Small-angle neutron scattering studies on an idealized diesel biofuel platform

Authors: RIFF, TIMOTHY - 1,4group, Inc; WEBB, MARK - 1,4group, Inc; Orts, William; ARAMTHANAPON, KRISTEN - 1,4group, Inc

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2017
Publication Date: 2/22/2017
Citation: Riff, T.J., Webb, M.A., Orts, W.J., Aramthanapon, K. 2017. Small-angle neutron scattering studies on an idealized diesel biofuel platform. Energy and Fuels. 31(4):3995-4002. https://doi.org/10.1021/acs.energyfuels.6b03185.
DOI: https://doi.org/10.1021/acs.energyfuels.6b03185

Interpretive Summary: Incorporation of ethanol into petroleum has been a goal for the U.S. and European fuel industries to reduce domestic reliance on imported petroleum, improve engine performance, decrease diesel particulate matter and nitrogen oxides, and potentially improve cold-flow properties. The ethanol market and its associated distribution network are more established than the biodiesel market; therefore, ethanol/diesel blends are likely to provide cost benefits over biodiesel. However, ethanol is only partly miscible with diesel and ethanol in diesel can cause corrosion, reduced energy content, reduced lubricity, poor ignition quality, instability, fuel clouding, and phase separation. Using ethanol is not as simple as mixing components together as previous attempts have resulted in limited success. The current stability and performance of ethanol/diesel mixes do not currently meet international fuel standards. Here, we explore a system based on microemulsions to better understand blend stability over a range of parameters, including water absorption and blend concentrations. Our results show that ethanol and water can successfully be mixed with an emulsifier to form stable microemulsions in diesel.

Technical Abstract: Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) were used to characterize the microstructure of a reverse micelle system consisting of ethanol, water, and surfactant in n-hexadecanes as an analytical framework to understand the structure and stability of a model platform for biofuel formulations. Best-fit modeling of SANS scattering data suggested that the micelles are better described as ellipsoids rather than spheres, with the (geometric) diameters of stable micelles increasing from 2.4 to 7.5 nm as a function of the increasing water content as well as surfactant concentration. Fitted diameters from DLS measurements followed similar trends, but DLS measurements overestimated the interior of the micelles by roughly 2-3 nm because DLS measurements are based on the full hydrodynamic radius, including the surfactant shell. SANS only detects the nanopool interior, a significant advantage. The choice of surfactant altered the stability at temperatures below 10 °C, but the micelles readily reassembled when the temperature was raised toward room temperature. This model framework was then used to quantitatively assess “real world” surrogate fuel systems consisting of ethanol, commercial ultra-low sulfur diesel, and a surfactant derived from minimally processed corn oil waste. These surrogate mixtures were probed over temperatures ranging from 10 to 60 °C, at concentrations up to 740 mM, and at various saturation levels with results similar to the model system. Results confirmed that this analytical framework can be used to understand optimization of biofuel formulations to meet industry standards for stability, cold-flow, and other performance requirements.