JPH0222057B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an oxidation process, in particular by the oxidation of p-toluic acid or a mixture of p-toluic acid and partially oxidized derivatives of p-xylene, such as p-xylene and/or p-tolualdehyde. The present invention relates to a method for producing terephthalic acid. Terephthalic acid is a substance of great industrial importance, increasingly used as a starting material for the production of polymeric resins such as polyesters from which fibers and films are formed. The known literature teaches many methods for obtaining aromatic carboxylic acids by liquid phase oxidation of aromatic compounds substituted with alkyl groups. One of the early patents in this field is U.S. Patent No. 2,245,528, which describes the production of alkyl aromatic compounds by molecular oxygen in the presence of a metal catalyst, a solvent such as acetic acid, and optionally an oxidation initiator. A one-step process for oxidizing compounds is described. However, even under such harsh conditions, the yield of dicarboxylic acids is low. For example, in acetic acid containing cobalt acetate and magnesium acetate as catalysts at 185 to 200°C.
When a mixture of xylenes is oxidized with air in the presence of diethyl ketone as an initiator at a temperature of
The main reaction products were toluic acid and other intermediate oxidation products. A number of other patents describe processes for the oxidation of p-xylene in one step to obtain terephthalic acid with improved yields. These patents primarily concern the use of special activators, such as bromine-containing compounds (US Pat. No. 2,833,816), ketones (US Pat. No. 2,853,514), or aldehydes (US Pat. No. 3,036,122). Although some of these methods are used industrially, they have significant drawbacks. For example, serious corrosion problems occur when bromine-containing activators are used. When a ketone or an aldehyde is used, a part of it is inevitably lost and the remainder is mainly transferred to acetic acid.
Acetic acid must be recovered, purified, and made into an economically viable product. However, despite these drawbacks, the use of activators is believed to be a fundamental necessity for the effective production of phthalic acid from xylene. In many cases, the use of solvents is also claimed to be necessary. Low molecular weight fatty acids, especially acetic acid, are widely used for this purpose. The amount of solvent added is such that the reactants and reaction products are in solution;
or at least in sufficient quantity to readily maintain it in suspension. In this way, the reaction mixture is easily stirred, oxygen dispersion is improved, by-product formation is minimized, and the heat of reaction is easily removed by evaporation of the solvent. However, under commonly employed reaction conditions, substantial amounts of solvent are lost through co-oxidation.
Furthermore, the solvent is separated from other components of the reaction mixture,
It must then be purified and recycled.
Obviously, such partial solvent consumption and residual solvent recovery operations result in additional operating costs. In order to avoid the serious problems mentioned above, it has been proposed to carry out the oxidation of p-xylene without the presence of a solvent. In this case, in order to obtain a liquid reaction mixture, it is necessary to carry out the reaction at a temperature clearly above the melting point range of p-toluic acid, ie at about 180.degree.
The choice of temperature is therefore limited. Furthermore, in the absence of a solvent, handling of the reaction mixture as well as separation and purification of terephthalic acid are difficult. Generally, the reaction is carried out to the point where the content of terephthalic acid in the mixture is no more than 60% by weight, preferably no more than 45% by weight. Beyond this point, it is difficult to handle the oxidation reaction mixture as a slurry and reaction operation is therefore adversely affected. This is explained in US Patent No.
No. 3883584. In the absence of solvent, the removal of the heat of reaction poses other difficulties in industrial scale production, since extensive fouling within the reactor occurs even when terephthalic acid is not present in large quantities. Thus, in U.S. Pat. No. 2,696,499 for the oxidation of toluic acid to xylene without the presence of a solvent,
It is shown that fundamental design issues inherent in the cooling of xylene oxide mixtures prevent precipitation of solids. US Pat. No. 3,406,196 shows a two-step process in which water is used as a suspending agent for terephthalic acid. In the first stage of this process, the alkylaromatic compounds, especially p-xylene, are oxidized by air without the presence of any additional solvent, and the partially oxidized compounds thereby formed are transferred to the second stage. Further oxidation is carried out at elevated temperatures in the presence of substantial amounts of water as suspending medium. To promote oxidation,
Bromine or a bromine-containing compound must be present. However, very high temperatures of 200 to 275°C, especially 225 to 250°C, are required to convert the partially oxidized compound to terephthalic acid. Corrosion problems that are similar or worse than in processes where acetic acid is used as the solvent therefore necessarily arise. Furthermore, as noted in the patent, significant loss of unreacted polyalkyl aromatic compounds due to degradation and other side reactions may result in such compounds being partially oxidized by the oxidation products produced in the first oxidation step. It tends to occur when products are exposed to the high temperatures necessary for efficient conversion to aromatic polycarboxylic acids. Apparently, the explanation in this patent is that the use of large amounts of water even in the presence of a bromine promoter does not give satisfactory results for the oxidation of p-xylin to terephthalic acid in one step. . In fact, it has long been known that water is a catalyst poison in oxidation reactions. This is shown in US Pat. No. 2,696,499. According to the most common opinion, water negatively affects the reaction rate by interfering with the initiation of the reaction. Usually, the presence of water is avoided as much as possible, whether or not solvents and/or activators are present. Thus, US Pat. No. 3,064,044 shows an improved means for maintaining the final (bromine-promoted) oxidation under nearly anhydrous conditions. U.S. Patent No. 1 on an oxidation process in which peracetic acid is used as an accelerator.
No. 3,519,684 states that water contents up to about 10% are acceptable, a minimum water content of less than 5% is preferred, but it is more preferred that nearly anhydrous conditions be employed. In a continuous process for the oxidation of xylene without the presence of any promoter, in which the partially oxidized intermediate is continuously removed, the water content in the reaction mixture is reduced to 15% of the total reaction mixture. Water is removed from the liquid effluent before recycling of the intermediate to achieve less than 5%, preferably less than 5%. This is shown in US Pat. No. 3,700,731. More recently, the oxidation of p-xylene to terephthalic acid has been unexpectedly performed without the presence of a bromine activator, which was previously considered to be fundamentally necessary. It was found that the method can be carried out in the presence of This process is described in US Patent Application Nos. 764,981 and 785,827. The process comprises p-toluic acid, water, and a heavy metal salt as a catalyst in the presence of an oxygen-containing This method includes a step of oxidizing p-xylene in the liquid phase using gas. However, since the mutual solubility of p-xylene and water is low at the operating temperature, such a mixture of water, p-xylene and p-toluic acid is difficult to maintain between the aqueous phase and the hydrocarbon-rich p-toluic acid present in the reaction mixture. - can be separated into two phases with an organic phase that also contains a significant portion of toluic acid. In this case, the oxidation reaction is
It occurs primarily in the organic phase where the concentration of water is relatively low. Therefore, the desired solvent effect of water is partially lost. Furthermore, this phase separation creates significant technical difficulties with respect to homogenization, oxygen dispersion and mass transfer effects. The object of the present invention is to obtain terephthalic acid with high yield and high purity, avoiding the above-mentioned drawbacks of the known technology.
