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Liquefaction of bamboo shoot shell for the production of polyols
Bioresource Technology 153 (2014) 147–153
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Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Liquefaction of bamboo shoot shell for the production of polyols Liyi Ye ⇑, Jingmiao Zhang, Jie Zhao, Song Tu ⇑ Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Bamboo (D.latiflorus Munro) shoot
shell was used as raw material for liquefaction. Bamboo (D.latiflorus Munro) shoot shell was liquefied efficiently to produce polyols. Liquefaction products were analysed by element analysis, TG, FT-IR, NMR, and GC–MS.
a r t i c l e
i n f o
Article history: Received 18 September 2013 Received in revised form 23 November 2013 Accepted 25 November 2013 Available online 1 December 2013 Keywords: Bamboo shoot shell Liquefaction Polyols Sulfuric acid Liquefaction percentage
a b s t r a c t Bamboo (Dendrocalamus latiflorus Munro) shoot shell (BSS) was liquefied in polyethylene glycol 400 (PEG400) and ethylene glycol (EG) catalyzed by sulfuric acid under atmospheric pressure. The effects of liquefaction conditions such as liquid–solid ratio, temperature, time, catalyst, solvents ratio, and material size on the liquefaction yield of BSS have been investigated. Methods including Elemental analysis, Thermogravimetric analysis, Fourier transform infrared spectroscopy, nuclear magnetic resonance and gas chromatography–mass spectrometry were selected to analyze the characteristics of products in three fractions: an aqueous fraction (AQ), an acetone-soluble fraction (AS) and a residue (RS), respectively. Results showed that the highest liquefaction percentage was 99.79% under the optimal conditions (liquid–solid ratio 6:1; temperature 150 °C; reaction time 80 min; raw size more than 40 mesh; catalyst mass percentage of solvent 4%; solvent volume ratio 3:1). Polyols could be obtained effectively by the liquefaction of BSS, an agricultural by-product. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Biomass has attracted great interest as a renewable raw material for the production of fuel oil (Samir et al., 2012), adhesives (Zhao et al., 2013; Huang et al., 2012), polyurethane material (Zou et al., 2012; Kurimoto et al., 2001; Ueno, 2007) and carbon fiber (Kadla et al., 2002). Biomass energy is inferior to coal, oil, natural gas and is the fourth largest energy. It cannot be ignored that biomass has significant effect on the world energy crisis and environmental problems due to it is a renewable and vast nature resource. Furthermore, as a resource it has many advantages such as quantity, variety, low content of S and N, zero carbon emission, ⇑ Corresponding authors. Tel./fax: +86 0592 2184887, +86 0592 2186020. E-mail addresses: [email protected] (L. Ye), [email protected] (S. Tu). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.11.070
etc. Recently significant efforts have been made to use renewable resources effectively through methods such as pyrolysis, gasification, and liquefaction. But liquefaction has attracted more attention due to its simple operation, high production level, high energy conversion, and powerful organic material treatment ability. Biomass liquefaction research focused on the liquefaction of modified raw material (Nakano, 1994) at the early stage. But because of its intense reaction conditions, complex methods and high cost, researchers trended to liquefy biomass directly, and tried to change the solvent and catalyst to make the liquefaction process more perfect. Recently, researchers pretreated the biomass by new technologies such as ultrasound (Kunaver et al., 2012) and microwave (Zhuang et al., 2012) before liquefaction. Up to now, the methods of liquefaction mainly include: liquefaction with solvent
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and catalyst (Duan and Savage, 2011), direct liquefaction with solvent (Elliott et al., 1991), liquefaction after pretreatment such as chemical modification or new technologies (Kunaver et al., 2012), liquefaction under high temperature and high pressure (Yuan et al., 2011), liquefaction with supercritical fluid (Sandeep and Ram, 2009; Tevfik and Mehmet, 2013), nanometer powder of material liquefaction and so on. Of course, different methods could be used together in the process. From the work of other researchers (Zou et al., 2009; D’Souza and Yan, 2013), it is known that three series of reactions including decomposition, esterification, and polycondensation mainly occurred during the liquefaction. And the reaction conditions always decide the intensity of the reaction, the structure and performance of the products. Now biomass liquefaction researchers have made a lot of work in such aspects as raw materials, solvents, and catalysts. Raw materials such as algae (Chow et al., 2013; Duan et al., 2013), giant reed (Tevfik and Mehmet, 2013), bagasse (Zhang et al., 2007), cop residue (Liu et al., 2013; Zhang et al., 2012), bark (D’Souza and Yan, 2013), wood (Rivas et al., 2013; Tekin and Karagoz, 2013; Cheng et al., 2010), sawdust (Xu et al., 2012), switchgrass (Sandeep and Ram, 2009), nannochloropsis (Faeth et al., 2013), straw (Yuan et al., 2009), poplar (Wu et al., 2008), manure (Theegala and Midgett, 2012) have been liquefied effectively. There are three series of solvents used: phenol, polyhydric alcohols, and cyclic carbonate, and various products are obtained by different types of solvents. The liquefaction products of phenol including phenolate derivatives, and it can react with formaldehyde to produce phenolic resin. The liquefaction product of polyhydric-alcohol is polyester or polyether polyols which riches in hydroxyl, and polyurethane materials with excellent properties can be obtained after putting in isocyanate. Moreover, excellent resin adhesive agent can also be obtained by reaction of liquefaction products of bagasse, wood and other plant fiber with additive such as cross-linking agent, curing agent. Besides alkali catalysts (Tekin and Karagoz, 2013) and acidic ionic liquids (Lu et al., 2013; Zhou et al., 2013), some inorganic acid (Zhang et al., 2007) can be used as catalyst, for example, perchloric acid, sulfuric acid (Zhuang et al., 2012) benzene sulfonic acid, hydrochloric acid, phosphoric acid and so on. However, almost all of biomass are solid and have complex composition, meanwhile, they are refractory, indissolvable, physically and chemically stable. The different molecular structure leads to different reaction mechanism (Zou et al., 2009) and reactivity, suggesting difficulty in studying liquefaction mechanism. So researchers usually analyze the liquefaction mechanism through the liquefaction of cellulose and lignin (Jin et al., 2011). Liquefaction mechanism can also be conjectured based on composition of liquefied production. So analysis of liquefied products is very important to survey on mechanism and the application of products. Elemental analysis and Thermogravimetric analysis, Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) (Leonardis et al., 2013), and gas chromatography– mass spectrometry (GC–MS) are usually selected to investigate the liquefied products. In this work, bamboo shoot shell (BSS) with annual output of 17.64–22.05 million tons in China (Yu and Wang, 2010) was used as raw material. As the by-products of agriculture and forestry processing industry, BSS either be burned directly or discarded. So the survey on the use of BSS can not only improve the added value of BSS, but also have important significance in protecting the environment. Polyhydric alcohol was chosen as liquefaction solvent due to phenol is damaged to the environment and the operation of carbonate liquefaction is complicated. As for catalyst, because of the low dosage and ultra-high catalytic potential, sulfuric acid was selected as catalyst. Experiments of BSS liquefaction were carried out under different liquid–solid ratio, liquefaction temperature, reaction time, raw material size, catalyst percent based on solvents
mass, and volume ratio of mixed solvents. In addition, it is worth stating that all of liquefaction reactions were carried out at atmospheric pressure with PEG400 as solvent, EG as co-solvent and sulfuric acid as catalyst. Subsequently, reaction products were separated and analyzed. 2. Methods 2.1. Materials Polyethylene glycol 400 (PEG400) is chemically pure; ethylene glycol (EG), sulfuric acid, and acetone are analytical grade. Bamboo (Dendrocalamus latiflorus Munro) shoot shell (BSS) was collected from a bamboo processing factory in Zhangzhou city, Fujian, China. It was crushed into particles and then sieved into four parts according to the particle size: less than 180 mesh, 80–180 mesh, 40–80 mesh, more than 40 mesh. Small lump BSS was also prepared as raw material for the reaction which side length was about 0.5–1.2 cm. All the raw materials were dried at 115 °C for 12 h, and then stored in a desiccator at room temperature. 2.2. Liquefaction The reaction was carried out in a 150 ml stand-up flask with a DF-101s hot type constant temperature heating stirrer. The solvents and catalyst were fed into the flask when the reactor was heated to the desired temperature. Then the BSS was added, and timing started when the temperature was stable to the desired temperature again. After completing the desired steady reaction time, heating was stopped and the reactor was rapidly cooled to room temperature. During the reaction, reflux condensation water was used for condensing volatile components from reactants. 2.3. Separation of liquefied products The liquefied products were separated by filtration through filter paper under vacuum. Filtrate was called aqueous fraction after collected and weighed. Filter cake was put into 50 °C oven to dry, and then was washed by acetone and filtrated under vacuum until the filtrate became colorless. The second filtrate was rotary steamed to remove acetone, then weighed and called acetonesoluble fraction. The last filter cake was scraped from the filter paper, and dried in an oven at 115 °C for 12 h, weighed, collected, and called residue. Generally, all the liquefied products were separated into three fractions: aqueous fraction (AQ), acetone-soluble fraction (AS), and residue (RS). The percentage of liquefaction and the AQ, AS percentage of liquid products were calculated with the following equations respectively:
Liquefaction percentage ð%Þ ¼ 100
residue mass 100 raw material mass ð1Þ
AQ percentage ð%Þ ¼
AQ mass 100 AQ mass þ AS mass
As percentage ð%Þ ¼ 100
AQ mass 100 AQ mass þ As mass
ð2Þ
ð3Þ
2.4. Product analysis 2.4.1. Elemental analysis C, H, N contents of samples were determined by a Vario EL III element analyzer. Oxygen content was estimated based on an
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assumption that the samples only contain the elements of C, H, N, and O. The Higher Heating Value (HHV) of the sample was calculated based on the Dulong formula.
