Biodiesel Blends

Energy & Fuels 2007, 21, 2363-2372

2363

Production and Fuel Properties of Pine Chip Bio-oil/Biodiesel Blends Manuel Garcia-Perez, Thomas T. Adams,* John W. Goodrum, Daniel P. Geller, and K. C. Das Faculty of Engineering Outreach SerVice and the Department of Biological and Agricultural Engineering, UniVersity of Georgia, Athens, Georgia 30602 ReceiVed October 24, 2006. ReVised Manuscript ReceiVed February 5, 2007

The use of pyrolysis-derived bio-oil as a diesel-fuel extender or substitute has long been a goal of the bio-oil research community. In this paper, a simple system to accomplish that goal is described. The production of pine-chip-derived bio-oils, the preparation, and fuel properties of bio-oil/biodiesel blends are presented. Pyrolysis-condensed liquids were obtained from the pyrolysis of pine chips and pine pellets in batch and auger slow-pyrolysis reactors. These liquids were composed of two phases: an oily bottom phase and an aqueous phase. The removal of most of the water present in the aqueous phase results in the formation of a second oily phase called, in this paper, polar oil. The oily bottom phases were more soluble in biodiesel than the polar oils. Monolignols, furans, sugars, extractive-derived compounds, and a relatively small fraction of oligomers were the main bio-oil compounds soluble in biodiesel. Water and low-molecular-weight compounds responsible for many of the undesirable fuel properties of bio-oils were poorly dissolved in biodiesel. Select fuel properties of bio-oil/biodiesel blends, such as viscosity, density, calorific value, water content, and pH, are reported.

1. Introduction Continued use of fossil fuels is generating concern because of the large amounts of carbon dioxide released into the atmosphere. The exploration, production, marketing, and transport of fossil fuels result in additional pollution as well as social and political unrest. Fuels produced from renewable resources, such as wood biomass, sugars, and vegetable oils, are attracting growing interest because their effect on the atmosphere is more carbon-neutral and they are less toxic in the environment. Ethanol, biodiesel, biogas, biomass, and bio-oils are the most common biofuels used today. The types of biofuels used depend upon a number of factors. Availability and cost of feedstock as well as technical and social conditions existing near the biomass resources are important factors when considering the production of biofuels. Technologies are needed that can convert diverse sources of biomass economically into transportation biofuels that may be used without major modification to engines. It would be desirable to have biomass conversion processes that are able to convert all of the energy in the biomass to a transportation fuel.1 In practice, it is impossible to do so, just as it is impossible to convert all of the energy in crude oil into gasoline and diesel fuels.1 When pyrolysis is compared with other processes that obtain liquid fuels from lignocellulose, it is one of the most thermally efficient processes. Biomass gasification to syngas and its subsequent conversion into liquid fuels is a well-established pathway. However, conversion of syngas to liquid fuels like Fischer-Tropsch alkanes, methanol, or ethanol is predicted to have overall process thermal efficiencies (PTEs) between 0.2 and 0.4.1 The PTE of ethanol * To whom correspondence should be addressed: Faculty of Engineering Outreach Service, The University of Georgia, Athens, GA 30602. Telephone: 706-542-0793. Fax: 706-542-0875. E-mail: [email protected]. (1) Huber, G. W.; Iborra, S.; Corma, A. Chem. ReV. 2006, 106, 40444098.

production from the fermentation of lignicellulosic sugars is expected to be around 0.49.1 The PTE of bio-oil production by fast pyrolysis ranges from 0.61 to 0.68.1 Refined hydrocarbons can be obtained after hydrotreating bio-oils, but the PTE drops to 0.5.1 The direct use of bio-oil molecules without hydrotreating in transportation fuels has evident advantages. Bio-oil. Bio-oil is derived from the rapid condensation of vapors released during the pyrolysis of biomass. It is a complex mixture of many organic molecules having diverse molar mass and structure. It is the lowest cost biofuel produced today from lignocellulosic materials.2 The chemical compounds found in bio-oils are derived from the breakdown of cellulose, lignin, hemicellulose, and biomass extractives, making these liquids very different from petroleum-derived fuels. Excellent reviews on the chemical composition of bio-oil and its applications as a source of fuels and chemicals can be found elsewhere.2-8 The complex chemical composition of crude bio-oil results in a multiphase, dark brown, relatively polar material, with an oxygen content typically between 33 and 45 mass %.9-12 Bio(2) Chiaramonti, D.; Oasmaa, A.; Solantausta, Y. Renewable Sustainable Energy ReV. 2007, 11, 1056-1086. (3) Czernik, S.; Bridgwater, A. V. Energy Fuels 2004, 18, 590-598. (4) Meier, D.; Faix, O. Bioresour. Technol. 1999, 68, 71-77. (5) Oasmaa, A.; Czernick, S. Energy Fuels 1999, 13, 914-921. (6) Diebold, J. P.; Bridgwater, A. V. Overview of fast pyrolysis of biomass for the production of liquid fuels. Fast Pyrolysis of Biomass: A Handbook; Bridgwater A. V., et al., Eds.; CPL Press: Newbury, U.K., 1999; pp 13-32. (7) Radlein, D. The production of chemicals from fast pyrolysis biooils. Fast Pyrolysis of Biomass: A Handbook; Bridgwater A. V., et al., Eds.; CPL Press: Newbury, U.K., 1999; pp 164-188. (8) Mohon, D.; Pittman, C. U.; Steel, P. H. Energy Fuels 2006, 20, 848889. (9) Garcıà-Pe´rez, M.; Chaala, A.; Pakdel, H.; Kretschmer, D.; Rodrigue, D.; Roy, C. Energy Fuels 2006, 20, 364-375. (10) Garcıà-Pe`rez, M.; Chaala, A.; Pakdel, H.; Kretschmer, D.; Rodrigue, D.; Roy, C. Energy Fuels 2006, 20, 786-795.

