阅读说明：本技术 一种高效利用电能进行煤氧化和二氧化碳还原的耦合工艺 (Coupling process for efficiently utilizing electric energy to perform coal oxidation and carbon dioxide reduction ) 是由 张秋民 范玉强 何德民 关珺 张轩轩 于 2020-12-07 设计创作，主要内容包括：本发明公开了一种高效利用电能进行煤氧化和二氧化碳还原的耦合工艺,包括阴极二氧化碳电还原、阳极水煤浆电氧化制备腐植酸以及二氧化碳循环鼓入三部分。与单独阴极二氧化碳电还原和单独阳极水煤浆电氧化相比,阴极和阳极耦合起来可以大大降低电解池的槽电压提高能量利用率；阴极配上气体缓冲罐使二氧化碳循环鼓入可以提高气态产物的最终浓度,降低分离难度；同时此工艺加入了反向脉冲,这一工艺的加入对于阴极可以大大的提高银电极的稳定性,使得其能配合阳极进行长时间的电解,对于阳极可以缓解煤颗粒在阳极表面的沉积,降低了煤中有机质的过度氧化产生无效的二氧化碳,使得电能更多的用来氧化煤中有机质增产腐植酸。(The invention discloses a coupling process for efficiently utilizing electric energy to carry out coal oxidation and carbon dioxide reduction, which comprises three parts of cathode carbon dioxide electroreduction, anode coal water slurry electrooxidation to prepare humic acid and carbon dioxide circular blowing. Compared with the single cathode carbon dioxide electroreduction and the single anode coal water slurry electrooxidation, the cathode and the anode are coupled, so that the cell voltage of the electrolytic cell can be greatly reduced, and the energy utilization rate is improved; the cathode is matched with a gas buffer tank to circularly blow carbon dioxide, so that the final concentration of a gaseous product can be improved, and the separation difficulty is reduced; meanwhile, reverse pulse is added in the process, the stability of the silver electrode can be greatly improved for the cathode by the addition of the process, the silver electrode can be matched with the anode to carry out long-time electrolysis, the deposition of coal particles on the surface of the anode can be relieved for the anode, the generation of ineffective carbon dioxide caused by excessive oxidation of organic matters in coal is reduced, and more electric energy is used for oxidizing the organic matters in the coal to increase the yield of humic acid.)

1. A coupling process for efficiently utilizing electric energy to carry out coal oxidation and carbon dioxide reduction combines the carbon dioxide reduction of a cathode and the oxidation of anode coal water slurry, and is characterized by comprising the following steps:

(1) crushing a coal sample to 150 meshes, adding a potassium hydroxide solution, stirring and then carrying out ultrasonic treatment to prepare anode coal water slurry with uniformly dispersed coal particles; preparing potassium bicarbonate cathode electrolyte;

(2) respectively filling the cathode electrolyte and the anode coal water slurry into a cathode-anode electrolytic cell, respectively filling a cathode electrode and an anode electrode, stirring the anode coal water slurry, and introducing quantitative pure CO into a gas buffer tank through a gas inlet (16)₂；

(3) The water bath is opened to set the reaction temperature of the cathode and anode, and CO is blown into the cathode₂；CO₂The blowing-in mode is a circulating blowing-in mode, and quantitative pure CO is blown into a buffer tank firstly₂Then the CO in the buffer tank is pumped by an air pump₂Bubbling into a cathode electrolytic cell, and introducing CO through an air outlet of the cathode electrolytic cell₂Circulating to buffer tank for 30min to make CO in catholyte₂The dissolution is saturated;

(4)CO₂after the dissolution is saturated, controlling the current and carrying out electrolysis by adopting a two-electrode system; in the reaction process, anode gas is collected by a gas collecting bag, cathode gas is collected by a gas collecting bag or a buffer tank according to different gas blowing modes, and CO is generated in the electrolysis process₂Continuously blowing in;

the electrolysis adopts constant current electrolysis, namely forward constant current electrolysis, reverse constant current pulse, forward constant current electrolysis and reverse constant current pulse are circulated; the current density of the forward constant current electrolysis is 8-80 mA/cm by taking the area of the anode electrode as a calculation reference^-2The forward constant current electrolysis time is 10-100 s; the current density of the reverse constant current pulse is 3-7 mA/cm by taking the area of the cathode electrode as a calculation reference^-2The time of the reverse constant current pulse is 1-3 s;

(5) and after the electrolysis is finished, performing centrifugal separation on the anode coal water slurry to obtain solid residual coal and filtrate, measuring the humic acid content in the residual coal and the filtrate, and discharging the gas in the gas buffer tank through a gas outlet (17) for detection and separation.

