Characterisation of products from pyrolysis of waste sludges

Bioresource Technology 108 (2012) 258–263

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Bioresource Technology

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Characterisation of the products from pyrolysis of residues after acid hydrolysisof Miscanthus

F. Melligan a, K. Dussan a, R. Auccaise b, E.H. Novotny b, J.J. Leahy a, M.H.B. Hayes a, W. Kwapinski a,⇑a Carbolea Research Group, Department of Chemical and Environmental Sciences, University of Limerick, Irelandb Embrapa Solos, RuaJardimBotânico 1024, Brazil

a r t i c l e i n f o a b s t r a c t

Article history:Received 9 August 2011Received in revised form 19 December 2011Accepted 20 December 2011Available online 28 December 2011

Keywords:BiorefineryBiocharBio-liquidPyrolysisAcid hydrolysis

0960-8524/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.biortech.2011.12.110

⇑ Corresponding author.E-mail address: [email protected] (W. Kwapi

Platform chemicals such as furfural and hydroxymethylfurfural are major products formed during theacid hydrolysis of lignocellulosic biomass in second generation biorefining processes. Solid hydrolysisresidues (HR) can amount to 50 wt.% of the starting biomass materials. Pyrolysis of the HRs gives riseto biochar, bio-liquids, and gases. Time and temperature were variables during the pyrolysis of HRs ina fixed bed tubular reactor, and both parameters have major influences on the amounts and propertiesof the products. Biochar, with potential for carbon sequestration and soil conditioning, composed abouthalf of the HR pyrolysis product. The amounts (11–20 wt.%) and compositions (up to 77% of phenols inorganic fraction) of the bio-liquids formed suggest that these have little value as fuels, but could besources of phenols, and the gas can have application as a fuel.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Second generation biofuels are produced from non-food crops.This involves the utilisation of lignocellulosic materials, such as agri-culture and forestry residues, some industrial waste materials, andalso dedicated lignocellulose crops. Acid hydrolysis processes areamongst the promising methods for converting such feedstocks intoplatform chemicals and energy. The process involves the hydrolysisof the cellulose and hemicellulose components in lignocellulose intoindividual sugar monomers, and these are then converted into arange of platform chemicals. This process involves dehydration ofthe hexoses to hydroxymethylfurfural (HMF) and rehydration ofthe HMF to levulinic acid (LA) and formic acid (FA, in equimolaramounts), and dehydration of the pentoses in hemicelluloses to fur-fural, which can also be transformed to LA. LA is an excellent plat-form chemical that can also be transformed into fuel additivessuch as ethyllevulinate, butan-2-ol, methyl tetrahydrofuran and c-valerolactone (Hayes et al., 2005). The FA when decarboxylatedcan be used as a source of hydrogen (Bulushev and Ross, 2011).

The solid residual material in the hydrolysis process is derivedmainly from lignin (Sharma et al., 2004), which resists hydrolysis,and cutin, cutan, and waxy materials in biomass, and also from con-densation reactions that involve reactive intermediates (such asHMF) in the degradation processes. Despite the highly recalcitrantnature of the lignin, it can be broken down to low molecular weight

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nski).

compounds (lignols) through a variety of routes (de Wild et al.,2009).

Mullen and Boateng (2010), Caballero et al. (1996), Baumlinet al. (2006), Liu et al. (2008) and Shen et al. (2010), amongst oth-ers, have looked at pyrolysis as a method of processing lignin forthe production of both energy and platform chemicals. Lignin,when pyrolysed yields much higher quantities of char than bothcellulose and hemicelluloses. There are several research papers(e.g. Bridgwater et al., 2002; Tange and Drohmann, 2005) thatpoint out how pyrolysis can be more attractive than combustionor gasification. The biggest advantages of pyrolysis are the valueadded products it provides such as char (which can be used as asequester of carbon, as a soil conditioner, an adsorbent, and as ahigher energy density fuel), and bio-oil (which can be used as asource of chemicals). In addition, the heat produced in the caseof combustion must be used immediately as it cannot be stored,and also the amount of waste gases from combustion is muchhigher. Char, when applied to soil is usually known as biochar. Itcan have a large surface area and porosity, and therefore have pos-sible uses as an adsorbent, and as a soil conditioner. Because of itsresistance to microbial attack, and because of its low content ofvolatiles, the carbon in biochar when added to soil can be regardedas sequestered carbon (Kwapinski et al., 2010).

