Method for preparing high-purity hydrogen through adsorption-enhanced formic acid dehydrogenation

Abstract

The invention belongs to the technical field of combustion chemical industry and materials, and particularly relates to a method for preparing high-purity hydrogen through adsorption-enhanced formic acid dehydrogenation. Through three steps of formic acid dehydrogenation reaction, adsorption-enhanced hydrogen production and adsorbent regeneration, the invention provides a method for preparing high-purity hydrogen through adsorption-enhanced formic acid dehydrogenation to solve the problems of catalyst poisoning, limited catalytic performance and to-be-improved H2 yield caused by high CO content in a gas product in the existing formic acid dehydrogenation technology. The invention aims to regulate and control the selectivity of a reaction gas product by adsorbing CO2, reduce the CO selectivity, prolong the service life of a catalyst, improve the H2 selectivity and improve the product quality. In addition, the CO2 adsorbent is desorbed and regenerated, CO2 is captured and utilized, the CO2 adsorbent can be recycled, and the overall economic effect of the system is improved.

Description

Technical Field

[0001] The invention belongs to the field of combustion chemical industry and material technology, and particularly relates to a method for producing high-purity hydrogen by adsorption-enhanced formic acid dehydrogenation. Background Art

[0002] Formic acid (FA) is the simplest carboxylic acid with the molecular formula HCOOH. It exists stably as a colorless transparent liquid at room temperature and pressure, has a pungent odor and is corrosive, and is miscible with water and most polar solvents. Formic acid has the following advantages in hydrogen storage: 1) Formic acid is a stable, low-toxic colorless liquid at room temperature, easy to handle, store and transport. Depending on its concentration, materials such as stainless steel, high-density polyethylene and polypropylene can be used for its safe and sealed storage and transportation; 2) Formic acid has a wide range of sources and a simple molecular structure. Under certain conditions, it only decomposes to generate several easily controllable small molecules, which can be directly used in fuel cells without producing exhaust gas; 3) The mass hydrogen content and volume hydrogen content of formic acid are 4.4wt.% and 53.4g / L, respectively.

[0003] Dehydrogenation reaction: HCOOH(l)→CO2(g)+H2(g) △G=-32.9kJ mol -1 (1-1)

[0004] Dehydration reaction: HCOOH(l)→CO(g)+H2O(l) △G=-12.4kJ mol -1 (1-2)

[0005] Formic acid generates CO2 and H2 through dehydrogenation. This pathway has a high atomic efficiency and 100% of the stored hydrogen can be used for catalytic storage. In contrast, methanol and methane can only store 66% and 50% of their hydrogen, respectively, because some of the hydrogen is lost in the form of water. However, formic acid may also undergo a dehydration reaction of formula (1-2) to generate CO and H2O, and the product CO can cause catalyst poisoning, leading to severe degradation or even inactivation of the catalytic activity. Therefore, it is necessary to avoid the occurrence of dehydration reactions and strictly control the CO concentration to a minimum. It can be seen that the dehydrogenation reaction is crucial for the efficient storage of hydrogen by formic acid, but it cannot proceed spontaneously at room temperature and pressure. It is necessary to select a suitable catalyst to promote dehydrogenation and inhibit the dehydration reaction. Therefore, the development of highly active and highly selective formic acid dehydrogenation catalysts is the key to building a formic acid hydrogen storage system, and is also the current research focus in the field of formic acid hydrogen production.

[0006] Therefore, it is of great significance to design high-performance catalysts to enhance the formic acid dehydrogenation reaction, regulate product selectivity, and increase H2 production. Compared with the traditional formic acid dehydrogenation reaction, adsorption-enhanced formic acid dehydrogenation technology has the following potential advantages: 1) CO2 adsorbent promotes the reaction equilibrium to move, increasing the hydrogen production rate; 2) Reduces CO selectivity, prevents catalyst poisoning, and increases the life of the catalyst; 3) Through CO2 adsorption regeneration, CO2 in the reaction is captured, and the CO2 adsorbent can be reused, improving the overall economic effect of the reaction. Summary of the invention

