BR112019007989B1 - METHOD FOR TREATING A WASTE STREAM CONTAINING HYDROCARBONS - Google Patents

Abstract

The present invention relates to methods for treating a hydrocarbon-containing waste stream to form a hydrocarbon-containing retentate and an aqueous permeate that is substantially free of hydrocarbons. The method includes passing the hydrocarbon-containing waste stream through a microporous membrane to produce the hydrocarbon-containing retentate and aqueous permeate. The membrane comprises a substantially hydrophobic polymer matrix and substantially hydrophilic finely divided particulate filler distributed throughout the matrix. The polymeric matrix has pores with a volumetric mean diameter of less than 1.0 microns, and at least 50 percent of the pores have a mean volumetric diameter of less than 0.35 microns.

Description

Field of invention

[0001] The present invention relates to waste stream purification processes containing hydrocarbons using microporous materials having filtration and adsorption properties.

History of the invention

[0002] According to the Department of Energy, 79.485 billion liters (21 billion gallons) of co-produced water are produced by oil and gas wells each year in the United States. The natural “oil” from a well is actually a multiphase oil/water/gas fluid. Generally, all three fluids are found in all hydrocarbon wells and well effluent.

[0003] Due to its value and environmental concerns, oil needs to be separated from this effluent. This is usually done by gravity sedimentation in large tanks, which requires significant capital and space that is not always available on site. The gas is easily separated in a mechanical separator or by reducing pressure within storage containers. In the case of heavy oils and many emulsified fluid systems, the crude fluids are heated to change the density of the oil and water by heating lighter ends and essentially agitating their molecular structures so that these fluids can be more easily separated. Water is then a byproduct.

[0004] Although co-produced water is common, it is a hazardous waste that is very inconvenient for operators and must be disposed of, sometimes with difficulty. Water that historically may have been sent down a stream or in a wooden barrel now needs to be piped into very large storage containers. At sea, these containers are fixed from above or hooked by hoses on old and retrofitted storage ships. This wastewater is stored for days to separate the oil from the water. The resulting aqueous product still contains some petroleum and other possible contaminants. This procedure, in addition to being expensive, is time-consuming, risky and consumes energy. In a deep-sea submarine environment, water storage containers are not viable.

[0005] Current superior water-oil separation processes are slow, environmentally hostile, and consume a large amount of energy in heating. Final wastewater must be discarded and cannot be released directly into the ocean. Often, stored water must be treated with chemicals to reduce surface tensions between phases and induce separation, creating an additional risk of chemical handling and potential spills. The volumes of water produced offshore can be thousands of barrels per day per well. In general, processing facilities are a large part of an ongoing footprint. Often, co-produced water is reinjected into the subsurface because overhead storage is a non-trivial problem. Sufficiently removing controversial chemicals and residual petroleum before any disposal is a process that involves regulatory bodies like the U.S. Environmental Protection Agency (EPA).

[0006] As mentioned above, in subsea operations there is simply no large volume water storage option available to the industry. Separation is ineffective: a significant amount of water in the oil remains in solution after subsea separation, resulting in inefficient separation and ultimately lower hydrocarbon recoveries. Most critically, oil-in-water concentrations are high (in the 5 percent range) due to lack of sufficient residence time, which will result in crude oil being injected into the disposal well along with the produced water. Consequently, the disposal zones eventually become connected and become ineffective for further disposal. Furthermore, oil in water that is pumped to disposal areas loses product and revenue for operating companies and loses royalties for the federal government.

[0007] It would be desirable to provide a simple and inexpensive technique that could overcome the aforementioned shortcomings. Such a technique can save the industry hundreds of millions of dollars in operational and maintenance costs, and increase revenues, in addition to saving space. Additionally, this method can eliminate many environmental concerns.

Summary of the invention

[0008] The present invention relates to a method for treating a hydrocarbon-containing waste stream comprising more than 0 to 2 weight percent hydrocarbons to form an aqueous permeate that is substantially free of hydrocarbons and a hydrocarbon-containing retentate, being that the method comprises passing the hydrocarbon-containing waste stream through a microporous membrane to produce the aqueous permeate and the hydrocarbon-containing retentate. The membrane comprises a substantially hydrophobic polymeric matrix and substantially hydrophilic finely divided particulate filler distributed throughout said matrix. The polymeric matrix has pores with a volumetric mean diameter of less than 1.0 microns, and at least 50 percent of the pores have a mean volumetric diameter of less than 0.35 microns.

Brief description of the figures

[0009] Figure 1 is a graph of the cartridge permeate rates of the experimental cartridge (Example 8) and the comparative cartridge (CE-9) disclosed herein.

[0010] Figure 2 is a graph of the oil concentration in the permeate of the experimental cartridge (Example 8) and the comparative cartridge (CE-9) disclosed here.

Detailed description of the invention

[0011] In addition to the operational examples, or unless expressly specified otherwise, all numbers expressing amounts of ingredients, reaction conditions and so on used in the specification and claims will be understood to be modified in all cases by the term “about” or “approximately”. Consequently, unless otherwise indicated, all numerical parameters presented in the specification following and in the attached claims are approximations that may vary depending on the desired properties to be obtained by the present invention. At a minimum, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted in light of the number of significant figures reported and applying customary rounding techniques.

[0012] Although the numerical ranges and parameters showing the broad scope of the invention are approximations, the numerical values presented in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors resulting from the standard variation found in their respective test measurements.

[0013] Likewise, it should be understood that any numerical range mentioned herein is intended to include all subranges included therein. For example, a range of “1 to 10” is intended to include all subranges between (and including) the mentioned minimum value 1 and the mentioned maximum value 10, i.e. having a minimum value greater than or equal to 1 and a maximum value less or equal to 10.

[0014] When used in this specification and the attached claims, the articles “a”, “an”, “the” and “a” include plural references, unless expressly and unambiguously limited to one referent.

[0015] Each of the various embodiments and examples of the present invention presented herein should be understood as being non-limiting with respect to the scope of the invention.

[0016] When used in the following description and claims, the following terms have the meanings indicated below.

[0017] The term “polymer” means a polymer including homopolymers, copolymers and oligomers.

[0018] When used herein, the term “formed from”, for example, “comprising”, indicates open claim language. As such, a composition “formed from” a list of mentioned components is intended to be a composition comprising at least these mentioned components and may further comprise other components not mentioned, during the formation of the composition.

[0019] When used herein, the term “polymeric inorganic material” means a polymeric material having a main chain repeating unit based on an element or elements other than carbon. For more information see James Mark et al., Inorganic Polymers, Prentice Hall Polymer Science and Engineering Series, (1992) on page 5, which is specifically incorporated herein by reference. Furthermore, when used herein, the term “organic polymeric materials” means synthetic polymeric materials, semi-synthetic polymeric materials, and natural polymeric materials, all of which have a carbon-based backbone repeating unit.

[0020] When used herein, an “organic material” means carbon-containing compounds in which carbon is typically bonded to itself and hydrogen, and often also to other elements, and excludes binary compounds such as carbon oxides, carbides , carbon disulfide, etc.; such ternary compounds as metal cyanides, metal carbonyls, phosgene, carbonyl sulfide, etc.; and carbon-containing ionic compounds such as metallic carbonates, for example, calcium carbonate and sodium carbonate. See R. Lewis, Sr., Hawley's Condensed Chemical Dictionary, (12th edition, 1993) at pages 761-762, and M. Silberberg, Chemistry The Molecular Nature of Matter and Change (1996) at page 586, which are specifically incorporated herein by reference.

[0021] When used herein, the term “inorganic material” means any material that is not an organic material.

[0022] When used herein, a “thermoplastic” material is a material that softens when exposed to heat and returns to its original condition when cooled to room temperature. When used herein, a “thermoset” material is a material that irreversibly solidifies or “hardens” when heated or otherwise cured.

[0023] When used herein, “microporous material” or “microporous sheet material” means a material having an interconnecting network of pores, where, on a coating-free, printing ink-free, impregnant-free and pre-free basis -bonding, the pores have a volumetric average diameter (i.e., an average pore size) ranging from 0.001 to 1.0 micrometer, and constitute at least 5 volume percent of the material as discussed herein below.

