ABSTRACT
This work evaluates the suitability of lignin as corrosion inhibitor when AISI 1018 carbon steel coupons were used as tests specimens. A stock solution of lignin powder, provided by an Albertan Pulp and Paper mill company, was tested for its inhibition efficiency in Rotating Cylinder Electrode (RCE) system according to ASTM G185-06. The testing environment consisted of modelled brackish water at different temperatures and pH values (30°C, 50°C and 85°C; pH=6 and 8).
The corrosion rates of the test specimens calculated by both linear polarization resistance (LPR) and weight loss methods indicated optimum lignin performance for all the temperature conditions tested and a pH of 6. The test medium containing lignin reduced the corrosion rate by more than 90% compared to the baseline corrosion rate measurement (medium without lignin).
The corrosion potential of the baseline test specimens were <-700 mV (more negative) and became more positive after lignin was added to the model brackish water system, indicating corrosion severity of the test medium in the absence of the inhibitor. Then after test optical imaging of the corrosion coupons showed no significant general corrosion and pitting in those test conditions containing lignin compared to the control specimens.
INTRODUCTION
The application of corrosion inhibitors is among the most cost effective methods to control internal corrosion issues in pipeline operations [1-3]. However, the selection of corrosion inhibitors should take into consideration factors such as toxicity and biodegradability [4-9]. Hence, industry efforts are leading to the development of non-toxic, biodegradable and more environmentally friendly “green” corrosion inhibitors [10-13] from renewable resources. As a result, naturally occurring compounds found in plant extracts with heterocyclic compounds [5], [14], having nitrogen [15-16], sulfur [17], phosphorus [18] as constituent atoms provided a viable alternative for the development of green inhibitors. However, certain limitations may exist when selecting its natural source, such as availability for their production volume on large industrial scales [19], and the fact that some specific plants might still be utilized for so many other applications in addition that they are seasonal [20]. Consequently, naturally abundant and environmentally friendly derivatives with anti-corrosion properties have more potential for mass production for the corrosion inhibition industry. Lignin, as the second most naturally abundant biopolymer substance in plant cell walls, exceeded only by cellulose [21], is one of the plant derived chemicals that fits this criterion. This biopolymer is available in large quantities as a byproduct of the pulp and paper industry and the annual production of lignin is over 70 million tons worldwide [22]; the most abundant industrial lignin is obtained from kraft and sulfite pulping processes [23].
