Method for calculating contribution coefficient of different pore diameters to VOCs adsorption capacity under different partial pressures

Abstract

The invention relates to the technical field of waste gas treatment, and discloses a method for calculating contribution coefficients of different pore diameters to VOCs (volatile organic compounds) adsorption capacity under different partial pressures, which comprises the following steps of: using two or more porous materials with concentrated pore diameter distribution as model adsorption materials; the change trend of the VOCs adsorption isotherm in different pressure areas is associated with the pore size of the material to obtain a regularity equation that the critical pore size of filling type adsorption and covering type adsorption changes along with pressure under corresponding adsorption conditions. According to the critical pore channel size equation and in combination with an influence rule of pore size difference and partial pressure change on a VOCs adsorption isotherm, contribution coefficients of different pore sizes in the adsorbent on filling type adsorption and covering type adsorption of VOCs adsorption and a regularity equation of the change along with the partial pressure are obtained respectively. The method can effectively guide the type selection of the adsorbent, and provides a reference basis for the development of efficient adsorption materials and technologies.

Description

Technical Field

[0001] The present invention relates to the technical field of waste gas treatment, and in particular to a method for calculating contribution coefficients of different pore diameters to VOCs adsorption under different partial pressures. Background Art

[0002] The emission of volatile organic compounds (VOCs) not only causes serious pollution to the environment, but also causes direct or indirect harm to human health. At present, the end-of-pipe treatment technologies of VOCs mainly include: catalytic combustion, biodegradation, low-temperature plasma, photocatalytic degradation, adsorption recovery, condensation and membrane separation. Among them, the adsorption method has the advantages of easy operation, high purification efficiency, wide application range, and the ability to be combined with other treatment technologies. It is one of the most widely used VOCs control technologies. The development of adsorption materials is an important foundation for the development of VOCs adsorption technology. The selection of adsorption materials needs to comprehensively consider many factors such as the structural properties of the materials, cost, adsorption amount, adsorption rate, regeneration performance and its matching relationship with the adsorbed VOCs waste gas.

[0003] Although adsorption technology has been widely used to treat VOCs, there are still many unresolved scientific problems in the study of the adsorption process of VOCs, such as the unclear precise matching relationship between the pore size of the adsorbent material and the amount of VOCs adsorbed. This is mainly due to the microscopic complexity of the adsorption process. The adsorption of VOCs by the adsorbent material will be affected by many factors. First, the properties of the adsorbent material, such as pore structure and surface properties, are the main factors affecting adsorption; secondly, there are many types of VOCs, and their physical and chemical properties (such as polarity, boiling point, molecular weight, etc.) vary greatly, resulting in the matching relationship between pore size and adsorption capacity during the adsorption process cannot be generalized; in addition, the temperature, humidity, and coexisting pollutants of the environment will also have an important impact on the adsorption process.

[0004] Although there are many factors that affect the adsorption process of VOCs, overall, it can be summarized as the matching relationship between the structural properties of the adsorbent and the physicochemical properties of the adsorbate under specific conditions. Increasing the pore volume or specific surface area under the pore size suitable for VOCs adsorption and improving the utilization rate of the pore volume or specific surface area of ​​the adsorbent material are the keys to improving the adsorption capacity of VOCs. Therefore, the key to the research is to study the effect of specific pore size on the adsorption capacity of volatile organic compounds. Existing research only provides a certain correlation trend, rather than an accurate relationship between pore size and adsorption capacity.

[0005] In current research, most of the influencing factors are mixed together, and only some trends such as positive or negative correlation between adsorption amount and parameters such as specific surface area, average pore size, and porosity can be obtained in a series of samples by the researchers themselves. For example, it is generally believed that the larger the specific surface area, the higher the adsorption capacity for VOCs. Micropores can provide stronger adsorption but also make desorption difficult. In general, these rules are generally general and insufficient to guide the development of VOCs adsorption process and adsorption materials. Further optimization of the pore structure of the adsorption material lacks a quantitative reference basis between pore size and adsorption performance. In practical applications, a lot of attempts and explorations are still needed to find possible more suitable adsorption materials.

[0006] At present, the research on the precise matching relationship between pore size and adsorption amount in the process of VOCs adsorption is still insufficient, which limits the optimization of the pore structure of the adsorption material and the development of adsorption technology. If there is a method for the contribution coefficient of pore size to VOCs adsorption, which can obtain the contribution coefficient of adsorbent pore size to VOCs adsorption under different partial pressures, it will provide a favorable reference for the development of adsorption technology and adsorption materials. Summary of the invention

[0007] Based on the above technical issues, it is necessary to explore the precise matching relationship between the amount of VOCs adsorbed and the pore size of the adsorbent from a new perspective. Volumetric filling adsorption is a common phenomenon in gas adsorption and is likely to be a breakthrough point in the exploration of the contribution coefficient of adsorption capacity. Based on the Kelvin formula, in nanopores close to the molecular scale, due to the limitation of the pore wall, the saturated vapor pressure on the concave liquid surface is less than the saturated vapor pressure on the flat liquid surface. Therefore, VOCs in the nanopores can condense at a partial pressure far below the saturated vapor pressure, forming volumetric filling adsorption in pores smaller than a specific pore size. Therefore, there is a critical pore size, which is the dividing size between volumetric filling adsorption and surface coverage adsorption. Therefore, the exploration of this critical pore size can provide a starting point for quantifying the contribution coefficient of pores of different pore sizes to the adsorption capacity of VOCs.

[0008] For VOCs adsorption under a specific pressure, after reaching adsorption equilibrium, it can be divided into two categories: volume filling adsorption and surface coverage adsorption. Therefore, for volume filling adsorption, the adsorption amount is related to the volume of pores filled with liquid-like VOCs, where the density of the adsorbed adsorbate is close to the density of the macroscopic liquid at the corresponding temperature. The pores that do not undergo volume filling adsorption (larger than the critical pore size) are surface coverage mechanisms for single-layer or multi-layer adsorption, and the adsorption amount of surface coverage adsorption is related to the corresponding specific surface area. Based on different adsorption types, it is very likely to calculate the contribution coefficients of different pore sizes to VOCs adsorption under specific partial pressures. Further combined with the law of changes in the critical pore size of filling adsorption with pressure, it will be possible to obtain the law of changes in the contribution coefficients of different pore sizes to VOCs adsorption with partial pressure. A method for calculating the contribution coefficients of different pore sizes to VOCs adsorption under different partial pressures is obtained.

