Patent Application
20240131449
Fluorinated fluids are used in many different applications. In some systems where fluids are recycled within a system, the conditioning (including filtration) of such fluids is necessary to maintain the fluid in optimal condition by, for example, removing contaminants and degradation products.
In one aspect, the present description relates to a fluid conditioning system. The fluid conditioning system includes an electrically non-conductive fluorinated fluid and a filter including desensitized activated carbon sorbent. The electrically non-conductive fluorinated fluid is in fluid communication with the filter, where electrically non-conduct means greater than 25 kV breakdown strength at a 2.5 mm gap according to ASTM D877 (1987).
In another aspect, the present description relates to a method of preparing a fluid conditioning system. The method includes providing activated carbon sorbent, desensitizing the activated carbon sorbent, placing the desensitized activated carbon sorbent into a filter housing, and placing the filter housing including the desensitized activated carbon sorbent in fluid communication with an electrically non-conductive fluorinated fluid.
In yet another aspect, the present description relates to a method of filtering fluorinated fluid. The method includes providing desensitized activated carbon sorbent, providing an electrically non-conductive fluorinated fluid, and introducing the desensitized activated carbon sorbent to the electrically non-conductive fluorinated fluid, such that the desensitized activated carbon sorbent is in fluid communication with the electrically non-conductive fluorinated fluid.
As used herein, “fluoro-” (for example, in reference to a group or moiety, such as in the case of “fluoroalkylene” or “fluoroalkyl” or “fluorocarbon”) or “fluorinated” means (i) partially fluorinated such that there is at least one carbon-bonded hydrogen atom, or (ii) perfluorinated.
As used herein, “perfluoro-” (for example, in reference to a group or moiety, such as in the case of “perfluoroalkylene” or “perfluoroalkyl” or “perfluorocarbon”) or “perfluorinated” means completely fluorinated such that, except as may be otherwise indicated, any carbon-bonded hydrogens are replaced by fluorine atoms.
As used herein, “fluid” refers to the liquid phase and/or the gaseous phase.
Fluorinated materials, including fluorinated fluids (fluid including both liquid and gas phases), are useful in numerous applications. This is at least in part to its electric non-conductivity at normal operating temperatures and environments, and its ability to prevent electrical short circuits (shorts). Electrical non-conductivity may be quantified by its breakdown strength at a given voltage, for a standard gap. For example, electrically non-conductive may mean greater than a 35 kV breakdown strength at a 2.5 mm gap, according to ASTM D877 (1987). In some embodiments, electrically non-conductive may mean greater than a 25 kV breakdown strength at a 2.5 mm gap, according to ASTM D877 (1987). In some embodiments, electrically non-conductive may mean having very high electrical resistivity, such as greater than 10∂Q cm.
The insulating properties of such fluorinated materials may make them particularly useful for insulating gasses (such as in electrical grid equipment) to prevent arcing electrical shorts, in fire-suppression applications to flood (and thereby remove heat or cut off oxygen from) electronic equipment without shorting it, and in immersion heat-transfer applications to efficiently transfer heat from electronic equipment without providing an electrically conductive medium to potentially allow short circuits to damage it.
For applications where fluorinated materials are in prolonged contact with electrical equipment, e.g., for insulating gasses or for immersion heat-transfer (cooling), it may be particularly important to avoid transfer of contaminants from the electrical systems into the fluid system. Accordingly, a conditioning system may be used to treat the fluid, filter the fluid, or otherwise remove or neutralize (or passivate) contaminants from the fluid.
Fluorinated materials having low global warming potential (GWP) are of particular interest for users of immersion cooling systems. Fluoroketones are an example of a class of materials that have low GWP and may be particularly suitable for immersion cooling. However, the same functional groups that enable the quick atmospheric breakdown (and thereby a low GWP) may also react with other elements within the immersion cooling system, including electronic components immersed therein, forming undesirable byproducts. For example, fluoroketones may undergo hydrolysis in the presence of water to form a highly corrosive acid (perfluoropropionic acid, or PFPA), which may circulate through the system and corrode or etch materials in contact with the circulating fluid. Along with PFPA, HFC-227ea (1,1,1,2,3,3,3 heptafluoropropane) is produced, which is a gas at room temperature. Because the gas may leave the system, such a process may be irreversible.
Certain fluorinated materials, such as fluoroketones, may also react with various organic molecules extracted from electronic components (for example, a —OH-containing plasticizer used in a polyvinyl chloride wire cladding) to form partially fluorinated esters and other degradation products. Partially fluorinated esters may also have considerably greater solubility in the overall fluorinated fluid system compared to the —OH molecules that preceded it, which makes filtration even more difficult.