10.1021/ef060533e CCC: $37.00 © 2007 American Chemical Society Published on Web 05/18/2007

2364 Energy & Fuels, Vol. 21, No. 4, 2007

oils can be broadly described as a mixture of (A) 5-30 mass % of water and very reactive organic volatile compounds, such as hydroxyl-aldehydes, hydroxyl-ketones, and carboxylic acids, with boiling points under 150 °C, (B) between 15 and 35 mass % of furans and mono-phenols, with boiling points similar to gasoline, (C) between 10 and 25 mass % of sugars, di-phenols, and extractive-derived compounds, with boiling or cracking temperatures similar to diesel fuels, and (D) between 10 and 30 mass % of oligomers, with a molecular mass between 500 and 10 000 g mol-1. Many of the poor fuel characteristics of bio-oils, such as acidity, low thermal stability, low calorific value, high viscosity, and poor lubrication, are generally associated with the low-molecular-weight organic molecules and water (fraction A) and the oligomers (fraction D). The furans and phenols as well as the sugars, diphenols, and extractivederived compounds (fractions B and C) are the fractions with more promising fuel properties. Direct use of crude bio-oil containing undesirable fractions (very small and very heavy molecules) is only possible if extensive operational and design modifications of diesel engines are undertaken to address its poor fuel properties. It has been proven that modified diesel engines can run smoothly using crude bio-oils;2 however, the cost associated with extensively revamping the engines and the damage that can be caused by the destructive properties of bio-oil are serious hurdles limiting the application of this approach.2,13 Several physical and chemical bio-oil-upgrading technologies, such as blending bio-oils with organic solvents and emulsification, have been tested at a laboratory scale.2,13,14 Solvent addition can impact bio-oil properties by two mechanisms: (1) physical dilution and (2) esterification and acetilization preventing chain growth.15 Blending pure pyrolysis oil with high-cetane-oxygenated compounds is another effective method to upgrade biooils for diesel engine applications.13 Tests on blends of pyrolysis oils with up to 56.8 mass % of dyglyme (diethylene glycol dimethyl ether), an oxygenated compound with a very high cetane number (112-130), has been reported.13,15,16 Minor differences were found when comparing the overall combustion performance of these blends with the one observed with diesel fuels. The economic feasibility of these approaches is limited by the high cost of cetane improvers, solvents, and emulsifiers. Biodiesel. Biodiesel is a renewable fuel derived from triglycerides. It is environmentally innocuous, safe to handle, and has a relatively high flash point. The heating value, density, and viscosity are comparable to those of the number 2 diesel from petroleum. Biodiesel is also a very good solvent. The work reported here seeks to create a new value-added market for chipped wood by converting virgin pine wood or its components, primarily underutilized or industry wood wastes, into a liquid transportation fuel suitable for use in diesel engines. The main purpose of this paper is to study how much and what fractions of bio-oil are soluble in biodiesel. The fuel properties of bio-oil/biodiesel blends are studied as a simple approach for (11) Garcıà-Pe`rez, M.; Chaala, A.; Pakdel, H.; Kretschmer, D.; Roy, C. Characterization of Bio-oils in chemical families. Biomass Bioenergy 2007, 31, 222-242. (12) Branca, C.; Di Blasi, C. Ind. Eng. Chem. Res. 2006, 45, 58915899. (13) Scholze, B.; Meier, D. J. Anal. Appl. Pyrolysis 2001, 60, 41-54. (14) Scholze, B.; Hanser, C.; Meier, D. J. Anal. Appl. Pyrolysis 2001, 58-59, 387-400. (15) Czernik, S.; Johnson, D. K.; Black, S. Biomass Bioenergy 1994, 7, 187-192. (16) Garcia-Perez, M.; Chaala, A.; Pakdel, H.; Kretschmer, D.; Rodrigue, D.; Roy, C. Energy Fuels 2006, 20, 786-795.

Garcia-Perez et al.

