Novel Materials for Facile Separation of Petroleum Products from Aqueous Mixtures Via Magnetic Filtration - Final Report

Period Covered by the Report: 8-1-00 to 7-31-01
Date of Report: 9-30-01
EPA Grant Number: R827015-01-0
Title: Novel Materials for Facile Separation of Petroleum Products from Aqueous Mixtures Via Magnetic Filtration
Investigators: Allen W. Apblett
Institutions: Oklahoma State University
EPA Project Officer: Bala Krishnan
Project Period: August 1, 2000 to January 31, 2001 (N/C Ext. to July 31, 2001)
Project Amount: $20,000
Research Category: Separations

Description:

The major objective of this research is to develop magnetic extractants that can be used in conjunction with a magnetic filter to efficiently and economically remove petroleum products from aqueous solutions and mixtures. The project will synthesize three types of magnetically-active materials that are capable of absorption of hydrocarbons so that the latter can be rapidly and efficiently removed from water using magnetic filtration technology. Initial tests were performed with aqueous mixtures of decane, a typical alkane. The possibility of using magnetic extractants for breaking of oil in water emulsions was also tested.

Several different approaches for the preparation of magnetic extractants were developed in this investigation.

We developed a method for making magnetically-active activated carbons that are simply prepared by impregnating paper towels with an aqueous solution of iron gluconate mixture and then firing at 500^oC under a nitrogen atmosphere. X-ray powder diffraction showed that the resulting material contained nanocrystalline magnetite while infrared spectroscopy demonstrated the presence of an activated carbon phase. A similar procedure using a nickel gluconate/ iron gluconate mixture yielded a nickel-ferrite impregnated activated carbon. Magnetic testing of the powders with a strong bar magnet indicated that the magnetite and ferrite-containing powders were strongly and completely ferromagnetic. Furthermore, none of the powders demonstrated any remnant magnetization outside of a magnetic field, an important property so that the powder will not stick to non-magnetized steel. Also, in the case of the magnetite, the lack of a remnant magnetization means that we have achieved our goal of creating particles too small to become permanently magnetized. As expected, the nickel ferrite-containing material exhibits the strongest response to a magnetic field. A second approach to higher surface area activated carbons that was investigated utilized sawdust and a conventional activated carbon preparation process that involved impregnating the sawdust with sulfuric acid before firing. In our experiments, iron and nickel salts were added to the sulfuric acid solution. Firing at 500^oC yielded magnetically-active carbon with surface areas between 250 and 300 m²/g. XRD analysis demonstrated the presence of magnetite or nickle ferrite particles with an average crystallite size less than 30 nm. Also present was calcite and calcium sulfate derived from calcium present in the sawdust.

Magnetically-Active Polydimethylsiloxane/Iron Composites

A recent report indicated that polydimethylsiloxane (PDMS) is a good absorbant for phenanthrene prompted us to prepare composites of PDMS with iron metal, hematite, and magnetite. These were prepared by cross-linking a PDMS polymer at moderate temperature (150^oC) in a mixture with the magnetic substrate. Two different PDMS oils were used as starting materials: a low viscosity (10 centistokes) material and a moderate viscosity material (1000 centistokes). These yielded strikingly different materials, a homogenous thinly-coated powder in the first case and a rubbery composite in the latter.

A composite material was prepared by coating a fine iron powder with poly-octadecyl methacrylate (average molecular weight of 170,000). The polymer was purchased as a toluene solution that was mixed with iron and allowed to evaporate yielding a waxy solid with imbedded iron particles. The proportions of the polymer and iron could be varied to provide a magnetic extractant that was neutrally buoyant (useful for removing soluble hydrocarbons) or which floats on water (useful for removing hydrocarbon slicks from water).

Magnetic extractants were prepared by treating iron and magnetite powders with octadecyltrimethoxysilane. This reagent condenses with surface hydroxyls on the iron or iron oxide surface, leading to a monolayer of pendant octadecyl groups grafted to the metal surface via a cross-linked silica layer.