[0009] Based on the above analysis, the present invention proposes a method for calculating the contribution coefficients of different pore sizes to the adsorption of VOCs under different partial pressures, and obtains the trend curves of the filling adsorption contribution coefficient and the covering adsorption contribution coefficient of each adsorbent material with pressure changes, and a unique equation. According to the contribution coefficients of different pore sizes to the adsorption of VOCs under specific partial pressures, it can effectively guide the selection of adsorbents, provide a reference basis for the development of adsorbent materials with special properties for the adsorption of specific types and concentrations of VOCs, and promote the development and optimization of adsorbent materials and technologies.

[0010] To achieve the above object, the present invention provides a method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures, comprising the following steps:

[0011] S1. Provide 2 or more porous materials with concentrated pore size distribution as model adsorption materials, test pore structure parameters, and test the adsorption isotherms of specific VOCs of the adsorption materials at specific adsorption temperatures;

[0012] S2. Obtain the pressure range corresponding to the filling adsorption of each model adsorption material according to the adsorption isotherm, and take the middle value of the pressure range as the critical pressure point P C The critical pressure point corresponds to the middle value of the pore size distribution of the adsorbent material, and the pore size is taken as the pressure point P C The critical pore size D for filling adsorption to occur C ;

[0013] S3, according to the pressure point P when the two or more adsorbent materials with concentrated pore size distribution undergo filling adsorption C and the corresponding critical pore size D C , the pressure point P is obtained by linear fitting method Cand critical pore size D C The linear relationship curve between them is formula 1:

[0014] D C =k×P C +D0 Formula 1;

[0015] In formula 1,

[0016] D C The pressure point P C Critical pore size for filling adsorption to occur under , nm;

[0017] P C For an aperture of D C The critical pressure corresponding to the filling adsorption in the pores, mbar;

[0018] k is the slope of the linear relationship between critical pore size and pressure, nm / mbar;

[0019] D0 is the linear relationship when the pressure approaches 0 mbar. C The value of , nm;

[0020] S4. According to the adsorption isotherms of the two or more adsorbent materials with concentrated pore size distribution at the same temperature, the adsorption amount at each pressure point on the adsorption isotherm is divided by the density at the corresponding temperature and the total pore volume of each adsorbent material, respectively, to obtain the trend curve of the filling adsorption coefficient (a=Q / V / ρ) of each adsorbent material with pressure change, and according to the high-pressure area after the filling adsorption in the adsorption isotherm is formed, combined with the influence of the pore size difference between different adsorbent materials on the curve, the calculation formula of the contribution coefficient (a) of the filling adsorption is obtained:

[0021] a=f(D A ,P)=(a0+a1×(D A -D0)+a2×P) Formula 2;

[0022] In formula 2, f(D A ,P) represents the coefficient of filling adsorption a is the pore size D A and pressure P;

[0023] a0 is the part of coefficient a that is not affected by changes in aperture size and pressure, and has no unit;

[0024] a1 is the coefficient of the part of coefficient a affected by the difference in aperture size, nm -1 ;

[0025] a2 is the coefficient of the part of coefficient a affected by pressure change, mbar -1 ;

[0026] D0 is the D when the pressure approaches 0 mbar in the linear relationship between critical pore size and critical pressure. C Value, nm;

[0027] D A is the average pore size of the pores where filling adsorption occurs, nm;

[0028] D A =4V C / (SS C ), S is the total specific surface area, m 2 / g;

[0029] V C is the pore volume below the critical pore size, cm 3 / g;

[0030] S C is the specific surface area of ​​pores above the critical pore size, m 2 / g;

[0031] P is any pressure point on the adsorption isotherm (mbar);

[0032] S5. According to the adsorption isotherms of the two or more adsorbent materials with concentrated pore size distribution at the same temperature, the adsorption amount at each pressure point on the adsorption isotherm is divided by the total specific surface area of ​​each adsorbent material to obtain the trend curve of the covering adsorption coefficient (b=Q / S) of each adsorbent material with pressure change. According to the low-pressure area gradually formed by the covering adsorption in the adsorption isotherm, combined with the influence of the pore size difference between different adsorbent materials on the curve, the calculation formula of the contribution coefficient (b) of the covering adsorption is obtained:

[0033] b=g(D AS ,P)=(b1+b2×P) Formula 3;

[0034] In formula 3,

[0035] g(D As ,P) represents the coefficient of filling adsorption a is the pore size D AS and pressure P;

[0036] b1 is the coefficient of the part of coefficient b that is affected by the difference in pore size, g / m 2 ;

[0037] b2 is the coefficient of the part of coefficient b that is affected by pressure change and pore size, g / m 2 / mbar;

[0038] P is any pressure point on the adsorption isotherm (mbar);

[0039] D AS is the average pore size of the pores where covering adsorption occurs, nm;

[0040] D AS =4(VV C ) / S C , V is the total pore volume, m 3 / g;

[0041] V C is the pore volume below the critical pore size, cm 3 / g;

[0042] S C is the specific surface area of ​​pores above the critical pore size, m 2 / g;

[0043] P is any pressure point on the adsorption isotherm (mbar);

[0044] S6. Since filling adsorption and covering adsorption do not occur simultaneously in the same pore size, when the pressure is sufficient to cause volume filling adsorption, the filling adsorption coefficient (a) is applicable, and when the pressure is insufficient to cause volume filling adsorption, the covering adsorption coefficient (b) of a specific size is applicable. Under a specific pressure, which adsorption model coefficient (a or b) should be used for a specific pore size depends on the size of the pore size relative to the critical pore size (the dividing point between volume filling adsorption and surface covering adsorption) at pressure P. The critical pore size at pressure P can be determined according to the equation (D C =k×P+D0) to obtain a one-to-one corresponding value. When the pore size is smaller than the critical pore size, filling adsorption occurs, and when the pore size is larger than the critical pore size, covering adsorption occurs.

