Catalytic pyrolysis of biomass
Dr Sanna recent research has focused on the development of metal oxide and zeolite catalysts towards the production of more stable and upgradable pyrolysis oils. We are developing catalysts able to improve the bio-oils properties and selectively control the products distribution towards aliphatic and aromatic products. Among the tested catalysts, Ni–Ce/Al2O3 was able to retain 59% of the algae starting energy in the bio-oil, lower the content of acids, improve the C/O molar ratio from 3.6 (without catalyst) to 5.1 and produce a bio-oil rich in aliphatics. CeO2 as such is instead particularly good in producing ketones, while metal doped zeolites are being developed for maximising the production of aromatics. Li-LSX-zeolite showed a good catalytic performance, principally for microalgae bio-oil denitrogenation (mainly in form of NH3), and good activity for olefins and aromatics production.
There are still research barriers to overcome for the catalytic conversion of algal biomass including that the deoxygenation results in C losses in coke formation due to removal of hydrogen from the algal biomass. Coke can be removed by successive pyrolysis/combustion cycles. Another limitation is represented by algae intrinsic high N-content, which can produce NOx if combusted and by their high ash content that can lead to catalysts deactivation.
Catalytic Membrane Reactors
The production of bio-fuels or chemicals from biomass derivates, such us pyrolysis/liquefaction bio-oils or cellulose hydrolysis, is a promising pathway to reduce the dependence on fossil fuels and reducing the emission of greenhouses gases. To decrease the oxygen content and convert highly reactive functionalities in more stable ones, intermediate bio-substrates can undergo hydrogenation reactions resulting in compounds with a higher economic value that can be used for the production of polymers, cosmetics, food additives or drop-in fuels.
In collaboration to the IMT-CNR, e are now developing novel metal- catalytic polymeric membranes for selective hydrogenation reactions. Unlike conventional methods, Catalytic Membrane Reactor (CMR) can overcome mass transfer limitations, resulting in low H2 requirements, high catalytic activity and high selectivity towards desired producs. In a recent work, the hydrogenation of furfural has been carried out in a customised catalytic membrane reactor under mild conditions: 70 ºC and 7 bar, exhibiting high catalytic activity towards furfuryl alcohol (selectivity >99%) with turnover frequency (TOF) as high as 48,000 h-1, 2 orders of magnitude higher than those obtained so far.
Dr Aimaro Sanna team is working on showing how bio-oils produced from biomass, can be upgraded into high commodity chemicals such as mono-alcohols, diols, light olefins and aromatic hydrocarbons — which are used in the production of plastics by hydrotreatment in aqueous phase. This is a promising and flexible integrated catalytic conversion pathway that would sensibly decrease the economical disadvantage of biomass compared with fossil fuels and would make possible the conversion of biomass on an industrial scale. Oxygenated gasoline additives, alcohols, and diols can be produced by increasing the intrinsic hydrogen content of bio-oil in a multi-stage continuous hydrogenation process. A Low Temperature Hydrogenation (LTH) step converts the aldehydes, ketones, and sugars in bio-oil to their corresponding alcohols with a Ru catalyst. The alcohols are thermally stable and can be further converted in the desired products by High Temperature Hydrogenation (HTH). Future advances in the field of metal catalysts, combined with reaction engineering, will lead to the design of even more efficient and economical processes to convert biomass resources to renewable chemical industry feedstocks.
High Temperature CO2 capture & BioCCS
Carbon capture and storage by mineralisation (CCSM has the potential to sequester billions of tonnes of CO2, but the current costs are too high for a widely spread deployment of this technology. Ex-situ mineral carbonation has been demonstrated in pilot and demonstration scale, with CO2 capture efficiencies of up to 80-90% using naturally occurring minerals, as well as wastes brines Mg/Ca rich. However, its application is currently limited by the high costs of this technology. Mineral carbonation cost ranges from $50 to $300/tCO2 sequestered, depending on resources and process used, with opportunities to decrease further the cost by direct flue gas capture, process optimisation, and system integration.
A promising way to sequester CO2 is by indirect pH swing mineral carbonation processes, which are able to produce marketable carbon neutral products from the sequestered CO2. However, the main drawback of this approach is linked to the large amount of energy required to recycle the chemicals used to accelerate the reactions. We have recently shown that the dissolution and carbonation steps of an alternative process that employs sodium-based salts can minimise energy requirements typically associated to ammonium based mineral carbonation processes at comparable CO2 capture efficiency.
In the proposed process, a Na-bisulphate solution is used to leach cations from silicate rocks into sulphates and NaOH to capture the CO2 into Na2CO3. The integration of cations-rich silicates and Ca/Mg-rich industrial wastes with the purpose to recycle the Na2SO4 remaining after the process and regenerate the required reagents, generating a range of Mg and Ca carbonates is considered.
The process is currently under development.
Co-gasification of marine biomass and coal
The recent use microalgae for energy production has received great attention due to their high production yield per area, high efficiency in CO2 capture and solar energy conversion and absence of competition for land with food crops. In the same time, coal is still the major energy resource in many countries, and its co-utilisation with biomass could provide many advantages, such as the reduction of CO2 and other gaseous pollutants emissions and improve the overall efficiency via synergistic effects.
We are therefore investigating the co-pyrolysis and co-gasification of microalgae in order to evaluate potential synergistic effects and the kinetic parameters, which are essential for advancing the co-utilization. In collaboration to Sotacarbo Spa, we are going to scale-up the co-utilisation studies using a bench scale fluidised bed reactor. Preliminary results indicate a strong synergistic effect during the co-gasification experiments (50/50wt% mixtures) due to the microalgae high alkali metals content promoted coal char gasification, resulting in a Ea decrease for the coal.