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The Potential Use of Whole-tree Biomassfor Bio-oil FuelsE. M. Hassan a , F. Yu a , L. Ingram a & P. Steele aa Department of Forest Products , Mississippi State University ,Mississippi State, Mississippi, USAPublished online: 20 Aug 2009.

To cite this article: E. M. Hassan , F. Yu , L. Ingram & P. Steele (2009) The Potential Use of Whole-treeBiomass for Bio-oil Fuels, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects,31:20, 1829-1839, DOI: 10.1080/15567030802463364

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Energy Sources, Part A, 31:1829–1839, 2009

Copyright © Taylor & Francis Group, LLC

ISSN: 1556-7036 print/1556-7230 online

DOI: 10.1080/15567030802463364

The Potential Use of Whole-tree Biomass

for Bio-oil Fuels

E. M. HASSAN,1 F. YU,1 L. INGRAM,1 and P. STEELE1

1Department of Forest Products, Mississippi State University,

Mississippi State, Mississippi, USA

Abstract Eight feed stocks were fast pyrolyzed at 450ıC in an auger reactor. Theyields of bio-oil, char, and non-condensable gases ranged from 40.3 to 60.1 wt%,

16.0 to 34.6 wt%, and 17.1 to 34.1 wt%, respectively. The composition of the non-condensable gases exit stream was determined by gas chromatography analysis and

was mainly composed of carbon monoxide, carbon dioxide, and methane. Bio-oils’physical properties of pH, water content, acid value, and viscosity were investigated.

Mean molecular weights and polydispersity were determined by gel permeation chro-matography. The chemical compositions for the bio-oils were also investigated by gas

chromatography-mass spectrometry analysis. Physical and chemical characterizationshowed that bio-oil produced from whole-tree pine is comparable to that from clear

wood feed stocks. Bio-oil produced from whole-tree cottonwood had high viscosityrendering it unsuitable for fuels production.

Keywords auger reactor, bio-oil, fast pyrolysis, fuels, whole tree

Introduction

Utilization of industrial sawdust and bark for energy biomass has been practiced by

industrial forest products companies for centuries. Higher-value wood chips from green

lumber production have had much higher value as feed stock for the production of

pulp and paper than for energy. However, lower demand for industrial wood chips as

pulp and paper operations have contracted in the U.S. has resulted in lower prices.

Therefore, utilization of forestry residue for energy production may now be economically

feasible.

Plantation pine silvical practices have been adopted for a rapidly increasing share

of timberlands in the southern softwood forest zone (Smith et al., 2001). Fast-grown

plantation pine thinnings frequently contain up to 80% of their volume in juvenile

wood (Zobel and Sprague, 1998). Presence of a large percentage volume of juvenile

wood in young southern pine stems results in serious problems in utilization of the

material harvested. Juvenile wood is characterized by lower density, lower transverse

Address correspondence to El Barbary Hassan, Department of Forest Products, MississippiState University, Box 9820, Mississippi State, MS 39762. E-mail: emhassan@cfr.msstate.edu

This is journal article no. FP-457 of the Forest and Wildlife Research Center, MississippiState University.

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1830 E. M. Hassan et al.

shrinkage, higher longitudinal shrinkage, lower strength, thinner latewood bands, more

compression wood, higher initial moisture content, thinner cell walls, and lower cellulose

to lignin ratio (Bendtsen, 1978). Pulp yields from juvenile wood are lower and lumber is

considerably weaker and very prone to warp (Zobel and Sprague, 1998). As plantation

pine trees add mature wood, following the initial 10-year juvenile wood period, the

relative percentage of this wood type decreases such that utilization problems from older

trees are reduced. For this reason, the most severe and objectionable lumber utilization

problems occur in trees from first and second thinnings rather than for older sawlog-sized

timber.

Lack of perceived economic viability has limited the research performed for utiliza-

tion of pine plantation materials for biomass production. Eight- to ten-year rotations for

plantations are typically applied when managing hardwood stands for biomass (Portland,

1994). If thinned by a similar early harvest schedule, the harvest of plantation pine at

age ten for biomass would release residual pine stems to increase their growth rates

with the growth rate increase roughly proportional to the severity of thinning. Faster

growth after ten years of age would act to solve the juvenile wood problem by increasing

the percentage of mature wood in relation to the juvenile wood core. By contrast, pine

plantation first thinning removal for pulpwood is usually practiced on stands at about 15

years of age. In addition to the earlier increased growth of the residual stand, there are

increased economic benefits to landowners if incomes from thinnings occur earlier in the

rotation (Bullard and Straka, 1998).

