Hydrothermal Liquefaction of Lignocellulosic Biomass Using

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Biofuels and Biomass

Hydrothermal liquefaction of lignocellulosic biomass using potassium fluoride doped alumina Koray Alper, Kubilay Tekin, and Selhan Karagoz Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b04381 • Publication Date (Web): 05 Mar 2019 Downloaded from http://pubs.acs.org on March 5, 2019

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Hydrothermal liquefaction of lignocellulosic biomass using potassium fluoride doped alumina Koray Alpera, Kubilay Tekinb, Selhan Karagöza,* a

Department of Chemistry, Karabük University, 78050 Karabük, Turkey

b

Department of Environmental Engineering, Karabük University, 78050 Karabük, Turkey.

Corresponding author: [email protected] (S. Karagöz) Tel.: + 90 370 433 82 10; fax: + 90 370 433 82 04 Submitted to Energy & Fuels

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ABSTRACT Hydrothermal liquefaction (HTL) of spruce wood was performed without and with the use of a potassium fluoride doped alumina catalyst (KF/Al2O3) in a bench-top reactor. HTL runs were performed at 250, 300 and 350 °C with residence times of 15, 30 and 60 min. The effects of the catalyst at different catalyst loadings (in concentrations from 10 to 40 wt% of the lignocellulose) on the bio-oil and solid residue yields as well as their properties were investigated. The use of the catalyst increased the bio-oil yields over two-fold and reduced char yields. GC-MS analysis revealed that the bio-oil from the non-catalytic and catalytic runs consisted of aldehydes, ketones, phenols, acids and esters. Among these components, phenolic compounds were dominant in both the non-catalytic and catalytic runs. The relative yields of phenolic compounds increased with catalyst use. The highest heating value was estimated to be approximately 29 MJ kg-1. The boiling point distributions of the bio-oils from both runs revealed that the total naphtha fraction (light and heavy) was comparable with that of crude oil. Keywords: Hydrothermal liquefaction, heterogeneous catalyst, lignocellulosic biomass


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INTRODUCTION In response to decreasing fossil fuel resources and concerns about environmental pollution, considerable research has been performed on the utilization of biomass. Alternative and renewable energy sources are indispensable to a sustainable society. Renewable energy sources, such as biomass, have been an important subject of research, particularly in the last two decades. Basically, biomass can be categorized into three groups: lipid-rich, carbohydrate-rich, and lignocelluloses 1. Lignocellulosic biomass, which primarily consists of lignin and holocellulose (cellulose and hemicellulose), is an important renewable biomass resource, particularly in countries with abundant agricultural and forestry resources. One effective way to fully utilize lignocellulosic biomass without fractionation is hydrothermal processing. In this process, lignocellulosic biomass is deconstructed and partially deoxygenated to produce biofuels 1. The process is suitable for any biomass type (i.e., algal biomass, lignocellulosic biomass, sludge, and food waste) and uses hot pressurized water as a reaction medium 2. Several studies on lignocellulose liquefaction via hydrothermal processing have been performed 3-6. Notably, lignocellulosic biomass is the most difficult biomass to process because of its inherent heterogeneous and recalcitrant structure 7. Although water at high temperatures behaves like a catalyst due to its high ionic product, it is necessary to use catalysts to efficiently deconstruct lignocellulosics. Homogenous base and basic salts are known to favor bio-oils and inhibit char formation 8. However, they are not recoverable. In addition, the separation of the resulting products is difficult when base and basic salts are used, particularly at high concentrations. Therefore, heterogenous catalysts have come to the forefront for the liquefaction of lignocellulose in hydrothermal media. There have been reports on the use of heterogenous catalysts for the efficient deconstruction of lignocellulosic biomass in hydrothermal media 9-12. ACS Paragon Plus Environment

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Hammerschmidt et al. used a homogeneous potassium carbonate (K2CO3) catalyst dissolved in the feed stream and a heterogeneous zirconium dioxide (ZrO2) catalyst in a fixedbed reactor for the hydrothermal liquefaction of three different types of sludge in a continuous process at 330 °C with a residence time of 10 min 9. The product yield and quality were changed depending on the feed type. A high yield of organic carbon was produced. Christensen et al. conducted hydrothermal liquefaction of dried distiller’s grains with solubles (DDGS) using a stop-flow reactor system at 350 °C with a residence time of 15 min at 25 MPa 10. They tested the catalytic effects originating from the reactor wall and ZrO2 on the product yield and quality. It was reported that neither the reactor wall nor ZrO2 had a significant effect on crude oil yields and properties. Notably, in HTL processing of biomass, a heterogenous catalyst will most likely be affected by sintering, poisoning, internal diffusion limitation, and inactivation 11. In a recent study, Remon et al. produced bio-oils from the microwave-assisted catalytic hydrothermal liquefaction of a mixture of pine and spruce biomass 12. The effects of the temperature (150-250 ºC), pressure (50-120 bar), time (0-2 h) and catalyst amount (NiCo/Al-Mg; 0-0.25 g catalyst/g biomass) on bio-oil yields were examined. The bio-oil yield ranged from 1 to 29 wt% 12. The highest bio-oil yield was 29 wt% and was obtained at 250 °C and 120 bar while employing 0.25 g catalyst/g biomass for 2 h. Substantially less research has been performed on the use of heterogenous base catalysts to deconstruct lignocellulose in hydrothermal media 13- 15. In those studies, the positive effect of either calcium oxide or calcium borate minerals on the yields of crude biooils from the decomposition of lignocellulose in hydrothermal media have been emphasized.


