Using Bio-oil Produced by Biomass Pyrolysis as Diesel Fuel - Energy

Publication Date (Web): October 29, 2013. Copyright © 2013 American Chemical Society. *Telephone: +55 51 33086308. Fax: +55 51 33087304. E-mail: ...
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Using Bio-oil Produced by Biomass Pyrolysis as Diesel Fuel Renato Cataluña,*,† Pedro M. Kuamoto,† Cesar L. Petzhold,† Elina B. Caramaõ ,† Maria E. Machado,† and Rosangela da Silva‡ †

Federal University of Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501-970 Porto Alegre, RS, Brazil Pontifical Catholic University of Rio Grande do Sul, Av. Ipiranga 6681, 90619-900 Porto Alegre, RS, Brazil

ABSTRACT: This study evaluated the effect of biomass (soybean oil, eucalyptus sawdust, and coffee grounds) pyrolysis oil on the formulation of diesel fuels. The parameters analyzed were ignition delay time, emission of particulate matter and unburned hydrocarbons, and specific fuel consumption. The fraction of pyrolysis oil used as fuel was obtained by vacuum distillation at 80− 240 °C. The use of this fraction resulted in a decrease in the ignition delay time in the combustion process, with the resulting increase in the cetane number due to the presence of phenolic groups in the pyrolysis oil, which modify the formation mechanism of peroxyl radicals by altering the temperature of the flame front. Additionally, particulate matter emissions are reduced significantly by up to 30% when compared with the base fuel. This is probably due to the high solubility of water in pyrolysis oil, which leads to the formation of an azeotropic mixture that lowers the boiling point and contributes to vaporize the fuel inside the combustion chamber, reducing the formation of particulate matter. These results indicate the promising potential of this fraction for use in the formulation of diesel fuel, decreasing ignition delay and increasing the cetane number, as well as significantly reducing particulate matter emissions. The main difficulty in using this fraction of pyrolysis oil is its chemical stability, since it has a strong tendency to form oligomers.

INTRODUCION Today’s energy matrix is largely dependent on fossil fuels, natural gas, and coal. Fossil-based products that supply the transport sector are expected to be replaced in the short and medium-term due to high growth rates, mainly in emerging countries. As a result, the transport sector will account for about one-third of the future growth in worldwide greenhouse gas emissions.1 The first generation biofuels, biodiesel and bioethanol, and, recently, those of the second generation derived from biomass, have shown significant growth in recent years.2−8 The generation of second generation biofuels is favored by the large supply of wastes produced in agriculture.9−11 In Brazil, a major producer of agricultural products12 and with extensive areas of reforestation area, the reuse of residual biomass plays an important role in the energy matrix, not only for economic reasons but also for environmental issues. The use of forest and agricultural residues stands out in the energy matrix, given their characteristic of not contributing to the phenomenon of global warming, and constituting a source of renewable fuels and of raw materials for the chemical industry. The use of rice husks, eucalyptus sawdust and fruit seeds in thermal conversion processes (pyrolysis) of biomass is an attractive option for many Brazilian regions, since it can take advantage of plentiful locally available residual biomass. Brazil produces approximately 5 Mton/year of agricultural wastes that could easily be converted into biofuels, with an estimated production of 2 Mton/year of bio-oil from thermal or delignification processes.13−19 The characteristics of fuels play an important role in the combustion process. The determination of the parameters that affect self-ignition and air pollutant emissions from diesel fuels enables the development of new and more efficient combustion processes, as well as the addition of new compounds to increase © 2013 American Chemical Society

the performance of the thermal cycle. Oxygenated compounds such as biodiesel alter the cetane number (CN) and the combustion mechanism, reducing the emission of particulate matter (PM).20,21 This paper discusses results of the characterization and performance of a biofuel, produced by fixed bed slow pyrolysis, using soybean oil, eucalyptus sawdust, and coffee grounds. The fraction of oil used as fuel was obtained by vacuum distillation at 80 to 240 °C. This fraction was characterized by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR), comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometric detection (GC × GC/TOFMS), and water content. Additionally, based on a diesel oil (S10) with low sulfur content (10 mg L−1) and a cetane number (CN) of 50, formulations were prepared with 10% m/m fraction of bio-oil and of soybean biodiesel, which are hereinafter referred to as S10po and S10bd, respectively. Performance tests were carried out in a diesel cycle engine to evaluate characteristics such as specific fuel consumption, ignition delay, and emissions of particulate matter and unburned hydrocarbons (HCs), using the S10 diesel and its S10po, S10bd formulations.


