The method for measuring absorption phase density of the Adsorbate Gas on adsorbate
Technical field
The present invention relates to a kind of methods of absorption phase density of measurement Adsorbate Gas on adsorbate, belong to shale gas and survey
Spy field.
Background technique
Domestic and foreign scholars (J.E.Fitzgerald et when the absorption property to coal measures mud stone and shale is studied
al,2005;Katsuyuki Murata et al,2001;Sommen J et al,1995;Moffat D H et al,
1955;Thomas Rupple et al,1974;Yee D et al,1994;Berhard M.Krooss,2008,2010,
2013;Cui Yongjun, 1999,2003;Zhou Li, 2000,2001) discovery, shale adsorbed methane is being tested using volumetric method
When, the presence for adsorbing phase volume will reduce the volume of free gas in sample cell, and then to the test result of shale adsorption capacity
It has an impact.However absorption phase is had ignored in " the high pressure isothermal adsorption test method volumetric method of GB/T 19560-2004 coal "
Volume exists, this will lead to the evaluation for adsorption capacity, and there are relatively large deviations.For such problems, domestic and foreign scholars
(Philippe Weniger et al,2012;YvesGensterblum et al,2013;MatusGasprik et al,
2014;Dongyong Li et al,2010;Thomas Rupple et al,1974;Yee D et al,1994;Cui Yongjun,
1999,2003;Zhou Li, 2000,2001) attempt to correct absorption phase volume from different angles to produced by adsorbed gas aptitude tests
Influence.However no matter influence to be corrected on caused by absorption phase volume in which way, conservation of matter original is followed at last
Reason, therefore the determination for adsorbing phase volume and density is the problem of can not avoiding, and the accuracy for adsorbing phase volume and density will be straight
Connect influence correction result.
In previous research, absorption phase density is usually assumed to be definite value, currently existing scheme one, two and three as described below.
However, methane molecule adsorbs close in illite crack type gap when different pressures can be observed by molecular simulation means
Degree distribution (as shown in Figure 1).As shown in Figure 1, absorption phase density is with pressure change, and not therefore definite value will adsorb phase in the past
The way that density is assumed to be definite value is obvious unreasonable.
Scheme one: theoretical hypothesis method, Yee D. (1994) think when temperature be higher than critical-temperature when (under normal conditions),
The limiting density that phase density is equal to gas compression is adsorbed, is 0.375g/cm with the absorption phase density of this inference methane3。Arri
(1992) assume that absorption phase density is the fluid density under atmospheric boiling point, be 0.421g/ with the absorption phase density of this inference methane
cm3.It is about 0.59g/cm that KatsuyukiMurayta (2001), which obtains methane adsorption phase density using empirical equation,3.Its its disadvantage
It is that will adsorb phase density as definite value, does not consider the influence that the conditions such as temperature, pressure generate.
Scheme two: German scholar Berhard M.Krooss and its team (2008,2010,2012,2013,2014) will
Gibbs about absorption definition in conjunction with langmuir equation, it is assumed that absorption phase density be definite value, will absorption phase density as to
Determine parameter, absorption phase density of the methane and carbon dioxide on coal measures mud stone and shale is evaluated from mathematical optimization angle.
The disadvantage is that assuming that absorption phase density is definite value, the influence of pressure is not considered, is runed counter to actual conditions.
Scheme three: similar, domestic scholars Zhou Li (2000,2001) is by Gibbs to the definition and D-A equation phase of absorption
In conjunction with, it is assumed that absorption phase density derives absolute adsorption amount model for definite value and as undetermined coefficient, carries out to adsorptivity density
Optimization is sought.The disadvantage is that assuming that absorption phase density is definite value, the influence of pressure is not considered, is runed counter to actual conditions.
Summary of the invention
The object of the present invention is to provide a kind of method of absorption phase density of measurement Adsorbate Gas on adsorbate, this hairs
It is bright to establish isotherm adsorption model based on adsorption mechanism, and then obtain absorption phase volume and adsorb phase density.
The method of absorption phase density of the measurement Adsorbate Gas provided by the present invention on adsorbate, including walk as follows
It is rapid:
1) excess adsorption and body phase density of the measurement Adsorbate Gas under at least three kinds of different pressures;
2) it according to the excess adsorption and the body phase density of modified isotherm adsorption model and step 1) measurement, obtains
To absorption phase volume;
3) according to modified isotherm adsorption model and isotherm adsorption model, the Adsorbate Gas is obtained in the adsorbate
On absolute adsorption amount;
4) absorption phase density of the Adsorbate Gas on the adsorbate is obtained according to formula (1), be denoted as
ρadsorption phase, unit g/cm3;
In formula (1), PSTPIndicate the pressure of standard state, unit MPa, TSTPIndicate that the temperature of standard state, unit are
K, ZSTPIndicating the compressibility factor of Adsorbate Gas in normal conditions, R indicates gas constant, be 8.314J/ (molK),
Vadsorption phaseIndicate absorption phase volume, unit cm3, VabsoluteIndicate the volume of absolute adsorption amount in normal conditions,
Unit is cm3/ g, M indicate the molal weight of the Adsorbate Gas, unit g/mol.
