wood/plastic copyrolysis in an auger reactor: chemical and physical analysis of the products

Fuel 88 (2009) 1251–1260

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Fuel

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Wood/plastic copyrolysis in an auger reactor: Chemical and physicalanalysis of the products

Priyanka Bhattacharya a, Philip H. Steele b, El Barbary M. Hassan b, Brian Mitchell b,Leonard Ingram b, Charles U. Pittman Jr. a,*

a Department of Chemistry, Mississippi State University, Mississippi State, MS 39762, United Statesb Department of Forest Products, Mississippi State University, Mississippi State, MS 39762, United States

a r t i c l e i n f o

Article history:Received 12 August 2008Received in revised form 14 November 2008Accepted 10 January 2009Available online 4 February 2009

Keywords:Bio-oilCopyrolysisSimultaneous pyrolysisPlastic

0016-2361/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.fuel.2009.01.009

* Corresponding author. Tel.: +1 6623257616.E-mail address: [email protected]

a b s t r a c t

Previous studies observed that slow copyrolysis of wood and plastic in enclosed autoclaves produced anupgraded raw bio-oil with increased hydrogen content. We now demonstrate that fast simultaneouspyrolyses of 50:50, w/w, pine wood/waste plastics in a 2 kg/h lab scale auger-fed reactor at 1 atm, witha short vapor residence time, generates higher heating value upgraded bio-oils. Three plastics: polysty-rene (PS), high density polyethylene (HDPE) and polypropylene (PP) were individually copyrolyzed withsouthern yellow pine wood at 525, 450 and 450 �C, respectively, to generate modified bio-oils upon con-densation. These liquids exhibited higher carbon and hydrogen contents, significantly lower oxygen con-tents, higher heats of combustion and lower water contents, acid values and viscosities than pine bio-oil.The formation of cross-over wood/plastic reaction products was negligible in the oils. Simultaneous pyro-lysis process design requires using a temperature at which the plastic’s thermal decomposition kineticsproduce vapors rapidly enough to prevent vaporized plastic from condensing on wood chars and exitingthe reactor.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction nitrogen and sulfur contents, it exhibits low heat values (15–

Plastics consumption has increased rapidly throughout theworld. The annual plastic consumption in United States was 30million tons in 2006 and 48.8 million tons in Western Europe in2003 [1,2]. In Asia, the consumption rate is less per person butgrowing faster than that of the US or Europe. Nearly 11.3% of allUS municipal solid wastes are plastics [1,2] and this is increasingannually. The rising cost of petroleum is increasing the price ofboth polymers and fuels, creating a huge opportunity to recyclethese plastic wastes or convert them to fuels.

Wood/plastic copyrolysis offers one route to liquid fuels. Pyro-lysis is a chemical recycling process that breaks organic macromol-ecules into small molecules at high temperatures in the absence ofoxygen via free radical degradation pathways [1,2]. Wood is com-posed of cellulose, hemicellulose and lignin and its fast pyrolysisproduces a liquid fraction called bio-oil (50–65%), a gaseous frac-tion (10–30%) and char (10–20%) [3–6]. Bio-oil is composed ofaldehydes, ketones, and hydroxy acetaldehydes (15–35%), organicacids (15–35%), anhydrous sugar fragments (levoglucosan), furanderivatives and phenolic compounds (6–15%) [3–6]. Water is alsoa major component of the bio-oil. The amount of oxygen presentin the bio-oil can range from �35 to 50%. While bio-oil has low

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(C.U. Pittman Jr.).

19 MJ/kg, 6450–8170 Btu/lb) [3], is corrosive and can oligomerizeand phase separate. Bio-oil has been tested as a fuel for diesel en-gines, turbines, furnaces and Stirling engines [7]. Upgrading bio-oilto allow petroleum refinery processing has been suggested [8,9]but deoxygenation is required [3] and this has led to catalyst cok-ing and remained uncommercialized.

Polyolefins contain higher hydrogen and carbon content thanwood and no oxygen. Therefore, plastic/wood copyrolysis may up-grade the bio-oil properties by increasing the carbon and hydrogencontents while reducing the oxygen present [10]. The elementalcontent of polyolefin plastics contains more hydrogen (approxi-mately 14% higher) and carbon than wood. Therefore, plastics pro-duce liquid products with higher hydrogen and carbon contentthan wood thermal degradation products [10]. Previous slow pyro-lysis (1–3 h) studies of polyolefins and wood/polyolefin copyrolys-es were conducted in a rotating autoclave under 0.1 MPa of argonat 360–450 �C that produced gas and liquid fractions [10–12].

In the slow autoclave copyrolysis of beech wood and atacticpolypropylene (aPP) (1:1 wt/wt ratio) in an autoclave, liquid andgas production increased somewhat as the temperature was in-creased (360, 380, 400, 430 and 450 �C). The amount of light liquidfraction was maximum (18.5%) at 400 �C, whereas the heavy liquidfraction decreased with increasing temperature. This may indicatecracking of the heavy liquid into a light liquid fraction at hightemperature. The amount of water fraction also decreased as

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1252 P. Bhattacharya et al. / Fuel 88 (2009) 1251–1260

temperature increased up to 450 �C. Liquid production increasedwith increasing pressure [10,11].

Autoclave copyrolysis of beech/atactic PP, pine/atactic PP andcellulose/atactic PP in ratios of 0/100, 20/80, 50/50, 80/20 and100/0 (w/w) at 400 �C produced higher heavy liquid fraction yieldsand lower amounts of water and gaseous as the plastic content inthe feed increased. The light liquid yield was highest at a wood/atac-tic PP 20:80 (w/w) ratios. Pyrolysis of atactic PP alone generatedmore gas phase olefins versus wood/atactic PP copyrolysis. Olefinicproducts derived from atactic PP reacted with wood depolymeriza-tion products or with wood char formed in the process [10,11].

The types of biomass and plastic used effect the copyrolysisproduct yields and product distributions. Copyrolyses of atacticPP with lignin, cellulose, beech wood or pine wood were conductedin 1:1 (w/w) ratios at 400 �C [10]. Lignin/aPP copyrolysis gave themost char and the least water and light liquid compared to theother three treatments. Cellulose produced the least char. Thebeech/atactic PP and pine/atactic PP copyrolyses produced similaramounts of char and gases. Beech/isotactic PP copyrolysis (1:1 w/w, 400 �C) produced more light liquid fraction than beech/PE, pre-sumably due to PE’s higher thermal stability [10].

The production of liquid increased and gas decreased withincreasing biomass/plastic feed ratios in 400–450 �C fast copyro-lyses under nitrogen in an autoclave [13–15]. In a related study,sugarcane bagasse was copyrolyzed (12 �C/min heating rate to500 �C) with petroleum residue (5%, 15%, 30% and 50%) for 1 h[16]. The organic liquid was a complex emulsion. Yields increasedand water content decreased with increasing petroleum residueconcentration [16].

