A method of obtaining a purified terephthalic acid (options)

 

(57) Abstract:

A method of obtaining a purified terephthalic acid, comprising the catalytic oxidation of para-xylene in the liquid phase with the aim of obtaining crude terephthalic acid containing 4-carboxybenzene as the main impurity and processing of crude terephthalic acid with hydrogen in the presence of a hydrogenation catalyst in the reaction vessel, resulting purified terephthalic acid containing 4-carboxybenzene in the number of fixed limit stationary manner, which involves improvement, which enables processing with rapid achievement of steady state after partial replacement of the deactivated catalyst to a new catalyst. This improvement consists in applying to the reactor crude terephthalic acid containing 4-carboxybenzene in excess of the amount in the steady state processing, and the processing of terephthalic acid up until this processing does not reach steady state. 2 S. and 3 C. p. F.-ly, 1 table.

The invention concerns a method of obtaining purified terephthalic acid. In particular, it relates to a impurity in the number of fixed small limit, stationary reception.

Purified terephthalic acid is required for the manufacture of polyester fibers. Such purified terephthalic acid previously received, for example, by the method described in Japan patent N 4116860. According to this method, the para-xylene catalytically oxidized in the liquid phase with the formation of crude terephthalic acid, usually containing 4-carboxybenzene as the main impurity in an amount of 0.1 to 4 wt. and this crude terephthalic acid is then fed in the form of an aqueous suspension in the reaction vessel and turns into an aqueous solution at high temperature and pressure and is processed by hydrogenation catalyst, for example a granular palladium catalyst on a carrier of activated carbon. When performing the processing of crude terephthalic acid stationary obtained purified terephthalic acid usually contains 1 to 25 hours/million 4-carboxybenzene.

However, the efficiency of processing of crude terephthalic acid to hydrogenation of 4-carboxybenzene into a pair methylbenzoic acid decreases with time during the above process of obtaining purified terephthalic acid for various reasons, mainly the certain time intervals during the process.

Typically, the hydrogenation catalyst has a high initial activity. So, when implementing the above-mentioned process of obtaining purified terephthalic acid, when the catalyst is deactivated and the deactivated catalyst is completely replaced by a new catalyst, the formation of undesirable side products in the violent reaction of the hydrogenation, but along with it an excessive amount of 4-carboxybenzene is reduced, thereby causing a decrease in the stability of the purity of the obtained terephthalic acid. Moreover, when you start processing raw terephthalic acid is adsorbed on charcoal catalyst, resulting in heat, and thus the catalyst tends to the destruction with the formation of separate pieces. This destroyed the catalyst can be mixed with the resulting terephthalic acid. Way, providing increased service life of the hydrogenation catalyst used in this process is described in the patent GDR N 212162 in which the deactivated catalyst in the reaction vessel is not completely replaced by a new and only partially updated, and detectiveagency catalyst is used again as such is th way can be increased service life of a small amount of catalyst, but it takes considerable time to have reached a stationary state in which the processing of crude terephthalic acid provides a stationary receiving purified terephthalic acid containing 4-carboxybenzene in a small quantity of the fixed limit after a partial update of the catalyst. Such a long time to achieve steady state leads to a significant loss of raw materials, as well as to undesirable obtaining terephthalic acid, does not meet the standard.

Thus, the object of the invention is an improved method of producing purified terephthalic acid, which includes the processing of crude terephthalic acid with hydrogen in the presence of a hydrogenation catalyst, the improvement, which enables the processing to achieve the stationary state immediately after partial replacement of the catalyst.

According to the invention provides an improved method of producing purified terephthalic acid, which comprises the catalytic oxidation of para-xylene in a liquid phase to obtain a crude terephthalic acid containing 4-carboxybenzene the organizations in the reaction vessel, the resulting purified terephthalic acid containing 4-carboxybenzene in the number of fixed limit, a stationary manner at a temperature within 255-300oC and a pressure of 10-110 kg/cm at a partial hydrogen pressure of 0.5-20 kg/cm, where the specified improvement is a partial replacement of the catalyst in the reaction vessel, when the catalyst is deactivated, a new catalyst, and subsequent submission to the reactor crude terephthalic acid containing 4-carboxybenzene more than in the steady state processing, to re-start processing of crude terephthalic acid, and treating this as terephthalic acid until then, until a stationary state is achieved.

