Neutralized amines

Cyclohexylamine is miscible with water, with which it forms an azeotrope (55.8% H2O) at 96.4°C, making it especially suitable for low pressure steam systems in which it acts as a protective film-former in addition to being a neutralizing amine. Nearly two-thirds of 1989 U.S. production of 5000 —6000 t/yr cyclohexylamine serviced this appHcation (69). Carbon dioxide corrosion is inhibited by deposition of nonwettable film on metal (70). In high pressure systems CHA is chemically more stable than morpholine [110-91-8] (71). A primary amine, CHA does not directiy generate nitrosamine upon nitrite exposure as does morpholine. CHA is used for corrosion inhibitor radiator alcohol solutions, also in paper- and metal-coating industries for moisture and oxidation protection. 

Neutralizing Amines. Neutralizing amines are used to neutralize the acid (H" ) generated by the dissolution of carbon dioxide or other acidic process contaminants in the condensate. These amines hydrolyze when added to water and generate the hydroxide ions required for neutralization ... 

By regulating the neutralizing amine feed rate, the condensate pH can be elevated to within a desired range (eg, 8.8—9.2 for a mixed copper—iron condensate system). 

Water-emulsifiable vehicles contain emulsifiers that may act as plasticizers after film formation, affecting the hardness. Water-soluble vehicles usually contain a neutralizing amine, the primary purpose of which is to solubihze the resin. These amines can influence the drying properties as they tend to complex the metal drier, thus affecting the catalytic activity. Acceptable results are usually obtained with trialkylamines such as dim ethyl eth a n o1 amine, trimethyl amine, and aminomethylpropan o1 (7). 

Environment Internal Cooling water containing neutralizing amine, oxygen scavenger, caustic... 

Carbon Dioxide CO2 Corrosion in water lines and particularly steam and condensate lines Aeration, deaeration, neutralization with alkalies, filming and neutralizing amines... 

Nucleophiles can also act as acids and bases, and this behavior substantially alters their nucleophilicity. At pH 5, trimethylamine exists mainly as its conjugate acid, trimethylammonium cation. First draw a Lewis structure, and then examine the electrostatic potential for trimethylammonium ion. On the basis of the map, which is the better nucleophile, the cation or the corresponding neutral amine At pH 12, phenol exists mainly as its conjugate base, phenoxide anion. First draw a Lewis structure (or series of Lewis structures), and then examine the electrostatic potential map for phenoxide anion. Which is the better nucleophile, phenoxide or phenol ... 

Carbon dioxide, from the decomposition in the boiler of temporary hardness salts present in some waters, causes corrosion of steel steam pipework and cast iron valves and traps. Corrosion inhibitors may be used, but the choice of inhibitor must take into account the other materials in the system. Neutralizing amines such as morpholine or cyclohexylamine are commonly used. 

Q Addition to the ketone or aldehyde carbonyl group by the neutral amine nucleophile gives a dipolar tetrahedral intermediate. 

In LP boilers with little returning condensate the requirement for MU is correspondingly high and may be relatively cool and partially oxygenated. Here it is not uncommon to observe the transport of ferrous bicarbonate [Fe(HC03)2] into the boiler (especially where no neutralizing amine is supplied) and the subsequent development of iron sludge, which settles on the top of combustion tubes and to the bottom of the boiler. 

Steam purity indicates the degree of inadvertent BW carryover, typically reflected by an increase in electrical conductivity from sodium and other ions present in the BW TDS. Iron and silica may also carry over, and the silica may be in a volatile form. Steam purity also is affected by the use of neutralizing amines (as an intentional measure). 

NOTE Neutralizing amines are often the first choice to neutralize carbonic acid in the condensate. In very small boiler plant applications they are... 

Filming amines generally produce a much worse fouling condition than neutralizing amines so where fdmers are required, the typical prac-... 

Condensate treatments include neutralizing amines such as morpholine and filming amines such as octadecylamine (ODA). 

Tannin-based multiblends cannot incorporate amines directly into their formulations (unlike sulfite-based multiblends). The neutralizing amine component must be added separately when using tannin multiblends. 

NOTE Acid phosphates and SHMP may attack chemical tanks and associated equipment, so acid-resistant equipment should be specified. Alternatively, the addition of caustic up to a pH level of 8.2 to 8.3 (the production of a pink color when tested with phenolphthalein) provides adequate protection. A further alternative is to add neutralizing amine to the tank. 

Ammonia is sometimes used to boost the pH but may be unsuitable where copper alloys are present. Hydrazine and the neutralizing amines produce ammonia as part of their breakdown process, so additional care is required here to minimize copper corrosion. 

