Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
1999-07-30
2001-03-27
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S653000, C134S010000, C134S013000
Reexamination Certificate
active
06207058
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the unexpected discovery of a class of surfactants which demonstrate improved surfactant recovery from aqueous solutions upon ultrafiltration.
Aqueous waste water solutions from industrial metal cleaning processes such as metal stamping, grinding, oil drilling and machining operations contain hydrocarbon and inorganic waste materials as well as the surfactants used in the cleaning process. Because of environmental and economic concerns, it is important to remove and desirably recover for reuse the active surfactant ingredients from these aqueous by-product or waste solutions. The recovery and recycling of surfactants from treated aqueous solutions not only reduces or eliminates the discharge of contaminated water into the environment but also reduces the overall cost of industrial processes. The separation and recovery of these surfactants from the waste water is of particular importance in processing aqueous solutions containing surfactants as they can be a costly component of the solution.
Ultrafiltration equipment can be used to overcome certain waste disposal problems in connection with aqueous solutions, whether using polymeric or sintered metal/sintered metal oxide filters. The economics of these processes in recovering surfactants have been seriously hampered since many of the conventional surfactants are not recoverable in the permeate. The ability to recycle and reuse these surfactants from aqueous solutions is significantly reduced thereby necessitating the addition of more surfactant to bring the amount in solution to the original level. This is a significant problem in the treatment of contaminated water systems since the loss of the original surfactant and the subsequent need for the addition of more becomes expensive.
Waste water treatment systems have been disclosed that claim significant recovery of water-based cleaning systems in the permeate upon ultrafiltration although in reality considerable dissatisfaction has been expressed concerning the filterability and recovery of existing water-based cleaning formulations. Whereas U.S. Pat. No. 5,205,937 to Bhave et. al. asserts to disclose aqueous cleaning systems wherein high percentages of the cleaner passes through the filter in the permeate for recycling, the amount of cleaner in the permeate is measured by HCI titration which is actually a measure of the caustic or sodium hydroxide present, not the surfactant. Most of the nonionic surfactants disclosed therein do not in fact pass through the membrane.
It is known that certain sultaine surfactants as disclosed in U.S. Pat. No. 4,891,159 to Nadolsky provide effective surfactant properties in highly alkaline cleaning solutions making them useful in paint stripping compositions, hard surface cleaners, oven cleaners, wax strippers, degreasers, aluminum cleaners, and bottle washing compositions. At lower alkalinities, they have proven effective in laundry and dish washing detergents and hand cleansers. However, these surfactants are not taught to provide any significant benefits when used in connection with an ultrafiltration-based water treatment and surfactant separation and recovery system.
As discussed above, U.S. Pat. No. 5,205,937 to Bhave et al. discloses a method for the recovery of a surfactant-containing solution from an aqueous contaminant stream using nonionic surfactants, among others. Whereas high yields of cleaning formulation is asserted to be recovered from the permeate, the amount that comprises the surfactant is really unknown since only the amount of sodium hydroxide present in the system is determined through the titration of the permeate with hydrochloric acid.
U.S. Pat. No. 5,654,480 to Dahanayake et al. on the other hand discloses the use of certain amphoteric surfactants, namely sultaines, in aqueous contaminant-containing streams. These surfactants, due to the nature of their pH dependent charge, are able to pass through the ultra-filtration membrane and are recovered in the permeate in very high amounts.
The present invention is directed to the finding that surfactant-containing aqueous compositions containing a certain class of nonionic surfactants unexpectedly provide improved surfactant recovery in the permeate after ultrafiltration. More particularly, it is discovered that a certain class of alcohol alkoxylate surfactants provide superior surface activity in aqueous cleaner systems while at the same time are able to pass through the filtration membranes for efficient recycling thereof.
SUMMARY OF THE INVENTION
It has unexpectedly been found that increased surfactant recovery can be obtained upon ultrafiltration of contaminated aqueous solutions containing certain nonionic surfactants which, when ultrafiltered, are able to pass through the ultrafiltration membrane resulting in increased surfactant recovery. More specifically, the present invention relates to a process for the recovery of high yields of several specific nonionic surfactants from the permeate of a recyclable cleaning system wherein said nonionic surfactants remain polar and are solvated at the higher operating temperatures of the ultrafiltration process.
The present invention also provides a process for the filtration of contaminants from an aqueous surfactant/contaminant-containing solution by passing it through an ultrafiltration membrane, preferably a metal oxide membrane on a ceramic support.
In another aspect, the present invention relates to a process for separating a surfactant in an aqueous solution containing contaminants such as oils, greases, waxes, emulsified lubricants, etc., by passing the solution cross-flow through a multi-channel sintered monolithic metal/metal oxide ultrafiltration membrane on a ceramic support to form a permeate of surfactant for recovery. The sintered metal oxide membrane has a nominal pore size in the range of about 50 to 1000 Angstroms.
DETAILED DESCRIPTION OF THE INVENTION
In an effort to provide superior water treatment recycle systems, it has been unexpectedly and surprisingly discovered that a high degree of surfactant recovery can be obtained using standard ultrafiltration membranes with certain aqueous nonionic surfactant systems. The particular nonionic surfactants useful in the process of the present invention are added to the contaminant-containing waste stream at standard operating temperatures and while the surfactants pass through the ultrafiltration membrane and are recovered in high concentrations in the permeate, the contaminants and other materials are collected by the filter in the retentate.
In general, the majority of non-ionic surfactants used in industry are non-polar at the standard operating temperatures of most ultra-filtration processes. In the non-polar state, these surfactants are not water soluble and are more oil-like when mixed in an aqueous system. As a result, most if not nearly all nonionic surfactants which otherwise exhibit superior surface active properties cannot pass through the ultra-filtration membranes to a large degree and are not easily recoverable from the system for recovery and re-use. The vast majority of the non-polar cleaners used in the prior art face this problem.
Without being bound by any theory, it is believed that when surfactants are mixed in aqueous systems, the surfactant becomes solubilized by forming hydrogen bonds with the surrounding water molecules. The surfactant thereby becomes hydrated. As the temperature of the system is increased, the surfactant/water hydrogen bonds are broken and the surfactant becomes dehydrated. This is known as the dehydration or cloud point. As this occurs, the non-polarity or hydrophobicity of the surfactant molecule increases and the molecules become insoluble in water but highly soluble in oil.
The temperature at which a solubilized surfactant's hydrogen bonds with water break is the dehydration point or cloud point for that surfactant. Whereas most compounds become more water soluble as the temperature of the system is increased, the non-ionic alkoxylate surfactants of the present i
Dahanayake Manilal S.
Ventura Mark E.
Fortuna Ana
Ohlandt Greeley Ruggiero & Perle L.L.P.
Rhodia Inc.
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