Characterization of the S10 Diesel. The S-10 diesel normally commercialized in the Brazilian market by Petrobras was used in this study as the base to prepare the two formulations, one containing 10% m/m of bio-oil and the other 10% m/m of soy biodiesel, referred to as S10po and S10bd, respectively. Received: August 19, 2013 Revised: October 28, 2013 Published: October 29, 2013 6831 | Energy Fuels 2013, 27, 6831−6838

Energy & Fuels


Table 1. Physicochemical Properties of Fuel S10


specific gravity (kg m−3)

T 10% (°C)

T 50% (°C)

T 90% (°C)

kinematic viscosity (mm2 s−1)

flash point (°C)

sulfur (mg L−1)


polycyclic aromatic hydrocarbons (% m)

D4052 839.4

D86 209

D86 264

D86 338

D445 2.85

D93 72

D7039 10

D613 50

D6591 1.61

Figure 1. Representative FTIR spectrum of the pyrolysis oil (film on KBr). The S10, with a maximum sulfur content of 10 mg kg−1, was developed by Petrobras to meet the requirements of the latest generation of diesel engines, which were designed to emit lower levels of particulate matter and NOx than those manufactured up to December 2011. In addition to its low sulfur content, this fuel has a high cetane number (at least 48), a narrow range of variation in specific mass (820 to 850 kg/m3), and a maximum distillation curve temperature of 370 °C for 95% of the products of evaporation. These properties also favor combustion and cold starting of engines. Table 1 describes these physicochemical properties and the respective methodologies employed. Characterization of the Bio-oil Produced by Pyrolysis. The pyrolysis oil was produced in a fixed bed reactor from a mixture of 1:1:1 soybean oil, coffee grounds and eucalyptus sawdust, applying a heating rate of 10 °C min−1 from room temperature to 700 °C and a holding time of 15 min. The oil thus produced was separated from the water and fractionated by vacuum distillation at a pressure of 50 mbar between 80 and 240 °C. The oil was characterized by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR), and Karl Fischer titration. The infrared spectrum of the pyrolysis oil fraction was obtained in the form of a film on a potassium bromide (KBr) wafer, using an FTIR spectrophotometer (Varian) in the frequency range of 4000−400 cm−1. A nuclear magnetic resonance (NMR) analysis was performed in deuterated chloroform, using a Varian VRMN-300 MHz spectrometer. The water content of the pyrolysis oil was determined by the Karl Fischer titration method, using an 870 Titrino Plus titrator from Metrohm. The analyses were performed in triplicate. The pyrolysis bio-oil composition was also determined by comprehensive two-dimensional gas chromatography with time-offlight mass spectrometric detection (GC × GC/TOFMS), using a Pegasus-IV system (LECO, St. Joseph, U.S.A.) equipped with a liquid nitrogen quad-jet modulator and CTC Combi PAL autosampler. The following columns were employed in the first and second dimension, respectively: a DB5 column (5% phenyl−95% dimethylpolysiloxane) 60 m in length, with 250 μm inner diameter (I.D.) and 0.25 μm of phase thickness, and a DB-17 ms column (50% phenyl−50% dimethylpolysiloxane) 2.15 m in length, with 180 μm I.D, and 0.18 μm of phase thickness (Agilent Technologies, J&W Scientific, Agilent,

