Title of Invention

AN IMPROVED PROCESS FOR THE REMOVAL OF PHENOLS FROM WASTE WATER

Abstract

An improved process for the removal of phenols from industrial waste water This invention relates to an improved process for the removal of phenols from industrial waste waters. In the process of the present invention liquid surfactant membranes is used to remove phenols from waste water. The process which is capable of treating phenolic waste waters containing high concentrations of phenol in excess of 1000 ppm by contacting a water-in-oil emulsion of strong alkali emulsified in hydrocarbon oil with the phenolic waste water in a micro porous hollow fiber contactor of shell-tube configuration, at ambient temperature.

Full Text

This invention relates to an improved process for the removal of phenols from waste waters. In the process of the present invention use is made of liquid surfactant membranes to relates to a process wmch is capable of treating phenolic waste waters containing high concentrations of phenol . Phenols are present in waste waters from several industries like petroleum refining, coal, coke oven plants,organic chemicals as well as in phenol producing plants . Typically phenol concentrations range from 20-1000 ppm in waste waters from oil refining and coal-based industries but in phenol producing units phenol concentrations may exceed 2000 ppm. The removal of phenols from waste waters becomes necessary, because of its extreme toxicity to plant and animal life and environmental regulations stipulate that treated effluents should not contain more than 1 ppm phenol. Conventional treatment procedures employed in industry for phenol removal are generally based on biological treatment,solvent extraction or carbon adsorption. These processes have several limitations. Thus biological treatment requires large land area and cannot handle shock loadings from high phenolic feeds. Solvent extraction processes ,due to solubility of solvents in water (even if limited) suffer from high solvent losses and can also create a potential environmental hazard due to discharge of solvent into the treated stream. Carbon adsorption, though an efficient removal process for relatively low phenol concentration feed waters, can become energy intensive especially with regard to the regeneration step. On the other hand it is known that the liquid surfactant membrane process (LSM) can effectively remove phenols from water. In this process , a water-in- oil emulsion is first made of aqueous alkali in a hydrocarbon oil using appropriate oil soluble emulsifier. This emulsion is then dispersed by agitation in the waste water containing phenol. During this dispersion, emulsion globules are formed and the interstitial oil between the microdrops of internal phase of the emulsion behaves as a liquid membrane and allows phenol to permeate across from the external waste water phase into the microdrops. Here the phenol reacts with the alkali hydroxide (NaOH) to form sodium phenate which being ionic is insoluble in the oil and cannot diffuse back. Phenol is therefore effectively trapped inside the emulsion globules. The liquid surfactant membrane process for phenol removal can use conventional liquid-liquid extraction equipment to disperse the emulsion in the waste water. Extraction rates are fairly high, typically phenol can be brought down from 1000 ppm to 1000ppm as such feeds require high concentrations of alkali in the internal phase for complete removal which in turn increases the leakage. It is further known that liquid-liquid extraction can be carried out efficiently under conditions of low shear by using microporous hollow fibre membrane modular devices in a shell-tube configuration in which the feed phase may be passed through the lumen of the fibers while the solvent is passed through the shell side of the module. The interface is maintained at the micropores in the fiber walls. It is also known that the extraction of copper from water at concentrations of up to l000ppm can be carried out with liquid surfactant membrane in a hollow fiber membrane deviceby passing the emulsion through the fiber lumen and waste water through the shell side. This method of contact minimises emulsion leakage and swell because of the low shear conditions prevalent in the contactor. Following references can be made to prior out. REFERENCES 1 Raghuraman, B. ; Wiencek, J., Extraction with emulsion liquid membranes in a hollow fibre contactor. AIChE J., 1993, 11, 39. 