Only a few very recent reports of the fast pyrolyses of biomasswith plastics have appeared [17–19]. Willow/polylactic acid flashcopyrolyses at an initial 600 �C temperature gave an upgradedbio-oil in improved yields [17]. Similar flash pyrolyses of willowwith polyhydroxybutyrate in various feed ratios generated en-hanced bio-oil yields and crotonic acid was readily separated [18].Finally, polypropylene copyrolyses in a fixed bed reactor at temper-atures from 450 to 600 �C under nitrogen were reported with sawdust, rice husks and corn cobs. The optimum pyrolysis temperaturewas 500–550 �C and fast heating rates were beneficial [19].

The objective of the research was reported here to produce up-graded bio-oil with lower oxygen and higher carbon and hydrogencontents by performing relatively fast, auger copyrolyses of plasticswith the woody biomass. In this auger reactor, feed is preheatedwithin a few seconds to 140 �C. Then, the temperature is furtherraised to �180–220 �C immediately before it enters the pyrolysiszone where it is exposed to the pyrolysis temperature (450 or525 �C). While the solid traverses the pyrolysis zone within 30 s,its rate of heating and the length of time within this zone that it gen-erates vapor and aerosol are unknown. The pyrolysis is ‘‘fast”, but itis not as fast as occurs in a fluidized-bed reactor. Vapors formed arerapidly cooled and condensed. The role of cross reaction productsbetween wood and its decomposition products with plastic decom-position products was sought. Because relatively fast heating ratesand low vapor residence times were employed, the role of crossreactions should be lower than that in slow autoclave pyrolyses.Therefore, wood and plastic mixtures were ‘‘auger-pyrolyzed” in apreviously described laboratory scale 1 kg/h auger-fed reactor [20].

2. Experimental

2.1. Materials

Southern yellow pine was copyrolyzed with commerciallyavailable (TDL Plastics Inc.) polystyrene (PS), polypropylene (PP)and high density polyethylene (HDPE).

2.2. Sample preparation

Pine wood chips (2–3 mm) were produced by chipping (Tho-mas-Wiley Laboratory Mill, Model 4) commercially available pinelumber which had been dried to about 15% moisture content. Chipswere dried to approximately 8 to 10% moisture content prior topyrolysis. The plastics were granulated (�2 mm). Each plasticwas mixed with pine chips in a 50:50 (w/w) ratio to give a totalof three wood/plastic feeds to use in the auger reactor for bio-oilproduction.

2.3. Equipment: copyrolysis in an auger reactor

A 1 kg/h auger-fed pyrolysis reactor, described previously [20],produced the required bio-oils. Pyrolysis occurs in a reactor tubeand vapor is rapidly expanded into a condenser train where it iscondensed to the bio-oil [20]. The initially formed vapor tempera-ture is within �30 �C of the set pyrolysis temperature (>400 �C) asthe vapor exits the reactor into a water-cooled first condenserwhere its temperature drops to �110 �C. A second condenser low-ers the temperature to 30–50 �C and a portion of the water in theexit gases is removed from the bottom of this condenser. Thus, thebio-oil finally collected from the condensers has a lower water con-tent than standard fast pyrolysis bio-oil. The water fraction re-moved contains a small amount of water soluble organiccompounds. Only a portion of water is removed in this second con-denser because none of the condensers are operating at full vapor/liquid equilibrium and because aerosol (fog-like) water continuedinto the third condenser. The non-condensable gases produced inthis process were collected in gas bags and analyzed using gaschromatography.

The preheating and pyrolysis zones, progress of the solid feedthrough the reactor and gas residence times in the pyrolysis zonehave been described [20]. The vapor residence time (<1.5 s) wasapproximated from the feed rate, the fraction of the feed convertedto vapor, the average molecular weight of the condensed products,gas analysis and the reactor dimensions.

The experimental volume of the gases at room temperature andthe approximate moles of product in the liquid fraction (obtainedby dividing the liquid fraction’s weight by the average molecularweight) and the moles of water condensed allow a reasonable esti-mate of the gas volume at the pyrolysis temperature to be madeusing the ideal gas law. Since, the reactor is continuously fed, theapproximate vapor volume produced per unit time in the knownreactor volume is determined. This volume defines how much timethe vapor can remain in the reactor. Using high end values of theaverage molecular weight in the liquid biases the estimated vaporresidence time in the reactor to a longer period. This gas residencetime is an approximation with an estimated +/� 25% uncertainty.The rate of temperature drop of the gas/aerosol leaving the reactorwithin the condenser was not established.

A pyrolysis temperature of 450 �C was selected based on anextensive pyrolysis-gas chromatography/mass spectrometry, Py-GC/MS study of the plastics, wood and wood/plastic mixtures[21,22] and the existing pyrolysis literature [10–12,23,24]. Theplastic and wood/plastic mixtures were fully pyrolyzed at 450 �Cwithin 10 s in Py-GC/MS studies, conducted at a heating rate of10 �C/ms, to give approximately optimum yields of liquid productsand lower char yields [4,21,22]. In the 400–500 �C range, the timerequired to complete the production of vapors differs as tempera-ture is increased. Lower temperatures require more time. Productdistributions differ as temperature changes. Analyzing all thesefeatures pointed toward forming highest yields of liquid productsin the vicinity of 450 �C (broadly 435–480 �C). Py-GC/MS studiesat both 10 �C/ms and 400 �C/s heating rates confirmed that reac-tion times of �10 s (>5 s) were required at 450 �C to allow plas-

P. Bhattacharya et al. / Fuel 88 (2009) 1251–1260 1253

tic/wood thermal decompositions to proceed to optimum liquidproduct and lower char yields. Larger solid char residues were ob-tained at shorter solid pyrolysis residence times (1 s and 5 s) in Py-GC/MS experiments. Repyrolyzing these residues generated furthervapor. Thus, the solid particles undergo pyrolytic decompositionover a time period that must be sufficient to permit all the vaporthat can be produced at a given pyrolysis temperature to form. Thisobservation can be compared to studies of bio-oil production fromwood in fluidized-bed reactors where longer solid residence timesincrease liquids production [3–7]. However, in fluidized beds, long-er vapor residence times decrease liquid yields.

When PP, HDPE or PS are present, sufficient time is required sothat polymer decomposition to vapors can provide high yields.When pyrolysing wood and plastics simultaneously, it is importantto recognize that the decomposition kinetics of the wood andplastics differ from each other at each temperature. Furthermore,in Py-GC/MS studies, we demonstrated from product analyses thatintimate wood/plastic mixtures pyrolyze largely like independentpyrolyses of the wood and plastics proceeding simultaneously[21,22]. Cross-over products between pyrolysis intermediates fromwood and those from plastics did not form in any significantamounts. The product distributions are almost entirely composedof products seen in independent pyrolyses of only wood and onlyplastics [21,22].

