The larger per gallon tax was dropped last year when the subsidy was dropped. What is left is only a 2.5% ad valorem tariff on the import of ethanol for use in fuel.
http://www.afdc.energy.gov/laws/law/US/393
2.5% is not an overly burdensome import tax.
The US has been a net exporter of fuel ethanol since Jan 2010. We produce more than we use. There is not a shortage.
http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=MFENT_NUS-Z00_2&f=M
In fact the last couple years we were exporting to Brazil as their demand exceeded their own supply. But the last few months we had small imports from them.
http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=MFENT_NUS-NBR_2&f=M
Brazil is the second largest producer of ethanol in the world after the United States. In 2010, Brazil produced 486,000 bbl/d of ethanol, up from 450,000bbl/d in 2009. A combination of high world sugar prices, a poor sugar cane harvest, and underinvestment caused a precipitous decline in ethanol production in 2011. While official numbers for the year have not been released, estimates place 2011 production around 390,000 bbl/d – close to a 20 percent drop year on year.This shortage forced Brazil to import corn ethanol from the United States.
http://www.eia.gov/countries/cab.cfm?fips=BR
The Brazilian government has taken measures to prevent future ethanol supply shortages and increase public involvement in the sector. The government lowered the blend requirement in gasoline from 25 percent to 20 percent. Additionally, it brought regulation of the ethanol sector under the jurisdiction of the ANP and announced plans to expand Petrobras' presence in the ethanol market. In the medium term, Brazil aspires to export ethanol to the United States, which recently removed tariffs on Brazilian sugar cane ethanol.