O-Methylation of the Phenolic Bio-oil with Dimethyl Carbonate in an Ionic Liquid [bmim]Cl

O-Methylation of phenols has been studied as an important organic reaction, and its products, aryl methyl ethers, are valuable intermediates in fine chemicals. The phenolic component is one of the factors leading to the thermal instability of biomass pyrolysis oils. O-Methylation of phenols is helpful to improve the stability of bio-oil. Using dimethyl carbonate (DMC) as a methylation reagent, model O-methylations of three phenols (phenol, guaiacol, and eugenol) have been investigated in an ionic liquid. 1-butyl-3-methyhmidazolium chloride ([bmim]Cl), in the presence of water and carboxylic acid, separately. In [bmim]Cl at 130 degrees C, both hydrolysis of DMC and esterification of acetic acid with DMC would occur and compete with the O-methylation of phenol and decrease the yield of the methylation. However, the esterification of carboxylic acids is helpful for bio-oil upgrading. Under the same reaction conditions, the methylation was performed for a phenolic which is the ether extractive from the bottom layer of phase separation of a biomass pyrolysis oil by adding a salt solution. Gas chromatography/mass spectrometry (GC/MS) analysis showed that phenolic compounds in the bio-oil were converted completely to the corresponding aryl methyl ethers and carboxylic acids were esterified to the corresponding methyl esters. The phenolic bio-oil after the modification has greatly enhanced the heating value, more than 30%. The methylation of the phenolic bio-oil with DMC in [bmim]Cl may be a potential method for upgrading of bio-oil.