Energy & Fuels 1991,5,427-436
stabilizing the C2HSO2radical. When air is used instead of oxygen in the reaction the nitrogen acta as a diluent, resulting in a lower conversion of the ethane. If recycling is to be effected under such conditions the unreacted ethane in the product must be separated from the nitrogen. This can be readily done by cooling the exit gas. The savings realized by not having to use pure oxygen may more than pay for the extra costs involved in separating out the nitrogen from the ethane, especially if efficient heat exchangers are used to conserve
427
energy. Though ethanol is a more valuable product than methanol, a blend of these oxygenated hydrocarbons could be added directly to gasoline as an octane enhancer. Acknowledgment. We are grateful to the Canadian
Gas Processors Association and Natural Science and Engineering Research Council of Canada for the financial support during the course of this work. Registry No. CzHe,74-84-0; CzHSOH,64-17-5; CHSOH,6756-1; HzO, 7732-18-5; CHSCHO, 75-07-0; CHI, 74-82-8.
Hydrocarbon Content of Liquid Products and Tar from Pyrolysis and Gasification of Wood H. Pakdel and C. Roy* Department of Chemical Engineering, Universite Laval, Ste-Foy, Quebec, Canada, GlK 7P4 Received October 2,1990. Revised Manuscript Received February 11, 1991 Vacuum pyrolysis of aspen poplar wood chips was performed in a multiple hearth furnace process development unit. Various pyrolysis oils were collected in a series of cooling traps installed in parallel at the reactor outlets (primary condensing unit, H-I to H-VI). An aqueous phase containing about 45% water (96% of the total pyrolysis water) was collected separately in a secondary condensing unit (C-1 to (2-3) which contained high-volatile and partially water soluble organic matter. Liquid-liquid and liquid-solid chromatographic techniques were developed to separate aliphatic and aromatic hydrocarbons. Preliminary characterization of the aliphatic and aromatic hydrocarbons was performed by gas chromatography and mass spectrometry (GC/MS). Aliphatic hydrocarbons represented between 0.08 and 0.44% of the oil phase and 0.01 and 0.02% of the aqueous phase. The aliphatic hydrocarbon fraction of the H-VI oil was dominated by n-alkanes in the range of n-Cls to n-C? Aromatic hydrocarbons contributed between 0.06 and 0.24% of the oil phase and were detected only m trace amounts in the aqueous phase. "MR and F"IR spectroscopic analyses of the aromatic fractions showed a complex mixture of highly branched aromatic hydrocarbons. Due to the highly branched nature of their aromatic fractions, neither phase is believed to have significant environmental and toxicological impact. The efficiency of the hydrocarbon separation technique was also tested on a tar sample from a 10 t/h wood gasifier which contained over 50% polycyclic aromatic hydrocarbons. Of this tar sample 85% was characterized by GC/MS.
Introduction Low-grade hardwoods such as aspen and other poplar species represent classes of renewable biomass materials which can be converted either to liquid fuels or to chemical feedstocks. Cellulose, hemicellulose, and lignin in different proportions are the three major lignocellulosic constituents. Depending on the conversion process and biomass constituent, oil composition changes considerably and usually reflects the reactor environment. However, oils produced via different thermochemical processes are very complex in chemical composition. Wood gasification is a high-temperature reaction and produces small amounts of tar mainly composed of hydrocarbon-type compounds.' Hydrocarbons produced under high-temperature gasification processes have been earlier reported to be mainly highly condensed polyaromatic hydrocarbons with a high level of mutagenic activity.* Low-temperature pyrolysis processes, on the (1) Elliott, D. C.; Baker, E. G.Biomass 1986, 9, 195-203. (2) Elliott, D. C. "Analysisand comparison of biomass pyrolysislgaeification condensates." Final report. DE-ACOB-76RLO,1830. Pacific Northwest Laboratory, Richland, WA, 1986.
0887-0624/91/2505-0427$02.50/0
other hand, yield significant amounts of oils with low hydrocarbon ~ o n t e n t . ~ Vacuum pyrolysis of wood produces high yields of pyrolysis oils4and carboxylic acids.6 The vacuum pyrolysis reactor used in our laboratory was designed to separate the oil phase from the aqueous phase.' In addition, our preliminary analytical results showed a fairly good fractionation of the oil in the reactor outlets according to their weight average molecular weight and various rare chemical compound^.^ Polycyclic aromatic compounds (PACs) are ubiquitous environmental pollutants and are formed from both natural and anthropogenic sources. The latter are by far the major contributors. Natural sources include forest fires! volcanoes,' and in situ synthesis from degradation of biological materials which has led to the formation of these (3) Pakdel, H.; Roy, C. &'rOlYSk oils from biomass; ACS Symposium Ser. 376; American Chemical Society: Washington, DC,1988;pp 203-219. (4) Roy, C.; Lemieux, R.; de Caumia, B.; Pakdel, H. Biotechnol. Bioeng. Symp. 1985, No. 15, 107-113. (5) Pakdel, H.; Roy, C. Biomass 1987, 13, 155-171. (6)Blumer, M.; Youngblood, W. W. Science 1976,188, 63-66. (7) Initsky, A. P.; Mischenko,V. S.;Shabad, L. M. Cancer Lett. 1977, 3, 227-230.
0 1991 American Chemical Society
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428 Energy & Fuels, Vol. 5, No. 3, 1991
PRIMARY
I
MICROPROCESSOR
I - UiSSOlVed in 250 m1 IN NROH 2- Extracted with 2 x 100 m1 I ol uene
CONDENSATE Washed with 250 nl
&O
I xtrnct-d with 2 Y PO rl CIL-Cl?
