A lithium and cobalt modified titanium silicon molecular sieve and its preparation method and application

Abstract

The present invention provides a lithium-cobalt modified titanium silicon molecular sieve and its preparation method and application, belonging to the field of adsorbent technology. The specific steps of the preparation method of the present invention are as follows: (1) preparing a salt solution: mixing lithium salt, cobalt salt and deionized water to obtain a salt solution; (2) mixing the ground titanium silicon molecular sieve with the salt solution in step (1), then filtering and separating, drying the filter residue obtained after separation, and finally roasting to obtain a lithium-cobalt modified titanium silicon molecular sieve. The present invention successfully prepares a lithium-cobalt modified titanium silicon molecular sieve by impregnating and modifying a salt solution with a specific lithium salt and cobalt salt dosage ratio. The preparation method is simple and low in cost. The prepared molecular sieve is used to separate N2 and CH4 mixed gas, and the adsorption amount of CH4 is extremely low, which can achieve effective separation of N2 and CH4. The molecular sieve prepared by the present invention can also be used to purify CH4 from coalbed methane, oilfield gas or landfill gas.

Description

Technical Field

[0001] The invention belongs to the field of adsorption technology and relates to a lithium and cobalt modified titanium silicon molecular sieve and a preparation method and application thereof. Background Art

[0002] In recent years, the development and application of natural gas denitrification technologies have attracted increasing attention. The main reasons are: (1) the soaring energy prices have led to the large-scale development of relatively cheap natural gas resources; (2) the natural gas produced by nitrogen injection as an enhancement of production (EOR) contains a large amount of nitrogen. Currently, there are five main natural gas denitrification processes at home and abroad: cryogenic separation process (CNR), pressure swing adsorption process (PSA), membrane separation process, solvent absorption process and hydrate separation process.

[0003] Pressure swing adsorption (PSA) is a room-temperature gas separation technology initially applied industrially for air drying and hydrogen purification. In recent years, it has been widely adopted in the gas separation industries of petroleum, natural gas, and chemicals. It primarily utilizes the differences in the adsorption characteristics of mixed gas components on solid adsorbent materials to achieve gas separation. Specifically, the solid adsorbent selectively adsorbs the easily adsorbed component in the mixed gas, while the remaining components are discharged. Gas separation and adsorbent recycling are achieved through a periodic pressure swing process. Adsorbent performance significantly influences the concentration efficiency of the process; PSA separation can only be performed when the adsorbent's equilibrium separation coefficient ratio is greater than 2. PSA boasts low investment, low energy consumption, and a simple process flow, making it widely used in industry. However, this process suffers from disadvantages such as low adsorption selectivity, limited adsorption capacity, and low methane recovery.

[0004] Currently, titanium silicate molecular sieves are widely used in the adsorbent field. Although titanium silicate molecular sieves have advantages such as surface acidity and molecular-sized pore size, their separation efficiency is low when used to separate mixed systems of CH4 and N2, so improvements are needed.

[0005] Chinese patent application CN 111889074 A discloses a selective adsorbent and its preparation method and application, belonging to the field of adsorbent technology. The technical problem solved by the present invention is to provide a method for preparing a selective adsorbent. The method comprises the following steps: impregnating a carbon molecular sieve with a metal salt solution, separating the solid and the liquid, drying the solid and then calcining it to obtain a selective adsorbent; wherein the metal salt contains Li + Cr 3+ 、Co 2+ and Mn 2+ , and Li + Cr 3+ 、Co 2+ and Mn 2+The molar ratio is 1:0.1-1:0.1-1:0.1-1. The present invention uses a specific type and ratio of metal salts to impregnate and modify a carbon molecular sieve. The resulting modified molecular sieve can be used as a selective adsorbent for N2 / CH4, O2 / CH4, or N2 / O2, and is particularly useful for separating N2 / CH4. However, this modified molecular sieve has relatively poor separation performance when used to separate a mixed system of nitrogen and methane.

[0006] Chinese patent application CN 107324307 A discloses a method for preparing a carbon molecular sieve for separating methane and nitrogen. The method mainly includes the following steps: (1) In the first step, a methane-nitrogen mixture containing a high concentration of methane is deposited at high temperature to roughly adjust the pore size of the carbon molecular sieve precursor; (2) In the second step, a methane-nitrogen mixture containing a low concentration of methane is deposited at low temperature to finely adjust the pore size of the carbon molecular sieve, thereby preparing a carbon molecular sieve with a high nitrogen adsorption capacity and a low methane adsorption capacity. However, this technology mainly involves the preparation of carbon molecular sieves and does not involve the modification of titanium silicon molecular sieves. Furthermore, it cannot solve the problems of titanium silicon molecular sieves in the separation of CH4 and N2, such as low nitrogen adsorption capacity and weak selective adsorption capacity.

