In a solvent extraction and recovery system in which a mixture of organic compounds is subjected to an extraction step by contact with furfural and the furfural is recovered from the extract by distillation in the presence of water, decomposition of the furfural and corrosion of the plant is inhibited by injecting an acid PICT:0649666/III/1 neutralizing substance into the aqueous furfural prior to separating the water phase therefrom, whereby the pH of the separated water phase is 5-7 and preferably nearly 7. The acid neutralizing substance is an oxide, hydroxide, carbonate or bicarbonate of an alkali or alkaline earth metal. The invention is applicable to the separation of (1) aromatic and unsaturated hydrocarbons from petroleum; (2) glyceride oils of varying degrees of unsaturation; and impurities from (3) anthracene; (4) anthraquinone; (5) animal and vegetable oils and fats; and (6) rosin. Crude petroleum lubricating oil fractions are treated in an extraction system 1 countercurrently with furfural from a storage vessel 2 and the raffinate containing furfural flows to a distillation column 3 from which the distilled furfural flows back to the vessel 2. Raffinate from the column 3 flows to a distillation column 4 into which steam is injected and the purified raffinate therefrom flows to storage whilst the distilled aqueous furfural flows into the reflux stream of a distillation column 6. The furfural solution of extracted aromatic and unsaturated compounds from column 1 flows into column 6 wherein dry furfural collects on a tray 7 and flows back to the vessel 2 and distilled wet furfural flows through a condenser 8 and line 9 into a separator 5. According to the invention a slurry of slaked lime in water is injected from a dosing tank 10 into line 9. Furfural from the separator 5 flows as reflux into the column 6 and the aqueous phase from the separator 5 having a pH of 5-7 is treated to recover furfural. The extract solution from column 6 flows into a pressure flash column 11 from which the flashed furfural flows to the vessel 2 and the extract flows into a distillation column 12 wherein it is subject to steam stripping; the distilled aqueous furfural flowing to the reflux stream of column 6 and the extract flowing to storage.
展开▼
