Aspects of storage and corrosion characteristics of biodiesel

Process and corrosion engineers have critically addressed compatibility of biodiesel components in petroleum refinery infrastructure because of different processing, storage and dispatching histories of shipments. Concerns were related to aging and corrosion and to accumulation of a bottom layer in the dedicated storage tank. Corrosion tests were executed in a microcosm test environment modified to the recommended practice of ASTM G4-01 procedure. Colloid chemical properties and technology of biodiesel refining operations can plausibly explain different material responses at different temperatures. The sampled bottom layer consisted mainly of glycerides, resembling characteristics of extract byproducts that are separated in trans-esterification in biodiesel synthesis. This bottom layer exerts both beneficial and detrimental effects. The positive side is that it extracts polar components and by this improves quality. The negative side is that it reduces resistance of the oil against aging. There was no risk of detrimental effects in terms of corrosion of storage tank materials. Overall progress of corrosion is controlled by the slightly alkaline bottom layer via neutralizing the oxidation products and exerting protection to metallic surfaces. Microbial degradation can only pose risks if normal and prudent conditions are not observed. Upon extended incubation microorganisms that are present in the bottom layer below the level detection limit, can develop countable colonies, if nutrients are available and conditions are favorable. It can be concluded that there is no risk of significant corrosion in storage and downstream infrastructure if the stored biodiesel meets standard quality specifications and storage conditions are normal.