Butoxylation of butyl biodiesel: Reaction conditions and cloud point impact

Abstract

A property of biodiesel that currently restricts its use to blends of 20% or less is its relatively poor lowtemperature properties (cloud point). Alkoxylation of the unsaturated fraction of biodiesel offers the potential benefit of reduced cloud point without compromising ignition quality or oxidation stability. In addition, the butoxylation of butyl biodiesel improves the renewable nature of biodiesel by substituting fossil-derived methanol with biobutanol. Butyl biodiesel derived from canola oil was epoxidized via the in situ peroxyacetic acid method for 6 h, resulting in a conversion of 46% of the unsaturated esters. Epoxy butyl biodiesel was butoxylated with n-butanol with sulfuric acid catalyst without the use of solvents. Conversion and selectivity for butoxy butyl biodiesel were optimized by examining reaction conditions including: temperature, reaction time, catalyst concentration, and molar ratio of alcohol to epoxy biodiesel. The optimal conditions for the butoxylation of epoxy butyl biodiesel were: 80 C, 2 wt % sulfuric acid, and a 40:1 molar ratio of n-butanol over a period of 1 h. Conversion of epoxy butyl biodiesel was 100%, and selectivity for butoxy biodiesel was 87.0%. The cloud point (CP) of butyl biodiesel was -3 C, as was the cloud point of butoxy butyl biodiesel produced under the aforementioned optimal conditions. Butoxylation of butyl biodiesel, at the conversion rate of 46%, therefore had no discernible impact on cloud point. To determine the impact of a higher conversion of unsaturated ester to butoxy ester, butyl biodiesel was subjected to 30 h of epoxidation, resulting in the conversion of 93% of the oleic portion. Subsequent butoxylation at the optimal conditions resulted in a butoxy content of 74%. The cloud point of this material was 2 C, representing an increase of 5 K over the original butyl biodiesel CP. Blends of the high conversion batch of butoxy biodiesel showed that cloud point was virtually unchanged at concentrations below 35% and then increased 1 K every 8 wt % to approximately 70 wt % butoxy biodiesel. The loss of unsaturated ester, due to conversion to butoxy ester, appears to have a significant effect on cloud point only after approximately one-third of the unsaturated ester is converted. Butoxy biodiesel is therefore able to prevent the earlier onset of crystallization due to the decrease in unsaturated content, but only at lower concentrations. © 2009 American Chemical Society.