The largest volume of biomass and the least amount of handling of stems would

occur if needles, branches, bark, and stems were harvested and utilized for a value-

added product. Previous studies by Oasmaa et al. (2003) proved that the bio-oil chemical

compositions of forestry residue (stem wood, needles, and bark) were similar to that of

clear wood pyrolysis oils.

Considerable research has been performed to develop short-rotation intensive culture

forestry plantations for energy. Traditionally, this research has focused on production

of energy from fast-growing hardwood species such as eastern cottonwood, American

sycamore, sweet gum, willow, and non-native species such as the eucalyptus (Bruce,

1994). Until recent years, the value of pine plantation thinnings for pulp and paper

feedstock has been so high that utilization of this resource for energy has been prohibitive.

However, current and future economic trends indicate that utilization of pine thinnings

for energy feedstock is becoming a viable alternative.

Fast pyrolysis processes to convert lignocellulosic materials to produce a liquid fuel,

generally referred as bio-oil, have been developed. The fast-pyrolysis process requires

the reduction of the biomass fuel to approximately sawdust size. Particles are heated to

between 400ıC and 650ıC very rapidly in the absence of oxygen followed by cooling to

condense the pyrolysis product. This high temperature treatment fractures the molecular

bonds converting the biomass to the final bio-oil. The charcoal by-product of the process

provides fuel to produce the required high pyrolyzation temperatures so that the process

is nearly energy neutral. The yield of bio-oil is relatively high at about 60% dry weight

basis or higher depending on the production process (Bridgewater, 2004).

Bio-oil chemical properties vary with the feedstock but woody biomass typically

produces a mixture of 30% water, 30% phenolics, 20% aldehydes and ketones, 10%

alcohols, and 10% miscellaneous compounds. As a fuel, bio-oil has environmental ad-

vantages when compared to fossil fuels, producing half the NOx and no SOx. As a fuel

derived from a renewable resource, bio-oil is considered CO2 neutral (Mulraney et al.,

2002). Research reports have shown that bio-oil can be burned directly in engines or

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Potential of Whole-tree Biomass for Bio-oil Fuels 1831

mixed with diesel oil. Electricity has been produced by diesel engines and turbines have

been specially modified to burn bio-oil (Mulraney et al., 2002). However, technical issues

such as acidity, immiscibility, viscosity change over time, and other problems must be

solved prior to widespread application for use in engines (Bridgewater, 2004).

The objective of this article was to determine if whole-tree feed stocks can produce

bio-oils for fuels production that are comparable to those produced from clear wood feed

stocks. Bio-oils were chemically and physically characterized to allow comparison of

each bio-oil type’s properties. Pine and cottonwood whole tree, clear wood, bark, leaves,

or needles feed stocks were pyrolyzed separately to allow determination of the influence

of the bark and leaves or needles components on whole-tree feed stock bio-oil charac-

teristics. The following physical tests were performed: pH, water content, acid value,

viscosity, and heating value. The bio-oils’ average molecular weights were determined

with gel permeation chromatography (GPC). The bio-oil chemical compositions were

characterized by gas chromatography-mass spectrometry (GC/MS) analysis and the exit

gas compositions were performed by gas chromatography (GC). The results of chemical

and physical characterization allowed evaluation of bio-oil quality for energy.

Experimental

Materials

Study pine trees were harvested from the Starr Memorial Forest of the Forest and

Wildlife Research Center, located ten miles south of Starkville, Mississippi. The pine

trees utilized were 4-year-old loblolly pine plantation stock. Four-year-old cottonwood

was harvested from Anderson Tully Company timberlands near the Mississippi River

in Coahoma County in the state of Mississippi. Both young pine and cottonwood trees

were approximately 3–4 inches in diameter. The harvested small-diameter trees were

transported to the Department of Forest Products, Mississippi State University. Trees

were randomly assigned to a whole tree chipping treatment or to a treatment in which

the bark, needles or leaves, and clear wood components were separated for pyrolysis by

component type. Whole trees and components were dried to 8–10% moisture content

by air drying to prevent loss of volatiles, particularly from needles and leaves that may

occur during oven drying. All dried whole trees and components were hammer-milled

followed by sieving with a vibrating screen to produce a feed stock with particle size

between 1–3 mm diameter.