2.4. Bio-oil characterization

The pyrolysis oil produced from each pine/plastic copyrolysiswas stored in a closed glass bottle at 4–5 �C [25].

2.4.1. Gas chromatography/mass spectrometry (GC/MS)Each bio-oil sample was analyzed on a Hewlett Packard 5890

series II Gas chromatograph/5971 series A mass spectrometerThe injector temperature was 270 �C. A 30 m � 0.32 mm internaldiameter � 0.25 l film thickness silica capillary column coatedwith 5% phenylmethylpolysiloxane was used at an initial 40 �C(4 min hold) followed by heating at 5 �C/min to a final temperatureof 280 �C. The mass spectrometer employed a 70 eV electron im-pact ionization mode, a source (detector) temperature of 250 �Cand an interface temperature of 270 �C.

A 0.1 mg representative sample of each pyrolysate liquid wasdiluted with 10 ml of dichloromethane. Only 1 ml of this solutionwas then transferred to the autosampler vial and 10 ll of internalstandard (4000 lg/ml concentration) was added. Then 2.0 ll ofthis sample was injected into the GC to acquire the respectivechromatogram. Six isotopically labelled compounds (US 108N,Ultra Scientific) were employed as internal standards including:1,4-dichlorobenzene-d4, naphthalene-d8, acenapthene-d10, phen-anthrene-d10, chrysene-d12 and perylene-d12. Internal standardswere used to verify the retention times and quantitate the amountsof thirty known compounds from a previously published list [25].In addition, a series of saturated hydrocarbon standards (ASTMD2887 quantitative calibration solution) were employed to quanti-tate some of the alkanes produced during HDPE pyrolysis. Toluene,styrene, ethylbenzene and a-methylstyrene were quantitated inpyrolyses containing polystyrene using naphthalene-d8 as thestandard. The compounds quantitated versus internal standardswere expressed as weight percents of the total bio-oil.

2.4.2. Gas analysisGas samples from each wood/plastic copyrolysis treatment

were analyzed on an Agilent 6890 Gas Chromatograph. A1 m � 0.75 mm ID ShinCarbon ST 100/120 micropacked columnwas used. Sample and calibrant were introduced using a VICI SeriesA-2 gas syringe. Four-point calibrations were prepared using 25,

50, 75 and 100 lL injections of the calibrants. Sample aliquot vol-umes of 50 lL were injected into GC for analysis.

2.4.3. Gel permeation chromatography (GPC)GPC molecular weight calibration was performed with polysty-

rene standards (0.5 g/10 ml) with peak molecular weights of 2900,1990, 1200, 1050, 580 and 162 according to the method developedfor bio-oil by Johnson and Chum [26]. Each bio-oil sample (0.3 g)was dissolved in 50 ml of THF. A Waters 600 E System Controllerand a Waters 410 Differential Refractometer were used. A VarionPolymer Labs Plgel 3 lm, 100 Å, 300 � 7.5 mm packed columnwas used with 100% THF mobile phase at a 1 ml/min flow rate.

2.4.4. 13C and 1H NMR spectroscopy13C NMR analyses of the pine wood/PS, pine wood/PP and pine

wood/HDPE pyrolysate liquids were performed in DMSO-d6 on aVARIAN Mercury 400 MHz spectrometer by accumulating 105scans for each spectrum using a 90� pulse width and broad bandproton decoupling. The integrated 13C NMR spectrum was dividedinto different chemical shift regions corresponding to alkyl, meth-oxy, carbohydrate, aromatic, carboxylic acid and ketone/aldehydecarbons [27,28]. The integrated peaks were summed and the per-centage was calculated according to the functional group typesusing a process developed at the National Renewable Energy Lab-oratory (NREL) [27,28].

1H NMR spectra of each pine wood/plastic pyrolysate liquidwere obtained on a Bruker AMX-600-A 600 MHz spectrometer.The integrated spectra were divided into different chemical shiftregions corresponding to hydrogens on different functions usingthe NREL protocol [27,28].

2.4.5. Elemental analysisElemental analyses for carbon, hydrogen, nitrogen and oxygen

and pyrolysate liquid heating values were determined by GalbraithLaboratories, inc., Knoxville, TN.

2.4.6. Physical analysisThe percent water, viscosity, density, pH and acid value of each

pyrolysate liquid were determined. Percent water was measuredby Karl Fisher titration with a Cole-Parmer Model C-25800-10titration apparatus. A 200 5B viscometer (Stony Brook Scientific)measured the viscosity and the pH was acquired with an expandedion analyzer EA 920 on 1 g of pyrolysate mixed with 50 ml ofwater. Density was calculated according to ASTM standard D4052. The acid value was determined by titrating 1 g of pyrolysatesamples dissolved in 50/50 v/v isopropanol/water and then titratedwith 0.1 N NaOH to a pH 8.5. At pH 8.5 over 99.9% of the carboxylicacids (formic, acetic, propanoic, oleic) are titrated. Less than 4% ofphenols (pKa of 9.89 or higher) are converted to phenoxides. Thepredominant phenolics in bio-oil are less acidic (methylated andmethoxylated phenols) and have pKa values greater than 9.89,decreasing the extent of over titration. A pH of 8.5 is in the rangewhere the clear color to red change of phenolphthalein begins tooccur during strong base titration.

3. Results and discussion

3.1. Pyrolysis temperature

Pyrolysis at 450 �C produced good quality liquid products fromthe 50/50 w/w PP/pine and HDPE/pine copyrolyses. However, at450 �C in PS/pine copyrolysis, a large amount of a sticky viscousoligomeric hydrocarbon was found coating the char whichemerged from the reactor. Incomplete chain scission of PS occurred(in the time available) to give these oily nonvaporized char


coatings, accounting for this behavior. A temperature above 450 �Cwas required to further fracture the PS to smaller fragments suchthat condensation did not occur prior to the condensers. At 475 �Cviscous liquid coatings still appeared on the char. At 525 �C, thePS pyrolyzed without generating the char coating. At this temper-ature, wood pyrolysis products will differ from those produced at450 �C. Thus, the 50/50 pine/PP and pine/HDPE mixtures were alsopyrolyzed at 525 �C for comparison. The gas yields were muchhigher and liquid bio-oil yield was much lower in these cases.Therefore, 450 �C temperature was selected for the PP and HDPEand 525 �C for PS in these copyrolyses.

