Environmental Friendly Bleaching of Eucalyptus tereticornis

Bhawana Bisht Kweera¹, Sanjay Naithani ²

¹Assistant Professor, Graphic Era University, Dehradun,

²Scientist, Forest Research Institute, Dehradun

ABSTRACT:

In this present paper a study has been carried out to develop an approach of minimum impact on environment during pulping and bleaching of Eucalyptus tereticornis. A new chemical additive (LpH) was used during pulping followed by single stage oxygen delignification and H-H-P sequence produced a pulp of higher pulp-yield, low kappa number, high brightness and better strength properties. In comparison to traditional modified cooking for lowering lignin content in pulp which are capital intensive additive pulping using a new chemical additive was preferred as a low cost alternatives. Among the addition of various doses of chemical additive the best results were obtained at 0.5% chemical additive dose .So the optimized condition for additive dose addition was 0.5%. In adopting bleaching sequence, OHHP sequence gave better strength properties, brightness in comparison to CEH sequence.

KEYWORDS: Extended delignification, Chemical additive (LpH), Kappa number, Chelating agent

INTRODUCTION:

Today environmental has become an important aspect and concerned efforts are going on throughout the world wide to improve the environment by reduced pollution. It has become a matter of importance whether to reduce the pollution at source or at the end of the pipeline. Intensive efforts are needed to reduce the pollution at source rather than going for treatment of the effluents. In fact Environment protection Agency of USA has issued in November,93 a proposed series of regulations to Clean Air Act and the clean water act that will necessitate use of Best Available Technology is either extended delignification or oxygen delignification and ClO₂ bleaching (1). Now a days in many developed countries the conventional bleaching sequence CEHH is replaced by chlorine dioxide partly or wholly in most of the pulp and paper mills(2).Other routes followed in developed countries are extended delignification before bleaching (i.e. cooking to lower kappa numbers) or oxygen bleaching.

The combination of delignification by chemical additive and extended delignification by oxygen bleaching played an important role in reducing chemical consumption in bleach plant, because this process makes it possible to reduce the kappa number of the pulp going into the bleach-plant by up to 50% (3). Such a reduction in kappa number will result in a reduction of the bleach plant effluent load by about 50% measured as COD, BOD, color and chlorinated compounds. The consumption of bleaching chemicals to reach certain brightness is related to the kappa number of the pulp entering the bleach plant. An oxygen delignification stage before bleaching will reduce the kappa number and thereby drastically decrease the required amount of bleaching chemicals. Oxygen delignification can reduce (4)color by 70-90%, BOD by 81% and COD by 67%.

As reported earlier by the author the new chemical additive explored, gave higher pulp yield, low kappa number, higher strength properties and higher brightness pulp when unbleached pulp was subjected to conventional CEH bleaching sequence (5). Further the bleaching studies were extended to OHHP bleaching sequence and its advantage on kappa number, pulp-yield, strength-properties and brightness of the pulp are discussed in the present paper.

EXPERIMENTAL:

Eucalyptus tereticornis (300gm O.D) chips were cooked by kraft process using chemical additive (LpH) under following conditions:

Total active alkali = 14%, Sulfidity = 20%, Raw material to liquor ratio = 1:3.5, Temperature of cooking = 170 ⁰C, Temperature at 170 ⁰C = 90 minutes, Chemical additive (LpH) dose = 0.2%. 0.5 %, 1.0 %, 1.5 %. The pulps were washed in a vibratory screener. The total unbleached pulp-yield was determined as usual.

Kappa number – The kappa number of pulps was determined as per Tappi method.

Bleaching- Eucaplytus tereticornis unbleached chemical pulps were bleached adopting OHHP sequence. Oxygen pre-treatment was carried out at optimized conditions; oxygen pressure, 6.0kg/cm ², treatment temperature 100⁰C, time 30 minutes and alkali charge 2.5% and hypochlorite treatment was carried out at 42 ± 2 ⁰C at 8% consistency for 2 hour. pH was maintained 10- 10.5 throughout the hypochlorite stage. As pH drops below 10, the viscosity starts to decrease sharply, if pH is too high (>11), the brightening reaction is retarded. H₂O₂ treatment was carried out at 80±2⁰C and consistency for 1 hour. MgSO₄ and sodium salt of ethylene diamine tetraacetic acid was added as chelating agent and sodium silicate as buffering chemicals. The bleached pulp yield was determined.

Pulp Evaluation: These bleached pulps were beaten; in PFI mill to a freeness level around 250 ml. standard sheet of 60± gsm were prepared. Strength properties of pulp sheets were determined as per ISO methods.

Brightness: Brightness of pulp pad was determined using Elerepho 2000 data color Brightness tester.

