WO2018039204A1 - Procédé d'élimination de l'huile de l'eau - Google Patents

Procédé d'élimination de l'huile de l'eau Download PDF

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WO2018039204A1
WO2018039204A1 PCT/US2017/047969 US2017047969W WO2018039204A1 WO 2018039204 A1 WO2018039204 A1 WO 2018039204A1 US 2017047969 W US2017047969 W US 2017047969W WO 2018039204 A1 WO2018039204 A1 WO 2018039204A1
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oil
cnts
carbon nanotubes
water
solution
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PCT/US2017/047969
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English (en)
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Ahmed Kayvani FARD
Muataz A. HUSSEIN
Tarik RHADFI
Marwan K. Khraisheh
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Qatar Foundation For Education, Science And Community Development
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
    • B01D17/02—Separation of non-miscible liquids
    • B01D17/0202—Separation of non-miscible liquids by ab- or adsorption
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D17/00—Separation of liquids, not provided for elsewhere, e.g. by thermal diffusion
    • B01D17/02—Separation of non-miscible liquids
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/288—Treatment of water, waste water, or sewage by sorption using composite sorbents, e.g. coated, impregnated, multi-layered
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/68—Treatment of water, waste water, or sewage by addition of specified substances, e.g. trace elements, for ameliorating potable water
    • C02F1/681—Treatment of water, waste water, or sewage by addition of specified substances, e.g. trace elements, for ameliorating potable water by addition of solid materials for removing an oily layer on water
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/281—Treatment of water, waste water, or sewage by sorption using inorganic sorbents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/283—Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/08—Nanoparticles or nanotubes

Definitions

  • the disclosure of the present patent application relates to the purification of water, such as industrial wastewater, groundwater and the like, and particularly to a method of removing oil from water using modified carbon nanotubes (CNTs).
  • CNTs modified carbon nanotubes
  • oil- water emulsion When oil mixes with the water, it forms an oil- water emulsion (or "floating film") that should be removed before it is discharged into the environment.
  • oil- water emulsion or "floating film"
  • Such water if treated to meet the environmental limits and regulations, can be used for aquifer recharge, irrigation, livestock or wildlife watering and habitats, as well as industrial applications (e.g., vehicle washing, power plant cooling water and fire control).
  • Numerous techniques are known for treating oil-contaminated water. Examples of such techniques include reverse osmosis, ultra-filtration and micro-filtration, a variety of flotation methods (e.g., dissolved air, column flotation, electro- and induced air), adsorption, gravity separation, activated sludge treatment, membrane bioreactors, biological treatment, chemical coagulation, electro-coagulation and coalescence. Adsorption/sorption is believed to be one of the most promising processes for the removal of oil from water due to its low operational and capital cost, in addition to its high removal efficiency. A variety of materials are known to be oil de-emulsifiers for oil-water treatment, such as natural sorbents, organic polymers (synthetic) and mineral materials (inorganic). Thus, a method of removing oil from water solving the aforementioned problems is desired.
  • flotation methods e.g., dissolved air, column flotation, electro- and induced air
  • adsorption e.g., dissolved air, column flotation, electro- and induced air
  • the method of removing oil from water includes contacting modified carbon nanotubes (CNTs) with the water to adsorb oil from the water, and then isolating the modified carbon nanotubes with the oil adsorbed thereon.
  • the modified carbon nanotubes may include carbon nanotubes doped with a metal, such as iron, silver, aluminum, zinc or copper, or oxides thereof.
  • the carbon nanotubes can be doped with iron oxide (Fe 2 0 3 ), also known as hematite.
  • the modified carbon nanotubes preferably have an outer diameter of about 10 nm to about 20 nm and a length between about 1 ⁇ and about 10 ⁇ .
  • Fig. 1 is a schematic diagram of the process of loading hematite (a-Fe20s) nanoparticles on a carbon nanotube (CNT) support.
  • Fig. 2 A is a scanning electron microscope (SEM) micrograph of undoped CNTs.
