extraction of holocellulose from bagasse using delignifying … · 2016. 7. 31. · umair aslam at...

Umair Aslam at al., J.Chem.Soc.Pak., Vol. 36, No. 1, 2014

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Extraction of Holocellulose from Bagasse using Delignifying Agents: A Comparative Study

Umair Aslam*, Syed Hassan Javed, Mohsin Kazmi and Nadeem Feroze

Department of Chemical Engineering, University of Engineering and Technology Lahore-54890, Pakistan. [email protected]*

(Received on 21st February 2013, accepted in revised form 30th May 2013)

Summary: In the present investigation, extraction of holocellulose from bagassae has been performed. NaOH, Na2SO3 and combination of NaOH and Na2SO3 were three delignifying agents being used. Different experimental conditions including cooking time, cooking temperature and concentration of delignifying agent were observed. Bagasse was initially washed, dried, grinded and screened to 80 mesh. Then its cooking was carried out. The liquid to solid ratio was 5:1. The washed and dried product was then tested to find the Kappa No. according to the Technical Association for Pulp and Paper Industry (TAPPI) T-236 method. Combination of NaOH and Na2SO3 rendered the best result at 140 oC, 5 hr and 30/70 mixture composition. X-Ray Fluorescence Spectrometry (XRF) and Scanning Electron Microscopy (SEM) results also confirmed the breakage of lignin.

Key Words: Delignifying Agents, Holocellulose, Kappa No., SEM, TAPPI, XRF. Introduction

Plant, plant derived materials including livestock manures are specified as Biomass. Lignocellulosic biomass is the non-starch, fibrous part of plant material and is an attractive resource as it is renewable [1]. Structural and chemical compositions of Lignocellulosic biomass are highly variable because of environmental and genetic influences and their interactions [2]. In agricultural areas, biomasses are abundantly available. Large amount of these agriculture wastes is burnt to cope with energy demands. Some biomasses like bagasse are also used for power production in industries. Air pollution is a serious problem due to burning of these residues. Disposal of unburnt biomasses is also a crucial environmental issue. Therefore, the use of these agricultural wastes in extraction of different hydrocarbon fragments, pulping or paper making can be advantageous as it will reduce the need for disposal and environmental deterioration through pollution. In Pakistan, annual production of sugarcane is 49,373 thousands metric ton per annum [3]. Sugarcane crop contains 33% bagasse [4].So total bagasse available is 16,293.09 thousands metric ton per annum [5].

Cellulose and hemicellulose are major constituents of all plant materials and form about 1/2 to 1/3 of plant tissues and are constantly restocked by photosynthesis. Cellulose and hemicellulose are collectively known as holocellulose. Cellulose is the most common organic substance in nature. It gives strength and stability to the plant cell wall. [6]. It is found in the cell wall as a network of microfibrils embedded in a non-cellulosic matrix [7]. Hemicelluloses are the second most abundant

biopolymers in the cell wall of cellulosic materials [8]. However, hemicelluloses are closely associated with cellulose by physical intermixing and hydrogen bonds and are linked to lignin by covalent bonds [9]. After cellulose and hemicellulose, lignin is the third most abundant natural polymer present in the nature. It is a major cell wall component. It provides rigidity, internal transport of water and nutrients and protection against attack by microorganisms. Lignin is an amorphous polymer consisting of phenylpropane units [10]. It basically holds cellulose, hemicellulose and inorganics together. It is partly soluble in aqueous alkaline solutions, and is readily attacked and solubilized by oxidizing agents [11].

To break lignin and extract cellulose and hemicellulose from biomass, different chemicals are used known as delignifying agents. NaOH was used to extract cellulose from hopstems [12]. Sisal fibers were treated with H2O2, NaClO2 [13]. Cellulose and hemicellulose were derived from sugar beet pulp by using NaOH [14]. Mixture of carboxyalic acids and H2O2 were reacted with wheat straw to obtain cellulose and hemicellulose [15]. Holocellulose was extracted from refined wheat straw by using KOH and boric acid [16].

