WO2015131059A1

WO2015131059A1 - Separating acetic acid from tpa and ipa

Info

Publication number: WO2015131059A1
Application number: PCT/US2015/018036
Authority: WO
Inventors: Paul MURDOCH; Victoria WILHELM; Randi Wytcherley; Kuen Yuan CHIU
Original assignee: Gtc Technology Us Llc
Priority date: 2014-02-27
Filing date: 2015-02-27
Publication date: 2015-09-03
Also published as: AR101437A1; TW201536735A

Abstract

The present invention provides a method and apparatus for separating high concentrations of acetic acid from terephthalic acid (TPA) and optionally TPA and isophthalic acid (IP A) mix, allowing the TPA or IPA/TPA mix to be further processed by a purification plant.

Description

SEPARATING ACETIC ACID FROM TPA AND IPA

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This Application claims the benefit under 35 U.S.C. § 119(e) of U.S.

Provisional Patent Application No. 61/945,685 filed February 27, 2014 which is incorporated herein by reference in its entirety as if fully set forth herein.

FIELD OF THE INVENTION

[0002] The present invention provides a method and apparatus for separating high concentrations of acetic acid from terephthalic acid (TPA) and optionally TPA and isophthalic acid (IPA) mix, allowing the TPA or IPA/TPA mix to be further processed by a purification plant.

BACKGROUND OF THE INVENTION

[0003] A number of oxidation reactions are known for forming the crude terephthalic acid (CTA) also known as TPA, from a variety of starting materials. The present invention may be used with substantially, any of these reaction systems. A common TPA reaction system involves the oxidation of paraxylene (p-xylene) in air; optionally, IPA which is converted from mixed xylenes in air, can also be used in the present invention.

[0004] Conventional TPA or IPA/TPA oxidation reactions, use acetic acid as the solvent to transfer the oxidized TPA or IPA/TPA throughout various sections of the oxidation plant; including, but not limited to crystallization, separation and the drying sections.

[0005] Acetic acid is generally used due to its recoverability properties, and because of the little negative impact it has on the oxidation reaction process. Generally, the oxidation drying section is located downstream of the oxidation filtration section. The drying system is designed to remove the majority of acetic acid from the filtered wet TPA cake, leaving a dry TPA powder, which is then stored in a TPA silo before being further processed by the purification plant.

[0006] 4-carboxybenzaldehyde (4-CBA) is considered as the main impurity in TPA, and due to the solubility properties of 4CBA, conventional hydrogenation purification plants have to first convert the 4CBA to paratoluic acid (p-TA) by hydrogenation. This process is carried out by the purification hydrogenation reactor at elevated pressures and temperatures. Post conversion, the newly converted impurity p-TA is soluble in water, allowing the hydrogenation purification plants to utilize water as their main solvent to convey the product throughout the plant, while allowing the soluble impurity p-TA to be separated from the Purified Terephthalic Acid (PTA) product by filtration or other separation means.

[0007] Hydrogenation purification plants generally do not process high

concentrations of acetic acid, as this would have a significant increase in capital costs, as the materials of construction would have to be changed to accommodate the high operating pressures and temperatures. The acetic acid would also have to be separated from the water; further increasing capital and operating costs.

[0008] The conventional oxidation process involves a number of steps to produce suitable quality TPA for the purification plant to process. One of these process steps is oxidation filtration.

[0009] The oxidation filtration step separates the TPA or IPA/TPA reaction intermediates, which are soluble in the acetic acid and therefore removed from the TPA or IPA/TPA mix cake as mother liquor, the main soluble intermediate being p-TA.

[00010] Generally, the filter cake, from the filtration process, will undergo washing with acetic acid to further remove product impurities from the filter cake such as catalysts cobalt (Co) and manganese (Mn), which are contained within the feed slurry mix to the filtration system. The result is a TPA cake with acceptable TPA product impurity concentrations; however, the TPA cake is saturated in acetic acid and cannot be processed by a purification plant without further treatment.

