Development of Novel Carbon Fiber Produced from Waste Fiber by Cabonization

Development of Novel Carbon Fiber produced from Waste Fiber by Cabonization Naohito Kawasaki＊ , Hisato Tominaga, Fumihiko Ogata, Kenji Inoue and Moe Kankawa Faculty of Pharmacy, Kinki University, (3-4-1, Kowakae, Higashi-Osaka, Osaka 577-8502, JAPAN)

Abstract: The volume of waste fiber has increased rapidly in recent years, and this trend is expected to continue. In this study, therefore, we attempted to convert waste fiber to carbonaceous materials by carbonization and investigated the basic properties of the resulting carbonized fibers. The results demonstrated that pores tend to form and specific surface areas change substantially, depending on the carbonization conditions. The carbonization conditions resulting in the largest specific surface areas included a temperature increase and retention times of 2 h. Carbonization temperatures resulting in the maximum values of 1000℃ were 900–1000℃ for wool and 1000℃ for both polyester and cotton. In particular, the specific surface area of cotton after carbonization at 1000℃ was 1253 m2/g, and scanning electron microscopy (SEM) micrographs showed that cotton retained its fibrous form after carbonization. Thus, it is possible to inexpensively convert waste fibers to carbonaceous material by carbonization. The results indicate that for cotton fiber in particular, the practical application of this process to the production of low-cost fibrous activated carbon would be possible, since cotton fiber retains its fibrous form under carbonization.

Key words: Waste Fiber; Carbonization; Pore Size Distribution; Conversion

1 INTRODUCTION responsibility in their pursuit of profits. However, recycling In recent years, increases in population and industrial rates for fiber products have not been rising, largely activity have led to many mutually related problems world- because of consumer resistance to the use of recycled wide concerning the environment, resources, and energy. products and the cost of recycling. Essentially, material cycle systems undergo breakdowns, People have used wool, cotton, and other natural fibers and effective use of waste materials as resources can con- throughout recorded history. The development of chemical tribute to the integrity of these systems. fibers began in 1884, and today they account for 60％ of With the declining prices of fiber products, their life the total volume of fiber use. Most of the chemical fibers cycle has shortened. In Japan alone, the annual volume of are petroleum-based polymers, and its effective utilization fiber waste discharge has reached some two million tons, is highly desirable. and the product life cycle has substantially shortened. Activated carbon, which is produced from materials such Moreover, the rapid rise in fiber imports appears to be as palm shell, petroleum pitch, and coal, is widely used for causing a rise in oversupply, dead stock, and subsequent the adsorption of organic compounds and harmful sub- disposal of unsold products. Approximately 10％ of all fiber stances4－7）. Fibrous activated carbon is characterized by a products are recycled, mostly in the form of incineration higher specific surface area, adsorption rate, and adsorp- and land reclamation. Other forms of recycling include tion efficiency than granular activated carbon8, 9）, but its chemical decomposition and regeneration of polyester production process is also more complex and expensive. In （PE）fiber, reuse of cotton as an automotive insulation ma- recent years, a trend has emerged for the production of terial, and export of used clothing to Southeast Asia and low-cost, useful carbonaceous materials from biomasses other regions. The use of these products as a reinforcing such as apricot shells10）, rubber wood sawdust11, 12）, material in walls and other applications has also been re- bamboo13）, jute fiber14）, and other agricultural by-products. ported1－3）. In recent years, in an effort to expand clothing An investigation has also been carried out on the produc- recycling, corporations have been asked to exercise social tion of activated carbon from cotton yarn using 4％ calcium

＊Correspondence to: Naohito Kawasaki, Professor Faculty of Pharmacy, Department of Pharmacy 3-4-1, Kowakae, Higashi-Osaka, Osaka 577-8502, JAPAN E-mail: [email protected] Accepted May 24, 2012 (recieved for review February 27, 2012) Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online http://www.jstage.jst.go.jp/browse/jos/ http://mc.manusriptcentral.com/jjocs

