Fast Pyrolysis of Forestry Residue and Pine. 4.Improvement of the Product Quality by Solvent Addition

Anja Oasmaa,*,† Eeva Kuoppala,† Johan-Fredrik Selin,‡ Steven Gust,‡ andYrjo Solantausta†

VTT Processes, P. O. Box 1601, 02044 VTT, Biologinkuja 3-5, Espoo, Finland, andFortum Oyj, P.O. Box 310, 06101 Porvoo, Finland

Received March 30, 2004

Addition of alcohols was found to improve the homogeneity, decrease the viscosity and density,lower the flash point, and increase the heating value of pyrolysis liquids. Alcohol addition alsolowered the viscosity and molecular mass increase during the aging of pyrolysis liquids. Thereduction in the viscosity change was primarily due to a stabilizing effect of alcohols on the water-insoluble high molecular mass lignin-derived fraction. Other effects include the formation ofacetals in reactions of alcohols with aldehydes, ketones, and anhydrosugars. Low (e5 wt %) alcoholadditions prevented aging reactions by a few months, while the higher (g10 wt %) ones retardedthem by almost a year. Methanol was the most effective alcohol of those tested (methanol, ethanol,isopropanol). By improving solubility, the alcohols also enhanced the separation of the extractive-rich top layer in the pyrolysis of forestry residue by decreasing its volume and increasing theconcentration of extractives and solids in the top layer.

Introduction

The advantage of pyrolysis liquids compared to pel-lets, wood chips, or other solid biomass will be their easeof use. All the customer has to do is to order the fueland perform annual maintenance. This in turn requiresthat the fuel is stable. Thus, to achieve customeracceptance, heating oils have to tolerate a storage periodof at least six months with the customer. Pyrolysisliquids are unstable1,2 due to their high amount ofreactive oxygen-containing compounds. The instabilityis seen as a viscosity increase during storage,3,4 which,connected with the formation of water, finally leads tothe separation of a lignin-rich bottom sludge.4 Thepyrolysis liquids consist of water, acids, alcohols, alde-hydes, ketones, carbohydrates, extractives, and de-graded lignin.5 The main changes6 upon aging ofpyrolysis liquids take place during the first six months

of storage. The amount of water-insoluble fractionincreases mainly due to polymerization and condensa-tion reactions.6 This causes an increase in the averagemolecular mass of the liquid and in viscosity.3 The watercontent increases due to condensation reactions. Thedecrease in volatile aldehydes and ketones raises theflash and pour points of the liquid.6 An increase in waterdecreases the heating value.6

Polar solvents have been used to homogenize pyrolysisliquids4,7 and to reduce the increase in their viscosity.8,9

Quantitative data is reported on the effects of water,10,11

methanol8,12 and furfural.13 The addition of solvents,

* To whom correspondence should be addressed. Fax: +358-9-460493. E-mail: anja.oasmaa@vtt.fi.

† VTT Processes.‡ Fortum Oyj.(1) Diebold, J. P. A Review of the Chemical and Physical Mecha-

nisms of the Storage Stability of Fast Pyrolysis Bio-oils. In FastPyrolysis of Biomass: A Handbook; Bridgwater, A., Ed.; CPL Press:Newbury, U.K., 2002; Vol. 2, pp 243-292.

(2) Oasmaa 2003: Oasmaa, A. Fuel Oil Quality Properties of Wood-based Pyrolysis Liquids. Academic dissertation. Research ReportSeries, Report: 99. Department of Chemistry, University of Jy-vaskyla: Jyvaskyla, Finland, 2003; 32 pp + appendices (251 pp).

(3) Czernik, S. Storage of Biomass Pyrolysis Oils. In Proceedings ofSpecialist Workshop on Biomass Pyrolysis Oil Properties and Combus-tion; Estes Park, CO, Sept 26-28, 1994; NREL Paper No. CP-430-7215, pp 67-76.

(4) Oasmaa, A.; Leppamaki, E.; Koponen, P.; Levander, J.; Tapola,E. Physical Characterisation of Biomass-Based Pyrolysis Liquids.Application of Standard Fuel Oil Analyses; VTT Publication 306;VTT: Espoo, Finland, 1997; 46 pp + appendices (30 pp).

