United States Patent: 6656238
The concept of a solid "foam", both firm and to some greater or lesser extent flexible, should be one pretty much familiar, through experience, to just about everyone by now.
Some commonplace examples would be the insulated cups you buy take-out coffee in and the cushions you plant your fanny on when you're driving your car. There are other examples, too, like insulation board, which, unlike the cups and cushions, is much more rigid; in a way, "stronger".
Actually, maybe unbeknownst to most folk, a lot of plastic items they deal with in their everyday lives are foams, sometimes referred to as foam composites; wherein the object in question looks and feels like a solid, rigid piece of plastic, but is surprisingly light.
Those plastic "foams" are made in a couple of different ways.
In some cases, the plastic resin the article is made with is of a type that, through one chemical pathway or another, i.e., reactions that generate gas, typically CO2, creates bubbles in the resin as it reacts and "cures", or hardens.
Other formulations rely on the addition of a basically inert chemical that remains liquid, sometimes in solution, in the resin, until "triggered", usually by the heat of the chemical reaction that forms the plastic, and turns into a gas at that juncture, forming "bubbles" that become "frozen" in the cured plastic.
The now-dreaded class of chemicals known generically as "CFC's" were once favored agents of foaming that were added to various plastic resins to achieve that effect.
Note that the parenthetical words we use to characterize the process aren't the technical terms used by the good folk knowledgeable in such matters; they're just our way of trying to describe it in a fashion that we might all be able to understand; in a way that was used to explain it to us.
There are other examples, and, it's all really beyond the scope of our discussion herein. The point being, that, by making a solid "foam", you can impart certain desired physical properties to an object formed out of the plastic which comprises the matrix of that foam. Insulating value is probably the most obvious example; but, again, foam can make an article more rigid, stronger in a way, but also lessen the weight of the object.
Impact resistance, too, is an important characteristic of foams. Whether soft and flexible, or rigid, they can absorb force; they can serve as protective cushions.
That figures in later on in our discussion herein; but, first, even though nearly all the useful foams most of us automatically think of are made of plastic, or, more generically and actually accurately, polymers, there are others.
Even concrete, and some metals, can be foamed.
And, as we previously documented in our report of:
West Virginia Coal Association | WVU Makes "Plastic" Coal Foam | Research & Development; concerning:
"United States Patent: 5888469 - Method of Making a Carbon Foam Material and Resultant Product;
(Method of making a carbon foam material and resultant product - West Virginia University); 1999; Alfred Stiller, et. al., WV; Assignee: West Virginia University; Abstract: A method of making anisotropic carbon foam material includes de-ashing and hydrogenating bituminous coal, separating asphaltenes from oils contained in the coke precursor, coking the material to create a carbon foam. In one embodiment of the invention, the carbon foam is subsequently graphitized. The pores within the foam material are preferably generally of equal size. The pore size and carbon foam material density may be controlled by (a) altering the percentage volatiles contained within the asphaltenes to be coked, (b) mixing the asphaltenes with different coking precursors which are isotropic in nature, or (c) modifying the pressure under which coking is effected. In another embodiment of the invention, solvent separation is employed on raw bituminous coal and an isotropic carbon foam is provided. A related carbon foam product is disclosed. The carbon foam materials of the present invention are characterized by having high compressive strength as compared with prior known carbon foam materials";
so can Coal.
And, the conversion of Coal into a plastic-like foam is done in ways that are actually related to some of the ways Coal can be converted into liquid hydrocarbons; that is, through the action of a Hydrogen-donating liquid solvent, as described, for one example, in:
WVU Hydrogenates Coal Tar | Research & Development; concerning: "Hydrogenation of Naphthalene and Coal Tar Distillate over Ni/Mo/Al2O3 Catalyst; Abhijit Bhagavatula; Thesis submitted to the College of Engineering and Mineral Resources at West Virginia University in partial fulfillment of the requirements for the degree of Master of Science in Chemical Engineering; John W. Zondlo, Ph.D., Chair; Elliot B. Kennel, M.S; Alfred H. Stiller, Ph.D; Department of Chemical Engineering; Morgantown, West Virginia. 2009. Abstract: The hydrogenation of naphthalene and coal-tar distillates has been carried out in a Trickle Bed Reactor ... for the hydrogenation of naphthalene (to make) the hydrogenated product, tetralin (1,2,3,4 Tetrahydronaphthalene) (which can serve to effect) the direct reaction between coal and hydrogen (and the) conversion of coal to refinable crude hydrocarbons, from which liquid fuels such as gasoline, diesel, kerosene, etc., can be produced".
