Patent GB-722180-A (GB)
Title: Process for purifying crude benzene
IPC: C07C7/00
Filed: 1950-07-26
Abstract: In the purification of crude benzene by sulphuric acid washing, the washing treatment is preceded by a catalytic treatment by which the unsaturated constituents of the crude benzene which tend to resinify are at least partially converted into aromatic hydrocarbons, said catalytic treatment consisting of passing the crude benzene in vaporized form at atmospheric pressure and at 250-650 DEG  C. into contact with a highly surface-active non-metallic catalyst material comprising silicon hydroxide gel, precipitated aluminium hydroxide gel, or active charcoal.  A carrier gas which may consist of inert gases or steam or of a non-oxidizing gas such as carbon monoxide or of mixtures of such gases is preferably added to the vapours. Hydrogen or hydrogen-containing gases may also serve as the carrier gas. Alkaline substances such as the oxides, hydroxides or carbonates of the alkali and alkaline earth metals may be added to the contact mass in an amount of 10 per cent to 20 per cent based on the total weight of contact material.  Compounds of the heavy metals vanadium, chromium, manganese, iron, cobalt and nickel such as the acetates or hydroxides of iron or chromium in a ratio of from 1 per cent to 20 per cent by weight of the surface-active catalyst material may also be added to the contact mass and it is preferred to include both an alkaline substance and such heavy metal compound.  The treatment of the crude benzene with the contact material may be preceded by passing the benzene vapours at elevated temperature over a desulphurization catalyst which may be alkalized bauxite or an iron compound such as "Lux-Mass" which contains precipitated iron hydroxide as the active ingredient.  The temperature of the desulphurization catalyst and the main contact material may be different and operation is generally effected with both at between 400 DEG  and 450 DEG  C.  The preparation of the contact agent may be effected by precipitating a heavy metal compound, e.g. ferric hydroxide at the same time as the main contact agent, e.g. aluminium hydroxide gel, the dried product containing about 2 per cent Fe2O3. Instead of precipitating ferric hydroxide, a chromic salt such as chromic sulphate, chromic chloride or chromic acetate may be used to form an activated gel containing chromic hydroxide, the dried product containing about 2 per cent of Cr2O3.  When such mixtures containing Cr2O3\t are used as the contact agent the prior treatment with a desulphurization catalyst may be dispensed with.  The process may be carried out continuously by removing the lower layers of contact material from the apparatus and adding fresh soot-free contact material at the top.  The inorganic gels, particularly the chromic oxide-aluminium hydroxide gel, may be regenerated by heating to light red heat and then again added at the top.  The treated benzene may be washed with sulphuric acid in a continuously operating washing apparatus in which the liquid benzene is passed in the form of fine droplets through one or more vessles containing sulphuric acid which may be an acid of 60-64 DEG  Be.  Preferably the benzene is allowed to flow through two or more washing vessels in succession, the acid being preferably passed countercurrently to the benzene by completely or partly withdrawing the spent acid at or near where the benzene enters and by adding fresh acid at the benzene exit.  The benzene is then preferably washed with caustic soda and then with water and may then be submitted to a final distillation.  Before washing with sulphuric acid the treated benzene is preferably subjected to a drying treatment, e.g. with solid caustic alkali and the pyridine present may also be recovered as pyridine sulphate by washing with sulphuric acid of about 37 per cent concentration before the usual sulphuric acid washing.  In examples: (1) crude benzene is distilled and the vapour passed at 400 DEG  C. through a small stove containing an auxiliary contact agent in the form of small grains consisting of precipitated ferric hydroxide from bauxite residues ("Lux-Mass") mixed with kieselguhr and clay. The vapour is then passed at 450 DEG C. into another stove which contains active charcoal.  The benzene is then condensed, washed with sulphuric acid in a continuously operating washing apparatus and then submitted to a final distillation; (2) steam distilled crude benzene is passed in vapour form through contact material consisting of alkalized bauxite heated to 450 DEG  C. and the vapour then passed into a contact stove heated to 450 DEG  C. and containing silicon hydroxide gel to which iron acetate and potassium carbonate has been added.  The product is then distilled and washed with sulphuric acid as in (1); (3) raw benzene is distilled and the vapours passed at 450 DEG  C. through granulated "Lux-Mass" with a soda content of 15 per cent to eliminate sulphur-containing ingredients and then through a contact stove maintained at the same temperature and containing a mixture of precipitated silicon hydroxide gel and a small amount of ferric oxide which has been obtained by saturating silicon hydroxide gel with a solution of iron acetate and drying.  After condensing the vapours the benzene is passed through a receptacle charged with solid sodium hydroxide and then successively through three sulphuric acid washing towers containing sulphuric acid of 78-98 per cent concentration the benzene being introduced into each tower in the form of fine droplets which rise through the acid.  The benzene is then passed through a tower filled with dilute caustic soda solution and then through a washing tower filled with water before submitting to a final distillation.  Specification 618,447 is referred to.