(5) Oasmaa, A.; Kuoppala, E.; Solantausta, Y. Fast Pyrolysis ofForestry Residue. 2. Physicochemical Composition of Product Liquid.Energy Fuels 2003, 17 (2), 433-443.

(6) Oasmaa, A.; Kuoppala, E. Fast Pyrolysis of Forestry Residue. 3.Storage Stability of Liquid Fuel. Energy Fuels 2003, 17 (3), 1075-1084.

(7) Oasmaa, A.; Kyto, M.; Sipila, K. Pyrolysis Liquid CombustionTests in an Industrial Boiler. In Progress in Thermochemical BiomassConversion; Bridgwater, A. V., Ed.; Blackwell Science, U.K., 2001; Vol.2, 1468-1481.

(8) Diebold, J. P.; Czernik, S. Additives to Lower and Stabilize theViscosity of Pyrolysis Oils during Storage. Energy Fuels 1997, 11,1081-1091

(9) Czernik, S.; Maggi, R.; Peacocke, G. V. C. Review of Methodsfor Upgrading Biomass-derived Fast Pyrolysis Oils. In Fast Pyrolysisof Biomass: A Handbook; Bridgwater, A., Ed.; CPL Press: Newbury,U.K., 2002; Vol. 2, p 424.

(10) Solantausta, Y.; Diebold, J.; Elliott, D. C.; Bridgwater, T.;Beckman, D. Assessment of Liquefaction and Pyrolysis Systems. VTTResearch Notes 1573; VTT: Espoo, Finland, 1994.

(11) Tiplady, I. R.; Peacocke, G. V. C.; Bridgwater, A. V. PhysicalProperties of Fast Pyrolysis Liquids from the Union Fenosa Pilot Plant.In Proceedings of the Second EC/Canada Workshop on ThermalBiomass Processing; Bridgwater, A. V., Hogan, E., Eds.; CPL ScientificInformation Services, Ltd.: Newbury, U.K., 1996; pp 164-174.

(12) Casanova, J. Comparative Study of Various Physical andChemical Aspects of Pyrolysis Bio-Oils Versus Conventional FuelsRegarding Their Use in Engines. In Proceedings of Specialist Workshopon Biomass Pyrolysis Oil Properties and Combustion; Estes Park, CO,Sept 26-28, 1994, NREL CP-430-7215, pp 343-354.

(13) Salvi, G.; Salvi, G., Jr. Pyrolytic Products Utilization AssessmentStudy, Commission of European Communities, Contract No. EN3B-0191-1(CH), 1991.

1578 Energy & Fuels 2004, 18, 1578-1583

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especially methanol, showed a significant effect on thestabilization. The rate of viscosity increase for the liquidwith 10 wt % of methanol was almost 20 times less thanfor the liquid without additives.8 It has been postu-lated8,14 that solvent addition can impact the liquidviscosity by three mechanisms:

(1) physical dilution without affecting the chemicalreaction rates,

(2) reducing the reaction rate by molecular dilutionor by changing the liquid microstructure, and

(3) chemical reactions between the solvent and theliquid components that prevent further chain growth.

The chemical reactions1,8 that have been suggestedto occur between the pyrolysis liquid compounds andmethanol or ethanol include esterification (Scheme 1)and acetalization (Schemes 2 and 3).15 Acetals serve asprotecting groups for aldehydes and ketones.15 Consid-ering the simplicity, the low cost of some solvents, andtheir beneficial effects on the liquid properties, alcoholaddition has been suggested to be the most practicalapproach for pyrolysis liquid quality upgrading.14 In thepresent study, confirmation of the suggested reactionsas well as new data on the effect of alcohol addition onphysicochemical changes of softwood liquids duringstorage are presented. This is the fourth part of a seriesof publications that have focused on fuel oil propertiesof fast pyrolysis liquids of forestry residue: optimizationof separation of extractives,16 physicochemical proper-ties,5 and storage stability.6

Experimental Section

Liquid Production. Pyrolysis was carried out by employ-ing a 20 kg/h capacity process development unit (PDU) atVTT.16,17 This transport bed reactor was initially designed anddelivered by Ensyn Technology in 1995, and it has beensubsequently modified by VTT. The ground, sieved (<3 mm),and dried (moisture 4-11 wt %) feedstock was fed to thereactor. The pyrolysis temperature was about 520 °C, andresidence time for pyrolysis vapors was 1-2 s. The productvapors were condensed in liquid scrubbers. Liquid yields(organics and water) from forestry residue ranged from 61 to64 wt % for dry feed and from 68 to 75 wt % for pine sawdust.17

Forestry residue and pine produced an extractive-rich toplayer, the amount of which varied from 1 to 25 wt %, dependingmainly on the content of extractives in the feedstock. Theextractive-rich top phase was separated from the bottom phaseafter 24 h of standing at 35 °C.16

Solvent Addition and Liquid Storage. Solvent (Table 1)was added either to the whole product liquid just aftercondensation or to the bottom phase of the liquid afterseparation of the top phase.

