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Effect of Acid Leaching of Bamboo and Hardwood Chips on Kraft Pulping and Pulp Bleaching

M. Sarwar Jahan
Pulp and Paper Research Division, BCSIR Laboratories, Dhaka, Dr. Qudrat-i-Khuda Road

S. Islam
Department of Applied Chemistry and Chemical Engineering, University of Dhaka, Dhaka- 1000

M. Moniruzzaman
Soil & Environment Research Division, BCSIR Laboratories, Dhaka, Dr. Qudrat-i-Khuda Road

M. A. Quaiyyum
Department of Applied Chemistry and Chemical Engineering, University of Dhaka, Dhaka- 1000

Abstract/ Executive Summary:

Acid leaching of chips prior to pulping is a proven method to reduce non-process elements in kraft pulping process. In this paper, acid leaching of bamboo and hardwood chips was carried out at pH 2 for 1h at 80°C prior to kraft pulping. Calcium removal in acid leaching from wood chips was 52.6% while for bamboo was only 17.4%. Acid leaching also reduced potassium (K) from 1258 mg/kg to 495.7 mg/kg for bamboo and 928 mg/kg to 562.5 mg/kg for wood chips. The effects of acid leaching on pulping, pulp bleaching, and papermaking characteristics were also determined. Acid leaching of both kinds of chips prior to kraft cooking resulted in a significant increase in the rate of delignification. Acid leached chips showed higher screen pulp yield and lower rejects at any kappa number. There was no significant difference of papermaking properties between pulps obtained from acid leached and non-leached chips. Using same ClO₂ charge, acid leaching improved pulp brightness by 1% and 1.1% for hardwood and bamboo, respectively. Acid leaching improved pulp viscosity from 10.1 mP.s to 12.1 mP.s for hardwood.

Keywords: Bamboo, Hardwood chips; Acid leaching; Pulp yield; Pulp bleaching

Location: Pulp and Paper Research Division, BCSIR Laboratories, Dhaka, Dr. Qudrat-i-Khuda Road

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Bamboo, Wood

Objectives:

In this study acid leaching of industrial chips of bamboo and mixed hardwoods was carried out with acidic water. The main objectives were to determine the impact of acid leaching on the kraft pulping and bleaching.

Methodology:

Raw materials Bamboo and mixed hardwood chips were collected from the KPM for acid leaching and subsequent pulping experiment. Acid leaching The acid leaching experiment of bamboo and mixed hardwood chips was carried out separately by acidic water in polyethylene bag. The chips (250g od basis) were treated with sulfuric acid-water under the following conditions: 1:10 material to liquor ratio, 80°C, 60 min and pH 2.0. After acid leaching, the liquor was collected for NPEs determination and chips were washed with distilled water. Pulping Acid leached and non-leached bamboo and mixed hardwood chips were used for subsequent pulping experiment. Pulping was carried out by kraft process in a thermostatically controlled electrically heated digester with capacity of 5 litres. Pulping conditions were as follows: -Active alkali was 16, 18 and 20 % on oven-dry (o.d) raw material as Na₂O -Cooking time was fixed for 2 h at maximum temperature (170 °C), with 90 min to raise maximum temperature (170 °C) from room temperature. -Liquor to material ratio was 4. -Sulphidity 25 % for kraft process. After digestion, pulp was washed until free from residual chemicals, and screened in a flat vibratory screener (Yasuda, Japan). The screened pulp yield, total pulp yield and screened reject were determined gravimetrically as percentage of o.d. raw material. The kappa number (T 236 om-99) of the resulting pulp was determined in accordance with Tappi Test Methods. Three replicates of all experiments were done and average reading was taken. Evaluation of pulps Pulps were beaten in a PFI mill to get drainage resistance (oSR) 25 and hand sheets of about 60 g/m² were made in a Rapid Kothen sheet making machine. The sheets were tested for tensile (T 494 om-96), burst (T 403 om-97) and tear strength (T 414 om-98) according to TAPPI Standard Test Methods. DEpD bleaching The acid leached and non-leached bamboo and mixed hardwood pulps were bleached by D0EpD1bleaching sequences (where D represents chlorine dioxide and Ep represents peroxide reinforced alkaline extraction). The ClO₂ charge was 2% and temperature was 70^oC for 45 min in the D0stage. The pH was adjusted to 2.5 by adding dilute H₂SO₄. Alkaline extraction was carried out with 2% NaOH and 0.5%, H₂O₂ charge, temperature was 70^oC for 120 min. In the D1stage, ClO₂ charge were 0.5, pH was adjusted to 4.5 by adding dilute alkali. The pulp consistency was 10% in all the stages. The brightness (T 452 om-92) and viscosity (T 230 om-99) of the bleached pulp were determined in accordance with Tappi Test Methods. NPEs determination NPEs were determined by atomic adsorption spectophotometer at the soil science laboratory of BCSIR Laboratories, Dhaka.

Source of Information: Bangladesh J. Sci. Ind. Res.51(4), 247-252, 2016

Article Link (Online Journal):

Funding Source:

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Total Budget (Tk.) :

Achievement/Findings:

Acid leaching of calcium is more difficult with bamboo chips compared to hardwood chips. Potassium, magnesium and manganese are leached similarly for both the chips. Acid leaching significantly improved delignification in subsequent kraft pulping. Acid leaching also reduced screening reject and slightly improved pulp yield. Improved pulp brightness and viscosity were observed on acid leached hardwood and bamboo chips. From the above results, it can be concluded that acid leaching of bamboo and hardwood chips prior to pulping is advantageous kraft pulping.

Knowledge Management: Journal