Characterization of biomass-based flash pyrolysis oils

CHARACTERIZATION OF BIOMASS-BASED FLASH

PYROLYSIS OILS

KAI SIPILAÈ , EEVA KUOPPALA, LEENA FAGERNAÈ S and ANJA OASMAA

VTT Energy, P.O. Box 1601, 02044 VTT, Espoo, Finland

(Received 25 November 1996; revised 29 August 1997; accepted 1 September 1997)

AbstractÐAn analytical scheme for the characterization of biomass-based ¯ash pyrolysis oils was devel-oped. The scheme was based on fractionation of the oils with water and on further extraction of thewater-soluble fraction with diethylether. The chemical composition of the fractions was analyzed by gaschromatography±mass spectrometry. The physical and chemical nature of straw, pine and hardwoodpyrolysis oils was determined and compared with each other. Correlations between the physical proper-ties and chemical composition of the oils were drawn. The characterization method will be utilized infurther work for stabilization and upgrading tests of ¯ash pyrolysis oils. # 1998 Elsevier Science Ltd.All rights reserved

KeywordsÐPyrolysis oil; bio-oil; characterization; properties; composition.

1. INTRODUCTION

The chemical composition of biomass-basedpyrolysis oils is complicated, comprisingmainly water, carboxylic acids, carbohydratesand lignin-derived substances. The oils areacidic, viscous, reactive and thermally un-stable. The composition and properties of theoils di�er considerably from those of pet-roleum-based fuel oils. Due to the specialproperties of pyrolysis oils many problemsarise in their handling and utilization.1±4

Research into biomass-based ¯ash pyrolysisoils at VTT Energy includes production,characterization, quality improvement, utiliz-ation and feasibility studies of the oils.5±8 Theaim of characterization work is to understandthe chemical behavior of the oils over thewhole chain from processing to utilization,and to solve the problems arising (Fig. 1). Theresults obtained with this characterizationmethod in these studies will be presented inother articles in the near future.

Standard fuel oil methods developed forpetroleum fuels may not all be suitable assuch for pyrolysis oils. The applicability ofthese methods to pyrolysis oils has recentlybeen evaluated.8 Chemical characterization ofpyrolysis oils has generally been based on thefractionation of the oils into di�erent classesof chemical functionality.7,9 In solvent extrac-tion, the oils have been divided mainly intoacidic, phenolic, basic, hydrocarbon and aqu-

eous fractions. In adsorption chromatography,the oils have been separated into di�erent hy-drocarbon and polar classes. Gas chromatog-raphy±mass spectrometry has been thetechnique most widely used in the analyses ofthe fractions. Fractionation methods with suc-cessive analyses of the fractions have oftenbeen quite complicated, elaborate and time-consuming.

In this study, a characterization scheme forpyrolysis oils was developed. The aim was to®nd a relatively simple, fast method thatwould give su�cient information with respectto chemical and physical properties. Thecharacterization procedure chosen was basedon the fractionation of the oils with water andon the analysis of the fractions separately. Inaddition to the analyses included in the basicscheme, additional analyses can be carried outif necessary. To investigate the e�ciency ofthe scheme, its applicability for three pyrolysisoils is presented. The aim was also to ®nd cor-relations between the physical properties andchemical composition of the oils.

2. MATERIALS AND METHODS

2.1. Pyrolysis oils

The pyrolysis oils studied were a mixedhardwood (oak±maple) oil, a Scots pine oiland a wheat straw oil. The hardwood oil wassupplied by Ensyn Technologies Inc., Canada.

Biomass and Bioenergy Vol. 14, No. 2, pp. 103±113, 1998# 1998 Elsevier Science Ltd. All rights reserved

Printed in Great Britain0961-9534/98 $19.00+0.00PII: S0961-9534(97)10024-1

103

The Scots pine oil and the wheat straw oilwere produced at VTT in an atmospheric ¯ui-dized-bed pyrolyzer (1 kg/h) at 5308C. The oilsamples were single samples from oils obtainedfrom di�erent raw materials. Hence, any morefar-reaching conclusions related to processconditions, recovery systems or oil ageingshould not be drawn.