L CHAR RECEIVER LVACUUM PUMP Figure 1. Schematic view of the vacuum pyrolysis unit.
compounds in various sediments and fossil fuels.8 Major anthropogenic sources include, for example, the burning of coal refuse banks, coke production, automobiles, commercial boilers and incinerators, wood stoves, and wood gasifiers. With rapid development of the industry throughout the world, the natural balance between the production and degradation of PACs has been disturbed. During the past 30 years, many studies have been undertaken to characterize the PACs. A bibliography of over 400 references on advanced analytical techniques for PACs analyses has been made.g Wood pyrolysis oils have a very complex nature compared to airborne particulate matter;O industrial effluent, work place atmosphere," water supplies,12 ~ e d i m e n t s , ' ~ f00d,14 and tobacco smoke.15 Techniques of separation and characterization of PACs have been extensively studied in those materials during the past several years? This paper presents a separation scheme for polycyclic aromatic hydrocarbons (PAHs) from pyrolysis oils which have not been analyzed in detail before. The oils were obtained in a multiple hearth vacuum pyrolysis process development unit.3 Efficiency of the separation scheme has also been tested on a tar sample from a large scale (10 t/h) wood gasification unit.ls
Experimental Section Pyrolysis. Debarked Populus deltoides (clone D-38) wood chip sieved between 1/4 and 1/2 in. Tyler meehes were pyrolyzed at a constant feeding rate of 0.8-4 kg/h in a six-hearth vacuum pyrolysis unit (runC025). The process development unit, shown in Figure 1,has been described in detail elsewhere? The organic vapors with about 40-8 residence time were removed from the reactor chamber by a mechanical vacuum pump and condensed to H-VI) installed in parallel at the in a series of condensers (H-I reactor outlet stages corresponding to the six reactor hearths. The noncondensed vapors from the primary condensing unit (PCU) were collected in a train of receivers (C-1 to C-3) which served (8) White, C. M.; Lee, M. L. Ceochim. Cosmochim. Acta 1980, 44,
1826-1832.
(9) Bartle, K. D.; Lee, M. L.; Wise, S. A. Chem. SOC.Rev. 1981,10, 113-168. - - - -. -. (10) Giger, W.; Schaffner, C. Anal. Chem. 1978,50, 243-249. (11) Blombrg, L.; Wannmnn, T. J. Chromtogr. 1979, 168, 81-88. (12) Bomeff, J. Adu. Enuiron. Sei. Technol. 1977,8, 393-408. (13) Wakeham, S. G.;Schaffner, G.; Giger, W. Geochim. Cosmchim. Acta 1980,44,416-429. (14) Lo,M. T.; Sandi, E. Residue Rev. 1978,69,35-86. (16) Hoffmann, D.; Rathkamp, G. Anal. Chem. 1972, 44,899-906. (16) Drauin, 0. Biothennica Intemntional Inc. (Montreal). 1990.
Private communication.
as a secondary condensing unit (SCU). The reactor hearth temperatures were stabilized at 200,263,327,363,401, and 448 "C from top to bottom. Average wood chips residence time on each hearth was about 5 min. Gasification. The Biosyn wood gasifier plant was located in St. Juste-de-Breteni6res,P. QuBbec, and used sawmill residues as feedstock with a nominal capacity of 10 t/h. The plant has now been dismantled. The experiments were carried out with a mixture of partially dried (15-22% moisture) softwood bark and sawdust. The gasifier was a fluidized bed reactor blown with oxygen at a pressure of 700-800 kPa. The temperature was kept at approximately 850 O C . The gasifier operated at a feed rate of 3 t/h during the experiment. Ash was removed at the secondary cyclone under atmospheric pressure througha seriea of lock hopper valves. During the demonstration program, the gas was simply flared without cleanup other than passage through the cyclones. An isokinetic pressurized sampler was used to accurately determine the mass flows of steam, particulates, and tars at various points of the gas circuit. This sampler was also used to recover the tar sample (run BY-005) which was subjected to further chemical analyses. More information on the Biosyn demonstration project will be found elsewhere.ls Separation. A typical separation scheme is outlined in Figure 2 and was applied to wood pyrolysis oil and aqueous phases, and the wood gasifier tar byproduct. A 10-g portion of the sample was dissolved in a diluted alkali solution. Toluene (100mL) was added to the mixture and stirred for 20 min. The toluene phnw was then separated from the aqueous phase. The aqueous phase was further extracted with another 100 mL of toluene. The toluene phases were mixed and evaporated to dryness under vacuum in a rotary evaporator. Acidic compounds, e.g., carboxylic acids and phenols, were separated. The remaining hydrophiliar were next removed by further extraction with distilled water as indicated in Figure 2. The polar compounds were removed by adsorbing on 15 g of silica gel (70-230 mesh, dichloromethane prewashed, and dried at 120 Oc for 2 h) packed in a glass column (30 x 1.5 cm i.d.) in n-pentane. The first fraction was collected
Liquid Hydrocarbons from Wood by eluting with 120 mL of n-pentane and 120 mL of 12% dichloromethane in n-pentane. The eluate was evaporated to dryness. A 40-mg portion of the extract was applied on a 20 X 20 cm prewashed and oven dried (at 120 "C for 1 h) TLC plate coated with 2-2.5 pm silica gel (containing 13% gypsum binder with 1 mm thickness). The plate was developed with n-pentane. All the solvents were previously distilled. The polycyclic aromatic and aliphatic hydrocarbons were recovered within RI ranges of 0.14-0.45 and 0.824.93, respectively, and analyzed by GC, GC/MS, FTIR, and FTNMR. RI value represents the ratio of the distance migrated by the sample compared to that travelled by the solvent front. Elution order and RI values of various hydrocarbons were previously determined by fractionation of a standard solution of various hydrocarbons, typically saturated and olefinic n-Cle,naphthalene, pyrene, and benzo[a]pyrene on a silica gel column and TLC plate under similar oil fractionation conditions. FT 'H NMR spectra of 20% solution in CDCl, were recorded on a XL200 Varian instrument. FRIR spectra were recorded on a Digilab FTS-60 spectrometer. Gas chromatographicanalysis were performed on a 6000 Varian gas chromatograph with FID detector and on-column injector. The capillary column was J & W fused silica: DB-1701, 15 m X 0.32 mm i.d. The carrier gas was helium and make-up gas was nitrogen. The oven temperature was maintained at 50 O C for 2 min, and then programmed to 90 "C at 30 "C min-' and finally to 280 "C at 4 "C min-'. A Waters 840 data chromatography control station with Digital Professional 350 computer were used as data processor. A HP-5890 gas chromatograph with split injector (1:40 split ratio at 290 "C) and flow ' rate was used with helium carrier gas with about 1 "inJ & W fused silica capillary column 30 m X 0.25 mm i.d. and 0.25 pm f i i of DB-5. The oven temperature was programmed from 50 to 100 "C at a rate of 30 "C m i d and then to 290 "C at a rate of 4 O C min-'. The end of the column was introduced into the ion source of a HP-5970 mass-selectivedetector. Typical mass spectrometer operation conditions were as follows: transfer line 270 "C, ion source 280 "C, electron energy 70 eV. Data acquisition was done with HP-UX Chemstation software using a HP-UNM computer and NBS library data baae. The masa range m/z 30400 Da was scanned every 1 8.