The above "naphthalene" is one type of Coal tar, or oil, first obtained as a byproduct from Coke ovens.
Less-fluid Coal tars are often lumped under the label "Pitch"; and, it's important that we establish a definition for that label, as in:
Coal-Tar Pitch Update; "In the processing of coal to make coke for steel making, volatile compounds are collected from the coking ovens, condensed, and separated, and become the base of hundreds of raw materials, including dyes, plastics, and a byproduct called coal-tar pitch. Coal-tar pitch is produced by distillation of the crude coke-oven tar (obtained during the high-temperature treatment of coal to make coke or natural gas). Pitch materials are usually thick, black, or dark brown liquids or semi-solids with a naphthalene-like odor."
For anyone old enough to have used them, "naphthalene-like odor" means it smells like mothballs. And, as a significant aside, note passing mention of the fact that Coal can be processed through a "high-temperature treatment ... to make ... (synthetic) natural gas".
And, such coke oven "pitch" is key to the process of making a carbon foam out of Coal we report to you herein, as seen in excerpts from the initial link in this dispatch to:
"United States Patent 6,656,238 - Coal-based Carbon Foam
Date: December, 2003
Inventors: Darren Rogers and Janusz Wladyslaw, Wheeling and Glen Dale, WV
Assignee: Touchstone Research Lab, Triadelphia, WV
(TRL Facilities | Touchstone Research Laboratory; "The Touchstone main facility is located at The Millennium Centre, an advanced technology park, located along Interstate 70, near Wheeling, WV, less than one hour from Pittsburgh, PA. Advanced Materials & Processes Magazine has called Touchstone, "One of the best equipped labs of its size in the country".
TRL Developments: CFOAM (R) | Touchstone Research Laboratory; "CFOAM(R) is a new structural material, made from coal in a cost-effective proprietary process, which is inexpensive, lightweight, fire-resistant, impact absorbing, can be thermally insulating or conducting, and whose electrical resistivity can be varied over nine orders of magnitude. This versatile, next-generation material has been under development since 1998, with both internal funding and funding made available through several SBIR program awards. During this period, manufacturing processes have been refined and extensive testing has been conducted to characterize the material’s unique properties.)
Abstract: A method for the manufacture of coal-based carbon foams from a coal particulate starting material that comprises blending from 1 to about 10% by weight of pitch with the coal particulate before foaming. Blends of coal-based particulate with 1 to about 10% by weight of pitch as well as coal-based carbon foams manufactured from such blends are also described.
Claims: A semi-crystalline, largely isotropic, porous coal-based product having a density of between about 0.05 and about 0.1 g/cm3 and a thermal conductivity below about 1 W/m/K produced from a blend comprising:
A) from about 90 to about 99% by weight of particulate coal exhibiting a free swell index of between about 3.5 and about 5.0 and of a small diameter; and:
B) from about 1 to about 10% by weight of pitch.
(For more than you could possibly want to know about the subject of "thermal conductivity" and the significance of "1 W/m/K", see: Thermal conductivity - Wikipedia, the free encyclopedia.
The word "isotropic", according to our dictionary, just means that the structure of the stuff is uniform throughout it's mass; that is, all the bubbles will be pretty much the same size and evenly distributed.)
The porous coal-based product ... wherein said coal exhibits a free swell index of between about 3.75 and about 4.5.
(The "free swell index" is a property of Coal that can help to determine whether or not it's suitable for making into Coke; and, it's explained fairly well in: Coal assay - Wikipedia, the free encyclopedia.)
The porous coal-based product ... having a compressive strength below about 6000 psi.
The porous coal-based product ... that has been carbonized (and/or) graphitized.
(In other words, after the "coal-based product" has been formed, it has to be "fired" to drive off all the remaining volatile constituents.)
Background and Field: The present invention relates to carbon foam materials derived from coal and more particularly to such foams that exhibit lower densities but equal strengths than similar prior art such materials.
Object and Summary: It is therefore an object of the present invention to provide a method for the production of coal-based carbon foams of lower density than but equal strength as those previously available in the prior art. It is another object of the present invention to provide a method for the manufacture of coal-based carbon foams that lends itself to the production of such materials from highly plastic precursor blends that simplify the formation and production of coal-based foam products, especially those possessing highly complex shapes.
