WO2015157009A1

WO2015157009A1 - Pure plant waste water purification and recycle

Info

Publication number: WO2015157009A1
Application number: PCT/US2015/022714
Authority: WO
Inventors: Finbar Mcdonnell; Ronojoy GOHO; Kristan WADROP
Original assignee: Invista North America S.A.R.L.
Priority date: 2014-04-08
Filing date: 2015-03-26
Publication date: 2015-10-15
Also published as: TW201544460A

Abstract

Disclosed are methods for purifying aqueous waste streams from a pure terephthalic acid (PTA) manufacturing plant and recycling of the purified water back into the PTA plant. Specifically, provided is a process for treating an aqueous eluent stream generated by a pure plant mother liquor solvent extraction process by raising the pH of the aqueous stream with an alkali, filtering the adjusted stream; and contacting the filtered stream with a reverse osmosis unit to form a demineralized water stream. Raising the pH of the aqueous stream with an alkali converts the soluble metal salts to insoluble compounds, while also converting both soluble and insoluble organic acids to the corresponding acid salts. The filter can be a standard ultrafiltration membrane, which removes the insoluble metal compounds and other remaining insoluble components. The reverse osmosis unit removes organic acid salts, including sodium salts, while balancing the pH.

Description

PURE PLANT WASTE WATER PURIFICATION AND RECYCLE

FIELD OF THE INVENTION

[0001] The invention is related to methods for purifying aqueous waste streams from a pure terephthalic acid (PTA) manufacturing plant and recycling of the purified water back into the PTA plant. The invention also relates to novel aqueous waste stream and purified water stream compositions.

BACKGROUND OF THE INVENTION

[0002] Poly(ethylene terephthalate) (PET) resins are widely produced and used, for example, in beverage and food containers, thermoforming applications, textiles, and as engineering resins. PET is a polymer formed from ethylene glycol and terephthalic acid (or dimethyl terephthalate). Terephthalic acid (1,4-benzenedicarboxylic acid) generally must be synthesized for use as a reactant. The terephthalic acid required as a reactant for PET production is a form of terephthalic acid known as "purified terephthalic acid" (PTA), which generally contains over 99.99 weight percent of terephthalic acid, and less than 25 ppm 4-carboxibenzaldehyde (4-CBA).

[0003] On the commercial scale, purified terephthalic acid (PTA) suitable for use in PET production is generally prepared in a two-stage process comprising paraxylene oxidation followed by purification of the crude oxidation product. First, paraxylene is oxidized (e.g., with air) to provide crude terephthalic acid (CTA), such as described, for example, in U.S. Patent No. 2,833,816 to Saffer et al.„ which is incorporated herein by reference. The oxidation reaction is generally conducted in a solvent comprising an aliphatic carboxylic acid (e.g., acetic acid) and in the presence of a metal catalyst (e.g., a cobalt or manganese salt or compound).

[0004] The crude terephthalic acid produced by this oxidation reaction is then purified, as it is typically contaminated by such impurities as 4-carboxybenzaldehyde, p-toluic acid, and various colored impurities that impart a yellowish color to the terephthalic acid. Purification of the CTA typically requires at least one chemical transformation in addition to at least one physical procedure (e.g., crystallization, washing, etc.). One common chemical transformation is hydrogenation of the CTA, which can transform one of the main impurities in the CTA, 4- carboxybenzaldehyde, to p-toluic acid, which is easier to remove. Thus, CTA is generally dissolved in water and subjected to hydrogenation in the presence of a Group VIII noble metal hydrogenation catalyst (e.g., a supported platinum or palladium catalyst) as a first step of purification. The purified terephthalic acid is recovered by one or more physical procedures. For example, PTA is generally obtained via crystallization of the product from water, as a majority of the impurities, including p-toluic acid, acetic acid, and small amounts of terephthalic acid remain in the solution. The PTA can be recovered by such means as filtration or centrifugation and washed to provide the pure desired material. The remaining solution is referred to as "pure plant mother liquor" (PPML).

[0005] The PPML remaining after production of purified terephthalic acid generally comprises some concentration of impurities. Although the PPML can be treated for release as effluent water on a commercial scale, it can be beneficially purified and recycled for use in the production of more terephthalic acid. Further, the impurities typically include crude terephthalic acid, which can be recovered and purified, as well as p-toluic acid, which can readily be converted into terephthalic acid. The recovery of these dissolved organic acids using solvent extraction is known as pure plant mother liquor solvent extraction (PPMLSX). The aqueous eluent from PPMLSX is not suitable for direct recycle within a PTA plant or for direct supply to a Reverse Osmosis (RO) based technology, such as those conventionally used for desalination of water, without further treatment.

