FORM-2
THE PATENT ACT, 1970
(39 Of 1970)
&
THE PATENT RULES, 2003
PROVISIONAL SPECIFICATION
(See Section 10 and Rule 13)
DEGRADATION OF CYCLO-ALIPHATICS
Nano Cutting Edge Technology Pvt Ltd
79/87, D.Lad Path, Kalachowki, Mumbai- 400 033, Maharashtra, India
Maharashtra (India)
:HE FOLLOWING SPECIFICATION DESCRIBES THE INVENTION

This invention relates to Halogenated Cyclo-Aliphatics.
Halogenated Cyclo-aliphatics (HCAs) such as chlorocyclohexanes and bromochlorocyclohexanes are highly stable, chemically nearly non-reactive under common conditions and persist in the environment. HCAs have long half-lives in soils, sediments, air or biota. Many of these pollutant sources are toxic and hazardous to human health.
A compound representative of the halogenated cyclo -aliphatics is y-hexachlorocyclohexane (commonly known as lindane). It is a broad spectrum organochlorine insecticide, widely used in veterinary medicine and as a household, gardening pesticide. It is neurotoxic, hepatotoxic and a convulsant agent, uterotoxic, an endocrine disrupter and a persistent organic pollutant (half life in water and soil is 300 days and 2-3 years respectively). Lindane is found in air, water, soil sediments, aquatic and terrestrial organisms throughout the world. It is also documented in human blood, human breast milk, human adipose tissue and amniotic fluid. This toxic insecticide is consistently ranked among the top chemicals of concern by the US Agency for Toxic Substances and Disease Registry.
It is banned and severely restricted in over 50 countries, including most of Europe and North America. But lindane production and usage continues in developing countries, especially India. India has a total installed capacity of lindane production of 1,300 tonnes per annum and has produced 5,387 tonnes of technical grade lindane between 1995-2005. Lax environmental laws and non-existent occupational safety regulations in India have resulted in huge stockpiles of highly persistent toxic wastes scattered and illegally disposed around the countryside. A study of human blood samples from villages in rural North India carried out by the Centre for Science and Environment, New Delhi in 2005 revealed lindane levels 605 times higher than those found in the United States.
Chemical methods of lindane elimination through dechlorination or dehydrochlorination reactions, i.e., combustion, hydrolysis, photolysis, thermal and base-assisted reduction, electrochemical and sonochemical processes result in toxic intermediates
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(trichlorobenzenes) and/or harmful byproduct (dioxins) formation. Microbial degradation pathways, both aerobic and anaerobic, suffer from incomplete and slow rates of biodegradation (24-100 h)’.
Fig. 1. of the accompanying drawings illustrates the Chemical structure of Lindane.
Recently, iron-based nanoparticles have attracted significant attention as potential catalysts for remediation of chloro-pollutants due to (i) their effective transportation by the flow of ground water (<100 nm Fe nanoparticle vs. 1000 run diameter of a bacterial cell), (ii) high specific surface area and (iii) their inexpensive and non-toxic nature. However, there are no reports on complete mineralization of these organic pollutants by Fe systems.
This invention envisages a process for the mineralization of n-halo-cylco-akanes.
This invention teaches that a Fe-Pd bimetallic nano-system will completely mineralize an aqueous solution of an n-halo-cylco-akanes, typically lindane in water, if hydroxyl radicals (a powerful oxidant with redox potential of + 2.8 V) are catalytically generated from a water molecule.
The process involves a three step reaction in which n-halo-cylco-akanes is degraded in water using nanoparticle Fe-Pd catalyst via hydroxyl radical in the formation of hydrocarbon radical during the mineralization process.
