Method of treating lignocellulosic biomass to produce cellulose

• US 6,419,788 B1
• Filed: 08/16/2000
• Issued: 07/16/2002
• Est. Priority Date: 08/16/2000
• Status: Expired due to Term

• Current Assignee: PureVision Technology, Inc.
• Original Assignee: PureVision Technology, Inc.
• Inventors: Wingerson, Richard C.
• Primary Examiner(s): Alvo, Steve
• Application Number:
  US09/640,815
• Time in Patent Office: 699 Days
• Field of Search: 162/26, 162/14, 162/19, 162/16, 162/18, 162/56, 162/63, 162/47, 162/78, 162/65, 162/67, 162/60, 127/1, 127/37, 127/29, 536/56, 536/57, 435/101, 530/500, 530/501, 530/502, 530/814, 426/635
• US Class Current: 162/14
• CPC Class Codes: D21C 1/02 with water or steam
• CPC Class Codes: D21C 3/02 with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
• CPC Class Codes: D21C 3/026 in presence of O2, e.g. air
• CPC Class Codes: D21C 3/028 in presence of O3
• CPC Class Codes: D21C 3/18 with halogens or halogen-generating compounds bleaching cellulose pulp D21C9/12
• CPC Class Codes: D21C 3/26 Multistage processes
• CPC Class Codes: Y02P 70/10 Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working

Abstract

A multi-function process is described for the separation of cellulose fibers from the other constituents of lignocellulosic biomass such as found in trees, grasses, agricultural waste, and waste paper with application in the preparation of feedstocks for use in the manufacture of paper, plastics, ethanol, and other chemicals. This process minimizes waste disposal problems since it uses only steam, water, and oxygen at elevated temperature in the range of 180° C. to 240° C. for 1 to 10 minutes plus a small amount of chemical reagents to maintain pH in the range 8 to 13. An energy recuperation function is important to the economic viability of the process.

Claims

1. A method of treating lignocellulosic biomass to produce purified cellulose containing less than 20% lignin, said method comprising the steps of:

providing a lignocellulosic feedstock having an average constituent thickness of at most 1″

;

introducing said feedstock into a pressure vessel having at least two reaction zones;

maintaining said feedstock in the pressure vessel for a residence time;

heating said feedstock in a first reaction zone to a temperature of from about 180°

C. to about 240°

C. to dissolve hemicellulose;

removing said dissolved hemicellulose from the heated feedstock

transferring said heated feedstock from said first reaction zone to a second reaction zone;

subjecting said transferring feedstock to a counterflow of hot wash water of pH of from about 8 pH to about 13 pH to create residual solids containing cellulose and a wash water containing dissolved materials; and

separating the residual solids containing purified cellulose from the filtered wash water, wherein said separated cellulose contains less than 20% lignin.

2. The method of treating lignocellulosic biomass according to claim 1 wherein the residence time of the solids in the pressure vessel is from 1 to 10 minutes and the average constituent thickness is at most ⅛

″

.

3. The method of treating lignocellulosic biomass according to claim 2 wherein the transferring step further includes the step of:

operating an auger at a predetermined rate.

4. The method of claim 3 further comprising the steps of:

operating the auger to perform at least one function selected from the group of functions consisting of kneading, stirring and compressing the transferring feedstock and thereby facilitating reaction processes.

5. The method of treating lignocellulosic biomass according to claim 1 wherein the method further comprises the steps of:

injecting water into the second reaction zone to rinse the residual solid containing cellulose to produce a rinsed cellulose product; and

discharging the rinsed cellulose product.

6. The method of treating lignocellulosic biomass according to claim 1 wherein the method further comprises the steps of:

adding an alkali reagent into at least one reaction zone to maintain the pH in the range of from 8 to 13.

7. The method of treating lignocellulosic biomass according to claim 6 wherein the alkali reagent includes lime.

8. The method of treating lignocellulosic biomass according to claim 1 wherein the method further comprises the step of:

adding an oxidizer to at least one reaction zone to decompose solid or dissolved material.

