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Thermal processing of soybean oil to obtain bio-based polymers and bio-oil
Industrial Crops and Products 66 (2015) 255–261
Contents lists available at ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Thermal processing of soybean oil to obtain bio-based polymers and bio-oil Vinicius M. Mello, Guilherme B.C. Martins, Mateus de A. Montenegro, Paulo A.Z. Suarez ∗ Laboratório de Materiais e Combustíveis, Universidade de Brasília, CP 4478, Brasília, DF 70910-970, Brazil
a r t i c l e
i n f o
Article history: Received 29 July 2014 Received in revised form 14 October 2014 Accepted 23 October 2014 Keywords: Soybean oil Thermal process Bio-oil Printing ink Nickel catalyst
a b s t r a c t In this study we evaluated the use of triacylglycerides to produce bio-based resins and bio-oils suitable to be used, respectively, as a binder in printing inks (offset) and as diesel-like fuel. Soybean oil was kept under nitrogen atmosphere at temperatures ranging from 260 ◦ C to 370 ◦ C up to 12 h in the presence or absence of a nickel complex as a catalyst precursor. It was observed that the reaction occurs in two steps. In the first one, occurs the consumption of the double bonds via Diels–Alder to form a polymer increasing the viscosity of the material. In a second step, the pyrolysis of ester groups and the alkyd chains takes place, reducing a viscosity of the polymers. Besides, using Nickel complex as a catalyst precursor it was observed a high activity to produce polymers with higher viscosity in a shorter time than when comparing with reactions without catalyst. It were also analyzed the bio-oil formed during the reaction. It was observed that without catalyst the pyrolysis leads to the formation of high amounts of carboxylic acids with short chain. However, the presence of Nickel complex increased the formation of hydrocarbons and reduced the amount of formed carboxylic acids, strongly indicating its activity in the deoxygenation. © 2014 Elsevier B.V. All rights reserved.
1. Introduction With the petroleum supply crisis in the 1970s, researchers were encouraged to develop products using biomass as raw materials. Particularly, the treatment of triacylglycerides at high temperatures proved to be an important way to produce new bio-products, such as fuels, lubricants, inks, additives and others (Suarez et al., 2007). In the early 1980s, American Newspaper Publishers Association reported the development of printing inks using a high viscosity bio-based polymer obtained from vegetable oils as a binder (Moynihan, 1985). When mixing this polymer with pigments and additives were obtained inks suitable to be used to print newspapers and magazines with very advantageous properties. Indeed, when compared these bio-based inks with traditional petroleum-based inks, was observed a better affinity with the carbon black pigment, making possible to reduce its amount in the formulation, a better degradation by fungi and a easier recycling of the paper, as well as a lower price (Moynihan, 1985; Erhan and Bagby, 1991, 1992, 1993, 1994, 1995). Because of these
∗ Corresponding author. Tel.: +55 6131073852; fax: +55 6132734149. E-mail address: [email protected] (P.A.Z. Suarez). http://dx.doi.org/10.1016/j.indcrop.2014.10.041 0926-6690/© 2014 Elsevier B.V. All rights reserved.
characteristics these bio-based inks were quickly accepted in the printing marked and are still in use. Nowadays, the search for renewable feedstock to produce materials and fuels is pointed out as an elegant solution to address environmental behaviors related to the petroleum industry as well as to address the increasing demand for organic materials and fuels. In this context, biobased polymers have received increasing attention and their use as binder in inks, paints, coatings and adhesives has proved to be viable from both economic and technical points of view (Suarez et al., 2007; Moynihan, 1985; Erhan and Bagby, 1991, 1992, 1993, 1994, 1995). However, there are few studies in the literature relating the thermal polymerization of vegetable oils (Archer Daniels Midland Company, 1938; Sims, 1957). It is well accepted that the reaction starts around 200 ◦ C, when the isomerization and the conjugation of double bounds to form trans conjugated dienes take place. Thus, the polymerization starts after 260 ◦ C when the formed dienes react by Diels–Alder to achieve tetra substituted cyclohexenes, forming a cross-link between chains (Sims, 1957), or via free radicals combination (Arca et al., 2012). Usually, the use of catalysts proved to diminish the reaction time, achieving higher viscosities in shorter times (Mello et al., 2013a). Thus, because of the high temperatures associated with thermal polymerization the use of catalyst are claimed to reduce energy consumption.