3.2. Product yields

Table 1 summarizes the copyrolyses liquid, char and gas (by dif-ference) yields. The pine/PS liquid yield produced at 525 �C was64.9%. This liquid yield was much higher than those from pine/HDPE (Y = �38.9%) and pine/PP (Y = �46%). The liquid yield forpine only pyrolysis at 450 �C was 50% (14.9% lower than pine/PS(at 525 �C) and 4% and 11.1% above than those of pine/PP andpine/HDPE (at 450 �C), respectively. Copyrolysis at 525 �C gavehigher liquid product yields from a 50/50 pine/PS feed. This repre-sents a trade off in some further pine conversion to gas while PS toliquid conversion increases. In contrast, a 450 �C temperature wasnearly optimized for liquid yields in pine/polyolefin (PP or HDPE)copyrolyses. Pine/PP and pine/HDPE copyrolyses at 525 �C causedconsiderable gasification to occur with substantial loss of liquidyield. At 450 �C, HDPE and PP fragmentation occured to generateproducts which were sufficiently volatile to prevent prematurecondensation on the char, but enough of these products were con-densable to produce reasonable liquid yields.

The char yields of all wood/plastic copyrolyses at both 450 and525 �C temperatures were summarized in Table 1. The char yieldsat 525 �C were 12.1% for pine/PS, 11.9% for pine/HDPE and 24.1%for pine/PP. At 450 �C, higher char yields were obtained: 25.9%for pine wood/HDPE and 32.2% for pine wood/PP as compared to19% for pine wood (at 450 �C) pyrolyzed alone. The gas yields were23%, 35.2% and 21.8%, respectively for pine/PS (at 525 �C), pine/HDPE and pine/PP (at 450 �C). Pine/HDPE and pine/PP gave muchhigher gas yields (79% and 48.5%, respectively) at 525 �C. Thehighest gas-flow rate at 450 �C was observed for pine/HDPE, thecopyrolysis which had lowest liquid yield. The total volumes ofthe non-condensable gases evolved from the PS/pine (measuredat 525 �C), HDPE/pine (at 450 �C) and PP/pine (at 450 �C) copyro-lyses were 0.034, 0.024 and 0.011 m3, respectively when theamounts of feedstocks processed were 240.5, 228 and 221 g,respectively. These non-condensable gases were mixtures of CO,CH4, CO2, ethane, propane and other hydrocarbons. The gas compo-sition was determined in each case by GC (see Section 2.4.2). Thus,the moles of non-condensable gas evolved per gram of the 1:1plastic/wood mixture pyrolyzed were 0.0063 (PS/pine), 0.0046(HDPE/pine) and 0.0022 (PP/pine).

Table 1Liquid, char and gas yields (wt%) produced from the copyrolyses of pine/PS 50:50 (wt/wt)

Sample ID Temperature (�C) Liquid y

PS/Pine 450b –50:50 (wt/wt) 525 64.9HDPE/Pine 450 38.950:50 (wt/wt) 525 9.1PP/Pine 450 4650:50 (wt/wt) 525 27.4Pine wood 450 50.1

Augur rotation rate was 12 rpm.a Calculated from: wt of feed � (wt of liquid + wt of char).b The yields were not reported since a PS sticky tar-like material coated the char and

3.3. Gas chromatography/mass spectrometry (GC/MS) study of the bio-oil

The GC/MS analysis of the liquid fraction from the PS/pine,HDPE/pine and PP/pine 50:50 (w/w) copyrolysis mixtures gaveproduct abundances based on GC area% and overall weight%. Theseare listed in Tables 2–4. By far the most abundant product in PS/pine copyrolysis was styrene (Table 2). Styrene constituted 30.2%of the total GC area% and, on quantitation versus naphthalene-d8,this represents 12.7 wt% of the bio-oil. Other major products in-cluded ethylbenzene, alpha-methylstyrene, naphthalene, andphenanthrene and 2-phenylnapthalene. All of these were producedfrom the PS pyrolysis as previously shown in the py-GC/MS resultsof 100% PS pyrolyses [22]. The presence of ethylbenzene indicatedthat some styrene hydrogenation occurred during decomposition.PS/pine 50/50 (w/w) copyrolyses also produced well known cellu-lose, hemicellulose and lignin thermal decomposition productsincluding furfural, 2-hydroxymethylfuran, 2-hydroxy-2-cyclopen-ten-1-one, phenol, 2-methylphenol, and 3-methylphenol, 2-methoxyphenol, 2,4-dimethylphenol, eugenol, cis-isoeugenol,trans-isoeugenol, levoglucosan and others. Identification of thesecompounds in bio-oil samples was based on comparison of boththe retention times and mass spectra of each compound withauthentic standards. All identified products have previously beenobserved in the individual pyrolyses of pine wood or PS. Thus, crossreactions between pine wood and polystyrene decompositionproducts did not play a significant role in the pyrolyses.

The most abundant products from HDPE/pine 50:50 (w/w)pyrolysis are listed in Table 3. These include 1-hydroxy-2-propa-none, isopropyl acetate, furfural, 2-hydroxy-2-cyclopenten-1-one,phenol, 2- and 4-methylphenols, 2-methoxyphenol, eugenol, cate-chol and other phenolic compounds, from the pine thermal decom-position. Some relatively long chain hydrocarbons, e.g., 1-undecne,dodecane, 1-tridecene, 1-tetradecene, tetradecane, 1-pentadecene,pentadecane, 1-hexadecene, hexadecane, heptadecane, nonade-cane and others formed from HDPE’s thermal decomposition.Again, no cross reaction products were identified. All the ob-served/identified products have previously been observed in eitherpine wood or HDPE individual pyrolyses.

Table 4 summarizes key products from PP/pine copyrolysis.These products include furfural, 2-furanmethanol, 2-methoxy-2-cyclopenten-1-one, 5-methyl-2-furancarboxaldehyde, 2-heptenal,3-buten-1-ol, phenol, 3-methylphenol, 4-methylphenol, 2-methoxyphenol, 2,4-dimethylphenol, 2,3-dimethylphenol andother phenolic derivatives, catechol, eugenol and oleic acid, all ofwhich were derived from pine decomposition. Products arisingfrom PP degradation included 2,2-dimethyl-3-octene, 2,4-dimeth-ylheptane, 5-methyl-1,6-heptadien-3-yne, 4-methyl-2,7-octadi-ene, cyclodecene, cyclododecane, and some other alkanes,alkenes, alkynes. No obvious cross-over products due to reactionbetween PP and pine decomposition products reacting with eachother were identified.

at 525 �C, pine/HDPE 50:50 (wt/wt), pine/PP 50:50 (wt/wt) and pine wood at 450 �C.

ield (%) Char yield (%) Gas yielda (%)

– –12.1 2325.9 35.211.9 7932.2 21.824.1 48.519.1 30.8

a significant fraction of the PS was not vaporized efficiently in the reactor.

Table 2Identification of selected products and amounts (GC area% and overall wt%) in the liquid fraction formed from the copyrolysis of pine and PS 50:50 (wt/wt) ratio at 525 �C andcompared with the pure pine bio-oil at 450 �C.

