Gas-Phase Catalytic Dehydration of Glycerol with Methanol to Methyl Glyceryl Ethers over Phosphotungstic Acid Supported on Alumina.

Glycerol can be dehydrated with methanol to produce methyl glyceryl ethers as biologicals and diesel fuel additives. Considering the high efficiency of mass transfer and product separation in the gas-solid catalytic process, a fixed-bed continuous-flow reactor was used to carry out the catalyst evaluation test of the process at 564 K. Compared with zirconium sulfate, lanthanum nitrate, and ammonium molybdate, phosphotungstic acid exhibits a higher target product selectivity. Through loading experiments, it was found that the optimal loading fraction of phosphotungstic acid on alumina is 10 wt %. After the alumina carrier is impregnated with nitric acid, the selectivity and yield of monomethyl glycerol ether can be effectively improved, and it has little effect on other products. A test of the addition amount of cerium nitrate as a promoter was carried out. It was shown in the test that when the addition amount of cerium nitrate is 10 wt %, the catalyst life increases from 2 to 3.5 h and the selectivity of dimethyl glycerol ether increases to 54.51%, which is twice the original. However, the selectivities of monomethyl glycerol ether and trimethyl glycerol ether decrease by one-half each. Through catalyst characterization, it was shown that carbon deposition on the catalyst surface is one of the reasons for catalyst deactivation.