Results and Discussion An understanding of the chemical and physical properties of pyrolysis oils is a necessary part of process development and enablea the identification of their potential applications or possible toxicity. The production of oils from biomass by thermal treatment depends on the pyrolysis temperature and residence time. The primary oxygenated oils produced during wood pyrolysis below 500 "C can be changed to highly aromatic, deoxygenated tar by additional thermal treatment at 700 "C or above." The concurrent decrease in phenols and increase in PAHs as a function of temperature was demonstrated earlier.2 The previous analytical results on vacuum pyrolysis oils produced from aspen showed no oxygen-free hydrocarbons.18 Ames away test was performed a few years ago to estimate the mutagenic activity of vacuum pyrolysis oil.lg The authors reported naphthalene and anthracene as the predominant aromatic hydrocarbons which showed a low mutagenic activity unless a large quantity of oil is considered. In their study, a HPLC system was used to characterize the aromatic fractions but the chromatograms suffered from very low resolution. The analytical procedure described in this paper is derived from a combination (17) Evan, R. J.; Milne, T. A. Energy Fuels 1987,1, 311-319.
(18) Elliott, D. C. 'Analyak and upgrading of biorrrrrrm liquefaction productd". Final report, Vol. 4. IEA Cooperative Project D1, Biomass Liquefaction Teat Facility. Project, Pacific Northwest Laboratory. . - . Richland, WA, 1983. (19) M6nard, H.;Belanger, D.; Chauvetta, G.; Gaboury, A.; Khorami, M.;G+, M.; Marta], A.; Pot+, E.; Roy, C.; Langlob, R. In Fifth Canodron Bioenergy R & D Semnar, Hmain, S., Ed.;Elsevier Applied Science Publiihen: New York, 1984; pp 418-434.
Energy & Fuels, Vol. 5, NO.3, 1991 429 Table I. Aromatic and Aliphatic Hydrocarbons in Vacuum Pyrolysis Oil sample oil, g PAHs4 AHs4 PCaa 0.11 0.17 0.13 377.4 H-I 0.22 0.24 0.44 278.4 H-I1 0.13 0.02 666.6 0.08 H-I11 0.15 0.13 0.04 H-IV 813.4 0.05 0.06 0.36 824.0 H-V 0.09 0.23 387.2 0.11 H-VI 0.02 CO.00 2869.0 CO.00 c-1 0.01 0.01 3269.0 0.01 c-2 0.01 0.00 581.6 0.01 c-3
aPAHs: polycyclic aromatic hydrocarbons (0.14 C Rf < 0.45); AHs: aliphatic and alicyclic hydrocarbons (0.82 < Rf C 0.93); PCs: polar compounds (0.0 C Rf C 0.14). All data in columns PAHs, AHa, and PCs are based on as-received (wt W )samples. of liquid-liquid, liquid-solid, liquid-gas chromatography and infrared (IR)and nuclear magnetic resonance (NMR) spectroscopy techniques. The analyses were performed on oil and aqueous phases and a tar byproduct obtained from vacuum pyrolysis and gasification processes, respectively. To our knowledge, there are only a few reports on PAHs composition of wood pyrolysis oils in the literature.'JJOZ1 Benzo[a]pyrene is the highest molecular weight PAH reported in wood pyrolysis? In the present study, the wood gasification tar sample showed benzo[a]pyrene and a trace of benzo[ghi]perylene as the highest molecular weight PAHs. Therefore, we have used pyrene and benzoIa1pyrene as the internal standard PAHs to monitor the separation steps (Figure 2). Vacuum Pyrolysis Oil. Six oil samples from the PCU and three aqueous samples from the SCU (Table I) were fractionated according to Figure 2. Aromatic and aliphatic hydrocarbon yields are reported in Table I. Aliphatic hydrocarbons are dominating over PAHs and maximum yield was achieved at 263 "C (H-11). On the h i s of similar reasoning for coal pyrolysis, most aliphatic and alicylic hydrocarbons are probably produced at low temperature as cracked hydrocarbons. In close agreement with early published results,22indeed the chromatograms of aliphatic hydrocarbon (AH) fractions of H-I to H-VIshowed a complex mixture of cracked hydrocarbons. We found for the first time n-alkanes in the range of n-C1, to n-CB and n-alkenes in the range of n-Clg to n-C% as the dominant compounds in the AHs fraction