MXPA00010181A - Preparation of organic acids - Google Patents

Abstract

This invention relates to a process for producing one or more org anic acids in high purity which process comprises (i) oxidizing in a liquid oxidation reactor one or more organic liquids with essentially pureoxygen or oxygen-enriched air containing at least about 50%oxygen, at a temperature sufficiently stable to prevent cycling of reaction rate, to produce a crude reaction product fluid, and (ii) refining said crude reaction product fluid to give said one or more organic acids in high purity. The oxidation temperature is preferably controlled to within about±3°C of a target temperature. The organic acids described herein are useful in a variety of applications, such as intermediates in the manufacture of chemical compounds, pharmaceutical manufacture and the like.

Description

'PREPARATION OF ORGANIC ACIDS " BRIEF SUMMARY OF THE INVENTION TECHNICAL FIELD This invention relates to a process for preparing organic acids by oxidizing in a liquid oxidation reactor an organic liquid with molecular oxygen or a gas containing molecular oxygen, to produce an organic acid.

BACKGROUND OF THE INVENTION The manufacture of petrochemicals through the oxidation of the liquid phase of hydrocarbons with a gaseous oxidant is a very significant commercial operation. Examples of consumer chemicals produced by this process are terephthalic acid, adipic acid and phenol. Air has traditionally been used as a gaseous oxidant in these processes, however, it has long been recognized that significant process advantages are offered by using pure oxygen as the oxidant. These advantages include, for example, transfer of improved oxygen mass to the phase liquid due to the driving force of increased concentration (partial pressure), improved chemical selectivity resulting from less serious operating conditions, reduced equipment size resulting in reduced gas throughput to the reactor, and reduced waste gas fired from the reactor. However, safety is always a problem when pure oxygen is used as the oxidant in any chemical process. There is a continuing need to provide safe and efficient processes for preparing organic acids, especially when oxigen is used as pure oxygen.

COMPENDIUM OF THE INVENTION This invention relates to a process for producing one or more organic acids in high purity, which process comprises (i) oxidizing in a liquid oxidation reactor one or more organic liquids with essentially pure oxygen or air enriched with oxygen containing at least about 50 percent oxygen, at a temperature stable enough to prevent cyclization of the reaction regime, to produce a crude reaction product fluid, and (n) to retinue the fluid of the crude reaction product to provide one or more organic acids in high purity. The oxidation temperature is preferably controlled to within about + 3 ° C of a boundary temperature. By controlling in this way the oxidation temperature, any of the temperature disturbances will not cause the release of oxygen quantities into the vapor space of the liquid oxidation reactor which may cause the vapor region to exceed LOV as defined below. . This invention also relates to a process for producing one or more high purity oxo acids whose process comprises (i) oxidizing in a liquid oxidation reactor one or more oxo-aldehydes with essentially pure oxygen or with air enriched with oxygen containing at least about 50 percent oxygen, where the mass transfer between one or more oxo aldehydes and the essentially pure oxygen or the oxygen enriched air containing at least about 50 percent oxygen, is sufficient to reduce the or to eliminate the formation of a by-product, to produce a fluid of the crude reaction product, and to refine the fluid of the crude reaction product to provide one or more oxo acids, in high purity. liquid as described herein, the forced circulation of the reagents, that is, the oxo-aldehyde and the pure oxygen or the oxygen enriched air containing at least about 50 percent oxygen, to break through quickly through the liquid fixation reaction system improves the transfer of heat and mass between the reactants, thus maximizing the volumetric productivity of the reactor and improving the selectivity of the desired product. This invention also relates to a process for producing one or more organic acids in high purity, which process comprises (i) oxidizing, in a reactor for oxidation of the liquid, one or more organic liquids with essentially pure oxygen or an air enriched with oxygen containing at least about 50 percent oxygen, to produce a fluid of the crude reaction product, and (n) refining the fluid of the crude reaction product to provide one or more organic acids in high purity; wherein the liquid oxidation reactor comprises: a) a vertically placed tube and a hull reactor vessel having a traction tube with the center thereof and heat exchanger tubes in the annular space between the hollow traction tube and the external wall of the reactor vessel, the reactor vessel has an upper space above of a hollow mixing chamber below the hollow traction tube and the heat exchanger tube; b) an impeller positioned within the hollow traction tube and adapted to cause the rapid flow of the organic liquid down through the hollow traction tube into the lower mixing chamber and rapidly upwards through the heat transfer tubes as a dispersion essentially uniform and towards the upper space in the reactor vessel; c) a top chamber positioned above and in fluid communication with the reactor vessel, the upper chamber having a vapor space above a desired liquid level; d) at least one generally horizontal gas containment baffle positioned between the upper chamber and the reactor vessel such that the vapor space above the liquid level in the upper chamber is maintained below both LOV and of LFL, the gas containment baffle being formed with a central hole to allow the impeller to extend generally concentrically through the hole in the gas containment baffle; e) at least one generally horizontal seal baffle placed within the space of steam in the upper chamber such that the vapor space above the seal baffle is maintained in an inert atmosphere, the seal baffle being formed with a central hole to allow the impeller to extend generally concentrically to through the hole in the seal baffle; f) a conduit for introducing the organic liquid into the reactor vessel and for introducing pure oxygen or air enriched with oxygen containing at least about 50 percent oxygen to the reactor vessel or the upper chamber for rapid recirculation with the organic liquid descending through the hollow drawing tubes towards the lower mixing chamber and rapidly upwards through the heat transfer tubes towards the upper space; g) a conduit for removing the liquid from the product from the reactor vessel; h) a conduit for flowing the cooling fluid into the reactor vessel for the removal and exothermic heat of the reaction generated within the reactor vessel; and i) a control means for maintaining the desired level of the liquid within the reactor vessel or within the upper chamber. Installing a baffle in the upper chamber, any equipment or parts that have the potential to generate heat of friction, eg, a seal through which the arrow of the agitator passes to the reactor of oxidation of the liquid, and will not impose a risk of ignition if it is prevented from Oxygen and organic vapors are brought into contact with this equipment or parts in an off-center condition such as the loss of agitation in the reaction zone. This invention is still further related to a process for producing one or more organic acids in high purity whose process comprises (i) oxidizing in a primary liquid oxidation reactor one or more organic liquids with essentially pure oxygen that is enriched with oxygen containing at least about 50 percent oxygen, to produce a first fluid of crude reaction product, (n) remove the first fluid of the crude reaction product from the primary liquid oxidation reactor, (ni) feed the first fluid of the product of crude reaction to at least one secondary liquid oxidation reactor or a flow reactor, (iv) oxidizing in the second liquid oxidation reactor or flow reactor in the first fluid of the crude reaction product with essentially pure oxygen or with oxygen enriched air containing at least approximately 50 percent oxygen to produce a second crude reaction product fluid, and (v) refining the second fluid of the crude reaction product to provide one or more organic acids in high purity. By configuring two or more liquid oxidation reactors in series or a liquid oxidation reactor followed in series by a flow reactor, the efficiency can be improved by increasing the conversion of the organic liquid.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a liquid oxidation reactor. Figure 2 illustrates the head of the condenser of a liquid oxidation reactor. Figure 3 illustrates a temperature control mechanism for a liquid oxidation reactor. Figure 4 illustrates a comparison of the discharge vapor composition for the reactor for oxidation of liquid and air converters with flammable scale. The liquid oxidation reactor operates below both LFL and LOV, while the air converters operate only below LOV. Figure 5 shows a comparison of the levels of by-product in a crude and refined product produced by the air converters and the liquid oxidation reactor.

