Article pubs.acs.org/EF
Development of the Basis for an Analytical Protocol for Feeds and Products of Bio-oil Hydrotreatment Anja Oasmaa,*,† Eeva Kuoppala,† and Douglas C. Elliott‡ †
VTT Technical Research Centre of Finland, Post Office Box 1000, 02044 Espoo, Finland Pacific Northwest National Laboratory (PNNL), 902 Battelle Boulevard, Richland, Washington 99354, United States
‡
ABSTRACT: Methods for easily following the main changes in the composition, stability, and acidity of bio-oil as a result of hydrotreatment are presented in this paper. The methods provide the basis for the development of an analytical protocol, which can be used for bio-oil, as well as the hydrotreated products from bio-oil. The correlation to more conventional methods is provided; however, the use of these methods for the upgrading products is different than previously recognized. The differences in the properties of bio-oil and the hydrotreated products will also create challenges for the analytical protocol. Polar pyrolysis liquids and their hydrotreated products can be divided into five main groups with solvent fractionation, and the change in the proportions of the groups as a result of handling or processing is easy to follow. Over the past 10 years, this method has been successfully used for comparison of fast pyrolysis bio-oil quality and the changes during handling and storage and provides the basis of the analytical protocol presented in this paper. This paper describes the use of the method for characterization of bio-oil hydrotreatment products. A discussion of the use of gas chromatographic and spectroscopic methods is also included. In addition, fuel oil analyses suitable for fast pyrolysis bio-oils and hydrotreatment products are discussed.
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INTRODUCTION Fast pyrolysis liquids (bio-oils) are completely different from mineral oils (Table 1). Therefore, the standard fuel oil analyses
determination for bio-oil are inconsistent, even though the measurements are conducted in certified laboratories. The reason for this variability is that the first flash is very difficult to observe because of the low amount of volatile compounds and high amount of water, which evaporates and suppresses the flame at various temperatures. Hence, a United Nations (UN) test method on sustained combustibility has been evaluated with fast pyrolysis bio-oils, and it has been shown that bio-oils are incapable of sustained combustion. It will be suggested to classify bio-oil as a nonflammable liquid.34 Because of the significant differences between pyrolysis liquids and mineral oils, new methods, such as solids content analysis, have also been developed. A first set of burner fuel specifications have been accepted for fast pyrolysis bio-oil in the form of American Society for Testing and Materials (ASTM) D7544. The solids content method within the burner fuel standard has been validated and has been issued as a standard method, ASTM D7579. Similar validation with bio-oil of the other methods listed in the standard will be required in the future. Fast pyrolysis bio-oil is chemically and thermally less stable than conventional petroleum fuels because of its high content of reactive oxygen-containing compounds. The instability of bio-oil can be observed as increased viscosity over time, i.e., “aging”, particularly when heated. It has been reported that the most significant reactions take place immediately after quenching of the liquid and cease during the first 3 months of storage.4,5 The principal changes during aging (Figure 1) include a reduction in carbonyl compounds, aldehydes and ketones, and an increase in the heavy water-insoluble (WIS) fraction.4,5 There is no change in the content of volatile acids.6
Table 1. Physical Properties of Pyrolysis Liquids and Mineral Oils7 analysis
pyrolysis liquids
light fuel oil (Tempera 15)
water (wt %) solids (wt %) ash (wt %) nitrogen (wt %) sulfur (wt %) stability viscosity, at 40 °C (cSt) density, at 15 °C (kg/dm3) flash point (°C) pour point (°C) LHV (MJ/kg) pH distillability
20−30 0.01−1 0.01−0.2 0−0.4 0−0.05 unstable 15−35 1.10−1.30 40−110 from −9 to −36 13−18 2−3 not distillable
0.025 0 0.01 0 0.2 stable 3.0−7.5 0.89 60 −15 40.3 neutral 160−400 °C
