Patent Publication Number: US-7591960-B2

Title: Preparation method for oil-based magnetic fluid

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a preparation method for magnetic fluid, especially to oil-based magnetic fluid that absorbs organic material, oil-based material and metal ions inside the fluid. Then by the application of the magnetic field, the absorbed material is separated from the fluid so as to achieve the purposes of fluid treatment or purification. 
     2. Description of the Related Art 
     Magnetic materials have been applied broadly to recording tapes, magnetic materials for memory such as magnetic disks or tapes, building materials such as ink, paint, and mechanical parts such as electromagnetic switches, or seals. By the development of new preparation method, magnetic materials are applied in more fields such as biomedicine for purification of drugs, protein and DNA or environmental waste treatment. 
     For example, U.S. Pat. No. 4,687,748 applied in 1987 discloses magnetically responsive spheres having an average diameter less than 1,000 nm, prepared by dissolving a carbohydrate polymer in a polar solvent and being applied to cell separation as well as affinity purification. Basically, such magnetic separation techniques have two types according to features of material being processed (1) apply the magnetic field to separate material itself with magnetic properties. (2) combine material without magnetic properties with magnetic material by chemical reactions and then apply the magnetic field for separation. In combination of the material without magnetic properties with magnetic material, various types and preparation methods of magnetic material play important roles. 
     There are various preparation methods for magnetic material according to users&#39; requirement. The most common is (1) grinding: refer to U.S. Pat. 4,604,222, applied in 1986, magnetic fluid is prepared by mixing of magnetic particles, dispersing agent such as a cationic surfactant and organic liquid carrier such as an ester or a glycol and then employing a grinding or ball mill technique so as to improve electrical conductivity and seal computer disc drives. (2) oxidation reaction: such as U.S. Pat. No. 6,140,001, applied in 2000, disclosing a method that mix a solution of a soluble phosphate compound such as sodium orthophosphate with a solution of ferrous ion, and alkali or alkaline hydroxide solution to form ferrous hydroxide. Then an oxidation step is performed by passing an oxygen-containing gas through the mixture. Finally, the iron oxide particles of the invention will precipitate from the solution. (3) chemical coprecipitation: refer to U.S. Pat. No. 6,743,371, applied in 2004, disclosing magnetic fluid prepared by mixture of magnetic sensitive particles such as nickel-zinc ferrite or manganese-zinc ferrite and conductive particles such as gold, silver, copper, aluminum and graphite. The magnetic fluid is utilized in electrical switching applications. Because the magnetic particles attract each other and thus aggregate, it is necessary to take surface treatment step during preparation process for effectively separation of particles. Not only the diameter of particles is smaller, but the particles are more easily to be dispersed inside the solvent. The ways of surface treatment are different depending on hydrophilic or lipophilic characteristics of the oil-based magnetic fluid being prepared. 
     As to the preparation of lipophilic oil-based magnetic fluid, refer to U.S. Pat. No. 5,124,060, applied in 1992, a method includes steps of adding the low boiling organic solvent and the dispersant having oleophilic groups to separate particles and heating the resulting material to evaporate the low boiling organic solvent thereby obtaining a magnetic fluid that is applied to seal vacuum apparatus. Moreover, U.S. Pat. 6,068,785, applied in 2000, disclosing a slurry is formed of particles of a non-magnetic oxide of iron (.alpha.-Fe.sub.2 O.sub.3), an oil carrier liquid and a surfactant. The slurry is then processed in an attrition mill to generate magnetic iron oxide particles for form an oil-based material. Due to direct grinding operation, oil and surfactant may attach on surface of magnetic particles so as to make the surface coating fall off. This leads to negative effect on yield rate. 
     Generally, magnetic fluid is more applied to magnetic materials for memory and design of mechanical seal. However, it&#39;s seldom used in eliminating organic compounds or oil inside the water and processing metal ions inside the inorganic wastewater. Conventionally, organic wastewater is processed by heat treating or chemically oxidation. This not only costs much but also generates secondary wastewater due to addition of chemicals. As to wastewater with metal ions, besides conventional chemical precipitation, physical treatment methods such as membrane technologies can also be used. Although there is no addition of chemicals, it requires higher equipment cost and more technical support. 
     In order to make the oil-based magnetic fluid have lipophilic interface and strong binding force between the magnetic metal oxide particles, the present invention adds surfactant with a carboxyl group during the preparation process of iron oxide so as to generate the magnetic material such as iron oxide with the carboxyl group. Then, the material further reacts with oil material to form oil-based magnetic fluid by crosslinking reaction. The bonding between the magnetic material and the compounds is formed by chemical reaction. Thus the final product has higher bonding force between molecules with better stability. 
     Thus the oil-based magnetic fluid in accordance with the present invention can react with oils, organic compounds, and metal ions inside water and then being separated by the application of magnetic field. The present invention has advantages of no addition of chemicals, simple equipment and easy operation. 
     SUMMARY OF THE INVENTION 
     It is therefore a primary object of the present invention to provide a preparation method for oil-based magnetic fluid that combines magnetic material with oil-based material by crosslinking reaction of functional groups to form chemical bonds therebetween. By the application of magnetic field, the oil-based magnetic fluid absorbs organic compounds or metal ions for separation from solution. Thus the purposes of fluid treatment or purification are achieved. 
