sugarcane bagasse organosolv delignification

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It was found that excluding the 1,4-dioxane data provided a better linear fit of RED vs delignification. The best solubility sphere for sugarcane bagasse lignin ...
SUGARCANE BAGASSE ORGANOSOLV DELIGNIFICATION: ANALYSIS OF WATER MISCIBILITY WITH 2-BUTANOL Lísias Pereira Novo(1) and Antonio Aprigio da Silva Curvelo(1,2) (1) Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São Carlense, 400, São Carlos, Brazil (2) Laboratório Nacional de Ciência e Tecnologia do Bioetanol (CTBE), Centro de Pesquisa em Energia e Materiais (CNPEM), Campinas, Brazil E-mail (contact author): [email protected] Keywords: Sugarcane bagasse, organosolv delignification, lignin, 2-butanol, Hansen solubility parameters, biorefinery. ABSTRACT In organosolv delignification water fragments lignin through hydrolysis, then organic solvent acts in the solubilization, thus the solubility of lignin in the solvent system is the key to the delignification extent. Therefore, knowing the water miscibility of the organic solvent in the specific conditions is essential to determine the solubility parameters. While water solubility in 2-butanol at room temperatures is partially soluble, at temperatures higher than the boiling point this is not easy to predict. This study is an attempt of understanding this behavior in mixtures of 10% of water (v:v) in 2-butanol at 125ºC. For that lignin solubility and delignification rates in various solvent systems were compared, considering both possibilities: miscibility and immiscibility. It was concluded that 2-butanol and water may be consider as immiscible and, therefore, only the solubility parameters of 2-butanol contributes for the solubility of lignin in an organosolv delignification of sugarcane bagasse. It was found that excluding the 1,4-dioxane data provided a better linear fit of RED vs delignification. The best solubility sphere for sugarcane bagasse lignin found is centered at δd 22.65, δp 8.07 and δh 22.53 with R0 16.02 MPa1/2. 1. INTRODUCTION The production of sugarcane in Brazil reached a production pick of about 720 million tons of sugarcane in 2010 [1]. Two main factors make this production increase through time: the cost of sugar in the international market and the need of the production/use of renewable fuels. Consequently, today, Brazil became the only country to deploy a large-scale use of a renewable fuel, alternative to petroleum [2]. For each ton of sugar cane processed, about 250 kg of bagasse with humidity of approximately 50%, are produced as a byproduct leading to a production in 2010 of about 180 million tons of sugarcane bagasse [2]. Nowadays, the majority of sugarcane bagasse is used as solid fuel in boilers to generate steam for the sugar and alcohol industrial production or to sale as electricity [2,3]. The high content of polysaccharide present in the sugarcane bagasse makes it a suitable feedstock to produce second-generation ethanol or other chemicals in a biorefinery context. To fully utilize this raw material it is necessary to separate the different macromolecules present in the vegetal tissues. In this context, we highlight the organosolv delignification processes. The utilization of organic solvent dissolves the lignin fragments produced by hydrolysis of some chemical bonds present in protolignin ("in situ" lignin) [4,5]. Among the delignification processes, the organosolv process is particularly interesting because of its possibility to recover the organic solvents used. It is also possible to use catalysts (acid or alkaline) and high pressures (reaction using subcritical and supercritical fluids) to optimize the reaction conditions [4-7].

The solubility of lignin fragments in the organic solvent is of great importance. In this context, a variable that can provide important information for understanding the solubility phenomena and for choosing the best solvent composition in the organosolv processes are the theories of solubility parameters. There are two main theories of solubility parameters: the Hildebrand theory and the Hansen theory. The first uses a one-component parameter (the internal energy density of the system) to describe the interaction between particles in the system, whereas the second uses a three-component parameter (dispersive interactions, polar interactions and hydrogen bonding) to describe the interaction between solute/solvent system. In many cases the Hildebrand solubility parameter theory cannot explain solubility behavior effectively, so it was found that the Hansen solubility parameters theory is best suited for systems in which several types of interaction occur [8-10]. Solubility parameters for solutions can be determined as been the sum of the individual parameters for each component multiplied by its volume fraction in the solution, thus with a solution containing 50% of a component "A" and 50% of a component "B" the solubility parameters of the solution will correspond to the geometric mean of its individual solubility parameters [9-11]. Hansen's theory states that a solvent may be described as a point (represented by the sum of three vectors) in a three dimensional space, been each dimension one of the tree parameters. Likewise, a polymer can be represented not as a point, but as a volume in the space. Therefore, for the solubilization of this polymer, the point representative of the solvent solubility parameter must be inside the volume corresponding to the solubility parameter of the polymer [10,12]. The solubility parameter of a polymer can be found experimentally through tests of solubility in solvents with known Hansen solubility parameters. The solvents data are placed in the tridimensional space and the volume containing only the solvent in which the substance was solubilized is delimited. Hansen proposes that the solubility volume of a solute should be described as a sphere of radius as small as possible, with the largest number of solvents that solubilize the solute and fewer solvents that don’t. The solubility parameter of the solute can be described as being the center of this sphere [10]. Thus, for a given polymer, as closer the solvent point is to the center of the sphere greater is its ability to solubilize the polymer. Thus, it is important to set the distance between the solubility parameter of a solvent and a polymer. This is geometrically defined by equation 1 [10,12,13]. Equation 1 Similarly, a parameter related to the affinity of a solvent with a given polymer is the relative energy difference (RED). This parameter is defined as the ratio between the distance of a solvent to the center of the polymer sphere and the radius (R0) of this sphere, as showed in equation 2 [10,12]. Equation 2 If RED is lower than "1.0" affinity between the solvent and the polymer is high. If RED is greater than "1.0" affinity between the solvent and the polymer is small and with the increase of this value gradually decreases the affinity between the two. The boundary condition of solubilization occurs when the value is equal or very close to "1.0" [10,12-14]. 2. EXPERIMENTAL SECTION 2.1. Sugarcane bagasse preparation The raw sugarcane bagasse collected from 2009 and 2010 harvest in the Iacanga sugar and alcohol plant was submitted to a washing process at 70°C for 1 h under constant stirring to remove residual sugars and land. Then, it was air dried until 10% moisture and stored.

