Sulfuric acid phase decomposition process and system in SI circulation

Abstract

The invention relates to the technical field of hydrogen preparation, in particular to a sulfuric acid phase decomposition process and a sulfuric acid phase decomposition system in SI circulation, the sulfuric acid phase decomposition process comprises a raw reaction, two-phase layering, sulfuric acid purification, sulfuric acid dehydration decomposition and hydrogen iodide decomposition, the purified sulfuric acid is concentrated to 75-90 wt%, the concentrated sulfuric acid reacts with phosphorus pentoxide to generate phosphoric acid and sulfur trioxide, and the sulfur trioxide reacts with phosphorus pentoxide to generate sulfur trioxide; sulfur trioxide is decomposed into sulfur dioxide and oxygen under the conditions of a catalyst and 923K-1023K, meanwhile, in-situ separation of oxygen is carried out by adopting a composite oxygen-permeable ceramic membrane, and sulfur dioxide gas without oxygen is returned and circulated to participate in the raw reaction. Sulfuric acid decomposition of the SI circulating system adopts a mode of matching chemical reaction with the membrane reactor, a step of decomposing sulfuric acid under a high-temperature condition is avoided, sulfur trioxide is prepared through dehydration reaction of phosphorus pentoxide, oxygen is separated in situ by the membrane reactor, the decomposition rate of sulfur trioxide can be increased, the decomposition temperature of sulfur trioxide can be reduced, and the sulfur trioxide can be recycled. The obtained oxygen is high in purity, and a byproduct is phosphoric acid.

Description

Technical Field

[0001] The present application relates to the technical field of hydrogen preparation, and in particular to a sulfuric acid phase decomposition process and system in an SI cycle. Background Art

[0002] As a recognized renewable clean energy, hydrogen energy is emerging in the era of low-carbon / zero-carbon energy. Among them, the thermochemical SI cycle hydrogen production method (hereinafter referred to as SI cycle) has attracted widespread attention as one of the most ideal cycles in thermochemical hydrogen production methods. The SI cycle system mainly includes the Bunsen reaction, sulfuric acid H 2 SO 4 There are three processes: decomposition and hydrogen iodide HI decomposition. Among them, sulfuric acid decomposition requires the highest temperature. 2 SO 4 Converted to SO at 573-773K 3 and H 2 O, and SO 3 It needs to be directly decomposed into SO at a high temperature above 1273K 2 and O 2 Even in the presence of a catalyst, SO 3 The thermal decomposition still requires a high temperature above 1173K. Summary of the invention

[0003] In view of the technical problem that sulfuric acid is difficult to decompose in the prior art, the present application proposes a method of combining chemical reaction with membrane reactor to improve the efficiency of sulfuric acid decomposition and the purity of oxygen products, thereby improving the hydrogen and oxygen production efficiency of the thermochemical sulfur-iodine hydrogen production system.

[0004] On the one hand, the present application proposes a sulfuric acid phase decomposition process in an SI cycle, the process comprising an S1 Bunsen reaction, a SO 2 ,I 2 Reacts with water to generate H 2 SO 4 S2 two-phase separation, adding excess elemental iodine to the mixed acid solution, the two phases are separated into the upper sulfuric acid solution and the lower I 2-HIx solution; S3 sulfuric acid purification and dehydration decomposition, sulfuric acid solution is taken out from the upper layer of the two-phase stratification to react with hydrogen peroxide, solid-liquid separation is performed to remove iodine solids, the purified sulfuric acid is concentrated to 75wt%-90wt%, it is slowly added and mixed with phosphorus pentoxide, phosphoric acid and sulfur trioxide are reacted, sulfur trioxide is decomposed into sulfur dioxide and oxygen under the conditions of 923K-1023K by platinum series, transition metal oxide and composite metal oxide catalysts, and composite oxygen-permeable ceramic membrane is used for in-situ separation of oxygen, and the sulfur dioxide gas with oxygen removed is returned to S1 for circulation to participate in the Bunsen reaction; S4 hydrogen iodide is decomposed, I is taken out from the lower layer of the two-phase stratification 2 -The HIx solution is cooled and solid-liquid separated to obtain elemental iodine, and the iodine-poor HIx solution obtained after solid-liquid separation is heated and decomposed to obtain elemental iodine and hydrogen; wherein the order of S3 and S4 is not limited.