DETAILED DESCRIPTION As used herein, the following abbreviations have the indicated meanings: Lower Flammable Limit (LFL) - a composition below which a mixture contains insufficient fuel to sustain combustion; Upper Flammable Limit (UFL) -a composition above which a mixture contains too much fuel to sustain combustion; and Value or Concentration of Oxygen Limit (LOV or LOC) - the oxygen content unless one mixture will not sustain combustion independently of another component composition. The liquid phase oxidation can be described as a two-step operation involving (i) mass transfer from inferium to oxygen to the liquid phase; and (n) chemical reaction of the dissolved oxygen and the hydrocarbon in the liquid phase through a free radical mechanism. The total oxidation regime is a function of both the physical transport phenomena and the speed of the chemical reaction. The transference of Oxygen from the gas to liquid phase is a critical aspect of the process and is often the regime limitation step since the solubility of oxygen in many hydrocarbon systems is inherently low. The mass transfer from gas to liquid is improved by increasing the contact area between the phases. In chemical reactors, this is typically achieved by introducing the gas through a submerged sprinkler designed to generate bubbles and promoting bubble dispersion and disintegration through the use of mechanical agitation. The liquid oxidation reactor has been designed with both a high degree of gas dispersion and gas-liquid mixing to promote the transfer of oxygen to the liquid phase and to minimize losses of chemical selectivity due to mass transfer deficiencies. The chemical reaction regime is influenced by the reaction temperature and the concentrations of the crude material. Reactions with low activation energy are not sensitive to temperature, however, those with a high activation energy may exhibit significant regime changes for only small temperature changes. For more intense exothermic reactions such as oxidations, this sensitivity to temperature is acute because the temperature deviation that affects the reaction rate impacts also the heat evolution regime. As an illustration, a small downward shift in the oxidation temperature which causes a reduction in the reaction rate correspondingly reduces the rate of thermal evolution, which in turn can result in a further reduction in the reaction temperature and the rate of reaction. The net result may be pronounced instability in the control of the reaction regime. For oxidation processes, the reaction instability can have serious safety consequences because the oxidation reactors maintain strict safety controls through the allowable oxygen concentration in a discharge gas in order to keep the discharge gas below of LOC. Due to reasons of improved mass transfer, oxidation processes are typically operated within a window where the level of oxygen passage under the LOC limit is maximized. Therefore, the stability of the reaction regime is of critical importance because the variations in the reaction regime cause the level of the passage of unreacted oxygen to the discharge gas to oscillate. These disorders can force the process to work well below the LOC limit in order to to prevent upward changes in oxygen concentration that exceed the LOC level. Due to this reason, commercial oxidation reactors often function purposefully in a regime where transport phenomena dominate the regime and the chemical selectivity advantages of oxidation are exempt from mass transfer limitations that change for improved stability. Organic liquids that can be employed in the process of this invention include, for example, aldehydes, alcohols, alkylbenzenes, cyclic aliphatic hydrocarbons and the like. Exemplary aldehydes include, for example, formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, 2-methylbutyraldehyde, iso-butyraldehyde, n-valeraldehyde, caproaldehyde, heptaldehyde, nonyl aldehyde, phenylacetaldehyde, benzaldehyde, o-tolualdehyde, m-tolualdehyde, p- tolualdehyde, salicylaldehyde, p-hydroxybenzaldehyde, anisaldehyde, vanillin, piperonal, 2-ethexaldehyde, 2-propheptaldehyde, 2-phenylpropionaldehyde, 2- [p-isobutylphenyl] propionaldehyde, 2- [6-methoxy? -2-naft? L] prop? Onaldeh? Do and like. Illustrative alcohols include, for example, 2-ethylhexanol, 2-propylheptanol, isobutyl alcohol, 2-methyl-1-butanol, and the like. The alkylbenzenes Illustrative include, for example, p-nitrotoluene, o-bromotoluene, ethylbenzene, n-butylbenzene, m-xylene, p-xylene, toluene and the like. Exemplary cyclic aliphatic hydrocarbons include, for example, cyclohexane, cyclooctane, cycloheptane, methylcyclohexane and the like. Illustrative of the appropriate organic liquids include those liquids of permissible starting material that are described in Kirk-Othmer's Encyclopedia of Chemical Technology, Third Edition, 1984, the pertinent portions of which are incorporated herein by reference. Preferred organic liquids include aldehydes, particularly aldehydes prepared by hydroformylation processes as disclosed, for example, in U.S. Patent Nos. 3,527,809, 4,148,830, 4,247,486, 4,593,127, 4,599,206, 4,668,651, 4,717,775 and 4,748,261. These aldehydes prepared by hydroformylation processes are referred to herein as "oxo aldehydes". The oxidizing agent useful in the process of this invention is pure oxygen or air enriched with oxygen containing at least about 50 percent oxygen. The oxygen enriched air may contain, for example, inert gases such as nitrogen, carbon dioxide or noble gases. The preferred oxidizing agent is pure oxygen. These oxidizing agents can be used in amounts which will be described below and in accordance with conventional methods. The oxidizing agent is used in an amount sufficient to allow complete oxidation of the organic liquid, e.g., the aldehyde. Preferably, the oxidizing agent is added at a rate, eg, oxygen partial pressure, sufficient to suppress or eliminate side reactions of the organic liquid such as decarbonylation of the aldehyde, and most preferably, an oxygen partial pressure of about .0703. kilogram per square centimeter or less to approximately 14,060 kilograms per square centimeter or greater. The oxidation step of the process of this invention can be carried out at a reaction pressure of about 3,518 to about 10,545 kilograms per square centimeter manométpca. The preferred operating pressure is from about 4,921 to about 8,436 kilograms per square centimeter gauge. The liquid oxidation reactor preferably operates at a pressure of approximately 7.03 kilograms per square centimeter gauge and can preferably be limited within a pressure range of approximately 5,624 to approximately 8,085. kilograms per square centimeter manométpca by means of automatic limits of high and low pressure. For aldehyde oxidations, it has been observed that the secondary reaction of aldehyde decarbonylation of Ci and Cn_ fragments is very low at partial oxygen pressures greater than 2,812 kilograms per square centimeter manométpca, but increases exponentially at partial oxygen pressures of less than 2,812 kilograms per centimeter square manometric, supposedly due to the increased acute impact of the oxygen mass transfer limitations. Other process conditions were consistent with commercial operating conditions (temperature of 65 ° C, reaction regime of <; 15 gmol / lit / hour). Therefore, for aldehyde oxidations, the operating pressure for the liquid oxidation reactor should preferably be greater than about 2,812 kilograms per square centimeter manometpca to minimize the selectivity of the organic acid product. The upper limit on the reaction pressure is determined by considerations of the thickness of the container wall. A deflagration that occurs in the vapor space of the liquid oxidation reactor will cause an increase in pressure to approximately 10 times the initial pressure. Designing the thickness of the wall of Container to contain the increase of a potential deflagration limits the normal operating pressure. The oxidation step of the process of this invention can be carried out at a reaction temperature of about -25 ° C or lower to about 125 ° C. Lower reaction temperatures can generally tend to minimize byproduct formation. In general, oxidations are preferred at reaction temperatures of about -10 ° C to about 100 ° C. The approach of this invention is in controlling the temperature of a kinetically controlled oxidation reaction thereby allowing improved product quality. This invention recognizes and directs the impact of temperature on the concentration of oxygen in the vapor space of the liquid oxidation reactor. Controlling a temperature sensitive oxidation reaction in a region that is not subject to mass transfer limitations, may result in improved product quality due to reduced byproduct formation. The operation of the reaction requires close control of the reaction temperature since the operation of a highly exothermic reaction with a high activation energy in a kinetically controlled rate can make the reaction extremely sensitive at the temperature. Sensitivity to temperature can cause fluctuations when oxygen is forced into the steam space of the reactor. Particularly, if the organic liquid A in an oxidation reactor of the liquid in organic acid B is oxidized in the following manner: xA + y02 = zB where x, y and z are stoichiometric constants, then the oxidation rate of the organic liquid A is provided by an expression of the form: RT rA = k * A * e * C "A * P" 'o2 wherein rA is the reaction regime of A; k, n, m are constants, A ^ is Arrhenius's constant, E is the activation energy, T is the absolute temperature, R is the universal gas constant, CA is the concentration of the organic liquid A, and Pg is the pressure partial oxygen If the reaction temperature changes by a small increment from T to T2 the change in the reaction regime? RA 'can be calculated as follows: -E ^ E R11 RT2? RA = k * A1 * [e - e] * C "A * P" '02 The impact on the oxygen consumption regime is: ? F02 =? RA * V * y / x where V is the volume of the reaction zone. A downward temperature change will cause a reduction in the oxygen consumption regime. If the rate of oxygen feed to the reaction zone is not reduced, the oxygen purge rate (Fg2) through the gas baffle will increase which is equal to: (F02) 2 = (F02) 1 +? F02 where (Fg2)? is the initial oxygen purge regime through the gas baffle. By preventing organic flow into the vapor space, the concentration of oxygen (CQ2) in the vapor space above the liquid level of the condenser will be equal to: (E02 '2 c02 N2 + < F02 > 2 where N2 is the regime of nitrogen purge through the vapor space. The following limit must be applied to maintain the vapor space in a safe operating region: C02 < LOC System It follows that the temperature controller of the reaction zone of the liquid oxidation reader should be able to maintain the reaction temperature within a range where the temperature disturbances do not cause the process to release quantities of oxygen into the vapor space, which can cause the vapor region to exceed LOC. This limit is within + 3 ° C, preferably + 2 ° C, and more preferably + 1 ° C, from the limit temperature of the oxidation reactions to preferred regimes of nitrogen purge through the vapor space. The limiting temperature is selected from a temperature ranging from about -25 ° C or less to about 125 ° C, preferably from about -10 ° C to about 100 ° C. These temperature disorders can cause cycling of the reaction rate. Cycling refers to periodic and extreme frequent changes in the reaction regime during the oxidation process. Cycling conditions interrupt the constant operation of the unit. A uniform temperature is required to eliminate cycling of the reaction rate. The oxidation reactor of the liquid preferably must be provided with a temperature control circuit sufficient to maintain or control the temperature of the reaction zone within the limits stated above. An illustrative design employs the strategy shown in Figure 3. In this project, the upper conical temperature is controlled by adjusting the inlet temperature of the cycle water. The water inlet temperature of the cycle is controlled by manipulating the amount of cycle water that is recycled from the return line of the hull to the hull inlet using the CVl and CV2 valves. These two motor valves have a slot flow area V that provides a highly linear flow response to require changes. Preferably, the upper conical temperature is controlled to within + 0.5 ° C, thus providing the desired stability and an acceptable variation in the level of oxygen passage in the vapor space. The importance of this invention is that the control of the reaction temperature is needed by the liquid deprivation reactor due to stability reasons and to capitalize on the advantages of the process of functioning in a controlled region of the chemical regime. The current means to achieve temperature control may be subject to different design variations. In a preferred embodiment for the oxidation of the aldehyde, a temperature control within + 1 ° C of the reaction temperature limit for oxidations carried out in the oxidation reactor of the liquid having an activation energy greater than 15 kilocalopes per mole and the exothermic heat of reaction of more than 100,000 BTU / pound-mol is desirable. The oxidation step of the process of this invention is carried out for a period of time sufficient to produce an organic acid. The exact reaction time employed depends, in part, on factors such as temperature, nature and proportion of starting materials and the like. The reaction time will normally be within the range of about one half to about 200 hours or more, and preferably, less than about one to about 10 hours. The oxidation step in the process of this invention can be carried out in a liquid state and can involve a batch or continuous liquid recycling system. The oxidation step of the process of this invention can be carried out in the presence of an organic solvent. Depending on the promoter and reagents used In particular, suitable organic solvents include, for example, alcohols, alkanes, esters, acids, amides, aromatics and the like. Any suitable solvent that does not unduly interfere in a detrimental manner within the proposed oxidation process may be employed and such solvents may include those commonly employed in the foregoing in known processes. Mixtures of one or more different solvents can be used, if desired. Solvents that partially or completely dissolve aldehyde and do not react with peracids can be useful. The amount of solvent employed is not critical to the invention and needs only to be that amount sufficient to provide the reaction medium with the specific substrate and the concentration of the desired product for a given process. In general, the amount of the solvent when employed can vary from about 5 weight percent to about 95 weight percent or more, based on the total weight of the reaction medium. In a preferred embodiment, when the required aldehyde product is provided by a hydroformylation reaction, appropriate solutions can be provided using liquid aldehydes or by melting the solid aldehydes. However, the appropriate solutions may consist of the aldehydes dissolved in a solvent appropriate (e.g., in the solvent in which the first step of the process of this invention was carried out). Any solvent that dissolves the aldehyde product and is unreactive with pure oxygen or air enriched with oxygen containing at least about 50 percent oxygen, can of course be used. Examples of suitable solvents are ketones (e.g., acetone), esters (e.g., ethyl acetate), hydrocarbons (e.g., toluene), and nitrohydrocarbons (e.g., nitrobenzene). A mixture of two or more solvents may be employed to maximize the purity and yield of the desired aldehyde. The solution used may also contain materials present in the crude reaction product of the aldehyde-forming reaction (e.g., a catalyst, coordinator group and heavy materials). Preferably, however, the solution consists essentially of only the aldehyde and the solvent. The concentration of the aldehyde in the solvent solution will be limited by the solubility of the aldehyde in the solvent. In one embodiment of this invention, the oxidation of the aldehyde occurs through a complicated free radical mechanism. This process can be simplified into two basic steps represented by (i) the formation of a peroxy acid from an aldehyde template and (n) the reaction of the peroxy acid with one additional mol of aldehyde to yield two moles of the acid product. Step (1) is believed to occur through a mechanism of free radical that can be represented by: Initiation RCHO + 02 > RCO * + H02"(1) Propagation RCO * + 02 > RC03 * (2) RC03"+ RCHO> RCO3H + RCO" (3) Termination RC02 * + RCHO > molecular product (4) The initiation step involves the production of an acyl radical (RCO *) of the reaction of the aldehyde with oxygen. An external promoter is not used to generate free radicals, instead, it is believed that the generation mechanism involves the decomposition of the peroxides either thermally or catalyzed by metal surfaces. However, other limitations may employ a promoter, such as a cobalt or manganese salt. During the chain propagation step, the acyl radical reacts rapidly with oxygen to forming a peroxyacyl radical (RC03-) which, in a subsequent slower step, reacts with one mole the aldehyde to form a peroxy acid and a new acyl radical. This propagation reaction proceeds until the chain is terminated after a large number of cycles by the formation of the non-radical products. In step (2), the peroxy acid reacts with one additional mole of the starting aldehyde to form a peroxy-aldehyde acid adduct, which is then decomposed to form two moles of the acid produced.