[0007] Therefore, it is necessary to explore a preparation method for titanium silicate molecular sieve with large capacity, strong selectivity, high separation ratio, easy regeneration, long service life and good economy. Summary of the Invention

[0008] The present invention addresses the problems of the prior art by providing a lithium- and cobalt-modified titanium silicalite molecular sieve, its preparation method, and its application. This modified titanium silicalite molecular sieve is modified with lithium and cobalt salts, altering both its structure and its acidity and alkalinity, allowing for molecular selection through different forces. Modification of the pore openings also results in unique geometric effects, enabling selection based on molecular size. Therefore, the present invention aims to enhance the molecular sieve's selective adsorption of nitrogen by modifying the titanium silicalite molecular sieve, thereby reducing its adsorption of methane and achieving effective separation of nitrogen and methane.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] First, a preparation method of lithium and cobalt modified titanium silicate molecular sieve is provided, comprising the following steps:

[0011] (1) preparing a salt solution: mixing lithium salt, cobalt salt and deionized water to obtain a salt solution;

[0012] (2) mixing the ground titanium silicon molecular sieve with the salt solution in step (1), filtering and separating the mixture, drying the filter residue obtained after separation, and finally calcining the mixture to obtain lithium and cobalt modified titanium silicon molecular sieve;

[0013] The ratio of the titanium silicate molecular sieve to the salt solution in step (2) is 4-6 g: 25-30 mL.

[0014] Furthermore, the lithium salt in step (1) includes one or more of lithium nitrate, lithium sulfate, and lithium chloride, and the cobalt salt includes one or more of cobalt nitrate, cobalt sulfate, and cobalt chloride.

[0015] Furthermore, in the salt solution in step (1), the concentration of lithium ions is 0.01-10 wt%, and the concentration of cobalt ions is 0.01-10 wt%. Preferably, the concentration of lithium ions is 0.1-5 wt%; the concentration of cobalt ions is 0.1-8 wt%.

[0016] Furthermore, the pore size distribution of the titanium silicate molecular sieve in step (2) is 1.4-3 nm.

[0017] Furthermore, the mixing method in step (2) is impregnation, and the impregnation is equal volume impregnation or excess impregnation.

[0018] Furthermore, the drying temperature in step (2) is set to 60-120° C. and the drying time is 10-14 h.

[0019] Furthermore, the calcination temperature in step (2) is set to 100-400° C. and the calcination time is 2-14 h.

[0020] Furthermore, the calcination in step (2) is a gradient temperature increase, and the gradient temperature increase program is set as: heating from 100°C to 200°C at a heating rate of 4°C / min, and keeping the temperature constant for 3 hours; then heating from 200°C to 300°C at a heating rate of 2°C / min, and keeping the temperature constant for 3.5 hours; then heating from 300°C to 400°C at a heating rate of 3°C / min, and keeping the temperature constant for 3 hours.

[0021] Furthermore, the preparation method obtains lithium and cobalt modified titanium silicon molecular sieve.

[0022] Furthermore, the lithium or cobalt modified titanium silicalite obtained by the preparation method or the lithium or cobalt modified titanium silicalite is used as a selective adsorbent for a nitrogen and methane mixed system, an oxygen and methane mixed system or a nitrogen and oxygen mixed system.

[0023] Furthermore, the lithium or cobalt modified titanium silicate molecular sieve obtained by the preparation method or the lithium or cobalt modified titanium silicate molecular sieve is used to purify methane in coalbed methane, oilfield gas or landfill gas.