[0005] In particular, the molar ratio of each substance in the S1 Bunsen reaction SO 2 :I 2 :H 2 O=1:1-1.5:12-20, react for 20-60 minutes after fully mixing, and the reaction temperature is controlled at 323-358K.

[0006] Particularly, the two phases of S2 are separated, the molar amount of elemental iodine added to the mixed solution after the Bunsen reaction is 2-4 times the amount of sulfur dioxide input in the Bunsen reaction in S1, the temperature of the solution is maintained at 323-358K, and the two phases are separated after standing for 20-40 minutes.

[0007] In particular, the S3 sulfuric acid is purified and dehydrated, the upper sulfuric acid solution reacts with a 60wt% hydrogen peroxide solution, a small amount of hydrogen iodide remaining in the sulfuric acid reacts with the hydrogen peroxide to generate iodine solid, and the sulfuric acid solution after filtering and separating the iodine is sent to the sulfuric acid concentration process.

[0008] Particularly, the concentrated sulfuric acid is slowly added and reacted with at least 20% excess phosphorus pentoxide solid, the reaction temperature is controlled below 423K, and after the sulfuric acid dehydration reaction is completed, water is added to react with excess unreacted phosphorus pentoxide to generate phosphoric acid.

[0009] In particular, the catalyst for decomposing sulfur trioxide into sulfur dioxide and oxygen is selected from Pt / TiO 2 、Pt / SiO 2 、Pt / Al 2 O 3 、Pt / ZrO 2 、Pt / CeO 2 Cr 2 O 3 , Fe 2 O 3 , CuO, CeO2 、NiO、Al 2 O 3 、FeTiO 3 、MnTiO 3 、NiFe 2 O 4 ,CuFe 2 O 4 、NiCr 2 O 4 , 2CuOCr 2 O 3 ,CuOCeO 2 .

[0010] In particular, the S4 hydrogen iodide decomposes, and the lower I 2 -HIx solution is cooled to 283K-293K, solid-liquid separation is performed to remove crystallized elemental iodine to obtain iodine-poor HIx solution, elemental iodine is returned to S2 for two-phase stratification and recycling, and then the solution is heated to 673-773K and thermally decomposed under the catalysis of the catalyst to obtain elemental iodine and hydrogen. The mixed gas is cooled to separate the insoluble hydrogen, and the residue is returned to S1 to participate in the Bunsen reaction.

[0011] On the other hand, the present application also proposes a sulfuric acid phase decomposition system in an SI cycle, the system implements the process as described above, the system includes at least two two-phase stratification tanks connected to the Bunsen reaction tank, the upper layer in the two-phase stratification tank is sent to a sulfuric acid purification tank, and the sulfuric acid purification tank is sequentially connected to an impurity separator, a sulfuric acid storage tank, a sulfuric acid concentrator, a concentrated sulfuric acid storage tank, and a sulfuric acid dehydration decomposition tank; the gas generated in the sulfuric acid dehydration decomposition tank is sent to a sulfur trioxide preheating tank, and the sulfur trioxide preheating tank is sequentially connected to a sulfur trioxide decomposer, a sulfur dioxide gas storage tank, and a Bunsen reaction tank to form a circulation loop, and the sulfuric acid purification tank is also connected to a hydrogen peroxide storage tank; the sulfuric acid dehydration decomposition tank is also respectively connected to a pure water tank, a phosphorus pentoxide storage tank, and a phosphoric acid storage tank; the sulfur trioxide decomposition tank is also connected to an oxygen storage tank.

[0012] Particularly, the internal space of the sulfur trioxide decomposer is divided into a first space and a second space in the upper and lower parts by a composite oxygen-permeable ceramic membrane, the lower part of the second space is filled with a sulfur trioxide decomposition catalyst, a sulfur trioxide gas inlet is provided at the lower part or the bottom of the sulfur trioxide decomposer, a sulfur dioxide gas outlet is provided on the upper side wall of the sulfur trioxide decomposer and located in the second space, and an oxygen gas outlet is provided at the upper part or the top of the sulfur trioxide decomposer and located in the first space.