[0024] “Plastomer” means a polymer that exhibits plastic and elastomeric properties.

[0025] The term “emulsion” means a colloidal suspension of two liquid phases in which droplets of one liquid are suspended in another liquid. In most embodiments of the present invention, a liquid is an aqueous liquid. Such emulsions may be unstable or optionally stabilized by surfactants or other emulsion stabilizers that are known in the art.

[0026] As mentioned above, the present invention relates to a method for treating a hydrocarbon-containing waste stream to form a hydrocarbon-containing retentate and an aqueous permeate that is substantially free of hydrocarbons. The method comprises passing the hydrocarbon-containing waste stream through a microporous membrane to produce the hydrocarbon-containing retentate and aqueous permeate. The membrane comprises a substantially hydrophobic polymeric matrix and substantially hydrophilic finely divided particulate filler distributed throughout said matrix, the polymeric matrix having pores having a volumetric average diameter of less than 1.0 microns, and at least 25 percent of the pores having an average diameter of less than 0.3 microns.

[0027] As mentioned above, the membrane comprises a substantially hydrophobic polymer matrix (discussed here below) and substantially hydrophilic finely divided particulate filler distributed throughout the matrix.

[0028] Membranes suitable for use in the method of the present invention typically include a microporous material. Suitable microporous membranes generally comprise: (a) a polyolefin matrix material present in an amount of at least 2 percent by weight; (b) particulate, substantially water-insoluble, finely divided, hydrophilic filler, e.g., any of those described below, distributed throughout the matrix, the filler constituting from about 10 percent to about 90 percent by weight of the material microporous, with the weight ratio of filler for polyolefin being greater than 0.3; and (c) at least 35 volume percent of an interconnecting network of pores communicating throughout the microporous material. In general, the microporous material is prepared using the following method: (I) mixing the polyolefin matrix material (a), the filler (b) and a processing plasticizer until a substantially uniform mixture is obtained; (II) introducing the mixture, optionally with additional processing plasticizer, into a heated barrel of an extrusion press and extruding the mixture through a laminate die to form a continuous sheet; (III) sending the continuous sheet formed by the die to a pair of heated calender cylinders acting cooperatively to form a continuous sheet of thickness less than that of the continuous sheet leaving the die; (IV) optionally stretching the web in at least one stretching direction above the elastic limit, with the stretching occurring during or immediately after step (II) and/or step (III), but before step (V ); (V) passing the sheet through a first extraction zone where the processing plasticizer is substantially removed by extraction with an organic liquid; (VI) passing the web through a second extraction zone where the residual organic extraction liquid is substantially removed by steam and/or water; (VII) passing the web through a dryer to substantially remove residual water and remaining residual organic extraction liquid; and (VIII) optionally stretching the web in at least one stretching direction above the elastic limit, the stretching occurring during or after step (V), step (VI) and/or step (VII) to form a microporous material.

[0029] It should be noted that although the polymeric matrix material can be heated and melted in an extruder as mentioned above in preparing the membrane sheet, it is not sintered; that is, “sintering” means a step that causes individual particles of material, e.g., polymer or resin, to adhere to each other in a solid porous matrix without the need for a separately introduced binder, while simultaneously retaining their individual identity as particles. discrete to a substantial extent in warming. Sintering of polymeric particles can be carried out by heating them in a furnace at a temperature such as 150 ° C for a period of time to allow the particles to adhere to each other, such as at least 1 hour. On the other hand, the polymeric matrix material used in the membranes in the process of the present invention undergoes fusion in such a way that the identity of the polymeric particles is not retained in the preparation of the membranes used in the present invention.

[0030] The microporous materials used in membranes may comprise a polyolefin matrix. The polyolefin matrix is present in the microporous material in an amount of at least 2 percent by weight. Polyolefins are polymers derived from at least one ethylenically unsaturated monomer. In certain embodiments of the present invention, the matrix comprises a plastomer. For example, the matrix may comprise a plastomer derived from butene, hexene and/or octene. Suitable plastomers are available from ExxonMobil Chemical under the trade name “EXACT”.

[0031] The matrix may comprise a different polymer derived from at least one ethylenically unsaturated monomer, which may be used instead of or in combination with the plastomer. Examples include polymers derived from ethylene, propylene and/or butene, such as polyethylene, polypropylene and polybutene. High-density and/or ultra-high molecular weight polyolefins, such as high-density polyethylene, are also suitable.

[0032] The polyolefin matrix may comprise a copolymer of ethylene and butene.

[0033] Non-limiting examples of ultra-high molecular weight (UHMW) polyolefins may include essentially linear UHMW polyethylene or polypropylene. To the extent that UHMW polyolefins are not thermosetting polymers having an infinite molecular weight, they are technically classified as thermoplastic materials.

[0034] Ultra-high molecular weight polypropylene can essentially comprise ultra-high molecular weight isotactic polypropylene. Often, the degree of isotacticity of such a polymer is at least 95 percent, for example, at least 98 percent.

[0035] Although there is no particular restriction regarding the upper limit of the intrinsic viscosity of UHMW polyethylene, in a non-limiting example, the intrinsic viscosity can vary from 18 to 39 dL/g, for example, from 18 to 32 dL/g . Although there is no particular restriction regarding the upper limit of the intrinsic viscosity of UHMW polypropylene, in a non-limiting example, the intrinsic viscosity can range from 6 to 18 dL/g, for example, from 7 to 16 dL/g.

[0036] For the purposes of the present invention, the intrinsic viscosity is determined by extrapolating to zero concentration the reduced viscosities or the inherent viscosities of various dilute solutions of UHMW polyolefin where the solvent is freshly distilled decahydronaphthalene to which 0.2 percent by weight of 3,5-diteriobutyl-4-hydroxyhydrocinnamic acid neopentanotetrayl ester [CAS Registry No. 6683-19-8]. The reduced viscosities or inherent viscosities of the UHMW polyolefin are determined from the relative viscosities obtained at 135°C using a Ubbelohde No. 1 viscometer in accordance with the general procedures of ASTM D 4020-81, except that various dilute solutions are employed. of different concentrations.

[0037] The nominal molecular weight of UHMW polyethylene is empirically related to the intrinsic viscosity of the polymer according to the following equation: M= 5.37 x 104 [ή]1.37where M is the nominal molecular weight and [ή] is the intrinsic viscosity of UHMW polyethylene expressed in dL/g (deciliter per gram). Similarly, the molecular weight of UHMW polypropylene is empirically related to the intrinsic viscosity of the polymer according to the following equation: M= 8.88 x 104 [ή]1.25where M is the nominal molecular weight and [ή] is the viscosity intrinsic value of UHMW polypropylene expressed in dL/g.

[0038] A mixture of substantially linear ultra-high molecular weight polyethylene and lower molecular weight polyethylene can be used. In certain embodiments, UHMW polyethylene has an intrinsic viscosity of at least 10 dL/g, and lower molecular weight polyethylene has a melt index (ASTM D 1238-86 Condition E) less than 50 g/10 min, e.g. e.g., less than 25 g/10 min, such as less than 15 g/10 min, and a melt index (ASTM D 1238-86 Condition F) of at least 0.1 g/10 min, e.g., of at least at least 0.5 g/10 min, such as at least 1.0 g/10 min. The amount of UHMW polyethylene used (as a weight percentage) in this embodiment is described in column 1, line 52 through column 2, line 18 of U.S. Patent No. 5,196,262, the disclosure of which is incorporated herein by reference. More particularly, the weight percentage of UHMW polyethylene used is described with reference to Figure 6 of U.S. Patent No. 5,196,262, i.e., with reference to the polygons ABCDEF, GHCL or JHCK of Figure 6, which is incorporated herein by reference. .