2.2. Fractionation of the oils

Chemical characterization of the oils wasbased on the fractionation of the oils withwater into water-soluble and water-insolublefractions, which were analyzed separately(Fig. 2). Pyrolysis oil was added slowly asdrops with constant stirring into distilledwater in 1:10 weight ratio. The powder-likewater-insoluble fraction was removed by ®l-tration (<0.1 mm). The fraction was furtherwashed with distilled water, vacuum-dried at

<408C, and weighed. The drying temperaturehad to be low, because the fraction becamedarker already at 608C and melted at 808C.

2.3. Chemical analyses

2.3.1. Whole pyrolysis oils. The pyrolysis oilswere dissolved in methanol, in which theywere soluble, and the solutions obtained wereanalyzed by mass-selective detection. The sys-tem (HP 5970) was controlled by an HP 9000series Pascal ChemStation computer. The in-terpretation of the mass spectra obtained bygas chromatography±mass spectrometry (GC±MS) was based on automatic library search(NBS REV_F/HP 9000 series 310) and on lit-erature data.10±19 The analysis was performedusing an HP Ultra 1 fused silica capillary col-umn (50 m� 0.32 mm i.d.; ®lm thickness0.52 mm). Helium was used as the carrier gas.The injector temperature was 2908C. The tem-

Fig. 1. Links between di�erent parts of the whole chain from biomass feedstock to utilization of pyrol-ysis oil.

K. SIPILAÈ et al.104

perature program was 2 min at 308C, then at108C/min to 3008C and 3 min at 3008C.2.3.2. Water-soluble fractions. The water-sol-

uble fractions were analyzed quantitatively forvolatile acids and alcohols. The low molecularmass C1±C6 carboxylic acids were analyzed astheir benzyl esters by GC with the method ofAleÂ n et al.,20 adapted for the purpose exclud-ing the treatment of the sample through anacidic cation exchange resin for liberating thesodium.

The low molecular mass aliphatic alcoholswere analyzed by an HP 5890 II gas chro-matograph using an HP Innowax column(60 m� 0.25 mm; ®lm thickness 0.25 mm). Theinjector temperature was 2408C. The tempera-ture program was 3 min at 708C, at 88C/minto 2308C and 20 min at 2308C. Helium wasused as the carrier gas. N-butanol was used asan internal standard after ensuring that it wasnot present in the sample.

The water-soluble fractions were furtherextracted with diethylether (1:1 v/v) immedi-

ately after separation. The diethylether solublefractions were analyzed by GC±MS asdescribed above. To measure the yields ofdiethylether solubles, ether was removed byevaporation, and the residues were vacuum-dried and weighed. In evaporation a part ofthe volatile compounds was lost.

The diethylether insoluble fractions wereevaporated in vacuo at <458C and the resi-dues vacuum-dried and weighed. The tempera-ture was held low in evaporation to avoiddegrading of carbohydrates. An aliquot of thisdried residue was dissolved in methanol, andthe solution analyzed by GC±MS as describedabove. Another aliquot was per(trimethylsily-lated) and analyzed then by GC±MS also asdescribed above. In the analyses of silylatedderivatives temperature program was, how-ever, di�erent; 48C/min from 100 to 3008Cand 10 min at 3008C. The evaporation residuesof the diethylether insoluble fractions werealso further pyrolyzed by pyrolysis (Py)±GC±MS presented below.

Fig. 2. Fractionation scheme with basic and additional analyses for pyrolysis oils. Additional analysesare marked with *.

Characterization of biomass-based ¯ash pyrolysis oils 105

2.3.3. Water-insoluble fractions. The water-insoluble fractions were pyrolyzed by Py±GC±MS like the diethylether insolubles of water-soluble fractions. In these analyses the sample(1±2 mg) was pyrolyzed in a quartz tube(1.25 cm� 1.0 mm i.d.) at temperatures 400,500, 600 and 7008C for the water-insolublefraction and at 600 and 7008C for the diethy-lether insoluble fraction (heating rate 18C/s;heating time 10 s) using a CDS Pyroprobe1000 heated ®lament pyrolyzer coupled to anHP 5890 gas chromatograph (interface tem-perature, 3508C), which in turn was interfacedto an HP 5970 mass-selective detector. TheGC analyses were also performed as those ofthe whole oil described above. The water-inso-luble fractions were also analyzed by infra-red(IR) spectroscopy using a Perkin-Elmer 683instrument.