HHVðMJ=kgÞ ¼ 0:3383 C þ 1:442 ðH O=8Þ
ð4Þ
In which C, H and O represent the weight percentage of carbon, hydrogen, and oxygen, respectively. 2.4.2. Thermogravimetric analysis Analysis was performed on a TG 209-F1 thermogravimetric analyzer, the samples of raw material and residue (less than 10 mg) were analyzed and high pure air was used as the purge gas. The temperature program was from 30 to 800 °C, heating rate was 10 °C/min. 2.4.3. Fourier Transform infrared Analysis was performed on a Nicolet 380 FTIR spectrometer using potassium bromide tableting method. 2.4.4. NMR Spectroscopy 1 H NMR and 13C NMR analysis were down on an Advance II 400 spectroscopy. The sample (20 mg for 1H, 40 mg for 13C) was dissolved in 1 ml DMSO. 2.4.5. Gas chromatography–mass spectrometry The AQ and AS were analyzed qualitatively by GC–MS [QP 2010 Plus; column, REX-5MS; 30 m 0.25 mm 0.25 lm; temperature program, 40 °C (hold for 5 min)–280 °C (hold for 15 min) (rate 5 °C/ min)]. The injector was kept at 200 °C in split mode (split ratio 20:1) with helium as the carrier gas. The sample volume was 0.6 lL, and compounds were identified using the NIST library of mass spectra. 3. Result and discussion 3.1. Effect of liquefaction conditions on liquefaction percentage
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liquid–solid ratio could promote diffusion of BSS into the liquefaction solvent. When the liquid–solid ratio became 6:1, the liquefaction percentage reached to 99.30%. It was adequate to liquefy BSS, so 6:1 was chosen as liquid–solid ratio for a determined condition to do other experiments. As shown in Fig. 1, the percentage of AQ was increased due to the enlargement of liquid–solid ratio. AQ is one of the biomass degradation products, and its degradation degree is higher than another product (AS). That is to say, when liquid–solid ratio increased, the degradation degree of BSS was increasing. As a result, the AQ percentage in the product was increase. 3.1.2. Effect of liquefaction temperature The liquefaction percentages of BSS liquefaction at different temperatures are shown in Fig. 2. It is obvious that the conversion of BSS can be enormously increased with increasing temperature. When the temperature was 110 °C, the conversion was only 28.79%, and when the temperature increased to 150 °C, the conversion came to 99.16%. That is to say, when BSS is heated, there is an attack on the glycosidic linkages which leads to dehydration, decarbonylation and cleavage of the molecules into smaller soluble fragments, and result in the liquefying of BSS finally. When temperature achieved 150 °C, BSS was almost reacted completely, so higher temperature conditions had not been investigated. And 150 °C was chosen as a determined condition for other experiments subsequently. Xu et al. (2012) liquefied sawdust in hot compressed ethanol, they realized the highest conversion 97.8% under the optimum operating condition (2.5% H2SO4 as catalyst, and the liquid–solid ratio was 7.5:1, then liquefied temperature was 250 °C, 1 h of reaction time). In our work, when the temperature reached 150 °C, the conversion already reached more than 99%, which was larger than the maximum conversion they had done, and the temperature was 100 °C lower than them. The conversion of BSS increased with increasing temperature, as for AQ percentage of liquid product, it increased with increasing temperature too. The results showed that heating not only facilitate BSS liquefied, but also amplify the degradation.
3.1.1. Effect of liquid–solid ratio The liquefaction percentages of BSS liquefaction at different liquid–solid ratios are shown in Fig. 1. When the liquid–solid ratio was at lower ratio (3:1) the percentage of liquefaction was very low. Whereas, the liquefaction percentage increased greatly when the liquid–solid ratio increased from 3:1 to 5:1, and then the increasing became slow. It indicated that the increasing of
3.1.3. Effect of liquefaction time The liquefaction percentages of BSS liquefaction at different liquefaction time are shown in Fig. 3. Along with the extension of liquefaction time, the liquefaction percentages of BSS have appreciable growth firstly, and then the growth gradually slows down. The slope of the liquefaction percentage-time curve
Fig. 1. Effect of liquid–solid ratio on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Temperature, 150 °C; Time, 120 min).
Fig. 2. Effect of temperature on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Liquid–solid ratio, 6:1; Time, 120 min).
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slightly. The result was basically similar to the analysis Zhang et al. (2012) made (They used glycerol as main solvent to liquefy acid hydrolysis residue). The effect of catalyst act on the AQ percentage is also presented in Table 1. It is obvious that addition of catalyst significantly enhanced the AQ yield of liquid products. For instance, the AQ percentage increased from 60.19 to 93.62% when catalyst mass percentage increased from 1 to 3%. It means that catalyst is very important not only to promote liquefaction reaction but also reinforce the extent of biomass decomposition. Thereafter, the AQ percentage was no longer increase with the rise of catalyst content, such as catalyst percentage was 6%, and AQ percentage was 93.60%.
Fig. 3. Effect of reaction time on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Liquid–solid ratio, 6:1; Temperature, 150 °C).