Vapours in pyrolysis processes give rise to syngas, and some va-pours condense to give bio-oil. Bio-oil has a number of unfavour-able properties, such as low pH, instability, high water andoxygen contents, and thus it will have low heating value. Hencethe usefulness of the bio-oil is limited. Because some valuable

Table 1Reaction parameters for the production of the hydrolysis residue materials.

Sample Temperature(�C)

Pressure(atm)

Time(min)

Acidconcentration(wt.%)

Residue(wt.%)

HR1 200 23 120 5 33.5HR2 200 23 10 1 36.6HR3 200 23 10 0.5 36.6HR4 175 11 10 1 37.6

F. Melligan et al. / Bioresource Technology 108 (2012) 258–263 259

platform chemicals can be extracted from bio-oil, it is important toknow how pyrolysis parameters will affect its chemical composi-tion. Caballero et al. (1996) found that with an increase in pyrolysistemperature the yields of methane, ethylene, propylene, propane,benzene, C4 hydrocarbons, and water increased. The polyphenolicstructure of lignin means that it is a rich source of phenolic com-pounds. de Wild et al. (2009) achieved up to 20 wt.% of a phenolicfraction in the bio-oil from the continuous fast pyrolysis of granitlignin (lignin prepared from a mixture of hardwoods via the Alcellorganosolv process), and 9 wt.% could be considered as low molec-ular weight phenolic compounds.

The work reported here investigates the pyrolysis of solid resi-dues (HRs) from the acid hydrolysis of a lignocellulosic substrateunder conditions that simulate biorefining processes. These resi-dues can be regarded as models for biorefinery residuals (BRs).The study investigates the properties of the pyrolysis productsand the potential usefulness of the products obtained.

2. Methods

2.1. Preparation of hydrolysis residue

Miscanthus x giganteus (M) samples, of particle size between 5and 10 mm were subjected to acid hydrolysis under the conditionsdescribed in Table 1, and the solid hydrolysis residual materials(HR) were recovered. The hydrolysis processes differ in the concen-trations of sulphuric acid used, and in the reaction time, tempera-ture and pressure of the hydrolysis process. The acid hydrolysiswas carried out in an aqueous medium. As the reaction tempera-ture increased the pressure also increased. The acid to solid ratioused was 9:1.

The liquid phase after the acid treatment was a mixture of com-pounds derived from the cellulose and hemicellulose components

Table 2Methods used for determinations of some properties and compositions of biomass and bi

Property Method

Moisture content of biomass The moisture contents of the feedstocks were meavalue was reached. Acc. ASTM d4442

C, H, N, S, O contents These analyses were carried out using an Elemendetermined by difference

Cellulose, hemicellulose andlignin content

Acc. ASTM E1758-01 ‘‘Standard method for the D

HHV The HHV was determined using the oxygen bombAcc. ASTM d240

Water content in bio-oil The water contents of the samples were determintitrated using hydranal Composite 5, and methan

pH The pH was determined at 25 �C using a pH meteChemical composition of bio-

liquidAgilent 7890a GC 5975c MS (GC/MS) instrument wVarian capillary column (30 m and i.d. 0.25 mm, 0filtered (0.45 lm filter), then acetone was added

Gas composition Agilent micro-GCVolatile matter Volatile material associated with the biochar was

standard procedure CEN/TS 15148:2005

of the biomass. That mixture contained platform chemicals, andare not dealt with in this manuscript.

