阅读说明：本技术 全氟磺酸树脂／改性木质素复合离子交换膜的制备方法 (Preparation method of perfluorosulfonic acid resin/modified lignin composite ion exchange membrane ) 是由 贾传坤 丁美 于 2020-03-20 设计创作，主要内容包括：本发明涉及液流电池所用离子交换膜领域,具体是一种全氟磺酸树脂/改性木质素复合离子交换膜的制备方法,解决现有商业化隔膜材料存在的离子渗透严重、稳定性差、离子选择性差以及在液流电池中性能差等瓶颈问题。以全氟磺酸树脂为基体骨架材料,将改性的木质素作为掺加的离子选择传导媒介,采用分步分散、溶液共混和溶液浇注等成膜方法来制备全氟磺酸树脂/离子化木质素复合质子交换膜。本发明制备的复合离子交换膜具有良好的离子选择传导率、超低的活性材料渗透性、良好的机械和化学稳定性以及优越的液流电池性能等优点,可广泛地应用于商业化液流电池领域。(The invention relates to the field of ion exchange membranes used for flow batteries, in particular to a preparation method of a perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane, which solves the bottleneck problems of serious ion permeation, poor stability, poor ion selectivity, poor performance in a flow battery and the like of the existing commercial diaphragm material. The perfluorinated sulfonic acid resin/ionized lignin composite proton exchange membrane is prepared by taking perfluorinated sulfonic acid resin as a matrix framework material and modified lignin as an added ion selective conduction medium by adopting film-forming methods such as stepwise dispersion, solution blending, solution casting and the like. The composite ion exchange membrane prepared by the invention has the advantages of good ion selective conductivity, ultralow active material permeability, good mechanical and chemical stability, excellent flow battery performance and the like, and can be widely applied to the field of commercial flow batteries.)

1. A preparation method of a perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane is characterized by comprising the following steps and process conditions:

(1) the lignin is derived from waste produced in the cellulose industry, paper industry or biofuel production process;

(2) lignin modification treatment: the modification treatment of the lignin is protonation, sodium ionization, potassium ionization or lithium ionization;

protonation treatment: soaking 1kg of lignin in 3-5 liters of an acid agent with the concentration of 0.5-2 mol/liter, stirring for 24-36 hours, centrifuging, filtering and drying to obtain protonated lignin;

sodium ionization treatment: soaking 1kg of lignin in 3-5 liters of sodium hydroxide or sodium chloride aqueous solution with the concentration of 0.5-2 mol/liter, stirring for 24-36 hours, centrifuging, filtering and drying to obtain sodium ionized lignin;

and (3) potassium ionization treatment: soaking 1kg of lignin in 3-5 liters of potassium hydroxide or potassium chloride aqueous solution with the concentration of 0.5-2 mol/liter, stirring for 24-36 hours, centrifuging, filtering and drying to obtain potassium ionized lignin;

lithium ionization treatment: soaking 1kg of lignin in 3-5 liters of lithium hydroxide, lithium chloride or lithium sulfate aqueous solution with the concentration of 0.5-2 mol/liter, stirring for 24-36 hours, centrifuging, filtering and drying to obtain lithium-ionized lignin;

(3) the preparation method of the perfluorinated sulfonic acid resin solution comprises the following steps: dissolving the dried perfluorinated sulfonic acid resin proton exchange membrane in a high-boiling-point organic solvent, wherein the mass-volume ratio is as follows: stirring a high-boiling-point organic solvent (1/40-1/10 g/mL) at a constant temperature of 100-160 ℃ for 0.8-5 h;

(4) adding the lignin modified in the step (1) into the perfluorinated sulfonic acid resin solution obtained after the reaction in the step (2), and stirring and performing ultrasonic treatment to prepare a perfluorinated sulfonic acid resin/lignin mixed solution with the modified lignin of which the mass percentage is 0.2-35%;

(5) and (4) adding the perfluorinated sulfonic acid resin/lignin mixed solution obtained in the step (3) into a grooved glass plate, forming a film by adopting a solution casting method, circularly heating and drying, and soaking in deionized water to obtain the perfluorinated sulfonic acid resin/lignin composite ion exchange membrane.

2. The method for preparing the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane according to claim 1, wherein in the step (2), the modification degree of lignin is 3-30 wt%, wherein an acid agent used in protonation treatment is one of sulfuric acid, nitric acid and hydrochloric acid.

3. The preparation method of the perfluorosulfonic acid resin/modified lignin composite ion exchange membrane according to claim 1, wherein in the step (2), the stirring speed is 300-1500 rpm.