An object of the present invention is to provide a method for oxidizing p-xylene to terephthalic acid. Another object of the invention is to provide a method that does not require highly corrosion-resistant equipment and can be carried out in conventional stainless steel equipment. Another object of the invention is to provide a process which can be carried out in the presence of substantial amounts of water without the need for any additional solvent. Another object of the invention is to provide a method by which terephthalic acid is produced by oxidizing a reaction mixture consisting essentially of a terephthalic acid precursor to be oxidized, water and an oxidation catalyst dissolved in water. It is about providing. Another object of the invention is to provide a process that does not require the use of promoters such as bromine compounds in addition to oxidation catalysts. Another object of the invention is to provide a process in which terephthalic acid can be easily recovered from an oxidized reaction mixture at relatively moderate temperatures. Another object of the invention is to provide a method in which the catalyst and oxidation intermediates can be recovered and reused for oxidation. Another object of the invention is to provide a method by which terephthalic acid can be produced in an industrial process at relatively low cost. Another object of the invention is to provide a process which can be carried out batchwise or continuously. Another object of the present invention is to provide a method by which the amounts of catalyst, water and p-toluic acid required to ensure efficient oxidation of the starting materials can be easily calculated. To achieve the above objectives according to the present invention,
A method for producing terephthalic acid is provided which includes the following steps. (a) at least one oxidizable terephthalic acid precursor selected from the group consisting of p-toluic acid and mixtures of p-toluic acid and oxidizable compounds; A substantially homogeneous reaction mixture consisting of 5 wt. Depending on the gas, about 140℃ to about 220℃
oxidizing at a reaction temperature under sufficient pressure to maintain at least a portion of the water in the liquid phase at this reaction temperature. Note that the oxidizable compound is p-xylene,
partially oxidized p-xylene derivatives and mixtures thereof; said oxidation catalyst is selected from manganese compounds, cobalt compounds and mixtures thereof; and said oxidation catalyst is selected from manganese compounds, cobalt compounds and mixtures thereof; The minimum amount M is defined by the following formula. M=Y(X+A)+BX/CX+D where Y is the molar ratio of water to p-toluic acid in the reaction mixture, and X is the molar ratio of manganese to the total amount of manganese+cobalt in the catalyst composition; A is about 0.200, B is about 10.9, C is about 4.35,
D is approximately 0.0724. (b) recovering the oxidized mixture containing terephthalic acid; By maintaining the catalyst concentration above the defined minimum value, effective oxidation of the starting material mixture to terephthalic acid in a homogeneous liquid phase reaction mixture is achieved. An important feature of the present invention is that the deleterious effects of water, which are widely recognized in the prior art, can be eliminated when the oxidation is carried out under the specific conditions mentioned above. Another feature of the invention is that it can be applied to the oxidation of various substrates consisting of p-toluic acid alone or in mixtures with p-xylene and/or partially oxidized p-tolualdehyde.
Yet another feature of the invention is that such substrates can be oxidized in a homogeneous aqueous solution when the amount of catalyst is selected in relation to the ratio of water to p-toluic acid present in the system. It is. The process of the invention can be carried out batchwise or continuously. The reactants are dissolved in water and then the catalyst is added to the resulting solution. Oxygen is then introduced into this mixture and under pressure
Oxidation is carried out at a temperature of 220°C. The pressure is adjusted to maintain the reaction mixture in substantially liquid form at the operating temperature. Terephthalic acid is separated from the reaction mixture as a white crystalline precipitate. In a continuous process, this precipitate is continuously removed by conventional solid-liquid separation means such as filtration, centrifugation, or settling and settling, and unconverted reactants and intermediate oxidation products are recycled to the oxidation zone. Ru. New reactants are continuously added to compensate for the terephthalic acid and by-product formation thus removed. Thus, the addition of chemicals unrelated to the production of terephthalic acid is unnecessary. However, in carrying out the process of the invention, one or more organic solvents that are relatively inert under the operating conditions can be added to the reaction mixture without interfering with the reaction. Examples of such compounds which can be used as solvents in mixture with water are benzoic acid and acetic acid. These compounds are actually produced in small amounts during the reaction and therefore accumulate to some extent in the reaction mixture. However, the advantages of the invention are obtained independently of the presence of such compounds. However, such compounds should not be present in an amount that exceeds the amount of water in the system. The amount of water suitably used in the method of the invention is:
Depending on various factors, it may vary over a wide range, for example from about 5 to about 80% by weight of the reaction mixture. As already mentioned, the basic contents of the present invention are:
The oxidation is carried out in a homogeneous aqueous system. Therefore, the amount of water is selected primarily to be sufficient to provide approximately uniform water solubility of the reactants, taking into account other process variables such as temperature and relative amounts of the various compounds to be oxidized. will be done.
For example, when the process is applied in the form of toluic acid alone or in a mixture with other relatively water-soluble oxygenated compounds such as p-tolualdehyde,
The amount of water will be selected to be sufficient to completely dissolve the p-toluic acid at the operating temperature. p to water
-The amount of water used can be decreased as the temperature increases, since the solubility of toluic acid increases rapidly at elevated temperatures. However, generally speaking the amount of water will not be less than 5% and preferably more than 10% of the weight of the reaction mixture. If p-xylene is also a component of the reaction mixture, it should not be in such an amount that separation of the mixture into two phases occurs. This amount obviously depends on the amount of p-xylene in the mixture. Figure 1 is 185
Figure 3 is a three-phase diagram (% by weight) of a mixture of p-xylene, p-toluic acid and water at °C. In this diagram, in zone A the system is a homogeneous solution and in zone B a two-phase system. As one skilled in the art can readily determine, the borders between these zones do not vary significantly with temperature. It can be seen that the amount of p-xylene must be limited to avoid the presence of a substantial organic phase. Therefore, when the oxidation of p-xylene according to the process of the invention is carried out in batches, p-xylene enters the reaction mixture progressively, intermittently or continuously at a rate such as to maintain the system in zone A. should be added. According to a preferred embodiment of the invention, the reaction is carried out in a continuous manner, whereby the unreacted p-xylene together with the intermediate oxidation products, ie mainly p-toluic acid, is continuously recycled into the reaction zone. In this case, the molar ratio of p-toluic acid to p-xylene in the reaction mixture at steady state will be from about 3 to about 15, depending primarily on temperature. In other words, the reaction mixture will be in the gray area of the diagram of FIG. This region lies mostly in zone A, ie corresponds to a largely homogeneous solution. From the above description it can be seen that the temperature and/or the amount of water used as solvent according to the invention can always be adjusted so as to obtain a homogeneous system. If the process of the present invention is carried out in continuous mode, US Pat.