O O HO O - O O \ / \ RC-H + RC-O-O-H > R-C C-R > 2RC-0-H (5) \ // H O aldehyde peroxy-acid adduct peroxy acid-aldehyde adduct There are several secondary reactions for mitered byproducts that compete with the aforementioned mechanism, under conditions of deficient mass transfer of oxygen to the liquid phase, the acyl radical involved in reaction 2, above can be broken down as follows: RCO "-> R * + CO (6) The remaining radical, R *, contains one carbon less than the initial acyl radical and may undergo additional oxidation to produce an aldehyde or alcohol. In the case of the oxidation of valeraldehyde, butyraldehyde or butanol may result from this step. The degree of generation of carbon monoxide and the rate of formation of compounds containing a carbon atom less (nl), than the hydrocarbon of the feedstock, are therefore measures of the degree of starvation of oxygen present at the conditions of reaction. The formation of the components of Cn_? it can impact the refining of the product if the same or the components formed by subsequent oxidation reactions have close volatility of the desired product. For example, the oxidation of valeraldehyde in valepco acid can produce small amounts of butyldehyde and butanol as undesirable byproducts of the oxygen starvation mechanism described above. Butyric aldehyde can still experience a additional oxidation to yield butyric acid, and butanol can be esterified with valeric acid to yield the butyl valerate. Both butyric acid and butyl valerate are difficult to separate from valeric acid in conventional refining columns because they are narrow boiling. The relative amounts of butyraldehyde and butanol present in the crude oxidation product are compared in Figure 5 for the liquid oxidation reactor and an air converter. After retinalization in similar fractionation processes, the amounts of butyric acid and butyl valerate remaining in the refined valeric acid are also shown in Figure 5. The reduction of butyric acid and butyl valerate correspond to quantitative improvements in purity of valepco acid. As indicated above, the forming process of the organic acid of the invention can be carried out in a batch or continuous manner, with the recycling of the raw materials not consumed if required. The reaction can be carried out in a single reaction zone or in a plurality of reaction zones, in series or in parallel, or it can be carried out batchwise or continuously in an elongated tubular zone or a series of these zones. The construction materials used must Be inert to the starting materials during the reaction, and the manufacture of the equipment must be able to withstand the temperatures and pressures of reaction. The means for introducing and / or adjusting the amount of starting materials or ingredients introduced batchwise or continuously into the reaction zone during the course of the reaction, can conveniently be used in the processes especially to maintain the desired molar ratio of the materials of departure. The reaction steps can be carried out by the incremental addition of one of the starting materials to the other. The processes can be carried out either in a glass lined equipment, stainless steel or a similar type of reaction equipment. The reaction zone can be equipped with one or more internal or external heat exchangers in order to control undue temperature fluctuations, or to prevent any of the possible "fugitive" reaction temperatures. As indicated above, the oxidation process of this invention is achieved by the use of pure oxygen or almost pure oxygen as the feed gas instead of the feed air and carrying out the oxidation reaction in a system of organic reaction, liquid instead of a conventional reaction system. The reactor technology described in present provides an advantageous and safe means to carry out the liquid phase oxidations with pure oxygen. This technology is referred to as the technology of the liquid oxidation reactor. Shown in Figure 1 is a schematic diagram of the liquid oxidation reactor technology. The liquid oxidation reactor consists of two discrete process zones divided by a gas containment deflector. Below the gas containment deflector there is a well-mixed reaction region where the oxidation of organic liquid occurs. Above the gas containment baffle there is a region of the condenser in which the discharged gases are treated before leaving the reactor. The reaction zone comprises a vertical hull and a tube heat exchanger with upper and lower tail heads mounted at either end of the leaves of the tube. Placed in the center of the bundle of tubes is a cylindrical traction tube containing a helical screw impeller of downward pumping. The oxygen and the organic liquid e.g., the aldehyde are fed to the upper conical head near the suction of the propellant. Oxygen is introduced through two sprinklers mounted on either side of the impeller shaft, the liquid organic through an open pipe in the wall of the container. The impeller dissipates the oxygen feed as a fine dispersion of gas bubbles and pumps down the resulting two-phase mixture through the tube and into the lower head. Three cross-shaped deflectors (quadrants) placed respectively in the suction mouth of the traction tube, under the impeller, and the outlet of the traction tube, ensure the pumping of the efficient axial traction tube minimizing the rotational oscillation. The fluid exiting the traction tube enters the lower conical head where a deflector as projected into the traction tube creates a roll wave where turbulent recirculation occurs before the fluids are returned to the head above the head. through the bunch of tubes. The heat of the reaction is removed by a side coolant of the helmet. The reaction zone is operated with the complete liquid and a level of liquid is maintained in the head of the condenser above the gas containment deflector controlling the rate at which the liquid product is withdrawn from the base of the reaction zone. The crude liquid product is removed in an ungassed form from below a baffle in the form of a bottom coma. Gas-liquid phase separation is achieved withdrawing the product through a narrow outer circumferential drain groove in the conical baffle at a low enough rate to allow the flotation forces to disengage the gas bubbles from the liquid product. The function of the gas containment baffle is to ensure high levels of oxygen consumption in the reaction zone by recirculating the unreacted oxygen released from the back of the upper tube sheet towards the traction tube. The baffle consists of a solid metal plate with a small degassing slot placed near the outer circumference. A small purge of gas has to be discharged from the reaction zone towards the head of the condenser through the degassing slot in order to prevent the accumulation of the inert gases formed as a by-product of the oxidation of aldehyde. The design of the deflector is to achieve an efficiency of oxygen consumption greater than 97.5 percent. This is achieved by limiting the ventilation rate of the gas through the degassing slot to a level that balances as much as possible the rate of production of the gaseous reaction byproducts. The gas containment deflector has a constant bearing comprising a split ring bucket mounted around the driving shaft and held in the gas containment deflector. The function of the constant bearing is to minimize the lateral movement of the driving shaft which can cause the metal to metal impact of the external tip of the impeller blades and the inner wall of the traction tube. A head of the direct contact condenser is placed above the gas deflector. The function of the condenser is to remove condensable organic vapors from the discharge gas and thus ensure that the composition of the discharge gas is below the LFL. To achieve this, the condenser liquid temperature is controlled at about -5 ° C to 25 ° C, depending on the organic vapor pressure of the system by externally circulating the process liquid through the evaporator of a refrigeration unit. To help ensure that the discharge gas is fuel-poor, a small recycle stream of acid is recirculated from the refining process and added to the circulation circuit of the condenser. The object of this stream is to provide a high localized concentration of the low volatility acid above the gas containment baffle. Above the liquid level of the condenser, a continuous purge of nitrogen is added to the vapor space to dilute the unreacted oxygen to a level well below LOV. The redundant oxygen analyzers continuously monitor the vapor space to ensure that the discharge oxygen is at safe levels. The nitrogen purge also serves to sweep the vapor space towards a vent header. A reactor pressure of 3,518 - 10,545 kilograms per square centimeter manometpca is maintained by controlling the ventilation regime of the discharge gas.

