KR820000093B1 - Meta-or phthalic acid preparation in benzoic acid-water solvent system - Google Patents

Abstract

Meta- or para-phthalic acids were prepd. by semi continuous or continuous air oxidn. of m- or p-xylene at 275≰C in monocarboxylic acid in the presence of transition metal catalysts and source of Br. The compns. of solvent system were 85-97 wt.% of BzOH and 15-3 wt.% of H2O and most used transition metal catalysts were Mn, Co and Ce.

Description

Method for preparing meta or paraphthalic acid

The present invention oxidizes meta- or paraphthalic acid by oxidizing m- or p-xylene to oxygen molecules at elevated temperatures and liquid phase conditions in the presence of a catalyst prepared by a combination of one or more transition metal oxidation catalysts and bromine source materials. In the process for the preparation, the use of a liquid solvent system consisting mostly of benzoic acid and from 3 to about 15% by weight of water allows commercial control of the oxidation temperature, which was not easy when oxidizing xylene, when the above catalyst system was free of water components. It is an improved method in that it is easy.

The unique catalysis of a combination of one or more transition metal oxidation catalysts and bromine source materials is described in US Pat. No. 2,833,816 and its foreign counterparts, which catalysts have one or more substituents that can be oxidized to carboxylic acid substituents. It is generally used to prepare aromatic carboxylic acids at elevated temperatures of 50 to 275 ° C. under pressure which maintains liquid phase conditions to oxidize aromatic hydrocarbons to oxygen molecules. The patent also describes the use of C ₂ -C ₈ carboxylic acids useful for such catalytic liquid oxidation.

This catalytic liquid oxidation has been developed in a world-leading way to commercially prepare isophthalic acid, terephthalic acid and trimellitic acid by air oxidizing m-xylene, p-xylene and pseudocumene in the presence of acetic acid.

This catalytic liquid oxidation is rare, but also applied to the commercial production of benzoic acid by air oxidation of toluene in the presence of benzoic acid as a solvent.

In the commercial production of benzene di- and tricarboxylic acid products, the use of acetic acid as a solvent is the most economically advantageous method, but has the disadvantage of simultaneously oxidizing on the order of 80 to 160 kg acetic acid per tonne of product produced (MT).

The least reactive acetic acid among the C ₂ -C ₈ aliphatic acids is oxidized in this process and converted to carbon oxides, water and methyl acetate.

Temperature control of this oxidation carried out in the presence of acetic acid solvent is not a problem for commercial production because the boiling point of acetic acid and by-product water is relatively similar and the concentration of water is 3 to 18% by weight of the solvent. A practical acetic acid-water solvent system is a single component system of mixed liquids and has a single degree of freedom when calculated from phase rates. Therefore, when operating at a constant volume, by setting the operating pressure constant, a constant operating temperature is determined accordingly.

In 1963, catalytic liquid air oxidation of a suitable methyl-substituted benzene in the presence of benzoic acid instead of acetic acid as a reaction solvent and in the presence of a specific combination of one or more transition metal oxidation catalysts and bromine sources already found, resulted in benzene di- and tricarboxylic acids. In particular, a continuous process for producing terephthalic acid has been published.

British Patent No. 1,088,183, published October 25, 1967, relates to oxidation carried out in the presence of a benzoic acid solvent and is described in detail. According to the patent, benzoic acid air-mixed at a temperature of 50 to 275 ° C. becomes a medium which corrodes the metals used in the production of the oxidation vessel at less than air-mixed acetic acid, is less volatile than acetic acid and less than acetic acid vapor at the reaction site. It is described that benzoic acid was chosen from C ₂ -C ₈ mono carboxylic acids because it is much easier to separate by-product steam from benzoic acid vapor. For example, the selective condensation of benzoic acid vapor with by-product water in the steam mixture can be carried out by simple partial condensation, but fractional distillation must be carried out to separate the mixture of acetic acid and by-product water vapor.

According to the British patent, another benefit of using benzoic acid solvents is that the oxidation rate is high using a high oxidation temperature (170 to 175 ° C.), and the liquid phase reaction using a high operating pressure (21 to 35 kg / cm ² ). The high oxygen concentration in the medium, the removal of by-product water as soon as possible, and the free operating temperature for this operating pressure.

