NATURAL GAS HYDRATE INHIBITOR

Abstract

A natural gas hydrate inhibitor having a structure of formula (1) or formula (2). The inhibitor of the present invention is synthesized on the basis of N-vinylpyrrolidone by introducing a new structural group to achieve terminal modification of the polymer chain, which thereby improves the inhibitory effect.

##STR00001## wherein R is a C.sub.1-8 hydrocarbon group.

Claims

1. A natural gas hydrate inhibitor, having a structure of formula (1) or formula (2): ##STR00003## wherein R is a C.sub.1-8 hydrocarbon group.

2. The natural gas hydrate inhibitor according to claim 1, wherein R is a phenylene group or a 1-methylcyclopentylene group.

3. A method of inhibiting a formation of natural gas hydrates, comprising the step of using the natural gas hydrate inhibitor of claim 1.

4. The method according to claim 3, wherein the natural gas hydrate inhibitor is used at a concentration of 0.5-3 wt % relative to water in a system, a pressure of 6-25 MPa, and a temperature of 2° C. to 4° C.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] The following examples are to further illustrate the present invention, but not to limit the present invention.

Example 1

Preparation of a Novel Inhibitor by Terminal Modification of Poly(N-vinylpyrrolidone) Using Trifluoromethylbenzene

[0016] 352 mg of azobisisobutyronitrile as the initiator and 20.0 g of N-vinylpyrrolidone were added to a three-neck flask provided with a thermometer, a reflux condenser, and a nitrogen gas pipe. The flask was then sealed with rubber plugs, and purged with nitrogen for three times to remove the air from the flask. Under a nitrogen atmosphere, 560 μL of trifluoromethylbenzene and 100 mL of N,N-dimethylformamide were added into the flask using syringes, followed by nitrogen purging for three more times. Then, under the nitrogen atmosphere and a 200 r/min magnetic stirring, the temperature was adjusted to 80° C. to allow reaction for 7 hours. The product was a transparent liquid. After the product was naturally cooled down, a rotary evaporation process was carried out to remove most N,N-dimethylformamide from the product. The product was naturally cooled down again and then added dropwise to 1000 mL of ether (about 0° C.), followed by a suction filtration process to obtain a solid product. The solid product was placed in a vacuum oven to carry out a drying process for 48 hours (at a temperature of about 45° C.) and a water removing process for 1 hour (at a temperature of about 105° C.), and then ground for later use.

Example 2

Preparation of a Novel Inhibitor by Terminal Modification of Poly(N-Vinylpyrrolidone) Using Trifluoroethane

[0017] 352 mg of azobisisobutyronitrile as the initiator and 20.0 g of N-vinylpyrrolidone were added to a three-neck flask provided with a thermometer, a reflux condenser, and a nitrogen gas pipe. The flask was then sealed with rubber plugs, and purged with nitrogen for three times to remove the air from the flask. Under a nitrogen atmosphere, 560 μL of trifluoroethane and 100 mL of N,N-dimethylformamide were added into the flask using syringes, followed by nitrogen purging for three more times. Then, under the nitrogen atmosphere and a 200 r/min magnetic stirring, the temperature was adjusted to 80° C. to allow reaction for 7 hours. The product was a transparent liquid. After the product was naturally cooled down, a rotary evaporation process was carried out to remove most N,N-dimethylformamide from the product. The product was naturally cooled down again and then added dropwise to 1000 mL of ether (about 0° C.), followed by a suction filtration process to obtain a solid product. The solid product was placed in a vacuum oven to carry out a drying process for 48 hours (at a temperature of about 45° C.) and a water removing process for 1 hour (at a temperature of about 105° C.), and then ground for later use.

Example 3

Preparation of a Novel Inhibitor by Terminal Modification of poly(N-vinylpyrrolidone) Using 1-trifluoromethyl-3-methyl-cyclopentane

[0018] 352 mg of azobisisobutyronitrile as the initiator and 20.0 g of N-vinylpyrrolidone were added to a three-neck flask provided with a thermometer, a reflux condenser, and a nitrogen gas pipe. The flask was then sealed with rubber plugs, and purged with nitrogen for three times to remove the air from the flask. Under a nitrogen atmosphere, 560 μL of 1-trifluoromethyl-3-methyl-cyclopentane and 100 mL of N,N-dimethylformamide were added into the flask using syringes, followed by nitrogen purging for three more times. Then, under the nitrogen atmosphere and a 200 r/min magnetic stirring, the temperature was adjusted to 80° C. to allow reaction for 7 hours. The product was a transparent liquid. After the product was naturally cooled down, a rotary evaporation process was carried out to remove most N,N-dimethylformamide from the product. The product was naturally cooled down again and then added dropwise to 1000 mL of ether (about 0° C.), followed by a suction filtration process to obtain a solid product. The solid product was placed in a vacuum oven to carry out a drying process for 48 hours (at a temperature of about 45° C.) and a water removing process for 1 hour (at a temperature of about 105° C.), and then ground for later use.