Biomass heating values (MJ/kg) and elemental analyses were performed by Hazen

Research, Inc., Golden, Colorado (Table 1). Elemental carbon, hydrogen, and nitrogen

analyses of the biomass samples were conducted by combustion in pure oxygen at

�950ıC and analysis of CO2, H2O, NOx, N2, and SO2. Oxygen was determined by

difference.

Pyrolysis

Pyrolysis of the feed stocks was conducted at an �3 kg/h feed rate in a proprietary

stainless steel auger reactor. Feed stocks were pyrolyzed at 450ıC at an auger speed of

13 rpm. Condensed bio-oil was collected in air-tight bottles and refrigerated immediately

at 4ıC. The char produced during pyrolysis was weighed to determine quantity produced.

All yields in this study are expressed on a dry and ash-free basis.

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Table 1

Characteristics of the eight study feed stocks

Characteristics

Pine

wood

Pine

whole

tree

Pine

bark

Pine

needles

Cotton-

wood

Cotton-

wood

whole

tree

Cotton-

wood

bark

Cotton-

wood

leaves

Ultimate analysis (%)

Sulfur 0.019 0.05 0.035 0.11 0.02 0.13 0.05 0.15

Carbon 52.64 51.96 53.99 53.48 51.08 47.98 47.13 52.14

Hydrogen 6.09 5.56 4.40 6.06 5.88 5.41 5.38 6.12

Nitrogen 0.09 0.47 0.37 1.25 0.08 0.97 0.39 1.71

Oxygena 27.96 33.03 17.68 28.94 36.06 32.82 34.89 33.12

Proximate analysis (%)

Moisture 11.0 8.54 15.1 6.69 6.15 7.66 6.88 7.14

Ash 0.2 1.39 4.43 3.47 0.73 4.03 5.28 4.81

Volatiles 73.54 71.74 61.16 72.28 79.69 71.88 70.55 71.14

Fixed carbon 15.26 18.33 19.31 17.56 13.43 16.43 17.29 16.91

Components analysis (%)

Lignin 26.03 30.77 40.43 36.72 22.88 27.43 33.74 31.6

Holocellulose 72.35 65.49 59.38 51.57 71.32 69.15 64.81 53.4

Heating value (MJ/kg) 21.9 19.8 18.3 19.8 18.4 17.6 16.6 16.8

aBy difference.

Bio-oil Characterization

Physical Properties

Bio-oil physical properties were characterized chemically and physically. Percent of water

was determined by ASTM Method D-1744. Viscosity was determined by Stony Brook

Model PDVa-100 viscometer (Stony Brook Scientific LTD., Norristown, PA). Acid value

was obtained by dissolving 1 g of bio-oil in an isopropanol/water mixture and titrating to

a pH of 8.5 with 0.1 N NaOH. The pH was determined indirectly by adding 1 g of bio-oil

to 50 mls of water, stirring, and measuring the pH with an Orion Model EA920 pH meter

(Orion Research Inc., Cambridge, MA). The density of bio-oil was determined at 20ıC.

The percent of filterable solids was determined by dissolving 5 g of bio-oil in 100 mls

of methanol and filtering through a 25 micron glass filter. The filter was dried at 105ıC

before and after collection of the particulate material. Percent of solids calculation was

based on weight increase after filtration. The heating value was measured as calorimetric

value (higher heating value) by a Parr 1341 oxygen bomb calorimeter (Parr Instrument

Co., Moline, IL).

GC/MS Analysis

The GC/MS analysis of the pyrolysis oil from the feed stocks was performed with a

Hewlett-Packard HP 5890-Series II gas chromatograph equipped with a Hewlett-Packard

HP 5971 series mass detector (MS) (Hewlett-Packard, Atlanta, GA). The calibration

method for determining bio-oil chemical components was described in a previous paper

reported by Ingram et al. (2007). Briefly, a representative sample (0.2 g) of each bio-

oil was weighed to the nearest 0.1 mg and diluted to 10 ml with methanol. One ml

of this solution was transferred to an auto-sampler vial and spiked with 10 �l of a

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Potential of Whole-tree Biomass for Bio-oil Fuels 1833

4,000 �g/ml (ppm) internal standard just prior to analysis. One �l of the diluted sample

was injected onto ZB-5 capillary column of (30 ml � 0.32 mm ID � 0.25 �m film

thickness). The initial oven temperature of the GC was 40ıC for 4 min and the temperature

was then programmed at a rate of 5ıC/min to 270ıC. The injector temperature and

detector temperature were 270ıC and 250ıC, respectively; the carrier gas was He of

99.99% purity. The m/z (ratio of mass to charge) values, which represent the fragment

ions of the compounds, were recorded for each compound.

