Microwave-assisted upgrading of fast pyrolysis bio-oil using structured zeolites on microwave-absorbing foam supports

Biomass is a key renewable feedstock to respond to the vital societal need for a step change in the sustainability of energy production required to combat climate change (80% reduction in greenhouse gas emissions by 2050 in the UK). Fast pyrolysis is one of the major technical routes to convert biomass to more valuable energy forms, i.e. bio-oil, with high yields of liquids of up to 75 wt%. However, it is not possible to realise the potential of bio-oil to be an effective energy carrier without removing the large amount of oxygen in bio-oil (about 38 wt%). From a process point of view, zeolites cracking is a promising technology to remove the oxygen from bio-oil at atmospheric pressure without the requirement of large amount of hydrogen. The catalyst deactivation caused by the coke formation remains a major concern for the bio-oil upgrading routes based on zeolite cracking and makes them not viable for further development. Therefore, the development of novel catalytic processes, which could suppress the coke formation and extend the life of zeolite catalysts, would be a major move in making a reality a cost-efficient bio-refinery.

The concept of this project is the development of a combination of emerging technologies for addressing the coking issue in bio-oil upgrading. This combination is based on (i) the exploration of the microwave-absorbing property of silicon carbide (SiC) open-cell foam supports with hierarchical characteristics (e.g. HZSM-5 or HY zeolites supported on SiC foams) and (ii) the development of microwave-assisted catalysis with enhanced heat and mass transfers. Under microwave irradiation, by using the microwave absorbing material of SiC as the catalyst support, heat is generated selectively at the support, and hence the heat flux is directed from the support surface to the bulk fluid via the zeolite layer. Mass transfer will also occur in the same direction due to the coupling vector facilitating the desorption of molecules from the active sites of the catalyst surface, as well as preventing the coking. This project, for the first time, proposes to use the combination of microwave-absorbing structured catalysts and microwave activation to address the coking issue in traditional zeolite bio-oil cracking systems. The proposed research consists of the feasibility study of the proposed catalytic system using model and real bio-oil as well as the evaluation of system energy efficiency in comparison with the conventional thermally activated systems. This proposal builds on the investigators' expertise in structured catalysts, microwave chemistry, heterogeneous catalysis, biomass thermo-chemical conversion and process development, aiming at delivering the proof-of-concept of a novel catalytic system with the enhanced catalyst longevity, low coke formation and high efficiency of deoxygenation of bio-oil.

In addition to the impact on academia of the work (see Academic Beneficiaries section), the successful outcome of this project would have a significant industrial, societal, economic and governmental impact.

The industry: The coke formation and associated catalyst deactivation impose high operating costs in the bio-oil upgrading contributed significantly (50-60%) to the conversion cost of biomass to fuel via the fast pyrolysis route. The project aims at investigating the feasibility of a novel catalytic technology for solving the coke formation problem in zeolite cracking of bio-oil, in which the local and global mass/heat transfer are promoted to suppress the carbon deposition during the cracking process. Therefore, the outcomes of this project should have a long-term impact on the biorefinery industry since the viable catalytic systems with long catalyst life is a key step to enable the integration of biomass derived fuels with today's refinery infrastructure. Additionally, considering the implementation of such a technology, the energy cost will be optimised since the energy to overcome the pressure drop of the open-cell configuration is generally 75% less than conventional packed-beds and the energy of microwave to activate the catalyst is about 90% less than thermal activation. The industrial partner in this project will contribute directly to this research helping to shape the project with their expertise in biomass conversion and ensure rapid take-up of the results. The concept of the proposed catalytic system is generic that can be transferred to other processes such as hydrodeoxygenation upgrading of bio-oil, low temperature VOC treatment and methane conversion to aromatic hydrocarbons supporting the innovation in other industries.

The society: Bio-oil from fast pyrolysis of biomass (with about 75% yield) is a promising source of renewable liquid transportation fuels/chemicals and potentially could substitute ca. 20% of the global consumption of chemicals and fuels by 2050, helping to cut the carbon emission and ward off climate change. The project is framed around the catalytic conversion of bio-oil to fuels with focus on addressing a crucial practical engineering challenge (coking) impeding its development. This project will contribute to the paradigm shift in the current energy system. The impact and benefit on our society of the proposed research will be multiple including: (1) dependency relief on fossil fuels by bringing in cheaper renewable energy; (2) reduced carbon emissions toward achieving climate security; and (3) creation of new jobs in the biorefinery sector. In general, this project has a great potential to improve the quality of life by developing key catalytic technology to enable the adoption of bioenergy by our society.

UK economy and public policy: The reduction of operating cost in bio-oil upgrading should encourage the adoption of this technology by the biorefinery industry in order to fulfil the 2008 Climate Change Act set by the UK environmental (the target of 80% CO2 emissions reductions by 2050). If the project is successful, it will stimulate (i) the formation of new, highly competitive SMEs in the area of catalyst development and catalytic upgrading of bio-oil or (ii) the technology transfer to relevant industries. Both can support the job creation and boost the UK economy. In the long term, the evidence base of the performance of novel catalytic systems developed by this project, which are applicable to a wide range of applications related to environment and manufacturing, is important for the UK policymakers and regulators to make relevant strategic decisions and develop relevant policies.