cannot always be used, as such, for bio-oils. Bio-oils exhibit unusual properties, which are not found in conventional hydrocarbon liquids.1,29 The standard analyses have been systematically tested for pyrolysis liquids,1−3 and modifications have been suggested when needed. On the basis of the wide range of properties assessed and evaluated in bio-oils, the following modifications (Table 2) to the standard methods are recommended for biooil analysis.1 One important method, flash point determination, demonstrates the great difference between bio-oil and petroleum hydrocarbons. The results from comparisons of flash point © 2012 American Chemical Society
Received: February 14, 2012 Revised: March 16, 2012 Published: March 19, 2012 2454
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Table 2. Fuel Oil Analyses for Fast Pyrolysis Liquids1 a analysis water (wt %) solids (wt %) particle size distribution carbon residue (wt %) ash (wt %) CHN (wt %) sulfur and chlorine (wt %) alkali metals (wt %) metals (wt %) density, at 15 °C (kg/dm3) viscosity, at 20 and 40 °C (cSt)
method
comment
ASTM E203 methanol/dichloromethane insolubles optical methods
b c
sample size 1g 30 g
d
1g
ASTM D189
e
2−4 g
EN 7 ASTM D5291 ion chromatography
f g h
40 mL 1 mL 2−10 mL
AAS ICP and AAS ASTM D4052
i j k
50 mL 50 mL 4 mL
ASTM D445
l
80 mL
analysis viscosity (mPa s) pour point (°C) heating value (MJ/kg) calorimetric (HHV) effective (LHV) flash point (°C) acidity total acid number (TAN) water insolubles (wt %) stability
method
comment
sample size
rotational viscometry ASTM D97
m n
40 mL 80 mL
DIN 51900
o
1 mL
ASTM D93 pH meter ASTM D664
p q
150 mL 50 mL
water addition
r
5 mL
80 °C for 24 h
s
200 mL
a
Sample size = minimum amount of pyrolysis liquid needed to carry out the analysis, including duplicates. bKarl Fischer titration, methanol/ chloroform (3:1) as a solvent, water addition method for calibration, HYDRANAL K reagents (Composite 5K and Working Medium K) in the case of a fading titration end point, a total of 50 mL of solvent for two determinations, sample size of about 0.25 g (water content > 20 wt %), and stabilization time of 30 s. c ASTM D7579, millipore or multiplace filtration system, 1 μm filter, sample size of 1−15 g to obtain 10−20 mg of residue, sample/solvent = 1:100, and solvent: methanol/dichloromethane (1:1). dMicroscopy with the photo analysis program or optical methods using high-speed cameras or light rays with programs. eControlled evaporation of water to avoid foaming. f Controlled evaporation of water to avoid foaming. gProper homogenization, for forest residue liquids, careful rolling of the sample bottle, sample size as large as possible, triplicates, and proper standard containing all elements measured at similar concentrations. hSample pretreatment by halogen combustion. iWet combustion as a pretreatment method. jWet combustion as a pretreatment method. In samples with a high amount of silicates, silicon can precipitate as SiO2 during the sample pretreatment. This may yield an error in the silicon. For accurate determination of Si, the sample should be ashed by dry combustion and a fusion cake prepared from the ash. kCareful mixing of foam-prone forest residue liquids to avoid air bubbles. lCannon−Fenske viscometer tubes at room temperature and for nontransparent pyrolysis liquids, no prefiltration of the sample if visually homogeneous, elimination of air bubbles before sampling, equilibration time of 15 min, and maximum allowed difference of duplicates of 5%. m Precise temperature measurement and cover the sample holder above 40 °C. nNo preheating of the sample. oUse of a fine cotton thread for ignition and lower heating value (LHV) obtained from a calorimetric heating value and hydrogen analysis. pElimination of air bubbles before sampling. Note that the flash point is not indicative for fast pyrolysis bio-oils and will be replaced by a sustained combustibility test; see UN Manual of Tests and Criteria, part III, subsection 32.5.2. qpH gives the level of acidity, with frequent calibration of the pH meter. TAN gives more accurate values for acidity, with a tight window to be chosen. The derivatization curve should be used. rAddition of 5 g of pyrolysis liquid into 100 g of water. sA total of 45 mL of pyrolysis liquid in 50 mL tight glass bottles, heating in a heating oven, measuring of the increase in viscosity and water, and viscosity determination at 40 °C according to ASTM D445.
