Carbon isotope fractionation of ethyl levulinate by liquefaction of composite solvents
Compound-specific stable isotope analysis(CSIA)can separate a single compound by gas chromatography or liquid chromatography,in which the stable isotope ratio of the element can be measured by isotope ratio mass spec-trometry.It elucidates the transformation process of compounds in chemical reactions by analyzing the stable isotope composition characteristics,variation laws and fractionation principles of specific elements in target compounds.CSIA was used to study the fractionation characteristics of carbon-stable isotopes during the liquefaction of C3 and C4 plant-derived feedstocks to ethyl levulinate(EL).The experimental results showed that,within the 15 min reaction,the re-action rates of C3 and C4 plant-derived feedstocks were as follows:tapioca starch was faster than corn starch,poplar cellulose was faster than corn straw cellulose,and poplar was faster than corn straw.The fractionation rate of EL car-bon isotope ratio generated by liquefaction of C3 plant-derived feedstocks was greater than that of C4 plant-derived feedstocks.The results indicated that the differences in carbon stable isotope composition of different feedstocks would affect the reaction rate of liquefaction.There was a direct relationship between the reaction rate and the fractionation rate,when the liquefaction reaction rate was large and the rate of change of δ13C value was also large.Combined with the Rayleigh equation to quantify the enrichment degree of 13C carbon stable isotope of EL during liquefaction,the en-richment factor in the liquefaction process of different raw materials was obtained as follows:εcorn starch＞εtapioca starch,εCS-C＞εP-C,εcorn straw＞εpoplar.The results showed that the enrichment degree of carbon isotopes during the liquefaction process was related to the δ13C value of the feedstocks,and the enrichment factor of C4 feedstocks with small carbon isotope ratio was larger.The degree of reaction progress in the liquefaction process was related to the carbon stable iso-tope of the feedstocks,and the fractionation trend can reflect the formation path of the product.There was no need to quantify the liquefied product.Due to the existence of kinetic isotope effect,the reaction rate of heavy isotope 13C was slower than that of light isotope 12C when chemical reactions occurred in organic compounds.This was because the difference in isotope mass resulted in the enrichment and dilution of heavy isotope 13 C in reactants and products re-spectively.13C isotope was enriched in the intermediate product 5-HMF,while 12C isotope was gradually enriched in the final product EL,indicating that the path of 5-HMF →EL was dominant in the experimental process,CSIA can be used to study the liquefaction process.
compound specific isotope analysisethyl levulinateliquefactioncarbon isotope fractionation
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