The British patent describes a method for preparing terephthalic acid by three-step continuous air oxidation of p-xylene, which yields 85-95 mol% (% of theory) and has a purity of 99-99.9 wt%.

However, despite the fact that terephthalic acid is produced in high yield and high purity in the presence of a liquid benzoic acid solvent, an important problem has been found in carrying out the British patent in a continuous process.

The problem occurred in the initial process of oxidizing p-xylene at operating pressures of 21 to 35 kg / cm ² while removing byproduct water as it was produced. This is because at such initial oxidation conditions, the operating temperature cannot be controlled and the benzoic acid and / or p-xylene or its partial oxidation products oxidize very quickly and become carbonized residues. In a specific example of the British patent, a stirring-tank-type oxidation vessel was not used, but if the liquid composition was not sufficiently stirred, insufficient air was dispersed and insufficient heat of reaction was distributed to the liquid phase to form a local "hot spot". The high oxidation rate results in part from the highly localized conditions of high temperature and high oxygen concentrations.

However, unstirred tubular reaction vessels are prepared by air oxidation of toluene in the presence of benzoic acid solution of one or more combinations of transition metals and bromine compounds, without carbonation of other oxidations, for example, reactants, products or benzoic acid solvents. Was successfully used. The lack of agitation therefore has no control over the formation of acute carbonation resulting from inadequate temperature control in the early stages of p-xylene oxidation.

We found that acute carbonization in the early stages of oxidation requires maintaining high operating pressures of 21 to 35 kg / cm ² as needed and removing byproduct water as it is produced. This was found by examining the effect on the initial operating temperature of the operating pressure 21 to 35kg / cm ² (the effect of the presence or absence of a small amount of water in the benzoic acid solvent) required by the British patent method.

When the water concentration of the liquid benzoic acid was changed from 5 wt% to 0 wt% at 25-35 kg / cm ^{2 in the} pressure range and the initial temperature of 205 ° C., the temperature increased by 110 ° C. without changing the pressure.

Such results from which acute carbonation is derived can be demonstrated from the results of the following investigation. 21 to 35 kg / cm of benzoic acid (boiling point 249 ° C. at 760 mmHg) containing 5% by weight of water²of Under pressure, it was heated to an initial temperature of 205 ° C. The temperature of the liquid benzoic acid was measured while changing its water content from the first 5% to 0%. The temperature of the liquid benzoic acid increased by 110 ° C. with no increase in the fixed pressure as the water dropped from 5% to 0%. This shows a specific temperature sensitivity to the water content of the liquid benzoic acid solvent, 21-35 kg / cm according to the required operating conditions of the British patent.²This is why the carbonized product is rapidly oxidized rapidly at the initial stage of oxidizing p-xylene at the pressure of.

Based on the findings of the dramatic increase in temperature observed during the experiments, we quickly remove the byproduct water as it is produced, keeping the water content near zero, and performing the initial oxidation reaction under high pressures such as 21 to 35 kg / cm ² . When carried out, it was concluded that the temperature control required for mass production operations to produce meta or paraphthalic acid by air oxidizing m- or p-xylene in the presence of liquid benzoic acid as a reaction solvent was concluded.

In addition to this initial stage, another problem arises in the continuous oxidation of m- or p-xylene into air in the presence of liquid benzoic acid as a solvent in accordance with the operating conditions of the British patent.

Even after the oxidation reaction has been initiated successfully by maintaining the proper initial and retentate content in the liquid benzoic acid to successfully control the temperature of the stirred liquid, the reaction temperature fluctuates greatly due to the change in the amount of water removed. Based on this test and the above test results, we do not need to remove the operating pressure of 21-35kg / cm ² too high and as soon as the by-product water is produced and the mass production continuous process is introduced. I concluded that

In the initial and general processes for the continuous air oxidation of commercially available m- or p-xylenes, solvent systems (85 to 97% by weight of liquid are obtained even if the operating pressure is in the range of 6 to 25 kg / cm ² and by-products are removed. We have found that this solvent system can be used for temperature control if the water content of benzoic acid and 15 to 3% by weight of water does not exceed 15% or fall below 3%. Under these operating conditions, an operating oxidation temperature of 175-235 ° C can and can be used.