2.2. Pyrolysis process

Pyrolysis of M and of the HR samples (HR1, HR2, HR3 and HR4)was carried out in a fixed bed tubular reactor (5 cm i.d.) at temper-atures of 600 �C with a heating rate of 70 �C/min and residencetime of 10 min. Pyrolysis at 600 �C was conducted for 30 and60 min in the cases of M and HR1. HR1 was also pyrolysed at400 and 500 �C, with heating rates of 65 and 70 �C/min, respec-tively, and a residence time of 10 min. A constant flow of N2

(50 cm3/min) was passed through the reactor. The pyrolysis vapourpassed through a condenser cooled to �10 �C, and the bio-liquidcondensate was collected for analysis and stored in air tight samplebottles. At the end of the run the solid residue (char) was allowedto cool to ambient temperature before recovery, and it was thenstored in air tight sample containers prior to analysis. The non-con-densable vapours were collected in gas sample bags for analysis.Each experiment was carried out at least three times, and the aver-age values are displayed in the figures and tables. The maximumerror for the bio-oil, char, and gas yields was less than 3%; however,the error was less than 1% for all the other measurements (elemen-tal analysis, volatiles, ash, moisture, cellulose, etc.). The analyticalprocedures used are summarised in Table 2.

2.3. Plant growth trials

Plant growth trials were carried out using 3 wt.% char in 500 gof soil. For each type of biochar five different pots were used, and10 corn (Zea mays L.) seeds were planted in each pot. Five controlpots were also used. All pots were then placed in a growth cham-berat 20 �C and exposed to 12 h of light per day. Water (50 cm3 perpot) was added to every pot twice a week for the duration of thetrial. After 10 days the five weakest plants were removed fromeach pot, and all remaining plants were harvested after 21 days.The green parts of plants were dried to constant weight in an ovenat 60 �C.

3. Results

3.1. Characterisations of pyrolysis products of hydrolysis residues andof Miscanthus biomass

Fig. 1 shows the thermogravimetric (TGA) and differential ther-mogravimetric (DTG) analysis of the pyrolysis products of the HRs

o-oil.

sured by placing the sample in an oven at 105 �C and weighing until a constant

tal Vario el Cube analyser. Sulphanilamide was used as a standard. Oxygen was

etermination of Carbohydrates by HPLC’’

calorimeter 6200 No. 442 m Parr company. Benzoic acid was used as a standard.

ed using a Karl–Fischer titration and a Mettler Toledo dl 31. The samples wereol-chloroform (3:1) was used as the solvent. Acc. ASTM D95r, type Orion 420ith an ion-trap detector was used for bio-oil analysis. GC was carried out using a.25 lm film thickness). To prepare samples for the GC/MS the bio-oil was first

to give a 6% sample solution

determined from weight loss on heating for 7 min at 900 �C, according to the

Fig. 1. TGA of hydrolysis residue feedstocks.

Table 4Some properties of Miscanthus before and after acid hydrolysis.

Biochar source Miscanthus HR1 HR2 HR3 HR4 ALMa

HHV (MJ kg�1) 18.7 21.4 25.9 25.8 20.2 n.d.C (wt.%) 46.6 62.6 65.1 64.8 55.7 62.05H (wt.%) 6.36 3.37 5.29 5.32 4.75 5.95N (wt.%) 0.41 0.23 0.58 0.61 0.37 n.d.O (wt.%)b 46.63 33.80 29.03 29.27 39.18 32.00

n.d. = not determined.a Results from Nowakowski et al. (2010).b By difference.