using bio-oil as a diesel extender or replacement in only slightly modified diesel engines. 2. Experimental Section 2.1. Feedstock Characterization. Biodiesel was provided by U.S. Biofuels (Rome, GA). The bioblend B100 fuel was prepared from a poultry fat feedstock and met or exceeded all standards specified in American Society for Testing and Materials (ASTM) D-6751. Fuel was used as shipped in 5 gallon containers. Two pine chip feedstocks were used in this study. The first one was supplied in a shredded form and shipped by Langdale Industries, Inc. (Valdosta, GA). The pine pellets were supplied from the Southern Shaving Co., Cherryville, NC. Both feedstocks were oven-dried overnight at 105 °C before pyrolysis. The pine pellets have a cylindrical shape with an average diameter of 6.46 mm (standard deviation of 0.23) and a length of 12.80 mm (standard deviation of 4.11). The pine chips had a more irregular rectangular shape with a thickness of 4.38 mm (standard deviation of 1.48), length of 28.38 mm (standard deviation of 9.72), and width of 16.55 mm (standard deviation of 7.38). The content of fat, mainly fatty acids, paraffin, and other extractives in pine samples was determined by petroleum ether extraction using a Soxtec HT6 system. The ANKOM200 method was used to measure the content of cellulose, hemicellulose, and lignin. The content of fat was determined by petroleum ether extraction in a Soxtec HT6 system. The oven-dried plant materials were further digested with neutral detergent solution (30.0 g of sodium lauryl sulfate, 18.61 g of ethylenediamine-tetraacetic disodium salt, 6.81 g of sodium phosphate dibasic, and 10.0 mL of triethylene glycol in 1 L of distilled water) and R-amylase to remove the soluble constituents, such as starch, sugars, pectin, amino acids, proteins, etc. The remaining solid formed by hemicellulose, cellulose, and lignin is commonly known as neutral detergent fiber (ANKOM200). The hemicellulose was determined as the fraction soluble in acid detergent solution [20 g of cetyl trimethylammonium bromide (CTAB) in 1 L of 1 N H2SO4]. The remaining solid (acid detergent fiber) was further extracted with a strong sulfuric acid (24 N or 72 mass % of H2SO4) to remove the cellulose. The lignin was the remaining solid residue. A detailed description of the methods used can be found elsewhere.17 The content of crude protein was determined by the combustion method in a separate analysis.18 Elemental analyses (CHNS-O) of studied feedstocks were carried out using two independent instruments: a LECO CNS-200 and a LECO CHN-200. The ash content was determined according to ASTM D-482. 2.2. Bio-oil Production. The studied bio-oils were produced in two different slow-pyrolysis units operating at atmospheric pressure. The shredded pine chips were converted in a batch reactor, while the pine pellets were pyrolyzed in a continuous auger reactor. A total of 1.4 kg of pine chips were pyrolyzed in a 230 mm long and 255 mm diameter batch reactor (Figure 1). The reactor was heated to 500 °C and maintained at that temperature for 30 min using a 30400 Thermolyne furnace. The pyrolysis vapors were rapidly evacuated across the biomass bed using 2 L min-1 of nitrogen as a carrier gas. Five ice-cooled traps connected in series were used as condensers. A trap containing cotton wool and a bubbling trap with water (not represented in Figure 1) were used to remove all of the aerosols from the pyrolysis gases. The charcoal solid residue was left behind in the reactor under nitrogen until the reactor reached room temperature to avoid oxidation. (17) Garcia-Perez, M.; Chaala, A.; Kretschmer, D.; De Champlain, A.; Hughes, P.; Roy, C. Spray characterization of a softwood bark vacuum pyrolysis oil. Proceedings of the Science in Thermal and Chemical Biomass Conversion Bridgwater and Boocock; Victoria, Vancouver Island, BC, Canada, August 30-September 2, 2004; p 1468. (18) Chiaramonti, D.; Bonini, M.; Fratini, E.; Tondi, G.; Gartner, K.; Bridgewater, A. V.; Grimm, H. P.; Soldaini, I. Biomass Bioenergy 2003, 25, 101-111.

Pine Chip Bio-oil/Biodiesel Blends

Energy & Fuels, Vol. 21, No. 4, 2007 2365

Figure 1. Batch pyrolysis installations and typical oven and biomass temperatures for pine chips. (1) Computer connected to thermocouples, (2) carrier gas cylinder, (3) mass-flow controller, (4) oven, (5) pyrolysis reactor, (6) chiller, and (7) condensing traps.

Figure 2. Continuous pyrolysis reactor used in the conversion of pine pellets. (1) Feeding hopper, (2) feeding valve, (3) auger motor, (4) auger conveyer, (5) cooler, (6) heater, (7) char container, (8) water cooler, (9) bio-oil traps, (10) ice chiller, and (11) vacuum pump. T ) temperature, and P ) pressure.

The pyrolysis of the pine pellets was conducted in an indirectly heated continuous-flow reactor fabricated from parts (Figure 2). Pine pellets were fed via a rotary valve at a feed rate of 1.5 kg h-1. The average amount of biomass used in each run was 6 kg. The reactor consisted of a 100 mm diameter stainless-steel tube placed in a Lindberg/Blue M (model HTF55322A at 1200 °C) furnace with an auger driven by a 1/4 hp motor. A cooler was installed between the hopper and the furnace to prevent the heating of the reactor feed. The auger speed was maintained at 2.2 rpm to obtain a solid retention time of 8.26 min, corresponding to 5.91 min in the heated zone. The charcoal was collected in a stainless-steel container located downstream of the auger. A vertical condenser followed by a series of ice-cooled traps was used to condense the pyrolysis vapors. The cooling system in the auger reactor is more complex than the one used in the batch. The main difference is the existence of an indirect water cooler. The ice chillers and bio-oil traps were similar in both systems. The pressure inside the reactor was maintained a few millimeters of mercury below atmospheric pressure using a vacuum pump with a valve to control the pressure inside the reactor. A total of 3 L min-1 of nitrogen was used as a carrier gas to maintain an inert atmosphere inside the reactor.

Condensed liquids were separated into an aqueous and an “oily bottom phase” using a separation funnel. The separation took place at 4 °C in a cooled room. The separation funnel valve was carefully controlled to allow for the viscous bottom phase sticking on the walls to flow to the bottom without the aqueous phase. The separation was done in two steps (3 h between steps). In the first step, most of the oil was separated. The second step was used to separate the bottom phase sticking on the walls that tends to flow very slowly to the bottom. The separation was stopped when the less viscous aqueous phase started to flow through the valve. The aqueous phase was subjected to an evaporation step at 60 °C under vacuum in a rotatory evaporator (Bu¨chi, RE 111). The goal was to reduce the water content to around 15 mass %. The resulting oil was called “polar oil”. A total of 5 mass % of methanol was added to all of the resulting oils to improve their thermal stability. The process used is presented in Figure 3. 2.3. Bio-oil Characterization. The water content of the biooils was determined by Karl Fisher titration (ASTM D-1744). Thermogravimetric and gas chromatography mass spectrometry (GC/MS) analyses were conducted for each of the obtained oils to have a more complete view of their chemical composition.


Garcia-Perez et al. Table 1. Elemental Composition of Pine Chips and Pine Pellets (Mass %) mass % organic basis feedstock

C

H

N

S

Oa

ash

pine chips pine pellets

49.5 48.0

6.0 5.9

0.06 0.05

0.02 0.05

43.9 44.9

0.5 1.1

a

Figure 3. Scheme used to produce bio-oil/biodiesel blends.