  • Figs. 2B, 2C, 2D, and 2E are SEM micrographs of CNTs doped with 1 wt%, 10 wt%, 30 wt%, and 50% Fe2C>3 nanoparticles, respectively.
  • Fig. 3A is a transmission electron microscope (TEM) image of unmodified CNTs.
  • Figs. 3B, 3C, 3D, and 3E are TEM micrographs of CNTs doped with 1 wt%, 10 wt%, 30 wt%, and 50% Fe 2 0 3 nanoparticles, respectively.
  • Fig. 4 are diffractograms comparing the powder X-ray diffraction (XRD) patterns of a-Fe 2 0 3 /CNT composites at 1, 10, 30, and 50 wt% Fe 2 0 3 nanoparticle loading, pure a-Fe 2 0 3 , and pure CNTs.
  • XRD powder X-ray diffraction
  • Fig. 5 are thermogravimetric analysis (TGA) plots of pure CNTs and a-Fe 2 0 3 /CNT nanocomposites having 1 wt%, 10 wt%, 30 wt% and 50 wt% Fe loadings.
  • Fig. 6 is a plot of N2 adsorption-desorption isotherms of CNTs and CNT/a-Fe 2 0 3 composites having 1 wt%, 10 wt%, 30 wt% and 50 wt% Fe loadings .
  • Fig. 7 is a plot of percentage removal of oil as a function of contact time comparing pure CNTs with CNTs loaded with 1, 10, 30, and 50 wt% Fe 2 0 3 .
  • Fig. 8 is a plot of percentage removal of oil as a function of adsorbent dosage comparing pure CNTs with CNTs loaded with 1, 10, 30, and 50 wt% Fe 2 0 3 .
  • Fig. 9 is a graph showing the Freundlich adsorption isotherms of oil adsorbed by pure CNTs and CNTs loaded with 1, 10, 30, and 50 wt% Fe 2 0 3 .
  • Fig. 10 is a plot showing the Temkin adsorption isotherms of oil adsorbed by pure CNTs and CNTs loaded with 1, 10, 30, and 50 wt% Fe 2 0 3 .
  • Fig. 11 is a plot showing the pseudo-first-order kinetics for the adsorption of oil by pure CNTs and CNTs loaded with 1, 10, 30, and 50 wt% Fe 2 0 3 .
  • Fig. 12 is a plot showing the pseudo-second-order kinetics for the adsorption of oil by pure CNTs and CNTs loaded with 1, 10, 30, and 50 wt% Fe 2 0 3 .
  • Fig. 13 is a plot showing the intra-particle diffusion model kinetics for the adsorption of oil by pure CNTs and CNTs loaded with 1, 10, 30, and 50 wt% Fe 2 0 3 .
  • the method for removing oil from water includes contacting modified carbon nanotubes (CNTs) with the water to adsorb oil from the water, and then isolating the modified carbon nanotubes with the oil adsorbed thereon.
  • the carbon nanotubes are doped with a metal, such as iron, silver, aluminum, zinc or copper, or an oxide of any of these metals, using thermal treatment.
  • the modified carbon nanotubes preferably have an outer diameter of about 10 nm to about 20 nm and a length between about 1 ⁇ and about 10 ⁇ .
  • Carbon nanotubes are molecules of pure carbon that are relatively long and thin, and which are shaped like tubes.
  • the modified carbon nanotubes for removing oil from water include carbon nanotubes doped with a metal or metal oxide.
  • the carbon nanotubes can be doped with iron oxide (Fe 2 0 3 ), i.e., hematite.
  • the method for removing oil from water can include the step of placing the carbon nanotubes impregnated with iron oxide into contact with wastewater to adsorb the oil, followed by isolating the carbon nanotubes with the adsorbed oil.
  • the iron oxide-modified carbon nanotubes may be fabricated by impregnating carbon nanotubes (CNTs) with iron oxide Fe2C>3 (hematite).
  • the iron oxide-impregnated carbon nanotubes possess an improved capacity to remove oil when compared against conventional oil adsorbents.