viscosity measured by stability testing conducted at 80 °C over a 24 h period.23 Because of the clear correlation between the methods, the results from different laboratories should be easily compared. A comprehensive overview of the stability of pyrolysis liquids was given by Diebold.4 The stability of pyrolysis liquids has to be improved before commercial energy use is possible. Fuel oils are typically preheated before combustion to lower their viscosity for better atomization. If a recirculation of the fuel is included, such as in diesel engines, polymerization and condensation reactions could lead to changes in properties, such as viscosity. The change in properties would require modifications in the fuel feeding system and/or adjustments in combustion conditions, which is not acceptable. The properties of the liquid have to be constant during the typical storage, at least 6 months at 15 °C. There are various methods for stability improvements, including dilution with alcohols,4,5,8−11 reduced pressure distillation,12 neutralization,13 and hydrotreatment.14−16 Dependent upon the final use, such as heating fuels or oil refinery feed, the upgrading requirement is different. The differences in the level of upgrading will create challenges for a comprehensive analytical protocol. In an earlier paper,21 methods for characterization of hydrodeoxygenation (HDO) products, especially the use of various nuclear magnetic resonance (NMR) spectra, were presented. This paper will focus on methods for easily following the main changes in the composition, stability, and
Figure 1. Main changes in softwood [forestry residue (FR) and pine saw dust] pyrolysis liquids during storage,7 presented on a dry basis. Ranges are based on observing the changes for four FR liquids and two pine saw dust liquids. The continuous lines have been drawn for the same green FR liquid.
There is a correlation with the change in the WIS content, increased molecular weight distribution,5−7 and viscosity.17 The viscosity increase-based stability test measures the change in viscosity of the pyrolysis liquid. The change in the carbonyl content of pyrolysis liquid correlates with the change in 2455
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present as microemulsion and cannot be removed by physical means, such as centrifugation.1 The water content is determined by Karl Fischer titration. It has been found that xylene distillation (EN 95 or ASTM D95) cannot be used because bio-oils contain a significant amount of volatile water-soluble compounds that end up being counted as part of the water fraction by this method.19,20 Water affects the physical properties of pyrolysis liquids. The density, viscosity, and heating value increase (Figure 4) when the water content decreases.1 Water improves the stability1 of the pyrolysis liquid until it starts to separate out (typically at above the 30 wt % water content level). In diesel engines, a high water content evens the temperature gradient and results in lower NOx emissions.22 During aging,4,9,10 water is formed in various condensation reactions, and hence, the water content of pyrolysis liquids is increased with time. The aging reactions are fast just after condensation and cease gradually. Most of the water can be removed by reduced pressure distillation at low (≤40 °C) temperatures,12 but simultaneously, a part of other organics will be removed. Acids. Pyrolysis oils contain below 10 wt % volatile carboxylic acids; the main acids as shown in Table 3 are acetic and formic acids.17 Acids can be analyzed quantitatively by capillary electrophoresis (CE), gas chromatograph−flame ionization detector (GC−FID), or as acidity by total acid number (TAN) or pH.1,6 CE and GC−FID (formic acid after derivatization) gave similar results.21 There is a clear correlation between acids in pyrolysis liquid by CE with acidity measured as TAN.6 The acidity of pyrolysis liquids causes material corrosion, and hence, the material choices in production, storage, and use are of utmost importance.1−3 The acids do not react with other bio-oil components (Table 2) at room temperature or at moderate temperatures (below ≤80 °C) to any significant degree over time.6 A part of acids can be removed by reduced pressure distillation of water at low (≤40 °C) temperatures, but simultaneously, some of the other volatiles will be lost.12 Carbonyl Compounds. Aldehydes and ketones are the main compounds (acids are ether-solubles but subtracted mathematically from this fraction) in the ether-soluble fraction of solvent fractionation. Most of the GC-eluted compounds are in this fraction. Aldehydes and ketones have been identified16,23 as the main reason for the instability of pyrolysis oils. Their amount decreases (Figure 1) gradually at room-temperature storage and faster at higher temperatures.7 This change is also seen by following the concentrations of carbonyl groups by titration (Figure 5)23 or GC−FID. During aging, aldehydes can react with each other to form polyacetal oligomers and polymers. For example, the poly(oxymethylene) polymer has limited solubility in water.4 This chemistry suggests a correlation between the decrease in carbonyl compounds and an increase in water insolubles. “Sugars”. This group is most challenging to identify; less than half of it is in the form of one to three ring anhydrosugars and hydroxy acids.17,18 It probably also contains higher molecular-weight anhydrosugar oligomers, sugar acids, and compounds, which chemically behave like sugars. The use of the Brix method of specific gravity correlation to the “sugars” concentration has been studied with these fractions and found to be a useful analytical method.18 This fraction causes some negative properties, for example, stickiness of pyrolysis liquids, which can be problematic. For example, in diesel engine use, the “sugars” have been indicated in fouling of the pistons.22 Water Insolubles. The WIS fraction is composed of degraded lignin,25,26,28 extractives,17,27 and solids. During aging, the WIS reaction products end up in this fraction. The amount of WIS increases (Figure 1) as the molecular weight (Mw) of the oil increases, which results in an increase in viscosity.5 Application of the Solvent Fractionation Scheme. Dividing bio-oils into component groups makes the comparison and studying the behavior of various pyrolysis oils easier. As shown in Figure 6, the main changes in bio-oil composition, e.g., decreased carbonyl compound content (aldehydes and ketones) paired with an increase in the WIS content, during storage are seen. The amount of volatile acids remains the same.
acidity of bio-oil and HDO products. Some of the pieces of the paper have been reported separately before, but this paper is meant to draw them all together into a single collection along with some new information, so that the total picture is presented at once. In a recent report of a similar effort, Fogassy et al.35 have published an analytical platform developed for the detection of biomass oxygenates and biocarbon in biogasoline produced by co-processing of HDO products and vacuum gas oil, but its focus is on the formation of a petroleum refinery feed.
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CHARACTERIZATION OF FAST PYROLYSIS BIO-OIL
The extensive work on bio-oil analysis is reviewed here (in part) to provide the basis for developing a comprehensive analytical protocol, which can be applicable to both bio-oil and the upgraded bio-oil products. Determination of Product Groups by Solvent Fractionation Methods. To determine the type and degree of required upgrading, the chemical composition of the whole bio-oil, especially the compound groups, has to be known. Bio-oil is a highly polar heavy liquid, and it cannot be adequately characterized using only conventional methods. Because of the low volatility of much of the bio-oil, gas chromatography/mass spectrometry (GC/MS) provides only a partial view of the composition. The high temperatures used in the injection systems may even lead to inaccurate conclusions because of further reaction of the bio-oil components as a result of its thermal instability. Using solvent fractionation at a moderate temperature17,18 (Figure 2), pyrolysis liquid can be divided into water-soluble and WIS fractions.
