Preparation of activated carbon fibers with large specific surface area from softwood acetic acid lignin

Softwood acetic acid lignin (SAL) free from a high-molecular-mass fraction could be spun at 220°C by a spinning machine equipped with an extruder. Although the resulting fibers required thermostabilization, this step could be conducted with a faster heating rate than that for fibers obtained from hardwood acetic acid lignin (HAL). The thermostabilized SAL fibers were converted to activated carbon fibers (ACF) by carbonization in a stream of nitrogen at 1000°C, followed by steam activation at 900°C. At an activation time of 40 min, the SAL-ACF had a larger specific surface area than the corresponding HAL-ACF. When the activation time for SAL carbon fibers was prolonged to 80 min, the adsorption capacities of resulting ACF against iodine and methylene blue were markedly increased, as was the surface area of the ACF. It was found that SAL-ACF had adsorption properties comparable to those of high-performance commercial ACF. Also, it had a tensile strength equal to that of a pitch-derived ACF.Part of this work was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999     

Preparation of activated carbon moldings from the mixture of waste newspaper and isolated lignins: mechanical strength of thin sheet and adsorption property

To expand the utilization of waste newspapers and lignin, activated carbon (AC) sheets, as an example of AC moldings, were prepared from those mixtures. The isolated lignins used were softwood and hardwood acetic acid lignins (SAL and HAL), softwood kraft lignin (KL), and wheat-straw lignin (WSL). The mixtures were molded into precursory sheets by thermal compression and then converted to AC sheets by carbonization and steam activation. The flexural strength of the precursory sheets was dramatically improved by additing the lignins compared to that of sheets without lignin. The strength of several sheets was more than 25 MPa. This suggested that lignins act as adhesives. SAL and HAL sheets with 40% newspaper were strengthened by the carbonization, whereas the strength of other lignin sheets was depressed. Finally, the AL-based AC sheets showed higher flexural strength (>6MPa) than others. Most of the AC sheets had adsorption ability comparable to that of commercially available AC powder and granules. The capacities were almost independent of paper content. Among the AC moldings tested, the AL-based AC sheets showed the fastest adsorption top-chlorophenol. Thus, viable AC moldings can be prepared from lignin-wastepaper mixtures, particularly SAL and HAL.     

Catalytic graphitization of hardwood acetic acid lignin with nickel acetate

 Catalytic graphitization of hardwood acetic acid lignin (HAL) with nickel (II) acetate was investigated regarding the production of highly crystalline carbon. Fusibility, one of the unique characteristics of HAL, was preserved with nickel acetate additions up to 0.3% (as the weight of nickel), although the thermal mobility of HAL was depressed by the addition of nickel acetate. An obvious effect of nickel salt as a catalyst on the development of carbon crystallite from HAL was observed for more than 0.2% addition. The development was found to proceed above 850°C. All the resulting carbons had turbostratic structure, and the apparent crystallite size (L _c) was increased with increasing amounts of catalyst, as determined by X-ray diffraction. Thus, highly crystalline carbon was produced from HAL by catalytic graphitization without compromising the fusibility of HAL by adding a small amount of organic nickel salt. Received: December 17, 2001 / Accepted: March 27, 2002 Present address: Department of Wood and Paper Science, North Carolina State University, NC 27695-8005, USA Part of this paper was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000 Correspondence to:Y. Uraki