Pyrolysis liquids were stored in closed bottles at roomtemperature. In addition, accelerated aging tests (stabilitytests) were carried out for studying the storage stability of theliquids. In the test, pyrolysis liquid was kept at fixed temper-ature for a certain time, and the increases in viscosity andwater content were measured. The conditions of the stabilitytest were 24 h at 80 °C, and 6 h at 80 °C. The temperature ofthe viscosity measurement was 40 °C. It has been presentedearlier6 that the chemical changes in the stability test at 80°C for 6/24 h correlated roughly with the changes in 3-4months/1 year storage at room temperature.

Liquid Analyses. Physical characterization of liquid prod-ucts was carried out by employing modified standard and newmethods.4,18 Chemical characterization was performed usingthe solvent extraction scheme5 based on water extraction. Withthe method, the following water-soluble fractions6 were ob-tained: carboxylic acids and alcohols, ether-solubles (mainlyaldehydes, ketones, and lignin monomers), water, and ether-insolubles (mainly anhydrosugars, anhydrooligomers, hydroxyacids C < 10). The water-insoluble fraction consisted ofdichloromethane-soluble [low molecular mass (LMM) ligninmaterial, extractives] and dichloromethane-insoluble [highmolecular mass (HMM) lignin material, solids] substances. Ofvolatile acids, only the main compounds,5 acetic and formicacids (about 90% of volatile acids), were quantified by using acapillary electrophoresis technique.

(14) Oasmaa, A.; Czernik, S. Fuel Oil Quality of Biomass PyrolysisOils - State of the Art for the End Users. Energy Fuels 1999, 13 (4),914-921.

(15) McMurry, J. Fundamentals of Organic Chemistry. Brooks/ColePublishing Co.: Pacific Grove, Albany, 1998; pp 566 + appendices.

(16) Oasmaa, A.; Kuoppala, E.; Gust, S.; Solantausta, Y. FastPyrolysis of Forestry Residue. 1. Effect of Extractives on PhaseSeparation of Pyrolysis Liquids. Energy Fuels 2003, 17 (1), 1-12.

(17) Solantausta, Y.; Oasmaa, A.; Sipila, K. Fast Pyrolysis ofForestry Residues. In Pyrolysis and Gasification of Biomass andWastesThe Future for Pyrolysis and Gasification of Biomass andWaste: Status, Opportunities and Policies for Europe; Strasbourg, FR,30 Sept-1 Oct, 2002. Bridgwater, A. V., Ed.; CPL Press: Newbury,U.K., 2003; pp 271-276.

(18) Oasmaa, A.; Peacocke, C. A Guide to Physical Property Char-acterisation of Biomass-Derived Fast Pyrolysis Liquids; VTT Publica-tion 450; VTT: Espoo, Finland, 2001; 65 pp + appendices (34 pp).

Scheme 1. Esterification of Aldehydes and Ketones15

Scheme 2. Hemiacetal and Acetal Formation fromAldehydes and Ketones15

Scheme 3. Acetal Formation from Monosaccharides15

Table 1. Properties of Alcohols Compared to Those ofPyrolysis Liquids

pyrolysis liquid methanol ethanol isopropanol

water, wt % 20-30 max 0.05 max 6 max 0.1viscosity at 20 °C,

cSt100-200 0.75 1.5 2.8

LHV, MJ/kg 13-18 19.9 26.6 28.7density at 20 °C,

kg/dm31.10-1.30 0.791 0.800 0.785

boiling point, °C - 64.6 78.0 82.2flash point, °C 40-110 11 12 12pour point, °C 27 DNAb -111a -89.5

a Freezing point. b DNA ) data not available.