It is preferable to employ the continuous process described in But other factors must also be taken into account. That is, since the desired product, terephthalic acid, is nearly insoluble in the reaction mixture, sufficient water must be added to obtain a workable slurry. However, there is no advantage to using large quantities of water such that, for example, more than 10% of the terephthalic acid dissolves at operating temperatures. A further factor that must be taken into account is the rate of reaction. That is, although it is possible within the scope of the present invention to carry out the oxidation reaction in a medium containing 80% by weight or more of water, the presence of excess water will adversely affect the reaction rate. Furthermore,
In some cases, a portion of the solvent may convert its catalytic function by forming a black compound that precipitates from the oxidizing medium. Furthermore, for economic reasons, it is disadvantageous to lose part of the reactor capacity by using excess and unnecessary amounts of water. Generally, for these various reasons, the amount of water present in the system will be less than 75%, and preferably less than 60%, by weight of the amount of reaction mixture. Suitably, the oxidation reaction is carried out at a temperature of 140°C or higher. Below this temperature, it is difficult to maintain a uniform temperature of the reaction mixture. On the other hand, operating temperatures above 220°C will result in increased peroxidation, undesirable side reactions and corrosion problems. In many cases,
The reaction temperature will be about 150°C to about 190°C. Pressure is adjusted as a function of temperature. Sufficiently high pressures above normal pressure must be employed to maintain the reaction mixture in liquid form at the operating temperature. Generally the pressure will be about 5 to about 40 kg/cm ² . The oxidation catalyst used in the process of the invention is characterized in that it is at least partially soluble in the reaction mixture;
or one or more metals selected from the group consisting of manganese compounds, cobalt compounds and compounds thereof, provided that they are soluble or can form at least partially soluble compounds with one of the reactants in this mixture. It can be a heavy metal compound composition consisting of a compound. Suitable metal compounds that can be used in the catalyst composition are salts. Particularly preferred are salts of carboxylic acids, such as acetates, naphthenates, toluates, and the like. Catalyst compositions other than cobalt and/or manganese compounds include, in particular, carboxylates of other metals commonly used as oxidation catalysts. A basic feature of the invention is that the minimum amount of catalyst required to carry out the oxidation in a homogeneous aqueous system depends on the respective amounts of water and p-toluic acid in said system. In fact, in a homogeneous aqueous solution of p-toluic acid and any p-xylene and/or partially oxidized derivative thereof, the amount of active catalyst is given by the following formula:
Below the critical concentration M, millimoles of metal compound per kg of reaction mixture, no oxidation can occur. M=Y(X+A)+BX/CX+D (1) where Y is the molar ratio of water to p-toluic acid, and X is the number of moles of metal catalyst relative to the total amount of manganese and cobalt in the metal catalyst. The amount of manganese is Mn/Mn+Co. A=approximately 0.200 B=approximately 10.9 C=approximately 4.35 D=approximately 0.0724 The above quantities A, B, C and D were determined experimentally and are therefore subject to measurement errors. According to calculations, the quantities with error ranges are each A=0.200±
0.031, B=10.9±1.3, C=4.35±0.17 and D=
It was 0.0724±0.0117. Therefore, given Y
The value of M calculated by equation (1) for the value of As one of ordinary skill in the art would understand,
This error range depends on the values of Y and X used in the calculation of M, but in special cases it can be calculated from the above data by applying Taylor's equation. Thus, for example, the critical concentration of a catalyst will be within the following error range: That is, 2.74 when Y=70 and X=0.5
±0.45. The critical concentration of a catalyst, as defined above, is the lowest concentration that can be used under given conditions. At lower concentrations the process will not work. It is clearly preferred in practice to use catalyst amounts higher than this minimum value. In fact, the oxidation rate increases as the catalyst concentration increases. However, catalyst concentrations higher than about 40 mmol of metal compound per kg of reaction mixture are economically disadvantageous.
A suitable amount of catalyst will be between a value slightly higher than the minimum value M calculated from equation (1) and about 30 mmol per kg of reaction mixture. As can be seen from equation (1), the concentration of water increases and p
-If the concentration of toluic acid decreases, the critical concentration of the catalyst increases. In other words, oxidation cannot occur in such aqueous solutions unless the concentration of p-toluic acid is above a critical value that increases as the catalyst concentration decreases. Thus, not only the catalyst but also p-toluic acid is the fundamental substance in producing oxidation in the presence of substantial amounts of water. In fact, the combined action of the catalyst and p-toluic acid used in suitable amounts according to the present invention allows the oxidation of p-xylene without resorting to the use of expensive and/or corrosive activators such as bromine compounds. It is possible to convert it into terephthalic acid. This effect of p-toluic acid is a completely unexpected feature since other carboxylic acids, even those of similar structure, such as benzoic acid, do not exhibit the same properties. Furthermore, the minimum concentration of catalyst required to carry out the oxidation in a homogeneous aqueous system also depends on the relative proportions of manganese and cobalt compounds in the catalyst employed. It turns out that manganese is more effective than cobalt. For example, a 50% by weight aqueous solution of p-toluic acid (molar ratio of water to p-toluic acid is 7.56)
The minimum amount of catalyst required to cause oxidation within is 4.5 or 20.9 mmol/Kg depending on whether manganese is used as the sole catalyst. However, for practical reasons, it is advantageous to employ a mixture of both metals, since cobalt generally has a beneficial effect on the reaction rate. Furthermore,
When a mixture of manganese and cobalt compounds is employed as a catalyst, less peroxidation occurs;
It has been found that generally higher yields of terephthalic acid are obtained than when each metal is used alone. For example, the combustion ratio (molar ratio of carbon dioxide evolved to absorbed oxygen) is generally between 0.06 and 0.09 in the first case, while in the second case it is approximately
It is 0.15. Indeed, the beneficial effects of using manganese and cobalt together as catalysts are a typical feature and a further advantage of the present invention. The reaction is then carried out in a two-phase system instead of a homogeneous solution as in the present process, and combustion ratios of 0.12 or even higher are regularly found, regardless of whether manganese or cobalt or mixtures thereof are used. . In most cases, values of X in formula (1) from about 0.1 to about 0.9 will be used with the advantage of providing active oxidation in a homogeneous aqueous medium and obtaining high yields of terephthalic acid. . For the same reasons mentioned above, it may be advantageous to use catalysts which, in addition to cobalt and/or manganese, also contain metal components such as nickel, lead or cerium. Such other metals undergo oxidation in a homogeneous aqueous medium, but provide practical improvements in, for example, purity and reaction rate. A surprising feature of the present invention is that the minimum concentration of catalyst employed to carry out the oxidation in an aqueous medium is
It can be calculated from equation (1) for reaction mixtures of any composition, and this equation is independent of important operating variables such as temperature. This is expressed by the results shown in Table 1, where the values of M experimentally obtained under a wide range of conditions are expressed by the formula
It is compared with the value calculated from (1). Most of these results were obtained using the following experimental methods. In a 1 liter corrosion-resistant autoclave equipped with a mechanical stirring device, a heating jacket, a gas inlet tube, a vent and a metering pump for injecting the liquid, the various components to be present in the oxidation reaction mixture, namely p-toluic acid , water and catalyst are introduced. The mixture is then heated while stirring and passing air through it. Once the oxidation has started, an aqueous solution of catalyst having the same catalyst concentration as the initial reaction mixture is progressively injected into the mixture. As a result, the reaction mixture is progressively diluted with water without any change in catalyst concentration. The degree of oxidation is observed by continuously measuring the oxygen content of the exhaust gas with an oxygen analyzer. As long as the concentration of p-toluic acid in the system is high enough to effect effective oxidation at the selected catalyst concentration, the reaction proceeds regularly at a rate that progressively decreases as a result of dilution.
