Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
  • C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids
  • C23F11/10—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids using organic inhibitors
  • C23F11/14—Nitrogen-containing compounds
  • C23F11/141—Amines; Quaternary ammonium compounds
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
  • C23F11/02—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in air or gases by adding vapour phase inhibitors

Definitions

• the present invention relates to compositions and methods for controlling the metal loss in boiler/­condensate steam systems.
• Iron and copper corrosion in steam condensate systems results in damage to piping and equipment as well as the loss of high quality water and energy.
• the corrosion products and process chemicals if returned to the boiler can contribute to the formation of damaging boiler deposits thereby reducing the reliability of the overall system and increasing operating and maintenance costs.
• Iron corrodes in water in the absence of oxygen because iron is less noble than hydrogen.
• the ferrous hydroxide (Fe(OH)2) formed by iron and water elevates the pH by providing hydroxide ions and ferrous irons. This reduces the amount of hydrogen ion which tends to retard corrosion.
• ferrous hydroxide is converted to magnetite (Fe3O4) in the absence of oxygen to form a somewhat protective film barrier.
• magnetite is formed based upon the overall reaction: 3 Fe + 4 H2 o ⁇ Fe3O4 + 4H2.
• cupric oxide In addition to iron corrosion in water which is augmented by the presence of oxygen, corrosion of copper by oxygen may also occur. Generally, the resulting formation of cupric oxide is self limiting. If, however, copper complexing agents such as, for example, ammonia are present, the copper oxide film cannot become permanently established. High concentrations of carbon dioxide in the condensate system, at lower pH values (less than 8), have an effect similar to ammonia in dissolving the copper oxide film.
• the ferrous bicarbonate is soluble under many conditions and can act as a corrosion reaction retardant. The stability of ferrous bicarbonate in solution is effected by heat, pH and the partial pressure of carbon dioxide above the condensate. Often, these conditions change from location to location within the boiler/condensate system.
• a second, more often utilized method of controlling carbonate-caused corrosion is the addition of amines to neutralize the carbonate and thereby increase the aqueous pH.
• amines Many different amines are utilized, but some commonly used materials include cyclohexylamine, morpholine, and methoxypropylamine.
• the most effective amines are those that possess high basicity and low molecular weight. The high basicity allows attainment of high pH after acid neutralization, and low molecular weight allows greater molar concentrations (and thus more neutralization).
• the addition of neutralizing amines neutralizes the acid (H+) generated by the solution of carbon dioxide in condensate.
• the amines hydrolyze in water to generate hydroxide ions required for neutralization.
• the condensate pH can be elevated to within a desired range (e.g. 8.5 to 9.01).
• Numerous amines can be used for condensate pH neutrali­zation and elevation.
• the selection of the appropriate amine is currently controlled by the basicity, stability and distribution ratio characteristics of the particular amine.
• the distribution ratio (DR) of an amine is expressed as formula DR equal to amine in vapour phase divided by amine in water phase (condensate) at some defined pressure or temperature.
• Amines with a distribution ratio greater than 1.0 have more amine in the vapour phase than the water phase.
• the distribution ratio is a function of the pressure and the temperature in a boiler/condensate system to be treated. Distribution ratios (at atmospheric pressure) for commonly used neutralizing amines are as follows: Morpholine 0.4; diethylaminoethanol 1.7; dimethylisopro­panol amine 1.7; cyclohexylamine 4.0; ammonia 10.0.
• the varying distribution ratios of commonly used neutralizing amines affect the loss of the amine from the system as well as the area in the system where the amine is most effective. Amines that have low distribution ratios provide excellent pH control at initial condensation sites, but poor neutralization at the final conden­sation sites. On the other hand, high DR amines are more likely to be found in remote sites in steam that has been in contact with the liquid phase as it passes through the steam distribution system.
• morpholine In boiler/condensate systems where the bulk of the steam produced is used for turbine supply, morpholine is most suitable or a blend having a high morpholine content.
