Investigation of the pyrolysis behaviour of brown algae before and after pre-treatment using PY-GC/MS and TGA

The pyrolysis behaviour of a number of brown macroalgae (seaweeds) collected in the UK such as Laminaria hyperborea and Fucus vesticulosus, are compared with the tropical algae Macrocystis pyrifera. Macroalgae contain a significant amount of alkali earth metals, halogens and a range of trace heavy metals. Pre-treatment of the algae has been performed to remove mineral matter in both water and weak acid. The pyrolysis behaviour of the residues has been investigated and the effect of processing on ash content and mineral composition has been determined. The pyrolysis behaviour of the raw samples and the residues from processing has been studied using thermal gravimetric analysis (TGA) and pyrolysis-GC/MS (Py-GC/MS). Total mineral matter has been determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) before and after pre-treatment. The Py-GC/MS pyrograms at 500 °C indicate the presence of a range of ketones, pentosans, nitrogen containing compounds and phenols. The residues from pre-treatment have different pyrolysis behaviours, particularly after acid treatment. The pre-treatment schemes investigated can remove a significant proportion of the mineral matter and halogens although they also selectively extract polymeric material. The residues have lower ash content and lower nitrogen content. Results for pre-treatment in water are consistent with the removal of mannitol, while results for pre-treatment in acid are consistent with the removal of fucoidan, mannitol and the partial removal of laminarin. Py-GC/MS of the residue from pre-treatment in acid produces a similar pyrogram to alginic acid in which furfural is a dominant product. There appears to be potential for the production of fuels and chemicals from brown algae by pyrolysis although the reduction of mineral matter and halogens by pre-treatment is advantageous.