[0007] In view of the problem that the gas product of the existing formic acid dehydrogenation technology has a high CO content, which leads to catalyst poisoning, limited catalytic performance, and the H2 yield needs to be improved, the present invention proposes a method for adsorption-enhanced formic acid dehydrogenation to produce high-purity hydrogen, which aims to regulate the selectivity of the reaction gas product by adsorbing CO2, reduce CO selectivity, increase catalyst life, increase H2 selectivity, and improve product quality. In addition, the CO2 adsorbent is desorbed and regenerated, which not only captures and utilizes CO2, but also can recycle the CO2 adsorbent, thereby improving the overall economic effect of the system.

[0008] To this end, the technical solution of the present application provides a method for producing high-purity hydrogen by adsorption-enhanced formic acid dehydrogenation, comprising the following steps:

[0009] (1) Formic acid dehydrogenation reaction: The preheated formic acid aqueous solution is introduced into a reactor containing a Pd / C catalyst using N2 as a carrier gas to carry out a dehydrogenation reaction to obtain a gas product containing H2, CO2, CO, and H2O;

[0010] (2) Adsorption-enhanced hydrogen production: The gas products containing H2, CO2, and CO are subjected to Na2CO3 adsorption reaction to obtain high-purity hydrogen and NaHCO3;

[0011] (3) Adsorbent regeneration: The NaHCO3 adsorbent is subjected to a regeneration reaction to obtain a regenerated adsorbent Na2CO3, which is used in step (2) to achieve a cycle of steps (2) and (3).

[0012] Furthermore, the preheating temperature in step (1) is 110°C.

[0013] Furthermore, the molar ratio of H2O / HCOOH in the aqueous formic acid solution in step (1) is 0.2 to 1.4, preferably 1.2.

[0014] Furthermore, the flow rate of the N2 carrier in step (1) is 0<N2≤50cm 3 / min, preferably 40cm 3 / min.

[0015] Furthermore, the flow rate of the formic acid aqueous solution when N2 is used as a carrier gas to pass into the reactor is 0.02 ml / min.

[0016] Furthermore, the dehydrogenation reaction temperature in step (1) is 50-120°C, preferably 80°C.

[0017] Furthermore, the dehydrogenation reaction pressure in step (1) is 2 -2 ~2 4 atm, preferably 1 atm.

[0018] Furthermore, the adsorption reaction temperature in step (2) is 40-140°C, preferably 80-90°C.

[0019] Furthermore, in step (2), the molar ratio of the adsorbent to formic acid is 1:1.

[0020] Furthermore, the regeneration reaction temperature in step (3) is 100-140°C, preferably 115-120°C.

[0021] The beneficial effects of the present invention are:

[0022] 1. The present invention proposes to enhance the formic acid dehydrogenation reaction by adsorbing CO2. In an N2 atmosphere, Pd / C is used as a catalyst for the dehydrogenation reaction, which helps to improve the yield and quality of H2 in the product, reduce the selectivity of CO, prevent catalyst poisoning, and ensure the stability of the catalyst.

[0023] 2. Based on the adsorption of CO2 to enhance formic acid dehydrogenation, compared with the existing formic acid dehydrogenation hydrogen production process, the invention introduces a CO2 adsorbent, HCOOH (l) → CO2 (g) + H2 (g) absorbs the reaction product, promotes the forward movement of the reaction equilibrium, and has a better CO2 capture capacity and high-quality hydrogen production capacity. Compared with the addition of Na2CO3 without CO2 adsorbent, the H2 concentration in the gas product is 97.91%, an increase of 16.37%. CO selectivity is reduced by 13.92%, which not only improves the H2 yield, but also ensures the catalyst life.