[0045] Preferably, the number of the adsorption materials having concentrated pore size distribution is ≥2.

[0046] Preferably, the step S1 further includes:

[0047] Using a commercial specific surface area and pore structure analyzer to test, the pore structure parameters of the adsorbent material are obtained through the DFT cylindrical pore calculation model, and the pore structure parameters include pore size distribution, pore volume within a specific pore size range, and specific surface area within a specific pore size range;

[0048] According to formula 1(D C =k×P C +D0), combined with the pore structure parameters of the adsorbent material, any critical pore size D C The pore volume V of the pores below the critical pore size corresponding to C and the specific surface area S of pores above the critical pore sizeC .

[0049] Preferably, the VOCs are one of hydrocarbon organic matter, oxygen-containing organic matter, halogen-containing organic matter, nitrogen-containing organic matter and sulfur-containing organic matter.

[0050] Compared with the related art, the method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures provided by the present invention has the following beneficial effects:

[0051] The present invention adopts a variable control method, by using two or more porous materials with concentrated pore size distribution as model adsorption materials, under specific conditions (specific VOCs type, temperature), to explore the critical pore size D of the pore size that can cause filling adsorption. C and its law of change with pressure.

[0052] Since the filling adsorption follows the volume filling mechanism of the adsorption space, and the density of the adsorbate in the pores is close to its density in the liquid state (ρ), the adsorption amount of this part is related to the density and the pore volume where the filling adsorption occurs; while the pores where the filling adsorption does not occur are the surface coverage mechanism of single-layer or multi-layer adsorption, and the adsorption amount of this part is related to the corresponding specific surface area. On this basis, by introducing the law of the change of critical pore size with pressure, the dividing point between filling adsorption and covering adsorption at a specific pressure and the regular equation of its change with pressure are obtained. By introducing the difference in pore size and the change in pressure, the calculation equations for the adsorption contribution coefficients of the two adsorption modes are obtained respectively, and the contribution coefficients of different pore sizes to the adsorption of VOCs under different partial pressures are obtained.

[0053] The method provided by the present invention for calculating the contribution coefficients of different pore sizes to the VOCs adsorption amount under different partial pressures has the advantages of simple calculation, clear physical meaning, high accuracy, and wide application range. It provides a reference basis for the selection of adsorption materials suitable for different VOCs, provides theoretical support for the design of efficient VOCs adsorption materials, the study of adsorption and desorption processes, and the optimization of VOCs adsorption processes, and has good scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a schematic diagram of the method for calculating the contribution coefficient of different pore sizes to the adsorption of VOCs in Example 1;

[0055] Figure 2 is the pore size distribution of the series of model adsorbent materials in Example 1;

[0056] Figure 3 is the middle pressure value of the adsorption isotherms of benzene of the series of model adsorbent materials at 25° C. normalized relative to the respective maximum adsorption amounts and the pressure region where filling-type adsorption occurs in Example 1;

[0057] Figure 4 In Example 1, the adsorption pressure P and the critical pore size D when filling adsorption occurs C The linear matching relationship between them;

[0058] Figure 5 is a trend curve of the filling adsorption coefficient (a=Q / V / ρ) of the series of model adsorption materials as a function of pressure in Example 1;

[0059] Figure 6 is a trend curve of the covering adsorption coefficient (b=Q / S) of the series of model adsorption materials as a function of pressure in Example 1;

[0060] Figure 7 The contribution coefficient trend diagram of benzene adsorption at 25°C in pores of different sizes with increasing adsorption pressure in Example 1: surface coverage adsorption contribution coefficient (b) and volume filling adsorption contribution coefficient (a);

[0061] Figure 8 The normalized adsorption isotherms of the series of model adsorbent materials for ethyl acetate at 25°C in Example 2, as well as the pressure and critical pore size D C The linear relationship between

[0062] Fig. 9 is a trend curve of the covering adsorption coefficient (b=Q / S) and the filling adsorption coefficient (a=Q / V / ρ) of the series of model adsorption materials for ethyl acetate adsorption at 25°C as a function of pressure;

[0063] Fig.10 The contribution coefficient trend diagram of ethyl acetate adsorption at 25°C in pores of different sizes with increasing adsorption pressure in Example 2: surface coverage adsorption contribution coefficient (b) and volume filling adsorption contribution coefficient (a);

[0064] Fig.11 The normalized adsorption isotherms of acetone adsorption by the series of model adsorbent materials at 35°C in Example 3, as well as the relationship between pressure and critical pore size D C The linear relationship between

[0065] Fig.12 The following are trend curves of the covered adsorption coefficient (b=Q / S) and the filled adsorption coefficient (a=Q / V / ρ) of the series of model adsorption materials for acetone at 35°C as a function of pressure;

[0066] Fig.13 The contribution coefficient trend diagram of acetone adsorption at 35°C in pores of different sizes with increasing adsorption pressure in Example 3: surface coverage adsorption contribution coefficient (b) and volume filling adsorption contribution coefficient (a);

[0067] Fig.14 In Comparative Example 1, there is a lack of correlation between the total pore volume or total surface area and the amount of benzene adsorption at different pressures (5, 10, 20 and 90 mbar). DETAILED DESCRIPTION

[0068] The method provided by the present invention for calculating the contribution coefficients of different pore sizes to the adsorption of VOCs under different partial pressures comprises the following steps:

[0069] S1. Provide 2 or more porous materials with concentrated pore size distribution as model adsorption materials, test pore structure parameters, and test the adsorption isotherms of specific VOCs of the adsorption materials at specific adsorption temperatures;

[0070] S2. Obtain the pressure range corresponding to the filling adsorption of each model adsorption material according to the adsorption isotherm, and take the middle value of the pressure range as the critical pressure point P C The critical pressure point corresponds to the middle value of the pore size distribution of the adsorbent material, and the pore size is taken as the pressure point P C The critical pore size D for filling adsorption to occur C ;