[0006] Water management is a growing issue for all industries globally, especially in areas where there is a shortage of fresh water. Currently, most PTA plants use demineralized water for purification of the product on a "once-through" mode. "Once-through" means that little or no recycling of water is employed; with a major portion of the water used in the process being discharged as liquid effluent. The costs associated with managing water are increasing and by employing better water recycle techniques; the overall operating cost of a PTA plant can be reduced while making it more environmentally friendly.

BRIEF SUMMARY OF THE INVENTION

[0007] The PPMLSX process permits recovery of a major portion of the organic acids from the PPML. In doing so, the process generates an aqueous waste stream, which combines the majority of the aqueous output of both oxidation and purification process steps, the recycle of which would offer potential environmental and economic benefits. The aqueous stream generated by the PPMLSX process is not suitable for direct recycle in a PTA plant, as it contains some soluble organic acids and metal salts, as well as suspended organic acid solids.

Furthermore, the combination of the preferred operating temperature range of the PPMLSX process and the presence of the aforementioned impurities means the stream cannot be satisfactorily processed by direct supply to a feed stream to an RO unit based on conventional known desalination membrane technology. This combination of temperature and composition will result in poor removal of dissolved acids and acetic acid by the RO process and may result in both scaling contamination of the RO membranes with organic acids and fouling of the RO membranes by dissolved metal salts and suspended solids.

[0008] Therefore, it would be advantageous to provide pre-RO process step(s) that can remove the metal salts, dissolved acids, and suspended solids. Such step(s) would allow the use of conventional RO processes in PPMLSX schemes, thereby making the PTA plant more environmentally friendly by increasing the output of clean water and reducing operating costs.

[0009] In one aspect of the invention is provided a process for treating an aqueous eluent stream generated by a pure plant mother liquor solvent extraction process comprising: raising the pH of the aqueous stream by contacting the aqueous stream with an alkali to form a pH adjusted stream; contacting the pH adjusted stream with a filter to form a treated stream; and contacting the treated stream with a reverse osmosis unit to form a demineralized water stream. Raising the pH of the aqueous stream with an alkali converts the soluble metal salts to insoluble compounds, while also converting both soluble and insoluble organic acids to the corresponding acid salts. The filter can be a standard micro-filtration or ultrafiltration membrane, which removes the insoluble metal compounds and other remaining insoluble components. The reverse osmosis unit removes organic acid salts, including sodium salts, while balancing the pH.

[00010] In another aspect of the invention is provided a process for using a demineralized water stream obtained from a pure plant mother liquor solvent extraction process comprising: raising the pH of an aqueous stream generated by a pure plant mother liquor solvent extraction process by contacting the aqueous stream with an alkali to form a pH adjusted stream; contacting the pH adjusted stream with a filter to form a treated stream; contacting the treated stream with a reverse osmosis unit to form the demineralized water stream; and sending the demineralized stream to other processes in a PTA plant. The other processes can include crude terephthalic acid crystallization, crystal water washing, terephthalic acid purification, distillation, scrubbing, gas scrubbing, separation, and steam generation.

[00011] In a further aspect of the invention is provided a process for converting organic acids to acid salts in an aqueous eluent stream generated by a pure plant mother liquor solvent extraction process comprising: contacting the aqueous eluent stream with an alkali, wherein the aqueous eluent stream has an organic acid concentration from about 600 ppm to about 5000 ppm prior to contact with the an alkali.

[00012] In yet another aspect of the invention is provided a process for removing cobalt and manganese hydroxides from an aqueous stream at a pH of at least 8 comprising: contacting the aqueous stream with a filter, wherein the aqueous stream has a sodium concentration from about 500 ppm to about 2000 ppm prior to contact with the filter.

[00013] In yet even a further aspect of the invention is provided a process for removing sodium salts from an aqueous stream at a pH of at least 8 comprising: contacting the aqueous stream with a reverse osmosis unit, wherein the aqueous stream has a cobalt concentration of less than 0.1 ppm and an acetate concentration from about 500 ppm to about 3000 ppm prior to contact with the reverse osmosis unit.

[00014] In a further aspect of the invention is provided a pure plant mother liquor solvent extraction aqueous eluent stream comprising: acetic acid at a concentration from about 600 ppm to about 3000 ppm; terephthalic acid at a concentration from about 50 ppm to about 450 ppm; and metals at a concentration from about 0.1 ppm to about 50 ppm, wherein the pH of the aqueous eluent stream in less than 5.

[00015] In yet another aspect of the invention is provided an aqueous stream: sodium salts from about 500 ppm to about 2000 ppm and metal hydroxides at a concentration from about 0.05 ppm to about 50 ppm, wherein the pH of the aqueous stream is at least 8.

[00016] In yet a further aspect of the invention is provided an aqueous stream comprising: cobalt from about 0 to about 0.1 ppm; and manganese from about 0 to about 0.1 ppm, wherein the pH of the aqueous stream is at least 8.

