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countries where water sanity is less possible. For instance in Uganda 60% of households’ tap water and communal drinking water supply is heavily contaminated by E.coli.”


Diamond’s Manchester Imaging Branchline team ( I13-2) collaborated with the researchers to conduct rapid high-resolution X-ray imaging of biomass. Diamond worked with them from the experiment feasibility, the complex measurements, to experimental setup of the furnace to create the correct environment and optimal X-ray imaging conditions, to mining the wealth of data generated.


How heat and duration applied affects


porosity and morphology of the nut shells: In function of the slow heating ramp applied the team distinguished four different regimes:


1. 100-225 degrees: no signifi cant changes 2. 225-350 degrees: swelling due to a phase transition, presumably by the lignin,


3. 350-500 degrees: moderate speed size reduction due to evaporation of constituents of the particle, pore development, more prominent at the particle surface


4. 500–650 degrees: faster reduction in size and pore development faster towards the centre of the particle


Holding at 650 degrees: constant size no reduction, progressive stabilisation of the carbon


Designing a reactor that also serves


Quartz tube reactor and imaging cell on stage with heating furnace. Credit - Queen Mary University of London and Diamond Light Source I-13


This allowed real-time tracking of particle morphology and porosity during pyrolysis. The results showed that the morphology and porosity of different nutshells evolved differently during pyrolysis. However, these differences were less pronounced in biomass pre-soaked with an alkaline solution. Almond shells shrank more but gained less porosity than walnut shells, which have thicker walled cells on average. The results suggest that the difference is related to how heat penetrates particles of biomass during pyrolysis. Porosity was found to accumulate towards the centre of particles during pyrolysis for the same reason.


sample has to remain thermally stable and also the radiation should not have an impact on the sample stability (radiation damage). The challenge is to avoid much movement between one tomography and the other one meaning that each tomography (which takes around one minute) should not involve too much change in temperature as this reduces the exposure time and therefore the contrast of the image.”


as an imaging cell Principal Beamline Scientist, Professor Christoph Rau explained; “The data is recorded with the very brilliant rapid and high resolution X-ray beam at I13-2. The very intense radiation permits short exposure times in the range of milliseconds. A complete 3-D tomographic data set with several thousands of projections is recorded within several minutes. To fulfi l the data acquisition strategy we had to fi rst scan with the sample under static conditions. This involved, starting the heating ramp, levelling to a given target temperature, tomographic scan, continuing heating ramp and so on. The tricky bit is to scan the sample under stable conditions. The trick to solve this issue was to design a reactor which also serves as an imaging cell. A quartz capillary tube that holds the sample particle which is heated by a fl ow of hot inert or reactive gas (Argon, CO2


). The


International Labmate I13 Beamline Visit - Copyright of Diamond Light Source 2023 Dr Roberto Volpe holding Sample at I13 2 - Copyright of Diamond Light Source 2023


The difference is related to how different chemical reactions occur in the confi ned space of evolving pores of biomass and how fast or how slow – the produced vapours are progressively released out of the particle through that evolving network of pores during pyrolysis. As such, as temperature is increased up to approximately 500°C, pores develop more towards the surface, while beyond 500°C, porosity starts to develop more towards the centre of particles. These heat and mass transport limitations are what make pyrolysis so challenging to resolve and control.


Dr Paul Quinn, Science Group Leader for Diamond explained; “Imaging techniques at Diamond allow the team to visualise the structure of the solid particle with enough detail to examine small gaps or pores and track any changes over time and with variations in temperature. This means that we can extract a great deal of detail about the evolution of these pores and their intricate geometry. This result sheds light on the fundamental behaviour of thermally treated biomass and at the same time allows Dr Volpe and his team to uniquely correlate the particle and pores geometry to temperature.”


The group is consciously developing an environmental cost-benefi t analysis for the use of biochar because of the energy needed to turn the biomass into it before it can then be used to adsorb pollutants. Dr Volpe commented: “This is very important. We are aiming at a fully circular approach where the char that is saturated with pollutants can be used as solid fuel to prepare new bio char from raw biomass. This will certainly favour the environmental benefi ts versus the cost when compared to using a traditional fossil- based activated carbon, yet a fully comprehensive analysis to quantify the benefi ts is to be done perhaps using a life cycle assessment method.”


Diamond Light Source Aerial Image - Copyright Diamond Light Source Ltd


One of Dr Volpe’s next moves will be to visit MIT and its ‘combustion group’ at the Department of Mechanical Engineering, on a Royal Society grant to combine his images with their mathematical models in an example two of the world’s leading groups on biomass conversion working together. He is also coming back to conduct further work at Diamond in April, as the group’s next step to increase the ‘tunability’ of biochar will be to resolve porosity at smaller resolution aiming at below the 100 nanometers.


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