Folsom, CA, U.S.A.). The carrier gas was helium under a constant flow rate of 1 mL min−1 and the sample injection volume was 1 μL. The injector temperature was 300 °C, and samples were injected in the splitless mode. The temperature program of the first column was set to begin at 40 °C for 1 min and reach a final temperature of 300 °C at 3 °C min−1, with 1 min of holding time. The transfer line was held at 300 °C and the electron impact ionization source itself was operated at 250 °C with collision energy of −70 eV. The mass range was 45−400 amu, and data acquisition rate was 100 Hz. The oven’s modulator period and offset temperatures were 8 s and 15 °C, respectively. The data were processed using integrated LECO ChromaTOF software, version 3.32. Engine Performance Tests. The tests to evaluate specific fuel consumption, ignition delay time, particulate matter and hydrocarbon emissions of S10 diesel fuel and its S10po and S10bd formulations were performed in a 250 cm3 Toyama 7.0 Hp single cylinder engine, using an Optrand inductive pressure sensor in the combustion chamber. The engine was run at 80% of maximum power, mechanical fuel injection at 20° before top dead center (TDC), with 150 bar average injection pressure, a compression ratio of 21:1, 3600 rpm, and 10% of O2 in the exhaust gases. The PM in the exhaust gas was quantified gravimetrically by direct filtration of the gas in a 47 mm diameter glass microfiber filter (Macherey-Nagel). The engine was especially instrumented22 to optimize its operation during the performance tests of each fuel. In addition, a differential pressure gauge in the filter was used to assess the accumulation of PM. The gas flow through the filter element was obtained with the aid of a vacuum pump, and after cooling, the flow rate was measured using a flow indicator/recorder (Sensirion), with a maximum rated capacity of 20 nL min−1. The quantification of PM in mg m−3 was based on the mass of PM trapped on the filter, divided by the volume of sampled gas. The average temperature of the filter element was set at 470 °C to keep the collected PM dry. The volatile condensable hydrocarbons (HCs) in the exhaust gases were collected together with the water generated in the combustion process, after separating the PM. The liquid fraction from the exhaust of diesel engines is composed of unburned and partially oxidized hydrocarbons (HCs) that condense along with the water formed in the combustion process. A portion of the water vapor in the exhaust gases is condensed by cooling the gas flow after the particulate matter has been collected. The total 6832 | Energy Fuels 2013, 27, 6831−6838

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Figure 2. 1H NMR spectrum of the pyrolysis oil. hydrocarbons in the form of methane were quantified using a technique similar to that of the ASTM D 659123 standard, by flowthrough oxidation of the sample in an oxygen atmosphere. Carbon dioxide (CO2) was analyzed in a gas chromatograph equipped with a thermal conductivity detector (Shimadzu GC-17A with TCD).

vibration of the CO bond of compounds derived from the fragmentation of soybean oil triglycerides. The absorption band at 1453 cm−1 is associated with the asymmetric deformation of the CH methyl and methoxyl26 groups, while the broadened band at 3367 cm−1 is characteristic of the stretching vibration of the OH bond. Figure 2 shows the 1H NMR spectrum of pyrolysis oil. Because this is a mixture of products, the NMR data confirm the presence of aromatic and vinylic hydrogens, indicated by the signals in the region of 5 to 7.5 ppm, as well as of hydrogens bound to oxygenated carbons (CH−O) between 3.5 and 4.8 ppm and of hydrogens neighboring carbonyl in the region of 1.9 to 2.9 ppm. The intense peaks between 0.7 and 1.5 are typical of aliphatic hydrogens. The same samples were also analyzed by GC × GC/TOFMS and the results are described in Table 2. A total of 89 compounds were tentatively identified, considering a minimum signal-to-noise ratio (S/N) of three. The compounds were tentatively identified when the similarity between the sample and library spectra was greater than 750 and after a detailed analysis of the spectra. Since no standards (reference substances) were used to confirm the identification, we considered only the indication listed in the library of the device. That is why we consider that the compounds were “tentatively identified.” For the same reason, the alkyl chains in some compounds were not completely defined. For example, a compound identified in the library as 2ethyl pyridine was only “tentatively identified” as C2-pyridine, where C2 represents an ethyl group or two methyl groups in an undefined position in the pyridine ring. In Table 2, the bio-oil composition is grouped by chemical class: alcohols, ketones, ethers, phenols, aromatics and aliphatic hydrocarbons and nitrogen compounds. The sample obtained by pyrolysis is composed mainly of ketones and nitrogen

