WO2001046517A1

WO2001046517A1 - Delignified corn grain fiber and methods of making and using

Info

Publication number: WO2001046517A1
Application number: PCT/US1999/030758
Authority: WO
Inventors: Manish M. Shah
Original assignee: Battelle Memorial Institute
Priority date: 1999-12-22
Filing date: 1999-12-22
Publication date: 2001-06-28
Also published as: AU2211900A

Abstract

The present invention is a corn grain fiber from which corn starch has been removed, having cellulose and hemicellulose, wherein the improvement is that the cellulose and hemicellulose are dissociated as a delignified corn grain fiber. A method of delignifying the corn grain fiber, has the steps of: (a) exposing the corn grain fiber to a liquid having water and oxidizer in a non-basic solution thereby delignifying the corn grain fiber into a delignified corn grain fiber; and (b) separating the delignified corn grain fiber from the liquid. The delignified corn grain fiber is useful for adding to cellulose in papermaking. The method of the present invention may be extended to add an enzyme to the delignified corn grain fiber for making cellulose derived compounds.

Description

DELIGNIFIED CORN GRAIN FIBER AND METHODS OF MAKING AND USING

FIELD OF THE INVENTION

The present invention is a corn grain fiber that has had the lignins removed. In addition, the method of removing the lignin and the methods of using the delignified corn grain fiber are part of the present invention. As used herein, the term grain refers to the kernels of the corn and does not include the stalk, leaves, cob or roots of the corn plant.

BACKGROUND OF THE INVENTION

Corn grain is the basis for many products including, for example corn starch. In the process of making corn starch, corn grain fiber is a waste material that is disposed of as landfill.

Thus, there is a need for a method of converting the waste corn grain fiber into a useful, higher value product.

SUMMARY OF THE INVENTION

The present invention is a corn grain fiber from which corn starch has been removed, having cellulose and hemicellulose, wherein the improvement is that the cellulose and hemicellulose are dissociated as a delignified corn grain fiber.

A method of delignifying the corn grain fiber, has the steps of:

(a) exposing the corn grain fiber to a liquid having water and oxidizer in a non-basic solution thereby delignifying the corn grain fiber into a delignified corn grain fiber; and

(b) separating the delignified corn grain fiber from the liquid. The delignified corn grain fiber is useful for adding to cellulose in papermaking. The method of the present invention may be extended to add an enzyme to the delignified corn grain fiber for making cellulose derived compounds.

The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a spectrograph of corn grain fiber.

FIG. 2 is a spectrograph of delignified corn grain fiber.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention is a corn grain fiber from which corn starch has been removed, having cellulose and hemicellulose, wherein the improvement is that the cellulose and hemicellulose are dissociated as a delignified corn grain fiber. The delignified corn grain fiber has a molecular weight distribution of about 400 to about 450 kDalton and may be characterized as having a lignin concentration less than a detectable limit of an NMR spectrometer. In addition, the delignified corn grain fiber is soluble in a carbohydrate dissolving solvent, for example DMA (di-methyl acetamide). Conversely, corn grain fiber is insoluble because the cellulose and hemicellulose is attached or associated by the lignin. Hence, corn grain fiber has characteristics of much higher molecular weight that does not go into solution so that a molecular weight range is not quantifiable.

A method of delignifying the corn grain fiber begins with exposing the corn grain fiber to a liquid having water and oxidizer in a non-basic solution thereby delignifying the corn grain fiber into a delignified corn grain fiber. The oxidizer is a strong chemical oxidizer including but not limited to sodium chlorite, ozone, superoxide (0₂ ^~ ), hydrogen peroxide (H₂O₂), hydroxyl radical (HO ), perchlorate, potassium superoxide and combinations thereof. The oxidizer may be provided as an added chemical or may be provided by generating it in solution. Superoxides and/or hydroxyls are found in solutions of cations with oxygenated anions including but not limited to O₂, HO, CO, NO, SO, SO₂, S₂O₅, SeO, SeO₂, CrO₂, U0₂, Np0₂, N0₂, PO, VO, Pu0₂, CIO, CI0₂, CI0₃, and combinations thereof. Alternatively, the superoxide may be generated in an electrochemical process including but not limited to, gas plasma, corona discharge and combinations thereof. A non-basic solution is a solution with a pH less than 9.0. It is preferred that the solution be about neutral or acidic. Preferred pH may be achieved by addition of an acid, preferably a mild acid, for example glacial acetic acid.

When a chlorinated oxidizer is used, it is preferred to provide a sweep gas to remove any chlorinated off gas. When ozone is used, a sweep gas is not needed.

The delignification reaction may foam. Such foaming may be reduced by addition of an anti-foaming compound, for example octyl alcohol.

The delignification reaction may be carried out at any temperature, but reaction kinetics are improved with increasing temperature. Accordingly, it is preferred to perform the reaction at temperatures above room temperature. At temperatures from about 40 °C to about 75 °C, reaction time is less than 1 hour, generally about 5 minutes. Reactions may be done at higher temperature, but because the mixture is aqueous, pressure containment is needed to preserve a liquid or supercritical phase. Temperatures below 100 °C are preferred to avoid the need for pressurized equipment.

