Solving corrosion problems in biofuels industry

Abstract

Ethanol is increasingly popular as fuel. It is renewable, cleaner than gasoline, and during the 2008 oil price peak, its costs of production without subsidies actually rivalled those of gasoline. The fuel grade ethanol producers are large consumers of stainless steel, in particular for cookers, fermentation tanks, and distillation columns as well as storage tanks for the finished product. The main reason is that cleanliness is important for the enzymes. However, contaminants play an important role in production as well as storage and distribution. Contaminants are causing a phenomenon called stress corrosion cracking. Biodiesel fuel is a mixture of fatty acid alcohol esters. Modern diesel engines are very sensitive to fuel quality and purity. Biodiesel is unstable, just like butter, which is going rancid in a matter of weeks. Biodiesel degradation is an oxidation process, which among others is speeded up by tiny amounts of metal ions leaching from production and storage vessels. Biodiesel vessels need to be designed in non-degradable materials of construction, as stainless steel. In addition, pretreatment of low cost feedstock and methyl recycling operations use strong acids, which also necessitate stainless steels. Biomass is gaining importance as a source for renewable fuels and hydrogen in addition to heat and electricity. Corrosion issues are numerous and include high temperature corrosion under ash and alkali salt deposits and metal dusting at gasification. Fuel grade ethanol, biodiesel and biomass represent three different corrosion issues, which can be solved using the correct stainless steel.