[0039] The nominal molecular weight of lower molecular weight polyethylene (LMWPE) is lower than that of UHMW polyethylene. LMWPE is a thermoplastic material and many different types are known. One method of classification is by density, expressed in g/cm3 (gram/cubic centimeter) and rounded to the nearest thousandth, in accordance with ASTM D 1248-84 (reapproved in 1989). Non-limiting examples of LMWPE densities can be found in Table A below.Table A

[0040] Any or all of the polyethylenes listed in Table A above can be used as the LMWPE in the microporous material matrix. You can use HDPE because it can be more linear than MDPE or LDPE. Processes for preparing the various LMWPE’s are well known and well documented. They include the high pressure process, the Phillips Petroleum Company process, the Standard Oil Company (Indiana) process, and the Ziegler process. The melt index (ASTM D 1238-86 Condition E, i.e., 190 °C and 2.16 kg load) of LMWPE is less than about 50 g/10 min. Often the Condition E melt index is less than about 25 g/10 min. The melt index (ASTM D 1238-86 Condition F, i.e., 190 °C and 21.6 kg load) of LMWPE is at least 0.5 g/10 min, such as at least 1.0 g /10 min.

[0041] UHMWPE and LMWPE can together constitute at least 65 weight percent, for example, at least 85 weight percent of the polyolefin polymer of the microporous material. Likewise, UHMWPE and LMWPE together can constitute substantially 100 weight percent of the polyolefin polymer of the microporous material.

[0042] The microporous material may comprise a polyolefin comprising ultra-high molecular weight polyethylene, ultra-high molecular weight polypropylene, high density polyethylene, high density polyethylene or mixture thereof.

[0043] If desired, other thermoplastic organic polymers may also be present in the microporous material matrix as long as their presence does not substantially adversely affect the properties of the microporous material substrate. The amount of the other thermoplastic polymer that may be present depends on the nature of such polymer. In general, a greater amount of the other thermoplastic organic polymer can be used if the molecular structure contains few branches, few long side chains, and few bulky side groups, than when there is a large amount of branches, many long side chains, and many side groups. bulky. Non-limiting examples of thermoplastic organic polymers that optionally may be present in the matrix of the microporous material include low-density polyethylene, high-density polyethylene, poly(tetrafluoroethylene), polypropylene, ethylene and propylene copolymers, ethylene and acid copolymers. acrylic and copolymers of ethylene and methacrylic acid. If desired, all or a portion of the carboxyl groups of the carboxyl-containing copolymer can be neutralized with sodium, zinc or the like. Generally, the microporous material comprises at least 70 weight percent UHMW polyolefin, based on the weight of the matrix. In a non-limiting embodiment, the other thermoplastic organic polymer described above is substantially absent in the matrix of the microporous material.

[0044] As mentioned previously, the membranes of the present invention further comprise substantially hydrophilic finely divided particulate filler distributed throughout the matrix. “Substantially hydrophilic” means that the fillers have polar properties and have a tendency to interact with, but are insoluble in, water and other polar substances.

[0045] Suitable fillers may include organic fillers such as hydrophilic polymers, hydrophilic microspheres, hydrophilic biopolymers and the like. Non-limiting examples of inorganic fillers include siliceous fillers and non-siliceous fillers. Such fillers include particles of silica, titanium oxide, iron oxide, calcium oxide, copper oxide, zinc oxide, antimony oxide, zirconium oxide, magnesium oxide, alumina, molybdenum disulfide, zinc sulfide, sulfate barium, strontium sulfate, calcium carbonate, magnesium carbonate and magnesium hydroxide. In a particular embodiment, the finely divided particulate filler comprises an inorganic filler material selected from the group consisting of silica, alumina, calcium oxide, zinc oxide, magnesium oxide, titanium oxide, zirconium oxide and mixtures thereof.

[0046] In particular embodiments of the present invention, the particulate filler comprises silica particles, such as precipitated silica particles. It is important to distinguish precipitated silica from silica gel as these different materials have different properties. Reference is made in this regard to R.K. Iler, The Chemistry of Silica, John Wiley & Sons, New York (1979), Library of Congress Catalog No. QD 181.S6144, the full description of which is incorporated herein by reference. Note especially pages 15-29, 172-176, 218-233, 364-365, 462-465, 554-564 and 578-579. Silica gel is usually commercially produced at low pH by acidifying an aqueous solution of a metal silicate, typically sodium silicate, with acid. Generally speaking, the acid used is a strong mineral acid, such as sulfuric acid or hydrochloric acid, although sometimes carbon dioxide is used. To the extent that there is essentially no difference in density between the gel phase and the surrounding liquid phase although the viscosity is low, the gel phase does not settle, i.e., does not precipitate. Thus, silica gel can be described as a rigid, coherent, non-precipitated, three-dimensional network of contiguous colloidal amorphous silica particles. The state of subdivision varies from large solid masses to submicroscopic particles, and the degree of hydration from nearly anhydrous silica to soft gelatinous masses containing on the order of 100 parts by weight of water per 1 part by weight of silica.

[0047] Precipitated silica is usually produced commercially by combining an aqueous solution of a soluble metal silicate, generally an alkali metal silicate such as sodium silicate, and an acid so that colloidal particles will grow in a weakly alkaline solution and be coagulated by the alkali metal ions from the resulting soluble alkali metal salt. Various acids can be used, including mineral acids, but the preferred acid is carbon dioxide. In the absence of a coagulant, silica does not precipitate from solution at any pH. The coagulant used to effect precipitation may be the soluble alkali metal salt produced during the formation of the colloidal silica particles, it may be an electrolyte such as a soluble organic or inorganic salt, or it may be a combination of both.

[0048] Thus, precipitated silica can be described as precipitated aggregates of final particles of colloidal amorphous silica that did not exist at any time as a macroscopic gel during preparation. Aggregate sizes and degree of hydration can vary widely.

[0049] Precipitated silica powders differ from silica gels that have been pulverized and typically have a more open structure, that is, a larger specific pore volume. However, the specific surface area of precipitated silica, measured by the Brunauer, Emmett, Teller (BET) method using nitrogen as the adsorbate, is often smaller than that of silica gel.

[0050] In the present invention, many different precipitated silicas can be employed, but the preferred precipitated silicas are those obtained by precipitation from an aqueous solution of sodium silicate using an appropriate acid such as sulfuric acid, hydrochloric acid or carbon dioxide. Such precipitated silicas are themselves known and processes for producing them are described in detail in U.S. Patent No. 2,940,830 and in West German Offenlegungsschrift No. 35,45,615, the disclosures of which are incorporated herein by reference, especially including processes for the preparation of precipitated silicas and the properties of the products.

[0051] The precipitated silicas used in the present invention can be produced by a process involving the following successive steps: (a) an initial stock solution of aqueous alkali metal silicate having the desired alkalinity is prepared and added to (or if prepare in) a reactor equipped with means for heating the contents of the reactor, (b) heat the initial stock solution within the reactor to the desired reaction temperature, (c) add, simultaneously, acidifying agent and solution of additional alkali metal silicate, with stirring in the reactor, simultaneously maintaining the alkalinity index and the temperature of the reactor contents at the desired values, (d) the addition of alkali metal silicate to the reactor is stopped, and more agent is added acidulant to adjust the pH of the resulting suspension of precipitated silica to a desired acid number, (e) separate the precipitated silica in the reactor from the reactant mixture, and wash to remove salt by-products, and (f) dry to form precipitated silica.

[0052] The washed silica solids are then dried using conventional drying techniques. Non-limiting examples of such techniques are oven drying, vacuum oven drying, rotary dryers, spray drying or flash drying. Non-limiting examples of spray dryers include rotary atomizers and nozzle spray dryers. Spray drying can be carried out using any suitable type of atomizer, in particular, a turbine, nozzle, pressurized liquid or dual fluid atomizer.

[0053] The washed silica solids cannot be a condition that is suitable for spray drying. For example, the washed silica solids may be too thick to be spray dried. In one aspect of the process described above, the washed silica solids, for example washed filter cake, are mixed with water to form a liquid suspension and, if necessary, the pH of the suspension is adjusted with dilute acid or dilute base. for example, sodium hydroxide, to a value of 6 to 7, for example 6.5, and then fed into the spray dryer inlet nozzle.

[0054] The temperature at which silica is dried can vary widely, but it will be below the melting temperature of silica. Typically, the drying temperature will vary from above 50°C to less than 700°C, for example from above 100°C, for example 200°C to 500°C. In one aspect of the process described above, the silica solids are dried in a spray dryer having an inlet temperature of approximately 400°C and an outlet temperature of approximately 105°C. The free water content of dry silica can vary, but is usually in the range of approximately 1 to 10% by weight, for example, 4 to 7% by weight. When used herein, the term “free water” means water that can be removed from the silica by heating it for 24 hours at a temperature of 100 °C to 200 °C, for example, 105 °C.