RESULTS AND DISCUSSION Characterization of the Pyrolysis Oil. The results of the Karl Fischer analysis indicated the solubility of 5000 ppm of water in the pyrolysis oil. This amount of water, even in small quantities, strongly affected the initial boiling point of the formulations, causing the fragmentation of the fuel to increase during injection because smaller droplets were generated. During the purification process the onset of vaporization is altered by the presence even of small amounts of water, suggesting that this is one of the determining factors in the reduced formation of particulate matter when pyrolysis bio-oil is used. In addition, albeit to a lesser degree, the presence of water in biodiesel may also lead to its hydrolytic oxidation.24 Water not only promotes biodiesel hydrolysis, which results in free fatty acids, but is also associated with the proliferation of microorganisms, causing corrosion and sediment deposition in storage tanks. Because biodiesel presents some degree of hygroscopicity, its water content should be monitored during storage. The FTIR spectrum in Figure 1 was used to investigate the chemical structure of pyrolysis oil. Since the pyrolysis oil obtained from the 1:1:1 mixture of soybean oil, coffee grounds, and eucalyptus sawdust, the absorption bands at 1592, 1453, 1414, 1379, 1253, 1236, 1166, and 824 cm−1 are characteristic of lignocellulosic materials and are consistent with the spectrum of pine wood.25 The absorption bands at around 3000 cm−1 are attributed to the symmetric and asymmetric vibration of saturated CH bonds. The signal at 1704 cm−1 is related to the stretching 6833 | Energy Fuels 2013, 27, 6831−6838

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Table 2. Identification of the Classes of Compounds in Bio-oil of by GC × GC/TOFMS retention time 1

TR D (min)

TR 2D (s)





area (%)

Alcohols 9.50 10.97 11.10 13.50

2.96 3.11 3.58 3.72

7.63 8.17 8.43 9.50 11.10 14.17 11.23 13.23 13.63 15.77 16.03 18.03 19.10 13.99 19.77 18.17 21.23 22.57 23.37 25.50 15.77 21.10 15.77 20.83 21.90 22.57 24.97 26.03 26.83 28.17 31.50 37.50

2.72 2.91 2.96 3.09 3.34 3.58 4.29 4.29 4.35 4.28 4.25 4.57 4.69 5.1 5.67 4.72 5.16 5.48 5.51 5.69 4.98 5.25 3.73 3.9 5.37 4.75 5.65 5.22 4.78 5.38 5.51 6.81

9.23 17.37 21.23 22.97

2.75 3.73 5.13 4.79

23.37 24.97 26.70

4.1 4.77 4.59

10.3 15.633 18.567 24.967 26.033 28.3

3.31 3.96 4.75 4.97 4.63 4.91

9.63 10.43 11.37 11.50

3.56 3.74 2.91 2.88

pentanol pentanol pentenol hexenol Ketones pentanone pentanone pentanone hexanone hexanone heptanone cyclopentanone cyclopentanone, C1(a) cyclopentanone, C1 cyclopentanone, C2 cyclopentanone, C2 cyclopentanone, C2 cyclopentanone, C2 cyclopentenone, C1 cyclopentenone, C1 cyclopentenone, C2 cyclopentenone, C2 cyclopentenone, C2 cyclopentenone, C2 cyclopentenone, C2 cyclohexanone cyclohexenone, C1 heptanone octanone cycloheptanone cyclopentenone, C3 acetophenone cyclohexenyl, ethanone cyclopentenone, C4 cyclohexanone, ethylidene cyclopentenone, C3 methylene indenone, hexahydro Ethers ethane, diethoxy furanmethanol furan, C2 furan, C2 Phenols phenol phenol, C1 phenol, C1 Hydrocarbons toluene benzene, C2 cyclopentane, methyl ethylidene cyclopentene, C3 cyclopentene, C3 cyclohexene, C4 Nitrogen Compouds pyrrole pyrrole, C1 piperidine, C1 piperidine, C1


