GB585772A - Improvements in the manufacture of furfural - Google Patents

Abstract

A process for the production of furfural comprises subjecting pentosan-containing vegetable raw material, which is non-finely divided, and without agitation, to heat and pressure in a stationary reaction vessel, together with an aqueous liquid in an amount such that under the reaction conditions all or substantially all of the said liquid is absorbed by the material, and passing steam through the reaction mass to remove the furfural; preferably, the steam is passed continuously so as to remove the furfural as it is formed. By using non-finely divided material, the reaction vessel can be substantially filled with it without it being entrained in the vapour stream. The reaction vessel should, preferably, have a ratio of length to greatest cross-sectional dimension of at least 2 : 1. Materials which may be treated include cereal husks, cotton seed hulls, maize cobs and stalks, bagasse, wood from, for example, various deciduous and coniferous trees, cereal straw, coconut shell and palm kernel shell. Fibrous material should be chopped into short lengths of not less than 1/4 inch, while the various woods should be used in fragments having a minimum dimension of 1/4 inch. Materials difficult to wet may be given a preliminary treatment with a wetting agent, such as "Lissapol N" (Registered Trade Mark) or Aerosol O.T., or a wetting agent may be incorporated in the aqueous liquid used in the process. In general, the ratio by weight of aqueous liquid to solid employed is from 1 : 3 to 2 : 1. Desirably, the reaction is carried out in the presence of added acids and/or salts, especially of strong mineral acids. Operating temperatures are generally between 150 DEG and 200 DEG C. and the pressure, at least in the early stages, that of saturated, but not wet steam. Uniform distribution of the aqueous liquid is desirable and may be effected by spraying the material as it is fed into the vessel by means of an inwardly-directed ring of jets in the upper part of the vessel or, where a conveyer band is used, by spraying the material in a fine layer thereon. The residual mass left in the vessel may be removed as a slurry by subjecting it to the action of jets of water situated near the base of the vessel. In typical examples: (1) a reaction vessel having a ratio of length to diameter of 15 : 1 and a steam inlet at the base and vapour outlet in the top, was charged with oat husks and steam passed through to maintain a liquidto solid ratio of 1 : 3 and a temperature of 188 DEG C. at a pressure of 150 lbs.; the issuing vapours of water and furfural were condensed, the yield of furfural based on the weight of dry husks being 9.8 per cent; (2) as in (1), the oat husks during the charging being sprayed with water containing 2 per cent of sulphuric acid based on the weight of the husks, the total quantity of liquid being such that, together with water from the steam used subsequently, the liquid solid ratio was 1 : 1. Specification 203,691, [Class 2 (iii)], is referred to.