[0071] S3, according to the pressure point P when the two or more adsorbent materials with concentrated pore size distribution undergo filling adsorption C and the corresponding critical pore size D C , the pressure point P is obtained by linear fitting method C and critical pore size D C The linear relationship curve between them is formula 1:

[0072] D C =k×P C +D0 Formula 1;

[0073] In formula 1,

[0074] D C The pressure point P C Critical pore size for filling adsorption to occur under , nm;

[0075] P C For an aperture of D C The critical pressure corresponding to the filling adsorption in the pores, mbar;

[0076] k is the slope of the linear relationship between critical pore size and pressure, nm / mbar;

[0077] D0 is the linear relationship when the pressure approaches 0 mbar. C The value of , nm;

[0078] S4. According to the adsorption isotherms of the two or more adsorbent materials with concentrated pore size distribution at the same temperature, the adsorption amount at each pressure point on the adsorption isotherm is divided by the density at the corresponding temperature and the total pore volume of each adsorbent material, respectively, to obtain the trend curve of the filling adsorption coefficient (a=Q / V / ρ) of each adsorbent material with pressure change, and according to the high-pressure area after the filling adsorption in the adsorption isotherm is formed, combined with the influence of the pore size difference between different adsorbent materials on the curve, the calculation formula of the contribution coefficient (a) of the filling adsorption is obtained:

[0079] a=f(D A ,P)=(a0+a1×(D A -D0)+a2×P) Formula 2;

[0080] In formula 2, f(D A ,P) represents the coefficient of filling adsorption a is the pore size D A and pressure P;

[0081] a0 is the part of coefficient a that is not affected by changes in aperture size and pressure, and has no unit;

[0082] a1 is the coefficient of the part of coefficient a affected by the difference in aperture size, nm -1 ;

[0083] a2 is the coefficient of the part of coefficient a affected by pressure change, mbar -1 ;

[0084] D0 is the D when the pressure approaches 0 mbar in the linear relationship between critical pore size and critical pressure. C Value, nm;

[0085] D A is the average pore size of the pores where filling adsorption occurs, nm;

[0086] D A =4V C / (SS C ), S is the total specific surface area, m 2 / g;

[0087] V C is the pore volume below the critical pore size, cm 3 / g;

[0088] S C is the specific surface area of ​​pores above the critical pore size, m 2 / g;

[0089] P is any pressure point on the adsorption isotherm (mbar);

[0090] S5. According to the adsorption isotherms of the two or more adsorbent materials with concentrated pore size distribution at the same temperature, the adsorption amount at each pressure point on the adsorption isotherm is divided by the total specific surface area of ​​each adsorbent material to obtain the trend curve of the covering adsorption coefficient (b=Q / S) of each adsorbent material with pressure change. According to the low-pressure area gradually formed by the covering adsorption in the adsorption isotherm, combined with the influence of the pore size difference between different adsorbent materials on the curve, the calculation formula of the contribution coefficient (b) of the covering adsorption is obtained:

[0091] b=g(D AS ,P)=(b1+b2×P) Formula 3;

[0092] In formula 3,

[0093] g(D As ,P) represents the coefficient of filling adsorption a is the pore size D AS and pressure P;

[0094] b1 is the coefficient of the part of coefficient b that is affected by the difference in pore size, g / m 2 ;

[0095] b2 is the coefficient of the part of coefficient b that is affected by pressure change and pore size, g / m 2 / mbar;

[0096] P is any pressure point on the adsorption isotherm (mbar);

[0097] D AS is the average pore size of the pores where covering adsorption occurred, nm;

[0098] D AS =4(VV C ) / S C , V is the total pore volume, m 3 / g;

[0099] V C is the pore volume below the critical pore size, cm 3 / g;

[0100] S C is the specific surface area of ​​pores above the critical pore size, m 2 / g;

[0101] P is any pressure point on the adsorption isotherm (mbar);

[0102] S6. Since filling adsorption and covering adsorption do not occur simultaneously in the same pore size, when the pressure is sufficient to cause volume filling adsorption, the filling adsorption coefficient (a) is applicable, and when the pressure is insufficient to cause volume filling adsorption, the covering adsorption coefficient (b) of a specific size is applicable. Under a specific pressure, which adsorption model coefficient (a or b) should be used for a specific pore size depends on the size of the pore size relative to the critical pore size (the dividing point between volume filling adsorption and surface covering adsorption) at pressure P. The critical pore size at pressure P can be determined according to the equation (D C =k×P+D0) to obtain a one-to-one corresponding value. When the pore size is smaller than the critical pore size, filling adsorption occurs, and when the pore size is larger than the critical pore size, covering adsorption occurs.

[0103] In this embodiment, the number of the adsorption materials having concentrated pore size distribution is ≥2.

[0104] In addition, the step S1 further includes: using a commercial specific surface area and pore structure analyzer to test, through the DFT cylindrical pore calculation model, to obtain the pore structure parameters of the adsorbent material, the pore structure parameters including pore size distribution, pore volume within a specific pore size range, and specific surface area within a specific pore size range; according to formula 1 (D C =k×P C +D0), combined with the pore structure parameters of the adsorbent material, any critical pore size D C The pore volume V of the pores below the critical pore size corresponding to C and the specific surface area S of pores above the critical pore size C In this solution, the VOCs are one of hydrocarbon organic matter, oxygen-containing organic matter, halogen-containing organic matter, nitrogen-containing organic matter and sulfur-containing organic matter.

[0105] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0106] Example 1

[0107] A series of ordered mesoporous silica MCM-41 materials with concentrated pore size distribution were used as model adsorption materials, namely M-2.6, M-3.0, M-3.4, and M-3.8. The pore size distribution of the material was obtained by using a commercial pore structure and specific surface area tester through the DFT cylindrical pore calculation model. The results are shown in the figure. Figure 2 As shown, it can be seen that the pore size distribution is concentrated at 2.6nm, 3.0nm, 3.4nm, and 3.8nm respectively.