  • ferric nitrate and iron oxide are dissolved in ethanol to form a first solution.
  • Carbon nanotubes (CNTs) are dissolved in ethanol to form a second solution.
  • the first and second solutions are then sonicated separately, followed by mixing the first solution and the second solution to form a third solution.
  • the third solution is sonicated to form a sonicated mixture, and the sonicated mixture is heated to provide a solid residue, which is then calcined.
  • the sonicated mixture can be heated in a furnace at a temperature ranging from about 60°C to about 90°C for a time period sufficient to evaporate the ethanol.
  • the solid residue can be calcined at about 350°C for about 4 hours to impregnate the iron oxide into the carbon nanotubes (CNTs).
  • the concentration of iron oxide used may be typically between 1% and 50%.
  • the sonication may be ultra-sonication and may be conducted for about forty-five minutes.
  • the Fe20 3 -modified carbon nanotubes may include single-walled and/or multi-walled carbon nanotubes.
  • Fig. 1 schematically illustrates the synthetic process used to produce CNTs impregnated with hematite (Fe2C>3).
  • the doped CNTs exhibited significantly enhanced removal efficiency of oil from water when compared against conventional oil adsorbents.
  • the CNTs may be doped with different metals or metal oxides using thermal treatment.
  • the CNTs may be doped with iron oxide or other metals or metal oxides to remove oil and other oil-derivatives from water.
  • Suitable metals that may be used with varying weight percentages include iron (Fe), silver (Ag), aluminum (Al), zinc (Zn), and copper (Cu).
  • the removal efficiency of modified CNTs can be at or near 100%.
  • Use of modified carbon nanotubes can provide a very effective and economical solution for removing oil from water.
  • Liquid ethanol (98% purity), used as a solvent, and ferric nitrate (Fe(N0 3 )3-9H 2 0) (99 % purity), used as a precursor of iron nanoparticles, were obtained from the Sigma-Aldrich, Inc. of St. Louis, Missouri.
  • Liquid gasoline used as an oil source, was purchased in Doha, Vietnamese, with an octane number of 97. All of the chemicals were used without further purifications.
  • the residue was calcined for four hours at 350°C in a furnace to prepare CNTs impregnated with 1% iron oxide.
  • CNTs were doped with different loadings of iron oxides by weight per cent, i.e., 1%, 10%, 30%, 50%, etc.
  • the product obtained had a purity of about 95%.
  • the modified carbon nanotubes had an outer diameter of about 10 nm to about 20 nm and a length of about 1 ⁇ to about 10 ⁇ .
  • Fig. 1 further illustrates the process by which CNTs loaded with hematite are produced.
  • XRD Powder X-ray diffraction
  • the Zeta potentials for a suspension of 50% of CNTs/Fe in deionized water (DI) solution were determined by a Zetasizer Nano ZS, manufactured by Malvern Instruments, Ltd. of the United Kingdom. Elemental analysis (Fe, C and O) was performed with energy- dispersive X-ray spectroscopy (EDX) analysis. The surface areas were measured by N2 adsorption at 77 K using a 15 -point BET technique on the analysis port of the analyzer, manufactured by Micromeritics ® of Georgia, to determine the amount of a-Fe20 3 present on the CNT surface. The thermogravimetric analyses (TGA) were performed with a TGA analyzer at a heating rate of 10°C/min in air.
  • TGA thermogravimetric analyses
  • the TGA analyzer was calibrated for temperature readings and mass changes using nickel reference material.
  • the gasoline concentration was measured using a combustion type total organic carbon (TOC) analyzer (model TOC-L, manufactured by the Shimadzu Corporation of Japan), with a detection range of 4 ⁇ g/L to 30,000 mg/L.
  • TOC combustion type total organic carbon
  • RE (%) TJ X 100 , (2) where C (mg/L) is the initial concentration of emulsified oil in the water, Cf (mg/L) is the final concentration of the remaining oil in the water, V (L) is the volume of the water, and W g is the mass of the CNTs.
