JP2879925B2 - Purification method of crude isophthalic acid - Google Patents

Description

The present invention relates generally to a method for catalytically purifying crude isophthalic acid and the catalyst system used therein, and more particularly to palladium-, platinum-, rhodium-,
It relates to the use in such a purification process of a catalyst bed consisting of a Group VIII noble metal component containing at least two of the ruthenium-, osmium- and iridium-containing components.

Polymer grade or "purified" isophthalic acid is one of the starting materials used in the production of unsaturated polyesters. Purified isophthalic acid is of relatively low purity industrial grade or "crude"
Meye on purification of crude terephthalic acid from isophthalic acid
No. 3,584,039 or Steck et al., U.S. Pat.
It is obtained by purifying using a noble metal catalyst of the type described in 4,405,809 and hydrogen. In this purification step, the crude isophthalic acid is dissolved in water at an elevated temperature and the resulting solution is preferably purified on a carbon support, as described in Pohlmann U.S. Pat.No. 3,726,915 for the purification of crude terephthalic acid. The hydrogenation is carried out in the presence of a hydrogenation catalyst containing the above precious metal, typically palladium. This hydrogenation step converts the various colored bodies present in the crude isophthalic acid into colorless products.

However, even after said purification, the purified isophthalic acid product contains colored bodies. It is therefore highly desirable to reduce the concentration of such colorants remaining in purified isophthalic acid. The color level of the purified isophthalic acid product is generally measured directly by measuring the optical density of a solution of the purified isophthalic acid or by measuring the b ^* -value of the solid purified isophthalic acid itself. The optical density of the purified isophthalic acid is 340 of its basic solution in a solvent such as sodium hydroxide or ammonium hydroxide.
And measured as absorbance at 400 nanometers (nm).

The measurement of the b ^* -value of a solid on the Hunter Colora Scale is based on Hunter's The Measurement.
of Appearance , Chapter 8, pp. 102-132 John Wiley & Son
Color Sci, such as s, NY, NY (1975), and Wyszecki
ence, Concepts and Methods, Quantitative Data and Fo
rmulae , 2nd edition, pp. 166-168, John Wiley & Sons,
NY, NY (1982).

More specifically, the b ^* -value of the purified isophthalic acid is determined, for example, by using a Diano Match Scan Spectrometer.
rophotometer) can be measured as follows.
The purified isophthalic acid is compressed into a pellet having a thickness of about 0.25 inches and a diameter of about 1 inch. The pellet was then irradiated with white light whose UV was removed by a filter. The spectrum of the visible light reflected from the sample was measured and the tristimulus values (X, Y and Z) were measured using a ClE Standard Obse
rver) is calculated using the function. Using the equidistant wavelength method, the tristimulus value is obtained from the following equation.

Where R _λ is the reflectance% of the object at wavelength λ, and
_λ , _λ , and _λ are ClE illuminants (CIE lllum
inant) Standard observer function at wavelength λ of D65. The color of the object is identified by a mixture of primary lights whose tristimulus values X, Y and Z visually match. However, tristimulus values are limited in their use as color standards.
This is because they do not correspond to visually meaningful counts of color appearance and the color spacing is not uniform compared to visual differences. As a result, the "Uniform Color Scale" (UCS) was adopted. It uses a simple equation to approximate the visual response. This UCS scale used by the Diano instrument provides tristimulus values for L ^* , a ^* , and b ^* − as shown below.
This is a CIE 1976 L ^* a ^* b ^* expression to be converted into a value.

The L ^* -value is a measure of the lightness or whiteness of an object where L ^* = 100 is pure white, L ^* = 0 is black and the middle is gray. This L ^* -value is exactly the tristimulus value Y
Is a function of. The b ^* -value is a measure of the yellowness-blueness count where a positive b ^* -value represents a yellow appearance and a negative b ^* -value represents a blue appearance. This b ^* -value is a function of both tristimulus values Y and Z.

In addition, even after purification, the purified isophthalic acid product often contains impurities,
About 390 and 40 when excited at ~ 320 nanometer wavelength
It fluoresces at a wavelength of 0 nanometers. It would be highly desirable to further reduce such fluorescence of the purified isophthalic acid product. Since the concentration of such impurities in purified isophthalic acid can vary considerably, specifications are often set for the amount of such fluorescence that can be tolerated in a purified isophthalic acid product. The problem of controlling such fluorescence by purified isophthalic acid is complicated. This is because some of the fluorescent impurities are soluble and can be removed by conventional isophthalic acid purification procedures, while other fluorescent impurities are insoluble and cannot be removed by such conventional procedures. Moreover, when chemically reduced during the purification of crude isophthalic acid, some impurities that do not fluoresce at wavelengths of 390 and 400 nanometers when excited at wavelengths of 260-320 nanometers. Converted to their reduced form,
39 when excited by a wavelength of 260-320 nanometers
Fluorescent at 0 and 400 nanometers.

