Thermochemical conversion of raw and defatted algal biomass via hydrothermal liquefaction and slow pyrolysis

Integrated biorefineries: CO2 utilization for maximum biomass conversion

“…In parallel, intensive research is devoted to CO 2 utilization for producing fuel and products [54], and among them microalgae cultivation has gained significant research interest [55,56]. The diverse array of the algae research activities includes microalgae strain selection and lipid yield enhancement, [57][58] microalgae cultivation and dewatering [59], oil-extraction and different upgrading methods [60][61][62][63][64][65][66][67] With the aim of enhancing the overall biofuel yields and improving the environmental impacts, the present research proposes an integrated biorefinery comprising of biomass pyrolysis, in addition to solvent-based carbon capture and utilization through microalgae cultivation. The process integration is based on the synergies between the processing steps of these processes, as shown in Fig.…”

Methods of energy extraction from microalgal biomass: a review

“…When drying of microalgal biomass was included pyrolysis used more energy than was produced as usable solid, liquid and gaseous fuels (Jena and Das 2011). The Energy Consumption Ratio for the production of bio-oil from microalgae, a ratio of the energy input for thermochemical treatment to the energy in the bio-oil, was found to be 0.44 to 0.63 for hydrothermal liquefaction and 0.92 to 1.24 pyrolysis due to the requirement for the moisture to be evaporated prior to pyrolysis (Vardon et al 2012); again indicating that pyrolysis can use as much, or more, energy than is generated as biofuels.…”

“…The ability of hydrothermal treatments to handle wet biomass make them some of the most interesting methods of producing biofuel from microalgae . Dunaliella with a moisture content of over 78 % has been treated by hydrothermal upgrading (termed liquefaction by the authors) at a laboratory scale (20 g of wet microalgae) yielding 37 % oil, based on the dry organic weight of the microalgal biomass (Minowa et al 1995); but hydrothermal liquation of biomass with a moisture content above 90 % is believed to have an unfavourable energy balance (Vardon et al 2012). …”

“…Bio-oil yield from the liquefaction of wet Nannochloropsis (79 % moisture content) has been found to be a maximum of 43 % of the biomass dry weight with recovery of 80 % the carbon and 90 % of the energy in the Nannochloropsis organic material (Brown et al 2010). Bio-oil yields from hydrothermal liquefaction, as a percentage of the mass of original dry microalgal biomass, have been reported as: up to 41 % for Spirulina (Jena and Das 2011), between 24 -45 % for Scenedesmus (Vardon et al 2012) and up to 49 % for Desmodesmus or 75 % recovery of the energy in the microalgal biomass as bio-oil . The cell wall of Desmodesmus has been found to be resistant to hydrothermal liquefaction ).…”

“…A more recent estimate reported the energy required for hydrothermal liquefaction of microalgal biomass with a moisture content of 80 % as between 44-63 % of the bio-oil energy produced (Vardon et al 2012). Although the liquefaction of microalgal biomass can be a net energy producer and the bio-oil has a high calorific value and can be readily refined into a variety of liquid fuels, it would appear that a complete process for the production of microalgal biofuel from liquefaction using existing microalgal growth and harvesting techniques may use more energy than is produced.…”