Kinetics Of Glucose Decomposition Catalyzed By Dilute Sulfuric Acid/Salts

The production of general chemicals from renewable biomass has become one of research hotpoints in the field of energy and resource.5-hydroxymethylfurfural and levulinic acid had wide use which could be prepared from biamass with large scale.Sulfuric acid above 1.5wt%was used as catalyst to hydrolyze cellulose currently, which caused serious equipment corrosion and environment pollution.So how to reduce pollution under the guarantee of yield had become a big problem in front us. Glucose was used as model compound to study the decomposition kinetics catalyzed by dilute sulfuric acid(0.05%-0.4wt%)and metal salts.Studying the kinetics of glucose decomposition catalyzed by dilute sulfuric acid was to investigate the feasibility of hydrolyzing biomass with less sulfuric acid.Studying the kinetics of glucose decomposition catalyzed by salts was to find out the cacalytic law of salts on glucose decomposition,which was facilitate to further studying on reaction mechanism and would provide basis for finding green catalysts with high activity and good selectivity.The decomposition kinetics of glucose and 5-hydroxymethylfurfural (intermediate of glucose decomposition)was systematically investigated at sulfuric acid concentration between 0.05%-0.4wt%and temperature ranged from 160℃to 190℃.A consecutive reaction with parallel by-reactions was proposed for data fitting. The kinetic parameters of 5-hydroxymethylfurfural decomposition catalyzed by sulfuric acid were obtained firstly,with the first-order kinetics equations,the activation energies evaluated were 78.5,98.0 kJ·mol^-1and the reaction orders to H⁺ concentration were 1.16,0.722 for main and side 5-hydroxymethylfurfural decomposition reactions under the experimental condition.Then the data of glucose decomposition catalyzed by sulfuric acid were proposed to fit.With the first-order kinetics equations,the activation energies evaluated were 129kJ·mol^-1,154 kJ·mol^-1 and the reaction orders to H⁺ concentration were 0.716,1.06 for main and side glucose decomposition reactions under the experimental condition.Through the analysis of kinetic equations,we could discover that the influence of sulfuric acid concentration on LA yield became small when sulfuric acid concentration increased to over 0.3wt%. By comprehensive consideration the factors of LA yield,sulfuric acid used and pollution problem,process for LA production catalyzed by dilute sulfuric acid(about 0.3wt%)had development prospect. Under the condition of initial concentration of 10 mg·mL^-1,temperature of 180℃, cation concentration of 0.0556mol·L^-1,the effect of anions(Cl^-,SO₄^2-)and cations(K⁺,Ca²⁺,Na⁺,Mg²⁺,Mn²⁺,Zn²⁺,Fe²⁺,Ni²⁺)on glucose decomposition and product selectivities for 5-hydroxymethylfurfural and levulinic acid were systematically investigated.The result indicated that sulfate had higher catalytic activity than chlorate.Catalytic activity of cations were close to metal activity,the more inactive of metal(except Zn and Na)was,the better catalytic activity on glucose decomposition and selectivity for levulinic acid the salt corresponding had.After investigated the effect of anions and cations on glucose decomposition,the kinetics of glucose decomposition catalyzed by Cu²⁺was systematically studied,the influences of anion,initial glucose concentration,temperature,catalyst loading and adding little other metal cation on levulinic acid yields were investigated.The result showed that CuSO₄ had higher catalytic activity than CuCl₂,but selectivity for levulinic acid was lower;under experimental condition,initial glucose concentration had little effect on glucose decomposition;higher temperature,more CuCl₂ loading would increase the yield of levulinic acid;The addition of a little MnCl₂,FeCl₂ or NiCl₂ would accelerate reaction,but the yield of levulinic acid would greatly decrease.The poineer investigations of this paper not only explore to solve the problem occurred in hydrolyzing cellulose currently,but also provide basic data for correlation study.