However, once the critical concentration of p-toluic acid is reached, the reaction rate drops rapidly to almost zero. The injection is then stopped and the reaction mixture is analyzed. The molar ratio of water and p-toluic acid determined in this way is clearly a critical value Y corresponding to a given catalyst concentration M, or, conversely, M is equal to water and p-toluic acid.
- is the minimum concentration of catalyst used to carry out the oxidation in the reaction mixture given the ratio Y to toluic acid. In practice, M depends on the composition of the catalyst, expressed as the molar ratio of manganese (X in Equation 1) to the total amount of manganese and cobalt in the catalyst composition used. Obviously, the determination of such numbers is subject to experimental error for a given reaction mixture (given Y and X). Therefore, it is expected that various values M _i will be obtained that are conveniently distributed around the actual value with standard deviation. various
The values of M _i thus determined for Y _i and X _i are shown in the table below. From these data, it can be estimated that the standard deviation of M _i from the value M calculated by equation (1) is 0.70. Therefore, any experimental value M _i does not differ from the calculated one by a standard deviation of 2 or more, that is, 1.4 or more, and can be considered to be consistent with equation (1). From the results given in Table 1, it is clear that: 1 Equation (1) is valid for any value of Y and X (for example, compare Experiments Nos. 1 and 7 for Y and Experiments Nos. 7 and 19 for X). 2 Equation (1) is independent of the presence or absence of p-xylene (for example, compare Experiments No. 8 and 13). 3 Equation (1) is independent of temperature (compare, for example, Experiments No. 3 and 9). 4 Equation (1) is independent of the presence of metals other than manganese and cobalt (compare, for example, Experiments No. 2 and 5).

TABLE The teaching of the prior art regarding the selection of metal compounds used to oxidize p-xylene and its partially oxidized derivatives to obtain terephthalic acid is quite confusing. However, the prior art generally holds that cobalt is the best catalyst, especially in the absence of a bromine activator, and that manganese is less active, if not inert. Manganese is inactive for the oxidation of p-toluic acid. (N.Ohta et al., Chem Abstr. 56 , 8620g
1962) or has oxidative inhibitory properties (VN
Aleksandrovet al., Kinet. Katal. 15 , 505,
1974). In other matters, although manganese exhibits catalytic activity, decolorization of terephthalic acid occurs when the amount of water is higher than 10% of the solvent weight or when the amount of manganese in the reaction mixture is high. Therefore, in the method of the present invention, manganese has a significant activity for causing an oxidation reaction in the presence of a large amount of water, and is further purified to the purity (fiber grade) required for the production of polyester fibers. It was completely unexpected that terephthalic acid could be obtained in high purity as a white crystalline precipitate, which is particularly suitable for the preparation of terephthalic acid. Examples of the present invention are shown below, but these are merely illustrative of the present invention and do not limit the scope of the present invention in any way. Example 1 The following materials were introduced into a 1 liter capacity corrosion-resistant autoclave equipped with a mechanical stirrer, a heating jacket, a gas injection tube and a vent. p-xylene 45.0g p-toluic acid 187.5g Various oxidized derivatives of p-xylene
4.5 g Water 63.0 g Manganese acetate 1.50 mmol Cobalt acetate 1.74 mmol The reactor was pressurized with air to 20 Kg/cm ² and the mixture was stirred and heated while flowing air at a flow rate of 92 liters/hour. In the above introduced material, the molar ratio (Y) of water and p-toluic acid is 63.0×136.15/18.02×187.5=2.54
and the molar ratio Mn/Mn+Co(X) in the catalyst
It was 1.50/1.50+1.74=0.46. By applying equation (1), the minimum concentration of catalyst required to carry out the oxidation in this case was calculated as follows: M=2.54(0.46+0.200)+10.9(0.46)/4.35(0.46
)+0.0724=3.2 mmol/Kg In fact, in this example the concentration of catalyst was 10.0 mmol/Kg, or about three times the minimum amount. In fact, upon heating the reaction started spontaneously and was vigorous, resulting in a rapid temperature increase and was maintained at 170° C. by controlled cooling. After a reaction period of 180 minutes, the oxygen absorption amounted to 40.9 liters (measured under air temperature and normal pressure). The introduction of air was then stopped and the reactor was shut down in order to recover unreacted p-xylene acid by stripping with water. Finally the reactor was cooled and opened. The precipitate contained therein was filtered, washed with water and dried under vacuum at about 80°C. Then acid titration, polarography,
The precipitate was analyzed by a combination of methods consisting of: and gas chromatography. As a result, 89.4
It was determined that % p-xylene and 23.1% p-toluic acid were converted to the following products. Terephthalic acid 90.2 g 4-Carboxybenzaldehyde 8.8 g Other intermediates 3.8 g Heavy by-products 2.2 g 4-Carboxybenzaldehyde and other intermediate products are recycled in a virtually continuous process, with the majority ultimately Taking into account the conversion to terephthalic acid, the yield of terephthalic acid in such a continuous process is:
Based on the amount of p-xylene consumed, it can be estimated that the amount is over 90 mole percent. In another operation carried out under the same conditions, the hot reaction mixture was subjected to filtration and the resulting cake was further washed on a filter with hot water and dried in vacuo. The analysis values of the dried product are as follows. Terephthalic acid 85.6% by weight p-Toluic acid 9.6 4-Carboxybenzaldehyde 3.6 The color of this sample was obtained by the method described in U.S. Pat. No. 3,354,802, except that a 5 cm cell was used instead of a 4 cm cell. It was therefore determined by measuring the optical density of its solution in dilute ammonia. The optical density values thus obtained are given in the table below and were compared with the optical density values obtained for commercial samples of terephthalic acid of greater than 99% purity.

