JPS62129248A - Purification of crude terephthalic acid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates generally to processes for the catalytic purification of crude terephthalic acid and catalyst systems used therein, and more particularly to layered catalyst beds and their use in such purification.

Polymer grade or "purified" terephthalic acid is the starting material for polyethylene terephthalate, which is polyester II
Ilt is the principal polymer used in the production of polyester films and resins used in bottles and similar containers. Purified terephthalic acid is produced from relatively impure technical grade or "crude" terephthalic acid, such as U.S. Pat. No. 3,584,039 or U.S. Pat. No. 4,405.

No. 809, it is derived by purification using hydrogen and a noble metal catalyst. In the purification process, crude terephthalic acid is dissolved in water at elevated temperature and the resulting solution is purified according to U.S. Pat.
, 915, preferably in the presence of a hydrogenation catalyst containing a noble metal, typically palladium, on a carbon support. Through this hydrogenation process,
Various colored substances present in the crude terephthalic acid are converted to colorless products.

However, even after purification, the purified terephthalic acid product contains colored substances.

It is highly desirable to reduce the concentration of such colored substances remaining in purified terephthalic acid. The color level of purified terephthalic acid products is generally measured directly, either by measuring the optical density of a solution of purified terephthalic acid or by measuring the b* value of the solid purified terephthalic acid itself. be done. Optics of purified terephthalic acid 11i! 7 degrees of its salt in a solvent such as sodium hydroxide or ammonium hydroxide
It is measured as the absorption of light at 340 tvn in a liquid solution.

Hunter Color Scale (LLlnter Co
The measurement of b"1iff of a solid on
of 8 to DQaranCQ ] , ] Chapter 8, Chapter 10
pp. 2-132, John Wiley & 5ons
, N, Y,.

N, Y., (1975) and Wiszeki-<
Wyszecki J et al.
ce Concept and Methods, Qu
an-titatiVC4oata and FORm
tllaeJ, 2nd edition, pp. 16B-168, John
14i1ey & 5ons, N, “i”,,
N,■,.

(1982).

More specifically, the b9 value of crude terephthalic acid can be determined using, for example, a Dianomatsu scan.

It can be measured using a Hatch 5can) spectrophotometer as follows. That is, crude terephthalic acid is compressed into pellets about 0.25 inches thick and about 1 inch in diameter. The pellet is then illuminated with U.sup.-filtered white light. The spectrum of visible light reflected from the sample is measured and tristimulus values (X, Y
and l) were calculated using the CI [standard observer function.

Using the equally spaced wavelength method, tristimulus values were obtained from the following equation:

where Rλ is the percent reflection of the object at wavelength λ, and y, yλ, and 7λ are standard observer functions at wavelength for CIE emitter D65.

The tristimulus values X, Y, and 2 perceive the color of the object as a mixture of elementary lights that visually match it.

However, tristimulus light has limited use as a color specifying device. This is because it is not related to visually meaningful attributes of color appearance and is not consistent with color fading, which is related to visual differences. In terms of results,
“Uniform color space” (UC3=Uniform color
5 pace) has been adopted using a simple formula that approximates the visual response.

The 008 scale used in the Diano instrument measures the tristimulus value as L.
CIE 1 to convert to *, a and b* as follows:
976L"a"b" type.

Bi=25(100Y/Y) 1/”-16a”
=500[(X/X) =(Y/Y)
]b” = 200 [(V/Y) = (7/Z
) 1L9 is a measure of the brightness or whiteness of an object and is a function of. The b' value is a measure of the yellowness-blueness attribute, with positive b'l representing yellowness, and negative b'
*Values represent blue tint. b” (direct is a function of both tristimulus values Y and Z.

Moreover, even after purification, purified terephthalic acid products often contain impurities that are excited at wavelengths 260-320 jun and emit fluorescence at wavelengths 390-400 jun. Further reduction of such fluorescence in purified terephthal is highly desirable. Because the Q degree of such impurities in purified terephthalic acid can vary significantly, normalization is often made to the range of such fluorescence allowed for purified terephthalic acid products. The problem with controlling such fluorescence with purified terephthalic acid is that while some fluorescent impurities are soluble and can be removed by conventional methods for purifying terephthalic acid, other fluorescent impurities are insoluble. This conventional method cannot eliminate the problem and is therefore complicated. Furthermore, during chemical reduction during the purification of crude terephthalic acid, it is excited at wavelengths between 260 and 320, and is excited at wavelengths between 390 and 400.
Some impurities that do not emit fluorescence of 1■ have a wavelength of 260-320n! Excited by n and wavelength 390 ~
400 tvn are converted to their reduced forms which fluoresce.

Pu5kas et al., U.S. Pat. Discloses the use of catalysts. These 29 patent specifications describe the use of rhodium-on-carbon catalysts under reduced pressure conditions and also the production of terephthalic acid by hydrogenation of 4-carboxybenzaldehyde, the major impurity of terephthalic acid, to p-toluic acid. Various known methods for producing the Vulgaris catalyst (2) with selectivity and activity suitable for acid purification are investigated.

However, since the hydrogenation solubility of p-toluic acid is also greater than that of terephthalic acid, such removal of p-toluic acid is mostly achieved, but in order to recover purified terephthalic acid, When crystallizing a hydrogenated terephthalic acid solution, a considerable amount of p-toluic acid is "trapped" in the purified terephthalic acid crystals.

In order to avoid the drawbacks associated with the separation of p-toluic acid, we carried out the simultaneous hydrogenation of one pure substance that may be present in the aqueous solution of crude terephthalic acid in the presence of a palladium/carbon catalyst. It has been proposed to decarbonylate 4-carboxybenzaldehyde to benzoic acid. This is because benzoic acid is more easily soluble in water than p-toluic acid. See, eg, Olsen US Pat. No. 3,456,001.

