Yield of Phenolic Monomers from Lignin Hydrothermolysis in

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Yield of phenolic monomers from lignin hydrothermolysis in subcritical water system Mohammad Nazrul Islam, Golam Taki, Masud Rana, and Jeong-Hun Park Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b05062 • Publication Date (Web): 19 Mar 2018 Downloaded from http://pubs.acs.org on March 19, 2018

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Industrial & Engineering Chemistry Research

Yield of phenolic monomers from lignin hydrothermolysis in subcritical water system Mohammad Nazrul Islam, Golam Taki, Masud Rana, and Jeong-Hun Park* Department of Environment and Energy Engineering, Chonnam National University, Gwangju 61186, Republic of Korea

Abstract Lignin is the most non-cellulosic based abundant natural organic polymer with the highest number of aromatic units. It is mainly extracted from wood in the Kraft pulping process and used as boiler fuel. However, the number of high-value applications of lignin remains small. The aim of this study is to explore the yield of phenolic monomers from lignin hydrothermal conversion in subcritical water. The hydrothermal experiments were carried out at different subcritical conditions to explore the influence of reaction temperature (200-350 °C), time (0-60 min) and lignin to water ratio (1:10-1:80). The results show that the yields of bio-oils (sum of crude-oil and water soluble organics regarded as light-oil) with a range of 28.9 - 44.7 wt.% (of dry lignin fed) was strongly influenced by these operating parameters. The crude-oil contained a small amount of monomers (0.1-2.8 wt.% of lignin), whereas a large amount of monomers were composed in the light-oil (1.2-6.3 wt.% of lignin). The most abundant monomers produced from hydrothermal reactions were guaiacol and cate-chol, with the highest yield of 1.18 wt.% (11.8 mg/g at 300 °C) and 1.88 wt.% (18.8 mg/g at 350 °C), respectively. Keywords: Lignin; Hydrothermal conversion; Phenolic monomers; Guaiacol; Crude-oil

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1. Introduction In the pulp and paper industry, lignin is treated as the waste material remaining from the production of cellulose and hemicellulose, and is utilized as a low-grade boiler fuel.1, 2 However, due to its unique structure and diverse chemical groups, lignin could be an effective source of bio-fuel and specialty chemicals such as phenolic monomers, including phenols, guaiacols, syringol, and catechols. It is well-known that these ‘green chemicals’ can be used as food additives and biopreservatives, pharmaceutical products, industrial products for resin, plastic and composites’ manufacture as well as commodity product (conversionbio-fuel or bio-jet fuel) by conversion using hydroprocessing reactions.3, 4 Recent studies on the hydrothermal conversion of lignin have shown that it can be converted into various monomers. The focus of most of the previous literature on lignin liquefaction is the use of either an aqueous-base solution or an organic solvent as the reaction medium.1, 5-7 Although the use of an organic/inorganic solvent has demonstrated a high product yield from lignin liquefaction1, 8, the water in the liquefaction process could be an alternative reaction medium that serves as the reagent, solvent, and catalyst due to its unique properties under sub- and supercritical conditions. Hot compressed water can hydrolyze many of the compounds that are catalyzed by enhanced ionic-water products, and can achieve the water-molecule hydrothermal cleavage while providing a homogeneous phase for the organic-substance dissolution reactions.9 Only a few works, however, have dealt with the waterbased hydrothermal decomposition of lignin, and catalytic cracking was performed in most of these. 5, 6, 10 To date, very little is known about the Kraft-lignin decomposition in sub- and supercritical water without a co-solvent or catalyst. A very low total oil yield from hydrothermal-lignin-liquefaction 2


