Production, distribution and storage
The storage and stability of ethanol blends are special issues due to ethanol’s affinity for water and the risk of phase separation. In addition, ethanol tends to clean impurities from fuel tanks and lines leading to risk of plugging the fuel filter.
The effect of water differs significantly depending on whether the water is dissolved in gasoline or is in a separate phase. A small amount of water in a homogeneous fuel has no adverse effect. If phase separation occurs, the ethanol/water mixture stays as a layer at the bottom of the tank and the octane number of the gasoline layer falls. The engine stalls if it takes in the ethanol/water phase. Furthermore, a mixture of ethanol and water is corrosive.
The risk of phase separation depends on the temperature and the aromatics and ethanol contents of gasoline. At low temperatures, the risk of phase separation increases. The higher the ethanol and aromatic contents of gasoline, the higher the proportion of water that can be absorbed by the fuel without phase separation. Phase separation may occur when the critical conditions change. For example, if a tank containing a little ethanol blend is filled with gasoline, the concentration of ethanol in the blend falls. In this situation, the presence of the water originally dissolved in the fuel may be sufficient to precipitate phase separation. The same may happen if the ambient temperature falls. The risk of phase separation is lower if stabilizing agents are used.
To avoid phase separation, anhydrous ethanol is used for low-level ethanol/gasoline blends. The whole chain from supplier to dispenser must be water-free. In practice, anhydrous ethanol is transported by tankers and stored in tanks specially designed for it. Low-level ethanol blends are typically blended at a product terminal or dispenser just before delivery to retail or the end user. Additional cleaning procedures may be needed for ethanol pipelines and tanks, depending on the market area (Owen and Coley 1995). E85 Handbook (2013) lists cleaning procedures, such as optic sweep, steam cleaning, filter agitator and chemical solvents.In the Netherlands, 15% hydrous ethanol (HE15) has been studied as fuel for gasoline cars (http://www.heblends.com/).
When non-oxygenated gasoline is used, water accumulates at the bottom of the tank. With alcohol-containing gasoline, alcohol content of this water layer increases, and gradually the tank "dries". Alcohol is sometimes added to fuel for this purpose. If there is a lot of water at the bottom of the tank, there is a risk of the alcohol/water layer being drawn into the engine.
An example of water tolerance of ethanol/gasoline blends is shown if the Figure 1 (link to Ternary phase diagrams).
Figure 1. An example of water tolerance of ethanol/gasoline blends at different temperatures (Filho 2008).
With neat ethanol, the vapor in the air space in the fuel tank is flammable over a wide temperature range of about 12-43 °C (Engelen et al. 2008). With gasoline the mixture is too rich, and with diesel too lean, to be ignitable in the normal ambient temperature range. For neat ethanol, the flammability limits are wide. Vapor barriers or vapor return systems may be needed in the refueling system to avoid the risk of explosion and poisoning (McCormick 2001). In a study by NREL headspace vapors of gasoline samples became flammable at temperatures below -19 °C. Ethanol and gasoline vapors are denser than air and tend to settle in low areas (E85 Handbook 2013). However, the flammability risk with E10 fuel is evaluated to be close to that of gasoline (Paasi et al. 2008).
Alcohol resistant foams are needed in fires with high concentration ethanol, whereas fire-fighting chemicals traditionally used for gasoline are insufficient. Neat ethanol burns without smoke or visible flames, whereas flame of fuel ethanol is visible in daylight. (Engelen et al. 2008, E85 Handbook 2013).
High electrical conductivity of fuel in general increases safety by dissipating static charge e.g. in refueling. However, capability of a substance to generate and accumulate electrostatic charge is a complex phenomenon. For example, impurities, immiscibles, and multiple phases can exacerbate electrostatic charges. (Stephenson 2004).
Denaturants are required in fuel ethanol to make it toxic. Denaturants can impact engine operation and thus only accepted denaturants should be used (Legislation and standards).
If fuel tanks leak, ethanol and gasoline get into the ground. If groundwater is present, ethanol dissolves in it and is biodegraded. One factor that has been studied is the effect of ethanol on the transportation of gasoline in the ground and in groundwater. Deep et al. (2002) reported the effect of ethanol on the rate of benzene biodegradation under non-limiting oxygen and nutrient conditions. The biodegradation of benzene was severely inhibited in the presence of ethanol. Ethanol is degraded preferentially to benzene, which means that ethanol has an impact on benzene plume lengths in subsurface environments. Model simulations indicated that benzene plume lengths are likely to increase by 16–34% in the presence of ethanol.
Lahvis (2003) reported the potential effects of low-volume releases of ethanol-blended gasoline in the vadose zone. Model results indicate that the migration of ethanol in the vadose zone is limited to less than 100 cm from the source for releases in sand. In sandy clay, ethanol transport is limited to less than 50 cm. Furthermore, the presence of ethanol in gasoline does not significantly affect benzene transport and mass loading to groundwater. Travel times to groundwater may be more than an order of magnitude greater for ethanol than for benzene, depending on conditions. The model results indicate that the impacts of ethanol and benzene on groundwater from low-volume releases of ethanol-blended gasoline in the vadose zone are not expected to be significant unless the release is near the water table (< 100 cm) or, in the case of benzene, its biodegradation is limited.