2.2. Organosolv delignification The organosolv delignification experiments were carried out using hydrochloric acid concentration of 0.05 mol.L-1, solvent/water ratio of 9/1 and solid/liquid ratio of 1/10 for all of the solvent systems. Since the only variable was the solvent system, it’s possible to correlate the solubility parameter of each solvent system with the capacity to solubilize the lignin fragments. The following solvents were used for the organosolv delignification (in mixture with water): 1,4-dioxane, 1-butanol, 2-butanol, acetone, acetonitrile, cyclohexane, ethanol, glycerol, isopropanol, methanol, methyl ethyl ketone, tetrahydrofuran and toluene. An experiment was also carried out using only water as the reaction solvent. These experiments were performed in a 195 cm3 stainless steel reactors with cap screws. It was equipped with a polytetrafluoroethylene o-ring. The heating was provided by a thermostatic bath of glycerol. The reactors were submerged into the glycerol bath when the bath was at 125ºC. After 60 minutes of reaction, the reactors were cooled in an ice bath to cease the reaction [3]. The pulps were separated from the pulping liquors by filtration under reduced pressure. The pulps were submitted to a defiber process with a 1% sodium hydroxide solution (by weight), in which the cellulosic fibers are separated from each other [15]. This procedure was previously determined as been indistinguishable to the extraction of the lignin fragments adsorbed on the bagasse fibers with a solution of water and the organic solvent used in delignification. After this procedure the pulps were filtered under reduced pressure and then washed with water until a pH around 6.5. The pulps were then air dried to moisture below 10%. 2.3. Characterization experiments The delignification experiments were characterized by the yield of the reactions and the lignin content of the pulps. The first consist on a simple gravimetric method in which the dry weight of the initial sample is compared to the dry weight of the final pulp, while the second consist on a modified Klason method [16] in which an acid solution digests the polysaccharides and precipitate the lignin, furthermore, the soluble lignin is quantified through UV-Vis. Through the comparison of the lignin content in the raw bagasse and in the pulps it’s possible to obtain the delignification extents [3]. 2.4. Lignin solubility sphere and evaluation of the water/2-butanol solubility From the determination of lignin solubility in several solvents Hansen and Björkman [12] showed that the Hansen solubility parameter for wood lignin was represented by the sphere centered in 21.9, 14.1, 16.9 (δD, δP, δH) with 13.7 MPa0,5 for Ro. However, since there is a great heterogeneity between lignins from different sources in addition to the method of extraction of the lignin (that has many ways of been fragmented) is highly probable that sugarcane bagasse lignin is centered differently. In order to determine the solubility parameter for organosolv lignin from sugarcane bagasse we apply the delignification extent obtained in the organosolv delignification as a measure of dissolving capability of the solvent. Since the solubility concept can be often stated as different phenomena, a relation between the delignification extents and the solubility of lignin in these solvents was done [10,13]. Thus, the delignification extent data can provide a new Hansen solubility parameter for sugarcane bagasse lignin. The solubility of the substrate in each solvent is expressed by a value of 1 or 0 for the solubility and insolubility, respectively [10,13]. To characterize the solubility of the lignin in the different solvents from the correspondent delignification extent different values of lignina removal it was established different delignification extent minimums to determine the solubility, i.e., when the delignification extent minimum was set in 70%, if a solvent system had a delignification extent higher than 70% the lignin can be considered soluble in this solvent system, and similarly if the delignification extent was lower than 70% lignin should be considered insoluble in this solvent system. For that, a program developed by Gharagheizi [13] for MatLab was used. In this program is necessary to input a database, containing the solvent systems used, the solubility parameters of the solvents and the solubility of the substrate for the calculation of the Hansen solubility parameters. The solubility parameter for 2-butanol/water mixtures were evaluated considering both miscibility and no miscibility in the reaction condition. These two possibilities were evaluated through the comparison

