JPH0811170B2 - Method for preventing decomposition of chelating agent used for removal of hydrogen sulfide and redox catalyst formulation used therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention is an improved system for removing hydrogen sulfide from a fluid stream.
Regarding the continuous circulation process, this process breaks the fluid flow.
Contact with a polyvalent metal catalyst solution and reused in the process
The catalyst solution for regeneration. More specifically, the book
The invention is based on the implementation of the hydrogen sulfide removal process of the above-mentioned form.
And excessive decomposition of aminopolycarboxylic acid chelating agent
And how to prevent loss. (Problems to be Solved by the Prior Art and Invention) A chelating iron catalyst for removing hydrogen sulfide from a gas stream
The use of aqueous solutions is well known. Sulfide water
Oxidize hydrogen sulfide to elemental sulfur by contacting it with an element-containing gas
At the same time, iron is reduced from ferric iron to ferrous state. This
Solution is contacted with an oxygen-containing gas to remove iron from ferrous iron.
Oxidized to ferric state, regenerated and reused. Many prior art patents in this area have limited small
Seems to be based on extensive experimental research. So
As a result, the disclosure of the above-mentioned patent shows that aminoporcarboxyl
This type of hydrogen sulfide removal process using acid chelating agent
Major operational problems in long-term, large-scale implementation
Not knowing, and even solving the above problems
Not intended. For example, many of the aforementioned prior art patents
Is a neutral or alkane that is most effective in removing hydrogen sulfide.
Acidic sulfur oxides such as thiosulfate at potash pH values
Is generated. In the prior art
Prevents or minimizes the formation of thiosulfate.
To this end, add organic amines, buffers, and other additives,
It is suggested to be added to the chelated iron solution. example
For example, in Meuly's U.S. Pat.
Alkali or alkaline salts of selected acids such as sulfuric acid
Is added to prevent the formation of thiosulfate.
Have been. Another way is to recycle the killer
A portion of the iron solution is collected periodically to accumulate thiosulfate
And the process is carried out at low pH values,
It has been suggested to interfere with the formation of thiosulfate. However, this type of process can be
If it is carried out over a period of time, it is necessary to produce and store thiosulfate.
It turns out that the product is not a serious problem. Further below
As we will see in detail,
Chemistry of required aminopolycarboxylic acid chelating agents
Decomposition and loss can result in large-scale
The most significant impact on the economic feasibility of implementation
I realized it was a driving problem. Some of the prior art researchers found that chelating iron solutions
The liquid is “unstable” and is not desirable for iron compounds
I knew that precipitation could occur. For example,
British Patent No. 999,799 discloses a chelate complex with a finely adjusted pH.
It is recommended to prevent decomposition of the body. British patent number 999,
800 is an iron chelate that carefully controls the regeneration of the catalyst solution.
Suggests that it protects against peroxidation. United States of Thompson
Patent No. 4,189,462 refers to ethylenediamine
Limiting the molecular ratio of acetic acid (EDTA) is a chelating molecule
Is an important consideration to avoid
Suggests that. Lynn US Patent No. 4,330,478
Is generally said to be highly resistant to oxidation.
Use of certain aliphatic polycarboxylic acid chelating agents
Suggests that. US Patent No. 3,62 to Roberts et al.
2,273 is a chelating iron complex with the addition of a selected buffer.
Maintains pH at a relatively high value, which is said to be highly stable
Is disclosed. Lynn et al. US Patent No. 4,27
8,646 has a low pH when the selected amine salt stabilizer is added.
The value suggests to obtain chelate stability. Diaz
U.S. Patent Number 4,382,918, Number 4,388,293, and Number
4,400,368 are various sulfur-containing compounds and nitrogen-containing
Compound is added as a stabilizer to reduce chelate decomposition rate
Proposal to do this, but look at the reported data
And the improvement in chelate loss is relatively small. Blytas
U.S. Pat. No. 4,421,733 of US Pat.
Add bisulfite ion to reduce chelate decomposition rate
Is disclosed. Prior art prior to the present invention was effective and
Of the problem of chelate decomposition that is environmentally acceptable and inexpensive.
There was no solution. Furthermore, in the hydrogen sulfide removal process
The mechanism by which the chelate exhibits instability was properly explained.
There was no. (Means for Solving Problems) A thorough experimental study on the problem of catalyst instability was conducted.
As a result, a chelate polyvalent metal complex is used during the oxidation regeneration of the catalyst solution.
Of the nitrogen-carbon bond of the aminopolycarboxylic acid moiety of
Aminopolycarbohydrate is produced by separation and destruction.
Increasing chemical degradation of xylate chelators
There was found. During the oxidation process of hydrogen sulfide, polyvalent metal
Nitrogen-iron bond when reduced to a lower valence state
Is released and the excited or activated nitrogen atom is
To be present and, subsequently, higher polyvalent metals
When regenerating the solution to oxidize to a higher valence state,
When the breaking of the nitrogen-carbon bond occurs at the site of the active nitrogen atom
Conceivable. In accordance with the present invention and based on the aforementioned chelate decomposition mechanism.
When we add some stabilizers to the catalyst solution,
It may cause the decomposition of the aminopolycarboxylic acid chelating agent.
To suppress or prevent the destruction of the nitrogen-carbon bond
It was discovered that it was very effective. Especially as a chelating agent
Nitrilotriacetic acid (NTA), Alkalithio as stabilizer
Very good results are obtained when using sulphates.
Other effective stabilizing additives include certain types of additives.