represents the liquefied rate. When the curve becomes flat, the slope is reduced, and signifying that the reaction rate is dropped for the material is consumed. It can be seen from the slope of curve in Fig. 3, during the liquefaction process, liquefied rate was great at the beginning and then gradually decreased. The liquefaction percentage has not changed obviously as the liquefaction time was prolonged, which means that liquefaction has been completed mainly. So liquefaction time 80 min was considered the most suitable for this system. Fig. 3 also shows that the AQ percentage of liquid products increased from 75.47 to 93.30% when liquefaction time prolonged from 20 to 80 min. Prolonging liquefaction time, the yield was beginning to float somewhat, the changing with no regular pattern. For instance, when liquefaction time was 110 min, the AQ percentage was 92.61%, when the time increased another 10 min, the percentage reduced to 86.21%. In the later stage of reaction, there was a competition between degradation and recombination among different reactants. The recombination just corresponded to the re-polymerization of cellulose and lignin degradation products during later stage. 3.1.4. Effect of catalyst percentage Many investigations had been performed for the influence of catalyst on the liquefaction percentage; the results are given in Table 1. Table 1 shows that the conversion increased evidently when H2SO4 was added in. For instance, the BSS was almost hadn’t been liquefied without catalyst, then 1% (percentage of solvent mass) H2SO4 was added into the reactor, the conversion increased to 44.99%. When 4% H2SO4 was added, the conversion came to 98.74%. Therefore, the use of H2SO4 showed marked catalytic effect on BSS decomposition. But when the percentage of the catalyst continued to increase, the liquefaction percentage changed
Table 1 Effect of catalyst percentage on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; Liquid– solid ratio, 6:1; Temperature, 150 °C; Time, 80 min.). Catalyst percentage (%)
Liquefaction percentage (%)
AQ (wt.%)
AS (wt.%)
1.0 2.0 3.0 4.0 5.0 6.0
44.99 92.86 96.98 97.49 98.74 98.08
60.19 85.54 93.62 93.30 84.18 93.60
39.81 14.46 6.38 6.70 15.82 6.40
3.1.5. Effect of solvents volume ratio The liquefaction percentages of BSS liquefaction at different liquefaction solvents volume ratios are shown in Table 2. It was found that solvents volume ratio affected the liquefaction percentage apparently. When EG or PEG was used alone, the liquefaction percentage was 81.96% and 88.30%, respectively. But when they were mixed together as blended solvents, liquefaction yields had different degrees of improvement, respectively. For example, when PEG and EG volume ratio was 1:1, the conversion was 95.83%, which obviously had high liquefaction percentage than PEG or EG alone used as liquefying solvent. The results also show that the highest conversion of BSS was 99.79% which obtained by triplex volume PEG and one volume EG as solvent. As shown in Table 2, mixed solvent facilitated the AQ percentage of products, and the effect of PEG was clearer compared with EG. For instance, when the volume ratio of PEG:EG changed from 1:1 to 1:5, the AQ percentage changed from 96.01 to 91.33%. Unlimited increased the EG content, AQ percentage turned to 90.57%. While the ratio of PEG:EG changed from 1:1 to 5:1, the AQ percentage changed from 96.01 to 86.84%, and the limit value of AQ percentage came to 76.73% when increased PEG unlimitedly. Overall, efficiency of PEG and EG as solvent for liquefaction was better than other alcoholic solvents relatively, such as n-octanol and ethylene glycol (the conversion was about 73.30% and 45.08%) (Zou et al., 2009), glycerol (the conversion was about 50.18%) (Zhang et al., 2012). 3.1.6. Effect of raw material size The liquefaction percentages of BSS liquefaction at different raw material size are listed in Table 3. All liquefaction percentages of five different size raw materials were above 92%, the highest conversion of BSS was 99.39% (raw material size: more than 40 mesh). And interestingly, the conversion of lump raw material was 96.07%, that is to say, the conditions of the reaction are suitable methods for biomass liquefied, and it provides some insight into raw material pretreatment step, which maybe leave out. At the same time, it Table 2 Effect of solvent volume ratio on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; H2SO4 wt%, 4%; Liquid–solid ratio, 6: 1; Temperature, 150 °C; Time, 80 min.). PEG/EG (V/V)
Liquefaction percentage (%)
AQ (wt.%)
AS (wt.%)
0:1 1:5 1:4 1:3 1:2 1:1 2:1 3:1 4:1 5:1 1:0
81.96 89.83 93.17 95.98 95.12 95.83 97.85 99.79 99.39 93.63 88.30
90.57 91.33 94.26 95.78 95.71 96.01 91.59 96.43 89.75 86.84 76.73
9.43 8.67 5.74 4.22 4.29 3.99 8.41 3.57 10.25 13.16 23.27
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Table 3 Effect of raw material size on liquefaction percentage and percentages of liquid products: AQ and AS. (PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Liquid–solid ratio, 6:1; Temperature, 150 °C; Time, 80 min.). Raw material
Liquefaction percentage (%)
AQ (wt.%)
AS (wt.%)
Lump >40 mesh 40–80 mesh 80–180 mesh <180 mesh
96.07 99.39 97.49 94.91 92.20
86.06 89.75 93.30 79.60 64.30
13.94 10.25 6.70 20.40 35.70
was found that the conversions changed small relatively compared with other alterative factors. Surprisingly, the results showed that the highest conversion was obtained by more than 40 mesh raw material even though it is widely acceptable that the smaller particle size, the greater contact area, so the higher conversion under the same other conditions. Due to PEG has high viscosity, when smaller particles are added to solvent, they tend to aggregate and lead to more difficult to disperse than larger particles, so the contact situation of smaller particles is not as good as larger particles at the liquefaction beginning. From another point of view, ash is difficult to be liquefied, which may be another reason that leads to the slight variation of liquefaction percentage. The ash content of BSS in different size particles parts had a slight changed after BSS was crushed. In more detail, ash content increased with the decrease of particle size after crushed (ash content: small lump, 1.97%; more than 40 mesh, 1.55%; 40–80 mesh, 1.61%; 80–180 mesh, 1.78%; less than 180 mesh, 3.35%), and which just fit the changes of liquefaction percentage.
3.2. Products characterization 3.2.1. Elemental analysis of BSS, AQ, AS and RS Table 4 shows the Elemental analysis and higher heating values of BSS, aqueous fraction (AQ), acetone-soluble fraction (AS) and solid residue (RS), respectively. The conditions of the reaction which obtained the samples were: raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; liquid–solid ratio, 6:1; temperature, 150 °C; reaction time, 120 min; and the conversion of the reaction was 99.54%. The elemental compositions of BSS were: carbon (44.96%), hydrogen (6.22%), nitrogen (1.80%) and oxygen (47.02%). And the HHV of BSS was about 15.70 MJ/kg. To obtain higher HHV product, it is required to detach oxygen atoms. Reactions such as dehydration (AH2O), decarbonylation (ACO) and decarboxylation (ACOO) can remove oxygen from biomass. The results show that the contents of oxygen of liquid products were reduced after reaction and the HHV of products were 20.07 MJ/kg (AQ) and 23.81 MJ/kg (AS), respectively. That is to
Table 4 Elemental components and heating values of BSS and Products (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Liquid–solid ratio, 6:1; Temperature, 150 °C; Reaction time, 120 min; and the conversion is 99.54%.). Samples
BSS 40–80 mesh Aqueous fraction Acetone-soluble fraction Residue
Elemental components (wt.%)
Higher heating value (MJ/kg)
C
H
N
O
44.96 42.87 47.13
6.22 9.55 10.60
1.80 2.05 1.13
47.02 45.53 41.14
15.70 20.07 23.81
30.11
4.83
0.95
64.11
5.60
Fig. 4. TG and DTG curves of the BSS and Residue (Raw material size, 80–180 mesh; PEG:EG (V/V), 3:1; H2SO4 wt%, 5%; Liquid–solid ratio, 7:1; Temperature, 150 °C; Time, 100 min, and the conversion is 99.20%).