[00011] Removing the acetic acid from TPA, generally involves several large key plant items including a rotary steam dryer, rotary valve, dryer scrubber, dryer gas blowers, dryer gas heater, and an intermediate silo to store the TPA, prior to it being processed by the PTA plant. [00012] In addition to high capital expenditure, there are also high operating costs associated with this technology; including, High, medium and low pressure steam usage, inert gas usage, acetic acid usage, and power usage.

[00013] In addition to expensive operating and capital costs, there are also environmental issues to consider:

• Dryer gas purge to atmosphere, which generally contains acetic acid and C0₂.

• Silo vent to atmosphere, which, generally contains PTA and acetic acid.

[00014] The dryer seals are also known to be problematic with common knowledge to those who are experienced in the art. Leakages of TPA from the dryer seals create a dust nuisance. However, there is a potential for a serious safety scenario, in the form of an overspill from the oxidation filtration section into the oxidation dryer, which can cause overpressure of the dryer seals leading to a dryer seal failure, which has the potential of creating a major toxic gas release.

[00015] Thus, there is a need for an improved method for separating the acetic acid from terephthalic acid and or a mixture of terephthalic acid and isophtalic acid.

SUMMARY OF THE INVENTION

[00016] The present invention is directed to a method and apparatus to separate high concentrations of acetic acid and product impurities from TPA or a TPA/IPA mix, the method comprising the use of a pressure filter, wherein the pressure filter separates the acetic acid and impurities from the TPA or TPA/IPA mix, thereby removing the need for the drying system and TPA storage. The present invention is also directed to a method and apparatus to separate high concentrations of acetic acid and product impurities from TPA or a TPA/IPA mix, the method comprising the use of a pressure filter, wherein the pressure filter separates the acetic acid and impurities from the TPA or TPA/IPA mix downstream of the oxidation crystallizer system, thereby removing the need for the downstream oxidation filtration, drying system and TPA storage. BRIEF DESCRIPTION OF DRAWINGS

[00017] FIG. 1 is an example of the conventional oxidation drying and storage system for TPA or IPA/TPA;

[00018] FIG. 2 shows a method and apparatus for displacing high

concentrations of acetic acid from TPA or IPA/TPA mix using the current invention with Techtiv-TA (TTA) and/or part recycled mother liquor as the solvent wash. The pressure filter is located downstream of the oxidation filter, removing the need for the oxidation drying system;

[00019] FIG. shows a method and apparatus for recovering the TTA solvent, solids, water and acetic acid;

[00020] FIG. 4 shows a method and apparatus for displacing high

concentrations of acetic acid from the TPA or IPA/TPA, using the current invention with TTA solvent, and/or recycled sour solvent, acetic acid and or recycled mother liquor as the pressure filter wash, removing the need for the oxidation filter and drying systems; and [00021] FIG. 5 shows a method and apparatus for displacing high

concentrations of acetic acid from the TPA or IPA/TPA, using the current invention with acetic acid and demineralized water wash and or recycled acetic acid and sour water, removing the need of the oxidation filter and drying systems.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS [00022] FIG. 1 shows a typical process for separating TPA or IPA/TPA, with high concentrations of acetic acid (typically 8-20%). (a) Cake high in acetic acid from the oxidation filter (1) enters a conveyor or conveyors (2). (b) The feed then enters a rotary steam dryer (3). (c) The acetic acid and other low boiling point components flash off from the TPA, TPA/IPA cake (typically at a temperature betweenll8°C - 155°C). The vapor phase enters a counter current gas stream (7). (d) The gas stream enters a scrubber (8). (e) Acetic acid is scrubbed from the gas stream by recirculated acetic acid, which is cooled by the circulation cooler (10). (f) The scrubbed gas stream is heated in the gas heater (11). (g) The stream pressure and flow are increased by a gas blower (12). (h) Some of the gas is further treated before being released to atmosphere (13). (i) The remaining gas is returned to the dryer (3). (j) The dried product is discharged from the dryer to a rotary valve (4). (k) A gas stream pneumatically transfers the product to a silo (5). (1) The gas stream is treated and discharged from the silo to atmosphere (14). (m) Product is discharged from the silo (6). [00023] Part I of the claimed invention relates to a method and apparatus to separate the high concentrations of acetic acid from the TPA or TPA/IPA mix, downstream of the oxidation filtration stage, thus removing the need for the drying system and storage stage mentioned previously. Part I of this invention, also relates to the method for the solvent recovery system to separate the TTA, solids, water and acetic acid. [00024] Parts II and III of the invention relate to a method and apparatus to separate high concentrations of acetic acid from the TPA or TPA/IPA mix; upstream of the oxidation filtration stage, thus removing the need for the oxidation filter and also removing the need for the drying system and storage mentioned previously.