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Above 350 ◦ C occurs a thermal cracking of triacylglycerides. In this process, the decomposition of the ester groups take place, converting the triacylglycerides into a mixture of different compounds, mainly hydrocarbons, carboxylic acids and other oxygenated compounds (Lima et al., 2004; Quirino et al., 2009). The composition of this mixture, known as bio-oil, varies according to the source of triacylglyceride used as a raw material, reaction conditions (temperature and time) and the catalyst used in this process (Lima et al., 2004; Quirino et al., 2009; Tami et al., 2011; Ramya et al., 2012; Botas et al., 2012). Because of their interesting physical and chemical properties (density, flash point, kinematic viscosity, calorific value and copper corrosion), the bio-oils have been pointed out as suitable to be used as liquid fuels (Lima et al., 2004; Quirino et al., 2009). In the literature several reports describe the use of triacylglycerides to produce bio-polymers and bio-oils (Moynihan, 1985; Erhan and Bagby, 1991, 1992, 1993, 1994, 1995). These studies are carried out at low temperatures (around 300 ◦ C) when aiming to obtain polymers and at high temperatures (above 400 ◦ C) when liquid fuels are desired. For instance, we have demonstrated the catalytic activity of different metal compounds to obtain polymers from different oils at low temperatures (Mello et al., 2013a) and the possibility to produce diesel-like fuels from different vegetable oils at high temperatures with (Quirino et al., 2009) or without (Lima et al., 2004) catalysts. For instance, we have recently published the use of bio-polymers obtained from soybean oil and frying oil in printing inks formulation (Mello et al., 2013b; Montenegro et al., 2013) and the production and storage stability of diesel-like fuel from soybean oil in a continuous pilot-plant (Barreto et al., 2012). However, as far as our knowledge, it was not yet studied simultaneously both processes, as well as the influence of the temperature and the use of catalyst in order to tune the selectivity. The aim of this work was to study the influence of temperature, in presence and absence of a nickel-based catalyst, in the bio-polymer and bio-oil yield. 2. Experimental 2.1. Materials Alkali-refined soybean were obtained from Bunge Alimentos (Valparaíso, GO, Brazil) and used as received. Nickel complex used as catalyst precursor was synthesized utilizing Ni2+ and carboxylate ligands derived from palm oil fatty acids, with the generic structure of Ni(carboxylate)2 , as previously described by Mello et al. (2013a,b). 2.2. Thermal reaction procedures Alkali-refined soybean oil (650 g) was added into a 1.0 L five necked round bottom flask equipped with a condenser, a nitrogen inlet, a thermocouple and a heating mantle. The experimental apparatus can be depicted from Fig. 1. When evaluating the catalytic activity of Ni(carboxylate)2 , the complex (0.65 g) was directly dissolved in soybean oil without any activation procedure. During the reaction, polymer samples were taken at different times. In order to take samples one of the flask neck was opened under a nitrogen flux and 20 mL were taken with a syringe. Thus, the sample was analyzed by FT-IR and its kinematic viscosity and acid index were determined. The FT-IR spectra were obtained using a Shimadzu Prestige-21 equipped with ATR (Attenuated Total Reflectance, from Pike Technologies), optical way 7 mm and 10 reflections, using nominal spectral resolution of 4 cm−1 and average of 32 interferograns. The kinematic viscosity was determined using an ubbelohde viscosimeter according to ASTM D445 standard
Fig. 1. Experimental apparatus used for thermal decomposition of soybean oil.
method. The acid index of the samples was obtained according to AOCS Cd 3d-63 standard method. Condensed Bio-oil samples were collected and analyzed by GC–MS in a CG-EM-QP5050 equipment from Shimadzu using a fused silica capillary column CBPI PONA with 50 m of length, 0.25 mm of diameter and 0.50 m width. The temperature of the injector was kept at 250 ◦ C, and the column temperature varied from 60 to 250 ◦ C, with 10 ◦ C/min heating rate, 39 min in total. Note that according to the experiment different time intervals were used to collect the bio-oil. The presence of nickel in the products was measured using an iCAP 6300 Duo ICP optical emission spectrometer (Thermo Fisher Scientific, Cambridge, England) equipped with axially and radially viewed plasma. The spectrometer was equipped with a simultaneous charge injection device detector allowing measurements from 166.25 to 847.00 nm and the Echelle polychromator was purged with argon. The introduction system was composed of a cyclonic spray chamber and a Meinhard nebulizer. The injector tube diameter of the torch was 2.0 mm. The precipitates in the polymeric product were analyzed by Xray diffraction powder using a Brucker diffractometer, model D8 Focus. The detection range (2Theta) was 10–90◦ with the step size of 0.05◦ (1◦ min−1 ). 3. Results and discussion 3.1. Mass relationship between polymer and bio-oil Initially, it was evaluated the mass relationship between the polymer and bio-oil formed at different temperatures during 1 h, with and without catalyst. It was observed that in a reaction without catalyst bio-oil was formed only above 350 ◦ C (Fig. 2A) and that in the presence of Nickel complex it was formed above 330 ◦ C, reducing the initial temperature by 20 ◦ C, clearly indicating a catalytic activity in pyrolysis. In sequence, it were analyzed the viscosities of the obtained bio-polymers, observing an increase in the viscosity values when increasing the temperature. Note that above 300 ◦ C the viscosity of the polymer is always higher when using Ni(carboxylate)2 than in the absence of catalyst. (Fig. 2B). 3.2. Polymer To evaluate the reaction parameters in the bio-polymer produced, soybean oil was kept at different temperatures during 12 h. It were taken samples at the times 0.0, 0.5, 1.0, 1.5, 2.0, 4.0, 6.0, 8.0, 10.0 and 12.0 h. The viscosities of the different samples are shown in Fig. 3. As can be depicted from Fig. 3, in the presence or absence of catalyst, it was not observed any increase in the viscosity during
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Fig. 2. Thermal reaction of refined soybean oil during 1 h: (A) mass relationship between distillated (,) and non-distillated (,) products in the absence (,) or presence of catalyst (,); (B) viscosity of the non-distillated products in the absence () or presence (䊉) of catalyst.