     It is another object of the present invention to provide a preparation method for oil-based magnetic fluid. The oil-based magnetic fluid has both magnetism and mobility of fluid. While being mixed with fluid such as wastewater, the oil-based magnetic fluid absorbing organic material and metal ions is insolvable with water. During the process of fluid treatment, there is no need to add catalyst, oxidizing agent or other chemicals. Not only the cost for treatment is saved, but also the recovery process of the catalyst is left out. At the same time, by magnetism, the oil-based magnetic fluid absorbing organic material and metal ions is separated with water rapidly and it&#39;s convenient to operate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein 
         FIG. 1  is a flow chart for preparation of an embodiment of oil-based magnetic fluid in accordance with the present invention; 
         FIG. 2  is a flow chart for preparation of another embodiment of oil-based magnetic fluid with organic extraction solvent in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Refer to  FIG. 1 , in step S 10 , a diamino compound is added into oleaginous material to form oil-based compound containing diamino group. Refer to step S 12 , the oil-based compound having a carboxyl group and a diamino group is obtained by adding carboxyl compounds into the oil-based material containing a diamino group. In step S 14 , iron solution is mixed with carboxyl compounds to get magnetic iron oxide with a carboxyl group. Refer to step S 16 , the oil-based compound having a carboxyl group and a diamino group is added into the magnetic iron oxide with a carboxyl group so as to obtain the oil-based magnetic fluid with particles whose diameter ranges from 60 to 100 nanometers. 
     In step S 10 , an embodiment is taking as an example. The compound containing a diamino group such as urea is dissolved into the water. Then add into the same amount of alcohol so as to make the concentration of the urea become 24 to 30% weight/volume ratio and the mixture is heated inside the reflux condenser at the temperature ranging from 70 to 90 Celsius degrees and 75 Celsius degrees is the preferable temperature. Moreover, take some oil (such as vegetable oil or other organic oils) and dilute it with equal volume of ethyl acetate. The diluted oil is dropped into the hot urea solution so as to make the volume ratio between the oil and the urea solution be two. Continuingly heat the resulting mixture for thirty minutes. After the solution cooling down to room temperature, wash it with water and centrifugate the solution to get the raw urea synthetic oil. Repeat the steps of washing and centrifugation several times, the product is urea synthetic oil. That&#39;s oil-based compound with a diamino group. 
     Take an embodiment for explanation of step S 12 . The urea synthetic oil is stirred and heated to 85 Celsius degrees in the reflux condenser. Then slowly add the carboxyl compound solution, such as undecenoic acid, oleic acid, lauric acid, or caproic acid, into the urea synthetic oil until the volume ratio of the carboxyl compound solution to the urea synthetic oil becomes 1/5. Continuingly heat the resulting mixture for 30 minutes. Then let it cool down to room temperature, add alcohol into the solution and washing the mixture. After centrifugation, oil-based material having carboxyl group and urea is obtained. The oil-based material having carboxyl group and urea made by condensation reaction between the undecenoic acid and an amino-terminal of the urea is an oil-based compound having a carboxyl group and a diamino group. 
     In step S 14 , ferrous chloride and ferric chloride are dissolved inside deoxidized water and the molecular ratio between them is from 1/2 to 1/3. The solution is heated to 80 Celsius degrees inside the reflux condenser. Then slowly add the carboxyl compound solution (such as undecenoic acid) about 2.4% volume ratio into the solution and continuingly heat the solution. Take an amount of 25% ammonia water, diluted with equal amount of alcohol and ethyl acetate and pour into solution inside the reflux condenser. The ammonia water occupies about 20% of the total volume. Keep heating at 80 Celsius degrees for thirty minutes. Then cool down the mixture to 65 Celsius degrees and keeps in this temperature for 5 hours and thirty minutes so as to get the precipitation of magnetic iron powder with a carboxyl group. Magnetically decant clear supernatant, wash the precipitation with alcohol several times and then preserve in a bit alcohol solution. Or after decanting clear supernatant, dry the precipitation at room temperature so as to get the magnetic iron powder with a carboxyl group. That&#39;s magnetic iron oxide coated with a carboxyl group. 
     In step S 16 , add carboxyl urea synthetic oil into magnetic iron powder with a carboxyl group and heat inside the reflux condenser at the temperature from 65 to 80 Celsius degrees for thirty minutes. The temperature is preferably 85 Celsius degrees. 
     After washing with alcohol, water, and separation, the stable oil-based magnetic solution is obtained. The composition of the solution includes iron oxide Fe 3 O 4 . 
     Refer to  FIG. 2 , in the step S 20 , mix iron solution with carboxyl compounds so as to obtain magnetic iron oxide with a carboxyl group. Take the step S 22 , mix the carboxyl compounds with organic extraction reagent to get organic extraction solution with a carboxyl group. In step S 24 , mix the magnetic iron oxide with a carboxyl group with the organic extraction solution with carboxyl group, then add the organic extraction solution with oleaginous material into the mixture so as to get oil-based magnetic fluid. 
     Dissolve 2.78 gm ferrous sulfate in 100 ml pure water and heat the solution to 85 Celsius degrees. Add 1 ml undecenoic acid into the solution, stir and heat at 85 Celsius degrees inside the reflux condenser. Add 10 cc 10% sodium hydroxide into the mixture drop by drop and keep heating the solution at 85 Celsius degrees in the reflux condenser for an hour. Magnetically decant the solution, wash with acetone for several times, put into the reflux condenser. Slowly add the mixture of 10 ml tributyl phosphate (TBP) with 1 ml undecenoic acid into the reflux condenser and heat for an hour. Again magnetically decant the solution, wash with acetone for several times, then wash several times again with 30% solution of tributyl phosphate in kerosene. Then the product is dispersed inside the 30% solution of tributyl phosphate in kerosene. This is oil-based magnetic fluid. 
     In summary, oil-based magnetic fluid in accordance with the present invention is used in combination with external magnetic field for absorption of floating oil on water surface and separation as well as treatment of organic compounds, metal ions and oil in wastewater. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.