2.4. Physical properties and fuel characteristics

Physical properties and fuel characteristicswere determined for the oils and their frac-tions using standard methods tested pre-viously.8 The solids were determined asethanol insolubles retained by a ®lter of0.1 mm after several washings and vacuum-dry-ing. Water content was analyzed by Karl±Fischer titration according to ASTM D 1744.The sample solvent was a mixture of chloro-form and methanol (3:1 v/v). Viscosity wasdetermined at 508C using glass capillariesaccording to ASTM D 445. Density wasmeasured at 158C by ASTM D 4052, andheating value according to DIN 51900. Ashwas determined according to EN 7,Conradson carbon residue (CCR) according toASTM D 189, and elemental analysis CHNaccording to ASTM D 5373-93. The oxygencontent was calculated by di�erence. Thechlorine and sulfur contents were determinedby capillary electrophoresis technique aftercombustion of the sample in an oxygen bombaccording to ASTM D 4239. Flash point wasmeasured according to ASTM D 93 and pourpoint according to ASTM D 97.

3. RESULTS AND DISCUSSION

3.1. Water fractionation method for pyrolysisoils

Addition of water into pyrolysis oil in a suf-®cient amount results in a phase separation.21

In the tests carried out for the hardwood oil,

in smaller water amounts than with the oil±water weight ratios of 1:3, the water-insolublefraction was heavy oil-like material. Higherwater amounts and addition of pyrolysis oil asdrops into water resulted in the formation of ahomogeneous powder-like fraction. The oil-water ratio of 1:10 was chosen to obtain allwater-solubles contained in the oils into thewater-soluble fraction.8

When adding pyrolysis oil too fast into thewater, the water-insoluble fraction contained,in addition to powder-like material, sticky ma-terial (less than 5 wt% of the oil). This stickymaterial was isolated, dissolved in methanoland analyzed by GC±MS. No eluted com-pounds were found. On the basis of CHNanalyses, the sticky fraction was of the samematerial as the powder-like fraction despitetheir di�erent appearance.

The stability of water-soluble fractions ofpyrolysis oils was studied by storing the frac-tions at room temperature for 2 months, whileprotected against light. After fractionationbrownish ¯akes were formed in the solutions.

The amount of ¯akes and simultaneouslythe pH of the solutions increased with thetime. The amount of ¯akes formed during 2months was for hardwood oil less than0.5 wt% of the oil and for straw oil and pineoil less than 0.2 wt%. For the hardwood oil,pH was increased from 2.6 to 2.8 and, respect-ively, the amount of acetic and formic acidsdecreased by 10%. No changes were found inthe hydroxy acid composition. The precipi-tation was dissolved when acetic and formicacids were added again into the solution. Withthe time the ¯akes changed into a tarry ma-terial, which was stuck on the surfaces of thebottle.

The ¯akes were dissolved in methanol andanalyzed by GC±MS. The compounds elutedfor hardwood oil were derivatives of syringolsand quaiacols with ketone, aldehyde, acid orhydrocarbon functionality. The main com-pound was syringaldehyde. For straw oil andpine oil the major compounds were quaiacolderivatives.

3.2. Water-soluble fractions

The yellow-colored water-soluble fractionscomprised a considerable part of the pyrolysisoils. The proportion of water-solubles rangedfrom about 60 to 80 wt% of the oils. Thehighest proportion was obtained for the strawoil. All the compounds in pyrolysis oils, eluted


on GC, were found in the water-soluble frac-tions.3.2.1. Volatile acids and alcohols. The highest

amount of separate organic compound groupsanalyzed in the oils consisted of low molecularmass carboxylic acids (Table 1). The highestamount of acids was obtained for the strawoil. The main acids were acetic and formicacids; their amount comprised 80±90% of thetotal amount of acids. The proportion of for-mic acid of the total acids was 34% for thepine oil, while it was 17±18% for the otheroils.

