Cellulase-assisted refining optimization for saving electrical energy demand and pulp quality evaluation

Transcription

1 Journal of Scientific & Industrial Research Vol 74, August 2015, pp Cellulase-assisted refining optimization for saving electrical energy demand and pulp quality evaluation R Singh 1, N K Bhardwaj 2 * and B Choudhury 3 1 Department of Paper Technology, Indian Institute of Technology Roorkee, Saharanpur Campus, Saharanpur , U.P., India *2 Avantha Centre for Industrial Research and Development, Yamuna Nagar , Haryana, India 3 Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee , U.K., India Received 9 September 2013; revised 15 July 2014; accepted 3 May 2015 Papermaking process necessitates fibers to be refined mechanically to develop greater bonding potential. This is achieved in refining step, which requires a huge energy demand. In the present paper, efficiency of biocatalysis was investigated for saving energy by taking different enzyme dosages, reaction times and conditions that were compatible for papermaking process. Bleached mixed hardwood pulp was taken as raw material along with cellulase as biocatalyst to get good quality paper as product. After the enzymatic pre-treatment, pulp was refined in PFI mill. Parameters were compared in terms of number of PFI revolutions required to achieve fixed level of Canadian standard freeness (CSF), ml without affecting the physical strength properties of paper. Action of cellulase on pulp was evaluated by reducing sugar analysis, pulp viscosity determination and amount of fines contents. This treatment achieved reduction in refining energy approx 29% (specific energy consumption reduced from 1.33 kwh/kg of pulp to 0.94 kwh/kg pulp) at an optimized dosage and time with improved pulp quality. Keywords: Cellulase, Enzyme biocatalysis, Optimization, Enzyme activity, Power consumption, Paper strength. Introduction Paper can be manufactured by taking a mixture of virgin or recycled pulps, known as stock or furnish, consisting of mainly cellulose, hemicelluloses and other chemical additives. In the papermaking process stock preparation is responsible to turn the fiber morphology to be suitable for desired paper properties 1. In paper mills this is achieved by the process of refining or beating. Generally, during refining fiber surface modifications occur due to (i) removal of outer primary layer (P1) and secondary layer (S1), by peeling mechanism, (ii) exposure of secondary cellulose rich wall (S2), (iii) swelling by hydration, (iv) increase of flexibility and change of shape from tubular to flat, thereby an increase of the fiber surface and specific volume, (v) decrease in length due to the cutting effect i.e. fiber shortening, (vi) internal fibrillation and (vii) external fibrillation 2.The ultimate problem in refining step is energy expenditure as it consumes up to 30% of the total electrical energy required by a paper mill. Thus, there is a need to decrease this energy demand. Enzymes are the biocatalysts which can offer Author for correspondence bhardwaj@avantharesearch.org potential advantages to paper industry like in biopulping 3, biobleaching 3,4, biodeinking 5 and effluent treatment 6, 7. Enzyme-assisted refining may result in a less energy requirement at mechanical operation stage 8-10 which is carried by valley beater or PFI mill in laboratories and conical or disc refiners in paper mill. Hence, energy conservation can be achieved. This can be beneficial to paper industry in terms of better paper quality with electrical energy savings. In the last few years, most of the research works in this area are mainly focused on mixtures or combinations of commercial cellulase, hemicellulase on softwood/ hardwood pulps from different origins 11. Our objective is to explore the refining for bleached mixed hardwood pulp of Indian origin by using a commercial enzyme composed of cellulase alone and its effect on pulp quality or paper strength properties and also to clarify the mechanism of enzymatic refining. Materials and Methods Pulp Bleached mixed hardwood pulp was provided by an integrated paper mill in north India. Enzyme A commercial enzyme Cell F composed of cellulase system was used in the present study. This