the entire reaction at 260 ◦ C. Thus, no polymer formation takes place at this temperature. However, even in the absence of catalyst it was observed an exponentially increasing of the viscosity at 300 ◦ C, achieving a high viscous polymer in 12 h (Fig. 3A). At temperatures from 330 to 370 ◦ C, it was noticed in the absence of catalyst a considerable increase in the viscosity values at initial times followed by its decrease at longer times. It is important to note that the reaction at 370 ◦ C was finished in 2 h because of a strong formation of light products, ending by an important mass loss inside the flask. Besides, in the presence of catalyst (Fig. 3B), it was observed a significant increase in the viscosity at initial times, demonstrating once again the catalytic activity of this catalyst in the polymerization. However, at 350 ◦ C the pyrolysis reaction becomes very important and, after 2 h, it was observed a reduction of the viscosity accomplished by the formation of light products (note that the reaction was stopped after 4 h because almost all material was converted into bio-oil). At 370 ◦ C, there is a substantial increase in the viscosity during the very initial times followed by a great loss of mass, and the reaction had to be stopped at 0.5 h. It is worth mentioning that in the absence of catalyst at 370 ◦ C this process took 2 h for the complete transformation of the material into biooil, once again evidencing the catalytic activity of Ni since the time was reduced by 75%. In sequence, it was evaluated the acid indexes of the polymer samples and the results are shown in Fig. 4. Without catalyst (Fig. 4A) it was observed that the acid index increased during all reaction at 260, 300 and 330 ◦ C. However, at 350 and 370 ◦ C the acid index decreased after achieving a maximum. This behavior is probably the result of the deoxygenation of the carboxylic acids formed during the thermal decomposition of esters, probably through decarbonylation and/or decarboxylation processes (Fabbri et al., 2005), which is favored at higher temperatures. In presence
of catalyst a similar behavior was obtained (Fig. 4B). However, in this case, it was already observed the formation of a maximum followed by a reduction in the acid index at 330 ◦ C, evidencing the catalytic activity of Ni also in the deoxygenation of carboxylic acids. These results are particularly important because polymers with small acid index lead to printing inks with higher hydrophobicity, which are known to have a better performance in lithographic and offset printing processes (Mello and Suarez, 2012). Thus, to obtain more information about the reaction mechanism, all the samples collected from the reaction bulk were analyzed by ATR-FT-IR. It were monitored the bands at wave numbers related to conjugate double bonds in trans configuration (987 cm−1 ), ester carboxyl group (1741 cm−1 ) and carboxylic acid carboxyl group (1708 cm−1 ). The obtained results are shown in Fig. 5 and Fig. 6. It is observed that the first transformation of triacylglycerides is the isomerization of double bonds to form conjugated trans dienes, as related in the literature (Sorensen, 1938), which are quickly consumed. Note that the velocity of formation and consumption of the trans dienes are strongly dependent on the temperature (Fig. 5A). Correlating the viscosity behavior from Fig. 3 and the formation and consumption of conjugated dienes from Fig. 5, it can be suggested that reactions involving conjugated double bonds (probably Diels–Alder or radical polymerization) are the most important reaction during the polymerization. Indeed, these results strongly suggest that the formation of conjugated dienes is needed before increasing the viscosity of the media. Carrying out these experiments in the presence of Ni it was observed a similar behavior with a higher reaction rate. As can be observed in Fig. 6, during the reaction the ester carboxyl groups (Fig. 6A and B) are consumed and carboxylic acids (Fig. 6C and D) are formed. Note that this process is strongly favored by the temperature. In the presence of catalyst the decomposition of the ester group is always more accentuated than in the
Fig. 3. Viscosity of the non-distillated products obtained by thermal decomposition of refined soybean oil at () 260 ◦ C; (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C in the absence (A) and presence (B) of catalyst.
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Fig. 4. Acid index of the samples collected from the reaction bulk during the thermal decomposition of refined soybean oil at () 260 ◦ C; (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C in the absence (A) and presence (B) of catalyst.
Fig. 5. Infrared absorbance of the samples collected from the reaction bulk during the thermal decomposition of refined soybean oil at obtained at () 260; (䊉) 300; () 330; () 350; and (*) 370 ◦ C: (1) absorbance at 987 cm−1 related to trans–trans conjugated double bonds in the absence (A) and presence (B) of Ni(carboxylate)2.
non-catalyzed reaction and occurs even at low temperatures (260 ◦ C). It is worth to mention that the deoxygenation of the carboxylic acids is also more pronounced in the presence of the catalyst.
It is important to highlight that we have repeated these reactions several times in the last 4 years and the polymer physical-chemical properties, as well as the reaction yields, present a very good reproducibility. Indeed, we have been producing polymers from soybean
Fig. 6. Infrared absorbance of the samples collected from the reaction bulk during the thermal decomposition of refined soybean oil at () 260; (䊉) 300; () 330; () 350; and (*) 370 ◦ C: absorbance at 1741 cm−1 related to ester carboxyl group in the absence (A) and presence (B) of catalyst. Absorbance at 1708 cm−1 related to carboxylic acid carboxyl group in the absence (C) and presence (D) of catalyst.
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Fig. 7. Percentage of heptanoic acid in distillated samples obtained by thermal decomposition of refined soybean oil at (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C: in the absence (A) and presence (B) of catalyst.
Fig. 8. Percentage of pentadecane in distillated samples obtained by thermal decomposition of refined soybean oil at (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C: in the absence (A) and presence (B) of catalyst.
oil and used soybean oil with tuned physical-chemical properties in order to formulate inks to be used in lithographic and xylographic prints, both in the presence or absence of nickel catalyst, and have always been able to reproduce the results. Indeed, we observed differences in the physical–chemical properties and the reaction yields only when changing the starting feedstock (Mello et al., 2013b). Note that some printings using inks formulated in our laboratory using these polymers have already been published in previous works (for instance, see references Mello et al., 2013b; Montenegro et al., 2013). 3.3. Bio-oil Bio-oil was collected during intervals of 0.5 h in the first 6 h and in intervals of 1 h until the end of the reaction, both in the
presence and absence of catalyst. It is important to highlight that was not observed the formation of bio-oil at 260 ◦ C and that at 300 ◦ C the formation of light products was observed only after 2 h. The collected samples were analyzed by GC–MS and acid index. The main results obtained from chromatographic analysis are shown in Figs. 7–9 and from acid index in Fig. 10. It was detected carboxylic acids with short chains (from 6 to 8 carbons) and hydrocarbons with large chains (from 15 to 17 carbons). It is important to highlight that the composition of the samples is strongly influenced by time, temperature and the presence of catalyst. For instance, in Figs 7–9 are shown the variation with time of selected compounds (respectively, heptadecanoic acid, pentadecane and heptadecane) wt.% in the samples at different temperatures. It becomes clear from Figs 7–9 that increasing the temperature and time and
Fig. 9. Percentage of heptadecane in distillated samples obtained by thermal decomposition of refined soybean oil at (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C: in the absence (A) and presence (B) of catalyst.
