(639c) Design and Assessment of Novel Thermochemical Lignocellulosic Biomass to Butanol Process Configurations

Production of liquid fuels from renewable sources such as biomass to replace traditional fossil fuels is an important strategy to help address the challenges posed by green house gas emissions and energy security. One such fuel receiving increased attention is biobutanol, as it is a better alternative to bioethanol as a gasoline replacement in current automobile engines and fuel pipeline networks [1]. Two major routes exist for biobutanol production; the biochemical route which primarily proceeds via fermentation of biomass feedstock to butanol, and the thermochemical route which proceeds via gasification of biomass feedstock to syngas and the conversion of syngas over catalysts to butanol.

Past research by Okoli and Adams [2] developed a novel continuous lignocellulosic biomass to butanol process using a thermochemical route which was shown to be economically competitive to the biochemical route, and economically feasible in comparison to gasoline under certain market conditions. However, this work made use of simplifying yield and conversion assumptions for modelling the mixed alcohol synthesis (MAS) reactor, which is the heart of the process. Another area identified for improvements by the authors is the separation section in which a conventional distillation sequence is used for butanol recovery. Potential exists for improvements of this section by utilizing process intensification technology based on dividing wall columns (DWCs) instead of conventional distillation columns. The use of DWCs can be significant as past research has shown that they can improve operating and capital costs of distillation by up to 30 % in comparison to conventional distillation sequences [3]. However, this has never been investigated on a plant-wide level for biofuel applications.

In this work, the modelling and assessment of different design configurations for the production of biobutanol from lignocellulosic biomass is considered. The major processing steps which were designed and modelled using Aspen Plus^®are biomass drying, biomass gasification, syngas cleanup and conditioning, mixed alcohol synthesis and alcohol separation. A key difference from the prior work is the modelling of the MAS reactor using a detailed kinetic model based on a modified high pressure methanol synthesis catalyst with good selectivity to butanol [4]. The use of a detailed kinetic model allowed the impact of design parameters such as feed composition, catalyst loading, temperature, and pressure on butanol production to be investigated for the different design configurations. Furthermore, additional configurations in which DWCs are used in place of conventional distillation columns for butanol recovery are assessed.

All design configurations are compared based on a techno-economic analysis using an assumption of n^thplant costs, with results showing that configurations with the DWC have very good prospects. The impact of different plant and cost parameters on the economics of the best configuration are also considered using a sensitivity analysis.

REFERENCES:

[1] M. Kumar and K. Gayen, “Developments in biobutanol production: New insights,” Appl. Energy, vol. 88, no. 6, pp. 1999–2012, Jun. 2011.

[2] C. Okoli and T. A. Adams, “Design and economic analysis of a thermochemical lignocellulosic biomass-to-butanol process,” Ind. Eng. Chem. Res., vol. 53, no. 28, pp. 11427–11441, Jun. 2014.

[3] N. Asprion and G. Kaibel, “Dividing wall columns: Fundamentals and recent advances,” Chem. Eng. Process. Process Intensif., vol. 49, no. 2, pp. 139–146, Feb. 2010.

[4] A. Beretta, E. Micheli, L. Tagliabue and E. Tronconi. Development of a process for higher alcohol production via synthesis gas. Ind. Eng. Chem. Res., vol. 37, no. 10, pp. 3896–3908, Sept. 1998.