Sugars Production from Wheat Straw Using Maleic Acid

Transcription

1 Sugars Production from Wheat Straw Using Maleic Acid G. KATSAMAS, D. SIDIRAS Department of Industrial Management and Technology University of Piraeus 80 Karaoli & Dimitriou, GR Piraeus GREECE Abstract: - In the present wor, the acid hydrolysis of wheat straw was studied using a 3.75 L batch reactor. This ind of hydrolysis was catalyzed by M maleic acid for 0-50 min at o C. The analysis of experimental data of reaction inetics indicates that this is a potential method for cellulose and hemicelluloses hydrolysis, due to a rapid hydrolysis reaction for adequately high reaction ending temperature. The inetics of the acid hydrolysis of cellulose and hemicelluloses can be simulated by a inetic model where the acidity of the liquid phase is affected by the acids produced within the complex networ of reactions and by the neutralization due to the wheat straw ash content. The temperature profile during the process and the p ending values were also studied. The reaction rate constants can be calculated according to this model using non-linear regression analysis. Process parameters investigated herein include variation in reaction ending temperature, maleic acid concentration and reaction time. The xylose and glucose monosaccharides and oligosaccharides produced by the acid hydrolysis process are appropriate for (i) fermentation in the bioethanol industry and (ii) high value chemicals production. Key-Words: - straw, maleic acid, hydrolysis, pretreatment, lignocellulosics, bioethanol 1 Introduction Lignocellulosic material contains mainly xylose, glucose, arabinose, mannose and galactose polymers. From these polymers, sugars can be produced by autohydrolysis [1] or acid hydrolysis [2] and can be processed to form maretable bioethanol [3]. Bio-ethanol is produced mostly from maize (USA) or from sugar cane (Brazil) [4] while Greece plans to produce bio-ethanol from sugar beets and cereals. Two of the five factories of the Gree National Sugar Industry will be modified to produce bio-ethanol instead of sugar. Several approaches have been examined for the hydrolysis of waste cellulose to sugars and the subsequent fermentation into bio-ethanol and other bio-products [5]. The main challenges in producing ethanol from lignocellulosics have been found in hydrolysis stage of the process. The hydrolysis of cellulose to glucose only occurs at economically viable yields when a catalyst is used. The three main catalyst classifications are: enzymatic, concentrated acid and dilute acid catalysts [6]. Pre-treatment is usually preformed before enzymatic hydrolysis by energy intensive physical methods, or the use of chemicals. Also, the presence of lignin can be inhibitory to the enzyme hydrolysis. Concentrated acid processes use relatively mild temperatures and the only pressure involved is that created in pumping materials from vessel to vessel. These low temperatures and pressures minimize the degradation of sugars to undesirable by-products. Concentrated acid disrupts the hydrogen bonding in the cellulose chain converting it from a crystalline to an amorphous state. The cellulose, once de-crystallized, forms a homogeneous gel with the acid, which allows hydrolysis reactions. Water can then be added at low temperatures to dilute the solution, providing conditions to form glucose. Straw has the potential to be a biomass feedstoc for ethanol production due to the high content of cellulose and hemicelluloses. emicelluloses can decompose at temperatures of C to form xylose and other sugars. owever, for the decomposition of crystalline cellulose, higher temperatures are usually required, with these generating problems with sugar degradation. At these higher temperatures, cellulose degrades into 5-hydroxymethyl furfural and xylose degrades into furfural [7-15]. Mosier et al. [16] showed that dilute maleic acid, a dicarboxylic acid, hydrolyzes cellobiose, the repeat unit of cellulose, and the microcrystalline cellulose Avicel as effectively as dilute sulfuric acid ISBN:

2 but with minimal glucose degradation. Maleic acid, superior to other carboxylic acids reported in Mosier et al. [16] paper, gives higher yields of glucose that is more easily fermented as a result of lower concentrations of degradation products. These results were especially significant because maleic acid, in the form of maleic anhydride, is widely available and produced in large quantities annually. Combined acid catalysis was employed by Guo et al. [17] as a pretreatment alternative with combined acid catalysts blending sulfuric acid with two biomimetic acids, trifluoroacetic acid (TFA) and maleic acid (MA), respectively. A synergistic effect on hemicellulose decomposition was observed in the combined acid hydrolysis, which greatly increased xylose yield, although TFA/MA would induce more total phenols. Fermentation tests of the acid-catalyzed hydrolysates with overliming showed that compared to 2 SO 4 pretreatment, TFA and MA pretreatments improved overall ethanol yield. Combined acid catalysis was shown as a feasible pretreatment method for its improved sugar yield, reduced phenols production and catalyst costs. The purpose of this wor was to study the acid hydrolysis of wheat straw using a batch reactor (3.75 L PARR autoclave). This ind of hydrolysis was catalyzed by maleic acid. The experimental data were analyzed to be available for the adaptation [18] of hydrolysis model. The inetics of acid hydrolysis of cellulose and hemicelluloses can be simulated using a inetic model where the maleic acid acidity will be taen into account. The temperature profile during the process and the p ending values were taen into account. The reaction rate constants can be calculated according to the model using nonlinear regression analysis (NLRA). Process parameters investigated herein include variation in reaction ending temperature ( C) maleic acid concentration ( M) and reaction time (0-50 min after the required for each endingtemperature preheating-period). 2 Materials and methods 2.1 Material Development The wheat straw used was obtained from Kapareli Village of Thebes, Greece, as a suitable source for full-scale industrial applications. The moisture content of the material when received was 9.0% w/w; after screening, the fraction with particle sizes between 10 and 20 mm was isolated. The composition of the raw material was as follows (expressed in % w/w on a dry weight basis): 29.9% cellulose, hemicelluloses 20.5%, 21.8% lignin and 27.9% others. 2.2 Acid ydrolysis process The acid hydrolysis process was performed in a 3.75-L batch reactor PARR 4843 (see Fig. 1). The hydrolysis time was 0, 30 and 50 min (not including the preheating time); the reaction was catalyzed by 0.01, 0.05 and 0.10 M maleic acid at a liquid-tosolid ratio of 20:1; the liquid phase volume (water) was 2000 ml and the solid material dose (wheat straw) was 100 g. The reaction ending temperature was 140, 180 and 220 C, reached after certain preheating time. Fig.1: The wheat straw was pretreated by maleic acid catalyzed hydrolysis in a 3.75-L batch reactor PARR Analytical Techniques The degree of crystallinity of barley straw cellulose was measured by X-ray diffraction [19] and by acid hydrolysis. The resisting-to-reaction hemicelluloses fraction (mainly xylan 1) was also measured by acid hydrolysis. The Saeman et al. [20] technique was used for the quantitative saccharification of the original lignocellulosic material and the acid hydrolysis reaction solid residues. The filtrates from the quantitative saccharification, as well as these from the autoclave (before and after secondary hydrolysis, i.e. post-hydrolysis with 0.9 N 2 SO 4 at 100 o C for 4.5 h) were analyzed for glucose, xylose and arabinose using high-performance liquid chromatography (PLC, Agilent 1200) with Aminex PX-87 Column, refractive index detector and 5 mm 2 SO 4 in water as the mobile ISBN:

3 phase. Cellulose was estimated as glucan and hemicelluloses were estimated as xylan and arabinan. Finally, the acid-insoluble lignin (Klason lignin) was determined according to the Tappi T222 om-88 method [21]. 3 Results and Discussion Cellulose fractions are hydrolyzed to water-soluble glucose, hemicelluloses are hydrolyzed mostly to water-soluble xylose and the acid-insoluble lignin fraction is not significantly affected by acid hydrolysis. The simulation model developed by the authors in an earlier wor [18] to describe the acid hydrolysis inetics is presented below and concerns the hydrolysis of polysaccharides. RR 1 3 WSO xyl 4 furfural ER 2 3 WSO xyl 4 furfural C1 C3 C4 CC WSOC glu 5 MF C2 C3 C4 AC WSOC glu 5 MF where: RR is the Reaction Resisting emicelluloses; ER the Easily Reacting emicelluloses; WSO the Water Soluble Oligosaccharides from emicelluloses; CC the Crystalline Cellulose; AC the Amorphous Cellulose; WSOC the Water Soluble Oligosaccharides from Cellulose; 5-MF the 5-hydroxymethyl furfural. A system of first-order inetic equations was applied to the hydrolysis of xylan 1 and xylan 2 (reaction-resisting and easily-reacting hemicelluloses, respectively) during the acid hydrolysis treatment. The acid activity is assumed to be constant during the acid hydrolysis process in the case where the initial acid concentration was constant. Moreover, the hydrolysis of amorphous and crystalline cellulose, the hydrolysis of oligosaccharides and the degradation of xylose/glucose can all be simulated by first-order inetic equations [1]. The following equations simulated the acid hydrolysis reactions of the lignocellulosic materials: dc i1 /dt = i1.c i1 (1) -dc i2 /dt = i2.c i2 (2) dc i3 /dt = i1.c i1 + i2.c i2 - i3.c i3 (3) dc i4 /dt = i3.c i3 - i4.c i4 (4) Eij / RT ij = pij a e (5) b a = A C a (6) where i=c for cellulose hydrolysis, i= for hemicelluloses hydrolysis, j = 1, 2, 3, or 4; p ij and E ij are the pre-exponential factor (min -1 ) and the activation energy (J/mol), respectively; a is the activity of the acid and can be estimated by the p equation a = 10 or p = log a ; C a is the acid concentration (Normality, N); A, b are empirical constants. The p was measured at 25 o C at the end of the cooling period in each experiment. All concentration values C ij (i = C or, j = 1, 2, 3, or 4) in this model were expressed in w/w units, based on the initial quantity of dry components in the reacting system. The rate constants, ij, were expressed in min -1, the reaction time t in min, and the reaction temperature T in K. C i1 +C i2 represents the concentration of the non-reacted polysaccharides (C i0 ), and C i3 +C i4 represents the concentration of total sugars in the liquid phase (C it ). The concentration of decomposition products (furfural, 5-MF), C i5, can be calculated from the expression 1-(C i0 +C it ). The concentrations of the acid hydrolysis products obtained from the polysaccharides (cellulose and hemicelluloses) are: Ci0,0 Cij i= C, C j = Ci0,0 i= C, (j=0, 3, 4, T) (7) where C i0,0 is the initial experimental concentration of straw cellulose and hemicelluloses. The solid residue yield, SRY, of (as a w/w fraction of initial dry material) is: SRY = Ci 0,0 C i0 + c (8) i= C, where the constant c is independent of the reaction conditions and is equal to the acid insoluble components fraction. The quantity of the acid insoluble lignin in the solid residue was relatively constant and approximately equal to that in the original wheat straw. The above model can simulate the nonisothermal reaction system of polysaccharide acid hydrolysis. It can also predict the concentration of polysaccharides under isothermal reaction conditions. The maleic acid hydrolysis temperature profiles for temperatures 140, 180, 220 o C are shown in Fig. 2. The experimental p values of the hydrolyzates ISBN:

4 Fig.2: Acid hydrolysis temperature profile (140 o C, 180 o C, 220 o C) vs. time. Fig.4: Acid hydrolysis Solid Residue yield vs. conditions severity; mild for 140 o C, 0.01 M, 0 min; moderate for 180 o C, 0.05 M, 30 min; and severe for 220 o C, 0.1 M, 50 min; solid ratio = 20:1. solution before and after acid hydrolysis are given in Table 1. The SRY, glucose and xylose are presented in Fig.3. SRY is also given in Fig.4. The glucose and xylose produced during hydrolysis are presented in Fig.5 and in Fig.6, respectively. The percentages of Cellulose, Xylan and Lignin are given in Fig.7 based on final solid and Fig.8 based on initial solid material. All these experimental data are given for mild (140 o C, 0.01 M, 0 min), moderate (180 o C, 0.05 M, 30 min) and severe (220 o C, 0.1 M, 50 min) conditions. Table 1. The experimental p values before and after acid hydrolysis are given Conditions p before p after 140 o C, 0.01 M, 0 min o C, 0.05 M, 30 min o C, 0.1 M, 50 min Fig. 5: Acid hydrolysis Glucose yield vs. conditions severity; mild for 140 o C, 0.01 M, 0 min; moderate for 180 o C, 0.05 M, 30 min; and severe for 220 o C, 0.1 M, 50 min; solid ratio = 20:1. Fig.3: Solid Residue Yield, Glucose and Xylose yields vs. conditions severity; mild for 140 o C, 0.01 M, 0 min; moderate for 180 o C, 0.05 M, 30 min; and severe for 220 o C, 0.1 M, 50 min; solid ratio = 20:1. Fig.6: Acid hydrolysis Xylose yield vs. conditions severity; mild for 140 o C, 0.01 M, 0 min; moderate for 180 o C, 0.05 M, 30 min; and severe for 220 o C, 0.1 M, 50 min; solid ratio = 20:1. ISBN:

5 monosaccharides and oligosaccharides produced by the acid hydrolysis process were appropriate for the bioethanol industry and high value chemicals production. Fig.7: Percentages of Cellulose, Xylan and Lignin vs. conditions severity (based on final solid); mild for 140 o C, 0.01 M, 0 min; moderate for 180 o C, 0.05 M, 30 min; and severe for 220 o C, 0.1 M, 50 min; solid ratio = 20:1. Fig.8: Percentages of Cellulose, Xylan and Lignin vs. conditions severity (based on initial solid); mild for 140 o C, 0.01 M, 0 min; moderate for 180 o C, 0.05 M, 30 min; and severe for 220 o C, 0.1 M, 50 min; solid ratio = 20:1. 4 Conclusion The acid hydrolysis of wheat straw, catalyzed by maleic acid, was studied using a batch reactor. This was proved to be a potential method for cellulose and hemicelluloses hydrolysis, due to a rapid reaction for adequately high reaction ending temperature. The cellulose and hemicelluloses hydrolysis inetics can be simulated by a model where the acidity of the liquid phase is affected by the acids produced within the complex networ of reactions and by the neutralization due to the wheat straw ash content. The temperature profile during the process and the p ending values plays a significant role. The effect of the variation of the reaction ending temperature, the maleic acid concentration and the reaction time on the polysaccharides degradation and sugars production was significant. The xylose and glucose References: [1] D. Sidiras, F. Batzias, R. Ranjan, M. Tsapatsis, Simulation and optimization of batch autohydrolysis of wheat straw to monosaccharides and oligosaccharides, Bioresource Technology, 102, 2011, pp [2] D.K. Sidiras. Simulation of Barley Straw Acid ydrolysis to Fermentable Oligosaccharides and Monosaccharides for Bioethanol Production. 19 th European Biomass Conference and Exhibition, Berlin, 2011, pp [3] J.D. Broder, R.A. arris and J.T. Ranney, Using MSW and industrial residues as ethanol feedstocs. Biocycle 42(10), 2001, [4] L. Dawson, R. Boopathy, Use of post-harvest sugarcane residue for ethanol production, Bioresource Technology, 98(9), 2007, pp [5] N. Lar, Y. Xia, C. Qin, C.S. Gong and G.T. Tsao, Production of ethanol from recycled paper sludge using cellulase and yeast, Kluveromyces marxianus, Biomass Bioenergy 12(2), 1997, pp [6] D.J. Schell, C.J. Riley, N. Dowe, J. Farmer, K.N. Ibsen, M.F. Ruth, S.T. Toon, R.E. Lumpin, A bioethanol process development unit: initial operating experiences and results with a corn fiber feedstoc, Bioresource Technology, 91(2), 2004, pp [7] J. Iranmahboob, F. Nadim, S. Monemi, Optimizing acid-hydrolysis: a critical step for production of ethanol from mixed wood chips, Biomass and Bioenergy, 22(5), 2002, pp [8] J. Zaldivar, J. Nielsen and L. Olsson, Fuel ethanol production from lignocellulose: a challenge for metabolic engineering and process integration, Applied Microbiology and Biotechnology, 56(1 2), 2001, pp [9] N. Mosier, C. Wyman, B. Dale, R. Elander, Y.Y. Lee, M. oltzapple, M. Ladisch, Features of promising technologies for pretreatment of lignocellulosic biomass, Bioresource Technology, 96(6), 2005, pp [10] B.P. Lavarac, G.J. Griffin, D. Rodman, The acid hydrolysis of sugarcane bagasse hemicellulose to produce xylose, arabinose, glucose and other products, Biomass Bioenergy 23(5), 2002, pp ISBN:

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