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Fig. 10. Acid index of distillated samples obtained by thermal decomposition of refined soybean oil at (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C: in the absence (A) and presence (B) of catalyst.
Fig. 11. DRX of the precipitate recovered from the polymer.
in the presence of catalyst the formation of the mentioned hydrocarbons is enhanced. Note that the acid index of the biooil samples (Fig. 10) corroborates these results, since the acidity decreases at higher temperatures and times and in the presence of catalyst.
reduced. Thus, nickel may be completely recovered from the products just by centrifuging or filtering the polymer phase.
3.4. Presence of nickel in the products
In summary, in this work was shown that the choice of time, temperature and the presence of nickel catalyst may drastically change the obtained products, switching from bio-polymers to biooils. It was also observed that the reaction parameters determine also the studied physical–chemical properties and chemical composition of the final products. It was observed that above 300 ◦ C the thermal decomposition of triacylglycerides occurs in two steps. In the first step occurs an increase in the viscosity of the media leading to high viscous biopolymers. In this step was observed the formation of conjugated trans–trans dienes followed by their consumption. In the second step occurs the reduction of viscosity of the material because of breaking carbon–carbon bonds and esters groups to form lighter products.
In order to understand what happened to the nickel complex after the reaction we studied the liquid and the polymeric products. In the liquid product we could no detect the presence of nickel cations using ICP-OES. Besides, we observed the formation of a precipitate in the polymeric phase. Thus, we isolated the precipitate by dissolving the polymer in hexane and centrifuging the mixture, washing the obtained solid with hexane. Analyzing the supernatant by ICP-OES it was also not possible to detect nickel cations. However, analyzing the obtained solid by DRX (see Fig. 11) it was observed that it was formed a mixture of metallic nickel and nickel carbide (Ni3 C), strongly indicating that at the reactions conditions the nickel complex decompose and the metallic cation is
4. Conclusions
V.M. Mello et al. / Industrial Crops and Products 66 (2015) 255–261
Studying the composition of the bio-oil, it was observed that in reactions without catalyst occur the formation of a large amount of carboxylic acids and small quantities of saturated and unsaturated hydrocarbons. However, in the presence of nickel catalyst it was observed a pronounced deoxygenation of the carboxylic acids to produce mainly saturated and unsaturated hydrocarbons, evidencing the catalytic activity of this catalyst in the decarbonylation and/or decarboxylation of the carboxyl groups. Acknowledgements The authors are thankful to INCT-Catálise, EMBRAPA, CAPES, FINEP, FAPDF and CNPq for financial support. The authors wish also to thank CNPq for their research fellowships. References Arca, M., Sharma, B.K., Price, N.P.J., Perez, J.M., Doll, K.M., 2012. Evidence contrary to the accepted Diels–Alder mechanism in the thermal modification of vegetable oil. J. Am. Oil Chem. Soc. 89 (6), 987–994. Archer Daniels Midland Company, 1938. US Patent US2213935. Barreto, C.C.K., Oliveira, C.C., Souza, G.G.S., Suarez, P.A.Z., Rubim, J.C., 2012. Evaluation of the stability during storage of a diesel-like fuel obtained by the pyrolysis of soybean oil. Biomass Bioenergy 37, 42–48. Botas, J.A., Serrano, D.P., García, A., de Vicente, J., Ramos, R., 2012. Catalytic conversion of rapeseed oil into raw chemicals and fuels over Ni- and Mo-modified nanocrystalline ZSM-5 zeolite. Catal. Today 195, 59–70. Erhan, S.Z., Bagby, M.J., 1991. Lithographic and letterpress ink vehicles from vegetable oils. J. Am. Oil Chem. Soc. 68, 635–638. Erhan, S.Z., Bagby, M.O., 1992. Gel permeation chromatography of vegetable-oil based printing ink vehicle. J. Appl. Polym. Sci. 46 (10), 1859–1862. Erhan, S.Z., Bagby, M.O.,1993. Taga Proceedings. Technical Association of the Graphic Arts, Chelsea, pp. 314–326.
