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Co-pyrolysis characteristics of the sugarcane bagasse and Enteromorpha prolifera
Energy Conversion and Management 120 (2016) 238–246
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Co-pyrolysis characteristics of the sugarcane bagasse and Enteromorpha prolifera Mei-Yu Hua, Bao-Xia Li ⇑ Department of Chemical Engineering, Huaqiao University, Xiamen, Fujian 361021, China
a r t i c l e
i n f o
Article history: Received 11 December 2015 Received in revised form 4 April 2016 Accepted 21 April 2016
Keywords: Co-pyrolysis Enteromorpha prolifera Biomass Bio-oil Mechanism Fixed-bed reactor
a b s t r a c t Enteromorpha prolifera, a green algae, has been spreading widely in China in recent years, resulting in a series of adverse impacts, such as the water eutrophication and the outbreak of green tides. Thus, it is necessary to develop an extensively available method to transfer marine biomass waste into highvalue products. In this study, Co-pyrolysis of sugarcane bagasse and E. prolifera was carried out in a fixed-bed reactor. The positive effects between sugarcane bagasse and E. prolifera were evidenced, as the acidity and density of the bio-oils from co-pyrolysis decreased and calorific value increased with respect to that of the merely biomass pyrolysis. When the ratio of the two components was 50/50, the bio-oil got the highest yield of 56.12 wt% and the high heating value of the bio-oil was 26.4 MJ/kg, which were 11.48%, 2.47% higher than the theoretical values, respectively. The acidity and density of the co-pyrolysis bio-oil at 50/50 blends were 51.62 mgKOH/g and 1.1185 g/cm3, which were 16.18%, 6.29% lower than the theoretical values, respectively. The analysis of bio-oil compositions showed that the bio-oil from co-pyrolysis of the blends could be a potential source of renewable fuel with lower content of acid, ketone, aldehyde, phenolic compounds and higher content of hydrocarbon, alcohol, ester compounds. In addition, the concentration of C2–C4 hydrocarbon gases produced through co-pyrolysis of the blends increased as the amount of E. prolifera increased in the blend. The co-pyrolysis chars had higher calorific values compared to that through pyrolysis of E. prolifera alone. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction With the development of world economy, energy consumption increases rapidly, and energy poverty is becoming more and more prominent. The exploration and development of safe and sustainable alternatives to fossil fuels are two of the most important global priorities today [1]. Bio-oil is a renewable and clean energy product, which is able to reduce dependence on fossil fuels, improve the security of supply, cut down greenhouse gas emissions, and create environmental benefits [2]. Biomass (such as agricultural crops and residues) that can be used as feedstock for the production of biofuels. The pyrolysis process of the biomass has received considerable attention. Many researchers [3–5] have investigated different pyrolysis conditions to determine the role of final temperature, sweeping gas flow rate and feed size on the product yields. They found that the highest liquid product yield was obtained at the final temperature of 500–550 °C, the sweeping gas rate of 0.1–2 L/min, and the particle ⇑ Corresponding author. E-mail addresses: [email protected] (M.-Y. Hua), [email protected] (B.-X. Li). http://dx.doi.org/10.1016/j.enconman.2016.04.072 0196-8904/Ó 2016 Elsevier Ltd. All rights reserved.
size less than 2 mm. Papari et al. [6] used a lab-scale pyrolysis unit to investigate the pyrolysis of sawmill residues under different pyrolysis conditions. The results showed that the pyrolysis temperature in the range of 500–550 °C, the N2 flow rate of 500 mL/min, and the average particle size of 0.3 mm were the optimum pyrolysis conditions. Others [7–9] investigated the catalytic pyrolysis of the biomass, the addition of the catalyst resulting in an improved yields and the properties of liquid organic products. Meanwhile, macro algae are gaining increasing interest as a feedstock for sustainable biofuels production. The chemical compositions of the seaweed mainly include fatty compounds, soluble polysaccharides, and proteins, which are easy to be pyrolyzed, different from the pyrolysis properties of terrestrial plants that are composed of cellulose, hemicellulose, and lignin. Ceylan and Goldfarb [10] used TG-FTIR to analyze the Ulva prolifera pyrolysis process, the apparent activation energy ranging from 130 to 152 kJ/mol, which was lower than other macroalgaes. Zhao et al. [11] researched the Enteromorpha prolifera in a free-fall reactor at different temperatures ranging from 100 to 750 °C, and the results showed that the average calorific value of the bio-oil was 25.33 MJ/kg and the oxygen content in the bio-oil was 30.27 wt%, which suggested that E. prolifera presented as a good bio-oil feedstock candidate.
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With research continued, more and more experts have already begun revealing the co-pyrolysis mechanism of biomass with different materials to improve the efficiency of pyrolysis reaction and the quality of the bio-oil. Li et al. [12] conducted the co-pyrolysis of rice straw and Shenfu bituminous coal in a fixed bed reactor under nitrogen atmosphere, and they found that the co-pyrolysis tar contained more phenolics, less oxygenate compounds than calculated values. Martínez et al. [13] conducted the co-pyrolysis of biomass with waste tyres, and the results showed that acidity, density and oxygen content in the co-pyrolysis biooil decreased, pH and calorific value increased with respect to that of the merely biomass pyrolysis liquid, leading to upgraded bio-oil. Brebu et al. [14] carried out the co-pyrolysis of pine cone with synthetic polymers, an increase in bio-oil yields and lower oxygenated compounds in the bio-oil were obtained compared to the pyrolysis of biomass alone. Samanya et al. [15] conducted co-pyrolysis of sewage sludge with wood, rapeseed and straw in a tubular furnace. They found that the maximum upper phase yield (33.2 wt%), the highest calorific value (34.8 MJ/kg) and the lowest acid number of the bio-oil were obtained with co-pyrolysis of 40% rapeseed. However, less works have been reported about co-pyrolysis of lignocellulose biomass with macroalgae. Wang et al. [16] researched the thermal behaviors of mixed rice husk and two types of seaweed by TG-FTIR, they found that the rice husk was mainly endothermic, the seaweed and the blended samples were exothermic, the synergistic effects existed in the co-pyrolysis of rice husk with seaweed. Nevertheless, the pyrolysis in a fixed bed reactor and the mechanism analysis of co-pyrolysis of lignocellulose biomass with seaweed has rarely been reported. The objective of present study is to investigate the impact of co-pyrolysis of lignocellulose biomass and seaweed at different mixed ratios on the products yields, characteristics of pyrolysis products and interaction mechanisms. E. prolifera (EP) and Sugarcane bagasse (BA) were chosen as the raw material, for the reason that EP is one specie of green algae which is widely distributed in the oceans, and BA is one kind of common lignocellulose material with low ash content. GC–MS was used to analyze the compositions of the bio-oils, which makes possible to better relate the liquid products compositions with the organic chemical compositions in the mixture samples. 2. Experimental 2.1. Materials and their characterization The EP used as the raw material for this study was obtained from the Dadeng island, Xiamen, Fujian. The BA was collected from the surrounding of Huaqiao University. The EP was washed with water 3 times to remove the impurities, then it was sundried for 5 days and milled to 90 mesh. The BA was pulverized in a disintegrator until it passed through a 90 mesh sieve, then dried by heating at 105 °C for 24 h. The samples were stored in a desiccator. The BA/ EP used were: 100/0, 70/30, 60/40, 50/50, 40/60, 30/70, 0/100. The proximate analysis of both materials were determined according to GB/T 28731-2012. The main constituents of the BA (hemicellulose, cellulose, lignin etc.) were determined by Van Soest [17]. The contents of crude protein, crude fat and carbohydrate in the EP were determined by Kjeldahl, Soxhlet extract and phenol-sulfuric acid method [18,19]. The crude fiber was determined by alkali-acid dissolve experiments [20]. Table 1 shows the feedstock characteristics. 2.2. Pyrolysis procedure The pyrolysis process was carried out in a laboratory scale reactor. The schematic diagram of experimental apparatus is shown in
Table 1 Properties of BA and EP. Proximate analysis on dry basis (wt%)
EP
BA
Moisture Volatiles Fixed carbon⁄ Ash
6.53 56.72 17.03 19.72
8.79 85.05 0.71 5.45
Main constituents on dry basis (wt%) Extractives Cellulose Hemicellulose Lignin Crude protein Crude fat Carbohydrates Crude fiber HHV (MJ/kg)
NDa NDa NDa NDa 13.11 1.06 44.95 14.63 13.23
24.33 38.01 33.27 4.01 NDa NDa NDa NDa 17.05
a ⁄
ND means not detected. Calculated value.