of the solubility sphere obtained with the input data of each case (miscibility, and therefore a solubility parameter for a solution, or immiscibility, and a solubility parameter for 2-butanol), and the adjustment of the data in the correspondent model generated. 3. RESULTS AND DISCUSSION In table 1 and 2 it can be visualized the solubility sphere generated for the different delignification extent minimums for the immiscibility and miscibility of 2-butanol/water, respectively. When the results of linear fit of table 1 and table 2 are compared individually it can be seen that for the sets 1, 3 and 5 the higher value of R2 occur for the immiscibility of 2-butanol/water in the reaction conditions, while for set 2 and 4 the miscibility provide higher values of R2. Comparatively, as higher is a linear fit, more accurate the model is to explain the behavior of the system, therefore, we have a first indicative that the mixture of 2-butanol/water in the reaction conditions is immiscible, since in most cases the R2 value is higher for this condition. The higher linear fit of data for table 1 occurred with delignification extent minimum of 70%, with a R2 equal to 0.84662, while for table 2 it can be seen that the higher linear fit of data occurred with delignification extent minimum of 72%, with a R2 equal to 0.81945, another indicative that the immiscibility is the real condition for the system. Table 1. Delignification extent minimum, generated sphere of solubility and linear regression coefficient of determination data for the immiscibility of water/2-butanol.

Delignification extent minimum (%)

1

70.0

0 0 0 0 1 1 1 1 1 0 0 0 0 22.65

8.07

22.53 16.02 0.84662

2

72.0

0 0 0 0 1 0 1 1 1 0 0 0 0 20.20

9.38

17.80 9.79

0.77758

3

75.0

0 0 0 0 1 0 0 0 1 0 0 0 0 20.37

9.95

16.75 9.58

0.72971

4

60.0

0 0 1 1 1 1 1 1 1 1 0 0 1 17.61

9.55

18.94 11.66 0.72936

5

50.0

0 0 1 1 1 1 1 1 1 1 0 1 1 16.45

9.60

17.35 15.42 0.67282

toluene cyclohexane methyl ethyl ketone tetrahydrofuran 1,4-dioxane methanol ethanol isopropanol 1-butanol 2-butanol water acetonitrile acetone

Set

Main solvent/Solubility

Solubility parameters (MPa1/2) Linear fit R2

Table 2. Delignification extent minimum, generated sphere of solubility and linear regression coefficient of determination data for the miscibility of water/2-butanol.

Set

Delignification extent minimum (%)

toluene cyclohexane methyl ethyl ketone tetrahydrofuran 1,4-dioxane methanol ethanol isopropanol 1-butanol 2-butanol water acetonitrile acetone

Main solvent/Solubility

1

70.0

0 0 0 0 1 1 1 1 1 0 0 0 0

26.51

-0.26 33.48 27.74 0.34857

2

72.0

0 0 0 0 1 0 1 1 1 0 0 0 0

21.36

6.64

20.55 11.61 0.81945

3

75.0

0 0 0 0 1 0 0 0 1 0 0 0 0

20.48

9.98

16.83

4

60.0

0 0 1 1 1 1 1 1 1 1 0 0 1

19.32

8.74

18.22 12.43 0.76437

5

50.0

0 0 1 1 1 1 1 1 1 1 0 1 1

16.45

9.69

17.60 15.53 0.65665

Solubility parameters (MPa1/2) Linear fit R2

9.89

0.7292

In figure 1 it’s possible to observe the distribution of the solvents data in both cases (2-butanol/water immiscible and miscible), for the best linear fit. It can be seen in figure 1 a better distribution of the data is for the immiscible case, since all the values are well scattered through RED axis, there is only one data distant to the linear fit (1,4-dioxane). For the miscible graph, it can be seen that in some cases the same RED value has a wide range of responses of delignification (for RED around 0,95 we have both values of approximately 65% and 90% of delignification extent) what indicates that this model cannot explain well the behavior of the system.

