Jun'ichi Hayashi

Preparation of activated carbon from lignin by chemical activation

Activated carbons were prepared from lignin by chemical activation with ZnCl2, H3PO4 and some alkali metal compounds. The influence of carbonization and activating reagent on the pore structure of the activated carbon was investigated. It was found that the maximum surface areas were obtained at the carbonization temperature of 600°C in both ZnCl2 and H3PO4 activation, and that the surface areas were as large as those of the commercial activated carbons. On the other hand, in alkali metal activation it was found that the maximum surface areas were obtained at the carbonization temperature of 800°C. Except for Na2CO3 maximum surface areas were much larger than those of the commercial activated carbons. The activated carbon prepared by K2CO3 activation showed a surface area of nearly 2000 m2/g. It was shown that ZnCl2 works effectively as dehydration reagent below 600°C. On the other hand, K2CO3 works effectively in two temperature ranges, below 500°C and above 600°C. Below 500°C, the carbonization behavior was modified by impregnation with K2CO3, but the pore structure changes little. Above 600°C, carbon was consumed by K2CO3 reduction and then the surface area was increased.

Preparing activated carbon from various nutshells by chemical activation with K2CO3

We have prepared activated carbons by chemical activation with K2CO3 from five kinds of nutshells: almond shell (AM), coconut shell (CN), oil palm shell (OP), pistachio shell (PT) and walnut shell (WN). When prepared at 1073 K, the activated carbons from all the nutshells had the maximum specific surface areas. According to the maximum values of specific surface areas, the activated carbons prepared were classified into two groups: Group-L and Group-S; the former group included activated carbons with high specific surface area and the latter included those with lower specific surface area, respectively. It was found that K2CO3 effectively worked as an activation reagent, but differently in the temperature ranges below 800 and above 900 K. Due to impregnation, cellulose and hemi-cellulose were modified by K2CO3 and accordingly the weight loss behaviors of the nutshells were changed in the temperature range below 800 K. In the temperature range above 900 K, carbon in the chars was removed as CO gas by the reduction of K2CO3 to increase the specific surface area and the pore volume. It was deduced that the difference between the specific surface areas of Group-L and those of Group-S correspond to the difference between weight loss behaviors in the temperature range above 900 K.

Activated carbon from chickpea husk by chemical activation with K2CO3: preparation and characterization

Activated carbon was prepared from chickpea husk by chemical activation with K2CO3. At 1073 K, the specific surface area of activated carbon prepared with an impregnation ratio of 1.0 yielded the maximum value of 1778 m2/g. From the results of the yield of the activated carbon and the reagent recovery ratio, it was concluded that the carbon involved in the husk char was removed as CO by reduction of K2CO3 above 1000 K. The fractal dimension changed slightly between 773 and 973 K, and it decreased rapidly between 973 and 1173 K. It was deduced that this decrease of the fractal dimension was due to the decomposition of the cross-linked structure and the small crystallite structure. The micropore volume and the specific surface area increased by the release of plugged pore due to the decomposition of the cross-linked structure. It was further deduced that the mesopore volume increased and the micropore volume decreased by combination of micropores due to the decomposition of small crystallites.

Production of molecular sieving carbon through carbonization of coal modified by organic additives

Abstract A new method was presented for producing molecular sieving carbon (MSC) from coal. Finely ground coal particles were mixed with coal tar pitch, phenol and formaldehyde at 95°C to be agglomerated through the formation of phenol-formaldehyde resin. Then the agglomerated particles were solely carbonized in an inert atmosphere to produce chars. The chars thus prepared have pore structure different from that of the chars prepared from the original coal. By changing the carbonization temperature and the mixing ratio of coal, pitch, phenol, and formaldehyde, we could prepare several kinds of molecular sieving carbons with sharp pore distributions around 0.35 nm in diameter. One of the MSCs thus produced is expected to be used successfully for the production of nitrogen from air by the pressure swing adsorption process.

Synthesizing activated carbons from resins by chemical activation with K2CO3

We prepared activated carbons from phenol–formaldehyde (PF) and urea–formaldehyde (UF) resins by chemical activation with K2CO3 with impregnation during the synthesis of the resins. The influence of carbonization temperature (773–1173 K) on the pore structure (specific surface area and pore volume) and the temperature range at which K2CO3 worked effectively as an activation reagent, were investigated. The specific surface area and micropore volume of PF–AC and UF–AC increased with an increase of carbonization temperature in the range of 773–1173 K. We prepared activated carbon with well-developed micropores from PF, and activated carbon with high specific surface area (>3000 m2/g) and large meso-pore volume from UF. We deduced the activation mechanism with thermogravimetry and X-ray diffraction. In preparing activated carbon from PF, K2CO3 was reduced by carbon in the PF char. The carbon was removed as CO gas resulting in increased specific surface area and pore volume above 1000 K. In preparing AC from UF, above 900 K the carbon in UF char was consumed during the K2CO3 reduction step.