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(in the range of 5.4% - 10.6%, depending on the reaction temperatures from 130 °C to 230 °C) was reported by Zhou et al.11, while the supercritical conditions (temperature above 380 °C) promoted secondary reactions that lead to the re-polymerization and carbonization of lignindecomposition products such as guaiacol and catechol.2 It seems that the yield of decomposition products such as aromatic monomers is particularly dependent on ideal reaction conditions. In this study, the lignin conversion was carried out in subcritical water under various conditions. In hydrothermal liquefaction, the operating factors (e.g. temperature, reaction time, solid-liquid ratio, etc.) could play a crucial role in the reaction pathways, thus affecting the products’ distribution. The influence of reaction temperature and time on lignin depolymerization has been studied by many researchers, most of whom recommended a suitable temperature in the range of 280 - 320 °C and reaction time of 15-60 min for the maximum bio-oil yield.2, 3, 12 The differences in the bio-oil yield according to the lignin conversion temperature or time could be explained by the reaction pathway of initial bio-oil formation followed by bio-oil decomposition. Further increases of temperature or time after their optimal condition can be promoted secondary reactions, leading to re-polymerization and condensation of degraded products.1, 13 Data from detailed quantitative analyses of the produced phenolic aromatic monomers in subcritical water as a function of different reaction temperatures, times, and solid-liquid ratios is limited. This work was aimed at preliminary understanding of the state of subcritical water which influenced the yields of liquid phenolic products under hydrothermal conditions studied. Therefore, this study provides detailed quantitative data of the phenolic monomers (% mass based on dry fed lignin) from the hydrothermal liquefaction of alkali lignin in subcritical water as a function of reaction temperature (200-350 °C), time (0-60 min), and lignin/water ratio (1:103



1:80). Clearly, this study provides data of phenolics after hydrothermal liquefaction of lignin and subsequent solvent extraction. 2. Experimental section 2.1. Feedstock and chemicals In this study, alkali-lignin was purchased from Sigma-Aldrich (CAS No. 8068-05-1) and used as the feedstock, which is a product of biomass treatment in alkali solutions. The results from the elemental analysis show that the relative content of C, H, O (calculated by difference), N, and S were 53.7%, 4.9%, 38.8%, 0.6%, and 2.1%, respectively. Element composition of used Kraft lignin shows a lower amount of carbon and higher amount of oxygen content than typical lignin used in other studies,7, 14 which might be attributed from the pulping process. The All of the chemicals (acetone, ethyl acetate, and diethyl ether) that were used in the separation and extraction processes were purchased from Honeywell Burdick & Jackson (Republic of Korea (ROK)) and are of an analytical grade. Phenol, guaiacol, syringol, and phenanthrene used for determining the relative response factor were purchased from Sigma-Aldrich and are of analytical grade (the purity of all chemicals was above 99%). 2.2. Hydrothermal conversion process The lignin-hydrothermal liquefaction experiments were carried out in a 300-mL-high-pressure Hastelloy-C-276 HR-8300 reactor (Hanwoul Eng. Ltd., ROK) (Fig. 1). A built-in control system was used to turn on/off heating, to control the reaction temperature and time, and magnetic drive stirrer coupled to a motor. The temperature and pressure limits of this reactor are 450 °C and 500 kg/cm2, respectively. Typically, a known amount of lignin powder was loaded into the reactor 4


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with a specific amount of deionized water (the lignin/water ratio was 1:10-1:80 w/v). Reactions were conducted by charging the reactor about two-third part that was filled with lignin and water, and the reactor was then sealed and purged with by nitrogen gas several times to remove inside air and for detecting possible leakages. The reactor was then heated using an electric furnace and cartridge heaters to the desired temperature (200-350 °C) at a heating rate of 10 °C/min, a process that required approximately 20-30 min in total, after which the reaction temperature was held for the pre-designed run times (0-60 min). It should be noted that the counting of run time began after the reactor temperature reached the set temperature. The mixture was stirred continuously at 200 rpm during the hydrothermal reaction. Upon completion, the heating was turned off, and the reactor was rapidly cooled using ice-water quenching. The gas-outlet valve was then opened to reduce the pressure from the gas level to the atmospheric level since the focus of the current study was the quantitative analyses of lignin derived phenolics only, which allowed the gas yield to be ignored. Next, solvent-based separation and extraction procedures were performed regarding the reaction products. 2.3. Separation, extraction, and analytical procedures Following the previous studies,15-17 the organics from the solid and liquid products were extracted by using the acetone and ethyl acetate, respectively. After the hydrothermal liquefaction, the resulting reaction mixture was poured into a beaker and centrifuged to separate the solid and liquid phases. The solid products were rinsed three times with acetone to obtain the solid residue and the acetone-soluble fraction. The solid residue, which composed of unconverted lignin, coke and/or char, was collected and dried in a convection oven, and noted the residual yield. The liquid phase was subjected to a liquid-liquid extraction with ethyl acetate. 5