593 N. Kawasaki, H. Tominaga, F. Ogata et al.

phosphate as an activator, and its ability to adsorb p-ni- sure of 0.025-0.99 and the desorption isotherm at a relative troaniline15, 16）has also been investigated. The various pressure of 0.1-0.99 were determined at the temperature methods of activated charcoal production that have been of liquid nitrogen. Then, the values were calculated by the reported generally include not only carbonization but also Dollimore-Heal method18）. The pores were considered to activation by processing with steam or chemical substanc- be cylindrical, and the average pore diameter（D）was cal- es. In the present study, we produced carbonaceous mate- culated using Eq.（2）from the specific surface area（S）and rials from various waste fibers by carbonization without ac- the pore volum（e P）19）. tivation. A method for carbonaceous material production 4P D＝（2） without activation has important advantages, including low S energy consumption and low environmental burden. The present study focused on the conversion of waste 2.3 Chemical properties of carbonaceous materials fibers to carbonaceous materials. Carbonaceous materials Base consumption was determined using the method of were produced from waste fibers, and their specific surface Boehm et al.20, 21）. A 0.1-g sample of the carbonaceous ma- area, pore volume, surface chemical properties, and effi- terial was weighed and placed in a vial, to which 20 mL of ciency in reduction of carbon dioxide emissions were in- 0.05 mol/L sodium hydroxide solution（Wako Pure Chemical vestigated. Industries, Osaka, Japan）was added; this was followed by shaking the vial at 100 rpm and 25℃ for 24 h. The solution was then filtered using 0.45-μm glass fiber filter paper（Ad- vantec, Tokyo, Japan）. The filtrate was titrated with 0.01 2 EXPERIMENTAL mol/L hydrochloric acid solution（Wako Pure Chemical In- 2.1 Production of carbonaceous materials dustries, Osaka, Japan）, using methyl red as the indicator, The carbonaceous materials were produced essentially and the base consumption was calculated using Eq.（3）. as follows. Wool, PE, or cotton was placed in a magnetic （0.05×a－0.01×b） B＝（3） furnace under a nitrogen gas flow of 1 L/min, and the tem- W perature was increased over 3 h to an end temperature where B is the base consumption（mmol/g）, a is the volume between 400 and 1000℃. The maximum temperature was of the sodium hydroxide solution（mL）, b is the volume of held for 0-2 h, and then, the materials were naturally the hydrochloric acid solution（mL）, and W is the carbona- cooled. The carbonized wool and PE were then pulverized ceous material weight（g）. Base consumption is an indica- and used as an adsorbent, and the cotton was used without tor of the number of carboxyl, phenolic hydroxyl, and other further processing because of its fibrous form. The result- acidic groups and the quantity of acidic substances present ing carbonaceous materials and the original fibers were ob- on the surface of the carbonized fibers. served on a JSM-5200 scanning electron microscope（JEOL, The pH was measured using the Japan Industrial Stan- Ltd., Tokyo, Japan）. dard JIS K1474 test method for activated carbon22）. To 50 The carbonaceous material yields Y（％）were calculated mL of purified water, 0.5 g of adsorbent was added; then, using Eq.（1）, the solution was boiled for 5 min and filtered using 0.45-μm M glass fiber filter paper; finally, the filtrate pH was measured Y＝ ×100 （1） M0 on a digital pH meter（Mettler-Toledo, OH, USA）. where M and M0 are the dry weights（g）of the carbonaceous material and the original fiber, respectively. The carbon, hydrogen, and nitrogen contents of the fibers and the carbonaceous materials were measured on a 3 RESULTS AND DISCUSSION Micro Corder JM-10（J-Science Co., Ltd., Kyoto, Japan）by 3.1 Surface shape of carbonaceous materials the Pregl-Dumas method. The SEM micrographs in Figs. 1-3 showed that the original wool and PE fibers lost their fibrous form and under- 2.2 Physical properties of carbonaceous materials went pore formation with an increase in carbonization tem- The specific surface area was obtained by first determin- perature. PE, which is produced by the condensation ing the adsorption isotherm at liquid nitrogen temperature polymerization of dicarboxylic acid and a diol and has a （－195.8℃）with high-purity nitrogen gas（99.999％）as the melting point of approximately 240℃, appeared to enter a adsorption gas on a Nova4200e（Quantachrome, FL, USA）. molten state at 400℃. As a result, the fibers formed an in- Next, curve fitting to the nitrogen adsorption isotherm at a creasing number of small pores with further increase in the relative pressure of 0.05-0.30 was carried out using the carbonization temperature. Cotton, on the other hand, re- Brunauer-Emmett-Teller（BET）equation17）. tained its fibrous form and SEM images showed no discern- Pore size distribution and pore volume were similarly able change with increasing carbonization temperatures. obtained. First, the adsorption isotherm at a relative pres- Since cotton is derived from plants, its main component is