2. The coupling process for performing coal oxidation and carbon dioxide reduction by efficiently utilizing electric energy according to claim 1, wherein the concentration of potassium hydroxide in the step (1) is 5-15 wt.%; the concentration of the potassium bicarbonate is 0.1-0.5 mol/L.

3. The coupling process for performing coal oxidation and carbon dioxide reduction by efficiently utilizing electric energy according to claim 1 or 2, wherein the cathode used in the step (2) is a silver electrode, and the anode is a nickel electrode; the area ratio of the silver electrode to the nickel electrode is 1: 1-10: 1.

4. The coupling process for efficiently utilizing electric energy to oxidize coal and reduce carbon dioxide according to claim 1 or 2, wherein the reaction temperature in the step (3) is 40-80 ℃.

5. The coupling process for performing coal oxidation and carbon dioxide reduction by efficiently using electric energy according to claim 3, wherein the reaction temperature in the step (3) is 40-80 ℃.

6. The coupled process for coal oxidation and carbon dioxide reduction with high efficiency of electric energy according to claim 1, 2 or 5, characterized in that the total electrolysis time of the step (5) is as follows: and 3-7 h, wherein the total electrolysis time is the total time from the start of electrifying electrolysis to the end of multiple cycles.

7. The coupled process for coal oxidation and carbon dioxide reduction with high efficiency of electric energy according to claim 3, characterized in that the total electrolysis time of the step (5) is as follows: and 3-7 h, wherein the total electrolysis time is the total time from the start of electrifying electrolysis to the end of multiple cycles.

8. The coupled process for coal oxidation and carbon dioxide reduction with high efficiency of electric energy according to claim 4, characterized in that the total electrolysis time of the step (5) is as follows: and 3-7 h, wherein the total electrolysis time is the total time from the start of electrifying electrolysis to the end of multiple cycles.

Technical Field

The invention belongs to the field of energy chemical industry, and particularly relates to the technical field of humic acid preparation through cathodic carbon dioxide electroreduction and anodic coal water slurry oxidation.

Background

Since the industrial revolution, the energy crisis is brought about by the heavy use of fossil energy, and the concentration of carbon dioxide in the atmosphere is increased from about 270ppm before the industrial revolution to about 400ppm nowadays, so that the ecological environment of the earth is seriously influenced by the greenhouse effect. And the waste of electric energy in China is serious, and the annual energy production of the three gorges hydropower station in 2018 is equivalent to 1000 hundred million kilowatt hours of wind, water and light abandonment in 2017. Therefore, scientists are researching a technology for reducing carbon dioxide into useful chemicals such as carbon monoxide, methane, ethylene or ethanol by using electric energy, the technology can not only consume electric energy and relieve greenhouse effect, but also can produce useful chemicals, and the technology is a technical scheme which is concerned at present; china has abundant coal resources, and currently, coal is mainly utilized as fuel for power generation. Coal has lower utilization rate of fuel, and the utilization of non-fuel is more valuable. In order to realize the transformation of coal economy from the traditional extensive type to the high-efficiency intensive type and realize the clean and high-efficiency utilization of coal, coal non-fuel utilization is more and more emphasized, the high-added-value utilization of coal resources containing humic acid is paid attention again, according to investigation, in the storage of the humic acid resources of the coal in China, the storage capacity of the lignite is 1264.6 hundred million tons, the world accounts for 4.82%, and the humic acid produced by the coal can repair soil in agriculture, prevent soil hardening, preserve water, resist drought, inhibit weed growth, promote the absorption of trace elements by plants, and finally improve the yield of crops.