The collected acetone- and ethyl acetate-solutions were evaporated under a vacuum pressure in a rotary evaporator. Upon removal of the acetone and the ethyl acetate, the liquid products were obtained and weighed, which were designated as crude-oil and light-oil, respectively. The yields of various products were defined by the following equations:

Crude − oil (%) =

Light − oil (%) =

Weight of acetone soluble organics × 100 Weight of dry fed lignin

Weight of ethyl acetate soluble organics × 100 Weight of dry fed lignin

Solid residue (%) =

Weight of dry solid residue (acetone insoluble) × 100 Weight of dry fed lignin

Gas + others (%) = 100 − (crude − oil + light − oil + solid residue)

The chemical compositions of the crude-oil and the light-oil were analyzed using gas chromatography-mass spectrometry (GC/MS), for which the Agilent 6890 device was equipped with a 0.25-mm-thick-film HP-5MS column (30 m x 0.25 mm x 0.25 µm). The temperature program is as follows: 40 °C (hold for 2 min) → 170 °C (10 °C/min, hold for 5 min) → 250 °C (10 °C/min, hold for 10 min) → 310 °C (10 °C/min, hold for 10 min). An electron-impact ionization mode was used to operate the mass selective detector, and the chemical compounds were identified through comparison of their mass spectra with those of the National Institute of Standards and Technology (NIST) library. The main aromatic monomers present in the crude-oil and light-oil with high content (based on peak area greater than 1%) were identified from the results of qualitative analysis, and were quantified using the response factors of a few selected pure compounds (phenol, guaiacol, and 6


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syringol), following the procedure described by Sing et al.18 and Arturi et al.12 Both crude-oil and light-oil samples were extracted with diethyl ether. Approximately 0.5 g of oil was mixed (1 h stirring) with 10 mL of solvent and a known amount of internal standard, and then filtered through a 0.45 µm syringe filter and used for GC-MS analysis. Phenanthrene was used as an internal standard since this was not formed in the conversion of lignin, and the relative response factors were used for quantification.

Response factor (RF) =

peak area concentration

Relative response factor (RRF) =

RF& RF'(

peak area X , 1 Yield of monomers X = × × concentration '( peak area '( RRF ,

where IS is the internal standard, X is the known pure compound, and X´ are unknown compounds.

3. Results and discussion 3.1. Product distribution Each operating factor, namely the reaction temperature, time, and solid-liquid ratio, were important control parameters of the hydrothermal decomposition process. Table 1 summarises the operating conditions for the experiments and the yield of various products. For each experiment, a calculated mass balance could be obtained by measuring the products yield based on the lignin mass fed into the reactor. The yield of crude-oil against temperature showed an increasing trend with a peak at 300 °C before decreasing at 350 °C. Yin et al.19 explained the 7



variation of the bio-oil yield due to conversion temperature by the three steps of bio-oil formation (biomass hydrolysis, bio-oil formation, and bio-oil decomposition) from the hydrothermal liquefaction of biomass. Regardless of other factors, the highest crude-oil was about 34.0 wt.%, obtained at 300 °C with a 6.2 wt.% yield of light-oil, which decreased to 30.5 wt% at 350 °C with an increased yield of light oil (14.1 wt.%). This can be explained by the enhanced lignin depolymerization at higher temperature via the competition between the hydrolysis and cleavage of ether and C-C bonds12, 20 and the favored solubilization in the liquid phase. Considering the yield of crude-oil and light-oil, the optimum temperature for lignin conversion was 350 °C (44.5 wt.%). The effects of residence time on lignin conversion and distribution of product yields are presented in Table 1. The highest amount of bio-oils (44.7 wt.%) was obtained at the residence time of 20 min. Values of the obtained crude-oil decreased from 39.2 wt.% to 29.1 wt.% with increasing the residence time from 20 min to 60 min; however, the light-oil increased from 5.5 wt.% to 6.2 wt.%. Overall, the yield of bio-oil was decreased when the residence time was extended to over 20 min. Most researchers reported similar observations that the bio-oil yield is higher with shorter residence times.19 Singh et al.1 and Jiang et al.21 both reported that after a certain reaction time, when the lignin depolymerization is essentially complete, any further increase in the residence time would favor the condensation or repolymerization of the produced lignin intermediates, thus promoting the formation of solid residue. We also report similar observations. By further increasing the reaction time beyond 40 min, the yield of solid residue increased from 30.5 wt.% to 36.5 wt.%, and the yield of crude-oil consequently decreased (Table