In above-mentioned method, the Adsorbate Gas is methane.
In above-mentioned method, the adsorbate is shale, and the shale is illite.
In above-mentioned method, in step 1), using the volumetric method adsorption isotherm experiment (high pressure of GB/T 19560-2008 coal
Isothermal adsorption test method) the measurement excess adsorption;According to temperature and pressure, by state equation (such as PR equation, specifically
With reference to Peng.D.Y.and Robinson.D.B.A New Two-Constant Equation of State, 1976) it calculates
The body phase density is sought, or is checked in by NIST (National Institute of Standards and Technology)
The body phase density.
In above-mentioned method, in step 2), shown in the modified isotherm adsorption model such as formula (2),
In formula (2), VLIndicate Langmiur volume, unit cm3/ g, PLIndicate Langmiur pressure, unit MPa, P
Indicate experimental pressure corresponding to upper different data point, unit MPa, ρ in adsorption isothermal curvebulkIndicate body phase density, it is single
Position is g/cm3, Vadsorption phaseIndicate absorption phase volume, unit cm3, MadsorbateIndicate mole of the Adsorbate Gas
Quality, unit g/mol, PSTPIndicate the pressure of standard state, TSTPIndicate the temperature of standard state, ZSTPIndicate that adsorbate exists
Compressibility factor under standard state, R indicate gas constant, are 8.314J/ (molK), VexcessIndicate the described of unit mass
The volume of excess adsorption corresponding to adsorbate in normal conditions, unit cm3/g。
In above-mentioned method, in step 3), shown in the isotherm adsorption model such as formula (3),
In formula (3), VabsoluteIndicate absolute adsorption amount corresponding to the adsorbate of unit mass in normal conditions
Volume, unit cm3/ g, VLIndicate Langmiur volume, unit cm3/ g, PLIndicate that Langmiur pressure, unit are
MPa, P indicate experimental pressure corresponding to different data point, unit MPa in adsorption isothermal curve.
The method of the present invention has the advantages that
This method method directly carries out on the basis of former isothermal adsorption test data, and scheme is simple and easy, easy to spread.
By molecular simulation to the research of absorption behavior it is found that the assumed condition of the method for the present invention is more reasonable, in terms of reasonability, hence it is evident that
Better than traditional prioritization scheme.From the point of view of calculated result, the method for the present invention coincide more to the calculating of absorption phase density and actual conditions
Good, precision is higher, hence it is evident that is better than traditional scheme.
Detailed description of the invention
Fig. 1 is methane gas density profile in illite crack type hole that aperture is 2nm.
Fig. 2 is the flow chart of the method for the present invention.
Fig. 3 is excess adsorption thermoisopleth.
Fig. 4 is the excess adsorption and original analog comparative result figure that the method for the present invention obtains.
Fig. 5 is to adsorb phase density with the variation diagram of pressure.
Specific embodiment
Experimental method used in following embodiments is conventional method unless otherwise specified.
The materials, reagents and the like used in the following examples is commercially available unless otherwise specified.
Absorption phase density of the methane on illite is measured according to flow chart shown in Fig. 2.
Step 1: model foundation
The Adsorption Models such as Langmiur, DR are for absolute adsorption amount, however adsorption isotherm experiment and molecular simulation
The adsorbance that means obtain is excess adsorption.Therefore, it is being optimized to excess adsorption using Adsorption Model
Before, first model is modified.
From the angle of intermolecular interaction, the interaction between gas molecule and adsorbent surface is with the two
The increase of distance and reduce, until disappear.By Van der Waals force and the Coulomb force mechanism of action it is found that phase between gas-adsorbent surface
Interaction is unrelated with the temperature and pressure of system, only related with gas-adsorbent distance between the surface.Therefore, for a certain system
For, adsorbent surface is a definite value to the sphere of action of gas molecule, is not changed with the temperature and pressure of system.The effect
Range is to adsorb phase volume VadsorptionPhase。
The present embodiment is modified model by taking Langmiur model as an example.
Excess adsorption is defined as total gas flow (absolute adsorption amount) in absorption phase and subtracts to deposit in absorption phase with body phase density
Gas flow:
Vexcess=Vabsolute-Vbulk(a)
In formula, Vexcess(cm3/ g STP) be excess adsorption corresponding to unit mass adsorption agent in normal conditions
Volume, Vabsolute(cm3/ g STP) it is the volume of absolute adsorption amount in normal conditions corresponding to the agent of unit mass adsorption,
Vbulk(cm3/ g STP) it is with gas flow existing for body phase density in absorption phase corresponding to the agent of unit mass adsorption in standard shape
Volume under state.
The archetype of Langmiur are as follows:
Formula (a) is combined with formula (3), then revised Langmiur isotherm adsorption model can be obtained:
In formula, VL(cm3/ g) it is Langmiur volume, PLIt (MPa) is Langmiur pressure.
