Specialty chemical company Evonik has introduced a bio-derived version of methyl tertiary-butyl ether (MTBE), an oxygenate that improves gasoline combustion, helps prevent engine knocking and decreases carbon monoxide and other emissions from vehicles. Evonik produces Bio-MTBE from isobutene and biomethanol in Marl (Germany) along with conventional MTBE; initial production of bio-MTBE began in March 2012.
MTBE has been a widely used antiknock agent for decades, and Bio-MTBE possesses the same technical attributes as its conventional counterpart: high energy density (86% of gasoline), low vapor pressure, low oxygen content, and very low solubility in water. It also means that Bio-MTBE can be handled safely in refineries and storage tanks and be conveyed by pipeline.
Because it is made from raw glycerine, which is itself a co-product of the biodiesel manufacturing process, bio-methanol is classified as a waste product according to the EU Renewable Energy Directive (RED)— doubling its value for determining bioenergy content. That makes Bio-MTBE a promising option for fuel manufacturers looking to meet EU specifications for biofuel use and CO2 reduction.
Bio-MTBE is the only commercially available, next-generation biofuel component for gasoline in Germany, and it doesn’t compete with food production, either.—Dr. Rainer Fretzen, who heads the Performance Intermediates Business Line at Evonik
While Evonik has primarily sold Bio-MTBE in Germany and the Netherlands, implementation of EU directives in other member states points toward additional growth potential for this biofuel component. Current European gasoline specification allows up to 15 vol. % MTBE and the revised FQD (Fuels Quality Directive) has enabled the specification to be expanded to up to 22 vol.% MTBE in gasoline.
If needed, Evonik can shift the full capacity of its plant (550,000 metric tons per year) over to production of Bio-MTBE.
Despite its potential benefits, MTBE has some properties that can be problematic. Much more soluble in water than most other components of gasoline, it can migrate faster and farther in the ground and can be more likely to contaminate public water systems and private drinking water wells if gasoline is spilled on the ground or leaks out of underground storage tanks.
In the US, MTBE was used in gasoline at low levels beginning in 1979 to replace lead as an octane enhancer. Since 1992, MTBE it was used at higher concentrations to fulfill the oxygenate requirements established in the 1990 Clean Air Act Amendments (CAA).
In the late 1990s, however, a number of community drinking water were analyzed with detectable levels of MTBE; since then, many areas have begun to phase out MTBE use in gasoline, commonly replacing it as an oxygenate with ethanol. (Earlier post.) Many states in the US subsequently passed laws limiting or banning the use of MTBE in gasoline.
With the Energy Policy Act of 2005, Congress removed the oxygen content requirement for reformulated gasoline. Subsequently, a number of companies removed MTBE from their gasoline due to state laws and concerns over possible legal liability.