[0013] Particularly, the lower layer in the two-phase stratification tank is sent to an iodine solid cooling and separation tank, the elemental iodine separated by the iodine solid cooling and separation tank is then sent to an iodine solid storage tank and then returned to the two-phase stratification tank, the hydrogen iodide solution remaining after the elemental iodine is separated by the iodine solid cooling and separation tank is sent to a hydrogen iodide decomposition tower, and the gas generated by the decomposition is then sent to a spray cooling tower, and the spray cooling tower is respectively connected to a water tank and a hydrogen storage tank.

[0014] On the basis of conforming to the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present application.

[0015] The above technical scheme has the following advantages or beneficial effects: The sulfuric acid decomposition of the SI circulation system of the present application adopts a chemical reaction combined with a membrane reactor, and the sulfur trioxide prepared by the dehydration reaction of phosphorus pentoxide only produces dry sulfur dioxide and oxygen after decomposition. Due to the absence of water vapor, the corrosion ability of sulfur dioxide gas to pipes, valves and other components is reduced, reducing the equipment's requirements for material corrosion protection. By separating oxygen in situ, the sulfur trioxide decomposition rate is increased by more than 10% at the same temperature, and while maintaining the same sulfur trioxide decomposition rate, the sulfur trioxide decomposition temperature can be reduced by 100-200K, and the resulting oxygen has high purity and does not require further purification. In addition to producing hydrogen and oxygen, this system can also produce high-value phosphoric acid. Of course, any technical scheme of the present application does not necessarily achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art description. Obviously, for those skilled in the art, other drawings can be obtained based on the provided drawings without creative work.

[0017] Figure 1 It is a schematic diagram of the principle of a sulfuric acid phase decomposition process in an SI cycle according to an embodiment of the present application.

[0018] Figure 2 It is a connection diagram of a sulfuric acid phase decomposition system in an SI cycle according to an embodiment of the present application.

[0019] Figure 3 It is a structural schematic diagram of a sulfur trioxide decomposer of a sulfuric acid phase decomposition system in an SI cycle according to an embodiment of the present application.

[0020] Among them, 1. Bunsen reaction tank; 2. Two-phase stratification tank; 3. Iodine solid cooling and separation tank; 4. Iodine solid storage tank; 5. Hydrogen iodide decomposition tower; 6. Sulfuric acid purification tank; 7. Impurity separator; 8. Sulfuric acid storage tank; 9. Sulfuric acid concentrator; 10. Spray cooling tower; 11. Water tank; 12. Sulfuric acid dehydration decomposition tank; 13. Sulfur trioxide decomposer; 131. Composite oxygen-permeable ceramic membrane; 132. First space; 133. Second space; 14. Sulfur trioxide preheating tank; 15. Concentrated sulfuric acid storage tank; 16. Phosphoric acid storage tank; 17. Pure water tank; 18. Phosphorus pentoxide storage tank; 19. Sulfur dioxide storage tank; 20. Oxygen storage tank; 21. Hydrogen storage tank; 22. Hydrogen peroxide storage tank. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application are clearly and completely described below in conjunction with the drawings of the present application. Obviously, the described embodiments are only part of the embodiments of the present application and are intended to be used to explain the inventive concept. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0022] The terms "first", "second", etc. used in the description are only used for descriptive purposes and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features specified as "first" or "second" may explicitly or implicitly include one or more of the features. The term "plurality" means two or more, unless otherwise clearly and specifically specified.

[0023] Unless otherwise clearly specified and limited, the terms "connected", "connected" and the like used in the description should be understood in a broad sense, for example, it can be fixedly connected, detachably connected, or integrated; it can be mechanically connected, electrically connected; it can be directly connected, indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments can be understood according to specific circumstances.

[0024] The term "a specific embodiment" used in the description means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0025] refer to Figure 1A specific embodiment of the present application proposes a sulfuric acid phase decomposition process in an SI cycle, which mainly includes the following reactions or operations. Bunsen reaction: SO 2 ,I 2 It undergoes redox reaction with water at 293-393K to generate H 2 SO 4 and HI mixed acid aqueous solution.

[0026] Two-phase separation: Two-phase separation requires H 2 SO 4 and HI are separated from the mixed acid produced by the Bunsen reaction to 2 SO 4 Adding excess elemental iodine to the mixed acid aqueous solution of HI can enhance the two-phase separation effect and reduce the impurity content in each phase.

