Oxalic Acid Process Chemistry ECF Bleaching - Generation
Art J. Ragauskas Institute of Paper Science and Technology Georgia Institute of Technology Oxalic Acid: Introduction
Oxalic Acid (Oxa) impacts operations and products – Ca:OxA scale formation impacts performance of bleaching equipment – Influences reduced water usage practices – Ca:OxA deposits have been noted on paper machine
[email protected] Oxalic Acid: Source
Wood: Bark/ (kg/ton) Wood (kg/ton) HW 9 –15 0.1 – 0.3 SW 4 -10 0.1 – 0.4 Pulp Lignin Oxidative Bleaching Agent Ox. Agent HO2C OxA OCH3 CO H CH3O 2 OH Slow Hydrolysis
OxA
[email protected] OxA Accomplishments
• Developed CIE analysis method to analyze OxA in bleach effluents • Demonstrated that [OxA] in bleach effluents can be increased upon heat treatment • OxA formation occurs under acidic and basic conditions
• Commercial HW D0 effluents contained approx. 20 mg OxA/L
• Heat treatment of HW D0 effluents increased [OxA] by 5 - 30%
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• Do (kf:0.25) effluent from an OD SW kraft pulp Reaction 0 1 2 5 Time/h
Initial pH 27 47 54 55 2.6(70oC)
Initial pH 27 33 34 61 11.5(70oC)
Initial pH 27 59 -- 61 2.6(90oC) [OxA] in effluents (mg/L)
[email protected] Oxalic Acid Research Goals
• Measure the amounts of oxalic acid in
commercial SW D0-stage effluents. • Determine the effect of temperature on post bleaching formation of oxalic acid. • Evaluate the effect of pulp kappa number on
oxalic acid formation from a D0-stage.
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Experimental Protocol
• Commercial samples acquired. • Bleach effluent samples were heated to 70oC for extended time period. • Aliquots were removed and analyzed for oxalic acid content.
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80 Initial 70 5 h at 75C 60 50 40
[OxA mg/L] [OxA 30 20 10 1. SW 2. SW 3a. HW 3b. SW 4. SW 5. HW
Increase in OxA is in the range of 10 - 30%.
[email protected] Oxalic Acid Results: Laboratory Studies
Goal: Determine the influence of pulping and bleaching conditions on OxA formation.
[email protected] Oxalic Acid Results: Laboratory Studies
Experimental Protocol Bleach series of SW kraft pulps with
0.1, 0.15, 0.20 kf ClO2.
Pulps Employed Conventional Extended Modified Continuous 31.9, 25.1, 22.4 29.1, 23.2, 19.4, 17.0
-all from the same tree
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[OxA] in D0 Effluents from SW Conventional Kraft Pulp 25
20
15 kf 0.10 kf 0.15 10 kf 0.20 [OXa mg/L] [OXa
5
0 CK 31.9 CK 25.1 CK 22.4 2-fold increase in D-charge increases OxA by ca 2.8
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[OxA] in D0 Effluents from Extended Modified SW Kraft Pulp
25
20
15 kf 0.10 kf 0.15 10 kf 0.20 [OXa mg/L] [OXa
5
0 EK 29.1 EK 23.2 EK 19.4 EK 17.0 2-fold increase in D-charge increases OxA by ca 2.7
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Heat Treatment of CK31.9 D0 Effluent
35 30 Heat treatment of 25 CK 31.9 Do o 20 effluent at 70 C kf 0.10 15 kf 0.15
[OXa mg/L] [OXa 10 kf 0.20 5 0 CK 31.9 0.5 h 1.0 h 2.0 h (70C) (70C) (70C)
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Heat Treatment of CK D0 Effluents
35 30 Results from 25 heat treatment 20 kf 0.20 of Do (0.20 kf) 15 70 C 1 h
effluent from mg/L] [OXa 10 SW CK 31.9, 25.1, and 22.4. 5 0 CK 31.9 CK 25.1 CK 22.4
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Heat Treatment of EK D0 Effluents
35 Results from 30 kf 0.20 initial 1 h 70C heat treatment 25 of D (0.20 kf) o 20 effluent from SW EK 29.1, 15 23.2, 19.4, and mg/L] [OXa 10 17.0 5 0 EK 29.1 EK 23.2 EK 19.4 EK 17.0
[email protected] Oxalic Acid Results: Heat Treatment EK D0 Effluents
20 18 kf 0.15 initial Results from heat 16 1 h 70C treating Do 14 (0.15 kf) 12 effluent from 10 8
SW EK 29.1, [OXa mg/L] 6 23.2, 19.4, and 4 17.0. 2 0 EK 29.1 EK 23.2 EK 19.4 EK 17.0
[email protected] Oxalic Acid Conclusion
• Factors contributing to OxA
– OxA generation is sensitive to D0 kf – OxA generation is sensitive to starting pulp kappa # • Heat generation of OxA
– higher pulp kappa # and D0 kf favors oxalic acid generation
[email protected] OxA Research: Value & Direction
• Any mill modeling of • Generation of OxA through OxA-scale formation bleaching mill needs to take into • Affinity of OxA for fibers account direct and • Control of OxA in bleached indirect OxA fiber line formation chemistry • develop new chemistry to • Bench marked OxA in control OxA several member mills >>Yield process and product improvements