say, during the liquefaction process, dehydration, decarbonylation, and decarboxylation, etc. may had taken place. 3.2.2. Thermogravimetric analysis of BSS and RS The pyrolysis process of BSS and RS were investigated in a Thermogravimetric analyser (Fig. 4). As we all know the pyrolysis behavior of biomass can be seen as the sum pyrolysis process of the three major components (cellulose, hemicelluloses, and lignin). The results just corresponded to the fact, that was in detail, the main pyrolysis of hemicellulose temperature range was 220– 330 °C, and as for cellulose, the range was 330–490 °C; the pyrolysis temperature range of lignin was wide, most major weight loss temperature was among 240–580 °C. That is to say, lignin was the most difficult one to be pyrolyzed, and hemicellulose was the easiest one. The thermal degradation of RS is also shown in Fig. 4. The reduction of sample quality was no longer obvious, residual quality of RS sample was about 45.33%, while BSS sample residual quality was only 1.96%, which just corresponded to the ash of BSS. The RS sample was obtained from the test with following conditions: raw material size, 80–180 mesh; PEG:EG (V/V), 3:1; H2SO4 wt%, 5%; liquid–solid ratio, 7:1; temperature, 150 °C; time, 100 min, and the conversion of this test was 99.20%. The quality of residue sample reduced slowly in the temperature range 240– 580 °C, it was conjectured as the degradation behavior of liquefaction residual lignin. TG curve of RS had no obvious degradation phenomenon about pyrolysis of cellulose and hemicellulose, which showed that the RS almost without cellulose and hemicelluloses, further suggested that, during the process of liquefaction, cellulose and hemicellulose were easy to be liquefied, and lignin was harder to be liquefied as a comparison. 3.2.3. Fourier transform infrared analysis of BSS, AQ, AS and RS The FT-IR spectra of the samples are shown in the Supplementary Fig. 1, the samples were BSS, AQ, AS, and RS (all products were obtained by the following conditions: raw material size, 80–180 mesh; PEG:EG (V/V), 3:1; H2SO4 wt%, 5%; liquid–solid ratio, 7:1; temperature, 150 °C; time, 100 min). In the picture, obvious peak of AQ and AS samples was the broad hydroxyl peak at 3430 cm1, it was the dominating feature of the samples, which implying a large amount of hydrogen groups. While, the two solid samples had relative small peak form at this location. Another strong peak of AQ and AS at 2880 cm1 corresponded to C-H stretching which may indicative of the O = C-H stretch, but BSS and RS almost had not peak at 2880 cm1. However, there was a
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small peak of BSS and RS at 2020 cm1, respectively suggesting the existence of two double or one triple bond. It might correspond to the two double bonds in the lignin structure, which showed that lignin had not been completely degraded after the reaction completed. The result was consistent with the consequence of TG analysis. The waves at 1720 and 1640 cm1 were attributed to carbonyl bond which was characteristic of ketone, aldehyde, or carbonyl acid and ester. The wave of BSS and RS at this location was inconspicuous. Absorption at 1460 cm1 indicated bending vibration of carbon hydrogen bonds (in ACH3 and ACH2). Another intense peak at 1110 cm1 was the ether bond absorption wave which might from C-O-C asymmetry stretching. Positions of peaks were almost the same in AQ and AS infrared spectrum, that is to say, they contained the same feature groups. But structure complexity of the product is different as to the different degree of biomass degradation; it can be seen by the 13C NMR spectra in the following content 3.2.4. Of course, two kinds of mixture products cannot be guaranteed one certain substance only exist in AQ or AS, so that AQ and AS infrared spectrum always has similar peaks. 3.2.4. NMR spectroscopy analysis of AQ and AS The chemical structure information of aqueous fraction (AQ) and acetone-soluble fraction (AS) is shown in Supplementary Fig. 2. The gemessen samples were obtained from the test with following conditions: raw material size, 80–180 mesh; PEG:EG (V/V), 3:1; H2SO4 wt%, 5%; liquid–solid ratio, 7:1; temperature, 150 °C; time, 100 min. It could be seen that a large amount of alcohol and ether present in the products (3.39, 3.49, 3.78, 3.88, 3.83 ppm in 1H NMR spectrum and 60.62, 63.06, 70.12, 72.54 ppm in 13C NMR spectrum). These different shifts of peaks were the most important and obvious in the spectra, and the locations met the result that D’Souza and Yan (2013) got (about 60.2, 62.8, 69.8, 72.5 ppm in 13C NMR spectrum), they used PEG/glycerol as solvent, sulfuric acid as catalyst to liquefied bark (1.67% H2SO4 as catalyst, liquid–solid ratio was 3.16, liquefied temperature was 160 °C, time was 120 min, and the experiment was carried out under a nitrogen environment). In addition, and in more detail, both in AQ and AS 1H NMR spectra, protons of saturated hydrocarbon were detected (0.82 and 1.20 ppm in the spectra). What’s more, the peaks among 1.8–2.1 ppm in 1H NMR spectra meant the presence of double or triple bond. As for the peaks among 7.0–8.2 ppm, it meant aromatic ring proton. This just corresponded to the peaks in the 13C NMR spectra (100–110, 148.35 and 156.65 ppm). It also illustrated the benzene ring may be connected to ether bond. Moreover, there were two small peaks at 208.22 and 178.29 ppm in AS 13C NMR spectra represented carbonyl, carboxyl and its derivatives, respectively. Therefore, it can be concluded that the AQ and AS contained a large amount of multi-hydroxyl compounds. 3.2.5. Gas chromatography–mass spectrometry of AQ and AS AQ and AS were obtained from 80–180 mesh raw material using 3:1(V/V) PEG:EG as solvent, 5 wt% H2SO4 as catalyst, and the liquid–solid ratio was 7:1, then liquefied at 150 °C for 100 min. They were identified by gas chromatography–mass spectrometry (GC– MS). It was found that AQ and AS involved a large amount of carbonyl compounds derivatived from cellulose and hemicelluloses. These compounds were 2, 2-dimethoxybutane, 1- (3, 4-methylenedioxybenzylidene) semicarbazide, propane, butanoic acid, 4(benzolmethyl) -6-methyl-2H-1, and aldehyde mainly. This result was in good agreement with the results of FT-IR and NMR analysis. 4. Conclusion Bamboo (Dendrocalamus latiflorus Munro) shoot shell (BSS) was effectively liquefied in PEG 400/EG blended liquefying solvents in
the presence of sulfuric acid as catalyst at ordinary pressure, the highest conversion is 99.79%. Six factors have different effect on the liquefaction. Catalyst, temperature, liquid–solid ratio affect the liquefaction evidently, while reaction time, raw material size and solvents volume ratio change the liquefaction relatively unconspicuous. The higher heating values of liquid products are 20.07 and 23.81 MJ/kg, and they contain hydroxyl and carbonyl abundantly, means that they have potential to make fuels and chemical products. Acknowledgements The authors would like to thank the financial support from the Key Planning Project of Science and Technology of Fujian Province, China (Grant number 2011N0035). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.biortech. 2013.11.070. References Cheng, S.N., D’cruz, I., Wang, M.C., 2010. Highly efficient liquefaction of woody biomass in hot-compressed alcohol-water co-solvents. Energy Fuels 24, 4659– 4667. Chow, M.C., Jackson, W.R., Chaffee, A.L., Marshall, M., 2013. Thermal treatment of algae for production of biofuel. Energy Fuels 27, 1926–1950. D’Souza, J., Yan, N., 2013. Producing bark-based polyols through liquefaction: effect of liquefaction temperature. ACS Sustain. Chem. Eng. 1, 534–540. Duan, P.G., Savage, P.E., 2011. Hydrothermal liquefaction of a microalga with heterogeneous catalysts. Ind. Eng. Chem. Res. 50, 52–61. Duan, P.G., Jin, B.B., Xu, Y.P., Yang, Y., Bai, X.J., Wang, F., Zhang, L., Miao, J., 2013. Thermo-chemical conversion of chlorella pyrenoidosa to liquid biofuels. Bioresour. Technol. 133, 197–205. Elliott, D.C., Beckman, D., Bridgwater, A.V., Diebold, J.P., Gevert, S.B., Solantausta, Y., 1991. Developments in direct thermochemical liquefaction of biomass: 1983– 1990. Energy Fuels 5, 399–410. Faeth, J.L., Valdez, P.J., Savage, P.E., 2013. Fast hydrothermal liquefaction of nannochloropsis sp. to produce biocrude. Energy Fuels 27, 1391–1398. Huang, Y.X., Liu, X., Zhang, S.B., 2012. Research and application on biomass adhesive at home and abroad. Wood Process. Machinery 1, 26–29. Jin, Y.Q., Ruan, X.M., Cheng, X.S., Lü, Q.F., 2011. Liquefaction of lignin by polyethyleneglycol and glycerol. Bioresour. Technol. 