| Br(?)nsted acidic ionic liquids(BAILs)are capable to both“dissolving cell wall”and“catalyzing transesterification”,thus,they are used to catalyze in-situ transesterification of wet algaefor biodiesel production.Water,methanol and other solvents are existed in Br(?)nsted acidic ionic liquids catalyzed in-situ transesterification of wet algae which probably affect the dual roles of BAILs and the,final biodiesel yield.However,how do methanol and water conditions affect the dual roles of BAILs is unclear.Herein,[Bmim][H2PO4],[Bmim]2[HPO4],and[Bmim][HSO4]are used to catalyze the in-situ transesterification of wet algae under different methanol and water conditions.The effect of solvent conditions on“dissolving cell wall”and“catalyzing transesterification”have been extensively investigated.The solubilities of cellulose in[Bmim][H2PO4]and[Bmim]2[HPO4]are higher than[Bmim][HSO4].The increase of methanol content is beneficial to the dissolution of cellulose in[Bmim][HSO4],while it is adverse to dissolution of cellulose in[Bmim][H2PO4]and[Bmim]2[HPO4].Lower content of water content is negative to the solubility of cellulose in[Bmim][H2PO4],[Bmim]2[HPO4]and[Bmim][HSO4],while it will effectively promote the dissolution of cellulose in[Bmim][H2PO4],[Bmim]2[HPO4]and[Bmim][HSO4]at higher water content.Both the cellulose solubility and FAME yield of[Bmim]2[HPO4]and[Bmim][HSO4]catalyzed in situ transesterification decrease with the increase of methanol dosage,while those of[Bmim][H2PO4]catalyzed in situ transesterification was positive to increase of methanl dosage.Similar to the effect of water content on“dissolving cell wall”,the presence of water was negative to the in-situ transesterification of wet algae catalyzed by[Bmim][H2PO4],[Bmim]2[HPO4]and[Bmim][HSO4].However,the continuous increase of water content was beneficial to in-situ transesterification of wet algae catalyzed by[Bmim][H2PO4],[Bmim]2[HPO4]and[Bmim][HSO4].In order to exploring the mechanism of solvent effect on“dissolving cell wall”and“catalyzing transesterification”,the crude oil composition,thermal stability,crystallinity of cellulose in situ transesterification of wet algae catalyzed by[Bmim][H2PO4],[Bmim]2[HPO4]and[Bmim][HSO4]were deeply analyzed.The results showed that the order of thermal stability and crystallinity of cell wall cellulose in situ transesterification of wet algae catalyzed by different BAILs was as follows:[Bmim][H2PO4]<[Bmim]2[HPO4]<[Bmim][HSO4].With the increase of water content,the contents of saturated ester(C16:0)and unsaturated component(C18:1)increased.The ratio of total saturated to unsaturated esters[Bmim][H2PO4]and[Bmim]2[HPO4]became smaller and smaller,while the ratio catalyzed by[Bmim][HSO4]became larger and tended to be 100%.In order to further explore the effect mechanism of[Bmim][H2PO4],[Bmim]2[HPO4]and[Bmim][HSO4]on“dissolving cell wall”and“catalyzing transesterification”under different solvent conditions,the hydrogen bonding interaction between BAILs and cellulose under different water content and its catalytic mechanism were analyzed by theoretical calculation.The p Ka of BAILs was calculated theoretically and the acid value of Hammett was determined by probe method.Three catalytic mechanisms were proposed:acidic catalytic process,neutral molecular catalytic process and alkaline catalytic process corresponding to[Bmim][HSO4],[Bmim][H2PO4]and[Bmim]2[HPO4]respectively.Combined with the conceptual density functional theory(CDFT)and the atomic theory in molecules(AIM),the catalytic sites are considered separately,the law of cellulose dissolution will be completely consistent with the calculation results.It can be seen that there is competition between the catalytic sites and the dissolved cellulose sites,but the competitive relationship will change with the increase of water content.The law of change can be found in the theoretical calculation part. |
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