U.S. Pat.Nos. 4,394,299 and 4,467,110 to Puskas et al.
The publication discloses the use of a combined noble metal catalyst on a porous carbonaceous surface, such as a palladium / rhodium catalyst, for the purification of aqueous terephthalic acid solutions. The two patents are also suitable for the use of a rhodium / carbon catalyst under reducing conditions and for the purification of terephthalic acid by converting the main impurity 4-carboxybenzaldehyde to p-toluic acid by hydrogenation. Have activity and selectivity
A variety of previously known processes for preparing Group VIII metal catalysts are outlined.

Now, palladium-, platinum-, rhodium-, ruthenium-, osmium- supported on activated carbon carrier particles
And a metal component containing at least two of the iridium-containing components used in the purification of the crude isophthalic acid described above, and passing an aqueous solution of the crude isophthalic acid through the bed of catalyst particles yields purified isophthalic acid. It has been found that the concentration of the colorant and the concentration of fluorescent impurities in the acid product are further reduced as compared to using a conventional palladium / carbon catalyst alone.

The present invention provides for purifying crude isophthalic acid in the presence of hydrogen at a temperature of from about 100 ° C. to about 300 ° C. and a pressure sufficient to maintain the solution in a substantially liquid phase. And passing it through a granular catalyst bed, wherein the granular catalyst bed has at least two of the palladium-, platinum-, rhodium-, ruthenium-, osmium- and iridium-containing components supported on activated carbon support particles. Comprising a seed-containing Group VIII noble metal-containing component, and separating the resulting hydrogenated aqueous solution from the solution by cooling and crystallizing the purified isophthalic acid. .

The process according to the invention is particularly suitable for the purification of crude isophthalic acid produced by continuous liquid-phase oxidation of m-xylene in a solvent with a catalyst, a solvent suitable for use in the catalytic liquid-phase oxidation of m-xylene. Is any aliphatic C ₂ ~
C ₆ monocarboxylic acids such as acetic acid, propionic acid, n- butyric acid, isobutyric acid, n- valeric acid, trimethylacetic acid and caproic acid, and water and mixtures thereof.
A mixture of acetic acid and water is preferred as the solvent, more preferably a mixture containing 1 to 20% by weight of water when introduced into the oxidation reactor. Since the heat generated in the highly exothermic liquid phase oxidation is at least partially dissipated by the vaporization of the solvent in the oxidation reactor, some of the solvent is removed from the reactor as vapor, which is then removed. It is condensed and recycled to the reactor. In addition, some of the solvent is removed from the reactor as a liquid in the product stream. After separating the crude isophthalic acid product from the product stream, typically at least a portion of the mother liquor (solvent) in the product stream is recycled to the reactor.

The oxygen content of the molecular oxygen source used in the oxidation step in the production of purified isophthalic acid can vary from oxygen content in air to oxygen gas. The preferred source of molecular oxygen is air. In order to avoid the formation of explosive mixtures, the oxygen-containing gas introduced into the reactor is 0.5 to 8% by volume
An exhaust gas-steam mixture containing oxygen (measured on a solvent-free basis) should be produced.

For example, by selecting an oxygen-containing gas supply rate sufficient to provide an amount of 1.5 to 2.8 moles of oxygen per methyl group, the gas-vapor mixture in the condenser can be reduced to such a 0.5-2.5 mole ratio.
Will have 8% by volume oxygen (measured based on no solvent).

The catalyst used in the oxidation step in the production of crude isophthalic acid consists of the cobalt, manganese and bromine components and may additionally contain promoters known in the art. In the liquid phase oxidation, the weight ratio of cobalt (calculated as elemental cobalt) to m-xylene in the cobalt component of the catalyst is from about 0.2 to about 1 per gram mole of m-xylene.
It is in the range of 0 milligram atoms (mga). In liquid phase oxidation, the weight ratio of manganese in the manganese component of the catalyst to cobalt in the cobalt component of the catalyst (calculated as elemental cobalt) (calculated as elemental manganese) was 1 mg of cobalt.
Within the range of about 0.2 to about 10 mga per gram. In liquid phase oxidation, the weight ratio of bromine in the bromine component of the catalyst to the total cobalt and manganese in the cobalt and manganese components of the catalyst (calculated as elemental cobalt and elemental manganese) (calculated as elemental bromine) is the total cobalt and manganese. Is in the range of about 0.2 to about 1.5 mga / mg.

