DE1091696B - Process for removing hydrogen sulfide from gases - Google Patents

Description

Method for removing hydrogen sulfide from gases The invention relates to a method for removing hydrogen sulfide from gases with the aid an iron-containing washing liquid that can be regenerated by oxidation.

In known methods of this type in which the liquid is alkaline is and from a suspension of iron oxide, iron oxide hydrate or basic iron carbonate and contains sodium or ammonium carbonate or bicarbonate, the reacts Hydrogen sulfide first with the alkali to form alkali sulfides, which in turn react with the iron in suspension to form iron sulfide. The reaction between soluble sulphides and iron suspension does not proceed instantaneously, and since the Solutions of alkali sulphides exert a partial pressure of hydrogen sulphide, the effect of this is the rapid and complete removal of the hydrogen sulfide from the gas, the resulting contaminated liquid is ventilated, to oxidize the iron, releasing sulfur, and the refreshed liquid is then ready for reuse for gas scrubbing.

This method has the disadvantage that influences are difficult to control when preparing the batch, the amount of reaction and the rate of reaction strongly affect.

In the method explained at the beginning, the use of a Washing fluid is known to contain certain hydroxy compounds such as glycols and glycelines and oxy acids such as citric acid, tartaric acid or their salts in addition to the iron hydroxide contains. These compounds have a dissolving or peptizing effect on the Iron hydroxide under neutral or alkaline conditions. A gas scrubbing liquid prepared in this way however, has the disadvantage that it is not easy to use and in particular can be oxidized for reuse after contact with the dirty gas.

Finally, it is known in the case of the method explained at the beginning to use an aqueous alkaline suspension of iron as washing liquid, in which the iron is partly or almost completely in the form of a solid complex Cyanide is contained and the complex cyanides mentioned are in colloidal or are in a coagulated or precipitated state. The reaction between the resulting alkali sulfides and the complex iron cyanides in the suspension Release of sulfur with the reduction of iron in the complexes from the ferric result in the Ferio state. The reduced complexes are then ventilated reoxidized and thus refreshed the suspension for reuse.

The above reduction and oxidation reactions are faster than the sulfiding and oxidizing reactions that occur when iron hydroxide is the reagent for binding and removing the hydrogen sulfide from the solution, and the aforementioned process therefore has advantages in terms of the extent of the Removal of hydrogen sulfide from the gas and the size required System. however, in both types of the process the reagent is iron as a suspension solid particles present and not in solution. The result is in all cases an inevitable and sometimes considerable loss of reagent that occurs with removal of the free sulfur from the system, for example by sedimentation and / or filtration processes is linked.

About the disadvantages of the relatively slow reaction and the loss of reagent as a result of the use of suspended solid reagents, it is necessary to to wash the gas with a dissolved reagent that is immediately and quantitatively using the hydrogen sulfide or with alkali sulfide reacting with any in the Gas scrubbing solution also present alkali can be formed.

In this case it is known, for example, to use a solution of a zinc salt, such as B. zinc acetate or zinc sulfate, to wash out the hydrogen sulfide To use gases. By this means the hydrogen sulphide is removed as it is dissolves, very quickly and completely bound as zinc sulfide, from the gas scrubbing liquid fails. By such a process, therefore, a gas can be made entirely of hydrogen sulfide to be freed. But the drawback remains that all of the zinc reagent is necessary from the liquid as sulfide for the Sulfur recovery and for freshening must be de-refined, which is not by such a simple step how ventilation can be achieved.

The invention is now based on the object of avoiding these shortcomings of the known methods. According to the invention, this object is achieved in that a solution of chelated iron in the ferric state is used as the washing liquid, in which the hydrogen sulfide from the ferric to the ferrous state and by oxidation treatment, e.g. B. aeration, from the ferrous to the ferric state to be transferred and in both oxidation stages remaining in solution iron as a complex compound with an amino acid of the type is present, in which at least two of the groups X consist of acetic acid or propionic acid or their alkali salts and in which R is an alkyl group with at least 2 carbon atoms in the chain, or cyclohexane, the groups are in the 1,2- (ortho) position of the cyclohexane as a substituent, or is a substituted benzene ring, the groups are in the 1,2- (ortho) position, and in which at least one chlorine or one methyl radical is present as a substituent in the 3- and 6-position of the benzene ring.

This solution reacts quickly and quantitatively with the hydrogen sulfide or with soluble alkali sulfides. Also, the dissolved substances remain in the regeneration by oxidation in solution. The sulfur released in the process can be easily removed, without losing a lot of washing liquid.

It is known that certain organic compounds known as chelating agents referred to, complexes with various metals, e.g. B. iron, and that that Metal in such a complex will remain in solution if the conditions otherwise the hydrogen ion concentration and / or the presence of other dissolved salts would cause her to fail. The stability at high temperatures is also a hallmark of some such complexes whose aqueous solutions, e.g. B. without decomposition of the complex and without precipitation of the metal, can be cooked.

