The delignification effects of white-rot fungal pretreatment on thermal characteristics of moso bamboo

Bioresource Technology 114 (2012) 437–442

Contents lists available at SciVerse ScienceDirect

Bioresource Technology journal homepage: www.elsevier.com/locate/biortech

The delignification effects of white-rot fungal pretreatment on thermal characteristics of moso bamboo Yelin Zeng, Xuewei Yang, Hongbo Yu, Xiaoyu Zhang, Fuying Ma ⇑ Key Laboratory of Molecular Biophysics of MOE, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, PR China

a r t i c l e

i n f o

Article history: Received 24 June 2011 Received in revised form 11 October 2011 Accepted 12 October 2011 Available online 20 October 2011 Keywords: Moso bamboo Thermogravimetric analysis White-rot fungi Delignification Lignocellulosic fractions

a b s t r a c t Moso bamboo (Phyllostachys pubesescens) is a major bamboo species which is widely used for temporary scaffolding in China. Its fast growing and low ash content make moso bamboo a potential renewable energy resource. In present work, thermal behaviors of moso bamboo and its lignocellulosic fractions were investigated using thermogravimetric analysis. Furthermore, to understand whether the delignification effect of white-rot fungi can promote the thermal decomposition of bamboo especially the lignin component, the changes in lignocellulose components as well as thermal behaviors of bamboo and acid detergent lignin were investigated. The results showed that the white-rot fungal pretreatment is advantageous to thermal decomposition of lignin in bamboo. The weight losses of ADL samples became greater and the thermal processes were accelerated after biopretreatment. The total pyrolysis weight loss increased from 57.14% to 65.07% for Echinodontium taxodii 2538 treated bamboo ADL sample. Ó 2011 Published by Elsevier Ltd.

1. Introduction The depletion of fossil fuels and climate changes have led to an increased interest in the development of thermal processing of sustainable biomass (Asif and Muneer, 2007; Haines et al., 2007). Pyrolysis is a promising thermochemical conversion route, converting biomass to energy-dense fuels and chemical feedstocks (Lu et al., 2009). Bamboo is a large woody grass of the tall graminaceous plants including 1250 species within 75 genera (Scurlock et al., 2000). Moso bamboo (Phyllostachys pubesescens) is a major bamboo species which is widely used for temporary scaffolding in China (Fu, 2001; Mui et al., 2008). Its fast growing, low ash content and alkali index make moso bamboo a potential renewable resource for obtaining biofuels. Furthermore, the heating value of bamboo is slightly lower than most woody biomass feedstocks but higher than most agricultural residues and grasses (Scurlock et al., 2000). However, there have been limited previous studies on the pyrolysis of bamboo, not to mention the thermal decomposition mechanism of individual lignocellulosic components in bamboo (Mui et al., 2008). Lignin is a major component of biomass accounting for 17–32.5% of the mass of bamboo (Mui et al., 2008), which consists of phenylpropane units (Bridgwater et al., 1999). Besides, lignin is the major by-product of biomass ethanol production and a major impurity in the process of wood pulping and papermaking (Lynd et al., 1991; Messner and Srebotnik, 1994). Due to its aromatic structure, it is attracting to convert lignin into valuable aromatic hydrocarbons ⇑ Corresponding author. Tel.: +86 27 87792128. E-mail address: [email protected] (F. Ma). 0960-8524/$ - see front matter Ó 2011 Published by Elsevier Ltd. doi:10.1016/j.biortech.2011.10.036

for biofuels and chemicals (Clark, 2007). Some of the previous researches focused on product distribution from pyrolysis of lignin in order to achieve higher yields of phenol and phenolics (Jiang et al., 2010). Studying on the kinetics of biomass pyrolysis is important to better understand the underlying processes and to provide useful information for design and scaling-up of pyrolysis reactors (Jiang et al., 2010; Orfao et al., 1999). Compared with pyrolysis of cellulose and hemicelluloses, lignin decomposes in an extensive temperature range with relatively low rates and is the principal source of the char (Bridgwater, 1999; Yang et al., 2006). It was hypothesized that the structure modification and degradation of lignin may make the lignin in biomass easier to thermal decomposition (Kim and Parker, 2008; McMillan, 1994; Yang et al., 2011).The lignin degrading white-rot fungi have been considered to be the most efficient microorganisms for biomass decomposition and depolymerization (Dinis et al., 2009). Pretreatment by white-rot fungi could efficiently convert the complex constituent of lignin to a relatively simple structure with mild conditions and low energy consumption (Sun and Cheng, 2002). In previous investigation, white-rot fungi Irpex lacteus CD2 and Echinodontium taxodii 2538 were found to have the ability to degrade biomass lignin (Yang et al., 2010; Yu et al., 2009). However, it is not yet known whether the delignification effect of white-rot fungal pretreatment can promote the thermal decomposition of bamboo and the lignin component. The purpose of this study was to explore the thermal behaviors of moso bamboo and its lignocellulosic fractions using thermogravimetric analysis. Furthermore, to understand the influence of biopretreatment on the pyrolysis of bamboo, the thermogravimetric characteristics of bamboo pretreated by white-rot fungi were