It can be seen that the crude sample obtained in this way by simple filtration and surface cleaning has better color properties than the commercial sample of better purity terephthalic acid. Example 2 An experiment similar to Example 1 was repeated, except that 63.0 g of water was replaced with the following mixture as solvent. Water 33.0g Acetic acid 30.0g After 180 minutes of reaction, oxygen absorption was 39.7 liters, i.e.
The amount was approximately the same as that in Example 1. The reaction mixture was then processed and analyzed as in Example 1.
As a result, 88.0% p-xylene and 23.5% p-
It was determined that toluic acid was converted to the next product. Terephthalic acid 89.4g 4-carboxybenzaldehyde 6.5g Other intermediates 4.8g Heavy by-products 3.2g By the same method as in Example 1, the yield of terephthalic acid was consumed in a continuous process under the same conditions p- It was estimated that the amount was about 90 mol% of the amount of xylene. Thus, these results are practically equivalent to those of Example 1, where water was used as the single component solvent. Example 3 The experiment of Example 2 was repeated except that formic acid was used instead of acetic acid. Therefore, the solvent used in this case was a mixture of 33.0 g water and 30.0 g phosphoric acid. After 180 minutes of reaction, the absorbed oxygen was 36.7 liters. By the same analytical procedure as in Example 1,
It was determined that 88.0% p-xylene and 15.6% p-toluic acid were converted to the following products. Terephthalic acid 66.7g 4-carboxybenzaldehyde 6.8g Other intermediates 7.0g Heavy by-products 3.7g By the same method as in Example 1, the yield of terephthalic acid was consumed in a continuous process under the same conditions p- It was estimated that the amount was about 85 mol% of the amount of xylene. Although these results are not as good as those of Examples 1 and 2, they show that large amounts of formic acid can be tolerated in the reaction mixture without significant negative effects on yield and reaction rate. . This is completely unexpected from the known literature, which always describes formic acid as a potent inhibitor of oxidation reactions. Since formic acid is always produced in such reactions, elaborate and expensive procedures generally have to be considered in order to avoid its significant accumulation in the reaction mixture. In the process of the invention, formic acid is combusted, as evidenced by the fact that the carbon dioxide produced in this experiment was 6.0 liters instead of the 3.8 liters measured in the experiment of Example 1. Therefore, the method of the present invention does not require any special operation to remove formic acid from the reaction mixture. Example 4 The experiment of Example 1 was repeated, except that cobalt was used as the sole catalyst. The actual substances introduced were as follows. p-xylene 45.0 g p-toluic acid 190.1 g various oxidized derivatives 1.9 g water 63.0 g cobalt acetate 3.48 mmol In this introduced material, Y is 2.50 and X is obviously 0. Therefore, in this case the critical amount of cobalt to carry out the oxidation is M=2.50
(0.200)/0.0724=6.9 mmol/Kg. The concentration of cobalt acetate in the initial mixture was 11.6 mmol/Kg, about twice the limit amount.
After 180 minutes of reaction, the absorbed oxygen was 41.5 liters. The reaction mixture was then processed and analyzed as previously described. In this way, 90.8% p
- It was determined that xylene and 19.5% of p-toluic acid were converted to the following products: Terephthalic acid 74.2g 4-carboxaldehyde 6.8g Other intermediates 1.5g Heavy by-products 3.7g From a comparison of these results with those of Example 1,
It can be seen that although the oxygen absorption is slightly higher, less terephthalic acid is produced. In fact, by estimating the yield of terephthalic acid carried out in a continuous process as in Example 1, a value of 81% is obtained instead of 90%. This difference clearly results in the advantageous yields resulting from using a mixture of manganese and cobalt instead of cobalt alone as a catalyst. Example 5 The experiment of Example 1 was repeated, except that manganese was used as the sole catalyst. The actual composition of the introduced raw materials was as follows. p-xylene 45.0 g p-toluic acid 182.8 g various oxidized derivatives 9.2 g water 63.0 g manganese acetate 3.00 mmol In this introduced material, Y was 2.60 and apparently X was 1.00. Therefore, the critical amount of manganese to carry out the oxidation was as follows. M=2.60 (1.00 + 0.200) + 10.9/4.35 + 0.0724 = 3.2 mmol/Kg In this example, the concentration of manganese was 10.0 mmol/Kg, or about three times the limit amount in Example 1. . After 180 minutes of reaction, the absorbed oxygen was 25.3 liters, ie significantly lower than in Examples 1 to 4. The reaction mixture was then processed and analyzed as previously described. In this way,
It was determined that 70.2% p-xylene and 5.8% p-toluic acid were converted to the following products. Terephthalic acid 31.2g 4-carboxybenzaldehyde 5.9g Other intermediates 6.3g Heavy by-products 5.1g By comparing these results with those of Examples 1 and 2, less reactants were consumed in this example. It will be clear that less terephthalic acid is produced. Furthermore, as in Examples 1-4, the yield of terephthalic acid for a continuous process estimated from these data is only 69%. Thus, in order to carry out the oxidation in the presence of water (as guaranteed by the lower value calculated for M, by comparison with the value calculated in the case of cobalt only), it is necessary to use manganese more than cobalt. is significantly more effective, but as in Example 1, there are clear advantages in using manganese with cobalt both in terms of reaction rate and yield. Example 6 The experiment of Example 1 was repeated except that manganese was used along with nickel. The actual composition of the introduced raw materials was as follows. p-xylene 45.0 g p-toluic acid 182.8 g various oxidized derivatives 9.2 g water 63.0 g manganese acetate 1.50 mmol nickel acetate 1.50 mmol In this introduced raw material, as in the previous example, Y is
2.60, and X was 1.00. In this way, M
It was 3.2 mmol/Kg (nickel was not taken into account in the calculation of M). In this example,
The concentration of manganese is 5.0 mmol/Kg, which is 1.8 excess over the limit amount. In fact, oxidation occurred actively. After 180 minutes, the absorption of oxygen is 29.2 liters,
The reaction mixture was analyzed as previously described.
