Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
  • C07C51/255—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting
  • C07C51/265—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting having alkyl side chains which are oxidised to carboxyl groups
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/582—Recycling of unreacted starting or intermediate materials

Definitions

• a process for the oxidation of organic compounds in the liquid phase by means of molecular oxygen or ozone characterised in that the oxidation is conducted with condensation of the overhead vapours, separation of water from the condensate, and reflux, under such conditions that the composition of the vapour over the liquid is in each stage of the oxidation outside the explosive range of compositions.
• Desired product can be recovered from the reaction product, for example by distillation.
• the oxidation may be conducted in a single stage or in several stages. Moreover, the process may be operated batchwise or continuously. It is desirable that cooling be provided in the process, for example by means of the latent heat of vaporization of a reactant or reactants or of an inert solvent, or by the use of a coil through which fluid is circulated, or by external heat transfer means. The last mentioned is especially important when the reaction mixture under the oxidation conditions atfords little self-cooling by evaporation of some of its components.
• the oxidation zone is preferably furnished with external heat transfer means, for example a jacket containing a liquid, for example water, boiling under pressure, and an associated condenser; the starting material is introduced near the top, and the oxidising gas near the bottom of the reaction zone; and the product is taken oil at or near the bottom thereof.
• external heat transfer means for example a jacket containing a liquid, for example water, boiling under pressure, and an associated condenser; the starting material is introduced near the top, and the oxidising gas near the bottom of the reaction zone; and the product is taken oil at or near the bottom thereof.
• the uncondensed vapours from the condenser are scrubbed with a liquid for recovery of residual starting material they contain.
• each of the stages may be furnished with the auxiliaries just described. Further, in processes comprising more than one stage any or all of the stages may comprise two or more sub-stages each similarly conducted.
• distillation columns are preferably provided between them and can be run either, (i) to yield as overheads unoxidised start ing materials and intermediate oxidation products for return to the prior oxidation stage, and as bottoms oxidation products for feeding to the next oxidation stage; or (ii) to yield as overheads unoxidised starting materials for return to the prior oxidation step and as bottoms intermediate and final oxidation products for feeding to the next oxidation step.
• the process can be operated firstly under such conditions that the concentration of organic compounds in the vapour over the liquid is below that corresponding to the lower explosive limit.
• the vapour in equilibrium with the liquid in the oxidation reactor has a concentration of organic compounds below that corresponding to the lower explosive limits; or to operate with a liquid, the equilibrium vapour of which would lie within the explosive limits, but to bring the composition of the vapour below the lower explosive limit by introducing sufiicient incombustible, inert diluent into the liquid or into the space above the liquid in the reaction zone.
• Suitable incombustible inert diluents are, for example, nitrogen, carbon monoxide and steam.
• the process can be operated secondly under such conditions that the concentration of organic compounds in the vapour over the liquid is above that corresponding to the upper explosive limit.
• this method of operation it may be arranged that the vapour in equilibrium with the liquid in the oxidation reactor has a concentration of organic compounds above that corresponding to the upper explosive limit, or to operate with a liquid of which the equilibrium vapour would lie within the explosive limits but to bring the composition of the vapour above the upper explosive limit by introducing sufiicient volatile organic liquid either into the liquid or into the space above the liquid, so that in result the concentration of organic compounds in the actual vapour above the liquid is above that corresponding to the upper explosive limit.
• this method of operation can be conducted by increasing the rate of boiling.
• Suitable organic liquids are, for example, benzene, acetic and propionic acids, halogenated benzenes, e.g., chlorbenzene and orthodichlorbenzene, and fully halogenated aliphatic hydrocarbons such as carbon tetrachloride.
• Another advantage of using such volatile organic liquids is that they function also to remove water formed in the reaction either as azeotrope, or by direct contribution of partial pressure. This water can be removed, for example, by means of a separator such as a Dean and Stark decanter situated in the exit line from the still of the reactor.
• a separator such as a Dean and Stark decanter situated in the exit line from the still of the reactor.