For this continuous oxidation, a suitable catalyst is dissolved in a solvent system to prepare a unique catalyst of a combination of one or more transition metals and bromine materials.

The continuous process of the present invention is carried out in a stirred oxidation zone that can effectively disperse air into the oxidation zone and effectively dissipate the reaction heat through the liquid phase of the oxidation zone.

The heat of reaction evaporates a small amount of benzoic acid and mainly water from the oxidation zone. Xylene hardly evaporates or does not evaporate at all because it is oxidized to a material that is difficult to evaporate under operating conditions. By cooling the steam to remove the heat of reaction and controlling the water content of the liquid (mainly water) refluxed to the oxidizing zone, satisfactory temperature control is achieved for almost constant operating conditions. The water content of the liquid reflux (usually 90-95% by weight) can be controlled by the operating temperature of the reflux condenser. Since the condensate contains only 5-10% by weight of benzoic acid, the change in oxidation temperature from the set operating temperature can be controlled by varying the rate of addition of the water recovered in the zone of oxidation.

For example, the rate of water recovery as reflux decreases or increases depending on how much the oxidation temperature of the oxidation zone decreases or increases from the set constant temperature. The method of changing the water content of the liquid reflux and the proportion of water recovered in the oxidation zone as described above is described later. This method can keep the change in temperature of the oxidation zone within or below 50 ° C. above the constant temperature of the selected oxidation zone.

Changes in the water ratio of this recovered liquid should not reduce the water content of the solvent system below 3% by weight. This is because under such conditions large uncontrolled temperature fluctuations occur again. Changes in the recovered liquid should not increase the water content of the solvent system to more than about 15% by weight (eg 18% by weight). This is because that amount of water partially or completely deactivates the catalysis system, reducing the oxidation rate beyond commercial use.

For the purposes of the present invention, m- or p-xylene oxidation is carried out with a weight ratio of benzoic acid-water solvent system to xylene of 2: 1 to 10: 1. The catalysis system is also suitably made of bromine source materials combined with one or more manganese, cobalt or cerium as transition metal oxidation catalysts. It is also desirable to minimize the amount of partial oxidation products and colored impurities in the recovered meta or paraphthalic acid product using an amount of air capable of providing 2 to 10 volume ratios of oxygen to the exhaust gas (based on no benzoic acid).

The process of the present invention can proceed to continuous pores by combining the pressure of 6-25 kg / cm ² with a specific benzoic acid-water solvent system to effectively control the temperature of the oxidation zone in the operating temperature range of 175-235 ° C.

In the continuous operation of the process of the present invention, the concentration of xylene is not relatively high at the start-up, i. The start-up process described above is different from the batch operation in that first, the catalyst and solvent-based components specific to the stirred oxidation zone are filled. The resulting solution is stirred and heated to a temperature at which oxidation starts, for example 160-170 ° C (but preferably an operating temperature of 175-235 ° C). Heat to the oxidation start temperature and pump m- or p-xylene into the stirring solution in the oxidizing zone and add approximately 1000 to 1500 N liters of air per kg of xylene until the temperature of the oxidizing zone reaches the operating temperature selected from 175-235 ° C. Inject into the stirring solution. The xylene is then pumped into the oxidizing zone and the air proportion is increased to about 3800 to 5900 N liters per kilogram of xylene so that 3 to 10% by volume of oxygen is included in the exhaust gas (benzoic acid and water free).

After the weight ratio of the originally filled solvent system to the total charged xylenes is in the range selected from 3 to 10: 1.0, the air injection rate is set to 3 to 10 volumes of oxygen in the exhaust gas to maintain the selected solvent to xylene weight ratio. The catalyst component solution of the benzoic acid-water solvent system was pumped at a rate of continuously pumping xylene while maintaining at 3800 to 5900 N liter / kg xylene to be%. The initial time to complete the continuous feed operation is relatively short, but it is time to adjust the operation of the cooler to remove the heat of reaction from the exhaust gas and to control the rate of water condensate recovered with the stirred condensate with the liquid condensate reflux. Once the oxidation zone of the oxidation zone has reached the volume of the air mixture to be operated, the flowable oxidation reaction mixture is withdrawn from the oxidation zone to the feed inlet to separate the meta or paraphthalic acid product from the liquid benzoic acid-water solvent system.

