JP5610271B2 - Thermochemical hydrogen production method - Google Patents

Description

The present invention relates to a thermochemical hydrogen production method excellent in hydrogen production efficiency, and more particularly to an improved thermochemical hydrogen purification process for purifying H ₂ SO ₄ and HIx phases in an iodine-sulfur (IS) hydrogen production cycle. It relates to a manufacturing method. In this improved hydrogen production method, as the stripping gas used in the above-described purification process, a mixed gas composed of oxygen and an inert gas is used in place of nitrogen that has been used so far.

Hydrogen is considered the best secondary energy and is also known as the next generation energy of mankind. However, conventional hydrogen production methods have been limited in the development of hydrogen energy due to drawbacks such as CO ₂ emission and low efficiency. As a result, more attention has been given to research on clean, efficient and sustainable hydrogen production methods. Among many thermochemical hydrogen production methods, the iodine-sulfur (IS) cycle, first proposed by General Atomic, among others, is clean, economical, and uses high-temperature nuclear thermal energy Seems to be a sustainable method of large-scale hydrogen production. However, in order to industrially produce hydrogen using the IS process, there are still some technical problems to be solved. One such challenge is the purification of the Bunsen reaction product consisting of H ₂ SO ₄ and HIx phases.

The above IS process is composed of the following three reactions.
Bunsen reaction: SO ₂ + I ₂ + 2H ₂ O = 2HI + H ₂ SO ₄ (1)
H ₂ SO ₄ decomposition reaction: H ₂ SO ₄ = SO ₂ + 1 / 2O ₂ + H ₂ O (2)
HI decomposition _{reaction: 2HI = H 2 + I 2} (3)

In the presence of excess iodine, the Bunsen reaction product is separated into two phases, a light H ₂ SO ₄ phase and a heavy HIx phase. It is unavoidable that small amounts of HI and H ₂ SO ₄ are generated in the H ₂ SO ₄ phase and the HIx phase, respectively, due to the distribution equilibrium. The presence of minor components in the two phases causes several side reactions such as sulfur formation (4) and hydrogen sulfide formation (5), as shown below.
Sulfur formation reaction: H ₂ SO ₄ + 6HI = S + 3I ₂ + 4H ₂ O (4)
Hydrogen sulfide formation reaction: H ₂ SO ₄ + 8HI = H ₂ S + 4I ₂ + 4H ₂ O (5)

Side reactions cause a number of serious problems such as impact on process raw material balance, overall efficiency degradation, and piping clogging that prevents closed-cycle continuous operation. Therefore, in order to prevent the occurrence of side reactions, it is indispensable to purify the H ₂ SO ₄ phase and the HIx phase and remove the minor components.

The purification principle currently known worldwide is the reverse Bunsen reaction (6).
Reverse Bunsen reaction: 2HI + H ₂ SO ₄ = SO ₂ + I ₂ + 2H ₂ O (6)

Researchers in Japan, Korea, and China, as reported in Non-Patent Documents 1, 2, and 3, respectively, employ the above purification reaction (6) and strip using nitrogen as the stripping gas. The column is designed to purify the H ₂ SO ₄ phase and the HIx phase.

There are several disadvantages in purifying the two phases using the process described above. A small amount of HI in the H ₂ SO ₄ phase is removed by the reverse Bunsen reaction, but at the same time, a certain amount of sulfuric acid must be consumed. Purification of the HIx phase using the process described above often involves side reactions such as sulfur or hydrogen sulfide generation that reduce the purification efficiency. One means for solving this problem is disclosed in Patent Document 1.

  In the above-mentioned patent document 1, addition of oxygen gas is proposed as a means for removing hydrogen sulfide generated as a result of a side reaction (see formula (5)) in the purification process. The following reaction proceeds by the addition of oxygen gas.

H ₂ SO ₄ + H ₂ S + O ₂ ⇒ 2SO ₂ + 2H ₂ O (7-1)
Further, hydrogen production efficiency can be improved by transporting sulfur dioxide and water, which are the products of this reaction, to (1) a vessel that proceeds with the Bunsen reaction to produce hydrogen. Furthermore, Patent Document 1 proposes the introduction of a filter as a means for removing sulfur produced as a result of (4) side reaction in the purification process. The following reaction proceeds by introducing oxygen gas into the filter in which sulfur is accumulated.

