1 INFLUENCE OF NITROGEN AND PHOSPHOROUS IN THE WATER VAPOR ADSORPTION ON ACTIVATED CARBONS J. Bedia, J. Rodrguez-Mirasol, and T. Cordero. Chemical Engineering Department. School of Industrial Engineering. University of MÆlaga. Campus de El Ejido, s/n, 29013 MÆlaga, Spain Corresponding author e-mail address: mirasol@uma.es Introduction Desiccants are designed to control humidity and ambient moisture in a certain range. The traditional desiccants are silica gel and zeolites. The former has high adsorption capacities and it is easy to regenerate. The latter has similar adsorption capacities but its regeneration is very slow at room temperature [1]. Activated carbons, that can be obtained from many raw materials, including carbonaceous waste, present a high capacity for water vapor adsorption, due to their large specific surface area and high porosity. Unfortunately, it is well known that carbon surface is essentially hydrophobic; this results in a Type V isotherm for water vapor adsorption, with very low uptake at low relative pressures. Despite of the strong influence of surface chemistry in water vapor adsorption, most of the work published in the technical literature is focused only in the effect of oxygen groups in the water vapor adsorption [2,3], however less attention has been directed to the behavior of activated carbons containing other elements. Mahajan et al [1] used oxidized carbons with high amounts of metal cations (Li, Na, K, Na) and show that the presence of these cations increases the water adsorption , especially, in the low relative pressure range, changing the isotherm shape from type V to type IV, and even to type I. Cossarutto et al [4] found that the presence of nitrogen on the carbon surface results in an enhancement of water vapor adsorption at low relative pressures and a decrease of the maximum amount of water adsorbed. More recently, our group have reported a paper [5] analyzing the presence of sodium on activated carbons obtained from Kraft lignin by means of CO 2 partial gasification. The sodium present on the carbon surface enhances the water adsorption capacities in the whole relative pressure range. In this paper we investigate the contribution of phosphorous and nitrogen to water vapor adsorption on activated carbons. Experimental Different phosphorous containing carbons were obtained by chemical activation of Alcell lignin with H 3 PO 4 as activating agent. Alcell lignin was mixed with H 3 PO 4 and water and was stirred. An impregnation ratio of 3/1 (weight of activating agent/weight of lignin) was used in this research. The mixture was dried at 333 K during 24 hours and heated to 773 K, in a N 2 flow (150 cm 3 STP/min) at a heating rate of 10 K/min. The sample was held at this temperature for 2 hours and cooled down in N 2 flow. The carbonized sample was