Figure 2. Solvent fractionation scheme for pyrolysis liquid characterization.17,18 DCM, dichloromethane; LMM, low-molecular-mass; HMM, high-molecular-mass; and EIS, “sugars” as an evaporation residue of the ether-insoluble fraction.17,18 It has been found that the water-soluble fraction is composed of four main groups: water, acids, carbonyl compounds (aldehydes and ketones), and “sugars”. These fractions are not pure, but their main compound types determine their properties. The WIS fraction can be divided by dichloromethane (DCM) extraction into two fractions: low-molecularmass (LMM) and high-molecular-mass (HMM) fractions. Water. Water in fast pyrolysis bio-oil is composed (Figure 3) of feedstock moisture and the water formed during pyrolysis (“pyrolysis water”). This water is either chemically dissolved in the bio-oil or
Figure 3. Pyrolysis yields from pine sawdust showing the origin of water in fast pyrolysis bio-oil. 2456
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Figure 4. Approximate correlation of the water content to density, viscosity, and heating value of pyrolysis liquids. Data points are shown in an earlier publication.1
Table 3. Acid Content and Acidity of Bio-oil at Various Temperatures over a Period of Time6 storage time at room temperature (months) acid (wt %)
0
3
6
stability test (80 °C for 24 h)
cold room, at 9 °C (6 months)
acetic glycolic formic total TAN
2.2 0.4 1.2 3.8 70
2.5 0.5 1.4 4.4 73
2.5 0.5 1.3 4.3 71
2.5 0.5 1.3 4.3 74
2.5 0.5 1.4 4.3 75
2.5 0.5 1.4 4.3 70
2.4 0.4 1.4 4.3 70
dissolved carbon in the aqueous phase following hydrotreating is a direct function of the extent of deoxygenation of the bio-oil.24 As reported earlier, severe hydrotreating can be used to decrease the oxygen content and resulting acidity of pyrolysis liquid (see Figure 7). When upgraded sufficiently, bio-oil hydrocarbon products can be characterized by conventional methods used in the oil refinery industry. Product Groups by Solvent Fractionation. During hydrotreatment, the solubility pattern of bio-oil changes. In an earlier study,21 it was shown that the basic fractionation scheme is informative for low-severity upgrading, even though product composition changes. In Figure 8, it can be seen that the ether-insoluble fraction (consisting mainly of sugar-type compounds) decreased with an increasing temperature in HDO. Therefore, the product of the conversion of “sugars” could be the source of the increase of the carbon recovery in the oil phase.25 The change in the “sugars” concentration in the aqueous phase can be measured easily by Brix. The oily phase contains only minor amounts of highly water-soluble “sugars”. Compound Identification by Gas Chromatography. Gas chromatograph−mass selective detector (GC−MSD) gives information on changes in GC-eluted compounds. In stabilization, the hydrogenation of aldehydes and “sugars” into alcohols might be seen as an increase in the diols. Also, the disappearance of diols with an increasing severity of hydrotreatment can be seen. At moderate levels of hydrotreating, to reduce residual oxygen contents to 10−15 wt %, unsaturated ketones and furans have been hydrogenated and some deoxygenated hydrocarbon products are detected. Some demethoxylation of the guaiacol structures to phenols is also seen.30 Severely hydrotreated products with residual oxygen contents, less than 1 wt %, have been reported to contain primarily cyclic hydrocarbons, both saturated naphthenes (alkyl cyclohexanes) and aromatics (alkyl benzenes), with some straight-chained and branched alkanes.30 For quantitative composition of aqueous phase compounds, GC−FID can be used. In GC−FID, the column HP-Innowax (cross-linked polyethylene glycol, 60 m, 0.25 mm, and 0.25 μm) was used. An aqueous phase was prepared by extracting
Figure 5. Change in carbonyl content over time at various storage temperatures for a pine pyrolysis liquid.23
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fridge, at 9 °C (6 months) freezer, at −17 °C (6 months)
CHARACTERIZATION OF HYDROTREATMENT PRODUCTS
Dependent upon the severity of hydrotreatment, one to three product fractions are obtained. At mild conditions, the bio-oil will undergo limited hydrogenation, primarily of the carbonyl functional groups, and will remain a single-phase oil. At moderate conditions, both a low-density hydrocarbon product phase will form and rise to the top of the aqueous phase with a heavy oxygenated oil phase on the bottom. At the most severe hydrotreating conditions, the hydrocarbon top phase becomes the only organic product. Water Content and Elemental Composition. The water content of polar oily phases was analyzed by Karl Fischer titration using Riedel de Haen: Hydranal Composite 1 solution. CHN was determined according to ASTM D5291. As reported earlier, a Van Krevelen plot16,21,25 with molar ratios of O/C (dry) versus H/C (dry), shows clearly the efficiency of hydrotreatment. The water content of the aqueous fractions was also analyzed by Karl Fischer titration. The carbon content of the aqueous phase can be determined with a Shimadzu total organic carbon/ total carbon (TOC/TC) analyzer. The relation of residual 2457