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1). Despite the different yields of crude-oil and residue according to residence time, no major change was observed for the yield of light-oil (4.2-6.2 wt.%) at 20-60 min (Table 1). An increase of lignin/water ratio to higher than 1:20 had a negative effect on the crude-oil yield; however, the yield of light-oil increased from 6.2 wt.% to 10.3 wt.% with increasing water content from 1:10 to 1:80, as shown in Table 1. The effect of a large amount of water might be connected to the secondary degradation of phenol-formaldehyde resins present in crude-oil, which may be attributed to the increased yield of light-oil. Malins et al.22 reported that hydrolysis reactions could occur more intensively in the presence of a large amount of water during hydroliquefaction reaction. 3.2. Yield of phenolic monomers Table 2 shows the quantified monomer and high molecular weight products (oligomers and other macromolecules) yields from the hydrothermal liquefaction of lignin at different experimental sets. The trend of the yield of monomers was complex, showing a steep increase and then decrease with the increase of temperature, time, and solid-liquid ratio. Among these three factors, the yield of phenolic monomers was strongly correlated to the conversion temperature, whereas the solid-liquid ratio had a minor influence in the case of light-oil. As can be seen in Table 2, no significant yield of phenolic monomers were identified in the crude-oil (only 0.1-2.8 wt.% of lignin), whereas the light-oil contained a large number of monomers (1.2-6.3 wt.% of lignin). For example, the products from a reaction at 350 °C for 40 min with a 1:10 solid-liquid ratio were composed of 2.8 wt.% of monomer and 27.7 wt.% of oligomer and other macromolecules in the

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crude-oil (a total crude-oil yield of 30.5 wt.%, Table 1), and 6.1 wt.% of monomeric and 8.0 wt.% of oligomeric and macromolecules in the light-oil (a total light-oil yield of 14.1 wt.%). 3.3. Monomers in the light-oil (as water soluble organics) Tables 3-5 show a list of the phenolic monomers derived from the GC-MS analysis of the diethyl ether-soluble fraction of the light-oil obtained at different conditions and their corresponding yields (% mass fraction based on the dry lignin fed to the reaction). The mono-aromatic compounds with aldehyde or acidic functions presenting a retention time higher than 20 min were not quantified due to their low concentration in all cases. The major products identified were mainly guaiacol, 4-methylguaiacol, 4-ethylguaiacol, pyrocatechol, 4-methyl pyrocatechol, syringol, vanillin, and homovanillic acid. The sum of the yield of these products accounted for 40-70 wt.% of the total monomers identified, depending on the different experimental conditions. Table 3 shows the effect of reaction temperature on the yield. The increase of reaction temperature from 200 to 350 °C increased the yield of monomers from 1.14 wt.% to 5.74 wt.% of lignin. Among the identified products, guaiacol is the primary product of alkali lignin decomposition with the maximum yield (1.18 wt.% of lignin) obtained at 300 °C; the yield then decreased with increasing temperature up to 350 °C, to the benefice of the highest yield of catechol (1.88 wt.% of lignin). This result concurs with those of similar studies conducted on the hydrothermal conversion of alkali lignin in which it was reported that catechol can be produced through the hydrolysis of guaiacol in subcritical water.5, 7, 12, 21 Similar to the study conducted by Jiang et al.21 on hydrothermal lignin decomposition, some components were not found within a specific temperature range. For example, vanillin, acetovanillone, homovanillic acid, and