Figure 1. Distribution of solvent data for the best linear fit. a) mixture of 2-butanol/water immiscible. b) mixture of 2-butanol/water miscible. However, in both cases it can be seen that the 1,4-dioxane data doesn’t fit well to other data, therefore, we remove this point and redo the linear fit. Figure 2 shows the new linear fit with the exclusion of

the 1,4-dioxane data, for both cases. It can be seen that the value of R2 has risen in both cases, indicating that 1,4-dioxane has a different behavior than the other solvents on the delignification of sugarcane bagasse (1,4dioxame is a particularly good solvent for lignin). It’s also possible to see that after the exclusion the linear fit of immiscible have resulted in a higher value of R2 (0.92549 versus 0.86288), indicating again that this case correspond to the real behavior of water in 2-butanol.

Figure 2. Distribution of solvent data with exclusion of 1,4-dioxane. a) mixture of 2-butanol/water immiscible. b) mixture of 2-butanol/water miscible.

4. CONCLUSIONS After analyzing the distribution of solvents data and the linear fit it was concluded that the miscibility behavior of water in the solvent 2-butanol is poor, i.e., it can be affirmed that water and 2-butanol in the conditions studied behave as immiscible components and, therefore, only the solubility parameter of 2butanol contributes to the solubilization of lignin in organosolv delignification. It was found that the best solubility sphere for sugarcane bagasse lignin is centered at δd 22.65, δp 8.07 and δh 22.53 with R0 16.02 MPa1/2. The exclusion of 1,4-dioxane data provided a better linear fit of RED vs delignification (R2 equal to 0.92549), for the conditions studied.

REFERENCES 1. Instituto Nacional de Geografia e Estatística (IBGE). Levantamento sistemático da produção agrícola, produção agrícola das safras de 2010. Rio de Janeiro, 2011. Available in: . Accessed in: May 5, 2011. 2. G. M. Zanin; C. C. Santana; E. P. S. Bon; R. C. L. Giordano; F. F. De Moraes; S. R. Andrietta; C. C. D. Neto; I. C. Macedo; D. L. Fo; L. P. Ramos; J. D. Fontana, “Brazilian bioethanol program”, Applied Biochemistry and Biotechnology, Vol. 84-6 (2000), p. 1147-1161. 3. L. P. Novo; L. V. A. Gurgel; K. Marabezi; A. A. S. Curvelo, “Delignification of sugarcane bagasse using glycerol-water mixtures to produce pulps for saccharification”, Bioresource Technology, Vol. 102 (2011), n. 21, p. 10040-10046. 4. A. A. S. Curvelo, “Processo de deslignificação organossolve”. 1992. 94 f. Tese (Livre Docência) Instituto de Física e Química de São Carlos, Universidade de São Paulo, São Carlos, 1992. 5. D. Pasquini, “Polpação organosolve/dióxido de carbono supercrítico de bagaço de cana-de-açucar”. 2004. 180 f. Tese (Doutorado) - Instituto de Química de São Carlos, Universidade de São Paulo, São Carlos, 2004.

6. D. T. BALOGH; A. A. S. CURVELO; R. A. M. C. DE GROOTE, “Solvent effects on organosolv lignin from Pinus caribaea hondurensis”, Holzforschung, Vol. 46 (1992), n. 4, p.343-348. 7. D. S. Perez, “Estudo cinético da deslignificação acetona-água do Eucalyptus urograndis”. 1996. 114 f. Dissertação (Mestrado) - Instituto de Química de São Carlos, Universidade de São Paulo, São Carlos, 1996. 8. A. Barton, “Solubility parameters”, Chemical Reviews, Vol. 75 (1975), n. 6, p. 731-753. 9. A. Barton, “Handbook of solubility parameters and other cohesion parameters”, 1983, CRC. 10. C. M. Hansen, “Hansen solubility parameters: a user's handbook”, 2007, CRC Press. 11. L. A. Utracki, and R. Simha, “Statistical thermodynamics predictions of the solubility parameter”, Polymer International, Vol. 53 (2004), n. 3, p. 279-286. 12. C. M. Hansen and A. Bjorkman, “The ultrastructure of wood from a solubility parameter point of view”, Holzforschung, Vol. 52 (1998), n. 4, p. 335-344. 13. F. Gharagheizi, “New procedure to calculate the Hansen solubility parameters of polymers”, Journal of Applied Polymer Science, Vol. 103 (2007), n. 1, p. 31-36. 14. R. E. Kirk and D. F. Othmer, “Kirk-Othmer encyclopedia of chemical technology”, 2004, Wiley. 15. D. Pasquini; M. T. B. Pimenta; L. H. Ferreira; A. A. S. Curvelo, “Sugar cane bagasse pulping using supercritical CO2 associated with co-solvent 1-butanol/water”, Journal of Supercritical Fluids, Vol. 34 (2005), p. 125-131. 16. L. P. Novo, “Determinação da relação dos parâmetros de solubilidade de Hansen de solventes orgânicos com a deslignificação organossolve de bagaço de cana-de-açúcar”. 2012. 139 f. Dissertação (mestrado) - Instituto de Química de São Carlos, Universidade de São Paulo, São Carlos, 2012.