[0055] Dry silica can also be sent directly to a granulator where it is compacted and granulated to obtain a granular product. Dry silica can also be subjected to conventional size reduction techniques, for example by grinding and pulverizing. An air-gas jet mill can also be used using air or superheated steam as the active fluid. Usually, the precipitated silica obtained is in the form of a powder.

[0056] Very often, precipitated silica is spin-dried or spray-dried. Spin-dried silica particles were observed to demonstrate greater structural integrity than spray-dried silica particles. They are less likely to break down into smaller particles during extrusion and other subsequent processing during the production of the microporous material than spray-dried particles. During processing the particle size distribution of spin-dried particles does not change as significantly as that of spray-dried particles. Spray-dried silica particles are more brittle than spin-dried silica particles, often providing smaller particles during processing. It is possible to use a spray-dried silica of a particular particle size such that the final particle size distribution in the membrane does not have a detrimental effect on water flow. In certain embodiments, the silica is reinforced, for example, it has a structural integrity such that porosity is preserved after extrusion. Most preferred is a precipitated silica in which the initial number of silica particles and the initial silica particle size distribution are substantially unaffected by stresses applied during fabrication of the membrane, such that a broad particle size distribution is present in the membrane. finished. Mixtures of different types of dry silica and different sizes of silica can be used to provide unique properties to the membrane. For example, a mixture of silicas with a bimodal particle size distribution may be particularly suitable for certain separation processes. It is expected that external forces applied to silica of any type can be used to influence and adapt the particle size distribution, providing unique properties to the final membrane.

[0057] The surface of the filler particles can be modified in any way known in the art, including, but not limited to, chemically or physically changing their surface characteristics using techniques known in the art. For example, the filler may be surface treated with an antifouling moiety such as poly(ethylene glycol), carboxybetaine, sulfobetaine and polymers thereof, molecules of mixed valences, oligomers and polymers thereof, and mixtures thereof. Another incorporation may be a mixture of charges in which one has been treated with a positively charged portion and the other has been treated with a negatively charged portion. The charge can also be superficially modified with functional groups such as cations and anions that allow targeted removal of specific contaminants in a fluid stream to be purified using the microporous membrane. Untreated filler particles can also be used. Filler particles coated with hydrophilic coatings can reduce fouling and can eliminate pre-wetting processing. Filler particles coated with hydrophobic coatings can reduce fouling and can aid degassing and ventilation of a system.

[0058] Suitable filler particles, for example, precipitated silica particles, typically have an average final particle size of 1 to 100 nm.

[0059] The surface area of filler particles, in particular, silica particles, is considered both the external surface area and the internal surface area due to the presence of pores. Such surface area can have a significant impact on performance. Fillers with high surface areas are materials of very small particle size, materials having a high degree of porosity, or materials exhibiting both characteristics. Typically, the surface area of the filler itself is in the range of about 125 to about 700 m2/g (square meter per gram) determined by the Brunauer, Emmett, Teller (BET) method in accordance with ASTM C 829-77 using nitrogen as adsorbate, but modified by degassing the system and sample for one hour at 130 °C. Often, the BET surface area is in the range of about 190 to 350 m2/g, more frequently, suitable filler particulates, in particular silica particulates demonstrate a BET surface area of 351 to 700 m2/g.

[0060] The BET/CTAB quotient is the ratio of the surface area of the fully charged particle (e.g., precipitated silica) including the surface area contained in pores accessible only by smaller molecules, such as nitrogen (BET), to the surface area external (CTAB). This ratio is referred to as a measure of microporosity. A high microporosity value, i.e. a high BET/CTAB ratio, is a high proportion of internal surface accessible to the small nitrogen molecule (BET surface area), but not to the larger particles to the external surface (CTAB).

[0061] It has been suggested that the structure, i.e. pores, formed within the filler, e.g. precipitated silica, during its preparation may have an impact on performance. Two measures of this structure are the BET/CTAB surface area ratio of the precipitated silica noted above, and the relative width (y) of pore size distribution is of the precipitated silica. The relative width (y) of pore size distribution is an indication of how widely the pore sizes are distributed within the precipitated silica particle.

[0062] Silica CTAB values can be determined using a CTAB solution and the method described below. The analysis is performed using a Metrohm Tirino 751 titrator equipped with a Metrohm interchangeable “pressure” 50 mL burette and a Brinkman Model PC 910 probe colorimeter equipped with a 550 nm filter. Additionally, a Mettler Toledo HB43 Moisture Analyzer or equivalent is used to determine moisture loss at 105°C from the silica and a Fisher Scientific Centrific™ Model 225 centrifuge can be used to separate the silica and residual CTAB solution. . Excess CTAB can also be determined by automatic titration with an Aerosol OT® solution until maximum turbidity is reached, which can be detected with the probe colorimeter. The maximum turbidity point is considered to correspond to a reading of 150 mV (milli-Volt). Knowing the amount of CTAB adsorbed for a given weight of silica and the space occupied by the CTAB molecule, the external specific surface area of the silica is calculated and reported as m2/g based on dry weight.

[0063] The solutions required for testing and preparation include a pH buffer equal to 9.6, cetyl{hexadecyl]trimethyl ammonium bromide (CTAB), dioctyl sodium sulfosuccinate (Aerosol OT®) and 1N sodium hydroxide. A buffer solution of pH 9.6 can be prepared by dissolving 3.101 g of orthoboric acid (99%; Fisher Scientific, Inc., technical grade, crystalline) in a 1 L volumetric flask containing 500 mL of deionized water and 3.708 g of potassium chloride solids (Fisher Scientific, Inc., technical grade, crystalline). Using a burette, 36.85 mL of 1N sodium hydroxide solution was added. The solution is mixed and diluted to volume.

[0064] Prepare the CTAB solution using 11.0 g ± 0.005 g of powdered CTAB (cetyl trimethyl ammonium bromide, also known as hexadecyl trimethyl ammonium bromide, Fisher Scientific, Inc., technical grade) in a dish. weighing. The CTAB powder is transferred to a 2 L beaker and the weighing pan is rinsed with deionized water. Approximately 700 mL of pH 9.6 buffer solution and 1000 mL of distilled or deionized water are added to the 2 L beaker and stirred with a magnetic stir bar. The beaker can be covered and stirred at room temperature until the CTAB powder is fully dissolved. The solution is transferred to a 2 L volumetric flask, rinsing the beaker and stir bar with deionized water. A large stir bar can be added and the solution mixed on a magnetic stirrer for approximately 10 hours. The CTAB solution can be used after 24 hours and for only 15 days. Aerosol OT® (dioctyl sodium sulfosuccinate, Fisher Scientific Inc., 100% solids) solution can be prepared using 3.46 g ± 0.005 g, which is placed in a weighing dish. The Aerosol OT® in the weighing pan is rinsed in a 2 L beaker, which contains approximately 1500 mL of deionized water and a large stir bar. The Aerosol OT® solution is dissolved and rinsed in a 2 L volumetric flask. The Aerosol OT® solution is diluted to the 2 L volume mark on the volumetric flask. The storage time for the Aerosol OT® solution is 2 months from the date of preparation.

[0065] Prior to surface area sample preparation, the pH of the CTAB solution should be checked and adjusted when necessary to a pH of 9.6 ± 0.1 using a 1N sodium hydroxide solution. For test calculations, a blank sample must be prepared and analyzed. 5 mL of CTAB solution is pipetted and 55 mL of deionized water is added to a 150 mL beaker and analyzed in a Metrohm Titrino 150 automatic titrator. The automatic titrator is programmed for blank and sample determination with the following parameters: measuring point density = 2, signal operation = 20, equilibration time = 20 seconds, start volume = 0 mL, stop volume = 35 mL , and fixed endpoint = 150 mV. The burette nozzle and colorimeter probe are placed exactly below the surface of the solution, positioned such that the tip and path length of the photo probe are completely submerged. Both the tip and the photo probe should be essentially equidistant from the bottom of the beaker and not touching. With minimal agitation (setting 1 on the Metrohm 728 shaker) the colorimeter is adjusted to 100% T before each blank and sample determination and the titration is started with the Aerosol OT® solution. The end point can be recorded as the volume (mL) of titrant at 150 mV.

