Study On Positive Synergistic Mechanism In Bio-oil Production On Hydrothermol Co-Liquefaction Of Spirulina And Spartina Alterniflora

Stable and reliable fossil fuels have played a crucial role in promoting the development of the world economy and the progress of civilization.However,the limited reserves and lack of cleanliness have also caused concern in the community.The development of biofuels,the most promising alternative to fossil fuels,seems to be a viable option that is expected to address the unsustainable and high emissions that previously existed in traditional fossil fuels.Hydrothermal liquefaction technology is a wide-ranging and efficient thermochemical conversion technology in many biofuel production technologies which does not require the cumbersome and high-energy drying process of the wet biomass raw materials,and the whole component utilization of the biomass can be realized by one-step conversion,and the high yield and high energy recovery rate of the biofuel are achieved at the same time.This thesis is aimed at the low-lipid microalgae spirulina that exists in nature and the invasive plant Spartina alterniflora in the coastal areas of China—two high-water content biomass.The hydrothermal co-liquefaction characteristics after blending were studied,and the synergistic effects of the reaction temperatures,residence time and blending ratio were also explored.Through the research on the synergistic characteristics of hydrothermal co-liquefaction of spirulina and the two main components of Spartina alterniflora—Cellulose and Lignin,respectively,the synergistic mechanism on hydrothermal co-liquefaction of Spirulina and Spartina alterniflora was revealed,to further improve the yield and quality of the bio-oil after the hydrothermal co-liquefaction of the blended raw materials,and to realize the efficient energyization of Spirulina and Spartina alterniflora.The main research contents and innovative research results are as follows:（1）The single-factor test combined with the response surface method was used to study the hydrothermal liquefaction characteristics of Spirulina and Spartina alterniflora.The results showed that it is a typical high-protein low-lipid microalgae whose protein content exceeds70wt.%and the lipid content is only 5wt.%.The model formula of Spirulina sample is CH_1.77O_0.57N_0.2,which shows that the theoretical higher heating value（HHV）is 18.51MJ/kg.The optimal bio-oil yield of Spirulina reached up to 40wt.%in subcritical water,the operating conditions at this time are:reaction temperature of 335℃,residence time of 45 min,raw material of 3g and water of 30mL.The characteristic analysis of the Spartina alterniflora raw material sample showed that was a typical lignocellulosic biomass whose the total content of cellulose and hemicellulose exceeds 65wt.%and the lignin content is over 10wt.%.The model formula of Spartina alterniflora sample is CH_1.66O_0.96N_0.02,which shows that the theoretical HHV is17.8MJ/kg;the bio-oil yield of Spartina alterniflora in subcritical water is not much different under the influence of reaction temperature and residence time.The optimal bio-oil yield is about15wt.%,whose requirement is at high reaction temperatures of 360℃,which is significantly lower than the bio-oil yield of Spirulina.（2）The research results on hydrothermal co-liquefaction the blended raw materials of Spirulina and Spartina alterniflora showed significant synergistic effect at different reaction temperature and reaction residence time,mainly in terms of the bio-oil yield and quality changing,and the optimal bio-oil yield was found in the operating conditions:reaction temperature of 360℃,residence time of 30min,blending ratio of 1:1,which is more than 30wt.%.More fatty acids was found in the bio-oil from the blended raw material compared with hydrothermal liquefaction Spirulina and Spartina alterniflora,respectively.At the same time,the HHV and the energy recovery rate of the blended raw materials bio-oil were higher at340³60℃,which was attributed to positive synergistic effect that changed part of the reaction pathways and improved the yield and quality of bio-oil.（3）The research on the hydrothermal co-liquefaction characteristics of Spirulina andα-Cellulose was carried out.The results showed that significant positive synergistic effect exists between Spirulina andα-Cellulose,resulting in a substantial increase in the synthesized bio-oil yield.At a reaction temperature of 300℃,a residence time of 30min,and a blending ratio of 2:1,the bio-oil yield exceeded 40wt.%.The synergistic effect SE exceeded 16wt.%compared with hydrothermal liquefaction of Spirulina orα-Cellulose under the same conditions,respectively,which is almost comparable to the gain effect of expensive catalysts;the possibility of carbonization was reduced,and the dehydration,polymerization,condensation,cyclization and Maillard reactions were enhanced on hydrothermal liquefaction of the blended raw materials,which led to the blended raw material bio-oil also contains a large amount of nitrogen-containing and oxygen-containing heterocyclic compound;the higher heating value（HHV）and the energy recovery rate analysis result show that the blended raw material bio-oil sample has a considerable energy recovery rate of 70⁸0%.（4）The blended raw materials of microalgae Spirulina and high purity Lignin were used as research objects in subcritical water to further explore the synergistic mechanism of hydrothermal liquefaction.The results showed that the quality of bio-oil from blended raw materials was significantly improved,and the bio-oil yield was not reduced any more when the reaction temperature was above 340℃.The operating conditions of Lignin bio-oil yield were optimized,at reaction temperature of 350℃,residence time of 50min and there was bio-oil yield of more than 23wt.%on hydrothermal liquefaction of Lignin in subcritical water.The operating conditions of the bio-oil yield of the blended raw material were also optimized,and the reaction temperature of 345℃,the residence time of 40 min,and the blending ratio of 2:1,which was closed to 32wt.%.The fatty acids content of the blended raw material bio-oil,especially the content of hexadecanoic acid was increased significantly compared with hydrothermal liquefaction Spirulina or Lignin,respectively.Interestingly,the nitrogen content of the blended feedstocks bio-oil was also significantly reduced.（5）The study on co-liquefaction of the Spirulina and Spartina alterniflora was also carried out to further improve the bio-oil yield and quality in ethanol-water co-solvent（EWCS）.The results showed that the bio-oil yield of from Spirulina,Spartina alterniflora and the blended raw materials was improved significantly after the addition of ethanol.The Spartina alterniflora bio-oil yield was the most obvious with the reaction temperature of 340℃,the residence time of30min and the ethanol volume fraction of 50vol.%,which reached 42wt.%;The yield of Spirulina bio-oil was increased and about 40wt.%bio-oil yield was achieved when the reaction temperature was only 280℃,the residence time was 30min,and the volume fraction of ethanol was 50vol.%.For the blended raw materials,the bio-oil yield was also significantly increased after the addition of ethanol,but to some extent weakened the synergistic effect between the blended raw materials.Interestingly,it was found that the lipid content of 25.85wt.%and the energy recovery rate of about 85%in the blended raw material bio-oil,which was superior to hydrothermal liquefaction of Spirulina and Spartina alterniflora in EWCS,respectively.Based on the study of the positive synergistic characteristics and mechanism on hydrothermal co-liquefaction of Spirulina and Spartina alterniflora,it can be seen that more yield and higher quality of bio-oil could be obtained on co-liquefaction of blending raw materials under suitable operating conditions.Thus,reasonable use of the positive synergistic effect between different biomass can not only produce biofuels more efficiently,but also solve the source problems of biomass raw materials due to seasonality and geography,to provide a variety of solutions for liquid biofuels conversion from biomass.