[00025] Part I of this invention separates the acetic acid from the TPA or TPA/IPA mix cake, using a pressure filter, hereinafter called the HAc Replace filter. The high concentrations of acetic acid and also catalysts are removed as mother liquor, which are then treated in an oxidation solvent recovery section; leaving the TPA or TPA/IPA mixed product, with reduced acetic acid concentration to be further processed by the purification plant. [00026] Parts I and II of this invention, specifically relate to the downstream purification plant being GT-PTA, which is a patented process by GTC Technology.

However, although this invention specifically relates to the downstream process as GT-PTA, it should also be taking into consideration that both part one and part two of this invention can be used as additional equipment, retrofitted to an existing hydrogenation PTA plant. [00027] For Part III of this invention, the downstream purification plant referenced, specifically relates to conventional hydrogenation purification plants.

[00028] The feed to the oxidation filter, with high concentrations of acetic Acid, can be either TPA, or TPA/IPA mixture (>80% TPA and <20% IP A). The invention also recognizes that TPA or TPA/IPA mixture with low concentrations of acetic acid can be used in this process. TPA/ TPA/IPA mix, contains impurities such as, 4-CBA, 3- carboxybenzaldehyde (3-CBA), and toluic acid isomers. Using the selective solvent TTA will also remove these impurities from the cake by up to 97%.

[00029] The referred to oxidation filtration stage can be either of the following: · A rotary vacuum filter system, whereas either TPA or a mixture of TPA & IPA cake is washed with acetic acid to remove the majority of impurities, leaving a high concentration of acetic acid; which cannot be processed by conventional PTA processes, however, can be processed by this invention, in connection with, GT- PTA purification plant.

· A pressure filter system, whereas either TPA or a mixture of TPA & IPA cake is washed with acetic acid to remove the majority of impurities, leaving a high concentration of acetic acid; which cannot be processed by conventional PTA processes; however, can be processed by this invention, in connection with GT- PTA purification plant. [00030] Further embodiments of this invention in particular parts II and III, also consider the upstream oxidation filtration system as part of this invention; these are:

• Part II, a pressure filtration system, where TPA or a mixture of TPA & IPA cake is washed with multiple zones consisting of acetic acid to remove the majority of the oxidation impurities and then further washed using TTA solvent to displace the acetic acid and some of the impurities such as 4CBA, 3CBA, BA, and p-TA.

Leaving a low concentration of acetic acid in the discharged TPA product. It can then be processed either by this invention or directly by the GT-PTA isothermal salt formation (ISF) section. · Part III, a pressure filtration system whereas TPA cake is washed with multiple zones consisting of acetic acid to remove the majority of the oxidation impurities and then further washed using demineralized water to displace the acetic acid, which leaves a low concentration of acetic acid in the TPA product, which can then be further processed by a conventional hydrogenation purification plant. Hi2h acetic acid displacement system (Part I)

[00031] In accordance with the present invention, there is provided a method and apparatus for reducing the acetic acid concentration within the liquid feed of oxidized TPA or TPA/IPA mix to the purification plant, without the need to dry the product as described previously.

[00032] It is taken, that the liquid feed in this invention has already been filtered by the oxidation filtration section; to remove the majority of acetic acid and other TPA or IPA/TPA impurities, typically Mn, Co and other color forming impurities. However, to remove the residual Co & Mn impurities, the TPA or IPA/TPA product, is exposed to acetic acid (80-99%) wash inside the oxidation filter system. This leaves the cake with reduced impurities of Co & Mn but high in acetic acid, typically between 5-30wt%.