The GC/MS analyses were conducted on samples diluted (1:10) in methanol. The GC/MS equipment has a HP 6890 GC oven with a HP 1973 MS detector in the scanning mode; HP 19091M-133 HP-5 columns were used (dimensions: 30 m × 0.25 mm × 0.5 µm). The method employed can be summarized as follows: the oven was initially maintained at 40 °C for 1 min and then heated at 6 °C min-1 to 260 °C. That temperature was kept for 12 min. The sample inlet temperature was maintained at 250 °C. A thermogravimetry (TG) Mettler Toledo thermogravimetric analysis (TGA)/SDTA851e was used for the thermogravimetric tests. All of the tests were conducted using initial masses of 5 mg. A total of 50 cm3 min-1 of nitrogen was used to obtain an inert atmosphere and to remove the evaporation and cracking products from the oven. The samples were heated from 25 to 600 °C at a heating rate of 10 °C min-1. 2.4. Preparation of Bio-oil/Biodiesel Blends. Each of the resulting separated bio-oils (oily bottom phase and polar oils) was blended separately with biodiesel. A total of 30 g of blends containing 10, 20, 40, and 50 mass % of bio-oils from pine chips and pine pellets (oily bottom and polar oil separately) and an ASTM 6751 standard biodiesel were prepared (see Figure 3). The blends were heated to 60 °C for 30 min in 50 mL sealed vials using a water bath. The vials were shaken every 10 min. The blends were left to cool to room temperature before decanting the formed phases. The less dense biodiesel-rich phase was carefully separated using a 10 mL syringe. Each of the resulting phases was weighed. Thermogravimetric analyses of products were accomplished under nitrogen at heating rates of 10 °C min-1. The scheme used to produce the studied blends is presented in Figure 3. 2.5. Fuel Properties of the Biodiesel-Rich Phase. Several properties of the biodiesel-rich phase (see Figure 3) were measured to determine the effect that bio-oil fractions could have on some fuel properties of biodiesel, such as viscosity, specific gravity, calorific value, and pH. Specific gravity was measured by a densitometer using a MooreVan Slyke-specific gravity bottle (Fischer Scientific, Pittsburgh, PA). The measurements were carried out at 20 °C (ASTM D-4809). The densitometer method required a small amount of sample and two weighing steps using an electronic balance. Viscosity was measured for each liquid sample in triplicate by using a Brookfield Synchrometric LVT viscometer with a UL adapter (Stoughton, MA). The viscometer was calibrated using a Brookfield 4:7 cP viscosity standard. This immersion-type concentric cylinder viscometer generated eight discrete shear rates between 0.32 and 34 s-1. A circulating temperature controller maintained temperatures at (0.5 °C. The calorific value was determined using a Parr 1351 oxygen bomb calorimeter operating under standard methods at 450 psi

By difference.

oxygen. Approximately 0.5 g of the sample was used for each run, and measurements were conducted in triplicate (ASTM D-4809). Karl Fisher titration was performed using a Mettler Toledo DL31 titrator. The water content method used is equivalent to International Organization for Standardization (ISO) 12937 and ASTM D-1744. A weighed portion of oil was injected into the titration vessel. When all of the water was titrated, excess iodine was detected by an electrometric end-point detector and the titration was terminated. Because of the inability of standard pH-meters to detect pH in oil-based systems, a water/oil emulsion system was used to determine the pH of bio-oil/biodiesel mixtures. A mixture of 50 mass % water/50 mass % bio-oil/biodiesel was initially formed at room temperature. The phases were separated after settling for 30 min. The water phase was collected, and its pH was measured using an Accument AR15 pH-meter.

3. Results and Discussion 3.1. Biomass Characterization. The elemental analyses of pine chips and pine pellets studied are presented in Table 1. The results were very similar in both feedstocks and close to the ones reported for other woody biomass.19,20 Table 2 presents the chemical proximate analyses for both feedstocks. 3.2. Bio-oil Production. Mass balances for the pine chip and pine pellet pyrolysis tests carried out in the batch and continuous auger reactors are presented in Table 3. The yield obtained for the charcoal was quite similar for both reactors (30 and 31 mass %) but was slightly larger than the one obtained by thermogravimetry for both feedstooks (24 mass %). This result suggests that the reactions leading to the formation of additional char, such as the secondary intra- and extra-particle reactions, are very similar for both systems and contributed to at least a 5 mass % increase in the yield of char. These reactions could be mitigated by reducing the particle size, increasing the heating rate, and reducing the residence time of pyrolysis vapor in contact with the partially converted biomass. The whole liquid condensate from pyrolysis, separated into two phases, had an aqueous phase (69 and 66 mass %), also known in other papers as pyroligneous water, and a more dense oily (bottom) phase (31 and 34 mass %), respectively (see Figure 3). The aqueous phase contained over 70 mass % water (see Table 3). The oily phase contained only 11.8 and 13.5 mass % of water and more than 86 mass % of organic compounds (see Table 3). The differences observed can be attributed to different heat- and mass-transfer phenomena between the two reactor configurations. Homo- and heterogeneous secondary reactions lead to the formation of more gases and water. 3.3. Bio-oil Characterization. The left side of Figure 4 presents the differential thermogravimetric (DTG) curves corresponding to the studied bio-oils. The use of thermogravimetric analyses to characterize bio-oils is relatively new.11,12 Contrary to GC/MS and high-performance liquid chromatography (HPLC), which are excellent techniques to quantify individual species, (19) Diebold, J. P.; Czernik, S. Energy Fuels 1997, 11, 1081-1091. (20) Suppes, G. J.; Natarajan, V. P.; Chen, A. Autoignition of select oxygenate fuels in simulated diesel engine environment, paper (74 e). Presented at the AIChE National Meeting; New Orleans, LA, February 26, 1996.