[0027] Decomposition of hydrogen iodide: I obtained after two phases are separated 2 -HIx solution, after cooling to 283K-293K, 80%-90% of elemental iodine crystallizes out from the solution. The iodine-poor HIx solution obtained after solid-liquid separation is heated to 673-773K and thermally decomposed to obtain elemental iodine and hydrogen using a metal-modified activated carbon catalyst, such as Pt / AC, Pt-Ni / AC, Ni / AC.

[0028] Purification and decomposition of sulfuric acid: In the two-phase separation process, the excess iodine increases the purity of the hydroiodic acid phase, but the hydrogen iodide in the sulfuric acid phase cannot be completely removed. The sulfuric acid phase needs to be further purified to ensure the purity of the sulfur dioxide produced by the decomposition of sulfuric acid. At this time, sulfuric acid purification uses a 60wt% hydrogen peroxide solution. The hydrogen peroxide reacts with the residual hydrogen iodide in the sulfuric acid phase to generate iodine and water. The specific chemical reaction formula includes: H 2 O 2 + 2HI= I 2 + 2H 2 O. Elemental iodine is insoluble in sulfuric acid solution and precipitates out. Through solid-liquid separation, sulfuric acid and iodine solids can be collected.

[0029] The purified sulfuric acid is concentrated to 75wt%-90wt%. The concentration process of sulfuric acid is relatively mature, such as the commonly used multi-stage flash evaporation. The concentrated sulfuric acid is decomposed into sulfur dioxide by two reactions, and the reaction temperature is reduced from above 1123K to 923-1023K. Including chemical reaction I: using phosphorus pentoxide to react with concentrated sulfuric acid to generate sulfur trioxide and phosphoric acid. Since the dehydration of phosphorus pentoxide is much stronger than concentrated sulfuric acid, phosphorus pentoxide can not only react with the residual water in concentrated sulfuric acid to generate phosphoric acid, but also remove the hydrogen and oxygen elements in the sulfuric acid molecules in the form of a molar ratio of 2:1. Thereby achieving the dehydration of concentrated sulfuric acid and generating phosphoric acid and sulfur trioxide. The specific chemical reaction formulas include: 3H2 SO 4 +P 2 O 5 →3SO 3 +2H 3 PO 4 , P 2 O 5 +3H 2 O→2H 3 PO 4 Chemical reaction II: In the presence of a catalyst, sulfur trioxide decomposes into sulfur dioxide and oxygen at 923-1023K. The catalyst mainly uses a platinum catalyst (such as Pt / TiO 2 、Pt / SiO 2 、Pt / Al 2 O 3 、Pt / ZrO 2 、Pt / CeO 2 ), transition metal oxide catalysts (such as Cr 2 O 3 , Fe 2 O 3 , CuO, CeO 2 、NiO、Al 2 O 3 ) and composite metal oxide catalysts (such as FeTiO 3 、MnTiO 3 、NiFe 2 O 4 ,CuFe 2 O 4 、NiCr 2 O 4 , 2CuOCr 2 O 3 ,CuOCeO 2 ). The oxygen generated by decomposition is separated in situ using a composite oxygen-permeable ceramic membrane. The composite oxygen-permeable ceramic membrane is a prior art, such as that disclosed in Chinese patent application CN102463039A. The in-situ separation of oxygen promotes the decomposition of sulfur trioxide: (1) At the same temperature, the decomposition rate of sulfur trioxide can be increased by more than 10%. For example, at 1073K, using CuO-CeO 2 The decomposition rate of sulfur trioxide is about 73%. The decomposition rate of sulfur trioxide can be increased to more than 90% by using ceramic oxygen permeable materials to separate oxygen in situ. (2) If the decomposition rate of sulfur trioxide is controlled to be around 73%, CuO-CeO 2 Catalysts and ceramic oxygen-permeable materials separate oxygen in situ, and the heating temperature can be reduced from 1073K to 973K.

