Study On The Production Of Levulinic Acid, A New Platform Chemical From Biomass

With the rapid consumption of non-renewable resources and approach of energy crisis, the utilization of renewable resources, instead of non-renewable ones, is attracting more and more attention wordwide. Especially, the utilization of lignocellulosic materials as promising renewable biomass to replace petroleum for producing important chemicals, is of important strategic significance. As a new kind of green platform chemicals, levulinic acid has highly attracted the attention for its wide range of applications. In this work, the degradation process, mechanism, kinetics as well as the separation and purification of levulinic acid production from biomass, such as wheat straw and wood powder, were evaluated at high temperature and catalyzed by acid. Furthermore, the synthesis of diphenolic acid with levulinic acid as raw material was also studied.Glucose is the product of cellulose hyddrolyzation and the precursor for levulinic acid synthesis, therefore, the degradation of glucose was studied at the temperature range of 170-210℃ and acid concentration range of 1-5%. It was found that the higher temperature and acid concentration were favorable for enhancing the glucose degradation and the rate of degradation was able to be described by first order kinetics. In the initial stage of glucose degradation, both isomerization and reversible reactions were also observed, and the intermediates and by-products were produced during the degradation process, such as 5-hydrornethylfurfural, humic, levulinic acid and formic acid. The production of by-products caused the productivity of levulinic acid lower than theoretical one. Based on the study of the degradation of glucose and the formation of 5-hydromethylfurfural and levulinic acid, a kinetic model was proposed, in which, the process was described by a series first-order reactions with parallel by-reaction. The model parameters were correlated from the experimental data and the results calculated by the model were in welll accordings with the experimental data.China is a main country in wheat production with plentful wheat straw. In this work, the production of levulinic acid from wheat straw was studied in the temperature range of 170-250℃ and acid concentration range of 1-5% . The effects of temperature, acid concentration, liquid/solid ratio, particle size and reaction time on the productivity of levulinic acid were evaluated. The results indicated that the effect of particle size of wheat straw on the productivity of levulinic acid was negeligible whereas the major effects were observed for other four factors. According to the experimental results from single-factor test, a response surface analysis methodology was applied to optimize the degradation process of wheat straw. The optimized conditions were: temperature 209.3209.3℃, sulfuric acid concentration 3.5%, liquid/solid ratio 15.6 and reaction time 37.6 mim. A verification experiment was performed and the productivity of levulinic acid was 19.86%, which is almost the same as the model prediction. Comparing the results from different raw materials, it was found that the degradation conditions were similar and the optimized conditions obtained in this work were good references for other raw materials.A modified high-pressure stirring tank reactor was applied to study the dynamic degradation process of the wheat straw and sawdust for levulinic acid production at different temperature(190℃,210℃ and 230℃) and acid concentration 1%, 3% and 5%). A mechanism model to describe the degradation of wheat straw to produce levulinic acid was suggested based on the analysis of experimental data obtained in this work and others from both domestic and international laboratories. A quasi first-order kinetic equation was derived and the parameters of the model were simulated from the experimental data. The curves calculated by the model were in accordings with the experimental data. Except the difference in the values of model parameters, the model was also appliable to the degradation process of sawdust.The traditional separation and purification process of levulinic acid was consisted of solvent extraction and high vaccumn distillation, which was low in product recovery, high in energy consumption and complex in process operation. In this work, a new process based on ion-exchange and high vaccumn distillation was developed. A weak alkalic ionexchange resin, D301, was screened out. The ion-exchange isotherms and kinetics of levulinic acid on D301 resin was measured. The isotherms belonged to preferential type and could be simulated by R-P equation. The ion-exchange rate was controlled by the intra-particle mass transfer resisstance. The both breakthrough and elution curves were further studied in a fixed bed ion-exchange column filled with D301 resin. The hydrolysate from the degradation of wheat straw was applied directly to pass through the column. The effects of levulinic concentration and flow rate of hydrolyzate as well as column height were examined. Hydrochloric acid was used as eluent and the effect of concentration and flow rate on the elution of levulinic acid was evaluated. The optimized conditions for ion exchange were: height/diameter ratio 15.5, flow rate 1 BV/h; and for elution: hydrochloric acid concentration 0.5 M and flow rate 1 BV/h. The recovery of levulinic acid in ion-exchange separation was 77.9%. The eluent was concentrated before vacuum distillation. The batch vacuum distillation was carried out at 0.00266 Mpa. The fraction between the temperature range of 130℃ and 160℃ wascollected and the levulinic concentration was 98%.Diphenolic acid is an important monomer for producing various polymers. The production of diphenolic acid from levulinic acid and phenol catalyzed by hydrochloric acid was studied. An asisstant catalyst, thioglycolic acid, was selected, which is able to enhance the reaction and less toxic. The amount of catalyst and asisstant catalyst, ratio of levulinic acid/ phenol, reaction temperature and time were examined for the synthesis of diphenolic acid. After orthogonal test and artificial neural network analysis, the optimal reaction conditions were: the ratio of catalyst: asisstant catalyst 0.02:1, molar ratio of phenol: levulinic acid 4.5:1, reaction temperature 65℃, reaction time 35 h, and molar ratio of hydrochloric acid: levulinic acid 3.5:1. The productivity of diphenolic acid was as high as 97.45%, which is higher than that in literature. The product was verified by FTIR and NMR as diphenolic acid.