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Erhan, S.Z., Bagby, M.O., 1994. Taga Proceedings. Technical Association of the Graphic Arts, Chelsea, pp. p313. Erhan, S.Z., Bagby, M.O., 1995. Vegetable-oil-based printing ink formulation and degradation. Ind. Crops Prod. 4 (3), 237–246. Fabbri, D., Baravelli, V., Chiavari, G., Prati, S., 2005. Profiling fatty acids in vegetable oils by reactive pyrolysis-gas chromatography with dimethyl carbonate and titanium silicate. J. Chromatogr. A 1100, 218. Lima, D.G., Soares, V.C.D., Ribeiro, E.B., Carvalho, D.A., Cardoso, E.C.V., Rassi, F.C., Mundim, K.C., Rubim, J.C., Suarez, P.A.Z., 2004. Diesel-like fuel obtained by pyrolysis of vegetable oils. J. Anal. Appl. Pyrolysis 71, 987–996. Mello, V.M., Suarez, P.A.Z., 2012. As Formulac¸ões de tintas expressivas através da história. Rev. Virtual Quim. 4 (1), 2–12. Mello, V.M., Oliveira, G.V., Mandarino, J.M.G., Carrão-Panizzi, M.C., Suarez, P.A.Z., 2013a. New metal catalysts active for thermal polymerization of vegetable oils. Ind. Crops Prod. 43, 56–60. Mello, V.M., Oliveira, G.V., Suarez, P.A.Z., 2013b. Turning used frying oil into a new raw material to printing inks. J. Braz. Chem. Soc. 24 (2), 1–6. Montenegro, M.A., Pereira, R.C., Hofmann-Gatti, T., Martins, G.B.C., Suarez, P.A.Z., 2013. The use of waste oils and fats to produce high value products: formulation of printing inks involving used frying oils. Rev. Virtual Quim. 5 (1), 26–37. Moynihan, J.T., 1985. American Newspaper Publishers Association, US Patent 4519841. Quirino, R.L., Tavarees, A.P., Peres, A.C., Rubim, J.C., Suarez, P.A.Z., 2009. Studying the influence of alumina catalysts doped with tin and zinc oxides in the soybean oil pyrolysis reaction. J. Am. Oil Chem. Soc. 86, 167–172. Ramya, G., Sudhakar, R., Joice, J.A.I., Ramakrishnan, R., Sivakumar, T., 2012. Liquid hydrocarbon fuels from jatropha oil through catalytic cracking technology using AlMCM-41/ZSM-5 composite catalysts. Appl. Catal. A: Gen. 433, 170–178. Sims, R.P.A., 1957. Possible mechanisms in thermal polymerization of vegetable oils: II. Polymer formation. J. Am. Oil Chem. Soc. 34 (9), 466. Sorensen, S.O., 1938. Konen, JC, US Patent US2213935. Suarez, P.A.Z., Meneghetti, S.M.P., Meneghetti, M.R., Wolf, C.R., 2007. Transformation of triglycerides into fuels, polymers and chemicals: some applications of catalysis in oleochemistry, Quim. Nova 30 (3), 667–676. Tami, H., Hasegawa, T., Shimouchi, M., Asami, K., Fujimoto, K., 2011. Selective catalytic decarboxy-cracking of triglyceride to middle-distillate hydrocarbon. Catal. Today 164, 410–414.
Contents lists available at ScienceDirect
Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop
Thermal processing of soybean oil to obtain bio-based polymers and bio-oil Vinicius M. Mello, Guilherme B.C. Martins, Mateus de A. Montenegro, Paulo A.Z. Suarez ∗ Laboratório de Materiais e Combustíveis, Universidade de Brasília, CP 4478, Brasília, DF 70910-970, Brazil
a r t i c l e
i n f o
Article history: Received 29 July 2014 Received in revised form 14 October 2014 Accepted 23 October 2014 Keywords: Soybean oil Thermal process Bio-oil Printing ink Nickel catalyst
a b s t r a c t In this study we evaluated the use of triacylglycerides to produce bio-based resins and bio-oils suitable to be used, respectively, as a binder in printing inks (offset) and as diesel-like fuel. Soybean oil was kept under nitrogen atmosphere at temperatures ranging from 260 ◦ C to 370 ◦ C up to 12 h in the presence or absence of a nickel complex as a catalyst precursor. It was observed that the reaction occurs in two steps. In the first one, occurs the consumption of the double bonds via Diels–Alder to form a polymer increasing the viscosity of the material. In a second step, the pyrolysis of ester groups and the alkyd chains takes place, reducing a viscosity of the polymers. Besides, using Nickel complex as a catalyst precursor it was observed a high activity to produce polymers with higher viscosity in a shorter time than when comparing with reactions without catalyst. It were also analyzed the bio-oil formed during the reaction. It was observed that without catalyst the pyrolysis leads to the formation of high amounts of carboxylic acids with short chain. However, the presence of Nickel complex increased the formation of hydrocarbons and reduced the amount of formed carboxylic acids, strongly indicating its activity in the deoxygenation. © 2014 Elsevier B.V. All rights reserved.
1. Introduction With the petroleum supply crisis in the 1970s, researchers were encouraged to develop products using biomass as raw materials. Particularly, the treatment of triacylglycerides at high temperatures proved to be an important way to produce new bio-products, such as fuels, lubricants, inks, additives and others (Suarez et al., 2007). In the early 1980s, American Newspaper Publishers Association reported the development of printing inks using a high viscosity bio-based polymer obtained from vegetable oils as a binder (Moynihan, 1985). When mixing this polymer with pigments and additives were obtained inks suitable to be used to print newspapers and magazines with very advantageous properties. Indeed, when compared these bio-based inks with traditional petroleum-based inks, was observed a better affinity with the carbon black pigment, making possible to reduce its amount in the formulation, a better degradation by fungi and a easier recycling of the paper, as well as a lower price (Moynihan, 1985; Erhan and Bagby, 1991, 1992, 1993, 1994, 1995). Because of these
∗ Corresponding author. Tel.: +55 6131073852; fax: +55 6132734149. E-mail address: [email protected] (P.A.Z. Suarez). http://dx.doi.org/10.1016/j.indcrop.2014.10.041 0926-6690/© 2014 Elsevier B.V. All rights reserved.
characteristics these bio-based inks were quickly accepted in the printing marked and are still in use. Nowadays, the search for renewable feedstock to produce materials and fuels is pointed out as an elegant solution to address environmental behaviors related to the petroleum industry as well as to address the increasing demand for organic materials and fuels. In this context, biobased polymers have received increasing attention and their use as binder in inks, paints, coatings and adhesives has proved to be viable from both economic and technical points of view (Suarez et al., 2007; Moynihan, 1985; Erhan and Bagby, 1991, 1992, 1993, 1994, 1995). However, there are few studies in the literature relating the thermal polymerization of vegetable oils (Archer Daniels Midland Company, 1938; Sims, 1957). It is well accepted that the reaction starts around 200 ◦ C, when the isomerization and the conjugation of double bounds to form trans conjugated dienes take place. Thus, the polymerization starts after 260 ◦ C when the formed dienes react by Diels–Alder to achieve tetra substituted cyclohexenes, forming a cross-link between chains (Sims, 1957), or via free radicals combination (Arca et al., 2012). Usually, the use of catalysts proved to diminish the reaction time, achieving higher viscosities in shorter times (Mello et al., 2013a). Thus, because of the high temperatures associated with thermal polymerization the use of catalyst are claimed to reduce energy consumption.
