Carboxyl-Grafted Welan Gum for Enhanced Green Corrosion Inhibition Performance in Acidic Environments Under Rising Temperatures

In this work, welan gum (WG) was investigated as a green corrosion inhibitor for metals in acidic petroleum drilling fluids. The side chain of WG was subsequently modified by grafting with 3-chloropropionic acid (WG-CAR), further improving the corrosion inhibition performance. At the same concentration, WG exhibited a better corrosion inhibition efficiency than the commercial β-cyclodextrin. Moreover, the graft-modified WG-CAR achieved 60.35% at a concentration as low as 100 ppm, whereas WG and β-cyclodextrin only reached 28.25% and 25.42%, respectively. These improvements are attributed to their electron-donating hydroxyl and carboxyl functional groups, through which the lone pair electrons in oxygen atoms can fill the unoccupied d-orbitals of iron atoms, forming coordination bonds. This promotes Langmuir chemisorption, thereby forming a protective layer on the steel surface that inhibits anodic and cathodic corrosion reactions. In addition, calculations show that the WG-CAR molecule possesses a larger dipole moment and enhanced electron-donating capacity, resulting in stronger coordination interactions for the protective layer. Even at a high temperature of 323 K, WG-CAR (200 ppm) maintains an inhibition performance of 36.80%, higher than that of WG (10.66%). This work broadens the application of WG and brings new perspectives for the development and design of corrosion inhibitors.