Study On The Effect Of Hydrothermol Liquefaction Of Spirulina Platensis With Aqueous Phase Recycling

In order to solve the fossil energy crisis and the environmental pollution caused by its combustion process,vigorously looking for alternative energy sources has become a top priority.Clean and renewable bio-fuels are considered to the most promising alternative fuels.At present,there are so many biomass conversion technologies,among which hydrothermal liquefaction is one of the most important.Hydrothermal liquefaction is most suitable for energy conversion of aquatic biomass,because it can reduce energy consumption without strict drying process of raw materials.In this paper,low-lipid microalgae(Spirulina Platensis)with wide distribution and faster growth rates was used as the main raw materials.Effects of different reaction conditions on circulating hydrothermal liquefaction products distribution of Spirulina Platensis were carried out.In addition,in order to provide a feasible utilization method for the aqueous phase from Spirulina Platensis,the study on co-liquefaction of the aqueous phase as a reaction solvent with α-Cellulose and Lignin was also attempted.In order to improve the quality of the bio-oil from circulating hydrothermal liquefaction of Spirulina Platensis,activated carbon was used for adsorption pretreatment of aqueous phase.At the same time,a series of circulating liquefaction experiments on the model compound——Phycocyanin were carried out to further explore the reaction mechanism.The main research contents and conclusions are as follows:(1)Spirulina Platensis is a typical low-lipid microalgae,protein content of that exceeds 70 wt.%,but lipid content is less than 6 wt.%.In the experiment of hydrothermal liquefaction of Spirulina Platensis with aqueous phase recycling,after the first recycle,the bio-oil yield sharply increased,however,the bio-oil yields obtained from the subsequent two recycling experiments were only slightly increased compared to the first recycle.When all the pure water was replaced with the organic aqueous phase,the bio-oil yield increased from 30 wt.% to 43.6 wt.%.The main components in the aqueous phase were N-containing compounds and organic acids,while the components in bio-oils were more complex,mainly composed of N-containing compounds,hydrocarbons,fatty acids,esters,ketones,and aldehydes.Significant amount of organic acids were found in the aqueous phase from hydrothermal liquefaction of Spirulina Platensis.And the content of organic acids in the aqueous phase reduced after recycling.Organic acids in the aqueous phase promoted the hydrolysis of Spirulina Platensis,resulting in the increase of N content in aqueous phase and bio-oil samples.(2)Effects of aqueous phase from Spirulina Platensis on the products distribution from hydrothermal liquefaction of a-Cellulose and Lignin were also studied in this paper.The results showed that the aqueous phase from Spirulina Platensis could promote the bio-oil yield from hydrothermal liquefaction of α-Cellulose,but it could inhibit the bio-oil yield from Lignin.The content of 5-hydroxymethylfurfural(5-HMF)in the bio-oil obtained from hydrothermal liquefaction of α-Cellulose in pure water was 28.8 %.After co-liquefaction with the aqueous phase from Spirulina Platensis,the content of 5-HMF dropped sharply,however,the content of organic acids and ketones increased significantly.In addition,the aqueous phase from Spirulina Platensis might aggravate the polymerization of phenolic compounds,leading to the decrease of the bio-oil yield from Lignin.(3)The research on adsorption pretreatment of recycled aqueous phase from Spirulina Platensis with activated carbon were carried out.160 mg of activated carbon and 40 min adsorption time was found to be the optimal adsorption conditions with bio-oil yield of 35.15 wt.% which was a bit lower than that of the untreated case,but still much higher than that of the one using pure water.This is mainly attributed to the reduction of N&O-heterocyclic compounds(20 %)in the aqueous phase by using the activated carbon as an adsorbent,while retaining organic acids that could promote yield and quality of the bio-oil.In addition,after the aqueous phase treatment,the nitrogen content in the bio-oil decreased and the carbon content changed in the opposite direction.Interestingly,the content of n-hexadecanoic acid in the bio-oil from pre-treated case was found significantly higher than that in pure water and recycling but untreated case.(4)Response surface methodology was used to research the hydrothermal liquefaction of Phycocyanin.The optimal bio-oil yield was 32.2 wt.% and found in the operating conditions: reaction temperature of 305 ℃,residence time of 35 min.Based on the above research,the effect of different reaction temperature and residence time on the circulating liquefaction process of Phycocyanin was carried out.The most suitable conditions for the aqueous phase recycling were the reaction temperature of 285 ~ 325 ℃,and the residence time of 25 ~ 55 min.Furthermore,the optimal bio-oil yield from circulating liquefaction of Phycocyanin was 37.4 wt.%(305 ℃,35 min).Higher reaction temperature and longer/shorter residence time would reduce the content of organic acids in the aqueous phase.Interestingly,the changes of the main components in the aqueous phase and bio-oil from the circulating liquefaction of Phycocyanin were similar to those of Spirulina Platensis.Based on the changes of the main components of the aqueous phase and bio-oil of Phycocyanin,the hydrothermal liquefaction reaction path of Spirulina Platensis with the aqueous phase recycling was preliminarily introduced.