As a result, 79.1% p-xylene and 3.3% p-
It was found that toluic acid was converted to the following product. Terephthalic acid 35.6g 4-carboxybenzaldehyde 6.6g Other intermediates 2.6g Heavy by-products 3.2g By comparing these results with those of the previous example, it was determined that only manganese was present at twice the concentration of this example. more oxygen is absorbed than when using
It can be seen that terephthalic acid is produced. This indicates that metals other than cobalt can be used with manganese to improve reaction rates. Example 7 The following materials were introduced into the same autoclave as in the previous example. p-xylene 45.0 g p-toluic acid 218.5 g various oxidized derivatives 6.5 g water 30.0 g manganese acetate 0.52 mmol cobalt acetate 0.45 mmol For this feedstock, the molar ratio of water to p-toluic acid (Y) is 1.04 The molar fraction (X) of manganese in the catalyst was 0.46. Therefore, by applying equation (1), the minimum concentration of catalyst used to carry out the oxidation in this case is M=2.7 mmol/Kg. In fact, in this example the catalyst concentration is 0.97 mmol or 3.2 mmol/Kg for 300 g of the initial mixture, ie only 0.5 mmol excess over the limit amount. However, oxygen absorption started spontaneously and was active. As a result, the temperature rises rapidly and with controlled cooling
The temperature was maintained at 170°C. After 395 minutes of reaction, 62.9 liters of oxygen had been absorbed. At that time, the introduction of air was stopped and the same procedure as in Example 1 was used to determine the composition of the reaction mixture. As a result, it was found that 98.8% of p-xylene and 29.2% of p-toluic acid were converted to the following products. Terephthalic acid 102.5 g 4-carboxybenzaldehyde 6.6 g Other intermediates 4.6 g Heavy by-products 3.6 Terephthalic acid achieved in a continuous process in which the intermediates are recycled by extrapolating from these data as in Example 1 The acid yield is
80% was obtained. This value is 10% lower than the yield estimated in Example 1. This difference in yield may be considered as further evidence of the advantages of oxidizing p-xylene in the presence of substantial amounts of water in accordance with the present invention. Comparative Example The same amounts of compounds were introduced as in the previous example, except that 0.30 mmol manganese acetate and 0.35 mmol acetic acid were used. The total concentration of metal catalyst was therefore 2.2 mmol/Kg, ie 0.5 mmol lower than the limit amount calculated in the previous example. When the mixture was oxidized in the presence of air flow under the same conditions as in the previous example, oxygen uptake started as well, but after about 70 minutes the oxygen uptake suddenly dropped to negligible levels. The absorption of oxygen was only 6.7 liters. Example 8 The following raw materials were introduced into the same autoclave as in Example 1. p-Tolualdehyde 45.0 g p-Toluic acid 187.5 g Various oxidized derivatives 4.5 g Water 63.0 g Manganese acetate 1.50 mmol Cobalt acetate 1.74 mmol This mixture is the same except that p-tolualdehyde has been replaced with p-xylene. It can be seen that these materials are very similar to the raw materials of Examples 1 to 5. The molar ratio of water to p-toluic acid was also 2.54 here.
By applying equation (1), the minimum concentration of catalyst used to carry out the oxidation is M=3.2 mmol/Kg. In fact, the concentration of catalyst is 10.8 mmol/Kg, ie 3 times higher. This mixture was heated in the presence of air as in the previous example. Oxygen absorption started spontaneously at about 30°C. With increased temperature and controlled cooling
The temperature was maintained at 170°C. After 180 minutes of reaction, the oxygen uptake was 25.6 liters. At that time, the introduction of air was stopped and then 180 ml was added with continued stirring and heating to extract the unreacted p-tolualdehye.
of n-heptane was injected into the reactor. The resulting mixture was then cooled and the reactor was opened. The precipitate therein is filtered, washed with n-heptane, dried under vacuum at 50°C, washed again with water,
Finally, it was dried at 70°C under vacuum. It was then analyzed using the same procedure as in the previous example. The filtration and washing solutions were combined, and the heptane extract was separated by sedimentation. The fractionated portion of this extract was analyzed by gas chromatography to determine p-tolualdehyde. The remaining portion was evaporated to dryness under vacuum and the residue was analyzed in the same manner as the first precipitate. These analyzes showed that 99.9% of p-tolualdehyde and 10.7% of p-toluic acid were converted to the following products. Terephthalic acid 58.4 g 4-carboxybenzaldehyde 7.1 g Other intermediates 6.1 g Heavy by-products 5.4 g Comparative Example 1 Same amounts as in the previous example, except that 0.3 mmol each of manganese and cobalt were used. Compounds were introduced into the autoclave. The total concentration of catalyst was therefore 2.0 mmol/Kg, ie 1.2 mmol below the limit amount calculated by equation (1). This mixture was heated in the presence of air under the same conditions as in the previous example. After 180 minutes of reaction, only 9.0 liters of oxygen was absorbed. The reaction mixture was then processed and analyzed as in the previous example.
As a result, it was found that p-tolualdehyde was completely converted to the following product. Terephthalic acid 2.3g p-Toluic acid 31.7g 4-Carboxybenzaldehyde 3.8g Other intermediates 0.9g Heavy by-products 2.0g In this example, p-tolualdehyde is primarily converted into p-toluic acid without substantial formation of terephthalic acid. - It can be seen that it was converted to toluic acid. Comparative Example 2 In this example, p-tolualdehyde was used as the single raw material to be oxidized. The actual raw materials introduced are as follows. p-Tolualdehyde 225.0 g Water 75.0 g Manganese acetate 1.50 mmol Cobalt acetate 1.50 mmol When this mixture was heated in the presence of air under the same conditions as in Example 8, oxygen absorption started as well but was significantly slower. . After about 240 minutes of reaction at 170°C, the oxygen uptake was 29.6 liters. By treating and analyzing the resulting reaction mixture as described above, it was found that 99.7% of p-tolualdehyde was converted to the following product. Terephthalic acid 4.6g p-Toluic acid 171.4g 4-Carboxybenzaldehyde 4.6g Other intermediates 1.3g Heavy by-products 1.3g In this example as well, p-Toluic acid is the main product from the oxidation of p-Toluic acid. , it can be seen that very little terephthalic acid was formed. This result clearly shows that in order to oxidize p-tolualdehyde to terephthalic acid according to the present invention, a sufficient amount of p-toluic acid must be present from the beginning of the reaction. Example 9 The experiment of Example 8 was repeated except that 3.48 mmol of cobalt acetate was used as the sole catalyst. By applying equation (1) it can be calculated that the minimum concentration of cobalt used in this case is M=7.0 mmol/Kg. Actually, the cobalt concentration in this example was 11.6 mmol/Kg. Oxygen absorption also started at low temperatures. However, heating was applied to maintain a temperature of 170°C. After approximately 210 minutes of reaction, the oxygen uptake was 20.8 liters. The reaction mixture was then processed and analyzed as in the previous example. As a result, it was found that 99.9% of p-tolualdehyde and 6.0% of p-toluic acid were converted to the following products. Terephthalic acid 49.1 g 4-carboxybenzaldehyde 6.9 g Other intermediates 6.5 g Heavy by-products 6.3 g Comparative Example The following raw materials were introduced into the same autoclave as in the previous example. p-Tolualdehyde 69.6 g p-Toluic acid 123.0 g Various oxidized derivatives 3.0 g Water 105.0 g Cobalt acetate 3.48 mmol Thus, the same amount of cobalt catalyst (11.6 mmol/Kg) as in the example above was used, but In this example, the molar ratio of water and p-toluic acid is not 2.54.