Of low molecular aliphatic alcohols metha-nol was detected in the oils. The methanolcontent was highest, 4 wt%, for the straw oil.

Formic and acetic acids seemed to have asigni®cant e�ect on the pH of the oils. Themain reason for the pH being lower in thepine oil than in the straw oil was the higheramount of formic acid, and the lower amountof water in the pine oil (Table 1).3.2.2. Diethylether solubles of water fractions.

The amount of diethylether solubles deter-mined as evaporation residues ranged from 4to 8 wt% of the pyrolysis oils. The residueswere bright yellow non-viscous ¯uids.

The diethylether solubles contained lowmolecular mass degradation products of ligninand polysaccharides (Figs 3 and 4). Theircomposition gave information on the raw ma-terial used and on the degree of thermal de-composition of the material. The ethersolubles of hardwood oil contained quaiacyl-syringyl lignin-derived compounds, and thoseof straw oil and pine oil quaiacyl lignin-de-rived compounds. The diethylether solubles ofstraw oil contained more lower molecularmass degradation products, such as aceticacid, glycolaldehyde, furaldehydes, phenols

and catechols, than those of pine oil. In ad-

dition, a larger part of the ether solubles

might have been volatilized from straw oil

than from pine oil during the evaporation of

ether.

The compounds volatilized from pyrolysis

oils were studied by rotary evaporation of the

straw oil, and by distillation of the hardwood

oil. The distillates from the experiments were

analyzed by GC±MS. The main compounds

evaporated from straw oil comprised water,

volatile acids (acetic and formic acids), ketones

(hydroxybutanone) and aldehydes (2-furalde-

hyde); and those distilled from hardwood oil

were aldehydes (formaldehyde, acetaldehyde),

ketones (2-propanone, 2-butanone) and esters

(acetic acid and formic acid methyl esters).

3.2.3. Diethylether insolubles of water frac-

tions. The diethylether insolubles determined

as evaporation residues comprised consider-

able proportions of the pyrolysis oils, from 25

to 40 wt%. The highest amount was for the

pine oil. The evaporation residues were dark

syrup-like substances.

Only a small part of the diethylether insolu-

ble fractions was eluted on GC. The main

compounds were levoglucosan and cellobiosan

(Figs 3 and 5). The highest amount of these

two compounds was for the pine oil; 4 wt% of

the oil. The straw oil contained a higher

amount of glycolaldehyde than the pine oil. In

addition to these compounds, mainly mono-

saccharides and hydroxy acids were found.

The total ion chromatogram of the diethy-

lether insoluble fraction for hardwood oil with

degradation pathway is shown in Fig. 5.

Pyrolytic decomposition pathways for cellulose

have been studied extensively by Evans and

Milne11 and Radlein et al.22

Table 1. The amounts (wt% of pyrolysis oil) of water-soluble compounds analyzed quantitatively in pyrolysis oils

Compound Straw oil Pine oil Ensyn oil (hardwood)

Water content of oil 19.9 11.1 23.2pH of oil 3.7 2.6 2.8Methanol 4.0 1.5 0.4Acids 10.8 7.3 6.2

Methanoic (formic) 1.85 2.47 1.10Ethanoic (acetic) 7.41 3.45 4.59Propanoic (propionic) 0.50 0.26 0.242-Methylpropanoic (isobutyric) 0.07 0.04 0.03Hydroxyethanoic (glycolic) 0.58 0.78 0.11Butanoic (butyric) 0.11 0.06 0.092-Hydroxypropanoic (lactic) 0.09 0.09 0.03Allyl acetic 0.08 0.07 0.03Pentanoic acid (valeric acid) 0.07 0.03 0.02Hexanoic (caproic) 0.05 0.06 Ð


