327 / 2018-07-28 20:31:58

Properties and Stability of Microalgae Bio-crude oil via Hydrothermal Liquefaction at different Storage Conditions

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Hydrothermal liquefaction (HTL) has been recognized as a promising technology to convert wet biowaste into bio-crude oil. The stability is a critical aspect for downstream oil refining, however, the stability of bio-crude oil via HTL was seldom documented. Here we investigated the stability and properties of bio-crude oil from microalgae at six different storage conditions: 4oC, 15oC and 35oC with/without protected N2 in dark place, over 12 weeks. The slight change of oil weight revealed that the bio-crude oil was not easy to volatilized. Significant changes of oil viscosity were observed when the storage temperature was shifted from 4oC to 35oC at air conditions. The addition of N2 protection led to similar viscosity changes at three storage temperatures. The TAN (total acid number) of bio-crude oil decreased (22.6~25%) when stored with N2 protection and increased (9.1~11.2%) without N2 protection. Interestingly, a layer of oil “Oxidation shell” up the bottle was formed, and the rigidity was increased with the storage temperature. And at the same temperature, the rigidity of oils that without N2 protected were harder than the oils with N2 protected. And TGA analysis also shows that the “Oxidation shell” of every bio-crude oil was aging more severely than the oil under the “Oxidation shell”. Although element contents and HHV of bio-crude oils (include the “Oxidation shell”) did not change obviously, its chemical compositions greatly changed. Specifically, some new oxygenated compounds occurred during the storage, indicating that the O2 in air especially in higher temperature may negatively impact the stability of bio-crude oil.