438

Y. Zeng et al. / Bioresource Technology 114 (2012) 437–442

investigated. The biopretreatment patterns of white-rot fungi and the alterations of biomass structures were evaluated by components losses of lignocellulose and FTIR analysis. TG/DTG analysis of bamboo and isolated lignocellulosic fractions were used to study whether the delignification effect of white-rot fungi promoted the biomass thermal reactions. 2. Experimental 2.1. Fungal strains and biopretreatment of bamboo The fungi used for pretreatment of bamboo were isolated from Shennongjia Nature Reserve (Hubei, China). The fungal strains were maintained on potato dextrose agar slant at 4 °C. Three to five disks cut from the margin of active fungal cultures on potato dextrose agar plates were inoculated into 250 mL Erlenmeyer flask with 100 mL of PDB medium (pH 5.5) and incubated at 28 °C, 150 rpm for 5–7 days on a reciprocal shaker. The mycelia in the flasks were gently homogenized, and 10 mL was used to inoculate fresh PDB medium each for 3 days to obtain the secondary seed culture under the same condition. Four years old moso bamboo without leaves was obtained from Xianning in Hubei province. Fungal pretreatment was carried out in 250 mL flasks containing 10 g (dry mass) of pulverized bamboo (grain diameter = 0.3–0.45 mm) and 15 mL of distilled water. After autoclaving (150 kPa, 45 min), 10 mL of homogenized secondary seed culture was inoculated. Uninoculated control samples were incubated under identical conditions. After 30 days of incubation at 28 °C and constant humidity, the pretreated bamboo was dried (in an aerated oven at 60 °C), milled and extracted with a benzene /ethanol mixture (80:20, v/v) in a Soxhlet apparatus.

and Testing Center, Huazhong University of Science and Technology. The temperature of the furnace and weight were calibrated according to the manufacturer’s recommendation. Temperature calibration was performed by measuring curie points of indium, tin and gold. Prior to thermogravimetric experiments, samples were ground to small chips through 0.15–0.2 mm screen. Initial sample masses of 5 mg were placed in the pan of the TGA microbalance, which was enough to fill the pan because of the low density of the ground samples. Nitrogen gas was used as carrier gas. Experiments were carried out on thermobalance at a linear heating rate of 10 °C min1, with the temperature range from 25 to 1000 °C, at a steady nitrogen flow of 100 mL min1. 3. Results and discussion 3.1. Compositional analysis The changes in weight losses and chemical composition of biopretreated bamboo were found to be different. After 30 days of pretreatment, the average weight losses on dry basis for I. lacteus CD2 and E. taxodii 2538 pretreated bamboo were 14% and 20%, respectively. As shown in Table 1, I. lacteus CD2 significantly degraded hemicelluloses, whereas the mass reduction of hemicelluloses in E. taxodii 2538 treated bamboo was limited. During the 30 days of biodegradation, both the white-rot fungi caused delignification of bamboo. The mass reduction of lignin was 13% for I. lacteus CD2 treated bamboo, and 29% for E. taxodii 2538 treated bamboo. At the same time, pretreatment by E. taxodii 2538 led to an apparent increase of cellulose percentage in bamboo, which was attributed to the relatively higher removal of lignin component and biomass weight loss. The results indicated that the fungus E. taxodii 2538 selectively degrade lignin to a great extent.