• the low DR for morpholine means that morpholine will be present in the initial condensate formed at the wet end of the turbine.
• a material with a high DR is more desirable.
• the best protection is typically provided by a blend of amine products containing a variety of materials with differing distribution ratios.
• Typical neutralizing amines have DR's from 0.1 to 10, but carbon dioxide has a DR of 100 or more depending upon temperature. Because of this difference in DR's, amines tend to concentrate in the condensate lines closest to the system boiler whereas carbon dioxide tends to concentrate in more remote areas of the condensate return system. Thus, conventional amine addition to the boiler feedwater is not sufficient to protect such remote areas from carbon dioxide induced corrosion, and often these lines are unprotected or require satellite feed of amines.
• DMA dimethylamine
• TMA trimethylamine
• DEA diethylamine
• TMA is an extremely strong base
• pKa extremely strong base
• DEA diethylamine
• TMA is between 2 to 5 times more volatile than cyclohexylamine at boiler pressures from 689.5 to 10342.5 kPa (100 to 1500 psig).
• DEA has a distribution ratio (at 6985 kPa (1000 psig)) of 28.
• Cyclohexylamine is the most volatile neutralizing inhibitor commonly used in the treatment of steam boiler/condensate systems.
• DMA, TMA, DEA and other low molecular weight amines would be more effective than cyclohexylamine and other amines used for condensate treatment in following and neutralizing carbon dioxide in the outlying areas of a condensate return system.
• the extreme volatility, i.e. flammability and high atmospheric vapour pressures, of low molecular weight amines has prevented the production of acceptable product formulations containing volatile, low molecular weight amines such as, for example, DEA, DMA and TMA for use in boiler/condensate system corrosion treatment.
• the present invention provides a composition and method for controlling corrosion in boiler/condensate aqueous systems.
• a method of controlling corrosion in boiler/condensate aqueous systems which comprises adding to the system an amount of at least one volatile, flammable, relatively low molecular weight amine by feeding to the system at least one, less volatile, relatively high molecular weight amine which when subjected to conditions of temperature and pressure in the system at least partially decomposes into the at least one relatively low molecular weight amine.
• a method of controlling corrosion in a boiler/condensate aqueous system which comprises treating the system with an amount of a mixture of amines of varying relative molecular weights and volatilities by feeding to the system an amine having a relatively high molecular weight and relatively low volatility which when exposed to conditions of temperature and pressure in the system at least partially decomposes into low molecular weight, higher volatility amines.
• the present invention also provides a corrosion control additive for boiler/condensate aqueous systems which comprises an amount of a mixture of amines of varying relative molecular weights, volatilities and flammabilities, the mixture including at least one relatively high molecular weight amine and the relatively low molecular weight decomposition products thereof.
• the method of the present invention comprises the addition of a relatively high molecular weight amine to the feedwater of a boiler/condensate water system.
• the high molecular weight amine partially decomposes at the conditions of temperature and pressure in the boiler/­condensate steam system, either through hydrolytic cleavage or thermal degradation, to provide more volatile lower molecular weight amines.
• the lower molecular weight amines in combination with undecomposed high molecular weight amine provides corrosion control which is superior to the control from a blend of neutralizing amines from a single amine feed. Such a combination provides corrosion control by amines with a range of distribution ratios.
• the high molecular weight amine is selected so that at the typical temperatures and pressures of the boiler/condensate steam system, at least partial decomposition to lower molecular weight amines such as, for example, monobasic alkyl amines occur.
• lower molecular weight amines such as DMA, TMA and DEA are highly volatile and flammable so their addition to the system feedwater in that form presents problems in handling and shipping.
• the feed of a single, relatively high molecular weight amine which is relatively easy to handle gives rise in the boiler system to a mixture of several amines which cover a broad range of distribution ratios and thus provides effective coverage of even complex boiler/condensate systems.