2 472 J SCI IND RES VOL 74 AUGUST 2015 enzyme was found to be active in the ph range of and temperature range of C. The enzyme was stored at 4 C. Optimization procedure Enzyme pre-treatment on pulps In order to match with industrial conditions, temperature was maintained at 45 C, initial ph was adjusted to 7.0 using a diluted H 2 SO 4 solution and pulp consistency was fixed to 5% for all the experiments. Five different cellulase dosages selected were 0.01, 0.03, 0.05, 0.07 and 0.09 IU/g oven-dry (o.d.) pulp for time duration 60, 90 and 120 min, respectively. Pre-treatment of pulps were carried out in plastic bags by keeping one variable fixed at a time. Pulp was pre-heated to reach the fixed temperature then cellulase dosage was added and mixed vigorously to ensure uniform distribution of enzyme before refining. This treatment was carried out in a thermostatic water bath for a particular reaction time. To terminate the reaction, pulps were submitted to boiling water for 10 min to make the enzyme inactive and after that finally washed thoroughly. Cellulase action on fiber Estimation of cellulase action was done by analyzing reducing sugar analysis, pulp viscosity determination and by amount of fines content. After the enzymatic treatment, the pulp was filtered in a Buchner funnel using a laboratory vacuum pump. The filtrate was recirculated to avoid loss of fines. Then the pulp was washed with water to remove the enzyme and prepared to perform refining studies. Control pulps were treated in a similar way except for the addition of enzyme. The reducing sugar released during enzymatic treatment from pulp was determined by using dinitrosalicylic acid method 12, fines (-200 screen) percentage by Tappi test method T 233 cm- 06 and viscosity determination before and after enzymatic treatment by ISO/FDIS mechanically without enzyme) and enzyme treated pulps (refined mechanically with enzyme) following the Tappi test method T 205 sp-02 and tested for physical properties as per Tappi test method T 220 sp-01. Tensile, tear, burst and double fold properties of paper were determined by Tappi test methods T 404 cm-92, T 414 om-98, T 403 om-97 and T 511 om-96 respectively. Testing was performed for all handsheets after conditioning at temperature 27 C and relative humidity 65%. All the experiments were carried out in triplicate and experimental results were represented as the mean±standard deviation at a confidence level of 95%. Results and Discussion Enzyme pre-treatment on pulp Optimization of enzyme dosage Energy consumption was strongly affected by increasing enzyme dosage. It decreased nearly by 50% (Fig. 1) at the expense of pulp/paper quality which got deteriorated (Table 1). Therefore, to achieve a decrease in energy requirement with enhanced tensile property, optimal dosage of cellulase was selected to be 0.07 IU/g o.d. pulp. Optimization of reaction time Optimal reaction time was found to be 90 min at an optimized enzyme dosage of 0.07 IU/g o.d. pulp. Further increase in reaction time resulted in decreased pulp/paper quality as shown in Table 1. For same enzyme dosage (0.07 IU) paper tensile property decreased by 17% with increase in reaction time from 60 to 120 min. This may be due to decrease in pulp viscosity 9. Effect on pulp and paper properties Energy requirement for pulp refining Laboratory beating of pulp by PFI mill was done to achieve freeness level of CSF ±10 ml as per Tappi test method T 248 sp-00 and freeness was measured by Tappi test method T 227 om-04. Strength properties The handsheets were prepared from unrefined and untreated pulps (without any mechanical and enzymatic treatment), control pulps (refined Fig.1- Graph showing energy reduction as a result of enzymatic refining at different enzyme dosages and reaction times