594 J. Oleo Sci. 61, (10) 593-600 (2012) Manufacture of Novel Carbon Fiber

No carbonization 400℃ 600℃

500µm 500µm 500µm

800℃ 900℃ 1000℃

500µm 500µm 500µm Fig. 1 SEM images of carbonaceous materials produced from wool at different temperatures. Carbonization condition: temperature increase and retention times were 2 h.

No carbonization 400℃ 600℃

500µm 500µm 500µm

800℃ 900℃ 1000℃

500µm 500µm 500µm Fig. 2 SEM images of carbonaceous materials produced from PE at different temperatures. Carbonization condition: temperature increase and retention times were 2 h.

No carbonization 400℃ 600℃

500µm 500µm 500µm

800℃ 900℃ 1000℃

500µm 500µm 500µm Fig. 3 SEM images of carbonaceous materials produced from cotton at different temperatures. Carbonization condition: temperature increase and retention times were 2 h.

595 J. Oleo Sci. 61, (10) 593-600 (2012) N. Kawasaki, H. Tominaga, F. Ogata et al.

cellulose. Cotton may retain its fibrous form after carbon- specific surface area generally increases with increasing ization, whereas wool and PE might melt by carbonization. micropore formation19）; this tendency was observed in the Moreover, the cotton before carbonization had microfibril carbonaceous materials. Shimakami et al.24）reported that structure, that structure may be come loose by carboniza- the specific surface area and the pore volume of cotton in- tion. As fibrous activated carbon has been reported to creased with increasing carbonization temperature. The exhibit higher adsorption rates than the particle form23）, it specific surface area of cotton produced at 600, 800, and may be possible to use carbonized cotton as carbonaceous 1000℃ was 496, 703, and 2192 m2/g, respectively24）. The material for various applications. pore volumes at those temperatures were 0.196, 0.270, and 1.082 mL/g, respectively24）. The pore volume of the carbo- 3.2 Specific surface area and pore size distribution of naceous materials produced from PE and cotton increased carbonaceous materials with increasing retention time. For all of the fibers, it was The specific surface areas and pore volumes of the car- found that exposure to increased temperature for 2 h was bonaceous materials obtained under carbonization with suitable and that subsequent retention was necessary, indi- different temperature increases and retention times at cating that the carbonaceous carbon activation and pore 1000℃ are listed in Table 1. These experiments were per- development proceeded under the high-temperature reten- formed to determine the production conditions that would tion. No single set of production conditions was found for yield carbonaceous materials most appropriate for use as all of the fibers in terms of maximum values for specific adsorbents. Activated carbon may generally be classified surface area and micropore formation, thus indicating a by pore diameter, as microporous（5 < r ≤ 20 Å）, mesopo- need to use different conditions for different fibers. As pro- rous（20 < r ≤ 500 Å）, and macroporous（500 Å < r）. The duction conditions for carbonaceous materials generally

Table 1 Physical properties of carbonaceous materials produced from waste fibers at 1000℃ at different temperature increase and retention times.