[00017] In yet another aspect of the invention is provided a clean water stream comprising: acetate at a concentration from about 0.5 ppm to about 20 ppm and sodium at a concentration from about 0.1 ppm to about 10 ppm, wherein the water stream has a pH from about 7 to about 10 and is substantially free of K, Mg, Ca, Co, Fe and Mn. BRIEF DESCRIPTION OF THE DRAWINGS

[00018] Figure 1 is a schematic process diagram of the steps of a system for the purification of PPML (PPMLSX system) according to the present disclosure, said PPML being generated from the production of PTA.

[00019] Figure 2 is a schematic process diagram of the steps of an exemplary system for the purification of the PPMLSX aqueous stream according to the present disclosure, said PPML being generated from the production of PTA.

DETAILED DESCRIPTION OF THE INVENTION

[00020] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. As used in the specification, and in the appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly dictates otherwise.

[00021] The present invention provides systems and methods for the production of purified terephthalic acid (PTA). More specifically, the invention provides systems and methods for purification of pure plant mother liquor solvent extraction (PPMLSX) aqueous eluent stream, generated during the purification of pure plant mother liquor (PPML) that is generated during the production of PTA. U.S. Application No. 61/720675 provides an exemplary description of the PPMLSX process, which is herein incorporated by reference in its entirety. Briefly, the

PPMLSX process and PTA process are described below.

[00022] The commercial production of PTA typically begins with the liquid-phase oxidation of a p-phenylene compound to give crude (i. e. , impure) terephthalic acid. The p-phenylene compound most commonly used is paraxylene (p-xylene); however, any phenylene having substituent groups subject to oxidation to form carboxyl groups at the para positions of the phenylene can be used. For example, exemplary substituent groups on the phenylene can include, but are not limited to, methyl, ethyl, propyl, isopropyl, formyl, acetyl, and combinations thereof. The substituents can be the same or different. 100023] The solvent used in the oxidation reaction can vary, but generally comprises acetic acid, which may optionally contain water. The oxidation reaction can be conducted under any conditions wherein oxygen is available. For example, the reaction can be conducted in air, wherein the oxygen in air can serve as the oxidant, and/or in an environment enriched with pure oxygen (e.g., an all-oxygen atmosphere or an inert gas atmosphere to which some concentration of oxygen is added). A transition metal catalyst and, optionally, a co-catalyst, are commonly used. The oxidation catalyst can vary and can, in some embodiments, comprise a heavy metal salt or compound (e.g., a cobalt, manganese, iron, chromium, and/or nickel-containing compound or salt, or a combination thereof) as described, for example, in U.S. Patent No.

2,833,816 to Saffer et al, which is incorporated herein by reference. Various co-catalysts and/or promoters can also be added, including, but not limited to, a bromine-containing compound, a bromide salt, a ketone (e.g., butanone, triacetylmethane, 2,3-pentanedione, methylethylketone, acetylacetone, or a combination thereof), a metalloporphyrin, a zirconium salt, or a combination thereof.

[00024] Oxidation is typically conducted at elevated temperature and/or elevated pressure. Generally, the temperature and pressure must be sufficient to ensure that the oxidation reaction proceeds, but also to ensure that at least a portion of the solvent is maintained in liquid phase. Therefore, it is generally necessary to conduct the oxidation reaction under both elevated temperature and elevated pressure conditions. The temperature required for the oxidation reaction may vary with the selection of the catalyst and optional co-catalyst and/or promoter. In certain embodiments, the reaction temperature is in the range of about 160 °C to about 220 °C; however, in some embodiments, the temperature can be maintained below 160 °C while still obtaining the oxidized product.

[00025] Following the oxidation reaction, the reaction mixture is typically cooled (e.g., by transferring the mixture to one or more crystallizer units, with decreased pressure). The resulting mixture generally comprises a slurry from which the crude terephthalic acid can be isolated. The means for isolating the crude terephthalic acid can vary and may comprise filtration,

centrifugation, and or any other suitable means for the separation of a solid phase and liquid phase. The solid phase is typically washed with fresh water and/or acetic acid to give isolated crystals of crude terephthalic acid. The liquid phase (typically comprising water, acetic acid, methyl acetate, and various other components) can, in some embodiments, be treated such that the acetic acid is separated from water and other low-boiling components. For example, in some embodiments, the liquid phase is vaporized and the steam is sent to a distillation apparatus (e.g., wherein it can undergo azeotropic distillation). Generally, azeotropic distillation can be an effective method for separating acetic acid from water and is done in the presence of an organic entrainer. Typically, within an azeotropic distillation apparatus, a bottoms product will form, comprising primarily acetic acid (which can, in some embodiments, be recycled into the oxidation reaction). The tops product may comprise organic entrainer, water, and methyl acetate and can subsequently be cooled to form a condensate.

