Synthesis Of Propylene Carbonate Form Glycerol, Hydrogen And Urea

A large amount of glycerol is formed as a by-product in biodiesel production process by transesterification of vegetable oils and animal fats. Seeking new utilization for glycerol by-product will improve the economy of the biodiesel production process. In the present work, the reaction integration of glycerol hydrogenolysis and urea alcoholysis was studied with glycerol as raw material to realize the reaction for synthesing propylene carbonate (PC) from glycerol, H2and urea.First of all, synthesis of PC from propylene glycol (PG) and urea was studied on a fixed-bed reactor. Zn-Al oxide catalysts were prepared by co-precipitation method and the effect of catalyst preparation conditions on the catalytic performance of Zn-Al oxides was investigated. The suitable preparation conditions were as follows:zinc nitrate and aluminium nitrate (n(Zn2+):n(Al3+)=3) as zinc source and aluminium source, sodium hydroxide and sodium carbonate (n(OH-):n(CO32-)=16) as the precipitant, using parallel-flow mixing manner, pH=9.5, aging temperature of40℃, calcination temperature of500℃, and calcination time of4h. The characterization results indicate that specific surface area is the main factor influencing the catalytic atcivity. The effect of reaction conditions on the reaction of PC synthesis was investigated over Zn-Al oxide catalyst prepared under the suitable preparation conditions. The suitable reaction conditions were as follows:n(PG):n(urea)=6:1, Zn-Al oxide catalyst volume of3mL, reaction temperature of140℃and LHSV=0.8h-1. The highest yield of PC reached87.4%. Zn-Al oxide catalyst showed a pretty high stability in the reaction for synthesizing PC from PG and urea; the yield of PC was still about86%until the reaction time reached60h.Secondly, the reaction of glycerol hydrogenolysis to PG was studied under atmospheric pressure on the fixed-bed reactor. Under the reaction conditions of Cu/y-Al2O3catalyst volume of3mL, pure glycerol feed, reaction temperature of190℃n(H2):n(glycerol)=100:1and LHSV of glycerol=0.2h-1, the conversion of glycerol was100%, the highest yield of PG was92.9%and the yield of PG was above85%untill the reaction time reached36h, demonstrating that Cu/γ-Al2O3catalyst exhibits a higher catalytic activity and stability in this reaction.Finally, the reaction integration of glycerol hydrogenolysis and urea alcoholysis to PC was implemented over Cu/y-Al2O3and Zn-Al oxide catalysts, which were separately filled in two sections of the fixed-bed reactors. The suitable reaction conditions were as follows: pure glycerol feed, atmospheric pressure, n(H2):n(glycerol)=60:1, n(urea):n(glycerol)=1:3, LHSV of glycerol=0.2h-1, reaction temperature of the upper stage=190℃, reaction temperature of the lower stage=150℃, and urea concentration=0.1g/(mL DMF). The conversion of glycerol was100%, and the yield of PG and PC was81.2%and16.3%, respectively. The selectivity of PC was60.5%based on the PG amount formed in glycerol hydrogenolysis. Furthermore, GC-MS was used for the analysis of the possible side-reactions and reaction pathway.