In conventional air-based liquid oxidation reactor technologies, the air flow is in a single pass upwardly through the reactor and the discharge gas is maintained at less than LOV by limiting the oxidant feed rate. This can cause undesirable consequences of mass transfer due to oxygen deficiency in the liquid phase, especially in the upper portion of the reactor where the concentration of oxygen is lower. In addition, the discharge gas is typically in thermal equilibrium with the liquid phase at the oxidation temperature, which causes the discharge gas to be above LFL for most volatile organic systems. In the liquid oxidation reactor, the combination of the condenser cooling, the addition of the recycle acid, and the nitrogen purge, ensures that the discharge composition is far enough away from the flammable region while allowing the reaction zone to operate at low partial pressures of oxygen very much in excess of conventional oxidation technologies. This is shown graphically in Figure 4 for the oxidation of valeraldehyde. The details of the upper portion of the oxidation reactor of the liquid that is used for aldehyde oxidation is shown in Figure 2. Ba or normal operating conditions, the composition of the vapor space is maintained less than both LOC and LFL. In addition, no ignition source is present. If mechanical agitation in the reaction zone of the liquid oxidation reactor is lost due to equipment malfunction or loss of energy, the oxygen gas dispersed in the reaction zone will be floated up through the gas baffle and will enter the vapor space of the liquid oxidation reactor. To prevent flammable conditions in the vapor space, the normal nitrogen purge through the vapor space is automatically increased by the reactor shutdown system to a level that will dilute the oxygen content to less than LOC. The arrow of the agitator passes to the liquid oxidation reactor vessel through a mechanical seal shown in Figure 2. The seal is cooled By means of the condensed material and under normal operating conditions there is no danger of ignition to the vapor space. However, it is conceivable that a mechanical failure of the seal can create a scenario where sufficient frictional heat is generated by the seal to present an ignition hazard. The seal can not present a danger of ignition if the oxygen and organic vapors are prevented from coming into contact with the seal in an off-center condition such as the loss of agitation in the reaction zone. One means to achieve this is to place a baffle comprising a flat metal plate immediately below the seal. The baffle is sealed in the wall of the container and contains a circular hole in its center sufficient to accommodate the arrow of the agitator with a small annular clearance of approximately 12.50 millimeters between the face of the arrow and the external tip of the baffle plate. A dedicated nitrogen purge is then introduced above the baffle at a rate of flow that is dimensioned to cause a slight increase in pressure above the baffle relative to the vapor space pressure below the seal baffle. The nitrogen is thus forced to pass in a downward movement away from the seal through the annular clearance space between the arrow and the tip of the deflector without upward mixing of the gas from the vapor space. In this way, a safe inert blanket is achieved around the seal. The vapor space of the liquid oxidation reactor is normally operated under non-flammable conditions. However, multiple equipment failures, such as those that cause the agitator to stop providing gas dispersion to the reaction zone, can cause the vapor space to become flammable. Under these conditions, it is important to ensure that there is no source of ignition of the vapor space. A conceivable ignition source can be generated by mechanical failure of the seal through which the arrow of the agitator passes into the vapor space. This seal failure can deform seal faces and generate sufficient frictional heat to ignite flammable gases that come into contact with the point of failure. The seal deflector ensures that no flammable gases come into contact with the seal. If the ignition of the vapor space occurs, it will result in an explosion of deflagration. This event involves the propagation of a flame front through the vessel at less than the speed of sound and an associated pressure wave that can approach 10 times the initial pressure. If a length of Sufficient functioning and turbulent mixing in the vapor space, a deflagration wave can rise up and become a detonation explosion. A detonation is a much more powerful event than a deflagration and generates a pressure shock wave that moves at a speed greater than the speed of sound. The wall thickness of the liquid oxidation reactor vessel can be designed to contain a maximum pressure resulting from a deflagration without loss of vessel integrity. A detonation is too powerful to contain with any reasonable wall thickness and will possibly result in the loss of container contents and shrapnel. A characteristic minimum cell diameter and a critical path length required for the transition from a deflagration to a detonation has been defined in the literature for a limited number of hydrocarbon systems. These values are sensitive to the specific geometry of the test apparatus and are not transferable to ascending scenarios with good accuracy. It is therefore difficult to obtain a design data defined in the cell size of the limit and a length required for the transition from a deflagration to a detonation in the liquid oxidation reactor. The volume of the vapor space in a liquid oxidation reactor it can be large enough to place the liquid oxidation reactor in a gray area where additional explosion protection must be considered since the potential for a blast in a blast can be considered difficult but unsafe. The seal baffle providing additional safety against ignition of the vapor phase is an important safety feature of liquid oxidation reactors where the volume of steam is large enough that the possibility of a leak occurring is not conclusively ruled out. transition from deflagration to detonation. In the oxidation of organic liquids, it is necessary to prevent a potentially explosive or flammable vapor-gas phase mixture that may develop in the upper gas phase. If the concentration and volume of the organic materials in the vapor space can not be adequately controlled, then the TNT equivalents can exceed the safe operation of the reactor vessel and thus impose a serious safety concern. A process and system of the liquid oxidation reactor as disclosed in U.S. Patent No. 4,900,480 has been found to be advantageous for these organic liquid oxidation applications.

