Compositions – Humidostatic – water removive – bindive – or emissive
Reexamination Certificate
1999-07-28
2003-01-07
Warden, Jill (Department: 1743)
Compositions
Humidostatic, water removive, bindive, or emissive
C252S389200, C252S389300, C252S389400, C252S389240
Reexamination Certificate
active
06503420
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to anti-corrosion solutions for air dehumidification systems, and in particular to air dehumidification solutions which include a phosphonate anti-corrosion agent.
BACKGROUND OF THE INVENTION
Alkali metal halide solutions and similar solutions, such as calcium chloride solutions, or their mixtures, are widely used in dehumidification processes and systems. In a typical air dehumidification system, humidified air to be conditioned is directed into a cooling system. The humidified air initially enters an air conditioning region where the air is cooled and then contacted with an absorbent solution of alkali metal halide, such as lithium chloride, alkaline earth metal halide, such as calcium chloride, or mixtures thereof. The absorbent solution removes water vapor from humidified stream of air by chemical absorption to provide an air stream with the desired relative humidity. Diluted solution is then routed to a regeneration region where the diluted solution is concentrated and thereafter directed back to the air conditioning region of the system.
Under poor environmental conditions, contaminants, such as carbon dioxide, sulfur oxide compounds (SO
x
), nitric oxides (NO
x
) or acidic vapors, can be present in the air stream to be treated. These conditions can adversely affect, that is reduce the pH of the absorbent solution, resulting in an acidic solution. Under acidic conditions, the absorbent solution becomes increasingly corrosive towards the metallic materials of the machine, such as carbon steel which is used to construct dehumidification equipment.
In current practice in the industry, molybdate, chromate or silicate anions or their salts are used as corrosion inhibiting additives. Because the dehumidification systems are open systems, new environmentally friendly and improved corrosion inhibitors are in demand for these systems. Use of chromate is limited due to environmental concerns. While more environmentally acceptable, simple alkali metal molybdate salts have limited solubility in aerated solutions. Silicates also exhibit limited solubility in this solution.
SUMMARY OF THE INVENTION
The present invention provides absorbent solutions which include one or more phosphonate corrosion inhibiting agents useful for air dehumidification applications. The solutions can offer comparable or improved anti-corrosion protection as compared to conventionally used corrosion inhibitors during repeated dehumidification cycles in closed or open systems. In addition, the solutions of the invention can be more environmentally acceptable. Still further, the phosphonates can be used in relatively small quantities, typically ranging from about 0.0005 to about 0.20 percent by weight and still provide high levels of corrosion protection even for dehumidification solutions having high concentrations of halide.
The solutions of the invention can also include one or more buffering agents to provide pH stable absorbent solutions useful for air dehumidification applications. The absorbent solutions can include inorganic buffers, such as boron-containing buffering agents. The absorbent solutions alternatively can include organic biological buffers, such as amino polyols and/or organic sulfonic acid buffering agents. The absorbent solutions can also include mixtures of the inorganic and/or organic buffering agents. The resultant solutions can exhibit stabilized pH through repeated fluid dehumidification cycles, even for fluid streams contaminated with carbon dioxide, sulfur oxide compounds (SO
x
), nitric oxides (NO
x
), acidic vapors, and the like.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described more fully hereinafter in connection with illustrative embodiments of the invention which are given so that the present disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. However, it is to be understood that this invention may be embodied in many different forms and should not be construed as being limited to the specific embodiments described and illustrated herein. Although specific terms are used in the following description, these terms are merely for purposes of illustration and are not intended to define or limit the scope of the invention.
Exemplary phosphonate corrosion inhibiting agents include without limitation phosphonocarboxylic acids, aminophosphonates, acylation products of phosphorous acid, phosphonoacetic acids, and the like and mixtures thereof.
