Patent GB-799603-A (GB)
Title: Process and apparatus for the continuous preparation of furfural from vegetable material containing pentosans
Inventor: LUDERT JEAN RODOLPHE ALFRED
IPC: C07D307/50
Filed: 1953-12-15
Abstract: Furfural is produced from vegetable material containing pentosans by a continuous process comprising treating said material in a vertical tower at an elevated temperature, removing a mixture containing furfural and water vapour from the top of the tower and separating furfural therefrom by rectification and purification, characterized in that the vegetable material is continuously supplied to the top of the tower in a finely divided condition without any addition of external moisture, a predetermined level of aqueous hydrochloric acid of strength less than 20 per cent by weight is maintained in the tower and aqueous hydrochloric acid is supplied to the tower below this level and heated to boiling, the level of aqueous hydrochloric acid being such that the vegetable material is contacted with moist hydrochloric acid vapour above said predetermined level and a substantially acid-free mixture of furfural and water vapour is removed as the top product for rectification, the residue of vegetable material and aqueous acid being removed at the bottom of the tower and the aqueous acid being regenerated and recycled. The regeneration of the acid may be accomplished by dilution with dilute aqueous acid obtained by rectification of the top product, the dilution preferably being effected by washing the residue of the vegetable material with the said dilute acid and adding the washing liquor to the acid to be regenerated.  Control of the flow of the vegetable material in the tower may be effected by employing one or more grids inside the tower and by the discharging means in the lower part of the tower.  The process may be carried out under atmospheric or superatmospheric pressure.  The aqueous acid may be heated by one or more steam coils, by electrical means or by one or more supplies of live steam.  The heating means may also be incorporated in the supply conduit for the acid to the tower so that the acid enters the tower partly in liquid and partly in vapour form.  The acid supplied to the tower may be a mixture of water and hydrochloric acid but a mixture of water, sodium chloride and sulphuric acid may be started from instead.  Examples describe the production of furfural by the treatment of ground corn cobs according to the above process with or without the introduction of live steam into the tower, and also the treatment of oat hulls with the introduction of sufficient live steam to make a significant contribution to the distillate.  Suitable apparatus comprises a vertical tower which is provided at the upper end with means, such as a screw, for supplying finely divided vegetable material, and with a discharge conduit for the vaporous top product, and which is provided with a supply conduit for the aqueous acid connecting the tower below the predetermined acid level with a container for the acid.  The tower is provided with a discharge conduit for the residue of vegetable material and aqueous acid with means for separating the residue of vegetable material from the aqueous acid, with means such as a pump for circulating the aqueous acid from the tower to the container, and from the latter back to the tower, and with heating means for keeping the aqueous acid at boiling point, together with a rectifying column for recovering from the top product an azeotrope of furfural and water, and a vessel wherein the azeotrope separates into a furfural phase and a water phase.