Carbon dioxide electroreduction research has focused on the improvement of current density and the improvement of faradaic efficiency of products. However, in these studies, only carbon dioxide reduction of the cathode is generally studied, the anode uses a platinum electrode to generate oxygen, and the anode only plays a role of forming a complete loop, but the oxidizability of the anode is not fully developed; although the faraday efficiency of the product is of great concern in these studies, separation is also made difficult due to the low product concentration; the extraction of humic acid from coal is mainly carried out by an alkali dissolution and acid precipitation method, and in order to improve the yield of humic acid, the raw coal is generally required to be subjected to pre-oxidation treatment. The oxidation of coal is generally divided into mild oxidation and deep oxidation. Mild oxidation is typically carried out with air or oxygen below 250 ℃, where oxidation of carbon oxides on the surface of the coal molecule occurs primarily; deep oxidation is generally carried out by dissolving coal in alkaline solution, heating and introducing into oxidizing substance such as air, oxygen, nitric acid, and the product is mainly high molecular organic acid soluble in alkali. When potassium permanganate or hydrogen peroxide is added. The product is then further oxidized to form a complex organic acid that is soluble in water. Benzene carboxylic acid is generated when the amount of the oxidant is increased and the reaction time is prolonged, and carbon dioxide and water are generated when the oxidation is completely performed. The pre-oxidation methods can greatly improve the content of humic acid in the coal. But also has certain disadvantages, such as strong oxidability of hydrogen peroxide, sensitivity to catalyst, metal iron and copper, impact and friction, easy explosion, poor safety and unsuitability for industrial production; the nitric acid oxidation has the problems of serious equipment corrosion, difficult nitric acid separation and recovery, serious environmental pollution problem caused by generated waste water and waste gas, certain use limit of the method and the like. In addition, the device has the disadvantages of large volume, expensive chemicals and the like. When the coal is pre-oxidized by adopting an electrooxidation method, the oxidizing agent in the traditional oxidation process can be replaced by the oxidation characteristic of the anode, the treatment difficulty of waste liquid is reduced, the pollution to the environment is reduced, the oxidizing strength of the anode can be changed by controlling the potential so as to control the type of the product, namely the content of the humic acid, the humic acid and the fulvic acid in the product can be changed by controlling the potential. In addition, the method for oxidizing the anode coal water slurry has the characteristics of mild operation conditions, simple equipment requirements, energy conservation and little pollution. However, similar to the carbon dioxide electroreduction, in the research of anode coal water slurry oxidation, the cathode only plays a role of forming a complete loop, and the reduction performance of the cathode is not really exerted.

The research is carried out by coupling the electric reduction of the cathode carbon dioxide and the electric oxidation of the anode coal water slurry, so that the reduction and oxidation effects of the cathode and the anode can be fully exerted, and compared with the current common single electric reduction of the carbon dioxide, the cell voltage can be lower, and the electric energy can be saved. The theoretical calculation of the electric energy consumed by the two is explained below.

At present, carbon dioxide electroreduction research takes carbon monoxide production as an example:

cathode: CO 2₂+2e^-+2H⁺→CO+H₂O; anode: h₂O–2e^-→1/2O₂+2H⁺(ii) a The theoretical decomposition tank voltage is 1.34V.

The process for coupling the reduction of cathode carbon dioxide to the oxidation of anode coal water slurry comprises the steps of producing carbon monoxide at the cathode and oxidizing anode C into CO₂For example, the following steps are carried out:

cathode: CO 2₂+2e^-+2H⁺→CO+H₂O; anode: c +2H₂O→CO₂+4H⁺+4e^-(ii) a The theoretical decomposition tank voltage is 0.33V.