Fast Pyrolysis of Forestry Residue and Pine Energy & Fuels, Vol. 18, No. 5, 2004 1579

Results and Discussion

Effect of Alcohol Addition on the Top Phase.Extractive-rich feedstocks, like forestry residue andpine, produced a separate top phase of 1-25 wt % ofthe total liquid product, which depended mainly on thetotal extractive content of the product liquid. Theformation of a top phase also separated the main portionof the solids into the top phase. The bottom phaseresembled the normal bark-free wood pyrolysis liquid.

The addition of alcohol into pyrolysis liquids enhancedthe solubility of poorly water-soluble compound groups,like lignin dimers and extractives, into the matrix. Thisreduced the amount of top phase (Figure 1). However,the concentration of extractives both in the top and

bottom phases increased (Figure 1). The concentrationof extractives in the top phase increased from ∼20 wt% to >50 wt %. In addition, the solid content of the topphase increased.

After the water content of the top phase decreased toabout 6-7 wt %, no further reduction of the top phasein any pyrolysis liquid was achieved by further alcoholadditions. This water content was typically achieved by5 wt % alcohol addition. There was no significantdifference between ethanol (EtOH) and isopropanol(IPA) in this respect.

Effect of Alcohol Addition on PhysicochemicalProperties of Pyrolysis Liquids. Addition of alcohol(Table 1) improved the homogeneity/solubility of hydro-phobic compounds (Figure 2) of the liquid; decreased its

Figure 1. Effect of 5 wt % isopropanol (IPA) addition on the amount and composition of phases of a brown forestry residueliquid.

Figure 2. Effect of isopropanol (IPA) addition on the homogeneity of a forestry residue liquid. Microscopic images.

1580 Energy & Fuels, Vol. 18, No. 5, 2004 Oasmaa et al.

viscosity (Figure 3), density, and flash point (Figure 4);and increased its heating value (Figure 5).

Homogeneity/Solubility. Alcohols are known4 to beefficient solvents for pyrolysis liquids. Figure 2 showshow another liquid phase (extractive material) dissolvesin the pyrolysis liquid matrix. The amount of alcoholaddition required for the dissolution of the extractivesvaried depending on the chemical composition of thepyrolysis liquid. As presented previously,6,19 the polarpyrolysis liquid compounds, like acids and alcohols,dissolved the hydrophobic lignin-derived and extractivematerial in the polar pyrolysis liquid matrix. If the ratioof hydrophobic to hydrophilic material increased sig-nificantly, the hydrophobic material, like lignin, sepa-rated out of the matrix. In aging, the increase inmolecular mass of the liquid caused the separation of

the lignin-derived material as a heavy bottom sludge.4,18

Addition of alcohols prevented the phase separationlonger. In the pyrolysis of forestry residue with a highextractive content, this phenomenon was seen as aseparation of an extractive-rich top phase.16

Viscosity. Alcohol addition decreased the viscosity ofthe liquid (Figure 3) depending on the viscosity of theadded solvent (Table 1). Pyrolysis liquids are typicallyNewtonian ones.16,18 The extractive-rich viscous topphase of forestry residue liquid caused a slight non-Newtonian behavior19 at lower temperatures, but thebehavior disappeared when heated, as the extractivesmelted.16

Density. Addition of alcohol into pyrolysis liquiddecreased expectedly its density. The difference betweenthe samples was marginal due to minor differences inthe densities of the alcohols (Table 1).

Flash Point. Addition of alcohols (Table 1) intopyrolysis liquids had a beneficial effect on the pourpoint, but it also decreased the flash point (Figure 4) ofthe liquid. The relative change in the flash pointdiminished when the amount of added alcohol wasincreased.

Chemical legislation in Finland limits the flash pointof a flammable liquid to 21 and 55 °C. In transportationlegislation the limit is 62 °C. The flash point of pyrolysisliquids typically falls into this category,4,18 if the producthas been condensed at low temperature. The flash pointof forestry residue liquids is lower than that of pinesawdust pyrolysis liquids, due to a larger amount ofvolatile compounds in the forestry residue feedstock(spruce, needles, bark). The flash point of pyrolysis

(19) Radlein, D. The Production of Chemicals from Fast PyrolysisBio-Oils. In Fast Pyrolysis of Biomass: A Handbook; Bridgwater, A.,Ed.; CPL Press: Newbury, U.K., 1999; Vol. 1, pp 164-188.

