Biomass Pyrolysis Challenge: A Multi-Scale Approach

Biomass pyrolysis challenge: A multi-scale approach

Sharifzadeh, Mahdi[1] , Shah, Nilay.

Centre for process Systems Engineering (CPSE), Imperial College London.

Biomass pyrolysis provides the cheapest pathway toward renewable liquid fuels. In this presentation, we provide an overview of our accomplishments at Centre for Process Systems Engineering (CPSE), Imperial College London, for research into production of fuels and chemicals from bio-oil, via the pyrolysis pathway. We adapted a multi-scale approach which spans from the structure of individual molecules to a country-wide supply chain network [1-5]. The research objective is to improve the overall economy of the biofuel production and mitigate carbon emissions in order to protect the environment.

The liquid product of pyrolysis reactions is called biomass pyrolysis oil, or simply bio-oil. Despite various incentives, bio-oil features some undesirable properties and is not immediately usable in the current energy infrastructure. Bio-oil contains a high amount of oxygenates and suffers from a low calorific value. Furthermore, it is highly acidic leading to thermal instability and increasing viscosity. Finally, due to high water content it is immiscible with petroleum-derived fuels. The technology for the removal of oxygen and other heteroatoms from pyrolysis oil is called “bio-oil upgrading”. We propose a novel framework for modelling the kinetics of the involved upgrading reactions based on connectivity of the oxygen atoms. We demonstrate that this approach is most effective for representing the highly interactive networks of the biomass upgrading reactions, involving a large number of species [2].

Furthermore, we conducted a comparative study [2] between two major bio-oil upgrading technologies, namely hydrodeoxygenation upgrading and hydrothermal treatment which identified the key characteristics of each technology. Based on such in-depth insights, we proposed a synergistic reaction networks which economically produce biofuels and is self-sufficient with respect to the required hydrogen.

Nevertheless, commercialization of biofuel technologies poses an important challenge; unlike crude oil, biomass has a high oxygen content (e.g., 58.28% mass fraction in the case of hybrid poplar). Therefore, in order to make the biofuels compatible with current energy infrastructures, the oxygen atoms should be removed resulting in a large amount of inevitable CO₂ by-product. For example, in the biomass pyrolysis pathway, from every two carbon atoms, almost one atom ends up in the CO₂ emissions. Therefore, CO₂ utilization is an indispensable element of future biorefineries. In a follow-up project [3], we developed a new biorefinery scheme based on processing synergies between bio-oil upgrading and biofuel production from microalgae. In the proposed scheme, the CO₂ generated via biomass pyrolysis and upgrading is captured using amine solutions and utilized for microalgae cultivation. We demonstrate that such process integration increases fuel conversion from 55% to 73%. Nevertheless, CO₂ capture and utilization reduces the CO₂ emissions from 45% in the stand-alone pyrolysis to 6% in the integrated scheme with another 19% in biomass residue waste streams.

In parallel, we studied the production of commodity products such as olefins and aromatics from biomass pyrolysis via integrated catalytic processing [4]. We provide the proof of concept that using such technology, naphtha can be replaced by biomass pyrolysis oil in conventional olefin processes. Such a retrofit results in up to 46% reduction in the emission of greenhouse gases, while the produced biochemicals are still economic in the current chemical market. 

Finally, we recently studied the biofuel production supply chain. Several production strategies were considered. They are (1) the centralized production strategy, where biomass pyrolysis and upgrading are performed at the same place, (2) the distributed production strategy, where the bio-oil is produced in distributed production facilities and the bio-oil is delivered to upgrading centres, and (3) mobile biofuel production where bio-oil is produced in mobile production facilities and sent to upgrading centres for biofuel production. A mixed integer linear optimization framework was programmed which enabled systematic decision-making regarding aforementioned alternative production strategies. The optimisation results suggested that a combination of geographically centralized pyrolysis and upgrading centres would suffice for supply chain management under deterministic conditions. However, under uncertain scenarios, it is advantageous to deploy mobile pyrolysers to add extra flexibility to the process operation. Further our analysis suggested that as the mobile pyrolysers are commercialized and their unit price is reduced, this technology has the potential to become a key member of future biofuel supply chains.

References

[1] Sharifzadeh M*, Richards C, Chadwick D, Shah N (2015). A generalized framework for modeling the kinetics of bio-oil hydrothermal reactions. In preparation, to be submitted to Biomass & Bioenergy.

[2] Sharifzadeh M^*, Richards CJ, Liu K, Hellgardt K, Chadwick D, Shah N. (2015). An integrated process for biomass pyrolysis oil upgrading: the synergistic approach. Biomass & Bioenergy. 76, 108–117, (Link).

[3] Sharifzadeh M^*, Wang L, Shah N, (2015). Integrated bio-refineries: CO2 utilization for maximum biomass conversion. Renewable and Sustainable Energy Reviews, 47, 151–161, (Link).

[4] Sharifzadeh M^*, Wang L., Shah N., (2015). Decarbonisation of olefin processes using biomass pyrolysis oil. Applied Energy, 149, 404–414, (Link).

[5] Sharifzadeh M^*, Cortada Garcia, M, Shah N., (2015). Supply chain network design and operation under uncertainty: centralized, distributed, and mobile production of biofuel via fast pyrolysis and upgrading, (minor revisions required by Biomass & Bioenergy).

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1 Corresponding author, Email: mahdi@imperial.ac.uk , Address: Room C603, Roderic Hill Building, Centre for Process Systems Engineering (CPSE), Department of Chemical Engineering, Imperial College London, South Kensington, London SW7 2AZ, UK.