The theoretical analysis shows that the process of coupling the cathode carbon dioxide reduction and the anode coal water slurry oxidation technology can greatly reduce the cell voltage of the electrolytic cell, thereby efficiently utilizing electric energy; on the basis of the combination of the cathode and the anode, the blowing-in mode of cathode carbon dioxide is changed from the traditional continuous blowing-in of pure carbon dioxide into the circulating blowing-in with a circulating tank, so that the concentration of the final gaseous product in the carbon dioxide can be improved, and the separation of the product is facilitated; in addition, reverse pulse is added in the electrolysis process, the stability of the silver electrode can be greatly improved by the addition of the reverse pulse to the cathode, so that the silver electrode can be matched with the anode to carry out long-time electrolysis, the deposition of coal particles on the surface of the anode in the electrolysis process can be relieved to the anode, organic matters in coal are prevented from being excessively oxidized into carbon dioxide, and the yield of humic acid is improved.

Disclosure of Invention

The invention aims to overcome the defects that the prior counter electrode is vacant when cathode carbon dioxide reduction is carried out alone and anode coal water slurry electrooxidation is carried out alone to prepare humic acid, the oxidation and reduction functions of the counter electrode cannot be effectively utilized, so that the potential of the counter electrode is wasted, the utilization rate of electric energy is low, and the product concentration of cathode carbon dioxide reduction is low and is not beneficial to separation. Compared with the process of singly carrying out carbon dioxide electroreduction, the process of coupling cathode carbon dioxide reduction and anode coal water slurry oxidation can greatly reduce the cell voltage and save electric energy; the blowing-in mode of cathode carbon dioxide is changed from the traditional continuous blowing-in of pure carbon dioxide into the circulating blowing-in with a circulating tank, so that the concentration of the final gaseous product in the carbon dioxide can be improved, and the separation of the product is facilitated; in addition, reverse pulse is added in the electrolysis process, the stability of the silver electrode can be greatly improved by the addition of the reverse pulse to the cathode, so that the silver electrode can be matched with the anode to carry out long-time electrolysis, the deposition of coal particles on the surface of the anode in the electrolysis process can be relieved to the anode, organic matters in coal are prevented from being excessively oxidized into carbon dioxide, and the yield of humic acid is improved.

The technical scheme of the invention is as follows:

a coupling process for efficiently utilizing electric energy to carry out coal oxidation and carbon dioxide reduction combines the carbon dioxide reduction of a cathode and the oxidation of anode coal water slurry together, and comprises the following steps:

(1) crushing a coal sample to 150 meshes, adding a potassium hydroxide solution, stirring and then carrying out ultrasonic treatment to prepare anode coal water slurry with uniformly dispersed coal particles; preparing potassium bicarbonate cathode electrolyte;

(2) respectively filling the cathode electrolyte and the anode coal water slurry into a cathode-anode electrolytic cell, respectively filling a cathode electrode and an anode electrode, stirring the anode coal water slurry, and introducing quantitative pure CO into a gas buffer tank through a gas inlet (16)₂；

(3) The water bath is opened to set the reaction temperature of the cathode and anode, and CO is blown into the cathode₂；CO₂The blowing-in mode is a circulating blowing-in mode, and quantitative pure CO is blown into a buffer tank firstly₂Then the CO in the buffer tank is pumped by an air pump₂Bubbling into a cathode electrolytic cell, and introducing CO through an air outlet of the cathode electrolytic cell₂Circulating to buffer tank for 30min to make CO in catholyte₂The dissolution is saturated;

(4)CO₂after the dissolution is saturated, controlling the current and carrying out electrolysis by adopting a two-electrode system; in the reaction process, anode gas is collected by a gas collecting bag, cathode gas is collected by a gas collecting bag or a buffer tank according to different gas blowing modes, and CO is generated in the electrolysis process₂Continuously blowing in;

the electrolysis adopts constant current electrolysis, namely forward constant current electrolysis, reverse constant current pulse, forward constant current electrolysis and reverse constant current pulse are circulated; the current density of the forward constant current electrolysis is 8-80 mA/cm by taking the area of the anode electrode as a calculation reference^-2The forward constant current electrolysis time is 10-100 s; the current density of the reverse constant current pulse is 3-7 mA/cm by taking the area of the cathode electrode as a calculation reference^-2The time of the reverse constant current pulse is 1-3 s;

(5) and after the electrolysis is finished, performing centrifugal separation on the anode coal water slurry to obtain solid residual coal and filtrate, measuring the humic acid content in the residual coal and the filtrate, and discharging the gas in the gas buffer tank through a gas outlet (17) for detection and separation.

