Patent GB-845287-A (GB)
Title: A process for the production of chlorinated phenols with recovery of hydrochloric acid
Inventor: SHELTON FREDERICK J
IPC: C07C37/62
Filed: 1956-10-29
Abstract: Chlorinated phenols comprising predominantly pentachlorophenol and having a minimum freezing point of 174 DEG C. when determined as specified below are prepared by chlorinating phenol in the presence, during at least the latter part of the chlorination reaction, of between 0,004 and 0,0085 mol. of anydrous aluminium chloride per mol. of phenols.  Preferably, the amount of aluminium chloride does not exceed 0,0075 mol. and the catalyst is not added until 1 to 3, and most preferably 2,3, atoms of chlorine have been combined per mol. of phenol.  Advantageously the chlorination in the absence of aluminium chloride is conducted at a temperature below 130  DEG C., although preferably above 70  DEG C., and the chlorination in the presence of aluminium chloride is conducted at a temperature between the melting point of the reaction mass and 200  DEG C.  The first step is preferably continued until the reaction mass has a melting point of at least 60  DEG C. and the catalyst thereafter added before the melting point exceeds 120  DEG C.  The first chlorination step is advantageously effected with dilute chlorine-containing off-gas from a later chlorination stage and the second step using an excess of chlorine gas, a suitable chlorination time being 5 to 15 hours.  In the first step the off-gas may be scrubbed substantially free of chlorine to give substantially chlorine -free hydrochloric acid gas, which may also be obtained by separate scrubbing of the off-gas from the process of the invention with hot molten phenol, mono-, di- or trichlorophenol or mixtures thereof (see Group III).  In an apparatus suitable for the chlorination process, described with the aid of a drawing, chlorine is fed through a flow measuring device to the lower portion of a primary reactor containing phenol, partially chlorinated phenol is withdrawn from the upper portion of this reactor and is fed to the lower portion of a scrubber-reactor also containing phenol and partially chlorinated phenol is then re-fed, wholly or partly, to the upper portion of the primary reactor, from the bottom of which pentachlorophenol product is withdrawn.  The apparatus also comprises means for isolation of the hydrogen chloride by-product as hydrochloric acid (see Group III).  In examples (1) the apparatus is used for the simultaneous preparation of pentachlorophenol and monochlorophenol (approximate compositions), the latter in the scrubber-reactor which is operated in the absence of catalyst and at a temperature of 70 DEG C. throughout and the former in the primary reactor, the temperature in which is gradually increased from 70 DEG  to 190 DEG C. and to which about 0,007 mols. of catalyst per mol. of phenols are added when the melting point of the product therein reaches 50 to 55 DEG C; and (2) pentachlorophenol and chlorinated phenol containing 2,68 atoms of chlorine per molecule of phenol are similarly prepared, the temperature in the primary reactor, which contains 0,005 mol. of catalyst per mol. of phenols, being first held at 130 DEG C. and then raised to 180 DEG C. and the temperature in the scrubber reactor being 60 DEG C. initially and 120 DEG C. finally. The procedures for the determination of chlorinated phenols expressed as per cent pentachlorophenol and for the determination of alkali-insoluble matter (desirably less than 1% in normal sodium hydroxide) and total chlorine in the product are described. The freezing point of the product is defined as the highest temperature at which the temperature remains constant for at least 15 seconds when the product is heated to about 10 DEG C above the expected freezing point in an enamelled cup or nickel tube and allowed to cool with constant stirring.  U.S.A. Specification 2,131,259 is referred to.ALSO:Substantially pure hydrochloric acid gas is obtained as a by-product in the chlorination of phenol or partially chlorinated phenols, (a portion at least of the chlorination being carried out in the presence of 0.004 to 0.0085 mol of anhydrous aluminium chloride catalyst per mol of phenols to produce chlorinated phenols having a minimum freezing point of 174.0 DEG C.), by scrubbing the off-gases from the chlorination with hot molten phenol, monochlorophenol, dichlorophenol or trichlorophenol or mixtures thereof to remove free chlorine.  In an apparatus suitable for the process, described with the aid of a drawing, chlorine is fed to the lower portion of a primary reactor containing phenol, partially chlorinated phenol is withdrawn from the upper portion of this reactor and is fed to the lower portion of a scrubber-reactor also containing phenol and partially chlorinated phenol is then re-fed wholly or partly, to the upper portion of the primary reactor, from which pentachlorophenol is withdrawn. From the upper end of the scrubber-reactor off-gases are withdrawn through a trap to the lower portion of an absorption tower through which water flows from the top, and concentrated hydrochloric acid is taken off from the lower portion of the tower and a portion thereof recirculated to the top of the tower, the remainder being withdrawn from the system.  Example describe the preparation of 36% hydrochloric acid by the process of the invention.  U.S.A. Specification 2,131,259 is referred to.