(71b) Techno-Economic Optimization of Xylose and Glucose Sugar Production Via Concentrated Acid Hydrolysis of Lignocellulosic Biomass

The gradual exhaustion of fossil fuel reserves coupled with substantial environmental concerns have led to an increasing interest in the development of sustainable technologies for production of energy, fuel, and chemicals. The lignocellulosic biomass is the only large-scale sustainable carbon source available[1] that is currently being explored for the synthesis of second-generation biofuel as well as various high-value commodity chemicals. This requires degradation of three major polymeric components[1] of lignocellulosic biomass, namely, cellulose, hemicellulose, and lignin to relatively smaller oligomeric or monomeric units.

Xylose (C5) and Glucose (C6) sugars are two of the most important platform intermedia generated through lignocellulose conversion. The production of these monomeric sugars can be viable through the hydrolysis process where the glycosidic linkages between the monosaccharides[2] are broken in presence of a catalyst. The conventional hydrolysis process rely on two approaches, namely, the thermochemical route (acid-catalyzed hydrolysis) and biochemical route (enzyme-catalyzed hydrolysis)[3]. Acid-catalyzed hydrolysis can be performed in presence of either concentrated acid(s) or dilute acid(s) as the catalyst. Concentrated acid hydrolysis (CAH) preceded by the biomass decrystallization step can result in a sugar yield closer to theoretical level[4]. CAH also has other advantages over dilute acid hydrolysis (DAH) such as lower operating temperature, and low degradation of sugars during the hydrolysis process. Despite several limitations of the CAH process, such as high utilization of concentrated acid(s) and requirement of corrosion-resistant MOC for reactors, the interest in CAH has been renewed recently due to the possibility of recovery of the acid catalyst and high flexibility of CAH for efficiently handling different types of biomass feedstocks[3]. Currently, most of the techno-economic analyses and commercialization studies focus on DAH process with only a handful of literatures have discussed the techno-economic assessment of CAH[5].

In this work, a kinetic model for the dynamic batch reactor for CAH is developed where the kinetic parameters are optimally estimated using dynamic optimization with orthogonal collocation on finite elements. Transient data from literature are used for parameter estimation by minimizing a weighted least squares objective function. Batch reactors used in the laboratory CAH process are scaled up to the commercial scale. Both commercial-scale batch reactors and continuous reactors are evaluated. Process models are also developed for the decrystallization of lignocellulosic biomass before CAH and recycling of the acid catalyst to enhance the economic feasibility of CAH. In addition, models of the separation section are also developed for separation of sugar products from the remaining unconverted reactants and catalyst present in the reactor outlet stream, followed by the formulation of another model aimed at recovering the acid from hydrolysate and recycling it. An economic model of the plant is developed with quantified uncertainty for the capital cost estimates. Techno-economic optimization is undertaken for maximizing the net present value by optimizing the key design variables such as the reactor dimensions as well as the key operating variables such as residence time, catalyst concentration and reaction temperature. Economics of optimal CAH process are compared with that obtained for the DAH.

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.