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Potassium fluoride doped alumina (KF/Al2O3) has been widely used in many organic synthesis reactions as a heterogenous solid base catalyst 16, 17. In addition, a small number of studies have examined the catalytic effect of KF/Al2O3 for the synthesis of biodiesel 18-20. This study was undertaken to investigate the effect of KF/Al2O3 on the bio-oil and solid residue yields from the direct liquefaction of lignocellulose in hydrothermal media. The experimental work was performed with the major objective of determining the effectiveness of the catalyst on crude bio-oils and solid residue yields as well as their properties. Thus, neither quantitative nor qualitative analyses of gas or aqueous phases were conducted. EXPERIMENTAL Materials Wood samples (spruce wood and beech wood) in the form of sawdust were supplied by a local wood-processing company in Karabuk, Turkey. Wood samples with average particle sizes of less than 0.5mm were used for the HTL runs. Table 1 shows proximate, ultimate and component analyses of the spruce wood. The components of the wood samples were determined according to a previous report 21. The beech wood revealed 76.75 wt% holocellulose, 22.16 wt% lignin, 41.70 wt% α-cellulose, 0.61wt% ash, and 1.52 wt% extractives. Aluminum oxide 90 active acidic (activity stage I) (0.063-0.200 mm) was purchased from Merck ((Darmstadt, Germany). Potassium fluoride (≥ 99.0 %) was purchased from Sigma-Aldrich (St. Louis, MO, USA). All other chemicals and solvents were of analytical-reagent grade.


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Preparation of potassium fluoride doped alumina catalyst In a previous work, it was demonstrated that that both the acidic and basic alumina support exerted stronger basic sites than neutral alumina 22. Thus, an acidic aluminum oxide was used as a catalyst support in this work. The KF/Al2O3 catalyst was prepared by wet impregnation according to the following procedure: 0.275 mol (~16 g) potassium fluoride was dissolved in de-ionized water (25 mL). Subsequently, 0.333 mol (~34 g Al2O3) and more de-ionized water (25 mL) were added to the solution under continuous stirring. Stirring was continued at room temperature for 24 h. The catalyst was separated from the water by filtration and then dried at 100 °C for 2 h. Subsequently, drying continued for another 2 h at 200 °C. Finally, the catalyst was calcined at 600 °C for 3 h. The KF content in the KF/Al2O3 was 32 wt%. The synthesized KF/Al2O3 catalyst was stored in a plastic bottle at room temperature and used for the HTL experiments. HTL Experiments The HTL experiments in this research were performed in a Parr batch reactor (Parr 4848 High Pressure Reactor, Parr Instrument Co., Moline, Illinois, USA. The details of the experimental set-up are described in a previous study 14. Briefly, the reactor was loaded with 15 g spruce wood and 150 mL ultrapure water. The loaded autoclave was purged and then pressurized with an initial pressure of 2 MPa nitrogen (N2). The reactor was then heated to the tested temperatures (250, 300 and 350 °C) for reaction times of 15, 30 and 60 min. After autoclaving was completed, the reactor was cooled to room temperature and depressurized to ambient conditions. Solid and liquid reaction products were collected from the reactor and placed in a beaker. Then, the reactor and vessel were washed with ultrapure water and dichloromethane (DCM). Solid and liquid products were separated using vacuum filtration. The liquid portion was extracted with DCM. Then, the aqueous and DCM phases were separated by using a separating funnel. The DCM phase was dried over anhydrous sodium ACS Paragon Plus Environment

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sulfate to remove water traces. Then, the mixture was filtered and evaporated under reduced pressure. After removal of DCM, the bio-oil was obtained. The remaining solid products on the filter paper from vacuum filtration were dried at 105 °C for 4 h. After drying, the filter paper and the remaining solids were removed from the oven, air equilibrated, and weighed. In the catalytic runs, the amount of solid residue was calculated by subtracting the catalyst mass from the total mass of the solid residue. Analytical methods The bio-oil was analyzed with an Agilent 6890 gas chromatograph equipped with a mass selective detector. The column was a phenyl methyl siloxane capillary column (30 m × 0.25 mm i.d. × 0.25 mm film thickness, Agilent 19091S-433). The injector temperature was 280 °C, and the injector was operated in split mode with a split ratio of 10:1 and a split flow rate of 9.9 mL/min. The carrier gas was helium. The total flow rate was 13.9 mL/min. The following temperature program was used. The initial oven temperature was set at 40 °C and held for 5 min. Then, the temperature was increased, first to 170 °C (rate: 2 °C/min, hold time: 5 min), then to 270 °C (rate: 5 °C/min, hold time: 10 min). Next, the temperature was increased to 280 °C (rate: 5 °C/min, hold time: 5 min). The compounds in the bio-oils were identified by comparing their mass spectra with the National Institute of Standards and Technology (NIST) mass spectral library. The qualitative and semi-quantitative analysis of the compounds was performed based on all peaks in the total ion chromatogram from the GC– MS analysis. The peak area of each identified compound in the bio-oils from the GC-MS analysis provided relative yields of identified compounds that were light enough to elute from the GC column. Elemental analysis (LECO CHNS 932 instrument) was performed on the raw material, bio-oils, and solid residue products. The reported results are the mean values of two repeated


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analyses. The heating values of the biomass, bio-oils, and solid residues were calculated according to the Dulong formula: HHV = 0.338C + 1.428(H–O/8) + 0.095S. The surface area measurements of the KF/Al2O3 catalyst were performed using N2 adsorption data measured at 77 K on a Micromeritics Gemini. The samples were subjected to degassing at 300 °C for 24 h before the analysis began. The total surface area (SBET) was calculated using the Brunauer–Emmett–Teller (BET) equation. The powder X-ray diffraction (XRD) patterns of Al2O3 and KF/Al2O3 were recorded on a Panalytical Empyrean diffractometer with Cu-Kα radiation (λ = 1.5406 Å) over a range 10-90° and while operating at 40 kV and 40 mA. The morphology of the catalysts and solid residues was investigated by scanning electron microscopy (SEM) using an FEI Quanta (FEG 450). The elemental compositions and mapping analyses were determined by energy-dispersive X-ray spectrometry (EDS-SDD APOLLO X) during the SEM analysis. The functional group chemical analysis of the catalyst support (Al2O3) and the catalyst (KF/Al2O3) was performed using Fourier transform infrared spectrometry (Perkin Elmer FTIR 100) according to the KBr disc method. A thermal gravimetric analyzer (EXSTAR TGA, 7200 system, SII Nano Technology Inc., Chiba, Japan) was used to estimate the boiling point distributions of the hydrocarbons in the bio-crudes according to a previous report by Anastasakis and Ross 23. The temperature was ramped up from 25 to 800 °C at a heating rate of 10 °C min-1 in the presence of nitrogen with a flow rate of 20 mL min-1 N2. RESULTS AND DISCUSSION Catalyst characterization