The concentration of the potassium hydroxide in the step (1) is 5-15 wt.%; the concentration of the potassium bicarbonate is 0.1-0.5 mol/L.

The cathode and anode electrodes in step (2) are electrodes of various materials and materials, including but not limited to the cathode silver electrode and the anode nickel electrode used in the examples cited in this patent. The area ratio of the silver electrode to the nickel electrode is 1: 1-10: 1.

The reaction temperature in the step (3) is 40-80 ℃.

The total electrolysis time range of the step (5) is as follows: and 3-7 h, wherein the total electrolysis time is the total time from the start of electrifying electrolysis to the end of multiple cycles.

The invention has the beneficial effects that: 1. the cathode and the anode are coupled, so that the electrolytic bath voltage can be greatly reduced, the electric energy is saved, and the utilization rate of the electric energy is improved. In order to combine the reduction of cathode carbon dioxide and the oxidation of anode coal water slurry, a common constant voltage electrolysis mode during the electrical reduction of carbon dioxide is changed into constant current electrolysis, and the area ratio and the current density of the cathode and anode electrodes are adjusted to enable the cathode and the anode to be well matched, so that the functions of the cathode and the anode can be played simultaneously. Compared with the single cathode carbon dioxide electroreduction, the process of coupling the cathode and the anode and matching constant current electrolysis can greatly reduce the cell voltage of the electrolytic cell from the theoretical and practical operation, thereby improving the utilization rate of electric energy; 2. the carbon dioxide circulation blowing mode can improve the concentration of the final cathode gaseous product and reduce the separation difficulty. The cathode is matched with a gas buffer tank, carbon dioxide is circulated between the cathode electrolytic cell and the buffer tank through a gas pump, and the gaseous product is continuously stored in the buffer tank, so that the final concentration of the gaseous product is improved, and the separation difficulty of the product is reduced; 3. the addition of the reverse pulse enables more electric energy to be used for oxidizing macromolecular structures of the coal to produce humic acid, so that the yield of the humic acid is improved. The technology of combining the cathode and the anode adds reverse constant current pulse on the basis of constant current electrolysis, and the addition of the technology can greatly improve the stability of the silver electrode for the cathode, so that the silver electrode can be matched with the anode to carry out long-time electrolysis, and the deposition of coal particles on the surface of the anode can be relieved for the anode, thereby not only reducing the damage of an anode sheet, but also relieving the generation of invalid carbon dioxide caused by excessive oxidation of organic matters in coal, and further leading the electric energy to be more used for oxidizing the organic matters in the coal to increase the yield of humic acid.

Drawings

FIG. 1 is a schematic view of an electrochemical reactor used in the present invention.

In the figure: 1 cathode gas collecting port, 2 anode gas collecting port, 3 cathode silver electrode, 4 anode nickel electrode, 5Nafion117 proton diaphragm, 6 water jacket water inlet, 7 water jacket water outlet, 8 cathode gas inlet, 9 anode coal water slurry stirrer, 10 water jacket, 11 cathode region, 12 anode region, 13 diaphragm pump, 14 gas buffer tank, 15 gas storage chamber, 16 gas inlet, 17 gas outlet.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the present invention is not limited to the specific examples.

The system is adopted to implement a coupling process for efficiently utilizing electric energy to carry out coal oxidation and carbon dioxide reduction, and the properties of coal samples used in experiments are shown in table 1.

Table 1 industrial and elemental analysis of lignite.

Note: is obtained by differential subtraction.

The humic acid content in the experimental lignite is 31.25 wt.%. Measured according to the national standard GB/T11957-2001 method for measuring the yield of humic acid in coal.

Table 2 specific process conditions for examples 1, 2, 3, 4, 5.

Table 3 examples the results of humic acid (both greater than 31.25% humic acid content in raw coal) as an anode product and the CO Concentration (CO) as a cathode product₂CO concentration in the cyclic blowing mode can reach more than 12%) and its faraday efficiency.