Hydrothermal Liquefaction Of Microalgae And Model Compounds In Hot Compressed Water

The improvement of our life cannot be separated from the support of energy.The growing demand for energy and the shortage of energy supply have made people urgently looking for alternative energy sources to cope with energy crisis that we faced nowadays.Many countries have begun to pay attention to the development of renewable energy,and one of the most significant and concerned research fields is biomass energy.As the representative of the 3^th generation of biofuels,microalgae has integrated the advantages of the first and second generations of biomass energy which are short life cycle and high yield,making it a biofuel with high commercial value and also characterized with environmental friendliness and carbon balance.Currently,research of the microalgae's utilization is increasingly focused on hydrothermal liquefaction,which could produce liquid biofuel product without drying of raw material.In this research,fused silica capillary reactor?FSCR?,polarized microscope real-time camera system and in-situ Raman spectroscopy were used to study the hydrothermal liquefaction process of microalgae and its model compounds,and fused quartz tube reactor?FQTR?,tubular heating furnace and GC/MS were used to study and analyze the liquefaction products of microalgae model compounds,presenting the possible hydrothermal liquefaction reaction pathways of microalgae model compounds.The pyrolysis process of microalgae and its model compounds can be divided into three stages:dehydration and depolymerization,volatilization and carbonization.On the other hand,the hydrothermal liquefaction process of microalgae and its model compounds can be divided into four stages:dissolution and diffusion of materials,degradation of materials and chemical reactions between them,production of bio-oil,dissolution and diffusion of bio-oil.An obviously synergistic effect can be observed during the thermal liquefaction process,reflected in material dissolving temperature,color changing,different of phase behavior and final form of the product.Due to the fluorescence emitted by organics during the hydrothermal liquefaction of microalgae model compounds,unsatisfactory Raman spectrum were captured.Among all the hydrothermal liquefaction products of microalgae model compounds,the maximum carbon number is C35,and the carbon number distribution is mainly between C12 and C18.The increase of the temperature of HTL will increase the yield of short-chain and long-chain products,decreasing the medium-chain product.The main products of HTL can be classified as hydrocarbon?aliphatic,alicyclic,aromatic,anthracene?,amino compound?amines,imines,amides,nitriles?,ester/ketone/alcohol/phenol,fatty acid and their derivatives?acids,aldehydes?,N-heterocyclic?pyrrole,pyridine?,di-N-heterocyclic?pyrazole,imidazole,pyrimidine,pyrazine?,N&O-heterocyclic?pyran,oxazole?.The yield of hydrocarbons increases as the temperature rises.The aminos do not change vastly at each temperature except260°C.The content of the esters/ketones/alcohols/phenols is complementary to the content of fatty acids and their derivatives,adding up to 80%of the total production.The N-heterocyclics have a little change between each temperature,and the di-N-heterocyclics only account for a small proportion,while N&O-heterocyclics barely have been detected.During the hydrothermal liquefaction of microalgae model compounds,glucose degraded into small molecules such as O-heterocyclic,ketones,cyclic hydrocarbons,phenols,cyclic ketones.Soy protein hydrolyzed first producing vast number of amino acid monomers,then underwent decarboxylation,deamination and other degradation processes at high temperatures,producing amines,carboxylic acids,aldehydes,alcohols.Lipid hydrolyzed initially into ricinoleic acid,through decarboxylation and decarbonylation,then alcohol and long-chain hydrocarbon were produced.The Maillard reaction between glucose and amino acids during the HTL could produce numbers of cyclic compounds containing N and O.The reaction between ricinoleic acid and glucose,and between ricinoleic acid and amino acids would all generate surfactant-like substances.