Figure 3. Effect of alcohol addition on viscosity of a brownforestry residue pyrolysis liquid (bottom phase): [, methanol;0, ethanol; 4, IPA.

Figure 4. Effect of solvent addition on the flash point of abrown forestry residue pyrolysis liquid (bottom phase): [,methanol; 0, ethanol; 4, IPA.

Figure 5. Effect of solvent addition on lower heating value(LHV) of a brown forestry residue pyrolysis liquid: [, metha-nol; 0, ethanol; 4, IPA.

Figure 6. Effect of alcohol on viscosity increase with room-temperature storage: 9, pine; 0, pine + 5 wt % EtOH; [,brown forestry residue (BFR); ], BFR + 5 wt % IPA; /, BFR+ 10 wt % IPA.

Figure 7. Viscosity increase (aging test for 6 h at 80 °C, whichcorrelates to 3-4 months storage at room temperature6) versusadded alcohol: [, methanol; 0, ethanol; 4, IPA.

Fast Pyrolysis of Forestry Residue and Pine Energy & Fuels, Vol. 18, No. 5, 2004 1581

liquid can be affected both by feedstock choice and bychanging the liquid condensation conditions.5

Heating Value. Addition of alcohols increased theheating value of pyrolysis liquid (Figure 5), which canalso be noticed by arithmetic calculations. The amountof the increase depended on the heating value of addedalcohol (Table 1). With forestry residue liquids, thesolvents also improved the solubility of high energyvalue16 extractives in pyrolysis liquids from the topphase to the bottom phase (Figure 1), which caused anadditional increase in the heating value.

Effect of Alcohol Amount on Aging. Addition ofalcohol diminished the increase in viscosity of pyrolysisliquids (Figure 6). Methanol was the most efficient agentfor decreasing aging, even though the differences be-tween the used alcohols were small (Figure 7).

There were some differences in chemical changesduring the storage of pyrolysis liquids with or without6

alcohol addition (Figure 8). Addition of 2 wt % alcoholdid not have any significant effect on stability improve-ment, but addition of 5 wt % alcohol prevented orretarded the aging reactions by a few months, especiallythe reactions of water-soluble compound groups. With5 wt % alcohol addition, after 3-4 months storage thechanges were fast, and within 6-7 months they reachedthe same level as without alcohol addition. Addition of10 wt % alcohol prevented clearly the aging reactions(Figure 8). The efficiency of alcohols decreased in thefollowing order: methanol, ethanol, isopropanol. Dieboldand Czernik8 drew a similar conclusion: a decrease inefficiency in the order methanol, acetone, methanol-acetone (1:1), ethanol, methyl isobutyl ketone-methanol(1:1), ethyl acetate.

Chemical Changes in Water-Soluble Fractionduring Storage. Acids. There was no significantchange in the amount of the main acids, acetic andformic acids, during 4-month storage of pyrolysis liquidswith or without6 alcohol addition.

Alcohols. The amount of alcohol in pyrolysis liquidsis very low (<1 wt %), but upon alcohol addition thereactivity of this group was clearly seen. The amountof alcohols decreased approximately by 20% (Table 2)during 1 year storage. The consumption of ethanol washigher than that of isopropanol during storage. Becauseacids do not react, the decrease in alcohols may be

Figure 8. Aging of brown (stored) forestry residue liquid with various amounts of ethanol.

Table 2. Change in Alcohols during Aging of a Brown Forestry Residue Liquid

fresh liquid, wt % aged (24 h at 80 °Ca) liquid, wt % change, wt %

water MeOH EtOH IPA water MeOH EtOH IPA water MeOH EtOH IPA

BFRb 26.7 1.04 0 0 28 0.82 0 0 28 -27 0 0BFR + 5 wt % EtOH 25.5 0.94 4.88 0 26.5 0.81 3.98 0 26 -16 -23 0BFR + 10 wt % EtOH 24.3 0.91 9.34 0 25.4 0.77 7.73 0 25 -18 -21 0BFR + 5 wt % IPA 25.5 0.94 0 5.19 26.6 0.75 0 4.44 26 -25 0 -17BFR + 10 wt % IPA 24.3 0.89 0 10.3 25.4 0.71 0 8.74 25 -25 0 -18

a Correlates with changes upon 1 year of storage at 20 °C.6 b Brown forestry residue.