Energy & Fuels, Vol. 21, No. 4, 2007 2367 Table 2. Proximate Analyses of Pine Chips and Pine Pellets (Mass %)

feedstock

moisture

extractives (fats)

protein

cellulose

hemicellulose

lignin

ash

others (sugars, starch, pectins)

pine chips pine pellets

3.0 7.7

0.5 0.6

1.2 1.0

52.9 45.0

9.6 11.4

26.0 23.2

0.5 1.1

6.3 10.1

Table 3. Yield of Products (Mass %) (Pyrolysis Final Temperature ) 500 °C) products

pine chips (batch reactor)

pine pellets (continuous reactors)

char total liquid water organics aqueous phase (%) water organics oily decanted phase (%) water organics gases (by difference)

31.2 50.4 26.2 24.2 34.8 (70.0%) 24.4 10.4 15.6 (11.8%) 1.8 13.8 18.4

30.0 57.8 30.9 26.9 38.3 (74.1%) 28.3 10.0 19.6 (13.5%) 2.7 16.9 12.2

thermogravimetry is very useful to obtain a global overview of bio-oil composition.11,12 The right side of Figure 4 corresponds to DTG curves of bio-oils after extraction with biodiesel. Each of the original DTG curves was multiplied by the yield obtained after extraction to clearly visualize the extracted groups of compounds. This figure will be discussed in the following section. The DTG curves were resolved into five major families of compounds using a method similar to the one described elsewhere.11,12 The mass % of volatiles assigned to each group is presented in Table 4. The global chemical composition presented in Table 5 was estimated considering that only the oligomeric fractions, families D and E, contribute to the formation of the residue. The first group of compounds (group A) is mainly formed from water and organic compounds with boiling points under 200 °C. The main compound of this group is water. The water content of the oils from pine chips was lower than the one for pine pellets. Organic constituents are low-molecular-weight acids, aldehydes, and alcohols (with a molecular weight lower than 110 g mol-1). These compounds are generally considered responsible for many of the poor fuel properties of bio-oils (low thermal stability, corrosion, low calorific value, and high flash point) representing between 14 and 24 mass % (see Table 5). The organic compounds in this group represent between 2 and 10 mass % of the whole oil. Monolignols and furans are the main compounds forming the second group (group B). This group is associated with species with boiling points between 100 and 300 °C. The peak observed in the oils derived from the water-soluble fractions is in general shifted to higher temperatures (perhaps a consequence of phenols and furans with higher polarity). The compounds commonly identified in this fraction by GC/MS (see Figure 5 and Table 6) are mainly alkylated and methoxylated phenols and benzenediols. It was possible to identify more compounds by GC/MS in pine-chip-derived oils than in pine chip pellet oils. Important amounts of furans and pyrans must also exist in group B, but unfortunately, they are not commonly identified by GC/MS.11 Compounds in group B have boiling points similar to gasoline, contributing between 28 and 45 mass % of the total mass of this phase (see Table 5). The yield obtained while applying TG directly to the whole bio-oil is considerably larger than the one obtained when applying TG to bio-oil fractions obtained after solvent extraction (yields between 17 and 27 mass %).11 This result indicates that part of the phenols and furans are lost while removing solvents during TG analysis of fuel blends.

The peaks A and B represent groups of compounds, which generally form a Gaussian distribution. However, some times, such as in the case of peaks A1 and A2 and B1 and B2, it is not possible to obtain unique Gaussian distributions. In these cases, it is necessary to subdivide the groups into more than one subgroup. Group C is mainly formed of sugars, extractive-derived compounds, and dimers. The boiling points of this group of compounds are between 200 and 300 °C. This range includes the boiling points of some monosugars and the cracking temperature of polysugars. Only levoglucosane (Mw ) 162 g mol-1) is commonly detected by GC/MS chromatograms. The oils derived from the aqueous phase were expected to be rich in sugars, while the bottom oils will be richer in extractivederived compounds and di-phenols.5 Extractive-derived compounds are also likely to appear in this group. Fatty and resin acids, paraffins, and phenanthrenes are found in this group (see Figure 5 and Table 6). Products of the reaction between monomers (dimers) are likely to be the main compounds forming the group (11-34 mass % of studied oils). The yields are similar to the ones obtained for other oils (between 13 and 52 mass %) but after separating the oils in fractions.11 Families D and E cannot be identified by GC/MS because of their high molar mass. The heavy compounds of lower molecular weight can be water-soluble or water-insoluble but CH2Cl2-soluble. These compounds will have molecular weights between 500 and 1000 g mol-1. The heavier oligomers (with a molecular mass larger than 1000 g mol-1) are insoluble in water and CH2Cl2. This fraction represents between 15 and 33 mass % of the studied oils. A detailed chemical characterization of the water-insoluble fractions (oligomers) can be found elsewhere.13,14 The thermal behavior of different bio-oil fractions11 shows that families D and E are responsible for most of the solid residues observed during crude bio-oil evaporation. The water/CH2Cl2-insoluble fraction, very rich in family D, generates around 40 mass % of solid residues. The water-insoluble/CH2Cl2-soluble fraction, with a lower content of family D, only produced around 20 mass % of solid residues. Fractions rich in families B and C, such as the water- and toluene-soluble fractions, produce less than 15 mass % of solid residues. All of the experimental evidence reported in the literature9,10,12-16 suggest that bio-oil rich in families D and E have a larger molar mass and viscosity. Liquid fuels with high viscosities tend to perform poorly during combustion. Fuel viscosity has a very important effect on spray droplet-size distribution.17 Table 7 presents the viscosity, calorific value, density, and pH of studied oils. As expected, the oily bottom phases (see Figure 3) have a higher calorific value than the polar aqueousphase oils. The viscosity of bio-oil obtained from pine chips in the batch reactor was higher than the one obtained from pine pellets and the biodiesel. The density of polar oil was higher than the oily bottom phase and the biodiesel. All of the biooils had pH values between 2.4 and 2.7, much lower than the biodiesel (pH 4.2). 3.4. Preparation of Bio-oil/Biodiesel Blends. Several blends were prepared using biodiesel/bio-oil ratios of 1, 1.5, 4, and 9 (bio-oil concentrations of 50, 40, 20, and 10 mass %). Each bottom oily phase and polar oil was used to prepare blends (see


Garcia-Perez et al.