Figure 2 of the accompanying drawings, illustrates the efficiency of these nanoparticles to degrade lindane. A 10 mg/L sample of lindane is completely degraded in 5 min by Fe-Pd (5 mg/10 mL) within the detection limit of GC-ECD (~ 10 pg). Figure 3a shows the GC-MS analysis of the control sample (10 mg/L lindane) and the treated sample (10 mg/L lindane + 5 mg/10 mL nano-Fe-Pd). The complete absence of any partially/fully dechlorinated metabolite from the degradation process, in corroboration with the GC-TCD (Figure 3b) results showed that lindane was completely degraded down toCO2. Using the internal standard method for GC analysis, the amount of CO2
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evolved from the mineralization of lindane was calculated as 5.85 mmol mmol -1 of lindane. Each lindane molecule contains 6 carbon atoms and hence each molecule would mineralize into 6 molecules of CO2. Thus, the efficiency of lindane mineralization by nanoparticle Fe-Pd catalyst was estimated to be 97.5 %.and is graphically illustrated in figures 4a, 4b, and 5 of the accompanying drawings.
The overall reaction mechanism for the complete mineralization of lindane can be speculated as shown in Figure 6 of the accompanying drawings):
Step 1: Dehaolgenation - Metallic or zero-valent iron (Fe°) present in Fe-Pd catalyst generates hydrogen through corrosion, which is then responsible for the dehalogeantion of n-halo-cylco-akane to give a cyclo alkane, typically cyclohexane.
Step la: Hydroxyl Radical Formation - XPS measurement showed the presence of Fe°, Fe11 and Pd° species (supplementary information). The presence of Fe11 along with Pd° on the surface, establishes the formation of a galvanic cell, i.e., Pd° mediates single electron transfer from Fe11 to water for producing hydroxyl radicals.
Step 2: Oxidation - Hydroxyl radicals, which are strong oxidants (redox potential + 2.8V), then initiate the formation of a cycloalkyl radical. The formation and stability of the cycloalkyl radical could be explained on the basis of sp2 hybridized state of the carbon atom involved. This sp2 hybridized carbon radical has a half life greater than its recombination rate, which gives cyclohexane molecule. In case of other aliphatic halogenated pollutants such as trichloroethylene (TCE), the generation of a secondary carbon radical is not possible. Hence, its degradation gets terminated at the dechlorination step only.
Step 3: Complete Mineralization - The surface cycloalkyl radical reacts with the superoxide anions to form carboxylates on the surface, which eventually leads to
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carbon dioxide formation according to the Kolbe reaction.
The oxidative conversion of cycloalkyl to carbon dioxide mediated by a hydroxyl radical was proved in a separate lindane degradation experiment in which ascorbic acid (10 mg/L) was added as a free radical scavenger. The reaction mixture, analyzed by GC-MS, showed that the degradation reaction was quenched at Stepla, i.e., at the dechlorination step, indicated by the presence of cyclohexane as the main product (Figure 4b). Since the free radical generation was interrupted by the scavenger, formation of hydroxyl radical responsible for the oxidation of cyclohexane to carbon dioxide was arrested. This proves that the hydroxyl radical is the key to lindane mineralization.
To establish the advantage of a Pd-coated nano-Fe catalyst, a systematic comparison of lindane degradation efficiency was carried out with commercial bulk Fe (300 mesh) and nano-Fe. The results are shown in Figure 5. It was clearly observed that monometallic Fe, even in nano form was not effective for the complete degradation of lindane. Although nano-iron provides a 4-fold increased surface area for dechlorination reaction (surface area 98 m /g compared to 26 m /g for Fe-Pd), it oxidizes rapidly in water, leading to formation of a surface-passivating oxide layer. This surface passivation is more rapid compared to the dechlorination reaction, thereby reducing the active surface area available on the nano-iron surface. In our Fe-Pd catalyst, the presence of Pd on the nano-Fe surface is responsible for the prevention of oxide layer formation and retaining the activity of the catalyst. Palladium further promotes the dechlorination reaction and hence nano Fe-Pd offers a double advantage over nano-Fe.
The economy of the catalytic process, which is a measure of the number of times a catalyst can be reused without sacrificing its efficiency, the repeated use of nanoparticles after continuous exposure to air and water was studied (supplementary information). The nano-catalyst showed only 5-6 % decrease in its original activity after 10 days of daily
recycles with a fresh lindane solution. Thus, the nano Fe-Pd catalyst has a relatively
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long life span, offering a better alternative material for large scale and large volume applications.