102, 3581–3583. Kadla, J.F., Kubo, S., Venditti, R.A., Gilbert, R.D., Compere, A.L., Griffith, W., 2002. Lignin-based carbon fibers for composite fiber applications. Carbon 40, 2913– 2920. Kunaver, M., Jasiukaityte, E., Cuk, N., 2012. Ultrasonically assisted liquefaction of lignocellulosic materials. Bioresour. Technol. 103, 360–366. Kurimoto, Y., Koizumi, A., Doi, S., Tamura, Y., Ono, H., 2001. Wood species effects on the characteristics of liquefied wood and the properties of polyurethane films prepared from the liquefied wood. Biomass Bioenergy 5, 381–390. Leonardis, I., Chiaberge, S., Fiorani, T., Spera, S., Battistel, E., Bosetti, A., Cesti, P., Reale, S., De Angelis, F., 2013. Characterization of bio-oil from hydrothermal liquefaction of organic waste by NMR spectroscopy and FTICR mass spectrometry. ChemSusChem 6, 160–167. Liu, H.M., Li, M.F., Sun, R.C., 2013. Hydrothermal liquefaction of cornstalk: 7-lump distribution and characterization of products. Bioresour. Technol. 128, 58–64. Lu, Z.X., Zheng, H.Y., Fan, L.W., Liao, Y.Q., Ding, B.J., Huang, B., 2013. Liquefaction of sawdust in 1-octanol using acidic ionic liquids as catalyst. Bioresour. Technol. 142, 579–584. Nakano, T., 1994. Mechanism of thermoplasticity for chemically modified wood. Holzforschung 48, 318–324. ~ oz, M.J., Vila, C., Santos, V., Parajól, J.C., 2013. Manufacture of Rivas, S., Gonza´lez-Mun levulinic acid from pine wood hemicelluloses: a kinetic assessment. Ind. Eng. Chem. Res. 52, 3951–3957. Samir, B., Romualdo, C., Debora, F., 2012. Direct liquefaction of ligno-cellulosic residues for liquid fuel production. Fuel 94, 324–332. Sandeep, K., Ram, B.G., 2009. Biocrude production from switchgrass using subcritical water. Energy Fuels 23, 5151–5159. Tekin, K., Karagoz, S., 2013. t-BuOK catalyzed bio-oil production from woody biomass under sub-critical water conditions. Environ. Chem. Lett. 11, 25–31. Tevfik, A., Mehmet, M.K., 2013. Liquefaction of giant reed by supercritical fluid extraction. Fuel 103, 758–763. Theegala, C.S., Midgett, J.S., 2012. Hydrothermal liquefaction of separated dairy manure for production of bio-oils with simultaneous waste treatment. Bioresour. Technol. 107, 456–463.
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Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Liquefaction of bamboo shoot shell for the production of polyols Liyi Ye ⇑, Jingmiao Zhang, Jie Zhao, Song Tu ⇑ Department of Chemical and Biochemical Engineering, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Bamboo (D.latiflorus Munro) shoot
shell was used as raw material for liquefaction. Bamboo (D.latiflorus Munro) shoot shell was liquefied efficiently to produce polyols. Liquefaction products were analysed by element analysis, TG, FT-IR, NMR, and GC–MS.
a r t i c l e
i n f o
Article history: Received 18 September 2013 Received in revised form 23 November 2013 Accepted 25 November 2013 Available online 1 December 2013 Keywords: Bamboo shoot shell Liquefaction Polyols Sulfuric acid Liquefaction percentage
a b s t r a c t Bamboo (Dendrocalamus latiflorus Munro) shoot shell (BSS) was liquefied in polyethylene glycol 400 (PEG400) and ethylene glycol (EG) catalyzed by sulfuric acid under atmospheric pressure. The effects of liquefaction conditions such as liquid–solid ratio, temperature, time, catalyst, solvents ratio, and material size on the liquefaction yield of BSS have been investigated. Methods including Elemental analysis, Thermogravimetric analysis, Fourier transform infrared spectroscopy, nuclear magnetic resonance and gas chromatography–mass spectrometry were selected to analyze the characteristics of products in three fractions: an aqueous fraction (AQ), an acetone-soluble fraction (AS) and a residue (RS), respectively. Results showed that the highest liquefaction percentage was 99.79% under the optimal conditions (liquid–solid ratio 6:1; temperature 150 °C; reaction time 80 min; raw size more than 40 mesh; catalyst mass percentage of solvent 4%; solvent volume ratio 3:1). Polyols could be obtained effectively by the liquefaction of BSS, an agricultural by-product. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Biomass has attracted great interest as a renewable raw material for the production of fuel oil (Samir et al., 2012), adhesives (Zhao et al., 2013; Huang et al., 2012), polyurethane material (Zou et al., 2012; Kurimoto et al., 2001; Ueno, 2007) and carbon fiber (Kadla et al., 2002). Biomass energy is inferior to coal, oil, natural gas and is the fourth largest energy. It cannot be ignored that biomass has significant effect on the world energy crisis and environmental problems due to it is a renewable and vast nature resource. Furthermore, as a resource it has many advantages such as quantity, variety, low content of S and N, zero carbon emission, ⇑ Corresponding authors. Tel./fax: +86 0592 2184887, +86 0592 2186020. E-mail addresses: [email protected] (L. Ye), [email protected] (S. Tu). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.11.070
etc. Recently significant efforts have been made to use renewable resources effectively through methods such as pyrolysis, gasification, and liquefaction. But liquefaction has attracted more attention due to its simple operation, high production level, high energy conversion, and powerful organic material treatment ability. Biomass liquefaction research focused on the liquefaction of modified raw material (Nakano, 1994) at the early stage. But because of its intense reaction conditions, complex methods and high cost, researchers trended to liquefy biomass directly, and tried to change the solvent and catalyst to make the liquefaction process more perfect. Recently, researchers pretreated the biomass by new technologies such as ultrasound (Kunaver et al., 2012) and microwave (Zhuang et al., 2012) before liquefaction. Up to now, the methods of liquefaction mainly include: liquefaction with solvent
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and catalyst (Duan and Savage, 2011), direct liquefaction with solvent (Elliott et al., 1991), liquefaction after pretreatment such as chemical modification or new technologies (Kunaver et al., 2012), liquefaction under high temperature and high pressure (Yuan et al., 2011), liquefaction with supercritical fluid (Sandeep and Ram, 2009; Tevfik and Mehmet, 2013), nanometer powder of material liquefaction and so on. Of course, different methods could be used together in the process. From the work of other researchers (Zou et al., 2009; D’Souza and Yan, 2013), it is known that three series of reactions including decomposition, esterification, and polycondensation mainly occurred during the liquefaction. And the reaction conditions always decide the intensity of the reaction, the structure and performance of the products. Now biomass liquefaction researchers have made a lot of work in such aspects as raw materials, solvents, and catalysts. Raw materials such as algae (Chow et al., 2013; Duan et al., 2013), giant reed (Tevfik and Mehmet, 2013), bagasse (Zhang et al., 2007), cop residue (Liu et al., 2013; Zhang et al., 2012), bark (D’Souza and Yan, 2013), wood (Rivas et al., 2013; Tekin and Karagoz, 2013; Cheng et al., 2010), sawdust (Xu et al., 2012), switchgrass (Sandeep and Ram, 2009), nannochloropsis (Faeth et al., 2013), straw (Yuan et al., 2009), poplar (Wu et al., 2008), manure (Theegala and Midgett, 2012) have been liquefied effectively. There are three series of solvents used: phenol, polyhydric alcohols, and cyclic carbonate, and various products are obtained by different types of solvents. The liquefaction products of phenol including phenolate derivatives, and it can react with formaldehyde to produce phenolic resin. The liquefaction product of polyhydric-alcohol is polyester or polyether polyols which riches in hydroxyl, and polyurethane materials with excellent properties can be obtained after putting in isocyanate. Moreover, excellent resin adhesive agent can also be obtained by reaction of liquefaction products of bagasse, wood and other plant fiber with additive such as cross-linking agent, curing agent. Besides alkali catalysts (Tekin and Karagoz, 2013) and acidic ionic liquids (Lu et al., 2013; Zhou et al., 2013), some inorganic acid (Zhang et al., 2007) can be used as catalyst, for example, perchloric acid, sulfuric acid (Zhuang et al., 2012) benzene sulfonic acid, hydrochloric acid, phosphoric acid and so on. However, almost all of biomass are solid and have complex composition, meanwhile, they are refractory, indissolvable, physically and chemically stable. The different molecular structure leads to different reaction mechanism (Zou et al., 2009) and reactivity, suggesting difficulty in studying liquefaction mechanism. So researchers usually analyze the liquefaction mechanism through the liquefaction of cellulose and lignin (Jin et al., 2011). Liquefaction mechanism can also be conjectured based on composition of liquefied production. So analysis of liquefied products is very important to survey on mechanism and the application of products. Elemental analysis and Thermogravimetric analysis, Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) (Leonardis et al., 2013), and gas chromatography– mass spectrometry (GC–MS) are usually selected to investigate the liquefied products. In this work, bamboo shoot shell (BSS) with annual output of 17.64–22.05 million tons in China (Yu and Wang, 2010) was used as raw material. As the by-products of agriculture and forestry processing industry, BSS either be burned directly or discarded. So the survey on the use of BSS can not only improve the added value of BSS, but also have important significance in protecting the environment. Polyhydric alcohol was chosen as liquefaction solvent due to phenol is damaged to the environment and the operation of carbonate liquefaction is complicated. As for catalyst, because of the low dosage and ultra-high catalytic potential, sulfuric acid was selected as catalyst. Experiments of BSS liquefaction were carried out under different liquid–solid ratio, liquefaction temperature, reaction time, raw material size, catalyst percent based on solvents
mass, and volume ratio of mixed solvents. In addition, it is worth stating that all of liquefaction reactions were carried out at atmospheric pressure with PEG400 as solvent, EG as co-solvent and sulfuric acid as catalyst. Subsequently, reaction products were separated and analyzed. 2. Methods 2.1. Materials Polyethylene glycol 400 (PEG400) is chemically pure; ethylene glycol (EG), sulfuric acid, and acetone are analytical grade. Bamboo (Dendrocalamus latiflorus Munro) shoot shell (BSS) was collected from a bamboo processing factory in Zhangzhou city, Fujian, China. It was crushed into particles and then sieved into four parts according to the particle size: less than 180 mesh, 80–180 mesh, 40–80 mesh, more than 40 mesh. Small lump BSS was also prepared as raw material for the reaction which side length was about 0.5–1.2 cm. All the raw materials were dried at 115 °C for 12 h, and then stored in a desiccator at room temperature. 2.2. Liquefaction The reaction was carried out in a 150 ml stand-up flask with a DF-101s hot type constant temperature heating stirrer. The solvents and catalyst were fed into the flask when the reactor was heated to the desired temperature. Then the BSS was added, and timing started when the temperature was stable to the desired temperature again. After completing the desired steady reaction time, heating was stopped and the reactor was rapidly cooled to room temperature. During the reaction, reflux condensation water was used for condensing volatile components from reactants. 2.3. Separation of liquefied products The liquefied products were separated by filtration through filter paper under vacuum. Filtrate was called aqueous fraction after collected and weighed. Filter cake was put into 50 °C oven to dry, and then was washed by acetone and filtrated under vacuum until the filtrate became colorless. The second filtrate was rotary steamed to remove acetone, then weighed and called acetonesoluble fraction. The last filter cake was scraped from the filter paper, and dried in an oven at 115 °C for 12 h, weighed, collected, and called residue. Generally, all the liquefied products were separated into three fractions: aqueous fraction (AQ), acetone-soluble fraction (AS), and residue (RS). The percentage of liquefaction and the AQ, AS percentage of liquid products were calculated with the following equations respectively:
Liquefaction percentage ð%Þ ¼ 100
residue mass 100 raw material mass ð1Þ
AQ percentage ð%Þ ¼
AQ mass 100 AQ mass þ AS mass
As percentage ð%Þ ¼ 100
AQ mass 100 AQ mass þ As mass
ð2Þ
ð3Þ
2.4. Product analysis 2.4.1. Elemental analysis C, H, N contents of samples were determined by a Vario EL III element analyzer. Oxygen content was estimated based on an
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assumption that the samples only contain the elements of C, H, N, and O. The Higher Heating Value (HHV) of the sample was calculated based on the Dulong formula.
HHVðMJ=kgÞ ¼ 0:3383 C þ 1:442 ðH O=8Þ
ð4Þ
In which C, H and O represent the weight percentage of carbon, hydrogen, and oxygen, respectively. 2.4.2. Thermogravimetric analysis Analysis was performed on a TG 209-F1 thermogravimetric analyzer, the samples of raw material and residue (less than 10 mg) were analyzed and high pure air was used as the purge gas. The temperature program was from 30 to 800 °C, heating rate was 10 °C/min. 2.4.3. Fourier Transform infrared Analysis was performed on a Nicolet 380 FTIR spectrometer using potassium bromide tableting method. 2.4.4. NMR Spectroscopy 1 H NMR and 13C NMR analysis were down on an Advance II 400 spectroscopy. The sample (20 mg for 1H, 40 mg for 13C) was dissolved in 1 ml DMSO. 2.4.5. Gas chromatography–mass spectrometry The AQ and AS were analyzed qualitatively by GC–MS [QP 2010 Plus; column, REX-5MS; 30 m 0.25 mm 0.25 lm; temperature program, 40 °C (hold for 5 min)–280 °C (hold for 15 min) (rate 5 °C/ min)]. The injector was kept at 200 °C in split mode (split ratio 20:1) with helium as the carrier gas. The sample volume was 0.6 lL, and compounds were identified using the NIST library of mass spectra. 3. Result and discussion 3.1. Effect of liquefaction conditions on liquefaction percentage
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liquid–solid ratio could promote diffusion of BSS into the liquefaction solvent. When the liquid–solid ratio became 6:1, the liquefaction percentage reached to 99.30%. It was adequate to liquefy BSS, so 6:1 was chosen as liquid–solid ratio for a determined condition to do other experiments. As shown in Fig. 1, the percentage of AQ was increased due to the enlargement of liquid–solid ratio. AQ is one of the biomass degradation products, and its degradation degree is higher than another product (AS). That is to say, when liquid–solid ratio increased, the degradation degree of BSS was increasing. As a result, the AQ percentage in the product was increase. 3.1.2. Effect of liquefaction temperature The liquefaction percentages of BSS liquefaction at different temperatures are shown in Fig. 2. It is obvious that the conversion of BSS can be enormously increased with increasing temperature. When the temperature was 110 °C, the conversion was only 28.79%, and when the temperature increased to 150 °C, the conversion came to 99.16%. That is to say, when BSS is heated, there is an attack on the glycosidic linkages which leads to dehydration, decarbonylation and cleavage of the molecules into smaller soluble fragments, and result in the liquefying of BSS finally. When temperature achieved 150 °C, BSS was almost reacted completely, so higher temperature conditions had not been investigated. And 150 °C was chosen as a determined condition for other experiments subsequently. Xu et al. (2012) liquefied sawdust in hot compressed ethanol, they realized the highest conversion 97.8% under the optimum operating condition (2.5% H2SO4 as catalyst, and the liquid–solid ratio was 7.5:1, then liquefied temperature was 250 °C, 1 h of reaction time). In our work, when the temperature reached 150 °C, the conversion already reached more than 99%, which was larger than the maximum conversion they had done, and the temperature was 100 °C lower than them. The conversion of BSS increased with increasing temperature, as for AQ percentage of liquid product, it increased with increasing temperature too. The results showed that heating not only facilitate BSS liquefied, but also amplify the degradation.
