Studies On The Carbonylation Of Glycerol To Glycerol Carbonate

Biodiesel is a regenerative and clean energy source substituted for fossilfuels and its production is increasing annually, resulting in the increase ofglycerol as a by-product in the biodiesel production. Therefore, it is important toimprove the efficiency of biodiesel production by transforming glycerol to highvalue-added products. The direct conversion of glycerol with CO2into glycerolcarbonate is very attractive due to converting two wastes into useful chemicals.However, this reaction is limited by thermodynamics because CO2is very stable.This work could break the reaction equilibrium by the hydrolysis of acetonitrile,and studied the structure-activity relationship of Cu-based catalysts and thereaction routes.Cu metal was loaded on different supports, and the catalytic performancewas valued in an autoclave. Besides glycerol carbonate, the products alsocontained glycerol monoacetin and diacetin due to the hydrolysis of CH3CN.The results showed that Cu played the decisive role in the synthesis of glycerolcarbonate from glycerol and CO2.The catalysts with base sites tended to favorthe formation of glycerol carbonate, and the acid sites accelerated the formationrate of monoacetin.Cu-based catalysts had obvious size effect in the reaction of glycerol withCO2. The conversion rate of glycerol increased with the decrease of Cu size.Under reaction conditions, more glycerol carbonate could be formed underhigher CO2pressure and higher reaction temperature. Both glycerol and CO2were activated by the adsorption on the surface of Cu/La2O3, so thecarbonylation of glycerol with CO2followed the mechanism ofLangmuir-Hinshelwood.The promoter Mn could improve the catalytic performance of Cu/La2O3inthe increase of selectivity to glycerol carbonate. However, Mn almost had noeffect on the conversion of glycerol. After adding Mn, the reduction and statusof Cu were changed in the process of calcinations, resulting in the decrease ofCu size. It was the reason that Mn could improve the catalytic performance ofCu/La2O3. Moreover, DMC (dimethyl carbonate) was used as coupling agent toovercome the thermodynamic constraint. Glycerol carbonate could be producefrom glycerol and CO2indirectly through DMC. Firstly, glycerol reacts withDMC to form glycerol carbonate and methanol, and then the formed methanolreacts with CO2to produce DMC. In the trickle bed reactor, Mg-Al-Zr catalystswere effective for both the transesterification of glycerol with DMC and thesynthesis of DMC from methanol and CO2. Therefore, the coupling reactioncould proceed. However, the formation of DMC from methanol and CO2wasreversible, and the coupling reaction was related to the equilibrium state.