Corrosion nonaqueous solvents

Activated tertiary amines such as triethanolamine (TEA) and methyl diethanolamine (MDEA) have gained wide acceptance for CO2 removal. These materials require very low regeneration energy because of weak CO2 amine adduct formation, and do not form carbamates or other corrosive compounds (53). Hybrid CO2 removal systems, such as MDEA —sulfolane—water and DIPA—sulfolane—water, where DIPA is diisopropylamine, are aqueous alkaline solutions in a nonaqueous solvent, and are normally used in tandem with other systems for residual clean-up. Extensive data on the solubiUty of acid gases in amine solutions are available (55,56). 

The original hot carbonate process developed by the U.S. Bureau of Mines was found to be corrosive to carbon steel (55). Various additives have been used in order to improve the mass transfer rate as well as to inhibit corrosion. Vetrocoke, Carsol, Catacarb, Benfteld, and Lurgi processes are all activated carbonate processes. Improvements in additives and optimization of operation have made activated carbonate processes competitive with activated MDEA and nonaqueous solvent based systems. Typical energy requirements are given in Table 9. 

On the other hand, the P—E bond is rather labile toward hydrolysis by even trace amounts of moisture in nonaqueous solvents, producing a series of corrosive products (Scheme 5). Thermal gravimetric analysis (TGA) reveals that, in a dry state, LiPFe loses 50% of its weight at >200 °C but that, in nonaqueous solutions, the deterioration occurs at substantially lower temperatures, for example, as low as 70 X. 

In a recent report, we described (15) how encapsulating the YBa Cu O- pellets in an epoxy matrix effectively fills the outer pores ana diminishes the problem with large background currents. These electrodes undergo reversible electron transfers with electroactive solutes in a variety of nonaqueous solvents, as observed by cyclic voltammetry. This reversible voltammetry was used as a phenomenological method for estimating the lifetime of such electrodes, in a variety of corrosive media, based on monitoring the voltammetric response as a function of exposure time to corrosive media. 

Corrosion in nonaqueous liquids such as fuels, lubricants, and edible oils is usually caused by the small amounts of water often present. Water is slightly soluble in petroleum products, and its solubility increases with temperature. If a nonaqueous solvent is saturated with water and the temperature is lowered, then some of the water will separate to attack steel that it contacts. Oils that have been subjected to high temperatures in air will contain organic acid that will be extracted by any water present to increase the rate of attack on steel. 

Small amounts of water inhibit corrosion in some nonaqueous solvents. Halogenated (containing chlorides, fluorides, bromides, or iodides), nonaqueous solvents can be particularly troublesome. 

It is clear from the situation just described that the latter situation is ideal for a stable chemical modification of the metal substrate and that molecules should be chosen that are able to interact strongly with the metallic substrate. However, there are some characteristic differences between corrosion inhibitors and molecular adhesion promoters whereas for corrosion inhibition the composition and structure of the metal surface are defined by the corrosive medium, the surface properties can be changed and adjusted to the stmcture of the adhesion promoter. Inhibitors must be soluble in the electrolyte (e.g., water) and can be applied only for well-defined reaction conditions. Adhesion promoters, however, may be applied from aqueous or nonaqueous solvents or even from the gas phase and the reaction conditions can be optimized for the given substrate. Therefore, some characteristic molecular features of inhibitors such as heteroatoms S, P, and O should be incorporated into the structure of the adhesion promoter however, the molecule itself should show minimum solubility in water and the possibility to bind a polymer onto the adhesion promoter. 

There are many nonaqueous solvents that are involved in corrosion problems too. Methanol or ethanol and pure liquid acetic acid show a weak self-dissociation like water as described by Equations 1.9 and 1.10. As fuels or solvents for chemical processes, they may cause corrosion of container materials. Similarly, liquid HP is an important solvent for many biological macromolecules, such as proteins, enzymes, vitamin B12, etc., which may be recovered without any damage to their composition and properties. Some liquefied gases like liquid NO2 or molten HgBr2 are solvents with weak self-dissociation (Equations 1.11 and 1.12). 

Because water is a common solvent we might think of it merely as a passive medium in which chemical reactions take place. However, water is a reactive compound, and an alien raised in a nonaqueous environment might consider it aggressively corrosive and be surprised at our survival. For instance, water is an oxidizing agent ... 

For all these reasons, the stability of the superconducting state and ways to control it are questions of prime importance. Many studies have addressed the degradation of the properties of HTSC under the influence of a variety of factors. They included more particularly the corrosion resistance of HTSC materials exposed to aqueous and nonaqueous electrolyte solutions as well as to water vapor and the vapors of other solvents. It was seen that the corrosion resistance depends strongly both on the nature (chemical composition, structure, etc.) of the HTSC materials themselves and on the nature of the aggressive medium. 

The single most important consideration in nonaqueous GPC is sample solubility. Although adsorption is not an infrequent problem, finding a solvent for a polymer is usually the hard step in analysis. The most common solvents for nonaqueous GPC are toluene, tetrahydrofuran, chloroform, and DMF. A number of potentially useful solvents are toxic, corrosive, or expensive,... 

Active metals such as lithium and sodium can be used as stable reference electrodes in nonaqueous solutions in which they are apparently stable. To a limited extent this may be true for the Mg/Mg2+, Ca/Ca2+ and A1/A13+ couples as well (though they must be checked separately for each specific solution). It is important to note that in most of the commonly used nonaqueous systems, the above active metals are thermodynamically unstable and react readily with the solvent, the salt anions and the unavoidably present atmospheric contaminants. However, the active metals are apparently stable in many systems because the above reaction products, which are usually insoluble (metal salts), precipitate as protective passivating surface films. These films prevent further corrosion of the active metals in solutions [21], Hence, the active metal covered by the surface films may... 

Historically, ionic liquids initial advances in electrochemistry were encouraged by difficulties and safety issues in the aluminum deposition process known as SIGAL (Siemens Galvano-Aluminium). Major concerns were related with the flammability of the aluminum precursors and of the volatile organic solvents used. In the search for low melting, nonvolatile, and nonaqueous electrolytes, pyridinium [25] and imidazolium chloroaluminates (III) were investigated [26]. These ionic liquids are able to dissolve various metal salts. Their biocompatibility is questionable due to their potential toxicity and because they are also corrosive and unstable in air and/or... 

Measurements of the pH in aqneous-organic solvent mixtures and in nonaqueous mixtures pose similar problems, but the need for such data is extensive, for instance for mobile phases used in chromatography, for electrochemistry, and for corrosion studies. When in cell (8.3) the solvent S is not pure water but its mixture with another solvent or a non-aqueous solvent altogether. Equation 8.4 still holds, but Ihe activity coefficient of the chloride ion must be changed, using the modified Bates-Guggenheim... 

This high dielectric constant with its ease of handling, low corrosivity, and low toxicity have made ethylene carbonate suitable as a solvent for specialized applications and for the preparation of binary mixed solvents with water, methanol, acetonitrile, sulpholane, and acetone. It is also used as an electrolyte in nonaqueous batteries, as a plasticizer, as a monomerer or reagent for the synthesis and modification... 

---