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The KF/Al2O3 catalyst had a BET specific surface area of 96 m2 g-1. The pore volume and pore size of the catalyst were 0.19 cm3.g-1 and 7.8 nm, respectively. The XRD patterns of the Al2O3 and KF/Al2O3 are shown in Figure 1. The XRD pattern of the KF/Al2O3 exhibited the characteristic peaks of Al2O3 (2Ɵ= 37º, 46º, 67º). The characteristic peaks assigned to potassium hexafluoroaluminate (K3AlF6) were observed at 2Ɵ =30º, 43º, 53º. The appearance of this new phase (K3AlF6) was also observed in previous reports 18, 22. The addition of aqueous KF to alumina resulted in the formation of potassium hexafluoroaluminate during the preparation of the catalyst according to the following reaction: 12𝐾𝐹 + 𝐴𝑙2 𝑂3 + 3𝐻2 𝑂 — > 2𝐾3 𝐴𝑙𝐹6 + 6𝐾𝑂𝐻 Aluminate and/or hydroxide are responsible for the nature of the actual basic species, which results in high reactivity of the KF/Al2O3 catalyst 24, 25. The XRD pattern of the KF/Al2O3 revealed that the actual basic species of the catalyst is due to K3AlF6 in this study. The FTIR spectra of the Al2O3 and KF/Al2O3 are shown in Figure 2. The peak at the 3436 cm-1 wavenumber is assigned to O–H stretching of physisorbed water. The absorption observed at 1634 cm-1 indicates physisorbed water and chemisorbed CO2 22, 26. The peak at 1422 cm-1 represents CO3 2- (chemisorbed CO2) ions weakly bonded with K+ on the surface of the KF/Al2O3 22. SEM images of the synthesized catalyst revealed a rough surface of various irregularly sized particles (Figure 3). SEM-EDS analysis revealed that the surface of the catalyst consisted of Al, K, O, and F elements. SEM-EDS mapping indicated high dispersion of potassium and fluorine particles on the surface of alumina. Bio-oil and solid residue yields Figures 4 and 5 show the effect of temperature and residence time on the bio-oil and solid residue yields from the HTL of lignocellulosic biomass. When the temperature was


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increased, the solid residue yields gradually decreased. The lowest bio-oil yield (3.9 wt%) was obtained at 250 °C. When the temperature was increased from 250 to 300 °C, the bio-oil yield slightly increased to 6.6 wt%, and a further increase in temperature to 350 °C resulted in a 4.9 wt% decrease. It is considered that some of the bio-oil was transformed into gaseous products at the highest temperature 27. The residence time had no significant effect on the bio-oil yields, which ranged from 5.8 to 6.6 wt%. The highest bio-oil yield was obtained at a residence time of 30 min. As the reaction time increased, the solid residue yields gradually decreased. Based on the data obtained from the non-catalytic HTL runs, the optimal temperature and residence time in this study were determined to be 300 °C and 30 min, respectively. Further experiments with catalysts were performed under these conditions. Figure 6 presents the effect of the KF/Al2O3 catalyst (in loadings from 10 to 40 wt% of the spruce wood sample) on the bio-oil and solid residue yields from the HTL of the lignocellulosic biomass. Catalyst loading at 10 and 20 wt% significantly promoted the bio-oil yields. The highest bio-oil yield (13.9 wt%) was obtained with a catalyst loading of 20 wt%, which was more than two-fold the yield obtained without a catalyst. At the highest catalyst loading (40 wt%), the yield of bio-oil decreased to 9.3 wt%, which was still higher than that of the run without a catalyst. It is probable that a high loading of solid base catalyst favors the Cannizzaro reaction, which produces alcohols and acids from aldehydes and further decomposition of these intermediates (alcohols and acids) to gaseous hydrocarbons. Thus, the highest catalyst loading produced low bio-oil yields. Notably, this study exclusively investigated bio-oil and solid residue products obtained from lignocellulosic biomass to demonstrate the effects of KF/Al2O3 in hydrothermal media. Thus, no attempts were made to quantify the gaseous and aqueous products in addition to their qualitative analysis. The solid residue yields from the catalytic runs were lower than that of the run with no catalyst. An