[0108] The adsorption amount of benzene by a series of adsorbent materials was tested at 25°C using an intelligent gravimetric analyzer (IGA) to obtain adsorption isotherms. The pressures corresponding to the midpoints of the rapid rise phases on the adsorption isotherms of the four MCM-41 adsorbent materials were 9.7, 14.0, 20.3 and 25.0 mbar, respectively, corresponding to the most probable pore sizes of the four adsorbent materials, 2.6, 3.0, 3.4 and 3.8 nm, respectively. Figure 2 Mesopore size distribution curve and Figure 3 As shown in the adsorption isotherm, it can be found that the larger the pore size of the adsorbent material, the greater the pressure required for the corresponding filling adsorption, and there is a linear relationship between the pressure and the corresponding critical pore size.

[0109] According to the most probable pore sizes of the four adsorbent materials and the corresponding pressures at the midpoints of the rapid rise phase on their corresponding adsorption isotherms, namely (9.7 mbar, 2.6 nm), (14.0 mbar, 3.0 nm), (20.3 mbar, 3.4 nm), and (25 mbar, 3.8 nm), the linear equation is obtained by linear fitting:

[0110] D C =0.0774*P+1.85 Formula 4

[0111] In formula 4,

[0112] D C is the critical pore size for filling adsorption to occur at the pressure point P, nm;

[0113] P is any pressure point on the adsorption isotherm (mbar);

[0114] The critical pore size for filling adsorption at any pressure can be obtained according to this formula. Pressure and critical pore size D C The linear relationship is as follows Figure 4 As shown, it can be used to calculate the critical pore size corresponding to different pressures for filling adsorption. For the model adsorbent materials used in the present invention, they all have a highly concentrated pore size distribution, while pores of other sizes can be ignored. Therefore, all the features of the isotherms in different pressure zones can be attributed to specific pore sizes.

[0115] In the first stage, the adsorption capacity increases slowly with the increase of vapor pressure, which can be attributed to the process that benzene molecules gradually form a monolayer or multilayer adsorption on the pore wall surface. In this stage, the pressure is not enough to cause volume filling adsorption.

[0116] In the second stage, the amount of benzene adsorption increases rapidly on the isotherm, which is caused by the volume filling adsorption occurring in the concentrated pores. In addition, this stage also includes a certain contribution from the surface coverage adsorption, because although the pore size distribution is very concentrated, there is still a certain range where the volume filling adsorption will preferentially occur in slightly smaller pores, while slightly larger pores are still surface coverage adsorption.

[0117] In the third stage, the isotherm reaches a flat state and the adsorption amount increases only slightly. The slight increase is mainly due to the rearrangement of the benzene molecules adsorbed in the pores of MCM-41 through volume filling adsorption.

[0118] Calculation method of contribution coefficient (a) of filled adsorption:

[0119] By dividing the adsorption amount at each pressure point on the adsorption isotherm of the adsorption material by the total pore volume and density, the trend of the filling adsorption coefficient (a) changing with pressure can be obtained. By dividing the adsorption amount at each pressure point on the adsorption isotherm by the total pore volume and density, the trend of the volume filling adsorption coefficient (a = Q / V / ρ) changing with pressure can be obtained, such as Figure 5 As shown. (The total volume (V) used here is calculated from the cumulative pore volume distribution curve using the cylinder N2-DFT model). In the volume filling adsorption coefficient (a), the part affected by the pore size is set to a1 = f(D), the part affected by the pressure is set to a2 = g(P), and the part not affected by the pressure and pore size is set to a0. Therefore, the filling adsorption coefficient a = a0 + f(D) + g(P).

[0120] It can be observed that the adsorption in the high-pressure region of the third stage of the adsorption isotherm basically completes the filling adsorption. At the same time, with the increase of pressure, the contribution coefficient (a) of the filling adsorption also shows a slightly increasing trend. This is mainly attributed to the fact that the VOCs molecules in the filling adsorption can undergo molecular rearrangement with the increase of pressure, resulting in a slight increase in the contribution coefficient (a) of the filling adsorption, while the contribution coefficient (a) of the volume filling adsorption of different pore sizes increases by the same magnitude, that is, the slope (0.001). Therefore, the change in coefficient a caused by pressure is a2 = 0.001 × P, as shown in Figure 5 shown.

[0121] In the high-pressure region of the third-stage adsorption isotherm, under the same pressure, the volume filling adsorption contribution coefficient (a) corresponding to different pore sizes also has certain differences, such as Figure 5 As shown, the coefficient a caused by the aperture difference is a1 = 0.08 × (D A-1.85). Among them, since pores smaller than 1.8 nm can also complete filling adsorption when P is close to 0 mbar, the value of the part not affected by pressure and pore size is a0=0.77.

[0122] According to the high-pressure area after the filling adsorption is formed in the adsorption isotherm, combined with the influence of the pore size difference between different adsorption materials on the curve, the calculation formula of the contribution coefficient (a) of the filling adsorption is obtained:

[0123] a=0.77+0.08×(D A -1.85)+0.001×P Formula 5;

[0124] In formula 5,

[0125] D A is the average pore size of the pores where filling adsorption occurs, nm;

[0126] D A =4V C / (SS C ), S is the total specific surface area, m 2 / g;

[0127] S C is the specific surface area of ​​pores above the critical pore size, m 2 / g;

[0128] P is any pressure point on the adsorption isotherm (mbar);

[0129] Calculation method of contribution coefficient (b) of surface coverage adsorption:

[0130] The surface coverage adsorption coefficient (b) can be studied by dividing the adsorption capacity by the total surface area of ​​the low pressure zone (b = Q / S), e.g. Figure 6 As shown. (The total surface area (S) used here is calculated based on the cumulative surface area distribution curve using the cylindrical N2-DFT model). In the adsorption isotherm in the low-pressure region, the adsorption capacity increases slowly, which is the process of the gradual formation of single-layer or multi-layer surface coverage adsorption. In this state, volume filling adsorption has not yet begun, so the trend of this state can be used to obtain the relationship between the coefficient b and pressure P.