By replacing the air with oxygen, the partial pressure of the oxygen-containing gas bubbles within the oxidation reactor is significantly greater than the oxygen partial pressure inherently limited in the air. Consequently, the driving force for the mass transfer is greater, and the possibility of oxygen starvation conditions that causes the formation of the by-product is less. The liquid oxidation reactor system is a well mixed stirred reactor system, with the oxygen bubbles evenly distributed through the reactive liquid. The approach of the liquid oxidation reactor, in its most common mode, uses a mixer impeller and traction tube placed to disperse and circulate the gas bubbles in the liquid phase. When used to safely react gaseous oxygen with flammable liquids, gas bubbles comprise a mixture of feed oxygen, flammable organic vapor and by-product gases. With gas bubbles dispersed as small bubbles through the liquid phase, the flammability risk associated with oxygen and the organic vapor mixture is mitigated by the thermal capacity of the surrounding liquid, which adsorbs the heat or reaction in the event of the ignition of the bubble, and because the flame of a single bubble can not propagate through the liquid phase. In the liquid oxidation reactor system as disclosed in US Patent Number 4,900,480, a recirculation liquid reaction zone is separated from, but remains in fluid communication with a still zone remaining in contact with the phase of superior gas. A deflector between the zones serves essentially to prevent the gas bubbles from being carried with the liquid in the area of the recirculating liquid to disengage from the liquid due to its flotation, thus ensuring that the bubbles are recirculated with the liquid and consume efficiently through reaction. Any of the gas bubbles that do not escape from the area of the recirculating liquid under the baffle, and which pass upwards through the still zone, are collected in the gas space above the still zone, where make them non-flammable by adding inert gas, eg, nitrogen, to the gas space. Since the liquid oxidation reactor system is a well-mixed stirred tank reaction system, oxygen bubbles are usually evenly distributed through the liquid. In this way, during the operation of the liquid oxidation reactor system in the practice of this invention, there are essentially no zones in the reactor that do not contain oxygen due to poor gas-liquid contact. Depending on the vapor pressure of liquid, which acts as a diluent, the average oxygen concentration in the gas bubble is much higher in a liquid oxidation reactor system than it is in a conventional reactor. In liquid oxidation reactor systems with a very low liquid vapor pressure, the average oxygen concentration can approach 95 percent or higher. This compares favorably with the average 5 percent oxygen concentration in a conventional air-based stirred tank reactor and the average of about 13 percent in an air-based bubble column reactor. For the oxidation of the aldehyde in the production of oxo acid, the higher total mass transfer rate associated with the technology of the oxidation reactor of oxygen-based liquid increases the amount of oxygen available for the reaction in the liquid phase and this way reduces selectivity losses that are associated with oxygen starvation conditions. In addition, for a given aldehyde conversion rate, the highest total mass transfer rate obtained with oxygen allows operation at lower temperatures and pressure than in the conventional air-based reaction systems. Since the concentration of oxygen in the gas phase is much higher in an oxygen-based system, a partial pressure of oxygen equal to a much lower total pressure than with air can be achieved. Also, since both the temperature and the oxygen concentration increase the reaction rate, a certain reaction rate can be maintained by increasing the oxygen concentration and decreasing the reaction temperature. Operation at this lower temperature also reduces the formation of the by-product and increases the selectivity of the product. An important advantage of the liquid oxidation reactor system is that it is a well mixed stirred tank reactor system having separate reaction and gas decoupling zones that are defined by the deflecting means disclosed in US Patent Number 4,900,480. Since the baffle or other means keeps most of the unreacted oxygen from decoupling the liquid before it is reacted, very little inert gas is required to ensure that the gas in the headspace is less than the flammable limit, that with margins of acceptable safety, is typically 5 percent oxygen or less.