Low molecular weight aliphatic alcohols, especially t-butanol and
And ethylene glycol. Therefore, the object of the present invention is to provide aminopolycarboxylates.
Touch of polyvalent metals chelated by acid chelating agents
Economy of the process of removing hydrogen sulfide using aqueous medium
It is to raise the real feasibility. A more specific object of the present invention is to provide a process of the above-mentioned form.
Of the aminopolycarboxylic acid chelating agent
New and improved methods to prevent major degradation and loss
To provide. A further object of the present invention is the aminopolycarboxylic acid key.
Relatively inexpensive to prevent excessive decomposition of rate agent
And an environmentally acceptable stabilizer in an appropriate amount
By mixing with a polyvalent metal aqueous solution,
Providing new and improved catalyst formulations for processes
It is in. (Example) The present invention will be described in more detail below with reference to the accompanying drawings.
Explained. Figures 1 and 2 show EDTA and oxidation, respectively
Iron in the ferric state and reduced with EDTA, ie ferrous iron
Schematic diagram of iron chelate complex in the state
Figure 4 shows the primary and secondary degradation products.
A graph showing the rate of primary and secondary decomposition, Fig. 5
Stabilized used in the preferred embodiment of the invention
It is a schematic diagram of an iron chelate complex. As mentioned above, sulfurization using an aqueous chelate iron catalyst solution
Some prior art patents on the removal of hydrogen are aqueous solutions.
Is "unstable" and precipitation of iron compounds occurs
Although admitting that there is a possibility
I was not aware of its importance. In addition, chelate iron solution
No proper explanation or understanding of the mechanism of liquid instability has been obtained.
did not exist. On the contrary, many prior art patents
The suspicion of formation and accumulation of thiosulfate in the catalyst solution
It seems that they are paying attention to some problems. Aminopolycarboxylic acid chelated iron solution
For laboratory research or small commercial operations,
Loss of chelating agent is not a serious problem, as hydrogen sulfide acid
Chelate along with sulfur slurry product
It seems that the cause is abandonment of the drug. But Naga
Have a large process unit in a commercial environment.
As a result of long-term operation, aminopolycarboxylate
Acid chelator consumption is based on laboratory processes
Clearly much more than predicted
Was. For small-scale operations, the total drug cost is
However, the loss of chelating agent is acceptable because it is relatively low
It may seem like a thing. This process can be
It will be carried out on a large scale for a long time of about 170 hours at least.
If you apply it, a slight unavoidable beauty
The loss of coating agent is relative to the chemical decomposition that occurs in this process.
It becomes insignificant when slipped, and it is a replenishing chelate.
Aminopolycal by chemical degradation requiring the addition of agents
Consumption of voxylic acid chelating agent implements this system
Is the most important issue in Furthermore, in most situations
Of hydrogen sulfide adsorption and oxidative regeneration of solution.
For this purpose, use a separate container or reaction area to
If the process is performed in an anaerobic system, thiosulfate
It has become clear that success is not a serious problem. Thiosulfur
Acid salt forms as a by-product in the process of removing hydrogen sulfide
However, its production is small, usually less than 5%, and
No or increased thiosulfate accumulation in the transfer solution
Almost never. As a result of thorough experimental research, we found that
Explain the mechanism of chemical decomposition of carboxylic acid chelating agents
Succeeded in understanding, and based on this mechanism,
Innovate extremely effective ways to delay or prevent solutions
I saw. The most effective polyvalent metal chelating agent for removing hydrogen sulfide
Most are ethylenediaminetetraacetic acid (EDTA) and its
Amides represented by homologues and closely related compounds of
It is widely known that it is of the nopolycarboxylic acid type.
Is recognized. But unfortunately, this kind of killer
The chelating agent is a chelating polyvalent metal water to remove hydrogen sulfide.
Regeneration of aqueous solutions using solutions and by oxidation or aeration
Rapid in cyclic hydrogen sulfide removal process
Disassemble into. Figures 1 and 2 show 4-Natri in aqueous solution.
1 is a schematic diagram of a complex formed by um-EDTA and iron. First
In Figure 1, the six ligands or "hooks" are
About ferric iron and its normal coordination requirements
Meets all. Four of the hooks are acetate ligands
Two between the iron and the two nitrogens of each EDTA molecule.
Filled by the bond. Shown in the schematic diagram of FIG.
But the seventh bond pair is the iron and hydroxyl ion
Exist between, or between the bridging oxygen to iron and another mirror image complex
It has been suggested in the literature. As is well known, EDTA-iron complex aqueous solution is used for gas flow.
In the case of adsorbing hydrogen sulfide from hydrogen, hydrogen sulfide is elemental sulfur.
At the same time iron is converted from polyvalent ferric iron to low atoms
Valence is reduced to ferrous iron, and the coordination number of iron changes from 6 to 4.
You. Figure 2 shows that iron is in the ferrous state, that is, in the low valence state.
The shape of this complex is shown in FIG. Iron coordination
Since the number changes from 6 to 4, there are two iron bonds, namely iron
-Carbon bond or iron-nitrogen bond must be broken
No. However, as shown in Figure 2, the release of the iron-nitrogen bond
Is responsible for the degradation of aminopolycarboxylic acid molecules
it is conceivable that. In Fig. 1, each nitrogen shares an electron pair with iron. This
The array of is the nitrogen of which attempts to relate all extranuclear electrons.
