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
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 OH OCH 3 Oxidative Bleaching Agent HO 2 C CH 3 O OxA Ox. Agent CO 2 H OxA Slow Hydrolysis
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 D 0 effluents contained approx. 20 mg OxA/L Heat treatment of HW D 0 effluents increased [OxA] by 5-30%
Oxalic Acid Generation Post-Do Do (kf:0.25) effluent from an OD SW kraft pulp Reaction Time/h Initial ph 2.6(70 o C) Initial ph 11.5(70 o C) Initial ph 2.6(90 o C) 0 1 2 5 27 47 54 55 27 33 34 61 27 59 -- 61 [OxA] in effluents (mg/l)
Oxalic Acid Research Goals Measure the amounts of oxalic acid in commercial SW D 0 -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 D 0 -stage.
Oxalic Acid Results: Commercial D 0 Effluents Experimental Protocol Commercial samples acquired. Bleach effluent samples were heated to 70 o C for extended time period. Aliquots were removed and analyzed for oxalic acid content.
Oxalic Acid Results: Commercial D o Effluents [OxA mg/l] 80 70 60 50 40 30 20 10 Initial 5 h at 75C 1. SW 2. SW 3a. HW 3b. SW 4. SW 5. HW Increase in OxA is in the range of 10-30%.
Oxalic Acid Results: Laboratory Studies Goal: Determine the influence of pulping and bleaching conditions on OxA formation.
xalic Acid Results: Laboratory Studies Experimental Protocol Bleach series of SW kraft pulps with 0.1, 0.15, 0.20 kf ClO 2. 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
Oxalic Acid Results: [OxA] in D 0 Effluents from SW Conventional Kraft Pulp 25 20 [OXa mg/l] 15 10 5 kf 0.10 kf 0.15 kf 0.20 0 CK 31.9 CK 25.1 CK 22.4 2-fold increase in D-charge increases OxA by ca 2.8
xalic Acid Results: OxA] in D 0 Effluents from Extended Modified SW raft Pulp 25 20 [OXa mg/l] 15 10 5 kf 0.10 kf 0.15 kf 0.20 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
Oxalic Acid Results: Heat Treatment of CK31.9 D 0 Effluent 35 Heat treatment of CK 31.9 D o effluent at 70 o C [OXa mg/l] 30 25 20 15 10 kf 0.10 kf 0.15 kf 0.20 5 0 CK 31.9 0.5 h (70C) 1.0 h (70C) 2.0 h (70C)
Oxalic Acid Results: Heat Treatment of CK D 0 Effluents 35 30 Results from heat treatment of D o (0.20 kf) effluent from SW CK 31.9, 25.1, and 22.4. [OXa mg/l] 25 20 15 10 5 0 CK 31.9 CK 25.1 CK 22.4 kf 0.20 70 C 1 h
Oxalic Acid Results Results: Heat Treatment of EK D 0 Effluents Results from heat treatment of D o (0.20 kf) effluent from SW EK 29.1, 23.2, 19.4, and 17.0 [OXa mg/l] 35 30 25 20 15 10 5 kf 0.20 initial 1 h 70C 0 EK 29.1 EK 23.2 EK 19.4 EK 17.0
Oxalic Acid Results: Heat Treatment EK D 0 Effluents Results from heat treating D o (0.15 kf) effluent from SW EK 29.1, 23.2, 19.4, and 17.0. [OXa mg/l] 20 18 16 14 12 10 8 6 4 2 0 kf 0.15 initial 1 h 70C EK 29.1 EK 23.2 EK 19.4 EK 17.0
Oxalic Acid Conclusion Factors contributing to OxA OxA generation is sensitive to D 0 kf OxA generation is sensitive to starting pulp kappa # Heat generation of OxA higher pulp kappa # and D 0 kf favors oxalic acid generation
OxA Research: Value & Direction Any mill modeling of OxA-scale formation needs to take into account direct and indirect OxA formation chemistry Bench marked OxA in several member mills Generation of OxA through bleaching mill Affinity of OxA for fibers Control of OxA in bleached fiber line develop new chemistry to control OxA >>Yield process and product improvements