As indicated above, it is convenient and generally desirable to use the liquid oxidation reactor system disclosed in U.S. Patent No. 4,900,480, but other embodiments thereof may also be employed in the practice of this invention. . Furthermore, even when purely pure oxygen, e.g., 99 percent pure oxygen, can be employed, such as the oxygen-containing gas used for the oxidation of organic liquids such as aldehydes, lower purity oxygen can also be used for this purpose. Therefore, oxygen containing gas having an oxygen concentration of about 50 volume percent or greater will offer improved selectivity through the use of feed air. The magnitude of the improved selectivity will generally increase in proportion to the concentration of oxygen in the oxygen-containing gas. In particular, oxygen of a purity greater than 90 percent will usually result in almost the same benefit that is obtained using 99 percent pure oxygen. Even though oxygen can be used salefully in bubble column reactors or gas lift bubble column to improve the operation in relation to the supply air in these reaction configurations due to the pressure partial higher oxygen available, a large amount of inert gas is necessary to make the upper space inert in these reactors, rendering the use of these reactors less desirable than the practice of this invention. The benefits of oxygen may also be obtained in other configurations of the stirred tank reactor b in mixing. However, as in the approach to the bubble column, the amount of unreacted oxygen escaping into the reactor head space will be greater than in the stirred tank systems of the non-liquid oxidation reactor. Therefore, the amount of inert gas required to maintain the non-flammable conditions in the headspace is typically much greater than the operations of the liquid oxidation reactor. The processes using these agitated non-liquid oxidation reactor tank systems again are economically unfavorable as compared to the use of a liquid oxidation reactor approach due to the high cost of nitrogen or other inert purge gas and the higher costs. elevated associated with the removal of organic compounds from the purge gas prior to discharge of the purge gas into the atmosphere. The liquid oxidation reactor employs a shell and tube reactor configuration in order to achieve a high heat transfer surface to the ratio of reactor volume together with improved thermal transfer due to forced circulation of the reaction liquid. Also, in the liquid oxidation reactor, means are provided to achieve gas flow through the entire reaction volume, thereby improving reaction productivity and reaction selectivity. The liquid oxidation reactor employed in this invention is particularly beneficial for reaction systems wherein the reactive gas can form a mixture of flammable gas with the vapor above the reactive liquid, such as in the oxygen-based oxidation of the substances organic chemicals In these cases, the oxygen gas is sprayed below the surface of the liquid directly into the suction of the impeller. A mixture of flammable gas is formed at the gas injection point. However, since the gas is dispersed within the liquid, it is not dangerous since the flame can not propagate through the liquid. The dispersion of the gas liquid is pumped down through the traction tube into the bottom mixing chamber and up through the heat exchanger tubes. The gas is then decoupled from the liquid phase and collected in the gas space above the liquid. This configuration takes advantage of the beneficial heat transfer and the fluid flow characteristics offered by the hull and tube design pumped since the reactive gas is circulated through the entire reactor volume. The productivity of the entire reactor volume is maximized, and the potential for starvation conditions of the reagent it can occupy is minimized. In one embodiment, a vertical heat exchanger reactor of hull and tube has a hollow traction tube positioned in the center thereof. The driving means are placed inside the traction tube, preferably in the upper portion, and are adapted to circulate the liquid down through the traction tube to the bottom cracking chamber, and up through the exchange tubes. thermal A liquid feed is passed through a feed line containing a flow control means preferably towards the upper portion of the reactor. Cooling water is passed into the reactor through an inlet and removed through an outlet. The liquid is caused to rise to a level of liquid in the upper portion that is in fluid communication with an upper chamber comprising a gas phase from which the gas is discharged through a gas discharge line that contains a means of flow control. The product is discharged from the bottom mixing chamber through a line containing a flow control means. The liquid level control means is adapted to receive input signals regarding the level of the liquid and to send an output signal to the flow control means in order to maintain the desired liquid level. A drive motor is connected to the driving shaft, adapted to drive the impeller. An upper baffle and a lower baffle are provided to facilitate the recirculation of the desired liquid down into the traction tube and upwardly into said tubes. In one embodiment, back pressure control means are provided to receive an input signal for pressure in the upper chamber and send an output signal to the flow control means in a gas discharge line. In addition, an inert purge line containing a normal flow control means is used, e.g., a valve to introduce a purge gas to the upper chamber or to the reactor above the liquid level. An oxygen analyzer is adapted to receive the input signals for oxygen concentration in the upper chamber and to send output signals to the emergency flow control means to allow additional quantities of the purge gas inert flow through the emergency flow line to the reactor to the upper chamber above the level of the liquid. At flammable ends such as those that exist in this invention, the potential to form flammable gas mixtures in the waste gas stream must be eliminated. For example, in the oxidation of an organic liquid with air, the oxygen content in the waste gas should be reduced to less than the flammable oxygen concentration which is typically between 8 percent and 12 percent. In practice, the oxygen concentration is reduced to less than 5 percent to provide an adequate safety margin. Nitrogen gas or other diluent gas can be added to the waste gas to reduce the oxygen concentration to less than 5 percent. If pure oxygen or near-pure oxygen is used, the oxygen must be reacted or an inert diluent added to the waste gas, but the operation of the mass transfer of the system is improved due to the higher oxygen concentration. The oxygen is used in the reactor system of the invention to improve the selectivity in the oxidation of the organic liquids in the corresponding organic acids. With oxygen, the partial pressure of oxygen in gas bubbles containing oxygen inside of the oxidation reactor is significantly higher than the oxygen partial pressure inherently limited in the air. Consequently, the driving force for mass transfer is greater, and the possibility of conditions of oxygen starvation that causes the formation of the byproduct is less, with oxygen. The oxidation reactor of the liquid useful in this invention is a stirred-mixed tank reactor system, consequently in the oxygen bubbles are evenly distributed through the liquid. In this way, with this reactor there are no zones where the oxygen is inanimate due to deficient contact of the gas with the liquid. Depending on the vapor pressure of the liquid acting as a diluent, the average oxygen concentration in the gas bubbles is much higher than in a conventional air reactor. In systems with a very low liquid vapor pressure, the average oxygen concentration can approach 95 percent or higher. This compares favorably with the average oxygen concentration of 5 percent in a conventional air-based stirred tank reactor and the average of 13 percent in a bubble column reactor. The highest total mass transfer rate results in improved oxygen mass transfer which increases the amount of oxygen available for the reaction in the liquid phase and thus reduces the selectivity losses that are associated with inanimate oxygen conditions. The higher total mass transfer rate that allows operation at a lower temperature also reduces the formation of the byproduct and increases the selectivity. Illustrative liquid oxidation reactors (which are also referred to as organic liquid reactors) and the useful reaction equipment for carrying out the oxidation step of the process of this invention are described, for example, in US Pat. Numbers 5,451,348, 5,371,283, 5,108,662, 5,356,600, 5,200,080, 5,009,816, 4,919,849, 4,965,022, 4,867,918, 4,544,207 and 4,454,077 and the European Patent Publications Numbers EP 0 792 683 A2, EP 0 781 754 Al, EP 0 796 837 Al and EP 0 792 865 Al, the exhibits of which are incorporated herein by reference. The liquid oxidation reactor preferably has a sufficient reactor volume to take advantage of economies of scale advantage, eg, a reactor volume of at least about 1892.50 liters or less, preferably at least about 3.785 liters and greater preference of at least about 7,570 liters or more.