3 BHARDWAJ et al.: CELLULASE-ASSISTED REFINING OPTIMIZATION FOR SAVING ENERGY 473 Table 1- Enzymatic refining optimization, its effect on PFI revolutions and pulp/paper properties Reaction time (min) CSF (±10 ml) Enzyme dosage (I.U./g o.d. pulp) PFI revolution (no.) Tensile index (N.m/g) Tear index (mn.m 2 /g) Burst index (kpa.m 2 /g) Folding endurance (Log 10. no. of double folds) U1 (0) ± ± ± ±0.062 C1 (0) ± ± ± ±0.041 E1 (0.01) ± ± ± ±0.054 E2 (0.03) ± ± ± ±0.042 E3 (0.05) ± ± ± ±0.090 E4 (0.07) ± ± ± ±0.073 E5 (0.09) ± ± ± ± U2 (0) ± ± ± ±0.049 C2 (0) ± ± ± ±0.046 E6 (0.01) ± ± ± ±0.055 E7 (0.03) ± ± ± ±0.036 E8 (0.05) ± ± ± ±0.054 E9 (0.07) ± ± ± ±0.044 E10 (0.09) ± ± ± ± U3 (0) ± ± ± ±0.054 C3 (0) ± ± ± ±0.045 E11 (0.01) ± ± ± ±0.067 E12 (0.03) ± ± ± ±0.034 E13 (0.05) ± ± ± ±0.052 E14 (0.07) ± ± ± ±0.055 E15 (0.09) ± ± ± ±0.046 U1, U2, U3 represents unrefined/untreated pulps i.e. without any mechanical and enzyme treatment for 60, 90, and 120 min reaction time respectively. C1, C2, C3 represents control pulps (refined mechanically with no enzyme). E1 to E15 represents enzyme treated pulps (refined mechanically with enzyme pre-treatment). Cellulase action on fiber Cellulase hydrolyses β-1, 4 glycosidic linkages in cellulose chain. The components of cellulase system are exoglucanase, endoglucanase and β-glucosidase that act in a synergistic sequence of events. Exoglucanase cuts the bonds at the end of fiber by disruption in cellulose hydrogen bonding in crystalline region. Endoglucanase cause hydrolysis of the accessible cellulose in the amorphous region and β-glucosidase acts on cellobiose units to release glucose 13.Enzyme hydrolytic efficiency of cellulosic material is expressed mostly by the quantity of sugar released from the treated matter. It increased with increasing time and dosage as shown in Fig. 2. This is due to release of glucose and reducing units from cellulosic chain. Pulp viscosity, which reflects polymerization degree of cellulose, displayed a decrease of 14% from 435 ml/g to 376 ml/g at an optimized enzyme dosage of 0.07 IU/g o.d. pulp for 90 min reaction time. The probable reason behind this decrease in viscosity may be the action of endoglucanase. This component of enzyme is responsible for viscosity changes of cellulosic chain as reported earlier by other authors 9, 10. They also Fig. 2- Reducing sugar (mg/g) analysis of pulp by taking enzyme dosage and reaction time variables reported the same trend of decrease in viscosity with increase in reducing sugar content. In the present study it was observed that fines content increased from 14% to 17% at a lower enzyme dosage. This may be due to lamina removal, peeling action and exposure of inner wall layers on which enzyme acted.

4 474 J SCI IND RES VOL 74 AUGUST 2015 A slight decrease was also noticed at higher dosage, which may be because of selective removal of fines by enzymatic hydrolysis 5. Effect on pulp and paper properties Energy requirement for pulp refining For control pulps required CSF was achieved by consuming 1.33 kwh/kg of pulp (based on PFI mill revolutions). Significant energy savings was observed with enzyme pre-treatment in range of 20-30%. It was found to be decreased by 20% (1.06 kwh/kg consumed) at an enzyme dosage 0.05 IU/g o.d. pulp with reaction time 120 min. Energy reduction of 25% was observed (1.00 kwh/kg consumed) at 0.07 IU/g o.d. pulp for 60 min treatment and 29% (0.94 kwh/kg consumed) for 0.07 IU/g o.d. with 90 min reaction time. Y. Kamaya 14 in an earlier work reported that mainly the endoglucanase component play the key role in refining behavior.in general, enzymes are known to act as protein catalyst. They speed up a chemical reaction by lowering down the activation energy. They are specific for the reaction catalyzed and substrate acted on 15. The main difference in energy requirement in our opinion is due to pre-treatment of pulp with enzyme, which may result in lowering down the activation energy and thereby speeding up the rate of changes required for fiber modifications. The cellulase action was verified with results obtained from reducing sugars analysis, pulp viscosity determination and fines contents. Strength Properties The physical strength properties of paper affected strongly with refining. Tensile and burst indices of enzyme treated pulp handsheets were found to be higher; folding endurance was increased slightly while tear index was lowered