[0066] To prepare the test sample, approximately 0.30 g of silica powder was weighed into a 50 mL container containing a stir bar. Granulated silica samples were quickly examined (before grinding and weighing) to obtain a representative subsample. A grinder of the type used in coffee grinding was used to grind granulated materials. Then 30 mL of the pH-adjusted CTAB solution was pipetted into the sample container containing 0.30 g of silica powder. Then, the silica and the CTAB solution were mixed in a mixer for 35 minutes. When mixing was complete, the silica and CTAB solution were centrifuged for 20 minutes to separate the silica and excess CTAB solution. When centrifugation was complete, the CTAB solution was pipetted into a clean container minus the separated solids, referred to as the “centrifuge”. For sample analysis, 50 mL of deionized water was placed in a 150 mL beaker containing a stir bar. Then, 10 mL of the centrifuged sample was pipetted for analysis into the same beaker. The sample was analyzed using the same technique and programmed procedure used for the blank solution.

[0067] To determine the moisture content, approximately 0.2 g of silica was weighed in the Mettler Toledo HB43 moisture analyzer, simultaneously determining the CTAB value. The moisture analyzer was programmed at 105 °C with the 5 drying criteria. Moisture loss was recorded to the nearest +0.1%.

[0068] The external surface area is calculated using the following equation, in which, V0 = volume in mL of Aerosol OT® used in the blank titration; V = volume in mL of Aerosol OT® used in sample titration; W = sample weight in grams; Vol = % moisture loss (Vol represents “volatiles”).

[0069] Typically, the CTAB surface area of the silica particles used in the present invention ranges from 120 to 500 m2/g. Silica often demonstrates a CTAB surface area of 170-280 m2/g.

[0070] In certain embodiments of the present invention, the BET value of the precipitated silica will be a value such that the quotient of the surface area of BET in m2/g to the surface area of CTAB in m2/g is greater than or equal to 1.0 . Often the BET/CTAB ratio is 1.0-1.5. Most often the BET/CTAB ratio is 1.5-2.0.

[0071] The BET surface area values reported in the examples of this patent application were determined according to the Brunauer-Emmett-Teller (BET) method in accordance with ASTM D 1993-03. BET surface area can be determined by fitting five relative pressure points from a nitrogen sorption isotherm measurement made with a Micromeritics TriStar 3000™ instrument. A Prep-060™ flow station provides heat and a continuous gas flow to prepare samples for analysis. Before nitrogen sorption, the silica samples are dried by heating at a temperature of 160 °C in flowing nitrogen (grade P5) for at least 1 hour.

[0072] Filler particles can constitute 10 to 90 percent by weight of the microporous material. For example, such filler particles may constitute from 25 to 90 percent by weight of the microporous material, such as from 30 to 90 percent by weight of the microporous material, or from 40 to 90 percent by weight of the microporous material, or from 50 to 90 weight percent microporous material, and up to 60 to 90 weight percent microporous material. Typically, the filler is present in the microporous material of the present invention in an amount of from 25 weight percent to about 85 weight percent of the microporous material. Often, the weight ratio of filler to polyolefin in the microporous material is greater than 0.3, often 1.4 to 3.5:1. Alternatively, the weight ratio of filler to polyolefin in the microporous material may be greater than 4:1, for example, as high as 10:1.

[0073] The microporous material used in the membrane used in the process of the present invention further comprises an interconnection network of pores communicating through the microporous material. Pores have a volumetric mean diameter of less than 0.1 micron, such as a volumetric mean diameter ranging from 0.01 to 0.9 microns, or from 0.02 to 0.7 microns, or from 0.02 to 0. 5 microns, or from 0.03 to 0.5 microns. Furthermore, at least 50 percent, such as at least 55 percent, or at least 60 percent, or at least 70 percent of the pores have an average diameter of less than 0.35 microns.

[0074] On an impregnant-free basis, such pores may comprise at least 15 volume percent, for example, at least 20 to 95 volume percent, or at least 25 to 95 volume percent, or 35 to 70 percent by volume of the microporous material. Often, the pores comprise at least 35 volume percent, or even at least 45 volume percent of the microporous material. Such high porosity provides greater surface area throughout the microporous material, which in turn facilitates the removal of contaminants from a fluid stream and greater flow rates from a fluid stream across the membrane.

[0075] As used herein and in the claims, the porosity (also known as void volume) of the microporous material, expressed as a percentage by volume, is determined according to the following equation: Porosity = 100[1-d1/d2 ] where d1 is the density of the sample, which is determined from the weight of the sample and the volume of the sample determined from measurements of the dimensions of the sample, and d2 is the density of the solid portion of the sample, which is determined from the weight of the sample and the volume of the solid portion of the sample. The volume of the solid portion thereof is determined using a Quantachrome™ stereopycnometer (Quantachrome Corp.) in accordance with the accompanying instruction manual.

[0076] The volumetric mean diameter, or mean pore diameter, of the pores of the microporous material can be determined by mercury porosimetry using an Auto Pore III porosimeter (Micromeritics, Inc.) in accordance with the accompanying instruction manual. The volumetric average pore radius for a single scan is automatically determined by the porosimeter. When operating the porosimeter, it scans the high pressure range (from 138 kPa absolute to 225 MPa absolute). If approximately 2 percent or less of the total volume shutoff occurs at the low end (138 to 250 kPa absolute) of the high pressure range, the volumetric mean pore diameter is considered to be twice the volumetric mean pore radius determined by the porosimeter. Otherwise, an additional scan is made in the low pressure range (from 7 to 165 kPa absolute) and the average volumetric pore diameter is calculated according to the equation: d = 2[v1r1/w1+v2r2/w2] /[v1/w1+v2/w2] where d is the average volumetric pore diameter, v1 is the total volume of mercury interfered in the high pressure range, v2 is the total volume of mercury interfered in the low pressure range, r1 is the mean volumetric pore radius determined from high-pressure scanning, r2 is the mean volumetric pore radius determined from low-pressure scanning, w1 is the weight of the sample subjected to high-pressure scanning, and w2 is the weight of the sample subjected to low pressure scanning. The volumetric average diameter of the pores is typically less than 1.0 microns (microns), and may be, for example, in the range of 0.001 to 0.7 microns, such as 0.02 to 0.7 microns, or 0.02 to 0.5 microns, or 0.3 to 0.7 microns. Also, as mentioned previously, at least 50 percent of the pores may have an average pore diameter of at least 0.35 microns. In the course of determining the volumetric mean pore diameter using the above procedure, the maximum detected pore radius is sometimes observed. This is determined from the low pressure range sweep, if it occurs; otherwise it is determined from high pressure range scanning. The maximum pore diameter is twice the maximum pore radius. To the extent that some production or treatment steps, for example coating processes, printing processes, impregnation processes and/or bonding processes, may result in the filling of at least some of the pores of the microporous material, and since Some of these processes irreversibly compress the microporous material, parameters regarding porosity, volumetric average pore diameter, and maximum pore diameter are determined for the microporous material before applying one or more of such production or treatment steps.

[0077] Porosity can also be measured using a Gurley densimeter, model 4340, manufactured by GPI Gurley Precision Instruments of Troy, New York. The porosity values reported are a measure of the rate of airflow through a sample or is the resistance to airflow through the sample. The unit of measurement for this method is a “Gurley second” and represents the time in seconds to pass 100 cm3 of air through an area of 2.54 cm2 (1 square inch) using a pressure differential of 12.40 cm (4.88 inches) of water. Lower values equate to less resistance to air flow (more air is allowed to pass freely). For purposes of the present invention, measurements are completed using the procedure listed in the model 4340 automatic densimeter manual.

[0078] In certain embodiments of the present invention, to prepare the microporous materials, filler, polymer powder (polyolefin polymer), processing plasticizer and smaller amounts of lubricant and antioxidant are mixed until a substantially uniform mixture is obtained. The weight ratio of filler for polymer powder employed in forming the mixture is essentially the same as that of the microporous material substrate to be produced. The mixture along with additional processing plasticizer is introduced into the heated barrel of an extrusion press. Attached to the extruder is a die, such as a laminate die, to form the desired final shape.

