Abstract: A method of gaseous acid catalysis which finds particular applications in the manufacture of furfural includes the steps of introducing a solid reactant containing one or more hydroxyl groups into a reactor (1); introducing superheated steam from a superheater (2) until the temperature within the reactor (1) is higher than that of the dew points of both water and the catalyst and the reactant is dry. The catalyst is then introduced into the superheated steam by vaporiser (3). Product gas formed is liquified in condenser (4) and the condensate collected in a buffer tank (5). Separation plant isolates the product gas and recovers the acid catalyst, preferably as its azeotrope with water, and recycles it into the vaporiser.

Abstract: Process for the manufacture of furfural wherein a pentosan-containing raw material acidified or not, is heated to a temperature T1 by admitting steam through valve 2 while the valves 3 and 4 are closed. During the very short heating process, the steam condenses, thus increasing the moisture content of the charge. Then, valve 2 is closed and a leak valve 3 is opened so as to produce a steady small flow of product vapor by gradual depressurization. This causes a slow drop in temperature. When a suitably chosen temperature T2 is reached, the leak valve 3 is closed to terminate the first “gradual depressurization”. If at the end of this period no more furfural was obtained, the digestion is completed by opening valve 4 to discharge the residue. If, however, furfural was still obtained, the reactor is reheated and submitted to another “gradual depressurization” period.

Abstract: A method of gaseous acid catalysis which finds particular applications in the manufacture of furfural includes the steps of introducing a solid reactant containing one or more hydroxyl groups into a reactor (1); introducing superheated steam from a superheater (2) until the temperature within the reactor (1) is higher than that of the dew points of both water and the catalyst and the reactant is dry. The catalyst is then introduced into the superheated steam by vaporiser (3). Product gas formed is liquified in condenser (4) and the condensate collected in a buffer tank (5). Separation plant 6 isolates the product gas and recovers the acid catalyst, preferably as its azeotrope with water, and recycles it into the vaporiser.

Abstract: A process for the production of furfural from lignosulphonate waste liquor which contains pentose is described, the process essentially comprising the maintenance of a boiling condition of the liquor at predetermined pressures for a sufficient time to convert the pentose to furfural and for the furfural produced to be removed without reacting with pentose, lignosulphonate or itself. Hot air or some other gas under pressure or hot mercury may be used to maintain the boiling of the liquor to ensure that the furfural produced transfers from the liquid to the gas phase and is transported from the reactor in the gas stream. Apparatus for carrying out the process includes a columnar reactor (4) with means (8) to control the pressure, an inlet for preheated liquor, an inlet for hot air under pressure at a low level, an outlet for spent liquor and an outlet for the gaseous phase, from which the furfural is recovered.

Abstract: A feed suspension of pentosan-containing organic raw materials in dilute sulfuric acid is passed with low residence time through a flow reactor heated by high-pressure steam to 170.degree.-230.degree. C. and then through a cooler in which it is cooled to 140.degree.-200.degree. C. before the suspension is admitted to a flash evaporating unit from which a furfural-rich vapor phase is separated from the residual suspension. Process water is recovered from the residual suspension and recycled for the preparation of the feed suspension. From the vapor phase, furfural is recovered by distillation, either directly or after liquefaction. In the latter case, partial condensation in a primary condenser can be used to increase the furfural concentration in the final condenser, the condensate of the primary condenser being recycled for the preparation of the feed suspension.

Abstract: A distillation or absorption column tray whose characteristic frequency is a specific function of the radius of circular apertures in its bottom wall, of the surface tension of the body of liquid therein at the operating temperature of the column and of the density of such liquid. This reduces the amplitude of vibrations of the tray under the action of ascending vapors and/or gases and hence increases the useful life of the tray.