Fig. 1 where the spatial distribution of the equipment can be seen. A mass of 16 g mixture samples was used for production of bio-oil. The reactor used was a cylindrical shaped quartz boat 29 cm in length with an internal diameter of 3 cm. In order to maintain an inert environment during the experiments, the reaction occurred under a high grade pure nitrogen atmosphere with a flow rate of 250 mL/min. The reactor with samples were introduced into the furnace at the initial temperature 30 °C which was heated at a rate of 20 °C/min until 550 °C and kept isothermal for 10 min. All the pyrolysis experiments were carried out in duplicate. The samples were dried, devolatilized, and finally decomposed to generate char, liquid, and non-condensable gas products. The volatiles evolved from the samples passed through two consecutive condensers placed in an ice bath. The non-condensable gas was collected in oxygen bags and analyzed by gas chromatograph (GC-9160) which equipped with a TDX-01 packed column (1 m 0.3 mm) and a thermal conductivity detectors (TCD). Argon was used as the carrier gas and the temperature of TCD and oven were 133 °C and 60 °C, respectively. The mass of noncondensable gas was calculated according to its total volume, average relative molecular mass and the molar volume of the gas, which is 24.45 L/mol at room temperature. The total volume of non-condensable gas was determined by Wet gas flow meter and its average relative molecular mass was obtained through GC analysis. The char was recovered after pyrolysis and directly weighed as solid fraction, and then the mass of liquid fraction was evaluated by subtracting the weight of gas and solid. The gas, char and oil yield were determined by using Eqs. (1)–(3):
Gas yield wt% ¼
mass of gas 100 mass of feedstock biomass mass of char 100 mass of feedstock biomass
ð2Þ
16-mass of gas-mass of char 100 mass of feedstock biomass
ð3Þ
Char yield wt% ¼ Oil yield wt% ¼
ð1Þ
After each experiment, the condenser and connection tubes were washed with acetone and the extraction liquid was identified by GC/MS-QP2010plus. The GC was fitted with a 30 m ⁄ 0.25 mm capillary column coated with a 0.25 mm thick film of polyethylene glycol (Rtx-Wax). The carrier gas flow (He) was 1.5 mL/min and the split ratio was 10:1. The initial oven temperature of 40 °C was kept isothermal for 4 min and then heated to 140 °C at 5 °C/min and maintaining this temperature for 5 min, followed by continuously heating it to 225 °C at 15 °C/min and maintaining this temperature for 3 min. The temperatures of MS source and injector were 250 °C.
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Fig. 1. A schematic diagram of the fixed-bed pyrolysis unit.
2.3. FTIR analysis
EP
Transmittance
The full-scan mode with mass to charge (m/z) ratios from 40 to 500 was used, and the solvent delay was 3.5 min. The chromatographic peaks were identified with the help of NIST mass spectral data library. A semi-quantitative analysis was used to compare the distribution of compounds in the liquid products. The relative proportions of compounds were calculated from the peak area of the total ion chromatogram (TIC). This method did not yield quantitative results but it was suitable for comparing the relative proportions of the compounds as used by other authors [21,22]. The higher heating values (HHVs) of the bio-oils and chars were determined by a ZDHW-2A automatic bomb calorimeter. Total Acid number (TAN) was measured according to GB/T 264-83 and the density of the bio-oils were determined by the method of pycnometer (GB/T 2540-81). All the products properties were carried out in triplicate, with the mean values taken for each experiment within the experimental error of less than ±2%.
BA
4000
3500
3000
2500
2000
1500
1000
500
-1
Wave number/cm The infrared spectrum of the feedstock was determined using a FTIR 8400S instrument. The sample was placed in the sample pool which was made from KBr. For each spectrum, a 32 scan adsorption interferogram was collected with a 4 cm1 resolution in the 4000–400 cm1 region at room temperature. 2.4. Interaction effect The products yields and properties were observed based on a comparison between the experimental pyrolysis results and the theoretical pyrolysis data to investigate the interaction between the co-pyrolysis of BA and EP. Theoretical values are calculated from each individual feedstock and their respective mass ratio, assuming that there are no interactions among the pyrolytic vapor molecules (Eq. (4)). Herein, x1 and x2 represent the product yield or physic-chemical property from BA and EP, respectively. While w1 and w2 are the mass proportion of the BA and EP in the mixture, respectively. Thus, if the experimental value better than the y value, it can be concluded that a synergetic effect occurs.
y ¼ w1 x1 þ w2 x2
ð4Þ
3. Results and discussion 3.1. Analysis of original samples Fig. 2 shows the microstructural aspects of original samples with the infrared solid tabletting method using FTIR 8400S transform infrared spectrometer. The spectrum for the original EP shows a very broad and strong absorption band between 3300 and 3800 cm1, which is caused by O–H and N–H stretching
Fig. 2. FTIR spectrum of BA and EP structure.
vibrations, indicating the existence of water and amines [16,20]. The peak at 2930 cm1 is assigned to stretching vibration of C–H, which proves the existence of the polysaccharide. The band at 3300–3500 cm1 and 1034 cm1 are characteristics of O–H and C–O–H group in phenols and alcohols [23]. The band at 1656 cm1 is contributed to the stretching vibration of carbonyl group. The absorption peak of –CONH– at 1546 cm1 is the mark of proteins in EP. There is previously a big difference between EP and BA due to the different main ingredients of algae biomass and terrestrial biomass. The BA belongs to lignocellulose biomass, which is mainly composed of cellulose, hemicellulose and lignin. The weak peaks of peptide bond are shown in BA. The moderate intensity bond of C–H at 2930 cm1 and the bond of asymmetric stretching vibration C–O–C are the indicator of pyranose ring structure (such as cellulose) in BA.
3.2. Product yields As known, the products yields of biomass pyrolysis depend on many parameters, such as temperature, particle size, heating rate and biomass species. Temperature plays a major role in biomass pyrolysis. In this study, the co-pyrolysis of BA and EP was carried out at 550 °C, which was determined by our previous work and that of other researchers [24]. Co-pyrolysis of BA and EP released gaseous and condensed products accumulated in the collector, part of initial material remaining inside reactor as residue. The condensed products consisted of an aqueous phase and an organic
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bio-oils and a decrease in the yields of gases compared to theoretical values. While the changes in the yields of chars are not so significant. The yield of the experimental bio-oil yield reaches a maximum value 56.12 wt% and 11.48 wt% higher than the theoretical value when the blend of BA/EP is 50/50 and the gas yield reaches a minimum value 8.37 wt%. Because of the high volatile content of BA and the high percentage of ash in the EP, it has been suggested by other researchers that macroalgae such as EP with lignocellulose biomass can lead to an increase of liquid products during thermal co-processing [26]. The yields obtained in our study for bio-oils from co-pyrolysis were close to those observed in literatures [24,27], which were 45.82–54.97%.
60
Product yield (%)
50
40
30
20
10 100/0
70/30
60/40
50/50
40/60
30/70
3.3. Liquid characterization
0/100
Blend (BA/EP) Oil Exp.
Oil Theor.
Gas Exp.
GasTheor.
Char Exp.
CharTheor.
Fig. 3. Distribution of the experimental and theoretical product yields for copyrolysis of BA and EP.
phase. They were considered together as bio-oil in calculation of liquid yield. The experimental and theoretical value of products yields from co-pyrolysis of BA and EP at various mixed ratios are given in Fig. 3. It is seen that the experimental yields of the co-pyrolysis are different from the theoretical ones calculated based on the yields from the individual pyrolysis of BA and EP. The yield of bio-oil is 57.71 wt% and 42.97 wt%, the char yield is 26.27 wt% and 44.44 wt%, from the sole pyrolysis of BA and EP, respectively. The higher char yield from seaweeds compared to terrestrial biomass is probably due to their higher alkali content in the ash. It is known that alkali and alkali earth metals serve as catalysts for char formation [25]. Adding EP to BA leads to an increase in the yields of
(a) 28.0
(b) 1.24
Exp. HHV Theo. HHV
27.5
1.20
Density (g/cm3)
26.5 26.0 25.5 25.0
1.18 1.16 1.14 1.12 1.10 1.08
24.5
1.06
24.0
1.04 70/30
60/40
50/50
40/60
30/70
0/100
100/0
70/30
60/40
Blend (BA/EP)
50/50
40/60
Blend (BA/EP)
(c) 80 Exp. TAN Theo. TAN
75
TAN (mgKOH/g)
HHV (MJ/kg)
Exp. density Theo. density
1.22
27.0
23.5 100/0
The properties of the bio-oils produced in the fixed bed reactor are presented in Fig. 4. The experimental results revealing a synergistic effect in all feedstocks seems to take place bringing about upgraded properties of the bio-oil such as higher calorific value and lower density (see Fig. 4a and b). The HHV is 26.4 MJ/kg for the 50/50 blend of BA/EP and shows an increase up to 2.47% than the theoretical value. The experimental values of density are lower than the theoretical values under all the mixed ratios. It is 1.1185 g/cm3 for the bio-oil obtained from the 50/50 blend and 6.29% lower than the theoretical value. As shown in Fig. 4c, the experimental value of TAN is lower than the theoretical value when the addition of EP is more than 50%. As pointed out by Bhattacharya et al. [28], TAN mainly reflected the presence of carboxylic acids, such as formic, acetic and propanoic acids, generated due to cellulose and hemicellulose pyrolytic degradation, whilst TAN gave a better tendency about the amount of acidic compounds present in the liquid. Tables 2 and 3 show the mainly compounds and classification in the bio-oils obtained from co-pyrolysis of BA and EP. Fig. 5 is the
70 65 60 55 50 45 100/0
70/30
60/40
50/50
40/60
30/70
0/100
Blend (BA/EP) Fig. 4. Properties of the liquid fraction produced in the fixed bed reactor.
