Organic hydration inhibitor

Based, in part, on the results of the previous section, we decided to investigate the use of several organic hydration inhibitors on PAA and Forest Products Laboratory (FPL)(92) sodium dichromate-sulfuric acid etched surfaces.(3.5,i3,9i,93) One of the inhibitors that is very successful is nitrilotris methylene phosphonic acid NTMP, N[CH2P(0)(OH)2]3. It provides hydration resistance for FPL surfaces in a manner similar to anodization in phosphoric acid, i.e., it forms a protective molecular layer that does not allow the aluminum oxide substrate to hydrate until the inhibitor complex dissolves. 

FIGURE 10. Wedge-test results (crack length vs. time) for FPl treated aluminum surfaces (a) FPL with FM-123 (moisture wicking), (b) FPL with FM-300 (moisture resistant), (c) FPL with an organic hydration inhibitor and FM-123, (d) FPL with BR-127 primer and FM-300. Data are compilations from References 14, 17, 22, and 47. FM-123, FM-300, and BR-127 are trademarks of American Cyanamid Corp., Havre de Grace, MD. 

NaClO, or else in the two-phase system but with a quaternary ammonium (viz. AUquat) ion as a phase-transfer catalyst, overoxidation to the corresponding carboxylic acid is obtained (entry 4). Therefore, by proper choice of the experimental conditions, a synthetically useful distinction in products formation can be made for the oxidation of primary alcohols, even though we are far from a satisfactory understanding of the reason behind this different behaviour. In fact TEMPO, as a well-known inhibitor of free-radical processes is allegedly responsible for the lack of overoxidation of an aldehyde to carboxylic acid (entry 3) this notwithstanding, TEMPO is also present under those conditions where the overoxidation does occur (eutry 4). Moreover, a commou teuet is that the formation of the hydrated form of an aldehyde (in water solution) prevents further oxidation to the carboxylic acid however, both entries 3 and 4 refer to water-organic solutions, and their... 

Certain oil additives are produced by reacting hydrated limes with alkyl phenates or organic sulfonates. The resulting calcium soaps act as wear inhibitors, help to prevent sludge build-up and neutralise acidity from products of combustion. 

Chem. Descrip. Basic zinc phosphate hydrate, organic treated Chem. Analysis 55.5% Zn, 38.5% PO4 CAS 7779-90-0 EINECS/ELINCS 231-143-9 Uses Corrosion inhibitor, pigment for primers and single-coat applies. Properties Wh. 3 m avg. particle size 0.01% 32 m sieve residue dens. 3.5 g/ml bulk dens. 1.1 g/ml (lapped) oil absorp. 20 pH 7 Toxicology Nontoxic Heucophos ZPZ [Heucotech Ltd]... 

Kinetic inhibitors are used on a smaller scale ( 0.5 %) and work by reducing the rate at which the hydrate is formed. The small amounts of hydrate that do form are simply carried along in fhe flow and dealt with at a later stage in the refinement process. Kinetic inhibitors are usually polymeric organic materials, such as poly(vinyl pyrrolidinone) (PVP). Generally, kinetic inhibitors or other anti-agglomerants (such as tetraalkyl ammonium salts) are not used without the presence of a thermodynamic inhibitor as well. 

Currently the most common flow assurance strategy is to rely upon injection of organic inhibitors, e.g. methanol, monoethylene glycol (MEG) in order to inhibit hydrate formation and to ensure unimpeded flow of hydrocarbons. The current trend for the gas industry is to favour the use of MEG over methanol for new developments. MEG loss to the vapour phase is very small and it has also the advantage that it can be effectively recovered, regenerated and recycled. 

Proposals for the mechanism of PPS formation include nucleophilic aromatic substitution (Sj Ar) (2radical-cation (27), and radical-anion processes (28,29). Some of the interesting features of the polymerization are that the initial reaction of the sodium sulfide-hydrate with NMP affords a soluble NaSH-sodium 4-(N-methylamino)butanoate mixture, and that polymers of higher molecular weight than pi edicted by the Caruthers equation are produced at low conversions. Mechanistic elucidation has been hampered by the harsh polymerization conditions and poor solubility of PPS in common organic solvents. A detailed mechanistic study of model compounds by Fahey provided strong evidence that the ionic S]s Ar mechanism predominates (30). Some of the evidence supporting the S s(Ar mechanism was the selective formation of phenylthiobenzenes, absence of disulfide production, kinetics behavior, the lack of influence of radical initiators and inhibitors, relative rate Hammet values, and activation parameters consistent with nucleophilic aromatic substitution. The radical-anion process was not completely discounted and may be a minor competing mechanism. 

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