Chemical composition of pyrolysis oil through thermal decomposition of sugarcane biomass

Cite this paper: Vietnam J. Chem., 2020, 58(6), 770-778 Article DOI: 10.1002/vjch.202000077 770 Wiley Online Library © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH Chemical composition of pyrolysis oil through thermal decomposition of sugarcane biomass Huynh Van Nam 1,2 , Dinh Quoc Viet 2 , Truong Thanh Tam 2 , Van Dinh Son Tho 1* 1 School of Chemical Engineering, Hanoi University of Science and Technology, 1 Dai Co Viet, Hai Ba Trung, Hanoi 10000, Viet Nam 2 Faculty of Natural Sciences, Quy Nhon University, 170 An Duong Vuong, Quy Nhon City, Binh Dinh 55000, Viet Nam Submitted May 5, 2020; Accepted June 7, 2020 Abstract The process of thermal decomposition of sugarcane biomass consists of 4 stages. On that basis, the research conducted the pyrolysis of sugarcane biomass to collect liquid products at different temperature stages and they were analyzed by GC-MS method to determine the chemical composition. Chemical composition of pyrolysis oil through thermal decomposition of sugarcane biomass was elucidated in this paper. It can be divided into 6 main groups, including: acids/esters, alcohols, aldehydes/ketones, furanic compounds (furans), phenolic compounds (phenols) and fragments of lignin containing methoxy groups (guaiacols). Acids are obtained mainly at 170 o C, followed by ketones and aldehydes, furans and alcohols, without phenols and guaiacols. At 318 o C, the content of acids decreases, the content of furans, phenols and guaiacols increase, the content of alcohols varies not much and this product segment doesn’t contain aldehydes and ketones. The composition of the resulting liquid product varies significantly from 318 to 400 o C with the phenols and guaiacols content account for the majority in liquid products, the rest are furans, alcohols, acids, ketones and aldehydes. The content of phenols and guaiacols in liquid products still accounts for the majority at the temperature stage of 400-500 o C and 500-600 o C while the furans content decreases compared to the previous temperature segments. The ring 6 edges compounds of phenols and guaiacols still account for the majority, followed by ring 5 edges compounds of furans, acids, ketones/aldehydes and alcohols in the product mixture of sugarcane pyrolysis at 600 o C. Keywords. Bio-oil, pyrolysis oil, sugarcane pyrolysis, kinetic analysis, thermal decomposition. 1. INTRODUCTION Pyrolysis oils are also known as bio-oils, bio-crude oils, wood fluids or wood oils, [1,2] it is a liquid produced from the vapor condensation of thermal depolymerization and decomposition of biomass structural components such as cellulose, hemicelluloses and lignin. [3] During pyrolysis, a large number of reactions occur, including: hydrolysis, dehydration, isomerization, hydrogenation, aromatization, condensation and coking reaction. So, the composition of pyrolysis oils are very complex, there are about 300 different types of compounds including: water, carboxylic acid, alcohols, aldehydes, esters, ketones, hydrocarbons, sugar compounds, phenolic compounds, furanic compounds, etc. [4] The properties and chemical components of bio-oil depend heavily on the pyrolysis process (type of pyrolysis reactor and reaction parameters), the nature of the material used (content of lignin, hemicellulose, cellulose, mineral content, extracted compounds, etc). [5] For example, pyrolysis oil from olive husk, hazelnut shell, spruce wood, and beech wood contain a large of the phenolic fraction, consisting of relatively small amounts of phenol, eugenol, cresols, and xylenols and much larger quantities of alkylated polyphenols. [3] Pyrolysis oil of waste paper contains four main different