30/70
0/100
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GC/MS total ion chromatogram of the bio-oil obtained from the co-pyrolysis of BA and EP. It can be observed that new compounds are formed during the co-pyrolysis process of BA/EP blends compared to the pyrolysis of the pure feedstock, such as decyloxirane, 2,3-anhydro-D-mannosan and 1-heptyl acetate. In addition, the compounds detected in the pyrolysis of solely BA and EP are also presented in the blend samples, including saccharides, phenols and amines, such as 1,4:3,6-dianhydro-a-Dglucopyranose, 4-methylphenol, 4-ethylphenol, succinimide and 3-hydroxypyridine. The content of furanone and 1,4:3, 6-dianhydro-a-D-glucopyranose increases when EP is added into the BA, for the sake of the intensive reactions of glucose monomer ring opening and reforming. This effect is more apparent at higher EP ratios since the presence of some additives in the EP, such as CaO, favors dehydration reactions [8]. The main compounds present in the bio-oil obtained from the co-pyrolysis of BA and EP are glucosan, furfural, phenols, acids, esters, aldehydes, ketones and hydrocarbons (see Table 3). During pyrolysis of holocellulose (hemicellulose and cellulose), two competing pyrolytic pathways are mainly responsible for its primary decomposition, depolymerisation and pyrolytic ring scission. Depolymerisation process forms various anhydrosugars, furans and other products [29]. As shown in Table 3, the furan area ratio is increased with increasing EP in the feedstock blend. It seems that secondary reactions between primary holocellulose decomposition products and radicals in the EP were likely to take place. In agreement with this, aldehydes and
Table 3 Composition classification of the oils obtained from co-pyrolysis of BA and EP (area %). Group
100/0
70/30
60/40
50/50
40/60
30/70
0/100
Hydrocarbons Acids Ketones Aldehydes Alcohols Esters Phenols Amines Pyridines Indoles Furans Others
6.62 4.59 12.09 10.09 14.41 – 33.31 3.44 9.07 – 6.38 –
14.51 5.04 10.54 – 22.87 4.48 16.04 5.61 13.68 – 7.23 –
14.03 4.52 6.14 – 18.92 3.33 26.58 6.15 12.93 – 7.4 –
13.58 2.39 5.22 – 16.73 9.98 24.68 9.2 11.31 – 6.91 –
2.12 1.84 3.57 – 23.33 12.04 20.19 7.7 15.47 2.48 8.35 2.91
4.32 4.78 1.88 3.11 11.37 11.88 24.6 6.21 13.03 1.17 17.65 –
16.02 7.74 6.81 4.76 9.3 2.93 19.69 7.45 14.59 9.54 – 1.17
– Means not detected.
ketones, which are the main products formed from the pyrolytic ring scission of holocellulose, are reduced according to the proportion of EP added to the BA. In addition, secondary degradation reactions may occur, since phenolic compounds tend to polymerized with aldehydes under acidic conditions [30]. The reduction of aldehydes could improve the stability of the crude bio-oil [31]. The area ratios of alcohols and ethers are increased under all the mixed ratios. The change in the content of hydrocarbons with EP added is not monotonic, which is increased maximum and then decreased, the proportion of the EP in the blend should be kept low as observed
Table 2 Compounds identified in the oils obtained from co-pyrolysis of BA and EP (area %). Retention time (min)
15.87 23.26 24.71 30.18 30.43 30.89 31.56 32.77 33.58 34.12 34.55 34.68 34.72 34.83 35.02 35.12 35.26 35.33 35.91 36.34
Molecular formula
C2H4O2 C2H5NO C6H8O2 C20H40O C4H7NO C7H10O3 C7H8O C8H10O C6H8O4 C5H8O3 C8H18 C8H8O C6H8O4 C5H5NO C5H4O3 C9H18O2 C4H5NO2 C5H8O3 C12H24O C5H12O5
Compounds
Acetic acid Acetamide 3-Methyl-1,2-cyclopentanedione Phytol 2-Pyrrolidinone 4-Methoxy-2,5-dimethyl-3(2H)-furanone 4-Methylphenol 4-Ethylphenol 2,3-Anhydro-D-mannosan Levulinic acid 2-Methylheptane 2,3-Dihydrobenzofuran 1,4:3,6-Dianhydro-a-D-glucopyranose 3-Hydroxypyridine 2-Furoic acid 1-Heptyl acetate Succinimide 5-Hydroxymethyldihydrofuran-2-one Decyloxirane Sorbitol
Retention time (min)
Molecular formula
Compounds
15.87 23.26 30.18 30.43 30.89 31.56 32.77 34.67 34.68 34.72 34.83 35.12 35.26 35.33 36.34
C2H4O2 C2H5NO C20H40O C4H7NO C7H10O3 C7H8O C8H10O C14H28 C8H8O C6H8O4 C5H5NO C9H18O2 C4H5NO2 C5H8O3 C5H12O5
Acetic acid Acetamide Phytol 2-Pyrrolidinone 4-Methoxy-2,5-dimethyl-3(2H)-furanone 4-Methylphenol 4-Ethylphenol 7-Tetradecene 2,3-Dihydrobenzofuran 1,4:3,6-Dianhydro-a-D-glucopyranose 3-Hydroxypyridine 1-Heptyl acetate Succinimide 5-Hydroxymethyldihydrofuran-2-one Sorbitol
– Means not detected.
Blend (BA/EP)
% match
100/0
70/30
60/40
50/50
1.34 – 3.95 – – – 6.10 8.13 – 0.91 3.42 6.38 5.70 9.07 2.34 – 3.44 2.67 – 0.95
– 1.24 – – 1.06 – 1.37 3.96 1.30 1.50 8.51 7.23 9.17 12.62 3.54 – 4.37 4.03 – 3.25
– 2.14 1.69 – 1.44 1.12 5.11 6.69 1.22 1.74 7.64 7.40 9.43 11.49 2.78 – 4.01 3.33 – 2.20
1.84 4.98 2.28 – 2.40 1.61 6.27 6.84 1.28 – 8.53 6.91 10.53 8.91 – 6.58 2.47 1.33 3.99 3.00
Blend (BA/EP)
99 99 91 86 94 86 92 95 90 88 81 92 91 94 80 86 92 94 84 87 % match
40/60
30/70
0/100
– 3.07 3.45 1.82 1.59 5.28 6.51 – 8.35 10.76 13.65 9.19 4.63 1.98 3.08
3.62 1.85 5.49 1.37 – 8.35 7.22 – 17.65 – 11.66 6.73 2.43 1.88 2.16
6.13 2.33 5.06 1.55 – 9.02 2.65 8.99 – – 13.04 – 3.59 – –
99 99 86 94 86 92 95 85 92 91 94 86 92 94 87
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Fig. 5. The GC/MS total ion chromatogram of the bio-oil obtained from the co-pyrolysis of BA and EP.
Fig. 6. Probable transform mechanisms of cellulose and protein in the co-pyrolysis process.
for the 50/50 blend. The increase of the HHVs of the bio-oils showed in Fig. 4a is consistent with the results of GC/MS analysis, which the increase of hydrocarbons, alcohols and ethers can lead to the increase of the HHVs of the bio-oils [32]. Contents of O&Ncontaining compounds in bio-oil obtained from co-pyrolysis of BA and EP also increased, implying that the interactions of protein and carbohydrates enhanced, since O&N-containing compounds mainly derived from the interaction of carbohydrates and protein.
Meanwhile, the deoxygenation and denitrogenation reaction played an important role in the co-pyrolysis process. Possible pyrolysis reaction pathways of these are shown in Fig. 6. The types of compounds identified above are consistent with the products described in previous reports [20]. Therefore, it can be concluded that an upgraded bio-oil is obtained with the addition of EP to the BA. Albeit a synergetic effect is observed for all blends this effect is more significant for the 50/50 blend.
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Table 4 GC analysis of gases obtained from co-pyrolysis of BA and EP (area %). Retention time (min)
Substance
0.41 1.42 4.25 10.64 22.69
H2 CO CH4 CO2 C mH n
Blend (BA/EP) 100/0
70/30
60/40
50/50
40/60
30/70
0/100
17.82 22.85 10.90 22.37 26.06
17.94 19.78 12.21 19.97 30.1
20.61 17.79 11.58 19.78 30.24
22.56 15.31 11.79 19.11 31.23
22.78 14.55 11.54 18.89 32.24
23.32 10.03 10.47 18.22 37.96
36.33 12.66 10.76 17.34 22.91
Fig. 7. Distribution of the experimental and theoretical concentrations of gas composition obtained from co-pyrolysis of BA and EP.
Table 5 The HHV of the char obtained from co-pyrolysis of BA and EP. Sample
Char HHV (MJ/kg) Exp.
Theor.