[00026] The crude terephthalic acid is then purified to provide PTA suitable for use in the production of poly(ethylene terephthalate). Various impurities are generally present in the crude terephthalic acid at this stage. For example, 4-carboxybenzaldehyde is one of the most common contaminants, as well as compounds that impart some degree of color to the crude terephthalic acid. Purification of the CTA typically requires at least one chemical transformation in addition to at least one physical procedure (e.g., crystallization, washing, etc.). The chemical

transformation can include various processes, including but not limited to catalytic

hydrotreatment, catalytic treatment, oxidation treatment, and/or recrystallization. Commercially, the most commonly used chemical transformation is hydrogenation, which can transform one of the main impurities in the CTA, 4-carboxybenzaldehyde, to p-toluic acid, which is easier to remove.

[00027] Various hydrogenation conditions can be used according to the invention. The CTA is generally dissolved in a solvent (e.g., water). In some embodiments, heat and/or pressure are required to dissolve the CTA in water. It is then subjected to hydrogenation in the presence of a Group VIII noble metal hydrogenation catalyst (e.g., a platinum, palladium, ruthenium, or rhodium catalyst) or an alternative type of catalyst (e.g., a nickel catalyst). The catalyst can be a homogeneous or heterogeneous catalyst and can be provided in an unsupported form or can be supported on any type of material suitable for this purpose. Support materials are generally porous materials including, but not limited to, activated carbon/charcoal, alumina, calcium carbonate, barium sulfate, silica powder, quartz powder, or a combination thereof. The hydrogen source is typically hydrogen gas, although this can vary as well. Although hydrogenation processes can, in certain cases, occur at atmospheric pressure and ambient temperature, on the commercial scale, heat and/or pressure are often applied. For example, in certain embodiments, the temperature is from about 200 °C to about 374 °C, e.g., about 250 °C or greater. The pressure is typically sufficient to maintain the CTA solution in liquid form (e.g., about 50 to about 100 atm). The amount of hydrogen required to effect hydro genation of the CTA is typically an excess of that amount required for reduction of dissolved impurities. The hydrogenation can occur, for example, within a pressure vessel, hydrogenator, or plug-flow reactor or can be accomplished by flow hydrogenation, wherein the dissolved CTA is passed over a fixed bed catalyst in the presence of hydrogen.

[00028] The purified terephthalic acid is recovered by one or more physical procedures. For example, PTA is generally obtained via crystallization of the product from solution (e.g., water), as a majority of the impurities, including p-toluic acid, acetic acid, and small amounts of terephthalic acid remain in the solution. Thus, the mixture in some embodiments, is passed through one or more crystallizers and depressurized (which generally cools the mixture and evaporates some water, giving a slurry of PTA crystals). The PTA can be recovered by such means as filtration and/or centrifugation, washed, and dried to provide the pure desired material. The remaining solution is known as pure plant mother liquor (PPML). The temperature at which this separation of PTA and PPML is conducted can vary; however, it is typically in the range of from about 70 °C to about 160 °C (e.g., about 100 °C or greater).

[00029] The PPML generally comprises water, along with some content of p-toluic acid, acetic acid, and small amounts of impure terephthalic acid. The PPML may also comprise benzoic acid and other intermediates and byproducts. According to the present invention, the PPML is purified by means of a process such as that exemplified in Figure 1, where like identifies refer to like components or streams. Although the process schematic in Figure 1 are not intended to be limiting of the invention, they represent exemplary systems that can employ the steps and features as described in the present application. Briefly, in some embodiments, PPML is contacted with an extractant in order to extract aromatic carboxylic acids (e.g., p-toluic acid and benzoic acid) therefrom. The extractant can take various forms and can be provided from various sources. The extractant advantageously can comprise an organic entrainer used in the distillation of the liquid phase obtained following the oxidation reaction of paraxylene to produce crude terephthalic acid.