S + O ₂ ⇒ 2SO ₂ (7−2)
And in the above-mentioned patent document 1, the hydrogen production efficiency can be improved by transporting sulfur dioxide, which is a product of this reaction, to (1) a vessel that proceeds with the Bunsen reaction to produce hydrogen. Have been described.

JP 2008-137824

Kubo S, Nakajima H, Kasahara S, Higashi S, Masaki T, Abe H, Onuki K Thermochemical Water-Splitting Iodine-Sulfur Process 233: 347-354 pages Nucl Eng December 2004 Ki-Kwang Bac, Chu-Sik Park, Chang-Hee Kim, Kyung-Soo Kang, Sang-Ho Lee, Bab-Jin Hwang, Ho-Sang Choi Thermochemical water splitting IS process, WHEC 16 / 13-16 2006 June Lyon France Guo HF, Zhang P, Bai Y, Wang LJ, Chen SZ, Xu JM Continuous purification of H2SO4 and HI phases by packed column in IS process Int.J Hydrogen energy, 2009 doi: 10.1061 / J.ijhydene.

Before describing the problem, definitions of terms used in this specification will be explained. That is, in the present specification, various symbols and formulas such as IF _HI and C _HI are used, and these are based on the definitions in Tables 1 and 2 below. For example, in the calculation formula of CHI (HI conversion rate) at the top of Table 2, OF _tHI and IF _HI indicate the total outflow amount of component HI and the inflow amount of component HI, respectively.

Now, it has been found that the oxygen addition described in Patent Document 1 has the following problems. That, H ₂ SO ₄ phase simulation solution results of oxygen gas were investigated reaction temperature effects on the system plus 0.5 mol / h, as described below, 100% even in the yield Y _SA is any temperature of the sulfuric acid Although kept close, a reaction temperature of 140 ° C. or higher is required in order to obtain an iodine selectivity S _I2 of nearly 100%. In this system, the following reaction is expected to have progressed.

4HI + O ₂ = 2I ₂ + 2H ₂ O (8)
2HI + 3O ₂ = 2HIO ₃ (9)
As a result of hydrogen iodide, which is an impurity in the sulfuric acid phase, reacting with oxygen, which is a reactive gas, it changed to iodine or HIO ₃ and the progress of the reverse Bunsen reaction (6) was hindered. it is conceivable that. In addition, it is considered that the stability of HIO ₃ is impaired at high temperatures, and the iodine selectivity S _I2 is improved. In addition, as a result of investigating the influence of the flow rate of oxygen gas added to the simulated solution of HIx phase with the reaction temperature kept at 120 ° C, the sulfur dioxide selectivity S _SO2 increases as the flow rate increases, but the conversion of sulfuric acid There was a decrease in rate C _SA and hydrogen iodide yield Y _HI .

Therefore, the two-phase purification method was further improved, the reaction temperature was reduced from 140 ° C in the H ₂ SO ₄ phase purification, and the sulfuric acid conversion rate and SO ₂ selectivity were simultaneously 100% in the HIx phase purification. There is a need to increase in the near future. Thus, the main object of the present invention is to provide an improved purification process for purifying the H ₂ SO ₄ and HIx phases in an iodine-sulfur cycle.

By adopting a process of purifying H ₂ SO ₄ phase and HIx phase using a mixed gas consisting of oxygen and inert gas instead of conventional oxygen and inert gas as the stripping gas, the above requirement Is satisfied and the problem is solved.

The present invention provides one process for purifying the H ₂ SO ₄ phase in an iodine-sulfur hydrogen production cycle. The characteristics of the process are as follows. In the following description, the features will be described in detail for easy understanding, but the present invention is not limited thereto.

Initially, the stripping tower temperature is controlled from 90 ° C to 200 ° C. Next, the H ₂ SO ₄ phase solution is pumped into the stripping tower from the top of the stripping tower. At the same time, a reactive stripping gas is flowed from the bottom of the stripping tower. Finally, the purified liquid is discharged from the stripping tower. Vapor exits from an outlet at the top of the stripping tower. Here, the reactive stripping gas, Ru mixed gas der consisting of oxygen and an inert gas. The above mentioned mixed gas consisting of oxygen and an inert gas, nitrogen, helium, and an inert gas one or several containing argon, a mixed gas of oxygen.