This operation through full continuous operation is undesirable from the beginning of charging the reactant and catalyzed solvent-based solutions and withdrawing the fluidized reaction compounds, but this is not the only solution to the water content of the solvent system that has the greatest impact on successful control of the operating temperature. It is a useful startup process that experiences temperature sensitivity.

After such experience, the startup of the process of the present invention can be simplified by retouching the desired startup conditions. For a preferred start-up, the solvent-based solution of the catalyst component necessary to reach the operating volume of the reactor is filled, stirred and heated to the selected operating temperature under the selected operating pressure.

Then, with the cooler reflux system sensitive to the temperature of the oxidation zone, xylene is pumped into the stirred solvent at a continuous operation ratio and air is injected. The fluid starts to separate when the total xylene filled to the selected initial solvent system is at the selected weight ratio of solvent system to xylene.

Continuous operation of the process of the present invention involves the use of a stirrer, reflux cooler (operated at a temperature near the melting point of benzoic acid (121.7 ° C.) to cool the benzoic acid as a liquid refluxed with agitated oxidizers) and a side arm cooler (byproduct water). Can be carried out in an oxidizing vessel attached thereto. The pressure regulating valve may be used between the coolers described above or preferably after the steam cooler (eg the outlet of the steam cooler). Uncondensed gases can be withdrawn from the condensate collection vessel described above via a pressure reducing valve. The reaction vessel must be equipped with a temperature and pressure measuring instrument and a tool for filling the solvent solution of the reactants and catalysis components and withdrawing the flowing oxidation effluent. The above-described apparatus can easily detect the water content control of the benzoic acid-water solvent system and control the water content within the range of 3-15% by weight based on the water content mass balance. Discard only the measured amount of the resulting by-product water and the equivalent water condensate, and return the remaining condensate back to the reaction zone to regulate the zone at constant pressure.

Meta or paraphthalic acid products, which are relatively insoluble in the solvent system, can be separated from the fluid oxidation effluent by solid-liquid separation methods such as filtration or centrifugation at temperatures at which the benzoic acid becomes liquid in the fluid oxidation effluent.

Since the flow effluent has a temperature of 175-235 ° C. (higher than the benzoic acid coagulation temperature) and a pressure of 6-25 kg / cm ² , the above product can be separated by depressurizing the effluent with premises cooling. Such decompression may be ambient or negative pressure. The cooled effluent is still a flowing effluent and is placed in the solid-liquid separator described above.

Preferably the effluent is depressurized to negative pressure so that no flash evaporation occurs in the solid-liquid separator.

The separated crystalline product is washed with hot fresh liquid benzoic acid and then with xylene, toluene or mixtures thereof to remove adhered benzoic acid. The washed product is dried and the xylene or xylene-toluene mixture removed by drying is recovered for reuse. Washing the product with xylene and / or toluene can be carried out in a solid-liquid separator, but preferably by suspending the solid product washed with benzoic acid in an aromatic hydrocarbon. Since the product is recovered at much higher temperatures than when using acetic acid as a solvent, there is an advantage that a high purity meta or paraphthalic acid product is obtained by the aforementioned separation and washing.

This separation at higher temperatures leaves more impurities in the mother liquor. In addition, because aromatic hydrocarbons such as xylene and / or toluene are better solvents than acetic acid for impurities, washing with xylene and / or toluene further removes the impurities.

In general, another advantage of the process of the present invention is that the oxidation reactor is less burned, the air flow is cleaner, less corrosive to the oxidation vessel, the series of transport and product recovery, and the reaction pressure is lower. Is lower than the price.

The combustion of the benzoic acid component of the solvent system is 50% lower than that of the acetic acid solvent using the same solvent to xylene weight ratio and the same operating temperature. Moreover, since benzoic acid combustion products are only water and carbon oxides, there is no need to separate them from solvents for the separation or removal of esters (methyl acetate) required when using acetic acid as a reaction solvent. In addition, non-condensable solvent vapor as much as the amount of solvent vapor generated when acetic acid is used as the reaction solvent is not exhausted. For this reason, a cleaner gas is exhausted in implementing the process of the present invention.