[00030] Referring first to Figure 1, "OR" represents an oxidation reaction of paraxylene, such as generally described above. Other discussion of such reactions is provided, for example, in U.S. Patent Nos. 5,705,682 to Ohkashi et al; and 6,143,926 and 6,150,553 to Parten, each of which is incorporated herein by reference. Stream B represents the overhead condensates formed during the oxidation reaction as well as the liquid and vapor phases obtained following the oxidation reaction and removal of the solid crude terephthalic acid. As such, stream B primarily comprises water and acetic acid (in liquid and/or vapor form). The primary component is generally acetic acid (e.g., at least about 50% by volume) and the remainder of the stream is generally water, although small amounts {e.g., less than about 5%, less than about 2%) of organic components {e.g., methyl acetate) can also be present in stream B. The liquid and/or vapor- containing stream B is brought into contact with an organic entrainer in distillation column 30. The entrainer can vary, but is advantageously a substance suitable for azeotropic distillation of a mixed solution of acetic acid and water. For example, in certain embodiments, the entrainer comprises toluene, xylene, ethylbenzene, methyl butyl ketone, chlorobenzene, ethyl amyl ether, butyl formate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, amyl acetate, methyl acetate, n-butyl propionate, diisobutyl propionate, propanol, water, or a combination of any two or more of these or other entrainers. Column 30 can be, for example, a trayed or packed column. A general discussion of azeotropic distillation processes to separate water from acetic acid is provided, for example, in U.S. Patent No. 5,980,696 to Parten et al, which is incorporated herein by reference.

[00031] Within column 30, organic entrainer is used to separate acetic acid and water. The acetic acid-containing phase can be removed from the bottom of the column as streams G and Jl. Typically, stream G comprises about 95% acetic acid and about 5% water and does not contain a significant amount of entrainer. Stream G is recycled to the column 30 through reboiler 60. The hot acetic acid stream Jl leaving column 30 is passed through heat exchanger 25 prior to passage back into the oxidation reaction. The organic stream Γ1 exiting the decanter 20 is also passed through heat exchanger 25 such that heat from acetic acid stream Jl is transferred to the organic stream Fl prior to its entry to the column 30 as stream F2. As such, organic stream F2 enters the column 30 at an increased temperature relative to the temperature upon exiting the decanter 20.

[00032] The vapor phase produced within column 30 generally comprises organic entrainer, as well as water and methyl acetate. Methyl acetate is advantageously removed from column 30 as it can, in some embodiments, interfere with the azeotropic separation within column 30. The vapor phase can be removed from the distillation column as stream C. This stream may be condensed within condenser 40 to provide condensate stream D. Condensate stream D generally comprises organic entrainer and may further comprise water, which can be removed from the mixture or maintained as a component of condensate stream D. The temperature of condensate stream D can vary; however, in exemplary embodiments, stream D is between about 60 °C and about 100 °C, such as between about 70 °C and about 90 °C, between about 75 °C and about 82 °C (e.g., about 78 °C or about 80 °C in certain embodiments). It is noted that the temperature of the condensate will vary somewhat depending upon the makeup of the condensate stream D (e.g., the specific entrainer used).

[00033] PPML stream A is brought into contact with stream D in a mixer 10. The weight ratio of stream A to stream D can vary and other components can be added to the mixer if desired (e.g., additional entrainer or water). The ratio of stream D to stream A is about 1 : 1 to about 5: 1 (e.g. , about 1.7: 1 to about 2.1 : 1). The nature of the mixer 10 can vary; it can comprise an extraction column, static mixer, dynamic mixer (e.g. , an agitating mixer), pump, or shaker.

[00034] The resulting mixture of stream A and stream D exits the mixer 10 as mixed stream E and is passed into a decanter 20. The decanter can be any component which can provide for separation of an organic (e.g., entrainer-rich) stream Fl from an aqueous stream K. Sometimes, a single decanter can be used, which can reduce the capital cost of the system and reduce the degree of hydrolysis of the entrainer. Also, certain organic impurities originally present in the PPML stream A (e.g., p-toluic acid, benzoic acid, etc.) are extracted into the organic phase and thus removed via organic stream Fl. Methyl acetate (originally present in stream C from distillation column 30) is partitioned into aqueous stream Kl .

[00035] The organic stream F2 is routed to the distillation column 30. Although the figures show entry of stream F2 at the middle of the distillation column, this is not intended to be limiting; stream F2 may enter the column at the top, middle, or bottom of the distillation column or at any stage in between. With the entry of certain organic components via stream F2, it is noted that the makeup of streams C and Jl leaving the distillation column 30 can be affected. Generally, the majority of the organic components that enter the distillation column via stream F2 are retained in the acetic acid phase and are removed from column 30 via stream Jl.