4. The method for preparing the perfluorosulfonic acid resin/modified lignin composite ion-exchange membrane according to claim 1, wherein in the step (3), the high-boiling-point organic solvent is one of N, N-dimethylformamide, dimethyl sulfoxide, N-dimethylacetamide, tetrahydrofuran and N-methylpyrrolidone.

5. The preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane according to claim 1, wherein in the step (4), the modified lignin is added into the perfluorinated sulfonic acid resin solution, the stirring speed is 700-1500 rpm, the stirring treatment is performed for 1-3 h, and the ultrasonic treatment time is 40-80 min.

6. The preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane according to claim 1, wherein in the step (4), a perfluorinated sulfonic acid resin/lignin mixed solution with the modified lignin content of 3-30% by mass is preferably prepared.

7. The method for preparing the perfluorosulfonic acid resin/modified lignin composite ion-exchange membrane according to claim 1, wherein in the step (5), the cyclic heating and drying treatment during the film formation by the solution casting method comprises the following steps: the first step is at 25-140 ℃, and the drying time is 1-2 h; the second step is drying at 140-160 ℃ for 10-24 h; the third step is 160-180 ℃, the drying time is 3-6 hours, and the temperature in the third step is gradually increased; and then, the circulation is performed in sequence as required.

8. The preparation method of the perfluorosulfonic acid resin/modified lignin composite ion exchange membrane according to claim 1, wherein in the step (5), the soaking time of deionized water is 16-30 h.

9. The preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane according to claim 1, wherein in the step (5), the prepared perfluorinated sulfonic acid resin/lignin composite ion exchange membrane is a proton type, sodium ion type, potassium ion type or lithium ion type composite membrane, and the thickness range of the membrane is 15-100 μm.

The technical field is as follows:

the invention relates to the field of ion exchange membranes used for redox flow batteries (flow batteries for short), in particular to a preparation method of a green perfluorosulfonic acid resin (Nafion)/modified lignin (lignin) composite ion exchange membrane.

Background art:

the flow battery is a large-scale and most feasible and potential energy storage technology which is used for matching novel clean energy (such as wind energy, solar power generation and the like) with peak clipping and valley filling of a national power grid. At present, the main problems restricting the commercialization of the flow battery are high cost and serious self-discharge. Among them, the high-cost ion exchange membrane material is a main determining factor of the cost of the flow battery system, and thus is a key material for restricting the commercial development of the flow battery. A good ion exchange membrane material for a flow battery should have good ion selectivity, good mechanical and chemical stability, excellent active ion barrier performance, excellent ion selectivity, low cost and the like, and at present, almost no commercial ion exchange membrane material meeting the conditions is available.

Currently, ion exchange membrane materials mainly adopted in the home and abroad flow battery exemplary engineering are Nafion series membranes (Nafion membranes are perfluorosulfonic acid proton exchange membranes) of the U.S. dupont company, but Nafion has poor active ion resistance, serious battery self-discharge phenomenon, poor circulation capacity retention rate and stability of the flow battery, high cost and other defects and restricts the application of the flow battery in the industrial development of the flow battery. Many companies and research institutions at home and abroad carry out modification research on ion exchange membranes, and although certain performance of the ion exchange membranes is enhanced, the application performance of the modified ion exchange membranes in the flow batteries is still not high, so that the commercialization process of the flow batteries is restricted. Meanwhile, researchers try to develop novel low-cost non-fluorine ion exchange membrane materials, but the ion exchange membrane materials have the defects of poor chemical stability, short cycle time, easiness in crushing and the like, and the requirements of ion exchange membrane materials required by commercialization of flow batteries cannot be met. In addition, the modification and preparation processes have the defects of complex process, difficult acquisition of raw materials and the like, and the key to the commercialization of the vanadium battery is how to reduce or avoid the problem of active ion permeation of the Nafion membrane. Meanwhile, the preparation and modification means of the diaphragm are only suitable for one flow battery, and the current market needs a diaphragm material suitable for multiple flow batteries urgently.

The invention content is as follows:

in order to overcome the defects of the prior art and break through the constraint of the traditional ion exchange membrane, the invention aims to provide a preparation method of a perfluorosulfonic acid resin (Nafion)/modified lignin (lignin) composite ion exchange membrane which is suitable for a flow battery, has low active ion permeability, high stability and excellent performance of the flow battery, and solves the problems of serious active ion permeability, high cost and unsuitability for various flow batteries existing in the conventional commercial Nafion membrane. The method can obtain the Nafion/lignin composite ion exchange membrane which has the active ion barrier property far higher than that of a Nafion membrane and the cost far lower than that of the Nafion membrane, can be suitable for multiple flow batteries, and has the advantages of good ion selectivity, high ion conductivity, good chemical stability, good performance in a single flow battery, suitability for multiple flow battery systems and the like.