  • aqueous solutions (20 ml) with 20 mg of undoped and doped CNTs were agitated at 400 rpm using a mechanical shaker at 27 °C.
  • the samples (1.2 ml) were taken from the solution at each preset time interval, and the final concentrations of oil were analyzed using a TOC analyzer.
  • TOC analyzer In order to find the maximum oil uptakes by CNTs and to interpret the experimental data acquired, three kinetic models (pseudo-first-order, pseudo-second-order and intra-particle diffusion) were used.
  • a linear fitting procedure was performed using software manufactured by the OriginLab Corporation of Massachusetts.
  • the Lagergren pseudo-first-order model proposes that the rate of sorption is proportional to the number of sites unoccupied by the adsorbate.
  • the pseudo-first-order equation can be written in linearized form as follows:
  • ⁇ n(Q e - Q t ) ⁇ n Q e - k 1 t ( 3 )
  • Q t is the sorption capacity (mg/g) at any preset time interval (i)
  • k 1 is the first- order rate constant (min -1 ).
  • a graph of ln(Q e — Q t ) as a function of time is plotted and the constant is found.
  • the adsorption data were analyzed using the pseudo-second- order kinetic mode.
  • the pseudo-second-order kinetic model can be written in linearized form as follows:
  • k 2 is the second-order rate constant (g/mg- min).
  • IPD intra- particle diffusion
  • the maximum adsorption capacity and the sorption energy of oil on CNTs were analyzed using the Freundlich, Langmuir, and Temkin isotherm models.
  • the Freundlich isotherm can be expressed as:
  • the Freundlich model does not consider the sorption saturation, as it assumes a heterogeneous adsorbent surface and an energy distribution for the different sites.
  • the Langmuir isotherm model assumes that the adsorption takes place at defined homogeneous sites on the surface of the adsorbent.
  • the Langmuir isotherm is expressed by:
  • the Langmuir constants K and X m (which are related to the constant free energy of sorption) can be determined by representing a linear plot of CJQ e vs. C e from the intercept and slope of the plot.
  • the Tempkin isotherm assumes that the sorption energy during the sorption process decreases linearly with increasing sorption site saturation rather than decreasing exponentially, as implied by the Freundlich isotherm.
  • the Temkin isotherm is given as:
  • the linearized isotherm coefficients were estimated using graphical methods by plotting Q e vs. In C e and are reported below.
  • FE-SEM field effect scanning electron microscopy
  • HR-TEM high resolution Transmission Electron Microscopy
  • TGA Thermogravimetry
  • XRD BET surface area
  • Zeta potential The surface morphologies of the undoped and doped CNTs adsorbents were observed using FE- SEM.
  • Fig. 2A is a SEM micrograph of undoped CNTs, which is used as a control.
  • Fig. 2B is a SEM micrograph of CNTs doped with 1 wt% Fe 2 C>3 nanoparticles.
  • Fig. 2C is a SEM micrograph of CNTs doped with 10 wt% Fe 2 03 nanoparticles.
  • Fig. 2D is a SEM micrograph of CNTs doped with 30 wt% Fe 2 03 nanoparticles.
  • Fig. 2E is a SEM micrograph of CNTs doped with 50 wt% Fe 2 C>3 nanoparticles. The diameter of the CNTs varied from 20 nm to 40 nm, the average diameter being 24 nm. It can be observed that there are no changes on the surfaces of doped CNTs after the doping, i.e., they are agglomerated and untangled, resembling a cotton-like structure.
  • Fig. 3A High Resolution Transmission Electron Microscopy (HR-TEM) was performed to characterize the structures, sizes and the purity of undoped and doped carbon nanotubes with iron oxide nanoparticles.
  • the TEM micrograph of the unmodified nanotubes is shown in Fig. 3A.
  • Fig. 3B is a TEM micrograph of CNTs doped with 1 wt% Fe 2 C>3 nanoparticles.
