Renewable and carbon neutral biofuels are necessary for environmental and economic sustainability. The viability of the first generation biofuels production is however questionable because of the conflict with food supply. Microalgal biofuels are a viable alternative. The oil productivity of many microalgae exceeds the best producing oil crops. This paper aims to analyze and promote integration approaches for sustainable microalgal biofuel production to meet the energy and environmental needs of the society. The emphasis is on hydrothermal liquefaction technology for direct conversion of algal biomass to liquid fuel.

No abstract

The understanding of the formation of silicate oligomers in the initial stage of zeolite synthesis is of fundamental scientific and technological importance. The use of different organic structure directing agents is known to be a key factor in the formation of different silicate species, and the final zeolite structure. Tetramethylammonium (TMA(+)), for example, is indispensable for the formation of the LTA zeolite type. However, the role of a TMA(+) template has not yet been elucidated at the molecular level. In this study, ab initio molecular dynamic simulations were combined with thermodynamic integration to arrive at an understanding of the role of TMA(+) in the formation of various silicate species, ranging from dimer to 4-ring. Free energy profiles show that trimer and 3-ring silicate are less favourable than other oligomers such as linear tetramer, branched tetramer and 4-ring structures. TMA(+) exhibits an important role in controlling the predominant species in solution via its coordination with silicate structures during the reaction process. This can explain that formation of D4R·8TMA crystals, as observed in experiment, is controlled by the single 4-ring formation step.

Wet torrefaction of typical Norwegian biomass fuels was studied within the temperature window of 175–225 °C, using a benchtop autoclave reactor of 250 mL in volume from Parr Instrument. Two types of local biomass fuels were employed as feedstock, Norway spruce (softwood) and birch (hardwood). Effects of process parameters including pressure, reaction temperature, holding time, and feedstock particle size on the yield and properties of the solid products were investigated. It appears that birch wood is more reactive and produces less solid products than spruce wood in the same wet torrefaction conditions. Increasing pressure above the saturated vapor pressure of water enhances the torrefaction rate. Both reaction temperature and holding time have significant effects on solid product yield and fuel properties of wet torrefied biomass. The yield of solid products is slightly reduced with decreasing feedstock particle size. The ash content of biomass fuel is significantly reduced by wet torrefaction. In addition, a comparison between wet and dry torrefaction supported by regression analyses and numerical predictions shows that wet torrefaction can produce solid fuels with greater heating values at much lower temperatures and shorter holding times.