Study On The Effect Of Biochar Based Nanocatalyst On Hydrothermal Liquefaction Of Spirulina Platensis To Produce High Quality Bio-oil

In order to meet the world’s growing demand for energy and keep moving towards the goal of carbon peak and carbon neutral,it is imperative to reduce the use of fossil fuels and vigorously develop clean,renewable and carbon-neutral energy sources.Liquid biofuel is a promising alternative fuel that could help achieve this goal.Among biomass energy conversion technologies,hydrothermal liquefication（HTL）has attracted much attention because of its advantages such as no need to dry the raw materials with tedious and high energy consumption and high conversion rate of raw materials.HTL is mostly applicable to the energy conversion of aquatic biomass and is one of the most important conversion technologies for biomass with high water content.Microalgae is a kind of aquatic biomass.As a raw material of biofuel,microalgae has many advantages,such as no occupation of cultivated land,wide distribution,high photosynthetic efficiency and short growth cycle,etc.Therefore,the low-lipid microalgae-spirulina platensis was used as the main raw material in this paper.The influence mechanism of biochar（BC）based catalyst on the production of bio-oil from spirulina platensis HTL was studied.The product utilization rate of microalgae HTL was improved and the energy consumption was reduced by activating the solid residue produced by spirulina platensis HTL to form BC catalyst.In addition,the activated BC was sulfonated,modified by alkali,modified by loaded metals and metal oxides,so as to further improve the yield and quality of bio-oil.The main research contents and conclusions are as follows:（1）This paper explored the influence of BC catalyst on the production of bio-oil by spirulina platensis HTL.Response surface methodology（RSM）was used to investigate the effects of reaction temperature,reaction residence time and catalyst dosage on the preparation of bio-oil.In the temperature range of 240～320℃,residence time of 10～60 min,and BC loading of 0～0.6 g（0～20 wt%）,the maximum bio-oil yield was 35.8 wt%,which occurred at 304℃,34.7 min,and0.32 g BC.（2）Single factor experiment was used to investigate the effect of temperature on bio-oil yield.The results showed that the BC catalyst improved the bio-oil yield obviously at low temperature,reaching 4 wt%at both 260℃ and 280℃.In addition,it was found that using appropriate amount of BC catalyst can make the parameter range corresponding to the optimal bio-oil yield move to the low energy consumption area,and the corresponding parameter range become larger.At the same bio-oil yield,the energy requirements of the liquefaction system can be reduced.（3）The above BC catalyst was modified with concentrated sulfuric acid and KOH to obtain acid-alkali modified BC catalysts KOH/BC and H₂SO₄/BC.The influence of acid-alkali modified BC catalysts on the production of bio-oil from spirulina platensis HTL under different temperatures and different dosage of catalyst was investigated.The results showed that under the condition of 0.15 g and 35 min,the effect of KOH/BC on the bio-oil yield was further expanded at low temperature,and the increase rate could be more than 8 wt%between 240℃ and 260℃.However,H₂SO₄/BC increased the bio-oil yield more obviously at low temperature,reaching 10.4wt%at 240℃.In addition,at 280℃ and 35 min,the bio-oil yield decreased with the increase of the amount of catalyst.When the amount of H₂SO₄/BC was 0.45 g,the bio-oil yield decreased significantly,even lower than the condition without the addition of catalyst.（4）The above BC were supported with metal Co,Niand their oxides CoOx and NiO to form Co/BC,Ni/BC,CoOx/BC,NiO/BC catalysts to explore the influence of different supported catalysts on the preparation of bio-oil.The results showed that at 280℃,35 min and 0.15 g,Ni/BC increased the bio-oil yield most obviously,reached 36.6 wt%,which was 6.4 wt%higher than that without catalyst,and 3.6 wt%higher than that with only BC.In addition,the Co/BC catalyst had a certain inhibitory effect on the bio-oil yield.（5）The bio-oil prepared by the above catalysts was characterized,and the results showed that KOH/BC had little effect on the bio-oil quality.H₂SO₄/BC played a positive catalytic role on the quality of bio-oil,which was reflected in the increase of hydrocarbon content in bio-oil,the increase of H/C and the decrease of O/C,thus increasing the higher heating value（HHV）of bio-oil,which could reach 36.65 MJ/kg.With the increase of temperature,H₂SO₄/BC improved the quality of bio-oil more significantly.CoOx/BC and NiO/BC also helped to increase the hydrocarbon content in bio-oil,and the HHV of NiO/BC bio-oil could reach 39 MJ/kg.Ni/BC could also improve the bio-oil quality,mainly in the aspect of nitrogen removal.The nitrogen content of Ni/BC bio-oil decreased by nearly 2 wt%compared with that without catalyst.（6）In summary,BC based catalysts had a good catalytic effect on the bio-oil yield of spirulina platensis HTL under mild conditions,and H₂SO₄/BC was the best one.For the quality of the prepared bio-oil,different BC based catalysts had different catalytic effects.NiO/BC had the strongest hydrogenation and deoxygenation ability,while Ni/BC had the best denitrification performance,and its energy recovery rate was also the highest among the prepared catalysts,reaching 74%.