• the vapour over the liquid has a concentration of organic compounds above the upper explosive limit
• a similar procedure may be adopted, when a gaseous inert diluent is used, the condensed starting material being returned to the oxidation step and also some of the inert gas if this is economically justifiable.
• the oxidising gas be distributed highly efficiently in the reaction mixture: this applies especially when operating above the upper explosive limit.
• Suitable distributors are, for example, rapidly rotating gas mixers, e.g., a cruciform stirrer, high efliciency atomisers, turbulent jets, or sinter glass: of these the first two are preferred. By using such distributors the oxygen content of the vapour above the liquid can be kept to a minimum.
• substantially pure oxygen is used as the oxidising gas, because the over-all velocity of the reaction is largely determined by the rate of diifusion of the gas. It is then particularly important that a highly efficient gas distributor be used, as already described. However, in fast oxidation processes, or when the solubility of oxygen in the liquid is high, air or oxygen diluted with inert gases may conveniently be used. If substantially pure oxygen is used for these oxidations it is economic to recycle the exit gas stream from the oxidation reactor after removing oxides of carbon, for
• limits of flammability normally refers to ignition at atmospheric pressure. Where ignition occurs in a closed system ignition is of the nature of an explosion and thus determination of the flammability limit is a suflicient index of the explosive limits (see, for example, Principles of Chemical Engineering, by Walker, Lewis and Mc- Adams (McGraw-Hill), Second Edition, Seventh Impression, page 206, second paragraph).
• the correct mixture to be tested can be prepared by passing a stream of the oxidising gas through a series of towers each containing an adsorbent such as kieselguhr loaded with the organic liquid.
• the towers are maintained at that temperature which yields a mixture with a partial pressure of organic compound corresponding to that which will be present in the reactor of the oxidation process. Care is taken to avoid condensation before feeding the mixture to the explosion tube by providing suitable heating means.
• the temperature in the explosion tube can be varied to correspond to the actual temperature in the oxidation process by providing the explosion tube with an external heating coil.
• the concentration of the organic compound will very often after condensation, which is a necessary step, fall within the explosive range. This may happen, due to inefliciency of condensation, even when the equilibrium mixture of the gas and organic compound would not normally be explosive at the temperature in the condenser. It is therefore preferred to make provision for the admission of sufiicient inert diluent, e.g., nitrogen, carbon dioxide or other inert gas, in close proximity to the potential hazard in order to eliminate it, for example in the exit gas line after the condenser.
• sufiicient inert diluent e.g., nitrogen, carbon dioxide or other inert gas
• the ozone, oxygen or oxygen-containing gas is brought into contact with the organic compound in the liquid phase under such conditions that the concentration of organic compounds in the vapour above the liquid is greater than corresponds to the upper explosive limit, at least part of the oxidise liquid is taken off continuously and fed to a separating column; the overhead from this comprising the starting material is recycled to the reactor and the bottoms comprising intermediate and final oxidation products are fed to a second reactor provided with a condenser, reflux and decanter, in which they are brought into contact with air or oxygen or ozone, run under such conditions that the concentration of organic compounds in the vapour over the liquid is less than that corresponding to the lower explosive limit.
• vapour from the second reactor emerging from the condenser may be subjected in the exit gas line to further cooling or scrubbing for recovery of valuable residual compounds, if this is economic.
• one or all of the intermediate products may be returned as overheads from the column to the first stage for oxidation there. in this process it is sometimes desirable to have present in the stage operated above the upper explosive limit, a more volatile combustible oxidation-stable solvent as already described.
• the ozone, oxygen or oxygen-containing gas is brought into contact with the organic compound in the liquid phase and partial oxidation is effected under such conditions that the concentration of organic compounds in the vapour above the liquid is greater than the upper explosive limits, at least a portion of the liquid mixture is withdrawn continuously to a second reactor in which the oxidation is continued and the composition of the vapour above the liquid is controlled outside the explosive limits by circulating it together with an inert in a closed system including a condenser and a purge line, and the liquid product from the second reactor is introduced into a third reactor in which it is reacted with oxygen or air under such conditions that the concentration of organic compound in the vapour is below the explosive limit.