The formation of a complex or chelate through the reaction of a chelating agent Agent with a metal is including the formation of one or more the MetaEion of comprehensive ring structures understood. You have the stability of the chelates attributed to the presence of such ring structures.

The term "chelated iron" is used in the following to denote such to designate a complex of ferrous or ferrous iron salt.

Examples of suitable amino acids are ethylenediamine-tetra-acetic acid, 1,2-diamine-cyclohexane-N, N .'-tetra-acetic acid, diethylene-triamine-penta-acetic acid and N-hydroxyethyl-ethylene-diamine-tri-acetic acid, but salts such as alkali metal salts can also be used of these acids are used.

The chelated iron solution for gas scrubbing is preferably by Dilute a concentrated solution of chelated iron prepared before the The dilution can be oxidized and ventilated for this purpose.

The chelated iron solution to the gas washing may be alkaline or non-alkaline as desired.

The chelated iron in the gas scrubbing liquid can be made from iron complexes exist that have arisen from multiple chelating agents.

The process can take place at atmospheric pressure and room temperature or at higher temperatures and pressures.

The following examples of chelated iron solutions are for the Use in the process according to the invention for the removal of hydrogen sulfide suitable from contaminated heating gases.

(1) 35 g of crystalline ferrous sulphate (Fe, S04 - 7 H, 0) are dissolved in 11 of water and this solution is poured into another liter of water, 24 g of anhydrous sodium carbonate, g between 50 and 70 Tetra sodium salt of ethylene -diamin-tatra-acetic acid and between 20 and 100 g of tri-ethanolamine. The resulting clear mixture is aerated until no further darkening in color is' after which it either with nine times the volume of water or with a nine-fold volume of 0.25 N sodium bicarbonate-carbonate solution (0.20 n bicarbonate, 0 , 05 n-carbonate) is diluted.

(2) 75 g of the tetra-sodium salt of ethylene-diamine-tetraacetic acid is dissolved in 11 % of water, and the hydrogen ion concentration of the solution is approximated to p. 7 set up. For this purpose, a solution is added 35 g kristaUinischen the ferrous sulfate in water and 11 aerates the solution and diluted with nine times its volume of water. The hydrogen ion concentration of the diluted solution is then set to about pl; 5.

(3) 35 g of crystalline ferrous sulfate are dissolved in 11 of water and the solution is poured into 11 of water, the solution 62.5 g in the sodium salt of di-ethylene-triamine-penta-acetic acid at pH 9 containing. The resulting solution is aerated until it contains a significant amount of chelated ferrous iron.

(4) 35 g of crystalline Feriosulfats are dissolved in 11 of water and the solution is poured into 11 of water, the solution 65.2 g in the tetra-sodium salt of cyclohexane-1,2-diamine-tetra-acetic acid contains. The resulting solution is aerated until all of the iron is present as chelated ferrous iron.

The aerated solutions of Examples (3) and (4) can be used for gas scrubbing undiluted or diluted with water (e.g. nine times their volume) as desired.

For example, when using ethylenediamine-tetra-acetic acid as the chelating agent, the following, more concentrated solution can be prepared: (5) 174 g of crystalline feriosulphate are dissolved in 11 % of water. This solution is added to a solution of 11 265 g ethylene diarnin tetraacetic acid sodium salt tetra-than and contains 75 g of tri-ethanol-amine. The resulting solution is aerated until all of the iron is present as ferric iron in the chelate.

This solution can be used undiluted for gas scrubbing.

The chelating agent can be ethylene-diamine-tetrapropionic acid or 1,2-diamine-cyclonhexane-N, N'-propionic acid contain. In all of the above named solutions, the chelating agent is present in an amount that is at least the stoichiometric equivalent of iron.

Claims (2)

PATENT CLAIMS: 1. A method for removing hydrogen sulfide from gases with the aid of an iron-containing scrubbing liquid which can be regenerated by oxidation, characterized in that a solution of chelated iron in the ferric state is used as scrubbing liquid, in which the hydrogen sulfide from the ferric in the ferrous state and duich oxidation treatment, e.g. B. aeration, from the ferrous to the ferric state to be transferred and in both oxidation stages remaining in solution iron as a complex compound with an amino acid of the type is present, in which at least two of the groups X consist of acetic acid or propionic acid or their alkali salts and both R an alkyl group with at least 2 carbon atoms in the chain, or cyclohexane, the groups are in the 1,2- (ortho) position of the cyclohexane as a substituent, or is a substituted benzene ring, the groups are in the 1,2- (ortho) position and in which at least one chlorine or one methyl radical is present as a substituent in the 3- and 6-position of the benzoin. 2. The method according to claim 1, characterized in that the washing out of the hydrogen sulfide and the regeneration of the washing liquid by venting the same takes place in continuous sequence in washing towers. 3. The method according to claim 1 or 2, characterized in that the washing process takes place at an elevated temperature.