[0131] By linearly fitting the adsorption isotherm in the low pressure zone, the equation of the coefficient (b) for different pore sizes can be obtained (b = b1 + b2 × P), where b1 is the intercept and b2 is the slope, which are affected by the pore size. For the pore at 2.6nm, the linear fitting result is b = 0.000024 × P + 0.000050, and for the pore at 3.8nm, the fitting result is b = 0.000013 × P + 0.000033. Assume that the pore size has a linear relationship with both the slope b1 and the intercept b2. Set the slope to the equation b2 = x × D AS +y, where D AS (D AS =4(VV C ) / S C ) is the average pore size of the pores for surface coverage adsorption. AS =2.6, b2 =0.000024) and (D AS =3.8, b2=0.000013) Input equation b2=x×D AS + y, we get b2 = 0.000048-0000009×D AS Using the same method, we can get the intercept equation b1 = 0.000087-000014×D AS Therefore, by introducing pore size and pressure as variables into the coefficient b, the equation for the surface coverage adsorption coefficient b during the adsorption of benzene at 25 °C is:

[0132] b=(8.7-1.4×D AS )×10 -5 +(4.8-0.9×D AS )×10 -5 ×P Formula 6

[0133] In formula 6,

[0134] D AS is the average pore size of the pores where covering adsorption occurs, nm;

[0135] D AS =4(VV C ) / S C , V is the total pore volume, m 3 / g;

[0136] V C is the pore volume below the critical pore size, cm 3 / g;

[0137] P is any pressure point on the adsorption isotherm (mbar);

[0138] Substituting different sizes into formula 4, according to P and D CThe linear relationship between C =0.0774*P+1.85), and the critical pore size for filling adsorption under any pressure is obtained. C Substituting into Formula 5 and Formula 6, the values ​​of the contribution coefficient (a) of filling adsorption and the contribution coefficient (b) of surface coverage adsorption in the adsorption process of benzene at 25°C with different pore sizes are obtained, as shown in Table 1 and Table 2

[0139] Table 1 Detailed quantification results of the filling contribution coefficients of pores of different sizes in benzene adsorption at 25 °C.

[0140]

[0141]

[0142] *The volume filling adsorption contribution coefficient (a) is given by formula (5) (a = 0.77 + 0.08 × (D A -1.85)+0.001×P) calculation can reflect the utilization rate of pore volume.

[0143] NA: Not applicable. It indicates that at a specific pore size, volume filling adsorption has not occurred at this pressure, but surface covering adsorption has occurred.

[0144] Application rule: Since filling adsorption and covering adsorption do not occur simultaneously at the same size, when the pressure is insufficient to cause volume filling adsorption, the size-specific covering adsorption coefficient (b) applies. Which coefficient (a or b) should be used for a specific pore size at a specific pressure is determined by the critical pore size equations (D C =k×P+D0).

[0145] Table 2 Detailed quantification results of the coverage contribution coefficients of pores of different sizes in benzene adsorption at 25 °C.

[0146]

[0147]

[0148] #Surface coverage adsorption contribution coefficient (b) is given by equation (6) (b = (8.7-1.4 × D AS )×10 -5 +(4.8-0.9×D AS )×10 -5 ×P) calculation can reflect the utilization rate of specific surface area.

[0149] NA: Not Applicable. Indicates that at a specific pore size, volume filling adsorption occurs at this pressure rather than surface coverage adsorption.

[0150] Application rule: Since filling adsorption and covering adsorption do not occur simultaneously at the same size, when the pressure is insufficient to cause volume filling adsorption, the size-specific covering adsorption coefficient (b) applies. Which coefficient (a or b) should be used for a specific pore size at a specific pressure is determined by the critical pore size equations (D C =k×P+D0).

[0151] Example 2

[0152] The ordered mesoporous silica MCM-41 material with the most probable pore diameters of 3.0 nm, 3.4 nm and 3.8 nm in Example 1 was used as a model adsorption material. The adsorption isotherms of the series of adsorption materials for ethyl acetate at 25° C. were obtained by the method of Example 1. Figure 8 Using the method of Example 1, the pressure P and the critical pore size D during the adsorption of ethyl acetate at 25°C were obtained. C The linear relationship is:

[0153] D C =0.0696×P+2.2 Formula 7

[0154] In formula 7,

[0155] D C is the critical pore size for filling adsorption to occur at the pressure point P, nm;

[0156] P is any pressure point on the adsorption isotherm (mbar);

[0157] Using the method of Example 1, the formula for the contribution coefficient (a) of the filled adsorption during the adsorption of ethyl acetate at 25° C. was obtained:

[0158] a=0.75+0.05×(D A -2.2)+0.001×P Formula 8

[0159] In formula 8,

[0160] D A is the average pore size of the pores where filling adsorption occurs, nm;

[0161] D A =4V C / (SS C ), S is the total specific surface area, m 2 / g;

[0162] S C is the specific surface area of ​​pores above the critical pore size, m 2 / g;

[0163] P is any pressure point on the adsorption isotherm (mbar);

[0164] like Fig. 9 As shown, during the adsorption process of ethyl acetate at 25°C, the surface coverage adsorption coefficients (b) at different pore sizes overlap, so the calculation process can be simplified by taking the average value. In the surface coverage adsorption coefficient (b), the part affected by pressure changes is set to b1=g(P), and the part not affected by pressure changes and pore size differences is set to (b0), and then the volume filling adsorption coefficient b=b0+g(P). In the first stage of adsorption, although there are certain differences in the lengths of the regions corresponding to different pore sizes, they can overlap well. Taking the average value of the first stage of adsorption, the equation for the surface coverage adsorption contribution coefficient can be obtained:

[0165] b=0.00024+0.000009×P Formula 9

[0166] In formula 9, P is any pressure point on the adsorption isotherm (mbar);

[0167] Substituting different sizes into formula 4, according to P and D C The linear relationship between C =0.0696×P+2.2), and the critical pore size for filling adsorption under any pressure is obtained. C Substituting into formula 8 and formula 9, the values ​​of the contribution coefficient (a) of filling adsorption and the contribution coefficient (b) of surface coverage adsorption under different pore sizes in the adsorption process of ethyl acetate at 25°C are obtained, as shown in Fig.10 And as shown in Table 3.

