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THERMODYNAMIC ANALYSIS OF METHANE PRODUCTION PROCESSES FROM LIGNINE (VANILLIN REPRESENTATIVE UNIT)
E. Baltierra-Trejo1, E. A.Mendoza-Chávez2, J. M. Sánchez-Yáñez3, L. Márquez-Benavides4, J. Saucedo-Luna5
INTRODUCTIONWorld reserves of petroleum are rapidly depleting, in recent years methane (CH4) from biogas has emerged as important alternative resource for fuel. Wheat is cultivated in 115 countries with an estimated production of 675 million tonnes year-1. It is estimated that as a by-product of wheat production, 877 tonnes of straw are generated (Talebnia et al. 2010). Commonly, in situ incineration is used to disposed, but this practice has a negative environmental impact.
Table 1. World production of agricultural residues
The straw is constituted by structural remnants of the plant cell wall: cellulose (39%), hemicellulose (38.7%) and lignin (17%). The lignin is a heterogeneous and highly stable polymer constituted by units of aromatics (Dekker et al. 2002). Due to its complex chemical structure and to the aromatic rings stability is a recalcitrant material in nature.
Lignin from residual wheat straw is usable if depolymerisation and aromatic oxidation is achieved; the chemical methods are expensive and a source of contaminants. A safer environmental option is the use of ligninolitic fungi (Chang et al. 2012).
The depolymerization of lignin by ascomycetes and oxidation of fatty acids may be associated with methanogenesis in anaerobic biogas production. It has been estimated that one ton of lignin could generate 296 kg of biogas. However the production of biogas from straws is a process poorly investigated.
The aim of this paper is to present a thermodynamic analysis for methane production from lignin-based aromatics (vanillin) with the method of Gibbs free energy minimization using the Aspen Plus® simulator.
1Programa de Doctorado Institucional en Ciencias Biológicas, UMSNH. [email protected]
2,5 Facultad de Ingeniería Química, Posgrado en Ciencias en Ingeniería Química, UMSNH. [email protected]ía Ambiental, Instituto de Investigaciones Químico-Biológicas, UMSNH. [email protected] Sólidos y Medio Ambiente, Instituto de Investigaciones Agropecuarias y Forestales, UMSNH. [email protected]
Crop Production (106 Ton/año)
Straw(106 Ton/año)
Maize 875 1,680 Wheat 675 877
Rice 718 862 Sugar cane 1,774 532
7.3 Ton/ha wheat straw
296 kg Biogas/Ton
wheat straw
1.17 barrels of oil
Universidad Michoacana de San Nicolás de Hidalgo
METODOLOGYEquilibrium compositions were calculated by the minimization of the Gibb’s free energy. Aspen Plus 7.3 software was used for the calculations. The RGibbs reactors were selected for the calculations using the UNIQUAC property method. The analysis was carried out using the interval 300-1500 K, feeding a H2O/Vanillin ratio (WVR) of 0.6 to 6.1, 1 atm.
RESULTS AND DISCUSIONThermodynamic analysis of the effects of process variables (WVR) on methane production was investigated. The results showed that the vanillin conversion was almost completed (Figure 1). Methane yields from 0.2 to 0.4 mol CH4/mol vanillin were obtained at high and low vanillin feed concentrations, respectively, when operating at low temperature (Figure 2). However CO2 production is parallel to methane (Figure 3) and very low CO (Figure 4).
This model predict that if there is 5.43 mole of an aromatic/kg lignin will occur theoretically 2.17 mol of CH4, which be equivalent to 48.6 L of CH4/kg lignin. Therefore it is necessary to introduce more variable simulation models to optimize experimental models.
CONCLUSIONProduction of methane as second-generation biofuels from renewable lignocellulosic resources may improve energy availability, decrease air pollution and diminish atmospheric CO2 emissions.The use of simulation models can be a tool to improve research in the use of agricultural straw for biogas production.
LITERATURA CITADAChang, A.J., Chang, E.J., Fan, J. & Wen, X. (2012). Screening of fungi capable of highly selective degradation of lignin in rice straw. International Biodeterioration & Biodegradation, 72, 26-30.Dekker, R.F., Barbosa, A.M., Sargent, K. (2002). The effect of lignin-related compounds on the growth and productionof laccases by the ascomycete, Botryosphaeria sp. Enzyme and Microbial Technology, 30, 374-380.Talebnia, F., Karakashev, D., Angelidaki, I. (2010). Production of bioethanol from wheat straw: An overview on pretreatment, hydrolysis and fermentation. Bioresource Technology, 101(13), 4744-4753.
Vanillin, aromatic from ligininLignin model
Figure 3. Production of CO2 from vanillin Figure 4. Production of CO from vanillin
Figure 1. Vanillin consume in simulated reactor Figure 2. Production of CH4 from vanillin
Conditions of operation UNIQUACTemperatures (OK) 300-1500
Pressure 1 atmWVR 0.6-6.1Feed 1 mol of vanillin
Objective High yield of methane
Table 1. Conditions of operation in simulated reactor