RT (min) Identified products Pine/PS 50:50 Pine

Areaa (%) Wt (%) Areaa (%) Wt (%)

1.76 1-Hydroxy-2-propanone 0.21 2.652.33 Isopropylacetate 0.02 0.682.67 Toluene 1.99 0.95 04.31 Furfural 0.2 0.01 0.88 0.094.86 2-Furanmethanol 0.2 0.01 2.3 0.165.04 Ethylbenzene 2.29 0.67 06.08 Styrene 30.19 12.72 06.42 2-Methyl-2-cyclopenten-1-one 0.34 0.04 0.31 0.076.7 2-(5H)-Furanone 0.53 0.22 0.78 0.57.17 2-Hydroxy-2-cyclopenten-1-one 0.11 1.528.36 5-Methyl-2-furancarboxaldehyde 0.1 0.05 0.28 0.048.39 3-Methyl-2-cyclopenten-1-one 0.1 0.05 1.56 0.479.01 a-Methylstyrene 3.26 1.02 09.29 Phenol 0.51 0.19 2.64 0.57

10.42 3-Methyl-1,2-cyclopentendione 0.43 0.22 1.23 0.4711.61 2-Methylphenol 0.23 0.12 1.62 0.2512.31 3-Methylphenol 0.33 0.22 3.03 0.4912.53 2-Methoxyphenol 0.24 0.17 1.52 0.1913.03 2,6-Dimethylphenol 0.03 0.02 0.12 0.0214.51 2,4-Dimethylphenol 0.63 0.13 2.02 0.2215.13 3-Ethylphenol 0.08 0.05 0.51 0.0915.28 2,3-Dimethylphenol 0.19 0.01 2.02 0.0315.32 Napthalene 3.02 1.32 2.67 0.0615.74 2-Methoxy-4-methylphenol 0.56 0.31 2.74 0.3116.14 1,2-Benzenediol (Catechol) 0.29 0.32 4.3 1.2916.81 5-(Hydroxymethylfurfural) 0.41 0.38 1.06 0.2118.21 4-Ethyl-2-methoxyphenol 0.33 0.1 1.06 0.0818.69 3-Methyl-1,2-benzenediol(3-methylcatechol) 0.36 0.29 1.38 0.8518.8 4-Methyl-1,2-benzenediol 0.28 0.13 4.15 0.3219.14 2-Methoxy-4-vinylphenol 0.39 1.5120.38 Eugenol 0.3 0.11 1.64 0.1120.55 2-Methoxy-4-propylphenol 0.03 0.03 0.0321.45 Vanillin 0.08 0.05 1.11 0.121.62 cis-Isoeugenol 0.12 0.61 0.89 0.621.78 3,4-Dimethylbenzoic acid 0.05 0.04 0.11 0.0422.68 trans-Isoeugenol 3.15 2.73 2.68 2.1423.53 Levoglucosan 0.36 0.05 12.7 0.4123.64 Acetovanillone 0.08 0.06 1.65 0.0824.43 Benzene, 1,10-(1,2-ethanediyl)bis- 1.94 030.22 Phenanthrene 2.49 034.11 2-Phenylnapthalene 2.85 037.4 Oleic acid 1.21 0.55 1.09 0.36

a These numbers give the area under each product peak divided by the sum of areas under all the product peaks (times 100 to express the number in percent).


3.4. Gas analysis

Table 5 gives the amounts of carbon monoxide (CO), carbondioxide (CO2) and methane (CH4) identified from the gaseous frac-tions of these copyrolyses. The other gases, such as ethane, ethene,propane, propene, butane, butene which generally evolve from theplastic thermal decomposition, were not individually quantified.CO and CH4 arising from the PS/pine copyrolysis (525 �C) consti-tuted 26.8 and 14.8 mol% of the total gases evolved, respectively.CO and CH4 evolved in much higher amounts in PS/pine copyroly-sis (26.8 and 14.8 mol%) than occurred from HDPE/pine and PP/pine copyrolyses (3.33, 0.44, and 9.39, 0.51 mol%, respectively).These higher CO and CH4 levels from PS/pine could be a conse-quence of the higher (525 �C) temperature employed in thatpyrolysis.

3.5. Gel permeation chromatography analysis

Gel permeation chromatography (also called size exclusionchromatography) was employed to determine the molecularweight distributions of the liquid fractions from the wood/plasticcopyrolyses (PS/pine at 525 �C, HDPE/pine and PP/pine both at

450 �C). A refractive index (RI) detector was used. The molecularweight distributions of these bio-oils are listed in Table 6. The aver-aged molecular weights (Mw) of the PS/pine, HDPE/pine and PP/pine liquids were 330, 330 and 370, respectively. These valuesare all lower than the Mw of 420 of the pine bio-oil prepared at450 �C in our laboratory [25]. Williams reported Mw values for purePS, HDPE and PP pyrolysis oils produced at 700 �C of 145, 240 and241, respectively [29]. The plastic-derived liquid products, pro-duced in our wood/plastic copyrolyses, should have higher averagemolecular weights than those reported by Williams since we usedlower pyrolysis temperatures. Nevertheless, incorporation of theplastics’ pyrolysis liquids lowered the overall molecular weightdistributions in the resulting oils. The number averaged molecularweights (Mn) of all three different plastic/pine pyrolysis oils wereabout 180. The polydispersities (Mw/Mn) of PS/pine, HDPE/pineand PP/pine oils were 1.83, 1.83 and 2.05, respectively. GPC analy-ses of pine wood/PS bio-oil exhibited bimodal peaks.

3.6. 13C and 1H NMR analysis

Table 7 summarizes the integrated 13C nuclear magnetic reso-nance (NMR) spectra of three copyrolysis oils (PS/pine at 525 �C,

Table 3Identification and amounts (GC area% and the overall wt%) of selected products in the liquid fraction formed by copyrolysis of pine and HDPE 50:50 (wt/wt) ratio at 450 �C andcompared with pure pine bio-oil at 450 �C.