[0024] 3. Based on the treatment process of step 1) of the present invention, the H2O / HCOOH molar ratio, formic acid dehydrogenation reaction temperature and reaction pressure are further coordinated and regulated, and a Pd / C high-performance catalyst is used to achieve a formic acid conversion rate of 99%. The NaCO3 / HCOOH molar ratio, adsorption enhancement reaction temperature, reaction pressure and adsorbent regeneration reaction temperature and reaction pressure are coordinated and controlled to improve the utilization rate of H atoms and achieve stable adsorption of CO2, which is helpful to improve the yield and quality of H2 in the product and reduce the selectivity of CO.

[0025] 4. Based on the adsorption enhancement treatment process of step 2) of the present invention, when the reaction temperature is 80°C, Na2CO3 can effectively adsorb CO2, and the absorption rate of carbon dioxide is 97.861% and the absorption rate is 1.88 kmol / h. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flow chart of a method for producing high-purity hydrogen by adsorption-enhanced formic acid dehydrogenation;

[0027] Figure 2-Figure 14 is the experimental result, among which,

[0028] Figure 2 is the change of hydrogen production rate and hydrogen atom utilization efficiency with dehydrogenation reaction temperature;

[0029] Figure 3 is the variation of H2, CO2 and CO concentrations with dehydrogenation reaction temperature;

[0030] Figure 4 is the change of formic acid conversion rate and system heat load with dehydrogenation temperature;

[0031] Figure 5 is the variation of H2 yield and H atom utilization efficiency with the pressure of the dehydrogenation reactor;

[0032] Figure 6 is the variation of H2, CO2 and CO concentrations with the dehydrogenation reaction pressure;

[0033] Figure 7 is the change of formic acid conversion rate and system heat load with dehydrogenation temperature;

[0034] Figure 8 is the change of hydrogen production rate and hydrogen atom utilization efficiency with the ratio of H2O / HCOOH;

[0035] Fig. 9 is the variation of H2, CO2 and CO concentrations with the H2O / HCOOH ratio;

[0036] Fig.10 is the change of formic acid conversion rate and system heat load with H2O / HCOOH ratio;

[0037] Fig.11 The concentrations of H2, CO2 and CO vary with the temperature of the adsorption enhanced hydrogen production reactor;

[0038] Fig.12 The CO2 absorption amount and CO2 adsorption rate change with the temperature of the adsorption enhanced hydrogen production reactor;

[0039] Fig.13 is the variation of H2, CO2 and CO concentrations with the Na2CO3 / HCOOH ratio;

[0040] Fig.14 The CO2 absorption amount and CO2 absorption rate change with the Na2CO3 / HCOOH ratio. DETAILED DESCRIPTION

[0041] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0042] The embodiment of the present application discloses a method for producing high-purity hydrogen by adsorption-enhanced formic acid dehydrogenation, comprising:

[0043] (1) Formic acid dehydrogenation reaction: The preheated formic acid aqueous solution is introduced into a reactor containing a Pd / C catalyst using N2 as a carrier gas to carry out a dehydrogenation reaction to obtain a gas product containing H2, CO2, CO, and H2O;

[0044] (2) Adsorption-enhanced hydrogen production: The gas product is subjected to Na2CO3 adsorption reaction to obtain high-purity hydrogen and NaHCO3;

[0045] (3) Adsorbent regeneration: The NaHCO3 adsorbent is subjected to a regeneration reaction to obtain a regenerated adsorbent Na2CO3, which is used in step (2) to achieve a cycle of steps (2) and (3).

[0046] Figure 1 The flow chart of this application method is as follows: Figure 1 As shown, this embodiment first enhances the formic acid dehydrogenation reaction by adsorbing CO2: First, in step (1) formic acid dehydrogenation reaction, HCOOH and Pd / C undergo dehydrogenation reaction under N2 carrier gas, and the reaction process is: 2HCOOH(l)→CO2(g)+H2(g)+CO(g)+H2O(l), thereby obtaining a gas product containing H2, CO2, CO, and H2O.

[0047] In this process, Pd / C is used as a catalyst, and the process is carried out in a quartz reactor. At the same time, by limiting the H2O / HCOOH molar ratio, the formic acid dehydrogenation reaction temperature, and the reaction pressure, a Pd / C high-performance catalyst is used to achieve a formic acid conversion rate of more than 99%.

