Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Waste paper or textile waste
Reexamination Certificate
1999-01-11
2001-06-26
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Waste paper or textile waste
C162S091000, C162S095000, C162S096000, C162S098000
Reexamination Certificate
active
06251221
ABSTRACT:
FIELD OF THE INVENTION
The invention disclosed herein provides a process for extracting lignin, cellulose and hemicelluloses from ligno-cellulosic matter. It also provides an improved method of converting cellulose to microcrystalline cellulose by a process that gives better control over the size and uniformity of the microcrystalline particles than was previously available.
Products obtained by the extraction process of the present invention may be (1) used directly without additional processing, (2) subjected to further processing using the methods of the invention or methods known in the art, or (3) used as chemical feed stocks for further manufacturing into fuel alcohol, livestock feed molasses, adhesives, plastics and many other commercially valuable products.
Ligno-cellulosic material used as the feed stock for a process described herein can include recycled wood products such as wastepaper, paperboard, cardboard and other paper products, as well as tree limbs, broken boards, recycled wood waste, and so forth. Materials such as these are typically discarded in landfills and constitute a major portion of the Nation's landfill mass. This ever-increasing burden on the limited number of landfill sites can be greatly alleviated using methods described herein to convert agricultural, industrial and domestic trash into useful products.
BACKGROUND OF THE INVENTION
A preferred liquor for use in preparation of pulp and extraction of lignin from wood has been described in U.S. Pat. Nos. 3,442,753 and 3,522,230 to Burkart, both of which are incorporated herein by reference in their entirety.
U.S. Pat. No. 4,826,566 discloses an improved method for treating ligno-cellulosic material to remove lignin and to obtain cellulose and other valuable products from paper, chips or other forms of cellulosic materials.
SUMMARY OF THE INVENTION
The invention provides an improvement over the prior art methods disclosed and claimed in U.S. Pat. No. 4,826,566 resulting from manipulating reaction parameters such as the water content of the feed stock, the temperature at which the reaction takes place and the length of time the material is allowed to react with the extraction liquor. Control of the time of reaction is improved by the incorporation of a quenching step into the extraction process.
The method of the invention involves treating cellulosic vegetable matter (the “Feed Stocks”) for the selective recovery of lignin (when present in the feed-stock), cellulose and hemicelluloses by: (1) reducing the material to be processed to an appropriate size; (2) adjusting the moisture content of the ligno-cellulosic feed stock to 15 percent to 30 percent water; (3) impregnating the ligno-cellulosic feed stock with an extraction liquor containing a glycol and an organic or Lewis acid; (4) rapid heating of said impregnated feed stock to a temperature of about 118° C. to about 145° C.; (5) maintaining the desired temperature for about 1 minute to about 6 minutes to solubilize the lignin therefrom (a period of about 2 minutes to about 5 minutes is preferred); (6) stopping the reaction immediately by lowering the temperature to <100° C. in a quenching bath of fresh or recycled liquor or other suitable liquid; (7) removing the lignin-enriched extraction liquor from the quenched impregnated matter and (8) recovering the extracted lignin. If the feed stock is non-ligneous (for example, cotton linters), the quenching step (step 6) may be combined with a wash (alcohol is exemplified) to remove the cooking liquor from the cooked material. The cellulosic material may then be recovered from the liquid using separatory means known in the art such as filtration, centrifugation or vacuum screening. Alcohol may be recovered by evaporation under reduced pressure. An improved means of converting the cellulose fraction to microcrystalline cellulose employs using ultrasonic means.
The triethyleneglycol solvent system described is easily adapted with modification to maximize the commercial usefulness of enormous quantities of cellulosic waste materials such as waste paper, poor quality or damaged cotton bales, used lumber, tree limbs, agricultural wastes, and so forth. The temperature at which the ligno-cellulosic material impregnated with liquor is heated is important for control of the process. Temperatures of about 118° C. to about 145° C. (a more preferred range being from 119° C. to 138° C.) are particularly appropriate for the recovery of products from pulped waste paper and wood.
The liquor dissolves the lignin leaving the residual carbohydrates in high yield. Liquor and lignin remaining in the pulp can be removed by washing the pulp with an alcohol such as ethanol followed by draining or centrifugation. The washing material such as ethanol may then be reclaimed by evaporation from the liquid under reduced pressure. Lignin can be reclaimed from the liquor by precipitation with water as disclosed herein. The extraction liquor can be recovered from the water/extraction liquor mix by evaporation of water at reduced pressure and recycled.
Microcrystalline cellulose can be produced either from the lignin-depleted pulp or from material which does not naturally contain lignin, such as cotton linters. In this embodiment, lignin-deficient or lignin depleted cellulosic material is impregnated with extraction liquor and cooked at about 135° C. to about 145° C. (a more preferred range being 139° C. to 145° C). This hydrolyses some of the amorphous areas of the cell wall microfibrils permitting reduction to micro-crystalline size by mild mechanical or ultrasound agitation. Ultrasound is a preferred method for use in this process.
DETAILED DESCRIPTION OF THE INVENTION
Using the process of the invention, lignin and other non-carbohydrate materials (such as ink in waste paper) are dissolved into the cooking liquor with very little degradation of the cellulose and hemicelluloses. The cooking time (which will vary with the species and particle size of the feed stock) is controlled by controlling the speed of the conveyor belt. During the digestion process, the particles and more dense the species of feed stock, the longer the time needed for cooking. Rapid cooling or quenching is necessary to prevent over-cooking which causes formation of undesired degradation products and reduction in pulp yields. The lignin-depleted paper or wood pulp that remains after lignin has been extracted into the liquor may then be processed to recover cellulosic and hemicellulosic materials. The lignin is reclaimed from the liquor as described above.
Materials that do not naturally contain lignin or which, by the methods described herein or elsewhere, have become depleted of their lignin content, are acceptable substrates for the production of microcrystalline cellulose for further processing into organic chemicals or alternate fuels A common source of naturally a-ligneous material is cotton linters or low grad cotton of a quality unsuitable for manufacture.
The following illustrative examples are provided not as limitations but as a means to teach specific methods for practicing the invention in greater detail.
MATERIALS AND METHODS
The liquor used in the process described below is prepared by mixing triethyleneglycol (TEG) with about 0.5 percent to about 1.5 percent (v/v) of an organic acid or Lewis acid as described in earlier patents. An appropriate acid is para-toluenesulfonic acid. After mixing the TEG and acid, the mixture is allowed to stand about 24 hours at room temperature before being applied to cellulosic materials. However, this reaction time may be shortened if the liquor is heated. For example, if the TEG/acid mix is heated to a temperature in the range of about 125° C. to about 135° C., the liquor can be used about an hour after mixing has occurred. After the cellulosic material has been impregnated, excess liquor can be removed by draining, pressure, or centrifugation of the impregnated material.
REFERENCES:
patent: 3081218 (1963-03-01), Ambuehl et al.
patent: 4826566 (1989-05-01), Burkart
patent: 5859236 (1999-01-01), Burkart
pate
Hendricks Glenna
Nguyen Dean T.
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