Yunqiao Pu, Arthur J. RagauskasDongho Kim

Institute of Paper Science and Technology, School of Chemistry and Biochemistry

Georgia Institute of Technology Atlanta, GA 30332

Improved Brownstock Quality Improved Brownstock Quality FY2007FY2007

TIP3 Year-end Project Review Meeting, Atlanta, GA August 8, 2007

Main Objectives:– Effect of carbon dioxide acidification washing for GA SW bleachable

grade: COD, carryover sodium, extractives, physical properties

– Effect of carbon dioxide acidification washing for GA SW kraft liner board: COD, carryover sodium, extractives, physical properties

– Effect of carbon dioxide acidification in combination with alcohol ethoxylates.

– Effect of carbon dioxide acidification on subsequent bleaching stage

Project Objectives and Key Questions

To evaluate the use of carbon dioxide acidification to improve pulp washing, reduce bleaching costs, and improve products performance for Georgia’s southern softwood resources.

Project Status - proposed vs. achieved

• Kraft SW brownstock to assess CO2 injection for improved washing – Done

• Kraft SW linerboard to assess CO2 injection for improved washing –Done

• Kraft SW brownstock to assess CO2 injection/ alcohol ethoxylates for improved washing – Done

• Kraft SW liner board to assess CO2 injection/ alcohol ethoxylates for improved washing - Done

• Evaluating improved D0(EO) bleaching – Done

• Evaluating physical properties of pulp and linerboard - Done

• Final report on FY 2007 project

Key Findings to-date• Depending on the different brownstock, carbon dioxide

acidification washing can reduce the carryover COD by 21%

• Carbon dioxide acidification washing can reduce the carryover sodium by 23%

• CO2 acidification washing can reduce extractives content by up to ~50%.

• The use of CO2 washing can improve drainage property

• After D(EO) bleaching, the CO2 washed pulp demonstrated slight improved physical/strength properties.

• After D(EO) bleaching, the CO2 washed pulp had lower AOX content by ~ 6.8% in the bleaching effluent.

Washing experimental

Laboratory Displacement Washer

• Employ 5 od gram sample

• pH3.7 CO2 solution (amount adjusted to obtain final pH 8.5), 2%CSC, DF- 2, 60oC, vacuum-7in.Hg• retention time 5~10 (1st displacement)-5~10 min (2nd displacement) -10min(3rd displacement)•Analyzed: Extractives, strength

properties, COD, Na

Linerboard pulp Filtrate pH Squeeze pH without CO2

Run #1 9.4 8.9 Run #2 9.3 8.7 Run #3 9.4 8.9

with CO2 Run #1 8.6 8.4 Run #2 8.7 8.4 Run #3 8.7 8.4

Brownstock without CO2

Run #1 8.6 8.4 Run #2 8.7 8.4 Run #3 8.8 8.5

with CO2 Run #1 8.4 8.2 Run #2 8.4 8.1 Run #3 8.4 8.1

Post-O2 without CO2

Run #1 8.8 8.5 Run #2 8.7 8.4 Run #3 8.7 8.5

with CO2 Run #1 8.6 8.3 Run #2 8.5 8.2 Run #3 8.6 8.3

pH value after washing

COD carryover in the washed pulp

0.02.0

4.06.0

8.010.0

12.0

w ithout CO2 w ith CO2

Linerboard pulpC

arry

over

CO

D(m

g/g

OD

Pu

lp)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

w ithout CO2 w ith CO2

Bleachable pulp

Car

ryov

er C

OD

(mg/

g O

D

Pulp

)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

w ithout CO2 w ith CO2

Post-O2 pulp

Car

ryov

er C

OD

(mg/

g O

D

Pulp

)

Laboratory Displacement Washer STDEV: 0.2~0.4

Metal ion content in washed pulp samples (mg/kg)

