Green corrosion inhibitors: amino acids and plant extracts

摘要

Corrosion inhibitors are chemicals that are used in many industries to control corrosion. As they are injected into process streams they have to be continually replenished in order to maintain protection. Many chemicals used are environmentally unfriendly highly toxic compounds including chromates and arsenic compounds. REACH legislation and PARCOM recommendations as well as general environmental concerns are driving an effort to find acceptable alternatives to conventional corrosion inhibitors. Promising initial work in the open literature has already identified several alternative green corrosion inhibitors, including plant extracts that have potential to be used as more environmentally acceptable corrosion inhibitors. However, to date a lot of the work has been done on a trial and error basis with little consideration of the mechanisms of inhibition or any detailed characterisation of the inhibited surface. Three candidate types of environmentally friendly corrosion inhibitors are identified as worth of further consideration: the amino acids histidine and tryptophan, aloe vera plant extract and plants with high inulin contents. Initial results on the effectiveness of the amino acids in protecting mild steel in an acidic environment are determined via immersion tests and weight loss measurements. The evolution of the inhibition film is studied using electrochemical measurements. Experiments are carried out at temperatures of 20 °C to 60 °C. Results are compared with those from the widely used corrosion inhibitor propargyl alcohol. The amino acids show some effectiveness as corrosion inhibitors in the environment used however further work on other candidate green corrosion inhibitors, including full lifecycle costing, is required to fully assess their potential.