Fig. 3. Total ion chromatograms of hardwood pyrolysis oil (A), and the diethylether solubles (B) andinsolubles (C) of the water fraction of the oil. Peak identi®cation: degradation products of polysacchar-ides: (1) acetic acid; (2) 1-hydroxy-2-propanone; (3) 1-hydroxy-2-butanone; (4) 2-furaldehyde; (5) 1-acet-yloxypropan-2-one; (6) (5H)-furan-2-one; (7) 2-methyl-2-cyclopenten-1-one; (8) 2-acetylfuran; (9) isomerof a-angelica lactone; (10) 5-methyl-2-furaldehyde; (12) 2-hydroxy-3-methyl-2-cyclopenten-1-one; (25)


Fig. 4. Total ion chromatograms of diethylether solubles of water fractions in the straw pyrolysis oil(A) and pine pyrolysis oil (B). Peak identi®cations: degradation products of polysaccharides: (1) aceticacid; (2) 1-hydroxy-2-propanone; (3) 1-hydroxy-2-butanone; (4) 2-cyclopenten-1-one; (5) 2-furaldehyde;(6) 2-methyl-2,3-dihydrofuran-3-one; (7) 1-acetyloxypropan-2-one; (8) 2-methoxy-2,5-dihydrofuran; (9)acetylfuran; (10) 2-methyl-2-cyclopenten-1-one; (11) isomer of a-angelica lactone; (12) 4-(hydroxy-methyl)tetrahydropyran-3-one; (13a) 5-methyl-2-furaldehyde; (13b) pent-4-enal-2-one; (15) 2-hydroxy-3-methyl-2-cyclopenten-1-one; (19) 3-hydroxy-2-methyl-(4H)-pyran-4-one; (24) 5-(hydroxymethyl)-2-fural-dehyde; (29) dimethylpyranone. Degradation products of lignin: (14) phenol; (16) 2-methylphenol; (17)3- or 4-methylphenol; (18) quaiacol; (20) 2,4- or 2,5-dimethylphenol; (21) ethylphenol; (22) catechol;(23) 4-methylquaiacol; (25) 3-methylcatechol; (26) 3-methoxycatechol; (27) 4-methylcatechol; (28) 4-vinylquaiacol; (30) dimethylcatechol; (31) eugenol; (32) 4-ethylcatechol; (33) vanillin; (34) isoeugenol(cis); (35) 4-propylquaiacol; (36) acetoquaiacone; (37) coniferyl alcohol (cis); (38) vanillic acid; (39) con-iferyl alcohol (trans); (40) a-oxypropioquaiacone; (41) dihydroconiferyl alcohol; (42) acetosyringone;

(43) coniferaldehyde; (44) syringyl acetone; (45) sinapaldehyde.

1,6-anhydro-b-D-glucopyranose (levoglucosan). Degradation products of lignin: (11) phenol; (13) 2-methylphenol; (14) 3- or 4- methylphenol; (15) quaiacol; (16) catechol; (17) 4-methylquaiacol; (18) 3-methylcatechol; (19) 3-methoxycatechol; (20) 4-ethylquaiacol; (21) syringol; (22) 4-ethylcatechol; (23)vanillin; (24) vanillic acid; (26) acetoquaiacone; (27) 4-ethylsyringol; (28) coniferyl alcohol; (29) 4-vinyl-syringol; (30) 4-allylsyringol; (31) syringaldehyde; (32) 4-propenylsyringol; (33) acetosyringone; (34) syr-

ingyl acetone; (35) propiosyringone; (36) sinapaldehyde.


When pyrolyzing the diethylether insolublefraction of the straw oil sample by Py±GC±MS, all compounds formed were mainlydegradation products of polysaccharides:gases, water, propanones, butanones, cyclo-pentenones, furaldehydes, levoglucosan andother anhydrosugars. The main compoundswere water and levoglucosan. The CHN analy-sis of the evaporation residue was close to thatof water-soluble polysaccharides-derived com-pounds.

3.3. Water-insoluble fractions

The amount of water-insoluble fraction inpyrolysis oils varied from about 20 to 40 wt%.The highest proportion was obtained for thehardwood oil.8

The water-insoluble fractions contained highmolecular compounds that were not eluted onGC. The IR spectrum of the fraction for thehardwood oil was comparable with that ofhardwood lignin. The CHN analysis of thefraction corresponded to that of lignin-derivedmaterial.