on H-VI sample. To our knowledge n-alkanes and n-alkenes have only been detected earlier in peat liquefaction products18and gasification tar byproduct.20 Wood extractives have not been reported earlier in the literature as a source of aliphatic hydrocarbons;23 thus, their occurrence in pyrolysis oils could be related to the decomposition product of long-chain alcohols or resins in extractives. The nature of PAHs fractions was investigated with some detailed characterization of the individual components in this paper. The chromatograms in Figure 3a,b as an example illustrate the evolution of various types of aromatic hydrocarbons at different temperatures. The hydrocarbon distribution becomes more complex with only (20) Soltes, Ed.J.; Elder, T. J. In Organic Chemicals from B i o m s ; Goldatein, I. S., Ed.;CRC Press: Boca Raton, FL, 1981; pp 63-99. (21) Solteg, E. J.; Lin, S-C. K. Production, Analysis, and Upgrading of Pyrolysis O b ; ACS Symposium Ser.; American Chemical Society: Washington, DC, 1987; Vol. 32, No. 2, pp 176-194. (22) Ami, E.; Davoudzadeh, F.; Coughlin, R. W. In Fundamental of Thermochemical B i o m e Conversion; Overend, R. P., Milne, T. A., Mudge, L. K., Eds.;Elsevier Applied Science Publiehen: New York, 1986; pp 329-343. (23) Goldatein, I. S. In Organic Chemicals from Biomass; Goldatein, I. S., Ed.;CRC Press: Boca Raton, FL, 1981; pp S18.
Pakdel and Roy
430 Energy & Fuels, Vol. 5, No. 3,1991
Table 11. Detailed Listing of Compounds in the Aromatic Hydrocarbon Fraction of E-I1 Pyrolysis Oil compound Rt*: min compound Rt*: min 1-ethyl-3-methylbenzene
(1,l-dimethylethy1)benzene 4-ethyl-l,2-dimethylbenzene 4-ethyl-1-phenylhydrazine 4-ethyl-l,2-dimethylbenzene 1,2,3,5-tetramethylbnzene 1-methyl-1-propenylbenzene 1-pentylbenzene naphthalene 1-hexylbenzene 1-methylnaphthalene 2-methylnaphthalene 1-heptylbenzene 1,l’-biphenyl 1,24imethylnaphthalene 2,3-dimethylnaphthalene 1,3-dimethylnaphthalene 1,4-dimethylnaphthalene dimethylnaphthalene acenaphthylene dimethylnaphthalene 1-octylbenzene 3-methylbiphenyl 1,2,3,4-tetrahydro-2,2,5,7-tetramethylnaphthalene 2 4 1-methylethyhaphthalene dibenzofurane 6 4 l,l-dimethylethyl)-1,2,3,4-tetrahydronaphthalene trimethylnaphthalene trimethylnaphthalene trimethylnaphthalene 1-nonylbenzene fluorene trimethylnaphthalene 4-methyldibenzofuran l-methyl-7-(1-methylethy1)naphthalene 1-decylbenzene 2-decylbenzene methylfluorene methylfluorene methylfluorene 2,4-dimethyl-l,l’-biphenyl
7-ethyl-1,4-dimethylazulene 1-undecylbenzene 2-undecylbenzene
10.35 13.11 13.24 14.00 14.27 14.41 15.37 15.37 16.42 18.68 19.78 20.28 21.67 22.17 22.89 23.29 23.41 23.85 23.91 24.10 24.27 24.50 25.01 25.16 25.56 25.89 26.01 26.24 26.66 27.05 27.18 27.59 27.72 28.85 29.07 29.68 29.80 30.43 30.58 30.85 31.06 31.24 32.08 32.16
phenanthrene le 1,6-dimethyl-4-(l-methylethyl)naphthalen 2,3-dimethylfluorene dimethylfluorene dimethylfluorene dimethylfluorene 1-dodecylbenzene 2-dodecylbenzene 2-methylanthracene methylphenanthrene methylphenanthrene 1-phenylnaphthalene 1-tridecylbenzene 2-tridecylbenzene dimethylphenanthrene dimethylphenanthrene dimethylphenanthrene dimethylphenanthrene fluoranthene 1-tetradecylbenzene dimethylphenanthrene pyrene brphenyl trimethylphenanthrene trimethylphenanthrene 1-pentadecylbenzene 2-pentadecylbenzene trimethylphenanthrene 2-(l,l-dimethylethyl)anthracene 2,3,5-trimethylphenanthrene methylpyrene benzo[ blfluorene 1-hexadecylbenzene 2-hexadecylbenzene 1-heptadecylbenzene 2,4,5,7-tetramethylphenanthrene benz[a]anthracene 1-octadecylbenzene 2-octadecylbenzene 1-nonadecylbenzene 2-nonadecylbenzene 5-methylchrysene 5&dimethylbenzo[ c ]phenanthrene
32.29 32.39 33.02 33.35 33.71 34.23 34.33 34.44 34.79 35.33 35.44 36.36 36.53 36.61 37.28 37.67 37.80 37.93 38.24 38.57 38.74 39.31 39.83 39.99 40.33 40.54 40.60 40.H 41.19 41.56 42.06 42.19 42.40 42.50 44.22 44.49 45.56 45.94 46.04 47.60 47.70 47.68 50.12
Retention time; see Figure 3a.
