(317e) Process Design for the Production of Xylitol in a Multi-Product Biorefinery

Xylitol is a sugar substitute with various beneficial health properties and a potential platform chemical that gained significant attraction in the last decade [1]. There exists a great potential for xylitol to be produced biotechnologically with engineered cell factories instead of the current chemical production process [2]. Moreover, the use of lignocellulosic biomass as feedstock for the biotechnological process adds further benefits in terms of sustainability. However, using lignocellulosic biomass as feedstock introduces several challenges for the conceptual design of the biotechnological processes, as considerations about potential value-added co-products, pretreatment technologies, and possibilities for process integration, amongst others [3].

In the presented study for a base-case process design, a synergistic optimization-based process design framework (S3O) is used to overcome the named hurdles and to design this process conceptually [4]. In this base case design, succinic acid and sustainable aromatic kerosene are chosen as value-added co-products and wheat straw as feedstock. Besides, the generation of heat as a product for possibly integrating it with the other products' downstream processes is considered. For all unit operations, mechanistic models are developed, validated, and assessed regarding their robustness via an uncertainty and sensitivity analysis. A design space exploration is performed to determine the most sensitive variables with respect to the objective function, and flowsheet sampling simulations are performed to fit different surrogate models for each flowsheet. As the combination of the surrogate model and optimization technique in the following superstructure optimization step has a crucial influence on the performance in the optimization problem, a benchmark of different options is performed and compared with previously obtained results [4,5]. The superstructure optimization step is a set of candidate process topologies, which are subsequently optimized in a simulation-based optimization approach to consolidate the process design under uncertainty [6].

As objective function in the framework, key performance indicators are selected, e.g., net present value or minimum selling price. The resulting base case process itself is evaluated against both the criteria of being economically viable and its sustainability. Potential options for process integration regarding the reuse of heat and CO₂ are assessed and compared to the base case design. Ultimately, the presented process design is evaluated regarding its feasibility compared to the established chemical production process, and potentials for further improvements considering the whole value chain and other potential value-added co-products and feedstocks are given.

Acknowledgments

The project is part of the Fermentation-Based Biomanufacturing Initiative at DTU and is funded by the Novo Nordisk Foundation under the grant NNF17SA0031362.

References

[1] A.F. Hernández-Pérez et al. 'Xylitol bioproduction: state-of-the-art, industrial paradigm shift, and opportunities for integrated biorefineries', Critical Reviews in Biotechnology, 2020, Vol. 39(7), pp. 924-943.

[2] Y.D. Arcaño et al.' Xylitol: A review on the progress and challenges of its production by chemical route', Catalysis Today, Vol. 344, 2020, pp. 2-14.

[3] T. Chaturvedi et al. 'Developing Process Designs for Biorefineries – Definitions, Categories and Unit Operations', Energies, 2020, Vol. 13(6), 1493.

[4] N.I. Vollmer et al.' Synergistic Optimization Framework for the Process Synthesis and Design of Biorefineries', Frontiers in Chemical Science and Engineering, under review.

[5] N.I. Vollmer et al.' Benchmarking of Surrogate Models for the Conceptual Process Design of Biorefineries', Computer-Aided Chemical Engineering, accepted.

[6] R. Al et al. 'Stochastic simulation-based superstructure optimization framework for process synthesis and design under uncertainty', Computers & Chemical Engineering, 2020, Vol. 143, 107118.