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Figure 6. Composition of pyrolysis liquid based on the solvent extraction scheme. Chemical characterization by measuring sugars by (A) solvent extraction as EISs and (B) Brix method. WIS = LMM + HMM fractions (including extractives and polymerization products).1
Figure 7. Relation of TAN (mg of KOH/g of oil according to ASTM D3339) to the oxygen content (wt %) in bio-oil and hydrotreated bio-oil.6
reported at a number of recent conferences.32,33 The hydrocarbon products produced from bio-oil display the same type of broad distillation range found in petroleum products. However, it must be pointed out that there is no consensus on the optimal method to be used. Also, the whole product might not be distillable, and hence, the possible non-GC-eluted fraction should be measured. Functional Groups by NMR Methods. The use of various NMR techniques has been compared in a previous paper.28 It was concluded that NMR is a useful tool for generating information on the reactions taking place during hydrotreatment, e.g., changes in carbonyl compounds, phenolics, and carbohydrates. The hydrogenation of aldehydes was clearly seen by both 1H and 13C NMR. 1H NMR also indicated the detachment of methoxyl groups from the aromatics. The increase in aliphatics/aromatics ratios after hydrotreatment showed that the hydrotreatment resulted in products with better physical properties than the pyrolysis liquid. In another study, distillate fractions from hydrotreated bio-oil products at three levels of residual oxygen content were analyzed by 13C NMR and compared.31 These results clearly showed the progression of the removal of the various oxygenated functional groups. While bio-oil as produced had a wide collection of oxygenates, the number and amounts of oxygenates were reduced through HDO to a level of 10 wt % or less. Limited amounts of carbonyls, carboxyls, and ethers were found mostly in the lighter distillate fractions (naphtha and
Figure 8. Results of VTT’s solvent fractionation technique applied to the aqueous phase product obtained at various HDO reaction temperatures.25
the sample with water (sample/water = 1:20). 1-Butanol was added to the aqueous extract as an internal standard. A total of 1 μL of sample was injected (split injection, ratio of 20:1) into the oven, with the following temperature program of the oven: 60 °C for 1 min, heating rate at 3 °C/min up to 230 °C, and hold time for 30 min. Identification and quantification of compounds was attained using reference compounds. Simulated Distillation. Simulated distillation (ASTM D2887) was applied to the hydrotreated products.31 Simulated distillation data for hydrotreated bio-oil products have been 2458
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When moving toward high-severity hydrotreatment and liquid hydrocarbon fuel production, the solvent fractionation scheme will be less informative and the routine analyses of mineral oil industry, such as distillation,35 are more appropriate. The transition in methods used on the basis of products being analyzed is depicted in Figure 9. Table 4 below summarizes briefly the main information obtained using various analyses within the protocol. As suggested in the table, the analytical protocol can be used to gauge a number of important process parameters and outcomes. These parameters and outcomes are considered to be the most important for elucidating the pyrolysis and upgrading process utility.
Figure 9. Applicable methods to be emphasized in the analytical protocol for bio-oil and HDO products.
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Table 4. Methods and Results from the Analytical Protocol information
sample type
mass and water balances carbon balances, H/C versus O/C carbon balances, H/C versus O/C amount of product groups change in “sugars”
oil, aqueous oil, solid
KF titration CHN
aqueous
TC and TOC
oil, aqueous
solvent fractionation
aqueous aqueous
ether insolubles, Brix, and HPLC TAN and pH
aqueous aqueous oil oil oil
CE GC−FIDa GC−MSD and GC−FID 1 H and 13C NMR simulated distillationb
acidity and total acid number amount of acids GC-eluted compounds GC-eluted compounds hydrogenation distillability
analytical methods
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Jaana Korhonen, Sirpa Lehtinen, Elina Paasonen, and Kaija Luomanperä are acknowledged for their analytical assistance. Metso, UPM, Fortum, Tekes, EU BIOCOUP, and VTT are acknowledged for funding, and the United States Department of Energy (DOE), Office of the Biomass Program funded the contribution from the Pacific Northwest National Laboratory through contract DE-AC05-76RLO-1830.
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a
HP-Innowax: cross-linked polyethylene glycol, 60 m, 0.25 mm, and 0.25 μm. bA comparison to conventional athmospheric distillation has to be made.
