Inhibitors polyphosphate

As an example of these types of inhibitors, polyphosphates, phosphates, silicates, and benzotriazole can be mentioned. The action of these inhibitors is highly dependent on the environmental factors such as pH and redox potential. Therefore, they are anodic under certain conditions and cathodic otherwise. 

Organophosphonates are similar to polyphosphates in chelation properties, but they are stable to hydrolysis and replace the phosphates where persistence in aqueous solution is necessary. They are used as scale and corrosion inhibitors (52) where they function via the threshold effect, a mechanism requiring far less than the stoichiometric amounts for chelation of the detrimental ions present. Threshold inhibition in cooling water treatment is the largest market for organophosphonates, but there is a wide variety of other uses (50). 

Temperature of the system When inhibitors are used in the 0-100°C range it is usually found that higher concentrations become necessary at the higher temperatures Other inhibitors can lose their effectiveness altogether as the temperature is raised. A prime example of this is the polyphosphate type of inhibitor. This is effective in circulating systems at temperatures below about 40°C, but at higher temperatures reversion to orthophosphate can occur and this species is ineffective at the concentrations at which it will then be present. If calcium ions are present, additional loss of inhibitor will occur due to calcium phosphate precipitation. 

Scale formation Controlled scale deposition by the Langelier approach or by the proper use of polyphosphates or silicates is a useful method of corrosion control, but uncontrolled scale deposition is a disadvantage as it will screen the metal surfaces from contact with the inhibitor, lead to loss of inhibitor by its incorporation into the scale and also reduce heat transfer in cooling systems. Apart from scale formation arising from constituents naturally present in waters, scaling can also occur by reaction of inhibitors with these constituents. Notable examples are the deposition of excess amounts of phosphates and silicates by reaction with calcium ions. The problem can be largely overcome by suitable pH control and also by the additional use of scale-controlling chemicals. 

In nitrogenous fertiliser solutions of the NH4NOJ—NHj —HjO type corrosion of steel can be prevented by 500 p.p.m. of sulphur-containing inhibitors, e.g. mercaptobenzothiazole, thiourea and ammonium thiocyanate. However, these inhibitors are not so effective where most of the NHj is replaced by urea. For these solutions phosphate inhibitors such as (NH4>2HP04 and polyphosphates were more effective... 

In the hydraulic transport of solids through steel pipelines, inhibitors of the sodium-zinc-phosphate glass type have been shown" to be effective. In the case of coal slurries the polyphosphate type was rejected because the de-oxygenating action of the coal lowered the inhibitor effectiveness. Hexavalent chromium compounds at 20 p.p.m. were more effective". ... 

Elsewhere, in a series of Japanese patents, mixtures of resorcinol + sodium nitrate, glycerine + sodium nitrate, lithium hydroxide + tungstate, etc., have been claimed to be effective. An example of the use of inhibited cooling mixtures of low toxicity is provided by a patent which describes a mixture of silicate-I- polyphosphate -I- a saccharide, e.g. sucrose or fructose, as the inhibitor formulation in a propylene glycol -I- potassium-hydrogen-carbonate mixture used in aluminium cooler boxes for ice-cream. 

Although the 3 - and 5 -polyphosphate derivatives mentioned above exhibit exquisite inhibitory potency these compounds are not cell permeable. To take advantage ofthepotency of such derivatives for studies with intact cells and tissues, there are two possibilities. One is chemically to protect the phosphate groups from exonucleotidases that also allows the compound to transit the membrane intact. The other is to provide a precursor molecule that is cell permeable and is then metabolized into an inhibitor by intracellular enzymes. The general term for such a compound is prodrug nucleotide precursors are also referred to as pronucleotides. Families of protected monophosphate derivatives were synthesized, based on (3-L- and 3-D-2, 5 -dd-3 -AMP, 3-L-2, 3 -dd-5 -AMP, and the acyclic 9-substituted adenines, PMEA and PMPA. Protective substituents were (i) -( -pivaloyl-2-thioethyl) ... 