• Both reactors are provided with reflux stills and with Dean and Stark decanters in the exit lines.
• the process can also be operated by distributing the organic compound to be oxidised in the oxidising gas by means of a packed tower or an atomizer nozzle, so that the liquid forms films.
• the process is of especial value in relation to the oxidation of organic compounds in the liquid phase by means of ozone or molecular oxygen in the presence of a catalyst comprising a metal of variable valence, e.g., manganese and/or cobalt and bromine, commonly under superatmospheric pressure.
• a metal of variable valence e.g., manganese and/or cobalt and bromine, commonly under superatmospheric pressure.
• Example 1 60 grams of ortho-xylene dissolved in grams of molten benzoic acid and containing as catalyst 0.33 gram of MnBr .4H O and 0.19 gram of CoBr .6H O was oxidized in the liquid phase at C. and atmospheric pressure by passing oxygen into it at a rate of 24 litres per hour through a high speed cruciform stirrer. Simultaneously 300 litres per hour of steam measured at 100 C. was blown over the liquid reaction surface. The vessel was provided with a reflux column and a Dean and Stark decanter in the gas exit line, and water was condensed from the exit gas stream. Analysis of the uncondense gas showed average oxygen absorption of approximately 3 litres per hour. 20 mls. of benzene were included in the reaction mixture with the object of avoiding blocking of the decanter by benzoic acid carried over, and this, with any unconverted ortho-xylene was continuously returned to the oxidation vessel by overflow.
• Example 2 40 grams of para-xylene dissolved in 200 grams of propionic acid was treated with well dispersed oxygen at 137 C. under reflux in the presence as catalyst of 0.33 gram of MnBr .4H O and 0.19 gram of CoBr .6H O, using an oxygen rate of 12 litres per hour.
• the boil-up rate was maintained at approximately 2 gram moles per hour of propionic acid to ensure that the concentration of the latter in the vapour was such that the vapour was above the higher inflammability limit.
• the vapours from the reaction vessel passed through a packed reflux column and were condensed in a decanter in the gas exit line.
• the bottom phase consisting of para-xylene dissolved in propionic acid, was returned to the oxidation reactor.
• Example 3 The proportions and procedural details were the same as in Example 2 except that the boil-up rate was decreased to 0.5 gram mole propionic acid per hour. 100 litres of propionic acid vapour (measured at 150 C.) was blown over the surface of the reaction medium at 150 C. in order to maintain the total composition of the vapour outside its upper infiammability limit.
• Example 4 40 grams of ortho-xylene dissolved in 200 grams of molten benzoic acid containing as catalyst 0.33 gram of and 0.19 gram of CoBr .6H- O together with 50 grams of benzene, was oxidised with a well dispersed stream of oxygen at 150 C. under atmosphereic pressure using 12 litres per hour of oxygen. The boil-up rate of the liquid was maintained at about 300 ml. of liquid hydrocarbon per hour, and the composition of the vapour thus maintained above its upper infiammability limit. The hydrocarbon vapours from the reaction zone after passage through a packed reflux column were condensed in a decanter in the gas exit line, the lower aqueous phase was removed from the system, and the hydrocarbon was recycled to the oxidation reactor.
• Example 5 The proportions of the reactants and the procedural details were the same as in Example 4 except that the boil-up rate of the liquid was decreased to 50 mls. of hydrocarbon per hour. 50 litres per hour of industrial nitrogen measured at 20 C. was blown over the reaction surface, whereby the upper inflammability limit was lowered, so that under these conditions the vapour over the liquid was non-inflammable.
• Example 6 For this run 40 grams of ortho-xylene and 0.5 gram of CoBr .6H O were added to the filtrate obtained after filtering oil the phthalic acid from the product obtained in Example 5. The other procedural details were the same, except that carbon dioxide at a rate of 50 litres per hour, measured at 20 C., was passed over the surface of the liquid.
• said solvent is selected from the group consisting of volatile benzene hydrocarbons, lower aliphatic acids, halogenated benzenes, and fully halogenated aliphatic hydrocarbons.
• said volatile organic liquid is selected from the group consisting of volatile benzene hydrocarbons, lower aliphatic acids, halogenated benzenes, and fully halogenated aliphatic hydrocarbons.

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• Engineering & Computer Science (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Citations (8)

• 0
  • BE BE562538D patent/BE562538A/xx unknown
• 1956
  • 1956-11-21 GB GB35564/56A patent/GB825429A/en not_active Expired
• 1957
  • 1957-10-28 US US692534A patent/US3155718A/en not_active Expired - Lifetime
  • 1957-11-09 ES ES0238493A patent/ES238493A1/es not_active Expired
  • 1957-11-21 FR FR1196029D patent/FR1196029A/fr not_active Expired

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