than those of control pulps (Table 1).The most important paper strength property i.e. tensile index was improved by 21% at an optimized dosage of 0.07 IU/g o.d. pulp for 90 min reaction time. It was improved nearly by 15% for 60 min reaction time and decreased at a higher reaction time i.e. 120 min by 5% at same dosage. Although a little difference in this property was noticed at lower enzyme dosages. This seems to be important when considering the enzyme dosage/cost, reaction time and energy requirement to achieve a higher tensile index. For example an enzyme dosage of 0.05 IU/g o.d. pulp for reaction time 120 min was showing nearly same result for tensile index, as of 0.07 IU/g o.d. pulp for reaction time 90 min i.e. consuming more time and energy. Conclusion The results obtained in this study showed that enzymes could be used to reduce energy demand during pulp refining taking into consideration the pulp quality. Optimization of enzymatic refining was performed using commercial cellulase on bleached mixed hardwood pulp of Indian origin. Refining energy reduction of 29% was achieved after optimizing enzyme dosage and reaction time. It was found to be 0.07 IU/g o.d. pulp for 90 min reaction time. At this optimized enzyme dosage and reaction time, specific energy consumption for pulp refining was reduced from 1333 kwh/t of pulp to 944 kwh/t pulp. Strength properties, namely tensile index improved by 21% and burst index by 19%, tear index decreased by 10%. It is suggested that paper mills can be benefited economically by reducing energy requirement for refining by applying enzyme pre- treatment on pulp. With increasing power costs in recent times, this process seems to have potential for industrial application. Acknowledgements The authors gratefully thank the Director, Central Pulp and Paper Research Institute (CPPRI), Saharanpur for certain experiments. The first author thanks Ministry of Human Resource Development, Government of India for providing MHRD scholarship. References 1 Bhardwaj N K, Bajpai P & Bajpai P K, Use of enzymes in modification of fibers for improved beatability, J Biotechnol, 51(1996) Stevens W V, in Refining: stock preparation, 3 rd edn, vol VI, edited by R W Hagemeyer, D W Manson & M J Kocurek, Pulp and paper manufacture Joint text book committee of the paper industry publishing, Tappi, 3 (1992) Helmy Samia M & Magda El-Meligi, Biopulping and biobleaching by white rot fungi, J Sci Ind Res, 61 (2002) Choudhury B, Aggarwal P, Gothwal R K, Mantri R, Mohan M K & Ghosh P, Biobleaching of non-woody pulps using xylanase enzyme of Bacillus brevis BISR -062, Appl Biochem Biotechnol,128 (2006) Pathak P, Bhardwaj N K & Singh A K, Optimization of chemical and enzymatic deinking of photocopier waste paper, BioResources, 6 (2011) Singh P & Thakur I S, Removal of colour and detoxification of pulp and paper mill effluent by microorganisms in two step bioreactor, J Sci Ind Res, 63 (2004) Ramanan V Venkat & Thakur I S, Treatment of pulp and paper mill effluent by 4-chlorosalicylic acid-degrading microbial community for analysis of toxicity of seedlings, J Sci Ind Res,61(2002)

5 BHARDWAJ et al.: CELLULASE-ASSISTED REFINING OPTIMIZATION FOR SAVING ENERGY Bajpai P, Mishra S P, Mishra O P, Kumar S & Bajpai P K, Use of enzymes for reduction in refining energy laboratory studies, Tappi J, 5 (2006) Lecourt M, Meyer V, Sigoillot J C & Conil M P, Energy reduction of refining by cellulases, Holzforschung, 64 (2010) Gil N, Gil C, Amaral M E, Costa, A P & Duarte A P, Use of enzymes to improve the refining of a bleached Eucalyptus globulus kraft pulp, Biochem Eng J, 46 (2009) Singh R, Bhardwaj N K, Enzymatic refining of pulps: An overview, Ippta J, 22 (2010) Miller G L, Use of dinitrosalicylic acid for determination of reducing sugar, Anal Chem, 31(1959) Akhtar M & Young R A, Environmentally friendly technologies for the pulp and paper industry (John wiley and sons. publication, New York) 1997, Kamaya Y, Role of endoglucanase in enzymatic modification of bleached Kraft pulp, J Fermen Bioeng, 82 (1996) Presscott L M, Harley J P & Klein D A, Microbiology 6 th edn (Mc- Graw Hill Publications) 2005,