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syringaldehyde were relatively more abundant at a lower temperature, whereas catechol, 4methylcatechol, and guaiacol were abundant products at the higher temperature runs (Table 3). The results of the yields of monomers in light-oil from the hydrothermal decomposition of lignin at varied subcritical water residence times at 300 °C are presented in Table 4. Increasing the residence time from 0 min to 40 min increased the monomeric yield of lignin from 1.44 wt.% to 4.36 wt.%. The monomeric yield of lignin then decreased to 2.05 wt.% for further prolonging reaction time up to 60 min due to the repolymerization or condensation of the lignin intermediate products since the yield of solid residue further increased beyond 40 min. A similar trend of the decrease in bio-oil yield with increasing reaction time was observed (Table 1). The yield of phenol, guaiacols, catechols, and homovanillic acid increased with the reaction time (up to 40 min) and then decreased (Table 4). Table 5 shows the results of the quantitative yield of monomers with different solid-liquid ratios. The effect of solid-liquid ratio on the monomers yield was similar to the effect of the increased reaction time with increasing water content, after which it decreased beyond 1:40. The largest yield of guaiacols (the sum of guaiacol products is 2.63 wt.%) and syringol (0.51 wt.%) was obtained at 300 °C, 40 min, and 1:40 in the light-oil (Table 5). 3.4. Monomers in the crude-oil The results of GC-MS analysis appear to confirm that the monomeric compounds identified in the light-oil (water phase) were mostly detected in the crude-oil (acetone soluble organics and residual phase), with the distribution between their phases depending on their polarity. However, as mentioned previously, the yield of monomers was very low in the crude-oil (Table 2). For 11



example, the best yield of monomers of 2.8 wt.% of lignin (9.18 wt.% of oil) was observed in the crude-oil at 350 °C for 40 min reaction, while it was about 6.1 wt.% ( 43.26 wt.% of oil) in the light-oil at the same condition (Table 2). With regard to the effect of operating conditions on the mass fraction of monomers, the same trends were observed as those for the light-oil, showing that the increase of reaction temperature led to the increased phenolic monomers (Table 6). Among the products, the guaiacol was the primary product and the mass of guaiacol was increased with increasing reaction temperature and time (Table 6). However, different longchained oligomeric products were mainly composed in the crude-oil (data are not presented).

4. Conclusions Detailed quantitative analyses of phenolic monomers produced from lignin hydrothermal conversion as a function of reaction temperature (200-350 °C), time (0-60 min), and lignin to water ratio (1:10-1:80) were reported. The maximum bio-oil (sum of crude-oil and light-oil) yield of 44.5 wt.% was obtained at 350 °C. Temperature higher than 300 °C, reaction time beyond 20 min, and lignin to water ratio higher than 1:20 had negative effect on crude-oil yield, while the water soluble organics regarded as light-oil increased within the experimental range. No significant phenolic monomers were identified in the crude-oil (0.1-2.8 wt.% of lignin), whereas the light-oil contained a large number of monomers (1.2-6.3 wt.% of lignin), depending on the reaction conditions. The major monomeric products were guaiacol, 4-methylguaiacol, 4ethylguaiacol, pyrocatechol, 4-methylcatechol, syringol, vanillin, and homovanillic acid. The highest amount of guaiacols (sum of guaiacol products) and catechols (sum of catechol products) 12


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were found to be approximately 2.63 wt.% (at 300 °C) and 3.66 wt.% (350 °C), respectively. However, these yields are still low and the development of better liquefaction protocol is required for improved product yield.

Author Information Corresponding author: Jeong-Hun Park *

E-mail: [email protected]; Tel: +82-62-530-1855; Fax: +82-62-530-1859

Note The authors declare no competing financial interest. Acknowledgment We would like to acknowledge the National Research Foundation (NRF) of the Republic of Korea (ROK) for its financial support (Grant No. 2016R1A2B4008115).

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17. Nazari, L.; Yuan, Z.; Souzanchi, S.; Ray, M. B.; Xu, C., Hydrothermal liquefaction of woody biomass in hot-compressed water: Catalyst screening and comprehensive characterization of bio-crude oils. Fuel 2015, 162, 74-83. 18. Singh, S. K.; Nandeshwar, K.; Ekhe, J. D., Thermochemical lignin depolymerization and conversion to aromatics in subcritical methanol: effects of catalytic conditions. New Journal of Chemistry 2016, 40, (4), 3677-3685. 19. Yin, S.; Dolan, R.; Harris, M.; Tan, Z., Subcritical hydrothermal liquefaction of cattle manure to bio-oil: Effects of conversion parameters on bio-oil yield and characterization of bio-oil. Bioresource Technology 2010, 101, (10), 3657-3664. 20. Kang, S.; Li, X.; Fan, J.; Chang, J., Hydrothermal conversion of lignin: A review. Renewable and Sustainable Energy Reviews 2013, 27, 546-558. 21. Jiang, W.; Lyu, G.; Wu, S.; Lucia, L. A., Near-critical water hydrothermal transformation of industrial lignins to high value phenolics. Journal of Analytical and Applied Pyrolysis 2016, 120, 297-303. 22. Malins, K.; Kampars, V.; Brinks, J.; Neibolte, I.; Murnieks, R.; Kampare, R., Bio-oil from thermo-chemical hydro-liquefaction of wet sewage sludge. Bioresource Technology 2015, 187, 23-29.