[0048] The obtained gas product containing H2, CO2, CO, and H2O is then subjected to an adsorption reaction by a Na2CO3 adsorbent. During this process, Na2CO3 adsorbs CO2 and H2O to generate NaHCO3, thereby obtaining high-purity hydrogen.

[0049] In this reaction, on the one hand, the introduction of Na2CO3 adsorbent promotes the absorption of reaction products during the reaction of HCOOH(l)→CO2(g)+H2(g), causing the reaction equilibrium to shift in the positive direction, thereby improving the CO2 capture capacity and the ability to produce high-quality hydrogen. On the other hand, since Na2CO3 adsorbs CO2 and H2O to generate NaHCO3, it reduces the selectivity of CO, thereby ensuring the life of the catalyst while improving the hydrogen yield.

[0050] In this reaction, the NaCO3 / HCOOH molar ratio, adsorption enhancement reaction temperature, reaction pressure and adsorbent regeneration reaction temperature and reaction pressure are coordinated to improve the utilization rate of H atoms and achieve stable adsorption of CO2, which helps to improve the yield and quality of H2 in the product and reduce the selectivity of CO.

[0051] Based on the above purpose, the present application proposes preferred parameter limits for the reaction process, for example: the preheating temperature in step (1) is 110°C; the H2O / HCOOH molar ratio in the formic acid aqueous solution is = 0.2 to 1.4, preferably 1.2; the flow rate of the N2 carrier is 0<N2≤50cm 3 / min, preferably 40cm 3 / min; the flow rate of formic acid aqueous solution into the reactor with N2 as carrier gas is 0.02ml / min; the dehydrogenation reaction temperature is 50-120°C, preferably 80°C; the dehydrogenation reaction pressure is 2 -2 ~2 4 atm, preferably 1 atm.

[0052] The adsorption reaction temperature in step (2) is 40-140° C., preferably 80-90° C.; the molar ratio of the adsorbent to formic acid is 1:1.

[0053] In this embodiment, after the above process is completed, the reacted NaHCO3 can also be regenerated by a regeneration reaction to achieve Na2CO3 regeneration, specifically, by thermal decomposition at 100-140°C, preferably 115-120°C to obtain Na2CO 3、 CO 2、 H2O, so that the regenerated Na2CO3 can continue to be put into step (2), so as to realize the cycle of step (2) and step (3), and further improve the economic effect of the system.

[0054] The technical effects of the present application will be described in more detail below with reference to specific embodiments and drawings.

[0055] In the following examples, the ratios of H2O / HCOOH and NaCO3 / HCOOH are molar ratios.

[0056] Embodiment 1 is the preferred embodiment of this application

[0057] 1) Formic acid dehydrogenation reaction: The preheated formic acid aqueous solution (50 ml, H2O / HCOOH=1.2) was preheated to 110°C to ensure the gasification of formic acid. Then it was introduced into the Pd / C dehydrogenation reactor and heated to 80°C at a heating rate of 10°C / min. The reaction pressure was 1atm. The main products were CO2 and H2, with a small amount of product CO.

[0058] 2) Adsorption enhanced hydrogen production: The gas product is passed into a Na2CO3 adsorption enhanced reactor (NaCO3 / HCOOH=1.0) with CO2 adsorbent placed therein, and enters the CO2 adsorption stage. The temperature is maintained at 80°C, CO2 is adsorbed, Na2CO3 is converted into NaHCO3, and the H2 concentration in the gas product is increased.

[0059] 3) Adsorbent regeneration: After the adsorption is completed, the adsorbent regeneration stage begins. The temperature is raised to 117.5°C at a heating rate of 10°C / min. CO2 is desorbed, and NaHCO3 is regenerated into Na2CO3, which then enters the adsorption enhanced reactor and continues to participate in the reaction as a CO2 adsorbent.