Also provides an additional improvement of the method, which is a partial replacement of the catalyst in the reaction vessel, when the catalyst is deactivated, the new catalyst and subsequent treatment of the crude terephthalic acid at a partial pressure of hydrogen is smaller than the partial pressure in a stationary state.

In the description of the invention under the stationary condition of the processing, there is traveling acids, contains 4-carboxybenzene in a small quantity of the fixed limit, in the processing of crude terephthalic acid containing 4-carboxybenzene, as the main impurity, hydrogen in the presence of a hydrogenation catalyst to obtain the purified terephthalic acid. Crude terephthalic acid obtained by the catalytic oxidation of para-xylene in the liquid phase.

Deactivation of the hydrogenation catalyst can be detected by the increase in the content of 4-carboxybenzene in the resulting purified terephthalic acid. In addition, the quality of the formed terephthalic acid is usually associated with the transmission coefficient at 340 nm. So, when industrial production of purified terephthalic acid purity terephthalic acid as the final product is determined by the content of 4-carboxybenzene and transmittance at 340 nm. These control values are stored for a fixed period of time, when you are processing a stationary manner. When these control values beyond a fixed limit, it is necessary that the catalyst in the reaction vessel was partially replaced by a new catalyst to increase effective the first acid is limited, the obtained purified terephthalic acid usually has a very small content of 4-carboxybenzene due to the high activity of the catalyst, and in accordance with that obtained purified terephthalic acid has a high transmittance at 340 nm.

Although it depends on the degree of deactivation of the catalyst, usually replaced by a new 20-70% of the deactivated catalyst in the reaction vessel.

After the deactivated catalyst in the reaction vessel is partially replaced by a new one as stated above, in the reaction vessel is introduced aqueous slurry of crude terephthalic acid and turns into an aqueous solution when exposed to high temperature and high pressure to re-start processing.

According to the invention the crude terephthalic acid containing 4-carboxybenzene in greater numbers than in the steady state, is fed into the reaction vessel, after which the reaction is stabilized until then, until a stationary state is achieved. As a possible variant, the reaction is carried out at a partial pressure of hydrogen is smaller than the partial pressure in the steady state. Crude terephthalic acid containing 4 the UD and processed at a partial pressure of hydrogen is smaller than the partial pressure in the steady state, up until not reached a stationary state of the reaction. This procedure reduces the time during which the reaction reaches steady state.

In the steady state processing of crude terephthalic acid is usually served in the reaction vessel in the form of an aqueous solution containing 24-30 wt. terephthalic acid. Hydrogenation treatment is usually performed at 255-300oC under pressure 10-110 kg/cm3and at a partial hydrogen pressure of 0.5-20 kg/cm2.

Used the hydrogenation catalyst includes, for example, palladium, ruthenium, rhodium, Osmi, iridium, platinum, platinum black, palladium black, iron or cobalt-Nickel, and each of them is applied to the activated carbon.

First reaction takes place, which is deactivated hydrogenation catalyst (used in the following example) to illustrate the activity of the catalyst.

The control example 1. Terephthalic acid in the amount of 30 g containing 3600 hours/million (ppm) of 4-carboxybenzene and 210 g of water, is injected into the autoclave with a capacity of 500 ml with 0.3 g of 0.5 wt. palladium on the carrier charcoal, and am, to the partial pressure of hydrogen was 7 kg/cm2(gauge), followed by one-hour processing of crude terephthalic acid.

The obtained purified terephthalic acid contains 400 hours/million 4-carboxybenzene.

Control example 2. 30 g of crude terephthalic acid containing 3600 ppm 4-carboxybenzene and 210 g of water, placed in an autoclave with a capacity of 500 ml with 0.3 g of 0.5% by weight of rhodium deposited on activated carbon, and the mixture is stirred while heating to 280oC. Then, to the autoclave, hydrogen is introduced to achieve a partial hydrogen pressure of 7 kg/cm2and processing of crude terephthalic acid are within one hours.

The obtained purified terephthalic acid contains 400 ppm of 4-carboxybenzene.

