Renewable Oxygenate Blending Effects on Gasoline Properties

Abstract

The oxygenates ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol (isobutanol), 1-pentanol, 3-methyl-1-butanol (isopentanol), methyl levulinate, ethyl levulinate, butyl levulinate, 2-methyltetrahydrofuran (MTHF), 2-methylfuran (MF), and 2,5-dimethylfuran (DMF) were blended in three gasoline blendstocks for oxygenate blending (BOBs) at levels up to 3.7 wt % oxygen. Chemical and physical properties of the blends were compared to the requirements of ASTM specification D4814 for spark-ignited engine fuels to determine their utility as gasoline extenders. Vapor pressure, vapor lock protection, distillation, density, octane rating, viscosity, and potential for extraction into water were measured. Blending of ethanol at 3.7% oxygen increased vapor pressure by 5–7 kPa as expected. 2-Propanol slightly increased vapor pressure in the lowest-volatility BOB, while all other oxygenates caused a reduction in vapor pressure of up to 10 kPa. Coefficients for the Wilson equation were fitted to the measured vapor pressure data and were shown to adequately predict the vapor pressure of oxygenate–gasoline blends for five individual alcohols and MTHF in different gasolines. Higher alcohols and other oxygenates generally improved vapor lock protection. Butyl levulinate blended at 2.7% oxygen caused the distillation end point to exceed 225 °C, thus failing the specification. Distillation parameters were within specification limits for the other oxygenates tested. Other than ethanol, MF, and DMF, the oxygenates examined will not produce blends with satisfactory octane ratings at these blend levels when blended into lower-octane blendstocks designed for ethanol blending. However, all oxygenates tested except 1-pentanol and MTHF produced an increase in octane rating. For ethanol, the propanol isomers, and methyl levulinate, 20 wt % or more of the oxygenate could be extracted into water in a room-temperature water tolerance experiment. For the butanol isomers and ethyl levulinate, the percent extracted ranged from about 4% to 8%. Extraction for other oxygenates was 2% or lower. Methyl levulinate separates from gasoline as a separate liquid phase at temperatures below 0 °C.