[0019] The synthesized products were determined by Fourier transform infrared spectroscopy and carbon NMR spectroscopy. Infrared spectra confirmed the expected structures of the inhibitors obtained in Examples 1-3.

Comparative Example 1

Preparation of Polyvinylpyrrolidone

[0020] 352 mg of azobisisobutyronitrile as the initiator and 20.0 g of N-vinylpyrrolidone were added to a three-neck flask provided with a thermometer, a reflux condenser, and a nitrogen gas pipe. The flask was then sealed with rubber plugs, and purged with nitrogen for three times to remove the air from the flask. Under a nitrogen atmosphere, 560 μL of methyl acetate and 100 mL of N,N-dimethylformamide were added into the flask using syringes, followed by nitrogen purging for three more times. Then, under the nitrogen atmosphere and a 200 r/min magnetic stirring, the temperature was adjusted to 80° C. to allow reaction for 7 hours. The product was a transparent liquid. After the product was naturally cooled down, a rotary evaporation process was carried out to remove most N,N-dimethylformamide from the product. The product was naturally cooled down again and then added dropwise to 1000 mL of ether (about 0° C.), followed by a suction filtration process to obtain a solid product. The solid product was placed in a vacuum oven to carry out a drying process for 48 hours (at a temperature of about 45° C.) and a water removing process for 1 hour (at a temperature of about 105° C.), and then ground for later use. The synthesized product was determined to be polyvinylpyrrolidone by Fourier transform infrared spectroscopy and carbon NMR spectroscopy.

Example 4

Assessment of Inhibitory Effect

[0021] The assessment was carried out using a device which mainly comprised: a constant-temperature air bath, a reactor, a magnetic stirrer, a data collecting module, a temperature sensor, and a pressure sensor. The reactor had a capacity of 1000 mL and a maximum allowable pressure of 25 MPa. The pressure sensor was a model CYB-20S with a precision of ±0.025 MPa. The temperature sensor was a model PT100 with a precision of ±0.1° C. The assessment employed a gas mixture of methane (95%) and propane (5%) while the inhibitor was applied at a concentration of 1%. To the reactor was introduced a prepared reaction solution of 197.0±0.5 g, and then a small amount of the gas mixture (below 1 MPa). The temperature of the reactor was then cooled down to a predetermined temperature of 4° C., followed by the introduction of the gas mixture to increase the pressure to about 6 MPa. After the pressure reached 6 MPa, the gas valve of the reactor was turned off and the gas supply was cut off. The magnetic stirrer was turned off to initiate the trial. Data was collected and the reaction was under observation. When the temperature first increased and then decreased to a value maintained stable for a long period, along with a significant decrease of pressure, the trial was terminated. The inhibitory effect of different inhibitors was determined by considering the induction times of hydrate formation.

[0022] In the assessment with the above device, polyvinylpyrrolidone (a weight average molecular weight of about 900000 Da) exhibited an inhibitory time of 480 minutes (at a temperature of 4° C. and a pressure of 6 MPa, wherein a mass concentration of polyvinylpyrrolidone in the aqueous solution of polyvinylpyrrolidone was 1%); an inhibitory time of 180 minutes at a temperature of 4° C., a pressure of 15 MPa, and a mass concentration of 3%; and an inhibitory time of 15 minutes at a temperature of 2° C., a pressure of 25 MPa, and a mass concentration of 0.5%.

[0023] The natural gas hydrate inhibitors of Examples 1-3 and the polyvinylpyrrolidone of Comparative Example 1 were tested for their inhibitory effect using the above device, with the mass concentrations indicated in Table 1. Results were as shown in Table 1.

TABLE-US-00001 TABLE 1 Inhibitory effect of different inhibitors Concentration Inhibitory time (wt %) Conditions (min) Example 1 0.5 275.15K, 25 MPa 80 1 277.15K, 6 MPa 1050 3 277.15K, 15 MPa 820 Example 2 0.5 275.15K, 25 MPa 30 1 277.15K, 6 MPa 850 3 277.15K, 15 MPa 230 Example 3 0.5 275.15K, 25 MPa 50 1 277.15K, 6 MPa 1200 3 277.15K, 15 MPa 560 Comparative 0.5 275.15K, 25 MPa 15 Example 1 1 277.15K, 6 MPa 480 3 277.15K, 15 MPa 180

[0024] The above examples are preferred embodiments of the present invention, but the present invention is not limited by the examples. Any other changes, modifications, substitutions, combinations, or simplifications, made without departing from the spirit and principle of the present invention, should fall within the scope of the present invention.