In the following examples, the deactivated catalyst is partially updated, and processed within one hour of crude terephthalic acid containing various amounts of 4-carboxybenzene and/or at different partial pressures of hydrogen to hydrogenation of 4-carboxybenzene.

Then checked, is there a stationary state when the specified Vasilevo acid. It can be assumed that in these examples, the stationary state is achieved when the content of 4-carboxybenzene and the resulting purified terephthalic acid is in the range of 10 to 12 hours/million, as illustrated below by examples 4 and 8.

Example 1. A mixture of 0.03 g of the same deactivated catalyst, and the control reference example 1, and 0.27 g of the new catalyst is used for processing as a catalyst for hydrogenation.

30 g of crude terephthalic acid containing 3600 hours/million 4-carboxybenzene and 210 g of water, is injected into the autoclave with a capacity of 500 ml with 0.3 g of the above catalyst, and the mixture is heated to 280oC with simultaneous stirring. Then in the autoclave, hydrogen is introduced so that the partial pressure of hydrogen was 2 kg/cm2(manometric.), followed by one-hour treatment.

The obtained purified terephthalic acid contains 10 hours/million 4-carboxybenzene.

Examples 2-9. Using 0.3 g of a mixture of the same deactivated catalyst that was used in the control example 1, and a new catalyst in the ratio given in the table, carry out the processing of crude terephthalic acid in the same obrazovanshchina and/or at different partial pressures of hydrogen to hydrogenation of 4-carboxybenzene.

Contents 4-carboxybenzene in the resulting purified terephthalic acid indicated in the table.

Examples 10-13. The reaction was carried out under the same conditions as in the previous examples, except that as the catalyst was used rhodium deposited on activated carbon. The results are presented in the table.

The procedures described in examples 1-3, is processed at a lower partial pressure of hydrogen (2.4 mg/cm2the gauge.), than the partial pressure of hydrogen (11 kg/cm2the gauge.) in the steady state (as in example 4, in which the crude terephthalic acid contains 3600 hours/million 4-carboxybenzene, and the resulting purified terephthalic acid contains 10-12 hours/million 4-carboxymethylthio).

Thus, examples 1-3 illustrate that the terephthalic acid of the same quality as in a stationary state is obtained within one hour after the re-start processing. In accordance with this, the partial pressure of hydrogen may be further increased to 11 kg/cm2(the gauge.) with the implementation of processing a stationary manner.

In examples 1-4 shows the progression of deactivation of the catalyst during the processing begins again at a lower partial pressure of hydrogen, than the partial pressure of hydrogen in a stationary state.

The procedures described in examples 5-7, is processed at a lower partial pressure of hydrogen (2-5 kg/cm2the gauge.), than the partial pressure of hydrogen (11 kg/cm2the gauge.) in the steady state (as in example 8, in which the crude terephthalic acid contains 2400 hours/million 4-carboxymethylthio).

So, examples 5-7 illustrate that terephthalic acid is of the same quality as when processing in a stationary state is obtained within one hour after the re-start processing. Next, the partial pressure of hydrogen can be increased up to 11 kg/cm2the gauge. while the content of 4-carboxybenzene in the crude terephthalic acid is reduced to 2400 hours /million to implement the processing of a stationary manner as described in example 8.

In examples 5 to 9 shows the progression of deactivation of the catalyst over time. These examples illustrate that the stationary state of the processing of crude terephthalic acid is achieved within one hour, when the processing begins again at a lower partial pressure of hydrogen than the pressure in a stationary state.

the gauge. and 5 kg/cm2the gauge. respectively) than the partial pressure of hydrogen (14 kg/cm2the gauge.) in the steady state (as in the example 12, where the crude terephthalic acid contained 3600 ppm 4-carboxybenzene, and the resulting purified terephthalic acid contained 14 ppm 4-carboxymethylthio).

Thus, examples 10 and 11 illustrate that terephthalic acid is of the same quality as in a stationary state is obtained after one hour after the resumption of processing. Accordingly, the partial pressure of hydrogen may then be increased to 14 kg/cm2the gauge. in order to carry out processing in a stationary state.