2 Goswami, A. N. ;Sharma, S.K.; Sharma, Anshu; Gupta, T.C.S.M., Removal of phenol from refinery waste waters using liquid surfactant membranes in a continous column contactor. Ind. J. Chem., 1992, 31A, 361. emulsion. At high alkali concentrations which are necessary to completely strip phenol present at high concentrations in the waste water, the emulsifier used to stabilize the emulsion may get hydrolysed and the emulsion gets inherently unstable. While such emulsions would break up significantly in a conventional mixer, in a hollow fiber contactor the small size of the micropores in the fiber walls (about 0.05 microns) prevents the internal phase micro drops (about 1-30 microns in diameter) from coming into contact with the external water phase. This prevents leakage so that it is possible to contact inherently unstable emulsions in a hollow fiber contactor. This method of emulsion waste water contacting will prevent leakage arising from both shear effects as well as emulsifier degradation arising from high alkali concentrations in the internal phase. Accordingly the present invention provides an improved process for the removal of phenols from waste water which comprises: emulsifying aqueous alkali such as sodium hydroxide in 2 to 6 % kerosene containing nonionic emulsifier such as herein described to form a water -in -oil emulsion, pumping the emulsion through the lumen of the hollow fiber membrane contractor (MHF) as shown in Figure 1 from one end at a flow rate in the range of 5 to 30 ml/min, at a pressure in the range of 1 to 4 psi, raw waste water containing phenol is pumped through the shell side of the contactor from the opposite end at a flow rate in the range of 20 to 50 ml/min at a pressure in the range of 5 to 10 psi, allowing to contact both the phases for a time in the range of 1 to 5 mins. at temperature range of 20 to 40 deg.C, collecting the treated water stream and spent emulsion separately. emulsion. At high alkali concentrations which are necessary to completely strip phenol present at high concentrations in the waste water, the emulsifier used to stabilize the emulsion may get hydrolysed and the emulsion gets inherently unstable. While such emulsions would break up significantly in a conventional mixer, in a hollow fiber contactor the small size of the micropores in the fiber walls (about 0.05 microns) prevents the internal phase micro drops (about 1-30 microns in diameter) from coming into contact with the external water phase. This prevents leakage so that it is possible to contact inherently unstable emulsions in a hollow fiber contactor. This method of emulsion waste water contacting will prevent leakage arising from both shear effects as well as emulsifier degradation arising from high alkali concentrations in the internal phase. Accordingly the present invention provides an improved process for the removal of phenols from waste water which comprises; emulsifying aqueous alkali such as sodium hydroxide in 4:hydrocarbon~et^keroseneJ containing nonionic emulsifier such as herein described to form a water -in -oil emulsion, pumping the emulsion through the lumen of (Formula Removed) the hollow fiber membrane contractor/as shown in/|t from one end at a flow rate in the range of 5 to 30 ml/min, at a pressure in the range of 1 to 4 psi, raw waste water containing phenol is pumped through the shell side of the contactor from the opposite end at a flow rate in the range of 20 to 50 ml/min at a pressure in the range of 5 to 10 psi, allowing to contact both the phases for a time in the range of 1 to 5 mins at temperature in the range of 20 to 40 deg.C, collecting the treated water stream and spent emulsion separately. The phenol molecules diffuse through the pores in the fiber walls from the waste water into the emulsion present in the fiber lumen. Here they transport across the hydrocarbon oil layer (which acts as a liquid membrane ) into the internal phase droplets containing alkali where they react to form sodium phenate. The sodium phenate being insoluble in the oil layer cannot diffuse back into the external water outside the fiber. The phenol is therefore effectively trapped in the emulsion flowing through the fiber lumen. The treated water is withdrawn from one end while the emulsion loaded with phenol (as sodium phenate) is withdrawn from the other end This loaded emulsion is sent for demulsification and phenol and emulsifier recovery. The operation is at ambient temperature. The said process for the removal of phenol from waste water can be carried out according to the following steps: 1. Emulsifying the aqueous alkali with a hydrocarbon like kerosene containing an oil-soluble emulsifier by high speed agitation in a mixer to give a water-in -oil. 2. Pumping the emulsion with a metering pump under pressure control at a specified rate through the tube side of a microporous polypropylene hollow fiber membrane contactor. 