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Above 350 ◦ C occurs a thermal cracking of triacylglycerides. In this process, the decomposition of the ester groups take place, converting the triacylglycerides into a mixture of different compounds, mainly hydrocarbons, carboxylic acids and other oxygenated compounds (Lima et al., 2004; Quirino et al., 2009). The composition of this mixture, known as bio-oil, varies according to the source of triacylglyceride used as a raw material, reaction conditions (temperature and time) and the catalyst used in this process (Lima et al., 2004; Quirino et al., 2009; Tami et al., 2011; Ramya et al., 2012; Botas et al., 2012). Because of their interesting physical and chemical properties (density, flash point, kinematic viscosity, calorific value and copper corrosion), the bio-oils have been pointed out as suitable to be used as liquid fuels (Lima et al., 2004; Quirino et al., 2009). In the literature several reports describe the use of triacylglycerides to produce bio-polymers and bio-oils (Moynihan, 1985; Erhan and Bagby, 1991, 1992, 1993, 1994, 1995). These studies are carried out at low temperatures (around 300 ◦ C) when aiming to obtain polymers and at high temperatures (above 400 ◦ C) when liquid fuels are desired. For instance, we have demonstrated the catalytic activity of different metal compounds to obtain polymers from different oils at low temperatures (Mello et al., 2013a) and the possibility to produce diesel-like fuels from different vegetable oils at high temperatures with (Quirino et al., 2009) or without (Lima et al., 2004) catalysts. For instance, we have recently published the use of bio-polymers obtained from soybean oil and frying oil in printing inks formulation (Mello et al., 2013b; Montenegro et al., 2013) and the production and storage stability of diesel-like fuel from soybean oil in a continuous pilot-plant (Barreto et al., 2012). However, as far as our knowledge, it was not yet studied simultaneously both processes, as well as the influence of the temperature and the use of catalyst in order to tune the selectivity. The aim of this work was to study the influence of temperature, in presence and absence of a nickel-based catalyst, in the bio-polymer and bio-oil yield. 2. Experimental 2.1. Materials Alkali-refined soybean were obtained from Bunge Alimentos (Valparaíso, GO, Brazil) and used as received. Nickel complex used as catalyst precursor was synthesized utilizing Ni2+ and carboxylate ligands derived from palm oil fatty acids, with the generic structure of Ni(carboxylate)2 , as previously described by Mello et al. (2013a,b). 2.2. Thermal reaction procedures Alkali-refined soybean oil (650 g) was added into a 1.0 L five necked round bottom flask equipped with a condenser, a nitrogen inlet, a thermocouple and a heating mantle. The experimental apparatus can be depicted from Fig. 1. When evaluating the catalytic activity of Ni(carboxylate)2 , the complex (0.65 g) was directly dissolved in soybean oil without any activation procedure. During the reaction, polymer samples were taken at different times. In order to take samples one of the flask neck was opened under a nitrogen flux and 20 mL were taken with a syringe. Thus, the sample was analyzed by FT-IR and its kinematic viscosity and acid index were determined. The FT-IR spectra were obtained using a Shimadzu Prestige-21 equipped with ATR (Attenuated Total Reflectance, from Pike Technologies), optical way 7 mm and 10 reflections, using nominal spectral resolution of 4 cm−1 and average of 32 interferograns. The kinematic viscosity was determined using an ubbelohde viscosimeter according to ASTM D445 standard
Fig. 1. Experimental apparatus used for thermal decomposition of soybean oil.
method. The acid index of the samples was obtained according to AOCS Cd 3d-63 standard method. Condensed Bio-oil samples were collected and analyzed by GC–MS in a CG-EM-QP5050 equipment from Shimadzu using a fused silica capillary column CBPI PONA with 50 m of length, 0.25 mm of diameter and 0.50 m width. The temperature of the injector was kept at 250 ◦ C, and the column temperature varied from 60 to 250 ◦ C, with 10 ◦ C/min heating rate, 39 min in total. Note that according to the experiment different time intervals were used to collect the bio-oil. The presence of nickel in the products was measured using an iCAP 6300 Duo ICP optical emission spectrometer (Thermo Fisher Scientific, Cambridge, England) equipped with axially and radially viewed plasma. The spectrometer was equipped with a simultaneous charge injection device detector allowing measurements from 166.25 to 847.00 nm and the Echelle polychromator was purged with argon. The introduction system was composed of a cyclonic spray chamber and a Meinhard nebulizer. The injector tube diameter of the torch was 2.0 mm. The precipitates in the polymeric product were analyzed by Xray diffraction powder using a Brucker diffractometer, model D8 Focus. The detection range (2Theta) was 10–90◦ with the step size of 0.05◦ (1◦ min−1 ). 3. Results and discussion 3.1. Mass relationship between polymer and bio-oil Initially, it was evaluated the mass relationship between the polymer and bio-oil formed at different temperatures during 1 h, with and without catalyst. It was observed that in a reaction without catalyst bio-oil was formed only above 350 ◦ C (Fig. 2A) and that in the presence of Nickel complex it was formed above 330 ◦ C, reducing the initial temperature by 20 ◦ C, clearly indicating a catalytic activity in pyrolysis. In sequence, it were analyzed the viscosities of the obtained bio-polymers, observing an increase in the viscosity values when increasing the temperature. Note that above 300 ◦ C the viscosity of the polymer is always higher when using Ni(carboxylate)2 than in the absence of catalyst. (Fig. 2B). 3.2. Polymer To evaluate the reaction parameters in the bio-polymer produced, soybean oil was kept at different temperatures during 12 h. It were taken samples at the times 0.0, 0.5, 1.0, 1.5, 2.0, 4.0, 6.0, 8.0, 10.0 and 12.0 h. The viscosities of the different samples are shown in Fig. 3. As can be depicted from Fig. 3, in the presence or absence of catalyst, it was not observed any increase in the viscosity during
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Fig. 2. Thermal reaction of refined soybean oil during 1 h: (A) mass relationship between distillated (,) and non-distillated (,) products in the absence (,) or presence of catalyst (,); (B) viscosity of the non-distillated products in the absence () or presence (䊉) of catalyst.