[0168] Table 3 Detailed quantitative results of the contribution coefficients of pores of different sizes to the adsorption of ethyl acetate at 25 °C.

[0169]

[0170]

[0171]

[0172] *The volume filling adsorption contribution coefficient (a) is given by equation (8) (a = 0.75 + 0.05 × (D A -2.2)+0.001×P) calculation can reflect the utilization rate of pore volume.

[0173] #The surface coverage adsorption contribution coefficient (b) is calculated by equation (9) (b = 0.00024 + 0.000009 × P), which can reflect the utilization rate of the surface area.

[0174] NA: Not applicable. It indicates that at a specific pore size, volume filling adsorption has not occurred at this pressure, but surface covering adsorption has occurred.

[0175] Application rule: Since filling adsorption and covering adsorption do not occur simultaneously at the same size, when the pressure is insufficient to cause volume filling adsorption, the size-specific covering adsorption coefficient (b) applies. Which coefficient (a or b) should be used for a specific pore size at a specific pressure is determined by the critical pore size equations (D C =k×P+D0).

[0176] Example 3

[0177] Using the method of Example 1, the pressure P and the critical pore size D in the adsorption process of acetone at 35°C were obtained respectively. C The linear relationship is:

[0178] D C =0.0103×P+2.4 Formula 10

[0179] In formula 10, D C is the critical pore size at which filling adsorption can occur under pressure point P, nm; P is any pressure point on the adsorption isotherm (mbar).

[0180] Using the method of Example 1, the formula for the contribution coefficient (a) of the filled adsorption during the adsorption of ethyl acetate at 35° C. was obtained:

[0181] a=0.61+0.12×(D A -2.4)+0.00035×P Formula 11

[0182] In formula 8, D A is the average pore size of the pores where filled adsorption occurs, nm; D A =4V C / (SS C ), S is the total specific surface area, m 2 / g;S C is the specific surface area of ​​pores above the critical pore size, m 2 / g; P is any pressure point on the adsorption isotherm (mbar).

[0183] Using the method of Example 2, the formula for the surface coverage adsorption coefficient (b) during the adsorption of ethyl acetate at 35° C. was obtained:

[0184] b=0.00017+0.0000017×P Formula 12

[0185] In formula 12, P is any pressure point on the adsorption isotherm (mbar).

[0186] Substituting different sizes into formula 10, according to P and D C The linear relationship between C =0.0103×P+2.4), and the critical pore size for filling adsorption at any pressure is obtained. C Substituting into formula 11 and formula 12, the values ​​of the contribution coefficient (a) of filling adsorption and the contribution coefficient (b) of surface covering adsorption in the adsorption process of acetone at 35°C with different pore sizes are obtained, as shown in Fig.13 And as shown in Table 4.

[0187] Table 4 Detailed quantitative results of the contribution coefficients of pores of different sizes to acetone adsorption at 35 °C.

[0188]

[0189]

[0190] *The volume filling adsorption contribution coefficient (a) is given by equation (11) (a = 0.61 + 0.12 × (D A -2.4)+0.00035×P) calculation can reflect the utilization rate of pore volume.

[0191] #The surface coverage adsorption contribution coefficient (b) is calculated by equation (12) (b = 0.000017 + 0.0000017 × P), which can reflect the utilization rate of the surface area.

[0192] NA: Not applicable. The same rules apply as in Table 3.

[0193] Comparative Example 1

[0194] like Fig.14As shown in the figure, at 90 mbar, when the adsorption isotherm is close to the saturated vapor pressure, the adsorption amount of benzene by MCM-41 shows a certain correlation with the total pore volume and total specific surface area of ​​the MCM-41 material. However, in practical applications, volatile organic waste gas rarely reaches the saturated vapor pressure. Therefore, it is necessary to consider the correlation between the adsorption capacity and the pore structure at lower pressures. However, in the pressure range where the adsorption isotherm is not close to saturation, the adsorption amount loses its correlation with the structural parameters (total pore volume and total specific surface area) of the adsorption material. For example, at 5 and 10 mbar, the adsorption amount of benzene by MCM-41 material has no correlation with the total pore volume of MCM-41. In addition, at a pressure of 20 mbar, the situation is slightly more complicated. For M-2.6 and M-3.0, their adsorption isotherms have reached the platform pressure area, while M-3.4 and MCM-41.3.8 have not. This results in a correlation between the adsorption capacity of M-2.6 and M-3.0 at 20 mbar pressure and the structural parameters of the materials, while there is no correlation between M-3.4 and MCM-41.3.8, as Fig.14 Therefore, by directly correlating the adsorption capacity with the pore volume, specific surface area or average pore size of the adsorbent, only relatively general rules can be obtained, such as smaller pore size leads to higher pore volume and specific surface area utilization.

[0195] It can be inferred that directly fitting the total pore volume (or total specific surface area) with the benzene adsorption at different pressures cannot produce an effective correlation law. At saturated vapor pressure, there is a good correlation between pore volume and adsorption, because at this pressure, the pore volume is fully utilized by volume filling adsorption. By directly correlating the adsorption capacity with the pore volume or specific surface area, a correlation can only be found in the pressure region where the adsorption isotherm approaches the saturated vapor pressure (such as 90 mbar), while there is no correlation at other pressure points (such as 5, 10, 20 mbar). Fig.14 Therefore, by directly fitting the total pore volume (or total specific surface area) with the benzene adsorption capacity at different pressures, an effective correlation relationship between the pore size and the adsorption capacity contribution coefficient cannot be obtained.