Temperature Retention time Speciﬁc surface Pore volume (mL/g) Mean pore Materials 2 increase time (h) (h) area (m /g) r ≦ 20Å r ≦ 500Å diameter (Å) 1 0 166 0 0 1.2 2 0 252 0.01 0.01 1.7 3 0 160 0 0.01 1.5 wool 1 1 237 0.02 0.02 4.2 1 2 146 0.01 0.02 5.6 2 1 213 0.02 0.02 4.3 2 2 133 0.01 0.01 4.3 1 0 582 0.01 0.00 0.4 2 0 699 0.01 0.02 1.0 3 0 626 0.01 0.02 1.0 PE 1 1 759 0.01 0.01 0.7 1 2 847 0.01 0.02 0.7 2 1 847 0.01 0.02 0.9 2 2 1019 0.02 0.04 1.4 1 0 371 0.02 0.02 2.3 2 0 528 0.02 0.04 2.9 3 0 435 0.02 0.03 2.6 cotton 1 1 472 0.02 0.02 1.7 1 2 808 0.04 0.07 3.6 2 1 642 0.04 0.06 3.7 2 2 1253 0.16 0.31 10.2 Temperature increase time was the reaching time of 1000℃. Retention time was the keeping time of 1000℃.

596 J. Oleo Sci. 61, (10) 593-600 (2012) Manufacture of Novel Carbon Fiber

include a 2 h temperature increase that was followed by the range of 900-1000℃. retention at this high temperature and because the carbo- In summary, in all of the tested fibers, it was possible to naceous materials obtained from most of the fibers under produce carbonaceous materials in which micropore devel- these conditions showed high specific surface area and mi- opment increased with increasing carbonization tempera- cropore values, they were applied in the following experi- ture at up to either 900 or 1000℃. In particular, cotton ments. carbonized at 1000℃ showed a specific surface density The specific surface areas and pore volumes obtained at greater than 1000 m2/g, which equals commercial activated various carbonization temperatures are listed in Table 2. carbon. Micropore and mesopore development, which The specific surface area was found to increase with in- relate to adsorption volume and adsorption rate, respec- creasing carbonization temperature for all of the fibers tively, indicate an excellent potential for commercial appli- throughout the temperature range of 400-900℃. The pore cation. volume and pore diameter distribution curves indicate that increasing the carbonization temperature effectively in- 3.3 Yield, base consumption, and pH of carbonaceous creases micropore development and specific surface area. materials At 1000℃, however, the results were different for different Measurements results for the fibers before and after car- tested fibers. The specific surface area of PE and cotton bonization at 400-1000℃, in terms of carbonaceous mate- carbonized at 1000℃ was higher than that at 900℃, but rial yield, base consumption, and pH, are listed in Table 3. that of wool at 1000℃ was lower than that at 900℃. In It can be seen that the yield generally decreased with in- short, the results indicate that small-pore development and creasing temperature, presumably because of an increasing specific surface area increase with increasing carbonization extent of carbonization. temperature throughout the range of 400-1000℃ for both Base consumption is an indicator of the number of func- PE and cotton, but only up to 900℃ for wool, in which tional groups and the quantity of acidic substances present baking densification apparently causes pore enlargement in on the surface of the carbonized fibers. This indicator for

Table 2 Physical properties of carbonaceous materials produced from waste fibers at different carbonization temperatures.

Carbonization Speciﬁc surface Pore volume (mL/g) Mean pore Materials 2 temperature (℃) area (m /g) r ≦ 20Å r ≦ 500Å diameter (Å) No carbonization 0 0 0 － 400 0 0 0 － 600 112 0 0 0.4 wool 800 238 0 0.01 0.8 900 328 0.02 0.02 2.5 1000 133 0.01 0.01 4.3 No carbonization 0 0 0 － 400 0 0 0 － 600 508 0.01 0.02 1.2 PE 800 614 0 0.01 0.5 900 796 0.01 0.02 0.9 1000 1019 0.02 0.03 1.4 No carbonization 0 0 0 － 400 186 0 0 0.3 600 381 0.01 0.01 1.3 cotton 800 564 0.03 0.06 4.1 900 698 0.05 0.11 6.6 1000 1253 0.16 0.31 10.2 Temperature increase time: 2 h Retention time: 2 h