260 F. Melligan et al. / Bioresource Technology 108 (2012) 258–263

of M biomass. The heating rate for the TGA was 10 �C/min. The ini-tial weight loss is primarily due to the evaporation of residualwater. The broad peak at 180–220 �C on the DTG plot for HR4 isattributable to the decomposition of glucose. HR4 was subjectedfor 10 min to a lower pressure (11 atm) and temperature (175 �C)and complete hydrolysis of the cellulose may not have taken placeunder these reaction conditions. The glucose content (14.5%, Table3), and the carbon (Table 5) contents for HR4, indicate incompletehydrolysis of the cellulose compared with less than 0.5% glucosecontent for HR1 (Table 3). The peak at 180–220 �C was not evidentfor the pyrolysis products of the other HR samples, further suggest-ing that most, or all of the cellulose and hemicelluloses were re-moved when the hydrolysis process was carried out attemperatures of 200 �C or greater. Characteristically hemicellu-loses decompose at a relatively low temperature (Yang et al.,2007). The rapid weight loss between 200 and 600 �C is due tothe breakup of inter-unit linkages and evaporation of monomericphenol units (Wörmeyer et al., 2011). Ferdous et al. (2001) founda linear transformation from about 28% to 60% for a temperaturerise from 350 to 650 �C, and a heating rate of 15 �C/min. Theyshowed that for a heating rate of 10 �C/min lignin conversionwas 60 wt.%. The conversion was 64 wt.% at 800 �C for a heatingrate of 15 �C/min. Hence, the heating rate has a small impact onthe overall lignin conversion. Above 600 �C the weight loss wassmall (Fig. 1), and the weight remained relatively constant above650 �C. Heo et al. (2010) contend that the temperature range forthe decomposition of lignin is very wide (150–900 �C). However,although the lignin would continue to decompose up to a temper-ature of 900 �C and beyond (Yang et al., 2007), the rate of degrada-tion above 600 �C would be slow, as can be seen from the TGA data.

From both the elemental analyses (Table 4) and the TG analysisof the hydrolysis residues it can be concluded that the acid concen-tration has a lesser effect than the reaction temperature on thecomposition of the residual material. The data in Table 4 show that

Table 3Biomass composition.

Biomass type Miscanthus

Moisture (wt.%) 8.82Cellulose Glucose (wt.%) 37.1

Hemicellulose Xylose (wt.%) 17.84Rhamnose (wt.%) 0.19

Lignin Klason lignin (wt.%) 20.1Ash (wt.%) 3.55Volatile matter (wt.%) 79.4

n.d. = not determined.a Results from Nowakowski et al. (2010); ALM lignin, manufactured by Asian Lignin Ma

non-woody plants (wheat straw and sarkanda grass (Saccharum munja)).

an increase of over 10% is obtained in the carbon content for a tem-perature increase of 25 �C. However, when the acid concentrationwas increased from 0.5% to 5% and the temperature remained con-stant, the difference in the carbon content was only about 2%.

Lenihan et al. (2010) observed that an increase in the reactiontemperature for acid hydrolysis of potato peelings caused boththe sugar production and decomposition reaction rates to increasesignificantly. When account is taken of the acid concentration andreaction temperature (Table 1) it can be deduced from compari-sons of the data for HR2 with HR4 in Table 3, that increasing thereaction temperature decreases the sugar yield.

3.2. Pyrolysis

In a separate set of experiments, pyrolysis of HR1 was carriedout at 400 �C with a heating rate 65 �C/min and residence time10 min, and the percentages measured of char, gas, and of bio-li-quid were of the order of 73, 23 and 4 wt.%, respectively. Withthe increase in temperature from 400 to 600 �C the amount of solidproduct decreased by almost 20 wt.%, and the volatile productgradually increased.

Fig. 2 presents results for the pyrolysis for 10 min at 600 �C ofMiscanthus and of the HR products. Pyrolysis of the HRs yielded verylow quantities of condensed liquid products and high levels of charwhen compared to the Miscanthus feedstock. Data from Nowakow-ski et al. (2010) in the same figure show that the pyrolysis productof ALM (an Asian Lignin Manufacturing India Pvt. Ltd. sulphur-freelignin) gave a gas, bio-liquid, and char distribution similar to thatfor HR4, and along the lines of the distributions for HR2 and HR3.ALM is a very stable lignin material (Nowakowski et al., 2010), andthe similarities with the relative abundances in the HR pyrolysisproducts highlights the importance of lignin as the major compo-nent of the HR products of the M used in the present study. TheALM lignin was pyrolysed in a batch reactor at 480 �C.

