Method for obtaining methane clath rates and recovering methane from methane clath rates

Abstract

The method of obtaining methane clathrates consists in the fact that pure methane or methane in a gas mixture not containing hydrocarbons other than methane in amounts not exceeding 1% is contacted with a mixture of alkanes from C7 to C16 and most preferably light paraffin oil containing alkanes from C10 to C14, at a temperature of 5 to 20° C. and absolute pressure above 1 bar, until the solvent is fully saturated.

Claims

1. A method of obtaining methane clathrates characterized in that pure methane or methane in a mixture of inert gases in amounts not exceeding 1% is contacted with a mixture of alkanes from C7 to C16 and most preferably with light paraffin oil at a temperature of 5 to 20° C. at absolute pressure above 1 bar, until the solvent is fully saturated.

2. The method according to claim 1, characterized in that the gas mixture comprises Ar, Kr, N.sub.2, O.sub.2, CO.sub.2, H.sub.2S, CO, H.sub.2.

3. The method according to claim 1, characterized in that the reaction takes place at an absolute pressure of 1.1 bar.

4. The method according to claim 1, characterized in that the mixture of alkanes comprises C10 to C14 alkanes.

5. A method of obtaining methane clathrates and recovery (desorption) of methane from clathrates, characterized in that pure methane or methane in a mixture of inert gases in amounts not exceeding 1% is contacted with a mixture of alkanes from C7 to C16 and most preferably light paraffin oil at a temperature of 5 to 20° C. at absolute pressure above 1 bar, until the solvent is fully saturated, the clathrates thus obtained are heated at a temperature above 20° C. and methane is released, and the solvent is preferably completely recycled.

6. The method according to claim 5, characterized in that the gas or inert gas mixture comprises Ar, Kr, N2, O2, CO2, H2S, CO, H2.

7. The method according to claim 5, characterized in that the reaction takes place at an absolute pressure of 1.1 bar.

8. The method according to claim 5, characterized in that the mixture of alkanes comprises C9 to C14 alkanes.

9. The method according to claim 5, characterized in that the temperature is increased to 70° C.

10. The method according to claim 5, characterized in that the decomposition temperature is controlled by pressure.

11. The method according to claim 9, characterized in that the decomposition temperature is controlled by pressure.

Description

EXAMPLE 1

[0028] Obtaining methane clathrates through its absorption in light paraffin oil (liquid paraffin).

[0029] Into the bubble absorber (“perlage”) with a capacity of 170 dm.sup.3 light paraffin oil containing C10 to C14 alkanes with a boiling point of +280° C. was introduced. The process was carried out in the temperature range of 17-20° C., with an overpressure of 0.1 bar.

[0030] In exhaust gas system from the absorber a methane sensor reacting to methane concentration above 4 ppm was placed. A mixture of methane and nitrogen gas was used for absorption in a volume ratio of 1:1 (0.6 m.sup.3hr CH.sub.4+0.6 m.sup.3/hr N.sub.2) with a total flow through the absorber 1.2 m.sup.3/hr. Gases were fed from gas bottle using mass flow regulators scaled for nitrogen and methane flow. After the process, the solvent volume increased to approx. 210 dm.sup.3, i.e. by 40 dm.sup.3. During the tests, no methane exceedance was observed in the waste gases above the sensitivity of the methane sensor used. Thus, the total methane absorption in the solvent was assumed. After the process was completed, as shown by the calculations, light paraffin oil should contain 14.512% by weight of methane. Calculations of the methane content in the solvent were made for the following assumptions:

[0031] d.sub.s (paraffin oil)=0.860 g/cm.sup.3—according to the manufacturer—measured at 20° C. −0.891 g/cm.sup.3. The measured value was taken for calculations, i.e. d.sub.s=0.891 g/cm.sup.3.

[0032] methane mole −16 g

[0033] Avogadro constant −1 mole contained in 22.4 dm.sup.3.

[0034] X.sub.Mole=36/0,0224=1607,142857

[0035] X.sub.kg=(X.sub.Mole*16)/1000=25,71428 kg

[0036] M.sub.s=170*d.sub.s=151,47 kg

[0037] X.sub.CH4=(X.sub.kg/(M.sub.s+X.sub.kg))*100%=14,512%

[0038] Solvent—light paraffin oil was tested after the process by the FTIR method (FTIR Nicolet iS50 with ATR attachment) and the presence of metastable sl methane clathrates was found. The content of alkanes in the solvant—light paraffin oil was also tested chromatographically using GC Shimadzu GC2010 plus with a plasma detector, ZB-1 capillary column 60 m long (manufacturer Shimadzu) using He (purity 99.9999%) as the carrier gas. The BID detector used for testing guaranteed detection of all gases absorbed in the solvent. The sensitivity of the BID detector working on helium as the carrier gas (99.9999% purity) relative to nitrogen and methane was below 1 ppm. Injection of samples on the chromatographic column was carried out by the automatic method (AOC 20i automatic injection column)—sample size—1μl—dispenser temperature 280° C. Analysis time with ramping up to 300° C.—detector 310° C.—45 minutes. Samples were diluted with n-hexane in a 1:1 ratio with n-hexane, thus constituting an internal standard. The concentration of methane contained in the sample was calculated using previously determined correction factors resulting from the detector characteristics for the hydrocarbons tested—methane and n-hexane, where the correction factor n-hexane in this case was assumed to be f.sub.1=1.0 and thus the correction factor for methane f.sub.2=9.5. Mathematical statistical analysis of the variability of the results of the determinations was based on the change in the size of the n-hexane peak area and the calculations carried out by the method of least squares, i.e. the Student's t-distribution. It was found that the average weight concentration of methane in the tested samples was X.sub.CH4=13.791±1.034%. The designated uncertainty area covers the calculation result. At the same time, chromatographic studies showed no change in the composition of paraffin oil used for absorption—called solvent.

[0039] The conditions for conducting the process of obtaining clathrates depend on the type of use of the method of contacting the solvent with methane or a mixture of methane together with gases not containing hydrocarbons other than methane. Thus, the contact time of the solvent with the gas or gas mixture also depends on the contacting method used. Any device can be used to contact the solvent with methane.

EXAMPLE 2

[0040] The invention also relates to the recovery of methane from clathrates obtained by dissolving methane in paraffins.

[0041] The clathrates obtained by the method of the first example were heated at 70° C. in a desorber, which caused the release of methane previously absorbed in the solvent, after which the separated methane was sent to the furnace in which it was used as heating fuel and the light paraffin oil used after cooling to 20° C. was returned whole to be recycled again.