Thus, there has been developed a nanoparticle Fe-Pd catalyst for complete mineralization of a highly halo -substituted organic pollutant molecule such as lindane. The complete mineralization by the bimetallic Fe-Pd catalyst was found to proceed through hydroxyl radical generated from water. This method of degradation demonstrates the formation of an efficient oxidant like hydroxyl radical from a simple molecule like water. In addition, this is a first demonstration case in which lindane dechlorination does not yield toxic intermediates, such as trichlorobenzenes, under such mild reaction conditions. This method holds tremendous potential in the oxidation area, e.g., for the ecofriendly degradation of several organic pollutants as well as for the activation of alkanes for the synthesis of value added chemicals.
Methods
Synthesis of Fe-Pd Nanoparticles. Synthesis of iron nanoparticles was achieved by adding 3.1 g of sodium borohydride (NaBH4) into 6.2 g of iron sulphate (FeS04.7H20). The solution was mixed vigorously at room temperature (25 ± 1 °C) for 15 min. The metal particles formed were then washed with large volumes (> 100 mL/g iron) ofmLtra-pure water for atleast 3 times. Palladized Fe nanoparticles were prepared by soaking freshly prepared iron particles in an ethanol solution containing 0.2 wt % of palladium acetate. This caused the reduction and subsequent deposition of Pd on the Fe surface. The palladized iron particles were then vacuum filtered, washed with ethanol followed by acetone and finally dried in a vacuum oven at 50 °C.
Materials characterization. BET surface area analysis was performed using nitrogen adsorption method with surface analyzer system CHEMBET 3000, Quantichrome Instruments, USA. XRD analysis of the particles was carried out using a Phillips
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diffractometer (model 1730). Nickel-filtered CuKα radiation source was used to produce X-rays (l=1.542 A) and scattered radiation was measured with a proportional counter detector at a scan rate of 4 °C/min. The X-ray photoelectron spectroscopy (XPS) analysis was carried out on a VG MicroTech ESCA 3000 instrument using Mg-Ka radiation (photo energy 1253.6 eV) at a pass energy of 50 eV and electron take off angle (angle between electron emission direction and surface plane) of 60°. The sample was placed in a container and was mounted on a sample probe taking care that the contact of air with sample was avoided. The sample was subjected to evacuation at 10 Torr during data collection. C Is spectra have been used as a reference with binding energy value of 284.6 eV and the spectra of different samples were corrected for surface charging. TEM measurements were performed on a JEOL Model 1200EX instrument operating at an accelerating voltage of 120 kV. Samples were loaded on carbon coated copper grids before being introduced in sample chamber. The complete characterization data is given in the supplementary information.
Batch experiments. All degradation experiments were performed at room temperature (25 ± 1 °C) in open 30 mL serum bottles with 10 mL of liquid volume. In each batch bottle, 10 mg/L lindane solution was prepared in N2-purged water (maximum solubility in water =12 mg/L). The solution contained a fixed amount of Fe-Pd particles in the range 0.005-0.01 mg. The pH of the reaction mixture was ~ 6.5. Solutions were stirred with an agitator to keep the particles in suspended form. Samples (100mL) were withdrawn from the bottles at fixed time intervals and lindane was extracted in HPLC grade hexane (1000mL). An aliquot of the sample (0.5mL) was then analyzed for the degradation of lindane using gas chromatography.
Chromatographic analysis. A gas chromatograph (ASXL, Perkin Elmer, USA) equipped with an electron capture detector and a capillary column SGE 3780B21 (length-25 m, type-bonded phase, material-silica, phase-BP5 non-polar, film thickness-0.5 urn) was used. The column temperature started at 50 °C, held for 10 min, ramped upto 150
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°C at 10 °C/min, held for 10 min, ramped to 240 °C at 10 °C and finally held for 15 min. The temperature of injector and detector was 230 °C and 280 °C respectively. The sample aliquot was eluted with nitrogen carrier gas at 35.0 mL/min. GC-MS analysis was performed on a Trace GC 2000, Thermo Instruments, USA equipped with a Mega 5 MS capillary column (30 m, 0.25 mm i.d. and 0.5mm film thickness). Electron impact mass spectrometry was carried out at 70 eV ionization potential and 230 °C ion source temperature. 15mL samples were injected each time.CO2 evolved was measured using a GC-TCD system (ASXL, Perkin Elmer, USA) with a capillary column Porapak Q (length-25 m, type-bonded phase, material-silica, phase-BP5 non-polar, film thickness-0.5 mm was used. The column temperature was 60 °C, injector temperature was 70 °C and detector temperature was 100 °C. Standard CO2 for calibration was purchased from BOC India Limited.
