Carrageenan from Chondracanthus Chamissoi Algae: Extraction process and experimental evaluation as green corrosion inhibitor for P22 steel in HCl

In this study, the extraction yield of carrageenan from the algae Chondracanthus Chamissoi and its efficiency as an ecological corrosion inhibitor for P22 steel in 1 M HCl at 65°C were evaluated. The extraction of carrageenan from the algae Chondracanthus chamissoi was carried out in cold water at 25°C (CC) and hot water at 80°C (HC), with different degreasing stages prior to the extraction (0, 1 and 2 stages). The codes of the six samples of carrageenan obtained were selected in terms of the production temperature and degreasing stages as: CC-0, CC-1, CC-2, HC-0, HC-1 and HC-2. All the carrageenan samples were characterized using: Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive spectrum. The CC shows crystallinity and is mainly composed of κ-carrageenan in the presence of KCl, NaCl and K3Na(SO4)2; while the degreasing stages reduce the content of KCl and NaCl. The HC presents an amorphous structure composed of κ/ι carrageenans. The highest carrageenan extraction yielded in cold water was 21.43%, without the degreasing stage (CC-0); while, the highest carrageenan extraction yielded in hot water was 28.96% with 2 degreasing stages (HC-2). The inhibition performance was investigated using gravimetric analysis, potentiodynamic polarization, linear polarization resistance, electrochemical impedance spectroscopy and electrochemical frequency modulation. The experimental results demonstrated that all six carrageenan inhibitors act as good corrosion inhibitors for P22 steel in 1 M HCl at 65°C. However, the CC-0 presented the maximum corrosion inhibition efficiency (IEc) of 85.53% (EIS technique). In the HC, the degrease does not significantly affect IEc, allows to obtain 82.56% without degrease (EIS technique). Based on the results obtained, the extraction CC-0 and HC-0 in the same extraction process, allows to obtain a semi-refined, economical carrageenan, with a total carrageenan yield of 45.91%, and with a high IEc.