  The present invention also provides a process for purifying the HIx phase in an iodine-sulfur hydrogen production cycle. The characteristics of the process are as follows. In the following description, the features will be described in detail for easy understanding, but the present invention is not limited thereto.

Initially, the stripping tower temperature is controlled from 90 ° C to 200 ° C. The HIx phase solution is then pumped into the stripping tower from the top of the stripping tower. At the same time, a reactive stripping gas is flowed from the bottom of the stripping tower. Finally, the purified liquid is discharged from the stripping tower. Vapor exits from an outlet at the top of the stripping tower. Here, the reactive stripping gas, Ru mixed gas der consisting of oxygen and an inert gas. Oxygen mixed gas consisting of inert gas above mentioned nitrogen, helium, and an inert gas one or several containing argon, a mixed gas of oxygen.

By using reactive stripping gas, the conventional purification reaction of H ₂ SO ₄ phase purification, ie reverse Bunsen reaction: 2HI + H ₂ SO ₄ = SO ₂ + I ₂ + 2H ₂ O, HI oxidation reaction: It is replaced with _{4HI + O 2 = 2I 2 +} 2H 2 O. By using a reactive stripping gas, the by-products H ₂ S and S ₂ produced from the purification of the HIx phase are oxidized to SO ₂ by the following reaction.
S + O ₂ = SO ₂ and H ₂ S + O ₂ = SO ₂

Compared with current technology, the present invention has the following advantages and significant technical effects. That is, the process of the present invention is different from the conventional purification mechanism, that is, the reverse Bunsen reaction: 2HI + H ₂ SO ₄ = SO ₂ + I ₂ + 2H ₂ O, HI oxidation: 4HI + O ₂ = 2I ₂ + by 2H ₂ O, without consuming H ₂ SO _4, complete purification of H ₂ SO ₄ phases can be realized. In the purification of the HIx phase using reactive oxygen or an oxygen-containing mixed gas as the stripping gas, oxygen reacts with the byproduct S or H ₂ S to form SO ₂ , so that the selectivity of SO ₂ can be increased.

It is the schematic which shows the process of the thermochemical hydrogen manufacturing method of this invention. FIG. 2 is a schematic diagram illustrating an example of a process for purifying an H ₂ SO ₄ phase and an HIx phase in an iodine-sulfur hydrogen production cycle. It is a figure for demonstrating the comparative example 1 of this invention, Comprising: It is a graph which shows the effect of the comparative example 1. FIG. It is a figure for demonstrating the comparative example 2 of this invention, Comprising: It is a graph which shows the effect of the comparative example 2. FIG. It is a figure for demonstrating the comparative example 3 of this invention, Comprising: It is a graph which shows the effect of the comparative example 3. FIG. It is a figure for demonstrating Example 1 of this invention, Comprising: It is a graph which shows the effect of Example 1. FIG. It is a figure for demonstrating Example 2 of this invention, Comprising: It is a graph which shows the effect of Example 2. FIG. It is a figure for demonstrating this invention. It is a figure for demonstrating the comparative example 4 of this invention, Comprising: It is a graph which shows the effect of the comparative example 4. FIG. It is a figure for demonstrating the comparative example 5 of this invention, Comprising: It is a graph which shows the effect of the comparative example 5. FIG. It is a figure for demonstrating Example 3 of this invention, Comprising: It is a graph which shows the effect of Example 3. FIG. It is a figure for demonstrating Example 4 of this invention, Comprising: It is a graph which shows the effect of Example 4. FIG.