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increase in catalyst loading resulted in a decrease in solid residue yields. It is well known that homogenous alkaline catalysts, such K2CO3, Na2CO3, KOH, and NaOH, improve the bio-oil yields from the HTL of lignocellulose and suppress the formation of char 28. The same trend was observed in this research for the heterogenous solid base catalyst. Based on previous reports and this study, one can conclude that the use of a base catalyst for the liquefaction of lignocellulose in hydrothermal media promotes bio-oils and inhibits char formation regardless whether homogenous or heterogenous. The raw material (spruce wood) used in this study is a softwood. We further performed HTL runs with a hardwood sample: beech wood. The results are shown in Figure 7 and compared with the results of the HTL processing of spruce wood under identical conditions. The KF/Al2O3 catalyst displayed sensitivity to both softwood and hardwood samples as it resulted in increased bio-oil yields and decreased char yields for both raw materials. The bio-oil yields from the catalytic runs changed depending on the wood type. The bio-oil yield was higher with the hardwood than the softwood. The bio-oil yields of the non-catalytic and catalytic HTL processing of the beech wood were 6.5 and 16.0 wt%, respectively. Lignin in wood samples primarily contributes to the formation of bio-oils from lignocellulose in hydrothermal media. The relative distribution of phenolic nuclei in lignin changes strongly depending on the plant species 29. Generally, hardwood lignin contains both guaiacyl (G) and syringyl (S) units, while softwood lignin exclusively includes G-units 29. Thus, catalytic deconstruction of hardwood produced a higher bio-oil yield than softwood in hydrothermal media. The reason is that the S-unit contains a lower fraction of carbon–carbon bonds than the G-units. The solid residue yield from the catalytic HTL processing of spruce wood (softwood) was 30.6 wt%, while it was 18.0 wt% for the beech wood (hardwood) sample. Both the bio-oil and solid residue yields from the catalytic HTL runs changed depending on the wood type. Table 2 shows yields, elemental compositions, and heating values of the bio-oils produced from the hydrothermal liquefaction of various lignocellulosic


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biomasses in the presence of homogeneous and heterogeneous catalysts. As can be seen from Table 2, the bio-oil yields obtained from the HTL of various lignocellulosic biomasses with homogenous catalysts were higher than those in the present report 30-33. However, the heating values of the bio-oils reported here are comparable with those of bio-oils in previous reports3033

.

Bio-oil compositions The bio-oil compositions from the non-catalytic and catalytic HTL of lignocellulose were analyzed using gas chromatography-mass spectrometry (GC-MS). Figure 8 shows the chemical class compositions of the crude bio-oils produced from the hydrothermal processing of spruce wood without and with the use of a catalyst. The identified compounds represented approximately 80 % of the sum of GC−MS and were classified as aldehydes, ketones, alkenes, phenol and acids. The main peaks are marked on the total ion chromatograms in Figure 9. The full list of identified compounds with their peak areas is provided in Table 3. The most abundant organic compounds in the bio-oils from both the non-catalytic and catalytic runs were phenolic compounds and phenol derivatives. It is well known that the formation of phenolic compounds and phenol derivatives from HTL of woody biomass is primarily responsible for the decomposition of lignin 14. Among the phenols, guaiacol had the highest relative abundance. Guaiacol is known to be the primary product of the thermal degradation of softwood lignin 34. The relative abundance of phenolic compounds increased with the use of catalyst. Previous studies also demonstrated that base-catalyzed depolymerization lignocellulosic biomass increased the relative abundance of phenolic compounds 35, 36. In the catalytic runs, in addition to lignin-derived phenolic species, carbohydrate derived-phenols occurred in the bio-oils. We believe that the carbohydrate portion of lignocellulose first deconstructs to furans in hydrothermal media. These intermediate furanic species transform into phenolic compounds via intramolecular aldol


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condensation in a base-catalyzed hydrothermal process 37. Cyclic ketones (i.e., cyclopentanone, 2-cyclopenten-1-one, and alkylated 2-cyclopenten-1-one) are also formed from furanic intermediates. Table 4 shows the elemental compositions and higher heating values of the bio-oils and solid residues obtained from the hydrothermal liquefaction of lignocellulosic biomass without and with the use of catalyst. The highest heating value was 29.42 MJ/kg, which was obtained from the run with highest catalyst loading (40 wt% KF/Al2O3). Notably, the O/C atomic ratio of all bio-oils was lower than that of raw lignocellulose, which suggests a high de-oxygenation degree. Base-catalyzed depolymerization of lignocellulose in hydrothermal media promotes dehydration and decarboxylation reactions 14. Increases in catalyst loadings resulted in decreased O/C atomic ratios of the bio-oils. The aromatic content of the bio-oils decreased with the use of catalyst compared with the bio-oil from the non-catalytic run because the H/C atomic ratio of the bio-oils from the catalytic runs was higher than that of the bio-oil from the non-catalytic run. The carbon content of the solid residue obtained from the non-catalytic run was 60.41 wt%. It decreased with the use of catalyst. The increase in catalyst loading resulted in decreased carbon content and heating values of the solid residues. We performed SEM-EDS analyses of the solid residues from HTL processing without and with the use of catalysts (Figure S1). The raw material had a smooth surface. After HTL processing, irregular small pores and a heterogenous surface were observed in all the solid residues from the run with no catalyst. In the solid residues from the catalytic runs, particles created by the catalyst were observed on the surface, which was confirmed by EDS analyses. Figure 10 shows the percentages of carbons recovered in the bio-oils and solid residues. The percentages of carbon recovered in the bio-oils from the catalytic runs were higher than in the run without a catalyst. At the highest catalyst loading, the recovered carbon percentage was ACS Paragon Plus Environment

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the lowest among the catalytic runs. We believe that the highest catalyst loading favored gasification of lignocellulose under hydrothermal conditions. The recovered carbon in solid residues decreased with the use of catalyst. The increase in catalyst loading resulted in a decrease in the recovered carbons of solid residues.

