Hydrogenolysis Of Glycerol To 1,2-propanediol Over Ni₃P-based Catalysts

Glycerol,as a by-product of biodiesel production,has a large amount and low price.1,2-propanediol,the glycerol hydrogenolysis product,is widely used in unsaturated polyester,medicine,food,cosmetics and other industries.The traditional preparation method of1,2-propanediol is the propylene oxide hydrolysis method using fossil resources as the raw material.The production process of this method is time-consuming and energy-intensive.Using glycerol as raw material to produce 1,2-propanediol not only solves the problem of excess glycerol production,but also provides a green way of production of 1,2-propanediol.In this paper,the reaction of glycerol hydrogenolysis to 1,2-propanediol was studied,and the metal promoter modified,citric acid（CA）modified and supported Ni₃P catalysts were prepared.The catalyst was characterized by XRD,N₂ physical adsorption,Raman spectroscopy,CO chemical adsorption,TEM and hydrogen temperature programmed reduction（H₂-TPR）,and the catalytic performance in the hydrogenolysis of glycerol and reforming hydrogenolysis of glycerol were investigated,and the reaction conditions were optimized to provide basic data for the industrial application of the catalyst.The bulk metal phosphides Ni₃P,Ni₂P,Co₂P,Fe₂P,Mo P were prepared by H₂-TPR method and applied in the hydrogenolysis of glycerol（glycerol hydrogenolysis under hydrogen atmosphere）.The results showed that Ni₃P exhibited the best catalytic activity.Ni₃P catalysts modified with metal promoters（Cu,Fe,Zn,Zr,Ce PO₄,W）were prepared by H₂-TPR method.The introduction of Ce PO₄ and W improved the catalytic performance of Ni₃P.The effects of the amount of promoters introduced on the catalytic activity were investigated.When Ce/Ni=0.1 and W/Ni=0.07,the catalyst had the best catalytic activity,the conversion of glycerol was 68.6%and 72.0%,and the selectivity of 1,2-propanediol was 71.0%and 72.3%respectively.Ni₃P catalysts supported on Si O₂,HZSM-5,SAPO-34 andγ-Al₂O₃were prepared by impregnation method.The evaluation results of the catalytic performance of the catalysts showed that Ni-P（3）/HZSM-5 exhibited the best performance.The effects of Si-Al ratio and Ni-P（3）loading on catalyst activity were investigated.The results showed that when Si-Al ratio was 46 and Ni-P（3）loading was 20 wt%,Ni-P（3）/HZSM-5 showed the best catalytic activity,with glycerol conversion and 1,2-propanediol selectivity of 69.8%and78.4%,respectively.The citric acid modified Ni₃P catalyst was prepared by H₂-TPR method and applied to glycerol reforming hydrogenolysis（glycerol hydrogenolysis under nitrogen atmosphere）.The addition of citric acid enhanced the dispersion of Ni species in the precursor and increased the specific surface area of the catalyst.When the molar ratio of CA/Ni was 1,the catalytic activity was the best.The effect of citric acid-modified precursor calcination atmosphere（N₂,air）on the performance of the catalyst was investigated.The residual carbon from the decomposition of citric acid inhibited the aggregation of Ni₃P particles and promoted the reduction of Ni species in the precursors.The influence of reaction conditions（temperature,pressure,time）was investigated.When the reaction condition was 210°C,0.5 MPa N₂,and 8h,the conversion of glycerol was 73.9%,and the selectivity of 1,2-propanediol was 64.3%.The stability study of CA（1）-Ni₃P in the glycerol reforming hydrogenolysis reaction showed:insoluble organics and polymers deposited on the catalyst surface during the reaction,covering the active sites of the catalyst,leading to a decrease in the activity of CA（1）-Ni₃P.