[0060] After the reaction, the gas products were collected, the gas component rate and the total gas yield were measured, the H atom utilization rate was calculated, and the effect of heat load on formic acid conversion was analyzed. The hydrogen production rate was 0.99989 kmol H2 / h, the hydrogen concentration was 97.905 vol% and the CO concentration was 11.97 ppm.

[0061] Example 2

[0062] Compared with Experimental Example 1, the only difference is that the temperature of the formic acid dehydrogenation reaction process is different.

[0063] 1) Formic acid dehydrogenation reaction: The preheated formic acid aqueous solution (50 ml, H2O / HCOOH=1.2) was preheated to 110°C to ensure the gasification of formic acid. Then it was introduced into the Pd / C dehydrogenation reactor and heated to 40°C, 60°C, 80°C, 100°C, 120°C and 140°C at a heating rate of 10°C / min. The reaction pressure was 1 atm. The main products were CO2 and H2, with a small amount of product CO.

[0064] 2) Adsorption enhanced hydrogen production: The gas product is passed into a Na2CO3 adsorption enhanced reactor (NaCO3 / HCOOH=1.0) with CO2 adsorbent placed therein, and enters the CO2 adsorption stage. The temperature is maintained at 80°C, CO2 is adsorbed, Na2CO3 is converted into NaHCO3, and the H2 concentration in the gas product is increased.

[0065] 3) Adsorbent regeneration: After the adsorption is completed, the adsorbent regeneration stage begins. The temperature is raised to 117.5°C at a heating rate of 10°C / min. CO2 is desorbed, and NaHCO3 is regenerated into Na2CO3, which then enters the adsorption enhanced reactor and continues to participate in the reaction as a CO2 adsorbent.

[0066] After the reaction, the gas products were collected, the gas component rate and the total gas yield were measured, the H atom utilization rate was calculated, and the effect of heat load on formic acid conversion was analyzed. The results showed that the hydrogen production rate and hydrogen atom utilization efficiency both showed an upward trend, reaching a peak at 80°C, and then showed a downward trend with the increase of formic acid dehydrogenation reaction temperature. Figure 2 (Chart showing the change of hydrogen production rate and hydrogen atom utilization efficiency with dehydrogenation reaction temperature). As the temperature of formic acid dehydrogenation reaction increases, the concentrations of H2 and CO2 show the same trend as the hydrogen production rate and hydrogen atom utilization efficiency, showing an upward trend before 80°C and reaching a peak at 80°C, while the effect of CO concentration is just the opposite, such as Figure 3 (H2, CO2 and CO concentrations as a function of dehydrogenation reaction temperature) The heat load in the dehydrogenation reactor decreases as the temperature increases, e.g. Figure 4 (Chart showing the conversion of formic acid and system heat load as a function of dehydrogenation temperature).

[0067] Example 3

[0068] Compared with Experimental Example 1, the only difference is that the pressure during the formic acid dehydrogenation reaction is different.

[0069] 1) Preheat the formic acid aqueous solution (50 ml, H2O / HCOOH=1.2) to 110°C to ensure the gasification of formic acid. Then pass it into the Pd / C dehydrogenation reactor and heat it to 80°C at a heating rate of 10°C / min. The pressure is 2 - 2 atm, 2 -1 atm, 0atm, 1atm, 2atm and 3atm. The main products are CO2 and H2, with a small amount of product CO.

[0070] 2) The gas product is passed into a Na2CO3 adsorption enhancement reactor (NaCO3 / HCOOH=1.0) in which CO2 adsorbent is placed, and enters the CO2 adsorption stage. The temperature is maintained at 80°C, CO2 is adsorbed, Na2CO3 is converted into NaHCO3, and the H2 concentration in the gas product is increased.

[0071] 3) After the adsorption is completed, the adsorbent regeneration stage is entered, and the temperature is raised to 117.5°C at a heating rate of 10°C / min. CO2 is desorbed, and NaHCO3 is regenerated into Na2CO3, which enters the adsorption enhanced reactor and continues to participate in the reaction as a CO2 adsorbent.