However, the above-mentioned decarbonylation of 4-carboxybenzaldehyde to benzoic acid produces equimolar carbon monoxide, a well-known poison for member metals such as palladium (e.g., Kimura et al. (See U.S. Pat. No. 4,201,872).

In an attempt to minimize catalyst poisoning, Kim
propose carrying out the decarbonylation at relatively low process pressures to minimize the dissolved carbon oxide concentration in the liquid reaction-6t#.

Processing pressure must also be controlled within strictly defined pressure ranges. The generated carbon monoxide is purged from the reactants as a gas.

We therefore used a catalyst system consisting of a first layer of catalyst particles containing the above-mentioned crude terephthalic acid supported and a second layer of palladium/carbon catalyst particles. and 1 of p-toluic acid produced during the purification of crude terephthalic acid by passing an aqueous solution of crude terephthalic acid through the first layer of rhodium/carbon catalyst particles and then through the second layer of palladium/carbon catalyst particles. We have found that it is possible to minimize the

Such a process using the above catalyst system does not cause the hydrogenation of 4-carboxybenzaldehyde to p-toluic acid, but instead causes the decarbonylation of 4-carboxybenzaldehyde to benzoic acid;
This or jp- Because it is more soluble in water than toluic acid, p-
It can be separated from terephthalic acid more easily than toluic acid during crystallization. This allows a feed solution with a relatively high 4-carboxybenzaldehyde content n to be achieved without the deleterious effects mentioned above of the dependent catalyst system.

Furthermore, the present inventors believe that a method using the above-mentioned catalyst system is
It has been found that the concentration of colored substances and fluorescent impurities in the resulting purified terephthalic acid is further reduced compared to the use of conventional palladium/carbon catalysts alone.

The present invention contemplates the purification of relatively impure aqueous solutions of crude terephthalic acid by hydrogenation in the presence of multiple noble metal catalysts. The substantial conversion of 4-carboxybenzaldehyde to benzoic acid is carried out in the same reaction vessel where the generated carbon monoxide is converted to hydrocarbon moieties such as methane, ethane, etc.
This is done at the same time as the mold reaction. Terephthalic acid of relatively high purity and having a relatively reduced content of colored substances and fluorescent impurities can be produced in this manner. If desired, the benzoic acid produced can be recovered as a commercially valuable by-product.

According to the invention, a relatively impure aqueous terephthalic acid solution containing preferably up to about 10,0Offlff 1 part of 4-carboxybenzaldehyde per 11 million parts of terephthal is prepared as a liquid containing multiple layers of different hydrogenation catalysts. Hydrogenation takes place in a packed bed of granular catalyst. In the catalyst bed are the oldest members of the periodic table of elements having one electron in their outermost orbit in the ground state: thenium, rhodium and platinum. A second catalyst layer is also present in the catalyst bed downstream of the first layer and contains palladium supported on an activated carbon support.

Hydrogenation is carried out at iU from about 100° C. to about 350° C. and at a pressure sufficient to maintain liquid phase C; typically about 200 psi.
g to about 1500 Psig with the generation of -carbon oxide. The solution of aqueous terephthalic acid to be treated is first passed through the first catalyst layer and then through the second catalyst layer both under reducing conditions, ie in the presence of hydrogen.

The generated carbon monoxide is converted into hydrocarbons such as methane and ethane in the reactants. - Oxidative carbon conversion also requires hydrogen, and therefore the amount of hydrogen present in the liquid-filled granular bed preferably causes a predetermined reduction of the 4-carboxybenzaldehyde content m in the aqueous solution and chemically necessary to convert at least a portion, preferably a majority, of the carbon oxide into hydrocarbon moieties.
at least equal to

The liquid effluent from the catalyst bed from the hydrogenated aqueous portion is then cooled to effect separation of the purified terephthalic acid produced from the solution by crystallization.

The process of the invention is particularly suitable for use in the purification of crude terephthalic acid prepared by continuous catalytic liquid phase oxidation of p-xylene in solvent. Suitable solvents for use in the catalytic liquid phase oxidation of p-xylene include any aliphatic C2-C6 solvent such as acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, trimethylacetic acid, and caproic acid. Includes monocarboxylic acids, water and mixtures thereof. Preferably, the solvent is a mixture of acetic acid and water, preferably containing 1 to 20% by weight of water, especially as introduced into the oxidation reactor. Because the heat generated in highly exothermic liquid phase oxidation is at least partially dissipated by evaporation of the solvent in the oxidation reactor, some of the solvent is recovered as a vapor from the reactor and then condensed into the reactor. Give back inside.

Additionally, some of the solvent is recovered from the reactor as a liquid in the product stream. After separating the crude terephthalic acid product from the product stream, at least a portion of the mother liquor (solvent) in the resulting product stream is typically reduced to the reactor.

The molecular oxygen source used in the oxidation step of the process for producing purified terephthalic acid can vary in molecular oxygen content from that in air to oxygen gas itself. Air is the preferred source of molecular oxygen.

To avoid the formation of explosive mixtures, the oxygen-containing gas fed into the reactor is an exhaust gas containing 0.5 to 8% by volume of oxygen (measured on a solvent-excluding basis). A gas-steam mixture must be released. For example, the feed rate of oxygen-containing gas sufficient to provide oxygen in an amount of 1.5 to 2.8 moles per methyl group is
The content of oxygen in the vapor mixture is between 0.5 and 8% by volume (measured without solvent).

The catalyst used in the oxidation stage of the process for producing crude terephthalic acid contains cobalt, manganese and bromine components and may additionally contain promoters known to those skilled in the art. The weight of cobalt (calculated as elemental cobalt) to p-xylene in the cobalt component of the catalyst in liquid phase oxidation is approximately 0 per Durham molecule of p-xylene.
, 2 to about 10 milligram atoms (Inga). The weight ratio of liquid phase acid cobalt (voiced as elemental cobalt) is from about 0.2 to about 10 IIl per mg of cobalt.
! It is within the range of Ja.

