FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
A process and device for recovering water and valuable chemicals in the aqueous effluent from the manufacture of polycarboxylic acids
APPLICANTS
Name : Reliance Industries Limited
Address : 5th Floor, Maker Chamber IV, Nariman Point,Mumbai 400 021,
Maharashtra, India
Nationality: Indian Company
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF INVENTION
This invention relates to a process and device for recovering water and valuable chemicals in the aqueous effluent from the manufacture of polycarboxylic acids.
BACKGROUND OF INVENTION
Polycarboxylic acids such as terephthalic acid, isophthalic acid, trimellitic acid or pyromellitic acid find applications, among others, in the manufacture
of fibres, dye and pigment intermediates, photographic films, paints or plastic articles. Purified terephthalic acid (PTA), in particular, is primarily used for manufacturing polyester fibres used in making fabrics and clothes. Purification of crude terephthalic acid (TA) formed in the oxidation section of a terephthalic acid manufacturing plant is carried out by dissolving the crude terephthalic acid in a solvent, usually water followed by
hydrogenation thereof at ~ 280°C using a palladium catalyst. During hydrogenation, aldehydic impurities present in the crude terephthalic acid such as benzaldehyde, 4- carboxy benzaldehyde or terephthaldehyde are
reduced to corresponding alcohols like benzyl alcohol, 4-(hydroxymethyl) benzoic acid, p-methyl benzyl alcohol or benzene-1, 4-dimethanol or to
alkanes such as toluene, para-toluvenic acid, p-methyl benzoic acid or paraxylene which remain present in the reaction mixture along with the colour causing impurities. Also present in the reaction mixture are some inorganics like cobalt and manganese catalysts used in the manufacture of crude terephthalic acid along with traces of corrosion metals like iron, nickel, chromium or sodium. On cooling the reaction mixture, purified terephthalic acid precipitates out and is separated by filtration. The organic and inorganic impurities remain dissolved in the aqueous mother liquor ie
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aqueous effluent comprising mostly water. The effluent, acidic in nature, is neutralized with caustic (NaOH) before it is sent to the effluent treatment plant. The effluent from a terephthalic acid plant has the following typical composition:
COD
(Chemical Oxygen Demand) 6000 - 10000 ppm
MLSS
(Mixed Liquid Suspended Solids) /
TSS
(Total Suspended Solids) 50 - 500 ppm
TDS
(Total Dissolved Solids) 4000 - 6000 ppm
Na 900-1500 wt ppm
Co 2 - 30 wt ppm
Mn 2-30 wt ppm
pH 5-7
Processes for the treatment of the aqueous effluent from the manufacture of polycarboxylic acids generally comprise cooling of the effluent usually at 70 to 80°C in a cooling arrangement such as cooling tower to 55 to 60°C followed by adjustment of the pH of the effluent between 6 to 7 with an
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alkali like caustic soda in an equalization tank. The effluent is further cooled in a cooler such as heat exchanger and subjected to aerobic digestion in an aerobic digestor. The effluent is clarified in clarifiers and the
supernatant from the secondary clarifier containing mostly water is discharged into the environment. The sludge or slurry at bottom of the secondary clarifier is concentrated in a decanter / thickner and filtered in a belt filter. The solids as about 15% solids are dried in driers and are either dumped in the environment or used as fuel in furnaces. The filtrate is sent back to the aerobic digestor. Some of the above processes employ the step of anaerobic digestion of the effluent in an anaerobic digester after the step of further cooling and prior to the step of aerobic digestion so as to generate methane gas for use as fuel. The treated water discharged into the environment typically has the following composition :
COD - 40-240mg/l
MLSS/TSS - 20 - 200 mg/1
TDS - 2000 - 2800 mg/1
Na - 800 -1400 wt ppm
Co - < 3 wt ppm
Mn - < 3 wt ppm
pH - 6.8 to 9.0
The treated water is not suitable for industrial reuse because of the presence of high amount of TDS and metals. Thus a large quantity of water is wasted alongwith valuable chemicals causing substantial economic losses.
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OBJECTS OF INVENTION
An object of the invention is to provide a process for recovering water and valuable chemicals in the aqueous effluent from the manufacture of polycarboxylic acids, which can be reused thereby rendering the process practically a zero discharge process.
Another object of the invention is to provide a process for recovering water and valuable chemicals in the aqueous effluent from the manufacture of polycarboxylic acids, which process is economical.
Another object of the invention is to provide a device for recovering water and valuable chemicals in the aqueous effluent from the manufacture of polycarboxylic acids, which device generates zero discharge.
