JPS5841701A - Thermochemical decomposition of water by magnesium- iodine system cycle - Google Patents

Abstract

PURPOSE:To evolve a highly-concentrated HI gas and to recover calorie effectively, by dividing an aqueous solution of MgI2 obtained by the reaction between MgO and I2 into two, adding MgO to one of them, heating the blend, absorbing evaporated substances in the other, decomposing the reaction product thermally. CONSTITUTION:In a Mg-I2 system cycle, MgO is reacted with I2 (the first step reaction) in the presence of water and excess I2. The formed Mg(IO3)2 is filtered off to give an aqueous solution of MgI2, which is divided into two. 3mol based on 1mol MgI2 of MgO is added to one of them, the prepared blend is evaporated under heating, 3Mg(OH) MgI2 is formed, generated steam and iodine vapor are absorbed in the other aqueous solution of MgI2, and vapor calorie is recovered. The diluted aqueous solution is returned to use it for the first step reaction, and the reaction product in a solid phase is decomposed at high temperature, to evolve a highly concentrated IH gas having a molar ratio of MgO to H2O of 1:1.

Description

[Detailed Description of the Invention] The present invention is based on a method for thermochemical decomposition of water using magnesium nonaride and iodine (Public Patent Publication No. 53-60), which has already been reported.
393), it provides a new operating method. The cycle in this method consists of the following four-stage reactions.

+Mg (■0.>,..., (1) Mll (IO2)2-Otsu00" (and-) MgO+I,
+2. sO, -・(2) 5MpI, +5H, 5M around O-u, 1ilO+10HI,, -(3) 300~70
0°C 10HI□5H, +5I, ---(4)6 Canopy 1,
From an operational point of view, this cycle converts the M I (IOs) precipitate from the mixture produced by reaction (l) into
After separating and concentrating the resulting M9I2 solution (containing excess iodine), HI gas is generated by reaction (3), which is a hydrolysis reaction of MpI2. This concentration process is to separate excess water and iodine, but by heating and evaporating it,
When the H20/JI I 2 molar ratio reaches a stage of about 6,
Thereafter, dehydration and the hydrolysis reaction of reaction (3) occur simultaneously. For this reason, there is a limit to the dehydration rate with simple concentration, and therefore, as is known from the reaction MpI2゜6H20→JIO+2HI+5H20, the final composition of the gas generated by the hydrolysis reaction of MpI is 1 mol of H At least 2.5 mol of water per mol of water is allowed to coexist.

The purpose of the present invention is to overcome these limitations and generate highly concentrated HI gas, while effectively recovering the excess water and iodine vapor generated in this concentration process. .

The water vapor and iodine gas generated during the reaction are absorbed into the other divided JII solution and the steam heat is recovered, and the thus diluted MpI solution is returned to the apparatus for reaction (1). 3Mf generated as? (OH),・
From MpI, ygo and H, O/H are produced by high temperature pyrolysis.
A gas with a molar ratio of 1/1 is generated.

The present invention will be explained in detail below.

When a mixture of MpI, JIO/M9I, and magnesium oxide added at a molar ratio of 3 is heated and evaporated, excess moisture is evaporated and solid content is 3M9 (OH).
- Generation of M, 9Il was observed. This substance is stable at temperatures below 300°C, and when heated to even higher temperatures, it decomposes while producing water vapor and hydrogen iodide, and the decomposition ends at temperatures above 350°C, leaving magnesium oxide as a solid content. That is, by this thermal decomposition, concentrated hydrogen iodide gas with a HI/H molar ratio of 20 can be recovered, which can be used in the subsequent reaction (4).
The process of producing hydrogen by reducing the handling and volume not only improves the operation, but also ultimately improves the thermal efficiency of hydrogen production per mole.

Magnesium iodide aqueous solution belongs to the category showing the highest boiling point among salt aqueous solutions. In general, an aqueous salt solution has the ability to condense water vapor at normal pressure at a higher temperature than the boiling point of water (100° C.) by the amount that increases the boiling point, but magnesium iodide has a particularly excellent boiling point increasing effect. Therefore, by utilizing this attribute, the latent heat of condensation of water vapor can be recovered at a higher temperature by absorbing it into the solution. Furthermore, the solution has the property of absorbing iodine vapor well.

From this, the above 3'JI (OH), ・JI I
Excess water vapor and iodine vapor generated during the production of 2 can be used, for example, in a shell-and-keep heat exchanger to heat water, for example. Therefore, if the medium is water, it can be used to generate steam at high temperature and pressure. In addition,
Collection of water vapor and iodine vapor (thus, the diluted magnesium iodide aqueous solution is poured into the apparatus for reaction (1),
It can be regenerated into a concentrated liquid by reaction (1).

The present invention will be explained below with reference to Examples.

Example 1 Magnesium iodide aqueous solution (concentration 55%, molar composition, M
pI, ・12,5H,O), M, 90/JII2
There was a stagnation of dehydration in the temperature range of 210°C, and active dehydration occurred again from 210°C, and magnesium hydroxyiodide was produced as a solid phase at 280°C. Calculation based on dehydration amount and X
From line analysis, it was determined to be 3Mg (OH)g-Mug. On the other hand, the above slurry contains 'v'Ml/T! The nine samples in which iodine was added at a -F-le ratio of 6 showed similar thermal loss curves, with almost all of the iodine evaporated by about 200°C, and the same <3 Mg(OH) at about 280°C. M,9I,
produced a composition of

This basic iodide is dissolved in an argon W atmosphere at normal pressure at about 3
Decomposition started at 20°C and ended at 380°C, leaving only magnesium oxide as a solid content.

Example 2 The vapor pressure of an aqueous magnesium iodide solution and a solution in which iodine was dissolved was measured using a hard glass Bourdon tube. The boiling points (1 atm) of magnesium iodide solutions with concentrations of 50.7% and 60.7% are 115°C and 136.5°C, respectively.
It was ℃. On the other hand, when iodine in a 12/Mg2 molar ratio of 4 was added to the 60.71 solution, the boiling point was 134°C.

Claims (1)

[Claims] (1) In the magnesium iodine cycle,
An aqueous solution of magnesium iodide, which is produced by the reaction of magnesium oxide and iodine (first stage reaction) in the presence of excess iodine in water and water, and which is obtained by separating magnesium iodate in a furnace, is
93 moles of magnesium oxide per mole of magnesium iodide were added, and the resulting mixture was heated and evaporated to produce magnesium hydroxyiodide (3M, ?).
(o) i), ・Ml, ) is produced, and the water vapor and iodine vapor generated at this time are absorbed into the other divided magnesium iodide aqueous solution to recover the vapor heat, and thus the diluted magnesium iodide The aqueous solution is returned for the first stage reaction, and the magnesium hydroxyiodide is decomposed into hydrogen iodide, water vapor and magnesium oxide by heating. Water thermochemistry using a magnesium-iodine cycle. Decomposition method.