WO2009064037A1

WO2009064037A1 - Recovery of catalysts, benzoic acid and aromatic acid

Info

Publication number: WO2009064037A1
Application number: PCT/KR2008/000180
Authority: WO
Inventors: Myron Myonkee Lee; Yong-Taek Park; Duk Jun Kwon; Dong Won Lee
Original assignee: ANT (ASIAN NEW TECH) Corp
Current assignee: ANT (ASIAN NEW TECH) Corp
Priority date: 2007-11-12
Filing date: 2008-01-11
Publication date: 2009-05-22
Anticipated expiration: 2010-05-12
Also published as: KR100897502B1

Abstract

A process is disclosed for the recovery of catalysts, benzoic acid and other aromatic acids from the solid wastes generated m a manufacturing process of an aromatic carboxylic acid. The catalysts are recovered from the solid wastes by using solvent extraction and filtration. The resulting solids are heated to dissolve benzoic acid in water and solid aromatic acids are separated by filtration. Benzoic acid is recovered from the liquid filtrate by using crystallization, filtration and drying.

Description

[DESCRIPTION]

[invention Title]

RECOVERY OF CATALYSTS, BENZOIC ACID AND AROMATIC ACID

[Technical Field]

This invention relates to a process for recovering catalysts, benzoic acid and other aromatic acids from solid wastes generated in a manufacturing process of an aromatic carboxylic acid.

[Background Art]

As the demand of various polymer resins increases, the production of raw materials for the polymer resins, such as terephthalic acid, isophthalic acid and trimellitic anhydride, has been increasing dramatically in recent years. A large amount of solid wastes are generated in the manufacturing processes of the above-mentioned aromatic acids. Presently, the worldwide generation of the solid wastes at the aromatic acid plants is estimated to be approximately 900,000 tons per year.

The said solid wastes contain many useful chemicals such as catalysts for oxidation reactions (0.7-1.4%), benzoic acid (17-32%) and other aromatic acids (7-15%) . The recovered catalysts can be reused in the oxidation reaction process of aromatic acids. The benzoic acid may be used as raw materials for dye intermediates, preservatives, insecticides, pharmaceuticals and plasticizers . Recently, the demand of benzoic acid has been increasing more rapidly due to the T) development of new processes for phenols and caprolactam, using benzoic acid as raw materials. The other aromatic acids recovered can be recycled back to the manufacturing process of the same aromatic acids or used in the manufacturing process of polyol resins. Since there are no economical processes

10 available to recover useful chemicals from the wastes, the solid wastes are presently sent to the wastewater treatment facilities, buried underground or burned in incinerators or boilers, causing environmental pollutions,

U.S. Patent 4,914,230 describes a method for recovering

If) catalysts from said solid wastes by using a centrifuge and solvent extraction and recycling recovered catalysts to the oxidation reactor. But this process has a disadvantage that the oxidation reaction rate decreases due to a large amount of water (more than 90%) contained in the recovered catalysts. In 0 addition, benzoic acid and other aromatic acids cannot be recovered.

U.S. Patent 4,910,175 teaches a method for recovering catalysts from said solid wastes by filtration and oxidation reaction, following precipitation of cobalt (Co) and manganese (Mn) catalysts by using oxalic acid and caustic soda. However, this process has several disadvantages such as: (1) bromine (Br) , benzoic acid and other aromatic acids can not be recovered; (2) the consumption of expensive oxalic acid is 5 high; (3) the reaction rate in the oxidation reactor of aromatic acids decreases due to introduction of the sodium ion which is a catalyst poison; and (4) the process is very complex, requiring high investment costs.

ROK Patent 1991-0003973 provides a method for recovering

10 benzoic acid from said solid wastes by using dehydration and distillation processes. Since this process requires distillation towers operating at temperatures higher than 200⁰C, it has several disadvantages such as high operating and investment costs, plugging problems of equipment and pipeline,

If) and the low purity of the product.

ROK Patent 1998-0009219 provides a method of recovering and purifying gaseous benzoic acid by using a gasifier and activated carbon. But this process has a number of technical difficulties to be overcome for commercialization, such as the 0 difficulty of separating benzoic acid from water (about 60% in said wastes) in the gas phase, the regeneration problem of used activated carbons, and plugging problems of equipment and pipelines . [Disclosure] [Technical Problem]

An object of the present invention is therefore to provide an improved, economical process for recovering 5 catalysts, benzoic acid and other aromatic acids simultaneously from the solid wastes generated in a manufacturing process of an aromatic carboxylic acid. Another object of the present invention is to eliminate the drawbacks of the prior art processes mentioned herein above. 10

[Technical Solution]

