| Hydrothermal liquefaction(HTL)technology has become a focus topic in the fie ld of biomass utilization.The HTL of undaria pinnatif ida residue treated with amines hydrothermal agent was conducted in this study.The main components of products were plant oil based compounds and organic acids,lactic acid,and glycolic acid with higher added value were separated from liquid phase.In this study,HTL of undaria pinnat ifida residue was carried out in reactor with amines as hydrothermal agent.The effects of different conditions on the distribution and composition of HTL products were studied.GC-MS and FT-IR were used to investigate plant oil based compounds products in the process of HTL.The results showed that the main components of plant oil based compounds were palmitic acid,which included alcohols,alkanes,ketones,amides and benzene derivatives.HPLC was used to investigate liquid phase in the process of HTL,and results showed that the main product of liquid phase was acid.Methylamine was selected as the hydrothermal agent for the preparation of glycolic acid;ethylamine was selected for lactic acid and propylamine for plant oil based compounds.Then study of recovery of hydrothermal agent was conducted,and results showed that the distribution and composition of products with recoverd amines had marginal changes with new amines.Response surface methodology was used to optimize preparation of glycolic acid with methylamine,lactic acid with ethyla mine,and plant oil based compounds with propylamine.The highest yield of glycolic acid was 36.46g/L,the highest yie ld of lactic acid was 23.77g/L,the highest yield of plant oil based compounds was 34.73g/L.Based on the composit ion of plant oil based compounds,the formation routes of each product were studied.Fatty acids were mainly obtained from hydrolysis of lipids in the residue of undaria pinnatif ida;alkanes were mainly obtained by elimination reaction under alkaline conditions with acids and alcohols;ketones were mainly composed of branched chain of chlorophyll.Through theoretical calculation and analysis,the influence of structure of glucose on nucleophilic attack of amine was investigated.The results showed that gylcolic acid was obtained by attacking the C3 position on the glucose carbon chain with methylamine,and lactic acid was obtained by attacking the C4 posit ion with ethylamine.In this study,the volume fraction of 100% TBP,100% A101 and 40%TO A +60% octanol were selected as extractants for extraction of lactic acid or glycolic acid.The single factor experiments were carried out and the optimum extraction condit ions were determined: extraction temperature 25℃,stirring speed 300r/min,stirring time 15 min,standing time 5min.In the process of extraction,the complex ratio of TBP with lactic acid or glycolic acid was 1:1;and the complex ratio of 40 TO A with lactic aicd was 2:1;the complex ratio of A101 with lactic acid was 2:1,and with glycolic acid was 3:1.The Gibbs free energy,entropy change and equilibrium constant of A101 and 40 TO A were higher than that of TBP in extraction process,which explained the higher distribution ratio of A101 or 40 TOA.The impurit ies in HTL solut ion were effective ly removed through pretreatment using activated carbon,whereas the majority of lactic acid and glycolic acid were retained.TBP was selected as extractant for the extraction of lactic acid and glycolic acid from HTL solution.After 5 stage cross flow extraction,the content of lactic acid or glycolic acid in solut ion was lower than 0.50g/L,and extraction rates were both higher than 98%;after 8 stage countercurrent extraction,the content of lactic acid or glycolic acid in solut ion was lower than 0.50g/L,and extraction rates were both higher than 98.50%.Higher temperature was found to be beneficial to the stripping process,under the condit ion of 55℃,stripping phase ratio of 2:1,the stripping rate of lactic acid was 34.90%,and glycolic acid was 56.51%.After 5 stage countercurrent extraction,the final glycolic acid stripping rate was 99.0 0%,and lactic acid was 75.60%,some lactic acid could be left in organic phase by stripping,which lead to the separation of lactic acid and glycolic acid.In the process of fractional extraction,the ratio of flow ratio was obtained by theoretical calculation: the flow ratio of VF:VS:VW=1.50:1:3,extraction series n=12,stripping series m=5 were selected for extraction.Under the condit ion of e xtraction temperature 25 ℃,stripping temperature of 55 ℃,stirring speed 300r/min,cascade extraction separation process was carried out.According to the calculation of matter balance,the stripping rate of glycolic acid was 99.77%,and lactic acid was about 67.49%.Finally,the purity of lactic acid reached 98.76%,and the purity of glycolic acid was 68.94%.Organic phase regeneration was invesitigated in this study: TBP can be recovered after regeneration by NaO H and washing with water for twice.In this study,the comprehensive utilization of biomass residue by hydrothermal liquefaction was studied.The effects of different amines on the product were investigated,and organic acids were separated by solvent extraction,these results will provide solid foundation for industrial applications. |
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