2.2. Isolation and calculation of bamboo lignocellulosic components 3.2. FTIR spectroscopy analysis Neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL) from biodegraded and undegraded bamboo were prepared via sequential detergence with neutral detergent reagent, acid detergent reagent and 72% H2SO4. In multiple-step detergence, NDF was performed first, followed by ADF and finally ADL (Gellerstedt and Pranda, 1994; Horwitz and William, 1980; Van, 1963). Hemicelluloses, cellulose and Klason lignin contents were calculated by the difference between NDF and ADF content, ADF and ADL content, ADL and ash content, respectively. 2.3. Fourier transform infrared spectroscopy (FTIR) FTIR spectra were recorded with a NEXUS 670 spectrometer (Thermo Nicolet Corp., Madison, WI), KBr pellets for FTIR spectroscopy were prepared using a Perkin-Elmer pellet die (2 mg of lignin sample in 40 mg of KBr) (Pandey and Pitman, 2003). Peak height and area was measured using OMNIC software version 1.2a (Nicolet Instrument Corp.). 2.4. Thermogravimetric analysis Thermogravimetric experiments were performed by using sensitive thermobalance (PerkinElmer, Diamond, China) by Analytical

3.2.1. FTIR analysis of bamboo FTIR analysis has been widely used to characterize changes in biomass decayed by fungi, since non-destructive and very small quantities of sample can be analyzed (Popescu et al., 2010). After 30 days of fungal degradation, relative changes in the intensity of lignin/carbohydrate characteristic bands were calculated in Table 2. Peak area values for lignin associated band at 1510 cm1 were rationed against carbohydrate reference peaks at 1734, 1373, 1161 and 898 cm1, respectively to provide relative changes in the composition of lignocellulosic components (Pandey and Pitman, 2003). Since most of the bands in FTIR spectra have contributions from all biomass constituents, the purely aromatic skeletal vibration of 1510 cm1 peak as a lignin characteristic band has been chosen. For the same reason, all carbohydrate peaks listed in Table 2 have no significant contribution from lignin (Pandey and Pitman, 2003). The assignment of bands to structural components according to references is provided as follow (Pandey and Pitman, 2003; Zhang et al., 2007): 1734 cm1 for unconjugated C@O in hemicelluloses, 1510 cm1 for aromatic skeleton in lignin, 1373 cm1 for C–H deformation in cellulose and hemicelluloses, 1161 cm1 for C–O–C vibration in cellulose and hemicelluloses, 898 cm1 for C–H deformation in cellulose. As shown in Table 2, there was a progressive decrease in

Table 1 Compositional analysis of untreated and biopretreated bamboo. Compositional analysis wt.% (on dry basis) Sample

Cellulose

Hemicelluloses

Lignin

Ash

Bamboo Bamboo pretreated by I. lacteus CD2 Bamboo pretreated by E. taxodii 2538

48.00 ± 0.53 48.20 ± 0.92 52.07 ± 1.14

23.60 ± 0.85 18.50 ± 0.97 22.70 ± 0.71

20.60 ± 0.87 17.87 ± 0.83 14.60 ± 0.40

0.93 ± 0.03 0.87 ± 0.23 1.07 ± 0.23

439

Y. Zeng et al. / Bioresource Technology 114 (2012) 437–442 Table 2 Ratios of the intensity of the lignin associated band with carbohydrate bands for untreated and biopretreated bamboo. Relative intensities of aromatic skeletal vibration against typical bands for carbohydrates I1510/I1734

I1510/I1373

I1510/I1161

I1510/I898

0.585 0.680 0.513

1.784 1.437 1.258

2.056 1.025 0.887

3.427 3.077 2.528

lignin content relative to carbohydrate in E. taxodii 2538 pretreated bamboo which also indicated that the white-rot fungus E. taxodii 2538 has great selective lignin degrading ability. In contrast, I. lacteus CD2 simultaneously degraded hemicelluloses and lignin in bamboo, which was evident from the increase in the lignin/carbohydrate ratio for 1734 cm1 band and the less decrease for other carbohydrate bands (at 1373, 1161 and 898 cm1) compared with E. taxodii 2538 treated sample. 3.2.2. FTIR analysis of acid detergent lignin (ADL) Compared with undegraded bamboo, there were great changes in the FTIR spectra of extracted ADL samples pretreated by white-rot fungi I. lacteus CD2 and E. taxodii 2538 for 30 days. The results were analyzed according to references (Collier et al., 1992; Pandey and Theagarajan, 1997; Zhang et al., 2007). As shown in Table 3, the aromatic skeletal vibration of white-rot fungi pretreated ADL samples at 1600, 1506, and 1460 cm1 decreased in intensity. Likewise, the intensity of aromatic bending vibration at 1029, 829 cm1 and C–C, C–O stretching vibration at 1220 cm1 in fungal degraded samples decreased. It is noteworthy that in the E. taxodii 2538 pretreated sample, the decreases in the intensity at aforementioned characteristic bands were much more compared to the I. lacteus CD2 treated sample. Furthermore, the intensity of all the lignin associated bands in the E. taxodii 2538 pretreated ADL sample decreased dramatically. The results from FTIR analysis indicated that both the white-rot fungi caused the weight loss and decomposition of bamboo lignin, whereas the fungus E. taxodii 2538 had greater selective lignin degrading ability. 3.3. Thermogravimetric characteristics analysis 3.3.1. TG–DTG analysis of bamboo The comparison of the TG (in wt.%) and DTG (in %/°C) curves, as well as the characteristic parameters in the thermogravimetric curves of untreated and biopretreated bamboo samples were shown in Fig. 1 and Table 4 (Entries 1–3). The pyrolysis of bamboo initiated at approximately 210 °C, then the reaction rate increased