When pyrolyzing the water-insoluble frac-tion of hardwood pyrolysis oil by Py±GC±MSat 400±7008C, the identi®ed products were thesame as the lignin-derived compounds of theoriginal oil. By increasing the temperature,their amount decreased and the amount of

gaseous products, mainly carbon monoxideand carbon dioxide, increased.

3.4. Whole pyrolysis oils

When determining the characteristics andbehavior of pyrolysis oils, both the physicalproperties (Table 2) and the chemical compo-sition (Fig. 6) of whole pyrolysis oils are ofimportance and correlations were foundbetween them.

The water-insoluble fraction contained highmolecular mass lignin-derived material (Fig. 6).The water-soluble fractions consisted of water,volatile acids, alcohols, evaporation residuesof diethylether insolubles and solubles andvolatilized compounds. The distribution of thecompounds eluted on GC in the hardwood py-rolysis oil, into the diethylether soluble andinsoluble fractions is shown in Fig. 3.

When comparing the straw and pine oilsproduced in the same pyrolysis conditions itcan be seen that the straw material haddegraded further than the pine one. The strawoil contained a higher amount of lower mol-ecular mass degradation products and loweramounts of ether insoluble and high molecularmass water-insoluble fractions than the pineoil.

The pysical properties of the pyrolysis oilscan be explained with the aid of their chemical

Fig. 5. Total ion chromatogram of diethylether insolubles of water fraction for hardwood oil, as sily-lated derivatives. Peak identi®cation: (1) glycolic acid; (2) glycolaldehyde; (3) 5-(hydroxymethyl)-2-fural-dehyde; (4) 2,4-dihydroxybutanoic acid; (5) 3,4-dideoxy-pentonic acids; (6) 2-hydroxyadipinic acid; (7)

arabinoses; (8) levoglucosan; (9) xyloses; (10) aldopentoses; (11) aldohexoses; (12) cellobiosan.


Table 2. Physico-chemical properties of di�erent pyrolysis oils

Analysis Straw oil Pine oil Hardwood oil

pH 3.7 2.6 2.8Water (wt%) 19.9 11.1 23.3Solids, (wt%) 0.35 0.18 0.30Density (kg/dm3) 1.186 1.266 1.233Viscosity, cSt, at 508C 11 46 50LHV (MJ/kg) 16.9 19.2 16.6LHV (MJ/kg)a 21.1 21.6 21.6C (wt%)a 55.3 56.4 58.4H (wt%)a 6.6 6.3 6.0N (wt%)a 0.4 0.1 0.1O (wt%)a 37.7 37.2 35.5Ash (wt%) 0.14 0.07 0.09CCR (wt%) 18 18 23Flash point (8C) 56 76 >106Pour point (8C) ÿ36 ÿ18 ÿ9Sulfur (wt%) 0.05 0.006 0.02Chlorine (wt%) 0.033 0.008 <0.001Water-insolubles (wt%) 23 28 40LHV (MJ/kg) 27.1 27.7 25.9C (wt%) 68.6 69.3 65.8H (wt%) 6.6 6.4 6.2N (wt%) 0.7 0.2 0.2O (wt%) 24.1 24.1 27.8

Water-solubles/ether-insol. (wt%) 28 41 25C (wt%) 47.2 45.7 44.7H (wt%) 6.5 6.3 6.4N (wt%) 0.6 0.2 0.1O (wt%) 45.7 47.8 48.8

aOn dry basis.

Fig. 6. The compositions of straw, pine and hardwood pyrolysis oils.


composition. The pH was a�ected mainly byvolatile acids and the diluting e�ect of water.Viscosity was lower in a higher water contentand in a lower proportion of water-insolublesof the oils, as seen when comparing straw andpine oils (Table 2). Viscosity was also a�ectedby alcohols: an addition of 5 wt% methanolinto hardwood pyrolysis oil with a low metha-nol content decreased its viscosity by 35%.The straw oil had the highest methanol con-tent of 4 wt%.