120527635820352035without CO2

122028232015601560with CO2

Post-O2 pulp

79530357347654765without CO2

85331255044754475with CO2

Linerboard pulp

100020256828302830without CO2

93019850623202320with CO2

Bleachable pulp

CaMgKNa

COD

21.312.720.3Before wash

Post O2 pulpBleachable pulpLinerboard pulp

washing conditions: 5g pulp, pH3.7 CO2 solution (amount adjusted to obtain final pH 8.5), 2%CSC, DF- 2, 60oC, vacuum-7in.Hg, retention time 5min-5min(1st displacement)-5min (2nd displacement) -10min(3rd displacement)

4.52.54.8with CO2 5.03.66.6without CO2

Post O2 pulp(Courtland)

Bleachable pulp(Cortland)

Linerboard pulp(Inland)

Effect of CO2 washing on TMP extractives content and strength properties.

0.920.11.3CO2 Washing

0.920.01.5Control Washing

0.818.82.4Original

Burst IndexkPa.m2/g

Tensile Index, Nm/gExtractives, %

Effect of CO2 washing on linerboard pulp extractives and strength properties.

19.125.348.90.4220.021CO2 washing

18.324.648.10.4170.041Control washing

STFI index(Nm/g)

Tear index(mN.m2/g)

Tensile indexNm/g

Density(g/cm3)

Extractives%

Drainage properties for linerboard pulp.

7189.12pH 8.5 pulp slurry adjusted by CO2 + 0.25% Alcohol ethoxylates

7268.86pH 8.5 pulp slurry adjusted by CO2

70710.94pH 11.5 pulp slurry + 0.25% Alcohol ethoxylates

71410.87pH11.5 pulp slurry - Control

CSF Freeness, mlTime to 700ml, sec

Initial extractive 4.45%

D(EO) bleaching

• Initial Kappa number of SW pulp (from InternationPaper, Augusta): with CO2- 27.3, without CO2 -27.5

• Bleaching conditions-- D: kf:0.2, 50oC, 3.5%CSC, 45min, Terminal pH-with CO2-2.07, without CO2-2.13, 10kg BLS/T pulp was added to the pulp slurry - EO: 90oC, 10% CSC, 60min, 3.6% NaOH, 35psi O2 for 15min-atmospheric for 45min, Terminal pH with CO2-11.9 without CO2-11.9; 10% of D stage filtrate was added to the pulp slurry

Extractives content for bleachable pulp

0.011Alcohol ethoxylate + CO2

0.010CO2 only

0.011Alcohol ethoxylate only

0.154Original

Extractives content (%)Bleachable

Effect of CO2 washing on D(EO) bleachingPulp properties after D(EO) bleaching sequence.

-25.750.52.9With CO2

-25.449.93.0Without CO2

with alcohol ethoxylates

2200026.451.12.9With CO2

2360026.250.23.1Without CO2

without alcohol ethoxylates

AOX(µg/L)

Viscosity(mPa.s)

TappiBrightness

Kappa number

0.2824.737.10.543with CO2

0.2624.136.40.538without CO2

with alcohol ethoxylates

0.2924.936.70.540with CO2

0.2724.236.40.539without CO2

without alcohol ethoxylates

Taber stiffness(mN m)

Tear index(mN.m2/g)

Tensile index(Nm/g)

Density(g/cm3)

Initial kappa #: with CO2 27.3; without CO2 27.5.

Relevance to Industry Needs – PotentialEconomic benefits

• The performance of many brownstock washers has been challenged as pulping capacity has been increased and mill closure technologies have been implemented.

• Improved brownstock washing is one of key processes which can reduce costs and improve final pulp properties.

• Important to know effects of CO2 acidification washing on Georgia’s southern SW pulp COD carryover, sodium carryover, extractives and drainage properties, as well as on the subsequent bleaching stage.

• The results of CO2 acidification washing provided mills with lower cost washing technology, lower bleaching cost and improved products performance.

• The improved brownstock quality with CO2 washing can be accomplished without additional modification to bleach plant equipment

AcknowledgementAcknowledgement