100

1.2

untreated bamboo I. lacteus CD2 E. taxodii 2538 1.0

80

0.8 60 0.6 40 0.4 20

Weight loss rate

Bamboo Bamboo pretreated by I. lacteus CD2 Bamboo pretreated by E. taxodii 2538

Weight loss (%)

Sample

0.2

0

0.0 200

400

600

800

Temperature Fig. 1. The TG and DTG curves of untreated and biopretreated bamboo at 10 °C min1 in nitrogen atmosphere (I. lacteus CD2 = bamboo pretreated by white-rot fungus I. lacteus CD2 for 30 days, E. taxodii 2538 = bamboo pretreated by white-rot fungus E. taxodii 2538 for 30 days).

linearly to 310 °C and rose sharply to the peak at approximately 350 °C. Beyond the temperature 370 °C, the TG and DTG curves became flat which reveal the slower decomposition dominated by the lignin. It could be observed that there were no significant differences in the weight loss rates as well as the maximum decomposition rates (DTGmax) between untreated and biopretreated bamboo. Besides, the weight loss of the original bamboo was comparable to, but slightly lower than, the bamboo pretreated by E. taxodii 2538 and higher than I. lacteus CD2 treated bamboo. The lowest pyrolysis weight loss of I. lacteus CD2 pretreated sample was probably due to the significant hemicelluloses degradation. 3.3.2. TG–DTG analysis of neutral detergent fiber (NDF) Fig. 2 and Table 4 (Entries 4–6) showed increases in the weight loss rates and the temperature for the maximum weight loss rates

Table 3 FTIR spectra analysis of untreated and biopretreated bamboo ADL. Wavenumber/ (cm1)

Attribution and description of FTIR absorption

1600 1506 1460

C@O stretching and aromatic vibration; S > G; condensed G > etherified G Aromatic skeletal vibration; G > S C–H bending vibration, CH3, CH2 asymmetric bending vibration aromatic skeletal vibration in lignin Aromatic skeletal vibration and C–H in-plane bending vibration S ring and 5-substituted G C–C and C–O stretching vibration C–H aromatic-plane bending vibration, characteristics of S ring; coincide with secondary alcohol C–O stretching vibration C–H aromatic in-plane bending vibration, G > S; primary alcohol C–O stretching vibration Aromatic C–H out-of-plane bending vibration S ring C–H out-of-plane bending vibration

1422 1329 1220–1221 1120–1121 1029–1031 913–914 829–831

Out of parentheses were the peak area values and in the parentheses were the corresponding peak heights.

Peak area and height of lignin associated bands Control

CD2

2538

9.280 (0.176) 5.109 (0.154) 2.415 (0.106)

8.494 (0.183) 5.058 (0.165) 2.377 (0.110)

5.379 (0.119) 3.502 (0.107) 1.548 (0.069)

1.111 2.604 4.051 4.750

1.298 1.950 3.178 4.765

0.810 1.000 1.945 3.241

(0.059) (0.058) (0.079) (0.120)

2.619 (0.047) 0.273 (0.013) 2.055 (0.043)

(0.069) (0.058) (0.074) (0.137)

1.816 (0.024) 0.275 (0.014) 2.002 (0.053)

(0.043) (0.034) (0.044) (0.087)

1.270 (0.017) 0.170 (0.008) 1.381 (0.035)

440

Y. Zeng et al. / Bioresource Technology 114 (2012) 437–442

Table 4 The thermogravimetric parameters of untreated and biopretreated bamboo, NDF, ADF and ADL samples in nitrogen atmosphere, at a heating rate of 10 °C min1. Entry

Sample

DTGmax (%/°C)

Tpeak (°C)

Char (%)