BA EP 30% EP 40% EP 50% EP 60% EP 70% EP
21.27 22.43 19.47 17.57 16.81 15.51 12.74
21.27 18.71 17.86 17.01 16.15 15.30 12.74
3.4. Non-condensable gas characterization The gaseous products were analyzed by GC to determine the volumetric concentrations of H2, CH4, CO, CO2 and CmHn, as shown in Table 4 and Fig. 7. The concentration of CmHn which mainly contain C2–C4 hydrocarbons [33] and CH4 increases as the amount of
EP increases in the feed, which is also consistent with previous studies [13]. It is worth pointing out that the incorporation of EP to the BA leads to the formation of C2–C4 hydrocarbons, such as C2H6 and C3H6 [34]. In contrast, the experimental values for H2, CO and CO2 are lower than the theoretical ones. The total contents of combustible gases (H2, CH4, CO, and CmHn) increase. This fact could be related to the interaction between EP and BA. In elucidation of the above contradiction, the gas-phase reaction of CO2 with H2 to form CH4 and CH4, C2H4 with H2 to form C2H6, H2 is considered to have an influence on the yields of gases [35]. The reaction might not arrive at a thermodynamic equilibrium so that reaction forward to the conversion of CO2 with H2 to CH4 and C2H4 with H2 to form C2H6. Likewise, one may have expected the formation of CH4 and H2O via the gas phase reaction of CO with H2. Indeed, this reaction could account for why H2, CO and CO2 decreased and CmHn increased during the co-pyrolysis process. The equation of gas reaction can be expressed as [36]:
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stretching vibration absorption peaks of C–Haromatic at 3030 cm1 increase at the co-pyrolysis of BA with EP 50/50, it may be due to the formation of aromatic hydrocarbons [42], which is one reason why the HHVs of the char from the co-pyrolysis of BA with EP increase compared with the theoretical ones. 4. Conclusions
Fig. 8. FTIR spectra of char at different mixed ratios (BA/EP: 100/0, 50/50, 0/100). 1
CO2 þ 4H2 $ CH4 þ 2H2 O DH ¼ 165 kJ=mol
ð5Þ
CO þ 3H2 $ CH4 þ H2 O DH ¼ 206 kJ=mol
1
ð6Þ
C2 H4 þ H2 $ C2 H6
ð7Þ
H2 is considered as a good indicator for secondary cracking of bio-oil [37] and CO is favored as a major secondary product from bio-oil cracking [38]. The experimental values for H2, CO are lower than the theoretical ones, which implies that co-pyrolysis of BA and EP would inhibit the secondary cracking of the bio-oil. However, it should be noted that the gas composition may not exclusively be the result of bio-oil cracking and the partial gasification of char due to the complicated interactions of the intermediate products, which would probably affect the final gas compositions. 3.5. Char characterization Table 5 lists the HHVs of solid residues. The HHV of char obtained from the sole pyrolysis of EP is 12.74 MJ/kg, which is lower than that of the original EP (13.23 MJ/kg). While the char obtained from co-pyrolysis is higher than the pyrolysis of EP alone. Due to the higher content of ash, the char obtained from seaweeds has a lower heating value than those from terrestrial biomass [39]. Similar increase trends are also observed by other researchers [14]. The high HHV shows the potential of solid residues to be regarded as a biofuel. The HHVs of the char from the co-pyrolysis of the blends increase, which are 15.51–22.43 MJ/kg. This perhaps maybe the fraction of oxygen in char was slightly reduced during the copyrolysis process or the fixed carbon content with high caloric value became the major part [40]. As products of co-pyrolysis of BA with EP, there should be a relationship between the chemical structure of char and the composition of other fractions. The FTIR spectra of char from co-pyrolysis of BA with EP at 100/0, 50/50, 0/100 are shown in Fig. 8. The functional characteristics of solid char are qualitatively similar with those of the original samples (Fig. 2). It can be observed that the stretching vibration absorption peaks of C–H between 2924 cm1 and 2852 cm1 disappear at the co-pyrolysis of BA with EP 50/50, because the C–H bonds of alkyls break lead to the decomposition of aliphatic hydrocarbon and give rise to some hydrocarbon gases, such as CH4 and C2H6 [41]. This also corresponds well with the previous observation of CH4 and C2–C4 hydrocarbons productions. The IR absorbance of C–O and the
Co-pyrolysis of BA and EP was performed in a fixed-bed reactor to investigate the effects of mixed ratios on product yields and characteristics. The characteristics of bio-oils obtained from the co-pyrolysis of BA and EP were changed, which the acidity and density decreased, calorific value increased compared to the merely BA pyrolysis bio-oil. The amount of acids, aldehydes and phenolic compounds in the bio-oil decreased with respect to the merely biomass pyrolysis liquid, leading to upgraded bio-oil. In the gas products, the H2, CO and CO2 decreased and CmHn increased during the co-pyrolysis process. Co-pyrolysis chars had higher HHVs compared to the pyrolysis of EP alone. The synergistic effect was the most significant at the blend of BA/EP (50/50). Co-pyrolysis of BA and EP is a promising process for both renewable fuel production and environmental improvement. Acknowledgements This work was sponsored by the key project of Science and Technology Plan of Fujian Province (2013Y0065), and the key project of Science and Technology Plan of Quanzhou city (2013Z25). References [1] Li D, Chen L, Zhang X, Ye N, Xing F. Pyrolytic characteristics and kinetic studies of three kinds of red algae. Biomass Bioenergy 2011;35:1765–72. [2] Li D, Chen L, Zhao J, Zhang X, Wang Q, Wang H, et al. Evaluation of the pyrolytic and kinetic characteristics of Enteromorpha prolifera as a source of renewable bio-fuel from the Yellow Sea of China. Chem Eng Res Des 2010;88:647–52. [3] Aysu T, Küçük MM. Biomass pyrolysis in a fixed-bed reactor: effects of pyrolysis parameters on product yields and characterization of products. Energy 2014;64:1002–25. [4] Abnisa F, Wan WM, Sahu JN. Optimization and characterization studies on biooil production from palm shell by pyrolysis using response surface methodology. Biomass Bioenergy 2011;35:3604–16. [5] Islam MR, Parveen M, Haniu H. Properties of sugarcane waste-derived bio-oils obtained by fixed-bed fire-tube heating pyrolysis. Bioresour Technol 2010;101:4162–8. [6] Papari S, Hawboldt K, Helleur R. Pyrolysis: a theoretical and experimental study on the conversion of softwood sawmill residues to biooil. Ind Eng Chem Res 2015;54:605–11. [7] Mullen CA, Boateng AA. Catalytic pyrolysis-GC/MS of lignin from several sources. Fuel Process Technol 2010;91:1446–58. [8] Kuan WH, Huang YF, Chang CC, Lo SL. Catalytic pyrolysis of sugarcane bagasse by using microwave heating. Bioresour Technol 2013;146:324–9. [9] Bakar MSA, Titiloye JO. Catalytic pyrolysis of rice husk for bio-oil production. J Anal Appl Pyrol 2013;103:362–8. [10] Ceylan S, Goldfarb JL. Green tide to green fuels: TG–FTIR analysis and kinetic study of Ulva prolifera pyrolysis. Energy Convers Manage 2015;101:263–70. [11] Zhao H, Yan HX, Liu M, Sun BB, Zhang Y, Dong SS, et al. Production of bio-oil from fast pyrolysis of macroalgae Enteromorpha prolifera powder in a free-fall reactor. Energy Sources, Part A: Recov, Util, Environ Effects 2013;35:859–67. [12] Li SD, Chen XL, Liu AB, Wang L, Yu GS. Study on co-pyrolysis characteristics of rice straw and Shenfu bituminous coal blends in a fixed bed reactor. Bioresour Technol 2014;155:252–7. [13] Martínez JD, Veses A, Mastral AM, Murillo R, Navarro MV, Puy N, et al. Co-pyrolysis of biomass with waste tyres: upgrading of liquid bio-fuel. Fuel Process Technol 2014;119:263–71. [14] Brebu M, Ucar S, Vasile C, Yanik J. Co-pyrolysis of pine cone with synthetic polymers. Fuel 2010;89:1911–8. [15] Samanya J, Hornung A, Apfelbacher A, Vale P. Characteristics of the upper phase of bio-oil obtained from co-pyrolysis of sewage sludge with wood, rapeseed and straw. J Anal Appl Pyrol 2012;10:120–5. [16] Wang S, Wang Q, Hu YM, Xu SN, He ZX, Ji HS. Study on the synergistic co-pyrolysis behaviors of mixed rice husk and two types of seaweed by a combined TG-FTIR technique. J Anal Appl Pyrol 2015;114:109–18. [17] Van Soest PJ. Use of detergents in the analysis of fibrous feeds. 2. A rapid method for the determination of fiber and lignin. J Assoc Off Agric Chem 1963;46:829–35.