597 J. Oleo Sci. 61, (10) 593-600 (2012) N. Kawasaki, H. Tominaga, F. Ogata et al.

Table 3 Characteristics of carbonaceous materials produced from waste fibers at different carbonization temperatures. Carbonization Base consumption Materials Yield (%) pH temperature (℃) (mmol/g) No carbonization － 1.05 5.2 400 27.4 0.88 6.2 600 19.4 0.89 6.1 wool 800 15.2 0.86 6.1 900 10.4 0.80 6.2 1000 9.9 0.65 5.6 No carbonization － 0.41 5.9 400 20 0.89 4.5 600 14.7 1.04 4.4 PE 800 11.6 1.25 4.4 900 10.7 1.35 4.4 1000 8.6 1.58 4.2 No carbonization － 0.45 6.6 400 24.1 2.65 5.2 600 15.5 0.96 7.5 cotton 800 10.2 0.95 8.0 900 7.4 0.82 8.4 1000 4.2 0.73 8.5 wool and cotton decreased with increasing carbonization tion temperature. temperature but that for PE increased. Wool fiber structur- ally consists of a surface cuticle layer and an inner“ para- 3.4 Reduction effect on carbon dioxide by conversion cortex” that is high in basic amino acid content. The de- from waste ber to carbonaceous materials crease in the base consumption of wool under The carbon, hydrogen, and nitrogen contents of the car- carbonization may be attributed to the disruption of the bonized fibers, as determined by elemental analysis, are cuticle surface structure and subsequent emergence of the listed in Table 4. The high carbon content of the carbona- basic functional groups to the surface of the fiber. In cotton ceous materials as compared to that of the non-carbonized fibers, the decrease in base consumption may be attributed fibers indicates that the carbonization effectively converted to a loss of functional groups at its cellulosic surface layer the fibers to adsorbent materials of high carbon content. under carbonization. In cotton, moreover, a microstructure Carbonized wool was substantially higher in nitrogen may develop in the structural spaces termed“ lumen” that content than the other two carbonized fibers, which was are normally present within the fiber25）during carboniza- presumably an effect of the protein-rich keratin composi- tion. Moreover, the base consumption of cotton carbonized tion of non-carbonized wool fiber. As a fossil-fuel deriva- at 400℃ was the largest. This result indicated that the tive, PE in the non-carbonized state has a substantially cotton before carbonization had microfibril structure, that higher carbon content than non-carbonized wool and structure may be come loose after carbonization at 400℃. cotton, but after carbonization, its carbon content of 85.2％ In contrast, in PE, the increase in base consumption with was nearly the same as that of carbonized wool（86.6％） carbonization temperature may be attributed to the disrup- and carbonized cotton（86.8％）. Thus, the overall results tion of its constituent ester bonds and consequential in- indicate that the maximum carbon content of the carbon- crease in acidic functional groups. ized fibers is in the vicinity of 85％. In pH measurements, both wool and PE were weakly The reduction in carbon dioxide emission, which may acidic or had neutral pH values and demonstrated a ten- result from carbonization of these fibers, was calculated on dency to shift toward increasing acidity with increasing the basis of their measured carbon contents. Disposal of 1 carbonization temperature. Cotton, in contrast, exhibited a ton of wool by complete incineration generates 1716 kg of shift toward increasing alkalinity with increasing carboniza- carbon dioxide, as calculated by carbon conversion. Car-

598 J. Oleo Sci. 61, (10) 593-600 (2012) Manufacture of Novel Carbon Fiber

Table 4 Elemental analysis of carbon, hydrogen, and nitrogen contents of carbonaceous materials produced from waste fibers. No carbonization (%) Carbonization at 1000℃(%) Materials Carbon Hydrogen Nitrogen Carbon Hydrogen Nitrogen wool 46.8 6.9 15.4 86.6 1.2 6.1 PE 62.2 4.3 0.0 85.2 1.7 0.1 cotton 42.9 6.3 0.2 86.8 1.6 0.2