Each of the cobalt and manganese components can be provided in any known ionic or combined form thereof that can provide a soluble form of cobalt, manganese and bromine in the reactor solvent. For example, if the solvent is an acetic acid medium, carbonate and / or manganese carbonate, acetate tetrahydrate, and / or bromide may be used. By using a suitable bromine source, the atomic ratio of bromine to milligrams of total cobalt and manganese is 0.2: 1.
0-1.5: 1.0 is obtained. Such bromine sources include elemental bromine (Br ₂ ) or ionic bromides (eg, HBr, NaB
r, KBr, NH ₄ Br, etc.) or an organic bromide known to release bromide ions at the oxidation operation temperature (eg, bromobenzene, benzyl bromide, mono-bromide).
And di-bromoacetic acid, bromoacetyl bromide, tetrabromoethane, ethylene-di-bromite, etc.). Total bromine in molecular bromine and ionic bromide is used to determine the atomic ratio of elemental bromine to total cobalt and manganese milligrams from 0.2: 1.0 to 1.5: 1.0. The bromide ions released from the organic bromide under the oxidizing conditions can be easily determined by known fractionation methods. For example,
Tetrabromoethane has been found to produce about 3 gram atoms of available bromine per gram mole at operating temperatures of 170 ° C to 225 ° C.

In operation, the minimum pressure maintained in the oxidation reactor is m
The pressure at which xylene and at least 70% of the solvent are kept substantially in the liquid phase. Solvents and m-xylene which are not in the liquid phase due to vaporization are removed from the oxidation reactor as a vapor-gas mixture, condensed and then returned to the oxidation reactor.
The solvent is acetic acid - if water mixture, suitable reaction gauge pressures in the oxidation reactor is about 0 kg / cm ² from about 35 kg / cm ² and typically about 10 kg / cm ² to about 30kg / cm ² It is.
The temperature in the oxidation reactor is generally about 120 ° C, preferably about 150 ° C.
C to about 240C. The solvent residence time in the oxidation reactor is generally from about 20 to about 150 minutes, preferably about 3
0 to about 120 minutes.

The resulting product is a relatively impure or crude slurry of isophthalic acid containing relatively large amounts of impurities such as 3-carboxybenzaldehyde, which may be present up to about 10,000 ppm by weight of isophthalic acid. These impurities can adversely affect the isophthalic acid polymerization reaction to produce unsaturated polyesters and can cause unwanted coloration in the unsaturated polyester polymer formed.

The specific method of the present invention is carried out at an elevated temperature and pressure in a fixed catalyst bed. Either a downstream reactor or an upward reactor can be used. The crude isophthalic acid to be purified is dissolved in water or a similar polar solvent. Water is preferred. However, as other suitable polar solvents, relatively low molecular weight alkyl carboxylic acids can be used alone or mixed with water. Hydrogenation of 3-carboxybenzaldehyde to m-toluic acid is one of the major reactions that takes place in the catalyst bed.

The reactor temperature during the purification, and thus the temperature of the isophthalic acid solution, can be from about 100 ° C (about 212 ° F) to about 300 ° C (about 572 ° F). Preferred temperatures are from about 200 ° C (about 392 ° F) to about
250 ° C (about 482 ° F).

The pressure condition of the reactor depends primarily on the temperature at which the purification operation is performed. Since the temperature at which practical amounts of impure isophthalic acid can be dissolved is substantially higher than the normal boiling point of the polar solvent, the pressure of this process is necessary to keep the isophthalic acid solution in the liquid phase. Significantly higher than the atmospheric pressure. If the reactor has a headspace, the reactor pressure can be maintained by gaseous hydrogen alone or a mixture of it with an inert gas such as steam and / or nitrogen in the headspace. The use of an inert gas mixed with hydrogen can provide a convenient means of adjusting the reactor hydrogen partial pressure, especially when the hydrogen partial pressure is relatively low. For this purpose, it is preferred to mix the inert gas with hydrogen prior to introduction into the reactor. Generally, the reactor pressure during hydrogenation is from about 689.5 kPa to about 6895 hPa (about 100 to about 10
00 psig), usually about 2068.5 to about 3102.75 kPa (about 300
~ 450 psig).

The hydrogenation reactor can be operated in several ways. For example, a predetermined liquid level can be maintained in the reactor,
The hydrogen can then be supplied at a rate sufficient to maintain a predetermined liquid level. The difference between the actual reactor pressure and the vapor pressure of the isophthalic acid solution present is the hydrogen partial pressure in the reactor vapor space. Alternatively, if hydrogen is supplied as a mixture with an inert gas such as nitrogen, the difference between the actual reactor pressure and the vapor pressure of the isophthalic acid solution present is the partial pressure of hydrogen and the inert gas mixed therewith. Is the sum. In this case, the hydrogen partial pressure can be calculated from the known relative amounts of hydrogen and inert gas present in the mixture.