Boiling point distributions of bio-oils The boiling point distributions of oxygenated organic compounds were estimated with the help of a miniature distillation apparatus using a thermal gravimetric analysis (TGA) data (Table 5). Hydrocarbons are classified (according to petroleum fractions) as light naphtha (343 °C). The amount of light naphtha in the bio-oils from catalytic runs was higher than that of the bio-oil from the non-catalytic run. The heavy naphtha fraction in the bio-oils from the catalytic runs was lower than that of the bio-oil from the non-catalytic run. The heavy naphtha fraction increased when the catalyst loading was increased. The total naphtha (light and heavy) fractions in the bio-oils were 32.7, 27.1, 28.3, and 28.8 wt% for the noncatalytic run at 10 wt% catalyst loading, 20 wt% catalyst loading and 40 wt% catalyst loading, respectively. These values are comparable with a typical crude oil fraction, in which the total naphtha fraction was 34.5 wt% 38. An increase in catalyst loading decreased the heavy gas oil fraction. Catalyst reuse Catalyst reusability experiments were conducted for three cycles. The used solid residue for the catalyst reusability runs was obtained from HTL of lignocellulosic biomass with catalyst at 300 °C for 30 min. The solid residue containing a mixture of char and catalyst was burnt in a muffle furnace at 550 °C for 2 h. The obtained solid particles (a mixture of ash and used


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KF/Al2O3 catalyst) were used for the catalytic runs. The bio-oil yields produced from HTL of lignocellulose in the presence of recovered catalyst are shown in Figure 11. The activity of catalyst decreased after each re-use. In the 3rd use, the bio-oil yield was found to be 8.1 wt%, which was still higher than that of the run without a catalyst (6.6 wt%). The loss in catalytic activity after each re-use might be the leaching of KF from the catalyst to the solution during the HTL processing. Conclusions The hydrothermal processing of lignocellulosic biomass was performed at 250, 300 and 350 °C for 15, 30 and 60 min. The main objective was to use a heterogenous catalyst in HTL processing of lignocellulose. The catalytic effect of KF/Al2O3 on bio-oil and solid residue products from HTL of spruce wood was investigated at 300 °C for 30 min. The main conclusions are as follows: 1. The use of KF/Al2O3 improved the bio-oil yields and suppressed the formation of char. The optimum catalyst loading, at which the highest bio-oil yield was obtained, was 20 wt% of the raw material. 2. The bio-oil yields from catalytic HTL processing of a hardwood sample were higher than the yields of a softwood sample. The opposite outcome was obtained for the solid residue yield. 3. The compounds identified in the bio-oils were aldehydes, ketones, phenols, acids, and esters. Among these compounds, the phenolic species were dominant in the bio-oil, both from the non-catalytic and catalytic runs. The use of KF/Al2O3 increased the relative yield of phenols and decreased the relative yield of aldehydes, ketones and acids. 4. The carbon content of the bio-oils increased with the use of catalyst. 5. The catalyst lifetime shortened after each re-use. ACS Paragon Plus Environment

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6. The highest heating value of the bio-oil was approximately 29 MJ. Kg-1, which was obtained with 40 wt% catalyst loading. 7. The O/C atomic ratio of spruce wood was 0.73, which decreased to 0.25 with the use of the catalyst. This result reveals a high de-oxygenation degree. 8. The aromatic content of the bio-oils decreased with the use of the catalyst compared with the bio-oil from the non-catalytic run. 9. The amount of light naphtha in the bio-oils from the catalytic runs was higher than that of the bio-oil from the non-catalytic run. Consequently, potassium fluoride doped alumina seems to be an effective catalyst for the deconstruction of lignocellulose to bio-oils in hydrothermal media. However, the catalyst lifetime must be improved. The catalytic effect of KF/Al2O3 using different types of biomass (i.e., algal biomass, food waste, sludge) should be investigated in future studies. Acknowledgements Financial support from Karabük University under the contract KBÜ-BAP-14/2-DR-010 is gratefully acknowledged. Referances [1]

Soh, L.; Eckelman, M. J. Green Solvents in Biomass Processing. ACS Sustain. Chem. Eng. 2016, 4 (11), 5821-5837.

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Elliott, D. C.; Biller, P.; Ross, A. B.; Schmidt, A. J.; Jones, S. B. Hydrothermal Liquefaction of Biomass: Developments from Batch to Continuous Process. Bioresour. Technol. 2015, 178, 147-156.

[3]

Jensen, M. M.; Djajadi, D. T.; Torri, C.; Rasmussen, H. B.; Madsen, R. B.; Venturini, E.; Vassura, I.; Becker, J.; Iversen, B. B.; Meyer, A. S.; Jørgensen, H.; Fabbri, D.; Glasius, M. Hydrothermal Liquefaction of Enzymatic Hydrolysis Lignin: Biomass Pretreatment Severity Affects Lignin Valorization. ACS Sustain. Chem. Eng. 2018, 6 (5), 5940-5949.

[4]

Yue, Y.; Kastner, J. R.; Mani, S. Two-Stage Hydrothermal Liquefaction of Sweet Sorghum Biomass - Part 1: Production of Sugar Mixtures. Energy and Fuels 2018, 32 (7), 7611-7619.

[5]

Liaw, S. B.; Yu, Y.; Wu, H. Association of Inorganic Species Release with Sugar


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Recovery during Wood Hydrothermal Processing. Fuel 2016, 166, 581-584. [6]

Mørup, A. J.; Becker, J.; Christensen, P. S.; Houlberg, K.; Lappa, E.; Klemmer, M.; Madsen, R. B.; Glasius, M.; Iversen, B. B. Construction and Commissioning of a Continuous Reactor for Hydrothermal Liquefaction. Ind. Eng. Chem. Res. 2015, 54 (22), 5935-5947.

[7]

Binder, J. B.; Raines, R. T. Simple Chemical Transformation of Lignocellulosic Biomass into Furans for Fuels and Chemicals. J. Am. Chem. Soc. 2009, 131 (5), 1979-1985.

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Tekin, K.; Karagöz, S.; Bektaş, S. A Review of Hydrothermal Biomass Processing. Renew. Sustain. Energy Rev. 2014, 40, 673-687.

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Hammerschmidt, A.; Boukis, N.; Hauer, E.; Galla, U.; Dinjus, E.; Hitzmann, B.; Larsen, T.; Nygaard, S. D. Catalytic Conversion of Waste Biomass by Hydrothermal Treatment. Fuel 2011, 90 (2), 555-562.