[0030] Through a two-step reaction, the sulfuric acid produced by the Bunsen reaction is converted into anhydrous sulfur dioxide gas and pure oxygen, while producing high-value phosphoric acid as a by-product. The anhydrous sulfur dioxide gas is passed into the Bunsen reaction tank and recycled as a reactant. In addition, compared with the traditional sulfur-iodine hydrogen production system, the oxygen produced by the decomposition of sulfuric acid does not contain impurities such as sulfur dioxide and water vapor, and has high purity and does not require further purification.

[0031] refer to Figure 2 and Figure 3 A specific embodiment of the present application proposes a system for producing hydrogen by SI cycle, comprising at least two two-phase stratification tanks 2 connected to a Bunsen reaction tank 1, wherein the upper layer of the two-phase stratification tank 2 is fed into a sulfuric acid purification tank 6, which is then sequentially connected to an impurity separator 7, a sulfuric acid storage tank 8, a sulfuric acid concentrator 9, a concentrated sulfuric acid storage tank 15, and a sulfuric acid dehydration decomposition tank 12. The gas generated in the sulfuric acid dehydration decomposition tank 12 is fed into a sulfur trioxide preheating tank 14, which is then sequentially connected to a sulfur trioxide decomposer 13, a sulfur dioxide gas storage tank 19, and a Bunsen reaction tank 1 to form a circulation loop.

[0032] The internal space of the sulfur trioxide decomposer 13 is divided into a first space 132 and a second space 133 in the upper and lower parts by a composite oxygen-permeable ceramic membrane 131. Preferably, the composite oxygen-permeable ceramic membrane 131 is in the shape of an array of tubes to increase the contact area. A sulfur trioxide decomposition catalyst is filled in the lower part of the second space 133. A sulfur trioxide gas inlet is provided at the lower part or the bottom of the sulfur trioxide decomposer 13. A sulfur dioxide gas outlet is provided at the upper side wall of the sulfur trioxide decomposer 13 and located in the second space 133. An oxygen gas outlet is provided at the upper part or the top of the sulfur trioxide decomposer 13 and located in the first space 132.

[0033] The sulfuric acid purification tank 6 is also connected to the hydrogen peroxide storage tank 22; the sulfuric acid dehydration decomposition tank 12 is also connected to the pure water tank 17, the phosphorus pentoxide storage tank 18, and the phosphoric acid storage tank 16 respectively; the sulfur trioxide decomposition tank 13 is also connected to the oxygen storage tank 19.

[0034] The lower layer of the two-phase stratification tank 2 is fed into the iodine solid cooling separation tank 3, and the elemental iodine separated by the iodine solid cooling separation tank 3 is then fed into the iodine solid storage tank 4 and then fed back to the two-phase stratification tank 2. The hydrogen iodide solution remaining after the elemental iodine is separated by the iodine solid cooling separation tank 3 is fed into the hydrogen iodide decomposition tower 5, and the gas generated by the decomposition is then fed into the spray cooling tower 10, and the spray cooling tower 10 is respectively connected to the water tank 11 and the hydrogen storage tank 21.

[0035] The system operation mode of the present application is as follows: (1) Bunsen reaction. After the system operates stably, the sulfur dioxide SO required for the Bunsen reaction is 2 , iodine I 2 and water H 2 O is introduced into the Bunsen reactor 1, and the molar ratio of each substance is SO 2 :I2 :H 2 O=1:1-1.5:12-20, fully mix to produce Bunsen reaction, reaction time is controlled at 20-60 minutes, reaction temperature is controlled at 323-358K.

[0036] (2) Two-phase separation: the mixed solution containing sulfuric acid, hydrogen iodide, elemental iodine and water produced by the Bunsen reaction enters the two-phase separation process. During the two-phase separation, the temperature of the mixed solution is maintained at 323-358K. Elemental iodine is added to the solution, and the molar amount of iodine input is 2-4 times the amount of sulfur dioxide input in the Bunsen reaction. After standing for 20-40 minutes, the upper layer is a sulfuric acid solution and the lower layer is an iodine-hydrogen iodide HIx solution.