[0024] In some specific embodiments, a method for preparing lithium and cobalt modified titanium silicalite comprises the following steps:

[0025] (1) preparing a salt solution: mixing lithium nitrate and cobalt nitrate with deionized water and stirring to completely dissolve the lithium nitrate and cobalt nitrate in the water to prepare a salt solution with a lithium ion concentration of 0.01-10 wt% and a cobalt ion concentration of 0.01-10 wt%;

[0026] (2) 4-6 g of the ground titanium silicate molecular sieve is mixed with 25-30 mL of the salt solution obtained in step (1) and stirred, and then placed in an ultrasonic oscillation mixer for mixing, and then filtered and separated. The filter residue obtained after separation is dried at 60-120 ° C for 10-14 h, and the dried sample is placed in a tube furnace and calcined under a nitrogen atmosphere. The calcination is a gradient heating program, and the gradient heating program is set to: heating from 100 ° C to 200 ° C at a heating rate of 4 ° C / min, and keeping the temperature constant for 3 h; then heating from 200 ° C to 300 ° C at a heating rate of 2 ° C / min, and keeping the temperature constant for 3.5 h; then heating from 300 ° C to 400 ° C at a heating rate of 3 ° C / min, and keeping the temperature constant for 3 h.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention uses a salt solution with a specific lithium salt and cobalt salt dosage ratio to impregnate and modify the titanium silicon molecular sieve, and successfully prepares lithium and cobalt modified titanium silicon molecular sieve;

[0029] (2) The preparation method of the present invention is simple and low-cost;

[0030] (3) The lithium and cobalt modified titanium silicalite molecular sieve prepared by the present invention is used to separate a nitrogen and methane mixed system with a large separation ratio, thereby achieving effective separation of nitrogen and methane. DETAILED DESCRIPTION

[0031] It is worth noting that the raw materials used in the present invention are all common commercially available products, and their sources are not specifically limited.

[0032] The following raw material sources are illustrative:

[0033] Titanium silicate molecular sieve: purchased from Shanghai Koraman Reagent Co., Ltd., product number 12173-28-3.

[0034] Example 1

[0035] Preparation of lithium and cobalt modified titanium silicalite molecular sieve:

[0036] (1) preparing a salt solution: mixing lithium nitrate and cobalt nitrate with deionized water and stirring to completely dissolve the lithium nitrate and cobalt nitrate in the water to prepare a salt solution with a lithium ion concentration of 0.5 wt% and a cobalt ion concentration of 10 wt%;

[0037] (2) Take 5 g of the ground titanium silicate molecular sieve and 25 mL of the salt solution obtained in step (1) and mix them, then place them in an ultrasonic oscillation mixer, and then filter and separate them. The filter residue obtained after separation is dried at 80°C for 12 hours. The dried sample is placed in a tube furnace and calcined under a nitrogen atmosphere. The calcination is a gradient heating program, and the gradient heating program is set to: heating from 100°C to 200°C at a heating rate of 4°C / min, and keeping the temperature constant for 3 hours; then heating from 200°C to 300°C at a heating rate of 2°C / min, and keeping the temperature constant for 3.5 hours; then heating from 300°C to 400°C at a heating rate of 3°C / min, and keeping the temperature constant for 3 hours.

[0038] The adsorption of nitrogen and methane by the modified samples was determined using a static adsorption method. The static adsorption method was performed according to the method disclosed in patent application 201911089480.2. The results are shown in Table 1.

[0039] Table 1

[0040]

[0041]

[0042] Example 2

[0043] Preparation of lithium and cobalt modified titanium silicalite molecular sieve:

[0044] (1) preparing a salt solution: mixing lithium nitrate and cobalt nitrate with deionized water and stirring to completely dissolve the lithium nitrate and cobalt nitrate in the water to prepare a salt solution with a lithium ion concentration of 9 wt% and a cobalt ion concentration of 1 wt%;

[0045] (2) Take 4 g of the ground titanium silicon molecular sieve and 30 mL of the salt solution obtained in step (1) and mix them, then place them in an ultrasonic oscillation mixer, and then filter and separate them. The filter residue obtained after separation is dried at 70°C for 14 hours. The dried sample is placed in a tubular furnace and calcined under a nitrogen atmosphere. The calcination is a gradient heating program, and the gradient heating program is set to: heating from 100°C to 200°C at a heating rate of 4°C / min, and keeping the temperature constant for 3 hours; then heating from 200°C to 300°C at a heating rate of 2°C / min, and keeping the temperature constant for 3.5 hours; then heating from 300°C to 400°C at a heating rate of 3°C / min, and keeping the temperature constant for 3 hours.

[0046] The static adsorption method in Example 1 was used to measure the adsorption capacity of nitrogen and methane by the modified sample. The results are shown in Table 2.