In a mode of operation in which the process is controlled by adjusting the partial pressure of hydrogen, the partial pressure of hydrogen in the reactor depends on the operating pressure of the reactor, the degree of contamination of impure isophthalic acid, the activity and lifetime of the individual catalyst used. About 68.95 kPa (about 10 psi) to about 1379 kPa, depending on pressure and other operating conditions.
(About 200 psi) or more.

Suitable palladium / carbon catalysts are described, for example, by Engelhard Corp.
oration, Newark, New Jersey, `` Palladium on Activ
ated Carbon Granules (Carbon Code CG-5) ". Similarly, suitable rhodium / carbon catalysts
Engelhard Corporation says `` Rhodium on Activated Ca
rbon Granules (Carbon Code CG-5) "and" Rhodi
um on Activated Carbon Granules (Carbon Code CG-2
1) Available under the name. Both of these rhodium / carbon catalysts have an N ₂ BET surface area of about 1000 m ² / gram and a particle size of 4 × 8 mesh in the US sieve series. Other suitable rhodium / carbon and palladium / carbon catalysts having similar dimensions and surface area are available from Johnson Ma
tthey Inc. from Seabrook, New Hampshire, `` 11766 Rhodiu
m, 1% on Steam Activated Carbon Granules, Anhydrou
available under the name "s". Similarly, suitable ruthenium / carbon, platinum / carbon and iridium / carbon catalysts are also commercially available.

The catalyst support is activated carbon, typically having a surface area of at least about 60.
_{^{0m 2 / g (N 2:}} BET method) preferably about 800 m ² / g to about 1500 m ² / g
Of coconut charcoal in the form of granules having However, other porous carbonaceous supports or substrates can be used as long as the surface area requirements are met. In addition to coconut charcoal, activated carbon from other plants or from animal sources can also be utilized.

The loading on each of the palladium, ruthenium, rhodium, platinum, osmium or iridium supports used is from about 0.01 to about 2% by weight, based on the total weight of catalyst or metal plus activated carbon support and calculated as elemental metal. . The loading of each catalytic metal used is preferably about 0.5% by weight.

In one embodiment of the method of the present invention, the Group VIII noble metal-containing component is supported on the same activated carbon carrier particles,
Each of the Group VIII noble metal-containing components is substantially uniformly distributed throughout the catalyst bed. In this embodiment, the individual activated carbon support particles contain all of the Group VIII noble metal-containing components, and the relative amount of Group VIII noble metal in the catalyst bed is the relative amount of the two Group VIII noble metals on each catalyst particle. Is adjusted by

Alternatively, one of the group VIII noble metal-containing components is supported on a first activated carbon carrier particle group, and the second group VIII noble metal-containing component is supported on a second activated carbon carrier particle group. And it is also preferable that the first particle group is separated and distinguished from the second particle group. In this embodiment, the particular activated carbon support particles contain only one of the Group VIII noble metal-containing components, and the relative amount of Group VIII noble metal in the catalyst bed depends on the Group VIII noble metal-containing component used in each group of activated carbon support particles. It is adjusted either by the relative amounts of the components or by the relative amounts of activated carbon carrier particles used in each group of activated carbon carrier particles. In this embodiment, when each of the first group and the second group of the activated carbon carrier particles is uniformly distributed throughout the catalyst bed,
The Group VIII noble metal-containing component is also uniformly distributed throughout the catalyst bed. Alternatively, in this embodiment, the catalyst bed is layered and (1) at least one layer containing substantially only the first group of particles and (2) substantially containing only the second group of particles. It may have at least one layer, and therefore the Group VIII noble metal-containing component may not be evenly distributed throughout the catalyst bed.

In this latter layered bed, the aqueous solution of isophthalic acid is
First passing through a first layer consisting essentially of only said first group of particles containing only the Group VIII noble metal-containing component and then from only said second group of particles containing only the second Group VIII noble metal-containing component Pass through a second layer that is substantially substantive. Typically, the weight ratio of the first layer to the second layer is about 1: 100, preferably about 1:20
To about 1: 2, preferably up to about 1: 4. Similarly, the residence time of the aqueous isophthalic acid solution in the first layer is from about 1: 2 to about 1: 100 of the total residence time of the solution in the catalyst bed. The aqueous solution is then removed directly from the catalyst bed or, for example,
A third particle group consisting essentially of only the first particle group containing only the group VIII noble metal-containing component or a third group consisting essentially of only the third particle group containing the third group VIII noble metal-containing component
Remove after passing the aqueous solution through the layer.

