Some of the most effective corrosion inhibitors for oil field pipeline applications are the oleic imidazoline (OI) class of molecules. However, the mechanism by which OIs inhibit corrosion is not known. We report atomistic simulations (quantum mechanics and molecular dynamics) designed to elucidate this mechanism. These studies lead to the self-assembled monolayer (SAM) model for corrosion inhibition, which explains the differences in corrosion inhibition efficiency for various OI molecules. The SAM model of OI inhibitors involves the following critical elements: (i) The function of the OI is to form a self-assembled monolayer on the native oxide surface of iron; this serves a protective role by forming a hydrophobic barrier preventing migration of H 2O, O2, and electrons to the Fe surface. (ii) The imidazoline head group serves as a sufficiently strong Lewis base to displace H2O from the Lewis acid sites of the iron oxide surface. (iii) These head groups self-assemble on the surface to form an ordered monolayer on the iron oxide surface. [ 3 × 3 for the (001) cleavage surface of R-Fe2O3.] (iv) The long hydrophobic tail (e.g., 2-oleic acid) tilts to form a tightly packed hydrophobic monolayer. [For R-Fe2O3(001) the tilt angle is about 72°with respect to the surface normal.] (v) This hydrocarbon tail must have a sufficient length to cover the surface. [For R-Fe2O3-(001) the chain length must be 12 or more carbon atoms.] (vi) The hydrophobic tail and the pendent group (e.g., -CH2CH2NH2) must lead to an octanol/water partition coefficient (log P) below a critical value in order to rapidly form the monolayer. This SAM model should be useful in developing both alternative environmentally benign corrosion inhibitors and higher temperature corrosion inhibitors.

Corrosion inhibition of mild steel by imidazolines and their precursors in a carbon dioxide (CO 2 )-containing environment was studied using rotating cylinder electrode (RCE) and linear polarization resistance (LPR) techniques. Corrosion rate-time/concentration profiles and minimum effective concentrations obtained for a series of imidazolines and amides were evaluated in terms of the respective contributions of their constituent parts (imidazoline ring, amide/amine group, and hydrocarbon chain) to overall corrosion inhibition. Formation of the inhibitor film was studied in terms of the bilayer/multilayer film model. FIGURE 9. Corrosion rate/potential-inhibitor concentration dependence for stearic amide/imidazoline constant concentration treatments.FIGURE 10. Corrosion rate/potential-time response for lauric imidazoline constant concentration treatment at 0 rpm and 6,000 rpm.

Periodic charge equilibration (PQEq) is used to study a few of the roles that the zeolite Y lattice might play in cracking catalysis. Comparison of the partial charge distributions of HY and Na 1 HY suggests that atoms within 10 Å of the sodium atom accept electrons from the sodium atom. The charge distributions of n-octane, benzene, and water adsorbed inside the supercage of zeolite Y and siliceous zeolite Y show that the lattice provides little perturbation to these molecules. In contrast, a local dipole in the zeolite Y lattice is found to induce a change in the partial charge distribution of a cracking hydride transfer transition state model (C 4 H 9 + plus n-octane). The polarization in this transition state model is attributed to the increased size of the transitionstate model in comparision to the size of n-octane. This polarization likely preferentially stabilizes species such as the transition state and is perhaps an explanation for the second-order dependence of hydrocarbon cracking rate on Al ion concentration in zeolite Y.