Additionally, at pressures over 7 psig (231 °F), hydrazine is also slightly volatile, and therefore hydrazine (together with its breakdown product ammonia) is considered a functional neutralizing amine. 

As a result of the limited solubility of MEKO, it is often formulated with other boiler treatment ingredients such as filming and neutralizing amines, sulfite, or erythorbates, which permit increased concentration, improved stability, and better overall effectiveness. 

Oxygen corrosion in condensate pipelines is recognizable as large pits and are a typical result. Where the condensate pH level is low (say, due to the presence of carbonic acid), the pits may be particularly large, but as the pH level rises (say, due to the use of neutralizing amines), the layer of iron oxide corrosion product becomes more protective and the resulting pits tend to be smaller. 

Condensation occurs constantly in steam pipes, and steam traps are installed to separate the steam from the condensate. In long steam-pipe runs most of the carbon dioxide remains in the steam phase, although if only a single neutralizing amine with a low DR is used, much of the amine will be present in the condensate. The result is that the amine feed quickly becomes depleted, and further down the steam/condensate pipe the pH level becomes progressively lower. 

Whether a blend of two or three neutralizing amines is required is debatable. It all depends on the needs of the specific steam-condensate... 

From a practical point of view, it is seldom possible to provide complete coverage from a twin-blend neutralizing amine program in a very large or difficult system. 

Under these conditions, because the neutralizing amine has no effect on oxygen ingress, it is common to supplement the neutralizing amine blend with a filming amine. Thefilmer may be applied separately (usually to a steam header) or blended with the neutralizers and added to the FW, or sometimes directly to the boiler. Care should be exercised when filmers are employed in previously corroded systems because it is very likely that old corrosion debris will be transported away to cause severe blockages in steam traps and valves. 

All neutralizing amines employed in water treatment formulations are based on single amine type or blends, drawn from this commercial stockpile. Unfortunately, they are not all drawn from a common class of amines, simply with progressively higher molecular weight or additional radical groups added instead they are drawn from a wide range of classes. For example,... 

Ammonia is usually classified as a neutralizing amine because it provides post-boiler section corrosion inhibition through the same carbonic acid neutralization mechanism as regular amines. Similarly, hydrazine and other VOSs that produce ammonia, may be classified as functional neutralizing amines. 

The various functional properties of neutralizing amines, such as basicity, neutralizing capacity, DR, and volatility often have little or no direct relationship with each other, but all these properties are significantly different at boiler temperatures. This vital consideration is often insufficiently highlighted in manufacturers data sheets. Consequently, some of the commonly available information comparing amines records data at ambient temperatures, making it next to useless. 

The relative neutralizing capacity (RNC) of amines can be calculated from the reaction mole ratios thus, from the reaction of ammonia with carbonic acid, shown here, the RNC is 17/44 = 0.386 ppm neutralizing amine required per ppm C02 ... 

Neutralizing capacity is not the only measure of a required amine feed rate. Once all acidic characteristics have been neutralized, amine basicity becomes the important issue because this raises the pH above the neutralization point, to a more stable and sustainable level. Consequently, in practice we are concerned with the level of amine necessary to raise the condensate pH to a noncorrosive level. This practical amine requirement is difficult to obtain from theoretical calculations because it must take account of the amine volatility, DR, and the boiler system amine recycling factor (as well as temperature). As noted earlier, the basicity of an amine has little or no relationship to its volatility or DR, so that reliable field results are probably a more important guide in assessing the suitability of an amine product than suppliers tables. 

A fundamental functional property of a neutralizing amine (vapor-phase amine) is its volatility. Derived from this function is relative volatility and the DR. 

Table 11.6 Some DR Values for C02, NH3, and Neutralizing Amines at Various Pressures...

Examples of neutralizing amine formulations reflecting the use of blends with different DR values are shown in the following formulatons. 

Standard Twin-Neutralizing Amine Blend Materials... 

Four Neutralizing Amine Blend for C02 and 02 Materials Control... 

Neutralizing amines are generally fed to the FW line but may be fed directly to the boiler or to the steam header. Day tanks may be polyethylene or carbon steel. 

The primary reason for employing vapor-phase or neutralizing amines in steam-condensate systems is to reduce the level of corrosion of both ferrous and nonferrous metals. A further beneficial consequence of this function is the reduction of metal transported back to the FW system. 

Under particularly difficult conditions, neutralizing amines are expensive and not always totally successful. The use of satellite dosing points and programs that combine neutralizers with filmers (either fed separately or as a combination product) may produce the desired result. Proof of effectiveness requires pH and Fe/Cu/Ni mass balance profile trials to be undertaken. 

---