Batch Experiments
Batch experiments were conducted in bottles with different sample volumes (25 mL, 150 mL, and 1000 mL) with same lindane concentration (10 mg/L). These solutions were treated with different amounts of nano Fe-Pd to study the correlation between amount of nanocatalyst and time of degradation with increase in sample volume. Sample volumes selected were less than the total capacity of the bottle to ensure the existence of a headspace that would improve mixing of nanoparticles. Accordingly, sample volumes of 15 mL, 100 mL and 500 mL were taken for the three batch experiments. Following addition of a weighed amount of nanoparticles to each set, all samples were agitated using magnetic stirrer. Samples (100mL) were withdrawn from the bottles at fixed time intervals and lindane was extracted in HPLC grade hexane (1000mL). An aliquot of the sample (0.5mL) was then analyzed for the degradation of lindane using gas chromatography.
The lindane degradation efficiencies were calculated for three different sample volumes containing a fixed amount of nano Fe-Pd catalyst. The following experimental sets were studied for the degradation efficiencies:
1. 15 mL aqueous solution containing 10 mg/L lindane + 10 mg Fe-Pd
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nanoparticles.
2. 100 rnL aqueous solution containing 10 mg/L lindane + 50 mg Fe-Pd nanoparticles.
3. 100 mL aqueous solution containing 10 mg/L lindane + 100 mg Fe-Pd nanoparticles.
4. 500 mL aqueous solution containing 10 mg/L lindane + 300 mg Fe-Pd nanoparticles.
In case of set 1, with a 1:1 stoichiometric ratio of nanoparticle weight (mg) with the sample volume (mL), 100 % lindane degradation was observed after 5 min of reaction time. However, with an increase in reaction volume (set 2), degradation efficiency showed a progressive increase with time. Figure 1(a) indicates that a 1:2 stoichiometric ratio results in only 90 % degradation of lindane after 60 min of reaction. However, increase in amount of nanoparticles from 50 mg to 100 mg (change in stoichiometry from 1:2 to 1:1) gave 100 % degradation efficiency in 15 min (Fig. 1(b)). Since the degradation of lindane occurs on the Fe-Pd surface, the nanoparticle surface area affects the degradation rate. As the nano Fe-Pd mass concentration increases from 50 to 100 mg, the reactive Fe site concentration and adsorptive Pd site concentration increase simultaneously, which in turn increases the total surface area. This leads to an increase of reaction rate and complete degradation is achieved in half of the reaction time.
Fig. 7. of the accompanying drawings shows the Degradation kinetics of 100 mL lindane aqueous solution using (a) 50 mg and (b) 100 mg Fe-Pd nanoparticle. As the sample volume was further increased to 500 mL (set 4), ~ 95 % lindane removal from solution was achieved after 15 min with a nanoparticles loading of 300 mg. Total absence of lindane in the solution was observed after 30 min. This indicates that a decrease in the 1:1 stoichiometric ratio of nanoparticles-to-sample volume results in an increase in reaction time for complete degradation of lindane.
On the basis of the above experiments, the amount of Fe-Pd nanoparticles required to degrade lindane with 100 % efficiency and minimum reaction time was correlated with the volume of the lindane solution to be treated. Figure 8 shows the relation
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between the amount of nanoparticles, the volume of treatment solution and fixed time of reaction. Thus, a minimum stoichiometric ratio of 1:1 is required for achieving faster degradation rates. This observation has huge implications in the selection of nano Fe-Pd mass concentrations for treatment of scaled-up volumes of lindane aqueous solutions.
Fig. 8. of the accompanying drawings shows the Correlation between amount of Fe-Pd
nanoparticles required to completely degrade lindane in different aqueous solution
volumes.