Satisfy the tendency and create an extremely stable configuration. ED
Long-term aqueous solution of TA-chelated ferrous iron and NTA-chelated ferric iron
It was aerated under atmospheric conditions for a period of time
There was no measurable decomposition of the chelating agent. I
Oxidation of hydrogen sulfide during the hydrogen sulfide removal process
When the iron in the complex is reduced from ferric iron to ferrous iron during
Is shown in Fig. 2 by the electron pair facing outward from the chelate ring.
As you can see, the pyramid structure of nitrogen is turned over,
There is one vacancy in the nitrogen complex formation site. Therefore,
In the configuration shown in Fig. 2, nitrogen is in the excited or active state.
During the subsequent oxidative regeneration of the catalyst solution due to
In addition, the nitrogen-carbon bonds along the backbone of the EDTA molecule are
It is considered that they are separated by the loss of unpaired electrons of nitrogen. The results we investigated using liquid chromatography techniques
The major decomposition product of EDTA is ethyl iminodiacetic acid (EID
A) and iminodiacetic acid (IDA), which are essentially these two
Of the class of substances that disappear from the catalyst solution during oxidative regeneration
It was confirmed that it occupied EDTA. Figure 3 shows the chemical composition of EDTA.
It is the figure which showed progress of decomposition. The main degradation product is EIDA
And IDA, but we also say that IDA
Raku N-methylglycine and glycine, or glycine
Decomposes into compounds related to syn and finally decomposes
It was revealed that acetic acid was produced as a substance. In addition, our research shows that a circulating hydrogen sulfide removal system
When using EDTA chelated iron solution in the process, EDT
The decomposition rate of A far exceeds the apparent loss rate of catalytic activity.
It turned out to exceed. IDA, which is the main decomposition product,
And its homologues do not degrade as fast as EDTA
However, their decomposition rate is very high in EDTA at regular intervals.
Or process with high iron concentration if not added continuously
Fast enough to make it impossible to do. Fourth
In the figure, the curve named "EDTA" is a repeating curve.
Use the EDTA chelated iron aqueous solution for hydrogen sulfide adsorption on the icicle
The rapid and incremental decomposition of EDTA during oxidative regeneration
It shows the loss. The curve named "IDA homologue" is
The concentration of primary decomposition products in the aqueous solution increased to the maximum,
Subsequent secondary degradation of IDA may reduce this concentration.
Is shown. The curve named "glycine" is a quadratic
As degradation progresses, glycine or glycine association becomes
It shows that the concentration of the compound increases complementarily. From the above experimental results, the iron loss in the aqueous solution was
In order to be well below the expected loss of EDTA, IDA and
And its homologues have some ability to chelate iron.
The conclusion was reached. In addition, IDA chelate iron
However, the gradual precipitation and loss of iron oxide
Hydrogen sulfide oxidation-catalyst regeneration circulation process without
He concluded that he had no ability to sustain. N-hydroxyethyl ethylenediamine triacetic acid (HEDT
A), diethylenetriaminepentaacetic acid (DTPA), and 1
Such as nitrilotriacetic acid (NTA), which has one nitrilo group
Other aminopolycarboxylic acid chelating agents
A similar test was performed on the rate iron solution, and the
The instability of the gut was investigated. All those substances are cyclic
Similar when used in the hydrogen sulfide oxidation catalyst regeneration process
It has been found to exhibit good chemical decomposition properties. According to the explanation of the chelate decomposition mechanism, iron is ferrous.
Steric reaction of the nitrogen atom of the chelated iron complex when reduced to water
Conversion and subsequent activation results in subsequent catalyst
At the time of oxidative regeneration of the solution, breaking of the nitrogen-carbon bond or
Leading to collapse. Other known nitrogen-free iron chelates
Agents such as acetylacetone or 2: 4 pentandio
Solution is used in aqueous solutions of neutral or weak pH to
It does not show the strong chelating effect needed to retain iron.
No. Thus, the tendency of nitrogen atoms to form complexes is
Not only cause decomposition problems, but also chelate iron sulfide water
The most effective aminopolycal in the element removal process
This is a distinctive feature of the voxylic acid chelating agent. According to
To increase the economic viability of this process
Is the excited or active state during the oxidative regeneration of the aqueous catalyst solution.
Suppresses the tendency of nitrogen present in
Need to bring an effective way to do. Stabilizing addition of various organic and inorganic substances
I explored its potential as a material, but only a few substances
Was found to have a remarkable effect. More cost, poison
Amino acid
Delay or prevent the decomposition of polycarboxylic acid chelating agents
To stop, alkali thiosulfate is the most convenient and
It was found to be an effective stabilizer. Hydrogen sulfide removal
Thiosulfate is formed in the process and is recycled.
Accumulation of thiosulfate in inverting solutions is highly desirable.
It ’s a bad thing, and we need to prevent it as much as possible.
In light of the ideas of prior art researchers based on many reasons
And this discovery was particularly amazing. The invention is
Thiosulfate must be mixed into the aqueous catalyst solution before
And keeping the thiosulfate at an appropriate concentration
To carry out hydrogen sulfide removal process on a large scale for a long time
Chelate decomposition to a level that is economically acceptable.
It was not known that it could be reduced by. Therefore, one specific embodiment of the present invention is directed to sulfide water.
In the circulation process of element removal-catalyst regeneration, aminopoly
It is possible to use an aqueous solution of polycarboxylic acid chelate.
And in the catalyst regeneration process, the chelating agent nitrogen-carbon
An effective amount to delay or prevent the breaking of elementary bonds.