[0079] In an exemplary manufacturing process, the material is shaped into a sheet or film, and a continuous sheet or film formed by a die is sent to a pair of heated calender rolls acting cooperatively to form a continuous sheet of thickness less than the of the continuous sheet coming out of the die. Final thickness may depend on the desired end-use application. The microporous material can have a thickness ranging from 17.8 to 457.2 microns and demonstrates a bubbling point of 6.9 to 551.6 kPa (1 to 80 psi) based on ethanol.

[0080] In certain embodiments, the sheet exiting the calender rolls is then stretched in at least one stretching direction above the elastic limit. Alternatively, stretching may occur during or after exit from the laminate die or during calendering, or several times, but typically it is done after extraction. The stretched microporous material substrate can be produced by stretching the intermediate or final product in at least one stretching direction above the elastic limit. Usually, the stretch ratio is at least about 1.1. In many cases, the stretch ratio is at least about 1.3, such as at least about 1.5. Often, the stretch ratio is in the range of about 1.5 to about 15. Often, the stretch ratio is in the range of about 1.7 to about 10. Preferably, the stretch ratio is in the range of about 2 to about 6.

[0081] The temperatures at which stretching takes place can vary widely. Stretching can be carried out at approximately room temperature, but elevated temperatures are usually used. The intermediate product can be heated by any of a wide variety of techniques before, during and/or after stretching. Examples of these techniques include radiative heating such as that provided by electrically or gas heated infrared heaters, convective heating such as that provided by recirculation of hot air, and conductive heating such as that provided by contact with heated cylinders. The temperatures that are measured for temperature control purposes may vary depending on the device used and personal preference. For example, temperature measuring devices can be placed to determine the surface temperatures of the infrared heaters, the interior temperatures of the infrared heaters, the air temperatures of points between the infrared heaters and the intermediate product, the temperatures of circulating hot air at points inside the apparatus, the temperature of the hot air entering or leaving the apparatus, the surface temperatures of the cylinders used in the stretching process, the temperature of the heat transfer fluid entering or leaving such cylinders, or the surface temperatures of the film. In general, the temperature or temperatures are controlled such that the intermediate product is stretched uniformly so that variations, if any, in the film thickness of the stretched microporous material are within acceptable limits and so that the amount of microporous material stretched outside those limits is acceptably low. It will be obvious that temperatures used for control purposes may or may not be close to those of the intermediate product itself, since they depend on the nature of the apparatus used, the locations of temperature measuring devices, and the identities of the substances or objects whose temperatures are being measured.

[0082] In view of the locations of the heating devices and the line speeds usually employed during stretching, varying temperature gradients may or may not be present across the thickness of the intermediate product. Furthermore, due to these line speeds, it is impractical to measure these temperature gradients. The presence of variable temperature gradients, when they occur, makes reference to a singular film temperature unreasonable. Consequently, film surface temperatures, which can be measured, are best used to characterize the thermal condition of the intermediate product.

[0083] These are normally equal across the entire width of the intermediate product during stretching, although they may be intentionally varied, such as to compensate for the intermediate product having a wedge-shaped cross section across the sheet. Film surface temperatures along the length may be approximately the same or may be different during stretching.

[0084] The surface temperatures of the film at which stretching occurs can vary widely, but, in general, they are such that the intermediate product is stretched approximately uniformly, as explained above. In most cases, film surface temperatures during stretching are in the range of about 20°C to about 220°C. Often such temperatures are in the range of about 50°C to about 200°C. A range of about 75°C to about 180°C is preferred.

[0085] Stretching can be carried out in a single step or in several steps, as desired. For example, when the intermediate product is stretched in a single direction (uniaxial stretching), the stretching may be carried out in a single stretching step or in a sequence of stretching steps until the desired final stretch ratio is achieved. Similarly, when the intermediate product is stretched in two directions (biaxial stretching), the stretching can be carried out by a single biaxial stretching step or by a sequence of biaxial stretching steps until the desired final stretch ratio is reached. Biaxial stretching can also be performed by a sequence of one or more uniaxial stretching steps in one direction and one or more uniaxial stretching steps in another direction. Biaxial stretching steps where the intermediate product is stretched simultaneously in two directions and uniaxial stretching steps can be performed sequentially in any order. Stretching in more than two directions is within the limits of contemplation. It can be seen that the various permutations of steps are quite numerous. Other steps, such as cooling, heating, sintering, annealing, winding, unwinding and the like, can optionally be included in the overall process as desired.

[0086] Various types of stretching apparatus are well known and can be used to perform stretching of the intermediate product. Uniaxial stretching is usually carried out by stretching between two cylinders, with the second cylinder or downstream cylinder rotating at a peripheral speed greater than that of the first cylinder or upstream cylinder. Uniaxial stretching can also be performed by simultaneously stretching in two different directions in a ramula. However, more commonly, biaxial stretching is performed by uniaxial stretching between two differently rotating cylinders as described above, followed by either uniaxial stretching in a different direction using a tumbler or by biaxial stretching using a tumbler. The most common type of biaxial stretching is where the two stretching directions are approximately at right angles to each other. In most cases where the web is being stretched, one direction of stretching is at least approximately parallel to the long axis of the sheet (machine direction) and the other direction of stretching is at least approximately perpendicular to the machine direction and is in the plane of the sheet (transverse direction).

[0087] Stretching sheets before or after extraction of the processing plasticizer allows for larger pore sizes than in conventionally processed microporous materials, thus making the microporous material particularly suitable for use in the microfiltration membranes of the present invention. It is also believed that stretching the sheets before extracting the processing plasticizer minimizes thermal shrinkage after processing.

[0088] The product passes through a first extraction zone where the processing plasticizer is substantially removed by extraction with an organic liquid that is a good solvent for the processing plasticizer, a poor solvent for the organic polymer, and more volatile than the processing plasticizer. Usually, but not necessarily, both the processing plasticizer and the organic extraction liquid are substantially immiscible with water. The product then passes through a second extraction zone where the residual organic extraction liquid is substantially removed by steam and/or water. The product then passes through a forced air dryer to substantially remove residual water and remaining organic extraction liquid. From the dryer, the microporous material can pass through a tension cylinder, when it is in the form of a sheet.

[0089] The processing plasticizer has little solvating effect on the thermoplastic organic polymer at 60 ° C, only a moderate solvating effect at elevated temperatures of the order of about 100 ° C, and a significant solvating effect at elevated temperatures of the order of about of 200°C. It is a liquid at room temperature and is usually a processing oil such as paraffinic oil, naphthenic oil or aromatic oil. Suitable processing oils include those that meet the requirements of ASTM D 2226-82, Types 103 and 104. Those oils that have a pour point less than 22°C, or less than 10°C, in accordance with ASTM D 97- 66 (reapproved in 1978) are used more frequently. Examples of suitable oils include Shellfex® 412 and Shellfex® 371 (Shell Oil Co.) solvent refined and hydrotreated oils derived from crude naphthenics. It is expected that other materials, including phthalate ester plasticizers such as dibutyl phthalate, bis(2-ethylhexyl phthalate), diisodecyl phthalate, dicyclohexyl phthalate, butyl benzyl phthalate and ditridecyl phthalate will function satisfactorily. as processing plasticizers.

[0090] There are many organic extraction liquids that can be used. Examples of suitable organic extraction liquids include 1,1,2-trichloroethylene, perchloroethylene, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, methylene chloride, chloroform, isopropyl alcohol, ether diethyl and acetone.

[0091] In the process described above for producing microporous material substrate, extrusion and calendering are facilitated when the load carries a lot of the processing plasticizer. The ability of the filler particles to absorb and hold the processing plasticizer is a function of the surface area of the filler. Therefore, the filler typically has a high surface area, as discussed above. To the extent that it is desirable to essentially retain the filler in the microporous material substrate, the filler must be substantially insoluble in the processing plasticizer and substantially insoluble in the organic extraction liquid when the microporous material substrate is produced by the above process.

[0092] The residual processing plasticizer content is usually less than 15 weight percent of the resulting microporous material and this can be further reduced to levels, such as less than 5 weight percent, by additional extractions using the same liquid of organic extraction or different organic extraction liquids.