REFERENCES
(1) Oasmaa, A.; Peacocke, C. A Guide to Physical Property Characterisation of Biomass-Derived Fast Pyrolysis Liquids. A Guide; VTT Publications: Espoo, Finland, 2010; VTT Vol. 731, ISBN 978951-38-7384-4, http://www.vtt.fi/inf/pdf/publications/2010/P731. pdf. (2) Oasmaa, A.; Peacocke, C.; Gust, S.; Meier, D.; McLellan, R. Energy Fuels 2005, 19 (5), 2155−2163. (3) Oasmaa, A.; Leppämäki, E.; Koponen, P.; Levander, J.; Tapola, E. Physical Characterisation of Biomass-Based Pyrolysis Liquids. Application of Standard Fuel Oil Analyses; VTT Publications: Espoo, Finland, 1997; VTT Vol. 306, ISBN 951-38-5051-X. (4) Diebold, J. P. A review of the chemical and physical mechanisms of the storage stability of fast pyrolysis bio-oils. In Fast Pyrolysis of Biomass: A Handbook; Bridgwater, A. V., Ed.; CPL Press: Newbury, U.K., 2002; Vol. 2, p 424. (5) Oasmaa, A.; Kuoppala, E. Energy Fuels 2003, 17 (4), 1075−1084. (6) Oasmaa, A.; Elliott, D. C.; Korhonen, J. Energy Fuels 2010, 24, 6548−6554. (7) Oasmaa, A. Fuel oil quality properties of wood-based pyrolysis liquids. Academic Dissertation, Department of Chemistry, University of Jyväskylä, Jyväskylä, Finland, 2003; Research Report Series, Report 99; ISBN 951-39-1572-7. (8) Oasmaa, A.; Kuoppala, E.; Selin, J.-F.; Gust, S.; Solantausta, Y. Energy Fuels 2004, 18 (5), 1578−1583. (9) Czernik, S. Storage of biomass pyrolysis oils. Proceedings of the Specialist Workshop on Biomass Pyrolysis Oil Properties and Combustion; Estes Park, CO, Sept 26−28, 1994; NREL Paper CP-430-7215, pp 67−76. (10) Czernik, S.; Johnson, D.; Black, S. Biomass Bioenergy 1994, 7 (1−6), 187−192. (11) Diebold, J. P.; Czernik, S. Energy Fuels 1997, 11 (5), 1081− 1091. (12) Oasmaa, A.; Sipilä, K.; Solantausta, Y.; Kuoppala, E. Energy Fuels 2005, 19 (6), 2556−2561.
gasoline), with phenolics becoming prominent in the jet/diesel/gas oil fractions when residual oxygen was at 8.2%. At 4.9 wt % residual oxygen, only phenolics were still detected. At 0.4 wt % residual oxygen, no detectible oxygen functional types were found in the distillate fractions tested in these NMR studies.
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SUMMARY The analytical protocol depends upon the objective of the research. Polar pyrolysis liquids and low-severity hydrotreatment products are much different from the highly upgraded bio-oil products, which are more like petroleum hydrocarbon fuels. Methods for analysis of the polar bio-oils have been developed over the years based on the specific requirements of the pyrolysis oil product. The water content, elemental analysis, and H/C and O/C molar ratios give a good indication of the effect of the process severity. By the solvent fractionation method, liquids can be divided into five main groups: water, acids, carbonyls, “sugars”, and a WIS fraction, and the amount of each can be followed during upgrading. The change in carbonyls, which are the main compounds causing instability of the bio-oil, can be measured in the aqueous fraction by KOH titration. The change in the “sugars” concentration in the aqueous fraction can be followed relatively conveniently by the fast Brix method. The change in acidity can be measured by TAN titration, which is commonly used in the petroleum industry. The use of NMR to track the changes in functional groups and aromaticity of the product has also been shown to provide useful information with the upgraded bio-oil products. 2459
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dx.doi.org/10.1021/ef300252y | Energy Fuels 2012, 26, 2454−2460
