DE2603690A1 - Prodn. of hydrogen and oxygen from water - using thermochemical continuous process in which carbon-oxygen cpds. is reacted with oxide as acceptor in presence of water and halogen - Google Patents

Abstract

Thermochemical continuous process for dissociation of water into H2 and O2 is carried out in several stages. Method comprises reacting a C-O cpd., e.g. CO, formaldehyde, (m)ethanol, or ethylene (with an oxide as acceptor) in presence of water and iodine to form a corresp. oxide with a higher O fraction and a cpd. such as ethane, converting the cpd., such as ethane, with the evolution of H, to the original cpd. e.g. ethylene, sepg. O from the cpd. recycling the prod. and ethylene to the process, and removing H and O from the process. The oxide used may be Sb, V, As, Bi, Te, U or Se and may be an alkali(ne earth) cpd. of the oxide. The method and choice of components avoid corrosion problems.

Description

Chemo-thermal cycle processes for the production of hydrogen and

Oxygen from water The invention relates to multistage cycle processes from chemical reactions to produce hydrogen and oxygen from water.

It is known that using heat and im Circle to lead chemical compounds or components in hydrogen and oxygen can be dismantled. This happens, for example, in the multi-stage processes of the iron-chlorine systems.

The disadvantages of such previously known circular processes exist on the one hand in the use of halogen or halogen compounds at temperatures that are essential lie above 5000 C and thus cause major corrosion problems, secondly in the necessary transport of large quantities of solids between reactors of the various Stages.

The object of the invention is therefore to provide a method for thermochemical To create water splitting, in which halogen compounds or

Isalogeno or also like halogen acting compounds only in process stage <'n If low temperatures are involved, the largest possible part of the process stages is operated with liquid or gaseous components and by the selection of the components corrosion problems can be largely excluded.

The object underlying the invention is achieved in that marl a carbon-oxygen compound from the group carbon monoxide, formaldehyde, Methanol and ethanol or ethylene with an oxide as an oxygen accessory in the present from water and iodine to the corresponding oxide with increased oxygen content and a Converts carbon-oxygen compounds with a lower proportion of oxygen or ethane, from this compound or the ethane with elimination of hydrogen the starting compound with a higher proportion of oxygen or ethylene forms back, from the oxide with increased Oxygen component splits off oxygen, the resulting oxide or

the ethylene re-enters the cycle in the process and hydrogen and removes oxygen from the process.

The reactions can advantageously be carried out in the gas phase, but also in the liquid phase. In all processes, the mechanism of the exothermic reaction consists of the following steps: Dissociation of iodine in water after: Oxidation of an oxide by hypoiodous acid with further formation of iodine-hydrogen.

Reduction of a hydrocarbon or a carbon-oxygen compound by iodine - hydrogen with the release of iodine.

When using an oxide in pure or aqueous form as the oxygen acceptor, the following cycle occurs with antimony oxide, for example: 200-4000C 9300 C, start of decomposition approx. 8000 C approx. 800-9000 C, reformer Methanol synthesis Conversion Instead of antimony III oxide, arsenic III oxide or vanadium IV oxide can also be used. In the first two stages, the reactions (J) (660-900 ° C).

If carbon monoxide is used instead of methanol, then, depending on the temperature (200 - 3500 C) and pressure (40 - 200 ata), lower oxygen contents are obtained in the product oxide than according to I 1. A characteristic cycle of this type results from the equations: or oxides with: 2/3> ME / O; D 1/2) Here, as in all of the following processes, oxygen acceptors with further oxidation states can also be used, so that the temperature necessary for the elimination of oxygen can be varied. In the case of vanadium, for example, the oxides V203, V204, V205, V305, V407, V6013 and many others are known. The same applies to uranium oxides. With antimony IV oxide, for. B. a process possible after approx. 200 ° C approx. 8000 C The use of arsenic oxides is particularly advantageous in terms of transportability in predominantly liquid form: 200 - 3500 C 650 - 8000 C With ethylene or formaldehyde, the cycle processes when using pure or aqueous oxides are: The analogous oxides can also be used here.

Underreaction of all processes is the formation of hydrogen iodide Oxidation of one of the oxides listed here. To achieve higher levels of oxidation to be able to, are usually alkali carbonates to generate a weakly alkaline Solution used.

The same effect can be achieved if the corresponding alkali or alkaline earth compounds of the oxides of antimony, vanadium, arsenic, bismuth, tellurium, @ran or selenium are used instead of the carbonates. For example, with carbon monoxide the following scheme results: approx. 9300 C The cycle is closed by reactions II 3. 4. and II 5..

The alkali or alkaline earth compounds can be used in various stoichiometric ratios to the water present and also to the oxide used, e.g. B. after: Oxygen is split off via the intermediate product Na 2 O As 2 O 3 at temperatures of 9000 C and more. In order to lower the temperature level, it is often more sensible to provide a more than stoichiometric oxide content, e.g. B. after: approx. 800 ° C The cycle processes V and VI are closed again by the reactions II, 3. 4. and II 5..

Compared to the pure oxides (method according to I; II and III) are the alkali oxide compounds are usually higher in water or

Soluble in water-alcohol mixtures, as hydrates have low melting points and often form eutectic melts, so their use with regard to portability is preferable.

It is of course possible to produce methanol from hydrogen and carbon dioxide to cover peak loads. This can take place particularly advantageously in the case of cycle processes using carbon monoxide / methane and also methanol / methane. In the special case of a half-open circuit, for example, carbon dioxide is taken from the flue gas of a coal-fired power plant and only methanol is produced from water and carbon dioxide: If iodine is used in stoichiometric amounts, other processes that use alcohols or their ethers can be carried out, e.g. B. according to the equations: 100 - 200 ° C 500 - 650 ° C

Claims (3)

Patent claims 4. Multi-stage thermochemical cycle processes for splitting of water into hydrogen and oxygen, characterized in that one Carbon-oxygen compound from the group consisting of carbon monoxide, formaldehyde and methanol and ethanol or ethylene with an oxide as an oxygen acceptor in the presence of Water and iodine to the corresponding oxide with increased oxygen content and a carbon-oxygen compound with a lower proportion of oxygen or ethane, from this compound or the Ethane, with elimination of hydrogen, is the starting compound with a higher proportion of oxygen or ethylene forms back, from the oxide with increased oxygen content oxygen splits off, the thus obtained oxide or the ethylene back in the cycle in the process starts and removes hydrogen and oxygen from the process. 2. The method according to claim 1, characterized in that one oxides of antimony, vanadium, arsenic, bismuth, tellurium, uranium or selenium is used. 3. The method according to claims 1 and 2, characterized in that alkali or alkaline earth compounds of the oxides are used.