3.3. Biochar

Table 5 gives some of the properties of the biochar from the fourdifferent HRs and from M, produced at 600 �C, and with theresidence time variously set at 10, 30 and 60 min, from the four

HR1 HR2 HR3 HR4 ALMa

5.98 5.67 5.49 6.21 n.d.0.36 0.38 1.4 15.4 0.2

0.1 n.d. n.d. 0.11 20.08 n.d. n.d. 0.17

85.5 95.5 93.6 76.2 941.92 1.58 1.59 1.86 <4

56.3 57.1 56.9 59.2 n.d.

nufacturing India Pvt. Ltd., is a sulphur-free lignin obtained from annually harvested

Fig. 2. Product distribution from the pyrolysis at 600 �C for 10 min of Miscanthusand HR materials, and of lignin (in a different reactor type). � Results fromNowakowski et al. (2010).

Fig. 3. 13C DP/MAS NMR spectra of A – HR4; B – char from HR4.

F. Melligan et al. / Bioresource Technology 108 (2012) 258–263 261

different HRs and from M. In order to produce biochar with opti-mum value for soil amendments and for carbon sequestration itis necessary to have relatively high temperatures and residencetimes. The residence time does not influence the elemental compo-sition of HR char, but it does the surface area which increases withthe time of pyrolysis (see data for HR1, Table 5). This is similar tothe results of Sharma et al. (2004). These show that the aromaticityand the carbonaceous nature of the char increase with reactiontemperature. This also holds for an increase in the residence time,as evident from Fig. 3.

Solid state NMR provides an excellent spectroscopic procedurefor following the changes in the compositions of biomass and ofbiochars that take place during pyrolysis. Kwapinski et al. (2010)have presented a 13C NMR DP/MAS spectrum that demonstratesaliphatic, aromatic, phenolic, methoxyl, and carbohydrate func-tionalities for M. The solid state NMR spectrum in Fig. 3A clearlyshows the aliphatic hydrocarbon (10–45 ppm) and the aromatic(110–140 ppm) resonances in the HR4 sample, but there is nodefinitive evidence for carbohydrate components. The resonancefor methoxyl at about 56 ppm, and the ‘shoulder’ at 140–150 ppm indicate resonances for lignin, or lignin alteration prod-ucts. The Gaussian shape of the spectrum shown in Fig. 4(b) ischaracteristic of the fused aromatic structures (centred around130 ppm) of biochars, and with no indications of the aliphaticand phenolic-type structures indicated in spectrum for HR4.

The process of pyrolysis maintains a large amount of the struc-tural architecture of the starting plant material, and a definite

Table 5Yields and some properties of biochars from pyrolysis at varying reaction times.

Char source M HR1 HR1 HR1 HR2 HR3 HR4

Pyrolysis time (min) 60 10 30 60 10 10 10Temperature (�C) 600 600 600 600 600 600 600Surface area

(m2 g�1)161 151 171 260 131 157 277

HHV (MJ kg�1) 32.5 27.9 27.9 27.7 29.3 28.6 26.1C (wt.%) 85.1 87.5 87.7 88.4 84.0 89.5 79.4H (wt.%) 2.40 2.15 2.12 1.99 3.12 2.14 2.18N (wt.%) 0.55 0.34 0.379 0.323 0.84 0.94 0.66O (wt.%)a 11.95 10.01 9.80 9.29 12.04 7.42 17.76Volatile matter

(wt.%)24.8 19.1 13.6 16.5 18.9 19.1 24.1

a By difference.