1 2 3

Bamboo Bamboo pretreated by I. lacteus CD2 Bamboo pretreated by E. taxodii 2538

1.082 1.091 1.073

343 344 343

17.62 20.69 16.91

4 5 6

NDF NDF pretreated by I. lacteus CD2 NDF pretreated by E. taxodii 2538

1.198 1.010 1.137

359 346 352

11.40 18.30 15.59

7 8 9

ADF ADF pretreated by I. lacteus CD2 ADF pretreated by E. taxodii 2538

2.096 2.213 2.212

325 324 322

12.47 11.27 10.01

10 11 12

ADL ADL pretreated by I. lacteus CD2 ADL pretreated by E. taxodii 2538

0.255 0.314 0.352

372 373 380

42.86 37.56 34.93

The char yield data of the TG curves, the peak height (DTGmax) and peak temperature (Tpeak) values of the DTG peaks were calculated.

100

untreated bamboo 1.2 I. lacteus CD2 E. taxodii 2538

2.5

80

untreated bamboo I. lacteus CD2 E. taxodii 2538 2.0

60

1.5

40

1.0

20

0.5

0.6 40 0.4 20

Weight loss rate

0.8

60

Weight loss (%)

1.0

Weight loss rate

Weight loss (%)

80

100

0.2

0

0.0 200

400

600

800

Temperature

0

0.0 200

400

600

800

Temperature

Fig. 2. The TG and DTG curves of untreated and biopretreated bamboo NDF at 10 °C min1 in nitrogen atmosphere (I. lacteus CD2 = bamboo pretreated by whiterot fungus I. lacteus CD2 for 30 days, E. taxodii 2538 = bamboo pretreated by whiterot fungus E. taxodii 2538 for 30 days).

Fig. 3. The TG and DTG curves of untreated and biopretreated bamboo ADF at 10 °C min1 in nitrogen atmosphere (I. lacteus CD2 = bamboo pretreated by whiterot fungus I. lacteus CD2 for 30 days, E. taxodii 2538 = bamboo pretreated by whiterot fungus E. taxodii 2538 for 30 days).

after the samples washed by neutral detergent reagent. Same results were observed in previous studies, which reported the changes of the thermal behaviors due to the mineral matter naturally present in biomass (Gómez et al., 2004; González et al., 2008). However, after biopretreatment, the weight loss rates and the weight losses of extracted NDF samples decreased. The total pyrolysis weight loss of E. taxodii 2538 pretreated NDF sample decreased from 88.6% to 84.4%, whereas the weight loss of I. lacteus CD2 treated sample was 81.7%. This can be explained by the fact that compared with biomass the degradation by white-rot fungi has greater influence on thermal decomposition of NDF fractions, which only includes cellulose, hemicelluloses, and lignin.

slightly higher than those of the untreated sample. The indistinctive changes in biopretreated ADF thermogravimetric characteristics were coincident with the limited degradation of cellulose by white-rot fungi I. lacteus CD2 and E. taxodii 2538. Since the major thermal decomposition of biomass is dominated by the decomposition of cellulose, the slight changes in thermal behaviors of biopretreated ADF samples have explained the insignificant changes in bamboo thermal behaviors to some extent.

3.3.3. TG–DTG analysis of acid detergent fiber (ADF) Thermal behaviors of ADF samples mainly represent the cellulose thermogravimetric characteristics because the relative content of cellulose in ADF was approximated to 80%. Thermal decomposition of untreated and biopretreated bamboo ADF samples were indicated by the features of the TG–DTG curves (Fig.3), as well as by the thermogravimetric parameters (Table 4, Entries 7–9). The decomposition of ADF samples became measurable at about 200 °C and main thermal reaction occurred in a relatively narrow range of temperatures between 280 and 360 °C. The weight losses and the maximum weight loss rates of biopretreated ADF samples had similar values in pyrolysis, and they were both

3.3.4. TG–DTG analysis of acid detergent lignin (ADL) Lignin is relatively more thermally stable compared to hemicelluloses and cellulose (Fatih Demirbas, 2009; Yang et al., 2006). The DTG peaks in pyrolysis of ADL samples were wider and flatter than those in pyrolysis of biomass and ADF samples. ADL samples started decomposing at the lowest temperature and its pyrolysis occurred in an extensive temperature range (between 100 and 800 °C) with relatively low rates. Owing to the delignification effects of white-rot fungi it is expected that the lignin in biopretreated bamboo will decompose easier during thermogravimetric experiments. As shown in Table 4 (Entries 10–12) and Fig.4, the weight losses of ADL samples became greater and the thermal degradation process were accelerated after biopretreatment. This could be explained by the decomposition of lignin and the depolymerization of bamboo when the biomass was degraded by white-rot fungi (Yang et al., 2010).