[00036] Aqueous stream Kl can be treated to allow water to be reused within the process (e.g., in the purification of CTA), recycled for other purposes, or disposed of as waste water. As shown in Figure 1, the heated effluent water LI exiting the recovery column 70 can be passed through the heat exchanger 65 in a heat exchange relationship with the aqueous stream Kl exiting the decanter 20. As such the aqueous stream K2 exiting the heat exchanger 65 can be delivered to the column 70 at a significantly increased temperature. The temperature of stream K2 can vary such that stream K2 can comprise an aqueous liquid and/or vapor phase. Provision of stream K2 at the increased temperature is beneficial in that the quantity of steam (via stream M) that must be introduced into column 70 to effectively strip the organic components can be significantly reduced. Undesirable methyl acetate, which can be present in aqueous stream K2 can be stripped from the aqueous phase of the PPML extraction in certain embodiments by passing the aqueous phase K2 through recovery column 70, which is designed to strip out any residual organic material. It is noted that a small amount of the organic phase (e.g. , comprising the organic entrainer) can also be present in stream K2 and in some embodiments, such residual organic material can also be removed via recovery column 70. Generally, the stripping of organic material from the aqueous phase is accomplished via contacting the aqueous phase stream K2 with steam, shown as stream M entering the column 70. Alternatively, a reboiler on column 70 can be used in place of stream M. In order to effectively strip the organic components, the stream to be treated generally should be heated to about 40 °C to about 140 °C, including 60 °C to 100 °C, e.g., about 95 °C. Cleaned water can exit the column, e.g., at the bottom thereof, via stream L2. Recovery column 70 can be further equipped with a condenser 50, which returns a reflux to the top of the column with a vapor purge and a liquid product.

[00037] Stream L2 contains impurities (e.g. carboxylic acids, metals) that make it unsuitable for use in other parts of the PTA plant. Further, because the operating temperature of the PPMLSX process and poor rejection of acetic acid at these temperatures, fouling and scaling of reverse osmosis membranes may occur. Surprisingly, it has been found that pre-treatment of stream L2 followed by reverse osmosis results in a demineralized water stream that is suitable for use in other parts of the PTA plant. Specifically, pre-treating L2 with an alkali solutions and micro or ultra-filtration makes reverse osmosis an economical and efficient method of obtaining demineralized water. Upon exiting the PPMLSX process, aqueous eluent stream L2, at a pH of less than or equal to 7, including 2-7, 4, 5, 6 and 7, has the following composition in Table 1 :

Acid and salts of acid expressed as w/w concentration of the acid.

Table 1

[00038] Prior to using L2 in a reverse osmosis process, L2 is treated to remove carboxylic acids and dissolved metals, and the pH is adjusted. Here, L2 enters neutralizer 100, wherein the aqueous stream is contacted with an alkali (e.g. sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, and mixtures thereof) to raise the pH to between 8-11, including 9 and 10. The concentration of the alkali in the aqueous stream can range from 5 wt.% to 90 wt.%, including 5 wt.% to 80 wt.%, 10 wt.% to 80 wt.%, 10 wt.% to 90 wt.%, 20 wt.% to 90 wt.%, 20 wt.% to 80 wt.%, 20 wt.% to 70 wt.%, 30 wt.% to 90 wt.%, 30 wt.% to 80 wt.%, 30 wt.% to 70 wt.%, and 30 wt.% to 60 wt.%. The concentration needs to be sufficient enough to reach an alkali concentration of 500 to 2000 ppm. Additionally, the dissolved and suspended carboxylic acids (e.g acetic acid, terephthalic acid, CBA, p-toulic acid, benzoic acid) are converted to their respective soluble salts. For example, if sodium hydroxide is used as the alkali, then acetic acid is coverted to sodium acetate. Additionally, the dissolved metals (e.g. cobalt, manganese) are converted to metal hydroxides and precipitate out in to the aqueous stream. Neutralizer 100 can be any device that results in sufficient contact between stream L2 and the alkali. For example, counter-current washer, gravity feed decanter (e.g. where L2 passes vertically through the alkali solution), static mixer, sparger can be used. Below is the composition of the pH adjusted stream N when sodium hydroxide is used as the alkali solution:

Acid and salts of acid expressed as w/w concentration of the acid

Table 2

[00039] Next, the pH adjusted stream N is sent to a pre-filtration unit 120, or optionally a holding tank 110 prior to unit 120, for removal of suspended solids. Here, pH adjusted stream N is contacted with at least one pre-filtration membrane to remove the metal hydroxides to form treated stream P. For example, the pre-filtration membrane can be an ultrafiltration membrane KMS HFMTM-180 with a pore size of around 0.1 micron has a rejection performance of >99.5% for cobalt and manganese hydroxides leaving a residual O.05 ppm cobalt and manganese in the treated stream. Typical pre-filtration units include ultra-filtration, micro-filtration, and other media filtration that removes metal hydroxides and other potentially fouling solids prior to the RO step. Ultra-filtration or micro-filtration with a separation range of less than or equal to 0.1 micron including Ultra-filtration Elements such as KMS HFM 180 can provide suitable protection of the reverse osmosis membrane. Below is the composition of the treated stream P when sodium hydroxide is used as the alkali solution:

Acid and salts of acid expressed as w/w concentration of the acid

Table 3

[00040] Treated stream P next passes into reverses osmosis unit 130, where sodium, acetate, and other ionic species are removed, along with a pH reduction to between about 7-10, thereby creating a demineralized water stream Ql and Q. Optionally, a second reverse osmosis unit 140 can be employed with unit 130 to further reduce the concentration of sodium, acetate, and other ionic species. Here, the first pass permeate Rl is fed into unit 140, and a demineralized stream Q2 is drawn off. Further, units 130 and 140 can be used in a loop type configuration, with a portion of the unit 140 permeate R2 being recycled back to unit 130. For example, treated stream P can pass through two reverse osmosis KMS Fluid Systems TFC-SW membranes can be arranged in series, resulting in a demineralized water stream Q with 0.97 ppm of sodium and 2.49 ppm of acetate, and pH of 6. Also, the present disclosure is not limited to one or two reverse osmosis units. Additional units can be employed in series or in loop type configurations with units 130 and 140 depending on application, size of plant, and location. Typical reverse osmosis units can include High Rejection Reverse Osmosis membranes, such as those used for sea water, brackish water, or waste water reclamation, including Fluid Systems®TFC®-SW, DOW™FILMTEC™SW30HRLE-400, FLUID SYSTEMS®TFC-FR, DO W™FILMTEC™BW30-400, Fluid Systems®TFC®-HR. Below is the composition of the demineralized water stream Q when sodium hydroxide is used as the alkali solution: Description Unit Typical Range

SODIUM ppm 0.3 0.1-10

ACETATE ppm 0.5-10

MANGANESE ppm <0.05 0-1

POTASSIUM ppm <0.05 0-1

CALCIUM ppm <0.05 0-1

MAGNESIUM ppm O.05 0-1

IRON ppm O.05 0-1

COBALT O.05 0-1

Table 4

[00041] As shown in Table 4, the demineralized water stream Q is substantially free of metal compounds, Mn, , Ca, Mg, Fe, and Co (i.e. a total metal concentration, excluding the alkali sodium, between 0.01 and 1 ppm, including between 0.01 ppm and 0.1 ppm, and between 0.01 ppm and 0.05 ppm), while also having low sodium and acetate concentrations.

[00042] The demineralized water stream Q can be used in other processes throughout the PTA plant. Such processes include: crude terephthalic acid crystallization, crystal water washing, terephthahlic acid purification, solvent recovery, distillation, separation, and steam generation. Furthermore, the demineralized water stream can be introduced into standard waste water treatment streams for downstream processing at waste water treatment plants.

Claims

CLAIMS What we claim is:

1. A process for treating an aqueous eluent stream generated by a pure plant mother liquor solvent extraction process comprising:

a. raising the pH of the aqueous stream by contacting the aqueous stream with an alkali to form a pH adjusted stream;

b. contacting the pH adjusted stream with a filter to form a treated stream; and c. contacting the treated stream with a reverse osmosis unit to form a demineralized water stream.

2. The process of claim 1, wherein the filter is an ultrafiltration membrane.

3. The process of claim 2, wherein the ultrafiltration membrane has an average pore size of 0.01 micron to 0.1 micron.

4. The process of claim 1, wherein the pH of the pH adjusted stream is from 8 to 12.

5. The process of claim 1 , wherein the alkali is selected from the group consisting of sodium hydroxide, potassium hydroxide, and mixtures thereof.

6. The process of claim 5, wherein the alkali is sodium hydroxide.

7. The process of claim 6, wherein the concentration of sodium metal is between 500 and 2000 ppm.

8. The process of claim 1, wherein the pH of the aqueous stream is from 3 to 5.

9. The process of claim 1 , wherein the treated stream contains metal compounds at a total metal concentration between 0.01 ppm and 1 ppm.

10. The process of claim 9, wherein the total metal concentration is between 0.01 ppm and 0.1 ppm.

11. A process for using a demineralized water stream obtained from a pure plant mother liquor solvent extraction process comprising:

a. raising the pH of an aqueous stream generated by the pure plant mother liquor solvent extraction process by contact the aqueous stream with an alkali to form a pH adjusted stream; b. contacting the pH adjusted stream with a filter to form a treated stream;

c. contacting the treated stream with a reverse osmosis unit to form the demineralized water stream; and

d. sending the demineralized water stream to other processes in a PTA plant.

12. The process of claim 11, wherein the filter is an ultrafiltration membrane.

13. The process of claim 12, wherein the ultrafiltration membrane has an average pore size of 0.01 micron to 0.1 micron.

14. The process of claim 11, wherein the pH of the pH adjusted stream is from 8 to 11.

15. The process of claim 11, wherein the alkali is selected from the group consisting of sodium hydroxide, potassium hydroxide, and mixtures thereof.

16. The process of claim 15, wherein the alkali is sodium hydroxide.

17. The process of claim 16, wherein the concentration of sodium metal is between 500 and 2000 ppm.

18. The process of claim 11, wherein the pH of the aqueous stream is from 3 to 5.

19. The process of claim 11, wherein the treated stream contains metal compounds at a total metal concentration between 0.01 ppm and 1 ppm.