[0093] The resulting microporous materials can be further processed depending on the desired application. For example, a hydrophilic or hydrophobic coating can be applied to the surface of the microporous material to adjust the surface energy of the material. Likewise, the microporous material can be adhered to a support layer such as a fiberglass layer to provide additional structural integrity, depending on the particular end use. Additional optional stretching of the web in at least one stretching direction may also be done during or immediately after any of the steps following extrusion in step (II). In the production of a microfiltration membrane, typically, the stretching step occurs after extracting the plasticizer.

[0094] Microporous materials prepared as described above are suitable for use as membranes in the processes of the present invention, and are capable of removing particulates from a fluid flow ranging in size from 0.05 to 1.5 microns. Membranes also serve to remove molecular contaminants from a fluid stream by adsorption and/or physical rejection due to molecular size, allowing separation of a hydrocarbon-containing waste stream into a hydrocarbon-containing retentate and an aqueous permeate.

[0095] The membranes can be in the sheet or housed (that is, as a component) in a filter assembly. Any suitable filter assembly known in the art may be used with the membrane described above used as the separation means. The membrane housed within the filter assembly may be in any practical configuration; Typically, it is configured to maximize surface area contact with the fluid being treated, such as bending. Non-limiting examples of suitable filter assemblies include spiral countercurrent filters described in U.S. Patent No. 8,454,829, Figures 1-8 and column 4, line 49 through column 8, line 47 of the reference which are incorporated herein by reference. The method of the present invention comprises contacting a hydrocarbon-containing waste stream with the membrane, typically passing the stream through the membrane, to form a hydrocarbon-containing retentate. The retentate has a higher concentration of hydrocarbons than the hydrocarbon-containing waste stream being treated. An aqueous permeate is also formed which is substantially free of hydrocarbons. When used herein with respect to the aqueous permeate produced by the method of the present invention, "substantially hydrocarbon-free" means that the aqueous permeate contains less than 50 parts per million (ppm) hydrocarbons, e.g., less than 45 ppm, or less than 40 ppm, or less than 30 ppm, or less than 25 ppm, or less than 20 ppm of hydrocarbons. The aqueous permeate produced by the method of the present invention is sufficiently purified from dissolved or emulsified hydrocarbons,

[0096] The hydrocarbon-containing waste stream can pass through several such membranes in series; however, a single pass is sufficient to produce the purities noted above, thus making the process of the present invention superior to conventional separation processes using conventional filters and membranes.

[0097] The waste streams containing hydrocarbons to be treated by the process of the present invention contain a hydrocarbon phase and an aqueous phase. Examples include crude oil well effluent (both inland and offshore oil production effluents) such as hydraulic fracturing effluents and conventional oil well drilling effluents. Other crude oil well effluents such as petroleum production wastewater streams including oil and gas drilling muds, drilling additives, polyacrylamide polymers and other hydrocarbon-based well additives and petroleum production brines are also appropriate fluid emulsions. The method of the invention can be used to treat hydrocarbon-containing waste streams comprising any weight percentage of hydrocarbons and/or water. For example, the process of the invention can be used to treat waste streams comprising hydrocarbons and water, with the hydrocarbons comprising at least 0.1 weight percent of the waste stream, e.g., at least 0.2 weight percent. , or at least 0.5 weight percent, for example, at least 1 weight percent, for example, at least 2 weight percent, for example, at least 5 weight percent. For example, the process of the invention can be used to treat hydrocarbon-containing waste streams comprising more than 0 to 2 weight percent hydrocarbons and at least 98 weight percent water. For example, the method of the present invention can be used in treating a hydrocarbon-containing waste stream comprising from 0.1 to 2.0 percent hydrocarbons, such as from 0.1 to 1.5 percent hydrocarbons, or from 0.1 to 1.0 percent hydrocarbons, or from 0.2 to 0.75 percent hydrocarbons.

[0098] For the purposes of the present invention, flow rates can be expressed in gallons/(ft2 x psi x day) (GFD/psi). The hydrocarbon-containing waste stream fluid to be treated usually passes through the membrane at a flow rate of 125 to 50000 (l/m2/h)/kPa (0.05 to 20 GFD/psi). Again, the waste stream to be treated passes through several membranes in series, but because of the high efficiency of the membranes used in the method of the present invention, typically a single pass is sufficient to achieve aqueous permeate purities that are in accordance with industry standards, described quantitatively above. Furthermore, in certain embodiments, the hydrocarbon-containing waste stream does not undergo any separation processes such as sedimentation in one or more tanks in series, distillation or centrifugation before passing through the membrane. No preliminary separation processes required.

[0099] In the method of the present invention, the hydrocarbon-containing waste stream to be treated is contacted with the membrane described above. The aqueous phase of the waste stream passes through the membrane forming an aqueous permeate. The hydrocarbon phase does not pass through the membrane and forms a retentate containing hydrocarbons. The hydrocarbon-containing retentate may be recirculated through the membrane at least once, either by itself for further purification or by mixing with additional feed of untreated hydrocarbon-containing waste stream.

[0100] A plurality of membranes configured in parallel filter assemblies may be used in the method of the present invention to achieve a desired flow rate, such as a flow rate of at least 473.12 liters (125 gallons/min). Minimal membrane fouling has been observed to occur during operation when used to treat oil well effluent, in contrast to conventional separation technologies used for oil well effluent. The membranes used in the process of the present invention are significantly more resistant to fouling than conventional separation systems. Therefore, in certain embodiments of the present invention, the flow rate of the hydrocarbon-containing waste stream during the process is at least 473.12 liters (125 gallons/min) during at least 168 hours of service time of the microfiltration membrane.

[0101] It is particularly noteworthy that the membrane can demonstrate a hydrocarbon retention rate, and the aqueous retentate and permeate produced by the method of the present invention have a purity that is generally independent (I) of the flow rate of the aqueous phase that passes through the membrane and (II) the pore size of the membrane. While not intending to be bound by theory, it is believed that surface interactions between the various phases of the fluid waste stream and the respective hydrophilic and hydrophobic components of the membrane contribute to the rate of hydrocarbon retention of the membrane and the purities of the aqueous permeate produced. by the method of the present invention. The present invention is more particularly described in the following examples which are intended to be illustrative only, as numerous modifications and variations will be apparent to those skilled in the art.

Examples Part I: Preparation of microporous materials in stretched sheets

[0102] The microporous membranes used in the following examples were prepared in two steps. First, the membranes were prepared according to the procedures described previously. Microporous Membrane A was prepared according to Example 2 of US 2014/0069862. Microporous Membrane B was prepared according to Example 3 of US 2014/0069862. Microporous Membrane C was prepared according to the procedure of Example 3 of US 2014/0069862, using 1000 parts of silica and 1330 parts of TUFFLO® 6056 (commercially obtainable from PPC Lubricants).

[0103] The membranes described above were then stretched to produce membranes with the desired properties and pore sizes. Stretching was performed by Parkinson Technologies, Inc., using the Marshall and Williams biaxial orientation plastic processing system. Machine direction oriented stretching (MDO) of materials, where indicated, was performed by heating the specified membrane material and stretching it in the machine direction through a series of cylinders maintained at the temperatures listed in Table 1.

[0104] After MDO stretching and where indicated, stretching was carried out with orientation in the transverse direction (TDO) by heating the resulting sheets according to the temperature conditions listed in Table 1, and stretching in the transverse (or crossed) direction in a structure tensioner, consisting of two horizontal chain rails, in which the clip and chain assemblies held the material in place. Table 1. Preparation of stretched microporous membrane

Comparative examples of membranes:

[0105] CE-5 was the stretched membrane prepared in Table 1 above.

[0106] CE-6 was the ULTRAFILIC® GE-Osmonics membrane, a treated polyacrylonitrile membrane sold commercially by Sterlitech Corporation for oil/water separation.

[0107] CE-7 was HFM® 180, a poly(vinylidene difluoride) ultrafiltration membrane, commercially obtainable from Sterlitech Corporation.