[0047] Table 2

[0048]

[0049] Example 3

[0050] Preparation of lithium and cobalt modified titanium silicalite molecular sieve:

[0051] (1) preparing a salt solution: mixing lithium nitrate and cobalt nitrate with deionized water and stirring to completely dissolve the lithium nitrate and cobalt nitrate in the water to prepare a salt solution with a lithium ion concentration of 5 wt% and a cobalt ion concentration of 5 wt%;

[0052] (2) Take 6 g of the ground titanium silicon molecular sieve and 27 mL of the salt solution obtained in step (1) and mix them, then place them in an ultrasonic oscillation mixer, and then filter and separate them. The filter residue obtained after separation is dried at 100°C for 10 hours. The dried sample is placed in a tube furnace and calcined under a nitrogen atmosphere. The calcination is a gradient heating program, and the gradient heating program is set to: heating from 100°C to 200°C at a heating rate of 4°C / min, and keeping the temperature constant for 3 hours; then heating from 200°C to 300°C at a heating rate of 2°C / min, and keeping the temperature constant for 3.5 hours; then heating from 300°C to 400°C at a heating rate of 3°C / min, and keeping the temperature constant for 3 hours.

[0053] The static adsorption method in Example 1 was used to measure the adsorption capacity of nitrogen and methane by the modified sample. The results are shown in Table 3.

[0054] Table 3

[0055]

[0056] Example 4

[0057] Preparation of lithium and cobalt modified titanium silicalite molecular sieve:

[0058] (1) preparing a salt solution: mixing lithium nitrate and cobalt nitrate with deionized water and stirring to completely dissolve the lithium nitrate and cobalt nitrate in the water to prepare a salt solution with a lithium ion concentration of 3 wt% and a cobalt ion concentration of 8 wt%;

[0059] (2) 5 g of the ground titanium silicate molecular sieve was mixed with 27 mL of the salt solution obtained in step (1) and stirred, and then placed in an ultrasonic oscillation mixer for mixing, and then filtered and separated. The filter residue obtained after separation was dried at 90°C for 10 h. The dried sample was placed in a tubular furnace and calcined under a nitrogen atmosphere. The calcination was a gradient heating program, and the gradient heating program was set as follows: heating from 100°C to 200°C at a heating rate of 4°C / min, and holding the temperature for 3 h; then heating from 200°C to 300°C at a heating rate of 2°C / min, and holding the temperature for 3.5 h; then heating from 300°C to 400°C at a heating rate of 3°C / min, and holding the temperature for 3 h.

[0060] The static adsorption method in Example 1 was used to measure the adsorption capacity of nitrogen and methane by the modified sample. The results are shown in Table 4.

[0061] Table 4

[0062]

[0063] Comparative Example 1

[0064] Preparation of lithium and cobalt modified titanium silicalite molecular sieve:

[0065] (1) preparing a salt solution: mixing lithium nitrate and cobalt nitrate with deionized water and stirring to completely dissolve the lithium nitrate and cobalt nitrate in the water to prepare a salt solution with a lithium ion concentration of 0.5 wt% and a cobalt ion concentration of 11 wt%;

[0066] (2) Take 5 g of the ground titanium silicate molecular sieve and 27 mL of the salt solution obtained in step (1) and mix them, then place them in an ultrasonic oscillation mixer, and then filter and separate them. The filter residue obtained after separation is dried at 80°C for 12 hours. The dried sample is placed in a tube furnace and calcined under a nitrogen atmosphere. The calcination is a gradient heating program, and the gradient heating program is set to: heating from 100°C to 200°C at a heating rate of 4°C / min, and keeping the temperature constant for 3 hours; then heating from 200°C to 300°C at a heating rate of 2°C / min, and keeping the temperature constant for 3.5 hours; then heating from 300°C to 400°C at a heating rate of 3°C / min, and keeping the temperature constant for 3 hours.

[0067] The static adsorption method in Example 1 was used to measure the adsorption capacity of nitrogen and methane by the modified sample. The results are shown in Table 5.

