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Effect of Spent Liquor Recirculation on Ns-aq Pulping of Jute

Dr. Samar Kanti Bose
Senior Research Officer
Pulp and paper Division, Bangladesh Forest Research Institute, P. O. Box 273, Chittagong-4000, Bangladesh.

Dr. A.F.M. Akhtaruzzaman
Divisional Officer
Pulp and paper Division, Bangladesh Forest Research Institute, P. O. Box 273, Chittagong-4000, Bangladesh.

Mr. Habibur Rahaman Khan
Research Assistant
Pulp and paper Division, Bangladesh Forest Research Institute, P. O. Box 273, Chittagong-4000, Bangladesh.

Abstract/ Executive Summary:

Neutral sulfite anthraquinone pulping produce kraft like pulp with a higher yield. This results in a spent liquor of low solids content. Re circulation of the pulping spent liquor substantially increases the solids content. As such, the fuel of the liquor is enhanced, resulting in reduced fuel cost in the evaporator section. However, the reuse of spent liquor for pulping retards delignification with a minor change in pulp yield and quality.

Keywords: Spent liquor, Neutral sulfite anthraquinone, Jute,Delignification, Physical properties.

Location: Pulp and paper Division, Bangladesh Forest Research Institute

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Jute

Objectives:

To study the effects of reusing spent liquor on the delignification of nonwood fiber and the strength development characteristics of the pulps.

Methodology:

Air-dried jute cuttings (bast fiber) from white B jute (Corcborus capsularies) were used as the fibrous raw material. The jute cuttings were mixed thoroughly to eliminate variability in the raw materials. Pulping: Pulping experiments were carried out with 250 g of jute on an o.d. basis in 2 L stainless steel autoclaves heated in a temperature controlled air bath. Analytical grades of Na₂SO₃, Na₂CO₃ and anthraquinone (AQ) were used. The following parameters were kept constant:

Liquor to fiber ratio 5:1
AQ dose 0.1% on OD jute
alkali ratio: 0.83
Temperature profile: ambient to 80°C in 30 min, 80°C to 173⁰C in 90 min
Cooking at maximum temperature (173°C): 180 min
Total alkali: 12-20% as NaOH on OD jute.

Five different doses of alkali (12, 14, 16,18 and 20%) were used to obtain different degrees of delignification. The spent liquors from these cooking’s were collected for subsequent pulping. Three series of cooks were done at each alkali dose in which the cooking liquor contained 25, 50 and 75% (v/v) spent liquor. The alkali doses were held constant after makeup with fresh chemicals. The pH of all the cooking liquors was measured at room temperature.Then, the autoclaves were cooled. The cooked materials were thoroughly washed and then disintegrated or mechanically refined. Then, defiberized pulps were screened and pressed to remove excess water and then stored.Analyses: The pulp yield, kappa number, sulfite consumption, and the pH and the solids content of the spent liquors were determined. The pulps were beaten to different freeness values in a PFI Mill. The paper making properties of the hand sheets made from the pulps were evaluated using SCAN standard methods after conditioning the sheets at 50 ±2% relative humidity and 23 ±1°C temperature.

Source of Information: Tappi Journal 82(5): 148-151 (1999).

Article Link (Online Journal):

Funding Source:

1. Government

Budget: 00

Total Budget (Tk.) : 00

Achievement/Findings:

An increased re circulation on spent liquor leads to a higher kappa number with only a minor change in pulp yield. The change in lignin content was higher at a low alkali dose. At higher alkali doses, the kappa number still increased, but the increase was smaller than it was with lower alkali doses. Sulfite consumption decreased gradually at a lower alkali charge, and the trend was reversed with higher alkali. The spent liquors contained unused chemicals at both the lower and higher.

Knowledge Management: Journal