The invention will be more clearly understood from the following detailed examples.

Examples 1-3 In each of Examples 1-3, a down-flow pilot plant reactor with a fixed catalyst bed of 2.54 cm (1 inch) in diameter and 16.51 cm (6.5 inches) in length was used.
The catalyst bed consisted of the commercial granular palladium / carbon catalyst (40 g, 0.5 wt% Pd, Engelhard) alone in Example 1,
Examples 2 and 3 consisted of a granular layer of this rhodium / carbon catalyst (4 g, 0.5 wt% Rh) and a granular layer of the same commercially available palladium / carbon catalyst (36 g). In Example 2, the palladium / carbon catalyst was in the upper layer, and in Example 3, the rhodium / carbon catalyst was in the upper layer.

The rhodium / carbon catalyst uses rhodium nitrate as a precursor and follows the procedure described in U.S. Pat. No. 4,728,630 and employs North American activated carbon as a support.
Prepared at pH 2 in water using G201. All catalysts were washed hot and aged for 72 hours in an autoclave in the presence of terephthalic acid and hydrogen. The reactor is about 221 ° C
(430 ° F) and a hydrogen partial pressure of about 275.8 kPa (about 40 psi). The total reactor pressure is about 2620.1 kPa (about 380 psi) each.
g). A crude isophthalic acid slurry containing about 20% by weight of isophthalic acid was fed to the reactor at a solution feed rate of 1.8 kg per hour. B ^* -of the purified isophthalic acid obtained
The values, fluorescence index, and optical densities at 340 and 400 nm were measured and the results are shown in Table 1 below.

Table 1 Example 1 Example 2 Example 3 b ^* -value 1.28 1.08 0.87 Fluorescence index 0.39 0.37 0.36 Optical density at 340 nm 0.81 0.62 0.56 Optical density at 400 nm 0.096 0.066 0.033 In the examples, only certain aspects were used. Although not shown, it is apparent that alternatives and various modifications would be apparent to those skilled in the art. These alternatives are equivalent to the present invention and fall within the spirit and scope of the present invention.

Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) C07C 63/24 C07C 51/487 C07C 51/43 C07B 61/00 B01J 23/40 WPI (DIALOG) EPAT (QUESTEL)

Claims (9)

(57) [Claims] 1. A solution of crude isophthalic acid in a polar solvent at 100 ° C.
At a temperature of 300300 ° C. and a pressure sufficient to keep the solution substantially in the liquid phase, it is passed through a granular catalyst bed in the presence of hydrogen, said granular catalyst bed being palladium-, platinum- A rhodium-, osmium- and iridium-containing component comprising a Group VIII noble metal-containing component comprising at least two, wherein the first Group VIII noble metal-containing component is supported on a first group of activated carbon carrier particles; Then, the second Group VIII noble metal-containing component is supported on the activated carbon carrier particles of the second group, and then the purified hydrogenated solution is cooled to produce purified isophthalic acid by crystallization from the solution. A method for purifying crude isophthalic acid, comprising separating. 2. A catalyst bed comprising at least one layer comprising only a first group of activated carbon support particles, and at least one layer comprising substantially only a second group of activated carbon support particles. The method of claim 1 having one layer. 3. The solution is first passed through a first layer containing substantially only the first group of activated carbon carrier particles and then through a second layer containing substantially only the second group of activated carbon carrier particles. The method of claim 2. 4. The third group of particles containing substantially the first group of activated carbon support particles or the third Group VIII noble metal-containing component after the solution has passed through the second layer and before being recovered from the catalyst bed. 4. The method of claim 3, wherein the third layer contains only one of the following. 5. The process according to claim 1, wherein the space velocity of the isophthalic acid solution passing through the catalyst bed is between 5 hr ^{-1 and} 25 hr ^-1 . 6. The process according to claim 5, wherein the residence time of the isophthalic acid solution in the first layer is 1: 100 to 1: 2 of the total residence time of the isophthalic acid solution in the catalyst bed. 7. The process of claim 1 wherein each of the Group VIII noble metals is present in the catalyst bed at the same or different concentrations, calculated as elemental metals, ranging from 0.01 to 2% by weight, based on the weight of the catalyst bed. 8. The process according to claim 1, wherein the two Group VIII noble metals are present in the catalyst bed in an atomic ratio calculated as elemental metal in the range from 1: 100 to 1: 1. 9. The method according to claim 1, wherein water is a polar solvent.