(315b) Optimal Production of Light Olefins from Lignocellulosic Biomass (BTO): Process Synthesis and Global Optimization

The growing interest toward alternative carbonaceous energy sources stems from concerns surrounding energy independency, energy affordability, and the generation of lower carbon energy, as stated in a recent perspective [1]. Specifically, there is a need for the development of sustainable and carbon neutral energy processes that have the potential to reduce global energy related carbon dioxide emissions. Lignocellulosic biomass is a potential feedstock that can serve as an alternative to fossil-fuels and offset the growing energy demand while simultaneously reducing the net carbon emissions due to the absorption of CO₂ during photosynthesis. The U.S. has the potential of sustainably supplying more than one billion tons of biomass annually [2,3]. Biomass has already been shown to be a viable feedstock for the production of liquid transportation fuels at low break-even oil prices [4]. However, the transportation fuel demand is expected to stall in the near future while the chemicals demand is expected to raise by 65% [5]. This increase in the chemicals demand is expected to be the major driver of the crude oil demand growth [5]. 

This work investigates the optimal production of light olefins from biomass within a process synthesis and global optimization framework. Light olefins are the most demanded class of petrochemicals and command two-thirds of the petrochemical commodities market [6]. These chemicals can be produced from carbonaceous feedstocks through several novel/competing process alternatives [7]. We propose a process superstructure with alternatives regarding (i) biomass conversion, (ii) synthesis gas cleaning, (iii) methanol production and conversion, (iv) olefins purification, (v) light gas recycle, and (vi) hydrogen and oxygen production among others. Simultaneous heat, power, and water integration is included to ensure minimum utility usage. The objective function of the proposed mathematical model maximizes the profit of the refinery. The resulting large-scale mixed integer nonlinear optimization model (MINLP) is solved to global optimality with a branch-and-bound global optimization framework. Several case studies are investigated to observe the effect of biomass type, plant scale, and topological decisions on the overall plant profitability. Significant reductions in the lifecycle GHG emissions are observed through the utilization of biomass.

 

[1]: Floudas, C. A.; Niziolek, A. M.; Onel, O.; Matthews, L. R. Multi-scale systems engineering for energy and the environment: Challenges and opportunities. AIChE Journal 2016, 62 (3), 602-623.

[2]: Department of Energy, Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply.

[3]: Department of Energy, US Billion-Ton Update: Biomass Supply for a Bioenergy and Bioproducts Industry.

[4]: Baliban, R. C.; Elia, J. A.; Floudas, C. A. Biomass to liquid transportation fuels (BTL) systems: process synthesis and global optimization framework. Energy Environ. Sci. 2013, 6 (1), 267-287.

[5]: ExxonMobil, The Outlook for Energy, A View to 2040

[6]: de Klerk, A. Fischer-Tropsch Refining; Wiley-VCH Verlag & Co. KGaA, 2011.

[7]: Onel, O.; Niziolek, A. M; Floudas, C. A Optimal Production of Light Olefins from Natural Gas via the Methanol Intermediate. Industrial & Engineering Chemistry Research 2016, 55 (11), 3043-3063.