GB1301101A - Improvements in the manufacture of carbon - Google Patents

Abstract

1301101 Active fibrous carbon DEFENCE SECRETARY OF STATE FOR 8 April 1970 [8 Jan 1969(3)] 1147/69 1148/69 and 1149/69 Heading C1A Strong flexible, i.e. a fibre or fabric which is sufficiently deformable to fold back on itself without fracture around a radius of curvature of 0À5 mm., activated fibrous carbon is produced by treating a fibrous carbohydrate material with a solution, which term includes a dispersion, of at least one Lewis acid which is a halide of zinc, aluminium, calcium, magnesium or iron, drying the fibrous carbohydrate material and flexing the material sufficiently to restore the major portion of any flexibility lost by contact with the Lewis acid solution, carbonizing the material by heating to a carbonizing temperature in an inert atmosphere and activating the carbonized material by contact at an elevated temp. with an activating gas until the activate has a carbon tetrachloride sorbency of at least 50% by weight. During carbonization, the material may be heated in an inert atmosphere up to the critical decomposition temp. range, i.e. the temp. range around the temps. at which the carbohydrate material starts to decompose and lose weight most rapidly, which extends for between 40 and 80‹ C. within the temp. limits 70‹ and 300‹ C. and maintaining the temp. within this critical range for a time which is at least 15 mins. for a 40‹ C. critical temp. range increasing progressively to at least 30 mins. for an 80‹ C. critical temp. range. Preferably the rate of heating up to the critical range does not exceed 10‹ C. rise per minute. The Lewis acid may be a chloride or a bromide and may be aluminium chloride, iron chloride or calcium chloride. The activation may be carried out at between 600‹ and 1000‹ C. The activating gas may be CO 2 or steam. The efficiency of activation may be improved by providing cations of Pb, BaCo or Ca in the carbonized material before activation. The cations may be provided as a halide salt or in the case of Pb as the nitrate or acetate. The proportion of cation incorporated into the fibrous carbon material is between 0À1 and 10% by weight. The carbonized material may be contacted with the activating gas for a period sufficient to achieve a weight loss of 40-70%. The activation improving cations may be incorporated by contacting the carbonized material with a suitable salt solution, alternatively the salt may be incorporated by contacting the carbohydrate material prior to carbonization. The fibrous carbohydrate material may be fibrous cellulose, e.g. a regenerated cellulose that may be viscose rayon or cuprammonium rayon. The Lewis acid may be incorporated into the fibrous carbohydrate material in a proportion of 0À1 and 10% by weight, and this may be achieved by immersing the material in a solution containing between 1 and 30% by wt. of the Lewis acid. The solution is preferably an aqueous solution. An excess of halide ion may be present in the aqueous solution to prevent excessive hydrolysis. The fibrous carbon produced may have a tensile strength of 40,000 lbs./ins.<SP>2</SP>, a bulk density of 1 gm./ml. in which about 50% of the fibre vol. constitutes usefully active pores and a carbon tetrachloride sorbency of at least 50%.