[00033] The basis of this invention is to mix the acetic acid saturated TPA cake or IPA/TPA cake, which typically contains <30wt% moisture at a temperature between 10°C and 90°C; with recycled and or reprocessed TTA solvent. Previous invention by Wytcherley & Chou patent (US 7,307,188 B2), claims that the TTA solvent, dissolves the TPA cake and the claim for this invention is that the high concentrations of acetic acid in the solution, coelutes, with the TTA solvent, allowing the solvent and acetic acid to be separated from the TPA or IPA/TPA mixture, thereby improving the TPA or IPA/TPA purity and lowering energy requirements.

[00034] At this point in the process, the mixture, which is now a slurry containing < 50% solids, is filtered using a pressure filter, with independent wash zones and wash collection points.

[00035] The mother liquor which is removed from the pressure filter will contain high concentrations of acetic acid, typically (5-45 wt%) and also TTA solvent. Further acetic acid is removed from the cake, by washing with TTA solvent with a temperature between 10-120°C) this reduces the acetic acid concentration in the discharged cake. The cake is further treated by GT-PTA.

[00036] The mother liquor removed from the filter contains TPA and or

TPA/IPA mix, TTA solvent, acetic acid and also TPA / IPA impurities. A portion of this mother liquor is returned back to the mixing vessel for re-slurrying the high acetic TPA or IPA/TPA mix feed, a portion is also returned to the wash system for further recycle use and the remaining mother liquor is purged from the system to a distillation apparatus, to allow the acetic acid, water and TTA solvent to be separated from the heavier phases of TPA or TPA/IPA, and their impurities. Recycled TTA solvent, is cooled and returned to the mixing vessel for re-slurrying purposes, or is reprocessed further by the downstream solvent recovery system, described later in this patent.

[00037] FIG. 2 is an example showing the method and apparatus for separating the high acetic acid feed from the oxidation filtration section, known in this invention as the HAc Replace filter, (a) Several liquid streams are fed to the re-slurry drum (2) to form a viscous slurry between 15-50% solids with a temperature between 20°C and 100°C. (b) The Re-slurry drum (2) is an agitated mixing vessel, designed to mix the contents of high acetic acid feed from the oxidation filter (l)recovered mother liquor and recovered TTA solvent from the solvent recovery plant, (15) (c)The mixed feed is pumped by the Re-slurry drum pump (3) to the HAc Replace filter (4). (d) The cake is separated from the majority of the mother liquor before being washed with recovered TTA solvent and or recycled mother liquor (5 &6) to remove HAc entrained in the cake, (e) The recovered wash discharged from the filter (7) is collected in the mother liquor drum (1 l)(f) The cake is dried using inert gas (8) and discharged to the GT-PTA ISF section (9).(g) The mother liquor exits the filter (10) and enters the mother liquor drum (11). (h) The mother liquor, mixed with wash liquor is transferred by the mother liquor pump (12), and mixed with recovered TTA solvent (5), before being transferred to the Re-slurry drum cooler (14), which cools the liquor between (20-100°C) (i) The cooled solvent and mother liquor (15), is transferred to the Re-slurry drum (2). (j) The remaining mother liquor is pumped by the mother liquor pump (12) to the solvent recovery section (13) to be further processed, or and recycled to the filter wash zones (6).

[00038] FIG. 3 represents the solvent recovery section of the invention, (a) Mother liquor (1) is transferred to the solvent stripper vessel (2). (b) Bottoms of the solvent stripper are circulated by the solids pump (3) and heated to 100 - 220°C by the solvent stripper heater (4). A portion of the concentrated solids are transferred for further processing (5). (c) Vapor from the solvent stripper passes to the Solvent Vacuum dehydrator (6). (d) The vacuum is created by the vacuum package (11). (e) The lighter phase condenses in the solvent vacuum dehydrator condenser (9). (f) Lighter phase is collected in the solvent vacuum dehydrator reflux drum (10). (g) The lighter phase is returned as reflux (13) and also sent for further processing (14). (h) A mixture of acetic acid and water is collected as a side stream (8) at between 80% to 98% acetic acid and sent for further processing (15). The acetic acid and water can also be recovered direct from the top of the column and condensed in the solvent vacuum dehydrator condenser (9). (i) The heavy phase, mainly TTA solvent, is heated by the solvent vacuum dehydrator reboiler (7) to remove the lighter phase components, mainly acetic acid and water, (j) The concentrated TTA solvent is cooled by the bottoms cooler (16) and transferred by the vacuum dehydrator bottoms pump (17) for further reuse (18). Oxidation filter, impurity and acetic acid displacement (Part II)