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Tables Table 1. Results of lignin depolymerization under different experimental conditions. Experimental conditions Run 1 2 3 4 5 6 3 7 3 8 9 10

a

Temp. (°C)

Time (min)

Lignin to water (g: mL)

200 250 300 350 300 300 300 300 300 300 300 300

40 40 40 40 0 20 40 60 40 40 40 40

1:10 1:10 1:10 1:10 1:10 1:10 1:10 1:10 1:10 1:20 1:40 1:80

Crude-oil (wt.% of lignin)

Light-oil (wt.% of lignin)

Solid residue (%)

25.9 27.7 34.0 30.5 35.4 39.2 34.0 29.1 34.0 35.7 33.6 25.7

3.0 4.1 6.2 14.1 4.2 5.5 6.2 6.2 6.2 9.0 10.0 10.3

40.5 38.6 30.5 27.4 39.0 37.3 30.5 36.5 30.5 30.8 28.8 28.0

Gases + others (%) b 30.6 29.6 29.3 28.0

21.4 18.0 29.3 28.2 29.3 24.5 27.6 36.0

a

The actual mass balance of each run can be calculated by: dry lignin fed (100%) = crude-oil + light-oil + solid residue + gases and other uncertainties. b Gases + others (%) = 100 – (crude-oil + light-oil + solid residue)

Table 2. Yields of monomer and oligomer and other macromolecule products in bio-oils. Light-oil (wt.% of lignin)

Crude-oil (wt.% of lignin) Run

Monomeric products

Oligomeric and other macromolecular products

Monomeric products

Oligomeric and other macromolecular products

1 2 3 4 5 6 3 7 3 8 9 10

0.1 0.8 1.8 2.8 0.9 2.5 1.8 2.4 1.8 2.0 1.8 0.4

25.8 26.9 32.1 27.7 34.4 36.7 32.1 26.6 32.1 33.7 31.8 25.2

1.2 1.3 4.7 6.1 1.5 1.6 4.7 2.4 4.7 5.8 6.3 6.1

1.8 2.8 1.5 8.0 2.7 3.9 1.5 3.8 1.5 3.2 3.7 4.2

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Page 18 of 22

Table 3. Yield of the presence of monomeric products in the light-oil under different temperatures.

RT (min)

Compound name

7.16

wt.% of dry fed lignin 200 °C

250 °C

300 °C

350 °C

Phenol

-

-

0.08

0.13

8.99

Guaiacol

0.18

0.23

1.18

0.72

10.56

4-methylguaiacol

-

0.02

0.35

0.25

10.71

Pyrocatechol

-

-

0.34

1.88

11.54

3-methylcatechol

-

-

0.21

0.19

11.60

3-methoxycatechol

-

-

-

0.30

11.82

4-ethylguaiacol

-

0.05

0.33

0.19

11.97

4-methylcatechol

-

-

-

0.79

12.81

Syringol

0.08

0.09

0.39

0.12

13.02

4-propylguaiacol

-

0.02

0.11

-

13.10

Pyrogallol

-

-

-

0.12

13.22

4-ethylcatechol

-

-

-

0.51

13.47

Vanillin

0.22

0.19

0.17

-

14.09

(E)-Isoeugenol

0.02

0.03

-

-

14.58

Acetovanillone

0.09

0.09

0.21

-

15.12

Methyl vanillylether

0.16

0.18

0.36

0.09

16.80

Homovanillic acid

0.29

0.29

0.65

0.15

17.00

Syringaldehyde

0.05

0.03

-

-

17.02

3,4-Dihydroxyacetophenone

-

-

0.07

0.13

18.46

Acetosyringone

0.06

0.04

-

-

1.14

1.26

4.43

5.74

Total

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Page 19 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 4. Yield of the presence of monomeric products in the light-oil under different reaction times.