the entire reaction at 260 ◦ C. Thus, no polymer formation takes place at this temperature. However, even in the absence of catalyst it was observed an exponentially increasing of the viscosity at 300 ◦ C, achieving a high viscous polymer in 12 h (Fig. 3A). At temperatures from 330 to 370 ◦ C, it was noticed in the absence of catalyst a considerable increase in the viscosity values at initial times followed by its decrease at longer times. It is important to note that the reaction at 370 ◦ C was finished in 2 h because of a strong formation of light products, ending by an important mass loss inside the flask. Besides, in the presence of catalyst (Fig. 3B), it was observed a significant increase in the viscosity at initial times, demonstrating once again the catalytic activity of this catalyst in the polymerization. However, at 350 ◦ C the pyrolysis reaction becomes very important and, after 2 h, it was observed a reduction of the viscosity accomplished by the formation of light products (note that the reaction was stopped after 4 h because almost all material was converted into bio-oil). At 370 ◦ C, there is a substantial increase in the viscosity during the very initial times followed by a great loss of mass, and the reaction had to be stopped at 0.5 h. It is worth mentioning that in the absence of catalyst at 370 ◦ C this process took 2 h for the complete transformation of the material into biooil, once again evidencing the catalytic activity of Ni since the time was reduced by 75%. In sequence, it was evaluated the acid indexes of the polymer samples and the results are shown in Fig. 4. Without catalyst (Fig. 4A) it was observed that the acid index increased during all reaction at 260, 300 and 330 ◦ C. However, at 350 and 370 ◦ C the acid index decreased after achieving a maximum. This behavior is probably the result of the deoxygenation of the carboxylic acids formed during the thermal decomposition of esters, probably through decarbonylation and/or decarboxylation processes (Fabbri et al., 2005), which is favored at higher temperatures. In presence
of catalyst a similar behavior was obtained (Fig. 4B). However, in this case, it was already observed the formation of a maximum followed by a reduction in the acid index at 330 ◦ C, evidencing the catalytic activity of Ni also in the deoxygenation of carboxylic acids. These results are particularly important because polymers with small acid index lead to printing inks with higher hydrophobicity, which are known to have a better performance in lithographic and offset printing processes (Mello and Suarez, 2012). Thus, to obtain more information about the reaction mechanism, all the samples collected from the reaction bulk were analyzed by ATR-FT-IR. It were monitored the bands at wave numbers related to conjugate double bonds in trans configuration (987 cm−1 ), ester carboxyl group (1741 cm−1 ) and carboxylic acid carboxyl group (1708 cm−1 ). The obtained results are shown in Fig. 5 and Fig. 6. It is observed that the first transformation of triacylglycerides is the isomerization of double bonds to form conjugated trans dienes, as related in the literature (Sorensen, 1938), which are quickly consumed. Note that the velocity of formation and consumption of the trans dienes are strongly dependent on the temperature (Fig. 5A). Correlating the viscosity behavior from Fig. 3 and the formation and consumption of conjugated dienes from Fig. 5, it can be suggested that reactions involving conjugated double bonds (probably Diels–Alder or radical polymerization) are the most important reaction during the polymerization. Indeed, these results strongly suggest that the formation of conjugated dienes is needed before increasing the viscosity of the media. Carrying out these experiments in the presence of Ni it was observed a similar behavior with a higher reaction rate. As can be observed in Fig. 6, during the reaction the ester carboxyl groups (Fig. 6A and B) are consumed and carboxylic acids (Fig. 6C and D) are formed. Note that this process is strongly favored by the temperature. In the presence of catalyst the decomposition of the ester group is always more accentuated than in the
Fig. 3. Viscosity of the non-distillated products obtained by thermal decomposition of refined soybean oil at () 260 ◦ C; (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C in the absence (A) and presence (B) of catalyst.
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Fig. 4. Acid index of the samples collected from the reaction bulk during the thermal decomposition of refined soybean oil at () 260 ◦ C; (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C in the absence (A) and presence (B) of catalyst.
Fig. 5. Infrared absorbance of the samples collected from the reaction bulk during the thermal decomposition of refined soybean oil at obtained at () 260; (䊉) 300; () 330; () 350; and (*) 370 ◦ C: (1) absorbance at 987 cm−1 related to trans–trans conjugated double bonds in the absence (A) and presence (B) of Ni(carboxylate)2.
non-catalyzed reaction and occurs even at low temperatures (260 ◦ C). It is worth to mention that the deoxygenation of the carboxylic acids is also more pronounced in the presence of the catalyst.
It is important to highlight that we have repeated these reactions several times in the last 4 years and the polymer physical-chemical properties, as well as the reaction yields, present a very good reproducibility. Indeed, we have been producing polymers from soybean
Fig. 6. Infrared absorbance of the samples collected from the reaction bulk during the thermal decomposition of refined soybean oil at () 260; (䊉) 300; () 330; () 350; and (*) 370 ◦ C: absorbance at 1741 cm−1 related to ester carboxyl group in the absence (A) and presence (B) of catalyst. Absorbance at 1708 cm−1 related to carboxylic acid carboxyl group in the absence (C) and presence (D) of catalyst.
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Fig. 7. Percentage of heptanoic acid in distillated samples obtained by thermal decomposition of refined soybean oil at (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C: in the absence (A) and presence (B) of catalyst.