Air-mixed wet (3-15% water) benzoic acid is generally less corrosive than air-mixed wet (5-10% water) acetic acid containing bromine at the operating temperature even if it contains a catalytic bromine component. Due to the generally less severe corrosiveness associated with benzoic acid-water solvents, SS 316 / type stainless steels, which are less expensive than relatively expensive metals such as titanium, which are used as solvents in acetic acid, can be used in manufacturing equipment (especially chillers).

The capital investment and running costs in the commercial practice of the invention are lower than when using acetic acid or benzoic anhydride as the reaction solvent. This lower cost uses less expensive metals for the process equipment, lower operating pressures on the oxidation reactor and its subcoolers and condensate collectors, reduces exhaust gas cleaning and reduces the later stages of crystallization (generally The use of acetic acid as a solvent is two or three steps) and the solvent fractionation process to recover the solvent to be recycled to oxidation is eliminated.

Unlike the process using the acetic acid solvent, the process of the present invention is not delayed in terms of speed because there is more than 5% by weight of water in the solvent system.

As mentioned above, the conditions essential for the implementation of the process of the present invention are 6-24, preferably 14-20 kg / cm ² operating pressure and benzoic acid capable of almost constant control of the selected operating temperature within the range of 175-235 ° C. (85-97 wt%) and water (15-3 wt%).

In a specific example, a combination of a solvent composition and an operating pressure that can well control an almost constant temperature (within ± 5 ° C) from the average operating temperature will be described. Those skilled in the art will select or devise other useful combinations. Can be.

Although it is important to carry out agitation in the reaction zone because air can be well dispersed in the liquid reaction mixture and heat can be well removed from the reaction mixture, this is usually sufficient for the stirring design of the art. For example, the usual design level of reactor and agitator-blade geometry, agitation mode, and stirrer power to suspend product crystals in a solvent system should be considered to allow for the necessary agitation. These criteria can be easily calculated from the published data and experimental data obtained easily by simple experiments with small scale devices.

Useful weight ratios of solvent system to m- or p-xylene are in the range of 2-10: 1.0 as described above.

Illustrative embodiments provide criteria for the process design engineer to select a ratio that fits a particular process design in the above range or to select a different ratio that fits the particular design devised.

The heat of reaction can be removed by adding water to the reaction zone to evaporate it from the reaction zone, as described below. The heat of reaction will be removed if 5 kg of water per kg of xylene to be oxidized evaporate. The reaction heat can also be removed by a known method of heat exchange liquid (for example, liquid flowing through the tubular coil in the reaction zone) and internal indirect heat exchange.

The heat of reaction can also be removed by any of the known external flow loop heat exchangers, in which the liquid reaction mixture flows from the oxidation zone to the external heat exchange loop, exchanging heat with indirect heat exchange, for example, water. And generate steam. The cooled reaction mixture is pumped back into the stirred reaction zone.

Many other useful methods for removing the heat of reaction can also be used.

The parameters of the catalysis component of 0.3 to 1.5 wt% total metal and 0.3 to 1.5 wt% bromine are not mentioned above and the proton ratios are calculated as elemental states based on xylene.

Preferably the heat of reaction is removed by evaporating the reaction solvent which is cooled by a three stage cooler. The H ₂ O of the reactor is removed at the last stage of the cooler and the other cooling liquid is returned to the reactor based on xylene.

Suitable sources of Mn, Co and Ce may be salts of these metals that can be dissolved in the benzoic acid-water solvent system.

Such salts include bromide as well as carboxylates (acetate, propionate, butyrate, taffetenate and benzoate), complex acetyl acetonates and ethylene diamine tetraacetate.

Bromine sources include elemental bromine, ionic bromine, including ammonium bromide, bromide of catalyzed transition metals, hydrogen bromide as is or bromic acid, sodium or potassium bromide or sodium or potassium bromate and organic bromide (tetrabromo Carbon, dibromoethylenebene, zylbromide and bromobenzene.

Such bromine source materials are known from US Pat. No. 2,833,816 and its foreign counterparts.

The following thirteen examples illustrate the practice of the process of the present invention by semi-continuous oxidation to produce terephthalic acid (TA) by air oxidizing p-xylene (PX). The oxidizer is a cylindrical oxidation vessel with a stirrer that stirs the reaction zone, and the amount of solvent-based and suspended products used after the p-xylene has been filled and airized, accounts for about 60% by volume of the total volume of the vessel. . The remaining 40 volume percent is intended to liberate gas and water vapor from the stirred liquor in the reaction zone.