compounds: anhydrosugars, carboxyl compounds, carbonyl compounds and aromatic compounds. [6] Therefore, studying the properties and composition of bio-oils can help determine the appropriate methods for producing, processing, storing and using these oils. At present, the mechanism of biomass pyrolysis has not been determined exactly. Due to the complex biomass structure, besides the three main components are cellulose, hemicellulose and lignin, there are a number of other components such as extraction compounds and ash. So, there are many factors that simultaneously affect the pyrolysis Vietnam Journal of Chemistry Van Dinh Son Tho et al. © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 771 process. Each component of biomass has been pyrolysis at different speeds with different mechanisms and pathways. According to a previously published study, [7] the thermal decomposition process of sugarcane consists of 4 stages. Stage 1 is mainly the process of moisture escape and extraction compounds from 25 to 170 °C with 6.5 wt%. Stages 2 and 3 occur the decomposition process of hemicellulose and cellulose from 170 to 318 o C and from 318 to 400 o C with 73.46 wt% of biomass. Stage 4 is mainly the decomposition of lignin to 700 o C with the corresponding weight reduction of 15.51 wt%. The activation energy of each stage is respectively 79.9 kJ/mol for stage 1, 103.1 kJ/mol for stage 2, 242.8 kJ/mol for stage 3 and 54.5 kJ/mol for stage 4. Except the stage 2 obeys 0.5 order kinetic, all other obey second-order kinetics. Therefore, the composition of pyrolysis oils formed in each stage will be different. Studying the composition of pyrolysis oils through these stages can assess the possibility of breaking the chemical bonds in biomass corresponding to those stages. From there is possible to identify the decomposition mechanism of biomass and there are possible to formulate suitable pyrolysis conditions to obtain the desired chemical compounds in pyrolysis oil. 2. MATERIAL AND METHODS 2.1. Material Sugarcane was collected from the sugar factory in the provinces in central Vietnam and then washed by mechanical devices and dried at 105 o C. Finally, it was grinded up to a size smaller than 2 mm. 2.2. Experimental methods Sugarcane pyrolysis process was conducted on continuous pyrolysis system at chemical engineering laboratory, Quy Nhon University. The pyrolysis reaction conditions: 50 mL/min flow rate of nitrogen carrier, 20-25 °C/min heating speed and 10 g/hr weight hourly space velocity (WHSV). The pyrolysis liquid samples obtained in the temperature range up to 170 o C, 170-318 o C, 318-400 o C, 400-500 o C, 500- 600 o C denoted respectively as L170, L318, L400, L500 and L600. LT is pyrolysis liquid sample obtained from the start until the end at 600 o C. FT-IR analysis spectra of liquid and solid sample are performed in Quy Nhon University. Gas chromatography-mass spectrometry (GC-MS) was used to determine the chemical composition of products and it was performed on GC-MS 7000D at laboratory of electrical - chemical - physics, the directorate for standards, metrology and quality of Viet Nam (STAMEQ). First, methanol (CH3OH) solution was used to dilute the pyrolysis oil in a ratio of 1:1 for GC/MS analysis. Then, the GC separation was performed using a DB- 5 capillary column (30 m×0.25 mm×0.25 μm). The prepared sample (2 µL) was injected into injection port set at 250 °C in a 50:1 split mode. High purity of helium (He) (99.999 %) was employed as a carrier gas in the column at a constant flow rate of 0.8 mL/min. The column temperature was set at 50 °C for 2 min and then it was increased up to 280 °C at 9 °C/min. The mass spectrometer ion source was operated at 280 °C with 70 eV in electron impact (EI) mode. The