It consists of incorporating the lucarithiosulfate into the solution. "A
The term "lucarithiosulfate" includes the alkali metal thiols.
Sulfate, alkaline earth metal thiosulfate, ammonium thiosulfate
And operating water such as hydrosulfide
The ability to produce thiosulfate ions in solution
Thiosulfate ion composed of other sulfur-containing compounds
It contains a precursor. Availability and cost
From a practical point of view, usually the first operating water
To prepare the solution, use ammonium thiosulfate or thiosulfate.
Sodium sulphate is used and the process is in progress
Maintain the thiosulfate concentration at the desired and effective level
Sometimes used as an additive when necessary
Would. The desired chelate-stabilizing effect is the thiol in the aqueous working solution.
Sulfate concentration ranges from about 0.3% to about 30% by weight, and
Within the range of about 3 g / l to about 300 g / l, preferably about 10 g / l
Obtained when in the range of 1 to about 50 g / l. Best results
In order to obtain the
At least 1 mole of thiosulfate is present for the offspring
Necessary, and more preferably effective stabilization
Has a molecular ratio of thiosulfate to nitrogen of about 1.5: 1
I need to keep it at 2: 1 level. Aminopolycarboxylic acid chelate used in the present invention
Agents include monoaminopolycarboxylic acid and polyaminopo
Licarboxylic acid, polyaminoalkyl polycarboxy
Acid, and polyamino hydroxyalkyl polycarbo
Contains xylic acid. Usually, chelating agents of the above type
Alone or as a mixture, their alkali metal salts, especially
Used in the form of the sodium salt. Polyaminopolyacetic acid
And polyaminohydroxyethyl polyacetic acid, or
Particularly preferred are their sodium salts. Belongs to the above class
Specific examples of useful chelating agents to be used include nitrilo triacetate.
Acid (NTA), ethylenediaminetetraacetic acid (EDTA), N-hydride
Roxyethyl ethylenediamine triacetic acid (HEDTA), and
And diethylenetriaminepentaacetic acid (DTPA). One preferred embodiment of the present invention is an aminopolycarboxylate.
Silicylate chelators and Thompson US Patent No. 4,189,4
The polyhydroxy type chelating agent disclosed in 62
Used in combination. Polyhydroxy type killer
For the agents, monosaccharides, disaccharides, reducing monosaccharides, reducing disaccharides
, Monosaccharide acids, and disaccharide acids, and their alkalis
Li metal salts are included. In particular, sorbitol is
It is a desirable chelating agent. Explained in Thompson's patent
As described above, when combined with a chelating agent, a wide range of
In aqueous solution at ambient pH and other process conditions
Can hold iron in. According to the present invention, nitrilotriacetic acid (NTA) is used as an aminopolyester.
When used as a carboxylic acid chelating agent,
Possible formation of two different complexes of diiron
Became clear. One of these complexes is iron-1
Another NTA molecule per molecule (monomer), another complex
Has two NTA molecules per iron molecule (dimer). Monomer
Of NTA-Iron complex of the same is used in the cyclic hydrogen sulfide removal process.
In the case of EDTA, the decomposition rate of the chelating agent is
It was found to be almost the same as the solution speed. But I was surprised
Notably, most iron is converted to 2 moles of NTA per mole of iron
Therefore, use a sufficient amount of NTA so that it is chelated.
Then, the decomposition rate is about 1 / of the decomposition rate when EDTA is used.
Reduced to 3. In addition, the alkali mixed in the catalyst solution
The decomposition-retarding action of lithiosulfate is due to the dimer of NTA-iron
It has been found to be particularly noticeable when using a pent complex.
won. Therefore, at least the preferred embodiments of the present invention are
Also uses an aqueous catalyst solution containing NTA and iron in a molecular ratio of about 2: 1
Then, virtually all of the iron is converted to a dimer of the NTA-iron complex.
Presence and substantially delays chelation degradation.
Or an effective amount of alkaline thiosulfate to prevent
It consists of mixing in the liquid. This preferred implementation of the invention
By using an embodiment, an aminopolycarboxylate
Uses a combination of EDTA and HEDTA as acid chelator
And as a polyhydroxy type chelating agent
Bitol is used to drive large-scale process operations.
Loss of aminopolycarboxylic acid chelating agents tested,
It could be reduced to 10% or less. By the mechanism described above, aminopolycarboxylic acid
The decomposition of the rate agent is caused by the nitrogen
It occurs due to the loss of unpaired electrons, resulting in alkali thiosulfate
Stabilizers form or associate with chelating agents, with iron being the first
When reduced from ferric iron to ferrous iron, it is released by nitrogen atoms.
By sharing the unpaired electrons emitted, the above decomposition
Would be delayed or blocked. Figure 5 shows thiosulfur
The phosphate ion associates with the dimeric NTA-iron complex and is reduced
Nitrogen bond is not broken during oxidation of iron complex
A schematic diagram of what is believed to be a way to stabilize the nitrogen atom
Is. As evidence of the configuration shown in Fig. 5, we use N
There is only 1 mol of sulfate per mol of NTA in the TA dimer
However, in contrast to having a remarkable stabilizing effect, EDTA
In a system using a
To prevent it from reaching a level that does not come,
It was confirmed that sulfate was required. Iron concentration in operating solution
The degree may be easier to quantify than the NTA concentration.
Depending on the iron content of the solution, the thiosulfate concentration
It would be convenient to monitor. For example, the
According to a preferred embodiment, a dimeric NTA-iron complex is used.