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[18] Saha SK, Brewer CF. Determination of the concentrations of oligosaccharides, complex type carbohydrates, and glycoproteins using the phenol-sulfuric acid method. Carbohydr Res 1994;254:157–67. [19] Miao XL, Wu QY. High yield bio-oil production from fast pyrolysis by metabolic controlling of Chlorella protothecoides. J Biotechnol 2004;110:85–93. [20] Li J, Wang G, Wang Z, Zhang L, Wang C, Yang Z. Conversion of Enteromorpha prolifera to high-quality liquid oil via deoxy-liquefaction. J Anal Appl Pyrol 2013;104:494–501. [21] Marin N, Collura S, Sharypov VI. Copyrolysis of wood biomass and synthetic polymers mixtures. Part II: characterisation of the liquid phases. J Anal Appl Pyrol 2002;65:41–55. [22] Menéndez JA, Inguanzo M, Bernad PL, Pis JJ. Gas chromatographic–mass spectrometric study of the oil fractions produced by microwave-assisted pyrolysis of different sewage sludges. J Chromatogr A 2003;1012:193–206. [23] Liu Q, Wang S, Zheng Y, Luo Z, Cen K. Mechanism study of wood lignin pyrolysis by using TG–FTIR analysis. J Anal Appl Pyrol 2008;82:170–7. [24] Bae YJ, Ryu C, Jeon JK, Park J, Suh DJ, Suh Y-W, et al. The characteristics of biooil produced from the pyrolysis of three marine macroalgae. Bioresour Technol 2011;102:3512–20. [25] Xu YP, Duan PG, Wang F. Hydrothermal processing of macroalgae for producing crude bio-oil. Fuel Process Technol 2015;130:268–74. [26] Maddi B, Viamajala S, Varanasi S. Comparative study of pyrolysis of algal biomass from natural lake blooms with lignocellulosic biomass. Bioresour Technol 2011;102:11018–26. [27] Mantilla SV, Gauthier-Maradei P, Gil PÁ, Tarazona Cárdenas S. Comparative study of bio-oil production from sugarcane bagasse and palm empty fruit bunch: yield optimization and bio-oil characterization. J Anal Appl Pyrol 2014;108:284–94. [28] Bhattacharya P, Steele PH, Hassan EBM, Mitchell B, Ingram L, Pittman CU. Wood/plastic copyrolysis in an auger reactor: chemical and physical analysis of the products. Fuel 2009;88:1251–60. [29] Branca C, Giudicianni P, Blasi C. GC/MS characterization of liquids generated from low-temperature pyrolysis of wood. Ind Eng Chem Res 2003;42: 3190–202.
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Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
Co-pyrolysis characteristics of the sugarcane bagasse and Enteromorpha prolifera Mei-Yu Hua, Bao-Xia Li ⇑ Department of Chemical Engineering, Huaqiao University, Xiamen, Fujian 361021, China
a r t i c l e
i n f o
Article history: Received 11 December 2015 Received in revised form 4 April 2016 Accepted 21 April 2016
Keywords: Co-pyrolysis Enteromorpha prolifera Biomass Bio-oil Mechanism Fixed-bed reactor
a b s t r a c t Enteromorpha prolifera, a green algae, has been spreading widely in China in recent years, resulting in a series of adverse impacts, such as the water eutrophication and the outbreak of green tides. Thus, it is necessary to develop an extensively available method to transfer marine biomass waste into highvalue products. In this study, Co-pyrolysis of sugarcane bagasse and E. prolifera was carried out in a fixed-bed reactor. The positive effects between sugarcane bagasse and E. prolifera were evidenced, as the acidity and density of the bio-oils from co-pyrolysis decreased and calorific value increased with respect to that of the merely biomass pyrolysis. When the ratio of the two components was 50/50, the bio-oil got the highest yield of 56.12 wt% and the high heating value of the bio-oil was 26.4 MJ/kg, which were 11.48%, 2.47% higher than the theoretical values, respectively. The acidity and density of the co-pyrolysis bio-oil at 50/50 blends were 51.62 mgKOH/g and 1.1185 g/cm3, which were 16.18%, 6.29% lower than the theoretical values, respectively. The analysis of bio-oil compositions showed that the bio-oil from co-pyrolysis of the blends could be a potential source of renewable fuel with lower content of acid, ketone, aldehyde, phenolic compounds and higher content of hydrocarbon, alcohol, ester compounds. In addition, the concentration of C2–C4 hydrocarbon gases produced through co-pyrolysis of the blends increased as the amount of E. prolifera increased in the blend. The co-pyrolysis chars had higher calorific values compared to that through pyrolysis of E. prolifera alone. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction With the development of world economy, energy consumption increases rapidly, and energy poverty is becoming more and more prominent. The exploration and development of safe and sustainable alternatives to fossil fuels are two of the most important global priorities today [1]. Bio-oil is a renewable and clean energy product, which is able to reduce dependence on fossil fuels, improve the security of supply, cut down greenhouse gas emissions, and create environmental benefits [2]. Biomass (such as agricultural crops and residues) that can be used as feedstock for the production of biofuels. The pyrolysis process of the biomass has received considerable attention. Many researchers [3–5] have investigated different pyrolysis conditions to determine the role of final temperature, sweeping gas flow rate and feed size on the product yields. They found that the highest liquid product yield was obtained at the final temperature of 500–550 °C, the sweeping gas rate of 0.1–2 L/min, and the particle ⇑ Corresponding author. E-mail addresses: [email protected] (M.-Y. Hua), [email protected] (B.-X. Li). http://dx.doi.org/10.1016/j.enconman.2016.04.072 0196-8904/Ó 2016 Elsevier Ltd. All rights reserved.
size less than 2 mm. Papari et al. [6] used a lab-scale pyrolysis unit to investigate the pyrolysis of sawmill residues under different pyrolysis conditions. The results showed that the pyrolysis temperature in the range of 500–550 °C, the N2 flow rate of 500 mL/min, and the average particle size of 0.3 mm were the optimum pyrolysis conditions. Others [7–9] investigated the catalytic pyrolysis of the biomass, the addition of the catalyst resulting in an improved yields and the properties of liquid organic products. Meanwhile, macro algae are gaining increasing interest as a feedstock for sustainable biofuels production. The chemical compositions of the seaweed mainly include fatty compounds, soluble polysaccharides, and proteins, which are easy to be pyrolyzed, different from the pyrolysis properties of terrestrial plants that are composed of cellulose, hemicellulose, and lignin. Ceylan and Goldfarb [10] used TG-FTIR to analyze the Ulva prolifera pyrolysis process, the apparent activation energy ranging from 130 to 152 kJ/mol, which was lower than other macroalgaes. Zhao et al. [11] researched the Enteromorpha prolifera in a free-fall reactor at different temperatures ranging from 100 to 750 °C, and the results showed that the average calorific value of the bio-oil was 25.33 MJ/kg and the oxygen content in the bio-oil was 30.27 wt%, which suggested that E. prolifera presented as a good bio-oil feedstock candidate.
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With research continued, more and more experts have already begun revealing the co-pyrolysis mechanism of biomass with different materials to improve the efficiency of pyrolysis reaction and the quality of the bio-oil. Li et al. [12] conducted the co-pyrolysis of rice straw and Shenfu bituminous coal in a fixed bed reactor under nitrogen atmosphere, and they found that the co-pyrolysis tar contained more phenolics, less oxygenate compounds than calculated values. Martínez et al. [13] conducted the co-pyrolysis of biomass with waste tyres, and the results showed that acidity, density and oxygen content in the co-pyrolysis biooil decreased, pH and calorific value increased with respect to that of the merely biomass pyrolysis liquid, leading to upgraded bio-oil. Brebu et al. [14] carried out the co-pyrolysis of pine cone with synthetic polymers, an increase in bio-oil yields and lower oxygenated compounds in the bio-oil were obtained compared to the pyrolysis of biomass alone. Samanya et al. [15] conducted co-pyrolysis of sewage sludge with wood, rapeseed and straw in a tubular furnace. They found that the maximum upper phase yield (33.2 wt%), the highest calorific value (34.8 MJ/kg) and the lowest acid number of the bio-oil were obtained with co-pyrolysis of 40% rapeseed. However, less works have been reported about co-pyrolysis of lignocellulose biomass with macroalgae. Wang et al. [16] researched the thermal behaviors of mixed rice husk and two types of seaweed by TG-FTIR, they found that the rice husk was mainly endothermic, the seaweed and the blended samples were exothermic, the synergistic effects existed in the co-pyrolysis of rice husk with seaweed. Nevertheless, the pyrolysis in a fixed bed reactor and the mechanism analysis of co-pyrolysis of lignocellulose biomass with seaweed has rarely been reported. The objective of present study is to investigate the impact of co-pyrolysis of lignocellulose biomass and seaweed at different mixed ratios on the products yields, characteristics of pyrolysis products and interaction mechanisms. E. prolifera (EP) and Sugarcane bagasse (BA) were chosen as the raw material, for the reason that EP is one specie of green algae which is widely distributed in the oceans, and BA is one kind of common lignocellulose material with low ash content. GC–MS was used to analyze the compositions of the bio-oils, which makes possible to better relate the liquid products compositions with the organic chemical compositions in the mixture samples. 2. Experimental 2.1. Materials and their characterization The EP used as the raw material for this study was obtained from the Dadeng island, Xiamen, Fujian. The BA was collected from the surrounding of Huaqiao University. The EP was washed with water 3 times to remove the impurities, then it was sundried for 5 days and milled to 90 mesh. The BA was pulverized in a disintegrator until it passed through a 90 mesh sieve, then dried by heating at 105 °C for 24 h. The samples were stored in a desiccator. The BA/ EP used were: 100/0, 70/30, 60/40, 50/50, 40/60, 30/70, 0/100. The proximate analysis of both materials were determined according to GB/T 28731-2012. The main constituents of the BA (hemicellulose, cellulose, lignin etc.) were determined by Van Soest [17]. The contents of crude protein, crude fat and carbohydrate in the EP were determined by Kjeldahl, Soxhlet extract and phenol-sulfuric acid method [18,19]. The crude fiber was determined by alkali-acid dissolve experiments [20]. Table 1 shows the feedstock characteristics. 2.2. Pyrolysis procedure The pyrolysis process was carried out in a laboratory scale reactor. The schematic diagram of experimental apparatus is shown in
Table 1 Properties of BA and EP. Proximate analysis on dry basis (wt%)
EP
BA
Moisture Volatiles Fixed carbon⁄ Ash
6.53 56.72 17.03 19.72
8.79 85.05 0.71 5.45
Main constituents on dry basis (wt%) Extractives Cellulose Hemicellulose Lignin Crude protein Crude fat Carbohydrates Crude fiber HHV (MJ/kg)
NDa NDa NDa NDa 13.11 1.06 44.95 14.63 13.23
24.33 38.01 33.27 4.01 NDa NDa NDa NDa 17.05
a ⁄
ND means not detected. Calculated value.