Gas samples were collected in Tedlar bags during pyrolysis from the exit flue of the

reactor. The bagged gas specimens were analyzed by Agilent 6890 gas chromatograph

with a thermal conductivity detector. Calibration and determination of unknown gas

concentrations was performed with a standard mixture of gases (RESTEK Scotty 14)

manufactured by Scott Specialty Gases (Bellefonte, PA). Gas samples and calibrant were

introduced with a VICI Series A-2 gas syringe (Precision Sampling, Inc., Baton Rouge,

LA). Four-point calibrations were prepared with 25, 50, 75, and 100 �L injections of

gas mixture. Sample aliquot volumes of 50 �l were injected into the GC column (1 m �

0.75 mm ID ShinCarbon ST 100/120 micropacked) (Restek Corporation, Bellefonte, PA).

Injector was 100ıC and 50 psi, oven was isothermal at 30ıC, temperature was 250ıC,

reference flow was 25 ml/min, and helium makeup flow was 5 ml/min. Gas components

(CO, CO2, and CH4) were identified as mole percentage values by this method.

GPC Analysis

GPC analysis was performed with a Waters HP system, consisting of a Waters 600E

system controller and a Waters 410 differential refractometer (Viscotek Corp., Houston,

TX). Molecular weight calibration was performed with five polystyrene standards with

peak molecular weights of 2,900, 1,990, 1,200, 1,050, 580, and 162. Approximately

80 �L aliquots of each standard and sample were individually flushed through a 20 �L

sample loop and injected for analysis with a 100 �L syringe. The analytical column was

a Varian Polymer Labs Plgel 3 �m 100A, 300 mm � 7.5 mm (Varian Inc., Palo Alto,

CA). The mobile phase was 100% tetrahydrofurane with a flow rate of 1 mL/min; total

sample run time was 16 min. Data from the differential refractometer was acquired and

processed by PC-based Viscotek GPC Software.

Results and Discussion

Pyrolysis Yield

Table 2 gives the pyrolysis product yields for the eight biomass samples from pine

wood, pine whole tree, pine bark, pine needles, cottonwood wood, cottonwood whole

tree, cottonwood bark, and cottonwood leaves. It is clear from the table that, for the

same species, clear wood produced higher bio-oil yields than bark; 60.1% for pine wood

compared to 48.2% for pine bark and 52.7% for cottonwood wood compared to 43.7% for

cottonwood bark. This result may be related to higher volatiles content of wood compared

to bark, 73.54% for pine wood compared to 61.16% for pine bark and 79.69% for

cottonwood wood compared to 71.55% for cottonwood bark (Table 1). The higher wood

volatiles content would be expected to produce higher bio-oil yield than for bark (Senelwa

and Sims, 1999). However, pine needles and cottonwood leaves had higher volatiles

content (72.28 and 71.14%, respectively) but they had somewhat lower bio-oil yields

compared to wood and bark. These results may be related to the higher concentrations

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Table 2

Yields and bio-gas analysis for the pyrolysis from different industrial feed stocks

Pine

wood

Pine

whole

tree

Pine

bark

Pine

needles

Cotton-

wood

Cotton-

wood

whole

tree

Cotton-

wood

bark

Cotton-

wood

leaves

Bio-oil (wt%) 60.1 53.7 48.2 49.7 52.7 44.1 43.7 40.3

Char (wt%) 19.1 28.1 34.7 27.0 16.0 24.3 26.1 25.6

Exit gas (wt%) 20.8 18.2 17.1 23.3 31.3 31.6 30.2 34.1

CO (mole%) 27.6 25.0 27.2 24.4 14.0 17.0 24.5 24.5

CH4 (mole%) 10.0 9.1 9.85 10.1 5.3 7.4 10.8 10.6

CO2 (mole%) 16.4 13.6 27.48 18.0 8.0 21.6 25.6 26.7

of volatile extractives in needles and similar leaves (Oasmaa et al., 2003), which may

be expelled as exit gas and accordingly decrease the bio-oil yield. Table 2 bio-oil yields

from pyrolysis of the pine and cottonwood whole-tree feed stocks at 53.7 and 52.7%,

respectively, were 6.4 and 8.6 percentage points lower than those for the clear wood yields

for the two species. These lower yields were the result of the presence of lower-yielding

bark and needles or leaves in the whole-tree feed stocks. Table 2 results also show that

bio-oil yield for all pine-derived feed stocks were higher than those for cottonwood.