441

Y. Zeng et al. / Bioresource Technology 114 (2012) 437–442 0.4

100

untreated bamboo I. lacteus CD2 E. taxodii 2538

80

60 0.2 40

0.1

Weight loss rate

Weight loss (%)

0.3

20

According to the references (Gómez et al., 2004; Manyà et al., 2003), first-order reaction model is suitable for hemicelluloses and cellulose. Therefore, the reaction order n in biomass, NDF and ADF samples is assumed to be 1. However, the pyrolysis of lignin is better described by a third-order reaction rate law which means the reaction order n in ADL samples is 3. The Coats-Redfern method utilizes the asymptotic series expansion for approximating the exponential integral in the right-hand side of Eq. (5), giving:

0

0.0 200

400

600

800

Temperature Fig. 4. The TG and DTG curves of untreated and biopretreated bamboo ADL at 10 °C min1 in nitrogen atmosphere (I. lacteus CD2 = bamboo pretreated by whiterot fungus I. lacteus CD2 for 30 days, E. taxodii 2538 = bamboo pretreated by whiterot fungus E. taxodii 2538 for 30 days).

There was only one main DTG peak of untreated ADL sample and the total weight loss was 57%. After biopretreatment, the weight loss increased to 62.44% for I. lacteus CD2 pretreated sample, and to 65.27% for E. taxodii 2538 treated sample. The DTG curves of biopretreated ADL samples presented two main peaks in the 200–350 °C and 350–600 °C temperature ranges, respectively. Furthermore, the weight loss rate of E. taxodii 2538 pretreated ADL sample was faster than that of the sample pretreated by I. lacteus CD2, which was implied by the shape of DTG curves and the calculated values of thermogravimetric parameters. The thermal decomposition of biopretreated ADL samples were more adequate and faster than control, which may attribute to the great lignin degrading and structure alteration ability of white-rot fungi especially E. taxodii 2538. 3.4. Kinetic parameters of bamboo and lignocellulosic fractions In the solid state reaction, the rate of conversion da=dt can be expressed in accordance with the Arrhenius equation:

  da E ð1  aÞn ¼ A exp  RT dt

wi  wt wi  wf

0

da A ¼ ð1  aÞn b

60.99 63.05

0.989 0.990

3.56  104

62.49

0.992

NDF NDF pretreated by I. lacteus CD2 NDF pretreated by E. taxodii 2538

2.05  104 5.29  104

60.75 64.52

0.996 0.991

1.85  104

60.17

0.991

6.43  108 9.77  108

112.85 110.06

0.952 0.949

8.70  108

109.32

0.945

ð4Þ

ADF ADF pretreated by I. lacteus CD2 ADF pretreated by E. taxodii 2538

4.77  103 1.57  104

65.86 62.67

0.962 0.992

ð5Þ

ADL ADL pretreated by I. lacteus CD2 ADL pretreated by E. taxodii 2538

3.38  104

58.58

0.994

ð3Þ

Z

T

T0

  E dT exp  RT

Table 5 Kinetic parameters in the active pyrolysis of untreated and biopretreated bamboo, NDF, ADF and ADL samples in nitrogen atmosphere, at a heating rate of 10 °C min1.

2.93  104 3.95  104

Upon integration, Eq. (4) gives: a

Plotting the Eq. (6) gives the kinetic parameters E and A from the slope and intercept respectively. As shown in Table 5, the apparent activation energy of biopretreated bamboo and NDF samples had similar values, and they were all slightly higher than those of the untreated samples. This was probably due to the indistinctive biodegradation of cellulose which is the main component in biomass pyrolysis. In addition, there was no significant difference in the values of activation energy between biomass and corresponding NDF samples. The results indicated that the neutral detergent extracted fractions of bamboo might have the similar apparent activation energy with lignocellulose. Of the three lignocellulosic components, it is cellulose that has the highest activation energy (Mui et al., 2008; Yang et al., 2006). After washed by acid detergence, the activation energy of ADF samples which mainly composed of cellulose became much higher than that of biomass and NDF samples. Pretreatment with white-rot fungi had little or no effect on the activation energy of cellulose, attested by the slight changes in the values of ADF activation energy pretreated by I. lacteus CD2 and E. taxodii 2538. In the case of ADL samples, the activation energy of biopretreated samples became lower than control. Moreover, the higher values obtained in biopretreated ADL samples for the pre-exponential factor may explain the faster thermal decomposition of biopretreated ADL samples.

