JPH0153201B2 - - Google Patents

Description

[Detailed Description of the Invention] Hydrogen sulfide contained in acid gas and natural gas discharged during oil refining is industrially treated by the Claus process, which involves partial combustion in air, and the sulfur content is removed by sulfur. The hydrogen content is recovered as water. From the standpoint of energy conservation, this treatment method cannot necessarily be said to be the best, as hydrogen sulfide has a large amount of effective energy.In particular, hydrogen for oil refining is used in the steam forming method, which consumes naphtha and natural gas. Considering the current state of production, if possible, the hydrogen content of hydrogen sulfide can also be
We want to collect it as hydrogen and reuse it.

First, let's take a look at the thermochemical data of the reaction that decomposes hydrogen sulfide to produce hydrogen and sulfur.The enthalpy change and free energy change in the standard state, △H° and △G゜, are expressed in Kcal/mol as follows. It is.

That is, △G゜₂₉₈ remains at 8.0 Kcal/mol, and theoretically it should be possible to electrolyze with 1/8.5 of the power consumption compared to electrolyzing 1 mole of water. However, it has not yet been put into practical use due to reasons such as the inability to find an electrolyte suitable for hydrogen sulfide. The present invention attempts to overcome this difficulty and realize the production of sulfur and hydrogen from hydrogen sulfide as follows. That is, the following two-step reaction is performed using the redox properties of iron ions in an aqueous solution state.

By blowing H ₂ S gas into a solution of ferric ions,
Sulfur is precipitated and separated by reaction (1), and then the solution is transferred to reaction (2), where divalent iron ions are regenerated into a trivalent state by electrolytic oxidation and hydrogen is generated at the same time. That is, the iron salt solution undergoes reactions (1) and (2).
As it circulates through channels connecting the two, it plays the role of forming sulfur in the former reaction and generating hydrogen in the latter without being consumed, forming a closed cycle.

It is well known that when hydrogen sulfide comes into contact with an aqueous solution of ferric ions, it is easily oxidized to produce sulfur. In reaction formula (1), ferric chloride in an aqueous solution state,
Under standard conditions where the activities of ferrous iron and hydrochloric acid are 1, the change in free energy, △G゜₂₉₈ , is - as shown above.
It was experimentally confirmed that sulfur coagulates and precipitates during the reaction, which predicts that the reaction will proceed smoothly at 27.5 Kcal/mol, and that it is insoluble and can be easily filtered and separated from the aqueous solution. The required concentration of ferric chloride solution is 0.1molKg ^-1
or more, preferably 0.5molKg ^-1 from room temperature
The reaction can be carried out at temperatures up to 150°C. This also applies when ferric sulfate or ferric phosphate is used instead of chloride. The problem is how to regenerate the reduced ferrous ions into ferric ions, but the present inventors performed the necessary oxidation (reaction equation 2) electrochemically at a low cell voltage. We discovered that this process can be carried out smoothly, and were able to propose a new closed cycle.

As the electrolytic cell, any conventional type may be used. Graphite is an example of an electrode material having acid resistance, and a diaphragm is provided between an anode and a cathode using graphite. The diaphragm is a hydrogen ion selectively permeable membrane, e.g.
When using Nafion 125 (DuPont) or NeoseptaC66-5T (Tokuyama Soda KK), an electrolyte solution on the cathode side is not required, and a porous gas diffusive electrode such as graphite fiber cloth, preferably platinum, etc., is directly connected to the diaphragm. may be contacted with a catalyst supported thereon. In this case, the resistance of hydrogen gas generation on the cathode surface is smaller than that in the case where hydrogen gas is generated as bubbles from the electrolyte solution, which has the advantage of making the structure of the cathode chamber itself more compact.

