride) was yellowish white. The composition of the compound was estimated to be between CF 1.30 and CF 1.59 by elemental analysis. Though the X-ray diffraction pattern of the pitch fluoride showed that its structure was similar to that of graphite fluoride, (CF) n with low crystallinity, it had some properties differing from (CF) n . First, the pitch fluoride was soluble in some fluorosolvents, such as C 6 F 6 , C 6 H 5 CF 3 , etc., while the graphite fluorides are insoluble in any solvent. Second, its thermal behavior was quite different from that of (CF) n ; (CF) n decomposes at temperatures higher than 500°C to amorphous carbon and gaseous fluorocarbons, such as CF 4 , C 2 F 6 etc., while the decomposition products of pitch fluoride were mainly solid fluorocarbons. An attractive feature of these compounds is that the thin film of the decomposed pitch fluoride could be formed on metal substrates by means of the vacuum-vapor-deposition method. The thin film of the decomposed pitch fluoride had a larger contact angle (113°) than PTFE (109°) against water, indicative of lower surface energy.