Perfluorinated sulfone are another class of fluorinated fluids that, like fluoroketones, can react with water and other various organic molecules, albeit at a slower rate, to form corrosive or highly soluble degradation products.
Besides being corrosive, certain contaminants and degradation and reaction products in fluorinated fluid systems may act as a co-solvent for other potentially harmful contaminants, such as solder flux residue, plasticizers, metal salts, and (other) degradation and reaction products. Moreover, these contaminants may compromise other properties of the fluid, including dielectric properties.
Activated carbon is well-known as a sorbent used in filtration systems. However, its usefulness in other systems, e.g., for drinking water filtration, do not necessarily provide for a close analogue in fluorinated fluid systems. In fact, residual water on the surface of activated carbon can react with certain fluorinated fluids (e.g., fluoroketones). Likewise, activated carbon is chemically or catalytically active, which can enable or exacerbate certain of the degradation and the other reactions described elsewhere.
In some embodiments, the fluid described herein may be or include one or more fluoroketones. In some embodiments, the fluoroketones may be perfluorinated. In some embodiments, the fluoroketones may include from 5 to 12 carbon atoms or from 5 to 8 carbon atoms. In some embodiments, fluoroketones may be present in the fluid in an amount of a least 80 wt. %, at least 90 wt. %, or at least 95 wt. %, based on the total weight of the fluid.
In some embodiments, the fluid described herein may be or include perfluorinated sulfones. In some embodiments, the perfluorinated sulfones may include from 3 to 7 carbon atoms or from 4 to 6 carbon atoms. In some embodiments, perfluorinated sulfones may be present in the fluid in an amount of at least 80 wt. %, at least 90 wt. %, or at least 95 wt. %, based on the total weight of the fluid.
In some embodiments, in addition to or in place of the fluoroketones or perfluorinated sulfones, the fluids may also include (individually or in any combination): ethers, alkanes, perfluoroalkenes, alkenes, hydrofluoroalkenes, aromatic fluoroalkenyl esters, haloalkenes, perfluorocarbons, perfluorinated tertiary amines (saturated or mono-unsaturated), perfluoroethers (saturated or mono-unsaturated), cycloalkanes, esters, oxiranes, aromatics, siloxanes, hydrochlorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroolefins, hydrochloroolefins, hydrochlorofluoroolefins, or hydrofluoroethers. Such additional components can be chosen to modify or enhance the properties of a fluid for a particular use.
In some embodiments, the fluids of the present disclosure may be hydrophobic, relatively chemically unreactive, and thermally stable. The fluids may have a low environmental impact. In this regard, the fluids of the present disclosure may have a zero, or near zero, ozone depletion potential (ODP) and a global warming potential (GWP, 100-year ITH) of less than 800, 500, 300, 200, 100 or less than 10. In some embodiments, the fluids of the present disclosure may have certain useful boiling points, for example, a boiling point between 30° C. and 75° C., or a boiling point between 130° C. and 150° C. In some embodiments, the fluids of the present disclosure may have a low dielectric constant, such as less than 4, or less than 2 at 1 kHz.
Fluid path 110 may be any suitable conduit for appropriate fluids to travel within and through the fluid conditioning system. Fluid path 110 may vary depending on the matter phases of the fluid. For example, fluid path 110 may be formed or created by piping or tubing. In some embodiments, fluid path 110 may be formed by ducting. In some embodiments, and differently from the illustration in
Pump 120 may be any suitable device or mechanism to circulate the fluid through the fluid conditioning system. Pump 120 may be a conventional fan or turbine to mechanically move fluid within fluid path 110. Pump 120 may be of any suitable style and its performance and characteristics may be selected based on the particular application and environment. Pump 120 may be powered by any suitable means, which are not illustrated in detail in
Container 130 may be any suitable space or volume, which may be fully or partially filled with the fluid of fluid conditioning system 100. For example, container 130 may be a tank in which servers, computers, and/or other electronics are fully or partially immersed in a liquid fluorinated fluid, for heat transfer applications. In some embodiments, container 130 may be a switchgear or other sensitive electrical device wherein a gaseous fluid is present in a sufficient quantity to prevent the arcing between high voltage components. In some embodiments, container 130 may be filled with both liquid and gaseous fluid. In some embodiments, container 130 may not always include a fluorinated fluid, but it may be filled in response to a certain event (e.g., fire suppression in response to a detected fire or fire risk). Container 130 may contain any suitable additional components to manage the pressure or ambient environment within the container. Container 130 may also contain (not illustrated) components selected for the particular application (e.g., server docks, electrical and network cables, circuit breakers, etc.), or other systems not directly related to the fluid conditioning. For example, a heat exchanger, compressor, or other thermal management device, or a system to be able to safely access and repair or install/remove components within container 130 (with or without human interaction or intervention: for example, a fully or partially automated robotic arm system). Container 130, in
Filter housing 140 may be any suitable filter housing and may include suitable filtration or sorbent media. Depending on the application, filter housing 140 may incorporate or utilize different flow schemes within, in order to place the fluid to be conditioned in contact with the appropriate media. Suitable housings and general filtration regimes will depend on the particular requirements of the applications (e.g., liquid versus gaseous filtration, acceptable pressure drop, nature and quantity of the expected contaminants, etc.). Filter housing 140 may be specifically configured in order to allow for the quick and easy change of any filtration/sorbent media. Note, that for the purposes of this description, filtration is not limited to the separation of solid phases (not dissolved) and liquid phases. Filtration as used herein includes separation of the bulk fluid from dissolved impurities, degradation or reaction products, or other undesired contaminants, whether or not dissolved or of the same phase.