traces of oxygenated hydrocarbons at low temperature. At high temperature, on the other hand, the aromatic hydrocarbon distribution is less complex but slightly oxygenated (Figure 3b). The GC/MS analyses of various collections of low- to high-temperature biomass gasification/pyrolysiss condensates under steam, nitrogen, air, oxygen, carbon dioxide, and methane pressure have been performed earlier.2J8 These authors have reported approximately 0.3-43.4 9a aromatic hydrocarbons produced at about 420-480 O C pyrolysis temperature range. Naphthalene, acenaphthylene, phenanthrene, and fluoranthene have been detected. A large number of aromatic hydrocarbons were identified by GC/MS in the vacuum pyrolysis oil. Their occurrence has not been reported earlier in the literature. Surprisingly, the H-I1 oil (Figure 3a) produced at 263 OC contained mainly aromatic hydrocarbons (Table 11) whereas H-VI oil produced at 448 O C contained partially oxygenated aromatic compounds. Several PAHs were quantified in H-I1 aromatic fraction by using external standards, as listed in Table 111. Although the chromatographic resolution was rather low, nevertheless the library matching waa satisfactory. However, we were unable to differentiate between various isomers. Two homologous series of monoalkylbenzenes, 1 and 2-phenylhexane to
Table 111. PAHs Quantified in the Aromatic Hydrocarbon Fraction of E-I1 Pyrolysis Oil amount: ppm in total pyrolysis oil compound 1-pentylbenzene to nonadecylbenzene* 11.8 2-pentylbenzene to nonadecylbenzeneb 13.0 naphthalene 4.9 acenaphthylene 1.0 acenaphthene 0.5 fluorene 3.8 phenanthrene 3.3 anthracene 0.5 fluroanthene 1.5 pyrene 2.5 benz[o]anthracene 1.1 chrysene 2.5 benzo[a]pyrene 0.2 benzo[k]fluoranthene 0.8 benzo[a Jfluoranthene 0.2 indeno(l,2,3-cd)pyrene 0.3 benzo[ghi]perylene 0.2 External standard method used for quantification. bCalculation was based on a similar detector’s response factor to naphthalene.
phenylnanodecane, were positively identified. Their mass spectra showed a large m/z 92 and 105 characteristic fragment ion peaks, respectively. Their crows scan m/z 92
Liquid Hydrocarbons from Wood
Energy & Fuels, Vol. 5, No. 3, 1991 431
a
b
Table IV. Percentage Hydrogen Distribution in Aromatic Fractions of Wood Vacuum Pyrolysis Oils chemicala ^L:c* oihb Ulllllr, hydrogen type symbol ppm H-I1 H-I11 H-V H-VI 24.0 38.0 29.5 29.0 H, 6-9 aromatic 3.6 2.9 3.2 2.6 Hf 3-4 Ar-CH2-Ar 24.1 27.4 26.3 32.1 H, 2-3 CHa; CH2 and CH a to ring CH, and CH of H, 1.5-2 15.8 11.1 15.1 9.4 naphthenes CH,; CH2 and CH Hp 1-1.5 23.5 14.7 17.0 16.6 @ or further away from ring CH, y or further H, 0.5-1 10.0 5.2 9,2 9,7 away from ring a 20% solution in CDCl* Oils are obtained from six reactor hearths (H-I to H-VI); see Table I.
fim (mln.) Figure 3. Total ion chromatograms of PAHs fractions of H-I1 (a) and H-VI (b) oils.
and 105 ion chromatograms are shown respectively in Figure 4, a and b. Investigation of the composition and structure of fuels has long provided one of the major field of industrial application of molecular spectroscopy.% For materials as complex as coal, petroleum, and biomass pyrolysis oils, preliminary subfractionation of the extracted oils is an essential prerequisite for successful exploitation of spect”pic techniques.% The potential merita of proton and C-13 nuclear magnetic resonance and GC/MS techniques in the separation and identification of the saturated and aromatic hydrocarbon fractions extracted from fossil fuels have been studied earlier.*% There is very limited information available in the literature on the spectroscopic study of wood liquid products which provided some additional confirmation of the chemical functional groups. The analyses have always been performed on the total oil and suffered from water interference and low resolution.2J8*as It is therefore not surprising why proton NMR has received even less attention than C-13 NMR for the pyrolysis oil analysis. However, utilization of NMR and IR can be considered as complementary analysis techniques if the oil samples are prefractionatd into compound classes to avoid spectra misinterpretation. Detailed high-resolution proton NMR spectroscopic analyses have been carried out on solutions of many single compounds associated with coal and related materials.30 (24) Friedel, R.A; Retcofsky, H.L.In Spectrometry o f h e & Friedel, R. A., Ed.: Plenum: New York, 1970; pp 37-45.
(25) W e , K.D.; Jones, D. W.; Pakdel, H.In Analytical Methods for Coal and Coal products; Karr, C., Ed.; Academic Prew New York, 1978; Vol. 11, pp 209-262. (26) w e , K.D.; Jones, D. W.; Pakdel, H.Anulytical Characterization Technrques; ACS Symposium Series 205; American Chemical Society: Washington, DC, 1982; pp 27-45. (27) Bartle, K. D.; Calimli, A.; Jones, D. W.; Matthewe, R. 5.;Oclay, A,; Pakdel, H.;Tugrul, T.Fuel 1979,68,423-428. (28) Jonw, D. W.; Pakdel, H.;Bartle, K. D. Fuel Sci. Technol. Int. 1990,8(9),Sp7-960. (29) Mckinley, J. W.;Barraee, G. In Research in Thermochemical Biomass Conuerdon; Bridgwater, A. V., Kuester, J. L., Eds.; Eleevier Applied Science Publirhen: New York, lBW, pp 236-250.