Exemplary phosphonocarboxylic acids include, for example, compounds of the formula
in which:
R is hydrogen, alkyl, alkenyl, or alkinyl radical having up to 4 carbon atoms, aryl, cycloalkyl or aralkyl radical or the radicals
R′ is hydrogen, alkyl radical having up to four carbon atoms or carboxyl radical; and
X is
Suitable phosphonocarboxylic acids include without limitation &agr;-methylphosphonosuccinic, phosphonosuccinic acid, 1-phosphonopropane-2,3-dicarboxylic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, &agr;-allyl-phosphonosuccinic acid, &agr;-p-chlorophenyl-phosphonosuccinic acid, &agr;-propargyl-phosphonosuccinic acid, &agr;-benzyl-phosphonosuccinic acid, &agr;-cyclohexyl-phosphonosuccinic acid, 2-phosphono-3-&agr;-methyl-carboxymethyl)-hexane-1,2,4-tricarboxylic acid, 2,2-diphosphono-butane-3,4-dicarboxylic acid, and the like and mixtures thereof.
Exemplary aminophosphonates include, for example, compounds having a methyl phosphonic acid or alkali metal or ammonium salt thereof bonded to a nitrogen atom. Such compounds can be generally described by the formula
wherein:
R is
R′ is R or —CH
2
CH
2
OH; and
R″ is R, —CH
2
CH
2
OH or
wherein M is hydrogen, NH
4
, alkali metal, or a combination thereof and n is 1, 2 or 3.
Other exemplary aminophosphates include without limitation amino tri(lower alkyidenephosphonic acids) or their water soluble salts, as defined by the formula
wherein X and Y represent hydrogen or lower alkyl having 1 to 4 carbon atoms. Illustrative compounds include amino tri(methylphosphonic acid) N(CH
2
P(O)(OH)
2
)
3
; amino(triethylidenephosphonic acid) (N((CH
3
)CHP(O)(OH)
2
)
3
; amino tri(isopropylidenephosphonic acid) (N((CH
3
)(CH
3
)CP(O)(OH)
2
)
3
, and the like and mixtures thereof.
Exemplary acylation products of phosphorous acid include, for example, compounds of the formula
wherein R is alkyl having 1 to 5 carbon atoms; alkali metal, ammonium and ethanolamine salts thereof; and mono- and dialkyl esters thereof with methanol, ethanol, propanol or butanol.
Exemplary phosphonates include, but are not limited to, 2-hydroxy-phosphonoacetic acid (HPA), tris-amino phosphonic acid (AMP), 1,1-hydroxyethylidine diphosphonic acid (HEDP), ethylene diamine tetra-methylenephosphonic acid (ENTP), hexamethylene diamine tetra-methylenephosphonic acid (HMTP), diethylene triamine penta-methylenephosphonic acid, 2-phosphono-1,2,4-butanetricarboxylic acid (PBTC), and the like, and mixtures thereof.
These and other phosphonates are well known in the art and are described in U.S. Pat. Nos. 3,214,454; 3,278,446; 3,336,221; 4,026,815; 3,959,360; 3,366,675; and 4,689,200, the entire disclosure of each of which is hereby incorporated by reference. The phosphonates can be present in an amount from about 0.0005 to about 0.20 percent by weight, preferably about 0.0025 to about 0.050 percent by weight, based on the total weight of the solution.
The phosphonate corrosion inhibiting agents are added to absorbent solutions which include at least one alkali metal halide, such as lithium chloride, alkaline earth metal halide, such as calcium chloride, or a mixture thereof, in conventional amounts. An exemplary alkali metal halide solution includes alkali metal halide in an amount from about 10 to about 45 weight percent, preferably about 20 to about 40 weight percent, based on the total weight of the solution.
Advantageously the solution further includes at least one buffering agent to stabilize pH of the dehumidification solution through repeated flu
Cross LaToya I
FMC Corporation
Myers Bigel Sibley & Sajovec P.A.
Warden Jill
LandOfFree
Anti-corrosion solutions for air dehumidification systems does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Anti-corrosion solutions for air dehumidification systems, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Anti-corrosion solutions for air dehumidification systems will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3040760