[00039] In accordance with the present invention there is also provided a method and apparatus for processing the high acetic acid feed, by replacing the upstream oxidation filtration system, with use of a pressure filter, utilizing several washing zones for both acetic acid and also TTA solvent, with separate collection points for each zone. This will have the same impact, as removing the oxidation dryer system and the oxidation filter system, both mentioned previously.

[00040] It is claimed, that the liquid feed to this invention typically consist of TPA or IPA/TPA mixture in an acetic acid solution with TPA or IPA impurities. This feed comes from the crystallizer section which is located downstream of the oxidation reaction. [00041] The liquid feed enters the pressure filter, where the majority of impurities and acetic acid, contained in the slurry, is filtered and removed as the mother liquor. The invention further claims, that the TPA or IPA/TPA cake then undergoes washing in one or more zones using acetic acid and or recycled mother liquor. This will remove impurities such as, Co & Mn, as well as other color forming impurities contained in the TPA or IPA/TPA cake. This leaves a TPA or IPA/TPA cake high in acetic acid concentration but reduced in impurities. The separated wash of removed impurities and acetic acid is fed directly to the mother liquor vessel, to be reprocessed by the oxidation plant; or used as recirculated wash solvent for this filter wash zones. [00042] The TPA or IPA/TPA mix is then separately washed by recycled TTA solvent mother liquor and or reprocessed TTA solvent at <120°C.

[00043] The TTA solvent comes into contact with the high concentrations of acetic acid and coelutes with the acetic acid in the filter cake. The acetic acid and TTA solvent, are then rejected via the pressure filter separated wash system return lines, to be further processed by downstream equipment and or used as recirculated solvent for this filter wash zones.

[00044] This invention will predominantly be used with GTC purification technology. However, this part of the invention should also be considered, that conventional hydrogenation PTA plants can also be retrofitted with this technology.

[00045] FIG. 4 is an example showing the method and apparatus of part 2 of this invention, (a) The filter feed from the oxidation crystallizer section will first be collected in the filter feed vessel (1). (b) Filter feed pump (2) transfers the feed to the oxidation TPA IPA/TPA rotary pressure filter (3). (c) The cake forms on the filter cloth as the filter rotates, and the cake then comes into contact with the first wash zone, where acetic acid wash (4) and or, recycled mother liquor, which has a high concentration of acetic acid (18), is used to remove impurities from the cake, mainly catalysts Co and Mn. (d) The wash zone can be either one or more wash zones, (e) The acetic acid and impurities are then collected separately (5) and mixed with the mother liquor in the mother liquor vessel (15). (f) The mother liquor is transferred by the mother liquor pump (16) to the oxidation plant for further processing (17), or returned to the filter as wash (18). (g) As the filter continues to rotate, the cake comes into contact with next wash zone, which may be one or more wash zones. In these wash zones, TTA Solvent (6), and or recycled sour TTA solvent (7) displaces the acetic acid, from the cake (8), it then enters the sour solvent vessel (9) (h) The sour solvent is transferred by the sour solvent pump (10) to the GT-PTA solvent recovery section (11) as mentioned in this invention (Solvent recovery section) or recycled back to the filter wash zones (7). (i) The cake is then dried by inert gas (12). (j) The product cake is then discharged for further processing by the GT-PTA technology (13). Oxidation filter, impurity and acetic acid displacement (Part III)

[00046] In accordance with the present invention there is also provided a method and apparatus for separating the high acetic acid and catalyst feed, by replacing the upstream oxidation filtration system with the use of a pressure filter. The pressure filter utilizes several washing zones, for both acetic acid and demineralized water, with separate collection points for each zone. This will have the same impact as removing the oxidation dryer system and the oxidation filter system, both mentioned previously.