mass spectrometer was conducted in scan mode in the range of 40-600 m/z. The chromatographic peaks were discriminated and analysed by mass spectral data library. The relative content of each component in the pyrolysis oil was determined by calculating the chromatographic area percentage. The solid, liquid and gas performance, the liquid yield in each pyrolysis stage are determined by the formula: o id performan e ( t ) ass of har after rea tion g ass of fed efore rea tion g × 00 (1) iquid performan e ( t ) ass of iquid after rea tion g ass of fed efore rea tion g × 00 (2) as performan e ( t ) 00 o id performan e ( t ) iquid performan e ( t ) (3) iquid ie d ( t ) ass of iquid after ea h stage g ass of tota iquid g × 00 (4) 3. RESULTS AND DISCUSSION 3.1. Product performance pyrolysis process by temperature According to the analysis results kinetic of pyrolysis stages shows that, for each stage of temperature occurs the decomposition of corresponding components in biomass. So the liquid products and Vietnam Journal of Chemistry Chemical composition of pyrolysis oil © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 772 solid products (char) in the pyrolysis stages will be different. Therefore, to demonstrate the ability to break the chemical bonds of biomass by temperature, the study conducted pyrolysis process to collect solid and liquid products in the temperature range below 170 °C, 170-318 °C, 318- 400 °C, 400-500 °C, 500-600 °C and 600-700 °C for evaluation. Results are shown in figure 1a. The products performance of pyrolysis by temperature show that at temperatures below 400 °C thermal decomposition rapidly occurs, corresponding to the weight of biomass rapidly decreases and liquid performance and gas performance increase. At 400 °C, liquid performance reaches 39.24 wt% and gas performance reaches 22.64 wt%. During this temperature period, the process of moisture evaporation, decomposition of extracted compounds, hemicellulose and cellulose should increase the efficiency of the product. At 500 °C, liquid performance and gas performance continue to rise but more slowly, with 44.85 wt% for liquid performance and 29.12 wt% for gas performance. When the pyrolysis temperature continues to rise to 600 °C, the liquid performance negligibly increases, reaching 45.97 wt%. The weight of biomass decreases during this period due to formation of gases and gas performance increases to 32.39 wt%. If the temperature continues to rise to 700 °C, no more liquid products are collected and only a small amount of biomass is pyrolysis to formed gas products. The gas performance at this temperature is 33.73 wt%. Depending on the biomass source and pyrolysis conditions, the performance of pyrolysis products is different. According to the research results of Li et al. (2005) [6] for pyrolysis of waste paper at pyrolysis temperature of 450 o C, yield oil was 47.03% with the heating rate of 10 o C min -1 and 48.34% with the heating rate of 30 o C min -1 . The research results of Demirbas (2009) [3] for pyrolysis of olive husk, hazelnut shell, spruce wood and beech wood, the pyrolysis oil contents and the higher heating values of pyrolysis oils vary from 32.1 to 49.3 % of dry and ash-free basis. Gerçel et al. (2006) [8] for pyrolysis of apricot stone, the product yields were significantly influenced by the process conditions. The pyrolysis temperature was increased, the percentage mass of char decreased while gas product increased. The bio-oil obtained 35.1 % at 550 °C, at which the liquid product yield was maximum. Therefore, with the purpose of the study collected liquid products, the most appropriate temperature for pyrolysis is 600 °C. Figure 1b shows the results of liquid yield in each temperature range and