Characteristics and humidity control capacity of activated carbon from bamboo.

Activated carbons were prepared from bamboo by chemical activation with K2CO3 or physical activation with CO2. The structural and surface chemical characteristics of the activated carbons were determined by N2 adsorption-desorption and Boehm titration, respectively. The water vapor adsorption properties of the activated carbons with various pore structures (preparation conditions) were examined. The relationship between water vapor adsorption capacity and pore properties, and the humidity control capacity of the prepared activated carbons are also discussed. The water adsorption isotherms show a region of rapidly increasing uptake of water vapor, and the relative humidity corresponding to those regions was different according to the preparation conditions, especially activation temperature. Water vapor adsorption capacity was improved with larger pore volume and surface area, but the humidity control capacity in a certain specific humidity region differed greatly according to the relative humidity corresponding to the steeply rising regions of the isotherms. In the typical operating conditions of an adsorption heat pump, RH 10-35%, the bamboo-sourced activated carbon that was prepared at 873K by potassium carbonate activation with impregnation ratio 1.0 had the highest humidity control capacity.

Fractal dimensions of activated carbons prepared from lignin by chemical activation

the form of adsorbents, catalysts and catalyst supports. In was mixed with one of the activating reagent and water,principle, there are two methods for preparing activated and was kneaded. An impregnation ratio [(the weight ofcarbons: physical activation and chemical activation. The activating reagent)/(the weight of lignin)] of 1.0 was usedphysical activation method comprises two steps: a carboni- in this work. The mixture was then dried at 383 K tozation step and an activation step. In chemical activation, a prepare the impregnated sample. The impregnated sampleraw material is impregnated with an activating reagent and was heated up to the carbonization temperature under N

Preparation and characterization of the carbonized material of phenol–formaldehyde resin with addition of various organic substances

Abstract We prepared carbonized materials of phenol–formaldehyde resins (PF) synthesized with the addition of organic substances such as ethylene glycol (EG), 1,6-hexanediol (1,6HD), polyethylene glycol (PEG), etc. We investigated the influence of the carbonization temperature, the organic additive species, and the additive ratio in synthesizing the PF resins on the pore structure of the carbonized PFs. Variation in the length of the added organic substance caused differences in the pore sizes of the carbonized PFs; when the length was short, the pore size of the carbonized PF became gradually smaller with increasing carbonization temperature, but when the length was long, the pore size gradually increased with increasing carbonization temperature. The difference in the additive organic species gave different pore sizes in the carbonized PFs such that the longer the length of the organic additive the greater the pore size in the carbonized PF. The additive ratio of EG did not give a large change in the pore size of the carbonized PF, but the variance in the average pore sizes were sharper than that of the carbonized PF without any additives. On the other hand, the pore sizes of the carbonized PFs with a high additive ratio of PEG20K were greater, and the carbonized PFs had mesopores. The BET surface area of the carbonized PFs with a 50% additive ratio of PEG20K was about 500 m2/g.

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

Abstract 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 CO2 and CH4, and others for separating C3H8 and C3H6. 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.

A shape-selective catalyst utilizing a molecular sieving carbon with sharp pore distribution

Abstract We have previously presented a new method for preparing molecular sieving carbon (MSC) from the coal modified by pitch and phenol-formaldehyde (PF) resin. By resorting to this method, we could prepare MSCs with sharp pore distributions around 0.37 to 0.45 nm in diameter. In this paper the possibility of using the MSC as a catalyst support that shows shape selectivity was examined. Methanol decomposition was performed at 350–450°C on the MSC supporting Ni as a model reaction. Methanol is known to be decomposed to CO and H 2 first, then CH 4 , CO 2 , and H 2 O are produced through reactions between CO and H 2 . It was possible to produce only CO and H 2 , by using MSCs with sharp pore distributions around 0.45 nm in diameter. On the other hand, all the products were detected by use of the activated carbon whose pore distribution was broadened through steam activation of the MSC. This difference was found to be derived from the difference in the pore distributions between the MSC and the activated carbon. Thus it was clarified that the MSC with sharp pore distribution can be utilized as a shape selective catalyst support.