The technical scheme of the invention is as follows:

a preparation method of a perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane comprises the following steps and process conditions:

(1) the lignin is derived from waste produced in the cellulose industry, paper industry or biofuel production process;

(2) lignin modification treatment: the modification treatment of the lignin is protonation, sodium ionization, potassium ionization or lithium ionization;

protonation treatment: soaking 1kg of lignin in 3-5 liters of an acid agent with the concentration of 0.5-2 mol/liter, stirring for 24-36 hours, centrifuging, filtering and drying to obtain protonated lignin;

sodium ionization treatment: soaking 1kg of lignin in 3-5 liters of sodium hydroxide or sodium chloride aqueous solution with the concentration of 0.5-2 mol/liter, stirring for 24-36 hours, centrifuging, filtering and drying to obtain sodium ionized lignin;

and (3) potassium ionization treatment: soaking 1kg of lignin in 3-5 liters of potassium hydroxide or potassium chloride aqueous solution with the concentration of 0.5-2 mol/liter, stirring for 24-36 hours, centrifuging, filtering and drying to obtain potassium ionized lignin;

lithium ionization treatment: soaking 1kg of lignin in 3-5 liters of lithium hydroxide, lithium chloride or lithium sulfate aqueous solution with the concentration of 0.5-2 mol/liter, stirring for 24-36 hours, centrifuging, filtering and drying to obtain lithium-ionized lignin;

(3) the preparation method of the perfluorinated sulfonic acid resin solution comprises the following steps: dissolving the dried perfluorinated sulfonic acid resin proton exchange membrane in a high-boiling-point organic solvent, wherein the mass-volume ratio is as follows: stirring a high-boiling-point organic solvent (1/40-1/10 g/mL) at a constant temperature of 100-160 ℃ for 0.8-5 h;

(4) adding the lignin modified in the step (1) into the perfluorinated sulfonic acid resin solution obtained after the reaction in the step (2), and stirring and performing ultrasonic treatment to prepare a perfluorinated sulfonic acid resin/lignin mixed solution with the modified lignin of which the mass percentage is 0.2-35%;

(5) and (4) adding the perfluorinated sulfonic acid resin/lignin mixed solution obtained in the step (3) into a grooved glass plate, forming a film by adopting a solution casting method, circularly heating and drying, and soaking in deionized water to obtain the perfluorinated sulfonic acid resin/lignin composite ion exchange membrane.

In the preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane, in the step (2), the modification degree of lignin is 3-30 wt%, wherein an acid agent adopted in protonation treatment is one of sulfuric acid, nitric acid and hydrochloric acid.

The preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane comprises the step (2), wherein the stirring speed is 300-1500 rpm.

In the preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane, in the step (3), the high-boiling-point organic solvent is one of N, N-dimethylformamide, dimethyl sulfoxide, N-dimethylacetamide, tetrahydrofuran and N-methylpyrrolidone.

The preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane comprises the step (4), adding modified lignin into a perfluorinated sulfonic acid resin solution, wherein the stirring speed is 700-1500 rpm, the stirring treatment is carried out for 1-3 hours, and the ultrasonic treatment time is 40-80 min.

In the preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane, in the step (4), a perfluorinated sulfonic acid resin/lignin mixed solution with the mass percent of the modified lignin of 3-30% is preferably prepared.

The preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane comprises the following steps of (5) cyclic heating and drying treatment during film formation by a solution casting method: the first step is at 25-140 ℃, and the drying time is 1-2 h; the second step is drying at 140-160 ℃ for 10-24 h; the third step is 160-180 ℃, the drying time is 3-6 hours, and the temperature in the third step is gradually increased; and then, the circulation is performed in sequence as required.

The preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane comprises the step (5), wherein the soaking time of deionized water is 16-30 h.

The preparation method of the perfluorinated sulfonic acid resin/modified lignin composite ion exchange membrane comprises the step (5), wherein the prepared perfluorinated sulfonic acid resin/lignin composite ion exchange membrane is a proton type, sodium ion type, potassium ion type or lithium ion type composite membrane, and the thickness range of the prepared perfluorinated sulfonic acid resin/lignin composite ion exchange membrane is 15-100 mu m.