Differential Column Reactor Experiments
COLUMN 1: A small scale differential column reactor was used to scale down a full-scale or pilot-scale reactor column to run such an experiment at the bench-scale. Glass columns of 1.5 cm diameter and 30 cm in length were used for packing of nanoparticles. The columns were packed while maintaining the packed materials under ultrapure water. A small portion of glass wool was used at the bottom of the column to prevent glass beads from plugging the bottom outlet of the column. Upon this glass wool, 5 mm glass beads were placed to support the packed bed nearer the middle of the column. More glass wool was placed on top of these beads to directly support the packed bed and ensure no nanoparticles could escape through the bottom of the column. 200-300 mg Fe-Pd nanoparticles were then added to the column and nanopure water was used to wash the nanoparticles down to the glass wool. More glass wool was packed on top of the packed bed, and finally more glass beads were placed on top of this glass wool until they reached the top of the column.
A schematic of the column setup is shown in Fig. 9 of the accompanying drawings which is a Small scale differential column reactor setup..
COLUMN 2. Differential columns were also prepared using sand-nanoparticle dual zone columns instead of glass beads-nanoparticle columns. The column was packed by first filling it with nanopure water and placing a small amount of glass wool at the bottom
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of the column. Horizontally on top of this glass wool, 5 g of pre-washed beach sand (the sand was first sieved through a 2 mm sieve and washed copiously with distilled water till the washings were colorless. The washed sand was then dried at 100 °C overnight) was added. After proper placement of the sand bed, 200-400 mg Fe/Pd nanoparticles were added to the column and allowed to settle on top of the sand bed. Different amounts of nanoparticles were added in separate DCR experiments to study the effect of nanoparticle bed volume on the column reactor efficiency. Upon leveling the surface of the nanoparticle bed, another 5 g of sand was slowly placed on top of the nanoparticle bed. Care was always taken to minimize compression of the bed during this step. Backwashing of the column at flow rate was performed three consecutive times while ensuring that nothing but fines escaped at the top of the column and the effluent leaving the top of the column ran clear. On the final backwashing step, the column was firmly tapped with a rod to encourage proper settling of the nanoparticles within the column.
METHODOLOGY: Test solutions for column experiments containing 10 mg/L lindane were stored in a 2 L glass tank and solutions were pumped through the packed beds using an Ismatec MCP 552 (Switzerland) peristaltic pump. Samples were collected directly from the column effluent tubing into 10 mL glass sample bottles. The outward flow rate was maintained between 2-3 mL/min. Samples collected were filtered through 0.2 um Whatman membrane filter paper. 100mL of sample was extracted with 1000mL of HPLC grade hexane and 0.5mL of extracted sample was used for lindane degradation studies using Gas Chromatography.
RESULTS: The lindane degradation efficiency of the column containing nanoparticles only (loaded alongwith glass beads) is shown in Fig. 10 of the accompanying drawings which shows the Lindane degradation efficiency of Fe-Pd nanoparticle-only in a differential column.. Complete removal of lindane was observed in the column effluent after passage of 60 bed volumes of lindane aqueous solution. The degradation efficiencies could not be monitored for additional bed volumes because the smaller particle sizes of the nano-Fe-Pd catalyst resulted in excessive pressure buildup. This led to bed compression and failure in the flow rate after the flow of 60 bed volumes.
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Differential column reactor containing beach sand-nanoparticles dual zones showed enhanced degradation efficiency, compared to the nanoparticle-only column. Figure 11 shows the working efficiency of the column showing Lindane degradation efficiency of beach sand-nanoparticle dual zone column. Complete removal of lindane was observed in the effluent after flowing 100 bed volumes of lindane aqueous solution. Thus, Fe-Pd nanocatalyst showed a sustained and efficient activity for lindane removal in a continuous column reactor.
To study the lindane adsorption characteristics of the beach sand, a column reactor containing a single sand bed was used as control reactor. Effluent collected by flowing 10 bed volumes of lindane aqueous solution was analyzed for residual lindane concentration. GC analysis showed that beach sand alone showed no lindane degradation efficiency.
Thus it is apparent that there has been provided, in accordance with the invention, a process that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the invention.
Dated this 4th day of August 2006.
Meman Dewan ofR.K.Dewan&Co Applicant's Patent Attorneys
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