Fig. 8. Percentage of pentadecane in distillated samples obtained by thermal decomposition of refined soybean oil at (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C: in the absence (A) and presence (B) of catalyst.
oil and used soybean oil with tuned physical-chemical properties in order to formulate inks to be used in lithographic and xylographic prints, both in the presence or absence of nickel catalyst, and have always been able to reproduce the results. Indeed, we observed differences in the physical–chemical properties and the reaction yields only when changing the starting feedstock (Mello et al., 2013b). Note that some printings using inks formulated in our laboratory using these polymers have already been published in previous works (for instance, see references Mello et al., 2013b; Montenegro et al., 2013). 3.3. Bio-oil Bio-oil was collected during intervals of 0.5 h in the first 6 h and in intervals of 1 h until the end of the reaction, both in the
presence and absence of catalyst. It is important to highlight that was not observed the formation of bio-oil at 260 ◦ C and that at 300 ◦ C the formation of light products was observed only after 2 h. The collected samples were analyzed by GC–MS and acid index. The main results obtained from chromatographic analysis are shown in Figs. 7–9 and from acid index in Fig. 10. It was detected carboxylic acids with short chains (from 6 to 8 carbons) and hydrocarbons with large chains (from 15 to 17 carbons). It is important to highlight that the composition of the samples is strongly influenced by time, temperature and the presence of catalyst. For instance, in Figs 7–9 are shown the variation with time of selected compounds (respectively, heptadecanoic acid, pentadecane and heptadecane) wt.% in the samples at different temperatures. It becomes clear from Figs 7–9 that increasing the temperature and time and
Fig. 9. Percentage of heptadecane in distillated samples obtained by thermal decomposition of refined soybean oil at (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C: in the absence (A) and presence (B) of catalyst.
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Fig. 10. Acid index of distillated samples obtained by thermal decomposition of refined soybean oil at (䊉) 300 ◦ C; () 330 ◦ C; () 350 ◦ C; and (*) 370 ◦ C: in the absence (A) and presence (B) of catalyst.
Fig. 11. DRX of the precipitate recovered from the polymer.
in the presence of catalyst the formation of the mentioned hydrocarbons is enhanced. Note that the acid index of the biooil samples (Fig. 10) corroborates these results, since the acidity decreases at higher temperatures and times and in the presence of catalyst.
reduced. Thus, nickel may be completely recovered from the products just by centrifuging or filtering the polymer phase.
3.4. Presence of nickel in the products
In summary, in this work was shown that the choice of time, temperature and the presence of nickel catalyst may drastically change the obtained products, switching from bio-polymers to biooils. It was also observed that the reaction parameters determine also the studied physical–chemical properties and chemical composition of the final products. It was observed that above 300 ◦ C the thermal decomposition of triacylglycerides occurs in two steps. In the first step occurs an increase in the viscosity of the media leading to high viscous biopolymers. In this step was observed the formation of conjugated trans–trans dienes followed by their consumption. In the second step occurs the reduction of viscosity of the material because of breaking carbon–carbon bonds and esters groups to form lighter products.
In order to understand what happened to the nickel complex after the reaction we studied the liquid and the polymeric products. In the liquid product we could no detect the presence of nickel cations using ICP-OES. Besides, we observed the formation of a precipitate in the polymeric phase. Thus, we isolated the precipitate by dissolving the polymer in hexane and centrifuging the mixture, washing the obtained solid with hexane. Analyzing the supernatant by ICP-OES it was also not possible to detect nickel cations. However, analyzing the obtained solid by DRX (see Fig. 11) it was observed that it was formed a mixture of metallic nickel and nickel carbide (Ni3 C), strongly indicating that at the reactions conditions the nickel complex decompose and the metallic cation is
4. Conclusions
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Studying the composition of the bio-oil, it was observed that in reactions without catalyst occur the formation of a large amount of carboxylic acids and small quantities of saturated and unsaturated hydrocarbons. However, in the presence of nickel catalyst it was observed a pronounced deoxygenation of the carboxylic acids to produce mainly saturated and unsaturated hydrocarbons, evidencing the catalytic activity of this catalyst in the decarbonylation and/or decarboxylation of the carboxyl groups. Acknowledgements The authors are thankful to INCT-Catálise, EMBRAPA, CAPES, FINEP, FAPDF and CNPq for financial support. The authors wish also to thank CNPq for their research fellowships. References Arca, M., Sharma, B.K., Price, N.P.J., Perez, J.M., Doll, K.M., 2012. Evidence contrary to the accepted Diels–Alder mechanism in the thermal modification of vegetable oil. J. Am. Oil Chem. Soc. 89 (6), 987–994. Archer Daniels Midland Company, 1938. US Patent US2213935. Barreto, C.C.K., Oliveira, C.C., Souza, G.G.S., Suarez, P.A.Z., Rubim, J.C., 2012. Evaluation of the stability during storage of a diesel-like fuel obtained by the pyrolysis of soybean oil. Biomass Bioenergy 37, 42–48. Botas, J.A., Serrano, D.P., García, A., de Vicente, J., Ramos, R., 2012. Catalytic conversion of rapeseed oil into raw chemicals and fuels over Ni- and Mo-modified nanocrystalline ZSM-5 zeolite. Catal. Today 195, 59–70. Erhan, S.Z., Bagby, M.J., 1991. Lithographic and letterpress ink vehicles from vegetable oils. J. Am. Oil Chem. Soc. 68, 635–638. Erhan, S.Z., Bagby, M.O., 1992. Gel permeation chromatography of vegetable-oil based printing ink vehicle. J. Appl. Polym. Sci. 46 (10), 1859–1862. Erhan, S.Z., Bagby, M.O.,1993. Taga Proceedings. Technical Association of the Graphic Arts, Chelsea, pp. 314–326.
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