The vessel is provided with a means for introducing air to the bottom of the oxidizing table, a means for introducing p-xylene and water to the top of the oxidizing table, a means for discharging the flowing oxidation effluent from the bottom of the vessel described above, and a free mixture of gas and vapor in the vessel Means for discharging from the top of the and for sealing the vessel for operation at pressures above the caution pressure.

The top discharge means is connected to a reflux condenser that cools the benzoic acid and the reflux and uncondensed gas and vapor are released to a side arm cooler that is operated to cool the water.

The steam cooler collects water condensate and connects the uncondensed gas (mixture of nitrogen, oxygen and carbon oxides) with a small amount of water vapor through a vent with a pressure regulating valve from the top.

The water freeze trap is located between the aforementioned pressure regulating valve (adjustable) and the instrument for sampling and analyzing the gas to be vented.

The p-xylene is pumped from the pressurized input tank and metered into the oxidizing zone. The water is filled with an oxidizing zone by the combination of a pressurized input tank (3.5kg / cm ² above the pressure of the oxidizing zone), the metering valve and the rotor meter. However, another side pipe through the ball valve is prepared to quench the reactants by adding a large amount of water to the reaction zone in case of an unforeseen increase in control of the reaction temperature without quenching the reactants.

Controllable means are first heated or cooled in the agitation liquid or flow contents in the oxidation zone system charged to the reaction vessel, and until the first introduction of p-xylene and air, if necessary until after the introduction of p-xylene. The solution is kept at operating temperature. The reflux cooler is heated with steam at a maximum pressure of 7 kg / cm ² introduced through an air pressurized steam regulator. By adjusting the air pressure, the operating temperature can be controlled by adjusting the steam pressure of 0-7kg / cm ² to the chiller. The air pressure is inversely adjusted in response to the temperature of the reaction rental. As such, the steam pressure is increased when the reaction temperature is decreased to adjust the cooler temperature corresponding to the temperature of the oxidation zone, and the steam pressure is decreased when the reaction temperature is increased. Increasing the vapor pressure in the premises reduces the water content of the solvent system and decreasing the vapor pressure increases the water content of the solvent system. The apparatus for controlling the reaction temperature by adjusting the temperature (steam injection pressure) of the reflux cooler described in the following examples is quite precise, and it is not necessary to add a large amount of water during cooling. However, when the outlet steam flow rate is slow and the temperature of the exhaust gas is difficult to control, a small amount of water is injected to make the temperature control more accurate.

Table I p-xylene oxidation in water solvent

ND means not detected.

* The total reaction effluent is obtained by pressurizing to ambient temperature. Thus the water component was flash evaporated.

The p-xylene oxidation of the following Examples 9-14 is carried out in the same manner as in Example 1-8 and in the same apparatus. In Example 14, however, a reaction solvent was prepared by combining 80% of the benzoic acid mother liquor from Example 13 with water, fresh benzoic acid, and manganese acetate tetrahydrate. Therefore, 4-CBA and p-toluic acid, which are intermediate products, accumulate and the color of the recovered product becomes dark.

Table II-Oxidation of p-xylene in benzoic acid-water solvent

＊ lowest-highest

The following p-xylene oxidation illustrates the continuous implementation of the oxidation process of the present invention. This continuous oxidation is carried out in the same type of device as described for the oxidation of the 14 embodiments described above, except that the components of the device are larger. The parts of the device are larger because of the higher p-xylene dosage per hour. Continuous oxidation begins in the same way as semi-continuous oxidation and is operated by pumping p-xylene until the weight ratio of solvent (first filled) to p-xylene is reached. The solvent solution of the catalysis component is then pumped into the reaction zone at a rate that maintains the solvent / xylene ratio and the TRE is withdrawn at a rate that can maintain the retention time as shown in Table III.

Table III P-Xylene Oxidation in Benzoic Acid-Water Solvent

When p-xylene oxidation was carried out in Comparative Example 1, water as a byproduct was not removed. That is, the reflux cooler was operated at a temperature where all the water and benzoic acid condensate returned to the oxidizing zone. This increases the water concentration of the benzoic acid-water solvent system from 10% to 18% by weight in normal operation.