9. The method of treating lignocellulosic biomass according to claim 8 further comprising the step of:

adding to at least one reaction zone a chemical agent selected from the group consisting of hydrogen peroxide, oxygen, air, chlorine dioxide and ozone.

10. The method of treating lignocellulosic biomass according to claim 1 wherein the method further comprises the steps of:

filtering the wash water with a filtration means; and

cleaning and scouring the filtration means by operation of the transferring feedstock step to prevent clogging.

11. The method of treating lignocellulosic biomass according to claim 1 wherein the method further comprises the step of:

injecting steam for heating into at least one reaction zone to create temperature differences between the at least two reaction zones.

12. The method of treating lignocellulosic biomass according to claim 1 wherein the pressure vessel includes a plurality of ports for the injection and discharge of wash liquid and the method further comprises the step of:

selectively removing soluble components of the transferred feed stock.

13. The method of treating lignocellulosic biomass according to claim 1 wherein the method further comprises the step of:

preheating the feedstock with flash steam from the discharge of cellulose solids.

14. The method of treating lignocellulosic biomass according to claim 1 wherein the method further comprises the step of:

heating input wash water to operating temperature by steam injection.

15. The method of treating lignocellulosic biomass according to claim 14, further comprising the step of:

using a final flash steam condensate in a liquid-liquid heat exchanger for initial preheat of the fresh wash water.

16. The method of treating lignocellulosic biomass according to claim 1 wherein the method further comprises the steps of:

providing input wash water;

obtaining effluent wash water; and

preheating the input wash water by heat exchange from the effluent wash water.

17. The method of treating lignocellulosic biomass according to claim 16 wherein the method further comprises the step of:

incorporating a multistage heat exchange process with stepwise reduction of pressure from the pressurized reaction vessel to atmospheric pressure, each stage having the steps of;

(a) discharging pressurized wash water through a control nozzle into a flash tank;

(b) conveying flash steam from said flash tank to a heat exchanger;

(c) condensing said flash steam to release heat; and

(d) transferring said heat to preheat said input wash water.

18. The method of treating lignocellulosic biomass according to claim 17, wherein the multistage process includes at least 3 stages of pressure reduction.

19. The method of treating lignocellulosic biomass according to claim. 17, further comprising the steps of:

(a) measuring temperatures and pressures in flash tanks and heat exchangers to produce temperature and pressure data;

(b) processing temperature and pressure data to provide control signals; and

(c) actuating variable nozzles controlling liquid flow into flash tanks based upon the control signals.

20. The method of treating lignocellulosic biomass according to claim 16, further comprising the step of:

removing entrained, non-condensible gases from effluent wash water before the heat exchange step.

21. The method of treating lignocellulosic biomass according to claim 1 further comprising the steps of:

acidifying flash liquor from one or more flash tanks at elevated pressure and temperature; and

providing holdup time sufficient for hemicellulose oligomers to decompose to monomers.

22. The method of treating lignocellulosic biomass according to claim 20 wherein the acidifying step includes the step of:

employing pressurized carbon dioxide as an acidifying agent.

23. A method of treating lignocellulosic biomass containing lignin to produce purified cellulose, said method comprising:

providing a lignocellulosic feedstock;

introducing said feedstock into a pressure vessel having at least two reaction zones;

heating said feedstock in a first reaction zone to a temperature of from about 180°

C. to about 240°

C;

removing hydrolized hemicellulose from the heated feedstock;

transferring said heated feedstock from said first reaction zone to a second reaction zone;

.

subjecting said feedstock in said second zone to a counterflow of hot wash water containing dissolved oxygen and having a pH of at least 11 to produce residual solids containing cellulose and a wash water containing lignin and other extractives; and

separating the residual solids containing purified cellulose from the filtered wash water, wherein the separated cellulose contains less than 20% lignin.