Examples 10 to 12 show the benefits from the deactivation of the catalyst over time. These examples illustrate that the stationary state is achieved within one hour, when the processing begins again at a lower partial pressure of hydrogen than the partial pressure of hydrogen in a stationary state.

In example 13, the processing is carried out at a lower partial pressure of hydrogen (5 kg/cm2the gauge. ) than the partial pressure of hydrogen (14 kg/cm2the gauge. in the steady state (as Reptilia acid contained 14 ppm 4-carboxymethylthio), whereas the original crude terephthalic acid contained 4200 ppm 4-carboxybenzene.

Thus, example 13 shows that terephthalic acid is of the same quality as in a stationary state is obtained within one hour after the resumption of processing. After that, the partial pressure of hydrogen can be increased to 14 kg/cm2the gauge. while the content of 4-carboxybenzene in the crude terephthalic acid is reduced to 3600 ppm, and the processing is carried out in a stationary state, as shown in example 12.

Examples 14 and 15. The reaction is carried out analogously to example 1, except that the used catalyst with catalytic value of the deactivated catalyst/catalyst equal to 6:4 (example 14) and 7:5 (example 15). The results obtained are summarized in the table.

Comparative examples 1-7. Using 0.3 g of a mixture of the same deactivated catalyst, as in test example 1, and a new catalyst in the ratio given in the table, carry out the processing of crude terephthalic acid in the same manner as described in example 1 at various partial pressures of hydrogen.

Contents 4-carboxybenzene in about what was found in the same conditions, as in the previous examples, except that as the catalyst was used rhodium deposited on activated carbon. The results are presented in the table.

Comparative examples 1 to 3 correspond to examples 1 to 3 in relation to the deactivation of the catalyst over time and in relation to the content of 4-carboxybenzene in crude terephthalic acid. However, processing is carried out at a partial pressure of hydrogen is not too low compared to the pressure in the steady state, namely, at a partial pressure of 7 kg/cm2. In these comparative examples, the content of 4-carboxybenzene in the resulting acid is very low after one-hour treatment, and a stationary state is not reached within one hour after the re-start processing.

Comparative examples 4 and 5 illustrate the process using more of the deactivated catalyst. In these examples does not work terephthalic acid desired degree of purity due to excessive deactivation of the catalyst.

Comparative examples 6 and 7 correspond to examples 5 and 8. As can be seen from example 5, in contrast to comparative example 6, the stationary state is th acid, when you start processing. However, when the catalyst is more active, as can be seen from comparative example 7, as compared with comparative example 6, the stationary state is not reached.

Comparative example 8 corresponds to example 10 and comes dezaktywizacja catalyst with time and the content of 4-carboxybenzene in crude terephthalic acid. However, processing was carried out at a partial pressure of hydrogen is not too low compared to the pressure in a stationary state, namely at a partial hydrogen pressure of 7 kg/cm2. Accordingly, in comparative example 8 contents 4-carboxybenzene in the obtained terephthalic acid was very low after the one-hour processing, and a stationary state is not reached within one hour after the beginning of processing.

Comparative examples 9 and 10 illustrate the process of using advanced deactivated catalyst. In these examples, terephthalic acid desired degree of purity is not obtained due to excessive deactivation of the catalyst.

The results are shown in the table.

1. A method of obtaining purified of terete is islote, containing as the main impurity 4-carboxybenzene, followed by processing it with hydrogen in the presence of a hydrogenation catalyst in the reactor, to obtain the purified terephthalic acid containing 4-carboxybenzene in the amount established for the stationary condition, in doing so, a partial replacement of the catalyst as it is decontamination, characterized in that the acid treatment with hydrogen is carried out at a temperature of 255 300oC and a pressure of 10 to 110 kg/cm2at a partial hydrogen pressure of 0.5 to 20.0 kg/cm2while partial replacement of the catalyst is conducted at 30 to 95% by mass, and before replacing the catalyst processing the raw acid stop, and after replacement of the catalyst charged to the reactor crude terephthalic acid with 4-carboxybenzene more than its content in Siri teraphtalate acid supplied during steady state, but not more than 10 times, followed by resumption of processing crude acid until then, until a stationary state.

