Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
2000-04-06
2003-12-30
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S304400, C428S307300, C428S307700, C428S312200, C428S312600, C428S312800, C428S319100, C428S318400, C428S457000, C428S698000
Reexamination Certificate
active
06670039
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to carbonized plants, and more particularly relates to the fabrication of materials using wood and other naturally fibrous plants as precursor materials. The carbonization process retains the anatomical features of the precursor plant while converting the composition of the plant to primarily carbon. The carbonized wood may then be formed to the desired shape. The shaped carbon product may be used to form composites such as carbon-carbon and carbon-polymer composites. The shaped carbon product may alternatively be converted to ceramic compositions, or further processed to form ceramic-containing composites such as ceramic-metal and ceramic-ceramic composites.
2. Background Information
Carbonization of wood for the manufacture of charcoal has been practiced since the beginning of history. Destructive distillation was practiced by the ancient Chinese. The Egyptians, Greeks and Romans carbonized wood and distilled the volatiles for embalming purposes and the filling of joints in wooden ships. In ancient times wood charcoal was used for the removal of odors, medicinal purposes, domestic cooking fuel, the making of gunpowder and the refining of ores. The Industrial Revolution brought about a heavy demand for charcoal, especially for the making of iron. Up until the late 1800's the largest portion of manufactured wood charcoal went into the reduction of iron ores. Today, coal derived cokes are used.
For many centuries charcoal was made in open air pits in the Western world. This entailed tightly piling bolts of air dried wood end to end forming a conical mound. This mound was then covered with several inches of leaves, grass, needles, branches or moss depending upon what was available. An additional few inches of dirt or sod then capped off the mound. Openings were left at the base for air supply and up the center to allow smoke to escape. The mound was then ignited at the base through an opening. The mound tender made certain just enough air entered to allow a smoldering combustion which could take from one to several weeks to complete.
The production of wood charcoal became a major industry by the end of the nineteenth century. The conventional open pit methods wasted the by-product gasses that are released when wood is thermally decomposed. An entire industry was formed around the distillation of the vapors evolved from wood carbonization. In the U.S. two branches of the industry formed due to the fact that denser hardwoods give different products than the lighter, more resinous softwoods. The products from destructive distillation of hardwoods included wood alcohol (methanol), acetate of lime and charcoal. The softwoods gave turpentine, tar, wood oils and charcoal. These products were made possible by carbonizing wood in a container designed such that the evolved gasses could be captured and distilled.
The first development beyond the open pit method was the use of brick kilns designed to both contain the wood charge and provide a means to tap into the exhaust. The brick kiln method meant a faster production rate since mounds were not needed and rapid loading was possible. This was also an asset for the iron industry which was rapidly expanding. The heat needed for decomposition was obtained from the wood charge itself, just as in the open pit method. One drawback of the brick kiln was that a large portion of the evolved vapors were lost through the bricks, thus giving limited yields.
The first high efficiency device for collecting carbonized wood vapors was the small cylindrical retort made of cast iron or steel measuring some 4 ft in diameter and 9 ft in length, capable of holding about two thirds of a cord. These were installed horizontally as pairs with batteries of 10 or more pairs in long rows enclosed by brick. Heating was able to be provided externally from below the retorts and fuel was typically in the form of charcoal, coal, wood gas, wood oil, wood tar or wood alone. A single run took about twenty four hours to complete. The vapors were collected and distilled in the form of pyroligneous acid which was later refined to produce acetic acid, methanol, acetone, furfural, tars and oils.
The cylindrical retort evolved into a large rectangular steel retort enabling the use of cars for loading and unloading. A common size was 50 ft long by 8 ft high and 6 ft wide. These retorts held more than ten cords of wood and considerably increased production rates while reducing the amount of labor involved. After a twenty four hour carbonization cycle the cars were removed to cooling retorts and held for another one or two days. Once removed from a cooling retort the cars were allowed to sit in the open for another two days thus giving a total time, from wood to marketable charcoal, of about ninety six hours. Some of the larger wood carbonization and distillation plants consumed as much as 200 cords per day.
In the beginning of the twentieth century wood charcoal and its distillation products had fallen behind the products derived from coal and petroleum in several of the markets. Eventually, due to dwindling supplies of wood and the availability of higher grades of coals, the metallurgical market share became dominated by coal derived cokes. The demand for wood charcoal began to decline in the late 1800's. Petroleum based products also began to take over some of the markets dominated by wood distillation products.
Currently in the U.S., the only significant markets for wood carbonization products are activated carbons and charcoal briquettes.
Thermal degradation of wood has been studied with the intent of gaining information on its ignition characteristics. In the U.S. wood is used on a large scale in construction, especially for residential housing. Increased public concern over fire safety has prompted forest product industries to investigate methods for eliminating or reducing the ignition temperatures of wood and wood based products. The most common approach was chemical treatment to suppress various decomposition reactions. Progress in many cases was limited due to the potential for production of poisonous, or noxious fumes when products did finally ignite. Additional problems such as degradation of wood mechanical properties and bonding characteristics has hindered wide scale manufacture of fire retardant products. In the 1980's construction grade fire resistant plywood entered the market and was widely installed as roof sheathing in many regions of the U.S. Unfortunately, the release to market was premature as the product suffered from ply delamination resulting in product recall and much negative publicity.
Several U.S. patents address wood treatment methods. U.S. Pat. No. 1,237,521 to Jennison discloses impregnating wood with preservatives such as tar.
U.S. Pat. No. 1,483,733 to Kozelek discloses the production of wood for musical instruments by heating the wood in air to a temperature of from 450 to 550° F. (232 to 288° C.). The heat treated wood, which has a yellow color, may then be treated with varnish prior to making the musical instrument.
U.S. Pat. No. 3,508,872 to Stuetz et al. discloses a process for the production of graphite fibrils using wood splinters less than 0.5 inch in length as a starting material. The splinters are first heated in air at 150 to 400° C., and are then charred at 2000 to 3000° C. The resulting graphite fibrils are then incorporated in a binder to form a composite.
U.S. Pat. No. 3,927,157 to Vasterling discloses the production of carbon-carbon composites using wood pulp as a starting material. Carbohydrate sugars are first chemically extracted from the wood, followed by heating the wood pulp at increasing temperatures of up to at least 3800° F. The fibers are then mixed with a carbonizable binder and the mixture is heated to form the carbon-carbon composite.
U.S. Pat. No. 4,170,668 to Lee et al. discloses a method for pre-charring the surface of wood in order to retard fire and rot.
U.S. Pat. No. 4,678,715 to Giebeler et al. discloses the impre
Byrne Christopher E.
Nagle Dennis C.
Petragallo, Bosick & Gordon
Towner, Esq. Alan G.
Turner Archene
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