Table V. Detailed Listing and Quantification of Compounds in Aromatic Hydrocarbon Fraction of Wood Gasification Tar Sample amount) comDound R+/min wt% ethylbenzene 6.5 0.68 dimethylbenzene 6.71, 7.35 1.62 7.27 0.68 1,3,5,7-cyclooctatetraene 0.79 phenol 9.94 0.14 benzofuran 10.48 4.07 propynylbenzene 12.01 0.14 7-methylbenzofuran 13.9 0.14 l-methyl-4-(1-propyny1)benzene 15.35 0.14 15.54 1-butynylbenzene 15.58 16.53 naphthalene methylnaphthalene 3.12 19.78, 20.28 2.17 ethenylnaphthalene 22.19, 23.57 0.27 dimethylnaphthalene 22.93, 23.33 7.72 acenaphthylene 24.16 0.54 acenaphthene 25.07 4-methylbiphenyl 0.14 25.30 1.63 dibenzofuran 25.89 1H-phenalene 27.14 0.27 fluorene 27.62 3.93 methyldibenzofuran 0.81 28.53, 28.86 0.41 methylfluorene 30.41, 30.82 phenanthrene 32.34 9.76 2.85 anthracene 23.52 ethenylanthracene 34.0 0.27 methylanthracene 1.76 34.80, 34.93, 35.12 1.76 38.30 4H-cyclopenta[deflphenanthrene methylphenanthrene 0.41 35.45 38.27 fluoranthene 3.93 4.2 39.32 pyrene 0.27 40.63 11H-benzo[b]fluorene 2.17 methylpyrene 41.15, 41.46 benz[a]anthracene 2.71 45.39 2.71 chrysene 45.58 46.16 7H-benz[de]anthracene-7-one nde 47.51 methylchrysene 0.41 benzo[a]pyrene 50.48 1.36 50.55 benzo[k]fluoranthene 2.17 benzo[ blfluoranthene 51.96 1.63 indeno[l,2,3-cd]pyrene 1.22 58.61 58.85 dibenzanthracene 0.41 dibenzanthracene 0.41 58.85 60.40 dibenzo[ghi]perylene nd total 84.99 a h t e n t i o n time; see Figure 7a. bWt % in total tar based on external standard quantification method. end = not determined.
For those analyses detailed consideration is required for the relation between chemical shifts and spin-spin coupling constants. For the aromatic hydrocarbon mixtures, however, with many closely similar chemical shifts, the (30)Bartle, K. D.; Jones, D. W. Ado. Org. Chem. 1972, 8, 317-423.
Pakdel and Roy
432 Energy & Fuels, Vol. 5, No. 3,1991 ,l-phenyldrcane
a
10
20
30 Time (mln.)
I
50
40
b
2-phenyldecane
2-pheny lpentadecae
10
20
30 ~ i m (mln.) e
40
50
Figure 4. Ion chromatograms of aromatic fraction of H-I1 oil: m / z 95 (a), and m / z 105 (b).
emphasis is much more on peak areas, patterns, and profiles than on shift-coupling relations. Indeed, very limited use has been made of spin-spin coupling constants in this area. Two instrumental developments in the past two decades have markedly favored the application of NMR to mixtures of closely similar compounds. One is the wider availability of high-field superconducting magnets and the second is the application of Fourier transform techniques. Usefulness of proton NMR recently has been shown for vacuum pyrolysis oil analysis after prefractionation into various classes of compound^.^ The FT 'H NMR spectra of the aromatic fractions (PAHs) of H-I1 and H-VI oil samples are shown for example in Figure 5, a and b, respectively. The resonance band assignments are reported in Table IV. From their 'H NMR spectra, the sharply defined peaks can be attributed to the fine aromatic structure with low molecular weight below 250. Due to their high noise/signal ratios, peak assignments of the 13C NMR spectra of the PAHs fractions could not be made but H-VI oil showed approximately 50% aromatic carbon. The 29.0% aromatic hydrogens in the same oil (Table IV), on the other hand, indicated its highly branched and partially condensed aromatic ring nature. Similar to their gas chromatograms, NMR spectra of H-VI oil (Figure 5a) had better resolution than H-I1 oil (Figure 5b) which could be further improved by using 600-MHz proton NMR spectrometer. FTIR spectra of all the aromatic fractions showed typical substituted aromatic hydrocarbon vibration bands. The FTIR spectrum of PAHs fraction of H-VI oil is shown, as an example, in Figure 6. Assignment of absorption bands is based on information in the literature.aa1a2 The bands at 2970,2958,and 2925 (31)Herget, H. L. In Lignin: Occurrence, Formution, Structure, and Reactiom; Sarkanen, K. V., Ludwing, C. H., Eds.; Wiley Interscience: New York, 1971; pp 267-293.