2. A method of obtaining a purified terephthalic acid, comprising the catalytic oxidation of p-xylene in a liquid phase to obtain the crude terephthalic acid is risotti hydrogenation catalyst in the reactor, obtaining purified terephthalic acid containing 4-carboxybenzene in the amount established for the stationary condition, in doing so, a partial replacement of the catalyst as it is decontamination, characterized in that the treatment with hydrogen is carried out at a temperature of 255 300oC and a pressure of 10 to 110 kg/cm2at a partial hydrogen pressure of 0.5 to 20.0 kg/cm2while partial replacement of the catalyst is carried out at 10 to 90% by mass, and before replacing the catalyst processing the raw acid stop, and after replacing the catalyst crude acid again downloads and resume processing at a partial pressure of hydrogen is lower than the partial pressure in the steady state until then, until a stationary state.

3. The method according to p. 2, characterized in that is carried out to replace the deactivated catalyst to a new 20 to 70% by mass.

4. The method according to PP.1 and 2, characterized in that the hydrogenation catalyst is granular palladium on a carrier of activated coal.

5. The method according to p. 1, characterized in that 30 to 70% by weight of the deactivated catalyst is exchanged for a new catalyst.

 

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FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a continuous method for preparing highly pure terephthalic acid. Method involves oxidation of p-xylene with oxygen-containing gas in acetic acid medium in the presence of catalyst comprising heavy metal salts, such as cobalt and manganese and halide compounds under increased pressure and temperature up to the definite degree of conversion of para-xylene to terephthalic acid at the first step and the following two-step additional oxidation of prepared reaction mixture and isolation of the end product. Mixing time of reagents is <25 s, oxidation at the first step is carried out at temperature 180-200°C up to conversion degree of p-xylene 95%, not above, oxidation at the second step is carried out at temperature 175-185°C and before feeding to the third step of oxidation the reaction mass is heated to 200-260°C, kept for 8-12 min and oxidized at temperature 180-200°C in the presence of catalyst comprising Ni and/or Zr salts additionally. As halide compounds method involves using XBr or XBr + XCl wherein X is H, Na, Li followed by isolation of solid products of oxidation after the third step and successive treatment with pure acetic acid and water in the mass ratio terephthalic acid : solvent = 1:3. Invention provides intensification of process and to enhance quality of terephthalic acid.

EFFECT: improved method for preparing.

1 tbl, 1 dwg, 14 ex

FIELD: industrial organic synthesis.

SUBSTANCE: aromatic carboxylic acid is obtained via liquid-phase oxygen-mediated oxidation of initial aromatic mix containing benzene bearing two or three oxidizable substituents in its ring or naphthalene bearing at least one oxidizable substituent in its ring in reaction medium containing initial aromatics, promoter, heavy metal-based catalyst, and solvent containing benzoic acid and about 5 to about 60 wt % water, percentage of solvent in reaction medium ranging from 1 to 40 wt %. Oxidation proceeds in reaction zone of double-phase stream reactor under reaction conditions to produce high-pressure emission gas at 160-230°C in first part of reaction zone and at 180-260°C in second part of reaction zone, while at least part of aromatic acid produced crystallizes from reaction medium in reaction zone. According to second embodiment of invention, aromatic carboxylic acid production process comprises (i) providing reaction mixture containing initial aromatic compound, heavy metal-based catalyst, bromine source, and solvent containing benzoic acid and water, initial aromatic compound being benzene bearing two oxidizable alkyl substituents in m- and/or p-positions of its ring or naphthalene bearing oxidizable alkyl substituents in its ring, percentage of solvent in reaction medium ranging from 1 to 40 wt %; (ii) bringing at least part of reaction medium into contact with oxygen-containing gas in first continuously stirred mixing reactor at 160-230°C to form first high-pressure gas stream and product containing crystalline aromatic dicarboxylic acid in liquid medium containing the same, heavy metal-based catalyst, bromine, water, benzoic acid, intermediate oxidation products, and by-products; and (iii) sending thus obtained product to second continuously stirred mixing reactor, wherein second high-pressure gas stream is formed and at least part thereof contacts with oxygen-containing gas at 180 to 260°C to produce aromatic dicarboxylic acid.

EFFECT: minimized toxic methyl bromide formation.

26 cl, 2 dwg

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