[0072] After the reaction is completed, the gas products are collected, the gas component rate and the total gas yield are measured, the H atom utilization rate is calculated, and the effect of heat load on formic acid conversion is analyzed. The hydrogen production rate and hydrogen atom utilization rate decrease steadily with the increase of dehydrogenation reaction pressure. Figure 5 (H2 yield and H atom utilization efficiency versus dehydrogenation reactor pressure) H2 and CO2 concentrations also have similar trends, decreasing with increasing dehydrogenation reaction pressure, e.g. Figure 6 (H2, CO2 and CO concentrations versus dehydrogenation reaction pressure). However, the heat load increases dramatically with the increase of dehydrogenation reaction pressure, such as Figure 7 (Chart of formic acid conversion and system heat load changing with dehydrogenation temperature).

[0073] Example 4

[0074] Compared with Experimental Example 1, the only difference is that the H2O / HCOOH in the formic acid dehydrogenation reaction process is different.

[0075] 1) Preheated formic acid aqueous solution (50 ml, H2O / HCOOH = 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4) was preheated to 110°C to ensure formic acid gasification. Then it was introduced into the Pd / C dehydrogenation reactor and heated to 80°C at a heating rate of 10°C / min and a pressure of 1 atm. The main products were CO2 and H2, with a small amount of product CO.

[0076] 2) The gas product is passed into a Na2CO3 adsorption enhancement reactor (NaCO3 / HCOOH=1.0) in which CO2 adsorbent is placed, and enters the CO2 adsorption stage. The temperature is maintained at 80°C, CO2 is adsorbed, Na2CO3 is converted into NaHCO3, and the H2 concentration in the gas product is increased.

[0077] 3) After the adsorption is completed, the adsorbent regeneration stage is entered, and the temperature is raised to 117.5°C at a heating rate of 10°C / min. CO2 is desorbed, and NaHCO3 is regenerated into Na2CO3, which enters the adsorption enhanced reactor and continues to participate in the reaction as a CO2 adsorbent.

[0078] As H2O / HCOOH increases, the hydrogen production rate continues to rise, while the hydrogen atom utilization rate gradually decreases, such as Figure 8 (Chart showing the variation of hydrogen production rate and hydrogen atom utilization efficiency with the H2O / HCOOH ratio). The concentrations of H2 and CO2 increase steadily with the increase of the H2O / HCOOH molar ratio, while the opposite is true for CO, e.g. Fig. 9 (H2, CO2 and CO concentrations versus H2O / HCOOH ratio) The heat load of the dehydrogenation system shows a gradual downward trend, e.g. Fig.10(Chart of formic acid conversion rate and system heat load changing with H2O / HCOOH ratio).

[0079] Example 5

[0080] Compared with Example 1, the only difference is that the CO2 adsorption reaction temperature is different.

[0081] 1) Preheated formic acid aqueous solution (50 ml, H2O / HCOOH=1) at 110°C to ensure formic acid gasification. Then pass into the Pd / C dehydrogenation reactor, and heat to 80°C at a heating rate of 10°C / min, with a pressure of 1 atm. The main products are CO2 and H2, with a small amount of product CO.

[0082] 2) The gas product is passed into a Na2CO3 adsorption enhancement reactor (NaCO3 / HCOOH=1.0) with CO2 adsorbent placed therein, and enters the CO2 adsorption stage at temperatures of 40°C, 60°C, 80°C, 100°C, 120°C, and 140°C. CO2 is adsorbed, Na2CO3 is converted into NaHCO3, and the H2 concentration in the gas product is increased.

[0083] 3) After the adsorption is completed, the adsorbent regeneration stage is entered, and the temperature is raised to 117.5°C at a heating rate of 10°C / min. CO2 is desorbed, and NaHCO3 is regenerated into Na2CO3, which enters the adsorption enhanced reactor and continues to participate in the reaction as a CO2 adsorbent.