RT (min) Identified products Pine/HDPE 50:50 Pine


1.76 1-Hydroxy-2-propanone 1.96 2.652.11 Formic acid, 1-methylethyl ester 0.37 02.33 Isopropylacetate 0.61 0.684.21 Furfural 0.59 0.04 0.88 0.094.86 2-Furanmethanol 0.15 0.11 2.3 0.166.42 2-Methyl-2-cyclopenten-1-one 0.09 0.07 0.31 0.076.7 2-(5H)-Furanone 0.90 0.42 0.78 0.57.17 2-Hydroxy-2-cyclopenten-1-one 0.92 1.528.36 5-Methyl-2-furancarboxaldehyde 0.31 0.08 0.28 0.048.39 3-Methyl-2-cyclopenten-1-one 0.58 0.09 1.56 0.479.29 Phenol 1.57 0.46 2.64 0.57

10.6 3-Methyl-1,2-cyclopentanedione 1.06 0.38 1.23 0.4711.65 2-Methylphenol 0.48 0.21 1.62 0.2512.36 3-Methylphenol 1.22 0.38 3.03 0.4912.5 2-Methoxyphenol 0.92 0.22 1.52 0.1912.65 1-Undecene 1.6 013.03 2,6-Dimethylphenol 0.13 0.02 0.12 0.0214.52 2,4-Dimethylphenol 1.06 0.17 2.02 0.2215.13 3-Ethylphenol 0.36 0.06 0.51 0.0915.28 2,3-Dimethylphenol 0.07 0.02 2.02 0.0315.3 Napthalene 1.6 0.24 2.67 0.0615.71 2-Methoxy-4-methylphenol 2.99 0.33 2.74 0.3115.97 Dodecane 0.45 0.26 016.28 1,2-Benzenediol (Catechol) 1.63 1.36 4.3 1.2916.84 5-(Hydroxymethylfurfural) 0.31 1.06 0.2117.14 3,4,5-Trimethylphenol 0.35 018.17 4-Ethyl-2-methoxyphenol 0.82 0.09 1.06 0.0818.59 1-Tridecene 1.57 018.7 3-Methyl-1,2-benzenediol 2.37 0.92 1.38 0.8518.8 4-Methyl-1,2-benzenediol 2.48 0.31 4.15 0.3219.14 2-Methoxy-4-vinylphenol 1.17 1.5120.32 Eugenol 0.62 0.11 1.64 0.1120.55 2-Methoxy-4-propylphenol 0.18 0.02 0.0321.28 1-Tetradecene 2.49 021.45 Vanillin 1.02 0.14 1.11 0.121.48 Tetradecane 0.93 0.54 021.64 cis-Isoeugenol 0.33 0.57 0.89 0.621.83 3,4-Dimethylbenzoic acid 0.07 0.04 0.11 0.0422.68 trans-Isoeugenol 2.13 2.36 2.68 2.1422.71 2-Methoxy-4-(1-propenyl)phenol 2.49 3.1123.81 1-Pentadecene 2.04 023.53 Levoglucosan 0.98 1.29 12.7 0.4123.64 Acetovanillone 0.61 0.11 1.65 0.0824 Pentadecane 0.46 0.19 024.73 1-(4-Hydroxy-3-methoxy)-2-propanone 4.77 026.2 1-Hexadecene 1.86 026.38 Hexadecane 0.62 0.33 028.46 1-Nonadecene 1.69 028.62 Heptadecane 0.56 0.16 030.76 2-Methyldodecane 0.71 032.67 1-Nonadecene 1.66 032.79 Nonadecane 0.51 037.45 Oleic acid 0.94 0.32 1.09 0.3641.72 Tetracosane 0.44 0.14 0



HDPE/pine at 450 �C and PP/pine at 450 �C) and that of pine bio-oil(at 450 �C). These spectra demonstrate that plastic/pine copyroly-sis oils contain higher aromatic contents than the pine bio-oil.However, the amounts of carboxylic acids, carbohydrates andmethoxy/hydroxy compounds are significantly lower than in all-pine bio-oil. The integrated 13C NMR spectra of these liquidsindicate that plastic/pine pyrolysis oils contain substantially lessoxygen content than pure pine bio-oil. The NMR spectra weredivided into several chemical shift regions that reflect differenttypes of hydrogens and carbons present in these complex mixturesof compounds. These NMR chemical shift regions, shown in Tables7 and 8, follow the standard protocol that was developed at theNational Renewable Energy Laboratory [27,28].

Table 8 summarizes the integrated 1H NMR spectra of the samethree plastic/pine oils and pine bio-oil. Aliphatic protons are foundin the chemical shift regions of 0–1.6 ppm and 1.6–2.2 ppm. Aliphatic–OH groups can also occur in this 1.6–2.2 ppm region. The tableshows that fewer aliphatic –OH protons are present in each plastic/pine copyrolysis oil compared to the pine bio-oil. Similarly, the –OCH3, –CHO, and –CH2O protons, which are found in chemical shiftregion of 3.0–4.2 ppm, are also less abundant in the plastic/pine oilsversus to the all-pine bio-oil. This result concurs with the 13C NMRspectra. The nonconjugated HC@C– protons are observed from 6.4–6.8 ppm and most of the aromatic protons appear from 6.8 to8.0 ppm. More aromatic protons and less nonconjugated olefinic pro-tons are present in the plastic/pine copyrolysis oils than in the pine

Table 4Identification and amounts (GC area% and overall wt%) of selected products in the liquid fraction formed from the copyrolysis of pine and PP 50:50 (wt/wt) ratio at 450 �C andcompared with pure pine bio-oil at 450 �C.

RT (min) Identified products Pine/PP 50:50 Pine


1.76 3-Butene-1-ol 0.58 02.33 Isopropylacetate 0.03 0.684.2 (E)-2-Heptenal 1.62 04.21 Furfural 0.43 0.01 0.88 0.095.04 2-Furanmethanol 0.07 0.03 2.3 0.166.38 2-Methyl-2-Cyclopenten-1-one 0.4 0.04 0.8 0.076.71 2-(5H)-Furanone 0.05 0.76 2.32 0.57.17 2-Hydroxy-2-cyclopenten-1-one 0.06 1.528.23 5-Methyl-2-furancarboxaldehyde 0.37 0.11 0.28 0.048.34 3-Methyl-2-cyclopenten-1-one 0.03 0.05 1.56 0.479.22 Phenol 0.07 0.08 2.64 0.57

10.6 3-Methyl-1,2-cyclopentanedione 0.20 0.09 1.23 0.4711.52 2-Methylphenol 0.09 0.33 1.62 0.2512.21 3,7-Dimethyl-6-octene-1-ol 0.55 012.36 3-Methylphenol 0.23 0.1 3.03 0.4912.47 2-Methoxyphenol 0.22 0.07 1.52 0.1912.87 2,6-Dimethylphenol 0.8 0.01 0.12 0.0214.44 2,4-Dimethylphenol 0.36 0.02 2.02 0.2215.06 3-Ethylphenol 0.87 0.01 0.51 0.0915.3 Napthalene 0.15 2.67 0.0615.22 2,3-Dimethylphenol 0.11 0.02 2.02 0.0315.71 2-Methoxy-4-methylphenol 0.37 2.74 0.3115.93 1,2-Benzenediol (Catechol) 0.42 0.12 4.3 1.2916.77 5-(Hydroxymethyl)furfural 0.15 0.22 1.06 0.2117.75 4-Methyl-1,2-benzenediol 0.19 0.07 4.15 0.3218.11 1,5-Hexadiyne 0.43 018.17 4-Ethyl-2-methoxyphenol 0.07 1.06 0.0818.58 3-Methyl-1,2-benzenediol 0.19 0.29 1.38 0.8518.97 2,2-Dimethyl-3-octene 1.41 019.14 2-Methoxy-4-vinylphenol 0.23 1.5120.19 2,4-Dimethylheptane 0.25 020.4 Eugenol 0.21 0.12 1.64 0.1120.58 2-Methoxy-4-propylphenol 0.30 0.16 0.0320.85 1-Methyl-cycloundecene 0.58 021.38 Vanillin 0.22 1.06 1.11 0.121.68 cis-Isoeugenol 0.45 3.54 0.89 0.621.85 3,4-Dimethylbenzoic acid 0.23 0.1 0.11 0.0422.69 trans-Isoeugenol 0.96 1.84 2.68 2.1422.69 5-Methyl-1,6-heptadien-3-yne 1.25 022.71 2-Methoxy-4-(1-propenyl)phenol 0.33 3.1123.62 Levoglucosan 0.23 0.77 12.7 0.4123.66 Acetovanillone 0.15 0.27 1.65 0.0823.79 4-Methyl-2,7-octadiene 1.46 037.45 Oleic acid 0.46 0.31 1.09 0.36