The ratio of thiosulfate to iron in solution,
Is at least 2 and preferably at least 3.5
You. Characteristics of the operating catalyst solution according to the preferred embodiment of the present invention
A solution containing approximately 1000 ppm of iron in a fixed formulation
Is sufficient to have a molecular ratio of NTA to iron of about 2: 1.
The molecular ratio of NTA and thiosulfate to iron is about 3.5: 1.
Sufficient sodium thiosulfate or thiosulfate
The molecular ratio of sorbitol to ammonium and iron
Contains sufficient sorbitol to be about 0.5: 1. The Stretford process uses vanadium salts and anthra
Uses an alkaline aqueous solution of quinone disulphonate (ADA)
In addition, it is a well-known process for removing hydrogen sulfide. Fent
US Patent No. 3,972,989, such as on, is a thiosulfate ion
Is added as a sacrificial agent to the aqueous solution, the process
Due to the hydrogen peroxide that is produced, preference for thiosulfate
Consumption of ADA may decrease due to static oxidation
Suggest that there is. However, in the present invention,
There is no significant consumption or loss of sulphate stabilizer
It was revealed. This means that the stabilization mechanism is Fenton.
What they presented about the Stretford process
It demonstrates different things. The preferred procedure for carrying out the invention is
When preparing the operating catalyst solution of the
It is to contain a sulfate. This way, fresh water
Since the solution is stable from the beginning, abnormal operating conditions and confusion
In the first operating phase of a process that often occurs,
The possibility of catalyst decomposition can be minimized. Recycling
In the continuous operation of the process using a circulating catalyst solution,
The desired concentration of thiosulfate can be
Concentration values can be obtained by collecting the used aqueous solution and further if necessary.
Maintain by adding fresh thiosulfate
be able to. Furthermore, in the hydrogen sulfide removal process
When using a chelating polyvalent metal solution,
It is also within the scope of the present invention to utilize the thiosulfate formed.
You. Also, if necessary, the main stream of circulating solution should be
To produce thiosulfate (eg by oxidation
The main circulation liquid flow.
Can be rejoined. In addition to the alkali thiosulfate, according to the invention there is
Of low molecular weight aliphatic alcohols as stabilizing additives
Can also be used to delay or prevent chelate degradation
Wear. 3 to 5 desirable substances belong to this category
Monohydric alcohols with carbon atoms, especially t-butanol
And organic chain alcohols such as isopropanol.
In addition, ethylene glycol and propylene glycol
You may use dihydric alcohols, such as a phenol. In the working solution
The concentration of added alcohol should be about 20g / l to about 100g / l.
No. Diaz US Pat. No. 4,402,930 claims to be a "regulator"
Certain aliphatic monohydric alcohols, especially C ₉ To C ₁₂ of
Add alcohol to the chelate metal solution and
It is difficult to separate from it, and sulfur is produced in a finely divided shape.
Disclosed to prevent being made. However, Diaz
Xu was unaware of the problem of chelate decomposition,
Teaching to Add Alcohol to Prevent Degradation
I haven't. In this specification, the present invention has been selected as a polyvalent metal.
The explanation is given with special emphasis on the use of iron.
Forms chelates with polycarboxylic acid chelating agents
Other polyvalent metals can also be used. This
Examples of polyvalent metals include copper, vanadium, manganese, and white.
Gold, tungsten, nickel, mercury, tin, and lead
is there. Any of the various methods well known to those skilled in the art
Of the required hydrogen sulfide-containing gas and the catalyst solution.
It can be used to achieve touch. Hydrogen sulfide acid
And regeneration of the catalyst solution occur simultaneously in the same reaction vessel
Aerobic system, or hydrogen sulfide oxidation and catalyst solution
Anaerobic cis with regeneration in a separate vessel or reaction zone
Tem is an example. These two types of process systems
See the aforementioned Thompson patent for a detailed description of the system.
I want to be illuminated. Hardison US Patent No. 4,238,462
An automatic recirculation process suitable for practicing the invention and
Apparatus and further US Patent No. such as Mancini
No. 4,011,304 describes control systems used for such processes.
Discloses the stem. The chelated iron solution of the present invention is preferably a suitable iron salt.
Is dissolved in water, the chelating agent is dissolved in another water,
By mixing the two solutions from to make a concentrate
Prepare. The pH of this concentrate is sodium hydroxide or
Is an alkaline substance such as sodium carbonate added in the required amount
Adjust by adjusting the desired neutral or alkaline
Use a concentrate of pH. Add the desired amount of iron to the appropriate amount of concentrate
Amount needed to prepare the desired amount of working solution to contain
Add water. Then add the required amount of alkali thiosulfate
Add as another aqueous solution. The iron content of the operating solution is
It can vary widely depending on the gas being treated and other factors.
It is possible to obtain Typically the iron content of the working solution
The amount ranges from about 5ppm to about 5000ppm, preferably 2
Adjust from 00ppm to 2000ppm. The amount of chelating agent should be small
Is sufficient to chelate all the iron in solution
However, it is desirable that the amount be slightly larger than this amount. Above
Thus, in the preferred embodiment of the present invention,
Uses a sufficient amount of NTA as an oxidizer,
Chelated by 2 moles of NTA per mole of iron
To do. The molecular ratio of NTA to iron is virtually all
Is present as a dimeric NTA-iron complex.
It should be at least 2: 1 but the ratio is slightly below 2: 1
Acceptable results are obtained even when spinning. Hydrogen Sulfide Containing Gas and Operating Dissolution in Hydrogen Sulfide Oxidation Process
Liquid contact often occurs at ambient temperature and pressure.