[10] Christensen, P. R.; Mørup, A. J.; Mamakhel, A.; Glasius, M.; Becker, J.; Iversen, B. B. Effects of Heterogeneous Catalyst in Hydrothermal Liquefaction of Dried Distillers Grains with Solubles. Fuel 2014, 123, 158-166. [11] Cao, L.; Zhang, C.; Chen, H.; Tsang, D. C. W.; Luo, G.; Zhang, S.; Chen, J. Hydrothermal Liquefaction of Agricultural and Forestry Wastes: State-of-the-Art Review and Future Prospects. Bioresour. Technol. 2017, 245, 1184-1193. [12] Remón, J.; Randall, J.; Budarin, V. L.; Clark, J. Production of Bio- Fuels and Chemicals by Microwave-Assisted, Catalytic, Hydrothermal Liquefaction (MAC-HTL) of a Mixture of Pine and Spruce Biomass. Green Chem. 2018, 21(2), 284-299. [13] 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. [14] Tekin, K. Hydrothermal Conversion of Russian Olive Seeds into Crude Bio-Oil Using a CaO Catalyst Derived from Waste Mussel Shells. Energy and Fuels 2015, 29 (7), 43824392. [15] Tekin, K.; Karagöz, S.; Bektaş, S. Hydrothermal Liquefaction of Beech Wood Using a Natural Calcium Borate Mineral. J. Supercrit. Fluids 2012, 72, 134-139. [16] Kabalka, G. W.; Pagni, R. M.; Wang, L.; Namboodiri, V.; Hair, C. M. MicrowaveAssisted, Solventless Suzuki Coupling Reactions on Palladium-Doped Alumina. Green Chem. 2000, 2 (3), 120-122. [17] Daştan, A.; Kulkarni, A.; Török, B. Environmentally Benign Synthesis of Heterocyclic Compounds by Combined Microwave-Assisted Heterogeneous Catalytic Approaches. Green Chem. 2012, 14, 17-37. [18] Bo, X.; Guomin, X.; Lingfeng, C.; Ruiping, W.; Lijing, G. Transesterification of Palm Oil with Methanol to Biodiesel over a KF/Al2O3 Heterogeneous Base Catalyst. Energy and Fuels 2007, 21, 3109-3112. [19] Boz, N.; Degirmenbasi, N.; Kalyon, D. M. Conversion of Biomass to Fuel: Transesterification of Vegetable Oil to Biodiesel Using KF Loaded Nano-γ-Al2O3 as Catalyst. Appl. Catal. B Environ. 2009, 89 (3-4), 590-596.


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[20] Teng, G.; Gao, L.; Xiao, G.; Liu, H. Transesterification of Soybean Oil to Biodiesel over Heterogeneous Solid Base Catalyst. Energy and Fuels 2009, 23 (9), 4630-4634. [21] Teramoto, Y.; Tanaka, N.; Lee, S-H.; Endo, T. Pretreatment of Eucalyptus Wood Chips for Enzymatic Saccharification Using Combined Sulfuric Acid-Free Ethanol Cooking and Ball Milling. Biotechnology and Bioengineering 2008, 99 (1), 75-85. [22] Murugan, C.; Bajaj, H. C.; Jasra, R. V. Transesterification of Propylene Carbonate by Methanol Using KF/Al2O3 as an Efficient Base Catalyst. Catalysis Letters 2010, 137, 224-231. [23] Anastasakis, K.; Ross, A. B. Hydrothermal Liquefaction of Four Brown Macro-Algae Commonly Found on the UK Coasts: An Energetic Analysis of the Process and Comparison with Bio-Chemical Conversion Methods. Fuel 2015, 139, 546-553. [24] Ando, T.; Clark, J. H.; Cork, D. G.; Hanafusa, T.; Ichihara, J.; Kimura, T. FluorideAlumina Reagents: The Active Basic Species. Tetrahedron Lett. 1987, 28 (13), 14211424. [25] Weinstock, L. M.; Stevenson, J. M.; Tomellin, S. A.; Pan, S. H.; Utne, T.; Jobson, R. B.; Reinhold, D. F. Characterization of the Actual Catalytic Agent in Potassium Fluoride on Activated Alumina Systems. Tetrahedron Lett. 1986, 27 (33), 3845-3848. [26] Rege, S. U.; Yang, R. T. A Novel FTIR Method for Studying Mixed Gas Adsorption at Low Concentrations: H2O and CO2 on NaX Zeolite and γ-Alumina. Chem. Eng. Sci. 2001, 56 (12), 3781-3796. [27] Tekin, K.; Akalin, M. K.; Karagöz, S. The Effects of Water Tolerant Lewis Acids on the Hydrothermal Liquefaction of Lignocellulosic Biomass. J. Energy Inst. 2016, 89 (4), 627-635. [28] Karagöz, S.; Bhaskar, T.; Muto, A.; Sakata, Y.; Oshiki, T.; Kishimoto, T. LowTemperature Catalytic Hydrothermal Treatment of Wood Biomass: Analysis of Liquid Products. Chem. Eng. J. 2005, 108 (1-2), 127-137. [29] Schutyser, W.; Renders, T.; Van Den Bosch, S.; Koelewijn, S. F.; Beckham, G. T.; Sels, B. F. Chemicals from Lignin: An Interplay of Lignocellulose Fractionation, Depolymerisation, and Upgrading. Chem. Soc. Rev. 2018, 47 (3), 852-908. [30] Sintamarean, I. M.; Grigoras, I. F.; Jensen, C. U., Toor, S. S.; Pedersen, T. H.; Rosendahl, L. A. Two-Stage Alkaline Hydrothermal Liquefaction of Wood to Biocrude in a Continuous Bench-Scale System. Biomass Convers Biorefin. 2017, 7(4), 425-435 and references therein. [31] Nazari, L.; Yuan, Z.; Souzanchi, S.; Ray, M. B.; Xu, C. C. Hydrothermal Liquefaction of Woody Biomass in Hot-Compressed Water: Catalyst Screening and Comprehensive Characterization Of Bio-Crude Oils. Fuel 2015, 162, 74-83. [32] Sun, P.; Heng, M.; Sun, S.; Chen, J. Direct Liquefaction of Paulownia in Hot Compressed Water: Influence of Catalysts. Energy 2010, 35(12), 5421-5429. [33] Tekin, K.; Karagoz, S. t-Buok Catalyzed Bio-Oil Production from Woody Biomass under Sub-Critical Water Conditions. Environ. Chem. Lett. 2013, 11(1), 25-31.