Another object of the invention is to provide a device for recovering water and valuable chemicals in the aqueous effluent from the manufacture of polycarboxylic acids, which device is simple in construction and easy and convenient to operate.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided a process for recovering water
and valuable chemicals in the aqueous effluent from the manufacture of
polycarboxylic acids, the process comprising the steps of:
i) cooling the effluent to 55 to 60 °C;
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ii) adjusting the pH of the effluent between 6.5 to 7.5 with an alkali;
iii) cooling the effluent to 30 to 40 °C;
iv) anaerobically digesting the effluent;
v) aerobically further digesting the effluent and filtering the effluent
in a membrane bioreactor at 20 to 40°C;
vi) further filtering the filtrate from the membrane bioreactor in a
filter; and
vii) subjecting the filtrate to reverse osmosis to obtain permeate
comprising demineralised water and reject comprising sodium
carbonate.
According to the invention there is also provided a device for recovering water and valuable materials in the aqueous effluent from the manufacture of polycarboxylic acids, the device comprising an aqueous effluent cooling arrangement for cooling the aqueous effluent from a polycarboxylic acid plant to 55 °C to 60 °C, an equalization tank for pH adjustment of the cooled effluent between 6.5 to 7.5, a cooler for further cooling the effluent to 30 to 40 °C, an anaerobic digestor for anaerobically digesting the further cooled effluent, a membrane bioreactor for aerobically further digesting the effluent and filtering the effluent, at least one filtrate collection tank for
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collecting the filtrate from the membrane bioreactor and a reverse osmosis module for reverse osmosis of the filtrate fed into the reverse osmosis module from the filtrate collection tank through a filter and a pump, the permeate and reject from the reverse osmosis module comprising demineralised water and sodium carbonate, respectively.
The following is detailed description of the invention with reference to the accompanying drawings, in which the sole Fig 1 is a block diagram of the device for recovering water and valuable chemicals in the aqueous effluent from the manufacture of polycarboxylic acids according to an embodiment of the invention.
The device 1 as illustrated in Fig 1 of the accompanying drawings comprises an aqueous effluent cooling arrangement 2 which can be a cooling tower. 3 is an equalization tank for pH adjustment of the cooled effluent. 4
is a cooler for further cooling the effluent and can be a heat exchanger. 5 is an anaerobic digester for anaerobically digesting the further cooled
effluent. 6 is a membrane bioreactor for aerobically further digesting the effluent and for filtering the effluent. A pair of filtrate collection tanks 7a, 7b are located one above the other and are connected to each other. 8 is a reverse osmosis module connected to the lower tank 7b through a filter 9 and
a pump 10. Preferably, the membrane bioreactor is outside-in hollow fibre type. Preferably, the reverse osmosis module comprises polyamide spiral wound type membrane. Preferably the filter 9 is cartridge type micron
filter.
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Aqueous effluent usually at 70 °C to 80 °C from a polycarboxylic acid manufacturing plants (not shown) is cooled in the cooling arrangement to 55 - 60 °C. The pH of the cooled effluent is adjusted to 6.5 to 7.5 in the equalization tank and the effluent is further cooled to 30 °C to 40 °C in the heat exchanger. The effluent is digested anaerobically in the digester and aerobically further digested at 20 - 40°C and filtered in the membrane bioreactor. The filtrate collected in tank 7a is allowed to flow down into the tank 7b under gravity by maintaining a level difference i.e. head between the filtrate levels in tanks 7a and 7b by draining the filtrate from lower tank 7b by pump 10. The filtrate 7b in the lower tank pumped into the reverse osmosis module by the pump 10 through the filter 9 is further filtered in the filter 9 and is subjected to reverse osmosis in the reverse osmosis module 8. The permeate comprising demineralised water and reject containing valuable chemicals mainly sodium carbonate are collected from the reverse osmosis module via the permeate outlet 8a and reject outlet 8b, respectively and reused by recycling them to the polycarboxylic acid manufacturing plant.
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Aqueous effluent from the terephthalic acid manufacturing plant having the following composition was treated according to the process of the invention:
COD
(Chemical Oxygen Demand) 7000 ppm
MLSS
(Mixed Liquid Suspended Solids) /
TSS
(Total Suspended Solids) 265 ppm
TDS
(Total Dissolved Solids) 5400 ppm
Na 1000 wt ppm
Co 11 wt ppm
Mn 16 wt ppm
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pH

6.3

The effluent was cooled in the cooling tower to 60 °C and its pH was adjusted to 7 in the equalization tank. The effluent was further cooled in the heat exchanger to 30 °C. Following this, the effluent was anaerobically digested and the anaerobically treated effluent had the following composition:
COD 998 ppm
MLSS/TSS 400mg/l
TDS 3500 mg/1
Na 1300wtppm
Co 3 wt ppm
Mn 18wtppm
pH 7.1
The effluent was aerobically further digested in a membrane bioreactor of the outside - in hollow fibre type at 25 °C and filtered. The filtrate was further filtered in a cartridge type micron filter and subjected to reverse osmosis in a reverse osmosis module comprising polyamide spiral wound
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type membrane. The permeate and the reject of the reverse osmosis module had the following composition :

The permeate comprising demineralised water can be reused for instance in the analyzer house or drier scrubber and drier stack of the plant. The reject containing sodium carbonate can be reused for instance in the equalization tank for pH adjustment of the aqueous effluent. According to the invention, the entire water and valuable chemicals mostly sodium in the effluent are recovered and recycled into the polycarboxylic acid manufacturing plant thereby rendering the process almost a zero discharge process and eliminating the waste disposal problem. As valuable chemicals like sodium and water are recovered and reused, the process and device are very
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economical. The device is also very simple in construction and easy and convenient to operate.
