Study On Hydrothermal Liquefaction Of Biomass For Bio-crude Production And Product Characterization

The renewable energy is of increasing concerned in recent years because they can mitigate rapid depletion of fossil fuel reserves, and provide clean sources of energy that have a much lower environmental impacts. As a promising technology, hydrothermal liquefaction（HTL） has the ability of using mixed feedstocks and producing products with better quality. HTL of lignocellulosic biomass and organic waste at different reaction parameters were conducted in two different types of batch reactor and compared to optimize its reaction conditions. The effect of reaction temperature, heating rate and catalyst on the HTL were investigated. Most importantly, the effect of reaction temperature and alkali catalyst on the products properties from barley straw was analyzed systematically and compared. As one of the co-product resulting from HTL process, aqueous phase was explored as well. Finally, HTL of woody biomass slurry was investigated in both continuous in order to evaluate the effect of process conditions on the products properties. The detailed results are as follows:Lower temperature favored the bio-crude oil production, irrespective of the heating rate and biomass type, while higher temperature improved the bio-crude properties. It was also found that the bio-crude oil yield and its properties were enhanced at a much higher heating rate. For example, the maximum bio-crude yield from barley straw and wood when treated at higher heating rate were 35.15 wt% and 42.97 wt%, respectively. The bio-crude oil composition was also tuned by adjusting reaction temperature. The compounds in bio-crude oil from HTL of barley straw at different temperatures were identified, which were mainly phenolics, carboxylic acids, aldehydes and alcohols, among which the relative contents of phenolics and carboxylic acids decreased with the increase of temperature.K₂CO₃ increased bio-crude oil yield with different feedstocks（bareley straw, wood, bark and sawdust） and inhibited solid residue formation when treated at 300 oC. Moreover, the bio-crude produced in the presence of a catalyst had better properties, in terms of higher heating value and lower O/C. For example, the bio-crude yield from barley straw was enhanced to 34.85 wt%. The major compounds identified in bio-crude from barley straw were carboxylic acids, phenolic compounds and ketones, irrespective of whether the catalyst was used. However, the distribution and relative content of these compounds were different. More phenolic compounds and less carboxylic acids were observed in the catalytic run. In addition, the carbon and energy recovery with the addition of K₂CO₃ were twice as high as that without catalyst, indicating an improvement in energy efficiency.After HTL of barley, the aqueous phase was recycled three times in HTL process. It was found that the aqueous phase was rich in organic acids and polyols, which accelerated the decomposition of barley. It raised the bio-crude yield gradually to 38.4 wt% after three cycles. The higher heating values of bio-crude from recycle runs were 28.4-29.4 MJ/kg, slightly higher than that from HTL with fresh water, while no obvious element difference can be found. As a result, it is feasible to recycle aqueous phase in HTL process.It was found that bio-crude oil yield was affected by reaction temperature, catalyst and biomass to water ratio significantly by Response surface methodology（RSM）. A maximum bio-crude oil yield was obtained at temperature of 304.8 oC, reaction time of 15.5 min, 11.7 wt% of catalyst（based on barley straw） and 18 wt% biomass（based on water） in this RSM mode. The predicted bio-crude yield was in agreement with the experimental results, suggesting the RSM mode was accurate in terms of optimization of HTL of barley straw.The results showed that the solid yield was strongly influenced by the type of reactor processing. Continuous processing improved the properties of the bio-crude oil with HHV of more than 38 MJ/kg.