  • Fig. 3C is a TEM micrograph of CNTs doped with 10 wt% Fe 2 C>3 nanoparticles.
  • Fig. 3D is a TEM micrograph of CNTs doped with 30 wt% Fe 2 C>3 nanoparticles.
  • Fig. 3A High Resolution Transmission Electron Microscopy
  • 3E is a TEM micrograph of CNTs doped with 50 wt% Fe 2 C>3 nanoparticles.
  • the TEM micrographs show that a highly ordered crystalline structure of CNTs exists.
  • the clear fringes of graphitic sheets are well separated by 0.34 nm and aligned with a tilted angle of about 2° toward the tube axis.
  • the TEM images of CNTs doped with Fe 2 C>3 nanoparticles were taken in order to verify the presence of nanoparticle ions on the surfaces of the CNTs (as shown in Figs. 3B and 3C).
  • the distribution and agglomeration of Fe 2 C>3 nanoparticles were also investigated.
  • Fe 2 03 nanoparticles there are formations of white crystal structures of Fe 2 03 nanoparticles with small sizes and irregular shapes. It can be seen that the Fe20 3 nanoparticles are spread widely on the surfaces of the carbon nanotubes, forming very small crystal particles with diameters varying from 1 nm to 5 nm. When the ratio is increased to 30% and 50%, the size of the Fe 2 03 nanoparticles is about 50 nm and agglomerate intensively, as seen in Figs. 3D and 3E, respectively. The doping of Fe20 3 nanoparticles on the surfaces of CNTs was also confirmed by energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD).
  • EDX energy dispersive X-ray spectroscopy
  • XRD X-ray diffraction
  • the EDX analysis of the undoped and doped CNTs which represents the atomic weight percentage (%) of the elements, such as Fe, O and C, with different percentage of a- Fe 2 C>3, is shown in Table 1 below.
  • the Fe/C ratios extracted from the EDX are close to the calculated values of the prepared samples.
  • Fig. 4 shows the X-ray diffraction patterns of undoped and doped CNTs and pure a- Fe2C>3. It has been observed that the XRD diffraction pattern of pure a-Fe20 3 is similar to doped Fe2C>3 nanoparticles, confirming the presence of a-Fe20 3 crystal nanoparticles on the surfaces of the CNTs. There is one characteristic peak of CNTs, which can be seen at 2 ⁇ of 27, while other characteristic peaks were found at 2 ⁇ values of 34.36, 42, 50, 54, 63, 65, 72 and 75, which correspond to a-Fe 2 03. These results revealed that the a-Fe 2 03 particles were successfully attached to the CNTs.
  • Thermogravimetric analysis was conducted to study the oxidation/combustion profile of CNTs and Fe2C>3 with different theoretical mole ratios of Fe on the CNTs (0%, 1%, 10 %, 20%, 30 % and 50%).
  • the TGA profiles of CNTs and modified CNTs with a-Fe20 3 at a heating rate of 10°C/min in air at temperatures ranging from 40°C to 900°C are presented in Fig. 5.
  • the graphs illustrate that CNTs completely oxidize in air at temperatures above 650°C, but the thermal stability of a-Fe20 3 /CNTs weakened and they began to decompose at 550°C. These results showed that the initial oxidation temperature of undoped CNTs under air starts approximately at 580°C and then reaches a complete oxidation at 670°C.
  • the initial temperature of doped CNTs with 1 wt%, 10 wt%, 30 wt% and 50 wt% reduces to 520°C, 480°C, 460°C, and 450°C, respectively, and the final oxidation temperatures reduce to 620°C, 600°C, 550°C and 500°C, respectively.
  • the loading of Fe20 3 nanoparticles doped on CNTs acts as a heating accelerator agent, which accelerated the heat transfer to the body of the CNTs, as can be seen by the faster combustion of the doped CNTs (i.e., oxidization) compared to undoped CNTs.
  • the TGA provides an accurate estimate of the loading of Fe2C>3 nanoparticles doped on CNTs by comparing the residue of the complete oxidation of doped and undoped CNTs.