There can be variations in the configuration and construction of the device by having more than one of each of the individual units (parts) thereof such as membrane bioreactor or reverse osmosis module. There can be also one or more than two filtrate collection tanks. The membrane bioreactor, filter and reverse osmosis module can be of different constructions. The effluent can be also treated anaerobically in an anaerobic digester for methane production prior to the aerobic treatment. Such variations in the invention are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention.
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We claim:
1. A process for recovering water and valuable chemicals in the aqueous effluent from the manufacture of polycarboxylic acids, the process comprising the steps of:
i) cooling the effluent to 55 to 60 °C;
ii) adjusting the pH of the effluent between 6.5 to 7.5 with an alkali;
iii) cooling the effluent to 30 to 40 °C;
iv) anaerobically digesting the effluent;
v) aerobically further digesting the effluent and filtering the effluent
in a membrane bioreactor at 20to40°C;
vi) further filtering the filtrate from the membrane bioreactor in a
filter; and
vii) subjecting the filtrate to reverse osmosis to obtain permeate
comprising demineralised water and reject comprising sodium
carbonate.
2. A process as claimed in claim 1, wherein the effluent is from the purified terephthalic acid manufacture.
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3. A process as claimed in claim 1, wherein the effluent is cooled in step
(i) in a cooling tower.
4. A process as claimed in claim 1, wherein the pH adjustment of the effluent in step (ii) is carried out in an equalization tank with sodium carbonate from step (vii).
5. A process as claimed in claim 1, wherein the cooling of the effluent in step (iii) is carried out in a heat exchanger.
6. A process as claimed in claim 1, wherein the effluent is an aerobically digested in step (iv) in an anerobic digester.
7. A process as claimed in claim 1, wherein the effluent is aerobically digested in step (v) in a membrane bioreactor of the outside-in hollow fibre type.
8. A process as claimed in claim 1, wherein the filtrate from the membrane
bioreactor is filtered in step (vi) in a cartridge type micron filter.
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9. A process as claimed in claim 1, wherein the reverse osmosis in step (vii) is carried out in a reverse osmosis module comprising polyamide spiral wound type membrane.
10. A device for recovering water and valuable materials in the aqueous effluent from the manufacture of polycarboxylic acids, the device comprising an aqueous effluent cooling arrangement for cooling the aqueous effluent from a polycarboxylic acid plant to 55 °C to 60 °C, an equalization tank for pH adjustment of the cooled effluent between 6.5 to 7.5, a cooler for further cooling the effluent to 30 to 40 °C, an anaerobic digestor for anaerobically digesting the further cooled effluent, a membrane bioreactor for aerobically further digesting the effluent and filtering the effluent, at least one filtrate collection tank for collecting the filtrate from the membrane bioreactor and a reverse osmosis module for reverse osmosis of the filtrate fed into the reverse osmosis module from the filtrate collection tank through a filter and a pump, the permeate and reject from the reverse osmosis module comprising demineralised water and sodium carbonate, respectively.
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11. A device as claimed in claim 10, wherein the effluent cooling arrangement comprises a cooling tower.
12. A device as claimed in claim 10, wherein the cooler is a heat-exchanger.
13. A device as claimed in claim 10, wherein the membrane bioreactor is outside-in hollow fibre type.
14. A device as claimed in claim 10, wherein the reverse osmosis module comprises polyamide spiral wound type membrane.
15. A device as claimed in claim 10, which comprises two filtrate collection tanks, located one above the other and connected to each other to allow the filtrate to flow down from the upper tank to the lower tank under gravity by maintaining a filtrate level difference in the tanks, the filtrate from the lower tank being fed to the reverse osmosis module through the filter.
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16. A device as claimed in claim 10 or 15, wherein the filter is cartridge type micron filter.
Dated this 17th day of January 2007

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ABSTRACT
A process and device for recovering water and valuable chemicals in the aqueous effluent from the manufacture of polycarboxylic acids. The effluent is cooled in a cooling arrangement to 55 to 60 °C and its pH is adjusted between 6.5 to 7.5 with an alkali in an equalisation tank. The effluent is further cooled to 30 to 40 °C in a cooler and anaerobically digested in an anaerobic digestor. The effluent is aerobically further digested and filtered in a membrane bioreactor at 20 to 40°C. The filtrate from the membrane bioreactor is further filtered in a filter and subjected to reverse osmosis to obtain permeate comprising demineralised water and reject comprising sodium carbonate (Fig 1).