Figure 4. DTG curves, showing families of compounds (A-E), of bio-oils before and after extraction.

Figure 3). The blends were stirred while being heated to 60 °C. The relationship between the ratio used in the preparation and the biodiesel-rich/bio-oil-rich phase equilibrium ratio obtained after separating the blends into bio-oil- and biodiesel-rich phases after being cooled to 25 °C is presented in Figure 6. The slope of the resulting straight lines can be used as a good indicator of the solubility of studied bio-oils in biodiesel. The oily bottom phases (see Figure 3) were considerably more soluble in the biodiesel (K ) 3.09) than the polar oils obtained

from aqueous phases (see Figure 3). The oils from pine chips obtained in the batch reactor were more soluble than the oils obtained from the pine pellets in the continuous reactor. These differences are due to feedstock composition and the reactors used to produce the oils.3,4,6,8,24-28 The slope of resulting experimental lines (K) (see Figure 6) can be used to calculate the concentration of bio-oil compounds in the biodiesel-rich phase knowing the initial biodiesel/bio-oil ratio (eq 1)



Table 4. Mass Fraction of Compounds in the Bio-oil Phase before (BE) and after (AE) Extraction for Each Group of Compounds (Mass % of Compounds)a pine chips polar oil group of compounds volatile compounds plus water (A1) (A2) total (A) mono-phenols plus furans (B1) (B2) total (B) sugars, extractive-derived compounds plus dimers (C) oligomers (D) oligomers (E) total solid residue (Rs) (mass %) a

pine pellets

oily bottom phase

BE

AE

BE

AE

20.0

1.0 24.0 25.0

8.0 8.0 16.0

8.0 3.0 11.0

51.0 13.0

14.0 11.0 25.0 14.0

37.5 37.0

5.0 11.0 100 11.0

6.0 9.0 79 10.3

3.5 6.0 100 9.0

polar oil

oily bottom phase

BE

AE

BE

AE

28.0

6.0 32.0 38.0

19.2

11.5

6.0 11.0

38.0 13.0

18.0 5.0 23.0 11.0

31.8 30.0

13.0 9.0

2.0 1.0 31 10.2

5.0 16.0 100 15.0

3.0 14.0 89 13.7

12.0 7.0 100 12.0

5.0 4.0 42.5 12.4

BE ) before extraction with biodiesel, and AE ) after extraction with biodiesel. Table 5. Estimated Chemical Composition of Bio-oils

group water volatile compounds total (A) mono-phenols plus furans total (B) sugars, extractive-derived compounds plus dimers (C) oligomers (D plus E) total

cbio-oil )

pine chips

pine pellets

mass %

mass %

polar oil

oily bottom phase

polar oil

oily bottom phase

8.3 9.5 17.8 45.4

11.8 2.8 14.6 34.1

14.5 9.3 23.8 32.3

13.5 3.4 16.9 28.0

11.6

33.7

11.1

26.4

25.2 100

17.6 100

32.8 100

28.7 100

mbio-oil sol (mbiodiesel + mbio-oil sol)

)

K-1 mbiodiesel K +1 mbio-oil

(

)

(1)

where cbio-oil is the mass fraction of bio-oil-derived compounds in the biodiesel-rich phase, mbio-oil sol is the mass of bio-oil soluble in the biodiesel-rich phase, mbiodiesel is the mass of biodiesel used, and mbio-oil is the mass of bio-oil used. Equation 1 is only valid if biodiesel solubility in the bio-oil matrix is very limited. This hypothesis was confirmed by GC/ MS analyses of the bio-oil-rich phase obtained. No biodieselderived compound was found in that phase. The concentrations of bio-oil in the biodiesel-rich phase for each of the studied blends can be observed in Figure 7. Biodiesel-rich phases with loads of up to 34 mass % of bio(21) Bertoli, C.; D’Alessio, J.; Del Giacomo, N.; Lazzaro, M.; Massoli, P.; Moccia, V. Running light duty DI diesel engines with word pyrolysis oil. SAE Technical Paper Series; International Fair Fuels and Lubricants Meeting and Exposition, Baltimore, MD, October 16-19, 2000; document number 2000-01-2975. (22) (22) ANKOM200 Fiber AnalysersOverview. ANKOM Technology, Macedon, NY, http://www.ankom.com/00_products/product_a200.shtml. (23) Sweeney, R. A. J. Assoc. Off. Anal. Chem. 1989, 72, 770-774. (24) Garcıà-Perez, M.; Chaala, A.; Pakdel, H.; Kretschmer, D.; Roy, C. J. Anal. Appl. Pyrolysis 2007, 78, 104-116. (25) Garcıà-Perez, M.; Chaala, A.; Pakdel, H.; Roy, C. J. Anal. Appl. Pyrolysis 2002, 65, 111-136. (26) Wang, X.; Kersten, S. R. A.; Prins, W.; van Swaaij, W. P. M. Ind. Eng. Chem. Res. 2005, 44, 8786-8795. (27) Branca, C.; Giudicianni, P.; Di Blasi, C. Ind. Eng. Chem. Res. 2003, 42, 3190-3202. (28) Atutxa, A.; Aguado, R.; Gayubo, A. G.; Olazar, M.; Bilbao, J. Energy Fuels 2005, 19, 765-774.