878 501 646 736

878 886 710 818

C5H12O C5H12O C5H10O C6H12O

0,24 0,01 2,24 0,00

791 887 945 853 759 775 924 889 905 809 615 825 777 952 937 815 888 868 877 846 869 820 925 927 916 745 863 861 726 774 789 806

813 887 945 908 902 882 924 906 905 840 842 825 848 952 937 818 888 868 877 869 878 820 925 927 924 758 903 879 789 776 873 854

C5H10O C5H10O C5H10O C6H12O C6H12O C7H14O C5H8O C6H10O C6H10O C7H12O C7H12O C7H12O C7H12O C6H8O C6H8O C7H10O C7H10O C7H10O C7H10O C7H10O C6H10O C7H10O C7H14O C8H16O C7H12O C8H12O C8H8O C8H12O C9H14O C8H12O C9H12O C9H12O

0,19 0,65 0,98 0,03 0,04 0,03 1,21 1,14 0,58 0,18 0,06 0,32 0,10 6,54 3,46 0,85 2,12 0,48 6,16 0,56 0,61 1,66 0,40 0,44 0,88 0,33 0,14 1,01 0,01 0,71 0,27 0,11

915 853 865 717

925 902 884 828

C6H14O2 C5H6O2 C6H8O C6H8O

1,99 8,35 4,23 0,37

908 651 714

914 840 843


2,00 0,06 0,78

871 595 765 718 652 755

871 790 779 747 741 755

C7H8 C8H10 C8H14 C8H14 C8H14 C10H18

0,22 0,02 0,58 1,41 0,74 0,35

715 931 693 787

909 931 846 828

C4H5N C5H7N C6H13N C6H13N

0,03 8,97 0,01 0,14 | Energy Fuels 2013, 27, 6831−6838

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Table 2. continued retention time 1

TR D (min)

TR 2D (s)





area (%)

Nitrogen Compouds 15.37 12.83 15.23 15.50 16.57 18.30 18.83 19.50 21.10 21.77 15.77 16.43 16.83 16.83 17.23 21.23 21.50 25.37 25.63 25.77 29.50 30.17 29.90 26.83 27.77 27.23 28.30 33.37 31.23 33.23 33.37 33.50 34.70 35.37 34.97 36.17 a

3.75 3.99 4.32 4.18 4.35 4.38 4.59 4.32 4.42 4.58 3.96 4.47 4.62 4.66 4.72 4.72 4.76 4.67 4.72 4.81 4.68 4.74 4.65 6.03 6.25 4.88 5.23 4.6 5.45 5.02 5.77 5.71 5.38 5.15 5.48 6.67

piperidine, C2 pyridine, C1 pyridine, C1 pyridine, C2 pyridine, C2 pyridine, C2 pyridine, C2 pyridine, C3 pyridine, C3 pyridine, C3 imidazole, C4 pyrazine, C2 pyrazine, C2 pyrazine, C2 pyrazine, C2 pyrazine, C3 pyrazine, C3 pyrazine, C4 pyrazine, C4 pyrazine, C4 pyrazine, C5 pyrazine, C5 pyrazine, C6 pyrrolidinone, C2 pyrrolidinone, C2 piperidinone, C4 pentanamide, C1 pyrazine, C6 imidazole, C3 pyrazole, C3 pyrazole, C4 imidazole, C4 pyrazole, C4 pyrazole, C4 pyridine, C1 propenyl pyrrolidinone, C2 methylidene

696 912 874 891 778 879 882 701 822 633 900 681 892 847 869 886 894 921 897 925 885 616 811 857 808 857 819 856 620 770 809 829 773 759 799 800

771 912 882 917 790 880 889 767 826 761 905 805 931 847 880 886 894 926 905 940 885 753 842 892 810 857 845 861 789 777 835 834 784 766 801 800

C7H15N C6H7N C6H7N C7H9N C7H9N C7H9N C7H9N C8H11N C8H11N C8H11N C7H12N2 C6H8N2 C6H8N2 C6H8N2 C6H8N2 C7H10N2 C7H10N2 C8H12N2 C8H12N2 C8H12N2 C9H14N2 C9H14N2 C11H18N2 C6H11NO C6H11NO C9H17NO C6H13NO C10H16N2 C6H10N2 C6H10N2 C7H12N2 C7H12N2 C7H12N2 C7H12N2 C10H13N C7H11NO