Fig. 1 where the spatial distribution of the equipment can be seen. A mass of 16 g mixture samples was used for production of bio-oil. The reactor used was a cylindrical shaped quartz boat 29 cm in length with an internal diameter of 3 cm. In order to maintain an inert environment during the experiments, the reaction occurred under a high grade pure nitrogen atmosphere with a flow rate of 250 mL/min. The reactor with samples were introduced into the furnace at the initial temperature 30 °C which was heated at a rate of 20 °C/min until 550 °C and kept isothermal for 10 min. All the pyrolysis experiments were carried out in duplicate. The samples were dried, devolatilized, and finally decomposed to generate char, liquid, and non-condensable gas products. The volatiles evolved from the samples passed through two consecutive condensers placed in an ice bath. The non-condensable gas was collected in oxygen bags and analyzed by gas chromatograph (GC-9160) which equipped with a TDX-01 packed column (1 m 0.3 mm) and a thermal conductivity detectors (TCD). Argon was used as the carrier gas and the temperature of TCD and oven were 133 °C and 60 °C, respectively. The mass of noncondensable gas was calculated according to its total volume, average relative molecular mass and the molar volume of the gas, which is 24.45 L/mol at room temperature. The total volume of non-condensable gas was determined by Wet gas flow meter and its average relative molecular mass was obtained through GC analysis. The char was recovered after pyrolysis and directly weighed as solid fraction, and then the mass of liquid fraction was evaluated by subtracting the weight of gas and solid. The gas, char and oil yield were determined by using Eqs. (1)–(3):
Gas yield wt% ¼
mass of gas 100 mass of feedstock biomass mass of char 100 mass of feedstock biomass
ð2Þ
16-mass of gas-mass of char 100 mass of feedstock biomass
ð3Þ
Char yield wt% ¼ Oil yield wt% ¼
ð1Þ
After each experiment, the condenser and connection tubes were washed with acetone and the extraction liquid was identified by GC/MS-QP2010plus. The GC was fitted with a 30 m ⁄ 0.25 mm capillary column coated with a 0.25 mm thick film of polyethylene glycol (Rtx-Wax). The carrier gas flow (He) was 1.5 mL/min and the split ratio was 10:1. The initial oven temperature of 40 °C was kept isothermal for 4 min and then heated to 140 °C at 5 °C/min and maintaining this temperature for 5 min, followed by continuously heating it to 225 °C at 15 °C/min and maintaining this temperature for 3 min. The temperatures of MS source and injector were 250 °C.
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Fig. 1. A schematic diagram of the fixed-bed pyrolysis unit.
2.3. FTIR analysis
EP
Transmittance
The full-scan mode with mass to charge (m/z) ratios from 40 to 500 was used, and the solvent delay was 3.5 min. The chromatographic peaks were identified with the help of NIST mass spectral data library. A semi-quantitative analysis was used to compare the distribution of compounds in the liquid products. The relative proportions of compounds were calculated from the peak area of the total ion chromatogram (TIC). This method did not yield quantitative results but it was suitable for comparing the relative proportions of the compounds as used by other authors [21,22]. The higher heating values (HHVs) of the bio-oils and chars were determined by a ZDHW-2A automatic bomb calorimeter. Total Acid number (TAN) was measured according to GB/T 264-83 and the density of the bio-oils were determined by the method of pycnometer (GB/T 2540-81). All the products properties were carried out in triplicate, with the mean values taken for each experiment within the experimental error of less than ±2%.
BA
4000
3500
3000
2500
2000
1500
1000
500
-1
Wave number/cm The infrared spectrum of the feedstock was determined using a FTIR 8400S instrument. The sample was placed in the sample pool which was made from KBr. For each spectrum, a 32 scan adsorption interferogram was collected with a 4 cm1 resolution in the 4000–400 cm1 region at room temperature. 2.4. Interaction effect The products yields and properties were observed based on a comparison between the experimental pyrolysis results and the theoretical pyrolysis data to investigate the interaction between the co-pyrolysis of BA and EP. Theoretical values are calculated from each individual feedstock and their respective mass ratio, assuming that there are no interactions among the pyrolytic vapor molecules (Eq. (4)). Herein, x1 and x2 represent the product yield or physic-chemical property from BA and EP, respectively. While w1 and w2 are the mass proportion of the BA and EP in the mixture, respectively. Thus, if the experimental value better than the y value, it can be concluded that a synergetic effect occurs.
y ¼ w1 x1 þ w2 x2
ð4Þ
3. Results and discussion 3.1. Analysis of original samples Fig. 2 shows the microstructural aspects of original samples with the infrared solid tabletting method using FTIR 8400S transform infrared spectrometer. The spectrum for the original EP shows a very broad and strong absorption band between 3300 and 3800 cm1, which is caused by O–H and N–H stretching
Fig. 2. FTIR spectrum of BA and EP structure.
vibrations, indicating the existence of water and amines [16,20]. The peak at 2930 cm1 is assigned to stretching vibration of C–H, which proves the existence of the polysaccharide. The band at 3300–3500 cm1 and 1034 cm1 are characteristics of O–H and C–O–H group in phenols and alcohols [23]. The band at 1656 cm1 is contributed to the stretching vibration of carbonyl group. The absorption peak of –CONH– at 1546 cm1 is the mark of proteins in EP. There is previously a big difference between EP and BA due to the different main ingredients of algae biomass and terrestrial biomass. The BA belongs to lignocellulose biomass, which is mainly composed of cellulose, hemicellulose and lignin. The weak peaks of peptide bond are shown in BA. The moderate intensity bond of C–H at 2930 cm1 and the bond of asymmetric stretching vibration C–O–C are the indicator of pyranose ring structure (such as cellulose) in BA.
3.2. Product yields As known, the products yields of biomass pyrolysis depend on many parameters, such as temperature, particle size, heating rate and biomass species. Temperature plays a major role in biomass pyrolysis. In this study, the co-pyrolysis of BA and EP was carried out at 550 °C, which was determined by our previous work and that of other researchers [24]. Co-pyrolysis of BA and EP released gaseous and condensed products accumulated in the collector, part of initial material remaining inside reactor as residue. The condensed products consisted of an aqueous phase and an organic
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bio-oils and a decrease in the yields of gases compared to theoretical values. While the changes in the yields of chars are not so significant. The yield of the experimental bio-oil yield reaches a maximum value 56.12 wt% and 11.48 wt% higher than the theoretical value when the blend of BA/EP is 50/50 and the gas yield reaches a minimum value 8.37 wt%. Because of the high volatile content of BA and the high percentage of ash in the EP, it has been suggested by other researchers that macroalgae such as EP with lignocellulose biomass can lead to an increase of liquid products during thermal co-processing [26]. The yields obtained in our study for bio-oils from co-pyrolysis were close to those observed in literatures [24,27], which were 45.82–54.97%.
60
Product yield (%)
50
40
30
20
10 100/0
70/30
60/40
50/50
40/60
30/70
3.3. Liquid characterization
0/100
Blend (BA/EP) Oil Exp.
Oil Theor.
Gas Exp.
GasTheor.
Char Exp.
CharTheor.
Fig. 3. Distribution of the experimental and theoretical product yields for copyrolysis of BA and EP.
phase. They were considered together as bio-oil in calculation of liquid yield. The experimental and theoretical value of products yields from co-pyrolysis of BA and EP at various mixed ratios are given in Fig. 3. It is seen that the experimental yields of the co-pyrolysis are different from the theoretical ones calculated based on the yields from the individual pyrolysis of BA and EP. The yield of bio-oil is 57.71 wt% and 42.97 wt%, the char yield is 26.27 wt% and 44.44 wt%, from the sole pyrolysis of BA and EP, respectively. The higher char yield from seaweeds compared to terrestrial biomass is probably due to their higher alkali content in the ash. It is known that alkali and alkali earth metals serve as catalysts for char formation [25]. Adding EP to BA leads to an increase in the yields of
(a) 28.0
(b) 1.24
Exp. HHV Theo. HHV
27.5
1.20
Density (g/cm3)
26.5 26.0 25.5 25.0
1.18 1.16 1.14 1.12 1.10 1.08
24.5
1.06
24.0
1.04 70/30
60/40
50/50
40/60
30/70
0/100
100/0
70/30
60/40
Blend (BA/EP)
50/50
40/60
Blend (BA/EP)
(c) 80 Exp. TAN Theo. TAN
75
TAN (mgKOH/g)
HHV (MJ/kg)
Exp. density Theo. density
1.22
27.0
23.5 100/0
The properties of the bio-oils produced in the fixed bed reactor are presented in Fig. 4. The experimental results revealing a synergistic effect in all feedstocks seems to take place bringing about upgraded properties of the bio-oil such as higher calorific value and lower density (see Fig. 4a and b). The HHV is 26.4 MJ/kg for the 50/50 blend of BA/EP and shows an increase up to 2.47% than the theoretical value. The experimental values of density are lower than the theoretical values under all the mixed ratios. It is 1.1185 g/cm3 for the bio-oil obtained from the 50/50 blend and 6.29% lower than the theoretical value. As shown in Fig. 4c, the experimental value of TAN is lower than the theoretical value when the addition of EP is more than 50%. As pointed out by Bhattacharya et al. [28], TAN mainly reflected the presence of carboxylic acids, such as formic, acetic and propanoic acids, generated due to cellulose and hemicellulose pyrolytic degradation, whilst TAN gave a better tendency about the amount of acidic compounds present in the liquid. Tables 2 and 3 show the mainly compounds and classification in the bio-oils obtained from co-pyrolysis of BA and EP. Fig. 5 is the
70 65 60 55 50 45 100/0
70/30
60/40
50/50
40/60
30/70
0/100
Blend (BA/EP) Fig. 4. Properties of the liquid fraction produced in the fixed bed reactor.
