Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-10-12
2001-08-28
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C137S003000, C137S013000, C585S015000, C585S950000
Reexamination Certificate
active
06281274
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for preventing or retarding the formation of gas hydrates, or for reducing the tendency of such hydrates to agglomerate, during the transport of a fluid comprising water and a hydrocarbon through a conduit, and, more particularly, to the addition to the fluid of a single phase composition of a copolymer of vinyl caprolactam and vinyl pyridine, or terpolymers thereof with vinyl pyrrolidone monomer, which is made in a polymerization solvent, and including a carrier solvent different from said polymerization solvent, to inhibit such gas hydrate formation.
2. Description of the Prior Art
It is well known In the art that the formation of gas hydrates in a conduit, e.g. in a pipeline, where an aqueous phase is inherently present, during the transport of liquids such as oil, and of gases, particularly lower hydrocarbons, e.g. methane, ethane, propane, butane, isobutane and natural gas, is a serious problem, especially in areas with a low temperature in the winter season or in the sea. Generally, the ambient temperatures in such areas are so low that gas hydrates are formed in the gas transportation pipeline, due to the inevitable presence of co-produced water therein. Insulation of the pipelines may decrease the opportunity for gas hydrate formation; however, if the field is relatively small and some distance from the production facilities, the cost of providing suitable insulation is too high to make such a field economically attractive. It is also known to add anti-freeze compounds, for example, ethylene glycol or methanol, during transport of such liquids and gases to minimize gas hydrate formation; however, large quantities of these highly flammable compounds are required to be effective which is expensive and unsafe.
Representative of the prior art in this field are U.S. Pat. Nos. 4,915,176; 5,420,370; 5,432,292; and 5,723,524; EPO 0323774A1; EPA 0457375A1; EPA 0526929A1; Can. Pat. Appin. 2,073,577; “Gas Hydrates and Hydrate Prevention”, 73 GPA Annual Convention, pages 85-93; WO 96/08456; WO 96/08636; WO 93/25798; WO 94/12761; WO 95/17579; and WO 95/32356.
A Accordingly, it is an object of this invention to provide an improved composition and method for retarding the formation of gas hydrate in a hydrocarbon gas pipeline.
SUMMARY OF THE INVENTION
What is described herein is a single phase composition for effectively preventing or retarding the formation of gas hydrates, or for reducing the tendency of gas hydrates to agglomerate, during the transport of a fluid comprising water and a hydrocarbon, through a conduit. The composition comprises a copolymer of (a) vinyl caprolactam and (b) vinyl pyridine; and, optionally, a terpolymer with vinyl pyrrolidone, preferably wherein the vinyl pyridine is 2- or 4-vinyl pyridine, optionally quaternized e.g. with a C
1
-C
18
alkyl halide, e.g. iodide, bromide, chloride or fluoride; having a cloud point >10° C., preferably >15°C.
Most preferably, the composition is made in a polymerization solvent which is a glycol ether, containing an alkoxy group having at least 3 carbon atoms, and most preferably, 2-butoxyethanol (BGE), and includes a carrier solvent different from the polymerization solvent, preferably, monoethylene glycol (MEG).
In preferred embodiments of the invention, the vinyl caprolactam monomer comprises about 70-97% of the polymer, and has a molecular weight of about 500 to 2500.
DETAILED DESCRIPTION OF THE INVENTION
The polymer which exhibits advantageous inhibitory characteristics in the composition of the invention is a copolymer of about 70-97% by weight of vinyl caprolactam and 3-25% by eight of vinyl pyridine, preferably 2- and 4-vinyl pyridine, and, optionally, terpolymers with up to 15% by weight of vinyl pyrrolidone.
Preferably vinyl caprolactam comprises 75-95% of the polymer and vinyl pyridine about 5-15%; optionally vinyl pyrrolidone up to 10%.
The polymers herein may be quaternized, suitably with a C
1
-C
18
alkyl halide; e.g. an alkyl iodide.
The composition herein is a single phase system having a cloud point >10° C., preferably >15°C.
The polymer is synthesized from its monomers in a polymerization solvent which preferably is a glycol ether containing an alkoxy group having at least 3 carbon atoms. Representative of such suitable glycol ethers are 2-butoxyethanol (ethylene glycol monobutyl ether); propylene glycol butyl ether; (diethylene glycol) monobutyl ether; and 2-isopropoxy-ethanol. 2-Butoxyethanol (BGE) is most preferred.
The product of the polymerization is a composition of the polymer in the polymerization solvent, e.g. BGE. Generally, the weight ratio of the polymerization solvent to the polymer is about 1:1.5 to 3:3 to 1, preferably about 1.5:1.
The composition is then provided with a suitable carrier solvent such as monoethylene glycol (MEG), methanol, ethanol, propanol, 1,4-butanediol, butanol, pentanol, hexanol, cyclohexyl pyrrolidone, propargyl alcohol, N-methylpyrrolidone and the like, preferably MEG. Preferably the concentration of MEG in the aqueous phase, i.e. under pipeline inhibition conditions, is about 2.5-10 wt. %, preferably 4-5 wt. %.
The thus-formed solution with carrier solvent can be further diluted with a dilution liquid, preferably water or methanol, or mixtures thereof, if desired, to form a use composition for injection into the pipeline. Suitable inhibitor composition to dilution liquid ratio are 0.5:1 to 5:1.
Generally, the polymer solution used in the composition of the invention is present in an amount of about 30 to 60%, preferably 45 to 55%, by weight in admixture with the polymerization solvent. The polymer inhibition concentration in the pipeline, i.e. in the aqueous phase, water being inherently present therein, is about 0.1 to 3%, preferably 0.5-1%, by weight. The solvent* inhibition concentration, accordingly, is about 1 to 9% by weight of the aqueous phase.
REFERENCES:
patent: 5723524 (1998-03-01), Cohen et al.
patent: 6117929 (2000-09-01), Bakeev et al.
patent: 61474 (1976-10-01), None
patent: 1015018 (1980-12-01), None
Bakeev Kirill N.
Chuang Jui-Chang
Drzewinski Michael A.
Graham David E.
Winkler Thomas
Davis William J.
ISP Investments Inc.
Katz Walter
Maue Marilyn J.
Wu David W.
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