GB759341A - Improvements in filters and filter material for use in filtering tobacco smoke - Google Patents

Abstract

The residual liquor obtained in the manufacture of paper pulp by the caustic soda process is concentrated by evaporation of water to a thick paste which is treated with weak acid, such as sulphuric or hydrochloric acid of 16 DEG to 22 DEG B<\>ae., to precipitate lignin, which is then separated by decantation, filtered and dried at a temperature not above 90 DEG C. The lignin so obtained is treated (a) with turpentine or alcohol at about 60 DEG C. to extract resins, &c. (b) with a mixture of three parts by volume of sulphuric acid and one part of hydrochloric acid at an elevated temperature below 100 DEG C. and (c) with concentrated sulphuric acid of at least 62 DEG B<\>ae. at above 220 DEG C., e.g. for five to six hours, the resultant carbon being treated with hydrochloric acid at normal temperature, washed with distilled water and dried at normal temperature. For use in tobacco smoke filters (see Group VI), the carbon is treated with steam, preferably after washing with sodium carbonate solution.ALSO:Filter material comprises cellulosic material in combination with porous or finely-divided carbon of at least 96 per cent, preferably over 99 per cent, purity, obtained by a wet process from lignin produced in the manufacture of paper by the soda process and heated as a step in the wet process with concentrated sulphuric acid at a temperature of over 220 DEG C. e.g. for five to six hours, the carbon being then steamed, preferably after alkaline washing. Details (see Group III) of a preferred wet process are given. The cellulosic material should be chiefly alpha cellulose and may be cellulose wool, tobacco or paper, with which the carbon is intimately associated, or the carbon may be situated between plugs of cellulose wool or paper. The filter material may be incorporated as filter tips into cigars or cigarettes or into expendible filter units for pipes or for cigar or cigarette holders which may themselves be of paper and expendible. According to the Provisional Specification, carbon derived from coconut shells heated in a closed retort, crushed and steamed may be used.