According to the present invention, there is provided a method for the manufacture of coal-based carbon foams from a coal particulate starting material that comprises blending from 1 to about 10% by weight of pitch with the coal particulate before foaming. Blends of coal-based particulate with 1 to about 10% by weight of pitch as well as coal-based carbon foams manufactured from such blends are also described.
The starting material coal may include bitumen, anthracite, or even lignite, or blends of these coals that exhibit a "free swell index" as determined by ASTM D720 of between about 3.5 and about 5.0, but are preferably bituminous, agglomerating coals that have been comminuted to an appropriate particle size, preferably to a fine powder below about -60 to -80 mesh.
The pitch may be ... coal-derived pitch (such as) Pittsburgh pitch ... . The chemistry and processing of carbon containing materials to extract pitch or to synthesize pitch are well known and have been discussed in numerous textbooks and publications.
(The "Pittsburgh pitch" is/was a product of Pittsburgh's Koppers Company. See:
http://www.koppers.com/docs/White_Papers/KOPHTC_TMS01.pdf; "Development of Binder Pitches From
Coal Extract and Coal-Tar Pitch Blends; Peter G. Stansberry and John W. Zondlo; West Virginia University,
Morgantown, WV; and: Robert H. Wombles; Koppers Industries, Inc.; Pittsburgh, PA"; and:
Koppers - Wikipedia, the free encyclopedia; "Koppers sources coal tar from around the world for further processing by distillation into carbon chemicals. One of Koppers' leading products is coal tar";
and, though somewhat off-topic, just for kicks:
West Virginia Coal Association | Pittsburgh 1942 Coal Gasification Utilizes CO2 | Research & Development; concerning: "United States Patent 2,302,156 - Process and Apparatus for the Production of Useful Fuel Gas; 1942; Assignee: Koppers Company, Pittsburgh, PA; Abstract: This invention relates to the production of fuel gas or high heating power out of dusty of finely granular fuels, such as black or brown coal, or coke or semi-coke made therefrom, the fuel being converted at a high temperature with air (oxygen), steam and carbon dioxide whereby a gas is produced which is rich in hydrogen and carbon monoxide".)
The production method of the present invention comprises:
1) heating a blend of:
A) coal particulate of preferably small i.e., less than about 1/4 inch particle size blended with:
B) from about 1 to about 10% by weight, based upon the weight of the coal particulate, of a pitch to a temperature at or just above the softening point of the pitch, generally, but no necessarily a temperature of from about 240C to below about 280C, to form a plastic blend;
heating the plastic blend thus formed in a "mold" and under a non-oxidizing atmosphere ... to a temperature of between about 300 and about 700C;
soaking at a temperature of between about 300 and 700C for from about 10 minutes up to about 12 hours to form a foam preform or finished product; and:
controllably cooling the preform or finished product to a temperature below about 100C. The non-oxidizing atmosphere may be provided by the introduction of inert or non-oxidizing gas into the "mold" at a pressure of from about 0 psi, i.e., free flowing gas, up to about 500 psi. The inert gas used may be any of the commonly used inert or non-oxidizing gases such as ... CO2.
After expanding the coal particulate/pitch blend as just described, the porous coal-based foam product is an open celled material. Several techniques have been developed for "sealing" the surface of the open celled structure to improve its adhesive capabilities for further fabrication and assembly of a number of parts. For example, a layer of a commercially available graphitic adhesive can be coated onto the surface and cured at elevated temperature or allowed to cure at room temperature to provide an adherent skin. Alternatively, the expansion operation can be modified by cooling the expanded coal/pitch blend product or preform rapidly, e.g., at a rate of 10C./min or faster after expansion. It has been discovered that this process modification results in the formation of a more dense skin on the preform or product which presents a closed pore surface to the outside of the preform or product. At these cooling rates, care must be exercised to avoid cracking of the preform or product.
After expanding, the porous coal/pitch blend-based preform or product is readily machineable, sawable and otherwise readily fabricated using conventional fabrication techniques as previously described in connection with earlier prior art coal-based foams that did not incorporate pitch as described herein.
Subsequent to production of the preform or product as just described, the preform or product may be subjected to carbonization and/or graphitization according to conventional processes to obtain particular properties desirable for specific applications of the type described hereinafter. Ozonation may also be performed, if activation of the coal-based expanded product would be useful in a final product application such as in filtering of air. Additionally, a variety of additives and structural reinforcers may be added to the coal-based preforms or products either before or after expansion to enhance specific mechanical properties such as fracture strain, fracture toughness and impact resistance. For example, particles, whiskers, fibers, plates, etc. of appropriate carbonaceous or ceramic composition can be incorporated into the porous coal-based preform or product to enhance its mechanical properties.