[0037] (3) Sulfuric acid purification and decomposition, after the two-phase separation is completed, the sulfuric acid solution separated from the upper layer is mixed with a 60wt% hydrogen peroxide solution, and a small amount of hydrogen iodide remaining in the sulfuric acid reacts with hydrogen peroxide to generate iodine solid. Through solid-liquid separation, the iodine solid is circulated back to the system, and the purified sulfuric acid solution is concentrated to 75-90wt% by a multi-effect evaporation process. 75-90wt% concentrated sulfuric acid enters the sulfuric acid dehydration decomposition process. In the sulfuric acid dehydration decomposition tank 12, concentrated sulfuric acid is slowly injected and dehydrated with phosphorus pentoxide solid to produce sulfur trioxide gas and release a large amount of heat. At this time, cooling water is required to control the reaction temperature below 423K. Since all sulfuric acid needs to be converted into sulfur trioxide gas, phosphorus pentoxide solid needs to be added in excess. Preferably, phosphorus pentoxide is in excess of more than 20%. After the sulfuric acid dehydration reaction is completed, an appropriate amount of water is added to convert the excess phosphorus pentoxide into phosphoric acid and prepare a phosphoric acid solution of about 85%.

[0038] (5) Sulfur trioxide decomposition, sulfur trioxide gas enters the preheating tank, and sulfur trioxide is preheated to 923-1123K. The preheated sulfur trioxide gas evenly enters several membrane decomposition units, and through catalytic decomposition, sulfur dioxide and oxygen are produced. The oxygen is separated in situ through the oxygen ceramic membrane separation tube and stored in the oxygen storage tank, and the sulfur dioxide enters the sulfur dioxide storage tank for use in the Bunsen reaction. High-temperature gas passes through the outside of the membrane decomposition unit to ensure that the temperature inside the unit is maintained at 923-1123K.

[0039] (6) Hydrogen iodide decomposition, iodine-hydrogen iodide HIx solution is extracted from the lower layer of the two-phase stratification tank 2 and sent to the hydrogen iodide cooling separation process. The iodine-hydrogen iodide HIx solution is cooled to 283-288K, at which time more than 90% of the elemental iodine is precipitated from the solution. The precipitated iodine is separated from the solution by a solid-liquid separation device, and the separated elemental iodine is added to the two-phase stratification tank 2 for recycling. The remaining hydrogen iodide solution, under the action of a catalyst, is temperature-controlled at 623-723K, and hydrogen iodide is decomposed into a mixed gas of hydrogen and iodine. The above mixed gas is sprayed with cooling to separate the insoluble hydrogen, and the elemental iodine is cooled to form a solid. Then the elemental iodine is sent back to the Bunsen reaction tank 1 to undergo a Bunsen reaction with sulfur dioxide and water. Example 1

[0040] After the system is stable, 135 mol of sulfur dioxide, 202.5 mol of elemental iodine, and 2700 mol of water are input into the Bunsen reaction tank 1. At 343K and normal pressure, the three react with the Bunsen reaction, and after 30 minutes of reaction, a mixed solution A is formed, in which 134.7 mol of sulfuric acid, 67.8 mol of elemental iodine, 269.5 mol of hydrogen iodide, and 2430.5 mol of water are formed. The mixed solution A enters the two-phase stratification tank 2, at which time 337.5 mol of elemental iodine is added to the mixed solution A, and the mixed solution B is formed after being stirred evenly. At 323K and normal pressure, the mixed solution B is static and stratified. After about 40 minutes, the two-phase material tends to equilibrium, with the upper layer being the sulfuric acid layer and the lower layer being the iodine-hydrogen iodide layer. In the sulfuric acid layer, sulfuric acid is 134.2 mol, iodine is 1.1 mol, water is 1214.5 mol, and hydrogen iodide is 0.5 mol; in the iodine-hydrogen iodide layer, sulfuric acid is 0.5 mol, iodine is 404.2 mol, water is 1216.0 mol, and hydrogen iodide is 269.0 mol. Next, the mixed solution B is separated into two phases to obtain a sulfuric acid solution and an iodine-hydrogen iodide solution, respectively.