3. Pumping the raw waste water feed with a metering pump under pressure control at a specified rate through the shell side of the same microporous hollow fiber contactor. Controlling the flow rates and fluid pressure conditions of the two phases so that a pressure differential of around 5 psi is maintained between the waste water phase and the emulsion phase in the contactor, with the emulsion being at the lower pressure. Allowing sufficient time of 30 to 45 rains to elapse so that steady state conditions are attained. Collecting the treated water stream and spent emulsion separately. e details of the above mentioned steps may be varied as Hows : The aqueous alkali concentration may vary from 0.5 to 1.5. The volume fraction of the internal phase may vary from 0.2 to 0.6, emulsifier concentration may vary from 1 to 6 wt % and the emulsifier Hydrophile Lipophile Balance number should be in the range of 2 to 5. The hydrocarbon oil used may be a kerosene fraction of boiling range 140-270°C. The emulsion may be prepared in a baffled mixer at agitation intensities of around 2000-6000 RPM for a period of 15 to 2 5 minutes. 2. The emulsion may be pumped through the tube side of the microporous hollow fiber contactor under pressure control. The flow rate of the emulsion may vary from 5 ml. min to 30 ml/min and the pressure may be maintained at 1 to 4 psi. 3 . The raw waste water feed containing phenol may be pumped through the shell side of the microporous hollow fiber contactor under pressure control . The flow rate of the waste water may be varied from 20 ml/min to 50 ml/min and the pressure can be maintained between 5 to 10 psi. 4. The phenol concentration in the waste water can vary from 10 to 600 0 ppm. 5. The operation is at ambient temperatures 20-40°C. The removal of phenol from waste water by liquid surfactant membranes can be carried out in a microporous hollow fiber contactor depicted in Figure-1. This contactor has 3600 microporous polypropylene hollow fibers of length 30 cm. o.d.210 microns,i.d. 180 microns and average wall pore size 0.05 microns. The fibers are potted with epoxy resin in a glass tube to give a module of a shell-tube configuration. To start the process a water-in-oil emulsion is first prepared in a mixer M by high speed agitation of known volumes of aqueous alkali of known concentration and kerosene containing known amount of oil soluble emulsifier Diatrolite SMO 80. This is a nonionic emulsifier of Hydrophile Lipophile Balance number 4.3. The emulsion is then transferred to reservoir Rl. Waste water containing known amount of phenol is taken in reservoir R2. This water is pumped through Line 3 by metering pump P2 to enter the microporous hollow fiber contactor MHF through the shell side. The water input flow rate is measured by the flow measuring burette B2. The treated water exits the contactor through the Line 4 under pressure control of valve NV 1, with flow rate monitored by flowmeter FM1 . The waste water inlet and outlet pressures are monitored by pressure gauges PG3 and PG2 respectively and these are maintained at around 5 to 7 psi with a pressure drop of around 0.2 psi. Emulsion from reservoir Rl is then pumped by metering pump PI through Line 1 to enter the microporous hollow fiber contactor MHF through the tube side. The loaded or spent emulsion exits the contactor through Line 2 under pressure control of valve NV 2. Emulsion input flow rate is measured by the flow measuring burette Bl and monitored by flowmeter FM2. Emulsion pressure at entry and exit points is recorded in pressure gauges PG1 and PG4 which are maintained 1-2 psi with pressure drop around 0.2 psi. Pumping of fluids is continued for about 30 to 45 mins. Samples of treated water are collected from Line 4 and analysed for phenol content by the 4- Amino antipyrine method of API-716-57 (AMERICAN PETROLEUM INSTITUTE) , This invention is further illustrated by the following examples the invention EXAMPLE 1 This example describes the removal of phenol from a synthetic aqueous feed containing 3750 ppm phenol by emulsion liquid membrane permeation in a hollow fibre contactor. A water-in-oil emulsion was first prepared in a mixer by mixing 400 ml of 0.75 N NaOH with 400 ml. of kerosene containing 4 vol % of oil-soluble emulsifier Diatrolite SMO-80 supplied by M/s Dai-Ichi Karkaria Ltd. (India), Bombay. The mixture was agitated at 4000 RPM for 20 minutes at ambient temperature (28-32°C). The internal hold-up in the resulting emulsion was 0.5. This emulsion was then taken in the emulsion reservoir and pumped