Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Continuous chemical treatment or continuous charging or...
Reexamination Certificate
1998-09-16
2001-05-08
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Continuous chemical treatment or continuous charging or...
C162S019000, C162S021000, C162S022000, C162S026000, C162S029000, C162S052000, C162S076000, C162S078000, C162S087000, C162S089000, C162S090000, C127S037000, C426S276000
Reexamination Certificate
active
06228213
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to a process for making microcrystalline cellulose (MCC). More specifically, the present invention relates to a process where microcrystalline cellulose is made by reactive extrusion.
Microcrystalline cellulose is obtained by hydrolysis of the amorphous portion of cellulose until a level-off degree of polymerization (LODP) product is obtained. MCC is comprised of highly crystalline regions of cellulose and usually has a LODP of 200-300.
Microcrystalline cellulose is useful for a number of different applications. Pieces of microcrystalline cellulose easily bond together without the use of an adhesive. Furthermore, MCC can be mixed with other substances so as to hold an additive while bonding to itself. It can be made into pharmaceutical-grade tablets, such as vitamins, pain relievers, and other medicines. It also may be used as a substitute for starch where starch is used as a smoothener, such as in suntan lotion.
The hydrolysis of cellulose to obtain MCC can be accomplished using mineral acid, enzymes or microorganisms. Although enzymatic methods are desirable because glucose, a useful by-product, is created, these methods are more expensive and create MCC products having a lower crystallinity. Thus, acid hydrolysis is the conventional method of choice for manufacturing MCC.
In conventional methods, MCC is formed by reacting cellulose with acid in a batch-type reaction vessel. Specifically, a large amount of acid solution is placed in a vat and then cellulose is added. Next, the acid hydrolyzes the cellulose, and MCC is formed. Such processes require significantly greater amounts of acid solution than cellulose. When this batch-type process is complete, a large amount of acid solution remains.
Acids that can be used in this process include hydrochloric acid, sulfuric acid, and phosphoric acid. At higher temperatures, sulfuric acid and phosphoric acid can peptize and surface modify (esterify) MCC. However, such MCC is difficult to purify and does not have the same visual and functional properties as underutilized cellulose produced with hydrochloric acid. One example of using hydrochloric acid involves a method using 2.5N hydrochloric acid, which is able to specifically cleave , 1-4 glucosidic linkages. More product can be created with such hydrochloric acid than with sulfuric acid at the same conditions. However, if used at high concentrations, hydrochloric acid is a strong corrosive agent.
MCC obtained by acid hydrolysis using conventional methods has a particle size of about 200 microns, although particle size can vary somewhat depending on the starting material used. The MCC can undergo mechanical grinding until the particles are of a desirable size.
Mechanical grinding can be accomplished by mixing the MCC with a water solution in either a blender or in a hammer mill. The MCC particle shape obtained after grinding depends mostly on the nature of the raw starting material, especially upon whether the cellulose is in its native or regenerated state.
Conventional methods do not contemplate the advantage of using pressure and high shear forces created by an extruder to aid in performing this acid hydrolysis reaction. Methods presently available also have extremely harmful impacts on the environment because they require large amounts of acid and thus create significant quantities of acid waste.
A process for producing microcrystalline cellulose is needed that has a shorter reaction time than previous processes. Furthermore, a process is needed that is a continuous process rather than a batch-type process. Still further, a process using a limited amount of acid is needed. In addition, a process that is able to produce small particles of microcrystalline cellulose without the need for mechanical grinding also would be advantageous.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for producing microcrystalline cellulose by means of reactive extrusion in order to provide a quicker process for producing microcrystalline cellulose.
Another object of the present invention is to provide a continuous process for producing microcrystalline cellulose so that MCC may be produced in a quick and efficient manner.
It is a further object of the present invention to provide a process of producing MCC that uses less acid than previous processes so that less acid waste is created.
Another object of the present invention is to provide a process for producing small particles of MCC so that there is no need for mechanically grinding the particles produced.
A further object of the present invention is to provide a simple, economical, and environmentally-friendly process for producing microcrystalline cellulose so that microcrystalline cellulose may be created for a variety of applications.
According to the present invention, the foregoing and other objects are achieved by a process for producing microcrystalline cellulose by means of reactive extrusion. This process can be a one-step process if pure cellulose is used as a starting material and is a two-step process if a lignocellulosic material is used as the starting material.
In the first step of this process, the lignocellulosic material is extruded with a basic aqueous solution in order to destroy the lignocellulosic complex. The lignocellulosic complex is broken into lignin, hemicellulose, and cellulose. Following extrusion, the lignin and the hemicellulose are extracted with a heated basic solution, and the remaining cellulose is washed. The cellulose can be bleached or further processed to microcrystalline cellulose without bleaching.
In the second step of this process, pure cellulose or the cellulose obtained from the lignocellulosic material undergoes reactive extrusion. The cellulose material is fed into an extruder with an acid solution. The cellulose, which is pressurized by the screw of the extruder, is hydrolyzed by the acid. After extrusion, the resulting microcrystalline cellulose product is washed, bleached and dried. The size of the resulting microcrystalline cellulose particles depends on the starting material used and the extrusion conditions.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
REFERENCES:
patent: 3954727 (1976-05-01), Toshkov et al.
patent: 4645541 (1987-02-01), DeLong
patent: 4728367 (1988-03-01), Huber et al.
patent: 4908099 (1990-03-01), DeLong
patent: 5106888 (1992-04-01), Kosinski
patent: 5879463 (1999-03-01), Proencal
Biby Gerald
Hanna Milford
Miladinov Vesselin
Halpern Mark
Shook Hardy & Bacon LLP
Silverman Stanley S.
University of Nebraska-Lincoln
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