In order to accomplish the above-mentioned objects, the present invention provides a process for the recovery of catalysts, benzoic acid and other aromatic acids from said l.^"ϊ solid wastes which comprises the following steps: a) separating the slurry mixture of residual aromatic wastes and water or an aqueous acetic acid solution from an extractor (3) into the first filtrate, containing catalysts, and wet cake, containing benzoic acid and other aromatic acids, 0 by means of both a filtration device 1 (5) and a filtration device 2 (8) or by using a filtration device 2 (8) only; b) feeding said first filtrate to an evaporator (10) , vaporizing excess solvent to recover a concentrated catalyst solution, reslurrying said wet cake with water (15) and feeding the resulting slurry to a filtration device 3 (18) to separate solids from filtrate, wherein the solids are sent to a dissolver (21) ; c) dissolving benzoic acid in the dissolver (21) and 5 feeding the resulting slurry to a filtration device 4 (24) to separate the second filtrate containing liquid-phase benzoic acid (31) from other solid aromatic acids (25) ; d) crystallizing benzoic acid by cooling the second filtrate.

10

An embodiment of the present invention will be described in detail by reference to Figures 1 and 2.

In Fig. 1, the solid wastes (1) generated in the manufacturing process of an aromatic acid are mixed with

IT) solvent (2) in an extractor (3) to extract catalysts such as cobalt (Co), manganese (Mn) and bromide (Br) ions, which are used as catalysts for the oxidation reaction. Preferred solvents (2) for the solvent extraction are water or an aqueous acetic acid solution. Desired ratios of the solvent

W feed rate relative to the solid wastes rate to the extractor (3) are 1.0 to 4.0 for water and 1.5 to 4.5 for the aqueous acetic acid solution. If the feed ratio of the solvent with respect to the solid wastes exceeds 4.0 for water and 4.5 for the aqueous acetic acid solution, the vaporization time of the solvent and energy required in the evaporator (10) become excessive, resulting in the increased operating costs. If the ratios of solvents are lower than 1.0 for water and 1.5 for the aqueous acetic acid solution, the extraction efficiency of T) catalysts decreases. The extractor (3) is preferably operated at a temperature within the range of 25 to 6O⁰C and at an agitator speed of 30 to 105 rpm with the extraction time of 0.3 to 1.5 hr.

The effluent slurry of the extractor (3) is separated

K) into a catalysts-bearing liquid and wet cake by using single- stage or multiple-stage filtration devices (4, 8) . When two- stage filtration devices are used as shown in Fig. 1, the effluent slurry of the extractor (3) is pumped through a filtration device 1 (5) and the filtrate (6) containing

IJ catalysts is sent to the evaporator (10) . The concentrated slurry is recycled back to the extractor (3) , while part of the concentrated slurry is fed through line 7 to a filtration device 2 (8) for separation of wet cake. Filtrate (9) of the filtration device 2 is sent to the evaporator (10) and the wet

?0 cake is sent to the holding tank 1(16) along with water (15) .

The feed rate of water (15) to the filtration device 2 (8) is preferably maintained at 1.0 to 3.0 times the wet cake rate for the high recovery rate and purity of benzoic acid.

In case the effluent slurry of the extractor (3) is processed by a single-stage filtration device, the effluent slurry is pumped to the filtration device 2(8), bypassing the filtration device 1(5) . Filtrate (9) containing catalysts is sent to the evaporator (10) and the wet cake is sent to the 55 holding tank 1(16) along with water (15) .

In case of using water as a solvent for the extractor (3) , the evaporator (10) is used to vaporize excess water in order to minimize the amount of water being recycled back to oxidation reactors along with the recovered catalysts, since

K) water decreases the oxidation rates of aromatic alkyl compounds. The concentrated catalysts solution (14) is recycled back to the oxidation reactors for reuse. The vaporized water is condensed in a condenser (11) and then sent to the wastewater treatment facility. The temperature of the

IT) evaporator (10) is preferably maintained in the range of 90 to 12O⁰C by a heater (13) . In case of using an aqueous acetic acid solution as a solvent for the extractor (3), the evaporator (10) can be used as a holding tank without using the heater (13) and the condenser (11) . 0 The slurry from the holding tank 1(16) is pumped to the filtration device 3(18) to separate liquid and wet cake in a similar way as for the filtration device 2(8) . The filtrate from the filtration device 3(18) is recycled back to the extractor (3) through a pipeline (20) and the wet cake, reslurried with water, is sent to a dissolver (21) . The feed rate of water to the filtration device 3 (18) for reslurrying is preferably maintained at 2.5 to 6.0 times the wet cake rate. If the feed ratio of water to the solid cake is more than 6.0, both energy consumption and equipment sizes increase, resulting in unfavorable process economics. If the feed ratio of water is less than 2.5, both the purity of benzoic acid and the recovery yield of other aromatic acids will decrease due to a higher temperature of dissolver (21) required to dissolve all benzoic acid.

