Let’s begin with the CAA 1970 and its subsequent amendments. The EPA originally approved MTBE as a gasoline oxygenate additive. It was not until gas station buried tank leaks led to water contamination issues (MTBE does not biodegrade readily) that the Oil Industry initially-voluntarily stopped the use of MTBE to avoid the obvious environmental issues. Benzene and other aromatics that were also uncontrolled early-on, are only toxic in pure-concentrated form (a fueling respiratory exposure issue that has been addressed by a combination of fueling pump/auto VR technologies). The original aromatics regulatory focus had to do with light vehicle CO/VOC tailpipe emissions, which involved the Auto & Oil Industries working with the EPA and state Governments to develop effective improvements. Hydraulic fracturing & Tier 3 is off subject.
I personally experienced the refining-pipeline-terminal-customer issues/equipment failures that developed with the original EPA oxygenate requirements (E-7.5 replaced MTBE). Ethanol is very corrosive to rubber and many synthetic materials (seals, tubing, etc.). Eventually the Oil and Auto Industries made material upgrades needed to avoid equipment failures (leaks). New vehicles and FFV’s don’t have an issue with increased E-10 to E-15, it’s the older vehicles that are at risk to leaks/fires. The EPA’s current solution is to post warning labels and place the responsibility on producers and customers. The EPA/DOE may believe the issue is resolved, but those ultimately responsible are not convinced yet. By the way, ethanol is definitely corrosive, but it can take a couple years for the failure to occur since the corrosion of fuel lines and seals can be relatively slow.
Ethanol full lifecycle cultivation-production-consumption is definitely very energy intensive. Corn ethanol consumes about 0.78 MBtu of fossil fuels for every 1.0 MBtu finished ethanol product. Read my post, it contains all the references including the DOE/EIA and the Argonne Lab (Wang’s outfit). The fossil fuels mix of course depends on where the corn ethanol bio-refinery is located (power grid fossil fuels mix) and how it’s designed. Some bio-refineries actually have coal fired steam plants used to provide process heat. As far as petroleum, its consumption is very significant. Beside corn fertilizer/cultivation equipment consumption ethanol must be transported (neat) via rail, marine and truck around much more efficient petroleum pipeline systems, for blending into gasoline at the local petroleum fuel terminals just prior to final truck shipment to retail outlets. Ethanol must be segregated due to its corrosive properties once again and its affinity for picking up water and solids.
I analyzed Wang’s GREET model in detail a few years ago. The corn ethanol lifecycle was reasonably accurate at that time, but the fossil fuels lifecycles were significantly in error (they used inaccurate international data rather than more accurate U.S. Refining data; which I shared the sources with them, but they have yet to correct the obvious errors in their model). Sugarcane (restricted by tariffs strongly supported by the U.S. Corn/Ethanol lobbies) and cellulosic ethanol are once again off subject. By the way, sugarcane ethanol production is much less energy intensive than corn ethanol, and cellulosic ethanol consumed (full lifecycle) fossil fuels are significantly greater than the finished biofuel's heat content (i.e. it has a large ‘negative’ NEV based on current state-of-art technologies).