The weight ratio of bromine (calculated as elemental bromine) in the bromine component of the catalyst to the total cobalt and manganese in the cobalt and manganese components of the catalyst in liquid phase oxidation is approximately 0.2 per m9a of total cobalt and manganese. It is in the range of about 1.5■a.

Each of the cobalt and manganese components may be provided in any known ionic or bound form thereof, such as to provide soluble forms of cobalt, manganese and bromine in the solvent in the reactor. cobalt and/or manganese carbonate, acetate tetrahydrate, for example when the solvent is an acetic acid medium;
and/or bromine can be used. 0.2:
1.0 to 1.52 1.0 bromine vs. Kobalusaki? A milligram atomic ratio of 1 to 1 is provided by a suitable bromine source.

Such bromine sources include elemental bromine (Br2) or ionic bromides (eg HBr, Na3r).

KBr, NH4Br, etc.) or organic bromides known to generate bromide ions at the operating temperature of oxidation (e.g. bromobenzene, benzylbromide, mono- or dibromoacetic acid, bromoacetylbromide, tetrabromomethane, ethylene-dipropylene). (Mido, etc.) is used to satisfy the total milligram atomic ratio of Ruto and Manganese. Bromine ion released from organic bromides under oxidizing operating conditions [can be easily measured by known analytical means]. For example, tetrabromoethane was found to produce about 3 effective grams of bromine per gram molecule at operating temperatures of 170°C to 225°C.

In operation, the minimum pressure maintained in the oxidation reactor is that which maintains the p-xylene and at least 70% of the solvent in substantially liquid phase. The p-xylene and solvent that are not in the liquid phase due to evaporation are removed from the oxidation reactor as a vapor-gas mixture, condensed, and then returned to the oxidation reactor. If the solvent is an acetic acid-water mixture, a suitable reaction gauge pressure in the oxidation reactor is about OKg/
ci to about 35 Kg/cm, and typically ranges from about 1 ONg/cm to about 30.9 kg/cm.

The temperature range within the oxidation reactor generally ranges from about 120°C, preferably about 150°C, to about 240°C, preferably about 230°C.
That's it.

The solvent residence time in the oxidation reactor generally ranges from about 20 to about 1
50 minutes and preferably about 30 to about 120 minutes.

The resulting product is approximately 1 part per million parts of terephthalic acid by weight.
The aqueous solution contains relatively large amounts of impurities such as 4-carboxybenzaldehyde, which can be present in amounts up to 0.000 parts. These impurities can adversely affect the polymerization reaction of terephthalic acid to produce polyethylene terephthalate or cause undesirable coloration of the polyethylene terephthalate polymer.

The method of carrying out the invention is carried out in a bed of fixed catalyst under elevated temperature and pressure. Both up-flow and counter-flow reactors can be used. The crude terephthalic acid to be purified is dissolved in water or a similar polar solvent. Although water is the preferred solvent, other suitable polar solvents are relatively low molecular weight alkyl carboxylic acids, alone or mixed with water.

The temperature in the reactor, i.e. during purification of the terephthalic acid solution, is approximately 10
It can range from 0°C (below about 212°C) to about 350°C (below about 660°C). Preferably the temperature is about 215°C (
530° C.) to about 300° C. (approximately 572° C. below).

Reactor pressure conditions depend primarily on the temperature at which the ta%l step is being conducted. Actual m of impure terephthalic acid
Since the temperature at which the aqueous solution is dissolved is substantially above the normal boiling point of the polar solvent, the process pressure will necessarily be significantly higher than the environmental pressure to maintain the aqueous solution in the liquid phase. If the reactor is hydraulically charged, the reactor pressure can be controlled by the feed pump speed. If the reactor has a headspace, the pressure in the reactor may be adjusted in the headspace alone or by an inert gas such as steam and/or nitrogen, especially at relatively low hydrogen partial pressures. This is an advantageous means for doing so. For this purpose, the inert gas is preferably mixed with hydrogen before being introduced into the reactor. Typically the reactor pressure during hydrogenation is about 20
0 to approximately 1,500 bonds/1 inch square gauge (ps
ig) and typically around 900
p3ig to approximately 1,200 psig.

Hydrogenation reactors can be operated in several ways. For example, a predetermined liquid level can be maintained in the reactor, and hydrogen is supplied for any given reactor pressure and at a rate sufficient to maintain the predetermined liquid level. can do. The difference between the actual reactor pressure and the vapor pressure of the terephthalic acid solution present is the hydrogen partial pressure in the vapor space of the reactor. Alternatively, if the hydrogen is supplied in a mixture with an inert gas such as nitrogen, the actual reactor pressure of the terephthalic acid present is the hydrogen partial pressure of the hydrogen present in the mixture and the inert gas. can be calculated from known relative quantities of.

In yet another method of operation, the reactor can be filled with terephthalic acid solution so that there is no vapor space in the reactor. That is, the reactor can be operated as a liquid-filled system with dissolved hydrogen fed to the reactor by flow control. In such cases, the hydrogen concentration of the solution can be adjusted by adjusting the flow rate of hydrogen to the reactor. If desired, the pseudohydrogen partial pressure value can alternatively be calculated from the solution hydrogen concentration, which can be correlated to the hydrogen flow rate to the reactor.

In methods of operation where process control is provided by adjusting the hydrogen partial pressure, the hydrogen partial pressure in the reactor is preferably from about 10 psi to about 200 psi depending on the activity and length of use of the particular catalyst used; It depends on similar process conditions.

In operating methods where process control is carried out by direct adjustment of the hydrogen concentration in the feed solution, this is usually not saturated with hydrogen and the reactor itself is filled with liquid. That is, adjusting the hydrogen flow rate to the reactor provides the desired control of the hydrogen concentration in the solution. Generally, a hydrogen gas that is too unstable to effect the desired hydrogenation under the reaction conditions used is fed to the purification reactor.