The testing of the extractants was initiated using a 104 ppm aqueous solution of decane. 20 g of solution was treated with 0.5 g of extractant. After filtration, 6 g the aqueous solution was extracted with 1 g hexane and the extracts were analyzed for decane by GC/MS. The results are as follows:

* Prepared using sawdust/sulfuric acid
** Below detection limit

Thus, all of the extractants tested (except for one) performed very well and can reduce the concentration of decane, a representative alkane, to the parts per billion level. t can be expected that less water-soluble alkanes will partition even better.The one exception was the activated cabon derived from sawdust. The behavior of this material is peculiar considering it’s high surface area. Since decane will adsorb to an iron oxide surface to some extent. the complete failure of this material implies a highly charged lipophobic surface. The best magnetic extractants for decane were the polydimethylsiloxane/iron composites. The results also suggest that organic content should be maximized and that a monolayer of C-18 chains does not provide the best results. Thus, the octadecylsilsesquioxane derivatives did not perform optimally.

A stable emulsion was prepared by diluting a 35:20:45 weight percent paraffin oil/triethanolamine/oleic acid mixture to 1000 ppm in water. This yielded an indefinitely stable white emulsion. Ten grams of this emulsion was treated with 0.5 g of the nickel ferrite/activated carbon extractant by briefly shaking the two materials together in a glass vial. The mixture was then passed through a magnetic filter consisting of a glass pipet packed loosely with steel wool and taped to the side of a bar magnet. The solution passed through the filter was much clearer. The extent of emulsion removal was then assessed by measuring the solution’s absorption at 500 nm. Before treatment the absorbance was 1.66 while after it was 0.21. In terms of transmission, an increase from 2 to 62% was observed. Thus, magnetic extractants are capable of breaking emulsions and these initial results suggest that optimization of the magnetic extractant could result in complete breaking of an oil in water emulsion. Notably, the emulsion used in this study was very high in surfactant and extremely stable and it is likely that real world samples may not be as challenging.

Future Activities

This project is still active and is being investigated by two OSU graduate students – one supported by SABIC and the other by a teaching assistantship. We are pursuing the PDMS composites and the activated carbons. Also testing of phenanthrene removal from water and emulsion breaking is being investigated.

Summary

This proof of concept proposal demonstrated that magnetic extractants in combination with magnetic filtration are capable of removing hydrocarbons from water and in breaking oil in water emulsions.

Publications/ Presentations:

Publications

A.W. Apblett, S. M. Al-Fadul, M. Chehbouni, and T. Trad "Removal of Petrochemicals from Water Using Magnetic Filtration" Proceedings of the 8th International Environmental Petroleum Consortium, 2001. http://ipec.utulsa.edu/Ipec/Conf/apblett_101.pdf.

A.W. Apblett, S. M. Al-Fadul, M. Chehbouni, and T. Trad "Ceramic-Derived Magnetic Extractants for Waste Water Treatment" Ceramic Transactions 2003. In Press.

A.W. Apblett, Sulaimon M. Al-Fadul, and Tarek M. Trad "Polydimethylsiloxane- Coated Iron and Iron-Oxides for Magnetic Separation of Organics from Water. Submitted to Environmental Science and Technology.

Presentations

"Removal of Petrochemicals from Water Using Magnetic Filtration" 8th Integrated Petroleum Environmental Consortium Conference, Houston, TX (November 9, 2001)

"Ceramic-Derived Magnetic Extractants for Wastewater Remediation" American Ceramic Society 104th Annual Conference, St. Louis, MO (April 30, 2002)

Supplemental Keywords:

water, drinking water, adsorption, solvents, organics, DNAPL, NAPL, effluent, discharge, remediation, cleanup, environmental chemistry, petroleum industry

Relevant Web Sites:

http://ipec.utulsa.edu/Ipec/10.d/10_Q3.pdf
http://ipec.utulsa.edu/Ipec/Conf/apblett_101.pdf
http://ipec.utulsa.edu/Ipec/10.d/Abstract.html