The pour point was lower for the straw oilthan for the pine oil. This was a�ected by thelower amount of water-insoluble material andby the higher total amount of volatiles, evap-oration residue of ether solubles, methanol,acids and water.

The total proportion of the evaporationresidue of ether solubles, and volatilesamounted to 14 wt% of the straw oil, whichwas higher than for the pine oil. This, in ad-dition to the higher methanol content, causedthe lower ¯ash point of the straw oil.

Hardwood oil had a high viscosity, pourpoint and ¯ash point. The oil did not containeasily vaporized volatile compounds, and hadlow contents of methanol and the evaporationresidue of ether solubles, resulting in a high¯ash point. The high pour point and viscositywere due to the high proportion of water-inso-luble material connected to the proportionallylower amounts of acids, alcohols, evaporationresidue of ether solubles and volatiles in theoil.

The ash content and the amounts of nitro-gen, sulfur and chlorine were higher for thestraw oil than for other oils due to their orig-inally higher amounts in straw than in wood.The solids content was also highest for thestraw oil.

The heating value of the pyrolysis oils wasa�ected by the composition of the oil. In ad-dition to the water-insoluble fraction, whichhad a high heating value (Table 2), the etherinsolubles of the water-soluble fraction had asigni®cant in¯uence on the heating value ofthe whole pyrolysis oil. Ninety percent of theheating value of the hardwood oil derivedfrom these two fractions. The heating value ofthe ether insoluble fraction for hardwood oilwas 18.3 MJ/kg (LHV). By using this heatingvalue for the respective fractions of pine andstraw oils the corresponding percentageswould be 80 and 70% of the heating value ofthe oils. The water-insoluble fraction con-

tained no GC-eluted compounds, and only asmall part of the ether insoluble one waseluted by GC. The heating values on a drybasis did not di�erentiate considerablybetween the oils.

4. CONCLUSIONS

The characterization scheme developed fordi�erent biomass-based pyrolysis oils provedto be a useful tool in determining the natureand behavior of pyrolysis oils, in comparingoils based on di�erent feedstocks and pyrolysisprocesses, and in drawing correlations betweenphysical properties and chemical compositionof the oils.

The basic scheme is a relatively simple pro-cedure consisting of the fractionation of oilwith water, analyses of water-soluble andwater-insoluble fractions, and of the furtherextraction of the water-soluble fraction withdiethylether. Determination of the evaporationresidues for the di�erent fractions was usefulto obtain a rough picture of the oil.

The method was selective in dividing thesubstances of di�erent molecular mass andorigin into di�erent fractions. The GC±MSanalyses of the whole oil and of the diethy-lether soluble fraction gave information aboutthe chemical composition of the oil. All com-pounds of pyrolysis oils eluted on GC weredissolved in water-soluble fractions. Of separ-ate compounds, water, volatile acids and alco-hols were easy to analyze quantitatively. Itwas found that these had a signi®cant e�ecton physical characteristics.

The characterization scheme can be used assuch or modi®ed for many purposes. Forexample, it is applicable in problem situationsfor ®nding out the changes occurred in pyrol-ysis oils, during handling, storing and utiliz-ation. It will be utilized in further work forstabilization and upgrading tests of pyrolysisoils.Associate Editor Ð D. O. Hall

AcknowledgementsÐFinancial support from theTechnology Development Center Finland (Tekes) throughthe Bioenergy Research Program (BIOENERGIA) andfrom the Finnish Corporations Vapo Oy, WaÈ rtsilaÈ DieselLtd, MetsaÈ -Serla Oy, and Neste Oy is gratefully acknowl-edged. Thanks are also due to Ms Johanna Levander, MrsRaili Silvasti and Mrs Sirkka Huru of VTT for skillfultechnical assistance, to Mr Vesa Arpiainen of VTT forproducing the straw and pine pyrolysis oil samples, and toMr Eero LeppaÈ maÈ ki of VTT for analytical advice. EnsynTechnologies Inc. is acknowledged for providing the hard-wood pyrolysis oil sample.


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Characterization of biomass-based flash pyrolysis oils

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