Bamboo Bamboo pretreated by I. lacteus CD2 Bamboo pretreated by E. taxodii 2538

Eq. (1) and (3) give:

Z

ð6Þ

A (1/s)

wi, wt, wf are initial sample mass, sample mass at time t and final mass of the sample, respectively. A is the pre-exponential factor, E is the apparent activation energy, t is the reaction time, n is reaction order, R is the universal gas constant, and T is the absolute temperature. Under nonisothermal condition, when the sample is heated at a constant rate or temperature ramp, the heating rate b:

  da A E ð1  aÞn ¼ exp  dT b RT

2

Sample

ð2Þ

dT b¼ dt

  ln ð1  aÞ

ð1Þ

where the fractional conversion of reactants a is defined in terms of mass change of the sample:

a¼



   AR 2RT E ¼ ln 1  ; when n ¼ 1 bE E RT T " #     ð1  aÞ2  1 1 AR 2RT E ln  2 ¼ ln 1  ; when n ¼ 3 2 bE E RT T

ln

E (kJ/ mol)

Correlation coefficients

442

Y. Zeng et al. / Bioresource Technology 114 (2012) 437–442

4. Conclusions The major aim of this study was to investigate the delignification effect of white-rot fungal pretreatment on thermal characteristics of moso bamboo. After biopretreatment the mass reduction of lignin was 13% and 29% for I. lacteus CD2 and E. taxodii 2538 treated bamboo, respectively. FTIR analysis showed that both the white-rot fungi caused the delignification of bamboo while the fungus E. taxodii 2538 had greater selective lignin degrading ability. The results of thermogravimetric experiments showed that the great lignin degrading ability of white-rot fungi especially E. taxodii 2538 made the thermal decomposition of bamboo lignin more adequate and faster. Acknowledgements The work was supported by National Basic Research Program (No. 2007CB21020), the Fundamental Research Funds for the Central Universities, HUST (2010MS039) and National Natural Science Foundation of China (30901137). The authors thank the Center of Analysis and Test of Huazhong University of Science and Technology for TG analysis. References Asif, M., Muneer, T., 2007. Energy supply, its demand and security issues for developed and emerging economies. Renew. Sustain. Energy Rev. 11, 1388– 1413. Bridgwater, A.V., 1999. Principles and practice of biomass fast pyrolysis processes for liquids. J. Anal. Appl. Pyrol. 51, 3–22. Bridgwater, A.V., Meier, D., Radlein, D., 1999. An overview of fast pyrolysis of biomass. Org. Geochem. 30, 1479–1493. Clark, J.H., 2007. Green chemistry for the second generation biorefinery – sustainable chemical manufacturing based on biomass. J. Chem. Tech. Biotechnol. 82, 603–609. Collier, W.E., Schultz, T.P., Kalasinsky, V.F., 1992. Infrared study of lignin: reexamination of aryl–alkyl ether C–O stretching peak assignments. Holzforschung 46, 523–528. Dinis, M.J., Bezerra, R.M.F., Nunes, F., Dias, A.A., Guedes, C.V., Ferreira, L.M.M., Cone, J.W., Marques, G.S.M., Barros, A.R.N., Rodrigues, M.A.M., 2009. Modification of wheat straw lignin by solid state fermentation with white-rot fungi. Bioresour. Technol. 100, 4829–4835. Fatih Demirbas, M., 2009. Biorefineries for biofuel upgrading: a critical review. Appl. Energy 86, S151–S161. Fu, J., 2001. Chinese moso bamboo: its importance. Am. Bamboo Soc. 22, 5–7. Gellerstedt, G., Pranda, J., 1994. Structural and molecular properties of residual birch kraft lignins. J. Wood Chem. Tech. 14, 467–482. Gómez, C.J., Manyà, J.J., Velo, E., Puigjaner, L., 2004. Further applications of a revisited summative model for kinetics of biomass pyrolysis. Ind. Eng. Chem. Res. 43, 901–906. González, J.D., Kim, M.R., Buonomo, E.L., Bonelli, P.R., Cukierman, A.L., 2008. Pyrolysis of biomass from sustainable energy plantations: effect of mineral