After dissolving benzoic acid in the dissolver (21) , the resulting slurry is pumped to the filtration device 4(24) to separate liquid and wet cake in a similar way as for the filtration device 2(8) . The filtrate (31) of the filtration device 4, mainly composed of benzoic acid, is sent to a crystallizer (32) and the wet cake is sent to a holding tank 2

(27) . The content of the holding tank 2 (27) , comprising of mainly aromatic acids (other than benzoic acid) and water, can be recycled back to the aromatic acid production process or used as a raw material for polyol resins.

The temperature of the dissolver (21) is preferably maintained in the range of 70 to 120⁰C by a heater (22) . If the temperature of the dissolver is higher than 12O⁰C, the purity of benzoic acid and the recovery rate of other aromatic acids decrease. If the temperature is lower than 7O⁰C, the purity of benzoic acid increases, but the recovery rate of benzoic acid decreases.

The aqueous benzoic acid solution fed to the ") crystallizer (32) is crystallized after cooling temperature to the range of 10 to 6O⁰C by using chilled water (33) and a cooler (34) . If the crystallizer temperature is higher than 60⁰C, the recovery yield of the benzoic acid becomes low since some dissolved benzoic acid cannot be crystallized. The

U) crystallizer temperature lower than 1O⁰C is not desirable, since both investment and operating costs increase.

Finally, the benzoic acid slurry is fed to a filtration device 5(40) to separate solid benzoic acid from filtrate m a similar way as for the filtration device 2(8) . The filtrate i^r) (36) mainly composed of water and a trace amount of benzoic acid is sent to the wastewater treatment facility and the solid benzoic acid is sent to a dryer (38) . The operating conditions of the dryer are preferably maintained at a temperature in the range of 60 to 120⁰C and at a pressure in O the range of 20 to 13OkPa with a drying time of 0.5 to 2.0 hr for the high purity and yield of benzoic acid.

Most filtration devices employed in this invention can be conventional pressure filters, rotary filters, tubular filters or centrifuges, which are commonly used m industrial applications for the solid- liquid separation. However, the filtration device 1(5) is of the tubular filter type and the same tubular type is preferred for other filtration devices for easier operation and maintenance. It is also desirable 1 that the material of construction for the tubular filters is stainless steel or titanium and the pore size of filter medium is m the range of 0.5 to 20μm. If its pore size is bigger than 20/ini, some solids of small size can not be filtered and fed with the filtrate to the subsequent processes, resulting m

K) yield losses, lower purity and other problems. If the pore size of filter medium is smaller than 0.5/Λn, the efficiency of the filtration process can be lowered due to the frequent plugging of filter medium by solid fines, the longer filtration time and the lower processing capacity. It is

11 desirable to use sintered metals of stainless steel or titanium for the tubular filter to prevent corrosions and process contamination.

According to the recovery method of this invention, the typical recovery yields from the solid wastes are about 80 to

Λ) 95% for benzoic acid and about 90 to 99.5% for catalysts and other aromatic acids such as terephthalic acid.

[Description of Drawings]

Fig. 1 and 2 are flow diagrams, showing the general configuration of this invention.

1: wastes 2: solvent

3: extractor 5: filtration device 1

6, 9: filtrate 1 8: filtration device 2

T) 10: evaporator 11: condenser

13, 22: heater 14: catalyst

15, 26, 33: water 16: holding tank 1

18: filtration device 3 21: dissolver

24: filtration device 4 27: holding tank 2 10 28: aromatic acids 31: filtrate 2

32: crystallizer 34: cooler

36: wastewater 38: dryer

39: benzoic acid 40: filtration device 5

4, 7, 12, 17, 19, 20, 23, 25, 35, 37: pipeline IT)

[Best Mode]

The present invention is further illustrated by the following specific examples, which are provided herein for illustration purposes only and are not intended to be limiting. 0 Example 1. Recovery of catalysts, benzoic acid and terephthalic acid

The type of the filtration devices used in the following example is tubular filters made of sintered stainless steel with the average pore size of Iμm. Batch tests were performed step-by-step at a pilot plant by using the solid wastes with the compositions shown in Table 1, which were simulated per a typical analysis of the solid wastes from a terephthalic acid plant. The extractor (3) in Fig. 1 was charged with 5 kg of the solid wastes and 17.5kg of de- ionized water and then catalysts were extracted at 45⁰C by stirring the extractor contents at 56 rpm for 60 minutes. The resulting slurry was fed to the filtration device 2(8) to separate solid and liquid. In this example, the filtration device 1(5) was not used.