To be useful, the delignified corn grain fiber is separated from the liquid. The separated delignified corn grain fiber may further be washed with water. Removal of water may be with acetone and drying.

The delignified corn grain fiber is useful for adding to cellulose in papermaking.

The method of the present invention may be extended to add an enzyme, for example cellulase, hemicellulase for example xylanase, arabinase and combinations thereof to the delignified corn grain fiber for making cellulose and/or hemicellulose derivatives, including but not limited to glucose, xylose, arabinose, polyols, cellulose acetate, cellulose ether and combinations thereof. Cellulose based products include but are not limited to paper.

Example 1

An experiment was conducted to demonstrate delignification of corn grain fiber. Waste corn grain fiber from a cornstarch processing plant was obtained. An amount of 5 g of the corn grain fiber was mixed with 120 mL of water for a ratio of 24 mL water per g corn grain fiber. The mixture was heated to 75 °C. An amount of 0.42 mL of glacial acetic acid was added to reduce the pH. An amount of 1.25 g sodium chlorite was gradually added. After 15 minutes the same quantities were added again and repeated for a total of 4 additions having 20 g corn grain fiber. Nitrogen gas N₂ was used as a sweep gas to displace CI0₂ reaction gas. Foaming was reduced by addition of 1 -2 drops octyl alcohol. After one hour, the reacted 20 g of corn grain fiber was rapidly cooled to 20 °C in an ice bath. The products were filtered to separate the delignified corn grain fiber from the liquid. The delignified corn grain fiber was washed with water to remove remaining acid, washed with acetone, then dried. A sample of corn grain fiber and a sample of delignified corn grain fiber were scanned from 250 nm to 650 nm on a spectrophotometer. Results are shown in FIG.'s 1 and 2. Results show that cellulose and hemicellulose peaks 100 are not altered but peaks 102 representing lignin component are absent in the 130 to 160 ppm region 104 after the treatment (FIG. 2). This suggests that the method is selective in removing lignin and conditions are mild and safe to use. These conditions are much better than those used in wood delignification which require extensive alkaline and sulfite treatments during delignification.

Example 2 An experiment was conducted to demonstrate conversion of delignified corn grain fiber to glucose. A buffered mixture was prepared having a ratio of 5 wt% delignified corn grain fiber to buffer. The buffer was selected to be compatible with the enzyme. The buffer was sodium acetate in an amount resulting in a pH of 5. The cellulase enzyme was added and permitted to act on the delignified corn grain fiber. A control containing no enzyme was identically prepared. Glucose was measured with a glucose enzyme kit.

Results are shown in Table E2-1. Table E2-1 Delignified Corn Grain Fiber Conversion to Glucose

Cellulase enzyme activity assay was performed showing one cellulase unit will produce 1 μmole/hr of glucose from a delignified corn grain fiber at pH 5.0 and 37 °C. Enzyme activity indicates the presence of glucose as a product. The control with no enzyme produced 0.0 units/mL enzyme activity.

CLOSURE

While a preferred embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

We claim: 1. A corn grain fiber from which corn starch has been removed, having cellulose and hemicellulose, wherein the improvement comprises: said cellulose and hemicellulose are dissociated as a delignified corn grain fiber having a molecular weight distribution of about 400 to about 450 kDalton.

2. The corn grain fiber as recited in claim 1 , wherein said delignified corn grain fiber has a lignin concentration less than a detectable limit of an NMR spectrometer.

3. The corn grain fiber as recited in claim 1 , wherein said delignified corn grain fiber is soluble in a carbohydrate dissolving solvent.

4. A method of delignifying a corn grain fiber, comprising the steps of:

(b) separating the delignified corn grain fiber from the liquid.

5. The method as recited in claim 4, wherein is said liquid has a pH less than 9.

6. The method as recited in claim 5, wherein the pH is about neutral or acidic.

7. The method as recited in claim 4, wherein the oxidizer is selected from the group consisting of sodium chlorite, ozone, superoxide, hydrogen peroxide, hydroxyl radical, perchlorate, potassium superoxide and combinations thereof.

8. The method as recited in claim 4, wherein the oxidizer is selected from the group consisting of 0₂, HO, CO, NO, SO, S0₂, S₂O₅, SeO, Se0₂, Cr0₂, UO₂, Np0₂, N0₂, PO, VO, PuO₂, CIO, CI0₂, CI0₃, and combinations thereof.

9. The method as recited in claim 4, further comprising the steps of:

(a) preparing a mixture of said separated delignified corn grain fiber with a buffer;

(b) adding a cellulase enzyme and obtaining glucose.

10. The method as recited in claim 4, further comprising the step of: adding the separated delingnified corn grain fiber to a fiber stream in a paper mill.

1 1. The method as recited in claim 4, wherein said oxidizer is obtained by generating the oxidizer in an electrochemical process.

12. The method as recited in claim 1 1 , wherein said electrochemical process is selected from the group consisting of gas plasma, corona discharge and combinations thereof.