[0084] The concentrations of H2 and CO2 decrease as the temperature of CO2 adsorption reaction increases, e.g. Fig.11 (Chart of the variation of H2, CO2 and CO concentrations with the temperature of the adsorption enhanced hydrogen production reactor). The CO2 absorption amount and CO2 absorption rate show the same trend, which decreases with the increase of CO2 adsorption reaction temperature, such as Fig.12 (Changes in CO2 absorption and CO2 adsorption rate with the temperature of the adsorption enhanced hydrogen production reactor).

[0085] Example 6

[0086] Compared with Example 1, the only difference is that the Na2CO3 / HCOOH ratio is different.

[0087] 1) Preheated formic acid aqueous solution (50 ml, H2O / HCOOH=1) at 110°C to ensure formic acid gasification. Then pass into the Pd / C dehydrogenation reactor, and heat to 80°C at a heating rate of 10°C / min, with a pressure of 1 atm. The main products are CO2 and H2, with a small amount of product CO.

[0088] 2) The gas product is passed into a Na2CO3 adsorption enhancement reactor (NaCO3 / HCOOH=0.4, 0.6, 0.8, 1.0, 1.2) with CO2 adsorbent placed therein, and enters the CO2 adsorption stage at a temperature of 80° C. CO2 is adsorbed, Na2CO3 is converted into NaHCO3, and the H2 concentration in the gas product is increased.

[0089] 3) After the adsorption is completed, the adsorbent regeneration stage is entered, and the temperature is raised to 117.5°C at a heating rate of 10°C / min. CO2 is desorbed, and NaHCO3 is regenerated into Na2CO3, which enters the adsorption enhanced reactor and continues to participate in the reaction as a CO2 adsorbent.

[0090] The CO2 concentration decreases to a stable level as the Na2CO3 / HCOOH ratio increases, e.g. Fig.13 (H2, CO2 and CO concentrations as a function of Na2CO3 / HCOOH ratio). However, H2 concentration shows the opposite trend, increasing with the increase of Na2CO3 / HCOOH ratio, such as Fig.14 (CO2 absorption amount and CO2 absorption rate as a function of Na2CO3 / HCOOH ratio).

[0091] Comparative Example 1

[0092] 1) Preheated formic acid aqueous solution (50 ml, H2O / HCOOH=1) at 110°C to ensure formic acid gasification. Then pass into the Pd / C dehydrogenation reactor, and heat to 80°C at a heating rate of 10°C / min, with a pressure of 1 atm. The main products are CO2 and H2, with a small amount of product CO.

[0093] 2) Compared with Example 1, the only difference is that no CO2 adsorbent is added and there is no adsorption enhancement reaction process.

[0094] Comparing the gas yields of Example 1 and Comparative Example 1, the H2 yield in Example 1 is increased by 16.37%, wherein the HCOOH conversion rate is 99%, which is increased by 9.62%.

[0095] Comparative Example 2

[0096] Compared with Example 1, the only difference is that there is no CO2 adsorption regeneration stage.

[0097] 1) Preheated formic acid aqueous solution (50 ml, H2O / HCOOH=1) at 110°C to ensure formic acid gasification. Then pass into the Pd / C dehydrogenation reactor, and heat to 80°C at a heating rate of 10°C / min, with a pressure of 1 atm. The main products are CO2 and H2, with a small amount of product CO.

[0098] 2) The gas product is passed into the CO2 adsorbent Na2CO3 adsorption enhancement reactor (NaCO3 / HCOOH=1.0) and enters the CO2 adsorption stage at a temperature of 80°C. CO2 is adsorbed and Na2CO3 is converted into NaHCO3.

[0099] In Comparative Example 1, the CO2 adsorbent was consumed quickly, resulting in a decrease in the CO2 adsorption amount and the CO2 adsorption rate.

[0100] The reaction conditions of the above Examples 1-6 and Comparative Examples 1-2 are shown in Table 1.