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[34] Brebu, M.; Vasile, C. Thermal Degradation of Lignin-A Review. Cellulose Chemistry & Technology 2010, 44 (9), 353-363. [35] Xu, C.; Lad, N. Production of Heavy Oils with High Caloric Values by Direct Liquefaction of Woody Biomass in Sub/Near-Critical Water. Energy and Fuels 2008, 22 (1), 635-642. [36] Aykaç, G. N.; Tekin, K.; Akalın, M. K.; Karagöz, S.; Srinivasan, M. P. Production of Crude Bio-Oil and Biochar from Hydrothermal Conversion of Jujube Stones With Metal Carbonates. Biofuels 2018, 9 (5),613-623. [37] Sınaǧ, A.; Kruse, A.; Schwarzkopf, V. Key Compounds of the Hydropyrolysis of Glucose in Supercritical Water in the Presence of K2CO3. Ind. Eng. Chem. Res. 2003, 42 (15), 3516-3521. [38] Speight J.G. Handbook of Petroleum Analysis. 2001, Wiley, New York


Energy & Fuels 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 Captions: Figure 1. XRD patterns of the Al2O3 and catalyst (KF/Al2O3). Figure 2. FTIR spectra of Al2O3 and KF/Al2O3. Figure 3. KF/Al2O3 catalyst a) SEM image; Elemental mapping images b) Al, c) O, d) K e) F, f) EDS spectrum. Figure 4. Bio-oil and solid residue yields produced from non-catalytic HTL processing of spruce wood at 250, 300 and 350 °C (PN2int.=2 MPa, t=30 min). Figure 5. Bio-oil and solid residue yields produced from non-catalytic HTL processing of spruce wood at residence times of 15, 30 and 60 min. (T=300 °C, PN2int.=2 MPa). Figure 6. Bio-oil and solid residue yields produced from HTL processing of spruce wood without and with catalyst (T=300 °C, t=30 min, PN2int.=2 MPa). Figure 7. Comparison of bio-oil and solid residue yields produced from HTL processing of spruce wood and beech wood without and with catalyst (T=300 °C, t=30 min, PN2int.=2 MPa, catalyst= 20 wt% KF/Al2O3). Figure 8. Chemical class composition of compounds identified in bio-oils from HTL processing of spruce wood without and with catalyst (T=300 °C, t= 30 min, catalyst= 20 wt% KF/Al2O3 of the raw material). Figure 9. Total Ion Chromatograms of bio-oils from non-catalytic and catalytic HTL

processing of spruce wood (T=300 °C, t=30 min, PN2int.=2 MPa, catalyst: 20 wt% KF/Al2O3). Figure 10. Percentages of carbon recovered from HTL processing of spruce wood without and with catalyst (T=300 °C, t=30 min, PN2int.=2 MPa). Others: refers to the sum of gas, water solubles, and losses during recovery of the bio-oil and solid residues, assuming that the total carbon balance closure is 100 %. Figure 11. Bio-oil yields from HTL processing of lignocellulose without and with catalyst (lifetime test) (T=300 °C, t=30 min, PN2int.=2 MPa).


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Figure 1.


Energy & Fuels 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 2.


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Figure 3.


Energy & Fuels

50 45 40 35 Yield (wt%)

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

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30 25 20 15 10 5 0 250

300 Temperature (°C) Solid residue Bio-oil

Figure 4.


350

Page 25 of 37

Energy & Fuels 50 45 40 35

Yield (wt%)

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

30

25 20 15 10 5 0 15

30

60

Time (min) Solid residue

Bio-oil

Figure 5.


Energy & Fuels

50 45 40 35 Yield (wt%)

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

Page 26 of 37

30 25 20 15 10 5 0 without catalyst

cat.1

cat.2

cat.1= 10 wt% KF/Al2O3 cat.2= 20 wt% KF/Al2O3 cat.3= 40 wt% KF/Al2O3 Solid residue

Bio-oil

Figure 6.


cat.3

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Figure 7.


Energy & Fuels

45 40 35 Peak area (%)

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

Page 28 of 37

30 25 20 15 10 5 0

Aldehydes

Ketones

Phenols

without catalyst

Acids

Esters

with catalyst

Figure 8.


Others

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Figure 9.


Energy & Fuels

100

Carbon recovery (%)

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

Page 30 of 37

80 60 40 20 0 without catalyst

cat.1 cat.2 cat.1= 10 wt% KF/Al2O3 cat.2= 20 wt% KF/Al2O3 cat.3= 40 wt% KF/Al2O3 Bio-oil

Solid residue

Others

Figure 10.


cat.3

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Figure 11.


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Table 1. Proximate, ultimate, and component analysis of spruce wood.

Proximate analysis (wt%)

Ultimate analysis (wt%)

Component analysis (wt%) a, b

Moisture Volatile matter Fixed carbona Ash C H N Ob HHVc (MJ/kg)

5.87 77.14 16.37 0.62 47.79 5.84 0.09 46.28 16.23

Extractives ɑ-cellulose Holocellulose Lignin

2.33 39.95 75.25 23.01

by difference Higher heating value

cHHV:


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Energy & Fuels

Table 2. Yield (wt%), Elemental Composition (wt%), and HHV (MJ.kg−1) of the bio-oils produced from the hydrothermal liquefaction of various lignocellulosic biomasses in the presence of homogeneous and heterogenous catalysts. Ref.