In a preferred embodiment of this invention, the liquid oxidation reactor comprises: a) a vertically placed tube and helmet reactor vessel having a hollow traction tube in the center thereof and heat exchanger tubes in the annular space between the hollow traction tube and the outer wall of the reactor vessel, the reactor vessel having an upper space above a hollow mixing chamber below the hollow traction tube and the heat exchanger tube; b) an impeller positioned within the hollow traction tube and adapted to cause the rapid flow of the organic liquid down through the hollow traction tube into the bottom mixing chamber and rapidly upwards through the heat exchanger tubes as a dispersion essentially uniform and towards the upper space in the reactor vessel; c) a top chamber positioned above and in fluid communication with the reactor vessel, the upper chamber having a vapor space above a desired liquid level; d) at least one generally horizontal gas containment baffle positioned between the upper chamber and the reaction vessel such that the vapor space above the liquid level and the upper chamber is kept below both LOV and LFL, the gas containment baffle being formed with a central hole to allow the impeller to extend generally concentrically through the hole in the gas containment baffle, e) a conduit for introducing the organic liquid into the reactor vessel and for introducing the pure oxygen into the oxygen enriched air containing at least about 50 percent oxygen in the reactor vessel , or the upper chamber for rapid recirculation with the organic liquid down through the hollow drawing tubes to the bottom mixing chamber and rapidly upwards through the heat transfer tubes into the headspace, f) a duct to remove the liquid produced from the reactor vessel, g) a conduit for flowing the cooling fluid towards the reactor vessel for the removal of heat from the exothermic reaction generated within the reactor vessel, and h) a control for maintaining a desired level of liquid within the reactor vessel or within the upper chamber In a particularly preferred embodiment, the liquid oxidation reactor further comprises at least one generally horizontal seal baffle placed within the vapor space of the upper chamber in such a manner, that the vapor space above the seal deflector is maintained below both LOV and LFL, preferably under an inert atmosphere, the seal baffle being formed with a central hole to allow the impeller to extend through General concentrically through the hole in the seal baffle. The configuration of two or more oxidation reactors of the liquid in series, or a liquid oxidation reactor followed in series by a plug flow reactor, allows the efficiency to be improved by increasing the conversion of the untreated organic material as will be described continuation. The liquid oxidation reactor is a close approximation to a gas-liquid reactor retro-mixed perfectly with a continuous stirred tank reactor (CSTR). This means that the concentration of all the components in the reaction zone is driven almost to uniformity by turbulent mixing and rapid loop circulation. As a consequence, the specific organic material, e.g., the aldehyde, the Concentration in the liquid product, the extraction will never be zero regardless of how long reaction time is provided by increasing the volume of the reactor. In this way, even though the CSTR mode ensures that there are no oxygen starvation regions (which would result in a byproduct formation), the operation of a single CSTR prevents the untreated material (aldehyde) from being driven until complete conversion in the manner of a plug flow reactor where untreated materials progressively consume up to extinction through the length of a unidirectional reactor flow path. The level of conversion can be increased in a CSTR by increasing the volume of the reactor, thus increasing the residence time in the reactor. This is not always desirable since as the reactor size increases, the reaction volume (and the associated release of reaction heat) more rapidly increases the available thermal transfer surface area, and the ability to maintain the reactor in a Well mixed mode also becomes increasingly difficult. The commercial processes of CSTR can overcome the disadvantage of the conversion of the untreated partial material by separating the unconverted material from the product and making it recycle to the reactor. This does not It is economical with processes where a by-product by-product is difficult to separate from untreated matter since the by-products would accumulate infinitely in a closed circuit. Oxo C5 acids are an example where a reaction by-product (butyl formates) does not readily separate from the unconverted aldehyde. Under these circumstances it is often desirable to configure several reactors remixed in series, in effect to simulate a multi-stage plug flow reactor, and thus to drive the untreated material to an economical level of conversion. This strategy also allows a good control of the generation of the by-product, limiting the conversion between stages and maintaining the associated temperature rise. The number of stages in a CSTR train is typically determined by changing the cost of capital of the multiple reactors against the level of the conversion of the untreated material achieved. When considering the placement of multiple liquid oxidation reactors in series, another factor that arises from the free radical mechanism of the oxidation processes must be taken into account. These free radical mechanisms involve the steps of initiation, propagation and termination as exemplified above for the oxidation of the aldehyde. When the concentation of the untreated matter is high, the initiation and propagation regime is high in relation to the free radical termination regime. However, when the concentration of the untreated material is low, the termination rate matches more closely with the initiation rate. This can cause a significant decrease in the oxidation regime observed in the last stages of a CSTR train. With the liquid oxidation reactor, an organic liquid level, e.g., of aldehyde, from 90 percent to 92 percent conversion can be achieved during a residence time of about 1 hour in a single stage; this can be increased to a total level of about 96 percent to 98 percent in a similar second stage. Beyond this, the aldehyde reaction regimes are very low and the additional steps are uneconomic unless the remaining aldehyde is concentrated by releasing the produced acid.

Alternatively, the conversion of the untreated material can be improved by sequencing a flow reactor, such as a bubble column, in series after a liquid oxidation reactor. The removal of adequate heat from the bubble columns is difficult to achieve with highly exothermic reactions such as oxidations. Adjusting the service in a column of bubbling so that it only serves with a polishing reactor, this problem can be avoided. The process of this invention is useful for preparing substituted and unsubstituted organic acids in high purity. Illustrative preferred organic acids prepared by the oxidation process of this invention include, for example, formic acid, acetic acid, co-own acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, laupco acid, femothetic acid, benzoic acid, italic acid, isophthalic acid, terephthalic acid, adipic acid, 2-et? lhexane? co acid, isobutyric acid, 2-met? lbut? r? co acid, 2-propylheptane? acid, acid 2- fen? lprop? omco, acid 2- (p-? sobut? lfeml) prop? omco, 2- (6-methox? -2-naphthyl) propionic acid and the like. Illustrative of the appropriate organic acids that can be prepared by the processes of this invention are those permissible organic acids described in the Chemistry Technology Encyclopedia of Kirk-Othmer, Third Edition, 1984, the relevant portions of which are incorporated in the present by reference. Preferred organic acids include carboxylic acids prepared from the oxidation of oxo aldehydes, e.g., valepco acid, 2-ethexanoacetate, 2-propylheptanoic acid and the like. These carboxylic acids oxo aldehyde preparations are referred to herein as "oxo acids". In accordance with this invention, the fluid of the untreated or crude reaction product is refined to provide one or more organic acids in high purity, that is, an organic acid purity of at least about 95 percent, preferably at least about 97 percent, and more preferably, at least about 99 percent or greater. Suitable refining methods include, for example, distillation, solvent extraction, crystallization, vaporization, phase separation, filtration and the like, including combinations thereof. Distillation is the preferred refining method for use in this invention. The refining can also be carried out in a single separation zone or in a plurality of separation zones. This invention is not intended to be limited in any way with respect to the permissible refining methods. The organic acids described herein are useful in a variety of applications, such as intermediates in the manufacture of chemical compounds, pharmaceutical manufacture and the like. For the purposes of this invention, the term "hydrocarbon" is intended to include all compounds permissible ones that have at least one hydrogen and one carbon atom. In a broad aspect, the permissible hydrocarbons include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and non-aromatic organic compounds, which may be substituted or unsubstituted. As used herein, the term "substituted" is intended to include all permissible substituents of the organic compounds unless otherwise indicated. In a broad aspect, the permissible substituents include acyclic and cyclic, branched and unbranched, carbocyclic and heterocyclic, aromatic and non-aromatic substituents of the organic compounds. Illustrative substituents include, for example, alkyl, alkyloxy, apho, aploxy, hydroxy, hydroxyalkyl, ammo, aminoalkyl, halogen, and the like wherein the number of carbon atoms may vary from 1 to about 20 or more, preferably from 1 to about 12. The permissible substituents may be one or more of the same or different for the appropriate organic compounds. This invention is not intended to be limited in any way by the permissible substituents of the organic compounds.

Certain of the following examples are provided to further illustrate this invention.

