Abstract:

In this work, the carbon isotopic fractionation characteristics of feedstocks with different stable carbon isotopic compositions during hydrothermal liquefaction for preparation of 5-hydroxymethylfurfural(5-HMF) were compared, and the effect of carbon stable isotope composition of raw materials on the yield of 5-HMF was studied. The results showed that the maximum yield of tapioca starch was 33.90%, which is higher than those of corn starch(29.93%), poplar cellulose(P-C, 31.00%), and corn straw cellulose(CS-C, 30.76%), respectively. The maximum yields of bamboo flour and poplar were 13.00% and 13.80%, which were higher than those of corn straw(11.6%) and corn cob(12.53%), respectively. At the reaction time of 15 min, the reaction rate of different raw materials: tapioca starch 0.301 g/(L·min) was greater than corn starch 0.128 g/(L·min), poplar cellulose 0.513 g/(L·min) was greater than corn straw cellulose 0.386 g/(L·min), and bamboo powder 0.133 g/(L·min) was greater than poplar 0.124 g/(L·min), which was greater than corn cob 0.117 g/(L·min) and greater than corn straw 0.097 g/(L·min). In the reaction process, the change rate of δ_¹³C value of raw materials with smaller δ_¹³C value(cassava starch, poplar cellulose, poplar and bamboo powder) in the initial stage of reaction was greater than that of raw materials with larger δ_¹³C value(corn starch, corn straw cellulose, corn straw and corn cob). There was a stable isotope kinetic effect in the hydrothermal liquefaction process. The ¹³C isotope required more energy to participate than the enriched raw materials in the reaction, the reaction rate was slow, and the yield of 5-HMF was low. In the process of liquefaction, the stable isotope fractionation of raw material with a simple structure has a great influence. The greater degree of liquefaction, the greater degree of change of δ_¹³C.

Key words: hydrothermal liquefaction, lignocellulose biomass, carbon isotope fractionation, 5-hydroxymethylfurfural, compound specific isotope analysis