0,09 0,65 1,31 0,89 0,16 0,11 0,07 0,05 0,09 0,05 0,11 0,04 0,55 0,15 0,06 0,14 2,68 1,42 2,60 8,02 7,78 0,10 0,20 0,05 0,67 0,24 1,02 0,30 0,08 0,39 0,15 1,51 0,55 1,63 0,39 0,75

Cx: represent an alkyl chain linked to structure where x is the number of carbon atoms.

cetane number (CN)). Each of these parameters is significant in determining the final concentration of NOx emission. The combustion control techniques take advantage of the kinetic mechanism of NOx formation by using the air flow or fuel flow controls (in stages) or by introducing inhibitors. A higher CN in fuels is favored by larger amounts of oxygenates, which, albeit supplying lower energy content, reduce not only the combustion flame temperature but also NOx emissions.21,27,28 Engine Performance Tests. Figure 4 illustrates the variation of chamber pressure as a function of the crankshaft angle with the fuel and its various formulations. As can be seen, with the three fuels evaluated here, the maximum pressure after the TDC occurs at a 13° angle, that is, the maximum pressure in the combustion chamber occurs near the 15° angle, which corresponds to maximum torque. Note, also, that the fuels formulated with 10% pyrolysis oil and biodiesel produce higher pressure in the combustion chamber at the TCD than the S10, indicating that the oxidation rates of both the biodiesel and the pyrolysis oil in the proportion of 10% m/m are higher than that of the base fuel.

compounds, with minor amounts of alcohols, ethers, phenols and hydrocarbons. The graph in Figure 3a shows the area percentage of different classes of compounds, while the graph in Figure 3b indicates the contribution of each group of compounds by referring to the number of compounds. As can be seen in these figures, the predominant classes in the sample were nitrogen and ketone compounds: 44.19% (41) nitrogen and 32.22% (33) ketone compounds. C1 pyrrole and C4 pyrazin predominated among the various nitrogen and ketone compounds. High percentages of furanmethanol and of C1 and C2 cyclopentenone were also observed (Table 2). The presence of high amounts of nitrogen compounds in the composition of pyrolysis oil may lead to the formation of oligomers and increase the emission of nitrogen oxide compounds (NOx) during the combustion process. However, the NOx emitted during combustion depends not only on the composition of the fuel but also on the mode of operation and the design of the burners and of the combustion chamber and on the fuel’s other physicochemical characteristics (e.g., its 6835 | Energy Fuels 2013, 27, 6831−6838

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Figure 3. Distribution of chemical classes for bio-oil produced by biomass pyrolysis according to (a) area percentage and (b) their number of compounds tentatively identified.

According to Shafizadeh,29 eucalyptus biomass is composed of 38−45% cellulose, 16% hemicellulose, 25−37% lignin, and 9−15% of other organic and inorganic compounds. Cellulose is a natural high molecular weight polymer with the generic empirical formula of H(C6H10O5)nOH with up to 10 000 monomer units and a molecular weight of 1 600 000 a.m.u.30,31 Hemicelluloses are formed with copolymers of glucose and a variety of other monomers, mainly hydrates of carbon. They are amorphous and have a lower degree of polymerization than cellulose.31 During the process of pyrolysis, these compounds are cracked, producing fractions of lower molecular weight while maintaining some of the characteristics of the original compounds. Each of these constituents plays a role in the combustion process. The molecule that has an unpaired electron, called a free radical, determines the speed of the oxidation reaction. The most important reactive radicals formed during the combustion process are hydroperoxyl (HOO•), hydroxyl (HO•), alkoxy (RO•), and peroxyl (ROO•). These radicals react with N2 and nitrogen oxides, forming N2O. CH•

Figure 4. Pressure profiles in the combustion chamber with S10 diesel and its S10bd and S10po formulations.