Table 5Partial gas analyses of Pine/PS, Pine/HDPE, Pine/PP copyrolysis gases and pine woodpyrolysis gases.

Sample ID Pyrolysis Temperature (�C) COa CH4a CO2

a

Pine and PS 450 – – –50:50 (w/w) 525 26.8 14.8 3.7Pine and HDPE 450 3.33 0.44 4.0350:50 (w/w) 525 5.3 3.1 2.5Pine and PP 450 9.39 0.51 11.450:50 (w/w) 525 6.9 4.0 3.9Pine wood 450 27.6 10.0 16.4

a Mol% in the gas phase.


bio-oil. Furthermore, the aromatic content is far higher in PS/pine oilsthan the others. This is expected since every PS monomer unit has aphenyl ring. 13C NMR spectra exhibited the same results.

3.7. Elemental analysis and heating values

Table 9 summarizes the elemental analyses of the plastic/pineand pine pyrolysis oils. The carbon content of PS/pine (66.3%),

HDPE/pine (74.4%) and PP/pine (79.7%) are each far greater thanthat of pine bio-oil (57.2%). Conversely, pine bio-oil has far moreoxygen in its organic compounds (32.2%) even after accountingfor the removal of all the water that is produced during the pyro-lysis of wood (20–40%). The HDPE/pine and PP/pine pyrolysis oilscontain 16.3 and 9.5% oxygen, respectively, giving them signifi-cantly higher energy for use as fuels than pine bio-oil. The PS/pinepyrolysis oil has more oxygen (27%), a possible consequence of itsproduction at 525 �C (versus 450 �C for the other oils). Copyrolyz-ing all three plastics, which are composed of only carbon andhydrogen, with wood produces oils with more carbon and lessoxygen.

The carbon, hydrogen and oxygen contents and liquid yields ofthe copyrolysis oils depend on the pyrolysis temperature. The onlysource of the oxygenated compounds in these oils is from the com-ponents of pine wood and its free moisture content in the feed. Abalance exists between the liquid yields and the oxygen contentof the liquids produced. Each plastic/wood feed ratio will give oilswith different C, H, O contents and heating values at each specifictemperature/time pyrolysis condition. The higher hydrogen con-tents of the HDPE/pine and PP/pine oils (9.1% and 10.6%) reflect

Table 6Molecular weight analyses by gel permeation chromatography (GPC) of pine/plastic copyrolysis oils and pine bio-oil.

RI detector Pyrolysis temperature

Pine:PS 50:50 (w/w)(Daltons)

Pine:HDPE 50:50 (w/w)(Daltons)

Pine:PP 50:50 (w/w)(Daltons)

Pine(Daltons)

525 �C 450 �C 525 �C 450 �C 525 �C 450 �C

Number average molecular weight(Mn)

180 180 230 180 270 330

Weight average molecular weight(Mw)

330 330 500 370 510 420

Polydispersity index (Mw/Mn) 1.83 1.83 2.17 2.05 1.89 1.27

Table 713C NMR integrations and general structure assignments for the pine/plastic copyrolysis liquids and pine bio-oil.

Chemical shift regionintegrated (ppm)

Type ofcarbon

Carbon content (integrated area% of all carbons)a

Pine:PS bio-oil 50:50 w/wproduced at 525 �C

Pine:HDPE bio-oil 50:50 w/wproduced at 450 �C

Pine:PP bio-oil 50:50 w/wproduced at 450 �C

Pine bio-oilproduced at 450 �C

1–54 Alkyl carbons 15.1 17.0 23.6 22.354–84 Methoxy/

hydroxy13.2 14.9 10.0 21.2

84–110 Carbohydrate 2.6 1.5 0.4 8.1110–163 Aromatic 62.6 48.9 58.2 38.5163–192 Carboxylic

acids3.5 2.1 3.9 6.3

192–215 Ketones/aldehydes

2.8 2.1 3.8 3.1

a Spectra were obtained at 25 �C in DMSO-d6 on a VARIAN Mercury 400 MHz spectrometer.

Table 81H NMR integrations of pine/plastic copyrolysis liquids and pine bio-oila.

Chemical shiftregion (ppm)

Type of protons Hydrogen content (integrated area % of all hydrogens)

Pine:PS bio-oil 50:50 w/wproduced at 525 �C

Pine:HDPE bio-oil 50:50 w/wproduced at 450 �C

Pine:PP bio-oil 50:50 w/wproduced at 450 �C

Pine bio-oilproduced at 450 �C

10.0–8.0 –CHO, –COOH,downfield ArH

7.7 8.1 10.4 2.6

8.0–6.8 ArH, HC@C–(conjugated)

39.8 6.5 9.0 4.4

6.8–6.4 HC@C– (nonconjugated) 1.9 4.2 3.6 5.36.4–4.2 –CHO, ArOH, HC@C–

(nonconjugated)10.7 20.3 26.2 16.5

4.2–3 CH3O–, –CHO, –CH2O– 3.1 28.3 25.5 37.63–2.2 CH3C@O, CH3Ar, –CH2Ar 8.1 6.3 4.8 9.02.2–1.6 –CH2–, Aliphatic OH 5.8 10.8 8.6 13.71.6–0 –CH3, –CH2– 22.9 15.4 11.8 10.9

a Spectra were obtained at 25 �C in DMSO-d6 on a VARIAN Mercury 400 MHz spectrometer.

Table 9Elemental analyses and heat of combustion values for pine/PS, pine/HDPE and pine/PP pyrolysis oils.