The open celled, coal-based preforms or products of the present invention can additionally be impregnated with, for example, petroleum pitch, epoxy resins or other polymers using a vacuum assisted resin transfer type of process. The incorporation of such additives provides load transfer advantages similar to those demonstrated in carbon composite materials. In effect a 3-D composite is produced that demonstrates enhanced impact resistance and load transfer properties."
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There is quite a lot more to it; and, our relatively-brief excerpts don't do a good job of fully explicating the technicalities of the process. But, the gist is, that, relatively lightweight, but strong and rigid, structures, with unique properties, such as "enhanced impact resistance", can be made out of, essentially, foamed Coal.
To give you some idea just how "high tech" that might really be, have a look at:
http://www.smdc.army.mil/FactSheets/Coal-basedCarbonFoam.pdf; concerning: "U.S. Army Space & Missile Defense Command/Army Forces Strategic Command; 'Coal-Based Carbon Foam'; Coal-based carbon foam is an enabling technology critical to improving the performance of a wide variety of next-generation material systems and components. Coal-based carbon foams are a new structural material made in a cost-effective proprietary process.
The result is an inexpensive, lightweight, fire-resistant, impact-absorbing material that can be thermally insulating or conducting, and whose electrical resistivity can be varied over many orders of magnitude.
Coal-based carbon foams offer systems designers alternatives to current design materials, extending the performance ranges in material systems where they replace more conventional materials whose peak performance levels have already been reached. With its ease of use, coal-based carbon foams can be cut, milled and turned with conventional equipment and tooling. Integration with other materials including impregnation with phenolic or other resins, and lamination with KevlarTM or other laminates, is straight-forward, creating a broad spectrum of potential applications to defense, aerospace and commercial markets.
Coal-based carbon foams are currently being developed for a variety of uses. Being a domestically produced material, it offers advantages in availability as well as cost, enhanced structural properties, fire resistance, radar cross-section, corrosion susceptibility, and low weight, making it ideal where these properties or combination of properties are coveted.
Benefits for Tomorrow’s Defense: Coal-based carbon foams will help to enhance capabilities and improve affordability, supporting today’s warfighter. Applications for coal-based carbon foams continue to be developed as the material is accepted as a mainstream structural building block for tomorrow’s technology. Current application examples include targeted advances in composite tooling, vehicle blast mitigation, radar
absorption, and ablation panels."
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The "vehicle blast mitigation" does have to do with the specified "enhanced impact resistance". And, the Army's two-page description of "Coal-based carbon foams" does lead to conjecture about the many uses to which it might be put outside the military arena.
In any case, the developments herein by Touchstone Research Lab, as disclosed via their "United States Patent 6,656,238 - Coal-based Carbon Foam", are not isolated, as the prior "US Patent 5,888,469 - Method of Making a Carbon Foam Material and Resultant Product", assigned to WVU, should attest.
And, make no mistake, this is fully-commercialized, on-the-market product, as the official, and legally required, Material, or Product, Safety Data Sheet:
http://www.cfoam.com/pdf/CFOAMProductDataSheet.pdf; "CFOAM carbon foam is applicable to a broad spectrum of commercial, defense and aerospace markets. It is an enabling technology for a host of next-generation material systems and components – replacing those currently based on more conventional materials such as balsa wood, intumescent mats, polymer matrices, metallic honeycombs, ceramic fibrous insulation, ceramic tile, Kevlar-based structures, polystyrene, plastics, fiberglass, rubber and various metals.
Carbon foams are currently being developed for a variety of uses including fire-resistant ship decking and
bulkheads, noise and impact mitigation for aircraft, structural panels and firewalls for automobiles, lightweight personnel and vehicular armor, modular construction, and as part of spacecraft thermal management systems";
should confirm.
There are a number of further advances in the making of Coal-based, polymer-like Carbon foams and composites, as we will document in coming reports. And, the potential exists, with at least some of them and some of their applications, to replace and displace somewhat related foams and composites based on various plastics, and on other petrochemical derivatives - nearly all of which we now import from OPEC.
All of which should point the way to a fuller employment of our domestic natural resources, and our domestic human resources, in a way that can improve certain of our products of manufacture; improve our balance of foreign trade; and, improve our overall quality of life in United States Coal Country.