RT (min)

Compound name

7.16

wt.% of dry fed lignin 0 min

20 min

40 min

60 min

Phenol

0.02

0.02

0.08

0.04

8.99

Guaiacol

0.31

0.38

1.18

0.65

10.56

4-methylguaiacol

0.06

0.11

0.35

0.18

10.71

Pyrocatechol

0.03

0.11

0.34

0.26

11.54

3-methoxycatechol

0.02

0.07

0.21

0.14

11.82

4-ethylguaiacol

0.09

0.11

0.33

0.15

12.81

Syringol

0.11

0.14

0.39

0.18

13.02

4-propylguaiacol

0.02

0.03

0.11

0.04

13.47

Vanillin

0.16

0.08

0.17

0.03

14.58

Acetovanillone

0.09

0.08

0.21

0.07

15.12


0.19

0.15

0.36

-

16.80

Homovanillic acid

0.28

0.27

0.65

0.29

17.00

Syringaldehyde

0.02

0.02

-

-

18.46

Acetosyringone

0.04

0.04

-

-

1.44

1.60

4.36

2.05

Total

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Page 20 of 22

Table 5. Yield of the presence of monomeric products in the light-oil under different solid-liquid ratios. RT (min)

Compound name

7.16

wt.% of dry fed lignin 1:10

1:20

1:40

1:80

Phenol

0.08

0.09

0.07

0.06

8.99

Guaiacol

1.18

1.48

1.51

1.39

10.56

4-methylguaiacol

0.35

0.44

0.41

0.29

10.71

Pyrocatechol

0.34

0.26

0.21

0.09

11.54

3-methoxycatechol

0.21

0.19

0.16

0.09

11.82

4-ethylguaiacol

0.33

0.50

0.56

0.50

12.81

Syringol

0.39

0.51

0.51

0.46

13.02

4-propylguaiacol

0.11

0.14

0.15

0.12

13.47

Vanillin

0.17

0.40

0.54

0.66

14.08

(E)-Isoeugenol

-

0.08

0.17

0.21

14.22

(4-Hydroxy-3-methoxyphenyl)propane

-

-

0.14

0.44

14.58

Acetovanillone

0.21

0.30

0.31

0.31

15.03

2,3,5-Trimethoxytoluene

-

0.09

0.09

0.08

15.12


0.36

-

0.53

0.50

16.80

Homovanillic acid

0.65

0.71

0.67

0.62

17.00

Syringaldehyde

-

0.09

0.09

0.10

18.46

Acetosyringone

-

0.08

0.09

-

4.43

5.36

6.21

5.92

Total

Table 6. Yield (wt.%) of major monomers identified in crude-oil. Temperature (°C)

Reaction time (min)

Lignin/water ratio

200

250

300

350

0

20

40

60

1:10

1:20

1:40

1:80

Phenol

-

-

-

0.04

-

-

-

-

-

-

-

-

Guaiacol

0.04

0.18

0.56

0.60

0.02

0.60

0.56

0.64

0.56

0.55

0.36

0.12

Pyrocatechol

-

-

-

0.19

-

-

-

-

-

-

-

-

4-ethylguaiacol

-

0.10

0.46

0.52

0.18

0.48

0.46

0.51

0.46

0.49

0.38

0.11

Syringol

-

0.04

0.14

0.07

0.05

0.19

0.14

0.16

0.14

0.10

-

-

4-propylguaiacol

-

0.07

0.34

0.29

0.11

0.32

0.34

0.39

0.34

0.31

0.22

0.04

20


Page 21 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure

Fig. 1. Schematic diagram of batch hydrothermal reactor. 1. Purging gas cylinder, 2. Gas inlet valve, 3. Reaction/inside pressure indicator, 4. Magnetic motor for stirring, 5. Electric furnace, 6. Reaction vessel, 7. Gas release valve, 8. Control box to maintain the reaction temperature, time and mixing, and TC: Thermocouple connected to the reactor to monitor the temperature.

21



TOC graph

22


Page 22 of 22

Yield of Phenolic Monomers from Lignin Hydrothermolysis in

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