cm-I indicate the stretchings of methylene and methyl groups, and the corresponding bands located at 1453 and 1378 cm-' indicate the bending motion of the methyl groups. The weak peak at 1602 cm-' can be assigned to the C = C bond moiety of benzene and the peaks at 875, 811, and 747 cm-' can be assigned as the out-of-plane bending modes of 1,2,3,adjacent hydrogens. The CH of the aromatic ring shows up at 3050 and 3017 cm-'. The two bands at 1030 and 1188 cm-' are probably benzene CH in-plane bending. Ether and carboxyl bands occur usually at 1200-1300 and 1720 cm-l, respectively. In general, the IR spectrum of H-VI aromatic fraction (Figure 5) is very similar to the IR spectrum of an aromatic fraction that has been separated from a coal pyrolysis tarsa Perhaps the most striking differences are the increase of the C-0 and C=O absorption frequencies in H-VI oil. Tables 11, 111, and IV and Figures 3,4,5, and 6 demonstrate that all the pyrolysis oils show a distribution of various aromatic hydrocarbons, differing in their degree of condensation, numbers of side chains, and chain length. Under the pyrolysis conditions used, a large number of aromatic hydrocarbons, with and without side chains, were produced at low bed temperature. Further increase in the bed temperature, from top to bottom of the reactor, favored the production of oxygenated aromatic compounds. Although there are various PAHs without or with only methylated side chains, all wood vacuum pyrolysis oils are mainly composed of moderately branched aromatic hydrocarbons with at list two carbon atoms in each chain. In general, polycyclic aromatic hydrocarbons without or with low branching have the greatest potential mutagenic activities. Wood Gasification Tar. The polycyclic aromatic hy(32) Hoestarey, B. L.; Winding, W.; Mey%laar,H. L. C.; Eyriae,E..M.; Grant, D. M.;puemire,R J. In Pyrolyels Olb from Womoss,Productron, Analyzing, and Upgrading;ACS Sympohm Ser. 376; American Chemical Society: Washington DC, 1988; pp 189-202.
Liquid Hydrocarbons from Wood
Energy & Fuels, Vol. 5, No. 3,1991 433
Figure 5. 'H NMR spectra of PAHs fraction of H-I1 (a) and H-VI (b) oils.
drocarbon fraction of wood tar produced in the gasifier unit was also separated following the same procedure shown in Figure 2. Unlike the vacuum pyrolysis oil, wood gasification yielded a small quantity of tar with a high percentage of PAHs (-90% dry, ash-free basis). Figure 7a,b shows the total ion chromatograms of the total tar and ita PAHs fraction, respectively. Earlier analyses of the biomass tars produced in the gasification reactors have been performed only on a minor portion of the organic compounds. The rest was mainly high molecular weight and/or high-polarity compounds derived from the high oxygen content.2 Table V shows a list of compounds identified by GC/MS in Figure 7a. Compared with the other tars reported in the literature,= this tar contains low amounts of oxygenated compounds. The quantitative analysis of the tar reported in this paper was baaed on an external reference solution of naphthalene, (33) Soltea, Ed.J.; Lin, SC. K.In Progress in B i o m e Conversion; Till", D.A., Jahn, E.C., Edm.; Academic Prew New York, IS*, Vol.
I, pp 1-67.
acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoroanthene, pyrene, benzo[a]anthracene, chrysene, benzo[a]pyrene, benz[ghi]perylene, and dibenzoanthracene. The other compounds were quantified on an estimated response factor basis. 'H NMR spectra of the wood gasification tar sample and ita PAHs fraction are shown in Figure 8, a and b, respectively. From Figure 8b, the following hydrogen types were calculated: H, (79%); Hf (4.0%); Ha (6.0%); H, (1.0%); H,(3.5%); and H.,(1.0%). The remaining 5.6% hydrogen was attributed to the olefinic hydrogens. A fairly wellresolved NMR spectrum in Figure 7b is indicative of a low molecular weight (250 at most) PAHs mixture with low branching, mainly methyl and partially ethyl and methylene bridge. Fine structure is usually attributed to individual compounds.M PAHs fraction of wood gasifier tar contributed to 84% of the total tar. The remaining 16% has not been characterized at this stage but it is believed (34) Bartle, K.D.;Smith, J. A. S . Fuel 1966, 44, 1W123.
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to be a mixture of highly oxygenated aromatic and phenolic compounds. 'H NMR spectrum of the initial tar (Figure 8a) is rather similar to the PAHs fraction (Figure 8b) but has low resolution and bands are significantly broadened. Line broadening in the NMR spectra of hydrocarbon mixtures, e.g., crude oil and coal tar fractions, has been shown to originate from the presence of free radicals and diamagnetic species.36 (35) Bartle, K. D.;Smith, J. A. S. Fuel 1S67,46, 28-46.
We found a significant difference between the chemical composition of Biosyn wood gasification tar (in this paper) compared with the other published results on air-blown wood gasification tar samplesa2 Their proton NMR spectra, however, appeared to be similar. Conclusion A separation method was developed to analyze aromatic and aliphatic hydrocarbon content of wood vacuum pyrolysis oils and gasification tars and their aqueous phases.
Liquid Hydrocarbons from Wood
Energy & Fuels, Vol. 5,No. 3, 1991 435 nrmtidkl
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Hydrocarbon distribution of vacuum pyrolysis oils is strongly dependent on the reactor bed temperature. Aliphatic hydrocarbon content ranged between 0.08 and 0.44% in the pyrolysis oils and 0.01 and 0.02% in the pyrolytic aqueous phase. Both the oil and the aqueous phase mainly contained cracked alkanes with some alkenes. Most aliphatic hydrocarbons were produced near the top of the pyrolysis reactor. H-VI oil at the bottom section of the reactor contained a significant proportion of n-alkanes and n-alkenes which have not been reported earlier in vacuum pyrolysis oils. Aromatic hydrocarbons contributed between 0.06 and 0.24% of the pyrolysis organic phase and only a trace quantity in the aqueous phase. GC/MS analyses of the
aromatic hydrocarbon fractions were made and their distributions were compared. Aromatic hydrocarbon fraction of the H-VI oil was less complex compared with H-I to H-V oils. PAHs fraction of H-I1 oil had surprisingly low oxygenated compounds compared with H-VI. FT-NMR spectroscopy further enabled UE to determine the hydrogen type distribution of the aromatic hydrocarbon fractions. Aliphatic side chain hydrogens of the aromatic fractions contributed approximately between 47 and 58% of the total hydrogens, indicating their long and highly branched nature and possibly their low mutagenic activity. Highly branched chain hydrocarbon nature of the aromatic fractions were confirmed by FTIR spectroscopic analysis. Wood gasification tar approximately contained 85%
436
Energy & Fuels 1991,5, 436-440
polycyclic aromatic hydrocarbons with low and short side chains. This tar may have a high mutagenic activity. Acknowledgment. Thanks are due to Professor s. Kaliaguine for permission to use the FTIR spectrometer. The assistance of Dr. J. L. Grandmaison to record FTIR spectra is also gratefully acknowledged. The gasification
tar sample was kindly provided by Biosyn (Montreal, P.Q.). The collaboration of Mr. Guy Drouin from Biothermica International Inc. (Montreal) is also acknowledged. This study has been by Mines and Canada and Energie et Ressources Qu6bec.