Temperature range from about 5 ℃ to about 65 ℃, the atmosphere
Use pressures below 100 bar and above
You may stay. pH range typically maintained at about 5.5 to about 10.5
But is mentioned in Thompson's patent number 4,189,462
, Especially the solution is a polyhydroxy type chelating agent
If it also contains, higher pH may be used.
In an anaerobic system, regeneration of the catalyst solution is
In the state, the used solution contains air or other oxygen-containing material.
It is performed by contacting with a gas. The following specific examples illustrate the invention.
You. Example I Separate Vessels for Hydrogen Sulfide Adsorption and Catalyst Regeneration
Using a small anaerobic pilot plant system,
Cyclic hydrogen sulfide removal-NTA in catalyst regeneration process
-Thiosulfuric acid added as a stabilizer into an iron chelate aqueous solution
The effect of sodium was evaluated. Each container has a pH meter and
Equipped with a redox electrometer. Same pilot plant
The unit was used for 92 hours of comparative operation. one
It was a test run, and the chelated iron solution was added with thiosulfate.
It contained a salt stabilizer. The other is control operation.
No thiosulfate was added to the rate iron solution. Adsorption capacity
In the reactor, contact the catalyst solution with undiluted hydrogen sulfide gas.
In addition, empty the used catalyst solution in the regeneration container.
Contacted with air, but the catalyst solution was continuous between the two vessels
Recycled. In each operation, use the same recirculation catalyst solution.
The same flow rate and hydrogen sulfide gas were kept at the same flow rate. Meaning
Although not shown, the air flow rate in the regeneration container is
Although it was higher in the control operation than in the test operation,
The redox potential inside the vessel is substantially the same in each operation.
Therefore, the difference in air flow rate was compared with the stability of chelate.
It did not affect. When preparing the catalyst solution for the control operation, ferric sulfate was used.
Is dissolved in water, and then an aqueous solution of NTA (sodium salt) is added.
Prepared separately, the pH was lowered from 11.0 to 6.3 with dilute sulfuric acid.
Then add the chelating solution to the ferric sulfate solution to dilute the pH.
Adjusted to 7.0 with sodium hydroxide. The concentrate obtained
Is diluted with a sufficient amount of water to reduce the iron content to approximately 1000 ppm.
Prepare the required amount of working solution with a molecular ratio of 2: 1 and NTA to iron.
It was Sodium thiosulfate is dissolved in water and added to the catalyst solution.
Except that the concentration of thiosulfate is about 50 g / l.
For example, use the same procedure to prepare the catalyst solution for the test run.
It was During the pilot plant operation, the pH during test operation
Only a minimum amount to maintain in the desired range of about 7.0
Need only add ammonium hydroxide once
However, in the control operation, the amount of ammonium hydroxide was increased.
It had to be added several times. Each pilot
At runt, periodically sample catalyst solution for analysis.
, And 53, 75 and 75 hours after the start of operation
Then, the sulfur generated in the adsorption container is taken out and operated.
Was done without any trouble. Sulfur production (sulfide water
Based on 100% conversion of the element)
It was the same amount. Trial of catalyst solution collected during pilot plant operation
The liquid used for liquid chromatography was NTA, and
Soluble iron and iodometry using optical spectrophotometry
Each of them was used for quantitative analysis of sodium thiosulfate. This
The results of these quantitative analyzes are shown in Table 1 below. Looking at the data in Table 1, the decomposition rate of NTA is
In (Test A), the concentration of NTA was significantly reduced,
It changed from 10.09g / l to 8.73g / l in 92.5 hours.
In lighting operation, NTA completely decomposed immediately after 47 hours.
I know that I have gone. Control of NTA degradation is controlled
Concentration of soluble iron from the beginning to the end of test A compared to
Is also proved to have been kept high. further
From the above table, thiosulfate is not so much produced in the control operation.
Not tested, and in Test A, thiosulfate was completely
It turns out that there is no solution or loss. Example II Using the same pilot plant equipment as in Example I,
Each of them carried out a series of tests for about 24 hours,
Various possible stabilizing additives other than thiosulfate are
The effect on the rate of decomposition of the soot was measured. Basic catalyst dissolution
The solution is an aqueous solution of NTA and iron with a molecular ratio of 2: 1 and a pH of about 7.0.
Adjusted to. The test solution should be based on the appropriate amount of the additive to be tested.
Add to this catalyst solution and dilute with water to obtain the desired iron concentration.
Prepared. Samples of catalyst solution were taken at 8h and 24h intervals
The NTA concentration was measured by liquid chromatography.
It was quantified using a fee. The results are shown in Table 2 below.
You Looking at Table 2, t-butanol used in Test C
Is equivalent to sodium thiosulfate in that it eliminates the decomposition of NTA.
In a controlled trial that was effective but did not use stabilizers,
It can be seen that substantially 50% of NTA was consumed. Further
In test B using ethylene glycol as an additive
Is shown by the fact that the decomposition of NTA was suppressed to about 10%.
As a result, it was very effective. Example III The same apparatus used in the examples described so far
A series of tests were performed using NTA and ferric sulfate with a molecular ratio of 2:
Thiosulfate when used as a stabilizing additive in solution 1
The effect of salt concentration was determined. Catalyst dissolution in each test
The flow rates of liquid, hydrogen sulfide supply gas, and oxidizing air are substantially
Are the same. Analysis of NTA is performed by liquid chromatography
I went by. The test results are shown in Table 3 below. Test H containing the lowest concentration of thiosulfate (3.1g / l)
In addition, the stability of NTA depends on the inclusion of thiosulfate in the solution.