Orthosilicates are not suitable for corrosion inhibitor purposes, and metasilicates are not generally used because they tend to increase the caustic alkalinity too much, leading to the potential for caustic-induced problems. However, glassy polysilicates are widely used. They have inhibition properties similar to those of polyphosphates and also have an indefinite crystalline structure. 

Although orthophosphates are themselves passivating, anodic inhibitors (and also cathodic inhibitors, forming a calcium phosphate barrier film), the film strength is weak, even in simple HW systems and they are not used for this purpose. Nevertheless, despite the thermal instability of sodium hexametaphosphate and other polyphosphates, phosphates in general have several important properties that make them useful in boiler plant operations. These properties include ... 

A solid, encapsulated scale inhibitor (calcium-magnesium polyphosphate) has been developed and extensively tested for use in fracturing treatments [1451-1453]. The inhibitor is compatible with borate- and zirconium-crosslinked fracturing fluids and foamed fluids because of coating. The coating... 

Scale inhibitors are used to prevent the formation of insoluble calcium salts when the drilling fluid contacts formation minerals and saline formation waters. Commonly used scale inhibitors include sodium hydroxide, sodium carbonate, sodium bicarbonate, polyacrylates, polyphosphates, and phosphonates. 

Because many cells maintain ATP, ADP, and AMP concentrations at or near the mass action ratio of the adenylate kinase reaction, the cellular content of this enzyme is often quite high. A consequence of such abundance is that, even after extensive purification, many proteins and enzymes contain traces of adenylate kinase activity. The presence of this kinase can confound the quantitative analysis of processes that either require ADP or are carried out in the presence of both ATP and AMP. Furthermore, the equilibrium of any reaction producing ADP may be altered if adenylate kinase activity is present. To minimize the effect of adenylate kinase, one can utilize the bisubstrate geometrical analogues Ap4A and ApsA to occupy simultaneously both substrate binding pockets of this kinase . Typical inhibitory concentrations are 0.4 and 0.2 mM, respectively. Of course, as is the case for the use of any inhibitor, one must always determine whether Ap4A or ApsA has a direct effect on a particular reaction under examination. For example. Powers et al studied the effect of a series of o ,co-di-(adenosine 5 )-polyphosphates (e.g., ApnA, where n =... 

The corrosion process can be inhibited by the addition of phosphate or polyphosphate ions [344], inorganic inhibitors as, for example, chromate ions [336], adsorbed alcohols [345], adsorbed amines, competing with anions for adsorption sites [339,] as well as saturated linear aliphatic mono-carboxylate anions, CH3(CH2)n-2COO , n = 7 — 11, [24]. In the latter case, the formation of the passive layer requires Pb oxidation to Pb + by dissolved oxygen and then precipitation of hardly soluble lead carboxylate on the metal surface. The corrosion protection can also be related to the hydrophobic character of carboxylate anions, which reduce the wetting of the metal surface. 

The first two components are the active surfactants, whereas the other components are added for a variety of reasons. The polyphosphate chelate Ca ions which are present (with Mg ions also) in so-called hard waters and prevents them from coagulating the anionic surfactants. Zeolite powders are often used to replace phosphate because of their nutrient properties in river systems. Sodium silicate is added as a corrosion inhibitor for washing machines and also increases the pH. The pH is maintained at about 10 by the sodium carbonate. At lower pH values the acid form of the surfactants are produced and in most cases these are either insoluble or much less soluble than the sodium salt. Sodium sulphate is added to prevent caking and ensures free-flowing powder. The cellulose acts as a protective hydrophilic sheath around dispersed dirt particles and prevents re-deposition on the fabric. Foam stabilizers (non-ionic surfactants) are sometimes added to give a... 

Utility systems for equipment and space heating and cooling frequently use heavy metal corrosion inhibitors in their heat transfer fluids. Chromate compounds are among the best corrosion inhibitors available. Nonchromate inhibitors that have proved to be feasible substitutes include polyphosphates, organophosphates, zinc, molybdates, and aromatic azoles. Some of these compounds have their own environmental impacts, however. Azoles, for instance, can be quite dangerous to human health. 