• the preferred relatively high molecular weight amine of the present invention is dimethylaminopropyl amine or N,N-dimethyl-1,3-propanediamine (DMAPA).
• DMAPA partially decomposes at common boiler conditions to provide monobasic amines such as, for example, dimethyl­amine (DMA) and trimethylamine (TMA). Methylamine and dimethylaminopropanol may also be produced.
• Other relatively high molecular weight amines may also be employed which will partially decompose at common boiler conditions. For example, dimethylaminoethanol (DEAE) will partially decompose at common boiler conditions to ethylaminoethanol (EAE) and diethylamine (DEA).
• the mechanism of decomposition is not clearly understood but it is believed to be a form of hydrolytic cleavage or thermal degradation.
• the inventors of the present invention attempted to produce acceptable boiler water/condensate system control agent formulations containing a DMA and TMA and other volatile low molecular weight amines.
• Research into the effectiveness of TMA as a condensation system corrosion control agent indicated that TMA was 2 to 5 times more volatile than cyclohexylamine.
• Attempts to develop product formulations containing low molecular weight amines which typically have extremely high atmospheric vapour pressures and are highly flammable were unsuccessful. These properties made the use of relatively low molecular weight amines such as, for example, DMA and TMA hazardous and complicated.
• DMA and TMA are hazardous to formulate and store, limiting their usefulness in commercial settings.
• a relatively high molecular weight amine could be formulated which when exposed to typical temperature and pressure conditions in a boiler system would partially decompose into the desirable, relatively volatile low molecular weight amines.
• a relatively high molecular weight amine By providing a relatively high molecular weight amine, only a single amine need be formulated, transported, stored and fed to a boiler system.
• the relatively high molecular weight of the feed amine results in a less volatile amine which is easier to transport, store and to feed.
• Proper formulation of the single relatively high molecular weight amine provides for partial decomposition at standard boiler temperature and pressure ranges.
• the relatively high molecular weight amine is formulated such that upon the partial decomposition relatively low molecular weight amines are formed.
• the single feed amine of the present invention provides for the in situ formation of a mixture of several amines in the boiler/condensate system. These several amines exhibit a broad range of distribution ratios to provide effective corrosion control even in complex boiler/­condensate systems.
• the preferred relatively high molecular weight amine of the present invention is dimethylaminopropyl-amine (DMAPA) or N,N-dimethyl-1,3-­propanediamine. It has been found that the DMAPA is relatively easy to formulate, transport, store and feed as a single amine. When DMAPA is subjected to common boiler temperatures and pressures of from 689.5 to 10342.5 kPa (100 to 1500 psig), the DMAPA will partially decompose. The partial decomposition of DMAP forms DMA and TMA.
• DMAPA dimethylaminopropyl-amine
• TMA TMA
• a research scale, electrically heated test boiler was charged with nitrogen sparged (a mechanical deaeration), demineralized water.
• the water was supplied by high pressure pump to a D-configuration stainless steel boiler having an internal volume of approximately 5 litres.
• Two 4000 watt Incoloy 800 resistance heaters produced a steam rate of approximately 7.7 kg/hr. (17 lbs/hr.) at a steam pressure of 9997.8 kPa (1 ,450 psig) (correspond to a temperature of 312 o C (593 o F)). Cycles of concentration were held at approximately 15 by controlling boiler blowdown rate to 0.50 kg/hr. (1.1 lbs/hr.).
• the saturated steam produced was routed back into the feed tank and mixed with the original feedwater.
• DEAE relatively high molecular weight amine diethylaminoethanol
• EAE volatile, relatively low molecular weight amines ethylaminoethanol
• DEA diethylamine

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)

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Cited By (4)

Citations (3)

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• 1989
  • 1989-04-18 CA CA 597045 patent/CA1339761C/en not_active Expired - Fee Related
  • 1989-04-19 NZ NZ22879789A patent/NZ228797A/en unknown
  • 1989-06-08 AU AU36209/89A patent/AU612491B2/en not_active Expired
  • 1989-06-29 EP EP89306603A patent/EP0351099A1/de not_active Withdrawn

Patent Citations (3)

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