oils were obtained when blending equal amounts of pine chip bottom phase bio-oils with biodiesel. 3.5. Analysis of Bio-oil and Biodiesel Rich Phases. The right side of Figure 4 shows the DTG curve of bio-oil-rich phases multiplied by the yield corresponding to the bio-oil-rich phases. The comparison with the left side of Figure 4 shows that fractions B and C from the oily bottom phases were the most soluble fractions in biodiesel. The mono-phenols and furans as well as dimers are likely to be the main compounds in these fractions. These compounds have boiling points in the range of petroleum gasoline and diesel and represent the most promising fractions for fuel applications. The water and low-molar-mass compounds (group A) were poorly soluble in biodiesel. This was a positive result because this fraction is responsible for many of the undesirable fuel properties observed in bio-oils, and the absence in the final fuel is desirable. Small amounts of oligomers (group D and E) were also soluble in biodiesel. Special attention must be paid to these compounds because they could increase the tendency of biodiesel to form carbonaceous residues in the injectors. This phenomenon will be further studied in diesel engine tests. The

Figure 5. GC/MS analysis of oily bottom phases.


Garcia-Perez et al. Table 6. GC/MS Tests of the Oily Bottom Phase

number

residence time

1 2 3 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

3648 4037 4272 4819 5053 5847 6068 6528 6942 728 7567 8389 8597 8793 9263 9694 10 126 10 506 10 584 11 016 11 409 12 263 15 013 15 369 15 870 16 562 16 662 16 887 17 256 17 945

32

18 619

33 34 35 36 37 38

18 964 19 353 19 945 20 489 21 749 23 236

compound name

pine chip

2,5-methyl, furan p-xylene tetrahydro-2,5-dimethoxy, furan 1-one,2-methyl-2-cyclopentent R-pinene 5-methyl-2-furancarboxaldehyde 5-methyl-2-furancarboxaldehyde phenol 3-methyl-1,2-cyclopentanedione 2-methyl-phenol 2-methoxy-phenol 2,4-dimethyl-phenol 2-methoxy-4-methyl-phenol 2-methoxy-4-methyl-phenol 2,6-dimethoxy-toluene 4-ethyl-2-methoxy-phenol 1-(2-hydroxy-5-methylphenyl)-ethanone eugenol 2-methoxy-4-propenyl-phenol eugenol 2-methoxy-4-(1-propenyl)-phenol 1-(4-hydroxy-3-methoxyphenyl)-2-propanone methyl ester hexadecanoic acid hexadanoic acid 2,2-dimethyl-3-bromo-1-oxa-2-sila-1,2-dihydro-naphthalene 9-hexadecenoic acid 3,5-dihydroxy-4,4-dimethyl-2-(1-oxopentyl)-2,5-cyclohexadien-1-one 2,3,5-trimethyl-phenanthrene 1-methyl-7-(1-methylethyl)-phenanthrene 1,2,3,4,4a,9,10,10a-octahydro-1,4a-dimethyl-7-(1-methylethyl), methyl ester 1-phenanthrenecarboxlic acid 1,2,3,4,4a,9,10,10a-octahydro-1,4a-dimethyl-7-(1methylethyl)-1-phenanthrenecarboxlic acid phthalic aid, di-isooctyl ester 1,5-diphenyl-2H-1,2,4-triazoline-3-thione 4H-1-benzopyran-4-one, 5-hydroxy-7-methoxy-2-(4-methoxyphenyl) 1H-naphtho(2,1-b)pyran-1-one, 3-acetyl-7,8-dimethoxy-2-methyl 2(3H)-furanone, dihydro-3,4-bis(4-hydroxy-3- methoxyphenyl)methyl), (3R-trans) ergosta-4,6,22-trien-3β-ol

pine pellets

X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X

X X X X X X X X X X X

X

X

X X X X X X

X X

Table 7. Fuel Properties of Obtained Oils pine chips

pine pellets

properties

polar oil

oily bottom phase

polar oil

oily bottom phase

biodiesel

dynamic viscosity at 25 °C (cP) high calorific value (MJ kg-1) pH density (kg dm-3)

125.6 17.9 2.6 1.1830

140.2 23.8 2.4 1.0880

44.8 19.5 2.7 1.2362

76.8 24.8 2.6 1.1337

6.4 39.0 4.2 0.8572

sugars (family C) and some oligomers (family D and E) that are not soluble in bio-diesel can be converted to hydrogen by supercritical reforming or to hydrocarbons and H2 by aqueousphase catalytic processes (APPs).1 These processes can be integrated into new bio-oil-based refinery concepts for a complete use of bio-oils.

Figure 8 presents the TG and DTG curves of biodiesel-rich phases obtained when blending with the oily bottom phases (see

Figure 6. Yield of biodiesel- and bio-oil-rich phases.

Figure 7. Bio-oil concentrations in the biodiesel-rich phase.



Figure 8. DTG curves of biodiesel-rich phases with different concentrations of bio-oil (arrows indicate solubility trends as the concentration of bio-oil increases).