4-Carboxybenzaldehyde (4-CBA) of the present invention
In purifying an aqueous terephthalic acid solution containing p-hydroxymethylbenzoic acid (HHBA),
- It is believed that the following principle reactions occur leading to the formation of toluic acid (TOL) and benzoic acid (8A).

A substantial portion of the hydrocarbon, HHBA, i.e. 4-carboxybenzaldehyde present in the crude terephthalic acid, is decarbonylated to benzoic acid while most of the remainder is converted to p-toluic acid in the same reactor. . Some decomposition of terephthalic acid to benzoic acid and hydrogenation of terephthalic acid to 4-carboxybenzaldehyde also occur, but these 29 are minor reactions.

Since carbon monoxide is known to inhibit the activity of hydrogenation catalysts, the presence of carbon monoxide in the 4-carboxybenzaldehyde hydrogenation reactor was thought to be a problem, but the present invention The method is Fisher-TrOp
This problem is avoided by carrying out the conversion of at least a substantial portion of the generated carbon monoxide to hydrocarbons, such as methane, in the reactor by what is considered to be an SCh type reaction.

Preferably, most of the carbon monoxide generated is converted to hydrocarbon moieties. The hydrocarbon byproducts formed are inert to purified terephthalic acid and can be easily separated from the resulting reaction product mixture by purging or other conventional methods.

It is believed that decarbonylation and conversion of carbon monoxide to hydrocarbon moieties occur substantially simultaneously in the first layer of the layered fixed catalyst bed of the present invention. The catalyst for decarbonylation and carbon monoxide conversion has 1 in its outermost orbital in the ground state.
Element I with electrons? ;lXg1#Ia It is a metal supported on a support of group 1 in Table 1.

A suitable periodic table of elements can be found in the “Handbook of Ch.
emistryand Physics J, 54th edition, Che+gical Rubber COIII)a
nV, C1eVeland, 0hio (1973
) can be found on the inside cover. Rhodium is the preferred catalyst, however ruthenium and platinum are also suitable. Such catalysts are commercially available.

Suitable palladium/carbon catalysts are available, for example, from Engelhard under the trade name “Palladium on activated carbon granules (carbon code CG
Similarly, suitable rhodium/carbon catalysts are available from Engelhard under the designation "Rhodium on activated carbon granules (carbon code CG-5)" and "Rhodium on activated carbon (carbon code CG-5)". 21)”. Both of these rhodium/carbon catalysts
2BET has a surface area of about 1,000 2/g and a particle size of 4
It has ×8 mesh U, S 5ieve 5eries. Other suitable rhodium/
The carbon catalyst is '11766 from Johnson Matsushi Co.
1%, anhydrous" on 0dium vapor activated carbon granules is available.

The catalyst support is activated carbon, usually derived from coconut charcoal, with a content of at least 600 TrL2/g (N2
; BET method) Preferably from about 800 m279 to about 1.5
It is in the form of granules with a surface area of 00 m279. However, other porous carbonaceous supports or substrates can also be used as long as surface area requirements are met. Besides coconut charcoal, activated charcoal derived from other plant or animal sources can also be used.

The ruthenium, rhodium, or platinum on the support makes up the total [i.e., metal plus activated carbon support]
It can be obtained from a range of about 0.01% by weight to about 2% by weight calculated as elemental metal. Preferably the catalytic metal loading is about 0.5% by weight.

Hydrogenation to 4-carboxybenzaldehydic acid is the principle reaction that occurs in the second layer of a layered fixed catalyst bed. This second W! J consists of a conventional palladium on activated carbon (Pd/C) granular catalyst. A typical palladium/carbon catalyst contains about 0 palladium, based on the total weight of the catalyst and calculated as elemental metal.
, 01 to about 2% by weight. The support or carrier for palladium is porous, inert, and preferably about 600TrL27g to about 15007FL2/9
It is an activated carbon with a surface area of . Suitable supports for palladium/carbon hydrogenation catalysts are well known;
See, inter alia, Heyer, US Pat. No. 3,584,039.

Although the relative thicknesses of the particulate catalyst layers in the hydrogenation bed can vary, the first catalyst layer preferably forms a minor portion of the fixed bed and the second catalyst layer forms a major portion of the catalyst bed. is doing. The first catalyst layer is always thick enough so that the aqueous crude terephthalic acid feed solution does not experience substantial flow drift within the catalyst layer as it passes therethrough. For this purpose, and as a practical matter, whatever the catalyst bed diameter, the first catalyst layer should be at least about 25M (approximately 1
(inch) thickness. Volumetrically, the first catalyst layer is preferably about 1710 of the volume of the second palladium/carbon catalyst layer, while the volume ratio of the catalyst *a of the first catalyst layer measure 2 is about 0. 001 to about 1.

The relative amounts of catalytic metal in the first catalytic layer and the second catalytic layer can vary. Generally, the desired Group 1 metals listed above for the first layer and palladium for the second layer are present in a molar ratio of about 1:1 to 1=1000, preferably about 1:10. .

The amount of hydrogen supplied under the reaction conditions is of course sufficient to effect the desired conversion of the carbon monoxide generated to hydrocarbons and the desired degree of hydrogenation of 4-carboxybenzaldehyde p-toluic acid. be. For the conversion of 4-carboxybenzaldehyde to p-toluic acid, the stoichiometric hydrogen requirement is 2 moles of hydrogen for each mole of 4-carboxybenzaldehyde converted.

For the conversion of 4-carboxybenzaldehyde to benzoic acid, the stoichiometric hydrogen requirement is dependent on the carbon monoxide generated. For the conversion of all generated carbon monoxide to methane, this requirement is 3 moles of hydrogen for each mole of 4-carboxybenzaldehyde converted to benzoic acid. Preferably, the amount of hydrogen fed to the catalyst bed is about twice that stoichiometrically required for the principle reaction described above taking place in the catalyst bed.

