Optimizaton of fast hydrothermal liquefaction of biomass
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Fossil liquid oil possesses many properties that have made it one of our primary sources of energy on which modern societies are highly dependent on. With the growing concern of fossil fuels impact on the environment, there is a huge potential for renewable and environmental friendly liquid fuels. Hydrothermal liquefaction (HTL) is a conversion method that can convert virtually any type of biomass to a liquid bio-oil, with similar properties to conventional oil, and gaseous and solid by-products. In order for HTL to be commercially successful, the yield of the produced oil must be optimized. Recent research indicates that high heating rate for the HTL process may be a key point to achieve this goal. The present project aimed to study the importance of high heating rate for achieving high oil yields, and to compare different kinds of biomasses subjected to high heating rates under HTL.In this work, three different heating methods were developed resulting in heating rates ranging from 66°C/min to 179°C/min, and the temperature profiles of these were studied. The highest heating rate was achieved by using micro quartz capillary reactors with an inner volume of 0.63 ml and 1mm wall thickness, in a preheated sand bath. The heating rate was then varied by using an otherwise identical reactor, but with a 2mm wall, heated in a sand bath or placed in a muffle furnace with air. All experiments were conducted with a set point temperature of 350°C and a total reaction time of 15 minutes, before the reactors were quickly cooled in a water bath at room temperature. The aqueous phase, solid residue and oil were collected and separated using a centrifugal separator and solvent dichloromethane (DCM). Using spruce wood as feedstock, the produced bio-oil increased significantly from 18.9wt% (weight basis) for the lowest heating rate, to 35.8wt% for the highest heating rate. Moreover, the solid yield decreased when the heating rate was increased, indicating that the high heating rate favoured the production of oil at the expense of solids. In addition to natural spruce, torrefied spruce and wild and cultivated batches of the macro algae Laminaria Saccharina were used as feedstock at the highest heating rate of 179°C/min. Of all the feedstocks used, the natural wood was most successful, and the oil yield decreased to 31.3wt% when torrefied wood was used. For the wild and cultivated samples of Laminaria Saccharina the bio-oil yield was much lower between 23wt% and 24wt%.