JPS6140758B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to corrosion control in steam condensate systems and other aqueous systems with relatively low mineral content. More particularly, the present invention relates to the use of methoxypropylamine in combination with hydrazine to inhibit corrosion in steam condensate systems or other low solids aqueous systems. Condensate corrosion protection is increasingly becoming an important aspect of equipment operation. In these energy-aware times, increases in condensate quantity and quality provide water and heat savings for the entire boiler system. Historically, the action of dissolved gases such as oxygen and carbon dioxide are the two main factors leading to condensate corrosion. To understand the role of oxygen and carbon dioxide in corrosion, one must understand the electrochemical nature of corrosion. Pure water has very little effect on pure iron, but such conditions are never encountered. Under most conditions iron tends to dissolve in water. Two electrons are then released for each atom that dissolves. These electrons are transferred to hydrogen ions present in the water and the ions are reduced to elemental gaseous hydrogen. If hydrogen remains on the surface of the metal, all effects cease at this point. This is because a protective film is formed that blocks the passage of electrons. However, substances that increase the number of hydrogen ions present in the water or cause removal of the protective film act to increase the corrosion rate. If carbon dioxide is dissolved, it reacts with water to form carbonic acid, which is then further exposed to the system to provide active hydrogen. Iron excretes hydrogen from this acid. Also, if oxygen is present in the water,
A double reaction occurs. Some oxygen molecules combine with the expelled hydrogen and thus expose the metal to new attacks. Other oxygen molecules combine with iron ions to form insoluble rust compounds. A corrosion effect greater than the mere dissolution tendency of iron is the presence of inhomogeneous surfaces in commercial irons and steels due to the presence of surface defects that tend to form couples with adjacent base metals. Electrons are released from the anodes of these couples to hydrogen ions at the adjacent cathode surfaces, thus increasing the corrosion area and slowing the corrosion rate. The initial products of corrosion are converted to ferric oxide. This is simply loosely bonded aggravated corrosion due to blocking off the area to oxygen access. These areas become anodes and iron oxide couples are obtained. The iron under the oxide deposit dissolves and the hole develops. Carbon dioxide attack results in metal thinning or groove formation. For these systems, the film-forming amine is
Provides condensate corrosion protection against oxygen and carbon dioxide. However, many industrial systems cannot tolerate film-forming amines and must use neutralized amines. An ideal neutralizing amine should have the following properties: 1 The distribution ratio must be high enough that a significant amount of the neutralized amine fed to the boiler ends up in the condensate.
This reduces loss of neutralized amine due to blowdown. 2 The distribution ratio shall not be too high in order to keep losses due to ventilation and exhaust to a minimum. The distribution ratio is the ratio of the amount of amine in the gas phase to the amount of amine in the liquid phase. 3 The basicity value must be moderately high or very high so that the amine effectively neutralizes any carbon dioxide it encounters. 4. The neutralized amine must have sufficient hydrolytic-thermal stability that it does not decompose to ammonia and other compounds in the boiler or in superheated or saturated steam. 5. Neutralized amines are convenient to supply because of their
Must be a water-soluble liquid. Neutralized amines such as cyclohexylamine and morpholine have been used, but these neutralized amines have several disadvantages. For example, cyclohexylamine has a high distribution ratio and therefore a substantial amount of cyclohexylamine escapes from the system via exhaust. Morpholine, on the other hand, has a low basicity value. This means that large amounts of morpholin are required to achieve high pH in condensate systems. Morpholine also has a very low distribution ratio. this is,
This means that a substantial amount is lost to emissions. The neutralized amines of the present invention overcome the aforementioned disadvantages of cyclohexylamine and morpholin.
Methoxypropylamine has a very desirable distribution ratio and fairly high basicity values. Methoxypropylamine can be used alone or in combination with oxygen corrosion inhibitors such as hydrazine. When using, 0.1 to 1000
mg/preferably a concentration of 1 to 100 mg/ has to be maintained in the steam condensate system. When used in combination with hydrazine or other oxygen corrosion inhibitors, the composition may contain from about 1 to 99% methoxypropylamine and from about 0.1 to 99% oxygen corrosion inhibitor, based on the active ingredients.
It should contain 50% preferably about 1-15%. The compositions of the invention can be fed by conventional liquid feed equipment to the steam condensate system to be treated or to the boiler feed water or directly to the steam feed line. The following examples illustrate the use of methoxypropylamine alone or in combination with hydrazine as a steam condensate corrosion inhibitor in accordance with the teachings of the present invention. Example 1 The distribution ratio of a number of neutralized amines is 100mg/each.
Calculated by preparing a solution of the amine with a concentration of and adding 500 ml of this solution to a saline bottle. This is heated gradually and uniformly so that 100 ml of distillate is obtained every 40 minutes. Furthermore, to keep the saline bottle solution at the 500ml mark,
The solution is manually introduced into the saline bottle every minute. Collect 100 ml aliquots of the distillate and measure the PH on three consecutive portions until a constant PH is obtained.
Take this as an indication of the establishment of equilibrium conditions.
At equilibrium, the brine and the final 100 ml were analyzed by gas chromatography to determine the amount of amine in each and the distribution ratio (DR).
is calculated by the following formula. DR=concentration of amine in final 100 ml/concentration of amine in brine Similarly, the basicity value (Kb), ie, the value of the amine's ability to react with carbon dioxide, is calculated by the following formula. K _b = [BH ⁺ ] [OH ^- ]/[B ⁰ ] In the formula, [BH ⁺ ], [OH ^- ] and [B ⁰ ] are defined as follows. [BH ⁺ ] = Concentration of dissociated amine [OH ^- ] = Hydroxide concentration [B ⁰ ] = Concentration of free, undissociated amine The results of these tests and calculations are shown in the table.

Table: Example 2 The hydrolytic-thermal stability of various neutralized amines is determined by tests. In this test, a concentration of 1000 mg/ml of neutralized amine was applied at 600 psi at 24
Autoclave for an hour (489〓) and measure the final concentration of ammonia. The results of this test are shown in the table below. Table Amine NH ₃ mg/ Methoxypropylamine <1.0 Morpholine 1.6 Cyclohexylamine 3.3 Diethylaminoethanol ^* 2.4 Aminomethylpropanol 124.0 *Diethylaminoethanol decomposes considerably to form diethylamine. Example 3 A condensate test system is used to evaluate neutralized amines. The system consists of a boiler capable of producing 45 Kg/hour of steam under a pressure of 200 psi, a cooling coil with a pump and metering device to regulate the composition of the blended water to the boiler, and a temperature control device to condense the steam. The condensate is recirculated through the test loop. Metal coupons and corrosion meters assess corrosion rates. The test water contains SO ₄ <1 mg/, Cl <1 mg/
, SiO ₂ <1 mg/ and CO ₂ 10 mg/. Table 1 shows the results of the corrosion tests.

EXAMPLE 4 The condensate test system of Example 3 is used to illustrate the effect of the addition of hydrazine to methoxypropylamine in inhibiting corrosion.

【table】

Claims (1)

Claims: 1. A steam condensate corrosion inhibition composition consisting essentially of methoxypropylamine and hydrazine. 2. A vapor condensate corrosion inhibiting composition according to claim 1 containing 1 to 15% by weight of hydrazine.