bonization of wool can reduce this emission by 39.8％. References Similar calculations show that the conversion of PE and 1） Ikeda, Y. The recycle of polyester textiles as resource cotton to carbonaceous materials can reduce carbon circulation（aiming at the forming of the circulation- dioxide emission by 23.0％ and 43.9％, respectively, as type society）. Sen’i Seihin Shohi Kagaku 46, 202- compared to disposal by incineration. The calculations in- 209（2005）. dicate that material transformation of fibers by carboniza- 2） Yagita, Y.; Yagita, H.; Inaba, A. Evaluation of the recy- tion, and therefore their regeneration, is a useful process cle for nylon 6 by life cycle inventory analysis. Nippon that may contribute to a reduction in the environmental Enerugi Gakkaishi 79, 1172-1181（2000）. burden and amelioration of global warming. 3） Kowalska, E.; Kijenska, M.; Czyzyk-Markiewicz, P. Me- chanical properties of composites with wool-contain- ing wastes. Przemysl Chemiczny 87, 951-958（2008）. 4） Kawasaki, N.; Ogata, F.; Yamaguchi, I.; Tominaga, H. 4 CONCLUSION Degradation characteristics of 17β-estradiol by ozone Pore formation was found to occur in carbonization of treatment with activated carbon. J. Oleo Sci. 58, 261- waste fibers, with a 2-h temperature increase and subse- 266（2009）. quent retention of temperature for 2 h in experimental 5） Kawasaki, N.; Kinoshita, H.; Oue, T.; Nakamura, T.; carbonization of three fibers at temperatures of 400- Tanada, S. Study on adsorption kinetic of aromatic hy- 1000℃. Investigations of the physical and chemical proper- drocarbons onto activated carbon in gaseous flow ties of these fibers were also conducted. Carbonization method. J. Colloid Interface Sci. 275, 40-43（2004）. temperatures of 900-1000℃ were found to result in 6） Sourja, C.; Sirshendu, D.; Sunando, D.; Jayanta, K. B. maximum micropore development and specific surface Adsorption study for the removal of basic dye: experi- area in carbonaceous materials produced from cotton and mental and modeling. Chemosphere 58, 1079-1086 PE but not in the carbonaceous materials produced from （2005）. wool. Maximum specific surface areas were observed for 7） Martin, M. J.; Artola, A.; Balaguer, M. D.; Rigola, M. Ac- PE and cotton carbonized at 1000℃ and for wool carbon- tivated carbon developed from surplus sewage sludge ized at 900℃. Carbonization of PE and cotton at 1000℃ for the removal of dyes from dilute aqueous solutions. resulted in a specific surface area of more than 1000 2m /g Chem. Eng. J. 94, 231-239（2003）. for both. The yields of carbonaceous materials generally 8） Suzuki M. Activated carbon fiber: fundamentals and decreased with increasing carbonization temperature. The applications. Carbon 32, 577-586（1994）. acidic functional group numbers in wool and cotton de- 9） Brasquet, C.; Cloriec, P. L. Adsorption onto activated creased with increasing carbonization temperature, but carbon fibers: application to water and air treatment. those in PE increased. The fibrous form of wool and PE Carbon 35, 1307-1313（1997）. was lost under carbonization, but that of cotton was re- 10） Karagozoglu, B.; Tasdemir, M.; Demirbas, E.; Kobya, M. tained. For cotton in particular, it was possible to produce The adsorption of basic dye（Astrazon Blue FGRL） carbonaceous material of fibrous form by carbonization. from aqueous solutions onto sepiolite, fly ash and apricot shell activated carbon: kinetic and equilibrium studies. J. Hazard. Mater. 147, 297-306（2007）. 11） Kalavathy, M. H.; Karthikeyan, T.; Rajgopal, S.; Miran- ACKNOWLEDGEMENT da, L. R. Kinetic and isotherm studies of Cu（II）adsorp-

This work was financially supported by the“ Antiaging tion onto H3PO4-activated rubber wood sawdust. J. Center Project” for Private Universities from the Ministry Colloid Interface Sci. 292, 78-82（2005）. of Education, Culture, Sports, Science and Technology 12） Prakash Kumar, B. G.; Miranda, L. R.; Velan, M. Ad- （MEXT）, Japan, 2008-2012. sorption of Bismark Browndye on activated carbons prepared from rubber sawdust（hevea brasiliensis）

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