Patent GB-774809-A (GB)
Title: A continuous process for the production of furfural and acetic acid from pentosan-containing material
Inventor: NATTA GIULIO
IPC: C07D307/50
Filed: 1954-07-29
Abstract: Furfural and acetic acid are produced from vegetal pentosan-containing material by a continuous process comprising heating said material in the presence of hydrochloric acid as a catalyst and wherein the furfural is stripped out by steam passed counter-currently to the material, characterized in that the extraction apparatus operates as a rectifying column fed at one extremity with the material to be processed and with a liquid reflux necessary for completely stripping the hydrochloric acid from the furfural-containing vapours traversing the extraction apparatus countercurrently to the material, so that the furfural-containing vapours leave the column free from hydrochloric acid; that the heating of the column is so effected that the extraction residuum will be dry and free from acids; and that the hydrochloric acid initially present in the middle part of the extraction apparatus is retained within said apparatus during the continuous operation of the plant by the liquid reflux.  The vapours issuing from the extraction apparatus are condensed to form a furfural-acetic acid-water mixture from which furfural may be recovered by azeotropic distillation.  The aqueous acetic acid solution remaining may be partially evaporated and the vapours superheated to provide the steam passing countercurrent to the pentosan-containing material.  This recirculation of acetic acid increases the acetic acid in the vapours from the extraction column, and the acetic acid from the evaporator is sufficiently concentrated to allow extraction by a solvent.  The liquid reflux feeding the apparatus may comprise a mineral acid-free stream of water equal to 30 per cent by weight of the dry pentosan-containing material.  It may be introduced by impregnation of the material with water so that the total of moisture present plus water added reaches the desired amount, or it may be introduced as a separate stream, obtained by condensation of the vapours leaving the column.  In order to increase the concentration of acetic acid produced, the aqueous acetic acid solution obtained after distillation of furfural may be used as the liquid reflux.  The heating at the base of the column may be effected indirectly by means of a heat-exchanger when heavy material like olive residuum is treated.  When a light porous material such as rice husks or corn cobs is treated, direct heating by means of superheated steam may be used, the steam being recirculated through a superheater.  Small additions of hydrochloric acid to compensate for losses thereof may be made by introducing gaseous hydrogen chloride, aqueous hydrochloric acid or chlorine.  The countercurrent principle with a liquid reflux is most suitably obtained with a vertical cylindrical extraction column but horizontal or inclined apparatus may be used wherein mechanical devices or rotational movement of the apparatus is used to obtain the desired direction of flow of material, liquid reflux and vapours.  Detailed examples are given of the treatment of rice hulls to obtain furfural and acetic acid.