Role of nitrogen in pore development in activated carbon prepared by potassium carbonate activation of lignin

The present work focuses on the role of nitrogen in the development of pores in activated carbon produced from lignin by K2CO3 activation, employing a fixed bed reactor under a high-purity He stream at temperatures of 500-900 degrees C. The specific surface area and pore volume obtained by activation of lignin alone are 230 m(2)/g and 0.13 cm(3)/g at 800 degrees C, and 540 m(2)/g and 0.31 cm(3)/g at 900 degrees C, respectively. Activation of a mixture of lignin and urea provides a significant increase in the surface area and volume, respectively reaching 3300-3400 m(2)/g and 2.0-2.3 cm(3)/g after holding at 800-900 degrees C for 1 h. Heating a lignin/urea/K2CO3 mixture leads to a significant decrease in the yield of released N-containing gases compared to the results for urea alone and a lignin/urea mixture, and most of the nitrogen in the urea is retained in the solid phase. X-ray photoelectron spectroscopy and X-ray diffraction analyses clearly show that part of the remaining nitrogen is present in heterocyclic structures (for example, pyridinic and pyrrolic nitrogen), and the rest is contained as KOCN at <= 600 degrees C and as KCN at >= 700 degrees C, such that the latter two compounds can be almost completely removed by water washing. The fate of nitrogen during heating of ligniniurea/K2CO3 and role of nitrogen in pore development in activated carbon are discussed on the basis of the results mentioned above. (C) 2016 Elsevier B.V. All rights reserved.