[0196] In summary, based on the theoretical basis that the adsorption of VOCs by porous materials includes two parts: filling adsorption and covering adsorption. According to the fact that the adsorption amount of filling adsorption is related to the density and the pore volume where filling adsorption occurs, and the adsorption amount of covering adsorption is related to the specific surface area where covering adsorption occurs, porous materials with concentrated pore size distribution are used as model adsorption materials. By correlating the change trend of VOCs adsorption isotherms in different pressure regions with the pore size of the material, the regular equation of the critical pore size of filling adsorption and covering adsorption under the corresponding adsorption conditions with pressure is obtained. According to the critical pore size equation, combined with the influence of pore size difference and partial pressure change on VOCs adsorption isotherms, the contribution coefficients of different pore sizes in the adsorbent to filling adsorption and covering adsorption of VOCs adsorption and the regular equation of their change with partial pressure are obtained respectively. According to the contribution coefficients of different pore sizes to VOCs adsorption under specific partial pressure, the selection of adsorbents can be effectively guided, providing a reference for the development of adsorption technology and materials.

Claims

1. A method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures, characterized in that: The following steps are involved: S1. Provide 2 or more porous materials with concentrated pore size distribution as model adsorption materials, test pore structure parameters, and test the adsorption isotherms of specific VOCs of the adsorption materials at specific adsorption temperatures; S2. Obtain the pressure range corresponding to the filling adsorption of each model adsorption material according to the adsorption isotherm, and take the middle value of the pressure range as the critical pressure point P C The critical pressure point corresponds to the middle value of the pore size distribution of the adsorbent material, and the pore size is taken as the pressure point P C The critical pore size D for filling adsorption to occur C ; S3, according to the pressure point P when the two or more adsorbent materials with concentrated pore size distribution undergo filling adsorption C and the corresponding critical pore size D C , the pressure point P is obtained by linear fitting method C and critical pore size D C The linear relationship curve between them is formula 1: D C =k×P C +D0 Formula 1; S4. According to the adsorption isotherms of the two or more adsorbent materials with concentrated pore size distribution at the same temperature, the adsorption amount at each pressure point on the adsorption isotherm is divided by the density ρ at the corresponding temperature and the total pore volume V of each adsorbent material, respectively, to obtain the trend curve of the filling adsorption coefficient (a=Q / V / ρ) of each adsorbent material with pressure change, and obtain the calculation formula of the contribution coefficient (a) of the filling adsorption: a=f(D A ,P)=(a0+a1×(D A -D0)+a2×P) Formula 2; S5. According to the adsorption isotherms of the two or more adsorbent materials with concentrated pore size distribution at the same temperature, the adsorption amount at each pressure point on the adsorption isotherm is divided by the total specific surface area of ​​each adsorbent material to obtain the trend curve of the covering adsorption coefficient (b=Q / S) of each adsorbent material with pressure change, and the calculation formula of the contribution coefficient (b) of the covering adsorption is obtained: b=g(D AS ,P)=(b1+b2×P) Formula 3; S6. The coefficient of the adsorption model to be used (a or b) is determined based on the pore size relative to the critical pore size at pressure P.

2. The method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures according to claim 1, characterized in that: The number of the adsorption materials having concentrated pore size distribution is ≥2.

3. The method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures according to claim 1, characterized in that: The step S1 also includes: The pore structure parameters of the adsorbent material are obtained by using a commercial specific surface area and pore structure analyzer and a DFT cylindrical pore calculation model. The pore structure parameters include pore size distribution, pore volume within a specific pore size range, and specific surface area within a specific pore size range.

4. The method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures according to claim 1, characterized in that: The adsorption material is one or more of ordered mesoporous silicon, ordered mesoporous carbon and molecular sieve.

5. The method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures according to claim 1, characterized in that: The VOCs are one of hydrocarbon organic matter, oxygen-containing organic matter, halogen-containing organic matter, nitrogen-containing organic matter and sulfur-containing organic matter.

6. The method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures according to claim 1, characterized in that: The formula D C =k×P C +D0: D C The pressure point P C The critical pore size for filling adsorption to occur under the condition of , in nm; P C For an aperture of D C The critical pressure corresponding to the filling adsorption in the pores of is mbar; k is the slope of the linear relationship between critical pore size and pressure, in nm / mbar; D0 is the linear relationship when the pressure approaches 0 mbar. C The value of is in nm.

7. The method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures according to claim 1, characterized in that: The formula a=f(D A ,P)=(a0+a1×(D A -D0)+a2×P), f(D A ,P) represents the coefficient of filling adsorption a is the pore size D A and pressure P; a0 is the part of coefficient a that is not affected by changes in aperture size and pressure, and has no unit; a1 is the coefficient of the part of coefficient a that is affected by the difference in aperture size, in nm -1 ; a2 is the coefficient of the part of coefficient a that is affected by pressure changes, in mbar -1 ; D0 is the value of D when the pressure approaches 0 in the linear relationship between critical pore size and critical pressure. C Numerical value, in nm; D A is the average pore size of the pores where filled adsorption occurs, in nm; D A =4V C / (SS C ), S is the total specific surface area, in m 2 / g; V C is the pore volume below the critical pore size, in cm 3 / g; S C is the specific surface area of ​​pores above the critical pore size, in m 2 / g.

8. The method for calculating the contribution coefficient of different pore sizes to VOCs adsorption under different partial pressures according to claim 1, characterized in that: The formula b=g(D AS ,P)=(b1+b2×P), g(D As ,P) represents the coefficient of filling adsorption a is the pore size D AS and pressure P; b1 is the coefficient of the part of coefficient b that is affected by the difference in pore size, in g / m 2 ; b2 is the coefficient of the part of coefficient b that is affected by pressure change and pore size, g / m 2 / mbar; P is any pressure point on the adsorption isotherm, in mbar; D AS is the average pore size of the pores where covering adsorption occurs, in nm; D AS =4(VV C ) / S C , V is the total pore volume, unit is m 3 / g; V C is the pore volume below the critical pore size, in cm 3 / g; S C is the specific surface area of ​​pores above the critical pore size, in m 2 / g; P is any pressure point on the adsorption isotherm, in mbar.

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