cumulative liquid yield to 600 o C. At temperature below 170 °C moisture escapes mainly and the volatile compounds in the biomass, accounting for 23.08 wt% of the total amount of liquid products. From 170 to 318 °C and318 to 400 °C, liquid yield obtains the highest, 100 200 300 400 500 600 700 0 20 40 60 80 100 P e rf o rm a n c e ( % ) Temperature ( o C) Solid Liquid Gas 0 10 20 30 40 2.42 12.20 29.79 32.51 600500400318 Liquid yield Cumulative liquid yield Temperature ( o C) L iq u id y ie ld ( % ) 170 23.08 20 40 60 80 100 C u m u la ti v e l iq u id y ie ld ( % ) (a) (b) Figure 1: (a) Product performance of pyrolysis by temperature; (b) The liquid yield according to the temperature range and the cumulative liquid yield to 600 o C Vietnam Journal of Chemistry Van Dinh Son Tho et al. © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 773 accounting for 32.51 wt% and 29.79 wt% of the total amount of liquid products. Thus, the cumulative liquid yield reaches for 62.30 wt% in this temperature range. As a result of kinetic analysis, in this temperature range occurs the decomposition of hemicellulose and cellulose, two components account for the highest levels of sugarcane biomass (61.75 wt%). [7] Therefore, this result fully consistent with the results of chemical composition analysis and analysis of the kinetics of phase thermal decomposition of sugarcane. At two remaining periods of temperature, from 400 to 500 o C and 500 to 600 o C, the liquid yield is low with 12.2 and 2.42 wt% of total liquid products, respectively. During this periods occur the decomposition process of lignin and the process of decomposition the remaining cellulose amounts of the previous period. Therefore, it is possible to predict that the liquid product in temperature below 170 o C is mainly water. The liquid composition will be the furanic compounds from 170 to 400 o C and phenolic compounds from 400 to 600 o C. This will be demonstrated through the results of the FT-IR spectrum and the GC-MS spectrum of liquid product samples. 3.2. FT-IR spectra of liquid products obtained after each pyrolysis periods Figure 2 shows FT-IR spectrum from the number waves 4000 to 400 cm -1 of liquid products which are obtained at different pyrolysis temperature ranges (L170, L318, L400, L500, L600). In contrast to solid product samples at temperature ranges, [7] FT-IR spectrum of L170 sample only appears oscillation vibrations of O–H group (3414 cm-1) and C=O group (1600-1700 cm -1 ), these bonds are of water and carboxylic acid that are generated by the decomposition of volatile components in sugarcane. At 318 o C, L318 sample began to appear oscillation vibrations of C–O–C, C=O, C=C of aromatic ring and O–H in phenols, guaiacols, alcohols, furans. These fluctuations are more pronounced at the next temperature range up to 600 o C. In these periods, the –CH2OH linkages in biomass are cracked and release the water, aldehydes, ketones, alcohols of low molecular mass. It is also observed that C–O of ether linkage (1250 cm -1 ) and C–O–C anti symmetric bridge (1159 cm -1 , 1163 cm -1 ) began to decompose and release furans, phenols and compound containing methoxy group (guaiacols). This proves that the breaking process of the hemicellulose, the cellulose and the lignin in biomass begin to occur when pyrolysis process is carried out above 170 o C. This result again demonstrated the ability to break down the chemical bonds of biomass by temperature, which has been studied in kinetic analysis and chemical bond breakage of sugarcane pyrolysis process. [7] 4000 3500 3000 2500 2000 1500 1000 500 Phenols, Guaiacols Acids C=O -OH L600 L500 L400 L318 R el at iv e tr an sm it ta n ce ( % ) Wave number (cm -1 ) L170 -OH -CH 2 , -CH 3 C=C C-O-C C=C C-H Acids