The design idea of the invention is as follows:

lignin (lignin) is a good ion exchange membrane filling material, and has rich ion conduction groups and excellent hydrophilic performance. Compared with other ion exchange membrane filling materials, the ion exchange membrane filling material has the advantages of low cost, environmental protection and the like, is a third-stored biopolymer on earth because of being a waste in the fiber industry, the paper industry and the biofuel production process, and has the advantage of easily obtained raw materials. The invention utilizes modification treatment lignin to improve the number of ion exchange groups on the surface of lignin, thereby improving the hydrophilicity, the dispersibility and the ion selectivity of lignin. And moreover, the Nafion/lignin composite ion exchange membrane prepared by the solution casting method has good ion conductivity, extremely low active ion permeability and excellent flow battery performance. The method for preparing the composite ion exchange membrane provides a new way for preparing the ion exchange membrane material for the industrial development of the flow battery, and is expected to become a preparation method of the commercial ion exchange membrane of the flow battery.

Compared with the prior art, the invention has the following remarkable advantages and beneficial effects:

1. lignin utilized in the present invention is combined with conventional filler materials (e.g., TiO)₂、WO₃、SiO₂Graphene and graphene oxide), has the advantages of rich lignin reserves, low recovery cost, good ion selectivity, low price, environmental protection, easily obtained raw materials and the like. Meanwhile, the surface is rich in a large number of ion exchange groups after modification treatment, the size of an ion transfer channel is easily regulated and controlled from a nanoscale, and ions are transported, so that the purpose of effectively realizing perfect screening of the proton exchange membrane material on the ions and active ion materials is achieved, and the ion conduction is blocked while the ion conduction is realized. In addition, the method can be suitable for various flow battery systems through different modification treatments.

2. The Nafion/lignin composite ion exchange membrane prepared by the method effectively improves the mechanical property and chemical stability of the ion exchange membrane, and further improves the stability of the composite ion exchange membrane in a vanadium battery. Due to the addition of the modified lignin, the interaction between the filling material and the matrix skeleton can be improved, the mechanical stability of the ion exchange membrane is improved, and the circulation stability of the ion exchange membrane in the battery is improved.

3. The modified lignin used in the invention is a good ion conduction carrier, and can effectively improve the water content and the ion conductivity of the composite ion exchange membrane, wherein the water content ranges from 25 wt% to 60 wt%, and the ion conductivity ranges from 4.86 ms/cm to 56.8 ms/cm.

4. The equipment used in the whole preparation process has the characteristics of low price, low raw material cost, convenient operation, environmental protection and other industrial practicability, and is beneficial to the development of the commercial ion exchange membrane material of the propulsion flow battery and the commercial production of the propulsion flow battery.

In a word, the Nafion/lignin composite ion exchange membrane prepared by the solution casting method is utilized. The composite ion exchange membrane has the advantages of good ion conductivity, low active ion permeation, good chemical stability, high capacity retention rate in a single flow battery, high efficiency, low self-discharge rate, suitability for multiple flow battery systems and the like. The swelling property can be reduced and the active ion permeability can be reduced by utilizing the modified lignin under the condition of improving the hydrophilic property, the ion conductivity, the electric conductivity and the mechanical property of the composite ion exchange membrane. Meanwhile, the Nafion/lignin composite ion exchange membrane has excellent capacity retention rate and cycle stability in the application of the flow battery, so that the composite ion exchange membrane prepared by the method is expected to realize industrialization in a multi-flow battery system.

Description of the drawings:

FIG. 1 is a graph comparing charge and discharge curves of a vanadium battery equipped with a composite ion exchange membrane of Nafion 212 and Nafion/protonated lignin

Fig. 2 is a graph of the capacity performance of a flow battery equipped with a Nafion 212 and Nafion/protonated lignin composite ion exchange membrane.

Fig. 3 is a graph of capacity performance versus flow cell performance for a flow cell equipped with Nafion 212 and a Nafion/potassium-ionized lignin composite ion exchange membrane.

Fig. 4 is a graph comparing the efficiency of flow batteries equipped with Nafion 212 and a Nafion/sodium-ionized lignin composite ion exchange membrane.

The specific implementation mode is as follows:

in the specific implementation process, perfluorosulfonic acid macromolecules (Nafion) are used as a matrix, a Nafion solution is prepared by a dissolution method, modified lignin (lignin) is used as an ion selection admixture, and a Nafion/lignin composite ion exchange membrane is prepared by film forming methods such as stepwise dispersion, solution blending and solution casting, wherein the thickness of the Nafion/lignin composite ion exchange membrane is 10-90 mu m. The modified lignin on the appearance of the obtained composite ion exchange membrane is uniformly dispersed, has no lignin dissolution phenomenon, and has better flexibility and mechanical property.

The present invention will be further described with reference to the following examples and the accompanying drawings.