The study of expired pharmaceutical drugs as corrosion inhibitor for carbon steel in acidic media using the design of experiment

Abstract

The performance of Bromhexine syrup has been investigated as a corrosion inhibitor for carbon steel (C-steel) in acid medium using the weight loss method and response surface methodology (RSM) of the design experiment. The effect of the concentration of the inhibitor, temperature and exposure time on inhibition efficiency and corrosion rate was studied. The experimental results revealed that expired drug is an effective inhibitor and its inhibition efficiency increases with the increasing concentration to attain a maximum of 97.23 % at 1.0 (v/v %) at 293 K. The thermodynamic parameters show that adsorption reaction on the C-steel surface is spontaneous and exothermic. Moreover, the energy barrier for the corrosion reaction increases in presence of the inhibitor. The individual and interactive effects of these three parameters were optimized for maximum response of inhibition efficiency using response surface methodology (RSM) within the experimental design. Second-order polynomial model was suggested to predict the inhibition efficiency as a function of three variables. The results from RSM gave a best second order polynomial model for the inhibition efficiencies (IE) with high R2= 0.998 and R2Adj= 0.997. Moreover, the value of Q2 greater than 0.9 indicating that the model used is excellent. This confirms a good agreement between experimental observed data and the predicted ones. The optimal inhibition efficiency (IE) obtained by RSM is 101.65 % for a concentration of 0.282 %, temperature of 20.87 °C and immersion time of 4h.