Study On The Catalytic Hydrothermal Liquefaction Of Low-lipid Microalgae And Process In Situ Analysis

The increasingly exhaustedoffossil resources promote the development of renewable fuels to meet the increasing demand for energy.Due to the strong photosynthesis and short growth cycle of microalgae,the production of biofuels with microalgae as the raw material had been becomes the hot topic.In order to avoid the energy consumption during the drying processes,hydrothermal liquefaction(HTL)of microalgaebecomes one of the main technologiesfor the transformation of microalgae.Herein,in this study,systematic research were paid on HTL of microalgae and in situ analysis technology of liquefaction process with the emphasis on the preparation of catalysts with high hydrothermal stability as well as their catalytic properties.The main results are thereas follows:At first,the catalysts with differentacid and alkaline were chosen to employ in catalytic HTL process of microalgae.The results showed that the alkaline catalyst is to improve the conversion of microalgae and bio-oil yield,while acidic catalyst is to improve the quality of the bio-oil.Due to different mechanisms,the introduction of the catalyst is beneficial to reduce the ash content of bio-oil,and can affect the chemical composition of bio-oil and boiling point distribution.Secondly,metals(Ni,Pd,and Co)supported carbon nanotubes(CNTs)were used as the catalyst for catalytic HTLof microalgae.The results show that the metal supported catalysts are to improve the conversion and bio-oil yield.The bio-oil obtained fromcatalytic HTL of microalgae was represented higher hydrocarbons content and low acid content.The type of catalyst has a significant impact on the chemical composition and the boiling point of distribution as well as the liquefaction reaction paths.Thirdly,the mesoporous catalysts with high hydrothermal stability were prepared through metal doping and alkylation grafting preparation,and used in catalytic HTL of microalgae.Results show that the metal doping and alkylation grafting are beneficial to improve the hydrothermal stability of mesoporous materials,and metal doped method is mainly to introduce the metal heteroatoms in the skeleton of mesoporous materials,and alkylation grafting method is to close surface hydroxyl groups in mesoporous materials by alkylating reagent.The mesoporous materials with high hydrothermal stability are largely depended on the doping metal species and the structure of grafting alkylating reagent.When the obtained mesoporous materials with high hydrothermal stability were used as the catalysts for catalytic HTL microalgae,the bio-oil with a higher percentage of hydrocarbons and a lower content of fatty acid was obtained as well as significantly low content of nitrogen-containing compounds.At last,the phase behavior and in situ Raman analysis of the model compounds of microalgae were carried out in quartz capillary reactor.Results show that single model compounds shows different phase behavior because of their different species and structure,whereas,the mixtures of model compounds showed significant interaction during the liquefaction process.The Raman characteristic peak related to the HTL reactionobtained from gas phase and water phase indicated that Raman spectroscopy can be used for the in situ analysis of HTL process.The HTL product components analysis from single model compound and its mixture show that the model compounds in HTL process hadobvious synergy effect,and the research results are consistent with the results of the phase behavior and the Raman analysis.