It was 6.45. Therefore, the minimum concentration of cobalt catalyst used in this case is M=17.8, i.e.
6.2 mmol more than the amount present in the introduced feedstock. This mixture was heated in the presence of air. Oxygen absorption occurred immediately in this example as well. However, after 45 minutes, oxygen uptake decreased to negligible levels. However, heating at 170°C continued. After 300 minutes of reaction, the oxygen absorption was only 10.0 liters.
The reaction mixture was then processed and analyzed as in Example 8. As a result, it was found that 90.1% of p-tolualdehyde was converted to the following product. Terephthalic acid 3.7g p-Toluic acid 53.5g 4-Carboxybenzaldehyde 3.3g Other intermediates 0.7g Heavy by-products 6.6g i.e. p-tolualdehyde converts to p-toluic acid without substantial formation of terephthalic acid It can be seen that it has been transformed into Example 10 The following raw materials were introduced into the same autoclave as in the previous example. p-Toluic acid 214.3 g Various oxidized derivatives 10.7 g Water 75.0 g Cobalt acetate 1.74 mmol Manganese acetate 1.50 mmol In this example, neither p-xylene nor p-tolualdehyde was used. The molar ratio (Y) of water to p-toluic acid was 2.64, and the molar fraction (X) of manganese in the catalyst was 0.46 as in Example 1. As calculated from equation (1), the minimum concentration of catalyst used is M=3.3 mmol/Kg. In fact, in this example, the catalyst concentration was 300% in the reaction mixture.
It was 3.24 mmol per g or 10.8 mmol/Kg, ie about three times the limit amount. This mixture was heated under the same conditions as Example 1 in the presence of air. In this example, the reaction also started spontaneously. After 180 minutes of reaction, 19.4 liters of oxygen were absorbed and the reaction was stopped by cooling.
The autoclave was opened and the precipitate therein was treated and analyzed as in Example 1. the result,
It was found that 33.2% of p-toluic acid was converted to the following product. Terephthalic acid 75.5 g 4-carboxybenzaldehyde 6.1 g Other intermediates 1.8 g Heavy by-products 0.1 g The net yield of terephthalic acid based on the converted p-toluic acid is 87 mole %. However, taking into account intermediate oxidation products such as 4-carboxybenzaldehyde, the actual yield of terephthalic acid as obtained in a continuous process in which intermediate products are recycled can be estimated to be 97 mol%. This example demonstrates that p-toluic acid can be effectively and in high yield oxidized to terephthalic acid according to the present invention even without the presence of p-xylene or other easily oxidizable compounds as promoters. clearly shows. Example 11 The following raw materials were introduced into the same autoclave as in the previous example. p-xylene 3.0 g p-toluic acid 142.6 g various oxidized derivatives 4.4 g water 150.0 g manganese acetate 1.05 mmol cobalt acetate 1.05 mmol In this example, water is 50% by weight of the initial mixture.
, Y was 7.95 and X was clearly 0.50.
By applying equation (1), the minimum concentration of catalyst used is M=4.9. In fact, in this example, the catalyst concentration was 7.0 mmol/Kg, or 2.1 mmol/Kg below the limit. Air was introduced into the reactor at a flow rate of 110 liters/hour under a pressure of 20 Kg/cm ² . When the temperature was about 170°C, a small amount of t was added to help start the reaction.
-Butyl hydroperoxide was added. As a result, absorption of oxygen occurred immediately. At that time the temperature rises rapidly and by controlling the cooling it reaches 185℃
was maintained. After 300 minutes of reaction, the absorption of oxygen is
It was 23.5 liters. The reaction is then stopped,
The resulting mixture was processed and analyzed as in Example 1. As a result, 95.0% p-xylene and 40.3
It was found that % of p-toluic acid was converted to the following products. Comparative Example 1 The same experiment as the previous example was repeated, except that half the amount of each metal catalyst was used. The total concentration of catalyst was therefore 3.5 mmol/Kg, ie 1.4 mmol below the limit amount. This mixture was heated in the presence of air under exactly the same conditions as in the previous example. Despite two successive additions of t-butyl hydroperoxide to help initiate the reaction, no oxygen uptake occurred by holding the mixture at 185° C. for 160 minutes. Considering the results obtained in the previous examples in which active and substantial oxidation occurs in the presence of large amounts of water, it is clear that such oxidation will occur when using the appropriate catalyst amounts specified in this invention. It is clear that it can be implemented. Comparative Example 2 The same experiment as Example 11 was repeated, except that part of the p-toluic acid was replaced with benzoic acid.
The actual composition of the raw materials is as follows. p-xylene 3.0 g p-toluic acid 44.5 g Benzoic acid 93.9 g Various oxidizing compounds 2.0 g Manganese acetate 156.6 g Cobalt acetate 1.05 mmol 1.05 mmol In this example, Y was 26.59. Therefore, the expression
By applying (1), the minimum concentration of catalyst used to carry out the oxidation of the mixture was 10.7 mmol/Kg, ie 3.7 mmol more than the amount actually present. By contrast, if benzoic acid has the same effect as p-toluic acid in carrying out the oxidation in an aqueous medium, it should be taken into account in the calculation of Y and M. In this case, Y=
(156.6/18.02)/(44.5/136.15+93.9/122.12)
=7.93, that is, Example 11 when active oxidation occurs
This is the same value as Y calculated in . This mixture was heated at 185° C. under the same conditions as Example 11. Again, t-butyl hydroperoxide was added to aid initiation. but,
No substantial oxidation occurred even when heating continued for 180 minutes. This shows that at least benzoic acid does not have the same activity as p-toluic acid for promoting oxidation in the presence of water carried out in the process of the invention. Comparative Example 3 The same experiment as Example 11 was repeated, except that part of the p-toluic acid was replaced with acetic acid. The actual composition of the raw materials was as follows. p-xylene 3.0 g p-toluic acid 52.7 g acetic acid 55.2 g various oxidizing compounds 1.3 g water 187.8 g manganese acetate 1.05 mmol cobalt acetate 1.05 mmol In this example, Y is 26.92, so M is 10.8;
That is, it was almost the same as the previous comparative example. even here,
In carrying out the oxidation in an aqueous medium, if acetic acid is
-If it has the same promoting effect as toluic acid,
This should be taken into account when calculating Y and M.