Pyrolysate liquid C (%) H (%) N (%) S (%) O (%) H2O (%) Heat of combustion (Btu/lb) (MJ/kg)

Pine:PS a 50:50 w/w produced at 525 �C 66.27 6.72 <0.5 <0.08 7.02 9.47 12217 (28.42)Pine:HDPEa50:50 w/w produced at 450 �C 74.38 9.11 <0.5 <0.005 6.33 10.65 11902 (27.68)Pine:PPa 50:50 w/w produced at 450 �C 79.7 10.64 <0.5 <0.05 9.5 5.44 15885 (36.94)Pine wooda produced at 450 �C 57.2 7.0 <0.09 <0.05 32.2 13 10800 (25.12)

a Elemental analysis on dry basis. The hydrogen and oxygen of water is not included here.


the higher percentage of hydrogen in the HDPE and PP versus thatin the wood. However, PS has a lower hydrogen weight percentthan HDPE and PP, accounting for the lower hydrogen content inthe PS/pine oil (6.7%). The heats of combustion of PS/pine, HDPE/pine and PP/pine oils were 12,217, 11,902, and 15,885 Btu/lb(28.42, 27.68 and 36.94 MJ/kg), respectively, compared to10,800 Btu/lb (25.12 MJ/kg) for the pine bio-oil. This value for pinebio-oil is higher than the range mentioned in the introduction(6450–8170 Btu/lb)3, because only 13% water was present. Thispine bio-oil was condensed in a condenser train attached to thereactor exit that was used to remove a portion of its water content.

3.8. Physical properties: water content, pH, acid value, density andviscosity

Table 10 summarizes the water content, pH value, acid value,density and viscosity for each of the four pyrolysis oils. The watercontent of PP/pine oil is 5.44% which is significantly lower than the10.65 and 9.47% water in HDPE/pine and PS/pine copyrolysis oils.The pine bio-oil had �13% water content as obtained from the con-denser system.

The pH values of all four bio-oils are similar but the acid valuesof the pine bio-oil is far higher (82.0) than that of PS/pine (30.6),

Table 10Comparison of percent water, pH, acid value, density and viscosity of pine wood/plastic copyrolysis oil and pine bio-oil.

Pyrolysate Liquid Water (%) pH Acid Value Density (g/ml) Viscosity (cSt)

Pine:PS 50:50 (wt/wt) produced at 525 �C 9.47 2.82 30.62 0.98 28.94Pine:HDPE 50:50 (wt/wt) produced at 450 �C 10.65 3.21 48.6 1.24 N.Oa

Pine:PP 50:50 (wt/wt) produced at 450 �C 5.44 3.02 38.12 1.09 23.6Pine wood produced at 450 �C 13 3.1 82.0 1.19 80.7

N.O.: not obtained.a Viscosities were not obtained because of the heterogeneous nature of the oil.


HDPE/pine (48.6) or PP/pine (38.1). The acid values reflect mainlythe presence of carboxylic acids, such as formic, acetic and propa-noic acids, generated due to cellulose and hemicellulose pyrolyticdegradation. Thus, higher wood content in the feed is expectedto give higher acid values.

3.9. Summary

Bio-oil produced from woody biomass can be unstable duringstorage, is corrosive due to organic acid content, has high densityand exhibits low heat content relative to petroleum fuels. Highoxygen contents of its organic components are responsible forthese undesirable properties. Copyrolyses at 450 and 525 �C ofPS, HDPE or PP with southern yellow pine wood in an auger-fed,2 kg/h reactor produced oils with lower oxygen contents, higherheating values, lower acid values, lower water contents, and lowerdensities. These copyrolysis oils are upgraded relative to bio-oilsproduced by a 100% pine wood feed because liquid componentsderived from the plastics are now present. These components con-tain only carbon and hydrogen, thereby raising the heating value.PS, HDPE and PP were each simultaneously pyrolyzed with pinewood in 50:50 wt ratios at temperatures of 450 and 525 �C. Thejoint condensation of the pine bio-oil components with the morehydrophobic hydrocarbon components of the plastics’ thermaldegradation allows a portion of the water to be removed in a con-denser train in series with the reactor. This together with the in-crease in percent C and H, due to the presence of the plastics’pyrolysis products, increases the heating value of the product oil.

These simultaneous pine/plastic pyrolyses did not producenoticeable cross reaction products between the pine and plasticsor their decomposition products. The individual wood and plasticpyrolytic decompositions occur mostly independent of one anotherin the auger reactor since the vapors formed have a short residencetime in the reaction zone. The major complication is the differenttime periods required for wood versus plastics to generate vaporphase products which can escape the reaction zone quickly. Plas-tics may require higher pyrolysis temperatures than wood toachieve high liquid product generation. Also, plastics do not under-go steam explosion-like disruption of the particles in the hot zonesince they contain no water. This difference contributes to howheat transfer rates differ within these two feed components. Whilepyrolysis is ‘‘fast” the heating rate is not as fast as in a fluidizedbed. Finally, the thermal decomposition activation energies of thewood and plastic components differ. Such factors cause the timesto differ for chemical degradation and vaporization of the woodand plastic feed components to proceed in high yields. If bothwood and plastic particles of the same mass were instantaneouslyheated to 450 �C, the time to complete the pyrolysis of these twodifferent substances would still differ. This difference may be exac-erbated because heating in the auger reactor is not instantaneous.Feed particle heating occurs over a short but finite (and not welldefined) time. Thus, heating rates and solid residence times inreactors will need to be carefully considered for each wood/plasticcomposition.

One benefit of simultaneous wood/plastic pyrolysis was theability to avoid molten plastic particle agglomeration into larger

mass aggregates which then can cause a variety of processingproblems. This problem may occur in auger reactor pyrolyses in400 to �530 �C temperature range when thermal degradation ratesto vapors are not fast enough to avoid melt aggregation. Theseproblems are a function of heat transfer rate and particle size.Blending wood and plastic particles increases the ease of process-ing in this temperature range, probably due to particle mixing andthe steam explosion-like degradation of wood, both of which re-duce the melt aggregation of plastics. Thus, wood/plastic copyrol-ysis in an auger reactor environment offers process flexibilityversus the pyrolysis of plastics alone.

Acknowledgement

This material is based upon work performed through the Sus-tainable Energy Research Center at Mississippi State Universityand is supported by the Department of Energy under Award Num-ber DE-FG3606GO86025.

Disclaimer: This report was prepared as an account of worksponsored by an agency of the United States Government. Neitherthe United States Government nor any agency thereof, nor any oftheir employees, makes any warranty, express or implied, or as-sumes any legal liability or responsibility for the accuracy, com-pleteness, or usefulness of any information, apparatus, product,or process disclosed, or represents that its use would not infringeprivately owned rights. Reference herein to any specific commer-cial product, process, or service by trade name, trademark, manu-facturer, or otherwise does not necessarily constitute or imply itsendorsement, recommendation, or favoring by the United StatesGovernment or any agency thereof. The views and opinions ofauthors expressed herein do not necessarily state or reflect thoseof the United States Government or any agency thereof.

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wood/plastic copyrolysis in an auger reactor: chemical and physical analysis of the products

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