Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
1999-12-22
2001-04-10
Reifsnyder, David A. (Department: 1723)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S781000, C210S787000, C175S066000, C175S206000, C208S013000, C516S136000
Reexamination Certificate
active
06214236
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention pertains to an effective, cost efficient method of separating even tightly emulsified oily waste sludges. The method can be used in treating used liquid petroleum products, and wastes generated from petroleum production and refining facilities, manufacturing plants, chemical plants, still mill sludges, municipal facilities, and other similar facilities and operations.
BACKGROUND OF THE INVENTION
Many industrial plants and municipal facilities generate waste products that are partial emulsions of water, oil and solids and are referred to as “sludges.” For example, petroleum refineries and manufacturing plants generate significant quantities of oily waste products that contain a variety of solids, such as suspended carbonaceous matter and inorganic matter such as rust scales, catalysts fines and the like. Furthermore, most of this waste is classified as hazardous and, therefore, must be treated before disposal in regulated landfills to meet concentration limits for certain organic compounds, cyanides and several heavy metals.
Refinery waste sludges are among the most difficult emulsions to break. Yet the disposal criteria for solids are expensive to reach, necessitating the separation of the water, oil and solid components to minimize the amount of wastes that require disposal. Further, the hydrocarbons can be recycled in the plant's processes and the water can be treated per normal waste water treatment processes, if sufficient amounts of solids are removed. Therefore, although refinery waste sludges are very difficult to break, it is often the most economical means of treating the waste.
An emulsion may be present in oily waste products other than refinery waste sludges. Emulsions may also be present in used oil. In the oil exploration industry, for example, drilling fluid may become saturated with cuttings, oil, water, and other materials. The saturated drilling fluid is no longer usable and must be discarded. The saturated drilling fluid may include an emulsion that includes the oil constituent of the drilling fluid. Unless the oil constituent of the saturated drilling fluid can be separated from the emulsion, the oil constituent will be discarded with the remainder of the saturated drilling fluid. If the saturated drilling fluid could be demulsified, the oil of the drilling fluid could be recovered and recycled as drilling fluid. Similarly, an emulsion may be present in other forms of used or spent oil. In the case of motor oil, the oil may become soiled with dirt and metal particles during use and an emulsion may be formed of the oil and other constituents of the used oil. Unless the oil constituent of the motor oil can be separated from the spent motor oil, the oil constituent will be discarded with remainder of the spent motor oil.
In order to understand the technology used to separate waste sludges, it is useful to review the theory of emulsion. An emulsion is an intimate mixture of two immiscible liquids, such as oil and water. Two types of oil and water emulsions are commonly encountered, based on the relative amounts of oil and water. The first is an oil dispersed in water (oil in water) emulsion, and the second is a water dispersed in oil (water in oil) emulsion.
A stable oil in water emulsion consists of electrically charged oil droplets dispersed in a polar medium such as water. The violent mixing and shearing of oily wastewater in transfer pumps disperses the minute oil droplets throughout the water, and the friction between the oil and water phases creates static electrical charges at the oil and water interphase and helps to stabilize the emulsion.
This emulsion can be further stabilized by a variety of chemical and physical mechanisms. Surfactants (such as soaps, cresylates, sulfides, and electrolytes) usually carry an electric charge and travel to the oil/water interface (the interfacial film) of the droplets, thus reinforcing the repulsion of the droplets. Fine, solid particles may also stabilize an emulsion if the particles are of the correct size and abundance. The solid particles adsorb at the oil/water interface, reinforce the interfacial film and prevent the droplets from coalescing. Thus, solid particles also reinforce the stability of the dispersion.
The “breaking,” or “resolution,” of an oil in water emulsion is done by neutralizing the charges at the surface of the droplets. This is performed with a cationic emulsion breaker because the dielectric constants of oil and water cause the oil droplets to carry a negative charge in water. Lowering the pH, with sulfuric acid for example, can also help by converting any carboxyl ions present in the surfactant into carboxylic acid. Once the charges are neutralized, the phases can be gravity separated in an API or CPI separator. This separation can be significantly accelerated by centrifuging the mixture. Treatments to break waste sludges include also floatation, ultrafiltration, activated carbon adsorption, coalescence and solvent extraction.
Water in oil emulsions are viscous, concentrated substances formed when oil comes into contact with water and solids. Where agitation is present, the water becomes dispersed in the oil. Finely divided solids, ranging from colloidal to 100 microns, are particularly effective in stabilizing these emulsions. Other stabilizing agents include soaps, sulfonated oils, asphaltic residue waxes, salt sulfides and mercaptans.
The breaking of a water in oil emulsion can be done with physical methods such as heating and centrifugation. Chemical treatment of water in oil emulsions is directed at destabilizing the dispersed water droplets and solids or at destroying the emulsifying reagents. Usually anionic reagents are employed to destabilize the water droplets because the water droplets tend to be positively charged. Acidification may also be effective if the acid dissolves some of the solids and thus reduces the amount of stabilizing solids. Another method of treatment involves potent demulsifying agents carrying both hydrophilic and lipophilic groups. The demulsifying agent displaces the original emulsifying agent because it has more potent surface active agents. Heating reduces the viscosity of the emulsion and increases the solubility and diffusion of the demulsifying agent in the emulsion. Usually, thorough mixing and heat are both necessary to help disperse the demulsifying agents in the emulsion and to facilitate the separation of the phases once the charges are neutralized. Here again, centrifugation is the key to accelerating the separation.
The emulsions encountered in refinery waste are very diverse because the waste itself is a very heterogeneous material coming from many different processes. Therefore, the separation of refinery waste into its constituents is a very tricky operation, far removed from the cleanliness of the theoretical resolutions described above. The state of the art includes multiple technologies, all attempting to enhance the efficiency of charge neutralization and the settling of the demulsified residual mixture. Myriads of chemical formulations have been created for breaking emulsions, showing by their number and diversity that there is no magic potion that can universally break refinery waste sludges.
Physical methods of resolving refinery waste sludges include sophisticated centrifuges that have been designed to apply high G forces and long residence times (a high &Sgr; factor) (see e.g., U.S. Pat. Nos. 4,810,393; 5,443,717). In U.S. Pat. No. 5,443,717 (the '717 patent), for example, a process for producing a quench stream for use in the quench cycle of a delayed coking process is described. A waste stream containing water, organic compounds and solids is treated by centrifugation in a vertical disk centrifuge. After being separated from the oil and water components of the stream, the particulate matter leaves the centrifuge at a very high exit speed and the impact of the solids on the exit shield causes attrition of the particle size. This particle attrition makes the solids produc
Baker & Botts L.L.P.
Reifsnyder David A.
LandOfFree
Process for breaking an emulsion does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for breaking an emulsion, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for breaking an emulsion will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2455710