20. The process of claim 9, wherein the total metal concentration is between 0.01 ppm and 0.1 ppm.

21. A process for converting organic acids to acid salts in an aqueous eluent stream generated by a pure plant mother liquor solvent extraction process comprising: contacting the aqueous eluent stream with an alkali, wherein the aqueous eluent stream has an organic acid

concentration from 600 ppm to 5000 ppm prior to contact with the an alkali.

22. The process of claim 21, wherein the organic acid concentration is from 1000 ppm to 5000 ppm.

23. The process of claim 22, wherein the organic acid concentration is from 2000 ppm to 5000 ppm.

24. The process of claim 21, wherein the organic acid concentration is from 1000 ppm to 3000 ppm.

25. The process of one of claims 21 to 24, wherein the organic acid is selected from the group consisting of: acetic acid, terephthalic acid, p-toluic acid, benzoic acid, and mixtures thereof.

26. A process for removing cobalt and manganese hydroxides from an aqueous stream at a pH of at least 8 comprising: contacting the aqueous stream with a filter, wherein the aqueous stream has a sodium concentration from 500 ppm to 2000 ppm prior to contact with the filter.

27. The process of claim 26 wherein the pH of the aqueous stream is from 8 to 11.

28. The process of claim 26 wherein the filter comprises an ultrafiltration membrane.

29. A process for removing sodium salts from an aqueous stream at a pH of at least 8 comprising: contacting the aqueous stream with a reverse osmosis unit, wherein the aqueous stream has a cobalt concentration of less than 0.1 ppm and an acetate concentration from 500 ppm to 3000 ppm prior to contact with the reverse osmosis unit.

30. The process of claim 29 wherein the pH of the aqueous stream is from 8 to 11.

31. The process of claim 29 wherein the acetate concentration is from 1000 ppm to 3000 ppm prior to contact with the reverse osmosis unit.

32. A pure plant mother liquor solvent extraction aqueous eluent stream comprising:

a. acetic acid at a concentration from 600 ppm to 3000 ppm;

b. terephthalic acid at a concentration from 50 ppm to 450 ppm; and

c. metals at a concentration from 0.1 ppm to 50 ppm, wherein the pH of the aqueous eluent stream is less than 5.

33. The aqueous eluent stream of claim 32 further comprising:

d. carboxybenzaldehyde at a concentration from 0 to 20 ppm;

e. p-toluic acid from 10 to 620 ppm; and

f. benzoic acid from 20 to 350 ppm.

34. An aqueous stream composition comprising:

a. sodium salts at a sodium concentration of 500 ppm to 2000 ppm; and

b. metal hydroxides at a metal concentration from 0.05 ppm to about 50 ppm, wherein the pH of the aqueous stream is at least 8.

35. The aqueous stream composition of claim 34 wherein the metal ion of the metal hydroxides are selected from the group consisting of cobalt, manganese, bromide, and mixtures thereof.

36. The aqueous stream composition of claim 34 or 35 further comprising:

c. carboxybenzaldehyde at a concentration from 0 to 20 ppm;

d. terephthalic acid salt at an acid concentration from 50 to 450 ppm;

e. p-toluic acid salt at an acid concentration from 10 to 620 ppm; and

f. benzoic acid salt at an acid concentration from 20 to 350 ppm.

37. An aqueous stream composition comprising:

a. cobalt from 0.01 to 0.1 ppm; and

b. manganese from 0.01 to 0.1 ppm, wherein the pH of the aqueous stream is at least 8.

38. The aqueous stream composition of claim 37 further comprising :

c. terephthalic acid salt at an acid concentration from 50 to 450 ppm;

d. carboxybenzaldehyde at a concentration from 0 to 20 ppm;

e. p-toulic acid salt at an acid concentration from 10 to 620 ppm; and

f. benzoic acid salt at an acid concentration from 20 to 350 ppm.

39. The aqueous stream of claim 37 or 38 further comprising sodium at a concentration from 500 to 2000 ppm.

40. A clean water stream composition comprising:

a. acetate at a concentration from 0.5 ppm to 20 ppm; and

b. sodium at a concentration from 0.1 ppm to 10 ppm, wherein the water stream has a pH from 7 to 10 and is substantially free of metals.

41. The clean water stream composition of claim 40, wherein the metals are selected from the group consisting of K, Mg, Ca, Co, Fe, Mn, and mixtures thereof.

42. The clean water stream composition of claim 40, wherein the concentration of metals is from 0.01 ppm to 1 ppm.

43. The clean water stream of claim 40 wherein the metals are Mg and Co, and the concentration of the metals is from 0.01 ppm to 0.05 ppm.