engleski

Application of pectin isolated from tomato waste as potential tin corrosion inhibitor

The possibility of utilizing the tomato waste from canning factory as a cheap source for pectin isolation and its application as a corrosion inhibitor was investigated to implement viable cyclical economy principle in solving the main problem of waste disposal. Pectin, from two tomato waste, batches A and B was extracted with ammonium oxalate/oxalic acid (under reflux), during 24 h in the first step, and then again with a fresh volume of extracting agent during 12 h in the second step. The isolated pectins were evaluated by characterisation of its physical properties, i.e. colour and viscosity. Subsequently, the sample with better rheological behaviours, i.e. pectin obtained from tomato peel batch A (A-I) was examined as corrosion inhibition substances of pure tin by electrochemical potentiodynamic analysis. The measurement was carried out in a mixture of 2 % NaCl, 1 % acetic acid and 0.5 % citric acid, at 25 °C in absence and presence of different concentrations (0.2 - 4.0 g/L) of A-I pectin. To compare the corrosion inhibition efficiency of this pectin, commercially available apple pectin (CAP) was analysed, too. In addition, the structure of pectin samples used in corrosion test was characterised by NMR spectroscopy. The results indicate that conducted extraction steps have shown a different effect on the viscosity and colour of pectin. The viscosity of brown coloured pectin samples (first step) was higher than viscosity of white coloured pectin samples (second extraction), which mean that each extraction step has a considerable influence on pectin gel properties, such as appearance, gel formation and strength. Corrosion results point out that pectin is efficient inhibitor (73 %) even at very low concentrations, much better then CAP (60 %). By addition of A-I to the tested solution, the change in the mechanism of corrosion process and an improvement in corrosion behaviour are obvious. This could be explained by physical adsorption process of pectin molecules via carbonyl, carboxylic and ionic carboxyl groups presented in galacturonate and methyl galacturonate units of A-I (confirmed by NMR experiment). These negatively charged groups could electrostatically bind positively charged tin ions, preventing further tin corrosion in aggressive medium by the formation and precipitation of complexes at the tin surface as a physical barrier. Therefore, this investigation points out that tomato peel waste could be used as a promising industrial resource for pectin production and its application as tin corrosion inhibitor, instead of ordinary chemical and toxic inhibitors.

corrosion inhibitor; NMR spectroscopy; pectin isolation; rheology; tomato waste

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