Preferably, the crude terephthalic acid feed to the catalyst bed in the reactor has a liquid flow width from the catalyst bed of less than about 2.5 p
L, I/L/ l'[! (TOL) vs. benzoin 1'l
(B8) Performed at a flow rate sufficient to maintain a high ffi ratio. More preferably, the p-toluic acid to benzoic acid weight ratio in the stream is maintained in the range of about 1.5 to about 0.5.

The space velocity of the aqueous crude terephthalic acid solution passing through the catalyst bed (
1 pound terephthalic acid solution/1 bond catalyst/hr) for about 5 hours to about 25 hours, preferably about 10 hours.
It is about 15 hours-1. The residence time of the terephthalic acid solution in the catalyst bed varies depending on the activity of the catalyst present.

Generally, however, the residence time of the aqueous terephthalic acid solution in the first catalyst bed is about 172 to 1/100 of the total residence time of the aqueous terephthalic acid solution in the catalyst bed.

The four fundamental factors that influence the degree of 4-carboxybenzaldehyde conversion in the catalyst bed are catalyst loading in the catalyst bed, catalyst activity, total bed and bed thickness, and feed throughput rate. However, as a practical matter, even under optimized process conditions, the 4-carboxybenzaldehyde content of the aqueous stream from the catalyst bed is still approximately 25% by weight relative to terephthalic acid. The amount is about 50 pp from While such 4-carboxybenzaldehyde contents are acceptable for some end uses of purified terephthalic acid, in other cases it is desirable to further reduce the 4-carboxybenzaldehyde content of the stream.

For this purpose, the catalyst bed is further provided with granular rhodium/carbon (Rh/C) downstream of the second catalyst layer mentioned above.
It has been discovered that it is possible to have a third catalytic layer of catalyst. This is more fully described in U.S. Pat. No. 785,321, entitled "Purification of Terephthalic Acid to Relatively Low Levels of 4-Carboxybenzaldehyde." This specification is incorporated by reference to the appropriate extent in Suimei mg.

Briefly, in such cases, the particulate rhodium/carbon inlay 1 constitutes the last layer through which the feed solution passes before exiting the reactor. This third catalyst layer of the fixed catalyst bed contains from about 0.01 to about 2'lt% rhodium, calculated as elemental metal based on the total weight of particulate catalyst present in the third layer.

If a third catalyst layer containing a rhodium/carbon catalyst is present, the catalyst layer is at least about 50 mm thick.
The thickness is . That is, the minimum thickness of the third catalyst layer is approximately twice the minimum thickness of the first catalyst layer of the catalyst bed. The maximum thickness of the third layer depends on the activity of the particular rhodium/carbon catalyst used, the reactor throughput speed, the thickness of the first catalyst layer, the 4-carboxybenzaldehyde content in the feed solution, etc. It can change depending on the conditions. However, the third catalyst layer is always less than 172 mm of the total catalyst bed thickness, ie it forms a minor portion of the total catalyst bed thickness.

A layered catalyst bed suitable for the hydrogenation of a relatively impure aqueous solution of terephthalic acid containing 4-carboxybenzaldehyde is shown in FIG. Downflow reactor 10 is shown hydraulically filled with the crude aqueous terephthalic acid solution 12 to be purified. This feed solution enters the reactor 10 via conduit 14, and a purified aqueous terephthalic acid solution with a relatively low content of 4-carboxybenzaldehyde enters the reactor 10 from the bottom as an effluent via conduit 16.
exit. The fixed granular catalyst bed 18 has a first catalyst layer 20, a second catalyst bed 20,
catalyst layer 22, and optionally a third catalyst layer 24.

First, the first catalyst layer is composed of a granular carrier such as activated carbon containing a metal of Group I of the Periodic Table of Elements having 1 (2) electrons in the outermost orbit in the ground state.

Metals mentioned for this purpose are ruthenium, rhodium, and platinum. The preferred metal is rhodium. The metal loading of the activated carbon support is the same as described above for Method I/ of the invention.

The second catalyst layer 22 is also comprised of a granular carrier such as activated carbon, and contains the same amount of palladium as described above for Z in the method of the present invention.

The optionally present third catalyst layer 24 consists of a granular carrier, such as activated carbon and rhodium, the latter having a content of about 0, calculated as an elemental metal based on the catalytic properties mentioned above.
．． 01 to about 2% by weight, preferably about 0.5% by weight.

As will be well known to those skilled in the art, the present invention finds other uses in the use of benzoates, benzoyl compounds, dyes, as food preservatives, as mordants in calico printing, inter alia.
It can also be used for the production of benzoic acid, a commercially important compound used as an intermediate for the production of . For this purpose, an aqueous solution of 4-carboxybenzaldehyde is prepared in a pressure vessel in the presence of hydrogen into granular particles containing one of the metals of the above group I, which has one electron in the outermost orbit in the ground state. Contact with catalyst. The reaction conditions for this purpose are the same as those described above for the purification of aqueous terephthalic acid solutions, but in this case there is no need to pass the aqueous solution through a bed or layer of balan shim/carbon catalyst.

As mentioned above, -carbon oxide is generated simultaneously with the decarbonylation of 4-carboxybenzaldehyde to benzoic acid. At that time, the -M carbon is separated from the resulting aqueous solution and the benzoic acid is recovered therefrom in a conventional manner.

The invention is further illustrated by the following examples.

A pilot plant reactor of the downflow type and equipped with a bed of immobilized catalyst 1 inch in diameter and 6.5 inches long was used. The catalyst bed was made of granular commercial palladium/carbon catalyst (40 g,
Is it only due to PdO, quintuplets, manufactured by Engelhard?
Alternatively, it consisted of an upper granular layer of rhodium/carbon catalyst (4 g, Rh 0.5% by weight) and a lower granular layer of palladium/carbon catalyst (40 g), also commercially available. A rhodium/carbon catalyst was prepared from rhodium nitrate as a precursor in al12 in water using North American activated carbon G-201 as a support. All catalysts were hot washed and aged in an autoclave in the presence of terephthalic acid and hydrogen for 72 hours. The reactor temperature is approximately 280°C (53°C
5 below), the hydrogen partial pressure is 50°100 and
Operated at 150 psi. The total reactor pressures were approximately 975.1025 and 11075 pSi, respectively.