3.1.1. Effect of liquid–solid ratio The liquefaction percentages of BSS liquefaction at different liquid–solid ratios are shown in Fig. 1. When the liquid–solid ratio was at lower ratio (3:1) the percentage of liquefaction was very low. Whereas, the liquefaction percentage increased greatly when the liquid–solid ratio increased from 3:1 to 5:1, and then the increasing became slow. It indicated that the increasing of
3.1.3. Effect of liquefaction time The liquefaction percentages of BSS liquefaction at different liquefaction time are shown in Fig. 3. Along with the extension of liquefaction time, the liquefaction percentages of BSS have appreciable growth firstly, and then the growth gradually slows down. The slope of the liquefaction percentage-time curve
Fig. 1. Effect of liquid–solid ratio on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Temperature, 150 °C; Time, 120 min).
Fig. 2. Effect of temperature on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Liquid–solid ratio, 6:1; Time, 120 min).
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slightly. The result was basically similar to the analysis Zhang et al. (2012) made (They used glycerol as main solvent to liquefy acid hydrolysis residue). The effect of catalyst act on the AQ percentage is also presented in Table 1. It is obvious that addition of catalyst significantly enhanced the AQ yield of liquid products. For instance, the AQ percentage increased from 60.19 to 93.62% when catalyst mass percentage increased from 1 to 3%. It means that catalyst is very important not only to promote liquefaction reaction but also reinforce the extent of biomass decomposition. Thereafter, the AQ percentage was no longer increase with the rise of catalyst content, such as catalyst percentage was 6%, and AQ percentage was 93.60%.
Fig. 3. Effect of reaction time on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Liquid–solid ratio, 6:1; Temperature, 150 °C).
represents the liquefied rate. When the curve becomes flat, the slope is reduced, and signifying that the reaction rate is dropped for the material is consumed. It can be seen from the slope of curve in Fig. 3, during the liquefaction process, liquefied rate was great at the beginning and then gradually decreased. The liquefaction percentage has not changed obviously as the liquefaction time was prolonged, which means that liquefaction has been completed mainly. So liquefaction time 80 min was considered the most suitable for this system. Fig. 3 also shows that the AQ percentage of liquid products increased from 75.47 to 93.30% when liquefaction time prolonged from 20 to 80 min. Prolonging liquefaction time, the yield was beginning to float somewhat, the changing with no regular pattern. For instance, when liquefaction time was 110 min, the AQ percentage was 92.61%, when the time increased another 10 min, the percentage reduced to 86.21%. In the later stage of reaction, there was a competition between degradation and recombination among different reactants. The recombination just corresponded to the re-polymerization of cellulose and lignin degradation products during later stage. 3.1.4. Effect of catalyst percentage Many investigations had been performed for the influence of catalyst on the liquefaction percentage; the results are given in Table 1. Table 1 shows that the conversion increased evidently when H2SO4 was added in. For instance, the BSS was almost hadn’t been liquefied without catalyst, then 1% (percentage of solvent mass) H2SO4 was added into the reactor, the conversion increased to 44.99%. When 4% H2SO4 was added, the conversion came to 98.74%. Therefore, the use of H2SO4 showed marked catalytic effect on BSS decomposition. But when the percentage of the catalyst continued to increase, the liquefaction percentage changed
Table 1 Effect of catalyst percentage on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; Liquid– solid ratio, 6:1; Temperature, 150 °C; Time, 80 min.). Catalyst percentage (%)
Liquefaction percentage (%)
AQ (wt.%)
AS (wt.%)
1.0 2.0 3.0 4.0 5.0 6.0
44.99 92.86 96.98 97.49 98.74 98.08
60.19 85.54 93.62 93.30 84.18 93.60
39.81 14.46 6.38 6.70 15.82 6.40
3.1.5. Effect of solvents volume ratio The liquefaction percentages of BSS liquefaction at different liquefaction solvents volume ratios are shown in Table 2. It was found that solvents volume ratio affected the liquefaction percentage apparently. When EG or PEG was used alone, the liquefaction percentage was 81.96% and 88.30%, respectively. But when they were mixed together as blended solvents, liquefaction yields had different degrees of improvement, respectively. For example, when PEG and EG volume ratio was 1:1, the conversion was 95.83%, which obviously had high liquefaction percentage than PEG or EG alone used as liquefying solvent. The results also show that the highest conversion of BSS was 99.79% which obtained by triplex volume PEG and one volume EG as solvent. As shown in Table 2, mixed solvent facilitated the AQ percentage of products, and the effect of PEG was clearer compared with EG. For instance, when the volume ratio of PEG:EG changed from 1:1 to 1:5, the AQ percentage changed from 96.01 to 91.33%. Unlimited increased the EG content, AQ percentage turned to 90.57%. While the ratio of PEG:EG changed from 1:1 to 5:1, the AQ percentage changed from 96.01 to 86.84%, and the limit value of AQ percentage came to 76.73% when increased PEG unlimitedly. Overall, efficiency of PEG and EG as solvent for liquefaction was better than other alcoholic solvents relatively, such as n-octanol and ethylene glycol (the conversion was about 73.30% and 45.08%) (Zou et al., 2009), glycerol (the conversion was about 50.18%) (Zhang et al., 2012). 3.1.6. Effect of raw material size The liquefaction percentages of BSS liquefaction at different raw material size are listed in Table 3. All liquefaction percentages of five different size raw materials were above 92%, the highest conversion of BSS was 99.39% (raw material size: more than 40 mesh). And interestingly, the conversion of lump raw material was 96.07%, that is to say, the conditions of the reaction are suitable methods for biomass liquefied, and it provides some insight into raw material pretreatment step, which maybe leave out. At the same time, it Table 2 Effect of solvent volume ratio on liquefaction percentage and percentages of liquid products: AQ and AS. (Raw material size, 40–80 mesh; H2SO4 wt%, 4%; Liquid–solid ratio, 6: 1; Temperature, 150 °C; Time, 80 min.). PEG/EG (V/V)
Liquefaction percentage (%)
AQ (wt.%)
AS (wt.%)
0:1 1:5 1:4 1:3 1:2 1:1 2:1 3:1 4:1 5:1 1:0
81.96 89.83 93.17 95.98 95.12 95.83 97.85 99.79 99.39 93.63 88.30
90.57 91.33 94.26 95.78 95.71 96.01 91.59 96.43 89.75 86.84 76.73
9.43 8.67 5.74 4.22 4.29 3.99 8.41 3.57 10.25 13.16 23.27
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Table 3 Effect of raw material size on liquefaction percentage and percentages of liquid products: AQ and AS. (PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Liquid–solid ratio, 6:1; Temperature, 150 °C; Time, 80 min.). Raw material
Liquefaction percentage (%)
AQ (wt.%)
AS (wt.%)
Lump >40 mesh 40–80 mesh 80–180 mesh <180 mesh
96.07 99.39 97.49 94.91 92.20
86.06 89.75 93.30 79.60 64.30
13.94 10.25 6.70 20.40 35.70
was found that the conversions changed small relatively compared with other alterative factors. Surprisingly, the results showed that the highest conversion was obtained by more than 40 mesh raw material even though it is widely acceptable that the smaller particle size, the greater contact area, so the higher conversion under the same other conditions. Due to PEG has high viscosity, when smaller particles are added to solvent, they tend to aggregate and lead to more difficult to disperse than larger particles, so the contact situation of smaller particles is not as good as larger particles at the liquefaction beginning. From another point of view, ash is difficult to be liquefied, which may be another reason that leads to the slight variation of liquefaction percentage. The ash content of BSS in different size particles parts had a slight changed after BSS was crushed. In more detail, ash content increased with the decrease of particle size after crushed (ash content: small lump, 1.97%; more than 40 mesh, 1.55%; 40–80 mesh, 1.61%; 80–180 mesh, 1.78%; less than 180 mesh, 3.35%), and which just fit the changes of liquefaction percentage.