Example 1 Oxidation of valeraldehyde was carried out with pure oxygen in a liquid oxidation reactor at the rate of 7 gram / liter / hour. The temperature of the reaction zone was operated at a point of 65 ° C. A nitrogen flow of 150 scfm was purged through the vapor space above the liquid level. The cooler is fed to the reactor shell to remove the heat of reaction. The reaction temperature was observed to oscillate approximately + 1.75 ° C around 65 ° C, with each cycle of oscillation occurring over a period of time of about 3 minutes. During the descending temperature phase of the oscillation, the concentration of oxygen in the vapor space was observed to rise to an average value of 0.8 mole percent to about 3.7 mole percent. The reactor was equipped with a 4-percent molar auto-off level to protect the vapor space and approach LOV. If the downward temperature cycle reduces the temperature from 65 ° C to 63 ° C, the oxygen concentration exceeded 4 percent molar and the reactor feeds were terminated.

Example 2 In a manner similar to Example 1, the oxidation of valeraldehyde was carried out, however, the temperature oscillation was restricted to + 1 ° C at a point of 65 ° C. The concentration of oxygen in the vapor space rose from an initial value of 0.8 mole percent to a maximum value of 2.5 mole percent during the falling temperature cycle. The continuous operation of the reactor under the shutdown level of 4 mole percent oxygen was maintained.

Example 3 The oxidation of valeraldehyde in valepco acid was carried out in a liquid oxidation reractor using pure oxygen and the untreated or crude product was refined in a conventional distillation project. The amounts of the decarbonate byproducts, ie, butyraldehyde and butanol in the untreated material were compared in Figure 5 for the oxygen-based liquid oxidation reactor and an air-based reactor.

During the refining of butyraldehyde you may undergo additional reaction to produce butyric acid and butanol which can be esterified with valepco acid to produce butyl valerate. The amounts of butyric acid and butyl valerate remaining in the refined valeric acid after processing in similar refining operations are also shown in Figure 5 for the oxygen-based liquid oxidation reactor product and an air reactor. Even though the invention has been illustrated by certain of the foregoing examples, it should not be construed as being limited by them; rather, the invention encompasses the generic area as disclosed in the foregoing. Various modifications and modalities can be made without deviating from the spirit and scope of it.

Claims (9)

CLAIMS:

1. A process for producing one or more high purity organic acids whose process comprises (i) oxidizing in a liquid oxidation reactor one or more organic liquids with essentially pure oxygen or air enriched with oxygen containing at least about 50 percent of oxygen, at a temperature stable enough to prevent cycling of the reaction regime, the temperature being controlled to within + 3 ° C of a limit temperature and the temperature limit being selected from an individual temperature within the range of approximately - 25 ° C or lower to about 125 ° C, in order to produce a raw or untreated reaction product fluid, and (n) to refine the fluid from the untreated or crude reaction product to provide one or more organic acids in high purity

2. A process for producing one or more high purity oxo acids whose process comprises (i) oxidizing in a liquid oxidation reactor one or more oxo aldehydes with essentially pure oxygen or air enriched with oxygen containing at least about 50 percent oxygen, where the mass transfer between one or more of the oxo aldehydes and the essentially pure oxygen or the air enriched with oxygen containing at least about 50 percent oxygen, is sufficient to minimize or eliminate the formation of the by-product, to produce a fluid of the untreated or crude reaction product, and (n) to refine the fluid of the product of raw or untreated reaction to provide one or more oxo acids in high purity.

3. A process for producing one or more high purity organic acids whose process comprises (i) oxidizing in a liquid oxidation reactor one or more organic liquids with essentially pure oxygen or oxygen enriched air containing at least about 50 percent oxygen to produce a raw or untreated reaction product fluid and (n) retinue the fluid of the crude or untreated reaction product to provide one or more organic acids in high purity; wherein the liquid oxidation reactor comprises: a) a vertically placed tube and helmet reactor vessel having a hollow traction tube in the center thereof and heat exchanger tubes in the annular space between the hollow traction tube and the external wall of the reactor vessel, the reactor vessel has an upper space above and a chamber hollow mixer below the hollow traction tube and the heat exchanger tube; b) an impeller positioned within the hollow traction tube and adapted to cause rapid flow of the organic liquid down through the hollow traction tube into the bottom mixing chamber and rapidly up through the heat transfer tubes as a dispersion essentially uniform and towards the upper space in the reactor vessel; c) a top chamber positioned above and in fluid communication with the reactor vessel, the upper chamber having a vapor space above a desired liquid level; d) at least one generally horizontal gas containment baffle placed between the upper chamber and the reaction vessel such that the vapor space above the liquid level in the upper chamber is maintained below both LOV and of LFL, the gas containment baffle being formed with a central hole to allow the impeller to extend generally concentrically through the hole in the gas containment baffle; e) at least one generally horizontal seal baffle placed within the space of steam in the upper chamber such that the vapor space above the seal baffle is maintained under an inert atmosphere, the seal baffle being formed with a central hole to allow the impeller to pass at least concentrically through the hole in the seal baffle; f) a conduit for introducing the organic liquid into the reactor vessel and for introducing pure oxygen or oxygen enriched air containing at least about 50 percent oxygen to the reactor vessel or the upper chamber for rapid recirculation with the organic liquid down through the hollow traction tubes into the phono mixing chamber and rapidly up through the heat exchanger tubes into the upper space; g) a conduit for removing the liquid produced from the reactor vessel; h) a conduit for flowing the cooling fluid to the reactor vessel for the removal of the exothermic heat of the reaction generated within the reactor vessel; and i) a control for maintaining a desired level of the liquid within the reactor vessel or within the upper chamber.

4. A process for producing one or more high purity organic acids whose process comprises (i) oxidizing in a primary liquid oxidation reactor one or more organic liquids with essentially pure oxygen or air enriched with oxygen containing at least about 50 percent of oxygen to produce a first fluid of the untreated or crude reaction product, (n) removing the first fluid from the raw or untreated reaction product of the primary liquid oxidation reactor, (m) feeding the first fluid of the reaction product raw or untreated to at least one secondary liquid oxidation reactor or a flow reactor, (iv) oxidizing in the secondary liquid oxidation reactor or flow reactor the first fluid of the untreated reaction product or crude with oxygen essentially pure or air enriched with oxygen containing at least about 50 percent oxygen to produce a second fluid of the reaction product. untreated or crude ion, and (v) refining the second raw or untreated reaction fluid to provide one or more organic acids in high purity.

The process of claim 4 wherein two or more liquid oxidation reactors are serially configured or a liquid oxidation reactor and a flow reactor are configured in series.

6. The process of claim 1, wherein the oxidation has an activation energy of more than about 15 kilocalopes per mole and an exothermic heat of reaction greater than about 100,000 BTU / pound-mole.

The process of claims 1, 3 or 4, wherein the organic liquid comprises one or more aldehydes, alcohols, alkylbenzenes or cyclic aliphatic hydrocarbons.

The process of claims 1, 3 or 4, wherein the organic acid comprises one or more of formic acid, acetic acid, propiomuco acid, butyric acid, valepco acid, caproic acid, caprylic acid, capric acid, lauric acid, Femlacetic Acid, Benzoic Acid, Italic Acid, Isophthalic Acid, Terephthalic Acid, Adipic Acid, Acid 2-Et? lhexane? co, Isobutyric Acid, Acid 2-Met? lbut? pco, Acid 2-Propylheptane? Acid 2 -femlprop? omco, acid 2- (p-isobutyl) propiomco and 2- (6-methox? -2-naphthyl) propiomco acid.

9. The process of claim 1, wherein the organic liquid comprises an oxo aldehyde and the organic acid comprises an oxo acid.