RESULT AND DISCUSSION:

Pulp yield and Kappa number of unbleached pulp:

Pulp yield and Kappa number results from kraft pulping with and without addition of additive are presented in Fig: 1. It was observe that pulping with chemical additive increases the pulp-yield and lowers the kappa number of the pulp in comparison to pulp which was obtained without addition of chemical additive during pulping. Addition of chemical additive 0.2 to 1.5% registered 1.1-3.3% pulp-yield (on control pulp-yield) advantage over the conventional Kraft (control) under identical pulping condition. As apparent from the Fig.1 that addition of 0.5% -of chemical additive (LpH) provided maximum pulp-yield (3.3%) improvement. There was no increase in pulp-yield at 1.0 to 1.5% addition of chemical additive.

To assess the effectiveness of chemical additive kappa number of control sample pulp and pulp which was obtained by chemical additive pulping was determined and it was found that under the same pulping condition the kappa number obtained with chemical additive addition is dropped from 21.23 to 19.00. The reduction of kappa number with higher pulp-yield in comparison to control may be due to stabilization of polysaccharides and disintegration of beta-phenyl ether bond. It is understood that even 1% increase in pulp-yield will result in enormous saving of raw material and maximizing production keeping economics of the additive cost. Reduction in kappa number is an added advantage and will definitely economics bleaching inputs.

Brightness and Pulp Yield of Bleached Pulp:

For a preliminary comparative study on the bleachability of pulps (control and chemical additive pulp) OHHP sequence was employed. The results are depicted in the following Table: 1

From the table:1 it was observed that bleached pulp produced by cooking with chemical additive has 1 or 2 points higher brightness than that of the control pulp. The total chlorine demand was given on the basis of kappa number which was obtained after oxygen treatment. The addition of this chemical additive not only help in increasing the brightness of the pulp but also preserve pulp-yield and allow providing a selection a milder cooking condition. It is possible to obtain the duplicate advantage in the manner as above with the chemical additive addition. Brightness and pulp-yield increases on increasing the additive dose up to 0.5% but after increasing it, from 0.5% dose there was no further increase in brightness and pulp-yield as shown in Fig: 2.The result indicates that chemical additive results in production of bleachable grade pulp and lignin present in the pulp is easily accessible during bleaching treatment as compared to control.

Table: 1 Bleaching results of 16%T.A.A (OHHP sequence)

Parameters	Blank		0.2%	0.5%	1.0%	1.5%
Kappa no. of unbleached pulp	21.23		20.20	19.00	18.99	18.99
Kappa no. after oxygen treatment	14.97		14.00	13.00	13.00	13.00
Total chlorine demand*(H₁H₂) as available chlorine (%) Temp.45⁰C Time 2 hours, Cy 8%	2.25		2.10	1.95	1.95	1.95
Peroxide treatment (%) **	0.5		0.5	0.5	0.5	0.5
Brightness, ISO	67.00		68.99	70.00	70.01	70.00
Pulp yield (%) ***	90.12		90.45	91.00	91.00	91.00
Kappa No. x 0.15 * NaOH 2.5%, Na₂SiO₃ 3%, EDTA.2%, MgSO₄.05%, Consistency 8%, Time1 hour, Temp.80 ⁰C		** * Pulp Yield on O.D. Pulp basis

Strength Properties of Bleached Pulp:

Fig: 3 and 4 reflects the strength properties of bleached pulp in term of tensile, tear and burst index. It is observed that up to 0.5% chemical additive treatment improves the strength properties. In case of pulps obtained with chemical additive when bleached showed higher strength properties and brightness in comparison to control may be due to more solubilization of lignin and stabilization of polysaccharide even at higher pulp-yield.

CONCLUSION:

The use of this new chemical additive (LpH) during chemical pulping for improving the pulp-yield without impairment in strength properties and bleachability showed that in situ modification of degraded lignin during pulping too produce compounds akin to anthraquinone, is very effective in accelerating delignification and carbohydrate stabilization resulting in increases pulp-yield(5). In addition to above bleaching of pulp by OHHP sequence gives better results rather than conventional methods. Strength properties, brightness and pulp-yield were on higher side in the pulp which was bleached by OHHP sequence instead of conventional method CEHH (6). Further investigations on economics aspects of the process with TCF bleaching sequence are in progress.

REFERENCES:

1. Berry,H.K., International Paper Maker, February,1994.

2. Singh, R.P.,editor, The bleaching of pulp Tappi Press, 1979.

3. Fossum,G., Paper technology, March,1992.

4. Carpenter, W.L.M.C, Kean, W.T.Barger, H.P., and Gelman, I, 8th International Pulp bleaching Conference proceedings. CPPA, Montreal, 1973.

5. Naithani, Sanjay, and Singh, S.V., IPPTA , Vol.11, No.3 September (1999)

6. Naithani, Sanjay, Bhawana and Singh, S.V., IPPTA , Vol.13, No.1 March2001

Received on 16.06.2011

Modified on 15.07.2011

Accepted on 07.08.2011

Research J. Science and Tech. 3(5): Sept.-Oct. 2011: 292-294