through the tube side of the microporous hollow fibre contactor at 10 ml/ min., and the tube side inlet and outlet pressures were maintained at 1.0 and 0.5 psi respectively. The synthetic.aqueous feed containing phenol was taken in the feed reservoir and pumped through the shell side of the hollow fibre contactor at 20 ml/min. The shell side inlet and outlet pressures were maintained at 5.0 and 4.5 psi respectively. The emulsion/aqueous feed treat ratio was 0.5. Pumping of fluids through the contactor was continued for 1 hour.. During this time samples of treated water coming out of the contactor were collected at 20, 30, 40 and 60 minutes. The samples were tested with litmus for leakage of alkali from internal phase and then analysed for phenol content by the 4-Amino antipyrine method of API 716-57. Further at the 15 minutes and 35 minutes run time a simultaneous measurement was made of the volume of emulsion pumped into the contactor over a five minute period and the volume of emulsion which exited the contactor over the same time period for an estimate of the emulsion swell in the contactor using the following relation: %Swell of emulsion=(output vol.emul.-input vol.emul.)xl00 input vol.emul. The phenol percentage removal was calculated as: % phenol removal = (Phenol cone in feed-Phenol cone in treated water) xlOO Phenol cone. in feed In this particular example no leakage of internal phase was detected and the phenol content in the samples collected were 1800, 1680, 1700, 1670 ppm. respectively. The average phenol percentage removal at steady state (after 3 0 mins. run time) was therefore 54.7. The percent swell of emulsion was essentially negligible. EXAMPLE 2 This example describes the removal of phenol from a synthetic aqueous feed containing 4400 ppm phenol by emulsion liquid membranes in a hollow fibre contactor as in Example 1 but with a higher concentration of alkali in the internal phase of the water-in-oil emulsion. The eraulsion was prepared as described in the above Example but with 1.0 N NaOH in the internal phase and internal hold up of 0.5. The emulsion was pumped into the tube side of the contactor at 10 ml/min while maintaining the inlet We Claim: 1. An improved process for the removal of phenols from waste water which comprises: emulsifying aqueous alkali such as sodium hydroxide in a hydrocarbon oil(kerosene) containing nonionic emulsifier such as herein described to form a water -in -oil emulsion, pumping the emulsion through the lumen of the hollow fiber membrane contractor as shown in the drawing accompanying the specification from one end at a flow rate in the range of 5 to 30 ml/min, at a pressure in the range of 1 to 4 psi, raw waste water (aqueous feed) containing phenol is pumped through the shell side of the contactor from the opposite end at a flow rate in the range of 20 to 50 ml/min at a pressure in the range of 5 to 10 psi, allowing to contact both the phases for a time in the range of 1 to 5 mins. at temperature range of 20 to 40 deg.C, collecting the treated water stream and spent emulsion separately. 2. An improved process as claimed in claim 1 wherein the aqueous feed mixture contain phenols in the range of 10 to 6000ppm 3. An improved process as claimed in claims 1 and 2 wherein the concentration of alkali in the emulsion is in the range of 0. IN to 1.5 N 4. An improved process as claimed in claims 1 to 3 wherein the water-in-oil emulsion prepared by mixing the oil and aqueous alkali phases in mixer at revolution per minute ranging from 2000 to 6000 for time in the range of 15 to 25 mins. 5. An improved process as claimed in claims 1 to 4 wherein the nonionic emulsifier is having Hydrophile Lipophile Balance number of 3-4 at a concentration in the range of 2 to 6% in kerosene. 6. An improved process as claimed in claims 1 to 5 wherein the kerosene which forms the oil phase of the emulsion used is having a boiling range of 120-270°C. 7. An improved process as claimed in claims 1 to 6 wherein the pressure differential between the fluid phases pressures in the contactor is in the range of 4 to 6 psi. 8. An improved process for the removal of phenol from waste water substantially as herein described with reference to the examples and Fig. 1 of the drawing accompanying the specification.

Documents:

498-del-1996-abstract.pdf

498-del-1996-claims.pdf

498-del-1996-correspondence-others.pdf

498-del-1996-correspondence-po.pdf

498-del-1996-description (complete).pdf

498-DEL-1996-Description (Provisional).pdf

498-del-1996-drawings.pdf

498-del-1996-form-1.pdf

498-del-1996-form-2.pdf

498-del-1996-form-4.pdf

498-del-1996-form-5.pdf

498-del-1996-form-6.pdf