‘honeycomb structure’ is preserved (Melligan et al., 2011) that ischaracteristic of the plant cell structure, and the surface area is in-creased (Kwapinski et al., 2010). The acid hydrolysis process re-sults in a breakdown of the cell structure and the absence of thewell defined ‘honeycomb structure’ is lost, as is evident inFig. 4(a). The evident differences between the SEMs in Fig. 4 areto be expected. The hydrolysis process removes a large amountof cellulose, which in combination with the hemicellulose and lig-nins are predominantly responsible for the structural integrity ofthe biomass. Hydrolysis conditions for HR1 were more energyintensive than those for HR4 (Table 1). In the case of HR4, the

Fig. 4. SEM of (a) char from HR1 (600 �C and 10 min); (b), char from HR4 (600 �Cand 10 min).

262 F. Melligan et al. / Bioresource Technology 108 (2012) 258–263

hydrolysis was carried out at a lower pressure and temperature,and incomplete removal of the cellulose had taken place (Table3), and aspects of the honeycomb structure were preserved(Fig. 4). The data in Table 5 show that the pyrolysis time is impor-tant in determining the surface area of the biochar.

Table 6Physical properties of bio-liquid produced at 600 �C in 10 min.

Bio-liquid source M HR1 HR2 HR3 HR4

3.3.1. Biochar as a fertiliser and soil ameliorantIt has been well documented that the application to soil of bio-

char from the pyrolysis of lignocellulosic feedstocks can be a keycomponent for sustainable biomass to bioenergy production sys-tems (Chan and Xu, 2009). There is abundant evidence to showthat applications of biochar to soil can promote plant growth. Bio-char increases the activity of soil symbiotic microorganisms andenhances soil water retention (Yamato et al., 2006). In addition,during pyrolysis a large proportion of the nutrients required forhealthy plant growth, such as Ca, Mg, K and P are concentratedin the char, and also about half of the N and S remain in the char(Laird et al., 2010). The char loses both hydroxyl and aliphaticgroups and the aromatic character increases quite rapidly above450 �C (Sharma et al., 2004). Therefore most of the nutrients canbe returned to the soil. Due to the highly aromatic nature of thebiochar it will potentially remain in the soil for millennia.

Fig. 5 compares the growth of maize (Zea mays L.) in soilamended with 3 wt.% HR1, with char from HR1, and with char fromM. Char produced from the M feedstock has a greater influence onplant growth than that from HR. The M char was shown to increaseplant productivity by up to 60% over a 21 day period, whereas thatfrom HR increased plant growth by about 10% during the same per-iod. Despite the fact that the growth promoting potential of charfrom HR materials is decreased, the biochars will, because of theirhigh carbon, low oxygen, and volatile matter contents, and theirpredominant fused aromatic structures, have potential as stablelong lasting soil conditioners, and will sequester carbon. Thus, eventhough the HR char was seen to be inferior to that from the parentM material for promoting plant growth it will have value insequestering carbon, in providing a habitat for soil microorgan-isms, in the retention of water, and in lowering the leaching lossesof nutrients.

Water content (wt.%) 36 74.0 65.5 63.8 n.d.pH 2.5 5.1 n.d. n.d. n.d.Density (g/cm3) 1.09 1.01 1.01 1.01 1.00C (wt.%) 43.1 3.09 4.86 5.11 8.34H (wt.%) 5.73 10.3 11.0 10.7 11.1N (wt.%) 0.28 0.73 0.65 0.72 0.34

n.d. = not determined.

3.4. Gas

The gas composition obtained from pyrolysis of HR at 600 �Cwas H2: 0.3–2 vol.%; CO: 13–28 vol.%; CO2: 14–24 vol.%; methane:12–20 vol.%; ethane: 0.1–5 vol.%; ethylene: 0.1–1.8 vol.%. As thecarrier gas for the pyrolysis process was nitrogen, it was assumedthat any nitrogen detected by the micro GC was not from biomass.Therefore the nitrogen content was subtracted and the concentra-

Fig. 5. Growth of maize after 21 days in soil amended with 3 wt.% biochar fromMiscanthus and HR1 before and after pyrolysis under various conditions.

tion of the remaining gases was then calculated on a dry base. Themajor components of the gas produced are CO and CO2. Shen et al.(2010) also found that CO and CO2 were the main gaseous productfrom the pyrolysis of wood lignin. They also found a high level ofmethane, along with small amounts of some light hydrocarbons,such ethane and ethylene were obtained. The hydrocarbons canmake up over 20 vol.% of the gas, resulting in an estimated heatingvalue of between 7 and 9 MJ/N m3.