A crude terephthalic acid slurry containing about 12% terephthalic acid and about 2700 ppm 4-carboxybenzaldehyde was fed to the reactor at a feed rate of 1.6 to 9 solutions/hour. The results obtained are summarized in the table below.

Table ■ Pd/C (7) MiTOL, 11pm 3227
3696 3990 (40grams) B8,
ppm 705 673 631
TOL/BA 4.5g 5.496.32Rh/C
(4(+) TOL, ppm 2433
2852 3371Pd/C (40 (11B eight,
I) l) III 1595 1587
1581TOL/BA 1.531.802.1
3 The above results show that the benzoic acid foot produced in the layered catalyst bed with an upper layer of rhodium/carbon and a lower layer of palladium/carbon is increased compared to the catalyst bed containing only palladium/carbon; And the amount of 4-carboxybenzaldehyde converted to p-toluic acid is decreasing.

Large [2 Commercially available palladium/carbon catalyst (4g, Pd0.5i
4! The selectivities of rhodium/carbon catalysts made as in Example 1 <49, rhodium 0.5ffl %/carbon) were compared in a 1 gallon titanium autoclave. . Crude terephthalic acid (approximately 2,909 g) in water (approximately 1,190 g)
It was melted at 7° C. (below about 530° C.), placed in an autoclave, and hydrogen was added thereto to give a partial pressure of about 50 pSi at the reaction temperature. The palladium/carbon or rhodium/carbon catalyst was then added to the autoclave.

An initial sample of the terephthalic acid solution was sampled before the addition of catalyst and at regular intervals thereafter. The samples were analyzed by liquid chromatography to determine the m of 4-carboxybenzaldehydoxymethylbenzoic acid (HHB^), TOL, and B^ present in the samples.

The results are summarized in Table ■.

The above results show that compared to the commercially available palladium/carbon catalyst, the rhodium/carbon catalyst has a surprising ability to decarbonylate 4-carboxybenzaldehyde under highly reductive conditions without adverse changes in the 4-carboxybenzaldehyde reduction rate. A commercially available palladium/carbon catalyst (
10 grams, PdO. a bed of rhodium/carbon catalyst (5 g.Rh
A crude aqueous terephthalic acid solution was mixed in a downflow pilot plant reactor with a bed consisting of an upper layer of palladium (0.5 wt%) and a lower layer of palladium/carbon catalyst (5 g, 0.5 wt% palladium/carbon, Engelhard). Used for hydrogenation.

The solution fed to the reactor is approximately 12ffXm of terephthalic acid.
% and 4-carboxybenzaldehyde approx. 2700p
It contained pm. Reactor conditions are as follows.

Temperature 2f30°C (535°F) Pressure
Power 975psig, 11025psi & 10
75psi gH2 partial pressure 50psi, 100ps
i & 150 psi residence time 063 minutes as shown in the 4-carpoxybenzaldegraph in the reactor effluent. Calculated p-toluic acid vs. benzoic acid (TOL/
B^) The weight ratios are shown in the following table ■.

Table ■ Leaf of -7 set and -] TOL/BA at si Catalyst bed 50 100 150Pd /C only 2.61 4.75 5.2 equivalent m (1)
Fr(DO,851,071,27Rh/
C and Pd/C The data in the table above shows that when using a layered catalyst bed with an upper rhodium/carbon layer and a lower palladium/carbon layer, a substantially lower p-toluic acid to benzoic acid weight ratio is achieved in the reactor effluent. This indicates that it is maintained in objects.

In a similar manner to Example 3, the performance of a 55 g catalyst bed containing only a commercially available palladium/carbon catalyst (Pd O, 51 ffi%: Engelhard) and a rhodium/carbon catalyst (Rh 0.5 wt. ) A down-flow pilot plant reactor was used to compare a catalyst bed containing two layers containing 5 g upper layer and 50 g lower layer of commercially available palladium/carbon catalyst (PdO05 wt%; Engelhard). It was done. All catalysts were aged in a titanium autoclave for 72 hours in the presence of prephthalic acid and hydrogen.

The solution fed to the reactor contains about 12% by weight terephthalic acid and about 2700 ppm 4-carboxybenzaldehyde.
It contained. Reactor conditions are as follows.

Temperature 280℃ (below 530℃) Pressure
975 psig, 1025 DSig &
1075 DsigH2 partial pressure 50 psi,
100 psi & 150 psi residence time 3.5
Benzoic acid, p-hydroxymethylbenzoic acid, and p-toluic acid in the reactor effluent were monitored. ll
! The results of a are summarized in Figure 2. The baton in Figure 2 is layer 1 and layer 2.
The average of four 1-number samples sampled at intervals of time and analyzed three times each is shown.

The calculated p-toluic acid to benzoic acid heavy R ratios are shown in Table 1 below.

Table ■ TOL/BAf at Naru Process 112 Partial Pressure (flsi) T:'s TOL/B^! l! L
l! l-and 50 100 150Pd/C(
Operation A) 2.9B 3.28 3.77R
h/C and Pd/C1,091,351,51 weight ratio 1
:1G (Run B) Rh/C and Pd /C 1,041,341,57 weight ratio 1:10 (Run B) The data presented in Figure 2 are based on layered rhodium/carbon and palladium/carbon catalysts. It is shown that as the p-toluic acid content of the reactor effluent decreases, there is a corresponding increase in benzoic acid of the effluent when a bed is used.