With reference to FIG.1 and FIG.2, the thermochemical hydrogen manufacturing method of this invention is demonstrated. FIG. 1 shows the whole process of the thermochemical hydrogen production method of the present invention, and FIG. 2 shows the details of the purification process of the H ₂ SO ₄ phase and the HIx phase shown in FIG. In FIG. 1, H ₂ SO ₄ phase and HIx phase are obtained from a raw material water H ₂ O by a two-layer separator by a Bunsen reaction. Thereafter, the H ₂ SO ₄ phase and the HIx phase are independently taken out and subjected to a purifier. In FIG. 1, the upper H ₂ SO ₄ phase is applied to the left closed loop purifier and the lower HIx phase is also applied to the right closed loop purifier. In these purifiers, each phase is purified using a reactive stripping gas. In the closed loop on the right side, H ₂ is produced by the HI decomposition reaction from the last purified HIx (purified solution) and taken out as a product. In addition, SO2 produced in the left closed loop and I ₂ produced in the right closed loop are recycled for hydrogen production. Next, a process for purifying each of the H ₂ SO ₄ phase and the HIx phase, which is a feature of the present invention, will be described in detail with reference to FIG.

  In FIG. 2, the purification process is handled as a batch process for convenience of explanation. However, it is extremely easy to install this apparatus in the closed loop of FIG. 1 using various valve mechanisms and piping. The description is omitted here. In FIG. 1, the waste heat from the HTGR is used as the heat source. However, it is sufficient that the desired temperature shown in FIG. 1 is obtained, and the waste heat from the steelworks, solar heat, etc. are used as the heat source. You may do it.

Please refer to FIG. The purification process of H ₂ SO ₄ phase and HIx phase consists of material tank 201 for H ₂ SO ₄ phase or HIx phase, pump 202, stripping tower 203, temperature controller 204, product tank 205, stripping gas tank 206, This is performed by an apparatus including a flow meter 207 and a valve mechanism 208. The stripping tower 203 is heated in advance to a desired temperature prior to performing the purification process. During the purification process, H ₂ SO ₄ phase or HIx phase is pumped into the heated stripping column 203 from its upper inlet and a reactive stripping gas whose flow rate is controlled by a flow meter 207 is It is introduced from the lower part of the ripping tower 203. Finally, the effluent from the stripping tower 203 is obtained as a purified liquid. Vapor exits from an outlet at the top of stripping tower 203.

Next, comparative examples and examples of the present invention performed using the above-described purification apparatus will be described with reference to FIGS. FIGS. 3 to 7 are explanatory diagrams showing experimental results regarding purification of sulfuric acid (H ₂ SO ₄ ) phase, and FIGS. 8 to 12 are explanatory diagrams showing experimental results regarding purification of polyhydroiodic acid (HIx) phase. FIG. Throughout each of the comparative examples and examples described below, the amounts of the sulfuric acid phase simulated solution and the polyhydroiodic acid phase simulated solution shown in paragraphs [0033] and [0039] were used, respectively.

These experimental results were calculated using ESP (The Environmental Simulation Program), a physical property estimation software manufactured by OLI Systems, Inc. of the United States. A feature of this software is the applicability of a thermodynamic database based on the MSE model (mixed solvent electrolyte thermodynamic model). In the calculation, the calculation was performed under the following condition setting [I1].
Parameters: Temperature, stripping gas flow temperature range: 60 ~ 160 ℃
Stripping gas: Nitrogen (as inert gas), Oxygen (as reactive gas)
H ₂ SO ₄ phase stripping gas flow range: N ₂ , 0 ~ 16mol%, O ₂ , 0 ~ 9mol%
HI phase stripping gas flow range: N ₂ , 0 ~ 4.7mol%, O ₂ , 0 ~ 2.4mol%
Pressure: 1atm
Equilibrium composition calculation: Bunsen reaction product composition without taking into account reaction rate: Equivalent to the measurement result of General Atomic
H ₂ SO ₄ phase impurity content: HI = 2 mol%
HIx phase impurity content: H ₂ SO ₄ = 1 mol%
Applicability of the present invention to the sulfuric acid (H ₂ SO ₄ ) phase

Comparative Example 1

Fig. 3 (Prior Art) shows the flow rate of nitrogen gas added to the simulated sulfuric acid solution of H ₂ SO ₄ : 1 mol / h, H ₂ O: 4 mol / h, HI: 0.1 mol / h at 100 ° C. Show the effect. As can be seen from FIG. 1, as the flow rate increases, iodine and sulfur dioxide selectivity S _I2 and S _SO2 improve to nearly 100%, but the sulfuric acid yield Y _SA decreases.

