Chemical Looping Pyrolysis-gasification Stage Conversion Of Microalgae Using Ca-Fe Oxygen Carrier

Biomass is a renewable energy to completely replace fossil energy,which can not only obtain various high-grade energy sources such as gas,liquid fuel and solid fuel,but also can be selectively converted into high value-added chemicals.As an important marine biomass resource,microalgae,posses the advantages of wide distribution,no occupation of cultivated land,strong photosynthesis and short growth cycle,has attracted huge amount attention.Compared with chemical conversion and biochemical conversion,thermochemical conversion provides a simple path for biomass.As a new type of thermochemical method,chemical looping technology provides new ideas for the thermochemical conversion of biomass.Owing to its merits of high-energy efficiency,controllable redox degree and product inherent separation,has been attracted tremendous interest.In this paper,microalgae was used as biomass material,and Ca-Fe composite oxygen carrier was employed to conduct a creative experimental study on the chemical looping pyrolysis-gasification of microalgae.Firstly,according to the different effects of oxidized and reducd CaFe₂O₄ oxygen carrier for microalgae pyrolysis stage,two chemical looping pyrolysis-gasification staged conversion routes were proposed.As to the oxidized oxygen carrier for microalgae pyrolysis,oxygen carrier is conducive to the aromatization reaction,with high valuable aromatic chemicals obtained.At 600 ^oC,the yield of toluene is up to10.26 area%.As to the reduced oxygen carrier for microalgae pyrolysis,the reduced oxygen carrier is beneficial to the formation hydrocarbons,in which the olefins yield is30.38 area%,and its high calorific value is 34.18 MJ/kg.Itindicated that bio-oil quality improved has been improved.The gasification process of microalgae pyrolysis semi-coke and oxygen carrier can produce H₂-rich or CO-rich synthesis gas,Meanwhile the oxygen carrier is reduced to its reduction stage.It proves the feasibility and flexibility of chemical looping in biomass pyrolysis-gasification stage conversion process.Secondly,in the view of the chemical looping process with oxidized oxygen carriers for microalgae pyrolysis,four kinds of oxidized Ca-Fe composite oxygen carriers?CF5,CF2,CF and C3F2?with different Ca-Fe molar ration were prepared.Further,their reaction characteristics in chemical looping pyrolysis-gasification of microalgae were evaluated.The Ca-Fe composite oxygen carrier in the oxidation state at the pyrolysis temperature is conducive to the production valuable products,among four oxygen carriers,CF2 and CF oxygen carriers are positive to the aromatization reaction,with the yield for toluene 10.26 area%and 31.99 area%,respectively,while CF5 and C3F2 oxygen carriers are favorable to the formation of 4-methyl,2-pentanol,with the area percentage 21.23 area%and 20.69 area%,respectively.During the reaction between oxidized CF2 as well as CF oxygen carrier and microalgae pyrolysis coke,both two oxygen carriers are beneficial to the generation of CO gas with steam as gasified agent,while they are in favour of the generation of H₂ gas with steam as gasified agent.Finally,with reduced oxygen carriers for microalgae pyrolysis,the reaction performances of four reduced Ca-Fe composite oxygen carriers in chemical looping pyrolysis-gasification of microalgae were studied.The results shown that the reduced Ca-Fe composite oxygen carriers are beneficial to produce high quality bio-oil.With four reduced composite oxygen carriers,the hydrocarbon content using reached to19.35,49.28,39.82 and 51.21 area%,respectively,while the olefin content is 14.87,30.38,22.24 and 40.71 area%,respectively,As a consequence,the combustion heat value increases from 20.51 MJ/kg to 35.28 MJ/kg,34.18 MJ/kg,36.04 MJ/kg and37.99 MJ/kg,respectively.Mechanism can be concluded as follows:CaO and Ca₂Fe₂O₅ facilitates the ketonization and hydrodeoxygenation reaction during the pyrolysis oil,which greatly reduces the oxygen and nitrogen content of the liquid phase,and improved the carbon chain length of the pyrolysis oil.Consequecely,both the pH value and thermal stability of the bio-oil was.In general,it provides a new way for biomass pyrolysis to produce high quality bio-oil.