In this case, Y=(187.2/18.02)/(52.7/136.15
+55.2/60.05)=7.95, that is, exactly the same value as Example 11. The above mixture was heated at 185° C. under the same conditions as Example 11. Again, t-butyl hydroperoxide was added to help initiate the reaction. Oxygen absorption for 300 minutes of reaction was only 3.8 liters. This result shows that the promoting effect of p-toluic acid exhibited in the method of the present invention is not exhibited by other carboxylic acids, that is, p-toluic acid is a specific one. Example 12 The following raw materials were introduced into the same autoclave as in the previous example. p-xylene 6.0 g p-toluic acid 183.3 g Various oxidized derivatives 5.7 g Water 105.0 g Manganese acetate 1.80 mmol In this example, Y = 4.33, and since manganese was used as the sole catalyst, X = 1.00. Therefore, by applying equation (1), the minimum concentration of manganese used in this example is M=3.6 mmol/Kg. In fact, in this example, the concentration of manganese is 6.0 mmol/Kg, well above the limit amount. This mixture should be heated at 170°C instead of 185°C.
Heated in the presence of air under exactly the same conditions as Example 11 except that the temperature was maintained at 0.degree.
After 305 minutes of reaction, the oxygen uptake was 21.2 liters. The reaction mixture was treated and analyzed as in the previous example and found to be approximately 96% p-xylene and 29.9%
It was found that p-toluic acid was converted to the following product. Terephthalic acid 44.8g 4-carboxybenzaldehyde 14.2g Other intermediates 0.9g Heavy by-products 1.2g Comparative Example Same amounts of compounds as in the previous example, except that only 0.60 mmol of manganese acetate was used as catalyst The concentration of catalyst in the mixture introduced into the reactor was therefore 2.0 mmol/Kg, or 1.6 mmol below the limit amount. As a result, even after adding t-butyl hydroperoxide to help initiate the reaction, no oxygen uptake occurred when the mixture was heated for 60 minutes in the presence of air under the same conditions as in the previous example. Example 13 The following raw materials were introduced into the same autoclave as in the previous example. p-xylene 6.3 g p-toluic acid 218.3 g various oxidized derivatives 2.2 g water 73.5 g cobalt acetate 3.48 mmol In this example, cobalt was used as the sole cobalt, ie X=0. On the other hand, Y is 2.54. By applying equation (1), the minimum concentration of cobalt used in this case is M=7.0 mmol/Kg. In fact, in this example the cobalt concentration was 11.6 mmol/Kg. Air at a pressure of 20 Kg/cm ² and a flow rate of 90 l/h was introduced into the reactor and the mixture was heated to 170°C. The reaction started spontaneously during heating and continued for 240 minutes. At the end of the reaction, the oxygen uptake was 29.8 liters. The reaction mixture was treated and analyzed as in Example 1 and found to have converted 89.3% p-xylene and 37.0% p-toluic acid to the following product. Terephthalic acid 81.5 g 4-Carboxybenzaldehyde 6.8 g Other intermediates 1.2 g Heavy by-products 3.0 g Comparative Example Same amounts of compounds as in the previous example, except that only 0.90 mmol of cobalt acetate was used as catalyst. was introduced into the reactor. Therefore, the catalyst concentration in the mixture is 3.0 mmol/Kg, i.e. less than the limit amount.
It was 4.0 mmol lower. As a result, even after repeated additions of t-butyl hydroperoxide, in the presence of air under the same conditions as in the previous example,
Heating the mixture for 240 minutes resulted in no oxygen uptake. It is to be understood that the above description of the basic and novel features of the invention is merely illustrative of preferred embodiments. Those skilled in the art will recognize many variations. For example, in carrying out the process of the invention, other compounds used as activators in other processes, such as aldehydes or ketones or bromine-containing compounds, can be added to the reaction mixture. Such additives are
For example, there may be advantages regarding reaction rates. These variations may be made without departing from the spirit of the invention.
would be within the scope of the invention.

[Brief explanation of drawings]

The figure shows a phase diagram of a mixture of p-xylene, p-toluic acid and water at 185°C.

Claims (1)

[Claims] 1. (a) an oxidizable terephthalic acid precursor consisting of p-toluic acid or a mixture of p-toluic acid and p-xylene; at least 5% by weight
of water and an oxidation catalyst in an amount sufficient to provide at least a minimum amount of catalytically active metal compound per kg of liquid reaction mixture, with a molecular oxygen-containing gas.
oxidizing at a reaction temperature of from about 140°C to about 220°C under a pressure sufficient to maintain at least a portion of the water in the liquid phase in the liquid phase at the reaction temperature; and (b) an oxidation comprising terephthalic acid. the oxidation catalyst is selected from the group consisting of manganese salts, cobalt salts of carboxylic acids, and mixtures thereof; A method for producing terephthalic acid, which is soluble and the minimum amount M (millimol) of the metal compound is defined by the following formula. M=Y(X+A)+BX/CX+D where Y is the molar ratio of water to p-toluic acid in the reaction mixture, and X is the molar ratio of manganese salt to the total amount of manganese salt + cobalt salt in the catalyst composition. , A is about 0.200, B is about 10.9, C is about 4.35, and D is about 0.0724. 2 The above A is about 0.200±0.031, B is about 10.9±1.3,
2. The method of claim 1, wherein C is about 4.35±0.17 and D is about 0.0724±0.0117. 3. The method of claim 1, wherein the amount of water in the reaction solution is about 5 to about 80% by weight of the reaction solution. 4 The amount of water is about 5 to about 75 of the weight of the reaction solution.
4. A method according to claim 3, wherein the amount is % by weight. 5. The amount of water is about 10 to about 75 of the weight of the reaction solution.
4. A method according to claim 3, wherein the amount is % by weight. 6 The amount of water is about 10 to about 60 of the weight of the reaction solution.
4. A method according to claim 3, wherein the amount is % by weight. 7. The reaction solution has a ratio of 0 to 100 relative to the amount of water.
The method of claim 1 further comprising % by weight of an inert organic solvent. 8. The method according to claim 7, wherein the organic solvent is acetic acid. 9. The method of claim 1, wherein the reaction temperature is about 150 to about 190°C. 10. The method of claim 1, wherein the reaction pressure is about 5 to about 40 kg/cm ² . 11 The amount of the oxidation catalyst is defined in claim 1.
Approximately per kg of reaction mixture with the minimum amount defined in Section 1.
2. The method of claim 1, wherein the amount is sufficient to provide an amount of catalytically active compound that is between 40 mmol. 12 The amount of the oxidation catalyst is defined in claim 1.
Approximately per kg of reaction mixture with the minimum amount defined in Section 1.
2. The method of claim 1, wherein the amount is sufficient to provide an amount of catalytically active compound that is between 30 mmol. 13. The method according to claim 1, wherein the catalyst is a mixture of a manganese compound and a cobalt compound. 14. The method of claim 13, wherein 14X is about 0.1 to about 0.9. 15. The method of claim 1, wherein the catalyst further comprises a compound of a metal selected from the group consisting of nickel, lead, and cerium. 16 Claim 1, wherein the molar ratio of p-toluic acid to p-xylene is about 3 to about 15.
The method described in section.