3.5. Bio-liquid

The vapour condensate from the pyrolysis of HRs formed a two-phase liquid. The bottom dark brown layer was only about 4% ofthe total volume. The physical properties of the upper layer, thebio-liquid produced from HRs at 600 �C in 10 min, are presentedin Table 6, and these are compared with the upper phase fromthe pyrolysis of M. Results from the pyrolysis of lignin in an inter-national collaboration study by Nowakowski et al. (2010) alsoshow a high water content for some of the bio-oil samples. Oneof the most notable differences between the bio-liquid from Mand that from its HR is the high water content and the low carboncontent in the product from the HR materials. The high water con-tents, in all bio-liquid from pyrolysis of HRs can explain their sim-ilar physical properties. However, some differences can be seen inthe levels of the organic compounds present (Fig. 6). The bars inFig. 6 represent normalised amounts, and the values on the barsare absolute yields of components with respect to the initial quan-tity of M. The absolute yields of organic compounds for HR4 weremore than were obtained for HR1 as the result of the incompleteacid hydrolysis in the case of the former. As expected, phenoland phenol derivatives were major organic products from the ther-mal decomposition of the HRs. These results have similarities withthose of Shen et al. (2010), which show that methoxy phenols are

Fig. 6. Distribution of functional groups in bio-liquid detected by GC/MS. All bio-liquid samples were produced with in a reaction time of 10 min. The numbersdisplayed on chart correspond to the approximate yields of the different groupswith respect to the initial mass of Miscanthus.

F. Melligan et al. / Bioresource Technology 108 (2012) 258–263 263

the most characteristic products of lignin pyrolysis, and phenol-2-methoxy, phenol-2,6-dimethoxy, and their derivatives includingalkyl guaiacol, eugenol, catechol-methoxy, vinyl guaiacol, alkylsy-ringol, and vinylsyringol, are the most abundant products. TheGC/MS results in Fig. 6 show that an increase in reaction tempera-ture results in an increase in the phenol contents. This is due to thesecondary cracking of alkyl guaiacol and alkyl syringol (Shen et al.,2010). There is a definite decrease in the level of hydrocarbons andof organic acids as the reaction temperature increases. The bio-li-quid has little or no value as a fuel because of its high water con-tent and a very small organic composition. However, the liquid canbe a source for the isolation of components such as phenols.Changing a pretreatment method from high temperature and acidconcentration (HR1) to lower temperature and acid concentration(HR4) results in the production of lower amounts of phenols andof higher amounts of oxygenates. Therefore it is possible to alterthe reaction parameters to influence the formation of certain phe-nol derivatives.

4. Conclusions

Pyrolysis, yielding bio-liquid, gas, and biochar provides a meth-od for utilising the residue from Miscanthus from hydrolysis biore-fining processes. The biochar is, arguably, the most useful product.It has high carbon content, an almost entirely fused aromatic struc-ture, and a large surface area. These properties are appropriate forapplications as a soil conditioner, and for carbon sequestration.There are limitations in the usefulness of the bio-liquid as a fuel.The organic fraction is primarily composed of phenols, which couldbe isolated. About 35% of the feedstock is converted to gas with aheating value of 7–9 MJ/nm3.

Acknowledgements

We acknowledge financial support of Science Foundation Ire-land under Grant number 06/CP/E007, and European Community’sSeventh Framework Programme (FP7/2007-2013) under Grantagreement number 227248-2.

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