[0041] The sulfuric acid solution is sent to the sulfuric acid purification tank 6, and 1.5 mol of hydrogen peroxide is added at the same time. After the reaction, 1.3 mol of elemental iodine is separated in the impurity separator 7, and the purified sulfuric acid is separated and sent to the sulfuric acid storage tank 8. It is then sent to the sulfuric acid concentrator 9 and concentrated to 75wt% by multi-effect evaporation process and stored in the concentrated sulfuric acid storage tank 15. Then the 75wt% concentrated sulfuric acid is sent to the sulfuric acid dehydration and decomposition tank 12. At this time, 190 mol of phosphorus pentoxide powder has been added to the sulfuric acid dehydration and decomposition tank 12. The concentrated sulfuric acid reacts with phosphorus pentoxide to produce 134.2 mol of sulfur trioxide gas. The sulfur trioxide gas enters the sulfur trioxide preheating tank 14 and is heated to 973K before entering the sulfur trioxide decomposer 13. The temperature in the sulfur trioxide decomposer 13 is maintained at 973-1023K. In the presence of the catalyst CuO-CeO 2Under the action of sulfur trioxide, sulfur trioxide is decomposed into sulfur dioxide and oxygen. Oxygen is separated through the oxygen separation tube. The decomposition rate of sulfur trioxide is about 92%. The generated sulfur dioxide and the remaining sulfur trioxide are returned to the Bunsen tank.

[0042] The iodine-hydrogen iodide solution enters the iodine cooling and separation process, at which the solution temperature is cooled to about 283K. After 15 minutes, about 90%, about 363.7 mol of iodine elemental substance precipitates from the solution. After separating the above-mentioned elemental iodine, 337.5 mol of elemental iodine is returned to the two-phase stratification process, and the remaining 26.2 mol of elemental iodine is added to the Bunsen reaction tank 1. The hydrogen iodide solution enters the hydrogen iodide decomposition hydrogen production process. Under the conditions of 723K and nickel-modified activated carbon catalyst, hydrogen iodide decomposes to produce hydrogen and elemental iodine. The elemental iodine returns to the Bunsen reaction tank 1, and about 134.5 mol of hydrogen is produced.

[0043] Although the embodiments of the present application have been shown and described above, it is to be understood that the above embodiments are exemplary and cannot be construed as limiting the present application. Without departing from the spirit and scope of the present application, the present application may also have various changes and improvements, which all fall within the scope of the present application to be protected.

Claims

1. A sulfuric acid phase decomposition process in an SI cycle, the process comprising S1 Bunsen reaction, SO2, I2 and water reacting to generate a mixed acid aqueous solution of H2SO4 and HI; S2 two-phase separation, adding excess elemental iodine to the mixed acid solution, and separating the two phases into an upper sulfuric acid solution and a lower I2-HIx solution; characterized in that: It also includes S3 sulfuric acid purification and dehydration decomposition, taking out sulfuric acid solution from the upper layer of the two-phase stratification to react with hydrogen peroxide, solid-liquid separation to remove iodine solid, the purified sulfuric acid is concentrated to 75wt%-90wt%, slowly added and mixed with phosphorus pentoxide, reacting to generate phosphoric acid and sulfur trioxide, sulfur trioxide is decomposed into sulfur dioxide and oxygen under platinum series, transition metal oxide and composite metal oxide catalysts and 923K-1023K conditions, and composite oxygen-permeable ceramic membrane is used for in-situ separation of oxygen, and the sulfur dioxide gas with oxygen removed is returned to S1 for circulation to participate in the Bunsen reaction; S4 hydrogen iodide decomposition, I2-HIx solution is taken out from the lower layer of the two-phase stratification, and elemental iodine is separated by cooling and solid-liquid separation, and the iodine-poor HIx solution obtained after solid-liquid separation is heated and decomposed to obtain elemental iodine and hydrogen; wherein the order of S3 and S4 is not limited.

2. The sulfuric acid phase decomposition process in the SI cycle according to claim 1, characterized in that: The molar ratio of each substance in the S1 Bunsen reaction is SO2:I2:H2O=1:1-1.5:12-20. After fully mixing, the reaction takes 20-60 minutes, and the reaction temperature is controlled at 323-358K.

3. The sulfuric acid phase decomposition process in the SI cycle according to claim 1, characterized in that: The S2 two-phase separation is carried out, and the molar amount of elemental iodine added to the mixed solution after the Bunsen reaction is 2-4 times the amount of sulfur dioxide input in the Bunsen reaction in S1. The temperature of the solution is maintained at 323-358K, and the two phases are separated after standing for 20-40 minutes.