Respectively, for the pine and cottonwood feed stocks the comparable yields were 60.1

vs. 52.7 for clear wood, 53.7 vs. 52.7 for whole tree, 48.2 vs. 43.7 for bark, and 49.7 vs.

40.3 for needles or leaves.

Pyrolysis of the eight pine and cottonwood feed stocks gave char yields ranging

from 16.0 to 34.7%. Respective pine and cottonwood char yields were 19.1 and 16.0 for

clear wood, 28.1 and 24.3 for whole tree, 34.7 and 26.1 for bark, and 27.0 and 25.6 for

needles and leaves. All pine feed stocks produced higher char yields than did cottonwood

feed stocks when compared by species type. This result is likely related to higher fixed

carbon and lignin content of pine compared to the cottonwood species (Table 1). The

high char yields for the barks of the two species may also be related to their higher

ash, fixed carbon, and low volatile matter contents (Table 1). Our bio-oil and char yield

results are similar to those reported by Sensoz (2003) for pyrolysis of wood barks.

In addition to the bio-oil products produced in the condensation stage, the rapid

pyrolysis process produces non- condensable gases as exit gas. Table 2 shows that the

weight of exit gas produced ranged from 17.1 to 34.1% by weight of the dry feedstock.

Pine needles and cottonwood leaves had the highest yield of exit gas (23.3 and 34.1,

respectively); this result may be due to the high volatile extractives concentrations in

needles and leaves. GC analysis provided the mole percentage values given in Table 2.

While values varied somewhat by feed stock type, these results indicate that CO and

CO2 are produced in roughly equal amounts with the exception of the pine wood and

pine whole-tree feed stocks which had considerably lower values for CO2. Amount of

CH4 produced was roughly less than half of the production of CO and CO2.

Physical Characterization of Bio-oils

The bio-oil physical characteristics of pH, acid value, water content, and viscosity for

the eight feed stocks are given in Table 3. The pH varied widely depending on the feed

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Potential of Whole-tree Biomass for Bio-oil Fuels 1835

Table 3

Bio-oil physical properties for the eight study feed stocks

Pine

wood

Pine

whole

tree

Pine

bark

Pine

needles

Cotton-

wood

Cotton-

wood

whole

tree

Cotton-

wood

bark

Cotton-

wood

leaves

pH 3.1 3.3 3.4 4.1 3.24 3.6 3.8 4.6

Acid value 80.6 45.6 18.1 16.8 107.5 49.5 17.6 15.0

Viscosity (cSt) 30.0 40.1 137.9 1,011.7 77.0 361.5 472.7 432.7

Water (%) 16.1 16.8 25.9 19.0 24.3 18.9 19.8 16.3

Heating value (MJ/kg) 23.02 24.67 24.47 25.60 21.38 23.31 25.02 26.12

stock type. Presence of organic acids, such as formic and acetic acids, causes nearly

all wood-based bio-oils to have pH values between 3.1 and 4.6. This acidity causes the

pyrolysis oils to be corrosive to mild steel, aluminum, etc. (Asadullah et al., 2008). Thus,

for application of bio-oil as fuel in turbine or diesel engines, it is preferable to produce

low acidity bio-oil. Lowest pH was observed for the bio-oils produced from clear wood,

with pH values of 3.1 and 3.2 for pine and cottonwood, respectively. Bark and needles

or leaves feed stocks had relatively higher respective pH values at 3.4 and 4.1 for pine

bark and needles and 3.6 and 4.6 for cottonwood bark and leaves. The higher pH values

for forest residues may be due to their lower ratio of acidic compounds (acid value) as

indicated in Table 3. Presence of components such as bark, needles, or leaves in the

whole-tree feed stocks resulted in respective pine and cottonwood whole-tree pH values

of 3.3 and 3.6, which clearly occurred due to the influence of the higher pH of bark and

needles or leaves.