Comparative Example 2

FIG. 4 (prior art) shows the effect of reaction temperature on a system in which 0.5 mol / h of nitrogen gas is added to a sulfuric acid phase simulated solution. As can be seen from FIG. 4, at 90 ° C. or higher, S _I2 and S _SO2 are improved to nearly 100%, but Y _SA is decreased and a decrease in sulfuric acid yield due to the reverse Bunsen reaction is expected.

Comparative Example 3

Next, the effect of adding only oxygen gas to the simulated sulfuric acid solution will be described. FIG. 5 (prior art) shows the effect of reaction temperature on a system in which oxygen gas is added at 0.5 mol / h to a simulated solution. From Figure 5, although the yield Y _SA sulfuric acid is maintained at nearly 100% even at any temperature, in order to obtain a selectivity S _I2 iodine nearly 100%, it is necessary to a reaction temperature above 140 ° C. I understand that. The reason for this is as described above in relation to Patent Document 1.

Next, the effect of adding a mixed gas of nitrogen and oxygen to the sulfuric acid phase simulated solution according to the present invention will be described. FIG. 6 shows the effect of the flow rate of oxygen gas added to the mixed system of the simulated solution and 0.5 mol / h nitrogen at 100 ° C. 0.025 mol / h was obtained as the oxygen flow rate capable of maintaining the sulfur dioxide selectivity S _I2 close to 0% while keeping the iodine selectivity S _I2 close to 100%.

FIG. 7 shows the effect of reaction temperature when a mixed gas of 0.5 mol / h nitrogen and 0.025 mol / h oxygen is added to the sulfuric acid phase simulated solution. Above 110 ° C., it is suggested that the yield of sulfuric acid _YSA and iodine selectivity S _I2 can be kept close to 100%.

From these results, it is expected that the following two effects will be exhibited by performing a purification process by adding a mixed gas of nitrogen and oxygen to the sulfuric acid phase.
(A) Yield of sulfuric acid close to 100% compared to addition of nitrogen gas alone (B) Reaction temperature drop from 140 ° C to 110 ° C compared to addition of oxygen gas alone As a result of (A) above, It is expected that the amount of sulfuric acid circulated will be reduced and the thermal efficiency of hydrogen production will be improved.
As a result of the above (B), it is expected that the operating temperature of the sulfuric acid phase refining process is reduced, leading to improvement of the hydrogen production thermal efficiency of the IS process.
Applicability of the present invention to polyhydroiodic acid (HIx) phase

First, the effect of temperature in the polyhydroiodic acid phase will be described.
In FIG. 8, the reaction temperature of the simulated solution of polyhydroiodic acid phase of HI: 2 mol / h, H ₂ O: 10 mol / h, I ₂ : 8 mol / h, H ₂ SO ₄ : 0.2 mol / h was changed. Show the effect. As the reaction temperature increases, the sulfuric acid conversion rate _CSA improves, but the hydrogen iodide yield _YHI decreases and the sulfur dioxide selectivity _SSO2 has a peak at 120 ° C. Therefore, experiments were performed as follows for the effect of various gases aiming to improve the C _SA and S _SO2 at the reaction temperature 120 ° C..

Comparative Example 4

The effect of adding only conventional nitrogen gas to the polyiodide phase was investigated.
Figure 9, HI at 120 ° C.: added to the simulated solution of polyiodide hydroacid phase of 0.2mol / h: 2mol / h, H 2 O: 10mol / h, I 2: 8mol / h, H 2 SO 4 The effect of the flow rate of nitrogen gas is shown. As the flow rate increases, the sulfuric acid conversion rate _CSA improves, but the sulfur dioxide selectivity _SSO2 and the hydrogen iodide yield _YHI decrease.

Comparative Example 5

Next, the effect of adding only oxygen gas, which is also a conventional technique, to the polyhydroiodic acid phase was examined.
FIG. 10 shows the effect of the flow rate of oxygen gas added to the simulated solution at 120 ° C. Accordance flow rate increases, although the improved selectivity S _SO2 sulfur dioxide, is observed reduction in yield Y _HI conversion of C _SA and hydrogen iodide sulfate. In this system, it is expected that the reaction according to the above formulas (8) and (9) has proceeded as in the case of the sulfuric acid phase.