The filtrate of the filtration device 2(8) was collected in the evaporator (10) and then boiled at 100⁰C for 30 min. to evaporate excess water. The total amount of catalysts (Co, Mn, Br) recovered was 98.3 gram and the recovery yield of catalysts is shown in Table 2.

The wet cake from the filtration device 2(8) was reslurried with 9 kg of water in the holding tank 1(16) and the resulting slurry was fed to the filtration device 3(18) to separate solid and liquid. The wet cake was washed with water and then mixed with 3 kg of water in the dissolver (21) . The contents of the dissolver (21) were heated to 96⁰C and well stirred at the same temperature for 30 minutes. The resulting slurry was filtered by the filtration device 4(24) . Amount of terephthalic acid recovered was 492.5 g and the recovery yield of terephthalic acid is shown in Table 2.

The liquid filtrate of the filtration device 4(24) was fed to the crystallizer (32) , wherein benzoic acid was crystallized at 34⁰C for 1 hour. The resulting slurry was filtered by means of the filtration device 5(40) . The wet cake thus obtained was dried at 80⁰C under a vacuum pressure 60 kPa for 2 hours. Amount of benzoic acid recovered was 1368.7 g and its recovery yield is shown in Table 2.

Table 1. Composition of Solid Wastes Used for Example

Table 2. Recovery Yields of Catalyst, Benzoic Acid and

Terephthalic Acid

[industrial Applicability]

The process of this invention provides a method of recovering catalyst, benzoic acid and other aromatic acid simultaneously from the solid wastes, while the prior art processes recover only one component from the wastes. The present invention also allows not only to obtain economic benefits by recovering most useful chemicals from the wastes but also to minimize the environmental pollution.

Claims

[CLAIMS]

[Claim l]

A process for the recovery of catalysts, benzoic acid and other aromatic acids from the solid wastes generated in a ό manufacturing process of an aromatic carboxylic acid, which comprises the following steps: a) separating the slurry mixture of residual aromatic wastes and water or an aqueous acetic acid solution from an extractor (3) into the first filtrate, containing catalysts, 10 and wet cake, containing benzoic acid and other aromatic acids, by means of both a filtration device 1 (5) and a filtration device 2 (8) or by using a filtration device 2 (8) only; b) feeding said first filtrate to an evaporator (10) , vaporizing excess solvent to recover a concentrated catalyst

If) solution, reslurrying said wet cake with water (15) and feeding the resulting slurry to a filtration device 3 (18) to separate solids from filtrate, wherein the solids are sent to a dissolver (21) ; c) dissolving benzoic acid in the dissolver (21) and 0 feeding the resulting slurry to a filtration device 4 (24) to separate the second filtrate containing liquid-phase benzoic acid (31) from other solid aromatic acids (25) ; d) crystallizing benzoic acid by cooling the second filtrate .

[Claim 2 ]

The process of Claim 1, wherein the filtrate of the filtration device 3 (18) in the above-stated Step b) is recycled to the extractor (3) . T) [Claim 31

The process of Claim 1, wherein the extractor

(3) is operated at a temperature within the range of 25 to 60⁰C.

[Claim 4]

The process of Claim 3, wherein either water or an 10 aqueous acetic acid solution is used as a solvent in the extractor (3 ) . [Claim 5]

The process of Claim 4, wherein the weight ratio of the solvent (2) to the solid wastes (1) is maintained within the If) range of 1.0 to 4.0 for water and within the range of 1.5 to 4.

5 for an aqueous acetic acid solution, respectively.

[Claim 6]

The process of Claim 1, wherein the temperature in the dissolver (21) is maintained within the range of 70 to 12O⁰C 0 in Step c) .

[Claim 7]

The process of Claim 6, wherein water is used as a solvent in the dissolver (21) .

[Claim 8] The process of Claim 7, wherein the amount of water used in said dissolver (21) is maintained within the range of 2.5 to 6.0 times the amount of wet cake from the filtration device 3(18) . 5

[Claim 9]

The process of Claim 1, wherein the crystallizer (32) in Step l.d is operated at a temperature within the range of 10 to 6O⁰C.

[Claim 10]

10 The process of Claim 9, wherein the solvent used in the crystallizer (32) is water.

[Claim 111

The process of Claim 1 or Claim 10, wherein the crystallized benzoic acid in Step l.d is used after drying and If) the dryer (38) is operated at a temperature within the range of 60 to 12O⁰C and at a pressure within the range of 20 to 130 kPa (absolute) .

[Claim 12]

The process of Claim 1, wherein the filtration devices 0 used in Step a) through Step d) are tubular type filters made of sintered metals.

[Claim 13]

The process of Claim 12, wherein the pore size of the filtration devices used in Step a) through Step d) is 0 ,5~20μm. 5