Figure 9. Change in ether-solubles (ESs, dry matter) withand without alcohol during storage for pine pyrolysis liquids:[, pine 1; ], pine 1 + 5 wt % IPA; 9, pine 2; 0, pine 2 + 5 wt% EtOH.

1582 Energy & Fuels, Vol. 18, No. 5, 2004 Oasmaa et al.

attributed to reaction of alcohols with aldehydes and/or ketones to form acetals. These reactions are catalyzedby acids (5-7 wt % volatile carboxylic acids in pyrolysisliquids), and their formation could explain the stabilityimprovement by alcohol addition. Water is formed inthe reaction, which was also observed with pyrolysisliquid.

Aldehydes and Ketones. Without any alcohol additionthe ether-soluble fraction (aldehydes, ketones, ligninmonomers) decreased steadily during aging.6 Withalcohol addition the reactivity of this fraction wassimilar within the first 2-3 months of storage. However,after that the alcohols seemed to protect aldehydes andketones toward further reactions (Figure 9), probablydue to acetal formation.

Anhydrosugars. Addition of alcohol stabilized little theaging of the sugar fraction (anhydrosugars, anhydro-oligomers), perhaps through acetal formation.

Chemical Changes in Water-Insoluble Fractionduring Storage. During the first six months of storage,alcohols were found to retard significantly the increase

in the water-insoluble fraction of pine and forestryresidue pyrolysis liquids. An alcohol addition of 5 wt %retarded the increase in water-insolubles by about 6months. The major factor affecting changes in water-insolubles was the HMM lignin fraction of water-insolubles. After 6 months the water-insoluble fractionstarted to increase and reached the same level aswithout the alcohol addition. An addition of 10 wt %alcohol retarded the changes in water-insolubles byalmost 1 year. Methanol reduced the change in water-insolubles (Figure 10) best. Ethanol was more effectivethan IPA. Increasing amounts of alcohols retarded theaging reactions (Figure 10).

Correlations of Changes in Physical Propertieswith Chemical Changes in the Liquid. Viscosity. Asearlier6 presented with pyrolysis liquids without anyalcohol additions, viscosity correlates with water-in-solubles (Figure 11) also when alcohol is added to theproduct liquid.

Conclusions

Addition of alcohols improved the homogeneity andphysical dilution of pyrolysis liquids through enhancingthe solubility of the hydrophobic compounds, which werehigh molecular mass lignin and extractives. Otherbeneficial effects of alcohols to the fuel oil quality ofpyrolysis liquids were the decrease in viscosity anddensity and the increase in heating value. A disadvan-tage was the decrease of flash point.

By improving the solubility of hydrophobic com-pounds, alcohols also enhanced the separation of extrac-tive-rich top layer in pyrolysis of forestry residue bydecreasing its volume and increasing the concentrationof extractives and solids in the top layer.

Alcohol addition decreased significantly the viscosityand molecular mass increase during aging of softwoodpyrolysis liquids. The change in viscosity correlated wellwith the change in the water-insoluble lignin-derivedfraction. With low (e5 wt %) alcohol additions, the agingreactions were prevented for a few months. With higher(g10 wt %) alcohol additions, the aging reactions wereretarded for almost 1 year. Methanol was the mosteffective of the alcohols tested (methanol, ethanol,isopropanol). Acetal formation of alcohols with alde-hydes, ketones, and sugars was observed.

Acknowledgment. The work was funded by Tekesunder contract 40921/99, Fortum Oyj and by EU Con-tract ERK5-CT1999-00011. Jukka-Pekka Nieminen andTuula Koskelo from Fortum are acknowledged forvaluable discussions. At VTT, Sirkka-Liisa Huru, SirpaLehtinen, Jaana Korhonen, and Mirja Muhola areacknowledged for the skillful analytical work, as arethose at Fortum Sirpa Hagg.

EF040038N

Figure 10. Effect of alcohol type on chemical changes (%) inthe water-insoluble fraction: [, methanol; 9, ethanol; 2, IPA.

Figure 11. The correlation of viscosity with water-insolublesof fresh and aged liquids with alcohol additions: 0, freshliquid; 9, aged liquid.

Fast Pyrolysis of Forestry Residue and Pine Energy & Fuels, Vol. 18, No. 5, 2004 1583