[0068] Table 5

[0069]

[0070] Comparative Example 2

[0071] Preparation of lithium and cobalt modified titanium silicalite molecular sieve:

[0072] (1) preparing a salt solution: mixing lithium nitrate and cobalt nitrate with deionized water and stirring to completely dissolve the lithium nitrate and cobalt nitrate in the water to prepare a salt solution with a lithium ion concentration of 5 wt% and a cobalt ion concentration of 5 wt%;

[0073] (2) Take 3.5 g of the ground titanium silicate molecular sieve and 32 mL of the salt solution obtained in step (1) and mix them, then place them in an ultrasonic oscillation mixer, and then filter and separate them. The filter residue obtained after separation is dried at 90°C for 10 hours. The dried sample is placed in a tube furnace and calcined under a nitrogen atmosphere. The calcination is a gradient heating program, and the gradient heating program is set to: heating from 100°C to 200°C at a heating rate of 4°C / min, and keeping the temperature constant for 3 hours; then heating from 200°C to 300°C at a heating rate of 2°C / min, and keeping the temperature constant for 3.5 hours; then heating from 300°C to 400°C at a heating rate of 3°C / min, and keeping the temperature constant for 3 hours.

[0074] The static adsorption method in Example 1 was used to determine the adsorption capacity of nitrogen and methane by the modified sample. The results are shown in Table 6.

[0075] Table 6

[0076]

[0077]

[0078] Comparative Example 3

[0079] Preparation of lithium and cobalt modified titanium silicalite molecular sieve:

[0080] (1) preparing a salt solution: mixing lithium nitrate and cobalt nitrate with deionized water and stirring to completely dissolve the lithium nitrate and cobalt nitrate in the water to prepare a salt solution with a lithium ion concentration of 5 wt% and a cobalt ion concentration of 5 wt%;

[0081] (2) 5 g of the ground titanium silicate molecular sieve was mixed with 27 mL of the salt solution obtained in step (1) and stirred, and then placed in an ultrasonic oscillation mixer for mixing, and then filtered and separated. The filter residue obtained after separation was dried at 80°C for 12 h. The dried sample was placed in a tubular furnace and calcined in a nitrogen atmosphere at a heating rate of 3°C / min from 100°C to 350°C, and kept at this temperature for 7 h.

[0082] The static adsorption method in Example 1 was used to determine the adsorption capacity of nitrogen and methane by the modified sample. The results are shown in Table 7.

[0083] Table 7

[0084]

[0085]

[0086] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing lithium and cobalt modified titanium silicon molecular sieve, characterized in that: The steps include: (1) preparing a salt solution: mixing a lithium salt, a cobalt salt and deionized water to obtain a salt solution; wherein the concentration of lithium ions in the salt solution in step (1) is 0.01-10 wt %, and the concentration of cobalt ions is 0.01-10 wt %; (2) mixing the ground titanium silicon molecular sieve with the salt solution in step (1), filtering and separating the mixture, drying the filter residue obtained after separation, and finally calcining the mixture to obtain lithium and cobalt modified titanium silicon molecular sieve; The dosage ratio of the titanium silicate molecular sieve to the salt solution in step (2) is 4-6 g: 25-30 mL; the pore size distribution of the titanium silicate molecular sieve in step (2) is 1.4-3 nm; the calcination in step (2) is a gradient temperature increase, and the gradient temperature increase program is set as: heating from 100°C to 200°C at a heating rate of 4°C / min, and keeping the temperature constant for 3 hours; then heating from 200°C to 300°C at a heating rate of 2°C / min, and keeping the temperature constant for 3.5 hours; then heating from 300°C to 400°C at a heating rate of 3°C / min, and keeping the temperature constant for 3 hours.

2. The preparation method according to claim 1, characterized in that The lithium salt in step (1) includes one or more of lithium nitrate, lithium sulfate, and lithium chloride, and the cobalt salt includes one or more of cobalt nitrate, cobalt sulfate, and cobalt chloride.

3. The preparation method according to claim 1, characterized in that The drying temperature in step (2) is set to 60-120° C. and the drying time is 10-14 h.

4. The preparation method according to claim 1, characterized in that The calcination temperature in step (2) is set to 100-400° C. and the calcination time is 2-14 hours.

5. The lithium or cobalt modified titanium silicalite obtained by the preparation method according to any one of claims 1 to 4.

6. Use of the lithium-cobalt modified titanium silicalite obtained by the preparation method according to any one of claims 1 to 4 or the lithium-cobalt modified titanium silicalite according to claim 5 as a selective adsorbent for a nitrogen and methane mixture system.

7. Use of the lithium or cobalt modified titanium silicate molecular sieve obtained by the preparation method according to any one of claims 1 to 4 or the lithium or cobalt modified titanium silicate molecular sieve according to claim 5 in purifying methane from coalbed methane, oilfield gas or landfill gas.

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