Much higher than the stability of the control run. Shown in the table
The half-life value is strict because the elapsed time of the test is not uniform.
The optimum thiosulfate concentration
Is about 12.5 g / l under pilot plant conditions
It is shown that. This is less expensive than NTA compared to control operation.
At the lowest concentration of thiosulfate that keeps qualitative properties 24 times higher
is there. However, even if the thiosulfate level is low,
A 10-fold improvement can be obtained compared to illuminated operation. Example IV Same pilot plant equipment as described in Example I
Addition of thiosulfate to EDTA in chelating iron solution
The effect on the decomposition of was investigated. The molecular ratio of EDTA and iron is about 1.
Using 1: 1 ferrous sulfate and EDTA (sodium salt), pH
Was adjusted to about 7.0 to prepare a catalyst condensate. For each test
The operating solution of the condensate was adjusted to an iron content of 1000 ppm.
And add the required amount of sodium thiosulfate
Prepared. The test results are shown in Table 4 below. Furthermore, for comparison, N
In a similar test using NTA iron solution with a TA to iron molecular ratio of 2: 1
The results obtained are shown. The duration of the test is not uniform, so a direct comparison is not possible
No, but if you look at the half-life values in Table 4, thiosulfate was added
In tests L and M, the stability of EDTA was comparable to the control run.
It can be seen that it has increased from 6 times to 10 times. these
Results show that excellent improvement was obtained
However, in Test J, a system using NTA-iron dimer was used.
The chelate stability is 24 times higher. In summary, the present invention provides a hydrogen sulfide removal-catalyst regeneration cycle.
When used in the ring process, it dissolves chelate polyvalent metal catalysts.
Excessive Degradation of Amino Polycarboxylic Acid Chelating Agent in Liquid
Is highly effective in preventing
It provides means that can be accepted on a borderline basis. So far
Acceptable for long-term, large-scale process operation
In contrast to the unbelievably high chelate consumption rate, the present invention
The rate of consumption of the chelating agent is determined by the chelating agent in the operating solution per day
It is possible to reduce to less than approximately 1-2% of the total amount of
You. Under normal operating conditions, a supplemental chelating agent
Costs below about $ 75 per ton of sulfur produced
It is considered to be one.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a chelate complex of EDTA with iron in an oxidized or ferric state, and FIG. 2 is a chelate complex of iron with EDTA in a reduced or ferrous state. Schematic diagram, Fig. 3
Figure 4 shows the primary and secondary degradation products of EDTA, Figure 4 shows ED
A graph showing the rates of primary and secondary decomposition of TA, FIG.
FIG. 1 is a schematic diagram of a stabilized iron chelate complex used in a preferred embodiment of the present invention, and Tables 1 to 4 show the test results of Examples I to IV, respectively.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 38/12 C10K 1/10 (56) References JP-A-60-153921 (JP, A) Special features Kaisho 62-197127 (JP, A)

Claims (1)

Claim: What is claimed is: 1. A method for preventing excessive decomposition of a chelating agent during long-term continuous hydrogen sulfide removal process operation using a chelate polyvalent metal catalyst solution. An aqueous solution of a polyvalent metal chelated with at least one chelating agent consisting of an acid or nitrilotriacetic acid is brought into contact with a hydrogen sulfide-containing fluid stream to oxidize hydrogen sulfide to elemental sulfur and at the same time to remove the aforementioned polyvalent metal. The catalyst solution is regenerated by reducing it from a high valence state to a low valence state, and then contacting the solution with an oxygen-containing gas to oxidize the polyvalent metal from the low valence state to the high valence state. However, the above-mentioned chelating agent is liable to be decomposed during the process, and therefore it is necessary to add a supplemental chelating agent. During the process operation, a stabilizer of a concentration effective enough to slow or prevent the decomposition rate of the above-mentioned chelating agent composed of aminopolycarboxylic acid or nitrilotriacetic acid is mixed into the above-mentioned catalyst solution, Stabilizers are those selected from the group consisting of alkali thiosulfates, t-butanol, isopropanol, ethylene glycol, substantially from the beginning to the end of the process run, if required. Maintaining the effective concentration of said stabilizer in said catalyst solution by incorporating an additional stabilizer into said solution or by removing the spent solution. . 2. One of the above-mentioned nitrogen bonds of the chelate complex is released during the reduction of the polyvalent metal to a low valence state, thereby giving an unpaired electron to the nitrogen atom, and further,
The above-mentioned stabilizer forms a complex with the chelating agent and shares the above-mentioned unpaired electron, thereby delaying the breaking of the above-mentioned bond between the nitrogen atom and the carbon atom during the subsequent regeneration of the catalyst solution. A method according to claim 1, characterized in that it comprises blocking. 3. The method according to claim 1, wherein said alkali thiosulfate is mixed in the first working solution to keep said alkali thiosulfate in said effective concentration throughout the process operation. The method according to claim 1. 4. A patent characterized in that said alkali thiosulfate is selected from the group consisting of alkali metal thiosulfates, alkaline earth metal thiosulfates, ammonium thiosulfate, and thiosulfate ion precursors. The method according to claim 1. 5. The method of claim 1 wherein said polyvalent metal is iron and said solution has an iron content of about 5 ppm to 5000 ppm. 6. The chelating agent as described above is selected from the group consisting of monoaminopolycarboxylic acids, polyaminopolycarboxylic acids, polyaminoalkylpolycarboxylic acids, polyaminohydroxyalkylpolycarboxylic acids, and alkali metal salts thereof. The method according to claim 1. 7. A process according to claim 1, characterized in that the solution also contains a polyhydroxy chelating agent. 8. Process according to claim 1, characterized in that the oxidation of hydrogen sulphide and the regeneration of the catalyst solution are carried out in separate reaction zones. 9. The thiosulfate concentration in the above solution is about 3 g / l.
