(643d) Plant-Wide Modeling and Techno-Economic Optimization for Production of Platform Intermediates through Concentrated Acid Hydrolysis of Lignocellulosic Biomass

The gradual exhaustion of fossil fuel reserves and growing environmental concerns have increased interest in developing sustainable technologies for production of energy, fuel, and chemicals. Lignocellulosic biomass, the only large-scale renewable carbon source available[1], is currently being explored for the synthesis of second-generation biofuels and high-value commodity chemicals. One key step in the potential conversion processes that this work focuses on is the degradation of the major polymeric components[1] present in the lignocellulosic biomass, to relatively smaller oligomeric or monomeric units.

Xylose (C5) and Glucose (C6) sugars are two of the most important platform intermediates obtained from lignocellulose conversion. These monomeric sugars are produced through the hydrolysis process where the glycosidic linkages between the monosaccharides[2] are cleaved in presence of an acid catalyst. The conventional hydrolysis process follows two approaches, namely, thermochemical (acid-catalyzed hydrolysis) and biochemical (enzyme-catalyzed hydrolysis)[3]. Acid-catalyzed hydrolysis can be performed using either concentrated or dilute acids as the catalyst – while concentrated acid hydrolysis (CAH) preceded by the biomass decrystallization step can result in a near-theoretical sugar yield [4]. Despite several challenges of the CAH process, such as high utilization of concentrated acid and requirement of corrosion-resistant MOC for reactors, the interest in CAH has been renewed recently due to improved acid recovery methods, lower operating temperature, lesser degradation of sugars and its adaptability to various biomass feedstocks [3].

In this work, a kinetic model for the dynamic batch reactor for CAH is developed where the kinetic parameters are optimally estimated by using dynamic optimization. Transient data from literature are used to estimate parameters by minimizing a weighted least squares objective function. As opposed to lumped models, this work develops an approach so that individual species can be identified and quantified as needed for their separation and economic evaluation. For commercial-scale production two scale up approaches are considered- commercial-scale batch reactor, commercial-scale continuous reactor. A configuration for the continuous scale reactor is proposed and modeled. Additionally, model for the separation section is also developed for separation of sugar products from the remaining unconverted reactants and acid catalyst present in the reactor outlet stream. In addition, the model of another unit operation is developed for converting the platform intermediates into value-added chemicals such as furfural and 5-hydroxymethylfurfural.

Models of a plant-wide CAH process have also been developed by incorporating steps like decrystallization of lignocellulosic biomass before CAH and recycling of the acid catalyst to improve economic feasibility of the overall valorization method. Techno-economic optimization is conducted to maximize net present value by optimizing key design variables including reactor dimensions as well as the key operating variables such as residence time, catalyst concentration and reaction temperature. The economics of the optimal CAH process are compared with that obtained for the dilute acid hydrolysis approach.

References:

[1] Z. Zhou, D. Liu, and X. Zhao, “Conversion of lignocellulose to biofuels and chemicals via sugar platform: An updated review on chemistry and mechanisms of acid hydrolysis of lignocellulose,” Renewable and Sustainable Energy Reviews, vol. 146. 2021. doi: 10.1016/j.rser.2021.111169.

[2] X. J. Shen, P. L. Huang, J. L. Wen, and R. C. Sun, “A facile method for char elimination during base-catalyzed depolymerization and hydrogenolysis of lignin,” Fuel Process. Technol., vol. 167, no. May, pp. 491–501, 2017, doi: 10.1016/j.fuproc.2017.08.002.

[3] Y. P. Wijaya, R. D. D. Putra, V. T. Widyaya, J. M. Ha, D. J. Suh, and C. S. Kim, “Comparative study on two-step concentrated acid hydrolysis for the extraction of sugars from lignocellulosic biomass,” Bioresour. Technol., vol. 164, pp. 221–231, 2014, doi: 10.1016/j.biortech.2014.04.084.

[4] F. J. Wolfaardt, L. G. Leite Fernandes, S. K. Cangussu Oliveira, X. Duret, J. F. Görgens, and J. M. Lavoie, “Recovery approaches for sulfuric acid from the concentrated acid hydrolysis of lignocellulosic feedstocks: A mini-review,” Energy Convers. Manag. X, vol. 10, no. December 2020, 2021, doi: 10.1016/j.ecmx.2020.100074.

[5] A. Athaley, P. Annam, B. Saha, and M. Ierapetritou, “Techno-economic and life cycle analysis of different types of hydrolysis process for the production of p-Xylene,” Comput. Chem. Eng., vol. 121, pp. 685–695, 2019, doi: 10.1016/j.compchemeng.2018.11.018.