In
In some embodiments, first sorbent 142 may be or include desensitized activated carbon. Desensitized activated carbon, also known as inert, dead, or passivated activated carbon, is activated carbon where surface oxides and other functional groups are removed or substantially removed, thereby making the sorbent material hydrophobic and catalytically inactive. In some examples, desensitized activated carbon may be helpful in significantly reducing the ability of the activated carbon sorbent (using standard activated carbon as a comparison) to chemically or catalytically react with fluorinated fluids to form undesirable products and, in particular, highly corrosive acids. In some embodiments, the desensitized activated carbon has also been dried in order to drive off any residual water content.
The particle/granule size and porosity of the desensitized activated carbon may be selected based on the particular application. In some embodiments, the desensitized activated carbon may be microporous, mesoporous, or macroporous, or may contain a combination thereof.
IUPAC has developed standard nomenclature for micro-, meso-, and macro-porosity. The term microporous refers to sorbents with pore diameters less than about 2 nm. The term mesoporous refers to sorbents with pore diameters greater than about 2 nm and less than about 50 nm. The term macroporous refers to sorbents with pore diameters greater than about 50 nm.
The desensitization or passivation process involves exposing the activated carbon to a de-oxidizing gas such as nitrogen or hydrogen at elevated temperatures (e.g. 700° C. to 1200° C.) to render the surface of the carbon free of oxygen-containing species, cooling the carbon under a de-oxidizing gas to a temperature of 30° C. to 500° C., contacting the carbon with a stabilizing or passivating substance such as ethylene, and further cooling to room temperature while in a de-oxidizing gas such as nitrogen. Such an exemplary process is described in U.S. Pat. No. 4,978,650 (Coughlin et al.).
When in contact with particular fluorinated fluids, for example, NOVEC 649 engineered fluid, available from 3M Company, St. Paul, Minn., (a fluoroketone) it has been observed that standard, commercially available activated carbon will produce a significantly higher level (e.g., 2 to 3 times or greater) of reaction products such as HFC-227ea as compared to the fluid without exposure to such a sorbent, where it is present but in trace amounts. Generation of such reaction products may be observed through nuclear magnetic resonance spectroscopy (NMR spectroscopy or simply NMR). Desensitized activated carbon produces significantly smaller increases in reaction products when exposed to NOVEC 649 and may in some cases be indistinguishable from the fluid without sorbent exposure.
In some embodiments, the suitable desensitized carbon mass necessary to achieve a desired contaminant level may be estimated based upon the measured adsorption isotherms of representative contaminants on the carbon and the anticipated organic burden in the container (e.g., an immersion cooling tank or other volume). This burden may be determined empirically or at least estimated by measuring or calculating extractable hydrocarbon levels in the polymers found or potentially found within the system, and tabulating the mass of contaminant in each. The desired filtration time constant (fluid mass/mass flow) dictates the mass flow through the filter. This time constant should be balanced with the residence time of the fluid within the filtration media (sorbent), which must be large enough to prevent breakthrough of contaminants which results in elevated contaminant levels and fouling of any additional filter media downstream of the carbon. The above method is merely exemplary and, of course, different optimizations, properties, and constraints should be considered depending on the specific application.
Optionally, filter housing 140 may include second sorbent 144. In some embodiments, second sorbent 144 may perform a different filtration/sorption function than first sorbent 142. In some embodiments, second sorbent 144 may be or include activated alumina. In some embodiments, the activated alumina may be pH-neutralized to remove hydroxyl groups. Suitable pH-neutralization methods may include, but are not limited to, water washing and subsequent drying or reactivation. Using activated alumina as a second sorbent may aid in removing acidic degradation products present in the fluid conditioning system. In some embodiments, the first and second sorbents may be present within the same filter housing. In some embodiments (not illustrated), the first and second sorbents may be present in separate filters or filter housings.