30/70
0/100
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GC/MS total ion chromatogram of the bio-oil obtained from the co-pyrolysis of BA and EP. It can be observed that new compounds are formed during the co-pyrolysis process of BA/EP blends compared to the pyrolysis of the pure feedstock, such as decyloxirane, 2,3-anhydro-D-mannosan and 1-heptyl acetate. In addition, the compounds detected in the pyrolysis of solely BA and EP are also presented in the blend samples, including saccharides, phenols and amines, such as 1,4:3,6-dianhydro-a-Dglucopyranose, 4-methylphenol, 4-ethylphenol, succinimide and 3-hydroxypyridine. The content of furanone and 1,4:3, 6-dianhydro-a-D-glucopyranose increases when EP is added into the BA, for the sake of the intensive reactions of glucose monomer ring opening and reforming. This effect is more apparent at higher EP ratios since the presence of some additives in the EP, such as CaO, favors dehydration reactions [8]. The main compounds present in the bio-oil obtained from the co-pyrolysis of BA and EP are glucosan, furfural, phenols, acids, esters, aldehydes, ketones and hydrocarbons (see Table 3). During pyrolysis of holocellulose (hemicellulose and cellulose), two competing pyrolytic pathways are mainly responsible for its primary decomposition, depolymerisation and pyrolytic ring scission. Depolymerisation process forms various anhydrosugars, furans and other products [29]. As shown in Table 3, the furan area ratio is increased with increasing EP in the feedstock blend. It seems that secondary reactions between primary holocellulose decomposition products and radicals in the EP were likely to take place. In agreement with this, aldehydes and
Table 3 Composition classification of the oils obtained from co-pyrolysis of BA and EP (area %). Group
100/0
70/30
60/40
50/50
40/60
30/70
0/100
Hydrocarbons Acids Ketones Aldehydes Alcohols Esters Phenols Amines Pyridines Indoles Furans Others
6.62 4.59 12.09 10.09 14.41 – 33.31 3.44 9.07 – 6.38 –
14.51 5.04 10.54 – 22.87 4.48 16.04 5.61 13.68 – 7.23 –
14.03 4.52 6.14 – 18.92 3.33 26.58 6.15 12.93 – 7.4 –
13.58 2.39 5.22 – 16.73 9.98 24.68 9.2 11.31 – 6.91 –
2.12 1.84 3.57 – 23.33 12.04 20.19 7.7 15.47 2.48 8.35 2.91
4.32 4.78 1.88 3.11 11.37 11.88 24.6 6.21 13.03 1.17 17.65 –
16.02 7.74 6.81 4.76 9.3 2.93 19.69 7.45 14.59 9.54 – 1.17
– Means not detected.
ketones, which are the main products formed from the pyrolytic ring scission of holocellulose, are reduced according to the proportion of EP added to the BA. In addition, secondary degradation reactions may occur, since phenolic compounds tend to polymerized with aldehydes under acidic conditions [30]. The reduction of aldehydes could improve the stability of the crude bio-oil [31]. The area ratios of alcohols and ethers are increased under all the mixed ratios. The change in the content of hydrocarbons with EP added is not monotonic, which is increased maximum and then decreased, the proportion of the EP in the blend should be kept low as observed
Table 2 Compounds identified in the oils obtained from co-pyrolysis of BA and EP (area %). Retention time (min)
15.87 23.26 24.71 30.18 30.43 30.89 31.56 32.77 33.58 34.12 34.55 34.68 34.72 34.83 35.02 35.12 35.26 35.33 35.91 36.34
Molecular formula
C2H4O2 C2H5NO C6H8O2 C20H40O C4H7NO C7H10O3 C7H8O C8H10O C6H8O4 C5H8O3 C8H18 C8H8O C6H8O4 C5H5NO C5H4O3 C9H18O2 C4H5NO2 C5H8O3 C12H24O C5H12O5
Compounds
Acetic acid Acetamide 3-Methyl-1,2-cyclopentanedione Phytol 2-Pyrrolidinone 4-Methoxy-2,5-dimethyl-3(2H)-furanone 4-Methylphenol 4-Ethylphenol 2,3-Anhydro-D-mannosan Levulinic acid 2-Methylheptane 2,3-Dihydrobenzofuran 1,4:3,6-Dianhydro-a-D-glucopyranose 3-Hydroxypyridine 2-Furoic acid 1-Heptyl acetate Succinimide 5-Hydroxymethyldihydrofuran-2-one Decyloxirane Sorbitol
Retention time (min)
Molecular formula
Compounds
15.87 23.26 30.18 30.43 30.89 31.56 32.77 34.67 34.68 34.72 34.83 35.12 35.26 35.33 36.34
C2H4O2 C2H5NO C20H40O C4H7NO C7H10O3 C7H8O C8H10O C14H28 C8H8O C6H8O4 C5H5NO C9H18O2 C4H5NO2 C5H8O3 C5H12O5
Acetic acid Acetamide Phytol 2-Pyrrolidinone 4-Methoxy-2,5-dimethyl-3(2H)-furanone 4-Methylphenol 4-Ethylphenol 7-Tetradecene 2,3-Dihydrobenzofuran 1,4:3,6-Dianhydro-a-D-glucopyranose 3-Hydroxypyridine 1-Heptyl acetate Succinimide 5-Hydroxymethyldihydrofuran-2-one Sorbitol
– Means not detected.
Blend (BA/EP)
% match
100/0
70/30
60/40
50/50
1.34 – 3.95 – – – 6.10 8.13 – 0.91 3.42 6.38 5.70 9.07 2.34 – 3.44 2.67 – 0.95
– 1.24 – – 1.06 – 1.37 3.96 1.30 1.50 8.51 7.23 9.17 12.62 3.54 – 4.37 4.03 – 3.25
– 2.14 1.69 – 1.44 1.12 5.11 6.69 1.22 1.74 7.64 7.40 9.43 11.49 2.78 – 4.01 3.33 – 2.20
1.84 4.98 2.28 – 2.40 1.61 6.27 6.84 1.28 – 8.53 6.91 10.53 8.91 – 6.58 2.47 1.33 3.99 3.00
Blend (BA/EP)
99 99 91 86 94 86 92 95 90 88 81 92 91 94 80 86 92 94 84 87 % match
40/60
30/70
0/100
– 3.07 3.45 1.82 1.59 5.28 6.51 – 8.35 10.76 13.65 9.19 4.63 1.98 3.08
3.62 1.85 5.49 1.37 – 8.35 7.22 – 17.65 – 11.66 6.73 2.43 1.88 2.16
6.13 2.33 5.06 1.55 – 9.02 2.65 8.99 – – 13.04 – 3.59 – –
99 99 86 94 86 92 95 85 92 91 94 86 92 94 87
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Fig. 5. The GC/MS total ion chromatogram of the bio-oil obtained from the co-pyrolysis of BA and EP.
Fig. 6. Probable transform mechanisms of cellulose and protein in the co-pyrolysis process.
for the 50/50 blend. The increase of the HHVs of the bio-oils showed in Fig. 4a is consistent with the results of GC/MS analysis, which the increase of hydrocarbons, alcohols and ethers can lead to the increase of the HHVs of the bio-oils [32]. Contents of O&Ncontaining compounds in bio-oil obtained from co-pyrolysis of BA and EP also increased, implying that the interactions of protein and carbohydrates enhanced, since O&N-containing compounds mainly derived from the interaction of carbohydrates and protein.
Meanwhile, the deoxygenation and denitrogenation reaction played an important role in the co-pyrolysis process. Possible pyrolysis reaction pathways of these are shown in Fig. 6. The types of compounds identified above are consistent with the products described in previous reports [20]. Therefore, it can be concluded that an upgraded bio-oil is obtained with the addition of EP to the BA. Albeit a synergetic effect is observed for all blends this effect is more significant for the 50/50 blend.
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Table 4 GC analysis of gases obtained from co-pyrolysis of BA and EP (area %). Retention time (min)
Substance
0.41 1.42 4.25 10.64 22.69
H2 CO CH4 CO2 C mH n
Blend (BA/EP) 100/0
70/30
60/40
50/50
40/60
30/70
0/100
17.82 22.85 10.90 22.37 26.06
17.94 19.78 12.21 19.97 30.1
20.61 17.79 11.58 19.78 30.24
22.56 15.31 11.79 19.11 31.23
22.78 14.55 11.54 18.89 32.24
23.32 10.03 10.47 18.22 37.96
36.33 12.66 10.76 17.34 22.91
Fig. 7. Distribution of the experimental and theoretical concentrations of gas composition obtained from co-pyrolysis of BA and EP.
