Experiments were carried out in industrial oils and model solutions presenting a wide range of concentration of free fatty acids and temperatures from 100°C to 290°C. As expected, the acid value has a strong impact on the corrosiveness of these bio-oils, quite similarly to naphthenic acids for conventional oils. For some test conditions, comparisons between neutral gas cap and H2 were carried out. A slight reduction of corrosion rate is measured in the presence of H2. Temperature also plays an important role in the range of 100°C to 290°C. It was observed that corrosion reactions for carbon and low alloy steels follow an energy activation Arrhenius law. For stainless steel grades, the positive influence of molybdenum was observed for highly acidic waste oils at high temperature.
To limit the impact of greenhouse gas emissions on climate change, the use of conventional hydrocarbons needs to be reduced significantly. The global demand for biofuels is thus expected to grow during the present decade. Hydrogenated Vegetable Oil (HVO) is one of the predominant biofuels produced by converting lipidic feedstocks (vegetable oils, animal fats, waste cooking oils, …) through a conventional refinery hydrotreatment (HDT) process. Material selection for the HDT process to convert lipidic oils and fats into usable end fuels is constantly under investigation. The presence of oxygenates is considered as an important factor in the material selection of the unit, notably in sections preceding the HDT reactor which includes transfer lines, heat exchangers, and injection nozzles. In their natural state, lipidic feeds are characterized by having large concentrations of fatty acids, either in the form of esters (triglycerides, diglycerides, monoglycerides) or as free fatty acids (FFA). The acids belong to the carboxylic group and mostly differ in their acid chain length (carbon number) and their degree of unsaturation (number of double bonds). The most common acids are found in the carbon chain range of 12 to 22 with some having up to 3 double bonds. These regularly exist in oils originating from conventional vegetable sources which are extracted by the trituration process of oil-bearing fruits or by solvent extraction of those with low fatty matter. While these lipidic oils are often characterized by fatty acids with similar molecular configurations (i.e. linear chain length and end chain carboxylic function), other types of bio-oils go beyond these structures and include more complex forms of acids. This is the case of tall oil fractions like TOFA (Tall Oil Fatty Acids) and DTO (Distilled Tall Oil), which are obtained from the pine wood pulping (Kraft process) in the paper manufacturing industry. Depending on the cut, the tall oil fractions usually include high concentrations of rosin acids (abietic, dehydroabietic, pimaric etc.) which contain three condensed naphthenic and/or aromatic rings in their overall configuration. Rosin acids also belong to the family of carboxylic acids and are miscible with linear chain FFA. Nonetheless, these tall oil fractions are also very rich in unsaturated fatty acids (mainly oleic and linoleic acid) except for the rosin acid content which is usually significantly higher in DTO compared to TOFA.