Ultrarapid Flashlamp Pyrolysis: Thermal versus Photochemical Reaction Pathways John H. Penn* and Walter H. Owens Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506-6045
Lawrence J. Shadle U S . Department of Energy, Morgantown Energy Technology Center, Morgantown, West Virginia 26505 Received October 22, 1990. Revised Manuscript Received December 18, 1990
A ;enon flashlamp has been used to rapidly heat organic substrates coated onto graphite particles by conversion of photochemical energy into thermal energy within the graphite particles, resulting in heating rates of 105"C/s (i-e.,ultrarapid pyrolysis). The compounds chosen for ultrarapid pyrolysis have been carefully selected to verify whether the reported reactions are due to photochemical or thermal activation. Bibenzyl yields primarily acetylene when subjected to flashlamp conditions. In contrast, traditional thermal or photochemical excitation yields products which may be rationalized by cleavage of the central C-C bond to yield benzyl radicals. 1,6-Diphenylhexanealso yields acetylene with a significant amount of ethylene when exposed to ultrarapid heating conditions. With traditional heating and photochemical reaction conditions, no products can be found. 1,4-Dibenzoylbutaneyields the normal Norrish type I1 cleavage products upon photoexcitation and no products upon thermal excitation at 650 OC. In contrast, ultrarapid pyrolysis yields acetylene and a small amount of benzaldehyde. Taken together these results indicate that photochemical reactions cannot be responsible for the observed reactions. Since the ultrarapid pyrolysis products differ from those observed with traditional heating techniques, the ultrarapid pyrolysis products are attributed to higher temperature (>lo00 "C) thermal activation.
Introduction A variety of studies, in a laboratory effort to emulate high heating rate industrial process conditions, such as fluidized bed reactors or entrained flow reactors, have shown that changes in the heating rate of fossil fuel substrates can dramatically change the relative quantities of the products formed in pyrolysis reactions.' These laboratory techniques for achieving high heating rates include wire-grid pyrolysis,2a shock tube reactions,2b flashlamp pyrolysis: laser pyrolysis,'*s fluidized sand bed pyrolysis,S (1)Solomon, P. R.;Hamblen, D. G. In Chemistry of Coal Conversion; SchJosberg, R. H., Ed.;Plenum Press: New York, 1986; Chapter 5. (2)(a) Cliff, D. I.; Doolan, K. R.; Mackie, J. C.; Tyler. R. J. Fuel 1984. 63,394. (b) Tyler, R. J. Fuel 1980,69,218. (3)(a) Freihaut, J. D.; Proecia, W. M. Energy Fuels 1989,3,625.(b) Freihaut, J. D.; Zabielski, M. F.; Seery, D. J. Ninteenth Symposium (Znternutional)on Combuntion;The Combustion Institute: Pithburgh, 1982;p 1159. (c) Freihaut, J. D.; Proecia, W. M.; Seery, D. J. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1987,32(3),129. (4) Phuoc, T. X.; Maloney, D. J. Symp. (Int.) Combunt., [ h o c . ] ,22 1988,125-134. (5)(a) Vaatola, F. J.; Pirone, A. J. Prepr. Pap.-Am. Chem. Soc., Diu. Fuel Chem. 1966,10,63.(b) Vaatola, F. J.; McGahan, L. J. Fuel 1987, 66, 886.
0887-0624/91/2605-0436$02.50/0
and even plasma pyrol~sis.~ A preferred technique for generating the fastest heating conditions utilizes the conversion of high-intensity light into thermal energy in an appropriate substrate. Granger and Ladne9 were the first to show that enhanced yields of low molecular weight (MW) gases resulted from ultrarapid flashlamp pyrolysis. Their studies revealed that enhanced yields of gases are obtained with increasing flash intensity for high vitrain coal particles from Coal Rank Code 902 to Coal Rank Code 203 in a flashlamp pyrolyzer. In an independent study, Calkins observed that flash pyrolysis of Pittsburgh No. 8 coal a t >700 "C produces low molecular weight hydrocarbons such as acetylene, ethylene, and propylene? while entrained flow pyrolyses of the same substrate at 445 "C, produced only aromatic compounds (6)(a) Calkins, W.H.; Tyler, R. J. Fuel 1984,63,1119.(b) Calkins, W . H.Energy Fuels 1986,1,59. (7)Bittner, D. K.; Baumann, H.; Klein, J. Fuel l9M,64, 1370. (8)Granger, A. F.; Ladner, W. R. Fuel 1970,49,17. (9)(a) Calkins, W.H. Prepr. Pap.-Am. Chem. SOC.Diu. h l Chem. 1983, 28, 85. (b) Calkins, W.H.; Hoveepian, B. K.; Drykacz, G. R.; Bloomquiet, C. A. A.; Ruecic, L.Fuel 1984,63,1226.
0 1991 American Chemical Society