In the anode chamber of the electrolytic cell, when a hydrochloric-acidic ferrous chloride solution, which corresponds to the left side of reaction equation (2), flows in, iron ions are electrolytically oxidized to a trivalent state. The cell voltage at this time is calculated to be 0.77V at 25℃ using the value of △G゜₂₉₈ = 35.5Kcal/mol under standard conditions, but in reality, it depends on the temperature of the solution, ferric ion / ferric ion / It varies depending on the molar ratio of iron ions and acid concentration. In particular, it has been found that when hydrochloric acid is used in excess as the acid, the cell voltage drops considerably. Here, excess hydrochloric acid means hydrochloric acid in a free state that does not participate in the redox reaction of iron ions, and the amount is approximately 0.5 to 15 ^{molKg -1} as a concentration.
is preferred. This effect is thought to be based on the property that the activity of hydrogen chloride is significantly increased in a concentrated hydrochloric-acidic solution. Thus, it is preferable that the electrolysis be carried out in the presence of excess hydrogen chloride. However, on the other hand, the hydrogen chloride vapor pressure exhibited by the trivalent iron ion solution flowing out from the electrolytic cell increases, and in this state the reaction (1)
If this is carried out, a large amount of hydrogen chloride gas will evaporate from the apparatus for reaction (1) together with non-reactive gas such as carbon dioxide originally contained in the raw material hydrogen sulfide gas. Therefore, in order to prevent losses due to this dissipation as much as possible, it is effective to control the operating temperature and introduce a condensation device for hydrogen chloride. Furthermore, another method is to limit the hydrogen chloride excess state of the iron salt solution to the residence period in the electrolytic cell, for example, by once distilling the outflow from the electrolytic cell under reduced pressure, and then returning the vapor phase to the electrolytic cell. It is also possible to take measures such as absorbing it back into the liquid and subjecting the distillation residue to reaction (1).

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

Example 1 This example describes the reaction of hydrogen sulfide with an aqueous ferric chloride solution. Hydrochloric acid acidic ferric chloride solution (composition, FeCl ₃ 1.16molKg ^-1 , HCl 4.8molKg ^-1 ) 18.8g
A conventional hard glass gas absorption device (capacity 150ml)
Hydrogen sulfide gas 200ml/min at 65℃
The solid sulfur was blown in at a high speed for about 5 minutes, and the solid sulfur produced was collected with a glass filter, dried at 150℃, and then weighed.
A yield of about 95% was obtained.

Example 2 This example describes the electrolysis of an aqueous hydrochloric acid solution containing ferrous chloride.

The electrolytic cells used were a pair of graphite cells (9.5 cm x 110
It is composed of a combination of outer shells (2 cm thick, 2 cm thick), and each outer shell has two communication ports, and from there, a large number of grooves (width 1 mm, depth 2 mm) are cut into the inner contact surface. It is possible to supply a raw material aqueous solution to the electrical part, or to discharge generated gas, etc. This current collector is made of graphite fiber cloth (1.7cm x 4.5cm,
A hydrogen ion permselective membrane (DuPont's NAFION-
125 membrane, 4 cm x 5 cm, thickness approximately 0.2 mm).
Therefore, the electric cell is composed of a lower cathode chamber (hydrogen gas generation chamber) and an upper anode chamber (ferrous electrolytic oxidation chamber) symmetrically around this permselective membrane.

The entire cell was placed in an air temperature chamber and a ferrous chloride aqueous solution containing excess hydrogen chloride (composition:
FeCl ₂ 2.5molKg ^-1 HCl4.8molKg ^-1 ) as a stock solution,
Argon gas containing saturated water vapor was supplied to the anode chamber at a flow rate of 5 ml/min under atmospheric pressure, while argon gas containing saturated water vapor was fed as a carrier to the cathode chamber at a rate of 80 ml/min. Electrolysis was performed at a cell voltage of approximately Starting at 0.45V, the current density at 0.65V was 100mA/ ^cm2 .
The hydrogen gas generated at the cathode was quantified using gas chromatography and the current efficiency was found to be over 95%.

Similarly, ferric chloride and ferrous chloride containing hydrogen chloride
Mixed aqueous solution of iron (composition, FeCl ₃ 1.16molKg
^-1 Fecl ₂ : 1.16molKg ^-1 , HCl : 4.8molKg ^-1 ) was used as the stock solution in a similar electrolytic experiment, and the cell voltage was
The current density at 0.75V is 100mA/ ^cm2 , and the current efficiency
It showed over 95%.

Claims (1)

[Claims] 1. In the decomposition of hydrogen sulfide, a solution containing sulfur and divalent iron ions is generated by a reaction between hydrogen sulfide and an aqueous iron chloride solution containing trivalent iron ions, and sulfur is separated from the reaction mixture, The resulting de-sulfurizing solution containing excess hydrogen chloride is sent to the anode chamber of the electrolytic cell, and the divalent iron ions are electrochemically regenerated into a trivalent state, while at the same time hydrogen is generated from the cathode chamber. On the other hand, a method for continuously producing hydrogen and sulfur by decomposing hydrogen sulfide, characterized in that an aqueous iron chloride solution containing trivalent iron ions discharged from an anode chamber is reused in a closed cycle method.