Part II: Membrane materials and physical properties

[0108] The physical properties of the membrane materials mentioned in the examples and comparative examples are summarized in Table 2. Table 2. Physical properties of membrane materials 1The thickness was determined using Ono Sokki's EG-225 thickness gauge. The reported thickness is an average of 9 measurements. 2Porosity was measured with a Gurley densimeter, model 4340, manufactured by GPI Gurley Precision Instruments of Troy, New York in accordance with operating instructions. 3ASTM F316-03 followed, using a 3G porosimeter manufactured by Quantachrome Instruments. POROFEL® Wetting Fluid, available from Quantachrome Instruments, was used to moisten the membrane prior to testing.4As stated in the product literature.

Part III: Oil/Water Crossflow Separation Test

[0109] The water flow test was performed using a cross flow test cell apparatus, model CF-042 obtainable from Sterlitech Corporation, WA, as described in the examples below. The test was performed on crude oil/water preparations with 0.125%, 0.25%, 0.5% and 0.75% by weight crude oil content. The cross-flow test results of crude oil in water for each oil concentration are presented, respectively, in Tables 4, 5, 6, 7 and 8.

Part IIIA: Aqueous Preparations of Model Crude Oil

[0110] For each oil concentration, 30.28 liters (8 gallons) of deionized water was charged into the feed tank and stirred with a 12.7 cm (5 inch) blade driven by a compressed air pressure of 206.84 kPa (30 psi). Designated amounts of the salts listed in Table 3 below were slowly added to the feed tank. The water and salts were mixed by stirring constantly for 30 min until a homogeneous solution was formed. Table 3. Salt composition in aqueous preparations

[0111] Then, designated amounts of Texas Raw Crude Oil (“Texas Raw Crude Oil”, obtained from Texas Raw Crude, Midland, TX) were slowly added to the feed tank to reach, respectively 0.125%, 0.25%,0 .50% and 0.75% crude oil content. The preparation was maintained by continuous stirring with a pneumatic motor during the cross-flow separation test described below.

Part IIIB: Crossflow Separation Test

[0112] The cross-flow test was performed on microporous membranes with the four crude oil/water preparation concentrations described above. For each test, the effective membrane area was 42 cm2. The apparatus contained 4 cells in parallel test lines. Each cell was equipped with a valve to open and close the feed flow and regulate the flow rate, which was set to 5.67 liters/min (1.5 GPM (gallon per minute)) in all tests. Pressure gauges were located at the inlet and outlet of the device. The pressure was maintained at transmembrane pressure (TMP) of 103.43 kPa (15 psi). The test apparatus was equipped with a temperature controller to maintain a temperature of (25 ± 2)°C and results were reported as gallons/(ft2 x psi x day), i.e., 24 hours (GFD/psi). The permeate sample was collected after 30 min of testing. The oil content in the permeate was measured following the EPA method 413.2. The oil retention rate (R) was determined using the following formula: R = 100*(Feed – Cpermeate)/Feed where Feed is the concentration of oil in the feed stream and Cpermeate is the concentration of oil in the permeate. The results for cross-flow separation tests at each crude oil concentration are shown, respectively, in Tables 4, 5, 7, and 8 below. Table 4. Cross-flow separation of 0.125% aqueous crude oil 2Turbidity was measured using a model 2100AN laboratory turbidimeter purchased from Hach Company. Table 5. Cross-flow separation of 0.25% aqueous petroleum Table 6. Cross-flow separation of 0.50% aqueous petroleum Table 7. Cross-flow separation of 0.75% aqueous petroleum 5Insufficient permeate collected.

Part IV: Oil/Water Cartridge Separation Test

[0113] The water flow test was also performed using 8040 spiral cartridges manufactured with an experimental membrane and a polyacrylonitrile membrane as described below. An 8040 cartridge was manufactured with the membrane of Example 1, comprising an effective membrane active area of 25.55 m2 (275 ft2), using a diamond feed spacer and thermoplastic mesh wrap. This is presented as Example 8. For Comparative Example CE-9, a GE MW 8040C1066 cartridge was purchased from Lenntech BV. This cartridge utilizes the ULTRAFILIC membrane demonstrated above as CE-6. The test was performed on a crude oil/water preparation starting at 0.25% by weight crude oil content.

Part IVA: Preparation of petroleum waste stream in water

[0114] The aqueous petroleum preparation for the cartridge separation test was prepared in the same proportions described in Part IIIA to obtain 1,135 liters (300 gallons) of solution and 0.25% by weight crude oil content. The preparation was maintained by continuous stirring with a pneumatic motor during the cartridge separation test described below.

Part IVB: Cartridge Separation Test

[0115] The water flow test on microporous membranes was carried out with the experimental cartridge (Example 8) and the comparative cartridge (CE-9) described above. The incoming feed flow was controlled at 340.65-397.42 liters/min (90-105 gallons/min), and the cartridge transmembrane pressure (TMP) was maintained between 55.15 to 82.73 kPa ( 8-12 psi). The permeate flow rate over time was recorded and reported as gallons/min. The test was run for approximately 12 continuous hours at a time, shutting down overnight. During the test, both the solution in the permeate and the solution from the flow outlet were returned directly to the 1,135 liter (300 gallon) tank. An additional 340 g of oil was added to the tank every 8 hours of operation. The results for the cartridge permeate rate and the oil concentration in the permeate are shown in Figures 1 and 2.

[0116] The data in Tables 4 to 7 demonstrate the ability of the microporous membranes of the present invention to effect good oil removal from the permeate while maintaining good flow rates compared to polyvinylidene difluoride and polyvinylidene difluoride membranes. commercially obtainable polyacrylonitrile. The robustness of the inventive membranes is further demonstrated in commercial-type cartridge configurations in Fig. 1 and Fig. 2, where the CE-9 commercial polyacrylonitrile cartridge assembly shows reduced flux and decreased effectiveness in removing oil from the permeate over time. when compared to Example 8, the cartridge configured with the membrane of Example 1.

[0117] Although particular embodiments of this invention have been described above for illustrative purposes, it will become apparent to those skilled in the art that numerous variations of the details of the present invention can be made without departing from the scope of the invention defined in the appended claims.

Claims (14)

1. Method for treating a hydrocarbon-containing waste stream comprising greater than 0 to 2 weight percent hydrocarbons to form an aqueous permeate containing less than 50 parts per million (ppm) hydrocarbons and a hydrocarbon-containing retentate, the method characterized by the fact that it comprises passing the flow of hydrocarbon-containing waste through a microporous membrane to produce the aqueous permeate and the hydrocarbon-containing retentate, the membrane comprising a hydrophobic polymer matrix and hydrophilic finely divided particulate filler distributed throughout said matrix , wherein the polymer matrix has pores with a volumetric average diameter of 0.3 microns to 0.7 microns, and wherein at least 50 percent of the pores have an average diameter of less than 0.35 microns. 2. Method according to claim 1, characterized in that the membrane comprises at least 35 in volume of an interconnecting network of pores communicating through the membrane. 3. Method according to claim 1, characterized in that the membrane is in the form of a sheet. 4. Method according to claim 1, characterized in that the polymeric matrix has pores with an average volumetric diameter ranging from 0.03 to 0.5 microns. 5. Method according to claim 1, characterized in that the finely divided particulate filler comprises an inorganic filler material selected from the group consisting of silica, alumina, calcium oxide, zinc oxide, magnesium oxide, titanium oxide , zirconium oxide and mixtures thereof. 6. Method according to claim 5, characterized in that the finely divided particulate filler comprises silica. 7. Method according to claim 6, characterized in that the finely divided particulate filler comprises precipitated silica present in the polymeric matrix in an amount ranging from 10 to 90 percent by weight. 8. Method according to claim 1, characterized in that the polymeric matrix comprises polyolefin. 9. Method according to claim 1, characterized in that the filler has been superficially modified with functional groups that react with or adsorb one or more materials in the fluid flow. 10. Method according to claim 9, characterized in that the filler has been superficially modified with hydrophilic functional groups. 11. The method of claim 1, wherein the hydrocarbon-containing waste stream comprises 0.1 to 1.0 percent by weight of hydrocarbons. 12. Method according to claim 11, characterized in that the hydrocarbon-containing waste stream comprises from 0.2 to 0.75 weight percent hydrocarbons. 13. Method, according to claim 1, characterized by the fact that said membrane is housed in a set of filters. 14. Method according to claim 13, characterized in that the set of filters is selected from the group consisting of a pleated filter and a spiral countercurrent filter.