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mixture, favoring vaporization with the formation of smaller diameter droplets. The greater the fragmentation of fuel in the injection process, the lower the formation of PM.35,36 As can be seen, HC emissions show a tendency unlike that of PM emissions. This is primarily due to the penetration of the jet in the combustion chamber. The higher the penetration the greater the likelihood of the fuel reaching the cold parts of the walls of the piston where the speed of oxidation decreases, increasing the emission of HCs. The higher emission of HCs does not significantly affect specific fuel consumption, since the maximum pressure in the combustion chamber is observed close to the 15° angle after TDC, the region of maximum torque, which keeps the engine’s power stable. During storage, the addition of small amounts of antioxidants to the fuel serves to suppress the formation of free radicals and interrupt their propagation for oligomer formation. In general, phenolic antioxidants (TBHQ, BHT, BHA, etc.) are added to biodiesel to prevent degradation.25 High oligomer formation was observed during the storage period of the pyrolysis oil and its respective formulation with the commercial diesel oil, even when stored at a low temperature. The addition of antioxidant additives to the fuel should reduce the formation of oligomers significantly and increase the fuel’s storage time.

and OH• radicals are formed continuously during the combustion process. In general, the presence of CH• radicals indicates low temperature in the inception phase and OH• radicals indicate reactions at high temperatures.32 During the combustion of biodiesel, the concentration of OH• radicals is lower while that of CH• radicals is higher.33 The high concentration of phenolic constituents in pyrolysis oil, which have a high potential for the formation of OH• radicals, explains the decrease in ignition delay and the increase in the speed of oxidation, with a consequent increase in the CN of the S10po fuel compared to the base fuel (S10). Figure 5 illustrates the differential pressure in the filter element resulting from the retention of particulate matter (PM)

CONCLUSIONS The pyrolysis oil fraction obtained by vacuum distillation at 80 to 240 °C and used in the formulation of diesel fuels showed good test results in terms of engine performance and air contaminant emissions. The use of this fraction reduces the ignition delay time in the combustion process, hence increasing the CN. The results obtained here indicate that the increase in the speed of oxidation at the onset of the combustion process may be due to the presence of phenolic groups in the pyrolysis oil. The fuels formulated with 10% of pyrolysis oil showed 30% lower formation of PM, which is attributed to the increase in water solubility in the oil, producing an azeotropic mixture that increases the fuel’s volatility during its injection, thus reducing the diameter of the droplets. The major difficulty in using the pyrolysis oil fraction in the formulation of diesel fuels is attributed to its chemical stability, since it has a strong potential to form oligomers.

Figure 5. Differential pressure in the filter element resulting from the retention of particulate matter (PM) as a function of gas sample volume with the S10 fuel and its S10bd and S10po formulations.

as a function of the volume of the gas sample for the S10, S10bd, and S10po fuels. The lowest differential pressure as a function of gas sample volume is observed for the formulation containing pyrolysis oil, because it generates less PM. Table 3 Table 3. Mass of PM in mg m−3 and the Emissions of Unburned HCs (%) of Sampled Gas from the Combustion Reaction of the S10 Fuel and Its S10bd and S10po Formulations fuel

PM (mg m−3)

HCs (%)

S10 S10bd S10po

33 30 25

0.87 0.84 0.97


Corresponding Author

*Telephone: +55 51 33086308. Fax: +55 51 33087304. E-mail: [email protected]

shows the mass of PM in mg m−3 and the emissions of unburned HC in percent (%) of sampled gas. The PM values found here underscore the results shown in Figure 5. Diesel fuels formulated with diphenyl-p-phenylenediamine (DPPD), which has phenolic groups, showed a similar effect in reducing the formation of PM.27 The use of 10% m/m of pyrolysis oil in the fuel reduces PM emissions by approximately 30%. The presence of aromatic compounds in pyrolysis oil should contribute to increase emissions of PM,34 but the presence of the hydroxyl of the phenolic compounds in pyrolysis oil contributes to augment the efficiency of combustion. The lower formation of particulate matter is related with the process of fuel injection and vaporization in the combustion chamber. Since the injection pressure remains approximately constant, the lower formation of PM with the S10po fuel is due to the presence of water, which reduces the boiling point of the


The authors declare no competing financial interest.


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