Phenols,Guaiacols Furans Figure 2: FT-IR spectra of liquid products after each pyrolysis periods 3.3. Composition of pyrolysis oil The study conducted GS-MS spectrum analysis to determine the chemical composition of pyrolysis oil each temperature range. The results were shown in table 1. This results only show the composition of Vietnam Journal of Chemistry Chemical composition of pyrolysis oil © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 774 Table 1: Components of the pyrolysis oil from sugarcane detected by GC-MS ID RT (min) Compound Formula Area (%) L170 L318 L400 L500 L600 LT 1 2.392 Acetic acid C2H4O2 48.96 100 40.32 - 22.39 11.37 2 3.200 Glyceraldehyde C3H6O3 - - - 53.45 - 5.90 3 3.353 Formic acid, ethenyl ester C3H4O2 5.78 27.1 10.69 16.73 - 2.90 4 4.314 Benzaldehyde C7H6O 16.04 - 11.44 11.61 - 2.90 5 4.918 Furfural C5H4O2 9.07 36.28 34.18 - - 8.93 6 5.037 2-Furanmethanol C5H6O2 - 10.66 11.42 9.9 6.38 4.79 7 6.525 1,3-Cyclopentanedione, 2- methyl- C6H8O2 - 7.0 35.83 29.88 9.59 25.82 8 7.646 2-Furancarboxaldehyde, 5- methyl- C6H6O2 - 9.12 14.36 - - 7.24 9 7.727 11-Hexadecyn-1-ol C16H30O - - 9.09 4.92 - 13.55 10 7.910 17-Octadecynoic acid C18H32O2 - - - 11.49 - 3.43 11 8.070 Phenol C6H6O 3.29 18.27 56.78 51.63 - 71.05 12 9.267 2-Cyclopenten-1-one, 2- hydroxy-3-methyl- C6H8O2 - - - 8.06 - 46.73 13 9.436 Phenol, 4-methyl- C7H8O - - 69.22 - - 2.97 14 9.773 Phenol, 2-methyl- C7H8O 1.18 - - 26.5 19.93 22.05 15 10.279 Phenol, 3-methyl- C7H8O 2.5 16.12 27.17 59.12 39.8 100 16 10.571 Phenol, 2-methoxy- C7H8O2 1.38 18.76 42.79 22.17 15.64 34.32 17 10.898 Phenol, 2-ethoxy- C8H10O2 - 9.59 23.18 100 - 28.68 18 11.185 Maltol C6H6O3 - 5.76 - 13.88 - 3.76 19 11.299 2-Cyclopenten-1-one, 3-ethyl- 2-hydroxy- C7H10O2 - 5.73 9.86 - - 12.85 20 11.906 Phenol, 2,5-dimethyl- C8H10O - - 21.87 12.15 10.08 14.15 21 12.309 Phenol, 2-ethyl- C8H10O 1.31 24.9 2.5 47.82 31.04 88.95 22 12.866 1,4-Benzenediol, 2,5-dimethyl- C8H10O2 - 15.97 - 21.84 48.08 23 12.949 Phenol, 2,6-dimethoxy C8H10O3 - 35.2 95.38 78.52 51.09 62.55 24 13.097 Hydroquinone C6H6O2 - - - 8.09 14.31 11.67 25 13.169 Phenol, 4-ethyl- C8H10O - - 100 - - 6.17 26 13.415 Benzofuran, 2,3-dihydro- C8H8O - 12.74 52.72 - - 5.26 27 14.253 4-Methoxybenzene-1,2-diol C7H8O3 - - 27.35 - 10.28 31.61 28 14.474 Tetradecanoic acid, 2-hydroxy- C14H28O3 - - - 4.87 - 4.65 29 14.641 Phenol, 4-ethyl-2-methoxy- C9H12O2 - 12.39 52.04 15.0 10.23 30.98 30 14.887 1,2-Benzenediol, 3-methyl- C7H8O2 - - 19.29 39.61 - 14.10 31 15.513 1,2-Benzenediol, 3-methoxy- C7H8O3 - - - 45.07 - 3.06 32 15.653 1,3-Benzenediol, 4-ethyl- C8H10O2 - - - 12.31 - 3.20 33 15.899 Dodecanoic acid, 3-hydroxy- C12H24O3 - 1.45 - 10.61 - 4.45 34 15.956 p-Cymene-2,5-diol C10H14O2 - - 5.96 5.71 8.1 4.48 35 16.115 2,4-Dimethoxyphenol C8H10O3 1.85 - - 12.72 36.12 81.69 36 16.395 Benzenemethanol, 3-hydroxy- 5-methoxy- C8H10O3 - - 6.29 10.64 - 12.00 37 16.708 3-Methyloxirane-2-carboxylic acid C4H6O3 - 21.98 11.15 69.99 - 14.73 38 17.484 Phenol, 3-ethyl-5-methyl- C9H12O - - 11.63 - - 5.44 Vietnam Journal of Chemistry Van Dinh Son Tho et al. © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 775 39 17.891 Phenol, 4-methoxy-3- (methoxymethyl)- C9H12O3 - 2.96 18.54 7.71 36.12 35.23 40 18.694 Phenol, 3-methoxy-2,4,6- trimethyl- C10H14O2 - 4.77 21.86 - 22.99 7.51 41 19.437 2-Propanone, 1-(4-hydroxy-3- methoxyphenyl)- C10H12O3 - - - 11.49 - 9.31 42 20.648 Phenol, 2,6-dimethoxy-4-(2- propenyl)- C11H14O3 - 5.74 11.76 6.61 - 4.64 compounds with sufficiently large concentrations that the measurement process can detect. Or some substances have the same boiling temperature so the peaks overlap and cannot be determined. However, the results also show the complexity of the chemical composition of sugarcane pyrolysis oil. T