The method according to claim 1, wherein the method is from about 300 g / l. 10. The concentration of thiosulfate in the solution is about 10.
A method according to claim 1 characterized in that it is from g / l to about 50 g / l. 11. The catalyst solution is neutral or alkaline.
The method according to claim 1, wherein the method is pH. 12. The method according to claim 1, characterized in that the solution also contains sorbitol. 13. The method of claim 1 wherein the molecular ratio of nitrilotriacetic acid to polyvalent metal in said solution is at least about 2: 1. 14. The polyvalent metal is iron, and the molecular ratio of nitrilotriacetic acid to iron in the solution is at least about 2: 1 so that most of the iron is iron 1.
Process according to claim 1, characterized in that it is chelated by 2 mol of nitrilotriacetic acid per mol. 15. A patent characterized in that said alkali thiosulfate is selected from the group consisting of alkali metal thiosulfates, alkaline earth metal thiosulfates, ammonium thiosulfate, and thiosulfate ion precursors. The method according to claim 14. 16. The method of claim 14 wherein the molecular ratio of thiosulfate to nitrilotriacetic acid is at least about 1: 1. 17. The catalyst solution as defined above is from about 5 ppm to about 5000 pp.
The method according to claim 14, characterized in that it consists of m iron. 18. The concentration of thiosulfate in said solution is about
The method according to claim 14, characterized in that it is from 3 g / l to about 300 g / l. 19. The concentration of thiosulfate in the above solution is about
A method according to claim 14, characterized in that it is from 10 g / l to about 50 g / l. 20. The catalyst solution comprises about 1000 ppm of iron, and the thiosulfate salt has a molecular ratio of thiosulfate salt to iron.
A sufficient amount of sodium thiosulfate or ammonium thiosulfate to be about 3.5: 1, and the above solution
The method according to claim 14, characterized in that it contains sufficient sorbitol so that the molecular ratio of sorbitol to iron is about 0.5: 1. 21. The method according to claim 1, wherein the polyvalent metal is iron. 22. The chelating agent as defined above is selected from the group consisting of monoaminopolycarboxylic acids, polyaminopolycarboxylic acids, polyaminoalkylpolycarboxylic acids, polyaminohydroxyalkylpolycarboxylic acids, and alkali metal salts thereof. A method as claimed in claim 1 characterized. 23. The method of claim 1 wherein said chelating agent comprises nitrilotriacetic acid. 24. The method according to claim 1, wherein said solution also contains a polyhydroxy chelating agent. 25. A patent characterized in that the above-mentioned t-butanol, isopropanol, ethylene glycol are incorporated into the first running aqueous solution and kept at the above-mentioned effective concentrations throughout the operation of the process. The method according to claim 1. 26. Process according to claim 1, characterized in that the oxidation of hydrogen sulphide and the regeneration of the catalyst solution are carried out in separate reaction zones. 27. The aforementioned t-butanol in the aforementioned solution,
The method according to claim 1, wherein the concentration of isopropanol and ethylene glycol alcohol is about 20 g / l to about 100 g / l. 28. A redox catalyst formulation for use in a process for removing hydrogen sulfide by oxidizing to elemental sulfur, comprising a neutral or alkaline solution of iron chelated with nitrilotriacetic acid, the method comprising the steps of: Triacetic acid is susceptible to decomposition during the process, and the molecular ratio of nitrilotriacetate to iron is at least about 2: 1, whereby most iron is chelated with 2 moles of nitrilotriacetic acid per mole of iron, In addition, the above solution should contain a sufficient concentration of the alkali thiosulfate stabilizer to slow the rate of decomposition of the nitrilotriacetic acid chelating agent and prevent its decomposition during process operation. A redox catalyst formulation characterized by: 29. The iron content of the above solution is from about 5 ppm to about
29. The catalyst formulation of claim 28, wherein the catalyst formulation is 5000 ppm and the molecular ratio of thiosulfate to nitrilotriacetic acid is at least about 1: 1. 30. The concentration of the above-mentioned alkali thiosulfate is about
A catalyst formulation according to claim 28, characterized in that it is from 3 g / l to about 300 g / l. 31. The concentration of the above-mentioned alkali thiosulfate is about
29. Catalyst formulation according to claim 28, characterized in that it is from 10 g / l to about 50 g / l. 32. The iron content of said solution is about 1000 ppm and said alkali thiosulfate is sufficient thiosulfate to have a molecular ratio of thiosulfate to iron of about 3.5: 1. A sodium or ammonium thiosulfate, further characterized in that the solution also contains sorbitol in an amount sufficient to give a molecular ratio of sorbitol to iron of about 0.5: 1. A catalyst formulation according to paragraph 28. 36. A method according to claim 1, characterized in that the solution also contains a polyhydroxy chelating agent.
A catalyst formulation according to paragraph 28. 37. Catalyst formulation according to claim 28, characterized in that the solution also contains sorbitol.