In formula, ρbulk(g/cm3) it is body phase density, Vadsorption phase(cm3) it is absorption phase volume, Madsorbate(g/
It mol is) molal weight of Adsorbate Gas, ZSTPFor the compressibility factor of Adsorbate Gas in normal conditions, R (8.314J/
It (molK)) is gas constant, TSTP(273.15K) is the temperature of standard state, PSTP(0.101MPa) is the pressure of standard state
Power.Wherein, ρbulkAnd ZSTPIt can be by the equation of gas state, NIST (National Institute of Standards and
Technology) or the approach such as molecular simulation obtain.
Step 2: calculating absorption phase volume
Adsorption isotherm experiment can only obtain excess adsorption, be unable to get the information such as absorption phase volume and absorption phase density.
Therefore, in order to verify the accuracy of the method for the present invention, the method for the present invention is applied by taking the result of molecular simulation as an example.
Potassium illite structure, molecular formula KAl are represented using pyrophyllite-1Tc4(Si7Al)O20(OH)4 1-3, each
Unit cell units have a silicon atom to be replaced by aluminium atom, and generated charge is balanced by potassium ion.With (0 0 1) of unit cell units
Face is inner surface, and establishing aperture is 2nm analogue unit, and each analogue unit is made of 5 × 3 × 1 structure cell.Utilize Clayff4,
Illite structure is described in the field of force, utilizes OPLS5Methane united stom model is described in the field of force.According to GCMC method
Absorption behavior to methane at 90 DEG C on illite surface carries out molecular simulation, obtains excess adsorption (as shown in table 1).It establishes
3nm × 3nm × 3nm empty packet, and methane united stom model is described with the field of force OPLS, using GCMC method to 90 DEG C
When load number of the methane in empty packet simulated, obtain the body phase density (as shown in table 1) of methane gas under different pressures.
Methane excess adsorption and body phase density in 1 aperture illite 2nm of table
P(MPa) |
Vexcess(cm3/g STP) |
Bulk Density(g/cm3) |
0.001 |
0.004850338 |
5.34443E-06 |
1 |
4.698618525 |
0.005359294 |
1.51 |
6.966251072 |
0.008140976 |
3.07 |
13.548311 |
0.016579137 |
6.27 |
24.61134366 |
0.034220358 |
10 |
30.89261022 |
0.055216582 |
13.05 |
35.40686447 |
0.072059194 |
16.57 |
37.85014498 |
0.090285288 |
23.68 |
36.70327158 |
0.125629946 |
27.2 |
34.77231219 |
0.140870379 |
30 |
32.92362587 |
0.153196569 |
34.02 |
30.53109143 |
0.167541041 |
For methane, ZSTPIt is 0.9976, MadsorbateFor 16g/mol.Excess adsorption and body phase density are substituted into
Formula (2), V in formulaL、PLAnd Vadsorption phaseNumber for undetermined coefficient, undetermined coefficient is less than equation number, is overdetermined equation,
Equation is optimized, V can be obtainedLFor 366.67cm3/ g, PLFor 35.59MPa, Vadsorption phaseFor 0.63cm3/
g.Model calculates gained excess adsorption and molecular simulation result is identical preferable (as shown in Figure 3) (as shown in table 1).By the two line
Sexual intercourse can be seen that (as shown in Figure 4) that the coefficient of X is 0.9994, illustrate the model calculation of the present invention and original analog knot
Fruit is very close, R2It is 0.9971, illustrates that the two correlation is fabulous.
Step 3: calculating absolute adsorption amount
In VLAnd PLIn the case where having obtained, absolute adsorption amount is sought according to formula (2), result is as shown in figure 3, absolutely
Adsorbance differs greatly with excess adsorption.
Step 4: absorption phase density is sought
In the case where absolute adsorption amount has been found out, phase density ρ is adsorbedadsorption phaseIt can be obtained by following formula:
Meanwhile it is improved based on the hypothesis that absorption phase density is definite value using Berhard M.Krooss team
Langmiur model (nex=nL·p/(PL+p)·(1-(ρbulk/ρadsorption phase), nexFor excess adsorption (mol/g), nL
For Langmiur maximal absorptive capacity (mol/g), PLIt is the experimental pressure in adsorption isothermal curve for Langmiur pressure (MPa), P
(MPa), ρbulkFor body phase density (g/cm3), ρadsorption phaseTo adsorb phase density (g/cm3)) calculated (such as document
High-pressure methane and carbon dioxide sorption on coal and shale samples
From the Paran á Basin, Brazil), obtain fixed absorption phase density, and with the obtained absorption of the method for the present invention
Phase density compares (as shown in Figure 5).
As seen from Figure 5, the obtained absorption phase density of the method for the present invention is gradually increased with pressure, with molecular simulation
The phenomenon that means are observed is consistent, and obtained absorption phase density matches with analog result.In contrast, early stage is false
If it is very big for the obtained absorption phase density of model and actual value deviation of definite value to adsorb phase density.The present invention from theoretical side more
Adduction reason, from the point of view of results of calculation, accuracy is much higher than early stage model, has wide application prospect.