ENVIRONMENTALLY BENIGN TCF BLEACHING SEQUENCES FOR AS/AQ WHEAT STRAW PULP

• US 20110114273A1
• Filed: 11/17/2009
• Published: 05/19/2011
• Est. Priority Date: 11/17/2009
• Status: Active Grant

• Current Assignee: Bushra Mateen, Ishtiaq-Ur-Rehman, Kausar Jamal Cheema, Naila Yaqoob, Sahibzada Rashad Hameed
• Original Assignee: Bushra Mateen, Ishtiaq-Ur-Rehman, Kausar Jamal Cheema, Naila Yaqoob, Sahibzada Rashad Hameed
• Inventors: Cheema, Kausar Jamal, Yaqoob, Naila, Mateen, Bushra, Ishtiaq-Ur-Rehman, Hameed, Sahibzada Rashad
• Granted Patent: US 8,080,129 B2
• Time in Patent Office: Days
• US Class Current: 162/23
• CPC Class Codes: D21C 3/02 with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
• CPC Class Codes: D21C 3/222 Use of compounds accelerating the pulping processes
• CPC Class Codes: D21C 5/00 Other processes for obtaining cellulose, e.g. cooking cotton linters obtaining fibres for spinning D01C; Processes characterised by the choice of cellulose-containing starting materials
• CPC Class Codes: D21C 9/1089 with dithionites
• CPC Class Codes: D21C 9/147 with oxygen or its allotropic modifications D21C9/16 takes precedence

Abstract

This invention reports an environmentally benign method of delignifying bleaching sequences to gain more than 80% ISO brightness for alkaline sulfite-anthraquinone (AS/AQ) wheat straw pulp comprising of AOPsYP₀, AOPsEP₀ and AOPsP₀P₁ sequences that yielded surprising results in the field of pulp and paper technology; wherein the selectivity of sequences resulted in the protection of α-cellulose from degradation, produced significant drop in acid soluble lignin and yielded low viscosity losses reducing ecological impact of effluent load.

Claims

1. A method of delignifying bleaching of alkaline-sulphite anthraquinone (AS/AQ) wheat straw pulp labelled as AOPsYP₀ comprising the steps of:

(a) Mechanical pressing of pulp to consistency greater than 15%;

(b) Acidification (A) with 2.0% sulphuric acid on the oven dried pulp;

(c) First wash with distilled water until the pulp shows neutral pH;

(d) Mechanical pressing of pulp to consistency greater than 10%, preferably between 15% and 20%;

(e) Delignification by oxygenation (0) using pure oxygen feed at 70-75 psig pressure in a revolving closed loop digester;

(f) Second wash with distilled water until the pulp shows neutral pH;

(g) Mechanical pressing of the pulp to consistency greater than 10%, preferably between 15% and 20%;

(h) Extended delignification and bleaching with 5.0% oxone (Ps) concentration on the oven dried pulp;

(i) Third wash with distilled water until the pulp shows neutral pH;

(j) Mechanical pressing of pulp to consistency greater than 10%, preferably between 15% and 20%;

(k) Reductive bleaching step (Y) using 0.2% sodium dithionite on oven dried pulp;

(l) Fourth wash with distilled water until the pulp shows neutral pH;

(m) Mechanical pressing of pulp to consistency greater than 10%, preferably between 15% and 20%;

(n) Oxidative bleaching using 3.0% hydrogen peroxide (P₀) on the oven dried pulp;

(o) Fifth wash with distilled water until the pulp shows neutral pH.

4. The method in the claim 1, wherein said reductive bleaching step (Y) with dithionite is conducted at 70°

C. temperature.

5. The method in the claim 1, wherein said dithionite bleaching (Y) is conducted for 30 minutes.

6. The method in the claim 1, wherein said dithionite bleaching (Y) is carried out at 3.0% pulp consistency.

10. The method of claims 1, 2 and 3, wherein said AS/AQ wheat straw pulp is sieved through 0.15 mm slot screen to remove shives prior to start of said delignifying bleaching.

11. The method in the claims 1, 2 and 3, wherein said acidification is performed at ambient temperature ranging between about 25-35°

C.

12. The method in the claims 1, 2 and 3, wherein said acidification is conducted for a period ranging between 10-15 minutes.

13. The method in the claims 1, 2 and 3, wherein said acidification is conducted at 15% consistency.

14. The method in the claims 1, 2 and 3, wherein said delignification by oxygen (O) is performed at 100°

C.

15. The method in the claims 1, 2 and 3, wherein said oxygen delignification (0) is conducted for a period of 60 minutes.

16. The method in the claims 1, 2 and 3, wherein said oxygen delignification (0) is conducted at 10% consistency.

17. The method in the claims 1, 2 and 3, wherein said delignification by oxygen (O) is conducted in an alkaline medium comprising the addition of a first solution of 0.3% magnesium carbonate followed by a second solution of 2.0% sodium hydroxide on the basis of oven dried pulp weight.

