| Supramolecular chemistry and its applications have gained widely attention since C. J. Peterson, D. J. Cram and J. M. Lehn won the Nobel Prize for chemistry for their contribution in this area. Our group has introduced the theory of supramolecular chemistry into the area of corrosion inhibition and obtained some achievements. Based on our previous results, this paper systematically explored the forming mechanism of supramolecular corrosion inhibitor, host-guest constructing model and basic applying problems through experimental and theoretical methods.According to the principle of supramolecular chemistry, the host material was selected as the hydroxypropyl-β-cyclodextrin (HP-β-CD) with the properties of high water solubility, low toxicity and environmental friendly. In order to lower the energy comsuption during the preparation process of HP-β-CD, super absorbent resin (crosslinking carboxymethyl cellulose grafting acrylamide) was used as the dehydrating agent instead of the water removing equipment under reduced pressure. By this method, not only could obtain the qualified product, the dehydration efficiency could also be15%higher than that used reduced pressure methods as well as the95%lower comsuption of energy.For the corrosion of carbon steel, the traditional corrosion inhibitor, octadecylamine (ODA, used under gas phase), was selected as the guest compound, with which, a supramolecular system was prepared through dry process using HP-P-CD as the host. The optimal experimental parameters were determined by single factor tests:HP-β-CD and ODA was mixed at a mass ratio of2/1, and grinded at85℃for15min. Meanwhile, a supramolecular inhibitor formed between β-CD and ODA was prepared by wet process. The results of proton nuclear magnetic resonance spectra (1H NMR) showed that ODA molecules could penetrate into the hydrophobic cavity of β-CD or HP-β-CD. It was found by phase solubility diagrams that the phase solubility curves of β-CD/ODA and HP-β-CD/ODA systems were both Bs type. This meant that a supramolecular complex could be formed with a stoichiometric ratio of1/1(host/guest, similarly hereinafter) at low concentrations of host compound (≤4mmol/L); with the increasing of host concentration, the solubility of complex kept stable and a new complex with the ratio of 2/1was formed. Fourier transform infrared spectroscopy (FT-IR) analysis showed that the characteristic peak of the-OH was shifted from3395.83cm-1to3416.83cm-1, which indicated the increased energy of chemical bond. Combined with the molecular structure of ODA, the conclusion could be made that hydrogen bond with-HC(H…O)-C-type was formed to fix ODA in the hydrophobic cavity of β-CD or HP-β-CD. X-ray diffraction (XRD) analysis showed that the crystalline state of supramolecular system based on ODA was dominated by the host compound. In contrast, the solubilization effect of ODA by HP-β-CD was better than that of p-CD.For the corrosion of copper and its alloys, benzotriazole (BTAH) was selected as the guest compound, which was used to perpare the supramolecular system with β-CD and HP-β-CD, respectively. Both β-CD and HP-β-CD had solubilizing effect for BTAH through the results of phase solubility diagrams, which were AL type. This meant that there was direct proportion relationship between the water solubility of BTAH and the dosage of host compound; the stoichiometric ratio of supramolecular complex based on BTAH were always1/1. In addition, the solubilization effect of BTAH by β-CD was better than that of HP-β-CD resulting from lacking of large substituent group.HP-β-CD/ODA complex was applied in the recycling of industrial condensate water. The corrosion rate of carbon steel in the condensate water was0.0098mm/a with a corrosion inhibition rate of96.1%after adding50mg/L complex according to the weight loss measurements. From the analysis of electrochemical polarization and impedance spectroscopy (EIS), HP-β-CD/ODA complex acted as the "mixed-type" corrosion inhibitor, which retarded the rate of anodic reaction much more than that of cathodic reaction. The complex could adsorb on the surface of metal and form a protective layer with a thickness of1.8nm according to the analysis of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS).β-CD/BTAH complex was applied in the research of circulating cooling water. This complex had a corrosion inhibition rate of over90%for copper and its alloys based on the results of weight loss. Through further inspection of XPS analysis, it was found that β-CD was not shown up on the surface of copper. Comparison the pre-film surface of copper in water and ethanol by surface enhanced Raman scattering (SERS), the conclusion could be made that Cu(I)BTA was formed between BTAH and Cu+to prevent copper and its alloys from corrosion.During the research of the application of supramolecular corrosion inhibitor in the recovering of blowdown wastewater from boilers, the optimal preparation process of high strength fly ash/clay ceramic substrate with its top attapulgite membrane (ATM) was also discussed. Through the filtration tests in dead-end mode, ATM could remove PO43-, SO42-and CO32-from blowdown water effectively through Donnan exclusion and dielectric effect. According to the sepecific data, the rejectio rate of PO43-by ATM could be around85%, while, that of SO42-and CO32-could reach over90%. The equipotential point of ATM in the blowdown wastewater was between pH=4and5after mearsuring. The continuous blowdown water from medium-and low pressure boilers could be reused as the make-up water based on the supramolecular corrosion inhibitor and ATM; in this way, the waste of large amount of water and heat could be avoided. |
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