Figure 3). The content of bio-oil for each of the biodiesel-rich phases obtained is indicated in the figure. Compounds with boiling points between 100 and 200 °C (phenols and furans) indicated by an increase in the shoulder under 200 °C and small amounts of oligomers (see an increase in DTG curves around 300 °C) were added to the biodiesel phase. The numbers indicated on the figure are the mass % of bio-oil-derived compounds present in the bio-diesel-rich phase. Only a small increase in the carbon residues, from 1.0 mass % for pure biodiesel to 2.0 mass % for a bio-diesel containing 34 mass % of bio-oil, was observed when bio-oils were added to the biodiesel. This increase is likely to be due to the addition of some oligomers to the bio-diesel. The thermal and oxidation stability of biodiesel containing bio-oil is an aspect that needs to be further studied. 3.6. Fuel Properties of Biodiesel-Rich Phases. The change in the density of the biodiesel-rich phase upon the addition of bio-oils is presented in Figure 9. The results obtained suggest an increase in 0.002 35 g mL-1 per mass % of bio-oil added. Figure 10 shows the change in the viscosity of biodieselrich phases at different concentrations of bio-oil. The addition of the pine chip oily bottom phase seems to cause a larger increase in viscosity than the pine-pellet-derived oils. This result could be explained by the larger amounts of fractions D and E soluble in the biodiesel (see Table 4). Some of the oligomers initially soluble could separate upon cooling; however, the remaining oligomeric material added to the biodiesel needs to be carefully controlled to protect fuel properties and engine injectors. The addition of bio-oils to biodiesel does not seem to greatly affect the calorific value of resulting blends (see Table 8). This result could be explained by the fact that almost all of the water and the most polar fractions in bio-oil responsible for the lowenergy values are not added to the biodiesel. These fractions are left in the bio-oil-rich phase (see Figure 4). The water content

Figure 9. Density of biodiesel/bio-oil blends (at 25 °C). Pine chip: (]) oily bottom phase and (O) polar oil. Pine pellet: (0) oily bottom phase and (4) polar oil.

in blends increases upon the addition of bio-oil-derived compounds. Water contents up to 1.65 mass % were obtained in blends prepared with 50 mass % bio-oil (Table 9). The pH of the biodiesel-rich blends is reduced as the bio-oil is added to the biodiesel (Table 10). This reduction in pH could be attributed to the solubility of some carboxylic acids. The biodiesel-rich phase was further extracted with an aqueous solution of sodium bicarbonate (5 mass %). The pH of the bicarbonate solution was maintained at approximately 8-9.5. A 3:1 bicarbonate solution/biodiesel-rich phase obtained after blending biodiesel with 50 mass % of the pine chip pellet oily phase was used. The aqueous bicarbonate phase/biodieselrich phase was vortexed for 30 s and left to settle for 2 h. The top biodiesel-rich phase was decanted. The bicarbonate solution extracts the strong organic acids and the highly polar compounds. The pH of the resulting biodiesel-rich phase increased to 6.9.


Garcia-Perez et al. Table 10. pH of the Biodiesel-Rich Phase (pH Biodiesel ) 4.15) pine chips

Figure 10. Viscosity of biodiesel/bio-oil blends (at 25 °C). Table 8. High Calorific Value of the Biodiesel-Rich Phase (MJ kg-1) (Biodiesel ) 39.02 MJ kg-1) pine chips

pine pellets

bio-oil/biodiesel blends (mass % of biodiesel)

polar oil

oily bottom phase

polar oil

oily bottom phase

10 20 40 50

37.0 35.8 35.6 36.1

38.5 37.5 36.0 39.0

36.2 38.0 38.5

35.5 35.4 36.7 35.6

Table 9. Water Content (Mass %) of the Biodiesel-Rich Phase (Biodiesel ) 0.1730 Mass % Water) pine chips

pine pellets


polar oil

oily bottom phase

polar oil

oily bottom phase

10 20 40 50

0.17 0.21 0.25 0.38

0.29 0.47 0.95 1.65

0.22 0.14 0.16 0.78

0.36 0.36 0.60 0.83

4. Conclusions The addition of processed bio-oils to biodiesel is a viable method to extract some of the best fuel fractions present in bio-

pine pellets


polar oil

oily bottom phase

oily bottom phase

polar oil

10 20 40 50

2.47 2.64 2.62 2.54

2.66 2.68 1.88 2.67

2.77 3.28 3.22 3.20

2.74 3.29 3.06 2.70

oils for use in a transportation fuel. This result is important because up to now the use of crude bio-oils as transportation fuel has been an elusive goal. Bio-oil is the least expensive liquid fuel obtainable from lignocellulosic materials. The use of some bio-oil fractions in transportation fuels could have huge economic implications. The fuel properties of biodiesel do not seem to be greatly changed by soluble fractions of bio-oils. Small increases in density and viscosity and a small change in the calorific value and solid residues were observed. The oily bottom phases were considerably more soluble in biodiesel than the polar oils obtained from the aqueous phases. Fuel blends of biodiesel and bio-oil require neutralization with a weak base, such as NaHCO3, to remove the organic acids soluble in biodiesel. Because the studies were carried out in blends prepared at 60 °C but left to cool to 25 °C, it is logical to suppose that our results represent only the equilibrium at ambient temperature. Separation could occur when the blends are cooled because the equilibrium between the phases is very dependent upon the temperature. Additional studies on the phase equilibrium of bio-oil/biodiesel blends at lower temperatures need to be carried out. Further studies will be conducted to study the performance of these blends in diesel engines and to develop methods to control the content of oligomers in the blends. Acknowledgment. The authors are very grateful to Joshua Pendergrass, Brian Bibbens, and Sempa Kissalita for their contributions in the experimental work. We thank the Fiber Committee of the Georgia Traditional Industries Pulp and Paper Research Program and the U.S. Department of Energy for financial support. Additionally, the authors greatly appreciate the guidance provided by our industrial research partner, especially, Mr. Wesley Langdale and Mr. Andres Villgas, Langdale Industries, Inc., Valdosta, GA. EF060533E

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