No abstract

Organic acids, typically derived from an oil-based value chain, are frequently used as corrosion inhibitors in industrial metal working fluids. The criteria for selection of these corrosion inhibitors have changed in the last decades, and are today not only performance-driven, but influenced by ecological considerations, toxicity and regulatory standards. We present scalable semisynthetic approaches to organic corrosion inhibitors based on phosphonic acids from renewable resources. They have been evaluated by chip filter assay, potentiodynamic polarization measurements, electrochemical impedance measurements and gravimetry for corrosion protection of iron and steel in an aqueous environment at slightly alkaline pH. The efficacy of several phosphonic acids tested was found to be strongly dependent on structural features influencing molecular self-assembly of protective layers, and the solubility of salts formed with di- and trivalent cations from the media or formed during corrosion. A carboxyphosphonic acid (derived from castor oil) was found to have remarkable anticorrosive effects in all media tested. We attribute the anticorrosion properties of this carboxyphosphonic acid to the formation of particularly stable protective layers on the metal surface. It might thus serve as a commercially attractive substitute for current acidic corrosion inhibitors, derived from renewable resources.

Amino alcohols, typically derived from an oil-based value chain, are frequently used as alkaline additives for neutralization of acidic corrosion inhibitors in industrial metal working fluids. The criterions for selection of these additives have changed in the last decades and are nowadays not only performance driven, but influenced by ecological considerations, toxicity and regulatory standards. We present amino acids as functional, nontoxic, non-hazardous, non-volatile, chemically stable and cheap alkaline additives for common acidic corrosion inhibitors. The resulting mixtures have been evaluated for Co, Ni and Cu-leaching and were analyzed by chip-filter assay, potentiodynamic polarization measurements, electrochemical impedance measurements and gravimetry for corrosion protection of iron and steel in aqueous environment at slightly alkaline pH. Of several amino acids tested, Glu and Tau were found to synergistically interact with several acidic corrosion inhibitors of the carboxylic acid and the phosphonic acid type. Glu had a particularly positive impact on the protective properties of phosphonic acids with low hard water compatibility and served as an antiscalant. Tau had also a positive effect on the anticorrosive properties of several acidic corrosion inhibitors and lead to low levels of Co and Ni-leaching. Glu and Tau might thus serve as commercially and ecologically attractive substitutes for current alkaline additives to acidic corrosion inhibitors.

We present alkali salts of amino acids as functional, non-toxic, non-hazardous, non-volatile, chemically stable, and cheap alkaline additives for common acidic corrosion inhibitors. The resulting mixtures have been evaluated for Co, Ni, and Cu leaching and were analyzed by chip filter assay, potentiodynamic polarization measurements, electrochemical impedance measurements, and gravimetry for corrosion protection of iron and steel in aqueous environment at slightly alkaline pH. Leaching of Co and Ni was found to depend on the corresponding complex stabilities. Taurine (Tau) as well as aminohexanoic acid (AHX) leads to low leaching of Co and Ni. Particularly AHX is an attractive low leaching additive leading to lower Co and Ni concentrations in solution than currently used amino alcohols. Glu and Tau were found to synergistically interact with several acidic corrosion inhibitors of the carboxylic acid and the phosphonic acid type. Tau had a particularly positive impact on the protective properties of carboxyphosphonic acids. Glu had also a positive effect on the anti-corrosive properties of several acidic corrosion inhibitors and served as an anti-scalant. Alkali salts of Glu and Tau might thus serve as commercially and ecologically attractive substitutes for current alkaline additives to acidic corrosion inhibitors.

Amino alcohols like triethanolamine (TEA), 2‐amino‐2‐methylpropanol (AMP), or 1‐aminopropan‐2‐ol (MIPA) are common ingredients in industrial metalworking fluids. They are used in large quantities as alkaline additives for the neutralization of acidic corrosion inhibitors and are typical industrial products from the oil‐based value chain. The criteria for the selection of these additives have changed in the last decades and are nowadays not only performance‐driven but influenced by ecological considerations, toxicity, and regulatory standards. In this study, we evaluate the sugar derivative N,N‐diethylglucamine (DEGA) for use as a functional, nonvolatile, chemically stable, and cheap alkaline additive for common acidic corrosion inhibitors. Electrochemical analyses confirm anticorrosive properties of DEGA comparable to the gold standard TEA for iron and steel in an aqueous environment at a slightly alkaline pH. In addition, DEGA leads to extremely low levels of Co, Ni, and Cu leaching and can thus also serve as a nonvolatile substitute for currently used low‐leaching additives such as AMP and MIPA. The diethylamino‐motif is a sweet spot among different glucamine derivatives tested because it combines easy synthetic accessibility with good water solubility and low‐leaching properties. Besides this, DEGA can be prepared in one step from glucose and diethylamine, both derived from renewable resources.