The effectiveness of rhodium/carbon catalyst (Rh 0.5 wt %) in the conversion of -merized carbon to methane is compared with the conventional palladium/carbon catalyst (Palladium 05 wt n 1%/Carbon) used for the purification of aqueous terephthalic acid solutions. )
was compared with that of

Both catalysts were first aged in a 1 gallon titanium autoclave in the presence of terephthalic acid and hydrogen for 12 hours. Thereafter, a small amount (4 g) of each catalyst was added to approximately 27 g.
4 in an autoclave maintained at 7°C (approximately below 530°C).
Time aqueous terephthalic acid solution (crude terephthalic acid 2909,
1160 g of water).

A mixture of hydrogen and carbon monoxide at the reaction temperature (1oo psi
H2 and 20 psi CO) were also added in the autoclave.
existed in

After the four hour interval described above, the heat to the autoclave was turned off, the autoclave was allowed to cool to about ambient temperature, and the gas sample was handled from the autoclave. The treated gas samples were then analyzed for carbon monoxide, carbon dioxide and methane. The results are shown in Table V below.

Table V Catalyst COC02C1+4 pct /CI5.64 0.56
0.01Rh/C14゜45 1.53
2.27 The above analysis shows that only the Rh/C catalyst converted significant parent carbon monoxide to methane.

Binding: Example 6 of Binding was produced by continuous liquid phase oxidation of p-xylene with oxygen-containing gas in the solvent in the presence of an oxidation catalyst and at elevated temperature and pressure in a commercially available unit. It involves 24 hours of operation per day in a commercial unit for continuous purification of crude terephthalic acid. The particular solvent, oxygen-containing gas, catalyst, temperature, pressure, and solvent distillation time used for the oxidation are all within the types and ranges set forth above.

Furthermore, the above-mentioned gas, solvent, catalyst, temperature, pressure and molten tIX? Each of the IO residence times is essentially the same in each run.

The operation of Example 6 or 2 sets 1 to 1 is included.

In both sets of runs, the aqueous solvent used in the purification reaction, temperature, pressure, and overall space velocity (mm of crude terephthalic acid per t4 of total catalyst per hour) were all of the general type and type described above. It was the same all around. In one set of runs, set Δ, the bed of catalyst particles is measured as elemental palladium and contains 0.5 palladium.
% by weight and total surface area 1000 m2/
gm and contained only palladium/carbon catalyst particles having a particle size of 4-8 mesh. Second
In the set of runs, Set B, 10% by weight of the total ω of palladium/carbon catalyst particles in the bed is removed from the top side of the bed and there is 0.0% rhodium, calculated as elemental rhodium. Contains 5% by weight and has a total surface area of 1000
m2/9 m was replaced with a layer of rhodium/carbon catalyst particles having a particle size of 4 to 8 mesh.
The same floor was used.

In each of Sets A and B, an aqueous solution of crude terephthalic acid was introduced into the top of the purification reactor and flowed down from the top of the catalyst bed to the bottom. Additionally, each of Set A and Set B was operated for at least 4 consecutive days with 24 hours of operation per day.

The data are for set A, the purified terephthalic acid obtained having an average optical density of 0.09 and an average b* value of 1.
18 showed that the average fluorescence index was 0.95. For set B, the obtained purified terephthalic acid has an average optical density of 0.08, an average b* value o, ai, and an average fluorescence index of 0.79, compared to set B. The purified terephthalic acid obtained showed substantially improved optical and fluorescent properties.

The specification and accompanying examples described above are intended to be illustrative rather than limiting. Further variations in process conditions and layered catalyst bed arrangements are possible and will occur to those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is a diagram of a reactor with a layered granular catalyst bed according to the invention, and FIG. 2 shows a R
First layer of Rh/C catalyst with h to Pd molar ratio and pd
Conversion of 4-carboxybenzaldehyde to benzoic acid at various hydrogen partial pressures in a layered catalyst bed with a second layer of Pd/C catalyst and the same conditions but with a non-layered Pd/C catalyst bed. Figure 3 is a bar graph showing a comparison of conversions conducted in a layered catalyst bed with a Rh to Pd molar ratio of approximately 1:1 and conversions conducted under the same conditions or in a non-layered Pd/C catalyst bed. This is a bar graph showing a comparison with .

Claims (1)

