Method for isolating alpha cellulose from lignocellulosic materials
The present invention involves an environmentally friendly process and apparatus for the delignification of lignin-containing materials, such as cardboard newspaper or agricultural or tree pruning wastes. This process produces cellulose using low temperatures and low concentrations of hydrogen peroxide. It can be performed using a column fitted with a semipermeable gasket that pressurizes the column by retaining oxygen released by action of the hydrogen peroxide on a lignin-containing material.
1. A method for delignification of a ligno-cellulosic material comprising:
blending a ligno-cellulosic material comprising cellulose and lignin with water to form an aqueous liquor,
contacting the aqueous liquor with hydrogen peroxide under non-alkaline conditions in a reaction column, wherein oxygen generated during said contacting increases internal pressure relative to ambient atmospheric pressure, or increases partial internal O2 pressure relative to ambient partial O2 pressure during said contacting,
removing dissolved lignin, and
recovering cellulose;
wherein a top of the column is closed to atmospheric pressure by a gasket, which gasket retains sufficient oxygen in the column to maintain a higher than atmospheric pressure in the column during said contacting; and
wherein the gasket comprises a fiber plug or membrane which fits over an open top of the reaction column and prevents escape of sufficient oxygen molecules and oxygen radicals produced by said hydrogen peroxide treatment to enhance efficiency of delinification compared to an otherwise identical method that does not comprise the gasket.
2. The method of claim 1 , wherein the ligno-cellulosic material is paper.
3. The method of claim 1 , wherein the ligno-cellulosic material is cardboard.
4. The method of claim 1 , wherein said contacting occurs in the absence of NaOH or aqueous ammonia.
5. The method of claim 1 , wherein said contacting occurs in the absence of chlorine dioxide; or in the absence of methanol, hydrochloric acid and sulfuric acid.
6. The method of claim 1 , further comprising contacting the ligno-cellulosic material with hydrochloric acid or another acid to remove calcium carbonate prior to contacting the aqueous liquor with hydrogen peroxide.
7. The method of claim 1 , wherein the aqueous liquor contains 0.5 to 5 wt % hydrogen peroxide at a liquid to solid ratio of 10:1 to 20:1.
8. The method of claim 1 , wherein the aqueous liquor contains 0.5 to 2 wt % hydrogen peroxide at a liquid to solid ratio of 10:1 to 20:1.
9. The method of claim 1 , wherein said oxygen increases the pressure at which said contacting occurs at least 5% above ambient atmospheric pressure.
10. The method of claim 1 , wherein said contacting occurs at a temperature ranging from 20 to 100° C.
11. The method of claim 1 , wherein said contacting occurs at a temperature ranging from 60 to 80° C.
12. The method of claim 1 , wherein said gasket comprises compressed cotton.
13. The method of claim 1 , wherein the gasket comprises a woven or nonwoven fiber.
14. The method of claim 1 , further comprising repeating the contacting under non-alkaline conditions, removing and/or recovering steps at least once, wherein repeating comprises removing a part of the aqueous liquor containing dissolved lignin and replacing it with a fresh solution containing hydrogen peroxide.
15. The method of claim 1 , wherein said contacting occurs at a pressure of at least 15 psia.
16. The method of claim 1 , wherein said contacting occurs at a pressure of at least 20 psia.