[0101] Table 1

[0102]

[0103] From the above analysis, it can be seen that the present invention proposes to enhance the formic acid dehydrogenation reaction by adsorbing CO2. In the formic acid dehydrogenation reactor, a Pd / C high-performance catalyst is used, an HCOOH aqueous solution is used for the dehydrogenation reaction, and the H2O / HCOOH molar ratio, formic acid dehydrogenation reaction temperature, and reaction pressure are coordinated and regulated to improve the yield of H2. In the adsorption enhancement reactor, Na2CO3 is used as a CO2 adsorbent to achieve stable adsorption of CO2, which helps to improve the yield and quality of H2 in the product, and reduce the selectivity of CO, prevent catalyst poisoning, and ensure the stability of the catalyst. In the adsorption regeneration reactor, the CO2 adsorbent NaCO3 is recycled, which has the following advantages compared with the existing formic acid dehydrogenation technology:

[0104] 1) Adsorption enhancement During the formic acid dehydrogenation reaction, Pd / C is used as a catalyst for the dehydrogenation reaction, which helps to improve the yield and quality of H2 in the product. Compared with the existing formic acid dehydrogenation hydrogen production process, HCOOH(l)→CO2(g)+H2(g) and the introduction of CO2 adsorbent to promote equilibrium movement have better CO2 capture capacity and high-quality hydrogen production capacity. Compared with the addition of Na2CO3 without CO2 adsorbent, the H2 concentration in the gas product is 97.91%, an increase of 16.37%. CO selectivity is reduced by 13.92%, ensuring the catalyst life.

[0105] 2) Further coordinate the H2O / HCOOH molar ratio, formic acid dehydrogenation reaction temperature, and reaction pressure, and use Pd / C high-performance catalyst to achieve a formic acid conversion rate of 99%. Coordinate the control of NaCO3 / HCOOH molar ratio, adsorption enhancement reaction temperature, reaction pressure, and adsorbent regeneration reaction temperature and reaction pressure to improve the utilization of H atoms and achieve stable adsorption of CO2. The absorption rate of carbon dioxide is 97.861% and the absorption rate is 1.88 kmol / h. This helps to improve the yield and quality of H2 in the product and reduce the selectivity of CO.

[0106] 3) Through the regeneration reaction of the CO2 adsorbent, at a reaction temperature of 117.5°C, CO2 is captured and Na2CO3 is regenerated and reused in the reaction system, thereby improving the economy of the system.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing high-purity hydrogen by adsorption-enhanced formic acid dehydrogenation, characterized in that: The steps include: (1) Formic acid dehydrogenation reaction: The preheated formic acid aqueous solution is introduced into a reactor containing a Pd / C catalyst using N2 as a carrier gas to carry out a dehydrogenation reaction to obtain a gas product containing H2, CO2, CO, and H2O; (2) Adsorption-enhanced hydrogen production: The gas product is subjected to Na2CO3 adsorption reaction to obtain high-purity hydrogen and NaHCO3; (3) Adsorbent regeneration: The NaHCO3 adsorbent is subjected to a regeneration reaction to obtain a regenerated adsorbent Na2CO3, which is used in step (2) to achieve a cycle of steps (2) and (3).

2. The method according to claim 1, characterized in that: The preheating temperature in step (1) is 110°C.

3. The method according to claim 1, characterized in that: In terms of molar ratio, H2O / HCOOH in the formic acid aqueous solution in step (1) is 0.2 to 1.

4.

4. The method according to claim 1, characterized in that: The flow rate of the N2 carrier in step (1) is 0<N2≤50cm 3 / min.

5. The method according to claim 1, characterized in that: The flow rate of the formic acid aqueous solution when N2 is used as a carrier gas to pass into the reactor is 0.02 ml / min.

6. The method according to claim 1, characterized in that: The dehydrogenation reaction temperature in step (1) is 50-120°C.

7. The method according to claim 1, characterized in that: The dehydrogenation reaction pressure in step (1) is 2 -2 ~2 4 atm.

8. The method according to claim 1, characterized in that: The adsorption reaction temperature in step (2) is 40-90°C.

9. The method according to claim 1, characterized in that: In step (2), the molar ratio of the adsorbent to formic acid is 1:

1.

10. The method according to claim 1, characterized in that: The regeneration reaction temperature in step (3) is 100-140°C.

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