  • the final remaining residual of undoped CNTs is 0.99 wt%, and the final remaining residuals of CNTs doped with 1 wt%, 10 wt%, 30 wt% and 50 wt% Fe 2 0 3 are 2.05 wt%, 8.8 wt%, 32 wt%, and 48 wt%, respectively.
  • BET surface area analysis was conducted to measure the surface area of undoped and doped CNTs. The interpretation of the BET results was based on the adsorption-desorption of liquid N2 at 77 K, as shown in Fig. 6.
  • the BET surface area values obtained for the undoped and doped CNTs with 1 wt%, 10 wt%, 30 wt% and 50 wt% Fe2C>3 nanoparticles were 137.7 m 2 /g, 226.6 m 2 /g, 295.4 m 2 /g, 128 m 2 /g, and 74.86 m 2 /g, respectively, as shown in Fig. 6.
  • iron oxide nanoparticles at 1 wt% and 10 wt% on surfaces of CNTs enhanced the surface area, thus increasing the number of sites for adsorption, while increasing the doping to 30 wt% and 50 wt% decreases their surface areas due to the aggregation and agglomeration of iron nanoparticles and the formation of a large cluster of nanoparticles that blocks the available surfaces on the CNTs.
  • the loading of Fe2C>3 nanoparticles on the negative surfaces of carbon nanotubes have a great impact on the stability of the oil emulsion breaking process, which substantially improves the adsorption capacity of the oil on the surface of the carbon nanotubes.
  • the existence of Fe 3+ on the surfaces of the carbon nanotubes will modify the liquid/liquid and liquid/air surface properties. For example, Fe 3+ serves to decrease the interfacial tension between the dispersed oil phase and the water, and then increases the interfacial tension between the air bubble and the oil phase.
  • loading Fe2C>3 nanoparticles on the surface of carbon nanotubes will increase oil droplet coalescence. Enhancing this coalescence will also facilitate the adsorption mechanism. This phenomenon can be explained through the zeta potential measurements.
  • Table 2 shows that the undoped carbon nanotubes have a negative charge of - 42.6 mV in the oil-in-water emulsion.
  • Loading Fe2C>3 nanoparticles on the negative surface of carbon nanotubes decreases the negative sign of the zeta potential by overcoming the repulsive effects of the electrical double layers to allow the finely sized oil droplets to form larger droplets through coalescence.
  • the zeta potential of oil droplets was not measured.
  • the literature indicates that oil droplets have a large negative zeta potential. This implies that electrostatic repulsion would make attachment between oil droplets highly unlikely.
  • Oil removal from produced water with both undoped and doped CNTs increases with an increase in contact time and reaches a maximum adsorption capacity after 20 min.
  • the presence of iron nanoparticle-doped CNTs enhances the removal efficiency and adsorption capacity compared to undoped CNTs.
  • the maximum removal efficiency of undoped and doped CNTs with 1 wt%, 10 wt%, 30 wt% and 50 wt% of Fe 2 0 3 nanoparticles was 87.0%, 96.09%, 96.37%, 96.62% and 98.52%, respectively.
  • the amount of sorbent oil particles increases rapidly at the initial stage and then progressively reaches 90% equilibrium capacity in 10-15 min adsorption time.
  • the high removal efficiency rate at the beginning of the contact time was due to the large number of vacant binding sites available for the adsorption of oil. These rapid uptakes coupled with a high sorption capacity were two of the most significant properties for oil sorption by CNTs. As the outside surfaces of CNTs become exhausted and saturated with oil particles, the rate of oil uptake starts to decrease and reaches equilibrium. The doped CNTs reach equilibrium faster than undoped CNTs by almost a factor of two. Compared against prior art magnetic CNTs, the present modified CNTs reached equilibrium three times faster.