As a result of the reaction of hydrogen iodide, which is a product in the polyhydroiodic acid phase, with oxygen, which is a reactive gas, it is considered that the yield of hydrogen iodide is reduced by changing to iodine or HIO ₃ . This oxidation reaction of hydrogen iodide is considered to suppress the competing side reactions (4) and (5), thereby increasing the degree of progress of the reverse Bunsen reaction and improving the SO ₂ selectivity. C _SA and S _SO2 are maximized at an oxygen gas flow rate of about 0.1 mol / h.

Next, the effect of adding a mixed gas of nitrogen and oxygen to the polyhydroiodic acid phase was investigated.
FIG. 11 shows the effect of the flow rate of nitrogen gas added to the mixed system of 0.1 mol / h oxygen, which is the optimum flow rate obtained by analysis of the simulated solution and pure oxygen gas addition at 120 ° C. Similar to the case of adding pure nitrogen gas into the simulated solution, according to the flow rate increases, although the improved conversion rate C _SA of sulfuric acid, a decrease in the yield Y _HI selectivities S _SO2 and hydrogen iodide, sulfur dioxide It was seen. However, for improvement rate of C _SA, reduction rate of S _SO2 is small, the pure oxygen gas as compared with the case of adding 0.1 mol / h, has become possible to optimize the as a purification process. In a flow rate of about 0.4 mol / h of nitrogen gas, C _SA and S _SO2 is maximized.

FIG. 12 shows the effect of reaction temperature when a mixed gas of 0.4 mol / h nitrogen and 0.1 mol / h oxygen is added to the simulated solution. According to the reaction temperature increases, but improves the conversion rate C _SA sulfuric acid, decreasing the yield Y _HI of hydrogen iodide, selectivity S _SO2 sulfur dioxide showed a peak at 110 ° C.. The reaction temperature at which C _SA and S _SO2 were maximized was 120 ° C.

From these results, it is expected that the following two effects are exhibited by performing a purification process by adding a mixed gas of nitrogen and oxygen to the polyhydroiodic acid phase.
(C) Equivalent sulfuric acid conversion rate and nearly 100% sulfur dioxide selectivity compared to addition of nitrogen gas alone (D) Equivalent sulfur dioxide selectivity and nearly 100% sulfuric acid compared to oxygen gas addition Conversion rate As a result of the above-mentioned (C), the progress of side reactions in the purification process can be suppressed, and the generation of elemental sulfur and hydrogen sulfide can be prevented.
As a result of the above (D), it is possible to prevent the inflow of impurities to the subsequent process and achieve the original function of the purification process.

  Based on the above facts, the addition of nitrogen gas alone and oxygen gas alone is incomplete as a purification process for polyhydrogen iodide gas, and the yield of hydrogen iodide is high for the first time using a mixed gas of nitrogen and oxygen to suppress side reactions. Purification process is possible.

201 ... (for H ₂ SO ₄ phase or HIx phase) material tank,
201 ... pump,
203 ... stripping tower,
204 ... temperature controller,
205 ... Product tank,
206 ... stripping gas tank,
207 ... Flow meter,
208… Valve mechanism

Claims (2)

Forming H ₂ SO ₄ and HIx phases from the raw material H ₂ O by the Bunsen reaction, separating the formed H ₂ SO ₄ and HIx phases, and then reactively stripping each phase Thermochemical hydrogen production comprising the steps of separately purifying impurities contained in each of the H ₂ SO ₄ phase and HIx phase using gas, and finally producing hydrogen from the purified HIx by HI decomposition reaction In the method
The method for producing thermochemical hydrogen, wherein the reactive stripping gas used in the purification step is a mixed gas composed of oxygen and an inert gas. In the thermochemical hydrogen production method according to claim 1,
  A method for producing thermochemical hydrogen, wherein the mixed gas comprising oxygen and an inert gas is a mixed gas of one or several kinds of inert gas containing nitrogen, helium and argon and oxygen.

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