Acid values (mL NaOH/g) track the acidity results measured by pH. The pine

and cottonwood species had the highest acid values for their clear wood (80.6 and

107.5) compared to needles and leaves (16.8 and 15.0). Pine and cottonwood barks

had comparable low acid values (18.1 and 17.6) to their needles and leaves values (16.8

and 15.0). The low acid value for the bio-oils from the bark, needle, or leaves was

responsible for the relatively low acid values for the pine and cottonwood whole-tree

bio-oils (45.6 and 49.5). These results confirm that the higher pH values for pine needles

and cotton-wood leaves was related to the presence of low concentrations of acetic or

formic acids. These data are similar to that obtained by Oasmaa et al. (2003) for the

fast pyrolysis of forestry residues. These results indicate that the presence of whole- tree

bark, needles, or leaf components can improve the bio-oil fuel properties, compared to

that from clear wood, by decreasing the acidity of the bio-oils.

Viscosity is another important factor for determining the suitability of bio-oil for

fuel applications as it affects the pumping and atomization of the bio-oil. In general, less

viscosity results in easier pumping, atomization, and, accordingly, easier combustion. The

typical viscosity value of the bio-oil can vary from 25 cSt to 100 cSt (measured at 40ıC)

or more depending on the feedstock and the water content of the oil (Diebold et al.,

1999). The viscosities of the bio-oils produced from the eight study feed stocks varied

widely, ranging from 30.0 to 4,327.1 cSt. Viscosity for the pine-based bio-oils increased

from 30.0 cSt for clear wood to 137.9 cSt for bark and to a very viscous 1,011.7 cSt

for needles. The cottonwood whole-tree bio-oil increased from 77.0 cSt to 472.7 cSt

for cottonwood bark to 432.7 cSt for cottonwood leaves. The high viscosity values for

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1836 E. M. Hassan et al.

the bio-oils produced from the two species’ bark and needles or leaves influenced the

whole-tree bio-oil viscosity values. Clear wood bio-oil viscosity increased slightly from

30.0 cSt to 40.1 cSt for whole-tree feed stock bio-oil, cottonwood bio-oil from clear

wood increased from 77 cSt to a very high 361.5 cSt for whole-tree feed stocks. This

result may be due to the increase of condensation reactions, which resulted from higher

lignin content in whole-tree feed stocks compared to clear wood as indicated in Table 1.

Moreover, very high viscosity values of pine needles and cottonwood leaves are probably

related to the condensation of phenolic extractives, such as phenols, stilbenes, lignans,

isoflavonoids, flavonoids, and condensed tannins, which are present largely in needles

and leaves (Larson, 1988).

For the investigation of the potential use of the bio-oil for fuel, the higher heating

values for the eight different bio-oils were measured. The higher heating values for the

eight bio-oils ranged from 21.38 to 26.12 MJ/kg. These heating values are relatively

higher than those reported for other bio-oils (15–18 MJ/kg) and approximately half (42

MJ/kg) of petroleum fuels (Boucher et al., 2000). This reduction in heating values is

due to the combined presence of water (16.0 to 26.0) and oxygenated compounds. When

comparing between feed stocks, one can see that the cottonwood leaves and pine needles

had relatively higher heating values than other feed stocks.

Chemical Characterization of Bio-oils

Average Molecular Weight

The weight-average molecular weight (Mw), number-average molecular weight (Mn),

and polydispersity index (PD D Mw=Mn) for the eight study bio-oils were determined

by GPC and the results are shown in Table 4. Mw for these bio-oils ranged between 400

and 790 g/mol while Mn ranged between 300 and 390 g/mol. The lowest Mw values

(400–410 g/mol) were obtained for the pine wood and cottonwood wood bio-oils. The

highest Mw values (590–790 g/mol) were obtained for the pyrolysis oils of pine needles

and cottonwood leaves. These results are consistent with the viscosity results and add

support to our hypothesis that condensation reactions occurred in the bio-oils of pine

needles and cottonwood leaves, probably as a result of high concentrations of phenolic

compounds. The ratio of Mw=Mn, which measures the homogeneity of the bio-oils was

found to increase in the same order of average molecular weight.

Table 4

GPC Mn and Mw characterization of the eight study bio-oils

Pine

wood

Pine

whole

tree

Pine

bark

Pine

needles

Cotton-

wood

Cotton-

wood

whole

tree

Cotton-

wood

bark

Cotton-

wood

leaves

Mw (g/mol) 400 430 470 590 410 440 470 790

Mn (g/mol) 315 330 340 340 300 320 330 370

Mw=Mn 1.26 1.30 1.73 1.78 1.36 1.37 1.42 2.13

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Potential of Whole-tree Biomass for Bio-oil Fuels 1837