matter reduction on kinetics and charcoal pore structure. Energy Sources Part A 30, 809–817. Haines, A., Smith, K.R., Anderson, D., Epstein, P.R., McMichael, A.J., Roberts, I., Wilkinson, P., Woodcock, J., Woods, J., 2007. Policies for accelerating access to clean energy, improving health, advancing development, and mitigating climate change. Lancet 370, 1264–1281. William, Horwitz, 1980. Official Methods of Analysis of the Association of Official Analytical Chemists. Assoc. Off. Analytic. Chem., Washington, DC, USA. Jiang, G., Nowakowski, D.J., Bridgwater, A.V., 2010. A systematic study of the kinetics of lignin pyrolysis. Thermochim. Acta 498, 61–66. Orfao, J.J.M., Antunes, F.J.A., Figueiredo, J.L., 1999. Pyrolysis kinetics of lignocellulosic materials – three independent reactions model. Fuel 78, 349– 358. Kim, Y., Parker, W., 2008. A technical and economic evaluation of the pyrolysis of sewage sludge for the production of bio-oil. Bioresour. Technol. 99, 1409–1416. Lu, Q., Li, W., Zhu, X., 2009. Overview of fuel properties of biomass fast pyrolysis oils. Energy Convers. Manage. 50, 1376–1383. Lynd, L.R., Cushman, J.H., Nichols, R.J., Wyman, C.E., 1991. Fuel ethanol from cellulosic biomass. Science 251, 1318–1323. Manyà, J.J., Velo, E., Puigjaner, L., 2003. Kinetics of biomass pyrolysis: a reformulated three-parallel-reactions model. Ind. Eng. Chem. Res. 42, 434–441. McMillan, J.D., 1994. Pretreatment of lignocellulosic biomass. In: Himmel, M.E., Baker, J.O., Overend, R.P. (Eds.), Enzymatic Conversion of Biomass for Fuels Production. American Chemical Society, Washington, DC, pp. 292–324. Messner, K., Srebotnik, E., 1994. Biopulping: an overview of developments in an environmentally safe paper-making technology. FEMS Microbiol. Rev. 13, 351– 364. Mui, E.L.K., Cheung, W.H., Lee, V.K.C., McKay, G., 2008. Kinetic study on bamboo pyrolysis. Ind. Eng. Chem. Res. 47, 5710–5722. Pandey, K., Theagarajan, K., 1997. Analysis of wood surfaces and ground wood by diffuse reflectance (DRIFT) and photoacoustic (PAS) Fourier transform infrared spectroscopic techniques. Eur. J. Wood Wood Prod. 55, 383–390. Pandey, K.K., Pitman, A.J., 2003. FTIR studies of the changes in wood chemistry following decay by brown-rot and white-rot fungi. Int. Biodeter. Biodegr. 52, 151–160. Popescu, C., Popescu, M., Vasile, C., 2010. Structural changes in biodegraded lime wood. Carbohydr. Polym. 79, 362–372. Scurlock, J.M.O., Dayton, D.C., Hames, B., 2000. Bamboo: an overlooked biomass resource? Biomass and Bioenergy 19, 229–244. Sun, Y., Cheng, J., 2002. Hydrolysis of lignocellulosic materials for ethanol production: a review. Bioresour. Technol. 83, 1–11. Van, S., 1963. Use of detergents in the analysis of fibrous feeds. A rapid method for the determination of fiber and lignin. J. Assoc. Off. Agric. Chem. 46, 829–835. Yang, H., Yan, R., Chen, H., Zheng, C., Lee, D.H., Liang, D.T., 2006. In-depth investigation of biomass pyrolysis based on three major components: hemicellulose, cellulose and lignin. Energy Fuel 20, 388–393. Yang, X., Ma, F., Yu, H., Zhang, X., Chen, S., 2011. Effects of biopretreatment of corn stover with white-rot fungus on low-temperature pyrolysis products. Bioresour. Technol. 102, 3498–3503. Yang, X., Ma, F., Zeng, Y., Yu, H., Xu, C., Zhang, X., 2010. Structure alteration of lignin in corn stover degraded by white-rot fungus Irpex lacteus CD2. Int. Biodeter. Biodegr. 64, 119–123. Yu, H., Guo, G., Zhang, X., Yan, K., Xu, C., 2009. The effect of biological pretreatment with the selective white-rot fungus Echinodontium taxodii on enzymatic hydrolysis of softwoods and hardwoods. Bioresour. Technol. 100, 5170–5175. Zhang, X., Yu, H., Huang, H., Liu, Y., 2007. Evaluation of biological pretreatment with white rot fungi for the enzymatic hydrolysis of bamboo culms. Int. Biodeter. Biodegr. 60, 159–164.