Hydrothermal Liquefaction Of Spirulina For Bio-crude Production: An Experimental Study On Aqueous Phase Circulation

As a third-generation biomass fuel,algae is an ideal source of biomass raw materials because of its advantages of fast growth rate,high biomass yield and no occupation of agricultural land.Hydrothermal liquefaction（HTL）converts algal biomass into bio-crude,while obtaining other by-products such as aqueous phase products,solid residues and gases.In order to improve carbon utilization rate,reduce process water consumption and reduce three-waste emissions,this paper proposes a technical route based on aqueous phase circulation as HTL medium,which can realize comprehensive utilization of various phase products.The high-protein spirulina was used as the raw material.The results of the aqueous phase cycle experiment showed that the bio-crude yield increased from 36.60%to 44.27%maximally and nitrogen enrichment occurred.The bio-crude nitrogen content increased from 7.67%to 8.27%maximally.Further the study about the effects of aqueous phase product components such as volatile aqueous phase products（VAPs）,non-volatile aqueous phase products（NAPs）,ash（Ash）recycling on product distribution and bio-crude properties.It was found that non-volatile water-soluble organic matter of NAPs is a key component for increasing the yield of bio-crude and causing nitrogen enrichment.The above conclusions were verified by the modeling experiment of the 2-piperidone component in NAPs.Thermal analysis studies the possible reaction characteristics of bio-crude in thermal processing.It was found that the reaction process was mainly divided into three stages.The first stage（373～442K）is mainly based on the distillation reaction of small organic matter;the second stage（442～877K）is mainly based on the thermal cracking and condensation of organic matter;the third stage（877～1073K）is mainly coke condensation,inorganic ash slowly decompose and volatilize.The DAEM model was selected and the non-preset function integration method was used for calculation.The pyrolysis activation energy of bio-crude in the second stage was 107.70～190.01k J/mol.The solid residue before and after pickling of 4%diluted hydrochloric acid was subjected to elemental analysis and BET detection,and it was found that the solid residue after pickling could not be used as a fuel and an adsorbent.Gas chromatography results showed that the gas contained 88.68%CO₂,which could be used as a carbon source to culture algae.