This 18% water content is higher than 15%, the upper limit for acceptable oxidation rates. In addition, 225 g of p-xylene is added to the initial fill of the solvent system containing the catalysis component and air is introduced to delay the p-xylene pumping up to the time (calculated) at which the initially charged p-xylene can be converted. Under these modified operating conditions, the temperature of the stirred zone is not controlled to the planned 217 ° C, but rather to a temperature significantly lower or higher than this temperature. In addition, the production of carbon oxides and the fluctuating oxygen content in the flue gas (which not only means poor control of the reaction temperature, but also mean that the oxygen concentration in the oxidation zone is too high or too low by air insertion) are constant. It was. The adverse effect of controlling the reactivity and the constant temperature is that it forms aromatic products and by-products in concentrations that will significantly reduce the desired rate of oxidation to TA.

The temperature of the reflux condenser was increased for the oxidation of Comparative Example II to remove water as a byproduct in the gas-vapor mixture at a temperature of 121 ° C. and maintain the water concentration in the solvent system at 10%.

However, p-xylene (908g) was prefilled again.

However, because the temperature of the oxidation zone was circulated again, constant temperature of 218 ° C could not be maintained and oxygen consumption was generally low.

Oxidation zone temperature was up to 226.5 ℃ and oxygen consumption was sharply increased at this temperature, it can be seen that the oxygen content outside the exhaust gas is enhanced to 75% in the premises.

In addition, p-xylene condensate was accumulated in the cooling trap in front of the exhaust gas sampling and analysis device. Therefore, most p-xylene evaporated and did not oxidize into the oxidation zone maintained at a pressure of 14.06 kg / cm ² . Close control of the reaction temperature was not possible because the temperature of the reflux condenser could not be maintained.

To implement Example 15, the operating temperature of the reflux condenser is maintained by water heated with an adjustable vapor stream added to a mechanism for inserting hot water into the chiller.

In this way, the temperature of the reflux cooler can be controlled closely in the range of 121 ± 0.5 ° C. Proximity control of the reflux cooler operation temperature and the indicated reaction zone pressure are used to achieve close control of the reaction temperature at 226.5 ° C. and oxygen consumption is normal.

In the above-described embodiment, m-xylene may be substituted for p-xylene to similarly produce high color and high purity isophthalic acid in 85-95 benzoic acid and 15-5% water system.

Claims (1)

Oxidation zone heated to 275 ° C in the presence of a monocarboxylic acid solution of a catalyst component consisting of one or more transition metal oxidation catalysts and bromine source, maintained in the liquid phase at an elevated temperature of 275 ° C by the elevated oxidation zone pressure In the process for producing meta or paraphthalic acid by oxidizing m- or p-xylene with air at 85 to 97% by weight of benzoic acid and 15 to 3% by weight of water, and the pressure of the oxidation zone is 6 to By maintaining the temperature at 25 kg / cm ² and cooling the exhaust gas from the oxidation zone, condensation of the benzoic acid in the reflux solution, removal of by-product water with steam, and the amount of water recycled to the oxidation zone, the temperature at which the oxidation zone is selected By varying the temperature within ± 5 ° C. from the range of ± 5 ° C. to manganese or cobalt and as transition metal components in a solvent system consisting primarily of liquid benzoic acid and water. M- or p at the temperature of the oxidation zone where either of the cerium is maintained almost constant at a predetermined temperature within the temperature range of 175 to 235 ° C. in the stirred oxidation zone containing the catalytic material in which the combination of water and manganese is used. -Xylene is air oxidized in a semi-continuous or continuous process, in which the weight ratio of solvent / xylene in the oxidation zone is in the range of 2 to 10: 1.0, and the catalyst component in the solvent system is the weight ratio of bromine / total metal to 1 weight of total metal. Bromine per 0.5 to 2.5 parts by weight while maintaining the range of 0.2 to 1.5% by weight of total metals and 0.2 to 1.5% by weight of bromine, based on xylene, the ratio of air / xylene charged in this reaction zone Method for producing meta or paraphthalic acid, characterized in that the oxygen content in the exhaust gas from the 3 to 10% by volume.