4. The sulfuric acid phase decomposition process in the SI cycle according to claim 1, characterized in that: The S3 sulfuric acid is purified and dehydrated, the upper sulfuric acid solution reacts with a 60wt% hydrogen peroxide solution, a small amount of hydrogen iodide remaining in the sulfuric acid reacts with the hydrogen peroxide to generate iodine solid, and the sulfuric acid solution after filtering and separating the iodine is sent to the sulfuric acid concentration process.

5. The sulfuric acid phase decomposition process in the SI cycle according to claim 1, characterized in that: The concentrated sulfuric acid is slowly added and reacted with at least 20% excess phosphorus pentoxide solid, the reaction temperature is controlled below 423K, and after the sulfuric acid dehydration reaction is completed, water is added to react with excess unreacted phosphorus pentoxide to generate phosphoric acid.

6. The sulfuric acid phase decomposition process in the SI cycle according to claim 1, characterized in that: The catalyst for decomposing sulfur trioxide into sulfur dioxide and oxygen is selected from Pt / TiO2, Pt / SiO2, Pt / Al2O3, Pt / ZrO2, Pt / CeO2, Cr2O3, Fe2O3, CuO, CeO2, NiO, Al2O3, FeTiO3, MnTiO3, NiFe2O4, CuFe2O4, NiCr2O4, 2CuOCr2O3, CuOCeO2.

7. The sulfuric acid phase decomposition process in the SI cycle according to claim 1, characterized in that: The S4 hydrogen iodide is decomposed, and the I2-HIx solution in the lower layer is cooled to 283K-293K, and the crystallized elemental iodine is removed by solid-liquid separation to obtain an iodine-poor HIx solution, and the elemental iodine is returned to S2 for two-phase stratification and recycling. The solution is then heated to 673-773K and thermally decomposed under the catalysis of a catalyst to obtain elemental iodine and hydrogen. The mixed gas is cooled to separate the insoluble hydrogen, and the remainder is returned to S1 to participate in the Bunsen reaction.

8. A sulfuric acid phase decomposition system in an SI cycle, the system implementing the process according to any one of claims 1 to 7, characterized in that: The system comprises at least two two-phase stratification tanks connected to the Bunsen reaction tank, the upper layer in the two-phase stratification tank is sent to a sulfuric acid purification tank, which is then connected in sequence to an impurity separator, a sulfuric acid storage tank, a sulfuric acid concentrator, a concentrated sulfuric acid storage tank, and a sulfuric acid dehydration and decomposition tank; the gas generated in the sulfuric acid dehydration and decomposition tank is sent to a sulfur trioxide preheating tank, which is then connected in sequence to a sulfur trioxide decomposer, a sulfur dioxide gas storage tank, and a Bunsen reaction tank to form a circulation loop, the sulfuric acid purification tank is also connected to a hydrogen peroxide storage tank; the sulfuric acid dehydration and decomposition tank is also respectively connected to a pure water tank, a phosphorus pentoxide storage tank, and a phosphoric acid storage tank; the sulfur trioxide decomposition tank is also connected to an oxygen storage tank.

9. The sulfuric acid phase decomposition system in the SI cycle according to claim 8, characterized in that: The internal space of the sulfur trioxide decomposer is divided into a first space and a second space in the upper and lower parts by a composite oxygen-permeable ceramic membrane. The lower part of the second space is filled with a sulfur trioxide decomposition catalyst. A sulfur trioxide gas inlet is provided at the lower part or the bottom of the sulfur trioxide decomposer. A sulfur dioxide gas outlet is provided on the upper side wall of the sulfur trioxide decomposer and located in the second space. An oxygen gas outlet is provided at the upper part or the top of the sulfur trioxide decomposer and located in the first space.

10. The sulfuric acid phase decomposition system in the SI cycle according to claim 8, characterized in that: The lower layer in the two-phase stratification tank is sent to the iodine solid cooling and separation tank, the elemental iodine separated by the iodine solid cooling and separation tank is then sent to the iodine solid storage tank and then returned to the two-phase stratification tank, the hydrogen iodide solution remaining after the elemental iodine is separated by the iodine solid cooling and separation tank is sent to the hydrogen iodide decomposition tower, and the gas generated by the decomposition is then sent to the spray cooling tower, and the spray cooling tower is respectively connected to the water tank and the hydrogen storage tank.

Images