In order to investigate the potential of holocellulose extraction from bagasse, three different treatments were comparatively studied. Chemical modifications in the samples were checked through kappa No. using Technical Association for Pulp and Paper Industry (TAPPI) T-236, X-Ray Fluorescence Spectrometry (XRF), and Scanning Electron Microscopy (SEM).

*To whom all correspondence should be addressed.


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Results and Discussion

In soda and sulfite processes, bagasse was cooked with NaOH and Na2SO3 respectively to extract holocellulose. The process parameters studied and optimized were concentration of NaOH (1 M-4 M) and Na2SO3 (1 M-3 M), cooking time (1, 3 and 5 hr) and cooking temperature (100 oC, 140 oC and 180 oC). While in combine process, different mixtures of NaOH and Na2SO3 were used and composition of the mixture of NaOH (3.5 M) and Na2SO3 (2.5 M) and cooking time were investigated and optimized. Then kappa No. of each sample was quantified by TAPPI T-236 method.

Fig. 1 shows the relationship of kappa No. of different samples with the concentration of NaOH at cooking time of 1 hr, 3 hr and 5 hr, at 100 oC. At the cooking time of 1 hr, as we are increasing the concentration of NaOH, the kappa No. reduces. Initially the reduction in kappa No. is sharp after that the change is not significant. The same trend was observed when cooking time is set as 3 hr and 5 hr. Cooking time of 3 hr and 5 hr reduce the kappa No. more than 1 hr. Fig. 2 and 3 also show the relationship of kappa No. with the concentration of NaOH at cooking time of 1 hr, 3 hr and 5 hr, at 140 oC and 180 oC respectively. Comparisons of Fig. 1-3 show that as we increase the temperature, it reduces the kappa No. At temperature of 140 oC and 180 oC the reduction in kappa No. was more than at 100 oC and in between 140 oC and 180 oC, the change is not significant.

Fig. 1: Changes in Kappa No. with change in time

and NaOH concentration at 100 oC.

Fig. 2: Changes in Kappa No. with change in time and NaOH concentration at 140 oC.

Fig. 3: Changes in Kappa No. with change in time and NaOH concentration at 180 oC.

Fig. 4-6 show the relationship of kappa No. of different products with the concentration of Na2SO3 at different cooking time and cooking temperature. One can observe the similar trend which means that higher temperature favors the delignification of bagasse. That’s why at 140 oC and 180 oC, kappa No. value is much lesser than at 100 oC. But there is not a significant difference between 140 oC and 180 oC.

Fig. 4: Changes in Kappa No. with change in time

and Na2SO3 concentration at 100 oC.


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Fig. 5: Changes in Kappa No. with change in time and Na2SO3 concentration at 140 oC.

Fig. 6: Changes in Kappa No. with change in time and Na2SO3 concentration at 180 oC.

Fig. 7 shows the relationship of kappa No. with different mixture of NaOH and Na2SO3 at cooking time of 1 hr, 3 hr and 5 hr, at 140 oC. When the cooking time is 1 hr, the trend depicts that as the content of Na2SO3 increases in the mixture, kappa No. reduces till NaOH/Na2SO3 is 30/70 then it increases. The same trend can be observed at cooking time of 3 hr and 5 hr but cooking time of 5 hr reduces the kappa No. more.

Fig. 7: Changes in Kappa No. with change in time and composition of NaOH-Na2SO3 mixture at 140oC.

Fig. 1-6 show that by increasing the temperature, cooking time and concentration of delignifying agent, kappa No. reduces. The rate of delignification increases by increasing the temperature [17]. Cooking time and concentration of delignifying agent has also the similar effect on lignin. By increasing the cooking time, reaction time increases and delignifying agents have more time available to break the lignin. Concentration also reduces the lignin content because more free ions will be available to attack and dissolve the lignin [18].