3.2. Products characterization 3.2.1. Elemental analysis of BSS, AQ, AS and RS Table 4 shows the Elemental analysis and higher heating values of BSS, aqueous fraction (AQ), acetone-soluble fraction (AS) and solid residue (RS), respectively. The conditions of the reaction which obtained the samples were: raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; liquid–solid ratio, 6:1; temperature, 150 °C; reaction time, 120 min; and the conversion of the reaction was 99.54%. The elemental compositions of BSS were: carbon (44.96%), hydrogen (6.22%), nitrogen (1.80%) and oxygen (47.02%). And the HHV of BSS was about 15.70 MJ/kg. To obtain higher HHV product, it is required to detach oxygen atoms. Reactions such as dehydration (AH2O), decarbonylation (ACO) and decarboxylation (ACOO) can remove oxygen from biomass. The results show that the contents of oxygen of liquid products were reduced after reaction and the HHV of products were 20.07 MJ/kg (AQ) and 23.81 MJ/kg (AS), respectively. That is to
Table 4 Elemental components and heating values of BSS and Products (Raw material size, 40–80 mesh; PEG:EG (V/V), 4:1; H2SO4 wt%, 4%; Liquid–solid ratio, 6:1; Temperature, 150 °C; Reaction time, 120 min; and the conversion is 99.54%.). Samples
BSS 40–80 mesh Aqueous fraction Acetone-soluble fraction Residue
Elemental components (wt.%)
Higher heating value (MJ/kg)
C
H
N
O
44.96 42.87 47.13
6.22 9.55 10.60
1.80 2.05 1.13
47.02 45.53 41.14
15.70 20.07 23.81
30.11
4.83
0.95
64.11
5.60
Fig. 4. TG and DTG curves of the BSS and Residue (Raw material size, 80–180 mesh; PEG:EG (V/V), 3:1; H2SO4 wt%, 5%; Liquid–solid ratio, 7:1; Temperature, 150 °C; Time, 100 min, and the conversion is 99.20%).
say, during the liquefaction process, dehydration, decarbonylation, and decarboxylation, etc. may had taken place. 3.2.2. Thermogravimetric analysis of BSS and RS The pyrolysis process of BSS and RS were investigated in a Thermogravimetric analyser (Fig. 4). As we all know the pyrolysis behavior of biomass can be seen as the sum pyrolysis process of the three major components (cellulose, hemicelluloses, and lignin). The results just corresponded to the fact, that was in detail, the main pyrolysis of hemicellulose temperature range was 220– 330 °C, and as for cellulose, the range was 330–490 °C; the pyrolysis temperature range of lignin was wide, most major weight loss temperature was among 240–580 °C. That is to say, lignin was the most difficult one to be pyrolyzed, and hemicellulose was the easiest one. The thermal degradation of RS is also shown in Fig. 4. The reduction of sample quality was no longer obvious, residual quality of RS sample was about 45.33%, while BSS sample residual quality was only 1.96%, which just corresponded to the ash of BSS. The RS sample was obtained from the test with following conditions: raw material size, 80–180 mesh; PEG:EG (V/V), 3:1; H2SO4 wt%, 5%; liquid–solid ratio, 7:1; temperature, 150 °C; time, 100 min, and the conversion of this test was 99.20%. The quality of residue sample reduced slowly in the temperature range 240– 580 °C, it was conjectured as the degradation behavior of liquefaction residual lignin. TG curve of RS had no obvious degradation phenomenon about pyrolysis of cellulose and hemicellulose, which showed that the RS almost without cellulose and hemicelluloses, further suggested that, during the process of liquefaction, cellulose and hemicellulose were easy to be liquefied, and lignin was harder to be liquefied as a comparison. 3.2.3. Fourier transform infrared analysis of BSS, AQ, AS and RS The FT-IR spectra of the samples are shown in the Supplementary Fig. 1, the samples were BSS, AQ, AS, and RS (all products were obtained by the following conditions: raw material size, 80–180 mesh; PEG:EG (V/V), 3:1; H2SO4 wt%, 5%; liquid–solid ratio, 7:1; temperature, 150 °C; time, 100 min). In the picture, obvious peak of AQ and AS samples was the broad hydroxyl peak at 3430 cm1, it was the dominating feature of the samples, which implying a large amount of hydrogen groups. While, the two solid samples had relative small peak form at this location. Another strong peak of AQ and AS at 2880 cm1 corresponded to C-H stretching which may indicative of the O = C-H stretch, but BSS and RS almost had not peak at 2880 cm1. However, there was a
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small peak of BSS and RS at 2020 cm1, respectively suggesting the existence of two double or one triple bond. It might correspond to the two double bonds in the lignin structure, which showed that lignin had not been completely degraded after the reaction completed. The result was consistent with the consequence of TG analysis. The waves at 1720 and 1640 cm1 were attributed to carbonyl bond which was characteristic of ketone, aldehyde, or carbonyl acid and ester. The wave of BSS and RS at this location was inconspicuous. Absorption at 1460 cm1 indicated bending vibration of carbon hydrogen bonds (in ACH3 and ACH2). Another intense peak at 1110 cm1 was the ether bond absorption wave which might from C-O-C asymmetry stretching. Positions of peaks were almost the same in AQ and AS infrared spectrum, that is to say, they contained the same feature groups. But structure complexity of the product is different as to the different degree of biomass degradation; it can be seen by the 13C NMR spectra in the following content 3.2.4. Of course, two kinds of mixture products cannot be guaranteed one certain substance only exist in AQ or AS, so that AQ and AS infrared spectrum always has similar peaks. 3.2.4. NMR spectroscopy analysis of AQ and AS The chemical structure information of aqueous fraction (AQ) and acetone-soluble fraction (AS) is shown in Supplementary Fig. 2. The gemessen samples were obtained from the test with following conditions: raw material size, 80–180 mesh; PEG:EG (V/V), 3:1; H2SO4 wt%, 5%; liquid–solid ratio, 7:1; temperature, 150 °C; time, 100 min. It could be seen that a large amount of alcohol and ether present in the products (3.39, 3.49, 3.78, 3.88, 3.83 ppm in 1H NMR spectrum and 60.62, 63.06, 70.12, 72.54 ppm in 13C NMR spectrum). These different shifts of peaks were the most important and obvious in the spectra, and the locations met the result that D’Souza and Yan (2013) got (about 60.2, 62.8, 69.8, 72.5 ppm in 13C NMR spectrum), they used PEG/glycerol as solvent, sulfuric acid as catalyst to liquefied bark (1.67% H2SO4 as catalyst, liquid–solid ratio was 3.16, liquefied temperature was 160 °C, time was 120 min, and the experiment was carried out under a nitrogen environment). In addition, and in more detail, both in AQ and AS 1H NMR spectra, protons of saturated hydrocarbon were detected (0.82 and 1.20 ppm in the spectra). What’s more, the peaks among 1.8–2.1 ppm in 1H NMR spectra meant the presence of double or triple bond. As for the peaks among 7.0–8.2 ppm, it meant aromatic ring proton. This just corresponded to the peaks in the 13C NMR spectra (100–110, 148.35 and 156.65 ppm). It also illustrated the benzene ring may be connected to ether bond. Moreover, there were two small peaks at 208.22 and 178.29 ppm in AS 13C NMR spectra represented carbonyl, carboxyl and its derivatives, respectively. Therefore, it can be concluded that the AQ and AS contained a large amount of multi-hydroxyl compounds. 3.2.5. Gas chromatography–mass spectrometry of AQ and AS AQ and AS were obtained from 80–180 mesh raw material using 3:1(V/V) PEG:EG as solvent, 5 wt% H2SO4 as catalyst, and the liquid–solid ratio was 7:1, then liquefied at 150 °C for 100 min. They were identified by gas chromatography–mass spectrometry (GC– MS). It was found that AQ and AS involved a large amount of carbonyl compounds derivatived from cellulose and hemicelluloses. These compounds were 2, 2-dimethoxybutane, 1- (3, 4-methylenedioxybenzylidene) semicarbazide, propane, butanoic acid, 4(benzolmethyl) -6-methyl-2H-1, and aldehyde mainly. This result was in good agreement with the results of FT-IR and NMR analysis. 4. Conclusion Bamboo (Dendrocalamus latiflorus Munro) shoot shell (BSS) was effectively liquefied in PEG 400/EG blended liquefying solvents in
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