Table 5 The HHV of the char obtained from co-pyrolysis of BA and EP. Sample
Char HHV (MJ/kg) Exp.
Theor.
BA EP 30% EP 40% EP 50% EP 60% EP 70% EP
21.27 22.43 19.47 17.57 16.81 15.51 12.74
21.27 18.71 17.86 17.01 16.15 15.30 12.74
3.4. Non-condensable gas characterization The gaseous products were analyzed by GC to determine the volumetric concentrations of H2, CH4, CO, CO2 and CmHn, as shown in Table 4 and Fig. 7. The concentration of CmHn which mainly contain C2–C4 hydrocarbons [33] and CH4 increases as the amount of
EP increases in the feed, which is also consistent with previous studies [13]. It is worth pointing out that the incorporation of EP to the BA leads to the formation of C2–C4 hydrocarbons, such as C2H6 and C3H6 [34]. In contrast, the experimental values for H2, CO and CO2 are lower than the theoretical ones. The total contents of combustible gases (H2, CH4, CO, and CmHn) increase. This fact could be related to the interaction between EP and BA. In elucidation of the above contradiction, the gas-phase reaction of CO2 with H2 to form CH4 and CH4, C2H4 with H2 to form C2H6, H2 is considered to have an influence on the yields of gases [35]. The reaction might not arrive at a thermodynamic equilibrium so that reaction forward to the conversion of CO2 with H2 to CH4 and C2H4 with H2 to form C2H6. Likewise, one may have expected the formation of CH4 and H2O via the gas phase reaction of CO with H2. Indeed, this reaction could account for why H2, CO and CO2 decreased and CmHn increased during the co-pyrolysis process. The equation of gas reaction can be expressed as [36]:
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stretching vibration absorption peaks of C–Haromatic at 3030 cm1 increase at the co-pyrolysis of BA with EP 50/50, it may be due to the formation of aromatic hydrocarbons [42], which is one reason why the HHVs of the char from the co-pyrolysis of BA with EP increase compared with the theoretical ones. 4. Conclusions
Fig. 8. FTIR spectra of char at different mixed ratios (BA/EP: 100/0, 50/50, 0/100). 1
CO2 þ 4H2 $ CH4 þ 2H2 O DH ¼ 165 kJ=mol
ð5Þ
CO þ 3H2 $ CH4 þ H2 O DH ¼ 206 kJ=mol
1
ð6Þ
C2 H4 þ H2 $ C2 H6
ð7Þ
H2 is considered as a good indicator for secondary cracking of bio-oil [37] and CO is favored as a major secondary product from bio-oil cracking [38]. The experimental values for H2, CO are lower than the theoretical ones, which implies that co-pyrolysis of BA and EP would inhibit the secondary cracking of the bio-oil. However, it should be noted that the gas composition may not exclusively be the result of bio-oil cracking and the partial gasification of char due to the complicated interactions of the intermediate products, which would probably affect the final gas compositions. 3.5. Char characterization Table 5 lists the HHVs of solid residues. The HHV of char obtained from the sole pyrolysis of EP is 12.74 MJ/kg, which is lower than that of the original EP (13.23 MJ/kg). While the char obtained from co-pyrolysis is higher than the pyrolysis of EP alone. Due to the higher content of ash, the char obtained from seaweeds has a lower heating value than those from terrestrial biomass [39]. Similar increase trends are also observed by other researchers [14]. The high HHV shows the potential of solid residues to be regarded as a biofuel. The HHVs of the char from the co-pyrolysis of the blends increase, which are 15.51–22.43 MJ/kg. This perhaps maybe the fraction of oxygen in char was slightly reduced during the copyrolysis process or the fixed carbon content with high caloric value became the major part [40]. As products of co-pyrolysis of BA with EP, there should be a relationship between the chemical structure of char and the composition of other fractions. The FTIR spectra of char from co-pyrolysis of BA with EP at 100/0, 50/50, 0/100 are shown in Fig. 8. The functional characteristics of solid char are qualitatively similar with those of the original samples (Fig. 2). It can be observed that the stretching vibration absorption peaks of C–H between 2924 cm1 and 2852 cm1 disappear at the co-pyrolysis of BA with EP 50/50, because the C–H bonds of alkyls break lead to the decomposition of aliphatic hydrocarbon and give rise to some hydrocarbon gases, such as CH4 and C2H6 [41]. This also corresponds well with the previous observation of CH4 and C2–C4 hydrocarbons productions. The IR absorbance of C–O and the
Co-pyrolysis of BA and EP was performed in a fixed-bed reactor to investigate the effects of mixed ratios on product yields and characteristics. The characteristics of bio-oils obtained from the co-pyrolysis of BA and EP were changed, which the acidity and density decreased, calorific value increased compared to the merely BA pyrolysis bio-oil. The amount of acids, aldehydes and phenolic compounds in the bio-oil decreased with respect to the merely biomass pyrolysis liquid, leading to upgraded bio-oil. In the gas products, the H2, CO and CO2 decreased and CmHn increased during the co-pyrolysis process. Co-pyrolysis chars had higher HHVs compared to the pyrolysis of EP alone. The synergistic effect was the most significant at the blend of BA/EP (50/50). Co-pyrolysis of BA and EP is a promising process for both renewable fuel production and environmental improvement. Acknowledgements This work was sponsored by the key project of Science and Technology Plan of Fujian Province (2013Y0065), and the key project of Science and Technology Plan of Quanzhou city (2013Z25). References [1] Li D, Chen L, Zhang X, Ye N, Xing F. Pyrolytic characteristics and kinetic studies of three kinds of red algae. Biomass Bioenergy 2011;35:1765–72. [2] Li D, Chen L, Zhao J, Zhang X, Wang Q, Wang H, et al. Evaluation of the pyrolytic and kinetic characteristics of Enteromorpha prolifera as a source of renewable bio-fuel from the Yellow Sea of China. Chem Eng Res Des 2010;88:647–52. [3] Aysu T, Küçük MM. Biomass pyrolysis in a fixed-bed reactor: effects of pyrolysis parameters on product yields and characterization of products. Energy 2014;64:1002–25. [4] Abnisa F, Wan WM, Sahu JN. Optimization and characterization studies on biooil production from palm shell by pyrolysis using response surface methodology. Biomass Bioenergy 2011;35:3604–16. [5] Islam MR, Parveen M, Haniu H. Properties of sugarcane waste-derived bio-oils obtained by fixed-bed fire-tube heating pyrolysis. Bioresour Technol 2010;101:4162–8. [6] Papari S, Hawboldt K, Helleur R. Pyrolysis: a theoretical and experimental study on the conversion of softwood sawmill residues to biooil. Ind Eng Chem Res 2015;54:605–11. [7] Mullen CA, Boateng AA. Catalytic pyrolysis-GC/MS of lignin from several sources. Fuel Process Technol 2010;91:1446–58. [8] Kuan WH, Huang YF, Chang CC, Lo SL. Catalytic pyrolysis of sugarcane bagasse by using microwave heating. Bioresour Technol 2013;146:324–9. [9] Bakar MSA, Titiloye JO. Catalytic pyrolysis of rice husk for bio-oil production. J Anal Appl Pyrol 2013;103:362–8. [10] Ceylan S, Goldfarb JL. Green tide to green fuels: TG–FTIR analysis and kinetic study of Ulva prolifera pyrolysis. Energy Convers Manage 2015;101:263–70. [11] Zhao H, Yan HX, Liu M, Sun BB, Zhang Y, Dong SS, et al. Production of bio-oil from fast pyrolysis of macroalgae Enteromorpha prolifera powder in a free-fall reactor. Energy Sources, Part A: Recov, Util, Environ Effects 2013;35:859–67. [12] Li SD, Chen XL, Liu AB, Wang L, Yu GS. Study on co-pyrolysis characteristics of rice straw and Shenfu bituminous coal blends in a fixed bed reactor. Bioresour Technol 2014;155:252–7. [13] Martínez JD, Veses A, Mastral AM, Murillo R, Navarro MV, Puy N, et al. Co-pyrolysis of biomass with waste tyres: upgrading of liquid bio-fuel. Fuel Process Technol 2014;119:263–71. [14] Brebu M, Ucar S, Vasile C, Yanik J. Co-pyrolysis of pine cone with synthetic polymers. Fuel 2010;89:1911–8. [15] Samanya J, Hornung A, Apfelbacher A, Vale P. Characteristics of the upper phase of bio-oil obtained from co-pyrolysis of sewage sludge with wood, rapeseed and straw. J Anal Appl Pyrol 2012;10:120–5. [16] Wang S, Wang Q, Hu YM, Xu SN, He ZX, Ji HS. Study on the synergistic co-pyrolysis behaviors of mixed rice husk and two types of seaweed by a combined TG-FTIR technique. J Anal Appl Pyrol 2015;114:109–18. [17] Van Soest PJ. Use of detergents in the analysis of fibrous feeds. 2. A rapid method for the determination of fiber and lignin. J Assoc Off Agric Chem 1963;46:829–35.
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