[00047] It is claimed, that the liquid feed to this invention typically consist of TPA or IPA/TPA mixture in an acetic acid and catalyst solution with TPA or IPA product impurities. This feed comes from the crystallizer section which is located downstream of the oxidation reaction section.

[00048] The liquid feed enters the pressure filter, where impurities and acetic acid, contained in the slurry, is filtered and removed as the mother liquor. The invention further claims, that the TPA or IPA/TPA cake then undergoes washing in one or more zones using acetic acid or recycled mother liquor. This will remove impurities from the product cake such as, Co & Mn. eaveing a TPA or IPA/TPA cake high in acetic acid concentration with reduced impurities. The separated wash of removed impurities, acetic acid and catalyst is reprocessed by the downstream oxidation plant; and or recirculated to the filter wash zones.

[00049] As well as washing the TPA or IPA/TPA mix with recycled mother liquor, the cake is also washed in a separate wash zone, or wash zones using demineralized water. The demineralized water, comes into contact with the high concentrations of acetic acid and coelutes with the acetic acid within the cake. The acetic acid and demineralized water are then rejected via separated wash system return lines, to be further processed by downstream separation equipment, such as the solvent recovery section, mentioned in this invention and or used as recirculated sour water for this and or previous filter wash zones.

[00050] This part of the invention is expected to be predominantly used with downstream conventional hydrogenation PTA plant technology; however, it should also be considered that the upstream oxidation plant can be retrofitted to accommodate the GT-PTA purification technology with this invention. [00051] FIG. 5 is an example showing the method and apparatus of part 3 of this invention, (a) The feed from the oxidation crystallizer section (1) is collected in the filter feed vessel (2). (b) The filter feed pump (3) transfers the feed to the TPA or IPA/TPA rotary pressure filter (4). (c) The cake forms on the filter cloth as the filter rotates, and comes into contact with first wash zone, where acetic acid (5) and or recycled mother liquor (6) is used as the wash to remove impurities from the cake mainly catalysts, Co and Mn. This wash zone, can either be one, or more wash zones, (d) The acetic acid and impurities are collected separately (7) and transferred with the mother liquor (8) to the mother liquor drum (9). (e) As the filter continues to rotate, the cake comes into contact with next solvent wash zone, which uses demineralized water as the solvent (12) or and recycled sour water (13). This washing section can also be one, or more wash zones, (f) The demineralized water displaces the acetic acid and is collected separately as sour water (14) for reprocessing, or and to be to recycled to the wash zones, (g) The filter continues to rotate into the drying zone, where inert gas (15) is used to dry the TPA or IPA/TPA cake, (h) The cake is then discharged for further processing either by conventional hydrogenation purification plant technology, or by the GT-PTA purification plant technology (16).

[00052] Those having skill in the art, with the knowledge gained from the present disclosure, will recognize that various changes could be made to the methods disclosed herein without departing from the scope of the present invention. Mechanisms used to explain theoretical or observed phenomena or results, shall be interpreted as illustrative only and not limiting in any way the scope of the appended claims.

Claims

1. A method to separate high concentrations of acetic acid and product impurities from TPA or a TPA/IPA mix, the method comprising: filtering a feed comprising TPA or TPA/IPA mix; providing a pressure filter in the filtration step, wherein the pressure filter separates the acetic acid and impurities as mother liquor from the TPA or TPA/IPA mix; performing a filtration wash on the mother liquor; and collecting the mother liquor for further treatment downstream of the filtration step.

2. The method of claim 1, wherein the filtration wash is carried out in one or more filter wash zones at a temperature between 30°C and 150°C

3. The method of claim 2, wherein demineralized water and/or recycled sour water, is used in the filtration wash.

4. The method of claim 1 wherein the further downstream treatment of the mother liquor is carried out between 50- 210°C.

5. The method of claim 1 wherein part or all of the further downstream treatment is operated under vacuum.

6. The method of claim 1, wherein solids are first separated from the lighter vapor phase in a solvent stripper vessel and the lighter vapor phases are further separated from the solvent in a vacuum distillation column.

7. An apparatus for performing the method of claim 1.