Type of Lignocellulose

30

Willow wooda

Catalyst

T (°C)

NaOH 400 (NaOH/Biomass ratio=0.40) 30 Willow woodb NaOH 400 (NaOH/Biomass ratio=0.40) 31 Birch wood K2CO3 (5 wt% of 300 the biomass) 31 Birch wood KOH (5 wt% of 300 the biomass) 32 Paulownia Iron powder (10 360 wood wt% of the biomass) 32 Paulownia Na2CO3 (5 wt% 360 wood of the biomass) 33 Scotch pine t-BuOK (10 wt% 300 wood of the biomass) 33 Scotch pine KOH (10 wt% of 300 wood the biomass) Present Spruce wood KF/Al2O3 (20 300 study wt% of the biomass) Present Beech wood KF/Al2O3 (20 300 study wt% of the biomass) a-Non-pretreated b-Alkaline pretreated. c-Heavy bio-oil

Reaction Yield Time (wt%) (min.) 10 31.0

C (wt%)

H (wt%)

N (wt%)

O* (wt%)

HHV & (MJ/kg)

84.00

9.40

1.60

5.00

40.92

10

42.0

82.00

9.00

1.60

7.40

39.25

30

38.5

65.60

6.20

0.06

28.14

26.00

30

39.5

66.50

6.10

0.09

27.31

26.31

10

36.3

73.50

7.08

-

19.42

31.49

10

31.9

70.29

6.01

-

23.70

28.11

0

41.9

69.23c

7.22

-

23.55

29.51

0

43.0

69.98c

6.97

-

23.05

29.49

30

13.9

68.34

6.82

0.05

24.79

28.42

30

16.0

67.54

6.62

-

25.77

27.71

*by difference & HHV was calculated according to the Dulong formula that is HHV = 0.338C + 1.428(H–O/8) + 0.095S.


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Page 34 of 37

Table 3. Identified compounds in the bio-oils obtained from the hydrothermal processing of spruce wood without and with the use of catalyst (T=300 °C, t= 30 min, cat.= 20 wt% KF/Al2O3 of the raw material). Peak No 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 1. 27 28 29 30 31 32

Compounds Cyclopentanone 2-Cyclopenten-1-one 2-Methyl-2-cyclopenten-1-one 1-(2-Furanyl)ethanone 2,5-Hexanedione γ-Valerolactone 3-Methyl-2-Cyclopenten-1-one Phenol 2-Hydroxy-3-methyl-2-cyclopenten-1-one 3-Methyl-1,2-cyclopentanedione 2,3-Dimethyl-2-Cyclopenten-1-one 2-Hydroxy-3,5-dimethylcyclopent-2-en-1-one 3-Ethyl-2-cyclopenten-1-one 2-Methoxyphenol 4-Methylphenol 3-Methylphenol 2-Methoxy-4-methylphenol 2,3-Dihydro-1H-inden-1-one 4-Ethyl-2-methoxyphenol 2-Methoxy-4-propylphenol Vanillin 4-Hydroxy-3-methoxyphenyl methyl ketone 4-(2-Hydroxyethyl)-2-methoxyphenol Homovanillic acid 4-Isopropylbipheny 5-Androsten-17,beta,-ol-3-one 1-Hydroxy-3,5,6-trimethoxyxanthen-9-one 3,4,5,6-Tetramethylphenanthrene Levopimaric acid methyl ester Palmitelaidic Acid Stearic acid Dehydroabietic acid Total


Area (%) without with catalyst catalyst 0.32 1.35 4.84 4.23 4.71 6.58 0.77 0.34 6.96 0.54 1.05 0.78 3.12 2.65 1.36 0.86 1.83 2.79 2.05 2.16 0.29 0.87 22.87 24.39 1.00 1.60 5.99 6.63 0.51 0.73 3.33 4.86 0.96 1.94 2.97 0.95 1.65 0.95 4.44 4.98 5.46 4.69 0.44 0.25 0.37 0.37 0.59 0.30 0.36 1.06 0.78 1.99 3.65 82.50 79.01

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Energy & Fuels

Table 4. Elemental composition (wt% and atomic ratio) of raw material, bio-oils and solid residues from the hydrothermal liquefaction of spruce wood without and with catalyst (T=300 °C, t=30 min, PN2int.=2 MPa). KF/Al2O3 (wt%)

without catalyst 10 20 40 without catalyst 10 20 40 a by difference

Product Type

C

H

N

Oa

H/C

O/C

HHV (MJ/kg)

Raw material Bio-oil Bio-oil Bio-oil Bio-oil Solid residue Solid residue Solid residue Solid residue

47.79 67.73 66.42 68.34 69.42 60.41 56.70 51.02 44.51

5.84 6.74 6.89 6.82 7.10 5.47 4.09 3.88 3.13

0.09 0.05 0.04 0.05 0.06 0.21 0.48 0.91 0.24

46.28 25.48 26.66 24.79 23.42 33.91 38.73 44.19 52.12

1.47 1.19 1.24 1.20 1.23 1.09 0.87 0.91 0.84

0.73 0.28 0.30 0.27 0.25 0.42 0.51 0.65 0.88

16.23 27.97 27.53 28.42 29.42 22.18 18.09 14.90 10.21


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Table 5. Boiling point distributions (wt%) of the crude bio-oils obtained from hydrothermal liquefaction processing of spruce wood without and with catalyst (T=300 °C, t=30 min, PN2int.=2 MPa).

KF/Al2O3 (wt%) 10 20 40

Light Naphtha 343°C

2.8 4.2 4.3 3.1

29.9 22.9 24.0 25.7

35.5 35.5 37.3 39.3

17.5 27.1 24.3 22.1


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Hydrothermal Liquefaction of Lignocellulosic Biomass Using

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