GC/MS Analysis

The GC/MS characterization of the eight study bio-oils is given in Table 5. Wood

biomass is composed mainly of cellulose, hemicellulose, and lignin. It is expected that

the major pyrolysis products should be derived from these components. Pyrolysis of

cellulose and hemicelluloses produce several degradation products such as levoglucosan,

furfural, 2-furanmethanol, 2-methyl-2-cyclopentene-1-one, 2-(5H)-furanon, 5-methyl-2-

furancarboxyaldehyde, 3-methyl-2-cyclopentene-1-one, acetaldehyde, hydroxyacetalde-

hyde, and acetic acid (Alén et al., 1996). Table 5 shows that cellulose and hemicelluloses

degradation products comprise a large proportion of all study bio-oils except those

produced from pine needles and cotton-wood leaves. These results were the result of

Table 5

GC/MS characterization for the bio-oil produced from different industrial feedstocks

Concentration, %

Compound name

Pine

wood

Pine

whole

tree

Pine

bark

Pine

needles

Cotton-

wood

Cotton-

wood

whole

tree

Cotton-

wood

bark

Cotton-

wood

leaves

Furfural 0.28 0.20 0.12 0.00 0.21 0.16 0.11 0.01

Levoglucosan 7.13 3.96 2.84 1.32 4.70 3.03 1.44 0.45

2-Furanmethanol 0.15 0.12 0.16 0.09 0.18 0.22 0.15 0.13

2-Methyl-2-cyclopenten-1-one 0.07 0.08 0.05 0.05 0.07 0.09 0.07 0.06

2-(5H)-furanone 0.49 0.30 0.29 0.18 0.44 0.43 0.31 0.17

5-Methyl-2-furancarboxaldehyde 0.04 0.07 0.06 0.02 0.03 0.04 0.03 0.01

3-Methyl-2-cyclopenten-1-one 0.11 0.07 0.05 0.12 0.09 0.06 0.04 0.01

Phenol 0.42 0.78 1.74 2.07 1.48 1.87 1.87 2.10

3-Methyl-1,2-cyclopentanedione 0.61 0.51 0.36 0.38 0.59 0.76 0.74 0.41

2-Methylphenol 0.23 0.30 0.38 0.54 0.30 0.53 0.62 0.76

3-Methylphenol 0.37 0.48 0.56 0.67 0.44 0.52 0.54 0.63

2-Methoxyphenol (o-Guaiacol) 0.30 0.30 0.23 0.35 0.16 0.22 0.18 0.22

2,6-Dimethylphenol 0.02 0.03 0.02 0.03 0.03 0.04 0.04 0.03

2,4-Dimethylphenol 0.22 0.28 0.19 0.16 0.14 0.21 0.17 0.14

3-Ethylphenol 0.08 0.11 0.10 0.09 0.07 0.12 0.12 0.07

2,3-Dimethylphenol 0.02 0.03 0.03 0.02 0.03 0.06 0.05 0.03

Naphthalene 0.01 0.06 0.01 0.09 0.06 0.05 0.05 0.05

2-Methoxy-4-methylphenol 0.33 0.33 0.33 0.10 0.11 0.15 0.11 0.07

1,2-Benzendiol 1.66 1.66 2.70 1.01 1.15 1.53 1.99 0.87

5-Hydroxymethyl-furfural 0.00 0.00 0.00 0.19 0.33 0.00 0.32 0.00

4-Methyl-1,2-benzenediol 0.34 0.31 0.34 0.16 0.27 0.37 0.33 0.14

4-Ethyl-2-methoxy-phenol 0.09 0.10 0.12 0.04 0.04 0.05 0.05 0.03

3-Methyl-1,2-benzenediol 1.13 1.05 1.51 0.37 0.42 0.64 0.54 0.21

2,6-Dimethoxy-phenol 0.00 0.00 0.00 0.05 0.30 0.32 0.26 0.13

Eugenol 0.13 0.13 0.08 0.05 0.06 0.09 0.07 0.05

2-Methoxy-4-propylphenol 0.03 0.03 0.02 0.01 0.01 0.02 0.01 0.01

Vanillin 0.15 0.13 0.10 0.00 0.06 0.09 0.07 0.02

Cis-isoeugenol 0.80 0.80 0.46 0.26 0.37 0.55 0.41 0.26

3,4-Dimethylbenzoic acid 0.00 0.04 0.04 0.00 0.00 0.00 0.00 0.00

Trans-isoeugenol 2.34 2.50 1.73 1.15 1.53 2.10 1.63 1.02

Acetovanillone 0.10 0.08 0.07 0.02 0.04 0.05 0.05 0.02

Oleic acid 0.48 1.06 0.72 0.53 0.29 0.46 0.49 0.33

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1838 E. M. Hassan et al.

the fact that pine needles and cottonwood leaves had the lowest holocellulose contents

(Table 1) such that these feed stocks would be expected to produce lower cellulose and

hemicelluloses degradation products.