18. The method in the claims 1, 2 and 3, wherein said extended delignification and bleaching (Ps) is conducted in the presence of 0.5% sodium hydroxide based on oven dried pulp.

19. The method in the claims 1, 2 and 3, wherein said extended delignification and bleaching stage (Ps) is conducted at 65°

C.

20. The method in the claims 1, 2 and 3, wherein said extended delignification and bleaching (Ps) is conducted for 30 minutes.

21. The method in the claims 1, 2 and 3, wherein said extended delignification and bleaching stage (Ps) is conducted at 10% consistency.

22. The method in the claims 1, 2 and 3, wherein said oxidative bleaching with hydrogen peroxide is carried out in presence of 1.5% sodium hydroxide and 0.1% concentration of a silicate-free hydrogen peroxide stabilizer on oven dried pulp.

23. The method in the claims 1, 2 and 3, wherein said oxidative bleaching with hydrogen peroxide is conducted at 90°

C.

24. The method in the claims 1, 2 and 3, wherein said oxidative bleaching with hydrogen peroxide is conducted for 60 minutes.

25. The method in the claims 1, 2 and 3, wherein said oxidative bleaching with hydrogen peroxide is conducted 10% consistency.

26. The method in the claims 1, 2 and 3, wherein said bleaching sequence yields a pulp with a brightness level of greater than 80% ISO and acid insoluble lignin of less than 2%.

2. A method of delignifying bleaching of alkaline-sulphite anthraquinone (AS/AQ) wheat straw pulp labelled as AOPsEP₀ comprising the steps of:

(a) Mechanical pressing of pulp to consistency greater than 15%;

(b) Acidification (A) with 2.0% sulphuric acid on the oven dried pulp;

(c) First wash with distilled water until the pulp shows neutral pH;

(d) Mechanical pressing of the pulp to consistency greater than 10%, preferably between 15% and 20%;

(e) Delignification by oxygenation (0) using pure oxygen feed at 70-75 psig pressure in a revolving closed loop digester;

(f) Second wash with distilled water until the pulp shows neutral pH;

(g) Mechanical pressing of the pulp to consistency greater than 10%, preferably between 15% and 20%;

(h) Extended delignification and bleaching with 5.0% oxone (Ps) concentration on the oven dried pulp;

(i) Third wash with distilled water until the pulp shows neutral pH;

(j) Mechanical pressing of the pulp to consistency greater than 6%;

(k) Conventional alkaline extraction (E) using 3.0% sodium hydroxide on the oven dried pulp;

(l) Fourth wash with distilled water until the pulp shows neutral pH;

(m) Mechanical pressing of the pulp to consistency greater than 10%, preferably between 15% and 20%;

(n) Oxidative bleaching using 3.0% hydrogen peroxide (P₀) on the oven dried pulp;

(o) Fifth wash with distilled water until the pulp shows neutral pH.

7. The method in claim 2, wherein said alkaline extraction (E) is conducted at 70°

C.

8. The method in claim 2, wherein said alkaline extraction (E) is conducted for 120 minutes.

9. The method in claim 2, wherein said alkaline extraction (E) is conducted at 10% consistency.

3. A method of delignifying bleaching of alkaline-sulphite anthraquinone (AS/AQ) wheat straw pulp labelled as AOPsP₀P₁ comprising the steps of:

(a) Mechanical pressing of the pulp to consistency greater than 15%;

(b) Acidification (A) with 2.0% sulphuric acid on the oven dried pulp;

(c) First wash with distilled water until the pulp shows neutral pH;

(d) Mechanical pressing of the pulp to consistency greater than 10%, preferably between 15% and 20%;

(e) Delignification by oxygenation (0) using pure oxygen feed at 70-75 psig pressure in a revolving closed loop digester;

(f) Second wash with distilled water until the pulp shows neutral pH;

(g) Mechanical pressing of the pulp to consistency greater than 10%, preferably between 15% and 20%;

(h) Extended delignification and bleaching with 5.0% oxone (Ps) concentration on the oven dried pulp;

(i) Third wash with distilled water until the pulp shows neutral pH;

(j) Mechanical pressing of the pulp to consistency greater than 10%, preferably between 15% and 20%;

(k) Oxidative bleaching using 3.0% hydrogen peroxide (P₀) on the oven dried pulp;

(l) Fourth wash with distilled water until the pulp shows neutral pH;

(m) Mechanical pressing of the pulp to consistency greater than 10%, preferably between 15% and 20%;

(n) Oxidative bleaching using 2.0% hydrogen peroxide (P₁) on the oven dried pulp;

(o) Fifth wash with distilled water until pulp shows neutral pH.