Among the three processes, combine process

is the best because in it both delignifying agents i.e. NaOH and Na2SO3 react with the lignin. NaOH breaks it while sulfite ion accelerates the rate of delignification by making smaller fragments of lignin which then make stable salts of sodium. At the same time being in small amount, NaOH attack on carbohydrate is reduced and yield of the process increases. SEM

Fig. 8 shows the SEM of bagasse. It is clear that bagasse has irregular structure due to the presence of lignin. Most of the lignin has been removed by the chemical treatment as shown by the regular and smooth surface of holocellose in Fig 9-11.

Fig. 8: SEM of bagasse.

Fig. 9 is showing that NaOH has not only broken the lignin but also affected the holocellulose. This behavior can also be seen in Fig. 11 while Fig. 10 do not have such structural deformations but more irregularities which shows that the lignin is more in it than others.


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Fig. 9: SEM of NaOH treated bagasse.

Fig. 10: SEM of Na2SO3 treated bagasse.

Fig. 11: SEM of NaOH and Na2SO3 treated bagasse. XRF

Table-1 shows the XRF analysis of Raw Bagasse and holocellulose obtained from three processes. Bagasse shows the maximum amount of silica while products have comparatively low amount. It means delignifying agents break and dissolve every inorganic and non-carbohydrate part as shown by the content of Si which also confirms the removal of lignin.

Table-1: XRF Analysis, Concentration (wt. %). Element Bagasse Soda Sulfite Combine

Na - 0.061 1.785 1.306 Al - - 0.301 0.486 Si 27.160 20.760 5.834 5.800 P - 0.244 0.121 - S - 0.405 17.062 0.646 K - - 0.363 - Fe - 5.157 1.484 1.847 Zr - - 0.135 0.267 Ca 24.928 22.987 13.794 10.510 Mg 0.783 8.682 0.450 0.512 Zn 4.593 - 14.724 16.253 Sr - - 0.463 0.694

Experimental

Materials

Sugarcane bagasse was obtained from a local sugar factory. It was first washed with distilled water and dried in sunlight and then cut into small pieces (1-3 cm). The cut bagasse was grinded to 80 mesh and dried again in an oven for 24 h at 80 oC. Delignifying agents used were NaOH and Na2SO3.

Holocellulose was extracted from bagasse using three different delignifying agents NaOH, Na2SO3 and combination of NaOH and Na2SO3 (chemical treatment). The main objective of these treatments was to eliminate lignin as it holds cellulose and hemicellulose together. A number of samples were prepared each weighing 5 grams. Different concentration of delignifying agents used were 1, 1.5, 2, 2.5, 3, 3.5 and 4 M. The cooking times were 1, 3 and 5 hr while cooking temperatures were 100 oC, 140 oC and 180 oC. The liquid to solid ratio was 5:1.

Fig. 12 shows the chemical treatment of samples. After the chemical treatment, each product was washed with distilled water until pH was 7. Then it was dried in oven for 24 hr at 80 oC.

Fig. 12: Scheme of holocellulose extraction.


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Methods

Kappa No. of each product was found out by using TAPPI T-236 method. Treated bagasse was coated with a thin layer of graphite and observed by an SEM (JEOL JSM-6490 LV) in order to study the surface morphology, particle size and shape. XRF analysis was performed using PANalytical 2830 ZT WD. Pellet was made by mixing sample (75%) and wax (25%). Conclusions

In this work, three different delignifying agents for holocellulose extraction were evaluated. Analysis of kappa No. showed that combine process is relatively the best process for the holocellulose extraction. SEM confirmed the breakage of lignin through structural deformations. XRF also showed the removal of lignin from bagasse as Si content was reduced. Acknowledgement

Authors are thankful to the Department of Chemical Engineering, University of Engineering And Technology, Lahore Pakistan for financial and technical support. References 1. R. D. Perlack, L. L. Wright, A. F. Turhollow, R.

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extraction of holocellulose from bagasse using delignifying … · 2016. 7. 31. · umair aslam at...

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