Bio-oils produced from lignocellulosic feed stocks, such as wood, that contains sig-

nificant quantities of lignin, have been shown to produce numerous phenolic compounds.

For our eight study bio-oils, phenol, isoeugenol, 1,2 benzenediol, 3-methyl-1,2-ben-

zenediol, 3-methyl-1,2-cyclopentanedione, 2-methylphenol, 3-methylphenol, 4-methyl-

1,2-benzenediol, 2-methoxy-4-methylphenol, 2-methoxyphenol, and 3-methyl phenol were

the most abundant chemicals observed from lignin degradation (Table 5). Most of these

compounds were observed to have relatively similar levels in all study bio-oils. However,

the amount of the phenolic compounds (phenol, 2-methylphenol, 3-methylphenol, and

2-methoxyphenol) was relatively higher in pine needles and cottonwood leaves. This

result may be due to the high needles and leaves concentrations of phenolic extractives,

which usually exist with large proportions in needles and leaves.

Conclusions

In this study, bio-oils for eight feed stocks (pine wood, pine whole tree, pine bark, pine

needles, cottonwood wood, cottonwood whole tree, cotton-wood bark, and cottonwood

leaves) were produced by an auger-fed reactor. Respectively, pine and cottonwood bio-

oil yields were 60.1 vs. 52.7 for clear wood, 53.7 vs. 52.7 for whole tree, 48.2 vs. 47.7

for bark, and 49.7 vs. 40.3 for needles or leaves. Therefore, whole-tree bio-oils yields

decreased for the whole-tree feed stocks as a result of lower bio-oil yields for the bark and

needles or leaves components. The economics of utilization of whole-tree feed stocks

will have to overcome this reduction in yield based on lower cost for the whole-tree

biomass type.

By feed-stock, char yields were largely the converse of bio-oil yields with those feed

stocks with higher bio-oil yields giving lower char yields and vice versa. Respectively,

pine and cottonwood char yields were 19.1 and 16.0 for clear wood and 28.1 and 24.3 for

whole-tree feed stocks. Loss of bio-oil yield for whole-tree feed stocks was 6.4 percentage

points compared to pine clear wood with a corresponding 9.0 percentage point increase

in char production. Likewise, cottonwood whole-tree feed stock bio-oil yield decreased

by 8.6 percentage points versus that for clear wood; char production increased by 8.3

percentage points. It is possible, therefore, that the shortfall in bio-oil revenue for whole-

tree feed stocks compared to clear wood may be partially offset if alternative markets

for the increased production of char are developed. This assumes that the increased char

yield is not required for pyrolysis energy production.

Viscosity of pine whole-tree bio-oil was 40.1 cSt compared to 30.0 cSt for pine clear

wood. This resulted from the high viscosities added by the bark and needles components

present in the whole-tree feed stocks. Likewise, whole-tree cottonwood bio-oil was 361.5

cSt compared to 77.0 cSt for bio-oil from the clear wood feed stock. Again, cottonwood

whole-tree viscosity increased from the influence of the higher-viscosity contributions of

the cottonwood bark and leaves. The pine whole- tree feed stock viscosity value of 40.1

cSt is a not a factor to eliminate bio-oil from this feed stock type as a fuel resource.

However, the high viscosity value for cottonwood whole-tree bio-oil (361.5 cSt) will

likely be problematic for utilization of the cottonwood whole-tree feed stock for bio-oils

intended as fuels.

With respect to acidity, the pH values for bio-oils whole-tree pine and cottonwood

are slightly higher than for clear wood. Acid values were much lower for the whole-tree

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Potential of Whole-tree Biomass for Bio-oil Fuels 1839

bio-oils. This result indicates better bio-oil properties for whole tree compared to clear

wood for utilization as a fuel.

These results show that bio-oil produce from whole-tree pine feed stock is compara-

ble chemically and physically to that produced from clear wood. The lower bio-oil yield

for whole-tree pine feed stock must be overcome by reduced cost of the whole-tree feed

stock compared to clear wood. Cottonwood bio-oil produced from whole-tree feed stocks

is probably not suitable for fuels production due to high viscosity.

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