Abstract
Macroalgae have emerged as a potential future source of feedstock for the production of chemicals and biofuels. The main drawbacks of macroalgae in terms of a biofuel feedstock are its low heating value (HHV), high halogen content, high ash content and high slagging and fouling propensity. In this investigation, three species of kelps; (i) Laminaria digitata (ii) Laminaria hyperborea and (iii) Alaria esculenta have been processed by hydrothermal carbonisation (HTC) in a batch reactor at two temperatures (200°C and 250°C). The yields and properties of the resulting hydrochars including their HHV, CHNS, mineral content and ash fusibility properties have been determined and compared to the starting material. Significant improvement in fuel quality is observed resulting in an increase in energy density from 10MJ/kg to typically 25MJ/kg, which is comparable to that of a low rank coal. The results indicate significant demineralisation of the fuel, in particular a significant removal of alkali salts and chlorine. This results in improved combustion properties due to a reduction in the slagging and fouling properties of the fuel. Analysis of the HTC water phase indicates the presence of high levels of soluble organic carbon consisting of sugars and organic acids, and high levels of potassium, magnesium and phosphorous. The potential for production of bio-methane and recovery of nutrients following anaerobic treatment of the water phase is assessed. A prediction of the bio-methane yields for the different seaweeds has been calculated. Processing of biomass collected throughout the growth season indicates the influence of seasonal variation on energy and nutrient recovery.
Highlights
Biofuels derived from aquatic biomass such as macroalgae offer an extensive and largely unutilised biomass resource which do not compete with agriculture or forestry for land and freshwater; overcoming drawbacks associated with using terrestrial biomass to produce biofuels
The results have shown a significant increase in energy density in the bio-coal, with the ‘as received’ calorific value (CV) of the fuel typically 22 MJ/kg for the 200 °C treatment and 25 MJ/kg for the 250 °C treatment
The hydrogen to carbon (H/C) ratios for seaweed bio-coals are similar at each temperature, which differ from lignocellulosic biomass, where the lower temperature bio-coals had both higher O/C and H/C ratios [20]
Summary
Biofuels derived from aquatic biomass such as macroalgae offer an extensive and largely unutilised biomass resource which do not compete with agriculture or forestry for land and freshwater; overcoming drawbacks associated with using terrestrial biomass to produce biofuels. Macroalgae offer a potentially large biomass resource, they are significantly different from terrestrial plants in terms of their chemical composition [26]. They do not contain high levels of lignocellulose and are instead predominantly comprised of carbohydrate in the form of mannitol, laminarin, fucoidan, alginic acid and other polysaccharides [35]. The remaining organic fraction includes protein and fucoidan which results in comparatively high levels of nitrogen and sulphur respectively [35]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