It is rare in actual applications that only one corrosion inhibitor is used. Synergistic blends of two or more inhibitors can take advantage of the strengths of each. Table 10-1 compares the performances of several of these blends to that of a chromate-zinc blend under different operating conditions. Note that while the chromate-zinc blend offers the best corrosion inhibition with no contaminants present and at high temperatures, other blends are close, and do not present the environmental problems that chromates do. With petroleum ether, hydrogen sulfide, or hexane contaminants present in the cooling water, the Polyphosphate-HEDP-Carboxylate blend performs the best, followed by Zinc-HEDP. 

Calculations based on Stiff and Davies stability index (Ref. 11 indicated that under normal producing temperatures formation water 1s not expected to form scale. However, the high skin temperature (up to 150° C) of the crude heaters will cause severe CaCO-scaling. This expectation was confirmed by laboratory tests using synthetic formation water. The result indicates a requirement to Inject scale inhibitor upstream of the heaters. A polyphosphate scale inhibitor was found to be effective in the laboratory tests. 

The whole question of the specificity was reopened with the discovery that E. coli phosphatase, contrary to an earlier statement (114), hydrolyzed a variety of polyphosphates including metaphosphate of average chain length 8 (97). It was subsequently reported that partially purified phosphatases from several mammalian tissues had appreciable PPi-ase activity at pH 8.5 (115). This was confirmed (116) and extended to include ATPase and fluorophosphatase activities (117). Proof that the same enzyme is responsible for the monoesterase and PPi-ase activities was afforded by heat inactivation studies, cross inhibition experiments, and inhibition of PPi-ase activity by L-phenylalanine, a specific inhibitor of intestinal phosphatase. It was also found that calf intestinal phosphatase couid be phosphorylated by 32P-PP and the number of sites so labeled agreed with the number of active sites determined with a monoester substrate using a stopped-flow technique (118). It would seem that the main reason for the confusion with regard to the PPi-ase activity results from the inclusion of Mg2+ in the assay. This stimulates the monoesterase activity but almost completely inhibits PPi-ase activity (117). 

In the preparation of amidine-containing substrates and inhibitors of trypsin, various nitriles have been synthesized as intermediates for these amidines. 15 In order to improve the yields of these nitriles and to preserve the optical activity of the amidines, many dehydrating agents such as POCl3, P2Os, TosCl/pyridine, and polyphosphate ester (PPE) and various dehydrating conditions have been evaluated. 101516 ... 

Oxygen, carbon dioxide and various chemicals used to reduce scaling can cause corrosion. Corrosion control is provided largely by the use of inhibitors such as chromates, polyphosphates, silicates and alkalies. 

Offline passivation involves treatment of equipment currently out of service. Treatment levels are typically higher consequently, passivation is completed more quickly. Passivation of nonchromate treatment generally uses either a polyphosphate, zinc, molybdate or other nonchromate-based inhibitor in combination with various surface-active cleaning agents. The passivation solution should be disposed of after the pretreatment stage, rather than dumped back into the cooling system where the potential for fouling can exist due to the precipitation of pretreatment compounds such as zinc or phosphate. Table 8.1 outlines both online and offline pretreatment procedures. 

Polyphosphates also act as corrosion inhibitors. They are cathodic polarizers and form a durable corrosion-inhibiting film that includes adsorbed calcium. 

In addition, they are anodic inhibitors, depositing iron metaphosphate, and forming y-Fe2C>3, thus stifling the anodic reaction. High and low pH or high temperatures will hasten the reversion (hydrolysis) of polyphosphate to orthophosphate. 

Zinc is almost never used on its own but is invaluable in synergizing with other inhibitors, such as polyphosphate, chromate, phosphonate, HPCA, and other organic inhibitors to reduce the total inhibitor requirement and to... 

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