[Claims] 1) Supported on an activated carbon support in the presence of hydrogen and containing a group VIII metal of the periodic table of elements having one electron in its outermost orbit in the ground state. an aqueous solution of crude terephthalic acid is maintained in a substantially liquid phase in a granular catalyst bed, which is a layered bed containing a first catalyst layer containing palladium and a lower catalyst layer containing palladium supported on an activated carbon support. passing at a temperature of about 100°C to about 350°C at a pressure sufficient to
The solution is first passed through the first layer and then the second layer, and then the hydrogenated aqueous solution is cooled to separate purified terephthalic acid produced from the aqueous solution by crystallization. A method for purifying crude terephthalic acid. 2) The solution is maintained at a temperature of about 245°C to 300°C and hydrogen is present in an amount of about twice the stoichiometrically required amount. the method of. 3) A process according to claim 1, characterized in that the space velocity of the aqueous terephthalic acid solution passing through the catalyst bed is from about 5 hours to about 25 hours. 4) A process according to claim 3, characterized in that the space velocity of the aqueous terephthalic acid solution passing through the catalyst bed is from about 10 hours to about 15 hours. 5) A patent claim characterized in that the residence time of the aqueous terephthalic acid solution in the first catalyst bed is about 1/2 to about 1/100 of the total residence time of the aqueous terephthalic acid solution in the granular catalyst bed. The method described in item 1 of the scope. 6) The method according to claim 1, wherein the Group VIII metal is rhodium. 7) Rhodium is present in the first catalyst layer at a concentration of about 0.01 to about 2% by weight, based on the weight of the catalyst in the first catalyst diagram and calculated as elemental rhodium. The method according to claim 6. 8) Crude terephthalic acid contains about 10,00 parts of 4-carboxybenzaldehyde per million parts by weight of terephthalic acid.
0 parts and characterized in that hydrogen is present in the granular catalyst bed in an amount at least equal to the amount stoichiometrically necessary to effect the desired reduction in the 4-carboxybenzaldehyde content. A method according to claim 1. 9) a first catalyst layer containing a Group VIII metal of the Periodic Table of the Elements supported on an activated carbon support and having one electron in its outermost orbit in the ground state in the presence of hydrogen; and a second containing palladium supported on an activated carbon support;
hydrogenating the aqueous solution of crude terephthalic acid at a temperature of from about 100° C. to about 350° C. at a pressure sufficient to maintain the aqueous solution of crude terephthalic acid in a substantially liquid phase in a granular catalyst bed, which is a layered bed containing a catalyst bed of; The hydrogenated aqueous solution is then cooled to effect separation of relatively pure terephthalic acid from the solution by crystallization, with the hydrogenation accompanied by the evolution of carbon monoxide and liquid effluent from the granular catalyst bed. The p-toluic acid:benzoic acid weight ratio in the liquid was maintained below about 2.5, and the hydrogen was generated in the granular catalyst bed with a predetermined reduction in the 4-carboxybenzaldehyde content. of crude terephthalic acid, characterized in that it is present in the granular catalyst bed in an amount at least equal to the amount stoichiometrically required to convert at least a portion of the carbon monoxide into hydrocarbon moieties. Purification method. 10) The method of claim 1, wherein the p-toluic acid:benzoic acid weight ratio is maintained in the range of about 1.5 to about 0.5. 11) A first catalyst diagram consisting of a granular activated carbon support containing a metal of group VIII of the Periodic Table of the Elements having one electron in the outermost orbit in the ground state; and a granular catalyst containing palladium. A layered catalyst bed suitable for the hydrogenation of a relatively impure aqueous solution of crude terephthalic acid containing 4-carboxybenzaldehyde, comprising a second catalyst layer constituted by an activated carbon support. 12) A layered catalyst bed according to claim 11, characterized in that the first catalyst layer constitutes a minor part of the catalyst bed and the second catalyst bed constitutes a main part of the catalyst bed. . 13) Group VIII metals, based on the combined weight of metals as carriers and calculated as elemental metals, have approximately 0.
12. A layered catalyst bed according to claim 11, characterized in that it is on a particulate support in an amount of from 0.01 to about 2% by weight. 14) The Group VIII metal is rhodium and is present in an amount of about 0.05% by weight, based on the combined weight of support and metal and calculated as elemental metal. Layered catalyst bed according to item 11. 15) The layered catalyst bed according to claim 11, wherein the Group VIII metal is ruthenium. 16) The layered catalyst bed according to claim 11, wherein the Group VIII metal is rhodium. 17) The layered catalyst bed according to claim 11, wherein the Group VIII metal is platinum. 18) The layered catalyst bed of claim 11, wherein the first catalyst layer is at least about 25 mm thick. 19) The layered catalyst bed of claim 11, wherein the volume ratio of the first catalyst layer to the second catalyst layer is from about 0.001 to about 1. 20) A layered catalyst bed according to claim 11, characterized in that the volume ratio of the first catalyst layer to the second catalyst layer is about 0.1. 21) The layered structure of claim 11, wherein the molar ratio of Group VIII metal in the first catalyst layer to palladium in the second catalyst layer is from about 1 to about 0.001. catalyst bed. 22) A layered catalyst bed according to claim 11, characterized in that the molar ratio of Group VIII metal in the first catalyst layer to palladium in the second catalyst layer is about 0.1. 23) The first catalyst layer is composed of a Rh/C catalyst,
The layered catalyst bed according to claim 11, wherein the second catalyst layer is made of a Pd/C catalyst. 24) The layered catalyst bed of claim 23, wherein the molar ratio of rhodium to palladium in the catalyst bed is from about 1 to about 0.001. 25) Claim 2, characterized in that the molar ratio of rhodium to palladium in the catalyst bed is about 0.1.
Layered catalyst bed according to item 3. 26) The rhodium concentration in the first catalyst layer is about 0.0 for each catalyst.
24. The layered catalyst of claim 23, wherein the palladium concentration in the second catalyst layer is from about 0.01 to about 2% by weight of each catalyst. floor. 27) The rhodium concentration in the first catalyst layer is about 0.0 for each catalyst.
24. The layered catalyst bed of claim 23, wherein the palladium concentration in the second catalyst layer is about 0.5% by weight of each catalyst. 28) A layered catalyst bed according to claim 11, comprising a third catalyst layer downstream of the second catalyst layer and composed of a granular activated carbon support containing rhodium. 29) The layered catalyst bed of claim 28, wherein the third catalyst layer is at least about 50 mm thick. 30) a first catalyst layer containing a Group VIII metal of the Periodic Table of the Elements supported on an activated carbon support and having one electron in its outermost orbit in the ground state in the presence of hydrogen; and a granular catalyst bed containing a low catalyst layer containing palladium supported on an activated carbon support at a pressure sufficient to maintain the aqueous solution of crude terephthalic acid substantially in the liquid phase. passing at a temperature of 100°C to about 350°C, the solution first passing through the first layer and then the second layer.
(hydrogen is present in an amount at least equal to that stoichiometrically required to effect the desired reduction of the 4-carboxybenzaldehyde content in the particulate catalyst layer; The residence time of the aqueous terephthalic acid solution in the bed is about 1/2 to about 1/100 of the total residence time of the aqueous terephthalic acid solution in the granular catalyst bed); the hydrogenated aqueous solution is then cooled to crystallize. A process for the purification of relatively impure terephthalic acid containing up to about 10,000 ppm by weight of 4-carboxybenzaldehyde, comprising separating the relatively pure terephthalic acid from said solution by.