Other sorbents may be suitable for substitution or combination with either the first or (optionally) second sorbent, such as silica or other oxides of main group elements.
The adsorbent materials (i.e. the activated carbons), treated and untreated, were first dried in a N2 inert furnace (available under the trade designation “BLUE M BOX FURNACE ATMOSPHERIC RETORT”, from Lindberg MPH, Riverside, MI). Approximately 50 grams of each adsorbent material was added to separate glass jars which were placed in a muffle furnace and the door was closed. Nitrogen flow was set to 90 standard cubic feet per hour (SCFH) and the furnace was purged for 10 mins. The nitrogen flow was then reduced to 20 SCFH, and the furnace was heated to 180° C. Drying was conducted at 180° C. for 16 hours. The jars were taken out of the oven at 180° C., capped and then allowed to return to room temperature. The samples were then placed in a dry N2 box for storage.
The dried Kuraray BGX and Kuraray RB activated carbon adsorbents were further treated using a process described by Coughlin et al. in U.S. Pat. No. 4,978,650, which is incorporated herein by reference in its entirety. This process involves exposing the activated carbon to a de-oxidizing gas such as nitrogen or hydrogen at elevated temperatures (e.g. 700° C. to 1200° C.) to render the surface of the carbon free of oxygen-containing species, cooling the carbon under a de-oxidizing gas to a temperature of 30° C. to 500° C., contacting the carbon with a stabilizing or passivating substance such as ethylene, and further cooling to room temperature while in a de-oxidizing gas such as nitrogen.
Compatibility of Adsorbents with NOVEC 649
One gram of the chosen adsorbent material (after all drying and treatment methods) was weighed out and added into a 30 ml poly bottle container, 10 ml of NOVEC 649 fluid was then dispensed into the container, a cap applied, and 3M vinyl tape wrapped around the cap to prevent accidental leakage. Finally, the container was placed on a rolling mill and mixed for 24 hours at room temperature. The bottles were set aside for at least 24 hours to allow for the adsorbent to settle out. A syringe was used to remove 3-4 ml of the supernatant fluid from the bottle and dispensed into an 8-ml poly bottle.
The liquid sample in the 8-ml poly bottle was analyzed with NMR to look for indication of reaction with the NOVEC 649. The 1H-NMR and 19F-NMR test methods were as follows. Neat aliquots (˜0.8-1.0 mL) of the NOVEC 649 sample fluids that were treated with the adsorbent material were transferred into pre-dried 5-mm outer diameter glass NMR tubes in a nitrogen-purged glove box. No extra standards of any kind were added to the sample fluids to avoid introduction of trace amounts of extra water. Initial 600.1 MHz 1H-NMR spectra and 564.7 MHz 19F-NMR spectra were acquired using a Bruker Avance-III HD 600 FT-NMR spectrometer (MAID #1467) that was operating with a helium cooled 5-mm inverse-detection gradient TCI cryoprobe (MAID 1472) at an analysis temperature of 25° C. The HFC-227ea impurity was used as the 1H/19F cross integration standard in place of the usual 1,4-bis(trifluoromethyl)benzene (p-HFX) standard to permit the cross correlation of the relative 1H and 19F signal intensities for quantitative purposes.
When NOVEC 649 reacted with an adsorbent, one by-product is 1,1,1,2,3,3,3 heptafluoropropane (CF3—CFH—CF3), designated as HFC-227ea, a colorless gas. Another by-product was hexafluoropropylene (CF3—CF═CF2), designated as HFP, another colorless gas. NOVEC 649 in the neat form contained a low level of HFC 227ea gas, designated by the symbol “(O)” in Table 1 (below), and typically has concentrations of HFP below the detection limit, designated by the symbol “(O)” Table 1. When these gases are present at levels ≥2-3 times the concentration of the neat fluid, this was an indication of reactivity of the adsorbent with the NOVEC 649, which was designated by the symbol “(X)” in Table 1.
The 19F-NMR and 1H-NMR spectra were used to measure the absolute weight percent concentrations of HFC-227ea and hexafluoropropylene (CF3—CF═CF2), HFP, in the NOVEC 649 samples treated with adsorbent material. The qualitative and quantitative compositional results that were derived from the single trial 19F/1H-NMR cross integration spectral analyses are summarized in Table 1.
The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the embodiments of the present invention. Thus, it should be understood that although the present invention has been specifically disclosed by specific embodiments and optional features, modifications and variations of the concepts herein disclosed may be resorted to by those of ordinary skill in the art, and that such modifications and variations are considered to be within the scope of embodiments of the present invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/052123 | 3/9/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63160536 | Mar 2021 | US |
