Research On Hydrolysis Of Sugar-rich Microalgae ?Chlorococcum Sp.? Into Lactic Acid And Mechanism Over La₂O₃ Catalysts

As a kind of renewable resources,the study on the utilization of biomass as a renewable energy to obtain high value-added bulk chemicals is attracting more and more attention.Microalgae is an aquatic single-celled organism with photosynthetic organs such as chloroplasts,which can quickly convert CO₂ into organic compounds by photosynthesis.And a new type of microalgae with high growth rate,stable heredity and rich in carbohydrates can be grown by modern biotechnology.The carbohydrates found in microalgae can be prepared by hydrothermal transformation to prepare the important small molecule containing oxygen,which is usually obtained by biological fermentation.According to the characteristics of sugar-rich microalgae and hydrothermal catalytic,he idea of"one-step"hydrolysis of sugar-rich microalgae to produce lactic acid was put forward in this paper.And how to obtain high yield of lactic acid in liquid phase and its reaction mechanism is the focus of this paper.Firstly,a system of hydrolysis of sugar-rich microalgae based on La₂O₃ catalyst to produce lactic acid was established.The influence factors analysis of hydrothermal catalytic conversion from sugar-rich microalgae to lactic acid showed that the lactic acid yield in liquid product increased with the increase of reaction time and catalyst dosage,but more gently by reaction time factors.And the lactic acid yield increased with the initial pressure in the reaction system.When the reaction temperature was200?,the reaction time was 120 min,catalyst dosage was 0.37M and the initial pressure of protection gas was 4MPa,the conversion of carbon and the yield of lactic acid in the liquid product reached the highest value,94.85%and 29.80%respectively.In the same condition,the hydrolysis production of corncob and chlorella in La₂O₃system was lactic acid,as the yield was 25.30%and 12.70%,respectively.Secondly,using glucose as a model compound with La₂O₃ as catalyst,and analyzes the influence of different reaction conditions on the yield of lactic acid by hydrolysis,and to explore the stability of La₂O₃ catalyst.The results show that the yield of lactic acid in liquid products increased firstly and then decreased with the increase of time and the amount of catalyst.The effect by reaction time factor is relatively smooth and the peak appeared at 30min,and with the initial pressure in the reaction system increased the yield of lactic acid showed a rising trend.When the molar ratio of catalyst to glucose was 7.5,the initial helium pressure is 4MPa,the reaction temperature is 200?,the reaction time is 30min,the yield of lactic acid is as high as 42.10%.Research on the stability of the catalyst showed that the stability of La₂O₃ decreased slightly in the first cycle,the lactic acid yield slightly decreased and then tended to be stable.Thirdly,the conversion mechanism of hydrolysis of sugar-rich microalgae to lactic acid was obtained,and the mechanism of C-C bond breaking and the mechanism of La₂O₃ catalyst were discussed.In this paper,the main intermediate products such as dihydroxyacetone,acetone aldehyde,pyruvate,glycerol and glyceraldehyde are selected to verify the main pathways of glucose conversion in the process of lactic acid,and the transformation path of intermediate state products is described.The mechanism of hydrothermally catalyzed conversion of sugar-rich microalgae to lactic acid was proposed,including hydrolysis to soluble intermediate glucose,and then isomerization to fructose under the action of Lewis acid.C-C bond between C-3 and C-4 on fructose was broken,glyceraldehyde was formed by reverse hydroxaldehyde condensation,and acetone aldehyde was further dehydrated to form acetone aldehyde.The intramolecular Cannizzaro reaction of acetone aldehyde was catalyzed by Lewis acid site on La₂O₃ to form lactic acid.In conclusion,the preparation of lactic acid from sugar-rich microalgae by hydrothermally catalytic conversion requires no pretreatment of microalgae,breaking walls,and so on.Under mild conditions,it can be directly converted to important small molecule oxygenated chemicals such as lactic acid.This provides a new way for efficient transformation of primary biomass with water as the medium.