  • the equilibrium adsorption is important in the design of adsorption systems. Equilibrium studies in adsorption indicate the maximum capacity of the adsorbent during the treatment process. The effect of initial concentration on oil adsorption was investigated by varying the initial concentration of oil (from 400 mg/L up to 7500 mg/L) at optimum experimental conditions (adsorbent dosage: 20 mg and contact time: 2 h). Equilibrium adsorption data were used to determine the maximum adsorption capacity of the undoped and doped CNTs. The Langmuir, Freundlich, and Temkin isotherm models were employed to demonstrate the adsorption data.
  • the Langmuir, Freundlich, and Temkin equations were used to describe the data derived from the adsorption of oil by the different adsorbents over the entire parameter range studied. Based on Figs. 7 and 8, the adsorption capacities (Q e ) and adsorption intensities were determined from the slope and the intercept of each adsorbent graph, respectively.
  • the Freundlich isotherm shows a better fitting model with higher correlation coefficients for both undoped and doped CNTs.
  • the Freundlich isotherm is commonly used to describe the adsorption characteristics for heterogeneous surfaces, as it is easier to handle mathematically in more complex calculations (e.g., in modeling the dynamic column behavior), where it may appear quite frequently. Therefore, the Freundlich isotherm model was employed to describe the adsorption of oil on the surface of all the adsorbents.
  • the Freundlich isotherm describes the adsorption process to be reversible and not restricted to the formation of a monolayer. Therefore, the amount of oil adsorbed on the CNTs is the summation of adsorption on all sites, with the stronger energy binding sites being occupied first, until the adsorption energies exponentially decreased upon the completion of the adsorption process.
  • the Temkin isotherm model analysis results are shown in Fig. 10 and Table 4.
  • the constants in the Temkin isotherm are found by plotting Q e as a function of In C e .
  • the correlation coefficient of 0.8 to 0.9 is obtained for the different adsorbents.
  • the A value which is an indication of binding energy, shows that there is a linear increase in the standard enthalpy of adsorption with surface coverage, and when the surfaces of the CNTs are doped with Fe 2 C>3 nanoparticles, the surface binding energy increases. This can be related to the zeta potential and increase in charge density by the introduction of Fe 2 C>3 nanoparticles.
  • Fig. 13 shows the plot of Q t vs. t 112 for the intra-particle diffusion model. It can be clearly seen that the plot does not show a linear trend over the entire time range. There are two almost linear regions, but the sorption time of 20 minutes for the oil uptake is far too short for an intra-particle diffusion mechanism. Nevertheless, the t 1/2 plot does give some visible insight to the mechanism by showing time regions.
  • the primary linear part may be explained as external surface adsorption, in which the oil particles diffuse through the solution to the external surface of the adsorbent.
  • the second and intermediate linear portion refers to a slower adsorption into the pores of the adsorbent with a slower rate than the first portion.

Abstract

Le procédé d'élimination d'huile de l'eau consiste à mettre en contact des nanotubes de carbone modifiés avec l'eau pour adsorber l'huile de l'eau, puis à isoler les nanotubes de carbone modifiés avec l'huile adsorbée sur celui-ci. Les nanotubes de carbone peuvent être dopés avec un métal, tel que le fer, l'argent, l'aluminium, le zinc ou le cuivre, ou un oxyde de l'un de ces métaux, à l'aide d'un traitement thermique. Afin de fabriquer des nanotubes de carbone modifiés par de l'oxyde de fer pour éliminer l'huile de l'eau, du nitrate ferrique et de l'oxyde de fer sont dissous dans de l'éthanol pour former une première solution. Des nanotubes de carbone sont dissous dans de l'éthanol pour former une seconde solution. Les première et seconde solutions sont ensuite soniquées séparément, suivies par le mélange de la première solution et de la seconde solution pour former une troisième solution, qui est ensuite soniqué pour former un mélange soniqué, et le mélange soniqué est chauffé pour fournir un résidu solide, qui est ensuite calciné.
PCT/US2017/047969 2016-08-24 2017-08-22 Procédé d'élimination de l'huile de l'eau WO2018039204A1 (fr)

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